Heat pump rectification system for tetrahydrofuran purification
By using a heat pump distillation system for cyclic pressurization and depressurization, the problem of heat waste in the tetrahydrofuran purification distillation column was solved, achieving efficient heat utilization and reduced energy consumption.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-07
- Publication Date
- 2026-04-07
AI Technical Summary
In the tetrahydrofuran purification distillation column, the temperature difference between the top and bottom of the column is large, the energy utilization efficiency is low, the steam consumption is large, and the heat waste is serious. Existing methods are difficult to further reduce energy consumption.
A heat pump distillation system is adopted, which combines a compressor, a bottom reboiler, a first heat exchanger, a working fluid storage tank, a flash tank, and a top condenser to achieve circulating pressurization and depressurization of the working fluid, recover the heat of the gas phase at the top of the distillation column, and use it to heat the material at the bottom of the column.
It effectively recovers heat from the top of the distillation column, reduces steam consumption in the reboiler at the bottom of the column, improves heat utilization efficiency, and reduces energy consumption and costs.
Smart Images
Figure CN224086027U_ABST
Abstract
Description
Technical Field
[0001] This utility model belongs to the field of heat pump distillation technology, specifically relating to a heat pump distillation system for the purification of tetrahydrofuran. Background Technology
[0002] Industrial polytetrahydrofuran (PTMEG) production units obtain tetrahydrofuran (THF) through the cyclization and dehydration of butanediol (BDO), followed by purification through a three-tower distillation process to obtain polymer-grade tetrahydrofuran. Furthermore, in the preparation of products such as polybutylene terephthalate (PBT) and polybutylene adipate terephthalate (PBAT) from BDO, water and tetrahydrofuran (THF) inevitably occur as byproducts under high-temperature conditions. These byproducts are also purified to over 99.9% purity through a three-tower distillation process to meet national standards and market demands. Currently, in the tetrahydrofuran purification distillation tower, distillation at atmospheric pressure removes impurities such as high-boiling-point homologues of tetrahydrofuran. The temperature difference between the top and bottom of the tower is approximately 25°C, and at least 0.6 tons of low-pressure steam are required per ton of product, resulting in significant steam consumption.
[0003] In the tetrahydrofuran purification distillation column, approximately 95% of the energy input to the bottom reboiler is carried away by the cooling water of the high-temperature gas phase at the top of the column, resulting in significant heat waste and low energy utilization efficiency. To reduce the energy consumed by the distillation column, methods such as increasing the number of trays, reducing the reflux ratio, adding intermediate reboilers and intermediate condensers, and using suitable insulation materials and high-efficiency packing can be employed. However, the effectiveness of these methods is limited. To further reduce energy consumption, it is necessary to recover the heat from the top of the distillation column. Utility Model Content
[0004] In view of this, the purpose of this utility model is to provide a heat pump distillation system for the purification of tetrahydrofuran, which can effectively recover the heat at the top of the distillation column and reduce the system energy consumption.
[0005] A heat pump distillation system for tetrahydrofuran purification, used to recover heat from a tetrahydrofuran purification distillation column, includes a compressor, a bottom reboiler, a first heat exchanger, a working fluid storage tank, a flash tank, and a top condenser connected in sequence. The bottom reboiler and the top condenser are respectively connected to the bottom and top of the distillation column. The bottom reboiler is connected to the outlet of the compressor. The first heat exchanger is connected to the outlet of the top condenser and the inlet of the compressor. The flash tank is connected to the inlet of the compressor. A first pressure reducing valve is provided on the pipeline connecting the working fluid storage tank and the flash tank.
[0006] The reboiler at the bottom of the distillation column heats the material at the bottom, while the condenser at the top cools the vapor phase at the top. During operation, the high-temperature, high-pressure working fluid vapor, obtained by compression, is sent to the reboiler at the bottom for condensation and heat release, providing heat to the bottom of the distillation column. The condensed working fluid vapor becomes liquid and is sent to the first heat exchanger to exchange heat with the vapor phase at the compressor inlet, then enters the working fluid storage tank in a subcooled state. Meanwhile, the subcooled liquid working fluid is depressurized by the first pressure-reducing valve and enters the flash tank for flash evaporation, producing both gaseous and liquid working fluids. The gaseous working fluid enters the compressor inlet to supplement the intake gas; the liquid working fluid enters the condenser at the top, exchanging heat with the vapor phase at the top of the distillation column to provide cooling. After heat exchange, the liquid working fluid absorbs heat and vaporizes into a gaseous working fluid, which is then sent to the first heat exchanger to exchange heat with the high-temperature liquid working fluid from the reboiler at the bottom, then enters the compressor in a superheated state for compression. In the compressor, the low-temperature, low-pressure gaseous working fluid is compressed to obtain high-temperature, high-pressure working fluid vapor, which is then sent to the reboiler at the bottom of the distillation column to provide heat to the bottom of the column. Through this cycle, the working fluid is pressurized and depressurized to ensure its circulation throughout the entire unit. This effectively recovers heat from the vapor phase at the top of the distillation column and uses this heat to heat the material at the bottom of the column, saving steam consumption in the reboiler and reducing costs.
[0007] Optionally, in one embodiment, a second pressure-reducing valve is provided on the pipeline connecting the flash tank and the top condenser of the tower.
[0008] In the above technical solution, a medium-pressure liquid working fluid is obtained after flash evaporation in the flash tank. After being throttled and depressurized by the second pressure reducing valve, it is sent to the top condenser of the tower.
[0009] Optionally, in one embodiment, the compressor is connected to the top outlet of the flash tank, and the top condenser is connected to the bottom outlet of the flash tank.
[0010] In the above technical solution, after flash evaporation in the flash tank, the gaseous working fluid enters the compressor through the top outlet, while the liquid working fluid enters the top condenser through the bottom outlet.
[0011] Optionally, in one embodiment, the pressure range of the flash tank is 0.7-1.0 MPaG.
[0012] In the above technical solution, the pressure range of the flash tank is controlled within 0.7-1.0 MPaG to ensure the normal operation of flash evaporation.
[0013] Optionally, in one embodiment, a separator tank is provided on the pipeline connecting the top condenser to the compressor.
[0014] In the above technical solution, the separator is used to further flash evaporate the gaseous working fluid sent from the top condenser of the tower to reduce liquid entrainment and allow the working fluid to be sent to the first heat exchanger in gaseous form for heat exchange.
[0015] Optionally, in one embodiment, the separator is provided with a demister located at the outlet of the separator.
[0016] In the above technical solution, the demister can effectively filter out liquid droplets in the gaseous working fluid, thereby reducing liquid droplet entrainment at the compressor inlet.
[0017] Optionally, in one embodiment, the first heat exchanger is a shell-and-tube heat exchanger, with the tube side of the first heat exchanger connected to the bottom reboiler and the working fluid storage tank, and the shell side of the first heat exchanger connected to the compressor and the top condenser.
[0018] In the above technical solution, the liquid working fluid entering the tube side of the first heat exchanger is after heat exchange in the reboiler at the bottom of the column, and the gaseous working fluid entering the shell side of the first heat exchanger is after heat exchange in the condenser at the top of the column. The two working fluids exchange heat in the first heat exchanger.
[0019] Optionally, in one embodiment, a second heat exchanger is provided on the pipeline connecting the first heat exchanger to the working fluid storage tank.
[0020] In the above technical solution, the second heat exchanger is used to further cool the liquid working fluid after heat exchange in the first heat exchanger, so as to ensure that it is sufficiently subcooled and sent into the working fluid storage tank in a cold state.
[0021] Optionally, in one embodiment, the compressor is a two-stage centrifugal compressor, the compressor is provided with a primary compression inlet and a secondary compression inlet, the first heat exchanger is connected to the primary compression inlet, and the flash tank is connected to the secondary compression inlet.
[0022] In the above technical solution, the compressor's primary compression inlet feeds a low-pressure working fluid, while the secondary compression inlet feeds a medium-pressure working fluid. The working fluid from the overhead condenser is in a low-pressure state and enters through the primary compression inlet; the gaseous working fluid after flashing in the flash tank is in a medium-pressure state and enters through the secondary compression inlet to supplement the compressor's intake air.
[0023] Compared with the prior art, the beneficial effects of this utility model are as follows:
[0024] The heat pump distillation system of this invention can effectively recover the heat in the gas phase at the top of the tetrahydrofuran purification distillation column by circulating the working fluid in two stages of pressurization and depressurization, and use this heat to heat the material at the bottom of the distillation column, thereby improving heat utilization efficiency, saving steam consumption in the bottom reboiler, and reducing energy consumption and cost. Attached Figure Description
[0025] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.
[0026] Figure 1 This is a schematic diagram of the heat pump distillation system in Example 1.
[0027] Figure 2 This is a schematic diagram of the heat pump distillation system in Example 2.
[0028] Explanation of the reference numerals in the figure:
[0029] T1 - Distillation column; C1 - Compressor; E1 - Bottom reboiler; E2 - Top condenser; E3 - First heat exchanger; E4 - Second heat exchanger; M1 - Working fluid storage tank; M2 - Flash tank; M3 - Separator; V1 - First pressure reducing valve; V2 - Second pressure reducing valve; L1 - Connecting pipeline. Detailed Implementation
[0030] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.
[0031] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.
[0032] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Example 1
[0033] Please refer to Figure 1This embodiment provides a heat pump distillation system for recovering heat from a tetrahydrofuran purification distillation column. It includes a compressor C1, a bottom reboiler E1, a first heat exchanger E3, a working fluid storage tank M1, a flash tank M2, and a top condenser E2 connected in sequence. The bottom reboiler E1 and the top condenser E2 are connected to the bottom and top of the distillation column T1, respectively. The bottom reboiler E1 is connected to the outlet of the compressor C1. The first heat exchanger E3 is connected to the outlet of the top condenser E2 and the inlet of the compressor C1, respectively. The flash tank M2 is connected to the inlet of the compressor C1. A first pressure reducing valve V1 is installed on the pipeline connecting the working fluid storage tank M1 and the flash tank M2.
[0034] The reboiler E1 at the bottom of distillation column T1 is used to heat the material at the bottom of the column, while the condenser E2 at the top is used to cool the vapor phase at the top of distillation column T1. During operation, the high-temperature, high-pressure working fluid vapor obtained after compression by compressor C1 is sent to the reboiler E1 at the bottom for condensation and heat release, providing heat to the bottom of distillation column T1. After condensation and heat release, the working fluid vapor becomes liquid and is sent to the first heat exchanger E3 to exchange heat with the inlet vapor phase of compressor C1 before entering the working fluid storage tank M1 in a subcooled state. On the other hand, the subcooled liquid working fluid, after being depressurized by the first pressure-reducing valve V1, enters the flash tank M2 for flash evaporation, producing gaseous and liquid working fluids. The gaseous working fluid enters the inlet of compressor C1 to supplement the intake gas; the liquid working fluid enters the top condenser E2, where it exchanges heat with the gas phase at the top of distillation column T1, providing cooling to the top of the distillation column. After heat exchange, the liquid working fluid absorbs heat and vaporizes into a gaseous working fluid, which is then sent to the first heat exchanger E3. After exchanging heat with the high-temperature liquid working fluid from the bottom reboiler E1, it enters the compressor C1 in a superheated state for compression. In compressor C1, the low-temperature, low-pressure gaseous working fluid is compressed to obtain high-temperature, high-pressure working fluid vapor, which continues to be sent to the bottom reboiler E1 to provide heat to the bottom of the distillation column. Through the above-mentioned cycle, the working medium is pressurized and depressurized to ensure the circulation of the working medium throughout the entire device. This effectively recovers the heat from the gas phase at the top of the distillation column T1 and uses this heat to heat the material at the bottom of the distillation column T1, saving steam consumption in the bottom reboiler E1 and reducing costs.
[0035] Preferably, the working fluid in this embodiment is R123. In addition, other working fluids that meet the requirements can also be selected.
[0036] In this embodiment, a second pressure reducing valve V2 is installed on the pipeline connecting the flash tank M2 and the top condenser E2. The liquid working fluid obtained after flashing in the flash tank M2 is at medium pressure. It needs to be throttled and depressurized by the second pressure reducing valve V2 before being sent to the top condenser E2 to meet the pressure requirements inside the top condenser E2.
[0037] In this embodiment, compressor C1 is connected to the top outlet of flash tank M2, and top condenser E2 is connected to the bottom outlet of flash tank M2. After flashing in flash tank M2, the gaseous working fluid enters compressor C1 through the top outlet, while the liquid working fluid enters top condenser E2 through the bottom outlet.
[0038] Preferably, the pressure range of the flash tank M2 is controlled within 0.7-1.0 MPaG to ensure the normal operation of flash evaporation.
[0039] In this embodiment, a separator M3 is installed on the pipeline connecting the top condenser E2 and the compressor C1. The separator M3 is used to further flash evaporate the gaseous working fluid sent from the top condenser E2, so that the working fluid is sent to the first heat exchanger E3 in gaseous form for heat exchange. In addition, a demister (not shown in the figure) is installed in the separator M3. The demister is located at the outlet of the separator M3. The demister can effectively filter out liquid droplets in the gaseous working fluid, thereby reducing liquid droplet entrainment at the inlet of the compressor C1.
[0040] Preferably, the demister is a wire mesh demister, which can effectively remove liquid droplets from the gas.
[0041] In this embodiment, the first heat exchanger E3 is a shell-and-tube heat exchanger. The tube side of the first heat exchanger E3 is connected to the bottom reboiler E1 and the working fluid storage tank M1, and the shell side of the first heat exchanger E3 is connected to the compressor C1 and the top condenser E2.
[0042] It should be noted that, in order to improve the heat transfer efficiency of the first heat exchanger E3, the gas usually enters the shell side of the first heat exchanger E3, and the liquid usually enters the tube side of the first heat exchanger E3. Therefore, the tube side of the first heat exchanger E3 is connected to the bottom reboiler E1 and the working fluid storage tank M1, and the shell side of the first heat exchanger E3 is connected to the compressor C1 and the top condenser E2, so that the liquid working fluid entering the tube side of the first heat exchanger E3 after heat exchange by the bottom reboiler E1, and the gaseous working fluid entering the shell side of the first heat exchanger E3 after heat exchange by the top condenser E2.
[0043] In this embodiment, the compressor C1 is a two-stage centrifugal compressor, which has a primary compression inlet and a secondary compression inlet. The first heat exchanger E3 is connected to the primary compression inlet, and the flash tank M2 is connected to the secondary compression inlet.
[0044] As shown in the diagram, the upper left side of compressor C1 has a primary compression inlet, and the lower right side has a secondary compression inlet. The primary compression inlet feeds a low-pressure working fluid, while the secondary compression inlet feeds a medium-pressure working fluid. The working fluid from the top condenser E2 is in a low-pressure state and enters through the primary compression inlet. After secondary compression by the compressor, it reaches the high-pressure state required for delivery to the reboiler E1 at the bottom of the column. The gaseous working fluid after flashing in flash tank M2 is in a medium-pressure state and enters through the secondary compression inlet to supplement the intake air of compressor C1. Specifically, the top outlet of flash tank M2 is connected to connecting pipe L1 via a pipeline, and the medium-pressure gaseous working fluid generated in flash tank M2 can enter the secondary compression inlet of compressor C1 through connecting pipe L1.
[0045] It is worth mentioning that, compared with single-stage compression, two-stage compression can effectively reduce energy consumption and achieve higher temperatures. Specifically, in this embodiment, the temperature required for heating the material in the reboiler E1 at the bottom of the distillation column T1 is 130°C. The working fluid vapor after two-stage compression by the compressor C1 can easily reach above 130°C, thereby providing heat to the reboiler E1 at the bottom of the column.
[0046] In addition, to ensure stable start-up and shutdown of compressor C1, two anti-surge control lines (not shown in the figure) are provided at the compressor outlet to flash tank M2 and separator M3.
[0047] Please refer to Figure 1 Taking compressor C1 as the starting point, the working principle of this utility model is as follows:
[0048] The high-temperature, high-pressure working fluid vapor from the outlet of compressor C1 enters the reboiler E1 at the bottom of the column for condensation and heat release, providing heat to the bottom of distillation column T1. After heat release, a high-temperature, high-pressure liquid working fluid is obtained. This liquid working fluid enters the tube side of the first heat exchanger E3 for further cooling, resulting in a cold liquid working fluid, which is then sent to a working fluid collection tank. The working fluid in the collection tank is depressurized through the first pressure reducing valve V1 and then sent to the flash tank M2 for flash evaporation. After flash evaporation, a medium-pressure gaseous working fluid and a medium-pressure liquid working fluid are obtained in the flash tank M2. The medium-pressure gaseous working fluid enters the secondary compression inlet of compressor C1 to supplement the intake air volume of compressor C1. The medium-pressure liquid working fluid in flash tank M2 is further depressurized by the second pressure reducing valve V2, becoming a low-pressure liquid phase. It is then sent to the top condenser E2, where it exchanges heat with the high-temperature tetrahydrofuran vapor at the top of distillation column T1, absorbing heat and vaporizing into a low-pressure working fluid. This vapor then enters the separator M3 for separation. After separation, it enters the shell side of the heat exchanger, exchanging heat with the high-temperature, high-pressure liquid working fluid in the tube side. After absorbing heat, it enters the first-stage compression inlet of compressor C1 in a superheated state, undergoing secondary compression within compressor C1. Compressor C1 compresses the two working fluids from flash tank M2 and separator M3, obtaining high-temperature, high-pressure working fluid vapor, which is then sent back to the reboiler E1 at the bottom of distillation column T1 to provide heat to the bottom of distillation column T1, thus completing the cycle.
[0049] By circulating and pressurizing the working fluid, heat in the gas phase at the top of distillation column T1 is recovered and used to heat the material at the bottom of distillation column T1. This effectively saves steam consumption in the bottom reboiler E1, reducing energy consumption and costs. Example 2
[0050] Please refer to Figure 2 In this embodiment, a second heat exchanger E4 is provided on the pipeline connecting the first heat exchanger E3 and the working fluid storage tank M1. The second heat exchanger E4 is used to further cool the liquid working fluid after heat exchange with the first heat exchanger E3, so as to make it sufficiently subcooled, ensuring that the liquid working fluid is sent into the working fluid storage tank M1 in a cold state, avoiding the temperature in the working fluid storage tank M1 from being too high, which is conducive to the normal operation of subsequent work.
[0051] The working fluid can be cooled by introducing cooling water or other cooling media into the second heat exchanger E4, allowing it to exchange heat with the incoming working fluid.
[0052] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the appended claims and their equivalents.
[0053] In the description of this utility model, it should be understood that terms such as "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.
[0054] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this utility model, "a plurality of" means two or more, unless otherwise explicitly specified.
[0055] In this utility model, unless otherwise explicitly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.
Claims
1. A heat pump distillation system for tetrahydrofuran purification, used to recover heat from the tetrahydrofuran purification distillation column, characterized in that, The distillation column includes a compressor, a bottom reboiler, a first heat exchanger, a working fluid storage tank, a flash tank, and a top condenser connected in sequence. The bottom reboiler and the top condenser are connected to the bottom and top of the distillation column, respectively. The bottom reboiler is connected to the outlet of the compressor. The first heat exchanger is connected to the outlet of the top condenser and the inlet of the compressor. The flash tank is connected to the inlet of the compressor. A first pressure reducing valve is provided on the pipeline connecting the working fluid storage tank and the flash tank.
2. The heat pump distillation system according to claim 1, characterized in that, The compressor is connected to the top outlet of the flash tank, and the top condenser is connected to the bottom outlet of the flash tank.
3. The heat pump distillation system according to claim 2, characterized in that, A second pressure reducing valve is installed on the pipeline connecting the top condenser of the tower to the bottom of the flash tank.
4. The heat pump distillation system according to claim 1, characterized in that, The pressure range of the flash tank is 0.7-1.0 MPaG.
5. The heat pump distillation system according to claim 1, characterized in that, A separation tank is installed on the pipeline connecting the top condenser of the tower to the first heat exchanger.
6. The heat pump distillation system according to claim 5, characterized in that, The separator is equipped with a demister, which is located at the outlet of the separator.
7. The heat pump distillation system according to claim 1, characterized in that, The first heat exchanger is a shell-and-tube heat exchanger. The tube side of the first heat exchanger is connected to the bottom reboiler and the working fluid storage tank, and the shell side of the first heat exchanger is connected to the compressor and the top condenser.
8. The heat pump distillation system according to claim 1, characterized in that, A second heat exchanger is installed on the pipeline connecting the first heat exchanger to the working fluid storage tank.
9. The heat pump distillation system according to claim 1, characterized in that, The compressor is a two-stage centrifugal compressor, which has a primary compression inlet and a secondary compression inlet. The first heat exchanger is connected to the primary compression inlet, and the flash tank is connected to the secondary compression inlet.