Rectifying tower waste heat recovery system for heat pump

Abstract

The invention provides a rectifying tower waste heat recovery system for a heat pump, the rectifying tower waste heat recovery system comprises a reaction and rectification unit, a segregation unit and a heat pump unit, the reaction and rectification unit comprises a raw material storage tank, a raw material preheater, a reactor and a rectifying tower which are sequentially communicated through a pipeline, and a tower kettle outlet of the rectifying tower outputs a tower kettle product; a tower top steam outlet of the rectifying tower is connected with the segregation unit, the segregation unit is used for separating VOC condensate and steam, and the steam provides a heat source for the heat pump unit. By additionally arranging the segregation unit, the tower top steam is separated into low-VOC steam and high-VOC condensate before entering the heat pump unit, and only the low-VOC steam enters the heat pump unit, so that VOC is prevented from being condensed and separated out in machinery equipment of the heat pump unit, and corrosion to the machinery equipment is eliminated from the source.

Description

Technical Field

[0001] This invention belongs to the field of energy-saving technology in chemical processes, and particularly relates to a waste heat recovery system for distillation columns used in heat pumps. Background Technology

[0002] During the esterification process, a large amount of steam at 80-120°C is generated at the top of the distillation column. This steam typically contains unreacted alcohols, trace amounts of acids, and water. These volatile organic compounds (VOCs) form corrosive liquid substances during condensation. Traditional water-cooling or air-cooling methods for direct condensation result in a significant waste of low-temperature heat. Recovering this waste heat using high-temperature heat pump technology, and then raising its temperature for use in feed preheating or reboiler heating, is a highly economical and energy-saving measure.

[0003] However, when the top steam of the tower is directly introduced into the heat pump evaporator, VOC components condense and precipitate on the cold wall surface of the evaporator, causing severe electrochemical corrosion and pitting on the heat exchange tube wall, which has become a fatal pain point restricting the application of this technology. Summary of the Invention

[0004] In view of this, the present invention provides a waste heat recovery system for a distillation column for a heat pump. The present invention separates the top steam of the column into low-VOC steam and high-VOC condensate before it enters the heat pump unit by adding a condensation unit. Only the low-VOC water vapor is allowed to enter the heat pump unit, thereby avoiding the condensation and precipitation of VOCs in the equipment of the heat pump unit and eliminating corrosion of the equipment from the source.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: This application provides a waste heat recovery system for a distillation column used in a heat pump, comprising: a reaction and distillation unit, a condensation unit, and a heat pump unit. The reaction and distillation unit includes a raw material storage tank, a raw material preheater, a reactor, and a distillation column connected in sequence by pipelines. The bottom product of the distillation column is output from the bottom outlet, and the top vapor outlet of the distillation column is connected to the condensation unit. The condensation unit is used to separate VOC condensate and vapor, and the vapor provides a heat source for the heat pump unit.

[0006] Preferably, it also includes a heat absorber, the high-temperature side of which is connected to the cooling water of the reactor, and an external medium enters the low-temperature side of the heat absorber to absorb heat. The medium that absorbs heat provides a heat source for the heat pump unit.

[0007] Preferably, the heat pump unit includes a primary heat pump cycle and a secondary heat pump cycle. The primary heat pump cycle includes an evaporator, a primary compressor, a heat exchanger, and a primary throttling valve. The secondary heat pump cycle includes a secondary compressor, a secondary throttling valve, and a heat exchanger. The water vapor separated by the condensation unit and the water flowing out from the low-temperature side of the heat absorber enter the high-temperature side of the evaporator to heat the working fluid of the first-stage heat pump cycle. The working fluid of the first-stage heat pump cycle flows out from the low-temperature side of the evaporator and enters the first-stage compressor, the high-temperature side of the heat exchanger, and the first-stage throttling valve in sequence, before returning to the low-temperature side of the evaporator. The working fluid of the secondary heat pump cycle flows out from the low-temperature side of the heat exchanger, enters the secondary compressor, the high-temperature side of the heat exchanger, and the secondary throttling valve in sequence, and returns to the low-temperature side of the heat exchanger. The water flowing out from the high-temperature side of the evaporator is returned to the distillation column.

[0008] Preferably, the system further includes an online purification unit, which includes a molecular sieve adsorption module, and the molecular sieve adsorption module is respectively disposed in front of the intake ports of the primary compressor and the secondary compressor.

[0009] Preferably, the online purification unit further includes a VOC sensor, a regeneration controller, and a molecular sieve adsorption module. The VOC sensor is respectively installed on the suction pipes of the primary compressor and the secondary compressor. The signal input terminal of the controller is electrically connected to the VOC sensor, and the control input terminal of the controller is electrically connected to the molecular sieve adsorption module.

[0010] Preferably, the low-temperature side of the heat exchanger is connected to the feed preheater and / or the reboiler of the distillation column to provide heat for the feed or the steam required by the reboiler.

[0011] Preferably, the condensation unit includes a condenser, the top vapor outlet of the distillation column is connected to the condenser, and the vapor outlet of the condenser is connected to the heat pump unit.

[0012] Preferably, the liquid phase outlet of the condenser is connected to the upper reflux port of the distillation column.

[0013] Preferably, the condensation unit further includes a steam tank and a condensate tank, the top steam outlet of the distillation column is connected to the condenser, the steam outlet of the condenser is connected to the steam tank, and the steam tank is connected to the heat pump unit; The liquid phase outlet of the condenser is connected to the condensate tank, and the condensate tank is connected to the upper reflux port of the distillation column.

[0014] Because of the above technical solutions, this invention has the following advantages and positive effects compared with the prior art: This invention provides a waste heat recovery system for a distillation column used in heat pumps, comprising a reaction and distillation unit, a condensation unit, and a heat pump unit. The system utilizes the heat pump unit to recover waste heat from the distillation column. Compared to existing technologies, a condensation unit is added before the heat pump unit, decoupling the VOC component separation and waste heat recovery processes. The condensation unit leverages the difference in dew points between VOC components and water vapor to create a gradient cooling condensation environment. By controlling the cooling rate and temperature, most VOC components (such as alcohols and trace acids) preferentially condense into the liquid phase, thus being separated before entering the heat pump unit. This results in the working fluid ultimately entering the heat pump unit becoming "clean water vapor" with extremely low VOC content, fundamentally eliminating the problem of VOCs condensing and precipitating on the cold walls of the heat exchanger in the heat pump unit, causing electrochemical corrosion and pitting of the heat exchange tubes. This protects the machine and ensures the long-term, efficient, and stable operation of the heat pump unit.

[0015] In a preferred embodiment of the present invention, the medium- and low-temperature heat from the reactor cooling circuit is further integrated and recovered through a heat absorber, and this heat is used as another heat source for the heat pump unit. Therefore, in this embodiment, the heat pump unit synergistically raises the temperature by combining two heat sources of different grades, which greatly improves the overall energy utilization efficiency and significantly reduces the system's energy consumption.

[0016] In a preferred embodiment of the present invention, an online working fluid purification module based on a molecular sieve adsorption module is added, which constitutes a second reliable line of defense against working fluid contamination and corrosion, effectively reducing the possibility of compressor failure. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a distillation column waste heat recovery system for a heat pump according to an embodiment of the present invention; Figure reference numerals: 1-Reaction and distillation unit; 101-Raw material storage tank; 102-Raw material preheater; 103-Reactor; 104-Distillation column; 105-Reboiler; 106-Top steam outlet of the column; 2-Fractional condensation unit; 201-Fractional condenser; 202-Steam tank; 203-Condensate; 204-First mixer; 205-Second mixer; 3-Heat pump unit; 301-Evaporator; 302-First stage compressor; 303-Heat exchanger; 304-First stage expansion valve; 305-Second stage expansion valve; 306-Second stage compressor; 307-Heat exchanger; 4-Online purification unit; 401-VOC sensor; 402-Controller; 403-Molecular sieve adsorption module; 5-Heat absorber. Detailed Implementation

[0018] The following detailed description, in conjunction with the accompanying drawings and specific embodiments, provides a further detailed explanation of the waste heat recovery system for a heat pump distillation column proposed in this invention. The advantages and features of the invention will become clearer from the following description.

[0019] A waste heat recovery system for a distillation column used in a heat pump includes: a reaction and distillation unit 1, a condensation unit 2, and a heat pump unit 3. The reaction and distillation unit 1 includes a raw material storage tank 101, a raw material preheater 102, a reactor 103, and a distillation column 104 connected in sequence by pipelines. The bottom product of the distillation column 104 is discharged from the bottom outlet. The top vapor outlet 106 of the distillation column 104 is connected to the condensation unit 2. The condensation unit 2 utilizes the difference in dew point between VOC components and water vapor to control the cooling rate and temperature, so that most VOC components (such as alcohols and trace acids) are preferentially condensed into liquid phase, thereby separating the VOC components in the liquid phase from the low-VOC vapor. The vapor provides a heat source for the heat pump unit 3.

[0020] In this embodiment, a condensation unit 2 is added before the heat pump unit 3 to decouple the two processes of VOC component separation and waste heat recovery. Only low-VOC steam is introduced into the heat pump unit 3 to provide a heat source for the heat pump unit 3. This fundamentally eliminates the problem of VOC condensation and precipitation on the heat exchange cold wall surface of the heat pump unit 3, which causes electrochemical corrosion and pitting corrosion to the heat exchange tubes, protects the machine, and ensures the long-term, efficient and stable operation of the heat pump system.

[0021] In some preferred embodiments, the waste heat recovery system of the distillation column 104 further includes a heat absorber 5. The high-temperature side of the heat absorber 5 is connected to the cooling water of the reactor 103. An external medium enters the low-temperature side of the heat absorber 5 to absorb heat, and the heat-absorbing medium provides a heat source for the heat pump unit 3. The heat absorber 5 further integrates and recovers the medium- and low-temperature heat cooled by the cooling circuit of the reactor 103, and uses this part of the heat as another heat source for the heat pump unit 3. Therefore, in this embodiment, the heat pump unit 3 coordinates two heat sources of different grades to raise the temperature, which greatly improves the comprehensive energy utilization efficiency and significantly reduces the system energy consumption.

[0022] Since the clean water vapor separated by the condensation unit 2 enters the heat pump unit 3, it provides a heat source for the heat pump unit 3. The heat absorber 5 absorbs the heat from the cooling circuit of the reactor 103. Preferably, external water enters the low-temperature side of the heat absorber 5 to absorb heat, thereby mixing with the clean water vapor separated by the condenser 201 and entering the heat pump unit 3. More preferably, a first mixer 204 is set before the heat pump unit 3. The low-VOC steam separated by the condensation unit 2 and the water flowing out from the low-temperature side of the heat absorber 5 enter the first mixer 204 for mixing, and then enter the heat pump unit 3.

[0023] In some embodiments, the condensation unit 2 includes a condenser 201, the top steam outlet 106 of the distillation column 104 is connected to the condenser 201, and the steam outlet of the condenser 201 is connected to the inlet of the first mixer 204.

[0024] In a preferred variation, the liquid outlet of the condenser 201 is connected to the upper reflux port of the distillation column 104. The condensate 203 of the VOC components separated by the condenser 201 is refluxed back to the distillation column 104, which avoids the entry of corrosion sources into the heat pump and recovers valuable raw materials. Further preferably, a second mixer 205 is provided, in which the water medium entering the heat pump unit 3, after being cooled by the working fluid of the heat pump unit 3, is mixed with the condensate 203 of the VOC components before being refluxed back to the distillation column 104.

[0025] In some variations, the condensation unit 2 further includes a steam tank 202 and a condensate tank 203. The top steam outlet 106 of the distillation column 104 is connected to the condenser 201, the steam outlet of the condenser 201 is connected to the inlet of the steam tank 202, and the outlet of the steam tank 202 is connected to the inlet of the first mixer 204. The liquid phase outlet of the condenser 201 is connected to the inlet of the condensate tank 203, the outlet of the condensate tank 203 is connected to the inlet of the second mixer 205, and the outlet of the second mixer 205 is connected to the upper reflux port of the distillation column 104.

[0026] In some preferred embodiments, the heat pump unit 3 includes a two-stage heat pump cycle to efficiently increase the temperature of the two heat sources. The two-stage heat pump cycle includes a primary heat pump cycle and a secondary heat pump cycle. The primary heat pump cycle includes an evaporator 301, a primary compressor 302, a heat exchanger 303, and a primary throttling valve 304. The secondary heat pump cycle includes a secondary compressor 306, a secondary throttling valve 305, and a heat exchanger 307. The mixed water flowing out of the first mixer 204 enters the high-temperature side of the evaporator 301 to heat the working fluid of the first-stage heat pump cycle. The cooled water flows out from the high-temperature side of the evaporator 301 and enters the second mixer 205. The working fluid of the first-stage heat pump cycle flows out from the low-temperature side of the evaporator 301, enters the high-temperature side of the first-stage compressor 302, the heat exchanger 303, and the first-stage throttling valve 304 in sequence, and returns to the low-temperature side of the evaporator 301. The working fluid of the secondary heat pump cycle flows out from the low-temperature side of the heat exchanger 303, enters the secondary compressor 306, the high-temperature side of the heat exchanger 307, and the secondary throttling valve 305 in sequence, and returns to the low-temperature side of the heat exchanger 303.

[0027] In the first-stage heat pump cycle, the working fluid flowing out from the low-temperature side of the evaporator 301 enters the first-stage compressor 302. After being heated and pressurized, it enters the high-temperature side of the heat exchanger 303. After heat exchange, the working fluid flows out from the high-temperature side of the heat exchanger 303 and enters the first-stage throttling valve 304. After throttling and depressurization, it returns to the low-temperature side of the evaporator 301 to absorb heat, thus completing the first-stage heat pump cycle.

[0028] In a two-stage heat pump cycle, the heat obtained from heat exchanger 303 is transferred to the working fluid of the two-stage heat pump cycle. The heated working fluid flows out from the low-temperature side of heat exchanger 303, enters the two-stage compressor 306 for further heating and pressurization, then enters the high-temperature side of exothermic device 307 to release heat and lower its temperature. It then enters the two-stage throttling valve 305 for throttling and pressure reduction, and finally returns to the low-temperature side of the mixed gas, completing the two-stage heat pump cycle. The low-temperature side of exothermic device 307 can utilize other media to absorb the increased temperature from the two-stage heat pump cycle for external heating or storage. Preferably, the increased temperature from the two-stage heat pump cycle is used for preheating the feedstock or heating the reboiler 105 in the distillation column. The low-temperature side of exothermic device 307 is connected to the feedstock preheater 102 and / or the reboiler 105 of the distillation column 104 to provide heat for the feedstock or the steam required by the reboiler 105. For example... Figure 1 As shown, water is used as the medium. External water enters the low-temperature side of the heat exchanger 307 to absorb heat. The heated water flows out from the low-temperature side of the heat exchanger 307 and can be divided into at least one path to flow into the raw material preheater 102 to heat the raw material, or flow into the reboiler 105 of the distillation column 104, or into two paths, flowing into the raw material preheater 102 and the reboiler 105 respectively, or into three paths, with the third path supplying heat or steam to the outside in addition to flowing into the raw material preheater 102 and the reboiler 105.

[0029] To further prevent contamination and corrosion of the heat pump circulating fluid and the machine, and to add a second line of defense, an online purification unit 4 is provided in some preferred embodiments. The online purification unit 4 includes a molecular sieve adsorption module 403, which is respectively installed before the suction ports of the primary compressor 302 and the secondary compressor 306. Even if trace amounts of VOCs corrode the heat exchange pipe wall of the evaporator 301 and penetrate into the working fluid, the molecular sieve adsorption module 403 adsorbs the trace amounts of VOCs before they enter the suction port of the primary compressor 302, allowing only clean working fluid to enter the primary compressor 302 and the secondary compressor 306. The molecular sieve adsorption module 403 includes at least one molecular sieve adsorption bed, and multiple molecular sieve adsorption beds are used in parallel. After one molecular sieve adsorption bed becomes saturated, another molecular sieve adsorption bed can be replaced.

[0030] Furthermore, the online purification unit 4 also includes a VOC sensor 401, a regeneration controller 402, and a molecular sieve adsorption module 403. The VOC sensor 401 is respectively installed on the suction pipes of the primary compressor 302 and the secondary compressor 306. The signal input terminal of the controller 402 is electrically connected to the VOC sensor 401, and the control input terminal of the controller 402 is electrically connected to the molecular sieve adsorption module 403. The VOC sensor 401 can monitor the purity of the working fluid in real time. When the VOC sensor 401 detects that the conductivity of the working fluid in any pipe continuously exceeds 4 μS / cm, the controller 402 can automatically switch the working fluid in the changed pipe to another molecular sieve adsorption bed in parallel.

[0031] For molecular sieve adsorption beds that have already adsorbed VOCs to saturation, they can be desorbed by heating. For example, the high-temperature working fluid discharged from the compressor can be introduced back into the saturated molecular sieve adsorption bed, and the desorbed trace amounts of VOCs can be exported and treated in an environmentally friendly manner.

[0032] The use of an online purification unit 4 ensures that the heat pump working fluid always maintains high purity, fundamentally avoiding COP decay and equipment corrosion caused by working fluid contamination.

[0033] Taking a production plant with an annual output of 100,000 tons of ethyl acetate as an example, this invention fully demonstrates the specific process flow, operating parameters and beneficial effects of the invention, but is not intended to limit the scope of protection of the invention.

[0034] 1. System Configuration and Initial Conditions The system used in this embodiment is as follows: Figure 1 As shown, it mainly includes: Reaction and distillation unit 1 includes a raw material storage tank 101, a raw material preheater 102, a reactor 103, a distillation column 104, and a reboiler 105.

[0035] Separation unit 2: A specially designed condenser 201.

[0036] Heat pump unit 3 includes a heat pump evaporator 301, a primary compressor 302, a heat exchanger 303 (serving as the secondary cycle evaporator 301), a secondary compressor 306, a heat exchanger 307, a primary throttling valve 304, and a secondary throttling valve 305.

[0037] Working fluid online purification unit 4: includes VOC sensor 401, controller 402 and molecular sieve adsorption module 403.

[0038] The initial process conditions are as follows: Raw materials: A mixture of acetic acid and ethanol, preheated to 25°C.

[0039] Reactor 103: operating temperature 110℃, the heat load to be removed due to the exothermic reaction is approximately 4500kW.

[0040] Distillation column 104: The operating pressure at the top of the column is 0.12 MPa (absolute pressure), the steam temperature at the top of the column is 92℃, the steam composition is approximately ethanol-water azeotrope (containing a small amount of ethyl acetate), the total heat load is approximately 5000 kW, and the required heat medium temperature for reboiler 105 is 135℃.

[0041] 2. Specific process flow and parameters Step 1: Esterification and Distillation The raw materials (acetic acid and ethanol) are pumped from the raw material storage tank 101, heated to 85°C in the raw material preheater 102, and then enter the reactor 103. Under the action of a catalyst, an esterification reaction is carried out at 110°C to produce ethyl acetate and water. The reaction product (crude ester) is discharged from the bottom of the reactor 103 and enters the distillation column 104 for separation. The bottom of the column yields ethyl acetate with a purity ≥99.5%, and the top of the column produces an ethanol-water-VOC vapor mixture at 92°C.

[0042] Step 2: Separation and VOC source interception The 92°C overhead steam mixture enters the condenser 201. By controlling the cooling water flow rate of the condenser 201, its internal temperature gradient is maintained between 85°C and 70°C. Under these conditions, most of the ethanol and higher-boiling-point VOC components are condensed.

[0043] High-VOC condensate 203 (temperature approximately 80°C, VOC concentration > 95 wt%) is returned to the upper part of distillation column 104 via second mixer 205 at a reflux ratio of 1.5. This step isolates more than 98% of the corrosive VOC components from heat pump unit 3.

[0044] Low-VOC vapor (temperature approximately 88°C, VOC concentration <200 ppm, mainly water vapor) is discharged from the top of the condenser 201 and enters the corrosion-resistant heat pump unit 3.

[0045] Step 3: Dual Heat Source Integration and Single-Stage Heat Pump Cycle Low-VOC vapor enters the heat pump evaporator 301 as the primary heat source for the first-stage cycle. Simultaneously, to remove the heat of the esterification reaction, the cooling medium of reactor 103 (heated from 110°C to 75°C by the reaction heat) is pumped to an absorber 5, where it absorbs heat, cools to 65°C, and returns to reactor 103. The heat absorbed by absorber 5 is transferred to an intermediate circulation working fluid, which then indirectly exchanges heat or mixes with the low-VOC vapor from the condenser 201 in the first mixer 204, jointly serving as the heat source for the heat pump evaporator 301, thereby increasing the total heat load of the evaporator 301 to approximately 6000kW.

[0046] Primary heat pump cycle: The working fluid (R1234ze) of the primary heat pump cycle evaporates at 35℃ / 0.3MPa in the evaporator 301; the evaporated working fluid gas is first purified by the molecular sieve adsorption module 403, and then enters the primary compressor 302, where it is compressed to 70℃ / 1.2MPa; the compressed high-temperature working fluid enters the heat exchanger 303, where it transfers heat to the working fluid of the secondary cycle. The working fluid of the primary heat pump cycle is then completely condensed, and the condensate 203 is throttled and depressurized by the primary throttling valve 304 before returning to the evaporator 301, completing the cycle.

[0047] Step 4: Two-stage heat pump cycle and high-temperature heating In heat exchanger 303, the heat released by the working fluid of the primary heat pump cycle causes the working fluid (R245fa) of the secondary heat pump cycle to evaporate.

[0048] Secondary heat pump cycle: The evaporated working fluid gas in the secondary heat pump cycle is also purified by the molecular sieve adsorption module 403, and then enters the secondary compressor 306, where it is compressed to 150℃ / 2.8MPa. This high-temperature and high-pressure working fluid enters the exothermic device 307, where it releases its latent heat of condensation to the medium water on the low-temperature side of the exothermic device 307. After the medium water is heated to 140℃, it is divided into three paths to provide heat to the raw material preheater 102, the distillation column 104, and the reboiler 105, and to supply hot water or steam to the outside. After being condensed in the exothermic device 307, the working fluid in the secondary heat pump cycle is throttled and depressurized by the secondary throttling valve 305 and returns to the heat exchanger 303, completing the cycle.

[0049] Step 5: Online working fluid purification and protection During system operation, VOC sensors 401 installed in the suction port pipes of the primary and secondary compressors 306 monitor the purity of the working fluid in real time; when the conductivity of either working fluid is detected to continuously exceed 4 μS / cm, the controller 402 automatically performs the following operations: The working fluid flow of this path is switched to another molecular sieve adsorption bed connected in parallel.

[0050] A portion of the high-temperature working fluid (approximately 150°C) discharged from the primary or secondary compressor 306 is introduced to the saturated adsorption bed for heating and regeneration. The desorbed trace amounts of VOCs are then extracted and properly treated.

[0051] Through the implementation of this embodiment, the system has achieved the following significant beneficial effects: Fundamentally solving corrosion problems and significantly extending equipment lifespan: In this embodiment, after treatment by the condenser 201, the VOC concentration of the steam entering the evaporator 301 is reduced from tens of thousands of ppm to below 200 ppm, eliminating the corrosion of the heat exchange tube walls by the VOC condensate 203 at the source. It is expected that the service life of key equipment such as the evaporator 301 can be extended from less than 2 years under the traditional direct recovery method to more than 10 years, synchronized with the unit's overhaul cycle, reducing maintenance costs by more than 70%.

[0052] The overall energy utilization efficiency is significantly improved, and energy consumption is drastically reduced: This embodiment successfully recovers the latent heat of steam at 92°C and the heat of reaction at 75°C, and raises it to 140°C for use in the esterification reaction process itself. The overall energy utilization rate of the system is more than 45% higher than that of the traditional process (cooling water for condensation at the top of the column, cooling water for the heat of reaction, and steam for reboiler 105). Specifically: Steam consumption: The steam required for reboiler 105 has been reduced from ~5.5 t / h to ~1.2 t / h, achieving an energy saving rate of over 78%; Cooling water consumption: The amount of cooling water used for condensation at the top of the tower and cooling of reactor 103 is reduced by approximately 85%; Heat pump performance: Thanks to the two-stage compression cycle, the system can still achieve a comprehensive COP of 5.8 under operating conditions with a temperature rise of up to 55°C, which is much higher than the COP of conventional single-stage heat pumps under the same operating conditions (about 3.0-3.5). Significant environmental benefits: The high-VOC condensate 203 separated by the condenser 201 is refluxed, so that almost all VOCs are consumed in the system. The total amount of VOCs emitted from the top of the tower is reduced by more than 98%, which is far below the national emission standards, thus achieving environmentally friendly production. The system operates stably and reliably: the dual-stage compression combined with the online working fluid purification unit enables the heat pump unit 3 to adapt to fluctuations in process load and always maintain efficient and stable operation, avoiding frequent shutdowns and performance degradation caused by corrosion and scaling.

[0053] In summary, this embodiment fully demonstrates the outstanding effects of the system described in this invention in solving corrosion problems, achieving deep energy conservation and consumption reduction, improving environmental protection levels, and ensuring long-term stable operation, and has extremely high industrial application value.

[0054] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments. Even if various changes are made to the present invention, if these changes fall within the scope of the claims of the present invention and their equivalents, they shall still fall within the protection scope of the present invention.

Claims

1. A waste heat recovery system for a distillation column used in a heat pump, characterized in that, include: The system includes a reaction and distillation unit, a condensation unit, and a heat pump unit. The reaction and distillation unit comprises a raw material storage tank, a raw material preheater, a reactor, and a distillation column, which are connected in sequence by pipelines. The bottom product of the distillation column is output from the bottom outlet, and the top vapor outlet of the distillation column is connected to the condensation unit. The condensation unit is used to separate VOC condensate and vapor, and the vapor provides a heat source for the heat pump unit.

2. The waste heat recovery system for a distillation column used in a heat pump according to claim 1, characterized in that, It also includes a heat absorber, the high-temperature side of which is connected to the cooling water of the reactor. An external medium enters the low-temperature side of the heat absorber to absorb heat, and the medium that absorbs heat provides a heat source for the heat pump unit.

3. The waste heat recovery system for a distillation column used in a heat pump according to claim 2, characterized in that, The heat pump unit includes a primary heat pump cycle and a secondary heat pump cycle. The primary heat pump cycle includes an evaporator, a primary compressor, a heat exchanger, and a primary throttling valve. The secondary heat pump cycle includes a secondary compressor, a secondary throttling valve, and a heat exchanger. The water vapor separated by the condensation unit and the water flowing out from the low-temperature side of the heat absorber enter the high-temperature side of the evaporator to heat the working fluid of the first-stage heat pump cycle. The working fluid of the first-stage heat pump cycle flows out from the low-temperature side of the evaporator and enters the first-stage compressor, the high-temperature side of the heat exchanger, and the first-stage throttling valve in sequence, before returning to the low-temperature side of the evaporator. The working fluid of the secondary heat pump cycle flows out from the low-temperature side of the heat exchanger, enters the secondary compressor, the high-temperature side of the heat exchanger, and the secondary throttling valve in sequence, and returns to the low-temperature side of the heat exchanger. The water flowing out from the high-temperature side of the evaporator is returned to the distillation column.

4. The waste heat recovery system for a distillation column used in a heat pump according to claim 3, characterized in that, The low-temperature side of the heat exchanger is connected to the raw material preheater and / or the reboiler of the distillation column to provide heat for the raw material or the steam required by the reboiler.

5. The waste heat recovery system for a distillation column used in a heat pump according to claim 3, characterized in that, It also includes an online purification unit, which includes a molecular sieve adsorption module, and the molecular sieve adsorption module is respectively installed in front of the air intake of the first-stage compressor and the second-stage compressor.

6. The waste heat recovery system for a distillation column used in a heat pump according to claim 5, characterized in that, The online purification unit also includes a VOC sensor, a regeneration controller, and a molecular sieve adsorption module. The VOC sensor is respectively installed on the intake pipes of the primary compressor and the secondary compressor. The signal input terminal of the controller is electrically connected to the VOC sensor, and the control input terminal of the controller is electrically connected to the molecular sieve adsorption module.

7. The waste heat recovery system for a distillation column used in a heat pump according to claim 1, characterized in that, The condensation unit includes a condenser, the top vapor outlet of the distillation column is connected to the condenser, and the vapor outlet of the condenser is connected to the heat pump unit.

8. The waste heat recovery system for a distillation column used in a heat pump according to claim 7, characterized in that, The liquid phase outlet of the condenser is connected to the upper reflux port of the distillation column.

9. The waste heat recovery system for a distillation column used in a heat pump according to claim 8, characterized in that, The condensation unit further includes a steam tank and a condensate tank. The top steam outlet of the distillation column is connected to the condenser, the steam outlet of the condenser is connected to the steam tank, and the steam tank is connected to the heat pump unit. The liquid phase outlet of the condenser is connected to the condensate tank, and the condensate tank is connected to the upper reflux port of the distillation column.

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