Mechanical vapor recompression rectification system and wastewater treatment method thereof

Abstract

The application relates to the technical field of wastewater purification, in particular to a mechanical vapor recompression rectification system and a wastewater treatment method thereof. The mechanical vapor recompression rectification system comprises a feed preheater, a wastewater degassing tank, a wastewater feed pump, an inlet-outlet heat exchanger, a steam heater, a rectification tower, a steam compressor and a reboiler; the cold side outlet of the steam heater is connected with the feed inlet of the rectification tower; the gas phase outlet at the top of the rectification tower is connected with a tail gas treatment device; the side line steam outlet of the rectification tower is connected with the inlet of the steam compressor; the outlet of the steam compressor is connected with the hot side inlet of the reboiler; the hot side outlet of the reboiler is sequentially connected with the hot side inlet of the inlet-outlet heat exchanger and the hot side inlet of the feed preheater; the liquid outlet at the bottom of the rectification tower is respectively connected with the cold side inlet of the reboiler and an evaporation crystallization system; and the cold side outlet of the reboiler is connected with the circulating feed inlet of the rectification tower. The mechanical vapor recompression rectification system has the advantages of good separation effect, high treatment efficiency, low energy consumption and high product purity.

Description

Technical Field

[0001] This application relates to the field of wastewater purification technology, specifically to a mechanical vapor recompression distillation system and its wastewater treatment method. Background Technology

[0002] MVR, or Mechanical Vapor Recompression, primarily utilizes secondary steam generated in the evaporator. This secondary steam is compressed by a compressor, increasing its pressure and temperature, and then returned to the evaporator as heating steam. Thus, during the entire evaporation process, only a small amount of live steam is needed at startup, while subsequent evaporation relies mainly on the cyclic compression of the secondary steam for heat, significantly reducing the demand for external live steam and achieving energy savings. It has wide applications in the food, pharmaceutical, chemical, and seawater desalination industries. Compared to traditional evaporation crystallization processes, MVR technology fully recovers and utilizes the heat energy of secondary steam, reducing dependence on external energy sources and significantly lowering energy consumption. Compared to traditional evaporation technologies, MVR systems can reduce energy consumption by 30%-80%. Because MVR systems do not require large amounts of external live steam during operation, they reduce emissions of greenhouse gases and pollutants such as carbon dioxide and sulfur dioxide, making them more environmentally friendly. MVR systems are highly automated and easy to operate. The control system allows for precise control of the evaporation process, ensuring stable system operation. MVR systems have a compact structure and require little floor space. Compared to traditional evaporation equipment, MVR systems can save a significant amount of space and are suitable for applications with limited space.

[0003] However, due to the single-effect evaporation of steam in traditional MVR processes, the presence of light components in the wastewater will significantly affect the efficiency of MVR and the purity of the purified water. Summary of the Invention

[0004] In view of this, embodiments of this application provide a mechanical vapor recompression distillation system and its wastewater treatment method, combining MVR and distillation. Energy saving is achieved through MVR, while the distillation process effectively separates purified water, light components, and solid components. It offers good separation effect, high treatment efficiency, low energy consumption, and high product purity.

[0005] The first aspect of this application provides a mechanical vapor recompression distillation system, including a feed preheater, a wastewater degassing tank, a wastewater feed pump, a feed and discharge heat exchanger, a steam heater, a distillation column, a steam compressor, and a reboiler;

[0006] The inlet end of the feed preheater is connected to the wastewater input pipeline, and the outlet end is connected to the inlet end of the wastewater degassing tank.

[0007] The inlet end of the wastewater feed pump is connected to the outlet end of the wastewater degassing tank, and the outlet end is connected to the cold side inlet of the feed-discharge heat exchanger.

[0008] The cold-side outlet of the feed heat exchanger is connected to the cold-side inlet of the steam heater, and the cold-side outlet of the steam heater is connected to the feed inlet of the distillation column.

[0009] The top vapor outlet of the distillation column is connected to the tail gas treatment device. The side steam outlet of the distillation column is connected to the inlet of the steam compressor. The outlet of the steam compressor is connected to the hot side inlet of the reboiler. The hot side outlet of the reboiler is connected in sequence to the hot side inlet of the feed heat exchanger and the hot side inlet of the feed preheater. The bottom liquid outlet of the distillation column is connected to the cold side inlet of the reboiler and the evaporation crystallization system, respectively. The cold side outlet of the reboiler is connected to the circulating feed inlet of the distillation column.

[0010] In one embodiment, the device further includes a purified water cooler, a purified water tank, and a purified water delivery pump. The hot-side outlet of the feed preheater is connected to the inlet of the purified water cooler, the outlet of the purified water cooler is connected to the inlet of the purified water tank, and the outlet of the purified water tank outputs purified water through the purified water delivery pump.

[0011] In one embodiment, a demister is provided at the gas phase outlet of the wastewater degassing tank, and the demister is any one of a wire mesh demister, a baffle demister, or a cyclone demister.

[0012] In one embodiment, the distillation column is a packed column or a plate column with side stream output, and the packing type includes any one or more of trays, structured packing, and random packing;

[0013] The distillation column is equipped with a thermally coupled control algorithm module, which is used to dynamically adjust the top gas flow rate and the side steam extraction rate according to the feed composition, column top temperature and pressure.

[0014] In one embodiment, the thermal coupling control algorithm module of the distillation column is further configured to:

[0015] Based on the content of non-condensable gas components in the feed, the initial control value of the gas phase flow rate at the top of the tower is solved using a temperature and pressure balance algorithm.

[0016] The gas flow rate at the top of the column is adjusted in real time based on the boiling point temperature of the non-condensable gas corresponding to the operating pressure at the top of the column.

[0017] In one embodiment, the steam compressor is a single-stage or multi-stage compressor used to pressurize the saturated steam extracted from the side stream to a pressure higher than the operating pressure at the bottom of the distillation column, serving as a heat source for the reboiler.

[0018] A second aspect of this application provides a wastewater treatment method for a mechanical vapor recompression distillation system, comprising:

[0019] The wastewater is preheated by the feed preheater and then fed into the wastewater degassing tank for flash degassing.

[0020] After degassing, the wastewater is pressurized by the wastewater feed pump, and then sequentially heated by the feed heat exchanger and the steam heater before being fed into the distillation column for separation.

[0021] Steam is drawn from the side stream of the distillation column, pressurized by the steam compressor, and then delivered to the reboiler as a heat source.

[0022] The concentrate at the bottom of the distillation column is partially circulated to the reboiler for heating via a bottom pump, and partially output to the evaporation and crystallization system.

[0023] The condensate generated by the reboiler is sequentially cooled by thermal coupling through the feed heat exchanger, the feed preheater, and the purified water cooler before being stored in the purified water tank and output through the purified water delivery pump.

[0024] In one embodiment, it also includes:

[0025] Using the composition and flow rate of wastewater as input values, the initial values ​​of the top gas phase output, side stream output, bottom gas output, and steam consumption are calculated, and the initial opening of the top regulating valve is obtained based on the initial values.

[0026] During operation, the temperature corresponding to the tower operating pressure and the temperature corresponding to the non-condensable gas component are coupled and solved to obtain the real-time control value. Based on the real-time control value, the tower top regulating valve is subjected to differential control.

[0027] In one embodiment, it also includes:

[0028] PID control is used to regulate the feed to the distillation column;

[0029] In addition, proportional-integral-derivative coupled frequency converter control is implemented for the distillation column side stream extraction rate and compressor power; including...

[0030] The side stream extraction amount is calculated based on the feed composition, and an initial value for control is assigned based on the side stream extraction amount to perform proportional control of the side stream extraction amount.

[0031] Based on the side stream outlet temperature under the tower operating pressure, the side stream extraction rate is coupled with differential control. At the same time, the control value of the side stream extraction rate is calculated based on the feed rate to perform integral control of the side stream extraction rate.

[0032] In one embodiment, it also includes:

[0033] The reboiler temperature and steam flow rate of the distillation column are controlled by a cascade proportional-integral control, including solving for the initial steam flow rate corresponding to the reboiler temperature using the operating pressure and reboiler composition.

[0034] The steam flow rate is integrally controlled based on the coupled solution of the extraction rate and the bottom temperature of the tower.

[0035] The mechanical vapor recompression distillation system provided in the first aspect of this application includes a feed preheater, a wastewater degassing tank, a wastewater feed pump, a feed-discharge heat exchanger, a steam heater, a distillation column, a steam compressor, and a reboiler; the inlet end of the feed preheater is connected to a wastewater input pipeline, and the outlet end is connected to the inlet end of the wastewater degassing tank; the inlet end of the wastewater feed pump is connected to the outlet end of the wastewater degassing tank, and the outlet end is connected to the cold side inlet of the feed-discharge heat exchanger; the cold side outlet of the feed-discharge heat exchanger is connected to the cold side inlet of the steam heater, and the steam... The cold-side outlet of the heater is connected to the feed inlet of the distillation column; the top vapor outlet of the distillation column is connected to the tail gas treatment device; the side-stream vapor outlet of the distillation column is connected to the inlet of the steam compressor; the outlet of the steam compressor is connected to the hot-side inlet of the reboiler; the hot-side outlet of the reboiler is sequentially connected to the hot-side inlet of the feed heat exchanger and the hot-side inlet of the feed preheater; the bottom liquid outlet of the distillation column is connected to the cold-side inlet of the reboiler and the evaporation crystallization system, respectively; and the cold-side outlet of the reboiler is connected to the circulating feed inlet of the distillation column. This system forms a closed-loop energy cycle system by integrating a pretreatment module (preheating, degassing), a distillation module (side-stream vapor compression and reuse), and a thermal coupling module (reboiler heat exchange). The pretreatment stage involves flash degassing of wastewater to eliminate the interference of non-condensable gases on the mass transfer efficiency of the distillation column. Side-stream steam, pressurized by a compressor, serves as a heat source for the reboiler, replacing the traditional method of relying on external steam for heating and reducing the need for external energy purchases. The bottom concentrate circulation loop design ensures stable reboiler heat load and avoids temperature gradient imbalance within the column caused by flow fluctuations. This process system combines MVR and distillation, achieving energy savings through MVR and effective separation of purified water, light components, and solid components through distillation. It offers good separation effect, high processing efficiency, low energy consumption, and high product purity. Compared to traditional MVR processes, in terms of removing light components, the temperature-controlled wastewater degassing tank flashes and removes dissolved light components from the wastewater, effectively reducing the soluble light components in the wastewater and lowering the heat load of the distillation column. By integrating the evaporator and distillation column, the unit achieves high equipment integration, occupies a small area, and reduces the workload of piping and equipment installation, significantly improving construction efficiency. Simultaneously, the reduced number of pipes and valves simplifies operation, increases production efficiency, and reduces the risk of operational errors and accidents. Due to its low investment, small footprint, and short construction period, this unit has found widespread application in coal chemical and petrochemical enterprises, effectively addressing environmental issues and generating substantial economic benefits.

[0036] It is understandable that the beneficial effects of the second aspect mentioned above can be found in the relevant descriptions in the first aspect mentioned above, and will not be repeated here. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a schematic diagram of the mechanical vapor recompression distillation system provided in one embodiment of this application.

[0039] In the diagram: 1. Feed preheater; 2. Wastewater deaeration tank; 3. Wastewater feed pump; 4. Feed and discharge heat exchangers; 5. Steam heater; 6. Distillation column; 7. Steam compressor; 8. Reboiler; 9. Bottom pump; 10. Purified water cooler; 11. Purified water tank; 12. Purified water transfer pump. Detailed Implementation

[0040] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of this application with unnecessary detail.

[0041] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0042] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0043] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0044] like Figure 1 As shown in the embodiment of this application, a mechanical vapor recompression distillation system includes a feed preheater 1, a wastewater degassing tank 2, a wastewater feed pump 3, a feed and discharge heat exchanger 4, a steam heater 5, a distillation column 6, a steam compressor 7, and a reboiler 8.

[0045] The inlet end of the feed preheater 1 is connected to the wastewater input pipeline, and the outlet end is connected to the inlet end of the wastewater degassing tank 2.

[0046] The inlet end of the wastewater feed pump 3 is connected to the outlet end of the wastewater degassing tank 2, and the outlet end is connected to the cold side inlet of the feed-discharge heat exchanger 4.

[0047] The cold side outlet of the feed heat exchanger 4 is connected to the cold side inlet of the steam heater 5, and the cold side outlet of the steam heater 5 is connected to the feed inlet of the distillation column 6.

[0048] The top vapor outlet of distillation column 6 is connected to the tail gas treatment device. The side steam outlet of distillation column 6 is connected to the inlet of steam compressor 7. The outlet of steam compressor 7 is connected to the hot side inlet of reboiler 8. The hot side outlet of reboiler 8 is connected in sequence to the hot side inlet of feed heat exchanger 4 and the hot side inlet of feed preheater 1. The bottom liquid outlet of distillation column 6 is connected to the cold side inlet of reboiler 8 and the evaporation crystallization system, respectively. The cold side outlet of reboiler 8 is connected to the circulating feed inlet of distillation column 6.

[0049] The entire process in this embodiment is divided into a wastewater light-weight wastewater removal process, a wastewater distillation process, and a vapor compression process. The wastewater light-weight wastewater removal process includes a raw material preheater and a wastewater degassing tank, where the wastewater is preheated and then flash-evaporated to remove light-weight wastewater. The wastewater distillation process includes a distillation column and a heat-coupled heat exchanger. The vapor compression process includes a multi-effect steam compressor and supporting facilities. These processes are organically integrated to transform wastewater into clean purified water and high-value-added solid salt products. This green and environmentally friendly MVRD process not only effectively treats complex industrial wastewater and solves the environmental problems associated with wastewater resource utilization, but also achieves good economic benefits, turning waste into treasure while addressing environmental issues. By integrating a pretreatment module (preheating and degassing), a distillation module (side-stream vapor compression and reuse), and a heat-coupled module (reboiler heat exchange), a closed-loop energy cycle system is formed. The pretreatment stage involves flash evaporation to degas the wastewater, eliminating the interference of non-condensable gases on the mass transfer efficiency of the distillation column. The side-stream steam is pressurized by a compressor and used as a heat source for the reboiler, replacing the traditional heating method that relies on external steam, thus reducing the need for external energy purchases. The bottom concentrate circulation loop design ensures stable heat load of the reboiler and avoids temperature gradient imbalance in the column caused by flow fluctuations.

[0050] In one embodiment, the system further includes a purified water cooler 10, a purified water tank 11, and a purified water delivery pump 12. The hot side outlet of the feed preheater 1 is connected to the inlet of the purified water cooler 10, the outlet of the purified water cooler 10 is connected to the inlet of the purified water tank 11, and the outlet of the purified water tank 11 outputs purified water through the purified water delivery pump 12.

[0051] This embodiment utilizes a purified water cooler and a storage tank to recover the condensate generated by the reboiler after staged cooling. The cooler and preheater form a counter-current heat exchange, utilizing the waste heat from the condensate to preheat the wastewater, further reducing the system's cooling source requirements. The purified water tank's buffer storage design resolves the conflict between intermittent condensate discharge and continuous reuse. The purified water purity meets industrial reuse standards, with a high recovery rate; and the cascaded utilization of condensate waste heat reduces cooling source energy consumption.

[0052] In one embodiment, a demister is provided at the gas phase outlet of the wastewater degassing tank 2. The demister is any one of a wire mesh demister, a baffle demister, or a cyclone demister.

[0053] This embodiment of the application installs a wire mesh / baffle / cyclone demister at the gas phase outlet of the wastewater degassing tank, removing entrained droplets through a multi-stage interception mechanism (inertial impaction, centrifugal separation). The wire mesh structure reduces the gas phase flow velocity to below the critical carry-over velocity, the baffles change the airflow direction to achieve gas-liquid inertial separation, and the cyclone enhances mist collection through centrifugal force. This reduces the content of entrained droplets in the gas phase, preventing mist from entering the steam compressor and causing impeller corrosion; it also improves the mass transfer efficiency of the distillation column and extends the service life of the steam compressor.

[0054] In one embodiment, the distillation column 6 is a packed column or a plate column with side stream output, and the packing type includes any one or more of trays, structured packing, and random packing.

[0055] Distillation column 6 is equipped with a thermally coupled control algorithm module, which is used to dynamically adjust the top gas flow rate and the side steam extraction rate according to the feed composition, column top temperature and pressure.

[0056] This application employs a combination of structured and random packing structures. By increasing the gas-liquid contact area and optimizing the flow channel distribution, the pressure drop across the trays is reduced. A thermally coupled algorithm dynamically adjusts the overhead gas flow rate based on the feed components, establishing a closed-loop feedback model of overhead pressure, temperature, and component concentration to match separation requirements in real time. This improves the separation efficiency of light components, reduces the amount of non-condensable gas residue at the top of the column, and lowers the packing pressure drop, thus reducing the power consumption of the steam compressor.

[0057] In one embodiment, the thermal coupling control algorithm module of distillation column 6 is also used for:

[0058] Based on the content of non-condensable gas components in the feed, the initial control value of the gas phase flow rate at the top of the tower is solved using a temperature and pressure balance algorithm.

[0059] The gas flow rate at the top of the column is adjusted in real time based on the boiling point temperature of the non-condensable gas corresponding to the operating pressure at the top of the column.

[0060] This application's embodiments establish a temperature and pressure balance model for non-condensable gas components based on the Antoine equation, and back-calculate the initial value of the overhead gas flow rate based on the real-time operating pressure. Through multi-parameter coupling of pressure sensors and temperature probes, the steam extraction rate is dynamically corrected, eliminating the mass transfer resistance caused by the enrichment of non-condensable gas at the top of the column. This reduces the fluctuation range of non-condensable gas concentration at the top of the column, improves the thermal efficiency of the steam compressor, enhances the system's resistance to feed composition fluctuations, and shortens the steady-state response time.

[0061] In one embodiment, the steam compressor 7 is a single-stage or multi-stage compressor used to pressurize the saturated steam extracted from the side stream to a pressure higher than the operating pressure at the bottom of the distillation column 6, serving as a heat source for the reboiler 8.

[0062] The single-stage compressor in this application is suitable for low-boiling-point wastewater, and the impeller speed is adjusted to match the steam load. The multi-stage compressor adopts an intermediate cooling design, compressing high-boiling-point steam stage by stage to avoid the risk of coking caused by overheating. The compressor has a high coefficient of performance (COP), which is improved compared to the single-stage design; it is suitable for complex wastewater treatment scenarios, and the steam pressurization stability is improved.

[0063] This application also provides a wastewater treatment method for a mechanical vapor recompression distillation system, comprising:

[0064] The wastewater is preheated by the feed preheater 1 and then fed into the wastewater deaeration tank 2 for flash deaeration.

[0065] After degassing, the wastewater is pressurized by the wastewater feed pump 3, and then sequentially heated by the feed heat exchanger 4 and the steam heater 5, before being fed into the distillation column 6 for separation.

[0066] Steam is drawn from the side stream of distillation column 6, pressurized by steam compressor 7, and then sent to reboiler 8 as a heat source;

[0067] The concentrate at the bottom of distillation column 6 is partially circulated to reboiler 8 for heating via bottom pump 9, and partially output to the evaporation and crystallization system;

[0068] The condensate generated by the reboiler 8 is cooled sequentially by the feed heat exchanger 4, the feed preheater 1, and the purified water cooler 10 through thermal coupling, and then stored in the purified water tank 11 and output through the purified water delivery pump 12.

[0069] This application's embodiment achieves a stepwise separation of organic components and salts through a four-stage process: flash degassing, multi-stage preheating, distillation separation, and steam reuse. The side-stream steam compression reuse and the bottom concentrate circulation form a thermodynamic coupling, overcoming the heat transfer temperature difference limitations of traditional multi-effect evaporation processes. This reduces energy consumption per unit of wastewater treated, and the concentrated liquid, with its high salt content, can directly enter the crystallization system, reducing mother liquor treatment costs.

[0070] In terms of energy saving, the use of MVR (Medium-Voltage Reduction) instead of traditional steam heating can significantly reduce the steam consumption of the unit. Energy consumption during the distillation process is controlled by PID (Peripheral Diagnostic Control). Partial differential equations are solved based on wastewater composition and flow rate, along with the operating parameters of the distillation column. Algorithm control is used to thermally couple the entire process system, enabling the entire unit to operate with the lowest energy consumption while meeting separation conditions, resulting in energy savings of approximately 80% compared to traditional distillation processes. The use of plate-packing mixing technology effectively improves the mass transfer and separation efficiency of the distillation column, significantly enhancing the mass transfer process and reducing separation energy consumption and costs.

[0071] In one embodiment, the method further includes: solving partial differential equations for the composition and flow rate of the wastewater and the operating parameters of the distillation column 6, and using algorithmic control to thermally couple the entire process system. Specifically:

[0072] Using the composition and flow rate of wastewater as input values, the initial values ​​of the top gas phase output, side stream output, bottom gas output, and steam consumption are calculated, and the initial opening of the top regulating valve is obtained based on the initial values.

[0073] During operation, the temperature corresponding to the tower operating pressure and the temperature corresponding to the non-condensable gas components are coupled and solved to obtain the real-time control value. Based on the real-time control value, the regulating valve at the top of the tower is controlled differentially to achieve precise extraction of non-condensable gas.

[0074] By coupling the side-stream outlet temperature at the top of the tower with the side-stream component temperature under operating pressure, the side-stream extraction rate is controlled differentially to achieve precise control of the side-stream extraction rate. By solving for the tower bottom temperature corresponding to the extracted concentration, the tower bottom extraction rate is controlled differentially to achieve precise control of the extracted concentration. By solving for the tower bottom gas phase temperature under operating pressure, the steam flow rate is controlled integrally to achieve minimum steam consumption.

[0075] In one embodiment, it also includes:

[0076] PID control is used to regulate the feed to distillation column 6;

[0077] In addition, proportional-integral-derivative coupled frequency converter control is implemented for the side stream extraction rate of distillation column 6 and the compressor power; including...

[0078] The side stream extraction amount is calculated based on the feed composition, and an initial value for control is assigned based on the side stream extraction amount to perform proportional control of the side stream extraction amount.

[0079] Based on the side stream outlet temperature under the tower operating pressure, the side stream extraction rate is coupled with differential control. At the same time, the control value of the side stream extraction rate is calculated based on the feed rate to perform integral control of the side stream extraction rate, thereby achieving optimal energy consumption.

[0080] In one embodiment, it also includes:

[0081] The reboiler temperature and steam flow rate of distillation column 6 are controlled by a cascade proportional-integral control, including solving for the initial steam flow rate corresponding to the reboiler temperature using the operating pressure and reboiler composition.

[0082] By solving the coupled extraction rate and the bottom temperature of the tower, the steam flow rate is integrally controlled to achieve the minimum steam consumption.

[0083] This application employs algorithm-integrated PID control to proportionally control the feed to the distillation column, and proportional-integral-derivative coupled control to control the side stream extraction rate and compressor power. Derivative control is added to the proportional control to increase the sensitivity of the unit's regulation, while integral control ensures the stability of the unit's production. Cascade proportional-integral control is used for the distillation column's reboiler temperature and compressor frequency to ensure the stability of the overall column temperature control and reduce the impact of temperature changes on the overall column operation. Proportional-derivative control is applied to the side stream steam flow rate and the distillation column's in-column temperature. Based on changes in flow rate, the side stream steam flow rate can be adjusted in a timely manner to achieve precise wastewater separation. Combined with the wastewater composition and flow rate, the entire process system is thermally coupled, enabling the entire unit to operate with the lowest energy consumption while meeting separation conditions. Due to the high integration of equipment and small footprint, the workload of piping and equipment installation is reduced, greatly improving the efficiency of unit construction. Simultaneously, the reduced number of pipes and valves simplifies operation, increases production efficiency, reduces operational errors, and lowers the risk of production accidents. Due to its low investment, small footprint, and short construction period, this device has been widely used in coal chemical and petrochemical enterprises, effectively solving environmental problems and bringing considerable economic benefits.

[0084] In one embodiment, a wastewater treatment method for a mechanical vapor recompression distillation system further includes:

[0085] Step 1: Wastewater degassing tank 2 performs flash evaporation and demisting separation on the dissolved gases in the wastewater;

[0086] Step 2: After degassing, the wastewater is pressurized by the wastewater feed pump 3 and enters the distillation column 6 in two streams. After being heated by the feed heat exchanger 10 and the steam heater 5 in stages, the wastewater enters the distillation column 6 from the column. The bottom of the distillation column 6 is heated by the reboiler 8 and the steam is compressed and heated by the steam compressor 7 to provide a heat source. The purified water at the bottom of the column is sent out by the bottom pump 9.

[0087] Step 3: Steam is cooled step by step through the reboiler 8, condenser feed heat exchanger 4, feed preheater 1, and purified water cooler 10 by thermal coupling, and then enters the purified water tank 11. The purified water is pressurized by the purified water delivery pump 12 and then sent out of the device.

[0088] In one embodiment, PID control is also used to regulate the feed to distillation column 6;

[0089] The side line extraction and compressor power are controlled by proportional-integral-derivative coupled frequency converter.

[0090] The reboiler temperature and steam flow rate of distillation column 6 are controlled by cascade proportional-integral control.

[0091] The composition and flow rate of the wastewater were solved using partial differential equations with the operating parameters of distillation column 6, and the entire process system was thermally coupled using algorithmic control.

[0092] In one embodiment, the MVRD process is illustrated using the treatment of BDO deionized wastewater as an example, as detailed below:

[0093] The composition of the deionized wastewater from a certain BDO unit is shown in Table 1.

[0094] Table 1

[0095]

[0096] Step 1: After the wastewater enters the wastewater degassing tank, the dissolved gases in the wastewater are separated by flash evaporation and demisting under operating conditions of 40-80℃ and 0.01-0.2MPaG.

[0097] Step 2: After oil removal, the wastewater is pressurized to 0.8–1.5 MPaG by a wastewater feed pump. It is then heated to 100–120°C through a series of heat exchangers and steam heaters before entering the distillation column. The distillation column operates at a pressure of 0.05–0.3 MPaG. Steam is drawn from a side stream, pressurized by a steam compressor, and used as a heat source for heat exchange with the reboiler. The light component content in the purified water at the bottom of the column is less than 20 ppm. This purified water is then pressurized to 0.5–1 MPaG by a bottom pump and sent to the evaporation crystallization unit. The MVRD unit saves approximately 80% more energy than traditional distillation processes.

[0098] Step 3: The steam is cooled to 40°C through the reboiler heat exchanger, condenser feed heat exchanger, feed preheater, and purified water cooler in a step-by-step thermal coupling process. The steam then enters the purified water tank. The purified water is pressurized to 0.5-1 MPaG by the purified water delivery pump and sent to the production water reuse device.

[0099] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A mechanical vapor recompression distillation system, characterized in that, It includes a feed preheater (1), a wastewater degassing tank (2), a wastewater feed pump (3), a feed and discharge heat exchanger (4), a steam heater (5), a distillation column (6), a steam compressor (7), and a reboiler (8); The inlet end of the feed preheater (1) is connected to the wastewater input pipeline, and the outlet end is connected to the inlet end of the wastewater degassing tank (2). The inlet end of the wastewater feed pump (3) is connected to the outlet end of the wastewater degassing tank (2), and the outlet end is connected to the cold side inlet of the feed heat exchanger (4). The cold side outlet of the feed heat exchanger (4) is connected to the cold side inlet of the steam heater (5), and the cold side outlet of the steam heater (5) is connected to the feed inlet of the distillation column (6). The top vapor outlet of the distillation column (6) is connected to the tail gas treatment device. The side steam outlet of the distillation column (6) is connected to the inlet of the steam compressor (7). The outlet of the steam compressor (7) is connected to the hot side inlet of the reboiler (8). The hot side outlet of the reboiler (8) is connected in sequence to the hot side inlet of the feed heat exchanger (4) and the hot side inlet of the feed preheater (1). The bottom liquid outlet of the distillation column (6) is connected to the cold side inlet of the reboiler (8) and the evaporation crystallization system, respectively. The cold side outlet of the reboiler (8) is connected to the circulating feed inlet of the distillation column (6). The distillation column (6) is a packed column or plate column with side stream output, and the packing type includes any one or more of tray, structured packing and random packing; The distillation column (6) is equipped with a thermally coupled control algorithm module, which is used to dynamically adjust the top gas flow rate and the side steam extraction rate according to the feed composition, column top temperature and pressure. The thermal coupling control algorithm module of the distillation column (6) is also used for: Based on the content of non-condensable gas components in the feed, the initial control value of the gas phase flow rate at the top of the tower is solved using a temperature and pressure balance algorithm. The gas flow rate at the top of the column is adjusted in real time based on the boiling point temperature of the non-condensable gas corresponding to the operating pressure at the top of the column. The wastewater degassing tank (2) is used to flash evaporate and demist separate the dissolved gases in the wastewater.

2. The mechanical vapor recompression distillation system as described in claim 1, characterized in that, It also includes a purified water cooler (10), a purified water tank (11), and a purified water delivery pump (12). The hot side outlet of the feed preheater (1) is connected to the inlet of the purified water cooler (10), the outlet of the purified water cooler (10) is connected to the inlet of the purified water tank (11), and the outlet of the purified water tank (11) outputs purified water through the purified water delivery pump (12).

3. The mechanical vapor recompression distillation system as described in claim 2, characterized in that, The wastewater degassing tank (2) is equipped with a demister at the gas phase outlet. The demister is any one of a wire mesh demister, a baffle demister, or a cyclone demister.

4. The mechanical vapor recompression distillation system as described in claim 2, characterized in that, The steam compressor (7) is a single-stage or multi-stage compressor used to pressurize the saturated steam extracted from the side stream to a level higher than the operating pressure at the bottom of the distillation column (6) as a heat source for the reboiler (8).

5. A wastewater treatment method based on the mechanical vapor recompression distillation system according to any one of claims 2 to 4, characterized in that, include: The wastewater is preheated by the feed preheater (1) and then fed into the wastewater degassing tank (2) for flash degassing. After degassing, the wastewater is pressurized by the wastewater feed pump (3), and then sequentially heated by the feed heat exchanger (4) and the steam heater (5) before being fed into the distillation column (6) for separation. Steam is drawn from the side stream of the distillation column (6), pressurized by the steam compressor (7), and then sent to the reboiler (8) as a heat source; The concentrate at the bottom of the distillation column (6) is partially circulated to the reboiler (8) for heating via the bottom pump (9), and partially output to the evaporation crystallization system; The condensate generated by the reboiler (8) is cooled sequentially by the feed heat exchanger (4), the feed preheater (1) and the purified water cooler (10) through thermal coupling, and then stored in the purified water tank (11) and output through the purified water delivery pump (12).

6. The wastewater treatment method as described in claim 5, characterized in that, Also includes: Using the composition and flow rate of wastewater as input values, the initial values ​​of the top gas phase output, side stream output, bottom gas output, and steam consumption are calculated, and the initial opening of the top regulating valve is obtained based on the initial values. During operation, the temperature corresponding to the tower operating pressure and the temperature corresponding to the non-condensable gas component are coupled and solved to obtain the real-time control value. Based on the real-time control value, the tower top regulating valve is subjected to differential control.

7. The wastewater treatment method as described in claim 5, characterized in that, Also includes: PID control is used to regulate the feed to the distillation column (6); In addition, proportional-integral-derivative coupled frequency conversion control is performed on the side stream extraction rate of the distillation column (6) and the compressor power; include The side stream extraction amount is calculated based on the feed composition, and an initial value for control is assigned based on the side stream extraction amount to perform proportional control of the side stream extraction amount. Based on the side stream outlet temperature under the tower operating pressure, the side stream extraction rate is coupled with differential control. At the same time, the control value of the side stream extraction rate is calculated based on the feed rate to perform integral control of the side stream extraction rate.

8. The wastewater treatment method as described in claim 5, characterized in that, Also includes: The reboiler temperature and steam flow rate of the distillation column (6) are controlled by a cascade proportional-integral control. include The initial value of steam flow rate corresponding to the reboiler temperature was obtained by calculating the operating pressure and reboiler composition. The steam flow rate is integrally controlled based on the coupled solution of the extraction rate and the bottom temperature of the tower.

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