MVR evaporation system for lactic acid production

Abstract

The utility model discloses an MVR (Mechanical Vapor Recompression) evaporation system for lactic acid production, which comprises a first-effect falling film evaporator, a second-effect falling film evaporator, a third-effect falling film evaporator, a first-stage steam compressor, a second-stage steam compressor and a third-stage steam compressor which are sequentially communicated in series along a material flowing direction, secondary steam generated by the second-effect falling-film evaporator and the third-effect falling-film evaporator is heated by the first-stage steam compressor and then enters the second-stage steam compressor to be compressed into secondary compressed steam, and one part of the secondary compressed steam enters the first-effect falling-film evaporator and the second-effect falling-film evaporator to evaporate and concentrate low-concentration lactic acid; the other part of secondary compressed steam and secondary steam generated by the first-effect falling film evaporator enter a third-stage steam compressor to generate third-time compressed steam, the third-time compressed steam enters a third-effect falling film evaporator to evaporate and concentrate lactic acid, and low-concentration lactic acid is evaporated and concentrated by using high-quality compressed steam; the consumption of fresh steam is effectively reduced, the energy consumption is reduced, and the evaporation and concentration cost is reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of production equipment for producing lactic acid by fermentation, in particular to an MVR evaporation system for lactic acid production which is used for concentrating low-concentration dilute lactic acid into high-concentration lactic acid products. Background Art

[0002] Lactic acid, also known as propionic acid and scientifically known as 2-hydroxypropionic acid, is one of the three most widely used organic acids in the world. It is widely used in food, pharmaceuticals, leather, textiles, environmental protection, and agriculture. The most promising application of lactic acid is in biomaterials, represented by polylactic acid (PLA). As the most promising biodegradable polymer, it has the potential to replace non-degradable plastics such as polypropylene, polyethylene, and polystyrene, eliminating "white pollution" and is a bio-friendly material with great application potential.

[0003] Lactic acid production methods include chemical synthesis, enzymatic methods, and microbial conversion. Microbial fermentation uses glucose or grains such as rice, corn, and potatoes as raw materials. Low-concentration lactic acid is obtained through microbial fermentation. This low-concentration lactic acid is then evaporated and concentrated to produce high-concentration lactic acid. Fermentation has become an important method for producing lactic acid due to its wide range of raw material sources, low production costs, and high product optical purity.

[0004] Since lactic acid is a heat-sensitive material, when evaporating and concentrating low-concentration lactic acid, if the evaporation temperature is too high, it is easy to cause lactic acid decomposition, affecting the quality of the finished lactic acid. Therefore, low-concentration lactic acid is currently concentrated using a multi-effect evaporator. However, multi-effect evaporation and concentration uses fresh steam as a heating heat source, which consumes a large amount of fresh steam, has high energy consumption, and high concentration costs. Utility Model Content

[0005] In summary, in order to overcome the shortcomings of the existing technical problems, the utility model provides an MVR evaporation system for lactic acid production, which adopts mechanical vapor recompression (MVR) technology and uses a steam compressor to compress the low-quality secondary steam generated in the evaporation process, so that the low-quality secondary steam is pressurized and heated into high-quality compressed steam, and the high-quality compressed steam is used to evaporate and concentrate low-concentration lactic acid, thereby effectively reducing the amount of fresh steam used, reducing energy consumption, and reducing the cost of evaporation and concentration.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] An MVR evaporation system for lactic acid production, comprising:

[0008] The falling film evaporation system comprises a first-effect falling film evaporator, a second-effect falling film evaporator and a third-effect falling film evaporator connected in series in the direction of material flow. The first-effect falling film evaporator, the second-effect falling film evaporator and the third-effect falling film evaporator are all multi-cavity falling film evaporators. The discharge port of the third-effect falling film evaporator discharges the material through a discharge pump and a discharge pipeline.

[0009] A steam washing tower is provided with a feed port at the upper portion of the steam washing tower, an air outlet at the upper end of the steam washing tower, an air inlet at the lower portion of the steam washing tower, and a discharge port at the lower end of the steam washing tower. The feed port of the steam washing tower is connected to a feed pump through a pipeline for feeding. The air inlet of the steam washing tower is connected to the secondary steam outlet of the second-effect falling film evaporator and the secondary steam outlet of the third-effect falling film evaporator through pipelines respectively. The discharge port of the steam washing tower is connected to the feed port of the first-effect falling film evaporator through a pipeline and a delivery pump.

[0010] The air inlet of the first-stage steam compressor is connected to the air outlet of the steam washing tower through a pipeline.

[0011] A two-stage steam compressor, the air inlet of the two-stage steam compressor is connected to the air outlet of the one-stage steam compressor and the secondary steam outlet of the first-effect falling film evaporator, the air outlet of the two-stage steam compressor is connected to the two-stage compressed steam pipeline, and the two-stage compressed steam pipeline is respectively connected to the air inlet of the three-stage steam compressor, the air inlet of the first-effect falling film evaporator and the air inlet of the two-effect falling film evaporator,

[0012] The air outlet of the three-stage steam compressor is connected to the air inlet of the three-effect falling film evaporator through a pipeline.

[0013] The secondary compressed steam pipeline is connected to a raw steam source.

[0014] Furthermore, the multi-cavity falling film evaporator comprises a distribution chamber, a heating chamber and a liquid collecting chamber arranged in sequence from top to bottom.

[0015] The distribution chamber is divided into a plurality of distribution chambers, the heating chamber is divided into a heating chamber, and the liquid collection chamber is divided into a plurality of collection chambers. The plurality of distribution chambers, the plurality of heating chambers and the plurality of collection chambers are connected one by one to form a plurality of evaporation chambers. The plurality of evaporation chambers are connected in series in sequence along the flow direction of the material.

[0016] The multi-cavity falling film evaporator has an air inlet connected to the shell side of the heating chamber, a condensed water outlet connected to the shell side of the heating chamber, and a secondary steam outlet connected to multiple collecting chambers.

[0017] The upper end of the multi-cavity falling film evaporator has multiple feed ports respectively connected to the multiple evaporation chambers, and the lower end of the multi-cavity falling film evaporator has multiple discharge ports respectively connected to the multiple evaporation chambers. One of the multiple feed ports is used for feeding, and the evaporation chamber connected to the feed port is a first-stage evaporation chamber. The evaporation chamber connected to the discharge port except the discharge port connected to the first-stage evaporation chamber is discharged, and the evaporation chamber connected to the discharge port is the last-stage evaporation chamber. The discharge port of the previous-stage evaporation chamber is connected to the feed port of the next-stage evaporation chamber through a pipeline and a transfer pump.

[0018] Furthermore, the single-effect falling film evaporator is a four-cavity falling film evaporator, which has four evaporation cavities connected in series; the second-effect falling film evaporator is a three-cavity falling film evaporator, which has three evaporation cavities connected in series; the three-effect falling film evaporator is a double-cavity falling film evaporator, which has two evaporation cavities connected in series.

[0019] The feed port of the first-stage evaporation chamber of the single-effect falling film evaporator is connected to the delivery pump through a pipeline, the discharge port of the fourth-stage evaporation chamber of the single-effect falling film evaporator is connected to the feed port of the first-stage evaporation chamber of the second-effect falling film evaporator through a first-effect output pump and a pipeline, the discharge port of the third-stage evaporation chamber of the second-effect falling film evaporator is connected to the feed port of the first-stage evaporation chamber of the triple-effect falling film evaporator through a second-effect output pump and a pipeline, and the discharge port of the second-stage evaporation chamber of the triple-effect falling film evaporator is connected to the discharge pump.

[0020] Furthermore, a demister is provided in the secondary steam outlet.

[0021] Furthermore, the first-effect falling film evaporator is provided with a first-effect liquid level sensor for detecting the material level of the collecting chamber of the four-stage evaporation chamber of the first-effect falling film evaporator; a second-effect feed valve is provided on the pipeline connecting the first-effect output pump and the feed port of the first-stage evaporation chamber of the second-effect falling film evaporator; the first-effect liquid level sensor is electrically connected to the second-effect feed valve, and the second-effect feed valve is controlled and adjusted by the first-effect liquid level sensor.

[0022] The two-effect falling film evaporator is provided with a two-effect liquid level sensor for detecting the material level of the collecting chamber of the three-stage evaporation chamber of the two-effect falling film evaporator. A three-effect feed valve is provided on the pipeline connecting the two-effect output pump and the feed port of the first-stage evaporation chamber of the three-effect falling film evaporator. The two-effect liquid level sensor is electrically connected to the three-effect feed valve, and the three-effect feed valve is controlled and adjusted by the two-effect liquid level sensor.

[0023] The three-effect falling film evaporator is provided with a three-effect liquid level sensor for detecting the material level of the collecting chamber of the secondary evaporation chamber of the three-effect falling film evaporator. The discharge pipeline is provided with a discharge valve. The three-effect liquid level sensor is electrically connected to the discharge valve. The discharge valve is controlled and adjusted by the three-effect liquid level sensor.

[0024] A steam washing level sensor is provided at the lower part of the steam washing tower, a delivery valve is provided on the pipeline connected to the discharge port of the delivery pump, the steam washing level sensor is electrically connected to the delivery valve, and the delivery valve is controlled and regulated by the steam washing level sensor.

[0025] Furthermore, it also includes a condensate water system, which includes a condensate water tank and a condensate water pump. The condensate water outlet of the first-effect falling film evaporator, the condensate water outlet of the second-effect falling film evaporator, and the condensate water outlet of the third-effect falling film evaporator are all connected to the water inlet of the condensate water tank through a pipeline. The water outlet of the condensate water tank is drained through the condensate water pump and the pipeline, and the air outlet of the condensate water tank is connected to the air inlet of the secondary steam compressor.

[0026] Furthermore, it also includes a preheating system, which includes a concentrated slurry material preheating device and a condensed water preheating device. The concentrated slurry material preheating device includes a second heat exchanger and a third heat exchanger connected in series, and the condensed water preheating device includes a fourth heat exchanger and a fifth heat exchanger connected in series.

[0027] The feed port of the second heat exchanger is connected to the feed pump through a pipeline, the discharge port of the second heat exchanger is connected to the feed port of the third heat exchanger through a pipeline, the discharge port of the third heat exchanger is connected to the feed port of the fourth heat exchanger through a pipeline, the discharge port of the fourth heat exchanger is connected to the feed port of the fifth heat exchanger, the discharge port of the fifth heat exchanger is connected to the feed port of the steam washing tower through a pipeline, and the discharge port of the steam washing tower is connected to the feed port of the first-effect falling film evaporator through a delivery pump and a pipeline.

[0028] The medium inlet of the third heat exchanger is connected to the discharge port of the discharge pump through a discharge pipeline, the medium outlet of the third heat exchanger is connected to the medium inlet of the second heat exchanger through a pipeline, and the medium outlet of the third heat exchanger is connected to the discharge pipeline.

[0029] The medium inlet of the fifth heat exchanger is connected to the outlet of the condensate pump through a pipeline, the medium outlet of the fifth heat exchanger is connected to the medium inlet of the fourth heat exchanger through a pipeline, and the medium outlet of the fourth heat exchanger is drained.

[0030] Furthermore, it also includes a non-condensable gas preheating device, which includes a first heat exchanger, a sixth heat exchanger and a seventh heat exchanger. The feed port of the first heat exchanger is connected to the feed pump through a pipeline, and the discharge port of the first heat exchanger is connected to the feed port of the second heat exchanger through a pipeline.

[0031] The feed port of the sixth heat exchanger is connected to the discharge port of the delivery pump through a pipeline, the discharge port of the sixth heat exchanger is connected to the feed port of the seventh heat exchanger through a pipeline, and the discharge port of the seventh heat exchanger is connected to the feed port of the first-effect falling film evaporator through a pipeline.

[0032] The medium inlet of the sixth heat exchanger is connected to the low-temperature non-condensable gas pipeline, which is respectively connected to the non-condensable gas outlet of the first-effect falling film evaporator and the non-condensable gas outlet of the second-effect falling film evaporator. The medium outlet of the sixth heat exchanger is connected to the medium inlet of the first heat exchanger, and the medium outlet of the first heat exchanger is exhausted.

[0033] The medium inlet of the seventh heat exchanger is connected to the non-condensable gas outlet of the triple-effect falling film evaporator, and the medium outlet of the seventh heat exchanger is connected to the medium inlet of the sixth heat exchanger.

[0034] The condensed water outlet of the first heat exchanger, the condensed water outlet of the sixth heat exchanger, and the condensed water outlet of the seventh heat exchanger are all connected to the condensed water tank.

[0035] The beneficial effects of the utility model are:

[0036] 1. The utility model adopts a three-effect falling film evaporator to evaporate and concentrate low-concentration lactic acid. The falling film evaporator adopts an integrated multi-cavity falling film evaporator. The inner cavity of the integrated multi-cavity falling film evaporator is divided into multiple evaporation chambers. The multiple evaporation chambers are connected in series with the transfer pump 40. The same falling film evaporator can be used to evaporate and concentrate low-concentration lactic acid multiple times, thereby achieving the purpose of multi-effect evaporation. At the same time, it can also reduce the residence time of lactic acid in the evaporator, avoid excessive temperature caused by prolonged heating of lactic acid in the evaporator, and prevent the denaturation and deterioration of lactic acid during the evaporation process.

[0037] 2. In the present invention, the secondary steam generated during the evaporation and concentration process first enters a first-stage steam compressor for compression into primary compressed steam. This primary compressed steam then enters a second-stage steam compressor for compression into secondary compressed steam. A portion of the secondary compressed steam enters the first- and second-effect falling film evaporators for heating and evaporation of low-concentration lactic acid. The two mechanical steam recompressions raise the secondary steam temperature by approximately 17°C, bringing the temperature of the secondary steam from approximately 85°C to approximately 102°C, fully meeting the evaporation and concentration requirements of the first and second effects. Another portion of the secondary compressed steam enters a third-stage steam compressor for compression into tertiary compressed steam, which then enters a third-effect falling film evaporator for evaporation and concentration of the lactic acid. The three mechanical steam recompressions raise the temperature of the secondary steam from approximately 85°C to approximately 111°C, meeting the requirements of the third-effect evaporation and concentration. During the entire evaporation process, fresh steam is used only during system initial operation and air replenishment, effectively reducing fresh steam usage and concentration costs.

[0038] 3. The utility model has a preheating system, which uses concentrated lactic acid, non-condensable gas and condensed water to preheat low-concentration lactic acid, and can effectively recover the waste heat in high-temperature and high-concentration lactic acid, the waste heat in non-condensable gas and the waste heat in condensed water, and can effectively recover the waste heat and reduce energy consumption.

[0039] 4. The utility model is provided with a steam washing tower. The low-concentration lactic acid preheated by the concentrated slurry material preheating device and the condensed water preheating device enters from the upper end of the steam washing tower, and the secondary steam flowing out of the two-effect falling film evaporator and the three-effect falling film evaporator enters from the lower part of the steam washing tower. In the steam washing tower, the low-concentration lactic acid flows from top to bottom, and the secondary steam flows from bottom to top. The preheated low-concentration lactic acid absorbs the lactic acid carried in the secondary steam, and the lactic acid is discharged from the discharge port at the lower end of the steam washing tower. The secondary steam flows out from the air outlet at the upper end of the steam washing tower and enters the first-stage steam compressor. The steam washing tower can realize both the washing of the secondary steam and the gas-liquid separation.

[0040] 5. The utility model has a simple structure, is easy to use, and has low cost. It can effectively realize the evaporation and concentration of low-concentration lactic acid, and evaporate and concentrate the low-concentration lactic acid produced by fermentation with a concentration of about 27% into a finished lactic acid with a concentration of about 85%, which can effectively improve the evaporation and concentration efficiency of lactic acid and reduce costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a structural diagram of the present utility model. DETAILED DESCRIPTION

[0042] The present invention will be described in further detail below with reference to the accompanying drawings.

[0043] like Figure 1As shown, an MVR evaporation system for lactic acid production, which includes: a preheating system, a falling film evaporation system, a steam scrubber 11, a first-stage steam compressor 14, a second-stage steam compressor 15, a third-stage steam compressor 17, a feed pump 1, a delivery pump 12 and a raw steam source. The feed pump 1 is used to deliver low-concentration lactic acid and provide power for system feeding. The discharge port of the feed pump 1 is connected to the preheating system through a pipeline. The preheating system includes a first heat exchanger 2, a second heat exchanger 3, a third heat exchanger 4, a fourth heat exchanger 5, a fifth heat exchanger 6, and a sixth heat exchanger connected in series in the direction of material flow. 7 and the seventh heat exchanger 8, the feed port of the first heat exchanger 2 is connected to the feed pump 1 through a pipeline, the discharge port of the first heat exchanger 2 is connected to the feed port of the second heat exchanger 3 through a pipeline, the discharge port of the second heat exchanger 3 is connected to the feed port of the third heat exchanger 4 through a pipeline, the discharge port of the third heat exchanger 4 is connected to the feed port of the fourth heat exchanger 5 through a pipeline, the discharge port of the fourth heat exchanger 5 is connected to the feed port of the fifth heat exchanger 6, and the discharge port of the fifth heat exchanger 6 is connected to the feed port of the steam scrubber 11 through a pipeline. The discharge port of the steam scrubber 11 is connected to the falling film evaporation system through a delivery pump 12 and a pipeline. A steam scrubber level sensor 38 is provided at the lower part of the steam scrubber 11, and a delivery valve 39 is provided on the pipeline connected to the discharge port of the delivery pump 12. The steam scrubber level sensor 38 is electrically connected to the delivery valve 39, and the delivery valve 39 is controlled and regulated by the steam scrubber level sensor 38.

[0044] The falling film evaporation system includes a single-effect falling film evaporator 13, a second-effect falling film evaporator 10 and a third-effect falling film evaporator 9 which are connected in series in the direction of material flow. The single-effect falling film evaporator 13, the second-effect falling film evaporator 10 and the third-effect falling film evaporator 9 are all multi-cavity falling film evaporators. The multi-cavity falling film evaporator includes a distribution chamber, a heating chamber and a liquid collecting chamber arranged in sequence from top to bottom. The distribution chamber is divided into a plurality of distribution chambers, the heating chamber is divided into a heating chamber, the liquid collecting chamber is divided into a plurality of collecting chambers, and the plurality of distribution chambers, the plurality of heating chambers and the plurality of collecting chambers are connected in one-to-one correspondence to form a plurality of evaporation chambers. The plurality of evaporation chambers are connected in series in sequence along the direction of material flow. The multi-cavity falling film evaporator The evaporator has an air inlet connected to the shell side of the heating chamber, a condensed water outlet connected to the shell side of the heating chamber, and a secondary steam outlet connected to multiple collecting chambers. A demister is provided in the secondary steam outlet. The upper end of the multi-cavity falling film evaporator has multiple feed ports connected to multiple evaporation chambers respectively, and the lower end of the multi-cavity falling film evaporator has multiple discharge ports connected to multiple evaporation chambers respectively. One of the multiple feed ports is fed, and the evaporation chamber connected to the feed port is a first-stage evaporation chamber. The evaporation chamber connected to the discharge port is the last-stage evaporation chamber, and the discharge port of the previous-stage evaporation chamber is connected to the feed port of the next-stage evaporation chamber through a pipeline and a transfer pump 40.

[0045] The single-effect falling film evaporator 13 is a four-cavity falling film evaporator having four evaporation cavities connected in series. The second-effect falling film evaporator 10 is a three-cavity falling film evaporator having three evaporation cavities connected in series. The triple-effect falling film evaporator 9 is a double-cavity falling film evaporator having two evaporation cavities connected in series. The feed port of the first-stage evaporation cavity of the single-effect falling film evaporator 13 is connected to the discharge port of the delivery pump 12 through a pipeline. The discharge port of the fourth-stage evaporation cavity of the single-effect falling film evaporator 13 is connected to the feed port of the first-stage evaporation cavity of the second-effect falling film evaporator 10 through a single-effect output pump 18 and a pipeline. The discharge port of the third-stage evaporation cavity of the second-effect falling film evaporator 10 is connected to the feed port of the first-stage evaporation cavity of the triple-effect falling film evaporator 9 through a single-effect output pump 19 and a pipeline. The discharge port of the secondary evaporation cavity of the triple-effect falling film evaporator 9 is connected to the feed port of the discharge pump 20. The discharge port of the discharge pump 20 is connected to the medium inlet of the third heat exchanger 4 through a discharge pipeline, the medium outlet of the third heat exchanger 4 is connected to the medium inlet of the second heat exchanger 3 through a pipeline, and the medium outlet of the second heat exchanger 3 is connected to the discharge pipeline. The second heat exchanger 3 and the third heat exchanger 4 use high-concentration lactic acid to preheat low-concentration lactic acid.

[0046] The secondary steam outlet of the two-effect falling film evaporator 10 and the secondary steam outlet of the three-effect falling film evaporator 9 are connected to the air inlet of the steam washing tower 11 through a pipeline. The low-concentration lactic acid preheated by the concentrated slurry material preheating device and the condensed water preheating device enters the steam washing tower 11 from the upper part of the steam washing tower 11. In the steam washing tower 11, the low-concentration lactic acid flows from top to bottom, and the secondary steam flows from bottom to top. The preheated low-concentration lactic acid absorbs the lactic acid in the secondary steam, and the lactic acid is discharged from the discharge port at the lower end of the steam washing tower 11. The secondary steam flows out from the air outlet at the upper end of the steam washing tower 11 and enters the first-stage steam compressor 14. The steam washing tower 11 can not only wash the secondary steam, but also realize gas-liquid separation.

[0047] The air outlet of the steam washing tower 11 is connected to the air inlet of the first-stage steam compressor 14, the air outlet of the first-stage steam compressor 14 and the secondary steam outlet of the first-effect falling film evaporator 13 are connected to the air inlet of the second-stage steam compressor 15 through a pipeline, the air outlet of the second-stage steam compressor 15 is connected to the second-stage compressed steam pipeline 16, the second-stage compressed steam pipeline 16 is respectively connected to the air inlet of the third-stage steam compressor 17, the air inlet of the first-effect falling film evaporator 13 and the air inlet of the second-effect falling film evaporator 10, the air outlet of the third-stage steam compressor 17 is connected to the air inlet of the third-effect falling film evaporator 9 through a pipeline, the second-stage compressed steam pipeline 16 is connected to the raw steam pipeline 37 through the air supply pipeline 29, and the raw steam pipeline 37 is connected to the raw steam source.

[0048] The condensate outlet of the first-effect falling film evaporator 13, the condensate outlet of the second-effect falling film evaporator 10, the condensate outlet of the third-effect falling film evaporator 9, the condensate outlet of the first heat exchanger 2, the condensate outlet of the sixth heat exchanger 7, and the condensate outlet of the seventh heat exchanger 8 are all connected to the water inlet of the condensate tank 27 through a pipeline. The water outlet of the condensate tank 27 is connected to the water inlet of the condensate pump 28 through a pipeline. The water outlet of the condensate pump 28 is connected to the medium inlet of the fifth heat exchanger 6 through a pipeline. The medium outlet of the fifth heat exchanger 6 is connected to the medium inlet of the fourth heat exchanger 5 through a pipeline. The medium outlet of the fourth heat exchanger 5 drains water. The fourth heat exchanger 5 and the fifth heat exchanger 6 use condensate to preheat low-concentration lactic acid. The air outlet of the condensate tank 27 is connected to the air inlet of the secondary steam compressor 15.

[0049] The non-condensable gas outlet of the first-effect falling film evaporator 13 and the non-condensable gas outlet of the second-effect falling film evaporator 10 are respectively connected to the low-temperature non-condensable gas pipeline 34 through pipelines, the low-temperature non-condensable gas pipeline 34 is connected to the medium inlet of the sixth heat exchanger 7, the non-condensable gas outlet of the third-effect falling film evaporator 9 is connected to the medium inlet of the seventh heat exchanger 8 through a pipeline, the medium outlet of the seventh heat exchanger 8 is connected to the medium inlet of the sixth heat exchanger 7 through a pipeline, the medium outlet of the sixth heat exchanger 7 is connected to the medium inlet of the first heat exchanger 2 through a pipeline, and the medium outlet of the first heat exchanger 2 is emptied. The sixth heat exchanger 7 uses the non-condensable gas generated by the first-effect falling film evaporator 13 and the second-effect falling film evaporator 10 to preheat the low-concentration lactic acid, the seventh heat exchanger 8 uses the non-condensable gas generated by the third-effect falling film evaporator 9 to preheat the low-concentration lactic acid, and the first heat exchanger 2 uses the tail gas to preheat the low-concentration soft acid.

[0050] The first-effect falling film evaporator 13 is provided with a first-effect liquid level sensor 21 for detecting the material level of the collecting chamber of the four-stage evaporation chamber of the first-effect falling film evaporator 13, and the first-effect output pump 18 is connected to the feed port of the first-stage evaporation chamber of the second-effect falling film evaporator 10. A second-effect feed valve 22 is provided on the pipeline, and the first-effect liquid level sensor 21 is electrically connected to the second-effect feed valve 22. The second-effect feed valve 22 is controlled and adjusted by the first-effect liquid level sensor 21. The second-effect falling film evaporator 10 is provided with a second-effect liquid level sensor 23 for detecting the material level of the collecting chamber of the three-stage evaporation chamber of the second-effect falling film evaporator 10. A three-effect feed valve 24 is provided on the pipeline connecting the second-effect output pump 19 and the feed port of the first-stage evaporation chamber of the three-effect falling film evaporator 9, and the second-effect liquid level sensor 23 is electrically connected to the three-effect feed valve 24, and the three-effect feed valve 24 is controlled and adjusted by the second-effect liquid level sensor 23. The three-effect falling film evaporator 9 is provided with a three-effect liquid level sensor 25 for detecting the material level of the collecting chamber of the secondary evaporation chamber of the three-effect falling film evaporator 9, and a discharge valve 26 is provided on the discharge pipeline. The three-effect liquid level sensor 25 is electrically connected to the discharge valve 26, and the discharge valve 26 is controlled and adjusted by the three-effect liquid level sensor 25.

[0051] The single-effect falling film evaporator 13 is provided with a single-effect pressure sensor 31, which is used to detect the pressure inside the single-effect falling film evaporator 13. The air supply pipeline 29 is provided with an air supply valve 30, and the single-effect pressure sensor 31 is electrically connected to the air supply valve 30, and the air supply valve 30 is controlled and adjusted by the single-effect pressure sensor 31.

[0052] The two-effect falling film evaporator 10 is provided with a two-effect pressure sensor 32, which is used to detect the pressure inside the two-effect falling film evaporator 10. A low-temperature non-condensable gas inlet valve 33 is provided on the low-temperature non-condensable gas pipeline 34, and the two-effect pressure sensor 32 is electrically connected to the low-temperature non-condensable gas inlet valve 33.

[0053] The three-effect falling film evaporator 9 is provided with a three-effect pressure sensor 35, which is used to detect the pressure inside the three-effect falling film evaporator 9. A high-temperature non-condensable gas inlet valve 36 is provided on the pipeline connecting the air inlet of the seventh heat exchanger 8 and the non-condensable gas outlet of the three-effect falling film evaporator 9, and the three-effect pressure sensor 35 is electrically connected to the high-temperature non-condensable gas inlet valve 36.

[0054] During use, when the system is initially operated, the air supply valve 30 on the air supply pipeline 29 is opened, and the fresh steam provided by the steam source enters the first-effect falling film evaporator 13 and the second-effect falling film evaporator 10 respectively through the steam pipeline and the secondary compression steam pipeline 16. The feed pump 1 delivers low-temperature and low-concentration lactic acid into the falling film evaporation system, and the fresh steam is used to evaporate and concentrate the lactic acid.

[0055] After the system runs stably and the steam pressure in the first-effect falling film evaporator 13 detected by the first-effect pressure sensor 31 reaches the set requirement, the air supply valve 30 is closed. The low-temperature, low-concentration lactic acid delivered by the feed pump 1 first enters the first heat exchanger 2, where the low-concentration lactic acid is preheated once using the non-condensable tail gas. After the preheating, the lactic acid enters the second heat exchanger 3 and the third heat exchanger 4 in turn. The second heat exchanger 3 and the third heat exchanger 4 use high-concentration lactic acid to preheat the low-concentration lactic acid twice and three times respectively. After the three preheating, the lactic acid enters the fourth heat exchanger 5 and the fifth heat exchanger 6 in turn. The fourth heat exchanger 5 and the fifth heat exchanger 6 use condensed water to preheat the low-concentration lactic acid four times and five times. After the five preheating, the lactic acid enters the fourth heat exchanger 5 and the fifth heat exchanger 6. The heated low-concentration lactic acid enters the steam washing tower 11, where the low-concentration lactic acid absorbs the materials carried in the secondary steam and separates the secondary steam. The low-concentration lactic acid flowing out of the lower end of the steam washing tower 11 enters the sixth heat exchanger 7 under the action of the delivery pump 12. In the sixth heat exchanger 7, the low-concentration lactic acid is preheated six times by using the non-condensable gas flowing out of the second-effect falling film evaporator 10 and the triple-effect falling film evaporator 9. After the six preheatings, the low-concentration lactic acid enters the seventh heat exchanger 8, and the seventh heat exchanger 8 uses the non-condensable gas flowing out of the triple-effect falling film evaporator 9 to preheat the low-concentration lactic acid for the seventh time.

[0056] After seven preheatings, the low-concentration lactic acid enters the first evaporation chamber of the first-effect falling film evaporator 13. Then, under the action of the transfer pump 40 of the first-effect falling film evaporator, the lactic acid flows through the first evaporation chamber, the second evaporation chamber, the third evaporation chamber and the fourth evaporation chamber of the first-effect falling film evaporator 13 in sequence, and finally flows out from the discharge port of the fourth evaporation chamber. Then, it enters the first evaporation chamber of the second-effect falling film evaporator 10 through the first-effect output pump 18. Then, under the action of the transfer pump 40 of the second-effect falling film evaporator 10, it flows through the first evaporation chamber, the second evaporation chamber and the third evaporation chamber of the second-effect falling film evaporator 10 once, and finally flows out from the discharge port of the third evaporation chamber.

[0057] The secondary steam separated by the steam washing tower 11 enters the primary steam compressor 14, and the primary steam compressor 14 performs the first compression on the secondary steam. The secondary steam is heated and pressurized for the first time to become the primary compressed steam. Then the primary compressed steam enters the secondary steam compressor 15. The secondary steam generated by the first-effect falling film evaporator 13 enters the secondary steam compressor 15. A part of the secondary compressed steam after being pressurized and heated by the secondary steam compressor 15 enters the first-effect falling film evaporator 13 and the second-effect falling film evaporator through the secondary compressed steam pipeline 16. In the first-effect falling film evaporator 10, the low-concentration lactic acid preheated seven times is heated by the secondary compressed steam to increase its temperature. The low-concentration lactic acid is evaporated and concentrated four times in the first-effect falling film evaporator 13. The lactic acid flowing out of the first-effect falling film evaporator 13 enters the second-effect falling film evaporator 10 under the action of the first-effect output pump 18. In the second-effect falling film evaporator 10, the lactic acid flowing out of the first-effect falling film evaporator 13 is heated by the secondary compressed steam to increase its temperature. The lactic acid flowing out of the first-effect falling film evaporator 13 is evaporated and concentrated three times in the second-effect falling film evaporator 10.

[0058] Another part of the secondary compressed steam flowing out of the secondary steam compressor 15 enters the tertiary steam compressor 17, and the tertiary steam compressor 17 compresses the secondary compressed steam for a third time to generate tertiary compressed steam. The tertiary compressed steam enters the three-effect falling film evaporator 9, and the lactic acid flowing out of the discharge port of the tertiary evaporation chamber of the second-effect falling film evaporator 10 enters the first evaporation chamber of the three-effect falling film evaporator 9 under the action of the second-effect output pump 19, and then enters the second evaporation chamber of the three-effect falling film evaporator 9 under the action of the transfer pump 40 of the three-effect falling film evaporator 9, and finally flows out of the discharge port of the second evaporation chamber as a high-concentration finished lactic acid. Under the action of the discharge pump 20, the finished lactic acid enters the third heat exchanger 4 and the second heat exchanger 3 in sequence to preheat the low-concentration lactic acid. After the finished lactic acid is cooled, it is discharged from the discharge pipeline.

[0059] In this embodiment, the concentration of the low-concentration lactic acid delivered by the feed pump 1 is 27.5%, and the temperature is about 35° C. The temperature of the lactic acid after preheating in the first heat exchanger 2 is about 40° C., the temperature of the lactic acid after preheating in the second heat exchanger 3 is about 46° C., the temperature of the lactic acid after preheating in the third heat exchanger 4 is about 52° C., the temperature of the lactic acid after preheating in the fourth heat exchanger 5 is about 66° C., the temperature of the lactic acid after preheating in the fifth heat exchanger 6 is about 86° C., the temperature of the lactic acid after preheating in the sixth heat exchanger 7 is about 93° C., and the temperature of the lactic acid after preheating in the seventh heat exchanger 8 is about 96° C. After the lactic acid with a temperature of about 96° C. and a concentration of about 27.5% enters the four evaporation chambers of the first-effect falling film evaporator 13 and is evaporated and concentrated four times, its temperature is about 97° C. and the concentration is about 44%. The lactic acid then enters the two-effect falling film evaporator 10. After four evaporation and concentration passes through the three evaporation chambers of the two-effect falling film evaporator 10, the temperature is about 98.5°C and the concentration is about 75%. The lactic acid then enters the three-effect falling film evaporator 9. After two evaporation and concentration passes through the two evaporation chambers of the three-effect falling film evaporator 9, the temperature is about 106.4°C and the concentration is about 85%.

[0060] The temperature of the secondary steam separated from the steam scrubber 11 is about 86°C, the temperature of the primary compressed steam compressed by the first-stage steam compressor 14 is about 93°C, the temperature of the secondary compressed steam compressed by the second-stage steam compressor 15 is about 102°C, and the temperature of the tertiary compressed steam compressed by the third-stage steam compressor 17 is about 111°C.

[0061] It should be noted that the above-described embodiments are illustrative rather than restrictive of the technical solutions of the present invention. Equivalent substitutions or other modifications made by ordinary technicians in the relevant technical field based on the existing technology should be included in the scope of rights required by the present invention as long as they do not exceed the concept and scope of the technical solutions of the present invention.

Claims

1. An MVR evaporation system for lactic acid production, characterized by: include: A falling film evaporation system, wherein the falling film evaporation system comprises a first-effect falling film evaporator (13), a second-effect falling film evaporator (10), and a third-effect falling film evaporator (9) which are sequentially connected in series along the material flow direction, wherein the first-effect falling film evaporator (13), the second-effect falling film evaporator (10), and the third-effect falling film evaporator (9) are all multi-cavity falling film evaporators, and the discharge port of the third-effect falling film evaporator (9) discharges material through a discharge pump (20) and a discharge pipeline. A steam washing tower (11), wherein a feed port is provided at the upper portion of the steam washing tower (11), an air outlet is provided at the upper end of the steam washing tower (11), an air inlet is provided at the lower portion of the steam washing tower (11), and a discharge port is provided at the lower end of the steam washing tower (11), the feed port of the steam washing tower (11) is connected to a feed pump (1) through a pipeline for feeding, the air inlet of the steam washing tower (11) is connected to the secondary steam outlet of the second-effect falling film evaporator (10) and the secondary steam outlet of the third-effect falling film evaporator (9) through pipelines, the discharge port of the steam washing tower (11) is connected to the feed port of the first-effect falling film evaporator (13) through a pipeline and a delivery pump (12), A first-stage steam compressor (14), the air inlet of the first-stage steam compressor (14) is connected to the air outlet of the steam scrubber (11) through a pipeline. A two-stage steam compressor (15), the air inlet of the two-stage steam compressor (15) is connected to the air outlet of the one-stage steam compressor (14) and the secondary steam outlet of the first-effect falling film evaporator (13), the air outlet of the two-stage steam compressor (15) is connected to the two-stage compressed steam pipeline (16), and the two-stage compressed steam pipeline (16) is respectively connected to the air inlet of the three-stage steam compressor (17), the air inlet of the first-effect falling film evaporator (13) and the air inlet of the second-effect falling film evaporator (10), A three-stage steam compressor (17), the air outlet of the three-stage steam compressor (17) is connected to the air inlet of the three-effect falling film evaporator (9) through a pipeline. The secondary compressed steam pipeline (16) is connected to a raw steam source.

2. The MVR evaporation system for lactic acid production according to claim 1, characterized in that: The multi-cavity falling film evaporator comprises a distribution chamber, a heating chamber and a liquid collecting chamber arranged in sequence from top to bottom. The distribution chamber is divided into a plurality of distribution chambers, the heating chamber is divided into a heating chamber, and the liquid collection chamber is divided into a plurality of collection chambers. The plurality of distribution chambers, the plurality of heating chambers and the plurality of collection chambers are connected one by one to form a plurality of evaporation chambers. The plurality of evaporation chambers are connected in series in sequence along the flow direction of the material. The multi-cavity falling film evaporator has an air inlet connected to the shell side of the heating chamber, a condensed water outlet connected to the shell side of the heating chamber, and a secondary steam outlet connected to multiple collecting chambers. The upper end of the multi-cavity falling film evaporator has a plurality of feed ports respectively connected to the plurality of evaporation chambers, and the lower end of the multi-cavity falling film evaporator has a plurality of discharge ports respectively connected to the plurality of evaporation chambers, one of the plurality of feed ports is fed, and the evaporation chamber connected to the feed port is a first-stage evaporation chamber, and one of the remaining discharge ports other than the discharge port connected to the first-stage evaporation chamber is discharged, and the evaporation chamber connected to the discharge port is a last-stage evaporation chamber, and the discharge port of the previous-stage evaporation chamber is connected to the feed port of the next-stage evaporation chamber through a pipeline and a transfer pump (40).

3. The MVR evaporation system for lactic acid production according to claim 2, characterized in that: The single-effect falling film evaporator (13) is a four-cavity falling film evaporator having four evaporation cavities connected in series. The second-effect falling film evaporator (10) is a three-cavity falling film evaporator having three evaporation cavities connected in series. The third-effect falling film evaporator (9) is a double-cavity falling film evaporator having two evaporation cavities connected in series. The feed port of the first-stage evaporation chamber of the first-effect falling film evaporator (13) is connected to the delivery pump (12) through a pipeline, the discharge port of the fourth-stage evaporation chamber of the first-effect falling film evaporator (13) is connected to the feed port of the first-stage evaporation chamber of the second-effect falling film evaporator (10) through a first-effect output pump (18) and a pipeline, the discharge port of the third-stage evaporation chamber of the second-effect falling film evaporator (10) is connected to the feed port of the first-stage evaporation chamber of the third-effect falling film evaporator (9) through a second-effect output pump (19) and a pipeline, and the discharge port of the second-stage evaporation chamber of the third-effect falling film evaporator (9) is connected to the discharge pump (20).

4. The MVR evaporation system for lactic acid production according to claim 2, characterized in that: A defoamer is provided in the secondary steam outlet.

5. The MVR evaporation system for lactic acid production according to claim 3, characterized in that: The first-effect falling film evaporator (13) is provided with a first-effect liquid level sensor (21) for detecting the material level of the collecting chamber of the four-stage evaporation chamber of the first-effect falling film evaporator (13); a second-effect feed valve (22) is provided on a pipeline connecting the first-effect output pump (18) and the feed port of the first-stage evaporation chamber of the second-effect falling film evaporator (10); the first-effect liquid level sensor (21) is electrically connected to the second-effect feed valve (22); and the second-effect feed valve (22) is controlled and adjusted by the first-effect liquid level sensor (21). The second-effect falling film evaporator (10) is provided with a second-effect liquid level sensor (23) for detecting the material level of the collecting chamber of the third-stage evaporation chamber of the second-effect falling film evaporator (10), a third-effect feed valve (24) is provided on a pipeline connecting the second-effect output pump (19) and the feed port of the first-stage evaporation chamber of the third-effect falling film evaporator (9), the second-effect liquid level sensor (23) is electrically connected to the third-effect feed valve (24), and the third-effect feed valve (24) is controlled and adjusted by the second-effect liquid level sensor (23). The triple-effect falling film evaporator (9) is provided with a triple-effect liquid level sensor (25) for detecting the material level of the collecting chamber of the secondary evaporation chamber of the triple-effect falling film evaporator (9), and a discharge valve (26) is provided on the discharge pipeline. The triple-effect liquid level sensor (25) is electrically connected to the discharge valve (26), and the discharge valve (26) is controlled and adjusted by the triple-effect liquid level sensor (25). A steam washing liquid level sensor (38) is provided at the lower part of the steam washing tower (11), and a delivery valve (39) is provided on the pipeline connected to the discharge port of the delivery pump (12). The steam washing liquid level sensor (38) is electrically connected to the delivery valve (39), and the delivery valve (39) is controlled and regulated by the steam washing liquid level sensor (38).

6. The MVR evaporation system for lactic acid production according to any one of claims 1 to 5, characterized in that: The utility model further comprises a condensed water system, wherein the condensed water system comprises a condensed water tank (27) and a condensed water pump (28); the condensed water outlet of the first-effect falling film evaporator (13), the condensed water outlet of the second-effect falling film evaporator (10), and the condensed water outlet of the third-effect falling film evaporator (9) are all connected to the water inlet of the condensed water tank (27) through a pipeline; the water outlet of the condensed water tank (27) is drained through the condensed water pump (28) and the pipeline; and the air outlet of the condensed water tank (27) is connected to the air inlet of the secondary steam compressor (15).

7. The MVR evaporation system for lactic acid production according to claim 6, characterized in that: The invention also includes a preheating system, wherein the preheating system includes a thick slurry material preheating device and a condensate water preheating device, wherein the thick slurry material preheating device includes a second heat exchanger (3) and a third heat exchanger (4) connected in series, and the condensate water preheating device includes a fourth heat exchanger (5) and a fifth heat exchanger (6) connected in series. The feed port of the second heat exchanger (3) is connected to the feed pump (1) through a pipeline, the discharge port of the second heat exchanger (3) is connected to the feed port of the third heat exchanger (4) through a pipeline, the discharge port of the third heat exchanger (4) is connected to the feed port of the fourth heat exchanger (5) through a pipeline, the discharge port of the fourth heat exchanger (5) is connected to the feed port of the fifth heat exchanger (6), and the discharge port of the fifth heat exchanger (6) is connected to the feed port of the steam scrubber (11) through a pipeline. The medium inlet of the third heat exchanger (4) is connected to the discharge port of the discharge pump (20) through a discharge pipeline, the medium outlet of the third heat exchanger (4) is connected to the medium inlet of the second heat exchanger (3) through a pipeline, and the medium outlet of the third heat exchanger (4) is connected to the discharge pipeline. The medium inlet of the fifth heat exchanger (6) is connected to the outlet of the condensate pump (28) through a pipeline, the medium outlet of the fifth heat exchanger (6) is connected to the medium inlet of the fourth heat exchanger (5) through a pipeline, and the medium outlet of the fourth heat exchanger (5) is drained.

8. The MVR evaporation system for lactic acid production according to claim 7, characterized in that: The non-condensable gas preheating device is also included, and the non-condensable gas preheating device includes a first heat exchanger (2), a sixth heat exchanger (7) and a seventh heat exchanger (8). The feed port of the first heat exchanger (2) is connected to the feed pump (1) through a pipeline, and the discharge port of the first heat exchanger (2) is connected to the feed port of the second heat exchanger (3) through a pipeline. The feed port of the sixth heat exchanger (7) is connected to the discharge port of the delivery pump (12) through a pipeline, the discharge port of the sixth heat exchanger (7) is connected to the feed port of the seventh heat exchanger (8) through a pipeline, and the discharge port of the seventh heat exchanger (8) is connected to the feed port of the first-effect falling film evaporator (13) through a pipeline. The medium inlet of the sixth heat exchanger (7) is connected to the low-temperature non-condensable gas pipeline (34), and the low-temperature non-condensable gas pipeline 34 is respectively connected to the non-condensable gas outlet of the first-effect falling film evaporator (13) and the non-condensable gas outlet of the second-effect falling film evaporator (10). The medium outlet of the sixth heat exchanger (7) is connected to the medium inlet of the first heat exchanger (2), and the medium outlet of the first heat exchanger (2) is exhausted. The medium inlet of the seventh heat exchanger (8) is connected to the non-condensable gas outlet of the three-effect falling film evaporator (9), and the medium outlet of the seventh heat exchanger (8) is connected to the medium inlet of the sixth heat exchanger (7). The condensed water outlet of the first heat exchanger (2), the condensed water outlet of the sixth heat exchanger (7), and the condensed water outlet of the seventh heat exchanger (8) are all in communication with the condensed water tank (27).

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