Citric acid concentration, evaporation, crystallization, and waste heat recovery device

Abstract

This utility model discloses a citric acid concentration, evaporation, crystallization, and waste heat recovery device, belonging to the technical field of citric acid production equipment. The device includes a tube bundle dryer, and pre-concentration first-effect, second-effect, and third-effect evaporators connected in series, each equipped with a separator. The citric acid liquid is piped to the top inlet of the first-effect pre-concentration evaporator. The exhaust gas outlet of the tube bundle dryer is connected to a cyclone separator. The exhaust gas from the top of the cyclone separator is connected to a waste gas scrubbing tower via a waste heat fan. The water outlet at the bottom of the scrubbing tower is connected to a primary flash tank, which is then connected to a secondary flash tank. The condensate outlet of the tube bundle dryer is connected to the tube bundle condensate flash tank, and its top outlet is connected to the shell side of the first-effect pre-concentration evaporator. The top outlets of the primary flash tank and the first-effect pre-concentration separator are both connected to the shell side of the second-effect pre-concentration evaporator, and the top outlets of the secondary flash tank and the second-effect pre-concentration separator are both connected to the shell side of the third-effect pre-concentration evaporator. This device utilizes waste heat to pre-concentrate citric acid, reducing steam consumption and improving heat utilization efficiency.

Description

Technical Field

[0001] This utility model relates to a citric acid production apparatus, and more particularly to a citric acid concentration, evaporation, crystallization, and waste heat recovery apparatus, belonging to the technical field of citric acid production equipment. Background Technology

[0002] In the industrial production process of citric acid, evaporation and crystallization is the core link between purification and finished product. Its technical level directly determines product quality, production efficiency and overall cost, and has an irreplaceable impact on the competitiveness of the entire industrial chain.

[0003] In terms of production efficiency and capacity, evaporation crystallization accounts for 30% to 40% of the entire citric acid production cycle, and its rate directly restricts the scale of output for enterprises. With the expansion of the citric acid industry and the increasing market demands for product quality, the drawbacks of this traditional crystallization process are becoming increasingly apparent. From an efficiency perspective, single-effect and double-effect crystallization largely rely on simple steam heating and evaporation, which limits heat transfer and mass diffusion rates, resulting in low crystallization efficiency and making it difficult to meet the rapidly growing market demand.

[0004] In terms of product quality, traditional processes struggle to precisely control key parameters such as temperature and supersaturation during crystallization. If supersaturation rises rapidly in the early stages of crystallization, a large number of crystal nuclei will form, resulting in fine and uneven crystal particles. In subsequent processes such as centrifugation and drying, these small crystal particles are prone to agglomeration and loss, reducing product purity.

[0005] Energy cost control is another important aspect of the value of evaporation crystallization. Currently, citric acid plants mostly use single-effect and double-effect crystallization processes in their evaporation crystallization operations. In single-effect crystallization, steam can only be used once, with a large amount of waste heat being directly emitted into the environment, resulting in a heat utilization rate of less than 30%. Although double-effect crystallization reuses steam, its heat recovery efficiency is still not ideal. With continuously rising energy costs, high steam consumption significantly compresses corporate profit margins. While single-effect and double-effect crystallization processes are characterized by simple equipment and low maintenance costs, they still have significant drawbacks: low product crystallization efficiency, long production cycles, uneven crystal particle size, and low purity; and high steam consumption.

[0006] Patent CN110960874B discloses "a citric acid evaporation, concentration, and crystallization apparatus and method". This technical solution uses live steam to heat citric acid solution and employs steam ejection technology, MVR evaporation technology, and single-effect crystallization to evaporate and crystallize citric acid. Although it saves some steam, the system operates stably, and has high thermal efficiency, it has the following drawbacks: First, MVR evaporation technology has high power consumption, which will increase production costs; second, it uses live steam as the heat source for heating, which results in relatively high steam consumption compared to waste heat evaporation.

[0007] In conclusion, the combination of waste heat pre-concentration and live steam falling film evaporation crystallization is of great significance in order to save steam consumption and ensure product quality. Utility Model Content

[0008] 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 present invention.

[0009] In view of the problems existing in the above and / or prior art, this utility model is proposed.

[0010] The purpose of this invention is to overcome the problems existing in the prior art and provide a citric acid concentration, evaporation, crystallization and waste heat recovery device, which can improve product crystallization efficiency, shorten the production cycle, make the crystallized particles more uniform, have higher purity, and have lower steam consumption.

[0011] To solve the above technical problems, this utility model provides a citric acid concentration, evaporation, crystallization, and waste heat recovery device, comprising a tube bundle dryer 401, a pre-concentration first-effect evaporator 413, a pre-concentration second-effect evaporator 415, and a pre-concentration third-effect evaporator 417 connected in series and each equipped with a separator; the outlet of the citric acid liquid pipe G17 is connected to the top inlet 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.

[0012] Furthermore, the shell-side inlet of the pre-concentrated triple-effect evaporator 417 is also connected to the outlet of the downstream fine filtrate flash vapor tube G21 and the dilute sulfuric acid flash vapor tube G22.

[0013] 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.

[0014] Furthermore, 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.

[0015] Furthermore, 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, and the upper outlet of the return auger 403 is connected to the feeding auger inlet of the tube bundle dryer 401.

[0016] Furthermore, the bottom of the cyclone separator 404 is connected to the middle inlet of the return auger 403 via an airlock 405.

[0017] 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.

[0018] 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 bottom 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 citric acid crystal slurry discharge pump 1612.

[0019] Furthermore, the top outlet of the crystallizer 1610 is also connected to the shell-side air inlet of the surface condenser 1613, and the shell-side condensate outlet of the surface condenser 1613 is connected to the condensate tank 412 through the condensate return pipe G16.

[0020] Compared with the prior art, the advantages or beneficial effects of the embodiments of this application include at least the following: 1. Citric acid evaporation crystallization accounts 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 device adopts a combination of waste heat pre-concentration and live steam falling film evaporation crystallization, which can reduce steam consumption, enhance waste heat recovery, and increase the heat utilization rate to over 60%; the steam consumption per ton of product is reduced by 0.5 to 1.2 tons.

[0021] 2. This device can improve crystallization efficiency and product purity, and shorten the production cycle.

[0022] 3. Evaporation and crystallization utilize the condensate generated from live steam for washing and filtration in a calcium salt process vacuum belt filter, thus achieving condensate recycling. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. 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 this utility model. Wherein: Figure 1 This is a flowchart of the drying and pre-concentration evaporation crystallization unit in this utility model; Figure 2 This is a flowchart of the concentration, evaporation, and crystallization unit in this invention; Figure label: Condenser 308; 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. Flash evaporator for downstream fine filtrate 704; Flash evaporator for dilute sulfuric acid 714; Citric acid 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. Feed distribution trough 1701; Steam pipe G05; Hot water reuse pipe G10; 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; Fine filtrate flash vapor pipe G21; Dilute sulfuric acid flash vapor pipe G22; Citric acid crystal slurry output pipe G23. Detailed Implementation

[0024] In the following description of this utility model, 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 this utility model and simplifying the description, and do not mean that the device must have a specific orientation.

[0025] To make the technical means, creative features, achieved objectives and effects of this utility model easier to understand, the present utility model will be further described below with reference to specific illustrations. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments.

[0026] 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.

[0027] like Figure 1 As shown, in the citric acid concentration, evaporation, crystallization, and waste heat recovery device of this utility model, 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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 714 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.

[0034] 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.

[0035] 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.

[0036] 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 section as washing water to clean the filter cake via the pre-concentration condensate pump 424 and condensate supply pipe G15.

[0037] 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.

[0038] 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.

[0039] Citric acid pre-concentration: using a multi-effect falling film evaporator.

[0040] After continuous ion exchange, impurity ions in the citric acid solution have been 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 section 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 along 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.

[0041] 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 device 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.

[0042] 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.

[0043] 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.

[0044] like Figure 2 As shown, 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-concentration 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. 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.

[0045] 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.

[0046] 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.

[0047] The bottom 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] The material coming out of crystallizer 1610 is detected by density sensor DT-1610. When it reaches a certain density, it is pumped to the citric acid drying section by citric acid slurry discharge pump 1612. A portion of it is pumped into forced evaporator 1609 by forced circulation pump 1611 to mix with new material and continue to evaporate and crystallize.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] Through the above process, steam consumption is reduced and waste heat recovery is enhanced; the combination of falling film concentration evaporation and single-effect crystallization improves crystallization efficiency and product purity.

[0057] The above description is merely a preferred embodiment of the present utility model, showing and describing the basic principles, main features, and advantages of the present utility model. It is not intended to limit the scope of patent protection of the present utility model. Those skilled in the art should understand that the present utility model is not limited to the above embodiments. In addition to the above embodiments, the present utility model may have other implementations without departing from the spirit and scope of the present utility model. Various changes and improvements to the present utility model are also possible. All technical solutions formed by equivalent substitutions or equivalent transformations fall within the scope of protection claimed by the present utility model. The scope of protection claimed by the present utility model is defined by the appended claims and their equivalents. Technical features not described in the present utility model can be implemented by or using existing technology, and will not be elaborated here.

Claims

1. A device for concentrated evaporation crystallization of citric acid and waste heat recovery, comprising a tube bundle drier (401), 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).

2. The citric acid concentration evaporation crystallization and waste heat recovery apparatus according to claim 1, characterized by: The shell-side inlet of the pre-concentrated triple-effect evaporator (417) is also connected to the outlet of the downstream fine filtrate flash vapor tube (G21) and dilute sulfuric acid flash vapor tube (G22).

3. The citric acid concentration evaporation crystallization and waste heat recovery apparatus according to claim 1, characterized by: 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).

4. The citric acid concentration evaporation crystallization and waste heat recovery apparatus according to claim 1, characterized by: The bottom outlet of the secondary flash tank (409) is connected to the upper spray port of the exhaust gas scrubbing tower (407) via a scrubbing tower circulation pump (410).

5. The citric acid concentration evaporation crystallization and waste heat recovery apparatus according to claim 1, characterized by: 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 connected to the feeding auger inlet of the tube bundle dryer (401).

6. The citric acid concentration evaporation crystallization and waste heat recovery apparatus according to claim 5, characterized by: The bottom of the cyclone separator (404) is connected to the middle inlet of the return auger (403) via an airlock (405).

7. The citric acid concentrating evaporation and crystallization and waste heat recovery apparatus as claimed in claim 1, wherein: 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).

8. The citric acid concentration evaporation crystallization and waste heat recovery apparatus according to claim 7, characterized by: 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 bottom 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).

9. The citric acid concentration evaporation crystallization and waste heat recovery apparatus according to claim 8, characterized by: The top outlet of the crystallizer (1610) is also connected to the shell-side air inlet of the surface condenser (1613), and the shell-side condensate outlet of the surface condenser (1613) is connected to the condensate tank (412) through the condensate return pipe (G16).

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