Citric acid fermentation refining device

Abstract

The utility model discloses a kind of citric acid fermentation fine filter devices, belong to citric acid production technical field.Device is composed of fermentation unit and fine filter unit: fermentation unit contains seed tank and fermentation tank, the feed inlet of seed tank is connected with syrup turbid liquid pipe, the feed inlet of fermentation tank is connected with syrup clear liquid pipe and syrup turbid liquid pipe, seed tank and fermentation tank are configured with steam, compressed air, defoaming agent, emptying and circulating water pipeline.Fine filter unit first removes most solid impurities with primary plate-and-frame filtration, then ceramic membrane fine filtration and anion and cation exchange impurity removal.Two-stage filter-pressing acid residue is dried after being thickened and then filter-pressing to be feed, and two-stage filtrate respectively enters subsequent process.The device can greatly reduce labor cost and failure rate, improve citric acid purity and yield, and meet the needs of large-scale, high-quality and green production.

Description

Technical Field

[0001] This utility model relates to a citric acid production device, and more particularly to a citric acid fermentation and filtration device, belonging to the technical field of citric acid production equipment. Background Technology

[0002] In the citric acid fermentation industry, technological innovation is crucial for improving production efficiency and product quality. Currently, most companies still use traditional operating methods, heavily relying on manual labor to perform various tasks on the production floor. From adding materials to the fermentation tank and real-time monitoring and control of fermentation process parameters (temperature, pH, dissolved oxygen, etc.) to periodic sample collection and testing, everything is done manually. This method not only consumes a lot of manpower but is also susceptible to human error, making it difficult to precisely match fermentation conditions between different batches, thus affecting product quality stability. For example, during manual inspections, uneven time intervals may cause the optimal parameter adjustment time to be missed, causing the fermentation process to deviate from its optimal state, resulting in citric acid yield fluctuations of up to 5%-10% and residual sugar content differences of up to 3g / L.

[0003] Manual operation also severely restricts the further expansion of production scale. As order volume increases, the inefficiency of manual operation becomes a bottleneck for capacity improvement, requiring companies to invest more in labor costs to maintain production and compress profit margins. According to statistics, manual operation accounts for 15%-20% of the production cost of citric acid, and production accidents caused by operational errors also occur frequently, increasing additional losses.

[0004] While automated control technology has been widely applied and achieved significant results in other fermentation fields (such as beer and antibiotic fermentation), its application in citric acid fermentation is still in its early stages. The main reason is the complexity of the citric acid fermentation process, involving multiple microbial metabolic pathways and the interaction of complex environmental factors, making the development of a suitable automated control system quite challenging. At the same time, some companies lack sufficient understanding of automation technology and worry about excessively high upfront equipment investment and system maintenance costs, hindering the pace of technological upgrades.

[0005] Chinese patent application CN101942487A discloses "a method for preparing citric acid by fermentation with added saccharifying enzyme." This technical solution involves manually adding saccharifying enzyme during the cooling process after sterilization of the fermentation medium, followed by inoculation with seed liquid, and manually monitoring the fermentation process. While this technical solution optimizes the saccharification process to some extent, it still relies on manual control of key operational points and fails to overcome the limitations of manual operation.

[0006] The fermented citric acid solution contains a large amount of insoluble materials from corn raw materials, such as fiber, germ, and ash. The presence of these impurities directly affects subsequent purification processes and the quality of the final product. Currently, the industry mainly uses plate and frame filter presses for filtration. Plate and frame filter presses can directly separate impurities through the mechanical interception of the 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 using plate and frame filter presses have gradually become apparent. Its filtration accuracy is relatively low, and it cannot effectively intercept fine ash particles, oil emulsified particles in the germ, and some soluble colloids, resulting in low purity of the filtrate. Subsequent processes need to additionally treat these impurities, thus affecting the quality of the final product.

[0007] 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.

[0008] Patent application CN102091453A discloses "a plate and frame filter press and its solid-liquid separation method for citric acid production." Using corn as raw material, without pre-removing fiber and ash from the corn, the process involves adding a flocculant to the citric acid fermentation broth after fermentation and stirring until homogeneous, followed by adding a filter aid and stirring until homogeneous again. A plate and frame filter press is then used for primary solid-liquid separation, and the filtrate is repeated for secondary solid-liquid separation to obtain a clear citric acid solution. This technical solution has the following drawbacks: relying entirely on plate and frame filtration to treat the fermented citric acid solution results in significant deficiencies in filtration efficiency, filtration effect, production cost, and production continuity. It cannot provide stable and qualified raw materials for subsequent production processes, hindering the efficient and stable production of citric acid.

[0009] Currently, some manufacturers are trying to filter citric acid residue using membrane filtration. However, in actual operation, the large amount of fiber and ash in the citric acid residue can easily wear down the ceramic membrane, leading to its failure.

[0010] In summary, to improve the stability of the fermentation process and the consistency of product quality, reduce labor costs and the risk of human error, and realize digital and intelligent management of the production process, it is of great significance to adopt a fully automated control system during fermentation. In addition, fermenting whole corn after crushing and using plate and frame filtration throughout can no longer meet the requirements for large-scale and high-quality citric acid production. Utility Model Content

[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 present invention.

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

[0013] The purpose of this invention is to overcome the problems existing in the prior art and provide a citric acid fermentation and filtration device. The fermentation process adopts a fully automated control system to solve the problem of citric acid contamination caused by human error, ensure product quality stability, and reduce labor costs.

[0014] To solve the above technical problems, this utility model provides a citric acid fermentation and filtration device, including a fermentation unit. The fermentation unit includes a seed tank 501 and a fermentation tank 502. The top material inlet of the seed tank 501 is connected to the outlet of the syrup turbid liquid pipe G11 through a turbid liquid feed regulating valve. The top exhaust port of the seed tank 501 is connected to the tank top exhaust pipeline G24 through an exhaust regulating valve. The top air inlet of the seed tank 501 is connected to the compressed air pipe G25 through a compressed air regulating valve. The top defoamer inlet of the seed tank 501 is connected to the defoamer pipeline G26 through a defoamer feed switch valve. A steam pipeline G05 is connected to the top inlet and bottom outlet of the seed tank 501 through a steam regulating valve. The bottom outlet of the seed tank 501 is connected to the top inlet of the fermentation tank 502 through a seed transfer switch valve and a seed transfer pipeline G27.

[0015] Furthermore, the top material inlet of the fermenter 502 is connected to the outlet of the syrup clear liquid pipe G12 via a clear liquid feed regulating valve, and to the outlet of the syrup turbid liquid pipe G11 via a turbid liquid feed regulating valve; the outlet of the condensate supply pipe G15 from the previous stage is connected to the outlet of the turbid liquid feed regulating valve; the top exhaust port of the fermenter 502 is connected to the tank top exhaust pipeline G24 via an exhaust regulating valve; the top air inlet of the fermenter 502 is connected to the compressed air pipe G25 via a compressed air regulating valve; the top defoamer inlet of the fermenter 502 is connected to the defoamer pipeline G26 via a defoamer feed switch valve; the steam pipe G05 is connected to the top inlet and bottom outlet of the fermenter 502 via steam regulating valves; and the bottom outlet of the fermenter 502 is connected to a citric acid output pipe G28.

[0016] Furthermore, the jacket inlets of the seed tank 501 and the fermentation tank 502 are both connected to the circulating water supply pipe G19, and the jacket outlets are both connected to the circulating water return pipe G20.

[0017] Furthermore, both the seed tank 501 and the fermentation tank 502 are equipped with temperature sensors, pressure sensors, pH sensors and defoaming sensors, and each sensor is interlocked with the corresponding regulating valve and switching valve for control.

[0018] Furthermore, the citric acid output pipe G28 is connected to the fermentation broth storage tank 601. 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.

[0019] 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 via the citric acid ion exchange discharge pump 616 and the citric acid fine filtrate pipe G30.

[0020] 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.

[0021] Compared to the prior art, the advantages or beneficial effects of the embodiments of this application include at least the following: 1. Ensure precise and consistent fermentation conditions across different batches to guarantee product quality stability. Through a fully automated control system, key parameters such as temperature, pH, dissolved oxygen, and pressure during the fermentation process are monitored and automatically adjusted in real time. This avoids fluctuations caused by manual operation, ensures the consistency of citric acid fermentation conditions for each batch, significantly reduces product quality differences caused by human factors, and improves citric acid yield and purity.

[0022] 2. Reduce labor costs and the risk of human error. 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 device 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.

[0023] 3. Achieve digital and intelligent management of the fermentation process to meet the needs of large-scale production. By linking sensors with automated valves, the fermentation process can be monitored and recorded in real time, facilitating data traceability and analysis. 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 bottlenecks of manual operation, meeting the capacity demands brought about by order growth, helping enterprises reduce costs, increase efficiency, and enhance market competitiveness.

[0024] 4. Optimize seed culture and fermentation processes to improve fermentation efficiency. The seed tank uses syrup turbidity as a substrate, retaining natural nitrogen sources and trace elements, which significantly enhances the activity and stress resistance of the seed cells. The fermentation tank ensures that the strains produce acid efficiently under optimal conditions through precise temperature and oxygen control, automated enzyme addition and transfer, shortening the fermentation cycle and improving the citric acid conversion rate.

[0025] 5. Reduce the risk of contamination and improve product purity. The fully automated sterilization process (both air and physical sterilization) and aseptic operation design avoid the contamination risks associated with manual operation, ensure the sterility of the fermentation environment, and significantly improve the purity and safety of citric acid products. Attached Figure Description

[0026] 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 fermentation unit in this utility model; Figure 2 This is a flowchart of the fine filtration unit in this utility model; Figure label: Concentrated sugar delivery pump 317; Pre-concentrated 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; fine filtrate buffer tank 701; mixed acid tank 901; Steam pipe G05; syrup turbid liquid pipe G11; syrup clear liquid pipe G12; acid residue pipe G14; condensate supply pipe G15; condensate return pipe G16; citric acid liquid pipe after ion exchange G17. Circulating water supply pipe G19; Circulating water return pipe G20; 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. Detailed Implementation

[0027] 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.

[0028] 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.

[0029] 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.

[0030] like Figure 1As shown, in the citric acid fermentation and filtration device of this utility model, the fermentation unit 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 through the syrup turbid liquid pipe G11, the turbid liquid feed flow meter, the turbid liquid feed regulating valve, and the turbid liquid feed switch valve. The top exhaust port of the seed tank 501 is connected to the top exhaust pipeline G24 through the exhaust regulating valve. The compressed air pipe G25 is connected to the top air inlet of the seed tank 501 through the compressed air regulating valve. The defoamer pipeline G26 is connected to the top defoamer inlet of the seed tank 501 through the defoamer feed switch valve. The steam pipe G05 is connected to the top inlet and bottom outlet of the seed tank 501 through the steam regulating valve. The steam regulating valve is controlled by the pressure sensor of the seed tank 501.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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%.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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 slurry tank 604. The outlet of the condensate supply pipe G15 is also connected to the inlet of the acid slag slurry tank 604 through a regulating valve. The outlet of the acid slag slurry 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. 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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 via fermentation broth discharge pump 602 for filtration. The clarified broth 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 broth and dilute citric acid produced after secondary filtration are sent to the primary neutralization stage via dilute citric acid clarified broth pipe G29. The acid residue after secondary filtration is sent to tube bundle dryer for drying via acid residue pipe G14, and then sold as feed.

[0062] 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.

[0063] 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.

[0064] Although the fermentation broth is pre-filtered by plate and frame filter and then finely filtered by ceramic membrane to remove solid impurities, it still contains a large number of soluble impurity ions, mainly including: cations: metal ions such as calcium, magnesium, iron, potassium, and sodium brought in by the raw materials; anions: inorganic salt ions that are not fully utilized, such as sulfate and phosphate ions. These impurity ions will significantly interfere with and damage the subsequent chromatographic separation. Therefore, before chromatographic separation, it is necessary to remove the residual impurity ions in the citric acid solution by ion exchange to create more suitable conditions for subsequent chromatographic separation and improve separation efficiency and product purity.

[0065] 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 stage via the citric acid ion exchange discharge pump 616.

[0066] 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.

[0067] 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 citric acid fermentation and filtration device, comprising a fermentation unit, characterized in that: The fermentation unit includes a seed tank (501) and a fermentation tank (502). The top material inlet of the seed tank (501) is connected to the outlet of the syrup turbid liquid pipe (G11) through a turbid liquid feed regulating valve. The top exhaust port of the seed tank (501) is connected to the top exhaust pipeline (G24) through an exhaust regulating valve. The top air inlet of the seed tank (501) is connected to the compressed air pipe (G25) through a compressed air regulating valve. The top defoamer inlet of the seed tank (501) is connected to the defoamer pipeline (G26) through a defoamer feed switch valve. The steam pipeline (G05) is connected to the top inlet and bottom outlet of the seed tank (501) through a steam regulating valve. The bottom outlet of the seed tank (501) is connected to the top inlet of the fermentation tank (502) through a seed transfer switch valve and a seed transfer pipeline (G27).

2. The citric acid fermentation and filtration apparatus according to claim 1, characterized in that: The top material inlet of the fermenter (502) is connected to the outlet of the syrup clear liquid pipe (G12) through a clear liquid feed regulating valve, and to the outlet of the syrup turbid liquid pipe (G11) through a turbid liquid feed regulating valve; the outlet of the condensate supply pipe (G15) from the previous stage is connected to the outlet of the turbid liquid feed regulating valve; the top exhaust port of the fermenter (502) is connected to the tank top exhaust pipeline (G24) through an exhaust regulating valve; the top air inlet of the fermenter (502) is connected to the compressed air pipe (G25) through a compressed air regulating valve; the top defoamer inlet of the fermenter (502) is connected to the defoamer pipeline (G26) through a defoamer feed switch valve; the steam pipe (G05) is connected to the top inlet and bottom outlet of the fermenter (502) through a steam regulating valve; and the bottom outlet of the fermenter (502) is connected to a citric acid output pipe (G28).

3. The citric acid fermentation and filtration apparatus according to claim 2, characterized in that: The jacket inlets of the seed tank (501) and fermentation tank (502) are both connected to the circulating water supply pipe (G19), and the jacket outlets are both connected to the circulating water return pipe (G20).

4. The citric acid fermentation and filtration apparatus according to claim 2, characterized in that: Both the seed tank (501) and the fermentation tank (502) are equipped with temperature sensors, pressure sensors, pH sensors and defoaming sensors, and each sensor is interlocked with the corresponding regulating valve and switching valve for control.

5. The citric acid fermentation and filtration apparatus according to claim 2, characterized in that: The citric acid output pipe (G28) is connected to the fermentation broth storage tank (601). The outlet of the fermentation broth storage tank (601) is connected to the inlet of the first-stage plate and frame filter press (603) through 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) through 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.

6. The citric acid fermentation and filtration apparatus according to claim 5, 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 through the citric acid ion exchange discharge pump (616) and the citric acid fine filtrate pipe (G30).

7. The citric acid fermentation and filtration apparatus according to claim 5, 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).

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