System for producing citric acid from degermed corn flour

Abstract

The invention discloses a system for producing citric acid from degermed corn flour, which is characterized in that a starch and protein mixing outlet of a corn degerming unit is connected with a crushing unit, an outlet of the crushing unit is connected with a size mixing unit after being metered, and an outlet of the size mixing unit is connected with a liquefying unit; an outlet of the liquefaction unit is connected with a seed tank of the fermentation unit and an inlet of the horizontal screw separation unit, and a seed liquid outlet of the seed tank and a syrup outlet of the horizontal screw separation unit are both connected with an inlet of the fermentation tank. And an outlet of the fermentation tank is sequentially connected with a filter pressing unit, a ceramic membrane filtering unit, an ion exchange unit, a chromatographic separation unit, a continuous ion exchange unit, a pre-concentration unit, an evaporative crystallization unit and a drying unit. The system can improve the additional value of by-products, increase the yield of citric acid, greatly reduce the consumption of calcium carbonate and the output of calcium sulfate by-products, relieve the treatment pressure of the by-products, reduce the unit consumption of energy and materials in the production process, improve the production continuity and stability, and finally realize the maximum utilization of corn raw materials by enterprises. The economic benefit and the environmental protection level are improved.

Description

Technical Field

[0001] This invention relates to a production system for producing citric acid, and more particularly to a system for producing citric acid from degermed corn flour, belonging to the technical field of citric acid production equipment. Background Technology

[0002] Citric acid, an essential organic acid indispensable in the food, pharmaceutical, and chemical industries, directly impacts the quality of industry development through the advancement of its production process. Currently, the traditional process of producing citric acid from corn in China, using whole corn crushing and fermentation followed by calcium salt purification, is widely employed. However, this process faces numerous unresolved issues in practical applications.

[0003] Patent CN109536541A discloses a "method for pretreatment of corn steep liquor and a method for producing citric acid." This method utilizes a complex protease to pretreat corn steep liquor, then uses the pretreated liquor for fermentation to produce citric acid. While this improves the microbial utilization of the corn steep liquor and reduces foaming during fermentation, the method uses corn starch mixed with water to form a slurry, without involving the pretreatment of whole corn kernels for citric acid production. From a raw material utilization perspective, the corn germ is not extracted during the whole corn fermentation process. This results in the high-value germ being crushed and fermented along with fibrin, ultimately ending up in the citric acid residue for low-priced animal feed. This not only wastes raw materials but also fails to fully realize the potential value of the germ. Furthermore, because the germ is not extracted, the citric acid residue has an excessively high fat content, posing significant challenges to subsequent separation and washing processes.

[0004] Patent CN1047442411A discloses "a method for purifying citric acid from citric acid fermentation broth," including a step of using an anion exchange resin chromatography system to perform chromatographic separation on the citric acid-containing fermentation broth to remove residual sugar and obtain purified citric acid. The drawbacks of this method are: 1. Although citric acid is obtained, the technical solution does not detail how to filter larger impurities from the citric acid fermentation broth before chromatographic separation, and the use of a simulated moving bed chromatography system results in higher investment and maintenance costs compared to ordinary chromatographic separation systems, and greater operational difficulty.

[0005] 2. Energy consumption is a particularly prominent issue during the production process. The purification stage requires a large amount of hot water for washing, resulting in significant heat demand. Furthermore, the evaporation of citric acid also consumes a large amount of steam, leading to persistently high overall energy consumption. In addition, corn has a high ash content. When using ceramic membranes for fine filtration, fibers and ash can easily cause the ceramic membrane to puncture, allowing impurities to enter the citric acid solution. This, in turn, leads to increased column pressure in the subsequent chromatographic separation system, resin contamination, and affects separation efficiency and equipment lifespan.

[0006] 3. The process also has significant shortcomings in terms of production continuity and automation. The fermentation process is difficult to automate, requiring frequent manual intervention, which not only increases labor intensity but also affects production stability. When the neutralization unit uses a continuous neutralization method, the connecting pipes often become clogged with sediment, causing production stoppages and requiring regular cleaning, severely impacting production efficiency.

[0007] 4. From an environmental protection and by-product treatment perspective, the calcium salt purification process generates a large amount of calcium sulfate as a by-product. Although calcium sulfate is a major raw material for gypsum board, the treatment of these by-products faces enormous pressure due to the saturation of the domestic construction industry. Simultaneously, the ion exchange process consumes large amounts of water and acids / alkalis, increasing production costs and indirectly leading to higher evaporation energy consumption. Furthermore, because citric acid has strong hygroscopic properties, it easily adheres to the sidewalls of the cyclone separator in the exhaust gas collection device during the drying process, forming accumulated material that affects drying efficiency and product quality.

[0008] Patent CN201482373U discloses a "hydraulic self-excited dust collector," which solves the dust removal problem in citric acid production without increasing operating equipment or additional power consumption. The advantages of this solution are its simple structure and strong anti-clogging ability; however, it has a low capture efficiency for fine dust (<5μm) (approximately 70-80%) and is prone to secondary dust dispersion due to water flow fluctuations.

[0009] In conclusion, the traditional process of producing citric acid by whole corn crushing and fermentation followed by calcium salt purification can no longer meet the current industry requirements for high efficiency, energy saving, environmental protection, and high raw material utilization. Therefore, optimizing new production processes in each production stage has significant practical importance and application value.

[0010] In the production of citric acid from corn, the current mainstream domestic process, namely the traditional whole corn crushing and fermentation followed by calcium salt purification, suffers from problems such as low raw material utilization, difficulty in handling by-products, high energy consumption, and poor production continuity. The main obvious drawbacks are as follows: 1. High energy consumption and large steam consumption. Currently, citric acid fermentation has relatively high energy consumption because a lot of hot water is needed for washing during the purification process of citric acid, which requires a large amount of heat. At the same time, the evaporation of citric acid also requires a large amount of steam. 2. The corn is directly crushed without extracting the germ. The germ can only be mixed with citric acid residue and sold as feed, which cannot maximize the value of the germ and greatly reduces its utilization value. At the same time, the high fat content of citric acid residue makes separation and washing difficult. 3. It is difficult to achieve automatic chaining in the fermentation process, which requires manual intervention and increases labor intensity; 4. The high ash content in corn often causes the ceramic membrane to break down during the ceramic membrane filtration process due to fiber and ash content. Impurities enter the citric acid solution, leading to increased column pressure in the subsequent chromatographic separation system and contamination of the resin. 5. During the continuous neutralization process in the neutralization unit, the connecting pipes are often prone to blockage, causing production to stop. It is necessary to clean the sediment in the connecting pipes regularly. 6. The calcium salt method for producing and purifying citric acid will generate a large amount of calcium sulfate as a byproduct. Calcium sulfate is the main raw material for gypsum board and can be used in the construction industry. However, the domestic construction industry is currently saturated, making it difficult to handle the byproducts. 7. Fixed-bed evaporation has high water and acid / alkali consumption, leading to increased evaporation energy consumption; 8. Because citric acid is hygroscopic, the drying exhaust gas collection device is prone to absorbing moisture, causing citric acid to stick to the side wall of the cyclone separator, resulting in material accumulation. Summary of the Invention

[0011] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, and such simplifications or omissions should not be construed as limiting the scope of the invention.

[0012] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0013] The purpose of this invention is to overcome the problems existing in the prior art and provide a system for producing citric acid from degermed corn flour. This system can increase the added value of by-products, improve the yield of citric acid, significantly reduce the consumption of calcium carbonate and the amount of calcium sulfate by-products, alleviate the pressure of by-product processing, reduce energy and material consumption per unit during the production process, improve the continuity and stability of production, and ultimately maximize the utilization of corn raw materials by enterprises, thereby improving economic benefits and environmental protection.

[0014] To solve the above technical problems, the present invention provides a system for producing citric acid from degermed corn flour, comprising a corn degerming unit, wherein the starch and protein mixing outlet of the corn degerming unit is connected to the inlet of a grinding unit, the outlet of the grinding unit is connected to the inlet of a slurry preparation unit after metering, the outlet of the slurry preparation unit is connected to the inlet of a liquefaction unit, the outlet of the liquefaction unit is connected to the inlet of a seed tank 501 of a fermentation unit and a horizontal screw separator, and the seed liquid outlet of the seed tank 501 and the syrup outlet of the horizontal screw separator are both connected to the inlet of a fermentation tank 502.

[0015] Furthermore, in the corn degerming unit, the outlet of the feeding port 101 is connected to the inlet of the cleaning screen 103 via a primary bucket elevator 102. The material outlet of the cleaning screen 103 is connected to the inlet of the destoner 104. The material outlet of the destoner 104 is connected to the material inlet of the hydrating auger 110 via a secondary bucket elevator 109. The outlet of the hydrating auger 110 is connected to the inlet of the corn temporary storage bin 112 via a modulator 111. The bottom outlet of the corn temporary storage bin 112 is connected to the inlet of the degerming machine 115 via a corn discharge auger 114. The outlet of the degerming machine 115 is connected to the inlet of the grading screen 117 via a tertiary bucket elevator 116. The larger particle outlet of the grading screen 117 is connected to the inlet of the degerming machine 115.

[0016] Furthermore, the coarse powder outlet of the grading screen 117 is connected to the inlet of the embryo selector 118, the fine powder outlet of the grading screen 117 is connected to the lower inlet of the four-stage bucket elevator 121, and the upper outlet of the four-stage bucket elevator 121 is connected to the inlet of the hammer mill 122 of the crushing unit. The germ outlet of the embryo selector 118 is connected to the germ output pipe G03; the germ-containing endosperm outlet of the embryo selector 118 is connected to the inlet of the degerminator 115; and the starch and protein mixed outlet of the embryo selector 118 is also connected to the lower inlet of the four-stage bucket elevator 121. The gas phase outlet of the embryo sorter 118 is connected to the inlet of the fiber separator dust collector 119, and the bottom fiber outlet of the fiber separator dust collector 119 is connected to the fiber output pipe G02.

[0017] Furthermore, the bottom of the hammer mill 122 is provided with a collection hopper 125, and the bottom of the collection hopper 125 is provided with a screw conveyor 126. The outlet of the screw conveyor 126 is connected to the inlet of the corn flour temporary storage bin 127. The outlet of the corn flour temporary storage bin 127 is connected to the inlet of the corn flour auger 129 through a vibrating unloader 128. The outlet of the corn flour auger 129 is connected to the inlet of the metering auger 130. The outlet of the metering auger 130 is connected to the feed port of the ribbon mixer 133 of the slurry preparation unit. The outlet of the sugar water tank 131 is connected to the inlet of the sugar water pump 132. The outlet of the sugar water pump 132 is connected to the slurry inlet of the ribbon mixer 133 through the electromagnetic flow meter FT-133 and the regulating valve FC-133. The output port of the ribbon mixer 133 is connected to the corn flour slurry output pipe G01.

[0018] Furthermore, the outlet of the corn flour output pipe G01 is connected to the corn slurry buffer tank 201 of the liquefaction unit, and the outlet of the corn slurry buffer tank 201 is connected to the main inlet of the static mixer 203 via the corn slurry discharge pump 202; the outlet of the primary enzyme metering pump 207 is connected to the enzyme inlet of the static mixer 203 via the primary enzyme flow meter 208; the outlet of the static mixer 203 is connected to the material inlet of the primary ejector 210 via the mixed flow meter 209, and the outlet of the primary ejector 210 is connected to the inlet of the first maintaining pipe 211. The outlet of the first maintaining pipe 211 is connected to the middle inlet of the first flash tank 212. The bottom outlet of the first flash tank 212 is connected to the lower inlet of the primary liquefaction column 219 via the laminar flow feed pump 213. The upper outlet of the primary liquefaction column 219 is connected to the middle inlet of the second flash tank 220. The outlet of the secondary enzyme metering pump 223 is connected to the enzyme inlet on the upper side wall of the second flash tank 220 via the secondary enzyme flow meter FT-223. The bottom outlet of the second flash tank 220 is connected to the primary liquefaction discharge pipe G06 via the primary liquefaction discharge pump 221.

[0019] Furthermore, the inlet pipe of the dilute alkali metering pump 205 is inserted into the lower part of the dilute alkali tank 204, and the outlet pipe of the dilute alkali metering pump 205 is also connected to the inlet of the corn syrup discharge pump 202; the steam pipe G05 is connected to the steam inlet of the primary injector 210. The primary liquefaction column 219 is provided with multiple columns connected in series. The top outlet of the previous liquefaction column is connected to the lower inlet of the next liquefaction column. The outlet of the laminar flow feed pump 213 is connected to the lower inlet of the first primary liquefaction column 219. The top outlet of the last primary liquefaction column 219 is connected to the middle inlet of the second flash tank 220. The bottom feed inlet of each primary liquefaction column 219 extends to the axis of the liquefaction column and then bends downward to form a bottom flushing device for flushing the bottom center.

[0020] Furthermore, the top secondary steam outlets of the first flash evaporator 212 and the second flash evaporator 220 are respectively connected to the hot side inlet of the first plate heat exchanger 214; the outlet of the cold sugar liquid pipe G07 is connected to the cold side inlet of the first plate heat exchanger 214, and the cold side outlet of the first plate heat exchanger 214 is connected to the inlet of the hot sugar liquid tank 217; the hot side outlet of the first plate heat exchanger 214 is connected to the middle inlet of the gas-liquid separator 215, and the bottom outlet of the gas-liquid separator 215 is also connected to the inlet of the hot sugar liquid tank 217; the outlet of the hot sugar liquid tank 217 is connected to the sugar water tank 131 through the hot sugar liquid pump 218 and the hot sugar liquid pipe G04.

[0021] Furthermore, the outlet of the primary liquefaction discharge pipe G06 is connected to the inlet of the secondary ejector 301, the outlet of the secondary ejector 301 is connected to the inlet of the second maintaining pipe 302, the outlet of the second maintaining pipe 302 is connected to the middle inlet of the third flash tank 303, and the top secondary steam outlet of the third flash tank 303 is also connected to the hot side inlet of the first plate heat exchanger 214; the bottom outlet of the third flash tank 303 is connected to the inlet of the secondary liquefaction column 305 via the secondary liquefaction feed pump 304. The top outlet of the final stage of the secondary liquefaction column 305 is connected to the middle inlet of the fourth flash tank 306. The bottom outlet of the fourth flash tank 306 is connected to the inlet of the liquefied liquid buffer tank 309 via the secondary liquefaction flash discharge pump 307 and the hot side of the condenser 308. The outlet of the liquefied liquid buffer tank 309 is connected to the seed tank 501 via the turbid liquid pump 310. The cold side inlet of the condenser 308 is connected to the outlet of the clear water pipe G09, and the cold side outlet of the condenser 308 is connected to the hot water return pipe G10.

[0022] Furthermore, the outlet of the liquefied liquid buffer tank 309 is also connected to the inlet of the first-stage horizontal decanter centrifuge 312 via the horizontal decanter feed pump 311 of the horizontal decanter separation unit. The heavy phase outlet of the first-stage horizontal decanter centrifuge 312 is connected to the inlet of the concentrated sugar buffer tank 316. The outlet of the concentrated sugar buffer tank 316 is connected to the fermentation tank 502 via the concentrated sugar transfer pump 317. The light phase outlet of the primary horizontal decanter centrifuge 312 is connected to the inlet of the sugar residue slurry tank 313. The outlet of the sugar residue slurry tank 313 is connected to the inlet of the secondary horizontal decanter centrifuge 315 via the slurry pump 314. The light phase outlet of the secondary horizontal decanter centrifuge 315 is connected to the cold side inlet of the first plate heat exchanger 214 via the cold sugar liquid pipe G07. The heavy phase outlet of the secondary horizontal decanter centrifuge 315 is connected to the feeding port of the tube bundle dryer 401 via the sugar residue pipe G13.

[0023] Furthermore, the pre-concentration first-effect evaporator 413, the pre-concentration second-effect evaporator 415, and the pre-concentration third-effect evaporator 417 are connected in series and each is equipped with a separator; the outlet of the citric acid liquid pipe G17 is connected to the top feed port of the pre-concentration first-effect evaporator 413. The exhaust outlet of the tube bundle dryer 401 is connected to the inlet of the cyclone separator 404. The top exhaust port of the cyclone separator 404 is connected to the air inlet of the waste gas scrubbing tower 407 through the waste heat fan 406. The bottom water outlet of the waste gas scrubbing tower 407 is connected to the middle inlet of the primary flash tank 408. The bottom outlet of the primary flash tank 408 is connected to the middle inlet of the secondary flash tank 409. The condensate outlet of the tube bundle dryer 401 is connected to the tube bundle condensate flash tank 411, and the top outlet of the tube bundle condensate flash tank 411 is connected to the shell inlet of the pre-concentration single-effect evaporator 413. The top outlets of the primary flash tank 408 and the pre-concentrating first-effect separator 414 are both connected to the shell-side inlet of the pre-concentrating second-effect evaporator 415, and the top outlets of the secondary flash tank 409 and the pre-concentrating second-effect separator 416 are both connected to the shell-side inlet of the pre-concentrating third-effect evaporator 417.

[0024] Furthermore, a steam tracing pipe is wound around the outer periphery of the cyclone separator 404, and the condensate outlet of the steam tracing pipe is also connected to the middle inlet of the tube bundle condensate flash tank 411. The bottom outlet of the tube bundle condensate flash tank 411 is connected to the condensate tank 412, and the outlet of the condensate tank 412 is connected to the condensate supply pipe G15 through the pre-concentrated condensate pump 424. The bottom outlet of the secondary flash tank 409 is connected to the upper spray port of the waste gas scrubbing tower 407 via the scrubbing tower circulation pump 410. The discharge port of the tube bundle dryer 401 is connected to the inlet of the three-way valve 402. The first outlet of the three-way valve 402 is connected to the cooling and packaging equipment. The second outlet of the three-way valve 402 is connected to the lower inlet of the return auger 403. The upper outlet of the return auger 403 is connected to the feeding auger inlet of the tube bundle dryer 401.

[0025] Furthermore, the bottom outlets of the pre-concentrating triple-effect evaporator 417 and the pre-concentrating triple-effect separator 418 are connected to the citric acid pre-concentration tank 1601 via the pre-concentrating triple-effect discharge pump 421, and the outlet of the citric acid pre-concentration tank 1601 is connected to the top inlet of the single-effect falling film evaporator 1603 via the citric acid pre-concentration feed pump 1602. Steam pipe G05 is connected to the inlet of steam jet pump 1600 via a regulating valve, and the outlet of steam jet pump 1600 is connected to the shell-side inlet of the first-effect falling film evaporator 1603. The lower part of the first-effect falling film evaporator 1603 is connected to the first-effect separator 1604, and the bottom outlets of both are connected to the inlet of the first-effect discharge pump 1605; the outlet of the first-effect discharge pump 1605 is connected to the top inlet of the second-effect falling film evaporator 1606; the top outlet of the first-effect separator 1604 is simultaneously connected to the suction port of the steam jet pump 1600 and the shell-side inlet of the second-effect falling film evaporator 1606.

[0026] Furthermore, the lower part of the double-effect falling film evaporator 1606 is connected to the double-effect separator 1607, and the bottom outlets of both are connected to the feed inlet of the crystallizer 1610 through the double-effect discharge pump 1608. The bottom outlet of the crystallizer 1610 is connected to the circulating liquid inlet of the crystallizer 1610 via a forced circulation pump 1611 and a forced evaporator 1609. The top outlet of the double-effect separator 1607 is connected to the shell-side inlet of the forced evaporator 1609; the top outlet of the crystallizer 1610 is equipped with a crystallizer discharge density sensor DT-1610 and is connected to the citric acid crystal slurry output pipe G23 through the discharge pump 1612.

[0027] Furthermore, the bottom outlet of the seed tank 501 is connected to the top inlet of the fermentation tank 502 via the seed transfer pipeline G27. The bottom outlet of the fermentation tank 502 is connected to the fermentation broth storage tank 601 via the citric acid output pipe G28. The outlet of the fermentation broth storage tank 601 is connected to the inlet of the first-stage plate and frame filter press 603 via the fermentation broth discharge pump 602. The filtrate outlet of the first-stage plate and frame filter press 603 is connected to the first-stage concentrated acid tank 607. The outlet of the first-stage concentrated acid tank 607 is connected to the inlet pipe of the membrane filtration circulation pump 609 via the first-stage concentrated acid pump 608. The outlet of the membrane filtration circulation pump 609 is connected to the inlet of the ceramic membrane filtration system 610. The concentrate outlet of the ceramic membrane filtration system 610 is connected to the inlet pipe of the membrane filtration circulation pump 609 and the return port of the fermentation broth storage tank 601, forming a partial concentrate return circulation.

[0028] Furthermore, the filtrate outlet of the ceramic membrane filtration system 610 is connected to the citric acid concentration tank 611. The outlet of the citric acid concentration tank 611 is connected in sequence to the cation exchange column 613 and the anion exchange column 614 via the citric acid concentration pump 612. The outlet of the anion exchange column 614 is connected to the citric acid ion exchange buffer tank 615. The outlet of the citric acid ion exchange buffer tank 615 is connected to the fine filtrate buffer tank 701 via the citric acid ion exchange discharge pump 616 and the citric acid fine filtrate pipe G30.

[0029] Furthermore, the slag outlet of the primary plate and frame filter press 603 is connected to the inlet of the acid slag conditioning tank 604, and the outlet of the condensate supply pipe G15 is also connected to the inlet of the acid slag conditioning tank 604 through a regulating valve. The outlet of the acid slag conditioning tank 604 is connected to the inlet of the secondary plate and frame filter press 606 through the acid slag slurry pump 605. The slag outlet of the secondary plate and frame filter press 606 is connected to the feed inlet of the tube bundle dryer through the acid slag pipe G14. The filtrate outlet of the secondary plate and frame filter press 606 is connected to the mixed acid tank 901 of the primary neutralization unit through the dilute citric acid clear liquid pipe G29.

[0030] Furthermore, the outlet of the filtrate buffer tank 701 is connected to the cold side inlet of the second plate heat exchanger 703 via the filtrate pump 702, the cold side outlet of the second plate heat exchanger 703 is connected to the middle inlet of the filtrate flash tank 704, the bottom outlet of the filtrate flash tank 704 is connected to the deoxycitric acid buffer tank 705, and the outlet of the deoxycitric acid buffer tank 705 is connected to the feed inlet of each chromatographic column 801 via the deoxycitric acid discharge pump 706. The outlet of the dilute sulfuric acid stock solution tube G32 is connected to the inlet of the dilute sulfuric acid buffer tank 707. The outlet of the dilute sulfuric acid buffer tank 707 is connected to the cold side inlet of the third plate heat exchanger 709 through the dilute sulfuric acid pump 708. The cold side outlet of the third plate heat exchanger 709 is connected to the middle inlet of the dilute sulfuric acid flash tank 710. The bottom outlet of the dilute sulfuric acid flash tank 710 is connected to the inlet of the deoxygenated dilute sulfuric acid buffer tank 711. The bottom of the deoxygenated dilute sulfuric acid buffer tank 711 is connected to the eluent inlet of each chromatographic column 801 through the deoxygenated dilute sulfuric acid pump 712. The chromatographic column 801 is provided with multiple columns connected in series. The reflux port of each column is connected to the reflux port of the fine filtrate buffer tank 701 through the citric acid reflux pipe G34. The eluent outlet of each column is connected to the reflux port of the dilute sulfuric acid buffer tank 707 through the dilute sulfuric acid reflux pipe G35. The extract outlet of each column is connected to the acid hydrolysis citric acid tank 1501 through the citric acid purification liquid pipe G36. The miscellaneous sugar outlet of each chromatographic column 801 is connected to the dilute citric acid buffer tank 1101 of the secondary neutralization unit through the miscellaneous sugar discharge pipe G37.

[0031] Furthermore, the hot-side inlets of the second plate heat exchanger 703 and the third plate heat exchanger 709 are both connected to the steam pipe G05, and the hot-side outlets of the second plate heat exchanger 703 and the third plate heat exchanger 709 are connected to the condensate tank 412 through the condensate return pipe G16. The top outlets of the fine filtrate flash evaporator 704 and the dilute sulfuric acid flash evaporator 710 are respectively connected to the shell-side heat source inlet of the pre-concentration triple-effect evaporator 417.

[0032] Furthermore, the inlet of the mixed acid tank 901 is also connected to the calcium hydrogen concentrated acid pipe G38 from the vacuum filtration and washing unit. The outlet of the mixed acid tank 901 is connected to the inlet of the mixed acid circulation pump 902 and the mixed acid discharge pump 903. The outlet of the mixed acid circulation pump 902 is connected to the return port of the mixed acid tank 901. The outlet of the mixed acid discharge pump 903 is connected to the feed port of each primary neutralization pot 904. The top inlet of each primary neutralization pot 904 is also connected to the defoamer pipe G26 and the calcium carbonate raw liquid pipe G39. The bottom outlet of each primary neutralization pot 904 is connected to the slurry distributor of the tricalcium citrate vacuum belt filter 1001 through the tricalcium citrate slurry pipe G40.

[0033] Furthermore, the tricalcium vacuum belt filter 1001 is provided with a feeding area, a filtration area, a washing and dehydration area and a cake discharge area in sequence along the filter cloth advancing direction, and the sugar water outlet below is connected to the inlet of the vacuum tank 1002 respectively. The exhaust port at the top of each vacuum tank 1002 is connected to the middle inlet of the gas-water separator 1003. The top of the gas-water separator 1003 is vented to the atmosphere through the vacuum pump 1004. Except for the final stage, the bottom outlet of each vacuum tank 1002 and the bottom outlet of the gas-water separator 1003 are connected to the inlet of the waste sugar water tank 1005. The outlet of the waste sugar water tank 1005 is connected to the waste sugar water pump 1006 and the wastewater treatment station.

[0034] Furthermore, the bottom outlet of the fifth-stage vacuum tank 1002-5 of the tricalcium vacuum belt filter 1001 is connected to the inlet of the sugar water tank 1007, and the sugar water tank 1007 is connected to the primary rinsing water inlet above the washing and dehydration zone via the sugar water pump 1008; the end washing water outlet of the tricalcium vacuum belt filter 1001 is connected to the inlet of the tricalcium washing water tank 1009, and the outlet of the tricalcium washing water tank 1009 is connected to the secondary rinsing water inlet above the washing and dehydration zone of the tricalcium vacuum belt filter 1001 via the tricalcium washing water pump 1010; the tertiary rinsing water inlet above the washing and dehydration zone is connected to the condensate supply pipe G15.

[0035] Furthermore, the filter cake discharge port of the tricalcium vacuum belt filter 1001 is connected to the tricalcium slurry preparation tank 1011, the slurry preparation water inlet of the tricalcium slurry preparation tank 1011 is connected to the condensate supply pipe G15, the outlet of the tricalcium slurry preparation tank 1011 is connected to the second secondary neutralization pot 1104 through the tricalcium slurry preparation pump 1012, and multiple secondary neutralization pots 1104 are connected in series. The discharge port of the end secondary neutralization pot 1104 is connected to the inlet of the secondary neutralization variable frequency circulation pump 1105 and the secondary neutralization discharge pump 1106, the outlet of the secondary neutralization variable frequency circulation pump 1105 is connected to the return port of the first secondary neutralization pot 1104, and the outlet of the secondary neutralization discharge pump 1106 is connected to the slurry distributor of the calcium hydrogen vacuum belt filter 1201.

[0036] Furthermore, the calcium hydrogen vacuum belt filter 1201 is provided with a feeding area, a filtration area, a washing and dehydration area and a cake discharge area in sequence along the filter cloth advancing direction, and the filtrate outlet below is connected to the inlet of the vacuum tank 1202 respectively. The exhaust port at the top of each vacuum tank 1202 is connected to the middle inlet of the gas-water separator 1203. The top of the gas-water separator 1203 is vented to the atmosphere through the vacuum pump 1204. The washing and dehydration zone is equipped with five vacuum tanks in sequence along the direction of filter cloth movement. The bottom outlets of the vacuum tank 1202-1, the first-stage vacuum tank 1202-2, the second-stage vacuum tank 1202-3, and the gas-water separator 1203 in the filtration zone are all connected to the inlet of the calcium hydrogen acid buffer tank 1205. The outlet of the calcium hydrogen acid buffer tank 1205 is connected to the calcium hydrogen acid pump 1206 and the mixed acid tank 901.

[0037] Furthermore, the outlet of the three-stage vacuum tank 1202-4 is connected to the first-stage calcium hydrogen acid tank 1207, and the bottom outlet of the first-stage calcium hydrogen acid tank 1207 is connected to the first-stage rinsing water inlet above the washing and dehydration zone through the first-stage calcium hydrogen acid pump 1208. The outlet of the fourth-stage vacuum tank 1202-5 is connected to the second-stage calcium hydrogen dilute acid tank 1209. The outlet of the second-stage calcium hydrogen dilute acid tank 1209 is connected to the second-stage rinsing water inlet above the washing and dehydration zone through the second-stage calcium hydrogen dilute acid pump 1210. The outlet of the five-stage vacuum tank 1202-6 is connected to the four-stage calcium hydrogen acid tank 1211. The bottom outlet of the four-stage calcium hydrogen acid tank 1211 is connected to the four-stage rinsing water inlet above the washing and dehydration zone through the four-stage calcium hydrogen acid pump 1212. The end of the calcium hydrogen vacuum belt filter 1201 is connected to the inlet of the calcium hydrogen washing water tank 1213. The outlet of the calcium hydrogen washing water tank 1213 is connected to the three-stage rinsing water inlet above the washing and dehydration zone through the calcium hydrogen washing water pump 1214. The five-stage rinsing water inlet above the washing and dehydration zone is connected to the condensate supply pipe G15.

[0038] Furthermore, the filter cake discharge port of the calcium hydrogen vacuum belt filter 1201 is connected to the calcium hydrogen slurry preparation tank 1215, the slurry preparation water inlet of the calcium hydrogen slurry preparation tank 1215 is connected to the condensate supply pipe G15, and the bottom outlet of the calcium hydrogen slurry preparation tank 1215 is connected to the calcium hydrogen slurry buffer tank 1301 of the acidolysis unit through the calcium hydrogen slurry preparation pump 1216. The outlet of the calcium hydrogen slurry buffer tank 1301 is connected to the inlet of the first acidolysis pot 1304-1 via the calcium hydrogen slurry pump 1302, and multiple acidolysis pots 1304 are connected in series. The bottom outlet of the concentrated sulfuric acid high-level tank 1307 is also connected to the acid inlet of the first acidolysis pot 1304-1. The outlet of the final acidolysis pot is connected to the inlet of the acidolysis variable frequency circulation pump 1305 and the acidolysis discharge pump 1306. The outlet of the acidolysis variable frequency circulation pump 1305 is connected to the circulation port of the first acidolysis pot 1304-1, and the outlet of the acidolysis discharge pump 1306 is connected to the slurry distributor of the acidolysis vacuum belt filter 1401.

[0039] Furthermore, the acid hydrolysis vacuum belt filter 1401 is provided with a feeding area, a filtration area, a washing and dehydration area and a cake discharge area in sequence along the filter cloth advancing direction, and the filtrate outlet below is connected to the inlet of the vacuum tank 1402 respectively. The exhaust port at the top of each vacuum tank 1402 is connected to the middle inlet of the gas-water separator 1403. The washing and dehydration zone is equipped with five vacuum tanks in sequence along the direction of filter cloth movement. The bottom outlets of the vacuum tank 1402-1, the first-stage vacuum tank 1402-2, the second-stage vacuum tank 1402-3, and the gas-water separator 1403 in the filtration zone are all connected to the inlet of the acid hydrolysis concentrated acid tank 1405. The outlet of the acid hydrolysis concentrated acid tank 1405 is connected to the acid hydrolysis concentrated acid pump 1406 and the acid hydrolysis citric acid tank 1501.

[0040] Furthermore, the outlet of the acid hydrolysis citric acid tank 1501 is connected to the inlet of the decolorization column 1503 via the acid hydrolysis citric acid pump 1502, and the outlet of the decolorization column 1503 is connected to the citric acid buffer tank 1504. The cation exchange system 1506 is a continuous rotary multi-column series-parallel structure. The resin columns are arranged in a ring around the circumference of the rotary table and are divided into a water washing top material zone, a compressed air top material zone, a primary exchange zone, a secondary exchange zone, a product top water zone, a regeneration water washing zone, a regeneration zone, and a pretreatment regeneration zone. The outlet of the citric acid buffer tank 1504 is connected to the inlet of the primary exchange zone in the cation exchange system 1506 via the cation exchange feed pump 1505. The outlet of the primary exchange zone is connected to the inlet of the secondary exchange zone via the primary cation exchange liquid tank 1507 and the primary cation exchange liquid feed pump 1508. The outlet of the secondary exchange zone is connected to the feed end of the anion exchange system 1520 via the secondary cation exchange liquid tank 1509 and the secondary cation exchange liquid feed pump 1510. The discharge end of the anion exchange system 1520 is connected to the inlet of the citric acid tank 1526. The outlet of the citric acid tank 1526 is connected to the feed port of the pre-concentration first-effect evaporator 413 via the citric acid liquid pump 1527.

[0041] Furthermore, the anion exchange system 1520 is a continuous rotary multi-column series-parallel structure, with the resin columns arranged in a ring around the circumference of the rotary table and sequentially divided into a water washing top material zone, a compressed air top material zone, a primary exchange zone, a secondary exchange zone, a product top water zone, a regeneration water washing zone, a regeneration zone, and a pretreatment regeneration zone. The primary and secondary exchange zones of the cation exchange system 1506 and the anion exchange system 1520 are both connected in parallel with five parallel channels, each channel consisting of a resin column. The cation exchange system 1506 and the anion exchange system 1520 each use three columns connected in series for the water washing top material zone. The compressed air top material zone and the product top water zone each use one resin column. The regeneration water washing zone each use four columns connected in series. The regeneration zone each uses two columns connected in series. The pretreatment regeneration zone each uses three columns connected in series. The outlet of the hydrochloric acid pipe is connected to the inlet of the regeneration zone in the cation exchange system 1506. The outlet of the regeneration water washing zone and the regeneration zone in the cation exchange system 1506 is connected to the inlet of the hydrochloric acid tank 1511. The outlet of the hydrochloric acid tank 1511 is connected to the inlet of the pretreatment regeneration zone in the cation exchange system 1506 through the hydrochloric acid pump 1512. The outlet of the pretreatment regeneration zone is connected to the waste liquid pipe.

[0042] Furthermore, the outlet of the RO water pipe is connected to the inlet of the washing top material area and the regeneration washing area in the cation exchange system 1506 and the anion exchange system 1520, respectively. The outlet of compressed air pipe G25 is connected to the inlet of the compressed air top material zone in cation exchange system 1506 and anion exchange system 1520, respectively. The outlets of the water washing top material area and the compressed air top material area in the cation exchange system 1506 are respectively connected to the inlet of the primary cation exchange liquid tank 1507. The outlet of the secondary exchange zone in the cation exchange system 1506 is also connected to the lower inlet of the product top water zone, and the top outlet of the product top water zone is connected to the inlet of the regenerated water washing zone.

[0043] Furthermore, the outlet of the alkali solution pipe is connected to the inlet of the regeneration zone in the anion exchange system 1520. The outlet of the regeneration water washing zone and the regeneration zone in the anion exchange system 1520 is connected to the inlet of the dilute alkali tank 1524. The outlet of the dilute alkali tank 1524 is connected to the inlet of the pretreatment regeneration zone in the anion exchange system 1520 through the dilute alkali pump 1525. The outlet of the pretreatment regeneration zone is connected to the waste liquid pipe. The outlets of the water washing top material zone and the compressed air top material zone in the anion exchange system 1520 are respectively connected to the inlet of the primary anion exchange liquid tank 1521. The bottom outlet of the primary anion exchange liquid tank 1521 is connected to the inlet of the secondary exchange zone in the anion exchange system 1520 through the primary anion exchange liquid feeding pump 1522. The outlets of the secondary exchange zone and the product top water zone are both connected to the inlet of the citric acid tank 1526.

[0044] Furthermore, the outlet of the citric acid crystal slurry output pipe G23 is connected to the inlet of the feed distribution tank 1701, the outlet of the feed distribution tank 1701 is connected to the inlet of the top-rotating centrifuge 1702, the bottom outlet of the top-rotating centrifuge 1702 is provided with a discharge auger 1703, the outlet of the discharge auger 1703 is equipped with a vibrating conveyor 1704, the outlet of the vibrating conveyor 1704 is connected to the feed inlet of the vibrating fluidized bed 1705; the discharge outlet of the vibrating fluidized bed 1705 is connected to the inlet of the gyratory screen 1709, the undersize outlet of the gyratory screen 1709 is connected to the inlet of the finished product buffer silo 1710, and the outlet of the finished product buffer silo 1710 is connected to the inlet of the packaging scale 1711.

[0045] Furthermore, the sieve outlet of the gyratory screen 1709 is connected to the inlet of the remelting tank 1718, the outlet of the pre-concentrated condensate pump 424 is connected to the slurry water inlet of the remelting tank 1718 through the condensate supply pipe G15, and the bottom outlet of the remelting tank 1718 is connected to the reflux port of the citric acid pre-concentration tank 1601 through the centrifugal pump 1719. The outlet of air filter 1712 is connected to the air inlet of finned heat exchanger 1713, and the air outlet of finned heat exchanger 1713 is connected to the air inlet of the drying section of vibrating fluidized bed 1705 through blower 1714; the outlet of air filter 1715 is connected to the air inlet of rotary dehumidifier 1716, and the air outlet of rotary dehumidifier 1716 is connected to the air inlet of the cooling section of vibrating fluidized bed 1705 through cooling fan 1717. The exhaust port of the vibrating fluidized bed 1705 is connected to the inlet of the self-excited hydraulic dust collector 1706, the outlet of the self-excited hydraulic dust collector 1706 is connected to the lower air inlet of the two-flow air-water film dust collector 1707, and the top air outlet of the two-flow air-water film dust collector 1707 is open to the atmosphere through the induced draft fan 1708; the compressed air inlet of the two-flow air-water film dust collector 1707 is connected to the compressed air pipe G25, and the spray water inlet of the two-flow air-water film dust collector 1707 is connected to the RO water pipe G41.

[0046] Compared to the prior art, the advantages or beneficial effects of the embodiments of this application include at least the following: 1. The citric acid production process has been optimized by extracting the germ before corn crushing. The extracted germ is then used to produce food-grade germ oil, increasing the added value of the by-product. The germ is completely separated from starch, protein, and fiber using a degerming device, reducing the ash content of the corn and ensuring that the germ is starch-free. This guarantees the stable operation of subsequent membrane filtration processes and improves the citric acid yield.

[0047] 2. The production process employing a two-stage injection and two-stage enzyme addition can fully convert large starch particles into dextrin, significantly improving the conversion rate of corn starch and reducing raw material consumption. The secondary steam generated by liquefaction flash evaporation is heated into hot water for washing in the slurry preparation and neutralization units, greatly improving heat energy utilization and reducing steam consumption. The liquefaction columns are multi-stage in series to ensure first-in, first-out (FIFO). A flushing device is installed at the bottom of each liquefaction column to reduce the sedimentation of insoluble impurities at the bottom of the laminar flow tank and avoid material blockage. The filtration method of the liquefied liquid after liquefaction is changed from plate and frame filtration to continuous horizontal screw centrifuge separation, which greatly reduces labor intensity, reduces downtime for slag removal, and extends effective production time.

[0048] 3. During the fermentation process, a fully automated control system monitors and automatically adjusts key parameters such as temperature, pH, dissolved oxygen, and pressure in real time, and performs automated sterilization to avoid fluctuations caused by manual operation. This ensures the consistency of citric acid fermentation conditions for each batch, significantly reduces product quality differences caused by human factors, and improves the yield and purity of citric acid.

[0049] 4. After fermentation, the fermentation broth undergoes plate and frame pre-filtration to efficiently remove a large amount of coarse, insoluble matter such as fibers. Ceramic membrane filtration then precisely retains fine ash particles and other residual impurities, significantly improving the purity of the citric acid solution. This provides high-quality raw materials for subsequent purification processes, effectively preventing impurities from interfering with chromatographic separation, ion exchange, and crystallization, resulting in more stable purity, color, and other indicators of the final product, meeting the production standards for high-quality citric acid.

[0050] 5. The filtered citric acid solution is then subjected to chromatographic separation to extract citric acid of higher purity. To reduce water consumption in the chromatographic separation system, the remaining citric acid in the residual sugars is extracted using the traditional calcium salt method. This method ensures the yield of citric acid while reducing the consumption of calcium carbonate and the output of calcium sulfate byproducts.

[0051] 6. The production process using a continuous ion exchange system significantly reduces acid and alkali consumption and water consumption during ion exchange, improves resin utilization, ensures the stability of citric acid products, and reduces energy consumption for subsequent evaporation and crystallization of citric acid.

[0052] 7. Utilize the waste heat generated from tube bundle drying and chromatographic deoxygenation for citric acid preconcentration to reduce steam consumption and enhance waste heat recovery.

[0053] 8. Adopting a combination of falling film concentration evaporation and single-effect crystallization process improves crystallization efficiency and product purity.

[0054] 9. The dual wet dust removal method, which combines a self-excited hydraulic dust collector and a two-stage air-water film dust collector, solves the problem of citric acid sticking and accumulating due to its easy absorption of moisture, thus improving the product recovery rate.

[0055] In summary, the improved process has comprehensively solved the problems of raw material waste, high energy consumption, poor stability, and heavy environmental pressure in traditional citric acid production, achieving the production goals of "high efficiency, energy saving, high quality, and environmental protection," which is in line with the industry's upgrading and development trend. Attached Figure Description

[0056] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. The drawings are provided for reference and illustration only and are not intended to limit the present invention. Wherein: Figure 1 This is a flowchart of the corn degerming, pulverizing, and pulping unit in this invention; Figure 2 This is a flowchart of the corn pulping and primary liquefaction unit in this invention; Figure 3This is a flowchart of the secondary liquefaction unit in this invention; Figure 4 This is a flowchart of the citric acid concentration, evaporation, crystallization, and waste heat recovery unit in this invention; Figure 5 This is a flowchart of the fermentation unit in this invention; Figure 6 This is a flowchart of the fine filtration unit in this invention; Figure 7 This is a flowchart of the chromatographic separation auxiliary unit in this invention; Figure 8 This is a flowchart of the chromatographic separation unit in this invention; Figure 9 This is a flowchart of a primary neutralization unit in this invention; Figure 10 This is a flow chart of the tricalcium citrate vacuum filtration and washing unit in this invention; Figure 11 This is a flowchart of the secondary neutralization unit in this invention; Figure 12 This is a flowchart of the calcium hydrogen citrate vacuum filtration and washing unit in this invention; Figure 13 This is a flowchart of the acidolysis unit in this invention; Figure 14 This is a flow chart of the calcium sulfate vacuum filtration and washing unit in this invention; Figure 15 This is a flowchart of the citric acid continuous cation exchange unit in this invention; Figure 16 This is a flowchart of the citric acid continuous anion exchange unit in this invention; Figure 17 This is a flowchart of the citric acid concentration, evaporation, and crystallization unit in this invention; Figure 18 This is a flowchart of the citric acid drying unit in this invention; Figure reference numerals: Feed inlet 101; Primary bucket elevator 102; Cleaning screen 103; Destoner 104; Pulse dust collector 105; Exhaust fan 106; Pulse dust collector 107; Exhaust fan 108; Secondary bucket elevator 109; Wetting auger 110; Flow meter FT-110; Regulating valve FC-110; Modulator 111; Corn temporary storage bin 112; Vibrating unloader 113; Corn discharge auger 114; Degerminator 115; Tertiary bucket elevator 116; Grading screen 117; Germ separator 118; Fiber separator dust collector 119; Exhaust fan 120; Four-stage bucket elevator 121; Hammer mill 122; Pulse dust collector 123; Exhaust fan 124; Collection hopper 125; Screw conveyor 126; Corn flour temporary storage silo 127; Vibrating unloader 128; Corn flour auger 129; Variable frequency motor EV-129; Metering auger 130; Weighing sensor WT-130; Sugar water tank 131; Sugar water pump 132; Ribbon mixer 133; Electromagnetic flow meter FT-133; Control valve FC-133; Corn syrup buffer tank 201; Corn syrup discharge pump 202; pH sensor PH-202; Static mixer 203; Dilute alkali tank 204; Dilute alkali metering pump 205; Frequency converter EV-205; Primary enzyme tank 206; Primary enzyme metering pump 207; Primary enzyme flow meter 208; Post-mixing flow meter 209; Primary injector 210; Injector needle valve TC-210; Steam regulating valve PC-210; Temperature sensor TT-210; Pressure sensor PA-210; First holding pipe 211; First flash tank 212; Primary and secondary steam regulating valve PC-212; Primary steam pressure sensor PA-212; Level gauge LT-212; Laminar flow feed pump 213; Variable frequency drive EV-213; First plate heat exchanger 214; Gas-liquid separator 215; Vacuum pump 216; Hot sugar tank 217; Hot sugar pump 218; Primary liquefaction column 219; Secondary flash tank 220; Level gauge LT-220; Secondary steam pressure sensor PA-220; Secondary steam regulating valve PC-220; Primary liquefaction discharge pump 221; Primary liquefaction discharge flow meter FT-221; Variable frequency drive EV-221; Secondary enzyme tank 222; Secondary enzyme metering pump 223; Secondary enzyme flow meter FT-223; Secondary injector 301; Injector needle valve TC-301; Temperature sensor TT-301; Steam regulating valve PC-301; Pressure sensor PA-301; Secondary holding pipe 302; Third flash tank 303; Pressure sensor PA-303; Secondary steam regulating valve PC-303; Level gauge LT-303; Secondary liquefaction feed pump 304; Frequency converter EV-304; Secondary liquefaction column 305; Fourth flash tank 306; Level gauge LT-306; Secondary liquefaction flash discharge pump; 307; Frequency converter EV-307; Condenser; 308; Liquefied liquid buffer tank; 309; Turbid liquid pump; 310; Horizontal screw feed pump; 311; Flow meter FT-311; Control valve FC-311; Primary horizontal screw centrifuge; 312; Sugar residue slurry tank; 313; Slurry pump; 314; Secondary horizontal screw centrifuge; 315; Concentrated sugar buffer tank; 316; Concentrated sugar transfer pump; 317; Tube bundle dryer 401; Three-way valve 402; Return auger 403; Cyclone separator 404; Airlock 405; Waste heat fan 406; Waste gas scrubbing tower 407; Primary flash tank 408; Secondary flash tank 409; Scrubbing tower circulation pump 410; Tube bundle condensate flash tank 411; Condensate tank 412; Pre-concentration single-effect evaporator 413; Pre-concentration single-effect separator 414; Pre-concentration double-effect evaporator 415; Pre-concentration double-effect separator 416; Pre-concentration triple-effect evaporator 417; Pre-concentration triple-effect separator 418; Pre-concentration single-effect discharge pump 419; Pre-concentration double-effect discharge pump 420; Pre-concentration triple-effect discharge pump 421; Pre-concentration surface condenser 422; Pre-concentration vacuum pump 423; Pre-concentration condensate pump 424. Seed tank 501; Fermentation tank 502; Fermentation broth storage tank 601; fermentation broth discharge pump 602; primary plate and frame filter press 603; acid residue slurry tank 604; acid residue slurry pump 605; secondary plate and frame filter press 606; primary filter concentrated acid tank 607; primary filter concentrated acid pump 608; membrane filtration circulation pump 609; ceramic membrane filtration system 610; citric acid concentrated acid tank 611; citric acid concentrated acid pump 612; cation exchange column 613; anion exchange column 614; citric acid ion exchange solution buffer tank 615; citric acid ion exchange solution discharge pump 616. 701 Filtrate buffer tank; 702 Filtrate pump; 703 Second plate heat exchanger; 704 Filtrate flash evaporator; 705 Deoxycitric acid buffer tank; 706 Deoxycitric acid discharge pump; 707 Dilute sulfuric acid buffer tank; 708 Dilute sulfuric acid pump; 709 Third plate heat exchanger; 710 Dilute sulfuric acid flash evaporator; 711 Deoxygenated dilute sulfuric acid buffer tank; 712 Deoxygenated dilute sulfuric acid pump; Column 801; Column circulation pump 802; Mixed acid tank 901; Mixed acid circulation pump 902; Mixed acid discharge pump 903; Primary neutralization pot 904; Tricalcium vacuum belt filter 1001; Vacuum tank 1002; Gas-water separator 1003; Vacuum pump 1004; Waste sugar water tank 1005; Waste sugar water pump 1006; Diluted sugar water tank 1007; Diluted sugar water pump 1008; Tricalcium cloth washing water tank 1009; Tricalcium cloth washing water pump 1010; Tricalcium slurry preparation tank 1011; Tricalcium slurry preparation pump 1012; 1101 dilute citric acid buffer tank; 1102 dilute citric acid transfer pump; 1103 plate heat exchanger; 1104 secondary neutralization pot; 1105 secondary neutralization variable frequency circulation pump; 1106 secondary neutralization discharge pump; Calcium hydrogen vacuum belt filter 1201; Vacuum tank 1202; Gas-water separator 1203; Vacuum pump 1204; Calcium hydrogen concentrated acid buffer tank 1205; Calcium hydrogen concentrated acid pump 1206; Primary calcium hydrogen dilute acid tank 1207; Primary calcium hydrogen dilute acid pump 1208; Secondary calcium hydrogen dilute acid tank 1209; Secondary calcium hydrogen dilute acid pump 1210; Quaternary calcium hydrogen dilute acid tank 1211; Quaternary calcium hydrogen dilute acid pump 1212; Calcium hydrogen cloth washing water tank 1213; Calcium hydrogen cloth washing water pump 1214; Calcium hydrogen slurry preparation tank 1215; Calcium hydrogen slurry preparation pump 1216. 1301 Calcium hydrogen slurry buffer tank; 1302 Calcium hydrogen slurry pump; 1304 Acidolysis kettle; 1305 Acidolysis variable frequency circulating pump; 1306 Acidolysis discharge pump; 1307 Concentrated sulfuric acid high-level tank. Acid hydrolysis vacuum belt filter 1401; Vacuum tank 1402; Gas-water separator 1403; Vacuum pump 1404; Acid hydrolysis concentrated acid tank 1405; Acid hydrolysis concentrated acid pump 1406; Acid hydrolysis primary washing solution tank 1407; Acid hydrolysis primary washing solution pump 1408; Acid hydrolysis secondary washing solution tank 1409; Acid hydrolysis secondary washing solution pump 1410; Acid hydrolysis quaternary washing solution tank 1411; Acid hydrolysis quaternary washing solution pump 1412; Acid hydrolysis cloth washing water tank 1413; Acid hydrolysis cloth washing water pump 1414. Citric acid hydrolysis tank 1501; Citric acid hydrolysis pump 1502; Decolorization column 1503; Citric acid buffer tank 1504; Cation exchange feed pump 1505; Cation exchange system 1506; Primary cation exchange liquid tank 1507; Primary cation exchange liquid feed pump 1508; Secondary cation exchange liquid tank 1509; Secondary cation exchange liquid feed pump 1510; Hydrochloric acid refill tank 1511; Hydrochloric acid refill pump 1512; Anion exchange system 1520; primary anion exchange liquid tank 1521; primary anion exchange liquid feed pump 1522; anion exchange liquid feed pump 1523; dilute alkali tank 1524; dilute alkali pump 1525; citric acid tank 1526; citric acid solution pump 1527; Steam jet pump 1600; Citric acid pre-concentration tank 1601; Citric acid pre-concentration feed pump 1602; Single-effect falling film evaporator 1603; Single-effect separator 1604; Single-effect discharge pump 1605; Double-effect falling film evaporator 1606; Double-effect separator 1607; Double-effect discharge pump 1608; Forced evaporator 1609; Crystallizer 1610; Crystallizer discharge density sensor DT-1610; Forced circulation pump 1611; Citric acid crystal slurry discharge pump 1612; Surface condenser 1613; Vacuum pump 1614. Feeding and distributing trough 1701; Top-rotating centrifuge 1702; Discharge auger 1703; Vibrating conveyor 1704; Vibrating fluidized bed 1705; Self-excited hydraulic dust collector 1706; Two-stage air-water film dust collector 1707; Exhaust fan 1708; Gyratory screen 1709; Finished product buffer silo 1710; Packing scale 1711; Air filter 1712; Finned heat exchanger 1713; Blower 1714; Air filter 1715; Rotary dehumidifier 1716; Cooling fan 1717; Remelting tank 1718; Centrifugal pump 1719; Corn flour output pipe G01; Fiber output pipe G02; Germ output pipe G03; Hot diluted sugar solution pipe G04; Steam pipe G05; Primary liquefaction discharge pipe G06; Cold diluted sugar solution pipe G07; Secondary steam pipe for tertiary distillation G08; Clear water pipe G09; Hot water recycling pipe G10; Turbid syrup pipe G11; Clear syrup pipe G12; Sugar residue pipe G13; Acid residue pipe G14; Condensate supply pipe G15; Condensate return pipe G16; Citric acid solution pipe after ion exchange G17; Citric acid pre-concentrated solution output pipe G18; Circulating water supply pipe G19; Circulating water return pipe G20; Flash steam pipe for fine filtrate G21; Dilute sulfuric acid flash steam pipe G21. Steam pipe G22; Citric acid crystal slurry output pipe G23; Tank top venting pipe G24; Compressed air pipe G25; Defoamer pipe G26; Seed transfer pipe G27; Citric acid output pipe G28; Dilute citric acid clear liquid pipe G29; Citric acid refined filtrate pipe G30; Deoxygenated citric acid discharge pipe G31; Dilute sulfuric acid stock solution pipe G32; Deoxygenated dilute sulfuric acid pipe G33; Citric acid reflux pipe G34; Dilute sulfuric acid reflux pipe G35; Citric acid purified liquid pipe G36; Mixed sugar discharge pipe G37; Calcium hydrogen acid concentrated acid pipe G38; Calcium carbonate stock solution pipe G39; Tricalcium citrate slurry pipe G40; RO water pipe G41; Chilled water pipe G42. Detailed Implementation

[0057] In the following description of the present invention, the terms "upper", "lower", "front", "rear", "left", "right", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not mean that the device must have a specific orientation.

[0058] To make the technical means, creative features, objectives, and effects of this invention easier to understand, the invention is further described below with reference to specific illustrations. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them.

[0059] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0060] The system for producing citric acid from degermed corn flour of the present invention includes a corn degerming, grinding, and slurry preparation unit; a corn slurry preparation and primary liquefaction unit; a secondary liquefaction unit; a drying and pre-concentration evaporation and crystallization unit; a fermentation unit; a fine filtration unit; a chromatographic separation unit; a primary neutralization unit; a tricalcium citrate vacuum filtration and washing unit; a secondary neutralization unit; a calcium hydrogen citrate vacuum filtration and washing unit; an acid hydrolysis unit; a calcium sulfate vacuum filtration and washing unit; a citric acid continuous ion exchange unit; a citric acid concentration evaporation and crystallization unit; and a citric acid drying unit.

[0061] like Figure 1 As shown, in the corn degerming, crushing, and slurry preparation unit of the present invention, the outlet of the feeding port 101 is connected to the lower inlet of the primary bucket elevator 102, the upper outlet of the primary bucket elevator 102 is connected to the inlet of the cleaning screen 103, the material outlet of the cleaning screen 103 is connected to the inlet of the destoner 104, the material outlet of the destoner 104 is connected to the lower inlet of the secondary bucket elevator 109, the upper outlet of the secondary bucket elevator 109 is connected to the material inlet of the water-lubricating auger 110, and the clean water pipe is connected to the flow meter FT-110 and the regulating valve FC-110. The water inlet of the sluice auger 110 is connected to the inlet of the modulator 111, the outlet of the modulator 111 is connected to the inlet of the corn storage bin 112, the bottom outlet of the corn storage bin 112 is connected to the inlet of the corn discharge auger 114 via the vibrating unloader 113, the outlet of the corn discharge auger 114 is connected to the inlet of the degerminator 115, the outlet of the degerminator 115 is connected to the lower inlet of the three-stage bucket elevator 116, and the upper outlet of the three-stage bucket elevator 116 is connected to the inlet of the grading screen 117.

[0062] The larger particle outlet of the grading screen 117 is connected to the inlet of the degerminator 115, the coarse powder outlet of the grading screen 117 is connected to the inlet of the embryo selector 118, and the fine powder outlet of the grading screen 117 is connected to the lower inlet of the four-stage bucket elevator 121.

[0063] The germ outlet of the embryo selector 118 is connected to the germ output pipe G03; the germ-containing endosperm outlet of the embryo selector 118 is connected to the inlet of the degerminator 115; and the starch and protein mixed outlet of the embryo selector 118 is connected to the lower inlet of the four-stage bucket elevator 121.

[0064] The gas phase outlet of the embryo separator 118 is connected to the inlet of the fiber separator dust collector 119. The exhaust port of the fiber separator dust collector 119 is vented to the atmosphere through the induced draft fan 120. The bottom fiber outlet of the fiber separator dust collector 119 is connected to the fiber output pipe G02.

[0065] The upper outlet of the four-stage bucket elevator 121 is connected to the inlet of the hammer mill 122. The bottom of the hammer mill 122 is equipped with a collection hopper 125, and the bottom of the collection hopper 125 is equipped with a screw conveyor 126. The outlet of the screw conveyor 126 is connected to the inlet of the corn flour temporary storage bin 127. The outlet of the corn flour temporary storage bin 127 is connected to the inlet of the corn flour auger 129 through a vibrating unloader 128. The outlet of the corn flour auger 129 is connected to the inlet of the metering auger 130. The outlet of the metering auger 130 is connected to the feed port of the ribbon mixer 133.

[0066] The hot sugar solution pipe G04 is connected to the inlet of the sugar solution tank 131, the outlet of the sugar solution tank 131 is connected to the inlet of the sugar solution pump 132, the outlet of the sugar solution pump 132 is connected to the slurry inlet of the ribbon mixer 133 through the electromagnetic flow meter FT-133 and the regulating valve FC-133, and the output port of the ribbon mixer 133 is connected to the corn flour slurry output pipe G01.

[0067] Corn is fed through the feeding port 101. Considering dust levels, a pulse dust collector 107 and a matching induced draft fan 108 are added to the feeding port. The corn is then conveyed to a cleaning screen 103 via a primary bucket elevator 102, where most impurities are removed. The corn, after impurity removal, passes through a destoner 104 for further impurity removal, specifically removing any embedded stones. Simultaneously, the destoner is further cleaned by a pulse dust collector 105 and an induced draft fan 106, reducing the ash content of the corn.

[0068] After stone removal, the corn is lifted by a two-stage bucket elevator 109 into a water-cooling auger 110. Since the initial moisture content of the corn is typically 12-13%, the kernels are quite hard, making the germ prone to breakage during the degerming process due to excessive mechanical force, hindering separation from the endosperm. To ensure efficient germ detachment during subsequent degerming, a certain amount of water is sprayed above the corn, with the water flow rate controlled by a flow meter FT-110 and a regulating valve FC-110. After watering, the corn enters a modulator 111 to allow moisture to penetrate through the corn seed coat into the kernel. To ensure a more even distribution of moisture among the germ, endosperm, and seed coat, the modulated corn is temporarily stored in a corn storage bin 112 for 20-60 minutes, bringing the moisture content to 14-16%. This ensures the hardness and resilience of the germ, making it easier to detach completely during degerming.

[0069] After being temporarily stored, the corn is discharged through a vibrating unloader 113 and a corn discharge auger 114. The frequency of the auger is adjusted by a variable frequency motor, which further regulates the flow rate to the degerming machine 115. Inside the degerming machine 115, the corn undergoes intense collisions under mechanical force, causing the endosperm to separate from the seed coat. Simultaneously, the endosperm is broken into smaller particles, while the germ, due to its good toughness, remains relatively intact. The degerming machine 115 separates the germ from the fiber, starch, and protein. The resulting corn flour is then lifted to a high position by a three-stage bucket elevator 116 and sieved through a grading screen 117, separating it into larger particles, coarse flour, and fine flour.

[0070] Larger particles that haven't had their germ completely removed are returned to the degerminator 115 for further degerming. The sieved fine powder, free of germ and fiber, is then sent to the subsequent grinding and liquefaction unit. The coarse powder is then passed through the separator 118 for further separation of the germ from fiber and protein starch, resulting in four products: germ, fiber, germ-containing endosperm, and a mixture of starch and protein. The separated germ is discharged through the germ output pipe G03 and can be sold as a product from which germ oil can be extracted.

[0071] Meanwhile, the embryo sorting machine is equipped with a fiber separator dust collector 119 and an induced draft fan 120. The fibers come out from the light phase air duct and are discharged from the bottom outlet of the fiber separator dust collector 119, and are output through the fiber output pipe G02 for grinding into feed. The germ and endosperm continue to return to the degerminator 115, while the starch and protein are mixed with the fine powder screened by the grading screen 117 for grinding and entering the grinding and liquefaction unit.

[0072] The sieved starch and protein are conveyed to the hammer mill 122 through a four-stage bucket elevator 121 for crushing. The fineness of the crushing is 30 mesh, and the sieve passing rate reaches 99%. At the same time, a pulse dust collector 123 and an induced draft fan 124 are equipped with a dust removal system. The crushed corn flour falls into the collection hopper 125 and is conveyed to the corn flour temporary storage bin 127 for buffering and temporary storage by a screw conveyor 126. Then, it is unloaded by a vibrating unloader 128 and conveyed by a corn flour auger 129 to a metering auger 130 for weighing and metering. Then, it is conveyed to the ribbon mixer 133, where water is added by a light sugar water pump 132 to mix and adjust the slurry. The corn flour auger 129 is equipped with a variable frequency motor EV-129, which is interlocked with the weighing sensor WT-130 of the metering auger 130, and also interlocked with the electromagnetic flowmeter FT-133 and the regulating valve FC-133 that control the flow of the diluted sugar water, ensuring that the discharge concentration of the ribbon mixer 133 is controlled at 28~30%, and is output through the corn flour slurry output pipe G01.

[0073] Through the above process, a large amount of ash adhering to the bran enters the feed process along with the fiber. After being crushed, it is used as feed, which significantly reduces the ash content in the corn flour and provides a guarantee for the stable operation of the ceramic membrane. At the same time, the early extraction of the germ increases the added value of the product and also creates favorable conditions for the effective separation of citric acid residue.

[0074] Traditionally, citric acid is produced from corn by crushing, slurrying, adding enzymes, and spraying liquefaction. This process reduces starch utilization, negatively impacting citric acid fermentation and consequently lowering citric acid yield and fermentation efficiency.

[0075] This corn degerming and pulping unit extracts the germ before corn grinding, using it to produce food-grade germ oil and increasing the added value of the by-product. The degerming equipment thoroughly separates the corn germ from starch, protein, and fiber, ensuring the germ is starch-free and improving citric acid yield. After degerming, only 1.4 tons of corn are needed to produce 1 ton of anhydrous citric acid, compared to 1.7 tons for the undegermed process. Producing lemons after degerming reduces raw material consumption by approximately 20% compared to the undegermed process. This unit also reduces the ash content of the corn, ensuring stable operation of subsequent membrane filtration processes, while using a dry extraction method to further increase the added value of the by-product. 8%-10% of the corn germ can be extracted after degerming for corn germ oil production, generating an additional economic benefit of approximately 80 yuan per ton of corn; whereas the germ of undegermed corn is mixed with fermentation residue and cannot be sold separately.

[0076] like Figure 2As shown, in the degermed corn syrup liquefaction and separation unit of the present invention, the outlet of the corn flour output pipe G01 is connected to the inlet of the corn syrup buffer tank 201, and the outlet of the corn syrup buffer tank 201 is connected to the inlet of the corn syrup discharge pump 202; the dilute alkali supply pipe replenishes 2%wt of dilute alkali solution into the dilute alkali tank 204, the inlet pipe of the dilute alkali metering pump 205 is inserted into the lower part of the dilute alkali tank 204, and the outlet pipe of the dilute alkali metering pump 205 is also connected to the inlet of the corn syrup discharge pump 202; the frequency converter EV-205 of the dilute alkali metering pump 205 is interlocked with the pH sensor PH-202 at the outlet of the corn syrup discharge pump 202.

[0077] The outlet of the corn syrup discharge pump 202 is connected to the main inlet of the static mixer 203; the inlet of the primary enzyme tank 206 is connected to the α-amylase tube; the inlet pipe of the primary enzyme metering pump 207 is inserted into the bottom of the primary enzyme tank 206; and the outlet of the primary enzyme metering pump 207 is connected to the enzyme inlet of the static mixer 203 through the primary enzyme flow meter 208.

[0078] The outlet of the static mixer 203 is connected to the material inlet of the primary injector 210 via the mixed flow meter 209. The frequency converter of the primary enzyme metering pump 207 is interlocked with the flow of the primary enzyme flow meter 208 and the mixed flow meter 209.

[0079] Steam pipe G05 is connected to the steam inlet of primary ejector 210 via steam regulating valve PC-210. A pressure sensor PA-210 is installed on the steam inlet pipe of primary ejector 210, and the opening degree of steam regulating valve PC-210 is interlocked with the pressure sensor PA-210. A temperature sensor TT-210 is installed at the outlet of primary ejector 210, and the opening degree of ejector needle valve TC-210 of primary ejector 210 is interlocked with the temperature sensor TT-210.

[0080] The outlet of the primary ejector 210 is connected to the inlet of the first maintaining pipe 211, the outlet of the first maintaining pipe 211 is connected to the middle inlet of the first flash tank 212, the bottom outlet of the first flash tank 212 is connected to the inlet of the laminar flow feed pump 213, and the frequency converter EV-213 of the laminar flow feed pump 213 is interlocked with the level gauge LT-212 of the first flash tank 212.

[0081] The primary liquefaction column 219 has multiple columns connected in series. The top outlet of the previous liquefaction column is connected to the bottom inlet of the next liquefaction column. The outlet of the laminar flow feed pump 213 is connected to the bottom inlet of the first primary liquefaction column 219. The top outlet of the last primary liquefaction column 219 is connected to the middle inlet of the second flash tank 220. The bottom outlet of the second flash tank 220 is connected to the inlet of the primary liquefaction discharge pump 221. The outlet of the primary liquefaction discharge pump 221 is connected to the primary liquefaction discharge pipe G06 through the primary liquefaction discharge flow meter FT-221.

[0082] Each primary liquefaction column 219 has a bottom inlet that extends to the axis of the liquefaction column and then bends downward to form a bottom flushing device that flushes the center of the bottom, thus reducing the sedimentation of insoluble impurities at the bottom of the laminar flow tank. Each primary liquefaction column 219 has a drain outlet at its bottom, and each drain outlet is connected to the inlet pipe of the primary liquefaction discharge pump 221.

[0083] The frequency converter EV-221 of the primary liquefaction discharge pump 221 is interlocked with the level gauge LT-220 of the second flash tank 220.

[0084] The inlet of the secondary enzyme tank 222 is connected to the α-amylase tube, and the inlet pipe of the secondary enzyme metering pump 223 is inserted into the bottom of the secondary enzyme tank 222. The outlet of the secondary enzyme metering pump 223 is connected to the enzyme inlet on the upper side wall of the second flash tank 220 through the secondary enzyme flow meter FT-223. The frequency converter of the secondary enzyme metering pump 223 is interlocked with the secondary enzyme flow meter FT-223 and also with the primary liquefaction discharge flow meter FT-221.

[0085] The top secondary steam outlet of the first flash tank 212 is equipped with a primary steam pressure sensor PA-212, and is connected to the hot side inlet of the first plate heat exchanger 214 through a primary steam secondary steam regulating valve PC-212; the top secondary steam outlet of the second flash tank 220 is equipped with a secondary steam pressure sensor PA-220, and is also connected to the hot side inlet of the first plate heat exchanger 214 through a secondary steam secondary steam regulating valve PC-220.

[0086] The outlet of the cold sugar liquid pipe G07 is connected to the cold side inlet of the first plate heat exchanger 214, and the cold side outlet of the first plate heat exchanger 214 is connected to the inlet of the hot sugar liquid tank 217; the hot side outlet of the first plate heat exchanger 214 is connected to the middle inlet of the gas-liquid separator 215, the top exhaust port of the gas-liquid separator 215 is vented to the atmosphere through the vacuum pump 216, the bottom outlet of the gas-liquid separator 215 is also connected to the inlet of the hot sugar liquid tank 217, the outlet of the hot sugar liquid tank 217 is connected to the inlet of the hot sugar liquid pump 218, and the outlet of the hot sugar liquid pump 218 is connected to the hot sugar liquid pipe G04.

[0087] The prepared corn flour from the corn flour output pipe G01 enters the corn flour buffer tank 201, and is then pumped into the primary ejector 210 for liquefaction via the corn flour discharge pump 202. Before liquefaction, the pH value needs to be adjusted to 5.5-6, which is achieved online through the dilute alkali tank 204 and the dilute alkali metering pump 205. The dilute alkali metering pump 205 is frequency-controlled and interlocked with the frequency converter EV-205 of the dilute alkali metering pump 205 via the pH sensor at the outlet of the corn flour discharge pump 202.

[0088] After the pH value is adjusted, the mixture enters the static mixer 203 for online addition of liquefying enzyme. The liquefying enzyme is added in a certain proportion through the primary enzyme metering pump (207), and the frequency of the primary enzyme metering pump (207) and the primary enzyme flow meter 208 are interlocked with the mixed flow meter 209.

[0089] After adjusting the pH and adding liquefying enzyme, the corn flour slurry enters the liquefaction jetting system. In the primary ejector 210, the corn flour slurry is mixed with steam. The ejector outlet is equipped with a temperature sensor TT-210. The opening of the ejector needle valve TC-210 is interlocked with the temperature measured by the temperature sensor TT-210, and the liquefaction temperature is controlled at 100~105℃ to achieve automatic control. At the same time, the steam regulating valve PC-210 and the pressure sensor PA-210 installed on the steam pipeline G05 are interlocked with each other. By controlling the opening of the steam regulating valve PC-210, the steam pressure of the primary ejector is controlled, maintaining the stable operation of the primary ejector 210 and achieving precise control.

[0090] The sprayed corn flour slurry enters the first holding pipe 211 and is maintained for 3-5 minutes to allow it to gelatinize rapidly at high temperature. The gelatinized corn flour slurry then enters the first flash tank 212 for flash cooling. The opening of the primary steam regulating valve PC-212 on the secondary steam pipeline is interlocked with the pressure value measured by the primary steam pressure sensor PA-212 at the flash tank outlet. By adjusting the opening of the primary steam regulating valve PC-212, the vacuum level of the first flash tank 212 is maintained, thereby controlling the temperature of the liquefied liquid in the flash tank 212 to 95-97℃. The flash-cooled liquefied liquid is then pumped into the primary liquefaction column 219 by the laminar flow feed pump 213 for liquefaction. The frequency converter EV-213 of the laminar flow feed pump 213 is interlocked with the level gauge LT-212 of the first flash tank 212 to control the level of the first flash tank 212.

[0091] Multiple primary liquefaction columns 219 are connected in series to ensure first-in, first-out (FIFO) material flow. At the same time, liquid is introduced from the bottom of each primary liquefaction column 219 to flush the bottom center, thereby reducing the precipitation of insoluble impurities at the bottom of the laminar flow tank.

[0092] After further liquefaction for 2.5-3 hours in the first liquefaction column 219, the starch enters the second flash tank 220 for further flash cooling. Usually, some large starch particles are not completely converted after the first enzyme addition liquefaction. To ensure the liquefaction effect, this unit adopts a two-stage injection and two-stage enzyme addition process. The liquefying enzyme is added in a certain proportion through the secondary enzyme metering pump (223). The two-stage enzyme addition fully converts the large starch particles into dextrin, thereby improving the conversion rate of corn starch.

[0093] The bottom discharge from the second flash tank 220 is sent to the secondary liquefaction unit via the primary liquefaction discharge pump 221 and the primary liquefaction discharge pipe G06. A primary liquefaction discharge flow meter FT-221 is installed on the primary liquefaction discharge pipe G06. The frequency converter EV-221 of the primary liquefaction discharge pump 221 controls the liquid level LT-220 of the second flash tank 220. The frequency converter frequency of the secondary enzyme metering pump (223) and the flow rate of the secondary enzyme flow meter FT-223 are interlocked with those of the primary liquefaction discharge flow meter FT-221.

[0094] The secondary steam generated by the first flash tank 212 and the second flash tank 220 enters the hot side of the first plate heat exchanger 214 to exchange heat with the cold syrup on the cold side. After heating, the syrup is discharged into the hot syrup tank 217. The condensate discharged from the hot side of the first plate heat exchanger 214 enters the gas-liquid separator 215 for gas-liquid separation. The non-condensable gas is extracted and vented by the vacuum pump 216. The separated condensate is discharged from the bottom of the gas-liquid separator 215 and also enters the hot syrup tank 217 to mix with the syrup. The mixed hot syrup is extracted by the hot syrup pump 218 and sent out through the hot syrup pipe G04 for use in the corn flour slurry preparation at the front end. This can greatly improve the liquefaction effect and reduce steam consumption.

[0095] like Figure 3 As shown, in the secondary liquefaction unit: the outlet of the primary liquefaction discharge pipe G06 is connected to the inlet of the secondary ejector 301; the steam pipe G05 is connected to the steam inlet of the secondary ejector 301 through the steam regulating valve PC-301; the steam regulating valve PC-301 is interlocked with the pressure sensor PA-301 at the steam inlet of the secondary ejector 301; a temperature sensor TT-301 is installed at the outlet of the secondary ejector 301; and the opening of the ejector needle valve TC-301 of the secondary ejector 301 is interlocked with the temperature sensor TT-301.

[0096] The outlet of the secondary injector 301 is connected to the inlet of the second maintaining pipe 302, and the outlet of the second maintaining pipe 302 is connected to the middle inlet of the third flash tank 303. The top secondary steam outlet of the third flash tank 303 is equipped with a pressure sensor PA-303, and is connected to the hot side inlet of the first plate heat exchanger 214 through the secondary steam regulating valve PC-303 and the secondary steam pipe G08.

[0097] The bottom outlet of the third flash tank 303 is connected to the inlet of the secondary liquefaction feed pump 304. The frequency converter EV-304 of the secondary liquefaction feed pump 304 is interlocked with the level gauge LT-303 of the third flash tank 303. The outlet of the secondary liquefaction feed pump 304 is connected to the inlet of the secondary liquefaction column 305. The secondary liquefaction column 305 consists of at least two columns connected in series. The top outlet of the first liquefaction column is connected to the lower inlet of the next liquefaction column. The bottom inlet of each secondary liquefaction column 305 extends to the axis of the liquefaction column and then bends downward to form a bottom flushing device for flushing the bottom center.

[0098] The top outlet of the final stage of the secondary liquefaction column 305 is connected to the middle inlet of the fourth flash tank 306. The top of the fourth flash tank 306 is emptied, and the bottom outlet of the fourth flash tank 306 is connected to the inlet of the secondary liquefaction flash discharge pump 307. The frequency converter EV-307 of the secondary liquefaction flash discharge pump 307 is interlocked with the level gauge LT-306 of the fourth flash tank 306.

[0099] The outlet of the secondary liquefaction flash discharge pump 307 is connected to the hot side inlet of the condenser 308. The cold side inlet of the condenser 308 is connected to the outlet of the clean water pipe G09. The cold side outlet of the condenser 308 is connected to the hot water return pipe G10. The hot side outlet of the condenser 308 is connected to the inlet of the liquefied liquid buffer tank 309. The outlet of the liquefied liquid buffer tank 309 is connected to the inlets of the turbid liquid pump 310 and the horizontal screw feed pump 311, respectively. The outlet of the turbid liquid pump 310 is connected to the seed tank 501 of the fermentation unit through the syrup turbid liquid pipe G11.

[0100] The outlet of the horizontal screw feed pump 311 is connected to the inlet of the first-stage horizontal screw centrifuge 312 via a flow meter FT-311 and a regulating valve FC-311. The heavy phase outlet of the first-stage horizontal screw centrifuge 312 is connected to the inlet of the concentrated sugar buffer tank 316. The outlet of the concentrated sugar buffer tank 316 is connected to the inlet of the concentrated sugar transfer pump 317. The outlet of the concentrated sugar transfer pump 317 is connected to the fermenter 502 of the fermentation unit via a syrup clear liquid pipe G12.

[0101] The light phase outlet of the primary horizontal decanter centrifuge 312 is connected to the inlet of the sugar residue slurry tank 313. The inlet of the sugar residue slurry tank 313 is also connected to the clear water pipe G09. The outlet of the sugar residue slurry tank 313 is connected to the inlet of the slurry pump 314. The outlet of the slurry pump 314 is connected to the inlet of the secondary horizontal decanter centrifuge 315. The light phase outlet of the secondary horizontal decanter centrifuge 315 is connected to the cold side inlet of the first plate heat exchanger 214 via the cold sugar liquid pipe G07. The heavy phase outlet of the secondary horizontal decanter centrifuge 315 is connected to the tube bundle dryer 401 of the tube bundle drying unit via the sugar residue pipe G13.

[0102] The liquefied liquid from the primary liquefaction outlet pipe G06, after secondary enzyme addition, enters the secondary liquefaction injection system. In the secondary injector 301, the liquefied liquid is mixed with steam. At the same time, the outlet of the secondary injector 301 is equipped with a temperature sensor TT-301, which is interlocked with the injector needle valve TC-301 to control the secondary liquefaction temperature at 120~130℃, thereby achieving automatic control.

[0103] Meanwhile, the steam regulating valve PC-301 and pressure sensor PA-301 installed on the steam pipeline are interlocked. By controlling the opening of the steam regulating valve PC-301, the steam pressure of the secondary ejector 301 is controlled, maintaining the stable operation of the secondary ejector 301 and achieving precise control.

[0104] After spraying, the liquefied liquid enters the second holding tube 302 and is maintained for 3-5 minutes to allow the incompletely liquefied liquid and large starch particles from the first liquefaction to be fully converted into dextrin. Then, it enters the third flash tank 303 for flash evaporation and cooling. The pressure sensor PA-303 at the outlet of the third flash tank 303 is interlocked with the secondary steam regulating valve PC-303 on its secondary steam pipeline. By adjusting the opening of the secondary steam regulating valve PC-303, the vacuum degree of the third flash tank 303 is further maintained, thereby controlling the temperature of the liquefied liquid in the third flash tank 303.

[0105] The secondary steam generated by the first flash tank 212, the second flash tank 220, and the third flash tank 303 is recovered by the vacuum pump 216. The secondary steam generated by the third flash tank 303 is also sent to the hot side of the first plate heat exchanger 214 through the secondary steam pipe G08. The first plate heat exchanger 214 is used to exchange heat with the clear liquid sugar from the secondary horizontal screw centrifuge 315, heating the sugar into hot sugar water, which is then sent back to the front end through the hot sugar water pipe G04 to adjust the corn flour slurry.

[0106] The liquefied liquid after secondary injection liquefaction flash evaporation is discharged from the bottom of the third flash tank 303 and pumped into the secondary liquefaction column 305 for further liquefaction by the secondary liquefaction feed pump 304. The secondary liquefaction column 305 consists of two columns connected in series, and the bottom of each column is flushed to the center. The secondary liquefaction feed pump 304 controls the liquid level of the third flash tank 303 through the frequency converter EV-304.

[0107] The liquefaction time of the secondary liquefaction column 305 is controlled at 1.5~2 hours. The sugar solution after secondary liquefaction enters the fourth flash tank 306 for further flash cooling, and the temperature after flash cooling is 95~97℃. The cooled sugar solution is discharged from the bottom of the fourth flash tank 306 and pumped into the hot side of the condenser 308 for further cooling via the secondary liquefaction flash discharge pump 307. The secondary liquefaction flash discharge pump 307 controls the liquid level of the fourth flash tank 306 via the frequency converter EV-307. The sugar solution on the hot side of the condenser 308 is sent to the cold side of the condenser 308 for heat exchange and cooling via the clean water pipe G09. The cooled sugar solution enters the liquefaction buffer tank 309 for buffering and is used for subsequent fermentation and horizontal decanter separation.

[0108] The hot water heated by the cold side heat exchange of condenser 308 is sent to the condensate tank 412 of the downstream citric acid crude extraction washing unit through hot water return pipe G10, so as to realize the recovery and utilization of heat and hot water.

[0109] The sugar solution from the liquefied liquid buffer tank 309 is divided into two parts and sent to different units. One part is pumped into the seed tank of the fermentation unit through the turbid liquid pump 310 and the syrup turbid liquid pipe G11 as a fermentation substrate for fermentation. The other part is pumped into the first-stage horizontal screw centrifuge 312 through the horizontal screw feed pump 311 for separation. The outlet pipe of the horizontal screw feed pump 311 is equipped with a flow meter FT-311 and a regulating valve FC-311, which controls the feed flow of the first-stage horizontal screw centrifuge 312 through interlocking.

[0110] After the sugar solution enters the primary horizontal screw centrifuge 312, the protein and syrup are separated. Compared with separation using a plate and frame filter press, this greatly reduces labor intensity. The separated syrup is discharged from the light phase outlet of the primary horizontal screw centrifuge 312 into the concentrated sugar buffer tank 316, and then transported to the fermentation unit as a nutrient source for fermentation via the concentrated sugar transfer pump 317 and the syrup clear liquid pipe G12.

[0111] The separated protein residue is discharged from the heavy phase outlet of the primary horizontal screw centrifuge 312 and enters the sugar residue slurry tank 313. Since the protein residue still contains a small amount of diluted sugar solution, a certain proportion of clean water is added for slurry preparation, and then pumped through the residue pump 314 into the secondary horizontal screw centrifuge 315 for further separation of the diluted sugar solution. The clean water pipeline is equipped with a flow meter and regulating valve, and the water flow rate is controlled by an automatic interlock. After centrifugation in the secondary horizontal screw centrifuge 315, the resulting light phase, diluted sugar solution, is discharged through the cold diluted sugar solution pipe G07 and sent to the cold side of the first plate heat exchanger 214. After heat exchange, it is sent to the corn slurry preparation unit. The heavy phase from the secondary horizontal screw centrifuge 315 is sugar residue, which is sent out through the sugar residue pipe G13 and sent to the tube bundle drying unit for feed production.

[0112] Traditional laminar flow tanks employ a tank structure, resulting in prolonged and uneven material residence time within the tank. This leads to starch granules depositing at the bottom and forming an adhesive layer. This blockage not only hinders material circulation but also causes localized temperature and enzyme concentration imbalances, resulting in incomplete liquefaction. Furthermore, the heat energy generated during liquefaction flash evaporation is not fully utilized, leading to high steam consumption per unit of product. In addition, separating the liquefied sugar residue is challenging, requiring multiple plate and frame separators, resulting in high labor costs.

[0113] The traditional laminar flow tank was replaced with parallel laminar flow tubes, with multiple spiral grooves on the inner wall of each tube to enhance the flowability of the liquefied liquid and further improve the liquefaction effect. However, the large number of parallel laminar flow tubes and the tendency for material to accumulate on the spiral grooves, along with the tendency for incompletely gelatinized starch granules to combine with residues on the spiral grooves, form difficult-to-remove lumpy deposits. Over time, this can lead to severe blockages, extended production cycles, and reduced production efficiency. Furthermore, the heat energy generated during the liquefaction flash evaporation process is not fully utilized, resulting in high steam consumption per unit of product. In addition, the separation of the liquefied sugar residue is difficult, requiring multiple plate and frame separators, leading to high labor costs and extended production cycles.

[0114] This degermed corn pulp liquefaction and separation unit can improve the conversion rate of corn starch and avoid material blockage during the liquefaction process; improve heat energy utilization; reduce labor costs and shorten the production cycle; after conventional single-enzyme liquefaction, some large starch particles are still not completely converted. This unit adopts a two-stage injection and two-stage enzyme addition process, which can fully convert large starch particles into dextrin, significantly improving the conversion rate of corn starch and reducing raw material consumption; the secondary steam generated by flash liquefaction is heated into hot water for washing in the pulp conditioning and neutralization units, greatly improving heat energy utilization and reducing steam consumption; the liquefaction columns are multi-stage in series to ensure first-in-first-out; and a flushing device is installed at the bottom of each liquefaction column to reduce the precipitation of insoluble impurities at the bottom of the laminar flow tank and avoid material blockage; the filtration method of the liquefied liquid after liquefaction is changed from plate and frame filtration to continuous horizontal screw centrifuge separation, which greatly reduces labor intensity, reduces downtime for slag removal, and extends effective production time.

[0115] like Figure 4 As shown, in the citric acid concentration, evaporation, crystallization, and waste heat recovery unit of the present invention, the outlets of the sugar residue pipe G13 and the acid residue pipe G14 are both connected to the inlet of the feeding auger of the tube bundle dryer 401. The outlet of the tube bundle dryer 401 is connected to the inlet of the three-way valve 402. The first outlet of the three-way valve 402 is connected to the cooling and packaging equipment. The second outlet of the three-way valve 402 is connected to the lower inlet of the return auger 403. The upper outlet of the return auger 403 is also connected to the inlet of the feeding auger of the tube bundle dryer 401.

[0116] Steam pipe G05 is connected to the steam inlet of tube bundle dryer 401 via steam regulating valve and is interlocked with the pressure sensor of steam inlet.

[0117] The exhaust outlet of the tube bundle dryer 401 is connected to the inlet of the cyclone separator 404. A shut-off valve 405 is installed at the bottom of the cyclone separator 404, and the outlet of the shut-off valve 405 is connected to the middle inlet of the return auger 403. A steam tracing pipe is wound around the outer periphery of the cyclone separator 404. The steam tracing pipe and the condensate outlet of the tube bundle dryer 401 are connected to the middle inlet of the tube bundle condensate flash tank 411 via a steam trap. The bottom outlet of the tube bundle condensate flash tank 411 is connected to the condensate tank 412. The hot water from the outlet of the condenser 308 in the liquefaction unit is also connected to the condensate tank 412 via a hot water reuse pipe G10. The outlet of the condensate tank 412 is connected to the condensate supply pipe G15 via a pre-concentrated condensate pump 424.

[0118] The top exhaust port of the cyclone separator 404 is connected to the suction port of the waste heat blower 406. The outlet of the waste heat blower 406 is connected to the air inlet of the waste gas scrubbing tower 407. The bottom outlet of the waste gas scrubbing tower 407 is connected to the middle inlet of the primary flash tank 408 through a regulating valve. The bottom outlet of the primary flash tank 408 is connected to the middle inlet of the secondary flash tank 409. The bottom outlet of the secondary flash tank 409 is connected to the inlet of the scrubbing tower circulation pump 410. The outlet of the scrubbing tower circulation pump 410 is connected to the upper spray port of the waste gas scrubbing tower 407.

[0119] The pre-concentration falling film evaporation unit for citric acid includes a pre-concentration first-effect evaporator 413, a pre-concentration second-effect evaporator 415, and a pre-concentration third-effect evaporator 417. The lower part of the pre-concentration first-effect evaporator 413 is connected to a pre-concentration first-effect separator 414. The lower part of the pre-concentration second-effect evaporator 415 is connected to a pre-concentration second-effect separator 416. The lower part of the pre-concentration third-effect evaporator 417 is connected to a pre-concentration third-effect separator 418.

[0120] The top inlet of the pre-concentrated first-effect evaporator 413 is connected to the outlet of the citric acid liquid pipe G17 after separation. The bottom outlets of the pre-concentrated first-effect evaporator 413 and the pre-concentrated first-effect separator 414 are connected to the inlet of the pre-concentrated first-effect discharge pump 419. The outlet of the pre-concentrated first-effect discharge pump 419 is connected to the top inlet of the pre-concentrated second-effect evaporator 415. The bottom outlets of the pre-concentrated second-effect evaporator 415 and the pre-concentrated second-effect separator 416 are connected to the inlet of the pre-concentrated second-effect discharge pump 420. The pre-concentrated second-effect discharge pump 420 is connected to the top inlet of the pre-concentrated third-effect evaporator 417. The bottom outlets of the pre-concentrated third-effect evaporator 417 and the pre-concentrated third-effect separator 418 are connected to the inlet of the pre-concentrated third-effect discharge pump 421. The outlet of the pre-concentrated third-effect discharge pump 421 is connected to the citric acid pre-concentration tank 1601 through the citric acid pre-concentrated liquid output pipe G18.

[0121] The top outlet of the tube bundle condensate flash tank 411 is connected to the shell-side inlet of the pre-concentrating first-effect evaporator 413. The top outlets of the primary flash tank 408 and the pre-concentrating first-effect separator 414 are both connected to the shell-side inlet of the pre-concentrating second-effect evaporator 415. The top outlets of the secondary flash tank 409 and the pre-concentrating second-effect separator 416 are both connected to the shell-side inlet of the pre-concentrating third-effect evaporator 417. The shell-side inlet of the pre-concentrating third-effect evaporator 417 is also connected to the fine filtrate flash vapor tube G21 at the top outlet of the subsequent fine filtrate flash tank 704 and the dilute filtrate flash vapor tube G21. The top outlet of the sulfuric acid flash tank 710 is connected to the dilute sulfuric acid flash vapor pipe G22; the top outlet of the pre-concentrating triple-effect separator 418 is connected to the shell-side inlet of the pre-concentrating surface condenser 422; the shell-side exhaust port of the pre-concentrating surface condenser 422 is vented to the atmosphere through the pre-concentrating vacuum pump 423; the tube-side inlet of the pre-concentrating surface condenser 422 is connected to the circulating water supply pipe G19; the tube-side outlet of the pre-concentrating surface condenser 422 is connected to the circulating water return pipe G20; and the shell-side condensate outlet of the pre-concentrating surface condenser 422 is vented.

[0122] The sugar residue separated by the horizontal screw centrifuge is sent out through the sugar residue pipe G13, and the acid residue from the plate and frame filter press is sent out through the acid residue pipe G14. Together, they are fed into the tube bundle dryer 401 by a feeding auger for tube bundle drying. Steam is introduced into the tubes of the tube bundle dryer 401, and the steam exchanges heat with the material through the tubes, evaporating the moisture in the material as waste heat exhaust gas, which is then discharged. The tube bundle drying exhaust gas enters the cyclone separator 404 for "coarse purification". The steam in the tubes of the tube bundle dryer 401 is discharged as condensate after heat exchange. The sugar residue and acid residue dried by steam heat exchange are discharged from the tail of the tube bundle, and then distributed through the three-way valve 402. To balance the moisture content of the material inside the tube bundle dryer 401 and ensure the quality stability of the product, part of it needs to be returned to the feeding auger of the tube bundle dryer 401 through the return auger 403 to mix with the wet material and further dry; the other part of the citric acid residue is discharged as product and sent for cooling and packaging.

[0123] The tube bundle dryer 401 is equipped with a waste heat recovery system. Because the exhaust gas from the tube bundle dryer 401 contains many impurities, after "coarse purification" by the cyclone separator 404, the waste heat fan 406 extracts the high-temperature exhaust gas separated and purified by the cyclone separator 404 and transports it to the waste gas scrubbing tower 407 for further washing and purification. The dust separated in the cyclone separator 404 contains some material, which is discharged through the bottom airlock 405 into the return auger 403.

[0124] Steam is introduced into the steam tracing pipes around the cyclone separator 404 to prevent the separated dust from becoming damp and clumping inside the cyclone separator 404, which could block the discharge port. The condensate in the steam tracing pipes of the cyclone separator 404 and the condensate in the tube bundle dryer 401 are discharged through steam traps and enter the tube bundle condensate flash tank 411 for flash evaporation and cooling. The secondary steam after flash evaporation is recovered as a heat source for the pre-concentration first-effect evaporator 413. The condensate discharged from the tube bundle condensate flash tank 411 is temporarily stored in the condensate tank 412 and then sent to the subsequent coarse extraction unit as washing water to clean the filter cake through the pre-concentration condensate pump 424 and condensate supply pipe G15.

[0125] In the exhaust gas scrubbing tower 407, the high-temperature exhaust gas is scrubbed and heat-exchanged by sprayed water. The hot water after heat exchange enters the primary flash tank 408 for flash evaporation and then enters the secondary flash tank 409 for further flash evaporation and cooling. The scrubbing water discharged from the secondary flash tank 409 is pumped back into the spray nozzles of the exhaust gas scrubbing tower 407 by the scrubbing tower circulation pump 410 for continued scrubbing and heat exchange, achieving recycling. The secondary steam generated from the two flash evaporations enters the citric acid evaporator to evaporate and concentrate citric acid, thus turning the low-quality heat source into a valuable resource and reducing the system's steam consumption.

[0126] The working principle of the pre-concentration evaporation crystallization unit is as follows: To save steam and ensure product quality, the evaporation and crystallization of citric acid is divided into two parts. One part is to pre-concentrate the citric acid using waste heat, and the other part is to use live steam to further concentrate, evaporate, and crystallize the pre-concentrated citric acid solution through falling film evaporation.

[0127] Citric acid pre-concentration: using a multi-effect falling film evaporator.

[0128] After continuous ion exchange, impurity ions in the citric acid solution are completely removed. The solution is then pumped by citric acid pump 1527 and ion-exchange-exchange citric acid pipe G17 into the pre-concentration evaporation unit for concentration. First, the solution enters the distributor at the top of the pre-concentration single-effect evaporator 413. The distributor then evenly distributes the material to each heating tube, forming a uniform downward-flowing film along the inner wall of the tube. A heating medium is introduced through the outside of the heating tube, and heat is transferred through the tube wall to the liquid film inside the tube, causing the water in the liquid film to rapidly heat to its boiling point and evaporate. The resulting secondary steam flows downwards in parallel with the liquid film. During this process, the liquid film is continuously concentrated, and its concentration gradually increases. The concentrated liquid and secondary steam enter the pre-concentration first-effect separator 414 together to separate the secondary steam from the concentrated liquid. The generated secondary steam serves as the heat source for the pre-concentration second-effect evaporator 415. The first-effect concentrated liquid is then pumped into the pre-concentration second-effect evaporator 415 again via the pre-concentration first-effect discharge pump 419 for further falling film concentration. The concentrated liquid and secondary steam then enter the pre-concentration second-effect separator 416 together to separate the secondary steam from the concentrated liquid. The generated secondary steam serves as the heat source for the pre-concentration third-effect evaporator 417. The second-effect concentrated liquid is then pumped into the pre-concentration second-effect discharge pump 420 for further concentration. The concentrated liquid is fed into the pre-concentrating triple-effect evaporator 417. The concentrated liquid and secondary steam enter the pre-concentrating triple-effect separator 418 together to separate the secondary steam from the concentrated liquid. The triple-effect concentrated liquid is sent to the concentration and crystallization system through the pre-concentrating triple-effect discharge pump 421 and the citric acid pre-concentrated liquid output pipe G18. The non-condensable gas generated is quickly separated from the material in the vacuum environment created by the pre-concentrating vacuum pump 423 and enters the hot side of the pre-concentrating surface condenser 422. It is condensed into condensate by the circulating cooling water on the cold side and discharged into the condensate tank 412 through the condensate return pipe G16.

[0129] To reduce steam consumption and increase waste heat recovery, the secondary steam generated from flashing in the primary flash tank 408 of the tube bundle dryer tail gas scrubbing and absorption unit is used as the heat source for the pre-concentrating double-effect evaporator 415, and the secondary steam generated from flashing in the secondary flash tank 409 is used as the heat source for the pre-concentrating triple-effect evaporator 417. The secondary steam generated from the flashing of the condensate discharged from the tube bundle dryer 401 in the tube bundle condensate flash tank 411 is used as the heat source for the pre-concentrating primary-effect evaporator 413.

[0130] The secondary vapor generated from flash deoxygenation before chromatographic separation in the downstream process is also used as a heat source for the pre-concentration triple-effect evaporator 417 via flash vapor tube G21 for fine filtrate and flash vapor tube G22 for dilute sulfuric acid.

[0131] The secondary steam generated above has stable heat transfer efficiency and temperature control, which can directly ensure concentration efficiency and product quality. This transforms a low-quality heat source into a valuable resource, reducing the system's steam consumption. Since waste heat is used for evaporation, the resulting condensate contains a small amount of impurities; therefore, this condensate is either discharged externally or collected in condensate tank 412.

[0132] like Figure 17 As shown, in the citric acid concentration, evaporation and crystallization unit of the present invention: the outlet of the pre-concentration triple-effect discharge pump 421 is connected to the inlet of the citric acid pre-concentration tank 1601 through the citric acid pre-concentrated liquid output pipe G18; the outlet of the citric acid pre-concentration tank 1601 is connected to the inlet of the citric acid pre-concentration feed pump 1602; and the outlet of the citric acid pre-concentration feed pump 1602 is connected to the top feed port of the single-effect falling film evaporator 1603.

[0133] Steam pipe G05 is connected to the inlet of steam jet pump 1600 via a regulating valve. The outlet of steam jet pump 1600 is connected to the shell-side inlet of first-effect falling film evaporator 1603. The lower part of first-effect falling film evaporator 1603 is connected to first-effect separator 1604. The bottom outlets of first-effect falling film evaporator 1603 and first-effect separator 1604 are connected to the inlet of first-effect discharge pump 1605. The outlet of first-effect discharge pump 1605 is connected to the top feed port of second-effect falling film evaporator 1606.

[0134] The top outlet of the first-effect separator 1604 is connected to the suction port of the steam jet pump 1600 and the shell-side inlet of the second-effect falling film evaporator 1606. The lower part of the second-effect falling film evaporator 1606 is connected to the second-effect separator 1607. The bottom outlets of the second-effect falling film evaporator 1606 and the second-effect separator 1607 are connected to the inlet of the second-effect discharge pump 1608. The outlet of the second-effect discharge pump 1608 is connected to the feed port of the crystallizer 1610. The bottom outlet of the crystallizer 1610 is connected to the inlet of the forced circulation pump 1611. The outlet of the forced circulation pump 1611 is connected to the lower tube-side inlet of the forced evaporator 1609. The upper tube-side outlet of the forced evaporator 1609 is connected to the circulating liquid inlet of the crystallizer 1610. The top outlet of the second-effect separator 1607 is connected to the shell-side inlet of the forced evaporator 1609.

[0135] The top outlet of the crystallizer 1610 is equipped with a crystallizer discharge density sensor DT-1610 and is also connected to the inlet of the citric acid slurry discharge pump 1612. The outlet of the citric acid slurry discharge pump 1612 is connected to the feed distribution tank 1701 of the citric acid drying unit through the citric acid slurry output pipe G23.

[0136] The top outlet of the crystallizer 1610 is connected to the shell-side air inlet of the surface condenser 1613. The shell-side exhaust port of the surface condenser 1613 is vented to the atmosphere through the vacuum pump 1614. The tube side of the surface condenser 1613 is connected to the circulating cooling water. The shell-side condensate outlet of the surface condenser 1613 is connected to the condensate tank 412 through the condensate return pipe G16.

[0137] The working principle of the citric acid falling film concentration evaporation and crystallization unit is as follows: To reduce steam consumption and improve product purity and crystallinity, citric acid falling film concentration evaporation and crystallization adopts multi-effect falling film evaporation + single-effect evaporation crystallization.

[0138] After pre-concentration, citric acid is pumped into the citric acid pre-concentration tank 1601 via the pre-concentration triple-effect discharge pump 421 and the citric acid pre-concentrated liquid output pipe G18. Then, it is fed into the distributor at the top of the single-effect falling film evaporator 1603 by the citric acid pre-concentration feed pump 1602. The distributor then evenly distributes the material to each heating tube, allowing it to flow downwards uniformly to form a thin film. A heating medium is introduced through the outside of the heating tubes, and heat is transferred through the tube walls to the liquid film inside the tubes, causing the water in the liquid film to rapidly heat to its boiling point and evaporate. The resulting secondary steam flows downwards in parallel with the liquid film. During this process, the liquid film is continuously concentrated, and its concentration gradually increases. The concentrated liquid and secondary steam enter the first-effect separator 1604 together to separate the secondary steam from the concentrated liquid. The generated secondary steam serves as the heat source for the second-effect falling film evaporator 1606. The first-effect concentrated liquid is then pumped into the second-effect falling film evaporator 1606 for further falling film concentration via the first-effect discharge pump 1605. The concentrated liquid and secondary steam then enter the second-effect separator 1607 together to separate the secondary steam from the concentrated liquid. The generated secondary steam serves as the heat source for the forced evaporator 1609. At this point, the concentrated liquid is concentrated to near saturation and is then pumped into the crystallizer 1610 via the second-effect discharge pump 1608 to begin evaporation and crystallization.

[0139] The nearly saturated citric acid concentrate enters the crystallizer 1610 for evaporation and crystallization. Then, it is pumped into the forced evaporator 1609 by the forced circulation pump 1611. The material is fed from the bottom and discharged from the top, ensuring full contact with the heat source outside the heating tube. It is concentrated to a saturated state. The liquid and secondary steam enter the crystallizer 1610 together. Under the vacuum created by the vacuum pump 1614, the saturated citric acid solution is further evaporated, becoming a supersaturated solution. Crystals precipitate out, and the secondary steam is separated from the citric acid solution containing crystals. The secondary steam enters the surface condenser 1613, where it is condensed into condensate by circulating water and discharged into the condensate tank 412.

[0140] When the material from crystallizer 1610 reaches a certain density as detected by density sensor DT-1610, it is pumped to the citric acid drying unit by citric acid slurry discharge pump 1612. A portion of it is then pumped into forced evaporator 1609 by forced circulation pump 1611 to mix with new material and continue evaporation and crystallization.

[0141] The heat source for falling film concentration evaporation and crystallization is live steam. To reduce steam consumption, a steam jet pump 1600 is used to recover the secondary steam from the first-effect separator 1604. A small amount of high-pressure saturated steam at 0.6 MPa is used as power to draw in and mix the low-pressure secondary steam from the first-effect separator 1604 within the steam jet pump 1600. The pressure of the mixed steam is then increased to the required process pressure through a diffuser and injected into the shell of the first-effect falling film evaporator 1603 as its heat source.

[0142] After heat exchange with the material in the first-effect falling film evaporator 1603, part of the secondary steam generated by the first-effect separator 1604 is drawn into the steam jet pump 1600, while the other part enters the shell of the second-effect falling film evaporator 1606 as a heat source for the second-effect falling film evaporator 1606. Then, the secondary steam generated by the second-effect separator 1607 is used as a heat source for the forced evaporator 1609 for evaporation and crystallization. The secondary steam generated by the crystallizer 1610 exchanges heat with the circulating water in the surface condenser 1613 and condenses into condensate water, which is discharged into the condensate tank 412 through the condensate water return pipe G16 for subsequent calcium salt purification and filter cake washing.

[0143] To conserve steam consumption and ensure product quality, the steam source for citric acid evaporation and crystallization in this unit is divided into two parts: one part utilizes the waste heat generated from the deoxygenation process before tube drying and chromatographic separation, which is then used to pre-concentrate the citric acid; the other part uses live steam for falling film concentration evaporation and crystallization of the pre-concentrated citric acid solution. The two steam sources are used in combination: live steam ensures stable operation of critical processes, while waste heat steam covers the energy needs of auxiliary processes. This approach effectively balances cost and efficiency, controlling production costs while meeting process stability requirements.

[0144] Citric acid evaporation and crystallization account for 40% to 50% of the total energy consumption in citric acid production, with steam consumption being particularly prominent. The heat utilization rate of single-effect crystallization is less than 30%. This unit combines waste heat pre-concentration with live steam falling film evaporation and crystallization, which can reduce steam consumption, enhance waste heat recovery, and increase the heat utilization rate to over 60%. Steam consumption per ton of product is reduced by 0.5 to 1.2 tons; crystallization efficiency and product purity are improved, and the production cycle is shortened. The condensate generated from the evaporation and crystallization is used for washing and filtration in the calcium salt process vacuum belt filter, achieving condensate recovery and utilization.

[0145] like Figure 5As shown, the fermentation unit in this invention includes a seed tank 501 and a fermentation tank 502. The outlet of the turbid liquid pump 310 in the corn syrup secondary liquefaction unit is connected to the top material inlet of the seed tank 501 via a syrup turbid liquid pipe G11, a turbid liquid feed flow meter, a turbid liquid feed regulating valve, and a turbid liquid feed switch valve. The top exhaust port of the seed tank 501 is connected to the top exhaust pipe G24 via an exhaust regulating valve. The compressed air pipe G25 is connected to the top air inlet of the seed tank 501 via a compressed air regulating valve. The defoamer pipe G26 is connected to the top defoamer inlet of the seed tank 501 via a defoamer feed switch valve. The steam pipe G05 is connected to the top inlet and bottom outlet of the seed tank 501 via steam regulating valves. The steam regulating valves are controlled by the pressure sensor of the seed tank 501.

[0146] The bottom outlet of seed tank 501 is connected to the top inlet of fermentation tank 502 via a seed transfer switch valve and seed transfer pipeline G27. The outlet of concentrated sugar transfer pump 317 is connected to the top material inlet of fermentation tank 502 via syrup clear liquid pipe G12, clear liquid feed flow meter, clear liquid feed regulating valve, and clear liquid feed switch valve. The outlet of syrup turbid liquid pipe G11 is connected to the top material inlet of fermentation tank 502 via turbid liquid feed flow meter, turbid liquid feed regulating valve, and turbid liquid feed switch valve. At the same time, the outlet of the pre-concentration condensate pump 424 is connected to the inlet of the turbid liquid feed switch valve via condensate supply pipe G15. The fermentation tank 502 is connected to the top exhaust port via an exhaust regulating valve to the top exhaust pipeline G24. The compressed air pipeline G25 is connected to the top air inlet of the fermentation tank 502 via a compressed air regulating valve. The defoamer pipeline G26 is connected to the top defoamer inlet of the fermentation tank 502 via a defoamer feed switch valve. The steam pipeline G05 is connected to the top inlet and bottom outlet of the fermentation tank 502 via steam regulating valves, which are controlled by the pressure sensor of the fermentation tank 502. The bottom outlet of the fermentation tank 502 is connected to the fermentation liquid storage tank of the fine filtration unit via a citric acid output pipeline G28.

[0147] The jacket inlets of seed tank 501 and fermentation tank 502 are connected to the circulating water supply pipe G19, and the jacket outlets of seed tank 501 and fermentation tank 502 are connected to the circulating water return pipe G20.

[0148] The fermentation unit first needs to be inoculated with strains from laboratory culture. The strains are inoculated into seed tank 501 using the flame inoculation method to expand the culture. The purpose of seed tank 501 is to cultivate the bacteria, to cultivate a sufficient number of vigorous and stable mycelia for large-scale fermentation. After fermenting in seed tank 501 for a certain period of time, the strains are then transferred to fermentation tank 502 to produce citric acid.

[0149] In the seed culture stage of citric acid fermentation, the substrate introduced into the seed tank 501 is unfiltered liquefied liquid from the turbid liquid pump 310 and the syrup turbid liquid pipe G11. The syrup turbid liquid is a key nutrient for the growth of seed strains, providing a nutrient substrate for the growth and reproduction of Aspergillus niger seeds. It is nutritionally complete, cost-effective, and far superior to filtered liquefied liquid.

[0150] On the one hand, the syrup contains carbon sources, including dextrin, maltose, and a small amount of glucose. These substances can be directly absorbed and utilized by Aspergillus niger, rapidly converted into energy and precursors for cell synthesis, significantly shortening the seed cell lag period and accelerating cell proliferation. On the other hand, it retains natural nitrogen sources and trace elements, mainly including protein degradation products from the corn raw material itself, such as small molecule peptides, amino acids, vitamins, and minerals. These substances are essential raw materials for Aspergillus niger to synthesize enzyme systems, cell membranes, and nucleic acids, significantly enhancing the activity and stress resistance of the seed cells, enabling them to tolerate the high sugar and high acid environment of the subsequent fermentation tank.

[0151] Incubator 502 is introduced with microbial inoculum and substrate. The inoculum is derived from the seed culture expanded in seed tank 501, providing the fermenter with sufficient, highly active, and stable acid-producing microorganisms. The substrate in the fermenter, including turbid and clear syrup, provides a carbon source for fermentation. After adding hot water from the pre-concentration condensate pump 424 via condensate supply pipe G15 to adjust the slurry, the sugar content of the fermentation substrate is stabilized at 15-18%, providing an optimal environment for microbial growth and acid production. Excessive sugar content will inhibit microbial growth due to high osmotic pressure, while insufficient sugar content will lead to inadequate acid production. Under stable conditions in the fermenter, the microorganisms begin to produce acid, converting the carbon source in the turbid and clear syrup into citric acid.

[0152] Citric acid is susceptible to microbial contamination during fermentation. Therefore, both the fermenter and the substrate need to be sterilized by steam before fermentation to ensure the purity of the fermented product.

[0153] The entire fermentation process is fully automated, with valves and instruments in each step controlled in an interlocking manner. It operates using a one-button start method to prevent human error from causing citric acid contamination.

[0154] I. Seed Tank Fermentation The seed tank fermentation process consists of the following steps: air sterilization—feeding—actual sterilization—cooling and oxygenation—inoculation—fermentation—transferring, as detailed below: 1. Empty space elimination: Before feeding, the seed tank 501 and its inlet and outlet pipelines must be sterilized. Before introducing steam, the relevant automatic control valves need to be opened to ensure that the seed tank and corresponding pipelines are thoroughly sterilized. First, open the vent regulating valve and its built-in small vent valve on the vent pipeline G24 at the top of the tank. Then, open the small vent valve on the turbid liquid feed valve on the syrup turbid liquid pipeline G11. During air sterilization, the turbid liquid feed valve should not be opened; only the outlet end of the turbid liquid feed valve and the corresponding pipeline should be sterilized. Then, open the small vent valve on the defoamer feed valve on the defoamer pipeline G26. During air sterilization, the defoamer feed valve should not be opened.

[0155] After opening the corresponding valves on the top of the tank, open the discharge valve and the small exhaust valve on the bottom of the tank, as well as the small exhaust valve on the seed discharge valve, and sterilize the pipeline in front of the seed discharge valve; then open the valve of the sampling port and sterilize the sampling pipeline during the sterilization process.

[0156] Finally, open the steam regulating valve and introduce steam from the bottom of the tank to sterilize all corners of the seed tank 501. The steam regulating valve is interlocked with the temperature sensor TT-501 on the seed tank 501. When the temperature of the seed tank 501 reaches 120~125℃, maintain it for 30 minutes to complete the sterilization. Then close the corresponding valves on the top and bottom of the tank and prepare for feeding.

[0157] 2. Feeding: After the seed tank 501 has been sterilized, there is no need to cool it down. Instead, syrup from the syrup turbid liquid pipe G11 is directly introduced. The feed switch valve, feed regulating valve and flow meter are opened. The substrate in the seed tank 501 is only syrup turbid liquid. When the liquid reaches the set flow rate, it means that the feeding of the seed tank is complete and it is ready for actual sterilization of the substrate.

[0158] 3. Actual consumption: After feeding is complete, close the feed valve and begin steam sterilization of the substrate. Before introducing steam, open the small exhaust valve to sterilize the feed line. After opening the corresponding valve, open the steam regulating valve on the top of the tank to introduce steam. This regulating valve is interlocked with the temperature sensor TT-501 in the seed tank. When the sterilization temperature reaches 120~125℃, maintain this temperature for 30 minutes, then close the steam regulating valve and the small exhaust valve. Sterilization is then complete.

[0159] 4. Cooling and oxygenation: After sterilization, cooling begins. First, the regulating valve on compressed air pipe G25 is opened to introduce sterile air into seed tank 501, ensuring adequate oxygenation. Then, the regulating valve on circulating water supply pipe G19 is opened to introduce circulating water into the jacket of seed tank 501 for cooling. The regulating valve is interlocked with the temperature sensor TT-501 of seed tank 501. After cooling to 37°C, inoculation begins.

[0160] 5. Vaccination: After the substrate is sterilized and cooled, inoculation begins. The laboratory-cultured strain is inoculated into the seed tank using the flame inoculation method to begin the large-scale culture of the strain.

[0161] 6. Fermentation: After inoculation, the microbial strain begins to multiply and grow within seed tank 501. Since citric acid fermentation is aerobic, compressed air is supplied to the seed tank via compressed air pipe G25. The venting regulating valve is interlocked with the pressure sensor on the top of the seed tank to maintain a pressure of 0.1 MPa, ensuring adequate dissolved oxygen levels. During fermentation, the microbial growth releases heat and produces a large amount of foam. Therefore, circulating water is supplied to the jacket via circulating water supply pipe G19 and then flows out via circulating water return pipe G20, maintaining the fermentation temperature in the seed tank at 37°C. Seed tank 501 is equipped with a defoaming sensor XP-501, which is interlocked with the defoaming agent feed valve on defoaming agent line G26. When the foam reaches a certain height, the defoaming agent feed valve automatically opens, adding defoaming agent. After approximately 35 hours of fermentation, the pH value in the seed tank is monitored online using the pH sensor PH-501, and a sample is taken to measure the citric acid level. Fermentation is stopped when the acidity reaches 3%.

[0162] 7. Transplanting: After the seed liquid is fermented and expanded in seed tank 501, it is compressed into fermentation tank 502 by compressed air to start the next step of fermentation.

[0163] II. Fermentation in Fermentation Tanks The fermentation process in a fermenter consists of the following steps: sterilization—feeding and volume adjustment—actual sterilization—cooling and oxygenation—enzyme addition and inoculation—fermentation, as detailed below: 1. Empty space elimination: Before feeding, the fermenter 502 and the inlet and outlet pipelines must be sterilized. Before steam is introduced, the relevant automatic control valves need to be opened to ensure that the fermenter 502 and the corresponding pipelines are thoroughly sterilized. First, open the vent regulating valve and its small vent valve on the vent pipeline G24 at the top of the tank. Then, open the small vent valves on the feed valves of the syrup turbid liquid pipeline G11 and the syrup clear liquid pipeline G12. During air sterilization, the two feed valves are not open; only the outlet end of the valves and the corresponding pipelines are sterilized. Next, open the small vent valve on the feed valve of the defoamer pipeline G26. During air sterilization, the defoamer feed valve is not open. Finally, open the transfer valve on the transfer pipeline G27.

[0164] After opening the corresponding valves on the top of the tank, open the discharge valve and the small exhaust valve on the bottom of the tank. Sterilize the pipeline in front of the discharge valve of the fermentation liquid. Then open the valve of the sampling port and sterilize the sampling pipeline during the sterilization process.

[0165] Finally, open the steam regulating valve and introduce steam from the bottom of the tank to sterilize all corners of the fermenter 502. The steam regulating valve is interlocked with the temperature sensor TT-502 on the fermenter 502. When the temperature of the fermenter 502 reaches 120~125℃, maintain it for 30 minutes to complete the sterilization. Then close the corresponding valves on the top and bottom of the tank and prepare for feeding.

[0166] 2. Feeding and volume determination: The substrate nutrient source in fermenter 502 is turbid syrup and clear syrup. After the sterilization of fermenter 502 is completed, the feed switch valve and feed regulating valve on the clear syrup pipe G12 are opened to introduce clear syrup; then the feed switch valve and feed regulating valve on the turbid syrup pipe G11 are opened to introduce turbid syrup; the substrate in seed tank 501 is only turbid syrup. When the liquid reaches the set flow rate, it indicates that the feeding of the fermenter is complete. Then water is added to make up the volume, and after making up the volume, the actual sterilization of the substrate begins.

[0167] 3. Actual consumption: After the feed volume is reached, close the feed valves on the turbid syrup pipe G11 and the clear syrup pipe G12, and begin steam sterilization of the substrate. Before introducing steam, open the small vent valve on the feed line to sterilize the feed line. After opening the corresponding valves, open the steam regulating valve on the top of the tank to introduce steam. This regulating valve is interlocked with the temperature sensor TT-502 of the fermenter. When the sterilization temperature reaches 120~125℃, maintain this temperature for 30 minutes, then close the steam regulating valve and the small vent valve. Sterilization is then complete.

[0168] 4. Cooling and oxygenation: After sterilization, cooling begins, and sterile compressed air is introduced to ensure adequate oxygenation within fermenter 502. First, the regulating valve on compressed air pipe G25 is opened to introduce sterile air into fermenter 502. Then, the regulating valve on circulating water supply pipe G19 is opened to introduce circulating water into the jacket of fermenter 502 for cooling. The circulating water regulating valve is interlocked with the temperature sensor TT-502 of fermenter 502. After cooling to 65°C, enzyme inoculation begins.

[0169] 5. Enzyme-added transfer: To improve the utilization rate of the fermentation substrate, saccharifying enzyme needs to be added before fermentation to promote the efficient synthesis of citric acid during fermentation. When the temperature of fermenter 502 drops to about 65℃, saccharifying enzyme is added to the fermenter, with the amount of saccharifying enzyme being 17-20% of the substrate. At this temperature, saccharification is carried out for about 1 hour. When the DE value is above 80, the higher the DE value, the better, indicating that saccharification is complete. Then, the temperature is further reduced to 37℃, and the seeds are transferred from seed tank 501.

[0170] Transplanting is a crucial step connecting seed culture and primary fermentation. Essentially, it involves transferring the "adapted-to-grow" microbial cells to an "acid-producing" environment, enabling the cells to quickly switch to an acid-producing metabolic mode after completing a certain growth phase, thus improving citric acid conversion. A batch of fermented seed culture is completely transplanted into fermenter 502, and fermentation begins after transplanting.

[0171] 6. Fermentation: After transplanting, a sufficient quantity of viable and metabolically stable production strains begins large-scale fermentation using the substrate in the fermenter. Since citric acid fermentation is aerobic, compressed air needs to be circulated in the seed tank. The venting valve is interlocked with the pressure sensor at the top of fermenter 502 to maintain a pressure of 0.05~0.07 MPa in fermenter 502, ensuring adequate dissolved oxygen levels. During fermentation, strain growth and product synthesis release heat and produce a large amount of foam; therefore, circulating water is needed to maintain the fermentation temperature at 37℃. Fermenter 502 is equipped with an XP-502 defoaming sensor, interlocked with the defoamer feed valve. When the foam reaches a certain height, the defoamer feed valve automatically opens, adding defoamer. After approximately 72 hours of fermentation, a sample is taken to test the reducing sugar content. Once the content falls below approximately 1%, fermentation is stopped, and the product is discharged through citric acid output pipe G28 to the fine filtration unit for sterilization and filtration.

[0172] like Figure 6 As shown, in the fine filtration unit of the present invention: the outlet of the citric acid output pipe G28 is connected to the inlet of the fermentation broth storage tank 601; the outlet of the fermentation broth storage tank 601 is connected to the inlet of the fermentation broth discharge pump 602; the outlet of the fermentation broth discharge pump 602 is connected to the inlet of the first-stage plate and frame filter press 603; the slag outlet of the first-stage plate and frame filter press 603 is connected to the inlet of the acid slag conditioning tank 604; the outlet of the condensate supply pipe G15 is also connected to the inlet of the acid slag conditioning tank 604 through a regulating valve; the outlet of the acid slag conditioning tank 604 is connected to the inlet of the acid slag slurry pump 605; the outlet of the acid slag slurry pump 605 is connected to the inlet of the second-stage plate and frame filter press 606; the slag outlet of the second-stage plate and frame filter press 606 is connected to the feed inlet of the tube bundle dryer through the acid slag pipe G14; and the filtrate outlet of the second-stage plate and frame filter press 606 is connected to the mixed acid tank 901 of the primary neutralization unit through the dilute citric acid clear liquid pipe G29.

[0173] The filtrate outlet of the primary plate and frame filter press 603 is connected to the inlet of the primary concentrated acid tank 607. The outlet of the primary concentrated acid tank 607 is connected to the inlet of the primary concentrated acid pump 608. The outlet of the primary concentrated acid pump 608 is connected to the inlet pipe of the membrane filtration circulation pump 609. The outlet of the membrane filtration circulation pump 609 is connected to the inlet of the ceramic membrane filtration system 610. The concentrate outlet of the ceramic membrane filtration system 610 is connected to the inlet pipe of the membrane filtration circulation pump 609 and the reflux port of the fermentation broth storage tank 601.

[0174] The filtrate outlet of the ceramic membrane filtration system 610 is connected to the inlet of the citric acid concentration tank 611. The outlet of the citric acid concentration tank 611 is connected to the inlet of the citric acid concentration pump 612. The outlet of the citric acid concentration pump 612 is connected to the inlet of the cation exchange column 613. The outlet of the cation exchange column 613 is connected to the inlet of the anion exchange column 614. The outlet of the anion exchange column 614 is connected to the inlet of the citric acid ion exchange buffer tank 615. The outlet of the citric acid ion exchange buffer tank 615 is connected to the inlet of the citric acid ion exchange discharge pump 616. The outlet of the citric acid ion exchange discharge pump 616 is connected to the fine filtrate buffer tank 701 through the citric acid fine filtrate pipe G30.

[0175] After citric acid fermentation is completed, the fermentation broth contains not only the target product citric acid, but also some microbial mycelia such as Aspergillus niger mycelia and spores, incompletely degraded corn residue, and metabolic byproducts generated during fermentation. Filtration is required to achieve the first step of purification from fermentation broth to product.

[0176] After fermentation in fermenter 502, the fermentation broth is temporarily stored in fermentation broth storage tank 601 via citric acid output pipe G28. It is then pumped into primary plate and frame filter press 603 for filtration via fermentation broth discharge pump 602. The clarified liquid after primary filtration enters primary concentrated acid tank 607, ready for subsequent ceramic membrane filtration. The filter residue after primary filtration enters acid residue slurry preparation tank 604 for further water addition and preparation, which can be done using hot water from upstream condensate supply pipe G15. Since the filter residue after primary filtration contains a small amount of citric acid, the prepared slurry is further pumped into secondary plate and frame filter press 606 via acid residue slurry pump 605 for further filtration. The clarified liquid and dilute citric acid produced after secondary filtration go to the primary neutralization unit via dilute citric acid clarified liquid pipe G29. The acid residue after secondary filtration goes to tube bundle dryer for drying via acid residue pipe G14, and is then sold as feed.

[0177] The concentrated acid, after pre-filtration by the primary plate and frame filter press 603, is temporarily stored in the concentrated acid tank 607. It is then pumped into the ceramic membrane filtration system 610 by the concentrated acid pump 608. Before entering the ceramic membrane filtration system, the membrane filtration circulation pump 609 needs to be started to increase the pressure and circulate. During the circulation process, small molecule citric acid solution permeates through the membrane pores to become permeate, i.e., citric acid clear liquid, which enters the concentrated acid tank 611 and then enters the subsequent purification process. Impurities such as bacteria and colloids are retained and form a concentrated liquid at the membrane module outlet, which flows back to the fermentation broth storage tank 601. After mixing with the new fermentation broth, it is filtered and circulated again.

[0178] The 610 ceramic membrane filtration system uses a ceramic membrane with an inner pore size of 3mm and a filtration accuracy of 50nm for fine filtration. Compared with the traditional ceramic membrane core with a pore size of 4mm and a filtration accuracy of 50nm, it can greatly reduce power consumption.

[0179] Plate and frame filter presses can directly separate substances through the mechanical interception of filter cloth, and are not easily rendered ineffective by fluctuations in the concentration of impurities in the feed in the short term. However, with the expansion of production scale and the increasing requirements for product quality, the shortcomings of plate and frame filter presses have gradually become apparent. Their filtration accuracy is relatively low, failing to effectively retain fine ash particles, oil emulsion particles in the germ, and some soluble colloids, resulting in low purity of the filtrate. Subsequent processes require additional treatment of these impurities, thus affecting the quality of the final product.

[0180] Meanwhile, fibers and germ tend to entangle and accumulate on the filter cloth of the plate and frame filter, quickly clogging the pores and causing a sharp increase in filtration resistance. This significantly shortens the operating cycle of the plate and frame filter, requiring frequent shutdowns for cleaning or replacement of the filter cloth, severely impacting production continuity and efficiency. Furthermore, the filter cake contains a large amount of residual citric acid, resulting in incomplete separation of impurities from effective components, leading to significant material loss and low raw material utilization. Combined with the increased consumable costs from frequent filter cloth replacements, as well as the rising costs of continuous energy consumption and manual cleaning, the overall operating cost is high.

[0181] This unit employs a combination of plate and frame pre-filtration and ceramic membrane fine filtration. Although the solid impurities are removed after plate and frame pre-filtration and ceramic membrane fine filtration of the fermentation broth, a large number of soluble impurity ions are still present, mainly including: cations: metal ions such as calcium, magnesium, iron, potassium, and sodium brought in by the raw materials; and anions: inorganic salt ions that are not fully utilized, such as sulfate and phosphate ions. These impurity ions will significantly interfere with and damage subsequent chromatographic separation. Therefore, before chromatographic separation, it is necessary to remove the residual impurity ions in the citric acid solution through ion exchange to create more suitable conditions for subsequent chromatographic separation, thereby improving separation efficiency and product purity.

[0182] The citric acid solution filtered through a ceramic membrane enters the citric acid concentration tank 611, and is then pumped into the cation exchange column 613 via the citric acid concentration pump 612 to remove cations such as calcium, magnesium, iron, potassium, and sodium. The citric acid solution after cation removal then enters the anion exchange column 614 to further remove anions. The ion-exchange citric acid solution enters the citric acid ion exchange buffer tank 615, and is then pumped into the subsequent chromatographic separation unit via the citric acid ion exchange discharge pump 616.

[0183] The improved system employs pre-degerming of corn flour, removing fiber and ash before fermentation. Furthermore, the degerming process removes oils and proteins from the germ, reducing complex impurities in the fermentation broth that can lead to product purity degradation. After fermentation, the resulting citric acid solution is pre-filtered using a plate and frame filter to remove a large amount of insoluble material, reducing the impurity load entering the ceramic membrane. The citric acid mixture, after removing insoluble materials, is then finely filtered through the ceramic membrane, reducing the impurity content to below 0.1%. This combined filtration method enhances product quality stability, provides high-quality raw materials for subsequent purification processes, significantly improves production efficiency, effectively reduces production costs, and achieves green and environmentally friendly production.

[0184] This unit ensures precise consistency of fermentation conditions across different batches, guaranteeing product quality stability. Through a fully automated control system, it monitors and automatically adjusts key parameters such as temperature, pH, dissolved oxygen, and pressure during the fermentation process in real time, avoiding fluctuations caused by manual operation. This ensures consistency of citric acid fermentation conditions for each batch, significantly reducing product quality differences caused by human factors and improving citric acid yield and purity.

[0185] Traditional manual operation accounts for 15%-20% of the cost of citric acid production and is prone to problems such as contamination and fermentation failure due to operational errors. This unit achieves fully automated control of the fermentation process, reducing manual intervention and labor costs, while effectively avoiding the risk of contamination and production accidents caused by human error, thus improving production safety and stability.

[0186] Through the coordinated control of sensors and automated valves, real-time monitoring and data recording of the fermentation process are achieved, facilitating the traceability and analysis of production data. This provides data support for process optimization and promotes the digitalization and intelligentization of citric acid fermentation. The automated system can stably operate large-scale fermentation production, overcoming the efficiency bottleneck of manual operation, meeting the capacity demands brought about by order growth, helping enterprises reduce costs and increase efficiency, and enhancing market competitiveness. The fully automated sterilization (both air and physical sterilization) and aseptic operation design avoids the contamination risks associated with manual operation, ensuring the sterility of the fermentation environment and significantly improving the purity and safety of citric acid products.

[0187] Optimize seed culture and fermentation processes to improve fermentation efficiency. The seed tank uses a syrup turbidity as a substrate, retaining natural nitrogen sources and trace elements, significantly enhancing seed cell activity and stress resistance. The fermentation tank ensures efficient acid production under optimal conditions through precise temperature and oxygen control, automated enzyme addition, and inoculation, shortening the fermentation cycle and increasing citric acid conversion rate.

[0188] like Figure 7 , Figure 8 As shown, in the chromatographic separation unit of the present invention, the outlet of the citric acid filtrate pipe G30 is connected to the inlet of the filtrate buffer tank 701, the outlet of the filtrate buffer tank 701 is connected to the inlet of the filtrate pump 702, the outlet of the filtrate pump 702 is connected to the cold side inlet of the second plate heat exchanger 703, the steam pipe G05 is connected to the hot side inlet of the second plate heat exchanger 703 through a steam regulating valve, the hot side outlet of the second plate heat exchanger 703 is connected to the condensate tank 412 through a condensate return pipe G16; the cold side outlet of the second plate heat exchanger 703 is connected to the middle inlet of the filtrate flash evaporator 704, and the top outlet of the filtrate flash evaporator 704 is connected to the shell-side heat source inlet of the pre-concentrated triple-effect evaporator 417 through the filtrate flash vapor pipe G21.

[0189] The bottom outlet of the flash evaporator 704 is connected to the inlet of the deoxycitric acid buffer tank 705. The outlet of the deoxycitric acid buffer tank 705 is connected to the inlet of the deoxycitric acid discharge pump 706. The outlet of the deoxycitric acid discharge pump 706 is connected to the inlet of each chromatographic column 801 through the deoxycitric acid discharge pipe G31.

[0190] The outlet of the dilute sulfuric acid stock solution pipe G32 is connected to the inlet of the dilute sulfuric acid buffer tank 707. The outlet of the dilute sulfuric acid buffer tank 707 is connected to the inlet of the dilute sulfuric acid pump 708. The outlet of the dilute sulfuric acid pump 708 is connected to the cold side inlet of the third plate heat exchanger 709. The steam pipe G05 is connected to the hot side inlet of the third plate heat exchanger 709 through a steam regulating valve. The hot side outlet of the third plate heat exchanger 709 is connected to the condensate tank 412 through the condensate return pipe G16. The cold side outlet of the third plate heat exchanger 709 is connected to the middle inlet of the dilute sulfuric acid flash evaporator 710. The top outlet of the dilute sulfuric acid flash evaporator 710 is connected to the shell-side heat source inlet of the pre-concentrated triple-effect evaporator 417 through the dilute sulfuric acid flash steam pipe G22. The bottom outlet of the dilute sulfuric acid flash evaporator 710 is connected to the inlet of the deoxygenated dilute sulfuric acid buffer tank 711. The bottom of the deoxygenated dilute sulfuric acid buffer tank 711 is connected to the inlet of the deoxygenated dilute sulfuric acid pump 712. The outlet of the deoxygenated dilute sulfuric acid pump 712 is connected to the eluent inlet of each chromatographic column 801 through the deoxygenated dilute sulfuric acid tube G33.

[0191] There are six chromatographic columns 801 connected in series. Each column 801 is equipped with a column circulation pump 802. The reflux port of each column is connected to the reflux port of the filtrate buffer tank 701 via a citric acid reflux pipe G34. The eluent outlet of each column is connected to the reflux port of the dilute sulfuric acid buffer tank 707 via a dilute sulfuric acid reflux pipe G35. The extract outlet of each column is connected to the acid hydrolysis citric acid tank 1501 of the citric acid continuous ion exchange unit via a citric acid purification liquid pipe G36. The sugar outlet of each column 801 is connected to the dilute citric acid buffer tank 1101 of the secondary neutralization unit via a sugar discharge pipe G37.

[0192] Citric acid filtrate pipe G30 draws citric acid solution from membrane filtration and after ion exchange into filtrate buffer tank 701. The filtrate is then pumped into the cold side of the second plate heat exchanger 703 via filtrate pump 702, where it exchanges heat with steam on the hot side to raise its temperature. The steam is condensed into condensate and returned to the condensate tank for subsequent unit washing. After heating, the citric acid solution enters the filtrate flash evaporator 704 for flash deoxygenation. The flash vapor passes through filtrate flash vapor pipe G21 to the pre-concentration triple-effect evaporator 417 of the citric acid evaporation unit, serving as one of its shell-side heat sources.

[0193] The citric acid solution after flash evaporation and deoxygenation enters the deoxycitric acid buffer tank 705, and is pumped into the feed port of the chromatographic column 801 in the chromatographic separation system through the deoxycitric acid discharge pump 706 and the deoxycitric acid discharge pipe G31.

[0194] The 0.2% dilute sulfuric acid from the dilute sulfuric acid stock solution tube G32, used as the eluent, also needs to be deoxygenated before entering the chromatography. The deoxygenation process is the same as that for citric acid solution. The 0.2% dilute sulfuric acid is temporarily stored in the dilute sulfuric acid buffer tank 707 and then pumped by the dilute sulfuric acid pump 708 to the cold side of the third plate heat exchanger 709, where it exchanges heat with the steam on the hot side to raise its temperature. The steam is condensed into condensate and returned to the condensate tank for subsequent unit washing. After being heated, the 0.2% dilute sulfuric acid enters the dilute sulfuric acid flash evaporator 710 for flash deoxygenation. The flash vapor passes through the dilute sulfuric acid flash vapor tube G22 to the pre-concentration triple-effect evaporator 417 of the citric acid evaporation unit, serving as one of its shell-side heat sources.

[0195] Normally, the secondary steam after flash evaporation is condensed by circulating water through a plate heat exchanger, requiring a vacuum system. This means the secondary steam heat source is not fully utilized, and it also increases circulating water consumption. This unit connects this portion of secondary steam to the citric acid evaporation unit for evaporating citric acid liquid. This utilizes this low-quality secondary steam while saving steam consumption across the entire system.

[0196] The 0.2% dilute sulfuric acid after flash deoxygenation enters the deoxygenated dilute sulfuric acid buffer tank 711, and is pumped into the eluent inlet of the chromatographic column 801 in the chromatographic separation system through the deoxygenated dilute sulfuric acid pump 712 and the deoxygenated dilute sulfuric acid tube G33.

[0197] In chromatographic separation, a citric acid mixture containing miscellaneous sugars is used as the target component, 0.2% dilute sulfuric acid is used as the eluent, and resin is used as the stationary phase. The citric acid mixture and ion exchange resin achieve the separation and purification of citric acid through ion adsorption and the essential difference in molecular structure.

[0198] The citric acid solution, after flash evaporation and deoxygenation, has its flow rate into the chromatography system regulated by a flow meter and a control valve to ensure a stable feed flow to the column. It enters column 801 at a specific flow rate and is circulated by the column circulation pump 802. After a certain circulation time, because the resins used in chromatographic separation are mostly strongly basic anion exchange resins, citrate ions are firmly adsorbed onto the resin surface and gradually enriched. Meanwhile, miscellaneous sugars, being neutral molecules, do not interact electrostatically with the resin and flow through the resin gaps with the solution, accumulating on a specific column.

[0199] The concentration of citric acid in the effluent is monitored to determine adsorption saturation; a sudden increase in concentration indicates adsorption saturation. Once the resin reaches saturation with citrate ions, the feed is switched to 0.2% dilute sulfuric acid as the eluent. The H₂ released from the 0.2% dilute sulfuric acid... + It will preferentially bind to the resin, displacing citrate ions from the resin. At this point, the eluent mainly consists of citric acid and contains almost no other sugars.

[0200] Chromatographic separation involves the following steps: Step A: Liquid circulation The citric acid mixture containing miscellaneous sugars is circulated in the chromatographic column by the column circulation pump 802-1~6 for a certain period of time. During this period, all discharge valves and feed valves are closed, while the circulating material valve is open, and the material is in a circulating state.

[0201] At this point, the first chromatographic column 801-1 and the second chromatographic column 801-2 mainly contain a mixture of citric acid, the third chromatographic column 801-3 contains a mixture of citric acid, the amount of miscellaneous sugars gradually decreases, the amount of citric acid gradually increases, and the amount of miscellaneous sugars in the fourth chromatographic column 801-4 and the fifth chromatographic column 801-5 gradually increases to the maximum. In step B, the miscellaneous sugars are removed.

[0202] Steps B and C: 0.2% dilute sulfuric acid is fed in, and citric acid is discharged; while the citric acid mixture is fed in, miscellaneous sugars are separated out.

[0203] Steps B and C are the feeding and discharging stages, where both products are processed simultaneously. This reduces the time required and increases the proportion of the entire separation section, resulting in a better separation effect.

[0204] The purified citric acid solution from the chromatographic separation system is further purified in the refining unit. In order to control the water consumption of the chromatographic separation system, some citric acid is extracted from the remaining sugars. This citric acid is extracted by the traditional calcium salt method. This can ensure the yield of citric acid, reduce the consumption of calcium carbonate, and reduce the production of calcium sulfate as a byproduct.

[0205] The conventional citric acid purification process in the industry mostly employs the calcium salt method. The core of this process involves the reaction of citric acid with calcium ions to produce calcium citrate and calcium hydrogen citrate. The precipitate is then separated and further acidified to obtain a high-purity citric acid solution. However, this method has significant limitations. Firstly, it consumes a large amount of calcium carbonate. The formation of calcium citrate precipitate requires a large amount of calcium carbonate as a reactant, directly increasing raw material costs. This is especially problematic when calcium carbonate prices fluctuate significantly, impacting the economic benefits of production companies. Secondly, the calcium salt method generates a large amount of calcium sulfate as a byproduct during the acidification stage. This calcium sulfate is not only of low purity and has limited application value, but it is also extremely difficult to dispose of. Large accumulations of calcium sulfate occupy significant land resources, and improper handling can lead to environmental pollution problems. This contradicts current green and environmentally friendly production concepts and increasingly stringent environmental policies, placing a heavy environmental burden and processing costs on enterprises.

[0206] The chromatographic separation method of this invention selectively adsorbs citric acid through resin, which can directly extract more than 90% of citric acid from the pretreated fermentation broth. The purity of the purified citric acid solution reaches more than 95%, and it is not affected by competition from other sugars. The yield of this step is 5%-10% higher than that of the neutralization step in the traditional calcium salt method. The residual citric acid in the remaining sugars can be extracted by the traditional calcium salt method with a recovery rate of more than 80%, which is equivalent to an additional recovery of 2.4%-4% of the total citric acid. The combination of chromatographic separation and calcium salt method reduces the consumption of calcium carbonate by about 50% compared with the traditional calcium salt method.

[0207] like Figure 9 As shown, in the primary neutralization unit of this invention, the dilute acid produced after the citric acid mixture is filtered by the two-stage plate and frame filter press 606 is introduced into the mixed acid tank 901 via the dilute citric acid clear liquid pipe G29. The concentrated calcium hydrogen acid from the downstream concentrated calcium hydrogen acid pump 1206 is also introduced into the mixed acid tank 901 via the concentrated calcium hydrogen acid pipe G38. The outlet of the mixed acid tank 901 is connected to the inlet of the mixed acid circulation pump 902 and the mixed acid discharge pump 903. The outlet of the mixed acid circulation pump 902 is connected to the return port of the mixed acid tank 901. The outlet of the mixed acid discharge pump 903 is connected to the inlet of each primary neutralization pot 904. The top inlet of each primary neutralization pot 904 is also connected to the defoamer pipe G26 and the calcium carbonate raw liquid pipe G39. The bottom outlet of each primary neutralization pot 904 is connected to the slurry distributor of the tricalcium citrate vacuum belt filter 1001 via the tricalcium citrate slurry pipe G40.

[0208] After the mycelium is removed from the citric acid fermentation broth by a two-stage plate and frame filter press 606, soluble inorganic salts and some residual sugars remain. These soluble impurities must be removed to obtain pure calcium citrate. The purpose of the first neutralization step is to react the calcium carbonate slurry with the dilute acid produced after filtration by the two-stage plate and frame filter press 606 and the concentrated calcium hydrogen acid sent from the calcium hydrogen acid tube G38 to generate insoluble calcium citrate. This removes the soluble inorganic salts and residual sugars, resulting in pure, impurity-free solid calcium citrate.

[0209] The citric acid mixture is filtered by a two-stage plate and frame filter press 606, and the resulting dilute acid is sent to the mixed acid tank 901 via the dilute citric acid clear liquid pipe G29. The calcium hydrogen acid concentrated acid pump 1206 is also sent to the mixed acid tank 901 via the calcium hydrogen acid concentrated acid pipe G38. After mixing in the mixed acid tank 901, in order to ensure the uniformity of acidity in the mixed acid tank 901 and the neutralization effect of each batch, the mixed acid circulation pump 902 is used for circulation mixing.

[0210] The diluted citric acid, after being mixed evenly, is pumped into the primary neutralization pot 904 through the mixed acid discharge pump 903, where it undergoes a primary neutralization reaction with 45%wt excess calcium carbonate from the calcium carbonate raw liquid pipe G39 to produce tricalcium citrate.

[0211] To prevent localized over-alkaliness during neutralization, a variable frequency stirrer is added to the primary neutralization tank. A large amount of foam is generated during the neutralization reaction, which can lead to unstable neutralization. To ensure the stability of the neutralized liquid, a foam sensor XP-904 is installed on the wall of the primary neutralization tank (tank 904), interlocked with the defoamer feed valve on the defoamer pipe G26. When foam reaches a certain height, the defoamer feed valve opens; when the foam drops to a certain height, the defoamer feed valve closes.

[0212] To detect the neutralization endpoint and reduce the labor costs associated with manual pH titration, an electromagnetic flow meter and regulating valve were installed on the calcium carbonate feed line. These were interlocked with the pH sensor PH-904 installed on the wall of the primary neutralization reactor 904 to monitor the pH value. When the pH reached 4-5 and the residual acid was 0.2-0.4%, the calcium carbonate feed valve was closed, and stirring continued for approximately 20 minutes. The pH and residual acid were then re-measured, indicating that the primary neutralization endpoint had been reached. Discharge then began, and the tricalcium citrate slurry was transported via the G40 pipe to the tricalcium citrate vacuum filtration and washing unit for filtration and washing.

[0213] like Figure 10 As shown, in the tricalcium citrate vacuum filtration and washing unit, the tricalcium citrate slurry pipe G40 is connected to the slurry distributor of the tricalcium vacuum belt filter 1001 through a flow meter and a regulating valve.

[0214] The tricalcium vacuum belt filter 1001 is provided with a feeding area, a filtration area, a washing and dehydration area and a cake discharge area in sequence along the filter cloth forward direction. The sugar water outlet below is connected to the inlet of the vacuum tank 1002. The exhaust port at the top of each vacuum tank 1002 is connected to the middle inlet of the gas-water separator 1003. The top of the gas-water separator 1003 is vented to the atmosphere through the vacuum pump 1004. Except for the final stage, the bottom outlet of each vacuum tank 1002 and the bottom outlet of the gas-water separator 1003 are connected to the inlet of the waste sugar water tank 1005. The outlet of the waste sugar water tank 1005 is connected to the waste sugar water pump 1006 and the wastewater treatment station.

[0215] The bottom outlet of the five-stage vacuum tank 1002-5 is connected to the inlet of the sugar water tank 1007. The sugar water tank 1007 is connected to the primary rinsing water inlet above the washing and dehydration zone via the sugar water pump 1008. The end washing water outlet of the tricalcium vacuum belt filter 1001 is connected to the inlet of the tricalcium washing water tank 1009. The outlet of the tricalcium washing water tank 1009 is connected to the secondary rinsing water inlet above the washing and dehydration zone via the tricalcium washing water pump 1010. The tertiary rinsing water inlet above the washing and dehydration zone is connected to the condensate supply pipe G15.

[0216] The filter cake discharge port of the tricalcium vacuum belt filter 1001 is connected to the tricalcium slurry preparation tank 1011. The slurry preparation water inlet of the tricalcium slurry preparation tank 1011 is connected to the condensate supply pipe G15. The outlet of the tricalcium slurry preparation tank 1011 is connected to the secondary neutralization pot 1104 through the tricalcium slurry preparation pump 1012.

[0217] The tricalcium citrate slurry also contains soluble inorganic salts and residual sugars. It is fed into the tricalcium vacuum belt filter 1001 through the tricalcium citrate slurry pipe G40 for solid-liquid separation to remove the soluble inorganic salts and residual sugars from the tricalcium citrate slurry and obtain pure tricalcium citrate salt.

[0218] The Tricalcium Vacuum Belt Filter 1001 is a continuous solid-liquid separation device. Its working principle is based on the combination of vacuum adsorption force and continuous movement of filter cloth. Through the synergistic effect of multiple processes, it realizes material feeding, filtration, washing, dewatering and cake discharge.

[0219] Feeding Zone: The tricalcium citrate slurry generated from the primary neutralization reaction flows into the slurry distributor of the tricalcium citrate vacuum belt filter 1001 at a stable flow rate through a flow meter and regulating valve, and is evenly distributed on the rotating filter cloth. The vacuum pump 1004 generates vacuum suction to form a vacuum chamber below the filter cloth, initially creating negative pressure. The tricalcium citrate slurry begins to permeate through the filter cloth into the vacuum chamber, and solid particles initially accumulate on the surface of the filter cloth to form an initial filter cake, which then enters the filtration zone.

[0220] Filtration Zone: The filter cloth, carrying the tricalcium citrate slurry, enters the main filtration zone with a high vacuum. Under continuous negative pressure, a large amount of liquid is drawn into the vacuum chamber, gradually increasing the thickness of the filter cake and compacting it. The vacuum chamber is connected to a vacuum pump via pipes. The extracted filtrate waste sugar water is separated by vacuum tank 1002 and gas-liquid separator 1003, and then enters waste sugar water tank 1005. It is then pumped away by waste sugar water pump 1006 for sludge removal, while the gas is discharged by the vacuum pump. Since the filter cake still contains a small amount of residual sugar, it needs to enter the washing and dehydration zone for further washing and dehydration.

[0221] Washing and dehydration zone: To ensure maximum washing efficiency and product recovery rate, a countercurrent washing method is adopted, utilizing the concentration gradient to reduce the amount of washing water used. In order to completely separate the residual sugar in the tricalcium citrate filter cake, a three-stage countercurrent washing is used: the third stage uses clean water, the second stage uses the collected filter cloth washing water, and the first stage uses the third-stage filtrate. The concentration of the filtrate obtained after washing also increases sequentially. The condensate from the pre-concentrated condensate pump 424 and condensate supply pipe G15 is used as the third-stage clean water to wash the filter cake. The flow rate of the clean water is controlled by controlling the flow meter and the opening of the regulating valve. The residual sugar is completely washed away. Under vacuum, the filtrate and residual sugar are pumped together into the fifth-stage vacuum tank 1002. Since the residual sugar concentration in the filtrate is low, it can enter the dilute sugar water tank 1007 as the first-stage washing water. The dilute sugar water pump 1008 pumps it to the first-stage washing area to wash the filter cake. The washed filtrate is pumped into the second-stage vacuum tank 1002. Its residual sugar concentration is higher, so it enters the waste sugar water tank 1005 for discharge. The completely cleaned and dried filter cake (tricalcium citrate) then enters the unloading area for unloading. After unloading, the water used to clean the filter cloth under high pressure flows into the tricalcium citrate washing water tank 1009. In order to recover the small amount of tricalcium citrate solid particles contained in the filter cloth water, it is used as secondary cleaning water and pumped by the tricalcium citrate washing water pump 1010 to clean the tricalcium citrate filter cake. The small amount of tricalcium citrate solid particles are trapped by the filter cloth to form a filter cake. The filtrate contains a certain amount of residual sugar, which is discharged into the waste sugar water tank 1005 through the third-stage vacuum tank.

[0222] After the filter cake from the tricalcium vacuum belt filter 1001 is unloaded, it enters the tricalcium slurry preparation tank 1011. After adding condensate from the pre-concentration condensate pump 424 and the condensate supply pipe G15 for slurry preparation, the tricalcium citrate slurry is sent to the secondary neutralization pot 1104 by the tricalcium slurry preparation pump 1012.

[0223] Currently, the production process uses a large amount of ordinary pressure cleaning water to flush the tail discharge area, but this still cannot deeply unclog the filter cloth pores. To solve the above problems, this unit introduces high-pressure water and compressed air into the filter cake cleaning area, forming two complementary cleaning systems: high-pressure water cleaning and back-flushing air. The tail discharge area of ​​the citric acid belt vacuum filter is equipped with an inside-out back-flushing air system. The main purpose is to use 0.2~0.3MPa compressed air to penetrate from the inside of the filter cloth to the outside in reverse, completely peeling off the residual filter cake adhering to the filter cloth, thereby solving the problem of incomplete discharge caused by material adhesion. After the back-flushing air removes large pieces of filter cake, high-pressure water at 8~12MPa is used for deep cleaning, achieving deep regeneration of the filter cloth and unclogging of pores, ensuring continuous and stable filtration efficiency.

[0224] Conventional calcium salt processes have significant limitations in practical applications. Firstly, they consume a high amount of calcium carbonate. The formation of calcium citrate precipitate requires a large quantity of calcium carbonate as a reactant, directly increasing raw material costs. This is especially problematic when calcium carbonate prices fluctuate significantly, impacting the economic benefits of production enterprises. Secondly, the acidolysis stage of the calcium salt process generates a large amount of calcium sulfate as a byproduct. This calcium sulfate is not only of low purity and has limited application value, but it is also extremely difficult to dispose of. Large accumulations of calcium sulfate occupy substantial land resources, and improper handling can lead to environmental pollution, contradicting current green and environmentally friendly production concepts and increasingly stringent environmental policies. This places a heavy environmental burden and processing costs on enterprises.

[0225] In this unit: the diluted citric acid solution produced after filtration of the citric acid mixture is mixed with the concentrated calcium hydrogen acid discharged from the calcium hydrogen citrate filter in a mixing tank. This mixture undergoes a neutralization reaction with excess calcium carbonate to produce tricalcium citrate, converting dissolved citric acid into a stable and easily separable solid tricalcium citrate. By controlling the excess calcium carbonate, complete reaction of citric acid to tricalcium citrate can be ensured, improving the citric acid recovery rate and purity.

[0226] By installing defoaming electrodes, online pH sensors, and automatic feeding systems on the neutralization tank, precise control of the neutralization process can be achieved through online foam detection and pH adjustment. Combined with stable automatic control programs, this ensures stable system operation and reduces labor costs.

[0227] A variable frequency stirring unit is installed on the primary neutralization tank to prevent local over-alkaliness, and a mixed acid reflux pump is added to ensure uniform acidity before the neutralization reaction.

[0228] Countercurrent washing is used during vacuum filtration and washing to reduce the amount of washing water by utilizing the concentration gradient. At the tail end, a dual cleaning system that combines high-pressure water cleaning and back-blowing air is used to deeply regenerate and unblock the pores of the filter cloth after vacuum filtration and washing, thereby extending the service life of the filter cloth, reducing production costs, and improving the recovery rate of citric acid products.

[0229] like Figure 11 As shown, in the secondary neutralization unit of the present invention, the miscellaneous sugar outlet of each chromatographic column 801 is connected to the inlet of the dilute citric acid buffer tank 1101 through the miscellaneous sugar and dilute citric acid discharge pipe G37. The outlet of the dilute citric acid buffer tank 1101 is connected to the inlet of the dilute citric acid transfer pump 1102. The outlet of the dilute citric acid transfer pump 1102 is connected to the cold side inlet of the plate heat exchanger 1103. The hot side inlet of the plate heat exchanger 1103 is connected to the steam pipe G05. The hot side outlet of the plate heat exchanger 1103 is connected to the condensate tank 412 through the condensate return pipe G16. The cold-side outlet of the plate heat exchanger 1103 is connected to the dilute acid inlet of the first secondary neutralization pot 1104. Multiple secondary neutralization pots 1104 are connected in series. The outlet of the last secondary neutralization pot 1104 is connected to the inlet of the secondary neutralization variable frequency circulation pump 1105 and the secondary neutralization discharge pump 1106. The outlet of the secondary neutralization variable frequency circulation pump 1105 is connected to the reflux port of the first secondary neutralization pot 1104. An online pH sensor is installed on the discharge pipe of the secondary neutralization discharge pump 1106 and connected to the slurry distributor of the calcium hydrogen vacuum belt filter 1201.

[0230] The chromatographic separation system generates citric acid from the residual sugars, which is discharged through the sugar and dilute citric acid discharge pipe G37 into the dilute citric acid buffer tank 1101. From there, it is pumped into the secondary neutralization vessel 1104 via the dilute citric acid transfer pump 1102. To accelerate the neutralization reaction and improve its efficiency, the dilute citric acid is heated to approximately 85-88°C before secondary neutralization by exchanging heat with steam on the hot side of the plate heat exchanger 1103. To control this heat exchange temperature, the steam regulating valve is interlocked with the temperature sensor TT-1103, which detects the temperature of the dilute citric acid.

[0231] The heated dilute citric acid is pumped into the first secondary neutralization vessel 1104. Three secondary neutralization vessels 1104 are connected in series. The dilute citric acid flow meter and regulating valve are interlocked with the level gauge LT-1104 on the secondary neutralization vessel. The level in the secondary neutralization vessel 1104 is controlled by adjusting the opening of the regulating valve. When the level in the first secondary neutralization vessel reaches approximately 30%, tricalcium citrate slurry from the primary neutralization unit is pumped into the second secondary neutralization vessel to begin the secondary neutralization reaction, producing calcium hydrogen citrate.

[0232] During the commissioning process, we found that the three-stage series secondary neutralization pot 1104 and the gravity flow pipe were prone to blockage, which led to unstable neutralization reaction and inability to stably control the acidity of the output.

[0233] To ensure stable acidity of the secondary neutralization output, a secondary neutralization variable frequency circulation pump 1105 is added at the discharge end to circulate the product. A certain amount of circulation back to the first secondary neutralization pot ensures stable acidity in all three neutralization tanks, guaranteeing stable production operation. Online pH sensors are added to the discharge pipes of the first and third secondary neutralization pots for precise control of the reaction process. To prevent precipitation and blockage, the series connection of the pipes between the three tanks is enlarged, and the number of small bends in the pipes is reduced to minimize the residence time of calcium citrate in the tanks. When the online detection shows that the pH value in the first secondary neutralization pot is 3.0~4.0 and the acidity in the third secondary neutralization pot is 3.0~4.5%, it indicates that the secondary neutralization reaction is complete, and the secondary neutralization discharge pump 1106 is started to discharge the product. To ensure continuous and stable discharge, a circulation rate of return material to discharge material of 5:1 is used. The calcium citrate discharged from the secondary neutralization discharge pump 1106 then enters the calcium hydride vacuum belt filter 1201 for filtration and washing.

[0234] like Figure 12 As shown, in the calcium dicalcium citrate vacuum filtration and washing unit, the calcium dicalcium vacuum belt filter 1201 is provided with a feeding area, a filtration area, a washing and dehydration area and a cake discharge area in sequence along the filter cloth advancing direction, and the filtrate outlet below is connected to the inlet of the vacuum tank 1202 respectively. The exhaust port at the top of each vacuum tank 1202 is connected to the middle inlet of the gas-water separator 1203. The top of the gas-water separator 1203 is vented to the atmosphere through the vacuum pump 1204. The washing and dehydration zone is equipped with five vacuum tanks in sequence along the direction of filter cloth advance. The bottom outlets of the vacuum tank 1202-1, the first-stage vacuum tank 1202-2, the second-stage vacuum tank 1202-3 and the gas-water separator 1203 in the filtration zone are all connected to the inlet of the calcium hydrogen acid buffer tank 1205. The outlet of the calcium hydrogen acid buffer tank 1205 is connected to the calcium hydrogen acid pump 1206 and the mixed acid tank 901. The outlet of the three-stage vacuum tank 1202-4 is connected to the first-stage calcium hydrogen acid tank 1207. The bottom outlet of the first-stage calcium hydrogen acid tank 1207 is connected to the first-stage rinsing water inlet above the washing and dehydration zone through the first-stage calcium hydrogen acid pump 1208. The outlet of the fourth-stage vacuum tank 1202-5 is connected to the second-stage calcium hydrogen dilute acid tank 1209. The outlet of the second-stage calcium hydrogen dilute acid tank 1209 is connected to the second-stage rinsing water inlet above the washing and dehydration zone through the second-stage calcium hydrogen dilute acid pump 1210. The outlet of the five-stage vacuum tank 1202-6 is connected to the four-stage calcium hydrogen acid tank 1211. The bottom outlet of the four-stage calcium hydrogen acid tank 1211 is connected to the four-stage rinsing water inlet above the washing and dehydration zone through the four-stage calcium hydrogen acid pump 1212. The end of the calcium hydrogen vacuum belt filter 1201 is connected to the inlet of the calcium hydrogen wash water tank 1213. The outlet of the calcium hydrogen wash water tank 1213 is connected to the three-stage rinsing water inlet above the washing and dehydration zone through the calcium hydrogen wash water pump 1214. The five-stage rinsing water inlet above the washing and dehydration zone is connected to the condensate supply pipe G15.

[0235] The filter cake discharge port of the calcium hydrogen vacuum belt filter 1201 is connected to the calcium hydrogen slurry preparation tank 1215. The slurry water inlet of the calcium hydrogen slurry preparation tank 1215 is connected to the condensate supply pipe G15. The bottom outlet of the calcium hydrogen slurry preparation tank 1215 is connected to the calcium hydrogen slurry buffer tank 1301 of the acidolysis unit through the calcium hydrogen slurry preparation pump 1216.

[0236] Tricalcium citrate slurry undergoes a secondary neutralization reaction with citric acid in residual sugars to produce calcium hydrogen citrate slurry. The slurry still contains a small amount of unneutralized citric acid and residual sugars. Therefore, it is necessary to perform solid-liquid separation using a calcium hydrogen vacuum belt filter 1201 to remove the citric acid and residual sugars from the calcium hydrogen citrate slurry and obtain pure calcium hydrogen citrate.

[0237] Feeding Zone: The calcium dicalcium citrate slurry generated from the secondary neutralization reaction flows into the slurry distributor of the calcium dicalcium vacuum belt filter 1201 at a stable flow rate through a flow meter and regulating valve, and is evenly distributed on the rotating filter cloth. The vacuum pump 1204 generates vacuum suction to form a vacuum chamber under the filter cloth, initially creating negative pressure. The calcium dicalcium citrate slurry permeates into the vacuum chamber through the filter cloth, and solid particles initially accumulate on the surface of the filter cloth to form an initial filter cake, which then enters the filtration zone.

[0238] Filtration Zone: The filter cloth, carrying the calcium hydride slurry, enters the main filtration zone with a high vacuum. Under continuous negative pressure, a large amount of liquid is drawn into the vacuum chamber, gradually increasing the thickness of the filter cake and compacting it. The vacuum chamber is connected to a vacuum pump via a pipe. The extracted filtrate waste sugar water is separated by the vacuum tank 1202-1 and the gas-liquid separator 1203 in the filtration zone, and then enters the calcium hydride concentrated acid buffer tank 1205. It is then pumped to the mixed acid tank 901 for neutralization via the calcium hydride concentrated acid pump 1206 and the calcium hydride concentrated acid pipe G38, while the gas is discharged by the vacuum pump. Since the filter cake still contains a small amount of residual sugar and citric acid, it needs to enter the washing and dehydration zone for further washing and dehydration.

[0239] Washing and Dehydration Zone: To ensure maximum washing efficiency and product recovery rate, a countercurrent washing method is adopted, utilizing the concentration gradient to reduce the amount of washing water used. To completely separate residual sugar and citric acid from the calcium dicalcium citrate filter cake, a five-stage countercurrent washing process is employed: stage five uses clean water, stage four uses stage five filtrate, stage three uses collected filter cloth washing water, stage two uses stage four filtrate, and stage one uses stage three filtrate, with the concentration of the filtrate increasing sequentially after washing. Condensate from condensate pump 424 is used as the fifth-stage clean water to wash the filter cake. The flow rate of clean water is controlled by adjusting the flow meter and regulating valve opening. Residual sugar and citric acid are completely washed away. Under vacuum, the filtrate, residual sugar, and citric acid are pumped together into the fifth-stage vacuum tank 1202-6. Since the concentration of residual sugar and citric acid in this filtrate is low, it can enter the fourth-stage calcium dicalcium acid tank 1211 as fourth-stage washing water, which is then pumped to the fourth-stage washing zone by the fourth-stage calcium dicalcium acid pump 1212 to wash the filter cake. The washed filtrate is pumped into the fourth-stage vacuum tank 1202-5, where the citric acid concentration increases. It then enters the second-stage calcium hydrogen dilute acid tank 1209 as secondary washing water. It is pumped into the secondary washing area by the second-stage calcium hydrogen dilute acid pump 1210 to wash the filter cake. The washed filtrate is pumped into the second-stage vacuum tank 1202-3, where the citric acid content is high. It flows into the calcium hydrogen concentrated acid buffer tank 1205 and is then pumped into the mixed acid tank 901 for primary neutralization via the calcium hydrogen concentrated acid pump 1206 and the calcium hydrogen concentrated acid pipe G38.

[0240] The thoroughly cleaned and partially dried filter cake (calcium citrate) enters the unloading area for discharge. After unloading, high-pressure water is introduced to clean the filter cloth, flowing into the calcium hydride cloth washing tank 1213. To recover the small amount of calcium hydride solid particles contained in the filter cloth water, this is used as tertiary washing water and pumped by the calcium hydride cloth washing pump 1214 to clean the calcium hydride filter cake. The small amount of calcium hydride solid particles are retained by the filter cloth, forming a filter cake. The filtrate contains a certain amount of citric acid and enters the primary calcium hydride dilute acid tank 1207 via the tertiary vacuum tank 1202-4 as primary washing water. This water is then pumped by the primary calcium hydride dilute acid pump 1208 to the primary washing area to clean the filter cake. The cleaned filtrate is pumped to the primary vacuum tank 1202-2. Since this filtrate has a high citric acid content, it enters the calcium hydride concentrated acid buffer tank 1205 and is then pumped to the mixed acid tank 901 via the calcium hydride concentrated acid pump 1206 and the calcium hydride concentrated acid pipe G38.

[0241] To ensure both washing effectiveness and water volume control during the washing process, this technology installs electromagnetic flow meters and regulating valves on each stage of the washing water pipeline. By controlling the opening of the regulating valves, the water volume at each stage is ensured to be uniform and stable.

[0242] Cake Discharge Area: The thoroughly cleaned and dried calcium dicalcium citrate filter cake enters the cake discharge area for unloading. The filter cake is automatically unloaded due to its own gravity and the assistance of a scraper. The calcium dicalcium citrate filter cake then falls into the calcium dicalcium slurry preparation tank 1215. After adding condensate from the condensate pump 424 and the condensate supply pipe G15 for slurry preparation, it is pumped into the calcium dicalcium slurry buffer tank 1301 of the subsequent acidolysis unit via the calcium dicalcium slurry preparation pump 1216.

[0243] In order to deeply unclog the filter cloth pores, high-pressure water and compressed air are introduced into the filter cake cleaning area for deep cleaning, so as to achieve deep regeneration of the filter cloth and unclogging of pores, and ensure the continuous and stable filtration efficiency.

[0244] This invention utilizes a calcium salt method to extract citric acid from residual sugars in a chromatographic separation system. This citric acid undergoes a secondary neutralization reaction with the tricalcium slurry after primary neutralization and filtration, generating calcium dicalcium citrate. This reduces water and acid consumption in the chromatographic separation system and increases the yield of citric acid. To ensure stable acidity in the secondary neutralization output, a variable frequency pump is added for circulation at the discharge stage, and an online pH sensor is installed on the discharge pipeline for precise control of the reaction process. By setting a specific circulation rate, the acidity in the three neutralization tanks is ensured to be uniform and stable, guaranteeing the normal operation of subsequent production. To prevent precipitate blockage, the diameter of the series pipes connecting the three tanks is increased, the number of small bends in the pipes is reduced, and the residence time of calcium dicalcium citrate in the tanks is shortened. Countercurrent washing is used during vacuum filtration and washing, utilizing the concentration gradient to reduce the amount of washing water used. A dual cleaning system combining high-pressure water cleaning and backflushing is used at the tail end to deeply regenerate and unblock the pores of the filter cloth after vacuum filtration and washing, extending the service life of the filter cloth, reducing production costs, and improving the citric acid product recovery rate.

[0245] like Figure 13 As shown, in the acidolysis unit of the present invention, the outlet of the calcium hydrogen slurry buffer tank 1301 is connected to the inlet of the first acidolysis pot 1304-1 via the calcium hydrogen slurry pump 1302, and multiple acidolysis pots 1304 are connected in series. The bottom outlet of the concentrated sulfuric acid high-level tank 1307 is also connected to the acid inlet of the first acidolysis pot 1304-1. The outlet of the final acidolysis pot is connected to the inlet of the acidolysis variable frequency circulation pump 1305 and the acidolysis discharge pump 1306. The outlet of the acidolysis variable frequency circulation pump 1305 is connected to the circulation port of the first acidolysis pot 1304-1, and the outlet of the acidolysis discharge pump 1306 is connected to the slurry distributor of the acidolysis vacuum belt filter 1401.

[0246] After secondary neutralization and filtration, the calcium hydrogen slurry of citrate is sent to the calcium hydrogen slurry buffer tank 1301 by the calcium hydrogen slurry adjusting pump 1216, and then pumped into the acid hydrolysis pot 1304 by the calcium hydrogen slurry pump 1302, where it reacts with concentrated sulfuric acid from the concentrated sulfuric acid high-level tank 1307 to produce citric acid and calcium sulfate.

[0247] If this unit adopts batch acidolysis reaction and relies on manual on-site inspection to observe the liquid level of concentrated sulfuric acid in the high-level tank and the clumping caused by excessive addition of concentrated sulfuric acid, on the one hand, it will cause the quality of acidolysis solution from each batch of acidolysis pot to be unstable, affecting the quality of subsequent products; on the other hand, it will cause process accidents due to operational errors.

[0248] To ensure stable product quality, a continuous acidolysis reaction is adopted, with three acidolysis reactors (1304-1 to 3) connected in series. Radar level gauges (GW-1304-1 and GW-1304-3) are added to the top of the acidolysis reactors to monitor the liquid level in real time. The feed flow rate is controlled by a flow meter and regulating valve on the feed pipeline. An online pH sensor (PH-1304-3) is added at the discharge point, interlocked with a flow meter and regulating valve on the concentrated sulfuric acid pipeline to control the discharge pH value. To ensure uniform acidolysis, a variable frequency circulating pump (1305) is used for circulation, which prevents clumping and ensures continuous and stable operation. When the pH sensor PH-1304-3 on the acidolysis tank 1304-3 detects that the pH is between 1.5 and 2.0, close the concentrated sulfuric acid discharge valve at the bottom of the concentrated sulfuric acid high-level tank 1307, keep stirring, and continue the reaction. Ensure that the stirring reaction time is greater than 2.5 hours, so that the calcium dicalcium citrate reacts completely with the concentrated sulfuric acid to produce pure citric acid and calcium sulfate precipitate. Turn on the acidolysis discharge pump 1306 to start discharging, and send the material to the acidolysis vacuum belt filter 1401 for solid-liquid separation.

[0249] To reduce the risk of process accidents, a liquid level sensor LT-1307 is added to the concentrated sulfuric acid high-level tank 1307, which is interlocked with the concentrated sulfuric acid feed valve KV-1307 at the raw material inlet. When the concentrated sulfuric acid high-level tank 1307 drops to a certain liquid level, the concentrated sulfuric acid feed valve KV-1307 automatically opens to feed, thus enabling online detection of feeding.

[0250] like Figure 14 As shown, in the calcium sulfate vacuum filtration and washing unit, the acid hydrolysis vacuum belt filter 1401 is provided with a feeding area, a filtration area, a washing and dehydration area and a cake discharge area in sequence along the filter cloth forward direction, and the filtrate outlet below is connected to the inlet of the vacuum tank 1402. The exhaust port at the top of each vacuum tank 1402 is connected to the middle inlet of the gas-water separator 1403. The top of the gas-water separator 1403 is vented to the atmosphere through the vacuum pump 1404. The washing and dehydration zone is equipped with five vacuum tanks in sequence along the direction of filter cloth movement. The bottom outlets of the vacuum tank 1402-1, the first-stage vacuum tank 1402-2, the second-stage vacuum tank 1402-3, and the gas-water separator 1403 in the filtration zone are all connected to the inlet of the acid hydrolysis concentrated acid tank 1405. The outlet of the acid hydrolysis concentrated acid tank 1405 is connected to the acid hydrolysis concentrated acid pump 1406 and the acid hydrolysis citric acid tank 1501.

[0251] The outlet of the three-stage vacuum tank 1402-4 is connected to the acid hydrolysis primary washing liquid tank 1407. The bottom outlet of the acid hydrolysis primary washing liquid tank 1407 is connected to the primary rinsing water inlet above the washing and dehydration zone through the acid hydrolysis primary washing liquid pump 1408. The outlet of the fourth-stage vacuum tank 1402-5 is connected to the acid hydrolysis secondary washing liquid tank 1409, and the outlet of the acid hydrolysis secondary washing liquid tank 1409 is connected to the secondary rinsing water inlet above the washing and dehydration zone through the acid hydrolysis secondary washing liquid pump 1410. The outlet of the five-stage vacuum tank 1402-6 is connected to the acid hydrolysis four-stage washing liquid tank 1411. The bottom outlet of the acid hydrolysis four-stage washing liquid tank 1411 is connected to the four-stage rinsing water inlet above the washing and dehydration zone through the acid hydrolysis four-stage washing liquid pump 1412. The end of the acid-dissolving vacuum belt filter 1401 is connected to the inlet of the acid-dissolving cloth washing water tank 1413. The outlet of the acid-dissolving cloth washing water tank 1413 is connected to the three-stage rinsing water inlet above the washing and dewatering zone through the acid-dissolving cloth washing water pump 1414. The five-stage rinsing water inlet above the washing and dehydration zone is connected to the condensate supply pipe G15.

[0252] Calcium hydrogen citrate slurry reacts with concentrated sulfuric acid to produce a mixture of citric acid and calcium sulfate. To separate the citric acid from the calcium sulfate, solid-liquid separation is required using an acid hydrolysis vacuum belt filter 1401. The citric acid in the calcium sulfate slurry is washed and filtered out to obtain pure citric acid.

[0253] Feeding Zone: The mixture of citric acid and calcium sulfate generated by the acidolysis reaction flows into the slurry distributor of the acidolysis vacuum belt filter 1401 at a stable flow rate through a flow meter and regulating valve, and is evenly distributed on the rotating filter cloth. The vacuum pump 1404 generates vacuum suction to form a vacuum chamber under the filter cloth, initially creating negative pressure. The calcium dicalcium citrate slurry seeps into the vacuum chamber through the filter cloth, and solid particles initially accumulate on the surface of the filter cloth to form an initial filter cake, which then enters the filtration zone.

[0254] Filtration Zone: The filter cloth, carrying the calcium sulfate slurry containing citric acid, enters the main filtration zone with a high vacuum. Under continuous negative pressure, a large amount of liquid is drawn into the vacuum chamber, gradually increasing the thickness of the filter cake and compacting it. The vacuum chamber is connected to a vacuum pump via pipes. The extracted citric acid filtrate is separated by the vacuum tank 1402-1 and the gas-liquid separator 1403 in the filtration zone, and then enters the acidolysis concentrated acid tank 1405. It is then pumped away from the ion exchange unit by the acidolysis concentrated acid pump 1406, while the gas is discharged by the vacuum pump. Since the filter cake still contains a small amount of residual sugar and citric acid, it needs to enter the washing and dehydration zone for further washing and dehydration.

[0255] Washing and Dehydration Zone: To ensure maximum washing efficiency and product recovery rate, a countercurrent washing method is adopted, utilizing the concentration gradient to reduce the amount of washing water used. To completely separate citric acid from the calcium sulfate slurry, a five-stage countercurrent washing process is employed: stage 5 uses clean water, stage 4 uses stage 5 filtrate, stage 3 uses collected filter cloth washing water, stage 2 uses stage 4 filtrate, and stage 1 uses stage 3 filtrate. The citric acid concentration in the resulting filtrate increases sequentially. Condensate from condensate pump 424 is used as the fifth-stage clean water to wash the filter cake. The flow rate of the clean water is controlled by adjusting the flow meter and regulating valve. The citric acid solution is completely washed off. Under vacuum, the citric acid solution is pumped into the fifth-stage vacuum tank 1402-6. Due to the low citric acid concentration in this filtrate, it can enter the fourth-stage acid hydrolysis washing tank 1411 as the fourth-stage washing water. This fourth-stage acid hydrolysis washing water is then pumped to the fourth-stage washing zone by pump 1412 to wash the filter cake. The washed filtrate... Citric acid is drawn into a four-stage vacuum tank 1402-5, where its concentration increases. It then enters the secondary acid hydrolysis washing tank 1409 as secondary washing water, which is pumped into the secondary washing area by the secondary acid hydrolysis washing pump 1410 to clean the filter cake. The washed filtrate is drawn into a secondary vacuum tank 1402-3, where its citric acid content is high. It then enters the concentrated acid hydrolysis tank 1405, and is pumped to the citric acid hydrolysis tank 1501 by the concentrated acid hydrolysis pump 1406 for ion-exchange purification. The completely cleaned calcium sulfate filter cake, after some moisture has been removed, is then unloaded in the cake discharge area. After unloading, the water used to clean the filter cloth under high pressure flows into the acid-cleansing water tank 1413. In order to recover the small amount of calcium sulfate solid particles contained in the filter cloth water, it is used as the third-stage cleaning water and pumped by the acid-cleansing water pump 1414 to clean the calcium sulfate filter cake. The small amount of calcium sulfate solid particles are trapped by the filter cloth to form a filter cake. The filtrate contains a certain amount of citric acid, so it enters the acid-cleansing first-stage washing liquid tank 1407 through the third-stage vacuum tank 1402-4 as the first-stage washing water. It is pumped by the acid-cleansing first-stage washing liquid pump 1408 to the first-stage washing area to clean the filter cake. The cleaned filtrate is pumped to the first-stage vacuum tank 1402-2. Since the filtrate has a high citric acid content, it enters the acid-cleansing concentrated acid tank 1405 and is pumped by the acid-cleansing concentrated acid pump 1406 to the acid-cleansing citric acid tank 1501 for ion-exchange purification.

[0256] To ensure both washing effectiveness and water volume control during the washing process, this technology installs electromagnetic flow meters and regulating valves on each stage of the washing water pipeline. By controlling the opening of the regulating valves, the water volume at each stage is ensured to be uniform and stable.

[0257] Unloading area: The calcium sulfate filter cake, which has been thoroughly cleaned and dried, enters the unloading area for unloading. The calcium sulfate filter cake is automatically unloaded due to its own gravity and the assistance of the scraper, and is sold as a by-product.

[0258] In order to deeply unclog the filter cloth pores, high-pressure water and compressed air are introduced into the filter cake cleaning area for deep cleaning, so as to achieve deep regeneration of the filter cloth and unclogging of pores, and ensure the continuous and stable filtration efficiency.

[0259] The citrate ion is released from the calcium salt through a metathesis reaction, generating a free citric acid solution. At the same time, a calcium sulfate precipitate that is insoluble in water is generated, realizing the key transformation from the intermediate product (salt) to the target product (acid), which directly determines the yield and purity of the subsequent citric acid.

[0260] To ensure stable product quality, this unit adopts a continuous acidolysis reaction process, with the acidolysis tanks set up in a three-stage series connection. A radar level gauge is installed on the top of the acidolysis tank to monitor the liquid level in real time. Flow meters and regulating valves are added to the feed pipeline and concentrated sulfuric acid pipeline, and an online pH meter and a variable frequency circulating pump are equipped at the discharge stage. This setup can effectively prevent clumping, ensure continuous and stable operation of the acidolysis process, reduce the amount of concentrated sulfuric acid used, and significantly reduce labor costs.

[0261] To reduce the risk of process accidents, a level sensor and an automatic feeding system are installed on the concentrated sulfuric acid high-level tank. When the concentrated sulfuric acid level in the high-level tank drops to the set value, the concentrated sulfuric acid feed valve automatically opens to replenish the tank, realizing online detection and automated control of the feeding process.

[0262] Countercurrent washing is used during vacuum filtration and washing to reduce the amount of washing water by utilizing the concentration gradient. At the tail end, a dual cleaning system that combines high-pressure water cleaning and back-blowing air is used to deeply regenerate and unblock the pores of the filter cloth after vacuum filtration and washing, thereby extending the service life of the filter cloth, reducing production costs, and improving the recovery rate of citric acid products.

[0263] like Figure 15 , Figure 16 As shown, in the citric acid continuous ion exchange unit of this invention, the citric acid extracted through chromatographic separation and neutralization acid hydrolysis contains a large number of metal ions, such as cations like calcium and magnesium ions and anions like sulfate ions, resulting in high conductivity, which seriously affects the crystallization quality of citric acid and causes excessive ash content. Ion exchange using an ion exchange resin deeply removes these impurity ions and reduces conductivity.

[0264] To reduce acid and alkali consumption and water consumption, improve resin utilization, and ensure product stability, a continuous ion exchange system is adopted.

[0265] This continuous ion exchange system consists of numerous small resin columns arranged in a ring on a rotating disc. The disc is driven by a drive system to rotate, thus rotating the resin columns. All resin columns are divided into several different zones along their circumference, using a series-parallel connection and switching via a rotary valve. A complete ion exchange process is completed when one resin column completes one revolution. Compared to a fixed-bed system, the continuous ion exchange system can save over 50% of resin, 50-70% of water consumption, and 30-55% of acid and alkali consumption.

[0266] Citric acid filtrate from the acidolysis reaction is fed into the acidolysis citric acid tank 1501 via acidolysis concentrated acid pump 1406. Purified citric acid from the column circulation pump 802 and citric acid purification tubing G36 is also temporarily stored in the acidolysis citric acid tank 1501. Then, it is pumped into the decolorization column 1503 via acidolysis citric acid pump 1502 to remove some pigment impurities. The decolorized citric acid enters the citric acid buffer tank 1504, waiting to enter the cation exchange system and anion exchange system.

[0267] The cation exchange system 1506 is divided into eight zones: water washing top material zone 1506-1~3, compressed air top material zone 1506-4, primary exchange zone 1506-5~9, secondary exchange zone 1506-10~14, product top water zone 1506-15, regeneration water washing zone 1506-16~19, regeneration zone 1506-20~21, and pretreatment regeneration zone 1506-22~24.

[0268] Primary exchange zone: The decolorized citric acid solution is pumped into the primary exchange zone 1506-5~9 via the centrifugal feed pump 1505, and the feed rate is controlled by a flow meter and regulating valve. The primary exchange zone 1506-5~9 consists of five parallel channels, each with one column, which diverts the liquid flow, reducing the flow rate and operating pressure of the equipment.

[0269] Secondary exchange zone: The primary effluent from the primary exchange zone 1506-5~9 is temporarily stored in the primary cation exchange tank 1507, and then pumped into the secondary exchange zone 1506-10~14 by the primary cation exchange pump 1508. The secondary exchange zone consists of five parallel channels, each with one column, to ensure that the cations not adsorbed in the primary effluent are completely adsorbed. After complete adsorption, the citric acid solution enters the secondary cation exchange tank 1509, and then is pumped to the anion exchange zone by the secondary cation exchange pump 1510 and the anion exchange pump 1523.

[0270] Product top water zone: The citric acid solution from the secondary exchange zone 1506-10~14 is partially used in the product top water zone to push out the water in the regenerated column, ensuring that the feed solution is not diluted during subsequent feeding.

[0271] Compressed air top-loading zone: After the resin column is saturated with adsorption, it enters the compressed air top-loading zone 1506-4, where compressed air pushes the liquid out into the primary cation exchange tank 1507. After the compressed air top-loading is complete, the saturated resin enters the water washing top-loading zones 1506-1~3, where a small amount of citric acid is washed off the resin.

[0272] Water washing top material zone: Water washing top material zones 1506-1~3 adopt a three-column series connection method for water washing, which can effectively reduce the amount of water used for top material washing. The topped material liquid enters the primary cation exchange liquid tank 1507.

[0273] Regeneration Zone: The saturated resin that has been eluted enters the regeneration zone, where it utilizes the H+ in the acid. + The cations exchanged on the resin are replaced, thereby allowing the resin to regain H+. + The goal is to regenerate the resin. The regeneration zone is divided into two parts: regeneration zone 1506-20~21 and pretreatment regeneration zone 1506-22~24. In the first part, regeneration zone 1506-20~21, two columns are connected in series. The columns pretreated in pretreatment zone 1506-22~24 are completely regenerated using a prepared 32% dilute hydrochloric acid solution. The used dilute hydrochloric acid enters the hydrochloric acid storage tank 1511 and is then pumped into pretreatment regeneration zone 1506-22~24 via hydrochloric acid storage pump 1512. Pretreatment regeneration zone 1506-22~24 uses three columns connected in series. The waste liquid after pretreatment regeneration contains a large number of exchanged impurity ions and is discharged as wastewater. The purpose of dividing the regeneration zone into two parts is to improve acid utilization and save acid consumption.

[0274] Regeneration water washing zone: After the column regeneration is completed, it enters the regeneration water washing zone 1506-16~19. The regeneration water washing zone adopts a four-column series water washing method. RO water is introduced through RO water pipe G41 to wash the pH value in the column back to neutral. The water after washing contains dilute hydrochloric acid, so it enters the hydrochloric acid refill tank 1511 for subsequent pretreatment regeneration.

[0275] like Figure 2 As shown, the anion exchange system 1520 is divided into 8 zones: water washing top material zone 1520-1~3, compressed air top material zone 1520-4, primary exchange zone 1520-5~9, secondary exchange zone 1520-10~14, product top water zone 1520-15, regeneration water washing zone 1520-16~19, regeneration zone 1520-20~21, and pretreatment regeneration zone 1520-22~24.

[0276] Primary exchange zone: Citric acid after cation removal is pumped into the primary exchange zone 1520-5~9 through the anion exchange liquid feed pump 1523. The primary exchange zone 1520-5~9 consists of five parallel channels, with one column in each channel, which diverts the liquid and reduces the flow rate and operating pressure of the equipment.

[0277] Secondary exchange zone: The primary discharge liquid flowing out from the primary exchange zone 1520-5~9 enters the primary anion exchange liquid tank 1521 and is then pumped into the secondary exchange zone 1520-10~14 by the primary anion exchange liquid feed pump 1522. The secondary exchange zone consists of five parallel channels, each with one column, to ensure that the unadsorbed anions in the primary discharge liquid are completely adsorbed. After complete adsorption, the citric acid liquid enters the citric acid tank 1526 and is then sent to the pre-concentration first-effect evaporator 413 of the pre-concentration evaporation crystallization unit through the citric acid liquid pump 1527 and the citric acid liquid pipe G17 after ion exchange.

[0278] Product top water zone: The citric acid solution that has been completely adsorbed in the secondary exchange zone is partially used in the product top water zone to push out the water in the regenerated column, ensuring that the feed solution is not diluted during subsequent feeding.

[0279] Compressed air top-loading zone: After the resin column is saturated with adsorption, it enters the compressed air top-loading zone 1520-4, where compressed air pushes the liquid out into the primary anion exchange tank 1521. After the compressed air top-loading is complete, the saturated resin enters the water washing top-loading zones 1520-1~3, where a small amount of citric acid is washed off the resin.

[0280] Water washing top material area: Water washing top material area 1520-1~3 adopts a three-column series connection method for water washing, which can effectively reduce the amount of top material water used. The topped material liquid enters the primary anion exchange tank 1521.

[0281] Regeneration Zone: The saturated resin that has been eluted enters the regeneration zone, where it utilizes the OH- in the alkali. - The anions on the resin are replaced, thereby allowing the resin to regain OH groups. - The goal is to regenerate the resin. The regeneration zone is divided into two parts: regeneration zone 1520-20~21 and pretreatment regeneration zone 1520-22~24. In the first part, regeneration zone 1520-20~21, two columns are connected in series. The columns pretreated in pretreatment zone 1520-22~24 are completely regenerated using a prepared 32% dilute alkali solution. The used alkali enters the dilute alkali tank 1524 and is then pumped into pretreatment regeneration zone 1520-22~24 via dilute alkali pump 1525. Pretreatment regeneration zone 1520-22~24 uses three columns connected in series. The waste liquid after pretreatment regeneration contains a large number of exchanged impurity ions and is discharged as wastewater. The purpose of dividing the regeneration zone into two parts is to improve the utilization rate of alkali and save on alkali consumption.

[0282] Regeneration water washing zone: After the column regeneration is completed, it enters the regeneration water washing zone 1520-16~19. The regeneration water washing zone adopts a four-column series water washing method. RO water is introduced to wash the pH value of the column back to neutral. The water after washing contains dilute alkali, so it enters the dilute alkali tank 1524 for subsequent pretreatment regeneration.

[0283] The above process optimizes the production process of the citric acid ion exchange system, significantly reduces acid and alkali consumption and water consumption during ion exchange, improves resin utilization, ensures the stability of citric acid products, and reduces energy consumption for subsequent evaporation and crystallization of citric acid.

[0284] Compared with fixed beds, this continuous ion exchange system can save more than 50% of resin, 50-70% of water consumption, and 30-55% of acid and alkali consumption; the cost of the ion exchange process per unit of citric acid product is reduced by 15%-25%; and the steam consumption in the subsequent evaporation process is reduced.

[0285] like Figure 18 As shown, in the citric acid drying unit of the present invention: the outlet of the citric acid slurry discharge pump 1612 is connected to the inlet of the feed distribution tank 1701 through the citric acid slurry output pipe G23; the outlet of the feed distribution tank 1701 is connected to the inlet of the top-rotating centrifuge 1702; a discharge auger 1703 is installed at the bottom outlet of the top-rotating centrifuge 1702; a vibrating conveyor 1704 is installed at the outlet of the discharge auger 1703; and the outlet of the vibrating conveyor 1704 is connected to the feed inlet of the vibrating fluidized bed 1705.

[0286] The outlet of air filter 1712 is connected to the air inlet of finned heat exchanger 1713, and the air outlet of finned heat exchanger 1713 is connected to the air inlet of the drying section of vibrating fluidized bed 1705 via blower 1714. Steam pipe G05 is connected to the steam inlet of finned heat exchanger 1713, and condensate from finned heat exchanger 1713 is discharged into condensate tank 412 via condensate return pipe G16.

[0287] The outlet of air filter 1715 is connected to the air inlet of rotary dehumidifier 1716. The air outlet of rotary dehumidifier 1716 is connected to the air inlet of the cooling section of vibrating fluidized bed 1705 via cooling fan 1717. Steam pipe G05 is connected to the steam inlet of rotary dehumidifier 1716 via steam regulating valve. The steam regulating valve is interlocked with the outlet temperature of rotary dehumidifier 1716. Chilled water pipe G42 is connected to the chilled water inlet of rotary dehumidifier 1716.

[0288] The discharge port of the vibrating fluidized bed 1705 is connected to the inlet of the gyratory screen 1709. The oversize outlet of the gyratory screen 1709 is connected to the inlet of the remelting tank 1718. The outlet of the pre-concentration condensate pump 424 is connected to the slurry inlet of the remelting tank 1718 via the condensate supply pipe G15. The bottom outlet of the remelting tank 1718 is connected to the reflux port of the citric acid pre-concentration tank 1601 via the centrifugal pump 1719. The undersize outlet of the gyratory screen 1709 is connected to the inlet of the finished product buffer silo 1710. The outlet of the finished product buffer silo 1710 is connected to the inlet of the packing scale 1711.

[0289] The exhaust port of the vibrating fluidized bed 1705 is connected to the inlet of the self-excited hydraulic dust collector 1706, the outlet of the self-excited hydraulic dust collector 1706 is connected to the lower air inlet of the two-flow air-water film dust collector 1707, and the top air outlet of the two-flow air-water film dust collector 1707 is vented to the atmosphere through the induced draft fan 1708.

[0290] The compressed air inlet of the two-flow air-water film dust collector 1707 is connected to the compressed air pipe G25, and the spray water inlet of the two-flow air-water film dust collector 1707 is connected to the RO water pipe G41.

[0291] The citric acid crystal solution after evaporation and crystallization contains a small amount of mother liquor. It is pumped into the feed distribution tank 1701 at a certain flow rate by the citric acid crystal slurry discharge pump 1612, and then centrifuged by the upward centrifuge 1702. The separated crystals are transported to the vibrating fluidized bed 1705 for drying by the discharge auger 1703 and the vibrating conveyor 1704.

[0292] The vibrating fluidized bed is divided into two parts: drying and cooling. In the drying section, hot air, generated by exchanging heat between outside air filtered by air filter 1712 and steam-introduced finned heat exchanger 1713, is blown into the drying section of the vibrating fluidized bed 1705 by blower 1714. The hot air contacts the citric acid crystals, converting the moisture in the crystals into hot gas, which is then discharged by the dust removal system. In the cooling section, outside air filtered by air filter 1715 is cooled and dehumidified by rotary dehumidifier 1716 and blown into the cooling section of the vibrating fluidized bed 1705 by cooling fan 1717. The dried citric acid crystals move forward with the vibration of the fluidized bed and enter the cooling section of the vibrating fluidized bed 1705. After contacting the cold air, they are cooled and discharged into a gyratory screen 1709 for sieving and separation. The unqualified products after sieving enter a remelting tank 1718, where water is added to dissolve them. Then, they are pumped by centrifugal pump 1719 to a citric acid pre-concentration tank 1601 for further evaporation, concentration, and crystallization. The screened finished product enters the finished product buffer chamber 1710, waiting to be packaged into products by the packaging scale 1711.

[0293] Because citric acid crystals easily generate dust during the drying process, many citric acid plants currently use dry dust removal methods, namely cyclone separators and bag filters, to collect dust. However, citric acid is hygroscopic, and the drying exhaust gas collection unit is prone to absorbing moisture, causing citric acid to stick to the side walls of the cyclone separator and the filter bags, resulting in material accumulation and affecting the dust removal effect.

[0294] Citric acid dust is highly hygroscopic and slightly acidic, so the dust removal system needs to consider preventing clogging and corrosion. This system adopts a dual wet dust removal method, consisting of a self-excited hydraulic dust collector 1706 and a two-flow air-water film dust collector 1707.

[0295] First-stage dust removal: Dust-laden gas first enters the self-excited dust collector 1706 for preliminary purification. The self-excited hydraulic dust collector is a wet dust removal device that utilizes the full contact between water and dust-laden gas to capture dust particles and purify the gas. The working process includes the following key steps: Dust-laden gas enters through the dust collector's inlet and, guided by the flow guiding device, rushes downwards towards the water surface, creating a strong impact. At this time, some larger dust particles will directly fall into the water due to inertia and be captured. Simultaneously, the gas impact on the water surface will agitate a large amount of water splashes and mist, forming an atomized zone filled with water droplets. As the dust-laden gas continues to flow upwards through this atomized zone, the fine dust particles in the gas will fully collide and contact with the water droplets and mist. Due to the adsorption effect of water, the dust particles will be adhered to the water droplets, forming dust-laden liquid droplets. The dust-laden gas first enters the self-excited dust collector for preliminary purification. The gas, carrying a small amount of water mist, enters the next stage.

[0296] Secondary dust removal: The 1707 water film dust collector with a two-flow air device enhances purification. This device, consisting of a dual-fluid nozzle composed of compressed air and water pipes, is installed in the middle of the dust collector, spraying water as ultrafine droplets of 0.1-10μm. Powered by 0.3-0.6MPa compressed air, the water is atomized into a mist, which mixes thoroughly with the rising dust-laden gas. Fine dust particles are adsorbed by the atomized droplets, forming "dust and droplet" aggregates. Some are further intercepted by the water film, while others are separated by the top dehydration device after rising with the airflow. Compared to traditional water film dust collectors, the additional introduction of auxiliary compressed air optimizes the flow field and water film morphology within the cylinder, enhancing the gas-liquid contact area and achieving higher dust removal efficiency.

[0297] A dual wet dust removal method is employed, combining a self-excited hydraulic dust collector and a two-flow gas-water film dust collector. The dust-laden hot gas discharged from the citric acid drying equipment first enters the self-excited hydraulic dust collector for preliminary purification, removing most of the coarse dust particles and reducing the gas temperature and acidity. The purified gas, carrying a small amount of dust and water vapor, then enters the water film dust collector containing the two-flow gas device for further purification, removing the remaining fine dust particles and acidic substances. Finally, the purified gas is treated by a dehydrator at the top of the water film dust collector (containing the two-flow gas device) before being discharged in compliance with standards.

[0298] Through the above process, the graded treatment of citric acid dust is achieved. The self-excited hydraulic dust collector first efficiently removes large dust particles, reducing the processing load of the secondary gas-water film dust collector, minimizing the impact and damage of fine dust on the water film, and improving the overall system stability and reliability. The secondary gas-water film dust collector then deeply captures the remaining fine dust, ensuring that the emitted gas meets stringent environmental standards. By addressing the "risk of coarse dust blockage" through self-excited pretreatment and resolving the issues of "fine dust escape" and "water film instability" through the secondary gas device, the triple goals of "high concentration tolerance + ultra-clean emissions + stable operation" are ultimately achieved. Its advantages are particularly significant for scenarios involving multi-particle-size, high-humidity, and easily hygroscopic dust, such as citric acid drying, as it not only meets stringent environmental standards but also increases product recovery rates, further improving product yield.

[0299] This unit, based on waste heat pre-concentration, employs live steam falling film evaporation crystallization, which reduces steam consumption, enhances waste heat recovery, and increases heat utilization rate to over 60%. Steam consumption is reduced by 0.5-1.2 tons per ton of product, controlling production costs while meeting process stability requirements. This unit combines falling film concentration evaporation with single-effect crystallization, improving crystallization efficiency and product purity, and shortening the production cycle. The condensate generated from the evaporation crystallization is used for washing and filtration in a vacuum belt filter, achieving condensate recovery. Citric acid drying utilizes a dual wet dust removal system. Self-excited pretreatment addresses the risk of coarse dust blockage, while a two-stage gas flow system solves the problems of fine dust escape and water film instability, ultimately achieving ultra-clean emissions and stable operation. For scenarios involving multi-particle size, high humidity, and easily hygroscopic dust, such as citric acid drying, its advantages are particularly significant, meeting stringent environmental standards while increasing product recovery rates and further improving product yield. It can not only reduce environmental pollution, but also recycle the collected dust, increase the product recycling rate, and has low operating costs and convenient maintenance, thereby reducing production costs, improving the economic benefits of enterprises, and achieving a win-win situation for both environmental and economic benefits.

[0300] The above description is merely a preferred embodiment of the present invention, showing and describing the basic principles, main features, and advantages of the present invention. It is not intended to limit the scope of patent protection of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. In addition to the above embodiments, the present invention may have other implementations without departing from the spirit and scope of the invention. Various changes and modifications to the present invention are possible, and all technical solutions formed by equivalent substitutions or equivalent transformations fall within the scope of protection claimed by the present invention. The scope of protection of the present invention is defined by the appended claims and their equivalents. Technical features not described in the present invention can be implemented by or using existing technology, and will not be elaborated here.

Claims

1. A system for producing citric acid from degermed corn flour, comprising a corn degermination unit, characterized in that: The starch and protein mixing outlet of the corn degerming unit is connected to the inlet of the crushing unit. The outlet of the crushing unit is connected to the inlet of the slurry preparation unit after metering. The outlet of the slurry preparation unit is connected to the inlet of the liquefaction unit. The outlet of the liquefaction unit is connected to the inlet of the seed tank (501) of the fermentation unit and the inlet of the horizontal screw separator unit. The seed liquid outlet of the seed tank (501) and the syrup outlet of the horizontal screw separator unit are both connected to the inlet of the fermentation tank (502).

2. The system for producing citric acid from degermed corn flour according to claim 1, characterized in that: In the corn degerming unit, the outlet of the feeding port (101) is connected to the inlet of the cleaning screen (103) via a primary bucket elevator (102). The material outlet of the cleaning screen (103) is connected to the inlet of the destoner (104). The material outlet of the destoner (104) is connected to the material inlet of the hydrating auger (110) via a secondary bucket elevator (109). The discharge port of the hydrating auger (110) is connected to the inlet of the corn storage bin (112) via a modulator (111). The bottom outlet of the corn storage bin (112) is connected to the inlet of the degerming machine (115) via a corn discharge auger (114). The discharge port of the degerming machine (115) is connected to the inlet of the grading screen (117) via a tertiary bucket elevator (116). The larger particle outlet of the grading screen (117) is connected to the inlet of the degerming machine (115).

3. The system for producing citric acid from degermed corn flour according to claim 2, characterized in that: The coarse powder outlet of the grading screen (117) is connected to the inlet of the embryo selector (118), the fine powder outlet of the grading screen (117) is connected to the lower inlet of the four-stage bucket elevator (121), and the upper outlet of the four-stage bucket elevator (121) is connected to the inlet of the hammer mill (122) of the crushing unit. The germ outlet of the embryo selector (118) is connected to the germ output pipe (G03); the germ-containing endosperm outlet of the embryo selector (118) is connected to the inlet of the embryo remover (115); and the starch and protein mixed outlet of the embryo selector (118) is also connected to the lower inlet of the four-stage bucket elevator (121). The gas phase outlet of the embryo selector (118) is connected to the inlet of the fiber separator dust collector (119), and the bottom fiber outlet of the fiber separator dust collector (119) is connected to the fiber output pipe (G02).

4. The system for producing citric acid from degermed corn flour according to claim 3, characterized in that: The bottom of the hammer mill (122) is provided with a hopper (125), and the bottom of the hopper (125) is provided with a screw conveyor (126). The outlet of the screw conveyor (126) is connected to the inlet of the corn flour storage bin (127). The outlet of the corn flour storage bin (127) is connected to the inlet of the corn flour auger (129) through a vibrating unloader (128). The outlet of the corn flour auger (129) is connected to the inlet of the metering auger (130). The outlet of the metering auger (130) is connected to the feed port of the ribbon mixer (133) of the slurry preparation unit. The outlet of the sugar water tank (131) is connected to the inlet of the sugar water pump (132). The outlet of the sugar water pump (132) is connected to the slurry inlet of the ribbon mixer (133) through the electromagnetic flow meter (FT-133) and the regulating valve (FC-133). The output port of the ribbon mixer (133) is connected to the corn flour slurry output pipe (G01).

5. The system for producing citric acid from degermed corn flour according to claim 4, characterized in that: The outlet of the corn flour output pipe (G01) is connected to the corn slurry buffer tank (201) of the liquefaction unit. The outlet of the corn slurry buffer tank (201) is connected to the main inlet of the static mixer (203) via the corn slurry discharge pump (202). The outlet of the primary enzyme metering pump (207) is connected to the enzyme inlet of the static mixer (203) via the primary enzyme flow meter (208). The outlet of the static mixer (203) is connected to the material inlet of the primary ejector (210) via the mixed flow meter (209). The outlet of the primary ejector (210) is connected to the inlet of the first maintaining pipe (211). The outlet of the maintenance pipe (211) is connected to the middle inlet of the first flash tank (212). The bottom outlet of the first flash tank (212) is connected to the lower inlet of the primary liquefaction column (219) via the laminar flow feed pump (213). The upper outlet of the primary liquefaction column (219) is connected to the middle inlet of the second flash tank (220). The outlet of the secondary enzyme metering pump (223) is connected to the enzyme inlet on the upper side wall of the second flash tank (220) via the secondary enzyme flow meter (FT-223). The bottom outlet of the second flash tank (220) is connected to the primary liquefaction discharge pipe (G06) via the primary liquefaction discharge pump (221).

6. The system for producing citric acid from degermed corn flour according to claim 5, characterized in that: The inlet pipe of the dilute alkali metering pump (205) is inserted into the lower part of the dilute alkali tank (204), and the outlet pipe of the dilute alkali metering pump (205) is also connected to the inlet of the corn syrup discharge pump (202); the steam pipe (G05) is connected to the steam inlet of the primary ejector (210). The primary liquefaction column (219) is provided with multiple columns connected in series. The top outlet of the previous liquefaction column is connected to the lower inlet of the next liquefaction column. The outlet of the laminar flow feed pump (213) is connected to the lower inlet of the first primary liquefaction column (219). The top outlet of the last primary liquefaction column (219) is connected to the middle inlet of the second flash tank (220). The bottom feed inlet of each primary liquefaction column (219) extends to the axis of the liquefaction column and then bends downward to form a bottom flushing device for flushing the bottom center.

7. The system for producing citric acid from degermed corn flour according to claim 6, characterized in that: The top secondary steam outlets of the first flash evaporator (212) and the second flash evaporator (220) are respectively connected to the hot side inlet of the first plate heat exchanger (214); the outlet of the cold sugar liquid pipe (G07) ​​is connected to the cold side inlet of the first plate heat exchanger (214), and the cold side outlet of the first plate heat exchanger (214) is connected to the inlet of the hot sugar liquid tank (217); the hot side outlet of the first plate heat exchanger (214) is connected to the middle inlet of the gas-liquid separator (215), and the bottom outlet of the gas-liquid separator (215) is also connected to the inlet of the hot sugar liquid tank (217). The outlet of the hot sugar liquid tank (217) is connected to the sugar water tank (131) through the hot sugar liquid pump (218) and the hot sugar liquid pipe (G04).

8. The system for producing citric acid from degermed corn flour according to claim 7, characterized in that: The outlet of the primary liquefaction discharge pipe (G06) is connected to the inlet of the secondary injector (301), the outlet of the secondary injector (301) is connected to the inlet of the second maintaining pipe (302), the outlet of the second maintaining pipe (302) is connected to the middle inlet of the third flash tank (303), and the top secondary steam outlet of the third flash tank (303) is also connected to the hot side inlet of the first plate heat exchanger (214); the bottom outlet of the third flash tank (303) is connected to the inlet of the secondary liquefaction column (305) via the secondary liquefaction feed pump (304), and the secondary liquid... The top outlet of the final stage of the liquefaction column (305) is connected to the middle inlet of the fourth flash tank (306). The bottom outlet of the fourth flash tank (306) is connected to the inlet of the liquefied liquid buffer tank (309) via the secondary liquefaction flash discharge pump (307) and the hot side of the condenser (308). The outlet of the liquefied liquid buffer tank (309) is connected to the seed tank (501) via the turbid liquid pump (310). The cold side inlet of the condenser (308) is connected to the outlet of the clear water pipe (G09), and the cold side outlet of the condenser (308) is connected to the hot water return pipe (G10).

9. The system for producing citric acid from degermed corn flour according to claim 8, characterized in that: The outlet of the liquefied liquid buffer tank (309) is also connected to the inlet of the first-stage horizontal decanter centrifuge (312) via the horizontal decanter feed pump (311) of the horizontal decanter separation unit. The heavy phase outlet of the first-stage horizontal decanter centrifuge (312) is connected to the inlet of the concentrated sugar buffer tank (316). The outlet of the concentrated sugar buffer tank (316) is connected to the fermentation tank (502) via the concentrated sugar transfer pump (317). The light phase outlet of the primary horizontal decanter centrifuge (312) is connected to the inlet of the sugar residue slurry tank (313). The outlet of the sugar residue slurry tank (313) is connected to the inlet of the secondary horizontal decanter centrifuge (315) via the slurry pump (314). The light phase outlet of the secondary horizontal decanter centrifuge (315) is connected to the cold side inlet of the first plate heat exchanger (214) via the cold sugar liquid pipe (G07). The heavy phase outlet of the secondary horizontal decanter centrifuge (315) is connected to the feed port of the tube bundle dryer (401) via the sugar residue pipe (G13).

10. The system for producing citric acid from degermed corn flour according to claim 9, characterized in that: The pre-concentrating single-effect evaporator (413), the pre-concentrating double-effect evaporator (415), and the pre-concentrating triple-effect evaporator (417) are connected in series and each is equipped with a separator; the outlet of the citric acid liquid pipe (G17) is connected to the top feed port of the pre-concentrating single-effect evaporator (413). The exhaust outlet of the tube bundle dryer (401) is connected to the inlet of the cyclone separator (404). The top exhaust port of the cyclone separator (404) is connected to the air inlet of the waste gas scrubbing tower (407) through the waste heat fan (406). The bottom outlet of the waste gas scrubbing tower (407) is connected to the middle inlet of the primary flash tank (408). The bottom outlet of the primary flash tank (408) is connected to the middle inlet of the secondary flash tank (409). The condensate outlet of the tube bundle dryer (401) is connected to the tube bundle condensate flash tank (411), and the top outlet of the tube bundle condensate flash tank (411) is connected to the shell inlet of the pre-concentration single-effect evaporator (413). The top outlets of the primary flash tank (408) and the pre-concentrating first-effect separator (414) are connected to the shell-side inlet of the pre-concentrating second-effect evaporator (415), and the top outlets of the secondary flash tank (409) and the pre-concentrating second-effect separator (416) are connected to the shell-side inlet of the pre-concentrating third-effect evaporator (417).

11. The system for producing citric acid from degermed corn flour according to claim 10, characterized in that: The outer periphery of the cyclone separator (404) is wrapped with a steam tracing pipe. The condensate outlet of the steam tracing pipe is also connected to the middle inlet of the tube bundle condensate flash tank (411). The bottom outlet of the tube bundle condensate flash tank (411) is connected to the condensate tank (412). The outlet of the condensate tank (412) is connected to the condensate supply pipe (G15) through the pre-concentrated condensate pump (424). The bottom outlet of the secondary flash tank (409) is connected to the upper spray port of the waste gas scrubbing tower (407) via a scrubbing tower circulation pump (410). The discharge port of the tube bundle dryer (401) is connected to the inlet of the three-way valve (402). The first outlet of the three-way valve (402) is connected to the cooling and packaging equipment. The second outlet of the three-way valve (402) is connected to the lower inlet of the return auger (403). The upper outlet of the return auger (403) is connected to the feeding auger inlet of the tube bundle dryer (401).

12. The system for producing citric acid from degermed corn flour according to claim 10, characterized in that: The bottom outlets of the pre-concentrating triple-effect evaporator (417) and the pre-concentrating triple-effect separator (418) are connected to the citric acid pre-concentration tank (1601) via the pre-concentrating triple-effect discharge pump (421), and the outlet of the citric acid pre-concentration tank (1601) is connected to the top inlet of the single-effect falling film evaporator (1603) via the citric acid pre-concentration feed pump (1602). The steam pipe (G05) is connected to the inlet of the steam jet pump (1600) via a regulating valve, and the outlet of the steam jet pump (1600) is connected to the shell-side inlet of the first-effect falling film evaporator (1603). The lower part of the first-effect falling film evaporator (1603) is connected to the first-effect separator (1604), and the bottom outlets of both are connected to the inlet of the first-effect discharge pump (1605); the outlet of the first-effect discharge pump (1605) is connected to the top inlet of the second-effect falling film evaporator (1606); the top outlet of the first-effect separator (1604) is simultaneously connected to the suction port of the steam jet pump (1600) and the shell-side inlet of the second-effect falling film evaporator (1606).

13. The system for producing citric acid from degermed corn flour according to claim 12, characterized in that: The lower part of the double-effect falling film evaporator (1606) is connected to the double-effect separator (1607), and the bottom outlets of both are connected to the feed inlet of the crystallizer (1610) through the double-effect discharge pump (1608). The bottom outlet of the crystallizer (1610) is connected to the circulating liquid inlet of the crystallizer (1610) via a forced circulation pump (1611) and a forced evaporator (1609); The top outlet of the double-effect separator (1607) is connected to the shell-side inlet of the forced evaporator (1609); the top outlet of the crystallizer (1610) is equipped with a crystallizer discharge density sensor (DT-1610) and is connected to the citric acid crystal slurry output pipe (G23) through a discharge pump (1612).

14. The system for producing citric acid from degermed corn flour according to claim 12, characterized in that: The bottom outlet of the seed tank (501) is connected to the top inlet of the fermentation tank (502) via a seed transfer pipeline (G27). The bottom outlet of the fermentation tank (502) is connected to the fermentation broth storage tank (601) via a citric acid output pipe (G28). The outlet of the fermentation broth storage tank (601) is connected to the inlet of the first-stage plate and frame filter press (603) via a fermentation broth discharge pump (602). The filtrate outlet of the first-stage plate and frame filter press (603) is connected to the first-stage concentrated acid tank (607). The outlet of the first-stage concentrated acid tank (607) is connected to the inlet pipe of the membrane filtration circulation pump (609) via a first-stage concentrated acid pump (608). The outlet of the membrane filtration circulation pump (609) is connected to the inlet of the ceramic membrane filtration system (610). The concentrate outlet of the ceramic membrane filtration system (610) is connected to the inlet pipe of the membrane filtration circulation pump (609) and the return port of the fermentation broth storage tank (601), forming a partial concentrate return circulation.

15. The system for producing citric acid from degermed corn flour according to claim 14, characterized in that: The filtrate outlet of the ceramic membrane filtration system (610) is connected to the citric acid concentrate tank (611). The outlet of the citric acid concentrate tank (611) is connected to the cation exchange column (613) and the anion exchange column (614) in sequence through the citric acid concentrate pump (612). The outlet of the anion exchange column (614) is connected to the citric acid ion exchange buffer tank (615). The outlet of the citric acid ion exchange buffer tank (615) is connected to the fine filtrate buffer tank (701) through the citric acid ion exchange discharge pump (616) and the citric acid fine filtrate pipe (G30).

16. The system for producing citric acid from degermed corn flour according to claim 15, characterized in that: The slag outlet of the primary plate and frame filter press (603) is connected to the inlet of the acid slag conditioning tank (604). The outlet of the condensate supply pipe (G15) is also connected to the inlet of the acid slag conditioning tank (604) through a regulating valve. The outlet of the acid slag conditioning tank (604) is connected to the inlet of the secondary plate and frame filter press (606) through the acid slag slurry pump (605). The slag outlet of the secondary plate and frame filter press (606) is connected to the feed inlet of the tube bundle dryer through the acid slag pipe (G14). The filtrate outlet of the secondary plate and frame filter press (606) is connected to the mixed acid tank (901) of the primary neutralization unit through the dilute citric acid clear liquid pipe (G29).

17. The system for producing citric acid from degermed corn flour according to claim 16, characterized in that: The outlet of the filtrate buffer tank (701) is connected to the cold side inlet of the second plate heat exchanger (703) via the filtrate pump (702). The cold side outlet of the second plate heat exchanger (703) is connected to the middle inlet of the filtrate flash tank (704). The bottom outlet of the filtrate flash tank (704) is connected to the deoxycitric acid buffer tank (705). The outlet of the deoxycitric acid buffer tank (705) is connected to the feed inlet of each chromatographic column (801) via the deoxycitric acid discharge pump (706). The outlet of the dilute sulfuric acid stock solution tube (G32) is connected to the inlet of the dilute sulfuric acid buffer tank (707). The outlet of the dilute sulfuric acid buffer tank (707) is connected to the cold side inlet of the third plate heat exchanger (709) via the dilute sulfuric acid pump (708). The cold side outlet of the third plate heat exchanger (709) is connected to the middle inlet of the dilute sulfuric acid flash evaporator (710). The bottom outlet of the dilute sulfuric acid flash evaporator (710) is connected to the inlet of the deoxygenated dilute sulfuric acid buffer tank (711). The bottom of the deoxygenated dilute sulfuric acid buffer tank (711) is connected to the eluent inlet of each chromatographic column (801) via the deoxygenated dilute sulfuric acid pump (712). The chromatographic column (801) is provided with multiple columns connected in series. The reflux port of each column is connected to the reflux port of the fine filtrate buffer tank (701) through the citric acid reflux tube (G34). The eluent outlet of each column is connected to the reflux port of the dilute sulfuric acid buffer tank (707) through the dilute sulfuric acid reflux tube (G35). The extract outlet of each column is connected to the acid hydrolysis citric acid tank (1501) through the citric acid purification liquid tube (G36). The sugar outlet of each chromatographic column (801) is connected to the dilute citric acid buffer tank (1101) of the secondary neutralization unit through the sugar discharge tube (G37).

18. The system for producing citric acid from degermed corn flour according to claim 17, characterized in that: The hot-side inlets of the second plate heat exchanger (703) and the third plate heat exchanger (709) are both connected to the steam pipe (G05), and the hot-side outlets of the second plate heat exchanger (703) and the third plate heat exchanger (709) are connected to the condensate tank (412) through the condensate return pipe (G16). The top outlets of the fine filtrate flash evaporator (704) and the dilute sulfuric acid flash evaporator (710) are respectively connected to the shell-side heat source inlet of the pre-concentrated triple-effect evaporator (417).

19. The system for producing citric acid from degermed corn flour according to claim 16, characterized in that: The inlet of the mixed acid tank (901) is also connected to the calcium hydrogen concentrated acid pipe (G38) from the vacuum filtration and washing unit. The outlet of the mixed acid tank (901) is connected to the inlet of the mixed acid circulation pump (902) and the mixed acid discharge pump (903). The outlet of the mixed acid circulation pump (902) is connected to the return port of the mixed acid tank (901). The outlet of the mixed acid discharge pump (903) is connected to the feed port of each primary neutralization pot (904). The top inlet of each primary neutralization pot (904) is also connected to the defoamer pipe (G26) and the calcium carbonate stock solution pipe (G39). The bottom outlet of each primary neutralization pot (904) is connected to the slurry distributor of the tricalcium citrate vacuum belt filter (1001) through the tricalcium citrate slurry pipe (G40).

20. The system for producing citric acid from degermed corn flour according to claim 19, characterized in that: The tricalcium vacuum belt filter (1001) is provided with a feeding area, a filtration area, a washing and dehydration area and a cake discharge area in sequence along the filter cloth forward direction, and the sugar water outlet below is connected to the inlet of the vacuum tank (1002). The exhaust port at the top of each vacuum tank (1002) is connected to the middle inlet of the gas-water separator (1003). The top of the gas-water separator (1003) is vented to the atmosphere through a vacuum pump (1004). Except for the final stage, the bottom outlet of each vacuum tank (1002) and the bottom outlet of the gas-water separator (1003) are connected to the inlet of the waste sugar water tank (1005). The outlet of the waste sugar water tank (1005) is connected to the waste sugar water pump (1006) and the wastewater treatment station.

21. The system for producing citric acid from degermed corn flour according to claim 20, characterized in that: The bottom outlet of the fifth-stage vacuum tank (1002-5) of the tricalcium vacuum belt filter (1001) is connected to the inlet of the sugar water tank (1007). The sugar water tank (1007) is connected to the first-stage rinsing water inlet above the washing and dehydration zone via the sugar water pump (1008). The end washing water outlet of the tricalcium vacuum belt filter (1001) is connected to the inlet of the tricalcium washing water tank (1009). The outlet of the tricalcium washing water tank (1009) is connected to the second-stage rinsing water inlet above the washing and dehydration zone of the tricalcium vacuum belt filter (1001) via the tricalcium washing water pump (1010). The third-stage rinsing water inlet above the washing and dehydration zone is connected to the condensate supply pipe (G15).

22. The system for producing citric acid from degermed corn flour according to claim 20, characterized in that: The filter cake discharge port of the tricalcium vacuum belt filter (1001) is connected to the tricalcium slurry preparation tank (1011), and the slurry preparation water inlet of the tricalcium slurry preparation tank (1011) is connected to the condensate supply pipe (G15). The outlet of the tricalcium slurry preparation tank (1011) is connected to the second secondary neutralization pot (1104) via the tricalcium slurry preparation pump (1012). Multiple secondary neutralization pots (1104) are connected in series. The outlet of the last secondary neutralization pot (1104) is connected to the inlet of the secondary neutralization variable frequency circulation pump (1105) and the secondary neutralization discharge pump (1106). The outlet of the secondary neutralization variable frequency circulation pump (1105) is connected to the return port of the first secondary neutralization pot (1104). The outlet of the secondary neutralization discharge pump (1106) is connected to the slurry distributor of the calcium hydrogen vacuum belt filter (1201).

23. The system for producing citric acid from degermed corn flour according to claim 22, characterized in that: The calcium hydrogen vacuum belt filter (1201) is provided with a feeding area, a filtration area, a washing and dehydration area and a cake discharge area in sequence along the filter cloth forward direction, and the filtrate outlet below is connected to the inlet of the vacuum tank (1202). The exhaust port at the top of each vacuum tank (1202) is connected to the middle inlet of the gas-water separator (1203). The top of the gas-water separator (1203) is vented to the atmosphere through a vacuum pump (1204). The washing and dehydration zone is equipped with five vacuum tanks in sequence along the direction of filter cloth movement. The bottom outlets of the vacuum tank (1202-1), the first-stage vacuum tank (1202-2), the second-stage vacuum tank (1202-3), and the gas-water separator (1203) in the filtration zone are all connected to the inlet of the calcium hydrogen acid buffer tank (1205). The outlet of the calcium hydrogen acid buffer tank (1205) is connected to the calcium hydrogen acid pump (1206) and the mixed acid tank (901).

24. The system for producing citric acid from degermed corn flour according to claim 23, characterized in that: The outlet of the three-stage vacuum tank (1202-4) is connected to the first-stage calcium hydrogen acid tank (1207), and the bottom outlet of the first-stage calcium hydrogen acid tank (1207) is connected to the first-stage rinsing water inlet above the washing and dehydration zone through the first-stage calcium hydrogen acid pump (1208). The outlet of the fourth-stage vacuum tank (1202-5) is connected to the second-stage calcium hydrogen acid tank (1209), and the outlet of the second-stage calcium hydrogen acid tank (1209) is connected to the second-stage rinsing water inlet above the washing and dehydration zone through the second-stage calcium hydrogen acid pump (1210). The outlet of the five-stage vacuum tank (1202-6) is connected to the four-stage calcium hydrogen acid tank (1211). The bottom outlet of the four-stage calcium hydrogen acid tank (1211) is connected to the four-stage rinsing water inlet above the washing and dehydration zone through the four-stage calcium hydrogen acid pump (1212). The end washing water outlet of the calcium hydrogen vacuum belt filter (1201) is connected to the inlet of the calcium hydrogen washing water tank (1213), and the outlet of the calcium hydrogen washing water tank (1213) is connected to the three-stage rinsing water inlet above the washing and dehydration zone through the calcium hydrogen washing water pump (1214). The five-stage rinsing water inlet above the washing and dehydration zone is connected to the condensate supply pipe (G15).

25. The system for producing citric acid from degermed corn flour according to claim 23, characterized in that: The filter cake discharge port of the calcium hydrogen vacuum belt filter (1201) is connected to the calcium hydrogen slurry preparation tank (1215), the slurry water inlet of the calcium hydrogen slurry preparation tank (1215) is connected to the condensate supply pipe (G15), and the bottom outlet of the calcium hydrogen slurry preparation tank (1215) is connected to the calcium hydrogen slurry buffer tank (1301) of the acidolysis unit through the calcium hydrogen slurry preparation pump (1216). The outlet of the calcium hydrogen slurry buffer tank (1301) is connected to the inlet of the first acidolysis pot (1304-1) via the calcium hydrogen slurry pump (1302), and multiple acidolysis pots (1304) are connected in series. The bottom outlet of the concentrated sulfuric acid high-level tank (1307) is also connected to the acid inlet of the first acidolysis pot (1304-1). The outlet of the final acidolysis pot is connected to the inlet of the acidolysis variable frequency circulation pump (1305) and the acidolysis discharge pump (1306). The outlet of the acidolysis variable frequency circulation pump (1305) is connected to the circulation port of the first acidolysis pot (1304-1), and the outlet of the acidolysis discharge pump (1306) is connected to the slurry distributor of the acidolysis vacuum belt filter (1401).

26. The system for producing citric acid from degermed corn flour according to claim 25, characterized in that: The acid hydrolysis vacuum belt filter (1401) is provided with a feeding area, a filtration area, a washing and dehydration area and a cake discharge area in sequence along the filter cloth forward direction, and the filtrate outlet below is connected to the inlet of the vacuum tank (1402) respectively. The exhaust port at the top of each vacuum tank (1402) is connected to the middle inlet of the gas-water separator (1403). The washing and dehydration zone is equipped with five vacuum tanks in sequence along the direction of filter cloth movement. The bottom outlets of the vacuum tank (1402-1), the first-stage vacuum tank (1402-2), the second-stage vacuum tank (1402-3), and the gas-water separator (1403) in the filtration zone are all connected to the inlet of the acid hydrolysis concentrated acid tank (1405). The outlet of the acid hydrolysis concentrated acid tank (1405) is connected to the acid hydrolysis concentrated acid pump (1406) and the acid hydrolysis citric acid tank (1501).

27. The system for producing citric acid from degermed corn flour according to claim 26, characterized in that: The outlet of the acid hydrolysis citric acid tank (1501) is connected to the inlet of the decolorization column (1503) via the acid hydrolysis citric acid pump (1502), and the outlet of the decolorization column (1503) is connected to the citric acid buffer tank (1504). The cation exchange system (1506) is a continuous rotary multi-column series-parallel structure. The resin columns are arranged in a ring around the circumference of the rotary table and are divided into a water washing top material zone, a compressed air top material zone, a primary exchange zone, a secondary exchange zone, a product top water zone, a regeneration water washing zone, a regeneration zone, and a pretreatment regeneration zone. The outlet of the citric acid buffer tank (1504) is connected to the inlet of the primary exchange zone in the cation exchange system (1506) via the ion exchange feed pump (1505). The outlet of the primary exchange zone is connected to the inlet of the secondary exchange zone via the primary cation exchange liquid tank (1507) and the primary cation exchange liquid feed pump (1508). The outlet of the secondary exchange zone is connected to the feed end of the anion exchange system (1520) via the secondary cation exchange liquid tank (1509) and the secondary cation exchange liquid feed pump (1510). The discharge end of the anion exchange system (1520) is connected to the inlet of the citric acid tank (1526). The outlet of the citric acid tank (1526) is connected to the feed port of the pre-concentration first-effect evaporator (413) via the citric acid liquid pump (1527).

28. The system for producing citric acid from degermed corn flour according to claim 27, characterized in that: The anion exchange system (1520) is a continuous rotary multi-column series-parallel structure. The resin columns are arranged in a ring around the circumference of the rotary table and are divided into a water washing top material zone, a compressed air top material zone, a primary exchange zone, a secondary exchange zone, a product top water zone, a regeneration water washing zone, a regeneration zone, and a pretreatment regeneration zone. The primary and secondary exchange regions of the cation exchange system (1506) and the anion exchange system (1520) are both connected in parallel with five channels, each consisting of a resin column; The cation exchange system (1506) and the anion exchange system (1520) are respectively equipped with three columns connected in series in the water washing top material zone, the compressed air top material zone and the product top water zone are respectively composed of one resin column, the regeneration water washing zone is respectively equipped with four columns connected in series, the regeneration zone is respectively equipped with two columns connected in series, and the pretreatment regeneration zone is respectively equipped with three columns connected in series. The outlet of the hydrochloric acid pipe is connected to the inlet of the regeneration zone in the cation exchange system (1506). The outlet of the regeneration water washing zone and the regeneration zone in the cation exchange system (1506) is connected to the inlet of the hydrochloric acid refill tank (1511). The outlet of the hydrochloric acid refill tank (1511) is connected to the inlet of the pretreatment regeneration zone in the cation exchange system (1506) through the hydrochloric acid refill pump (1512). The outlet of the pretreatment regeneration zone is connected to the waste liquid pipe.

29. The system for producing citric acid from degermed corn flour according to claim 28, characterized in that: The outlet of the RO water pipe is connected to the inlet of the washing top material area and the regeneration washing area in the cation exchange system (1506) and the anion exchange system (1520), respectively; The outlet of the compressed air pipe (G25) is connected to the inlet of the compressed air top material zone in the cation exchange system (1506) and the anion exchange system (1520), respectively; The outlets of the water washing top material area and the compressed air top material area in the cation exchange system (1506) are respectively connected to the inlet of the primary cation exchange liquid tank (1507); The outlet of the secondary exchange zone in the cation exchange system (1506) is also connected to the lower inlet of the product top water zone, and the top outlet of the product top water zone is connected to the inlet of the regenerated water washing zone.

30. The system for producing citric acid from degermed corn flour according to claim 29, characterized in that: The outlet of the alkali solution pipe is connected to the inlet of the regeneration zone in the anion exchange system (1520). The outlet of the regeneration water washing zone and the regeneration zone in the anion exchange system (1520) is connected to the inlet of the dilute alkali tank (1524). The outlet of the dilute alkali tank (1524) is connected to the inlet of the pretreatment regeneration zone in the anion exchange system (1520) through the dilute alkali pump (1525). The outlet of the pretreatment regeneration zone is connected to the waste liquid pipe. The outlets of the water washing top material zone and the compressed air top material zone in the anion exchange system (1520) are respectively connected to the inlet of the primary anion exchange liquid tank (1521). The bottom outlet of the primary anion exchange liquid tank (1521) is connected to the inlet of the secondary exchange zone in the anion exchange system (1520) through the primary anion exchange liquid feeding pump (1522). The outlets of the secondary exchange zone and the product top water zone are both connected to the inlet of the citric acid tank (1526).

31. The system for producing citric acid from degermed corn flour according to claim 13, characterized in that: The outlet of the citric acid crystal slurry output pipe (G23) is connected to the inlet of the feed distribution tank (1701), the outlet of the feed distribution tank (1701) is connected to the inlet of the top-rotating centrifuge (1702), the bottom outlet of the top-rotating centrifuge (1702) is provided with a discharge auger (1703), the outlet of the discharge auger (1703) is equipped with a vibrating conveyor (1704), the outlet of the vibrating conveyor (1704) is connected to the feed inlet of the vibrating fluidized bed (1705); the discharge outlet of the vibrating fluidized bed (1705) is connected to the inlet of the gyratory screen (1709), the undersize outlet of the gyratory screen (1709) is connected to the inlet of the finished product buffer silo (1710), and the outlet of the finished product buffer silo (1710) is connected to the inlet of the packing scale (1711).

32. The system for producing citric acid from degermed corn flour according to claim 31, characterized in that: The sieve outlet of the swing screen (1709) is connected to the inlet of the remelting tank (1718), the outlet of the pre-concentration condensate pump (424) is connected to the slurry water inlet of the remelting tank (1718) through the condensate supply pipe (G15), and the bottom outlet of the remelting tank (1718) is connected to the reflux port of the citric acid pre-concentration tank (1601) through the centrifugal pump (1719). The outlet of the air filter (1712) is connected to the air inlet of the finned heat exchanger (1713), and the air outlet of the finned heat exchanger (1713) is connected to the air inlet of the drying section of the vibrating fluidized bed (1705) through the blower (1714); the outlet of the air filter (1715) is connected to the air inlet of the rotary dehumidifier (1716), and the air outlet of the rotary dehumidifier (1716) is connected to the air inlet of the cooling section of the vibrating fluidized bed (1705) through the cooling fan (1717); The exhaust port of the vibrating fluidized bed (1705) is connected to the inlet of the self-excited hydraulic dust collector (1706), the outlet of the self-excited hydraulic dust collector (1706) is connected to the lower air inlet of the two-flow air-water film dust collector (1707), and the top air outlet of the two-flow air-water film dust collector (1707) is vented to the atmosphere through the induced draft fan (1708); the compressed air inlet of the two-flow air-water film dust collector (1707) is connected to the compressed air pipe (G25), and the spray water inlet of the two-flow air-water film dust collector (1707) is connected to the RO water pipe (G41).

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