Polyimide waste heat recovery system

Abstract

This application relates to the field of refrigeration and waste heat recovery technology, specifically disclosing a polyimide waste heat recovery and utilization system, including a first evaporator connected to a first refrigerant inlet pipe and a first refrigerant outlet pipe connected to a casting film forming section; a second evaporator connected to a second refrigerant inlet pipe and a second refrigerant outlet pipe connected to a polycondensation reaction section; an incinerator for receiving and incinerating organic waste gas generated during the production of polyimide films; a waste heat boiler connected to the incinerator via a flue gas pipe, which uses the high-temperature flue gas generated in the incinerator to heat water inside to generate superheated steam; and a waste heat refrigeration unit connected to the waste heat boiler via a steam pipe, which uses the superheated steam for refrigeration and supplies liquid refrigerant to the first evaporator through a first pipe and to the second evaporator through a second pipe. This application has the effect of reducing energy waste and lowering the power consumption for refrigeration in production.

Description

Technical Field

[0001] This invention relates to the field of refrigeration and waste heat recovery technology, and in particular to a polyimide waste heat recovery and utilization system. Background Technology

[0002] Polyimide (PI) film is an organic polymer film material with excellent comprehensive performance. It has the characteristics of high temperature resistance (long-term operating temperature can reach 250-280℃), high insulation, chemical corrosion resistance, and high mechanical strength (tensile strength of about 200MPa). It is widely used in flexible circuit boards, motor insulation, aerospace, 5G communication and other fields.

[0003] The mainstream production process for PI film is a two-step method. The first step involves a polycondensation reaction of dianhydride monomers and diamine monomers in a polar solvent such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), or N-methylpyrrolidone (NMP) to generate a polyamic acid (PAA) solution. This polycondensation reaction is exothermic and must be carried out at a low temperature of -15 to -20°C to suppress the reverse reaction, reduce monomer volatilization, and prevent premature imidization and precipitation of PAA. The second step involves casting the PAA solution onto a steel strip or roller to form a wet film, which is then dried and subjected to high-temperature imidization in a stepped-heating tunnel (100°C → 400°C) to dehydrate and cyclize the PAA into PI. Finally, the film is wound up to obtain the PI film product. The casting stage requires stable workshop and steel strip surface temperatures, necessitating cooling and temperature control with chilled water at approximately 7°C.

[0004] The organic waste gas generated during production is sent to an incinerator for oxidation treatment at 800–1000℃. The high-temperature flue gas produced by incineration carries a large amount of high-grade heat energy, which is directly discharged into the atmosphere in the current process, resulting in a huge waste of energy. At the same time, the polycondensation reaction section requires a continuous flow of cryogenic liquid at -15 to -20℃ to remove the heat of polymerization, and the casting film-forming section requires 7℃ chilled water to maintain the surface temperature of the steel strip and the workshop environment. Currently, all of the above cooling capacity is provided by electric compression refrigeration units, which consume a lot of electricity.

[0005] Therefore, the existing PI film production process suffers from serious waste of waste heat and high power consumption for refrigeration, and there is an urgent need for a system solution that can recover waste heat from incineration for process refrigeration. Summary of the Invention

[0006] In order to reduce energy waste and lower the refrigeration power consumption in the production of polyimide films, this application provides a polyimide waste heat recovery and utilization system.

[0007] The polyimide waste heat recovery and utilization system provided in this application adopts the following technical solution: A polyimide waste heat recovery system, comprising: The first evaporator is connected to a first refrigerant inlet pipe and a first refrigerant outlet pipe that are connected to the casting film section; liquid refrigerant enters the first evaporator, evaporates and absorbs heat, and cools the first refrigerant flowing through the first evaporator. The second evaporator is connected to a second refrigerant inlet pipe and a second refrigerant outlet pipe that are connected to the polycondensation reaction section; liquid refrigerant enters the second evaporator, evaporates and absorbs heat, and cools the second refrigerant flowing through the second evaporator. An incinerator is used to receive and incinerate the organic waste gas generated during the production of polyimide films. The waste heat boiler is connected to the incinerator through a flue gas pipe, and uses the high-temperature flue gas generated by the incinerator to heat the water inside to produce superheated steam. The waste heat refrigeration unit is connected to the waste heat boiler through a steam pipe, uses superheated steam for refrigeration, and supplies liquid refrigerant to the first evaporator through a first pipeline and to the second evaporator through a second pipeline.

[0008] Optionally, the waste heat refrigeration unit includes a first refrigeration cycle; the first refrigeration cycle includes a first generator, a first condenser, a first absorber, a first solution pump, and a first GAX heat exchanger; superheated steam enters the first generator through a steam pipe, heating the rich solution inside to desorb the refrigerant; the gaseous refrigerant is condensed and liquefied by circulating water in the first condenser, and then enters the first evaporator under reduced pressure; the gaseous refrigerant in the first evaporator enters the first absorber and is absorbed by the lean solution to form a rich solution; the rich solution is transported to the first GAX heat exchanger by the first solution pump, exchanges heat with the high-temperature lean solution from the first generator, and then returns to the first generator.

[0009] Optionally, the waste heat refrigeration unit further includes a second refrigeration cycle; the second refrigeration cycle includes a second generator, a second condenser, a GVX heat exchanger, a second absorber, a second solution pump, and a second GAX heat exchanger; superheated steam enters the second generator through a steam pipe, heating the rich solution inside to desorb the refrigerant; the gaseous refrigerant is condensed and liquefied by circulating water in the second condenser, then enters the GVX heat exchanger to exchange heat with the gaseous refrigerant from the second evaporator to cool down, and then depressurizes before entering the second evaporator; the gaseous refrigerant in the second evaporator is heated by heat exchange in the GVX heat exchanger, then enters the second absorber to be absorbed by the lean solution to form a rich solution; the rich solution is transported to the second GAX heat exchanger by the second solution pump, exchanges heat with the high-temperature lean solution from the second generator, and then returns to the second generator.

[0010] Optionally, the waste heat refrigeration unit includes a third generator, a third condenser, a medium-pressure GVX heat exchanger, a low-pressure GVX heat exchanger, a medium-pressure absorber, a low-pressure absorber, and a third GAX heat exchanger; superheated steam enters the third generator through a steam pipe, heating the rich solution inside to desorb the refrigerant; the gaseous refrigerant is condensed and liquefied by circulating water in the third condenser, and then flows through branch pipes to the medium-pressure GVX heat exchanger and the low-pressure GVX heat exchanger respectively, and then depressurizes before entering the first evaporator and the third GAX heat exchanger respectively. Two evaporators; the gaseous refrigerant discharged from the first evaporator is heated by heat exchange in the medium-pressure GVX heat exchanger and then enters the medium-pressure absorber; the gaseous refrigerant discharged from the second evaporator is heated by heat exchange in the low-pressure GVX heat exchanger and then enters the low-pressure absorber; the rich solution in the low-pressure absorber is pressurized and then sent to the medium-pressure absorber, and the rich solution in the medium-pressure absorber is pumped by a third solution pump into the third GAX heat exchanger, where it exchanges heat with the high-temperature lean solution from the third generator and then returns to the third generator.

[0011] Optionally, the waste heat refrigeration unit includes a third generator, a third condenser, a medium-pressure GVX heat exchanger, a low-pressure GVX heat exchanger, a medium-pressure absorber, a low-pressure absorber, and a third GAX heat exchanger. Superheated steam enters the third generator through a steam pipe, heating the rich solution inside to desorb the refrigerant. The gaseous refrigerant is condensed and liquefied by circulating water in the third condenser, then flows sequentially through the medium-pressure GVX heat exchanger and the low-pressure GVX heat exchanger, and then depressurizes before entering the first evaporator. The unevaporated liquid in the first evaporator... The gaseous refrigerant is depressurized and enters the second evaporator; the gaseous refrigerant discharged from the first evaporator and the second evaporator is heated by heat exchange in the medium-pressure GVX heat exchanger and the low-pressure GVX heat exchanger, respectively, and then enters the medium-pressure absorber and the low-pressure absorber, respectively; the rich solution in the low-pressure absorber is pressurized and sent to the medium-pressure absorber, and the rich solution in the medium-pressure absorber is pumped by the third solution pump to the third GAX heat exchanger, where it exchanges heat with the high-temperature lean solution from the third generator and then returns to the third generator.

[0012] Optionally, it also includes a primary condenser, a secondary condenser, and a tertiary condenser; the organic waste gas generated during the production of polyimide film sequentially enters the primary condenser, the secondary condenser, and the tertiary condenser; the primary condenser is supplied with circulating water as a cold source, the secondary condenser is connected to the first refrigerant produced by the first evaporator through a first refrigerant pipeline as a cold source, and the tertiary condenser is connected to the second refrigerant produced by the second evaporator through a second refrigerant pipeline as a cold source; the exhaust gas condensed by the tertiary condenser flows to the incinerator through a tertiary pipeline.

[0013] Optionally, a fourth condenser is also included, which is connected in series to the pipeline that supplies liquid refrigerant to the second evaporator, and is connected to the low-temperature exhaust gas after the third-stage condensation through the pipeline, so as to use the low-temperature exhaust gas to cool down the liquid refrigerant in the pipeline.

[0014] Optionally, a first heat exchanger is included, which is connected in series in the three-stage pipeline. The first heat exchanger is connected to the waste heat boiler through an exhaust pipe, and the exhaust gas from the waste heat boiler is used to preheat the tail gas flowing through the three-stage pipeline before it is sent into the incinerator.

[0015] Optionally, a second heat exchanger is included, which is connected in series in the organic waste gas pipeline leading to the first-stage condenser to receive high-temperature organic waste gas; at the same time, it is connected to the waste heat boiler through the water supply pipeline to preheat the water supply flowing through the water supply pipeline using the high-temperature organic waste gas.

[0016] Optionally, a subcooler is included, which is connected in series to the refrigerant inlet pipe of the secondary condenser and is connected to the low-temperature exhaust gas after the tertiary condenser through the pipe. The low-temperature exhaust gas is used to pre-cool the refrigerant flowing through the refrigerant inlet pipe.

[0017] In summary, this application includes at least one of the following beneficial technical effects: 1. The high-temperature flue gas waste heat generated during the incineration of organic waste gas in the PI film production process is recovered and used to drive the waste heat refrigeration unit for refrigeration. Different temperatures of cooling capacity are supplied to the casting and film forming section and the polycondensation reaction section respectively, which replaces the traditional electric compression refrigeration unit, realizes the effective utilization of waste heat resources, and greatly saves refrigeration power consumption. 2. Through a three-stage condensation recovery system, the organic waste gas is condensed in stages using the cooling capacity of different temperature levels generated by waste heat refrigeration, which efficiently recovers organic solvents and reduces solvent consumption and waste emissions. 3. Through multiple sets of heat exchangers, multi-stage cascade recovery and utilization of flue gas waste heat, organic waste gas sensible heat and low-temperature tail gas waste cooling are realized. The system has high energy utilization efficiency, and each set of heat exchangers is a passive heat exchanger, which does not increase the additional operating energy consumption. 4. The waste heat refrigeration unit can adopt a dual-cycle GAX architecture or a single generator dual-pressure stage architecture to flexibly adapt to the cooling needs of production lines of different scales. It has a compact structure and is easy to operate and adjust. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the waste heat recovery and utilization system in Embodiment 1 of this application.

[0019] Figure 2 This is a schematic diagram of the waste heat refrigeration unit in Embodiment 1 of this application.

[0020] Figure 3This is a schematic diagram of the waste heat recovery and utilization system in Embodiment 2 of this application.

[0021] Figure 4 This is a schematic diagram of the waste heat recovery and utilization system in Embodiment 3 of this application.

[0022] Figure 5 This is a schematic diagram of the waste heat recovery and utilization system in Embodiment 4 of this application.

[0023] Figure 6 This is a schematic diagram of the waste heat recovery and utilization system in Embodiment 5 of this application.

[0024] Figure 7 This is a schematic diagram of the waste heat recovery and utilization system in Embodiment 6 of this application.

[0025] Figure 8 This is a schematic diagram of the waste heat recovery and utilization system in Embodiment 7 of this application.

[0026] Figure 9 This is a schematic diagram of the waste heat recovery and utilization system in Embodiment 8 of this application.

[0027] Figure 10 This is a schematic diagram of the waste heat recovery and utilization system in Embodiment 9 of this application.

[0028] Explanation of reference numerals in the attached figures: 01. Polycondensation Reaction Section; 02. Casting and Film Forming Section; 03. High-Temperature Imidide Chemical Processing Section; 1. First Evaporator; 11. First Refrigerant Inlet Pipe; 12. First Refrigerant Outlet Pipe; 13. First Refrigerant Pump; 2. Second Evaporator; 21. Second Refrigerant Inlet Pipe; 22. Second Refrigerant Outlet Pipe; 23. Second Refrigerant Pump; 3. Incinerator; 31. First Waste Gas Pipe; 32. Second Waste Gas Pipe; 33. Flue Gas Pipe; 4. Waste Heat Boiler; 41. Exhaust Pipe; 42. Steam Pipe; 5. Waste Heat Refrigeration Unit; 51. First Generator; 52. First Condenser; 53. First Absorber; 54. First Solution Pump; 55. First GAX Heat Exchanger; 56. Second Generator; 57. Second Condenser; 58. GVX Heat Exchanger 59. Second absorber; 510. Second solution pump; 511. Second GAX heat exchanger; 512. Third generator; 513. Third condenser; 514. Medium-pressure GVX heat exchanger; 515. Low-pressure GVX heat exchanger; 516. Medium-pressure absorber; 517. Low-pressure absorber; 518. Third GAX heat exchanger; 519. Third solution pump; 520. Pressurization pump; 6. First-stage condenser; 61. First-stage piping; 7. Second-stage condenser; 71. Second-stage piping; 72. First inlet branch pipe; 73. First outlet branch pipe; 8. Third-stage condenser; 81. Third-stage piping; 82. Second inlet branch pipe; 83. Second outlet branch pipe; 91. Fourth condenser; 92. First heat exchanger; 93. Second heat exchanger; 94. Subcooler. Detailed Implementation

[0029] The following is in conjunction with the appendix Figures 1-10 This application will be described in further detail. Example 1

[0030] This application discloses a polyimide waste heat recovery and utilization system. (Refer to...) Figure 1 and Figure 2 The production process of polyimide (PI) film is as follows: Polycondensation reaction section 01: Dianone monomers and diamine monomers undergo a polycondensation reaction in a polar solvent to generate a polyamic acid (PAA) solution; Casting film formation section 02: The PAA solution is cast and coated onto a steel belt or roller to form a wet film; High-temperature imide chemical section 03: PAA cast into a wet film enters a stepped heating oven (100℃→400℃) for drying and high-temperature imidization, causing PAA to dehydrate and cyclize into PI, and finally it is wound up to obtain PI film product.

[0031] The waste heat recovery and utilization system includes a first evaporator 1, a second evaporator 2, an incinerator 3, a waste heat boiler 4, and a waste heat refrigeration unit 5.

[0032] The first evaporator 1 has a first refrigerant inlet pipe 11 and a first refrigerant outlet pipe 12 connected to its tube side. The liquid refrigerant evaporates and absorbs heat in the shell side of the first evaporator 1, cooling the first refrigerant flowing through the tube side. The first refrigerant inlet pipe 11 and the first refrigerant outlet pipe 12 are connected to the casting film forming section 02. The first refrigerant inlet pipe 11 is connected to a first refrigerant pump 13, and the first refrigerant enters the casting film forming section 02 through the first refrigerant inlet pipe 11.

[0033] The second evaporator 2 has a second refrigerant inlet pipe 21 and a second refrigerant outlet pipe 22 connected to its tube side. Liquid refrigerant evaporates and absorbs heat in the shell side of the second evaporator 2, cooling the second refrigerant flowing through the tube side. The second refrigerant inlet pipe 21 and the second refrigerant outlet pipe 22 are connected to the polycondensation reaction section 01. A second refrigerant pump 23 is connected to the second refrigerant inlet pipe 21, and the second refrigerant enters the polycondensation reaction section 01 through the second refrigerant inlet pipe 21.

[0034] Organic waste gas generated in the casting film section 02 flows to the incinerator 3 through the first waste gas pipe 31, and organic waste gas generated in the high-temperature imide chemical section 03 flows to the incinerator 3 through the second waste gas pipe 32. The high-temperature flue gas generated by the combustion of organic waste gas in the incinerator 3 flows to the shell side of the waste heat boiler 4 through the flue gas pipe 33. In the shell side, the high-temperature flue gas heats the water supplied to the tube side of the waste heat boiler 4 to generate superheated steam. The high-temperature flue gas, after being heated in the waste heat boiler 4, is discharged to the outside through the exhaust pipe 41. The superheated steam generated in the waste heat boiler 4 enters the waste heat refrigeration unit 5 through the steam pipe 42. The waste heat refrigeration unit 5 uses the superheated steam for refrigeration and introduces depressurized liquid refrigerant into the shell side of the first evaporator 1 and the second evaporator 2 through pipelines.

[0035] The organic waste gas generated from the casting film-forming section 02 and the high-temperature imide chemical section 03 enters the incinerator 3 for combustion. The high-temperature flue gas generated from combustion enters the shell side of the waste heat boiler 4. The high-temperature flue gas heats the water in the tube side of the waste heat boiler 4 to produce superheated steam. The superheated steam enters the waste heat refrigeration unit 5, which uses the superheated steam for refrigeration. The waste heat refrigeration unit 5 delivers liquid refrigerant to the shell side of the first evaporator 1 through pipelines. The liquid refrigerant evaporates and absorbs heat in the shell side of the first evaporator 1, cooling the first heat transfer fluid flowing through the tube side of the first evaporator 1. The first heat transfer fluid is cooled to 7°C, which in turn cools the casting film-forming section 02. Waste heat refrigeration unit 5 supplies liquid refrigerant to the shell side of the second evaporator 2 through pipelines. The liquid refrigerant evaporates and absorbs heat in the shell side of the second evaporator 2, cooling the second refrigerant flowing through the tube side of the second evaporator 2. The second refrigerant is cooled to -15 to -20°C, thus cooling the polycondensation reaction section 01. Utilizing the waste heat generated during the polyimide film production process to produce cold energy, which is then supplied to the casting film section 02 and the polycondensation reaction section 01, replaces the traditional electric compression refrigeration unit. This reduces waste heat waste and saves electricity.

[0036] Reference Figure 2 The waste heat refrigeration unit 5 includes a first generator 51, a first GAX heat exchanger 55, a first absorber 53, a first condenser 52, a second generator 56, a second GAX heat exchanger 511, a second absorber 59, a second condenser 57, and a GVX heat exchanger 58. Superheated steam enters the tube side of the first generator 51 and the tube side of the second generator 56 through steam pipes 42, respectively.

[0037] In the first refrigeration cycle, superheated steam heats the rich solution in the shell side of the first generator 51 within the tube side, causing the refrigerant in the rich solution to desorb. The gaseous refrigerant enters the shell side of the first condenser 52. Circulating water is introduced into the tube side of the first condenser 52 to condense and liquefy the gaseous refrigerant in the shell side. The liquefied refrigerant is then depressurized by a pressure reducing valve and enters the shell side of the first evaporator 1. The liquid refrigerant evaporates in the shell side of the first evaporator 1, and the gaseous refrigerant then enters the shell side of the first absorber 53. Circulating water is introduced into the tube side of the first absorber 53, and the lean solution in the first absorber 53 is sprayed onto the outer surface of the tube bundle to form a falling film that absorbs the gaseous refrigerant in the shell side, forming a rich solution. The rich solution is delivered to the tube side of the first GAX heat exchanger 55 by the first solution pump 54, and exchanges heat with the high-temperature lean solution delivered from the shell side of the first generator 51 (the high-temperature lean solution goes through the shell side of the first GAX heat exchanger 55). After heat exchange, the rich solution enters the first generator 51, and the lean solution enters the first absorber 53 after depressurization.

[0038] In the second refrigeration cycle, superheated steam heats the rich solution in the shell side of the second generator 56 within the tube side, causing the refrigerant in the rich solution to decompose. The gaseous refrigerant enters the shell side of the second condenser 57, where circulating water condenses and liquefies the gaseous refrigerant. The liquefied refrigerant enters the tube side of the GVX heat exchanger 58, where it exchanges heat with the gaseous refrigerant exiting the shell side of the second evaporator 2, cooling it down. The gaseous refrigerant then flows through the shell side of the GVX heat exchanger 58, while the cooled liquid refrigerant, after being depressurized by a pressure reducing valve, enters the shell side of the second evaporator 2. The liquid refrigerant evaporates in the shell side of the second evaporator 2, and the gaseous refrigerant enters the shell side of the GVX heat exchanger 58 for heat exchange and heating up. The heated gaseous refrigerant then enters the shell side of the second absorber 59. Circulating water flows through the tube side of the second absorber 59. The lean solution in the second absorber 59 is sprayed onto the outer surface of the tube bundle to form a falling film, which absorbs the gaseous refrigerant in the shell side to form a rich solution. The rich solution is delivered to the tube side of the second GAX heat exchanger 511 by the second solution pump 510, where it exchanges heat with the high-temperature lean solution delivered from the shell side of the second generator 56 (the high-temperature lean solution flows through the shell side of the second GAX heat exchanger 511). After heat exchange, the rich solution enters the second generator 56, while the lean solution enters the second absorber 59 after depressurization.

[0039] The workflow of this embodiment is as follows: The organic waste gas generated in the casting film section 02 is collected through the first waste gas pipe 31, and the organic waste gas generated in the high-temperature imide chemical section 03 is collected through the second waste gas pipe 32 and sent to the incinerator 3 for incineration. The high-temperature flue gas generated in the incinerator 3 enters the shell side of the waste heat boiler 4 through the flue gas pipe 33, where it exchanges heat with the feedwater in the tube side. After the flue gas is cooled by heat exchange, it is discharged to the outside through the exhaust pipe 41. The water in the tube side absorbs the heat of the flue gas and becomes superheated steam. The superheated steam is split through the steam pipe 42 and enters the tube side of the first generator 51 and the tube side of the second generator 56.

[0040] In the first generator 51, superheated steam heats the rich solution in the shell side within the tube side, causing the refrigerant in the rich solution to decompose into a gaseous state. The gaseous refrigerant enters the shell side of the first condenser 52 and is condensed and liquefied by the circulating water in the tube side. The liquid refrigerant, after being depressurized by a pressure reducing valve, enters the shell side of the first evaporator 1 to evaporate and absorb heat, absorbing the heat of the first heat transfer fluid in the tube side. The first heat transfer fluid is cooled to 7°C and, driven by the first heat transfer fluid pump 13, circulates into the casting film forming section 02 to cool it down. The gaseous refrigerant generated by evaporation in the shell side of the first evaporator 1 enters the shell side of the first absorber 53 and is absorbed by the lean solution sprayed on the outer surface of the tube bundle. The heat released by the absorption is carried away by the circulating water in the tube side. The rich solution formed by absorption is pressurized by the first solution pump 54 and sent to the tube side of the first GAX heat exchanger 55, where it exchanges heat with the high-temperature lean solution from the first generator 51 in the shell side, and then returns to the first generator 51, completing the first refrigeration cycle.

[0041] In the second generator 56, superheated steam heats the rich solution in the shell side within the tube side, causing the refrigerant in the rich solution to decompose into a gaseous state. The gaseous refrigerant enters the shell side of the second condenser 57 and is condensed and liquefied by the circulating water in the tube side. The liquid refrigerant enters the tube side of the GVX heat exchanger 58 and exchanges heat with the gaseous refrigerant from the second evaporator 2 in the shell side to achieve subcooling. The subcooled liquid refrigerant is then depressurized by a pressure reducing valve and enters the shell side of the second evaporator 2 to evaporate and absorb heat, absorbing the heat from the second refrigerant in the tube side. The second refrigerant is cooled to -15 to -20°C and circulates into the polycondensation reaction section 01 under the drive of the second refrigerant pump 23 to cool the polycondensation reaction section 01. The gaseous refrigerant generated by evaporation in the shell side of the second evaporator 2 first exchanges heat and heats up in the shell side of the GVX heat exchanger 58 before entering the shell side of the second absorber 59 to be absorbed by the lean solution. The rich solution formed by absorption is pressurized by the second solution pump 510 and sent to the tube side of the second GAX heat exchanger 511. After exchanging heat with the high-temperature lean solution from the second generator 56 in the shell side and being heated, it returns to the second generator 56 to complete the second refrigeration cycle.

[0042] The implementation principle of the polyimide waste heat recovery and utilization system in this application embodiment is as follows: The high-temperature flue gas waste heat released from the combustion of organic waste gas generated by the PI film production line in incinerator 3 is used to generate superheated steam through waste heat boiler 4. This superheated steam drives waste heat refrigeration unit 5 to produce 7°C chilled water and -15 to -20°C cryogenic liquid, respectively. The 7°C chilled water is used for temperature control in the casting film forming section 02, while the -15 to -20°C cryogenic liquid is used in the polycondensation reaction section 01 to remove the heat of polymerization. The system uses waste heat as its driving energy, eliminating the need for electrical energy consumption for refrigeration and achieving effective utilization of waste heat resources.

[0043] The waste heat refrigeration unit 5 adopts a dual-cycle GAX absorption refrigeration architecture, with two refrigeration cycles operating independently. The operating parameters of each cycle can be independently adjusted according to the cooling load of the corresponding process section without interference. The GAX heat exchanger recovers the sensible heat of the solution between the generator and the absorber, reducing the heating load on the generator. The GVX heat exchanger 58 performs regenerative subcooling on the liquid refrigerant in the second refrigeration cycle, increasing the subcooling of the refrigerant entering the second evaporator 2 and improving the refrigeration efficiency of the second refrigeration cycle. Example 2

[0044] This application discloses a polyimide waste heat recovery system. The difference from Example 1 is that, referring to… Figure 3 The waste heat refrigeration unit 5 includes a third generator 512, a third GAX heat exchanger 518, a low-pressure absorber 517, a medium-pressure absorber 516, a low-pressure GVX heat exchanger 515, a medium-pressure GVX heat exchanger 514, and a third condenser 513.

[0045] Superheated steam enters the tube side of the third generator 512 through steam pipe 42, heating the rich solution in the shell side of the third generator 512 and causing the refrigerant in the rich solution to decompose. The gaseous refrigerant enters the shell side of the third condenser 513, where circulating water is circulated through the tube side to condense and liquefy the gaseous refrigerant in the shell side.

[0046] The liquefied refrigerant flows through system distribution branches to the tube side of the low-pressure GVX heat exchanger 515 and the tube side of the medium-pressure GVX heat exchanger 514, respectively. A portion of the liquid refrigerant in the tube side of the low-pressure GVX heat exchanger 515 exchanges heat with the gaseous refrigerant flowing from the second evaporator 2 into the shell side of the low-pressure GVX heat exchanger 515 for cooling, while another portion of the liquid refrigerant in the tube side of the medium-pressure GVX heat exchanger 514 exchanges heat with the gaseous refrigerant flowing from the first evaporator 1 into the shell side of the medium-pressure GVX heat exchanger 514 for cooling.

[0047] Liquid refrigerant flowing out of the tube side of the low-pressure GVX heat exchanger 515 is depressurized by a pressure reducing valve and then enters the shell side of the second evaporator 2. Liquid refrigerant flowing out of the tube side of the medium-pressure GVX heat exchanger 514 is depressurized by a pressure reducing valve and then enters the shell side of the first evaporator 1. The liquid refrigerant evaporates in the shell side of the first evaporator 1 and the shell side of the second evaporator 2. Gaseous refrigerant flowing out of the shell side of the first evaporator 1 enters the shell side of the medium-pressure GVX heat exchanger 514 for heat exchange and temperature increase before entering the shell side of the medium-pressure absorber 516. Gaseous refrigerant flowing out of the shell side of the second evaporator 2 enters the shell side of the low-pressure GVX heat exchanger 515 for heat exchange and temperature increase before entering the shell side of the low-pressure absorber 517. Circulating water is circulated in the tube sides of both the medium-pressure absorber 516 and the low-pressure absorber 517.

[0048] The lean solution in the low-pressure absorber 517 and the medium-pressure absorber 516 is sprayed onto the outer surface of the tube bundle to form a falling film, which absorbs the gaseous refrigerant in the shell side to form a rich solution. The rich solution in the low-pressure absorber 517 is delivered to the medium-pressure absorber 516 by the pressurization pump 520. The rich solution in the medium-pressure absorber 516 is delivered to the tube side of the third GAX heat exchanger 518 by the third solution pump 519, where it exchanges heat with the high-temperature lean solution delivered from the shell side of the third generator 512 (the high-temperature lean solution goes through the shell side of the third GAX heat exchanger 518). After heat exchange, the rich solution enters the third generator 512, and the lean solution enters the low-pressure absorber 517 after depressurization.

[0049] In this embodiment, superheated steam enters the tube side of the third generator 512, heating the rich solution in the shell side and causing refrigerant vapor to be released. The refrigerant vapor enters the shell side of the third condenser 513 and is condensed into liquid by the circulating water in the tube side. The liquid refrigerant is distributed into two paths as needed by the system distribution branch: one path enters the tube side of the medium-pressure GVX heat exchanger 514, where it exchanges heat with the gaseous refrigerant (flowing through the shell side) from the shell side of the first evaporator 1 to achieve subcooling. The subcooled liquid refrigerant is throttled to the corresponding evaporation pressure by the pressure reducing valve and then enters the shell side of the first evaporator 1 for evaporation, providing 7°C of cooling capacity for the casting film forming section 02; the other path enters the tube side of the low-pressure GVX heat exchanger 515, where it exchanges heat with the gaseous refrigerant (flowing through the shell side) from the shell side of the second evaporator 2 to achieve subcooling. The subcooled liquid refrigerant is throttled to the corresponding evaporation pressure by the pressure reducing valve and then enters the shell side of the second evaporator 2 for evaporation, providing -15 to -20°C of cooling capacity for the polycondensation reaction section 01.

[0050] The gaseous refrigerant produced in the shell side of the first evaporator 1 is reheated in the shell side of the medium-pressure GVX heat exchanger 514 and then enters the shell side of the medium-pressure absorber 516, where it is absorbed by the lean solution sprayed on the outer surface of the tube bundle. The gaseous refrigerant produced in the shell side of the second evaporator 2 is reheated in the shell side of the low-pressure GVX heat exchanger 515 and then enters the shell side of the low-pressure absorber 517, where it is absorbed by the lean solution. The rich solution in the low-pressure absorber 517 is pressurized by the pressurization pump 520 and then sent to the medium-pressure absorber 516, where it is combined with the rich solution in the medium-pressure absorber 516. The combined rich solution is pressurized by the third solution pump 519 and sent to the tube side of the third GAX heat exchanger 518, where it exchanges heat with the high-temperature lean solution from the third generator 512 in the shell side and then enters the third generator 512. The lean solution is then depressurized and enters the low-pressure absorber 517, completing the cycle.

[0051] The implementation principle of the polyimide waste heat recovery system in this embodiment is as follows: A GAX absorption refrigeration architecture with a single generator and dual-pressure-stage absorbers is adopted. Liquid refrigerant is generated using the same generator and condenser. The liquid refrigerant is distributed as needed to two evaporator loops with different evaporation pressure levels via system distribution branches, producing 7°C chilled water and -15 to -20°C cryogenic refrigerant respectively. Each of the two evaporation pressure stages achieves regenerative subcooling of the liquid refrigerant through a corresponding GVX heat exchanger 58. The rich solution produced by the low-pressure absorber 517 is pressurized and then flows into the medium-pressure absorber 516 to form a series absorption process, resulting in a higher concentration of the rich solution at the generator inlet and improving the generator's desorption efficiency. Compared with the dual-cycle scheme of Embodiment 1, this embodiment uses only one generator and one condenser, reducing the number of devices and making the system structure more compact. Example 3

[0052] This application discloses a polyimide waste heat recovery system. The difference from Example 1 is that, referring to… Figure 4The waste heat refrigeration unit 5 includes a third generator 512, a third GAX heat exchanger 518, a low-pressure absorber 517, a medium-pressure absorber 516, a low-pressure GVX heat exchanger 515, a medium-pressure GVX heat exchanger 514, and a third condenser 513.

[0053] Superheated steam enters the tube side of the third generator 512 through steam pipe 42, heating the rich solution in the shell side of the third generator 512 and causing the refrigerant in the rich solution to decompose. The gaseous refrigerant enters the shell side of the third condenser 513, where circulating water is circulated through the tube side to condense and liquefy the gaseous refrigerant in the shell side.

[0054] The liquefied refrigerant flows sequentially through the tube side of the medium-pressure GVX heat exchanger 514 and the tube side of the low-pressure GVX heat exchanger 515, and then flows into the shell side of the first evaporator 1 after pressure reduction. The unevaporated refrigerant in the shell side of the first evaporator 1 then flows into the shell side of the second evaporator 2 after pressure reduction. The liquid refrigerant exchanges heat with the gaseous refrigerant flowing from the shell side of the first evaporator 1 into the shell side of the medium-pressure GVX heat exchanger 514 in the tube side, achieving the first cooling subcooling. In the tube side of the low-pressure GVX heat exchanger 515, it exchanges heat with the gaseous refrigerant flowing from the shell side of the second evaporator 2 into the shell side, achieving the second cooling subcooling.

[0055] Liquid refrigerant evaporates under reduced pressure in the shell side of the first evaporator 1, and the resulting gaseous refrigerant enters the shell side of the medium-pressure GVX heat exchanger 514 to exchange heat with the liquid refrigerant flowing through the tube side. The liquid refrigerant cools down, while the gaseous refrigerant warms up. The unevaporated liquid refrigerant in the shell side of the first evaporator 1 then enters the shell side of the second evaporator 2 to evaporate under reduced pressure. The resulting gaseous refrigerant enters the shell side of the low-pressure GVX heat exchanger 515 to exchange heat with the liquid refrigerant flowing through the tube side. The liquid refrigerant cools down further, while the gaseous refrigerant warms up.

[0056] Gaseous refrigerant flowing from the shell side of the low-pressure GVX heat exchanger 515 enters the shell side of the low-pressure absorber 517 and is absorbed by the lean solution to form a rich solution. Gaseous refrigerant flowing from the shell side of the medium-pressure GVX heat exchanger 514 enters the shell side of the medium-pressure absorber 516 and is absorbed by the lean solution to form a rich solution. Circulating water flows through the tube sides of both the low-pressure absorber 517 and the medium-pressure absorber 516. The rich solution in the low-pressure absorber 517 is pressurized by the pressurization pump 520 and transported to the medium-pressure absorber 516. The rich solution in the medium-pressure absorber 516 is then transported by the third solution pump 519 to the tube side of the third GAX heat exchanger 518, where it exchanges heat with the high-temperature lean solution from the shell side of the third generator 512 (the high-temperature lean solution flows through the shell side of the third GAX heat exchanger 518). After heat exchange, the rich solution enters the third generator 512, and the lean solution is depressurized before entering the low-pressure absorber 517.

[0057] In this embodiment, unlike the split-flow liquid supply method in Embodiment 2, a series subcooling method using liquid refrigerant is employed. The liquid refrigerant from the shell side of the third condenser 513 first enters the tube side of the medium-pressure GVX heat exchanger 514, exchanging heat with the gaseous refrigerant (flowing through the shell side) from the shell side of the first evaporator 1, achieving the first subcooling. The liquid refrigerant flowing out of the tube side of the medium-pressure GVX heat exchanger 514 then enters the tube side of the low-pressure GVX heat exchanger 515, exchanging heat with the gaseous refrigerant (flowing through the shell side) from the shell side of the second evaporator 2, achieving the second subcooling. After two subcooling processes, the liquid refrigerant first passes through the first pressure-reducing valve and then enters the shell side of the first evaporator 1. The liquid refrigerant in the shell side of the first evaporator 1 evaporates and absorbs heat, providing 7°C of cooling capacity to the casting film section 02. The unevaporated liquid refrigerant in the shell side of the first evaporator 1 is further throttled by the second pressure reducing valve and enters the shell side of the second evaporator 2, where it completely evaporates and absorbs heat at a lower evaporation temperature, providing -15 to -20°C cooling capacity for the polycondensation reaction section 01.

[0058] The gaseous refrigerant generated in the shell side of the first evaporator 1 enters the shell side of the medium-pressure GVX heat exchanger 514, where it exchanges heat with the liquid refrigerant in the tube side and is heated. Then, it enters the shell side of the medium-pressure absorber 516 and is absorbed by the lean solution. The gaseous refrigerant generated in the shell side of the second evaporator 2 enters the shell side of the low-pressure GVX heat exchanger 515, where it exchanges heat with the liquid refrigerant in the tube side and is heated. Then, it enters the shell side of the low-pressure absorber 517 and is absorbed by the lean solution. The remaining absorption, generation, and solution circulation processes are the same as in Example 2.

[0059] The implementation principle of the polyimide waste heat recovery system in this embodiment is as follows: a refrigeration architecture using liquid refrigerant in series with cascaded subcooling and evaporators in series. The liquid refrigerant flows sequentially through a medium-pressure GVX heat exchanger 514 and a low-pressure GVX heat exchanger 515 to achieve gradual subcooling. Then, it partially evaporates in the first evaporator 1 at the medium-pressure evaporation pressure, generating 7°C of cooling capacity. The unevaporated liquid refrigerant then enters the second evaporator 2 at the low-pressure evaporation pressure for complete evaporation, generating -15 to -20°C of cooling capacity. Unlike the parallel flow scheme in Embodiment 2, the liquid refrigerant in this embodiment flows in series. The amount of liquid refrigerant entering the second evaporator 2 is determined by the evaporation rate of the first evaporator 1; that is, the greater the evaporation rate of the first evaporator 1, the less liquid refrigerant remains. The system can automatically adjust the amount of refrigerant entering the second evaporator 2 according to changes in the two cooling loads, exhibiting a certain degree of load self-balancing capability, while also simplifying the system piping. The liquid refrigerant flows in series through the medium-pressure GVX heat exchanger 514 and the low-pressure GVX heat exchanger 515, achieving a deeper subcooling than in Example 2, further improving the refrigeration efficiency. Example 4

[0060] This application discloses a polyimide waste heat recovery system. The difference from Example 1 is that, referring to… Figure 5The waste heat recovery and utilization system also includes a primary condenser 6, a secondary condenser 7, and a tertiary condenser 8.

[0061] Organic waste gas generated in the film casting section 02 flows to the shell side of the primary condenser 6 through the first waste gas pipe 31, while organic waste gas generated in the high-temperature imide chemical section 03 flows to the shell side of the primary condenser 6 through the second waste gas pipe 32. Circulating water flows through the tube side of the primary condenser 6, and the organic waste gas exchanges heat with the circulating water in the shell side. The liquid solvent condensed in the shell side of the primary condenser 6 is discharged to the outside for recycling and reuse, while the non-condensable gas flows to the shell side of the secondary condenser 7 through the primary pipe 61.

[0062] A first inflow branch pipe 72 connects the secondary condenser 7 and the first refrigerant inlet pipe 11, and a first outflow branch pipe 73 connects the secondary condenser 7 and the first refrigerant outlet pipe 12. A first refrigerant pump 13 is connected to the first refrigerant outlet pipe 12, and a portion of the first refrigerant enters the tube side of the secondary condenser 7 via the first inflow branch pipe 72 as a cold source. The non-condensable organic waste gas exchanges heat with the first refrigerant in the tube side of the secondary condenser 7. The liquid solvent condensed in the shell side of the secondary condenser 7 is discharged to the outside for recovery, and the non-condensable gas flows to the shell side of the tertiary condenser 8 through the secondary pipeline 71.

[0063] A second inflow branch pipe 82 connects the third-stage condenser 8 to the second refrigerant inlet pipe 21, and a second outflow branch pipe 83 connects the third-stage condenser 8 to the second refrigerant outlet pipe 22. A second refrigerant pump 23 is connected to the second refrigerant outlet pipe 22, and a portion of the second refrigerant enters the tube side of the third-stage condenser 8 via the second inflow branch pipe 82 as a cold source. The non-condensable organic waste gas exchanges heat with the second refrigerant in the tube side of the third-stage condenser 8. The liquid solvent condensed in the shell side of the third-stage condenser 8 is discharged to the outside for recovery, and the non-condensable gas flows to the incinerator 3 through the third-stage pipeline 81.

[0064] In this embodiment, during operation, the organic waste gas generated in the casting film forming section 02 is sent to the shell side of the primary condenser 6 through the first waste gas pipe 31, and the organic waste gas generated in the high-temperature imide chemical processing section 03 is sent to the shell side through the second waste gas pipe 32, where it exchanges heat with the circulating water flowing through the tube side. The solvent components and water vapor with higher boiling points in the organic waste gas first reach the dew point temperature and condense into liquid and are discharged and recovered. The uncondensed non-condensable gas enters the shell side of the secondary condenser 7 through the primary pipe 61. The tube side of the secondary condenser 7 contains the first refrigerant at 7°C, which is drawn from the outlet of the first evaporator 1 and transported through the first outflow branch pipe 73 and the first inflow branch pipe 72. The non-condensable gas is further cooled down by exchanging heat with the first refrigerant in the tube side, and the residual solvent vapor continues to condense and be discharged. The non-condensable gas then enters the shell side of the tertiary condenser 8 via the secondary pipeline 71. Inside the tube side of the tertiary condenser 8 flows a second refrigerant at -15 to -20°C, drawn from the outlet of the second evaporator 2 and transported via the second outflow branch pipe 83 and the second inflow branch pipe 82. The non-condensable gas undergoes deep cooling by exchanging heat with the second refrigerant in the shell side and tube side, resulting in almost complete condensation and discharge of residual solvent vapors. The clean exhaust gas after tertiary condensation is sent to the incinerator 3 for treatment via the tertiary pipeline 81. The liquid solvent discharged from each stage of condensation can be collected and reused. Through the three-stage condensation system with progressively decreasing temperatures, the solvent recovery rate in the organic waste gas is significantly improved.

[0065] The implementation principle of the polyimide waste heat recovery and utilization system in this application embodiment is as follows: A three-stage condenser 8 is added to the waste heat refrigeration system of Embodiment 1. The first-stage condenser 6 uses circulating water as a cold source to cool the organic waste gas; the second-stage condenser 7 uses the 7°C first refrigerant produced by the first evaporator 1 as a cold source to further cool the non-condensable gas; and the third-stage condenser 8 uses the -15 to -20°C second refrigerant produced by the second evaporator 2 as a cold source to deeply cool the non-condensable gas. The cold source temperature of the three-stage condensers decreases progressively, corresponding to the saturated vapor pressure of different boiling point solvent components in the organic waste gas at different temperatures. Solvents within the corresponding concentration range are recovered at each condensation temperature, ultimately achieving efficient, stepwise recovery of solvents from the organic waste gas. The recovered liquid solvents can be directly reused in the PAA synthesis section after regeneration treatment.

[0066] The cooling capacity of the 7°C chilled water and -15 to -20°C cryogenic liquid produced by the waste heat refrigeration system is simultaneously supplied to process cooling and organic waste gas condensation and recovery, achieving cross-system sharing of cooling capacity. One refrigeration system meets two types of cooling needs. Compared with single-stage condensation using circulating water alone, three-stage condensation significantly improves solvent recovery rate, reduces solvent procurement costs and waste emissions. At the same time, the organic matter content in the exhaust gas entering incinerator 3 is significantly reduced, reducing the processing load and auxiliary fuel consumption of incinerator 3. The cooling source of the three-stage condenser 8 is all from the waste heat-driven refrigeration system, without consuming additional electricity, achieving zero additional energy consumption in the solvent recovery process. Example 5

[0067] This application discloses a polyimide waste heat recovery system. The difference from Example 2 is that, referring to… Figure 6 The waste heat recovery and utilization system also includes a primary condenser 6, a secondary condenser 7, and a tertiary condenser 8, which are connected in the same way as in Example 4.

[0068] This embodiment combines the single-generator dual-pressure-stage GAX refrigeration architecture of Embodiment 2 with a three-stage condensation recovery system. The organic waste gas flows sequentially through the shell side of the first-stage condenser 6 (heat exchange with the circulating water in the tube side), the shell side of the second-stage condenser 7 (heat exchange with the first refrigerant at 7°C from the first evaporator 1 in the tube side), and the shell side of the third-stage condenser 8 (heat exchange with the second refrigerant at -15 to -20°C from the second evaporator 2 in the tube side). The solvent in the organic waste gas is recovered through cascaded condensation by cooling at three stages with decreasing temperatures.

[0069] The waste heat refrigeration section operates according to the principle described in Example 2. The refrigerant is distributed through system distribution branches to the medium-pressure GVX heat exchanger 514 and the low-pressure GVX heat exchanger 515 for subcooling, and then enters the two evaporators for refrigeration. At the same time, it provides a cold source for the corresponding process cooling section and the condensation recovery section of the same temperature level. The recovered liquid solvent can be reused.

[0070] The implementation principle of the polyimide waste heat recovery system in this application embodiment is as follows: A single-generator, dual-pressure-stage GAX absorption refrigeration system is integrated with a three-stage organic waste gas condensation and recovery system. The same waste heat refrigeration unit 5 simultaneously meets the cooling capacity requirements for process cooling and solvent condensation and recovery. The 7°C cooling capacity produced by the medium-pressure evaporator and the -15 to -20°C cooling capacity produced by the low-pressure evaporator are supplied to the corresponding temperature-grade process sections and condensers, respectively, achieving a unified distribution of cooling capacity according to temperature grade. This embodiment integrates three major functions—waste heat refrigeration, process cooling, and high solvent recovery rate—with a compact single-generator architecture. Example 6

[0071] This application discloses a polyimide waste heat recovery system. The difference from Example 3 is that, referring to… Figure 7 The waste heat recovery and utilization system also includes a primary condenser 6, a secondary condenser 7, and a tertiary condenser 8, which are connected in the same way as in Example 4.

[0072] This embodiment combines the refrigeration architecture of liquid refrigerant series-connected cascade subcooling with evaporator series connection from Embodiment 3 with a three-stage condensation recovery system. The three-stage condensation recovery process for organic waste gas is the same as in Embodiment 4.

[0073] On the refrigeration side, the liquid refrigerant flows sequentially through the tube side of the medium-pressure GVX heat exchanger 514 and the tube side of the low-pressure GVX heat exchanger 515, undergoing two subcooling processes. It then enters the shell side of the first evaporator 1 (medium-pressure evaporation) for partial evaporation, generating 7°C of cooling capacity to supply the casting film forming section 02 and the secondary condenser 7. The unevaporated liquid refrigerant in the shell side of the first evaporator 1 then enters the shell side of the second evaporator 2 (low-pressure evaporation) for complete evaporation, generating -15 to -20°C of cooling capacity to supply the polycondensation reaction section 01 and the tertiary condenser 8.

[0074] Because the liquid refrigerant flows in series, the evaporation rate of the first evaporator 1 directly determines the amount of liquid refrigerant entering the second evaporator 2. That is, an increase of 7°C in the cooling capacity consumed by the secondary condenser 7 will increase the load on the first evaporator 1, leading to a greater amount of refrigerant evaporation within the first evaporator 1. Consequently, the amount of liquid refrigerant remaining entering the second evaporator 2 will decrease, and the cooling capacity produced by the second evaporator 2 will decrease accordingly. The system has a certain self-balancing capacity for cooling load.

[0075] The implementation principle of the polyimide waste heat recovery system in this application embodiment is as follows: Based on a refrigerant series-cascade evaporation refrigeration architecture, a three-stage waste gas condensation and recovery system is integrated. The refrigerant evaporates sequentially in two evaporation pressure stages, corresponding to the process cooling section and condensation recovery section at two temperature levels, respectively. The refrigerant series evaporation automatically achieves adaptive distribution of cooling capacity between the medium-pressure and low-pressure stages, eliminating the need for additional refrigerant flow distribution and adjustment devices. The staged condensation of waste gas in the three-stage condenser 8 and the staged evaporation of refrigerant in the two evaporators form a dual-cascade utilization architecture, achieving efficient utilization of energy and materials according to temperature and grade. Example 7

[0076] This application discloses a polyimide waste heat recovery system. The difference from Example 4 is that, referring to… Figure 8 The waste heat recovery and utilization system also includes a fourth condenser 91, a first heat exchanger 92, a second heat exchanger 93, and a subcooler 94.

[0077] The fourth condenser 91 is connected in the pipeline between the second condenser 57 and the GVX heat exchanger 58. The tube-side inlet of the fourth condenser 91 is connected to the liquid refrigerant outlet pipeline of the second condenser 57, and the tube-side outlet of the fourth condenser 91 is connected to the liquid refrigerant inlet pipeline of the GVX heat exchanger 58. Before entering the GVX heat exchanger 58, the liquid refrigerant flows through the tube side of the fourth condenser 91 to cool the exhaust gas flowing through the shell side of the fourth condenser 91.

[0078] The first heat exchanger 92 is connected to the exhaust pipe 41. The tube-side inlet of the first heat exchanger 92 is connected to the tertiary pipeline 81, receiving the exhaust gas after tertiary condensation. The tube-side outlet of the first heat exchanger 92 is connected to the inlet pipeline of the incinerator 3. The shell-side inlet of the first heat exchanger 92 is connected to the exhaust pipe 41 of the waste heat boiler 4, and the shell-side outlet of the first heat exchanger 92 opens to the atmosphere. The exhaust gas exchanges heat with the flue gas from the waste heat boiler 4 within the tube side and shell side. The shell side of the fourth condenser 91 is connected to the tertiary pipeline 81, and the tube side of the first heat exchanger 92 is also connected to the tertiary pipeline 81. The first heat exchanger 92 is located between the fourth condenser 91 and the incinerator 3.

[0079] The second heat exchanger 93 is connected to the second waste gas pipe 32 of the first-stage condenser 6 and the high-temperature imide chemical section 03. The shell-side inlet of the second heat exchanger 93 is connected to the second waste gas pipe 32, receiving the high-temperature organic waste gas generated by the high-temperature imide chemical section 03. The shell-side outlet of the second heat exchanger 93 is connected to the waste gas inlet pipe of the first-stage condenser 6. The tube-side inlet of the second heat exchanger 93 is connected to the feed water pipe of the waste heat boiler 4, and the tube-side outlet of the second heat exchanger 93 is connected to the inlet of the waste heat boiler 4. The high-temperature organic waste gas exchanges heat with the feed water in the tube side within the shell side. The water supplied to the waste heat boiler 4 first flows into the tube side of the second heat exchanger 93, and then flows into the waste heat boiler 4.

[0080] Subcooler 94 is connected to the first inflow branch pipe 72 between the secondary condenser 7 and the first refrigerant inlet pipe 11. The tube-side inlet of subcooler 94 is connected to the first inflow branch pipe 72, receiving the first refrigerant before it enters the secondary condenser 7. The tube-side outlet of subcooler 94 is connected to the tube-side inlet of the secondary condenser 7. The shell-side inlet of subcooler 94 is connected to the tertiary pipeline 81, receiving the low-temperature exhaust gas after tertiary condensation. The shell-side outlet of subcooler 94 is connected to the shell-side inlet of the fourth condenser 91. Before entering the tube side of the secondary condenser 7, the first refrigerant from the first evaporator 1 flows through the tube side of subcooler 94, exchanging heat with the low-temperature exhaust gas flowing through the shell side from the outlet of the tertiary condenser 8. The first refrigerant is further cooled before entering the tube side of the secondary condenser 7, reducing the actual condensation temperature of the secondary condenser 7 and improving the solvent recovery rate of the secondary condenser. After the low-temperature exhaust gas absorbs heat in the shell side of the condenser 94, its temperature rises slightly, and then it enters the shell side of the fourth condenser 91 to continue releasing residual heat.

[0081] This embodiment adds four sets of heat exchangers to the existing embodiment 4. The energy utilization process during system operation is as follows: Before entering the primary condenser 6, the high-temperature organic waste gas generated in the high-temperature imide chemical section 03 first enters the shell side of the second heat exchanger 93 through the second waste gas pipe 32, where it exchanges heat with the feedwater of the waste heat boiler 4 in the tube side. The organic waste gas is pre-cooled and cooled down, while the feedwater of the waste heat boiler 4 is pre-heated and then enters the waste heat boiler 4, reducing the feedwater heating load of the waste heat boiler 4.

[0082] Before entering the GVX heat exchanger 58, the liquid refrigerant from the second condenser 57 flows through the tube side of the fourth condenser 91, where it exchanges heat with the low-temperature exhaust gas from the outlet of the third-stage condenser 8 in the shell side. The liquid refrigerant further absorbs cold from the low-temperature exhaust gas to achieve subcooling, increasing the cooling capacity after entering the second evaporator 2.

[0083] Before entering the tube side of the second-stage condenser 7, the first refrigerant from the first evaporator 1 flows through the tube side of the cooler 94 and exchanges heat with the low-temperature tail gas after the third-stage condensation from the third-stage pipeline 81 to achieve pre-cooling and cooling. This allows the non-condensable organic waste gas in the shell side of the second-stage condenser 7 to be further condensed and liquefied at a lower condensation temperature, thereby improving the solvent recovery rate in the second-stage condensation stage.

[0084] The low-temperature exhaust gas flows sequentially through the three-stage pipeline 81, the shell side of the subcooler 94, and the shell side of the fourth condenser 91 before entering the tube side of the first heat exchanger 92. There, it exchanges heat with the flue gas from the exhaust pipe 41 of the waste heat boiler 4 within the shell side. After being preheated by the flue gas, it is sent to the incinerator 3. The cold energy carried by the low-temperature exhaust gas is first precooled by the secondary condenser refrigerant in the subcooler 94, and then subcooled by the liquid refrigerant in the fourth condenser 91. This two-stage recovery of cold energy before it is preheated by the waste heat from the flue gas optimizes both the utilization of cold energy and the heat recovery efficiency of the low-temperature exhaust gas.

[0085] The implementation principle of the polyimide waste heat recovery system in this application embodiment is as follows: Based on three-stage condensation recovery and dual-cycle GAX refrigeration, multiple stages of energy recovery and utilization are achieved through four sets of additional heat exchangers. High-temperature organic waste gas transfers sensible heat to the feedwater of the waste heat boiler 4 via the second heat exchanger 93, reducing the cooling load of the subsequent condensation system and improving the thermal efficiency of the waste heat boiler 4. Liquid refrigerant further absorbs cold from the low-temperature exhaust gas via the fourth condenser 91 to achieve deep subcooling, improving the refrigeration efficiency of the second refrigeration cycle. The first refrigerant is pre-cooled by the low-temperature exhaust gas via cooler 94, reducing the condensation temperature of the second-stage condenser 7 and improving the solvent recovery rate in the second-stage condensation stage. The low-temperature exhaust gas absorbs heat from the exhaust gas of the waste heat boiler 4 via the first heat exchanger 92 and enters the incinerator 3 at a higher temperature, reducing the auxiliary heating requirements of the incinerator 3 and further reducing the final exhaust gas temperature of the system. All heat exchangers in the entire system are passive heat exchangers, without increasing additional operating energy consumption. Example 8

[0086] This application discloses a polyimide waste heat recovery system. The difference from Example 5 is that, referring to… Figure 9 The waste heat recovery system also includes a fourth condenser 91, a first heat exchanger 92, a second heat exchanger 93, and a subcooler 94. The connection method and function of each additional heat exchanger are the same as in Embodiment 7.

[0087] This embodiment integrates the single-generator dual-pressure-stage GAX refrigeration architecture of Embodiment 5 with a three-stage condensation recovery system, and adds four additional heat exchangers. While realizing the three major functions of waste heat refrigeration, process cooling and solvent recovery, it further improves the refrigeration efficiency by deep subcooling the liquid refrigerant through the fourth condenser 91, reduces the heating load by using the high-temperature organic waste gas to preheat the feedwater of the waste heat boiler 4 through the second heat exchanger 93, improves the secondary condensation solvent recovery rate by precooling the secondary condensation refrigerant through the subcooler 94, and reduces the auxiliary heating demand of the incinerator 3 by using the exhaust gas of the waste heat boiler 4 through the first heat exchanger 92. This realizes multi-stage cascade recovery and utilization of energy in the entire system. Example 9

[0088] This application discloses a polyimide waste heat recovery system. The difference from Example 6 is that, referring to… Figure 10 The waste heat recovery system also includes a fourth condenser 91, a first heat exchanger 92, a second heat exchanger 93, and a subcooler 94. The connection method and function of each additional heat exchanger are the same as in Embodiment 7.

[0089] This embodiment integrates the liquid refrigerant series cascade evaporation refrigeration architecture of Embodiment 6 with a three-stage condensation recovery system, and adds four additional heat exchangers. While the refrigerant series evaporation automatically achieves adaptive cooling capacity distribution, the four additional heat exchangers enable multi-stage energy recovery across the entire system: the fourth condenser 91 deeply subcools the liquid refrigerant, the second heat exchanger 93 preheats the feed water using high-temperature organic waste gas, the subcooler 94 precools the secondary condensation refrigerant, and the first heat exchanger 92 preheats the exhaust gas using flue gas. The three-stage progressive condensation of waste gas and the two-stage progressive evaporation of refrigerant form a dual-cascade utilization architecture, achieving efficient utilization of both energy and materials according to temperature and grade.

[0090] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A polyimide waste heat recovery and utilization system, characterized in that, include: The first evaporator (1) is connected to a first refrigerant inlet pipe (11) and a first refrigerant outlet pipe (12) that are connected to the casting film section (02); the liquid refrigerant enters the first evaporator (1) to evaporate and absorb heat, thereby cooling the first refrigerant flowing through the first evaporator (1); The second evaporator (2) is connected to a second refrigerant inlet pipe (21) and a second refrigerant outlet pipe (22) that are connected to the polycondensation reaction section (01); the liquid refrigerant enters the second evaporator (2) to evaporate and absorb heat, thereby cooling the second refrigerant flowing through the second evaporator (2); Incinerator (3) is used to receive and incinerate the organic waste gas generated during the production of polyimide film; Waste heat boiler (4) is connected to the incinerator (3) through flue gas pipe (33) and uses the high temperature flue gas generated by the incinerator (3) to heat the water inside to generate superheated steam. The waste heat refrigeration unit (5) is connected to the waste heat boiler (4) through a steam pipe (42), uses superheated steam for refrigeration, and supplies liquid refrigerant to the first evaporator (1) through a first pipeline and to the second evaporator (2) through a second pipeline.

2. The polyimide waste heat recovery system according to claim 1, characterized in that: The waste heat refrigeration unit (5) includes a first refrigeration cycle; the first refrigeration cycle includes a first generator (51), a first condenser (52), a first absorber (53), a first solution pump (54), and a first GAX heat exchanger (55); superheated steam enters the first generator (51) through a steam pipe (42) and heats the rich solution inside to desorb the refrigerant; the gaseous refrigerant is condensed and liquefied by circulating water in the first condenser (52) and then enters the first evaporator (1) under reduced pressure; the gaseous refrigerant in the first evaporator (1) enters the first absorber (53) and is absorbed by the lean solution to form a rich solution; the rich solution is transported to the first GAX heat exchanger (55) by the first solution pump (54), and after exchanging heat with the high-temperature lean solution from the first generator (51), it returns to the first generator (51).

3. The polyimide waste heat recovery system according to claim 2, characterized in that: The waste heat refrigeration unit (5) further includes a second refrigeration cycle; the second refrigeration cycle includes a second generator (56), a second condenser (57), a GVX heat exchanger (58), a second absorber (59), a second solution pump (510), and a second GAX heat exchanger (511); superheated steam enters the second generator (56) through a steam pipe (42) to heat the rich solution inside and cause the refrigerant to decompose; the gaseous refrigerant is condensed and liquefied by circulating water in the second condenser (57) and then enters the GVX heat exchanger (511). 58) The gaseous refrigerant from the second evaporator (2) is cooled by heat exchange and then depressurized before entering the second evaporator (2); the gaseous refrigerant in the second evaporator (2) is heated by heat exchange in the GVX heat exchanger (58) and then enters the second absorber (59) to be absorbed by the lean solution to form a rich solution; the rich solution is transported to the second GAX heat exchanger (511) by the second solution pump (510), and after heat exchange with the high-temperature lean solution from the second generator (56), it returns to the second generator (56).

4. The polyimide waste heat recovery system according to claim 1, characterized in that: The waste heat refrigeration unit (5) includes a third generator (512), a third condenser (513), a medium-pressure GVX heat exchanger (514), a low-pressure GVX heat exchanger (515), a medium-pressure absorber (516), a low-pressure absorber (517), and a third GAX heat exchanger (518). Superheated steam enters the third generator (512) through a steam pipe (42) to heat the rich solution inside and cause the refrigerant to decompose. After the gaseous refrigerant is condensed and liquefied by circulating water in the third condenser (513), it flows through branch pipes to the medium-pressure GVX heat exchanger (514) and the low-pressure GVX heat exchanger (515), and then enters the first evaporator (1) and the second evaporator (2) under reduced pressure. The gaseous refrigerant discharged from the first evaporator (1) enters the medium-pressure absorber (516) after heat exchange and temperature rise in the medium-pressure GVX heat exchanger (514); the gaseous refrigerant discharged from the second evaporator (2) enters the low-pressure absorber (517) after heat exchange and temperature rise in the low-pressure GVX heat exchanger (515); the rich solution in the low-pressure absorber (517) is pressurized and sent to the medium-pressure absorber (516), and the rich solution in the medium-pressure absorber (516) is sent to the third GAX heat exchanger (518) by the third solution pump (519), and returns to the third generator (512) after heat exchange with the high-temperature lean solution from the third generator (512).

5. The polyimide waste heat recovery system according to claim 1, characterized in that: The waste heat refrigeration unit (5) includes a third generator (512), a third condenser (513), a medium-pressure GVX heat exchanger (514), a low-pressure GVX heat exchanger (515), a medium-pressure absorber (516), a low-pressure absorber (517), and a third GAX heat exchanger (518). Superheated steam enters the third generator (512) through a steam pipe (42) to heat the rich solution inside and cause the refrigerant to decompose. After the gaseous refrigerant is condensed and liquefied by circulating water in the third condenser (513), it flows sequentially through the medium-pressure GVX heat exchanger (514) and the low-pressure GVX heat exchanger (515), and then depressurizes before entering the first evaporator (1). The unevaporated liquid in the first evaporator (1) The gaseous refrigerant is depressurized and enters the second evaporator (2); the gaseous refrigerant discharged from the first evaporator (1) and the second evaporator (2) is heated by heat exchange in the medium-pressure GVX heat exchanger (514) and the low-pressure GVX heat exchanger (515), respectively, and then enters the medium-pressure absorber (516) and the low-pressure absorber (517), respectively; the rich solution in the low-pressure absorber (517) is pressurized and sent to the medium-pressure absorber (516), and the rich solution in the medium-pressure absorber (516) is sent to the third GAX heat exchanger (518) by the third solution pump (519), and after heat exchange with the high-temperature lean solution from the third generator (512), it returns to the third generator (512).

6. The polyimide waste heat recovery system according to claim 1, characterized in that: It also includes a primary condenser (6), a secondary condenser (7), and a tertiary condenser (8); the organic waste gas generated during the production of polyimide film enters the primary condenser (6), the secondary condenser (7), and the tertiary condenser (8) in sequence; the primary condenser (6) is supplied with circulating water as a cold source, the secondary condenser (7) is connected to the first refrigerant produced by the first evaporator (1) through the first refrigerant pipeline as a cold source, and the tertiary condenser (8) is connected to the second refrigerant produced by the second evaporator (2) through the second refrigerant pipeline as a cold source; the tail gas condensed by the tertiary condenser (8) flows to the incinerator (3) through the tertiary pipeline (81).

7. A polyimide waste heat recovery system according to claim 6, characterized in that: It also includes a fourth condenser (91), which is connected in series to the pipeline that supplies liquid refrigerant to the second evaporator (2) and is connected to the low-temperature tail gas after the third-stage condensation through the pipeline, so as to cool the liquid refrigerant in the pipeline by using the low-temperature tail gas.

8. A polyimide waste heat recovery system according to claim 6, characterized in that: It includes a first heat exchanger (92), which is connected in series to the three-stage pipeline (81). The first heat exchanger (92) is connected to the waste heat boiler (4) through an exhaust pipe (41). The exhaust gas from the waste heat boiler (4) is used to preheat the tail gas flowing through the three-stage pipeline (81) before it is sent to the incinerator (3).

9. A polyimide waste heat recovery system according to claim 6, characterized in that: It includes a second heat exchanger (93), which is connected in series to the organic waste gas pipeline leading to the first-stage condenser (6) to receive high-temperature organic waste gas; at the same time, it is connected to the waste heat boiler (4) through the water supply pipeline to preheat the water supply flowing through the water supply pipeline using the high-temperature organic waste gas.

10. A polyimide waste heat recovery system according to claim 6, characterized in that: It includes a subcooler (94), which is connected in series to the refrigerant inlet pipe of the secondary condenser (7) and is connected to the low-temperature exhaust gas after the tertiary condenser through the pipe. The low-temperature exhaust gas is used to pre-cool the refrigerant flowing through the refrigerant inlet pipe.

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