MVR system for methanol recovery and its application in vitamin C production

Abstract

The present invention discloses a methanol distillation (MVR) system for methanol recovery and its application in vitamin C production. The system comprises a raw material tank, a raw material pump, a preheater, a crude distillation tower, a crude distillation tower reboiler, a first steam compressor, a second steam compressor, a distillation tower, a distillation tower reboiler, a methanol tank, a discharge pump, a stripping tower, a first flow regulating valve, a second flow regulating valve, and a finished product heat exchanger. Such a system: 1. It solves the problem of a large temperature difference between the tower top and the tower bottom, which limits the application of MVR technology in methanol distillation systems. 2. The system has a low operating load, low energy consumption, and high product output. It also solves the problem of residues in the feed being denatured and clogging the distillation tower equipment after prolonged heating. 3. It fully utilizes the potential of the steam at the top of the distillation tower, saving a large amount of steam energy and reducing production costs. 4. Compared with traditional methanol multi-effect distillation, it can save 30% of raw steam and circulating cooling water, achieving significant energy-saving and environmental protection effects.

Description

Technical Field

[0001] The present invention relates to a methanol recovery technology, in particular to a rectification MVR system for methanol recovery in vitamin C production and application thereof in vitamin C production. Background Art

[0002] Vitamin C, also known as L-ascorbic acid, is widely used as a drug and additive in pharmaceutical, food and feed production.

[0003] Currently, the industrial production of vitamin C primarily utilizes a two-step fermentation process to prepare the vitamin C intermediate 2-keto-L-gulonic acid. This is followed by a transesterification reaction between 2-keto-L-gulonic acid and methanol to produce sodium vitamin C. The sodium vitamin C is then subjected to exchange, decolorization, concentration, crystallization, and filtration to obtain vitamin C. The vitamin C production process generates a large amount of methanol mother liquor, with a methanol content ranging from 60% to 90%, with significant fluctuations. It also contains impurities such as intermediates and inorganic salts. Currently, methanol recovery is commonly achieved through distillation, including conventional distillation and multi-effect distillation. Conventional distillation consumes a high energy consumption, consuming approximately one ton of steam for every ton of methanol recovered. Multi-effect distillation, which includes double-effect distillation and triple-effect distillation, can save 40% to 60% of steam, but energy consumption remains high, resulting in high recovery costs.

[0004] With the continuous rise in energy prices, the production of vitamin C urgently needs to further reduce the energy consumption of methanol recovery and improve the utilization rate of distillation steam.

[0005] MVR is a steam mechanical recompression technology. It is an energy-saving technology in which the MVR evaporator reuses the energy of the secondary steam it generates, thereby reducing the demand for external energy. In addition to replenishing some heat loss caused by heat loss, the operation of this technology no longer requires steam after normal operation. The main energy consumption is the electricity consumed by the compressor, so it can significantly reduce energy consumption. In view of this, scientific and technological workers are willing to introduce it into the distillation system. However, in the distillation system, the temperature difference between the top and the bottom of the tower is too large, and direct introduction will greatly limit the effectiveness of MVR technology.

[0006] CN114632343B discloses an MVR heat pump distillation system and method. The system includes a distillation tower, an overhead heat exchanger, a steam compressor, a first-stage reboiler, a circulating heat exchanger, and a circulating feed pump. The top of the distillation tower, the overhead heat exchanger, the steam compressor, and the first-stage reboiler are sequentially connected by pipelines. The bottom of the distillation tower is connected to the bottom of the first-stage reboiler by a pipeline, and the top of the first-stage reboiler is connected to the distillation tower by a pipeline. The first-stage reboiler, the circulating heat exchanger, the circulating feed pump, and the distillation tower are sequentially connected by pipelines. The overhead heat exchanger partially replaces the heat generated by the steam compressor with heat, thereby reducing process energy consumption and achieving energy conservation. The overhead steam of the distillation tower is preheated and compressed by the steam compressor, then used as a heating medium to preheat the kettle liquid, achieving reboiler liquid reboiler, thereby fully utilizing the latent heat of the overhead steam and the kettle liquid of the distillation tower, thereby saving a large amount of energy and operating costs. In order to solve the problem that "the gas phase at the top of the distillation tower is in a saturated state, and direct compression with a compressor is prone to liquefaction, which can easily affect the life of the compressor", such a system uses a top heat exchanger to preheat the gas phase at the top of the distillation tower before compressing it to avoid liquefaction. However, this increases energy consumption and reduces system efficiency.

[0007] CN106237643A discloses an MVR heat pump distillation system. The MVR heat pump distillation system includes a distillation tower, a reboiler, a steam compressor, a jet pump, a fan, a first gas-liquid separator, a second gas-liquid separator, a third gas-liquid separator, a heat exchanger, and a condenser. While this MVR heat pump distillation system utilizes the latent heat of the distillation tower overhead vapor and the bottom liquid, it primarily recovers the latent heat of the bottom liquid, resulting in a low heat recovery rate.

[0008] The above-mentioned new heat pump distillation technology has not been able to completely solve the problem of large temperature difference of 40°C between the top and bottom of the methanol distillation tower, resulting in that the effectiveness of the MVR technology cannot be fully utilized; it has not considered the impact of the residue contained in the methanol mother liquor on denaturation and clogging of the distillation tower equipment after long-term heating, and is not suitable for methanol recovery in vitamin C production. Summary of the Invention

[0009] The object of the present invention is to overcome the deficiencies of the prior art and to provide a distillation MVR system for methanol recovery in vitamin C production.

[0010] The purpose of the present invention is achieved through the following technical solutions:

[0011] A distillation MVR system for methanol recovery in vitamin C production comprises a raw material tank, a raw material pump, a preheater, a crude distillation tower, a crude distillation tower reboiler, a first steam compressor, a second steam compressor, a distillation tower, a distillation tower reboiler, a methanol tank, a discharge pump, a stripping tower, a first flow regulating valve, a second flow regulating valve and a finished product heat exchanger. The liquid outlet of the raw material tank is connected to the liquid inlet pipeline of the preheater through the raw material pump and the pipe line of the finished product heat exchanger; the liquid outlet of the preheater is connected to the feed inlet pipeline of the crude distillation tower; the top steam outlet of the crude distillation tower is connected to the feed inlet pipeline of the distillation tower through the first steam compressor, and the bottom tower kettle liquid outlet and the bottom tower kettle liquid outlet of the distillation tower are both connected to the feed inlet pipeline of the stripping tower; the top steam outlet of the stripping tower is also connected to the feed inlet pipeline of the distillation tower, and the bottom tower kettle liquid outlet is connected to the feed inlet pipeline of the stripping tower. The kettle liquid outlet serves as a wastewater discharge outlet, and the wastewater is discharged to an environmental protection facility for treatment, and the steam inlet is connected to a steam supply pipeline; the top steam outlet of the distillation tower is connected to the steam inlet pipeline of the crude distillation tower reboiler, and is also connected to the steam inlet pipeline of the distillation tower reboiler through a second steam compressor; and the condensate outlets of the crude distillation tower reboiler and the distillation tower reboiler are both connected to the inlet pipeline of the methanol tank; the bottom outlet of the methanol tank is connected to the reflux inlet pipeline of the distillation tower through a discharge pump, and then through a first flow regulating valve, and is connected to the shell-side inlet pipeline of the finished product heat exchanger through a second flow regulating valve; the tube-side inlet of the finished product heat exchanger is connected to the outlet pipeline of the raw material pump, the tube-side outlet is connected to the liquid inlet pipeline of the preheater, the shell-side inlet is connected to the outlet pipeline of the second flow regulating valve, and the shell-side outlet serves as a finished product collection outlet. When such a distillation MVR system for methanol recovery is working, the methanol mother liquor in the raw material tank enters the finished product heat exchanger under the drive of the raw material pump, takes the waste heat of the extracted finished product through the finished product heat exchanger, and then is sent to the preheater for heating. After heating, the methanol mother liquor enters the rough steam tower for rough steaming. The top steam generated by the rough steaming is pressurized and heated by the first steam compressor and then sent to the distillation tower for distillation, and the discharged bottom liquid is introduced into the stripping tower for stripping; the top steam generated by the stripping tower is sent to the distillation tower for distillation, and the discharged bottom liquid is sent to the environmental protection facility for wastewater treatment; and during the distillation tower rectification, part of the steam discharged from the top of the tower is directly introduced into the rough steam tower. The tower reboiler is used as the motive steam for crude distillation, and part of it is pressurized and heated by the second steam compressor and then introduced into the distillation tower reboiler to be used as the motive steam for distillation. The bottom liquid discharged from the bottom of the tower is introduced into the stripping tower together with the bottom liquid discharged from the bottom of the crude distillation tower for stripping; the methanol liquid discharged from the condensate outlet of the crude distillation tower reboiler and the distillation tower reboiler is introduced into the methanol tank; during the operation of the system, the methanol entering the methanol tank flows out through the liquid outlet at the bottom of the methanol tank, and is driven by the discharge pump to be diverted through the first flow regulating valve and the second flow regulating valve, with part of it refluxed to the distillation tower as reflux liquid, and part of it is extracted after shell-side heat exchange in the finished product heat exchanger.

[0012] In the above technical solution, the crude steam tower reboiler and the distillation tower reboiler are preferably falling film evaporators or wound heat exchangers; the steam compressor is preferably a twin-screw compressor and preferably a dry gas seal; the stripping tower is preferably a plate tower; and the distillation tower is preferably a packed tower.

[0013] In the above technical solution, the bottom temperature of the crude distillation tower is designed to be 50-90°C, the top temperature of the crude distillation tower is designed to be 40-80°C, and the reboiler pressure of the crude distillation tower is designed to be 0.02-0.20 MPa (gauge pressure).

[0014] In the above technical solution, the bottom temperature of the stripping tower is designed to be 90-140°C, the top temperature of the stripping tower is designed to be 70-120°C, and the bottom pressure of the stripping tower is designed to be 0.05-0.30 MPa (gauge pressure).

[0015] In the above technical solution, the bottom temperature of the distillation tower is designed to be 70-120° C., and the top pressure of the distillation tower is designed to be 0.020-0.20 MPa (gauge pressure).

[0016] Such a distillation MVR system for methanol recovery, 1. uses the overhead steam generated in the distillation process as the motive steam for crude distillation and rectification, and uses the finished product heat exchanger to recover the waste heat of the extracted finished product. During operation, only the preheater heats the methanol mother liquor and the stripping tower strips the bottom liquid discharged from the crude distillation tower and the distillation tower, which consumes raw steam. Apart from this, the main energy consumption is the electricity consumed to maintain the operation of the steam compressor. Therefore, a large amount of steam energy can be saved, which significantly reduces energy consumption, reduces production costs, and gives full play to the efficiency of the system; 2. A part of the overhead steam generated in the distillation process is used to directly supply the crude distillation tower reboiler, and a second steam compressor is designed to pressurize and heat the remaining refined methanol. The top steam generated during the distillation process is supplied to the reboiler of the distillation tower. Although the design is simple, it solves the problem that the temperature difference between the top and bottom of the crude distillation tower and the distillation tower is too large, which limits the effectiveness of the MVR technology. 3. The system adopts a three-tower distillation process of "crude distillation + distillation + supplemented by steam stripping recovery". During operation, crude methanol can be quickly evaporated, and then distilled through the distillation tower to improve product quality. The system has a low operating load, which is conducive to reducing production energy consumption. The design uses a steam stripping tower to recover the methanol component in the bottom liquid. While increasing product output, it also removes residues in the feed, solving the problem that the residues in the feed will denature and clog the distillation tower equipment after long-term heating.

[0017] Beneficial effects of the present invention:

[0018] 1. Solved the problem that the large temperature difference between the tower top and the tower bottom limits the application of MVR technology in methanol distillation system.

[0019] 2. The system has low operating load, low energy consumption, high product output, and solves the problem that the residues contained in the feed will denature and clog the distillation tower equipment after long-term heating.

[0020] 3. It makes full use of the potential of the steam at the top of the distillation tower, which can save a lot of steam energy and reduce production costs.

[0021] 4. Compared with traditional methanol multi-effect distillation, it can save 30% of raw steam and circulating cooling water, achieving significant energy-saving and environmental protection effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic structural diagram of a distillation MVR system for methanol recovery in vitamin C production provided by the present invention;

[0023] Markings in the figure: 1. Raw material tank; 2. Raw material pump; 3. Preheater; 4. Crude distillation tower; 5. Crude distillation tower reboiler; 6. First steam compressor; 7. Second steam compressor; 8. Distillation tower; 9. Distillation tower reboiler; 10. Methanol tank; 11. Discharge pump; 12. Stripping tower; 13. First flow regulating valve; 14. Second flow regulating valve; 15. Finished product heat exchanger. DETAILED DESCRIPTION

[0024] In order to facilitate those skilled in the art to better understand the technical solutions of the present invention, the present invention is further described below with reference to the accompanying drawings and embodiments.

[0025] With reference to the accompanying drawings, an embodiment of the present invention provides a distillation MVR system for methanol recovery in vitamin C production, which comprises a raw material tank 1, a raw material pump 2, a preheater 3, a crude distillation tower 4, a crude distillation tower reboiler 5, a first steam compressor 6, a second steam compressor 7, a distillation tower 8, a distillation tower reboiler 9, a methanol tank 10, a discharge pump 11, a stripping tower 12, a first flow regulating valve 13, a second flow regulating valve 14 and a finished product heat exchanger 15. The liquid outlet of the raw material tank 1 is connected to the liquid inlet pipe of the preheater 3 through the pipe line of the raw material pump 2 and the finished product heat exchanger 15; the preheater 3 , the liquid outlet is connected to the feed inlet pipeline of the crude steam tower 4; the crude steam tower 4, the top steam outlet is connected to the feed inlet pipeline of the distillation tower 8 through the first steam compressor 6, the bottom tower kettle liquid outlet and the bottom tower kettle liquid outlet of the distillation tower 8 are both connected to the feed inlet pipeline of the stripping tower 12, the bottom temperature is designed to be 71 ° C, the top temperature is designed to be 80 ° C, and the feed flow rate is designed to be 20000 kg / h; the crude steam tower reboiler 5 adopts a falling film evaporator, the pressure is designed to be 0.08 MPa (gauge pressure), and is connected to the crude steam tower 4 pipeline; the stripping tower 12 is a plate tower, and the bottom temperature is designed to be 128 ℃, the tower top temperature is designed to be 106 ℃, the tower top steam outlet is also connected to the feed inlet pipeline of the distillation tower 8, the tower bottom kettle liquid outlet is used as a wastewater discharge port, and the wastewater is discharged to the environmental protection facility for treatment, and the steam inlet is connected to the steam supply pipeline; the distillation tower 8 is a packed tower, and the tower top steam outlet is connected to the steam inlet pipeline of the crude steam tower reboiler 5, and is connected to the steam inlet pipeline of the distillation tower reboiler 9 through the second steam compressor 7. The tower bottom temperature is designed to be 105 ℃, and the tower top temperature is designed to be 85 ℃; the distillation tower reboiler 9 adopts a falling film evaporator, which is connected to the distillation tower 8 pipeline; and the The condensate outlets of the crude distillation tower reboiler 5 and the rectifying tower reboiler 9 are both connected to the inlet pipe of a methanol tank 10. The bottom outlet of the methanol tank 10 is connected to the reflux inlet pipe of the rectifying tower 8 via a first flow regulating valve 13, and to the shell-side inlet pipe of a finished product heat exchanger 15 via a second flow regulating valve 14. The tube-side inlet of the finished product heat exchanger 15 is connected to the outlet pipe of the feed pump 2, the tube-side outlet is connected to the liquid inlet pipe of the preheater 3, and the shell-side inlet is connected to the outlet pipe of the second flow regulating valve 14. The shell-side outlet serves as the finished product production outlet. The system is designed to produce 16,000 kg / h of methanol product.

Claims

1. A methanol recovery distillation MVR system, characterized by: It consists of a raw material tank (1), a raw material pump (2), a preheater (3), a crude steam tower (4), a crude steam tower reboiler (5), a first steam compressor (6), a second steam compressor (7), a distillation tower (8), a distillation tower reboiler (9), a methanol tank (10), a discharge pump (11), a stripping tower (12), a first flow regulating valve (13), a second flow regulating valve (14) and a finished product heat exchanger (15). The raw material tank (1) has a liquid outlet connected to the raw material pump (2), the finished product The tube side of the heat exchanger (15) is connected to the liquid inlet pipe of the preheater (3); the liquid outlet of the preheater (3) is connected to the feed pipe of the crude steam tower (4); the top steam outlet of the crude steam tower (4) is connected to the feed pipe of the distillation tower (8) through the first steam compressor (6), and the bottom tower kettle liquid outlet and the bottom tower kettle liquid outlet of the distillation tower 8 are both connected to the feed pipe of the stripping tower (12); the top steam outlet of the stripping tower (12) is also connected to the feed pipe of the distillation tower (8). The feed inlet pipe is connected, the bottom kettle liquid outlet is used as a wastewater discharge port, and the steam inlet is connected to the steam supply pipe; the distillation tower (8), the top steam outlet is connected to the steam inlet pipe of the crude steam tower reboiler (5), and is connected to the steam inlet pipe of the distillation tower reboiler (9) through the second steam compressor (7); and the condensate outlets of the crude steam tower reboiler (5) and the distillation tower reboiler (9) are both connected to the inlet pipe of the methanol tank (10); the bottom outlet of the methanol tank (10) is connected to the steam inlet pipe of the distillation tower reboiler (5). The outlet is connected to the reflux inlet pipe of the distillation tower (8) through the discharge pump (11), and then connected to the shell-side inlet pipe of the finished product heat exchanger (15) through the first flow regulating valve (13), and connected to the shell-side inlet pipe of the finished product heat exchanger (15) through the second flow regulating valve (14); the tube-side inlet of the finished product heat exchanger (15) is connected to the outlet pipe of the raw material pump (2), the tube-side outlet is connected to the liquid inlet pipe of the preheater (3), the shell-side inlet is connected to the outlet pipe of the second flow regulating valve (14), and the shell-side outlet serves as the finished product collection outlet.

2. The methanol recovery distillation MVR system according to claim 1, characterized in that: The bottom temperature of the crude distillation tower (4) is 50-90°C, the top temperature of the crude distillation tower (4) is 40-80°C, and the pressure of the crude distillation tower reboiler (5) is 0.02-0.20 MPa; the bottom temperature of the stripping tower (12) is 90-140°C, the top temperature of the stripping tower (12) is 70-120°C, and the bottom pressure of the stripping tower (12) is 0.05-0.30 MPa; the bottom temperature of the rectifying tower (8) is 70-120°C, and the top pressure of the rectifying tower (8) is 0.020-0.20 MPa.

3. The methanol recovery distillation MVR system according to claim 2, characterized in that: The bottom temperature of the crude distillation tower (4) is 71°C, the top temperature of the crude distillation tower (4) is 80°C, and the pressure of the crude distillation tower reboiler (5) is 0.08 MPa; the bottom temperature of the stripping tower (12) is 128°C, the top temperature of the stripping tower (12) is 106°C; the bottom temperature of the distillation tower (8) is 105°C, and the top temperature of the distillation tower (8) is 85°C.

4. The methanol recovery distillation MVR system according to claim 1, characterized in that: The crude steam tower reboiler (5) and the distillation tower reboiler (9) are selected from falling film evaporators or wound heat exchangers; the first steam compressor (6) and the second steam compressor (7) are selected from twin-screw compressors and dry gas seals; the stripping tower (12) is selected from plate towers; and the distillation tower is selected from packed towers.

5. Use of the methanol recovery distillation MVR system according to claim 1, 2, 3 or 4 in vitamin C production.

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