A method for treating VOC S Multi-stage gradient indirect condensation device and process for waste gas

Abstract

The invention discloses a method for treating VOC S The multi-stage gradient indirect condensation device and process of waste gas, which involves the technical field of waste gas treatment, respectively forms waste gas condensation channel A and waste gas condensation channel B, which are connected in parallel, and the condensers of the same stage are connected in parallel to the same cooling device and each forms a cooling loop with the cooling device, each cooling device is connected to a refrigeration unit, and the last stage refrigeration unit is connected to a heat carrier, and the condensers of the same stage are connected in parallel to the heat carrier and each forms a heat carrier loop with the heat carrier. The cooling medium is used as a buffer for the heat balance in the system to ensure that the VOC-containing S The waste gas obtains a stable condensation temperature and recovery treatment effect when the gas volume and composition change.

Description

Technical Field

[0001] The present invention relates to a VOC-containing S The technical field of waste gas treatment, particularly a method for treating VOC S Multi-stage gradient indirect condensation device and process for waste gas. Background Art

[0002] The petroleum and chemical industries produce VOCs during the production, storage and transportation of oil products. S The exhaust gas discharged into the atmosphere will cause air pollution, and due to the flammable and toxic properties of organic matter, direct exhaust gas discharge will also cause safety hazards in the factory area. S The exhaust gas discharged into the atmosphere causes environmental pollution and brings potential safety hazards. According to the requirements of relevant national laws and regulations, it is necessary to S The exhaust gas is treated to reduce the VOC S It can only be discharged into the atmosphere when the content drops below the prescribed limit.

[0003] Existing VOC S The waste gas treatment process includes two types: recovery method and destruction method. The recovery method includes condensation method, absorption method, adsorption method, and membrane separation method. The destruction method includes thermal storage combustion method, catalytic oxidation method, and direct combustion method. S Concentration exceeds 30000mg / Nm 3 In the process of waste gas treatment, the recovery method is given priority to recover the effective components in the waste gas, reduce the waste of resources, and obtain certain economic benefits while reducing pollution. S It will be separated in liquid form and is the most commonly used VOC S Waste gas treatment process.

[0004] The traditional condensation process is to pass the exhaust gas directly into the evaporator of the mechanical refrigeration system, and use the evaporation heat absorption of the refrigerant to achieve the purpose of cooling the exhaust gas. According to the relevant standards for the treatment of volatile organic compounds, the treatment device needs to be designed according to the maximum load, and the volume and composition of the exhaust gas generated during the storage and transportation of oil products are always in a variable state and the range of variation is very wide. At the lowest point, no exhaust gas is even generated, which causes the exhaust gas treatment device to operate under low load for most of the time. For mechanical refrigeration devices, when the load is less than 50%, the refrigeration compressor cannot operate stably, which not only affects the condensation treatment effect of the exhaust gas, but also causes frequent shutdown alarms of the equipment, or even damage.

[0005] Therefore, in order to ensure that the VOC STo achieve the condensation treatment effect of exhaust gas, it is necessary to improve the traditional condensation process to enhance the stability of the condensation process and its adaptability to refrigeration load fluctuations. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a method for treating VOC S The multi-stage gradient indirect condensation device of the exhaust gas includes a condenser and a refrigeration unit.

[0007] The condenser includes a multi-stage exhaust gas condenser A and a multi-stage exhaust gas condenser B. The multi-stage exhaust gas condenser A and the multi-stage exhaust gas condenser B each include at least two condensers connected in series to form an exhaust gas condensation channel A and an exhaust gas condensation channel B respectively. The exhaust gas condensation channel A and the exhaust gas condensation channel B are connected in parallel and then connected to the same exhaust gas recovery device. All condensers are connected to the same VOC S Recovery device;

[0008] The same-stage condensers of the exhaust gas condensation channel A and the exhaust gas condensation channel B are connected to the same cooling device in parallel and each forms a cooling loop with the cooling device. Each stage of the cooling device is connected to a refrigeration unit. Each stage of the cooling device and each stage of the refrigeration unit are equipped according to the condensation temperature and the refrigeration load to form a multi-stage gradient condensation.

[0009] The last stage refrigeration unit is connected to a heat carrier, and the same stage condensers of the exhaust gas condensation channel A and the exhaust gas condensation channel B are connected to the heat carrier in parallel and each forms a heat carrier circuit with the heat carrier, and all condensers are connected to the same heat carrier.

[0010] Technical effect: The present invention introduces a cooling medium, and during the operation of the device, the cooling medium is used to store and transfer cold to indirectly cool the VOC-containing S Exhaust gas, through the temperature of the refrigerant, adjusts the operating load of each level of refrigeration units and controls the start and stop of the units. When the amount or composition of exhaust gas changes and the required cooling capacity becomes smaller, the cold capacity stored in the refrigerant can play a buffering role, avoiding frequent fluctuations in the operating load of the refrigeration unit or start and stop, which may cause unstable operation or damage of the refrigeration compressor, so that the device can operate stably for a long time.

[0011] The technical solution further defined in the present invention is:

[0012] A method of treating VOC as described above S The multi-stage gradient indirect condensation device for exhaust gas, the multi-stage exhaust gas condenser A includes a primary exhaust gas condenser A, a secondary exhaust gas condenser A and a tertiary exhaust gas condenser A, and the multi-stage exhaust gas condenser B includes a primary exhaust gas condenser B, a secondary exhaust gas condenser B and a tertiary exhaust gas condenser B.

[0013] A method of treating VOC as described above SA multi-stage gradient indirect condensation device for exhaust gas, wherein the cooling device comprises a primary cooling device, a secondary cooling device and a tertiary cooling device, wherein the primary cooling device comprises a primary cooling medium pump and a primary cooling medium storage tank, the secondary cooling device comprises a secondary cooling medium pump and a secondary cooling medium storage tank, the tertiary cooling device comprises a tertiary cooling medium pump and a tertiary cooling medium storage tank, and the cooling medium pump, the cooling medium storage tank and the condenser form a cooling circuit.

[0014] A method of treating VOC S A multi-stage gradient indirect condensation device for exhaust gas, the refrigeration unit includes a primary refrigeration unit, a secondary refrigeration unit and a tertiary refrigeration unit, the primary refrigeration unit includes a primary refrigeration evaporator and a primary refrigeration compressor, the secondary refrigeration unit includes a secondary refrigeration evaporator and a secondary refrigeration compressor, the tertiary refrigeration unit includes a tertiary refrigeration evaporator, a tertiary low-temperature side refrigeration compressor and a tertiary high-temperature side refrigeration compressor, the tertiary low-temperature side refrigeration compressor and the tertiary high-temperature side refrigeration compressor operate independently.

[0015] A method of treating VOC S The multi-stage gradient indirect condensation device of the exhaust gas, the heat carrier device comprises a heat carrier pump and a heat carrier storage tank, the heat carrier pump, the heat carrier storage tank and the condenser form a heat carrier circuit.

[0016] A method of treating VOC S Multi-stage gradient indirect condensation device for exhaust gas, VOC S The recovery device includes a recovery oil storage tank and a recovery oil delivery pump. The rear end of the recovery oil storage tank is connected to the recovery oil delivery pump. The exhaust gas condensation channel A and the exhaust gas condensation channel B are connected to the recovery oil storage tank through the recovery oil circuit A and the recovery oil circuit B respectively. Each stage of the condenser of the exhaust gas condensation channel A is connected to the recovery oil circuit A respectively, and each stage of the condenser of the exhaust gas condensation channel B is connected to the recovery oil circuit A respectively.

[0017] A method of treating VOC S Multi-stage gradient indirect condensation device for exhaust gas, VOC S The recovery device also includes a liquid level meter, which is arranged on the recovery oil storage tank.

[0018] A method of treating VOC S In a multi-stage gradient indirect condensation device for exhaust gas, the cooling medium and the heating medium adopt the same organic matter.

[0019] A method of treating VOC S The multi-stage gradient indirect condensation device of the exhaust gas, the switching of the exhaust gas condensation channel A and the exhaust gas condensation channel B, and the switching of condensation and heating are automatically controlled by the switch valve.

[0020] Another object of the present invention is to provide a method for treating VOC SThe multi-stage gradient indirect condensation process of waste gas specifically includes:

[0021] S1. According to the VOC content in the exhaust gas S The concentration and type of each condenser are selected to select the appropriate condensation temperature and evenly distribute the VOC at each level. S Condensation capacity: each stage of condenser is equipped with a refrigeration unit and a cooling device according to the condensation temperature and refrigeration load;

[0022] S2. After each refrigeration unit is in operation, the cooling medium enters the refrigeration unit to cool down, bringing the cooling capacity of the system out of the refrigeration unit, and the low-temperature cooling medium enters the corresponding condenser;

[0023] S3. When the temperature of the cooling medium reaches the set value, VOC S The exhaust gas enters the condensers at each level in turn, and the exhaust gas temperature gradually decreases. S Most of it is condensed and separated from the gas, becoming liquid or solid at low temperatures;

[0024] S4. Due to VOC S Solid or high-viscosity liquid will be formed at low temperatures. After running for a period of time, the pressure in the exhaust gas condensation channel will increase, and the substances attached to the pipe wall will affect the heat exchange efficiency between the exhaust gas and the cooling medium. Therefore, after the exhaust gas condensation channel A has been running for a period of time, it is necessary to switch to the exhaust gas condensation channel B to continue condensing the exhaust gas;

[0025] S5. At the same time, the exhaust gas condensation channel A enters the heating stage. First, the cooling medium in each condenser in the exhaust gas condensation channel A is discharged into the respective cooling devices, and then the heating medium at 45°C is introduced, and the heating device is started to heat the condenser to melt the solid matter, so that the VOC separated in the condensation operation stage is S Inflow of VOC S Recovery device;

[0026] S6. After the exhaust gas condensation channel A completes heating and defrosting, the heat-carrying medium in each level of condensers is exhausted, and the cooling medium is injected again to pre-cool the exhaust gas condensation channel A. After the exhaust gas condensation channel B has been condensing for a period of time, it is switched to the exhaust gas condensation channel A to continue condensing the exhaust gas, and the exhaust gas condensation channel B enters the heating stage. During the operation of the device, the exhaust gas condensation channel A and the exhaust gas condensation channel B are cyclically switched to perform condensation and heating operations;

[0027] S7. The condensed low-temperature exhaust gas is heated to above 5°C through the exhaust gas heat regenerator using the heat generated by the refrigeration unit during operation, and then sent out of the device.

[0028] The beneficial effects of the present invention are:

[0029] (1) In the present invention, the heat carrier and the cooling medium are made of the same organic compound, so that when the condenser switches between condensation and heating operations, the cooling medium and the heat carrier can still maintain their quality and performance in the presence of residues and exchanges between them;

[0030] (2) The heat of the heat carrier in the present invention is taken from the heat generated during the operation of the refrigeration unit, and the heat carrier is heated by the heat exchanger, thereby reducing the operating cost of the device and improving the economic benefits;

[0031] (3) In the present invention, the organic matter in the condensed and recovered waste gas is collected in a recovered oil storage tank and then sent out of the device by a recovered oil delivery pump for recycling;

[0032] (4) In the present invention, appropriate condensation temperatures are selected for each condenser to evenly distribute VOC at each level. S Condensation capacity, to avoid a large amount of organic matter condensing in a certain stage of condenser, which will cause the resistance to increase rapidly;

[0033] (5) The present invention uses a cooling medium to indirectly cool the exhaust gas. The system controls the temperature of the cooling medium. When the exhaust gas condensation channel is switched, the condensation temperature fluctuates slightly, which can ensure the condensation treatment effect and obtain a stable VOC S Removal rate;

[0034] (6) The present invention utilizes a cooling medium to store cold energy, and the refrigeration unit can be shut down when the load is low. According to the characteristics of oil storage and transportation exhaust, the device operates at a low load most of the time. When it operates for a long time, it can save electricity and reduce the operating cost of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic diagram of the system of the present invention;

[0036] Among them: 1. Primary exhaust gas condenser A; 2. Primary exhaust gas condenser B; 3. Secondary exhaust gas condenser A; 4. Secondary exhaust gas condenser B; 5. Third-stage exhaust gas condenser A; 6. Third-stage exhaust gas condenser B; 7. Exhaust gas regenerator; 8. Primary cooling medium pump; 9. Primary cooling medium storage tank; 10. Primary refrigeration evaporator; 11. Primary refrigeration compressor; 12. Secondary cooling medium pump; 13. Secondary cooling medium storage tank; 14. Secondary refrigeration evaporator; 15. Secondary refrigeration compressor; 16. Third-stage cooling medium pump; 17. Third-stage cooling medium storage tank; 18. Third-stage refrigeration evaporator; 19. Third-stage high-temperature side refrigeration compressor; 20. Recovery oil storage tank; 21. Recovery oil delivery pump; 22. Heat carrier storage tank; 23. Third-stage low-temperature refrigeration compressor; 24. Heat carrier pump. DETAILED DESCRIPTION

[0037] This embodiment provides a method for treating VOC SMulti-stage gradient indirect condensation device for exhaust gas, such as Figure 1 As shown, it includes a multi-stage exhaust gas condenser A and a multi-stage exhaust gas condenser B. The multi-stage exhaust gas condenser A includes a primary exhaust gas condenser A1, a secondary exhaust gas condenser A3 and a tertiary exhaust gas condenser A5. The multi-stage exhaust gas condenser B includes a primary exhaust gas condenser B2, a secondary exhaust gas condenser B4 and a tertiary exhaust gas condenser B6, which are connected in series to form an exhaust gas condensation channel A and an exhaust gas condensation channel B, respectively. The exhaust gas condensation channel A and the exhaust gas condensation channel B are connected in parallel and then connected to the same exhaust gas recovery device. The switching of the exhaust gas condensation channel A and the exhaust gas condensation channel B, as well as the switching of condensation and heating are automatically controlled by the switch valve.

[0038] All condensers are connected to the same VOC S Recovery device, VOC S The recovery device includes a recovery oil storage tank 20 and a recovery oil delivery pump 21. The recovery oil storage tank 20 is connected to the recovery oil delivery pump 21 at the rear end. A liquid level gauge is also provided on the recovery oil storage tank 20. The exhaust gas condensation channel A and the exhaust gas condensation channel B are connected to the recovery oil storage tank 20 through the recovery oil circuit A and the recovery oil circuit B respectively. Each stage of the condenser of the exhaust gas condensation channel A is connected to the recovery oil circuit A respectively, and each stage of the condenser of the exhaust gas condensation channel B is connected to the recovery oil circuit A respectively.

[0039] The same-level condensers of the exhaust gas condensation channel A and the exhaust gas condensation channel B are connected to the same cooling device in parallel and each forms a cooling loop with the cooling device. Each level of cooling device is connected to a refrigeration unit. Each level of cooling device and each level of refrigeration unit are equipped according to the condensation temperature and refrigeration load to form a multi-stage gradient condensation. The refrigeration unit adopts circulating water or air cooling. The cooling device includes a first-level cooling device, a second-level cooling device and a third-level cooling device. The first-level cooling device includes a first-level cooling medium pump 8 and a first-level cooling medium storage tank 9. The second-level cooling device includes a second-level cooling medium pump 12 and a second-level cooling medium storage tank 13. The third-level cooling device includes a third-level cooling medium pump 16 and a third-level cooling medium storage tank 17. The cooling medium pump, the cooling medium storage tank and the condenser form a cooling loop. The refrigeration unit includes a primary refrigeration unit, a secondary refrigeration unit and a tertiary refrigeration unit. The primary refrigeration unit includes a primary refrigeration evaporator 10 and a primary refrigeration compressor 11. The secondary refrigeration unit includes a secondary refrigeration evaporator 14 and a secondary refrigeration compressor 15. The tertiary refrigeration unit includes a tertiary refrigeration evaporator 18, a tertiary low-temperature side refrigeration compressor and a tertiary high-temperature side refrigeration compressor 19. The tertiary low-temperature side refrigeration compressor and the tertiary high-temperature side refrigeration compressor 19 operate independently.

[0040] The last stage of the refrigeration unit is connected to a heat carrier. The condensers of the same stage of the exhaust gas condensation channel A and the exhaust gas condensation channel B are connected to the heat carrier in parallel and each forms a heat carrier loop with the heat carrier. All condensers are connected to the same heat carrier. The heat carrier includes a heat carrier pump 24 and a heat carrier tank 22. The heat carrier pump 24, the heat carrier tank 22 and the condenser form a heat carrier loop. The cooling medium and the heat carrier use the same organic matter.

[0041] The process flow of the above device is as follows:

[0042] When in use, the first-stage cooling medium storage tank 9, the second-stage cooling medium storage tank 13 and the third-stage cooling medium storage tank 17 are filled with cooling medium, and the heat medium storage tank 22 is filled with heat medium, and the first-stage cooling medium pump 8, the second-stage cooling medium pump 12 and the third-stage cooling medium pump 16 are started to make the cooling medium of each stage begin to circulate, and the cooling medium circulates through the first-stage exhaust gas condenser A1, the second-stage exhaust gas condenser A3 and the third-stage exhaust gas condenser A5, and the first-stage refrigeration compressor 11, the second-stage refrigeration compressor 15, the third-stage high-temperature side refrigeration compressor 19 and the third-stage low-temperature side refrigeration compressor are started, and the mechanical refrigeration unit starts to work, and the refrigerant in each stage of the refrigeration unit evaporates in the first-stage refrigeration evaporator 10, the second-stage refrigeration evaporator 14 and the third-stage refrigeration evaporator 18, and absorbs the heat of the circulating cooling medium during the evaporation process to reduce the temperature of the cooling medium. When the temperature of the circulating cooling medium at each stage drops to the set value, the VOC-containing S The exhaust gas is introduced into the exhaust gas condenser A1, the second exhaust gas condenser A3 and the third exhaust gas condenser A5 in sequence. The temperature of the exhaust gas is gradually reduced, and the VOC in the exhaust gas is S The components are separated from the exhaust gas due to supersaturation and converted into solid or high-viscosity liquid under low-temperature conditions. The low-temperature exhaust gas at the outlet of the three-stage exhaust gas condenser A5 enters the exhaust gas reheater 77 and is heated to above 5°C before exiting the device. At the same time, the heat generated by the three-stage refrigeration compression work is used to heat the heat carrier in the heat carrier storage tank 22.

[0043] After the exhaust gas is condensed in the condensers of the exhaust gas condensation channel A for a period of time, the VOC S The substances adhere to the surface of the condenser, increasing the resistance of the condenser and reducing the heat exchange efficiency of the condenser. In order to ensure the operation effect of the device, the system switches the exhaust gas condensation channel in the device. Before switching, the first-stage exhaust gas condenser B2, the second-stage exhaust gas condenser B4 and the third-stage exhaust gas condenser B6 in the exhaust gas condensation channel B are filled with cooling medium to pre-cool the condenser of the exhaust gas condensation channel B. Then, the exhaust gas and the cooling medium are circulated and switched into the first-stage exhaust gas condenser B2, the second-stage exhaust gas condenser B4 and the third-stage exhaust gas condenser B6 at the same time. At this time, the exhaust gas enters the exhaust gas condensation channel B to continue cooling and separate the VOCs therein. S substance.

[0044] The exhaust gas condensation channel A enters the heating stage. Before heating, the cooling medium in the first-stage exhaust gas condenser A1, the second-stage exhaust gas condenser A3 and the third-stage exhaust gas condenser A5 in the exhaust gas condensation channel A is discharged into the respective cooling medium storage tanks. After being discharged, the heat carrier pump 24 is started to send the heat carrier into the first-stage exhaust gas condenser A1, the second-stage exhaust gas condenser A3 and the third-stage exhaust gas condenser A5 and start circulation. The heat carrier heats the condenser in the exhaust gas condensation channel A, so that the VOC attached to the condenser tube wall is S The material heats up and flows into the recovery oil storage tank 20. A level gauge is provided on the recovery oil storage tank 20. When the recovered oil reaches a certain level, the recovery oil delivery pump 21 is started to send the recovered oil out of the device for reuse. After the condenser in the exhaust gas condensation channel A has finished heating up, the heat carrier is discharged into the heat carrier storage tank 22. After it is completely discharged, the first-stage exhaust gas condenser A1, the second-stage exhaust gas condenser A3 and the third-stage exhaust gas condenser A5 are filled with cooling medium for pre-cooling in preparation for the next switch. After the exhaust gas has been condensed for a period of time through the exhaust gas condensation channel B, it is switched again according to the change in resistance drop. The exhaust gas condensation channel A condenses the exhaust gas, and the exhaust gas condensation channel B enters the heating stage.

[0045] During operation, the exhaust gas condensation channel A and the exhaust gas condensation channel B are switched cyclically according to the operation conditions to ensure the long-term stable operation of the device. When the refrigeration load decreases due to changes in the exhaust gas volume and composition, the refrigerant plays the role of storing cold capacity. The refrigeration compressors in the refrigeration units at all levels adjust the operating load or start and stop according to the temperature of the refrigerant storage tank, and control the temperature of the refrigerant at all levels within a certain range. While ensuring the exhaust gas cooling effect, it can avoid operating failures or equipment damage caused by the refrigeration compressor working under low load.

[0046] The invention is reasonably designed and can ensure that the device operates stably and the exhaust gas condensation effect is stable when the exhaust gas volume and composition change. S The removal rate of substances is stable, and the cold storage function of the refrigerant allows the refrigeration compressor to shut down at low load, reducing the operating energy consumption of the device and saving costs.

[0047] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. A method for treating VOC S The multi-stage gradient indirect condensation device of exhaust gas comprises a condenser and a refrigeration unit, and is characterized in that: The condenser includes a multi-stage exhaust gas condenser A and a multi-stage exhaust gas condenser B. The multi-stage exhaust gas condenser A and the multi-stage exhaust gas condenser B each include at least two condensers connected in series to form an exhaust gas condensation channel A and an exhaust gas condensation channel B respectively. The exhaust gas condensation channel A and the exhaust gas condensation channel B are connected in parallel and then connected to the same exhaust gas recovery device. All condensers are connected to the same VOC S Recovery device; The condensers of the same level of the exhaust gas condensation channel A and the exhaust gas condensation channel B are connected to the same cooling device in parallel and each forms a cooling circuit with the cooling device. Each level of the cooling device is connected to the refrigeration unit. Each level of the cooling device and each level of the refrigeration unit are equipped according to the condensation temperature and the refrigeration load to form a multi-stage gradient condensation. The last stage of the refrigeration unit is connected to a heat carrier, and the condensers of the same stage of the exhaust gas condensation channel A and the exhaust gas condensation channel B are connected to the heat carrier in parallel and each forms a heat carrier circuit with the heat carrier, and all condensers are connected to the same heat carrier; The refrigeration unit comprises a primary refrigeration unit, a secondary refrigeration unit and a tertiary refrigeration unit, the primary refrigeration unit comprises a primary refrigeration evaporator (10) and a primary refrigeration compressor (11), the secondary refrigeration unit comprises a secondary refrigeration evaporator (14) and a secondary refrigeration compressor (15), the tertiary refrigeration unit comprises a tertiary refrigeration evaporator (18), a tertiary low-temperature side refrigeration compressor and a tertiary high-temperature side refrigeration compressor (19), the tertiary low-temperature side refrigeration compressor and the tertiary high-temperature side refrigeration compressor (19) operating independently; The heat carrier device comprises a heat carrier fluid pump (24) and a heat carrier fluid storage tank (22); the heat carrier fluid pump (24), the heat carrier fluid storage tank (22) and a condenser form a heat carrier circuit.

2. A method for treating VOC according to claim 1 S The multi-stage gradient indirect condensation device for exhaust gas is characterized by: The multi-stage exhaust gas condenser A comprises a primary exhaust gas condenser A (1), a secondary exhaust gas condenser A (3) and a tertiary exhaust gas condenser A (5), and the multi-stage exhaust gas condenser B comprises a primary exhaust gas condenser B (2), a secondary exhaust gas condenser B (4) and a tertiary exhaust gas condenser B (6).

3. A method for treating VOC according to claim 2 S The multi-stage gradient indirect condensation device for exhaust gas is characterized by: The cooling device comprises a primary cooling device, a secondary cooling device and a tertiary cooling device; the primary cooling device comprises a primary cooling medium pump (8) and a primary cooling medium storage tank (9); the secondary cooling device comprises a secondary cooling medium pump (12) and a secondary cooling medium storage tank (13); the tertiary cooling device comprises a tertiary cooling medium pump (16) and a tertiary cooling medium storage tank (17); the cooling medium pump, the cooling medium storage tank and the condenser form a cooling circuit.

4. A method for treating VOC according to claim 1 S The multi-stage gradient indirect condensation device for exhaust gas is characterized by: The VOC S The recovery device comprises a recovery oil storage tank (20) and a recovery oil delivery pump (21); the recovery oil storage tank (20) is connected to the recovery oil delivery pump (21) at the rear end; the exhaust gas condensation channel A and the exhaust gas condensation channel B are connected to the recovery oil storage tank (20) via a recovery oil circuit A and a recovery oil circuit B, respectively; each stage of the condenser of the exhaust gas condensation channel A is connected to the recovery oil circuit A, respectively; and each stage of the condenser of the exhaust gas condensation channel B is connected to the recovery oil circuit A, respectively.

5. A method for treating VOC according to claim 4 S The multi-stage gradient indirect condensation device for exhaust gas is characterized by: The VOC S The recovery device also includes a liquid level meter, which is arranged on the recovered oil storage tank (20).

6. A method for treating VOC according to claim 1 S The multi-stage gradient indirect condensation device for exhaust gas is characterized by: The cooling medium and the heating medium adopt the same organic matter.

7. A method for treating VOC according to claim 1 S The multi-stage gradient indirect condensation device for exhaust gas is characterized by: The switching between the exhaust gas condensation channel A and the exhaust gas condensation channel B, and the switching between condensation and heating are automatically controlled by a switch valve.

8. A method for treating VOC S The multi-stage gradient indirect condensation process of waste gas is characterized by: Applicable to any one of claims 1 to 7, specifically comprising: S1. According to the VOC content in the exhaust gas S The concentration and type of each condenser are selected to select the appropriate condensation temperature and evenly distribute the VOC at each level. S Condensation capacity: each stage of condenser is equipped with a refrigeration unit and a cooling device according to the condensation temperature and refrigeration load; S2. After each refrigeration unit is in operation, the cooling medium enters the refrigeration unit to cool down, bringing the cooling capacity of the system out of the refrigeration unit, and the low-temperature cooling medium enters the corresponding condenser; S3. When the temperature of the cooling medium reaches the set value, VOC S The exhaust gas enters the condensers at each level in turn, and the exhaust gas temperature gradually decreases. S Most of it is condensed and separated from the gas, becoming liquid or solid at low temperatures; S4. Due to VOC S Solid or high-viscosity liquid will be formed at low temperatures. After running for a period of time, the pressure in the exhaust gas condensation channel will increase, and the substances attached to the pipe wall will affect the heat exchange efficiency between the exhaust gas and the cooling medium. Therefore, after the exhaust gas condensation channel A has been running for a period of time, it is necessary to switch to the exhaust gas condensation channel B to continue condensing the exhaust gas; S5. At the same time, the exhaust gas condensation channel A enters the heating stage. First, the cooling medium in each condenser in the exhaust gas condensation channel A is discharged into the respective cooling devices, and then the heating medium at 45°C is introduced, and the heating device is started to heat the condenser to melt the solid matter, so that the VOC separated in the condensation operation stage is S Inflow of VOC S Recovery device; S6. After the exhaust gas condensation channel A completes heating and defrosting, the heat-carrying medium in each level of condensers is exhausted, and the cooling medium is injected again to pre-cool the exhaust gas condensation channel A. After the exhaust gas condensation channel B has been condensing for a period of time, it is switched to the exhaust gas condensation channel A to continue condensing the exhaust gas, and the exhaust gas condensation channel B enters the heating stage. During the operation of the device, the exhaust gas condensation channel A and the exhaust gas condensation channel B are cyclically switched to perform condensation and heating operations; S7. The condensed low-temperature exhaust gas is heated to above 5°C through the exhaust gas regenerator (7) using the heat generated by the refrigeration unit during operation, and then sent out of the device.

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