Working mode switching method for VOCs recovery using indirect heat exchange condensation method

Abstract

The present invention belongs to the field of gas recovery technology and relates to a method for switching working modes for VOCs recovery using an indirect heat exchange condensation method. The method utilizes a carrier circulation system, which includes a first heat exchanger, a second heat exchanger, a heat carrier tank, a coolant tank, and a valve assembly for controlling the flow direction of the carrier. The method includes obtaining the current states of the first heat exchanger and the second heat exchanger and switching the opening and closing states of the valve assembly according to demand; switching from condensation mode to defrost mode, allowing the coolant to flow into the heat exchanger, and after flowing out, first passing into the heat carrier tank, and then into the coolant tank; when switching from defrost mode to condensation mode, allowing the heat carrier to flow into the heat exchanger, and after flowing out, first passing into the coolant tank, and then into the heat carrier tank. The present invention can avoid significant temperature changes in the coolant tank and the heat carrier tank, ensure that the temperatures of the coolant and the heat carrier remain stable during the switching process, and do not affect the condensation effect of VOCs and the defrosting effect of the heat exchanger.

Description

Technical Field

[0001] The invention relates to a working mode switching method for recovering VOCs using an indirect heat exchange condensation method, and belongs to the technical field of gas recovery. Background Art

[0002] VOCs (Volatile Organic Compounds), a significant pollutant affecting air quality, are emitted from a variety of sources, including petrochemical process exhaust, associated gas from resource extraction, and combustion products. With the acceleration of global industrialization, VOC emissions have been increasing annually, posing a serious threat to the atmospheric environment and human health.

[0003] Condensation is an effective VOC treatment method. Through multi-stage continuous cooling, the temperature of each component in the VOC gas is reduced to below its freezing point, thereby converting the gas into a liquid state and facilitating subsequent recycling. During the condensation process, indirect heat exchange is typically employed to improve heat exchange efficiency and avoid potential contamination from direct contact between the refrigerant and the VOC gas. This involves the refrigerant first exchanging heat with an intermediate refrigerant (or heat carrier), which then exchanges heat with the VOC gas.

[0004] However, in actual applications, the moisture in VOCs gas condenses into frost during the condensation process. Over time, the frost layer gradually thickens, causing the VOCs channel of the heat exchanger to become clogged, affecting the heat exchange effect and gas circulation, and thus affecting the normal operation of the VOCs recovery system. To solve this problem, it is necessary to add a defrost mode. However, when switching between condensation mode and defrost mode, the following problems arise:

[0005] When switching from condensing mode to defrosting mode, the original low-temperature refrigerant in the heat exchanger (for a two-stage condensing device, the temperature is about -35~-40℃; for a three-stage condensing device, the temperature is about -75~-80℃) will be gradually pushed out by the high-temperature heat carrier and passed into the heat carrier tank (the heat carrier temperature in the heat carrier tank is generally >20℃), causing the temperature in the heat carrier tank to suddenly drop significantly. This will not only affect the defrosting effect of the heat exchanger and prolong the defrosting time, but also cause fluctuations in the heating load of the refrigeration system, affecting the stability of the refrigeration system operation. Similarly, when switching from defrost mode to condensation mode, the original high-temperature heat carrier (>20℃) in the heat exchanger will be gradually pushed out by the low-temperature refrigerant and passed into the refrigerant tank (for a two-stage condensing device, the refrigerant temperature in the refrigerant tank is about -35~-40℃; for a three-stage condensing device, the refrigerant temperature in the refrigerant tank is about -75~-80℃), causing the temperature in the refrigerant tank to suddenly rise sharply, which will not only directly affect the condensation effect of the heat exchanger, causing the VOCs gas temperature to rise and affecting the recovery efficiency, but also cause the cooling load of the refrigeration system to fluctuate, further affecting the stability of the refrigeration system operation.

[0006] Therefore, a working mode switching method for VOCs recovery by indirect heat exchange condensation is needed to ensure the stable operation of the refrigeration system.

[0007] It should be noted that the above information disclosed in this Background section is only for understanding the background of the present inventive concept and therefore it may contain information that does not constitute the prior art. Summary of the Invention

[0008] The purpose of the present invention is to provide a new technical solution to improve or solve the technical problems existing in the prior art as described above.

[0009] The technical solution provided by the present invention is as follows: a method for switching working modes for VOCs recovery using an indirect heat exchange condensation method, utilizing a carrier circulation system comprising a first heat exchanger, a second heat exchanger, a heat carrier tank, a coolant tank, and a valve assembly for controlling the flow of the carrier, comprising the following steps: obtaining the current states of the first heat exchanger and the second heat exchanger, and switching the opening and closing states of the valve assembly according to demand;

[0010] S1. When the first heat exchanger needs to be switched from the condensing mode to the defrosting mode, and the second heat exchanger needs to be switched from the defrosting mode to the condensing mode at the same time: first, obtain the state of the valve assembly before switching, then switch the valve assembly to allow the brine to flow from the brine tank into the second heat exchanger, and after flowing out, first enter the heat carrier tank for a duration of T1, and then enter the brine tank; then allow the heat carrier to flow from the heat carrier tank into the first heat exchanger, and after flowing out, first enter the brine tank for a duration of T2, and then enter the heat carrier tank;

[0011] S2. When the first heat exchanger needs to be switched from the defrost mode to the condensing mode, and the second heat exchanger needs to be switched from the condensing mode to the defrost mode at the same time: first obtain the state of the valve assembly before switching, then switch the valve assembly to allow the refrigerant to flow from the refrigerant tank into the first heat exchanger, and after flowing out, first pass into the heat carrier tank for a duration of T3, and then pass into the refrigerant tank; allow the heat carrier to flow from the heat carrier tank into the second heat exchanger, and after flowing out, first pass into the refrigerant tank for a duration of T4, and then pass into the heat carrier tank.

[0012] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects: in the working mode switching method of the present invention, when the condensing mode is switched to the defrosting mode, the refrigerant with a lower temperature originally in the heat exchanger is first pushed into the refrigerant tank by the heat carrier; when the defrosting mode is switched to the condensing mode, the heat carrier with a higher temperature originally in the heat exchanger is first pushed into the heat carrier tank by the refrigerant, thereby avoiding large changes in the temperature in the refrigerant tank and the heat carrier tank, ensuring that the temperatures of the refrigerant and the heat carrier remain stable during the switching process, without affecting the condensation effect of VOCs and the defrosting effect of the heat exchanger, and avoiding fluctuations in the heating and cooling loads of the refrigeration system.

[0013] On the basis of the above technical solution, the present invention can also be improved as follows.

[0014] Furthermore, the first heat exchanger and the second heat exchanger are connected in parallel, and the valve assembly includes a first refrigerant inlet valve, a first refrigerant outlet valve, a second heat carrier inlet valve, a second heat carrier outlet valve, a second refrigerant inlet valve, a second refrigerant outlet valve, a first heat carrier inlet valve and a first heat carrier outlet valve. The first heat exchanger is connected to the refrigerant tank through the first refrigerant inlet valve and the first refrigerant outlet valve to form a first refrigerant circulation path; the second heat exchanger is connected to the refrigerant tank through the second refrigerant inlet valve and the second refrigerant outlet valve to form a second refrigerant circulation path; the first heat exchanger is connected to the heat carrier tank through the first heat carrier inlet valve and the first heat carrier outlet valve to form a first heat carrier circulation path; the second heat exchanger is connected to the heat carrier tank through the second heat carrier inlet valve and the second heat carrier outlet valve to form a second heat carrier circulation path.

[0015] The beneficial effect of adopting the above-mentioned further scheme is that the carrier circulation system of the present invention adopts two sets of heat exchangers in parallel, that is, the first heat exchanger and the second heat exchanger are arranged in parallel, and each has an independent refrigerant and heat carrier circulation path, one set is used for condensing VOCs gas, and the other set is used for heating and defrosting the frost layer. When one set of heat exchangers affects the condensation efficiency of VOCs gas due to the thickening of the frost layer, it can be quickly switched to the other set of heat exchangers to continue working, and the frosted heat exchanger can be defrosted at the same time, which not only ensures the continuity and efficiency of the VOCs recovery process, but also effectively avoids the problem of drastic fluctuations in the refrigeration system load caused by mode switching in traditional systems, thereby improving the stability and operation efficiency of the entire system.

[0016] Furthermore, it also includes a coolant pump and a heat carrier pump, the coolant pump is arranged at the outlet of the coolant tank for pumping coolant, and the heat carrier pump is arranged at the outlet of the heat carrier tank for pumping heat carrier.

[0017] The beneficial effect of adopting the above further solution is that by adding a coolant pump and a heat carrier pump and arranging them at the outlets of the coolant tank and the heat carrier tank respectively, efficient and stable pumping of the coolant and the heat carrier is achieved.

[0018] Furthermore, in step S1, the state of the valve assembly before switching is that the first refrigerant inlet valve and the first refrigerant outlet valve are in an open state; the refrigerant pump is in an open state; the second refrigerant inlet valve, the second refrigerant outlet valve, the first heat carrier inlet valve, the first heat carrier outlet valve, the second heat carrier inlet valve and the second heat carrier outlet valve are in a closed state, and the heat carrier pump is in a closed state. The valve assembly opening and closing switching process is as follows:

[0019] S11, opening the second coolant inlet valve and the second heat transfer outlet valve;

[0020] S12, delaying for a period of time T1, closing the second heat transfer medium outlet valve, and opening the second coolant outlet valve;

[0021] S13, closing the first coolant inlet valve and opening the first heat transfer agent inlet valve;

[0022] S14, turning on the heat transfer agent pump;

[0023] S15, delaying for a period of time T2, closing the first refrigerant outlet valve and opening the first heat transfer outlet valve;

[0024] S16, for a period of time TT1, turn off the heat transfer agent pump;

[0025] S17, closing the first heat carrier inlet valve and the first heat carrier outlet valve.

[0026] The beneficial effect of adopting the above further solution is that, in step S1, a smooth transition from the condensing mode to the defrosting mode is achieved through the opening and closing switching process of the valve assembly.

[0027] Furthermore, in step S2, the state of the valve assembly before switching is that the second refrigerant inlet valve and the second refrigerant outlet valve are in the open state; the refrigerant pump is in the open state; the first refrigerant inlet valve, the first refrigerant outlet valve, the second heat carrier inlet valve, the second heat carrier outlet valve, the first heat carrier inlet valve and the first heat carrier outlet valve are in the closed state, and the heat carrier pump is in the closed state. The valve assembly opening and closing switching process is as follows:

[0028] S21, opening the first coolant inlet valve and the first heat transfer outlet valve;

[0029] S22, delaying for a period of time T3, closing the first heat transfer medium outlet valve, and opening the first coolant outlet valve;

[0030] S23, close the second coolant inlet valve and open the second heat transfer agent inlet valve;

[0031] S24, turning on the heat transfer agent pump;

[0032] S25, delaying for a period of time T4, closing the second refrigerant outlet valve and opening the second heat transfer outlet valve;

[0033] S26, delay for a period of time TT2, and turn off the heat transfer agent pump;

[0034] S27, close the second heat carrier inlet valve and the second heat carrier outlet valve.

[0035] The beneficial effect of adopting the above further solution is that, in step S2, a smooth transition from condensing mode to defrost mode is achieved through the valve assembly opening and closing switching process. By utilizing the refrigerant pump and heat transfer pump, as well as the valve assembly opening and closing switching process, the present invention not only improves the overall performance of the carrier circulation system, but also achieves a smooth transition from condensing mode to defrost mode and back again, effectively avoiding system load fluctuations caused by mode switching. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0037] Figure 1 Schematic diagram of the structure of the carrier circulation system of the present invention;

[0038] In the figure, 1. first heat exchanger; 2. second heat exchanger; 3. heat carrier tank; 4. coolant tank; 5. coolant pump; 6. heat carrier pump; 7. first coolant inlet valve; 8. first coolant outlet valve; 9. second heat carrier inlet valve; 10. second heat carrier outlet valve; 11. second coolant inlet valve; 12. second coolant outlet valve; 13. first heat carrier inlet valve; 14. first heat carrier outlet valve. DETAILED DESCRIPTION

[0039] Component numbers herein, such as "first" and "second," are used solely to distinguish the components being described and do not imply any sequential priority or specific technical meaning. Furthermore, unless otherwise specified, the terms "connected" and "coupled" used in this application encompass both direct and indirect connections.

[0040] When interpreting the description of this application, it is important to clarify that the directions or positional relationships indicated by terms such as "upper," "lower," "front," "back," "left," "right," "vertical," "horizontal," "top," "bottom," "inside," "outside," "clockwise," and "counterclockwise" are based on the perspectives and layouts shown in the accompanying drawings and are intended to facilitate explanation and simplify the description process. They are not intended to be absolute limitations on the actual directions, constructions, and operating modes of the devices or components described. Therefore, these terms should not be construed as restrictive of the content of this application.

[0041] The principles and features of the present invention are described below with reference to examples. The examples are only used to explain the present invention and are not used to limit the scope of the present invention.

[0042] like Figure 1 As shown, a method for switching working modes for VOCs recovery using an indirect heat exchange condensation method utilizes a carrier circulation system. The carrier circulation system includes a first heat exchanger 1, a second heat exchanger 2, a heat carrier tank 3, a coolant tank 4, and a valve assembly for controlling the flow direction of the carrier. The method includes the following steps: obtaining the current status of the first heat exchanger 1 and the second heat exchanger 2, and switching the opening and closing status of the valve assembly according to demand;

[0043] S1. When the first heat exchanger 1 needs to be switched from the condensing mode to the defrosting mode, and the second heat exchanger 2 needs to be switched from the defrosting mode to the condensing mode at the same time: first, obtain the state of the valve assembly before switching, then switch the valve assembly to allow the brine to flow from the brine tank 4 into the second heat exchanger 2, and after flowing out, first enter the heat carrier tank 3 for a duration of T1, and then enter the brine tank 4; allow the heat carrier to flow from the heat carrier tank 3 into the first heat exchanger 1, and after flowing out, first enter the brine tank 4 for a duration of T2, and then enter the heat carrier tank 3;

[0044] S2. When the first heat exchanger 1 needs to be switched from the defrost mode to the condensing mode, and the second heat exchanger 2 needs to be switched from the condensing mode to the defrost mode at the same time: first obtain the state of the valve assembly before switching, and then switch the valve assembly to allow the refrigerant to flow from the refrigerant tank 4 into the first heat exchanger 1, and after flowing out, first pass into the heat carrier tank 3 for a duration of T3, and then pass into the refrigerant tank 4; allow the heat carrier to flow from the heat carrier tank 3 into the second heat exchanger 2, and after flowing out, first pass into the refrigerant tank 4 for a duration of T4, and then pass into the heat carrier tank 3.

[0045] The first heat exchanger 1 and the second heat exchanger 2 are connected in parallel, and the valve assembly includes a first refrigerant inlet valve 7, a first refrigerant outlet valve 8, a second heat carrier inlet valve 9, a second heat carrier outlet valve 10, a second refrigerant inlet valve 11, a second refrigerant outlet valve 12, a first heat carrier inlet valve 13 and a first heat carrier outlet valve 14. The first heat exchanger 1 is connected to the refrigerant tank 4 through the first refrigerant inlet valve 7 and the first refrigerant outlet valve 8 to form a first refrigerant circulation path; the second heat exchanger 2 is connected to the refrigerant tank 4 through the second refrigerant inlet valve 11 and the second refrigerant outlet valve 12 to form a second refrigerant circulation path; the first heat exchanger 1 is connected to the heat carrier tank 3 through the first heat carrier inlet valve 13 and the first heat carrier outlet valve 14 to form a first heat carrier circulation path; the second heat exchanger 2 is connected to the heat carrier tank 3 through the second heat carrier inlet valve 9 and the second heat carrier outlet valve 10 to form a second heat carrier circulation path. The carrier circulation system of the present invention adopts two sets of heat exchangers in parallel, that is, the first heat exchanger 1 and the second heat exchanger 2 are arranged in parallel, and each has an independent refrigerant and heat carrier circulation path, one set is used for condensing VOCs gas, and the other set is used for heating and defrosting the frost layer. When one set of heat exchangers affects the condensation efficiency of VOCs gas due to thickening of the frost layer, it can be quickly switched to the other set of heat exchangers to continue working, and at the same time, the frosted heat exchanger is defrosted. This not only ensures the continuity and efficiency of the VOCs recovery process, but also effectively avoids the problem of drastic fluctuations in the refrigeration system load caused by mode switching in traditional systems, thereby improving the stability and operation efficiency of the entire system.

[0046] The system further includes a coolant pump 5 and a heat carrier pump 6. The coolant pump 5 is disposed at the outlet of the coolant tank 4 for pumping the coolant, while the heat carrier pump 6 is disposed at the outlet of the heat carrier tank 3 for pumping the heat carrier. By adding the coolant pump 5 and the heat carrier pump 6, and disposing them at the outlets of the coolant tank 4 and the heat carrier tank 3, respectively, efficient and stable pumping of the coolant and heat carrier is achieved.

[0047] In step S1, the valve assembly is in the state before switching, that is, the first refrigerant inlet valve 7 and the first refrigerant outlet valve 8 are in the open state; the refrigerant pump 5 is in the open state; the second refrigerant inlet valve 11, the second refrigerant outlet valve 12, the first heat carrier inlet valve 13, the first heat carrier outlet valve 14, the second heat carrier inlet valve 9 and the second heat carrier outlet valve 10 are in the closed state, and the heat carrier pump 6 is in the closed state. The valve assembly opening and closing switching process is as follows:

[0048] S11, opening the second coolant inlet valve 11 and the second heat transfer outlet valve 10;

[0049] S12, delaying for a period of time T1, closing the second heat transfer medium outlet valve 10, and opening the second coolant outlet valve 12;

[0050] S13, close the first coolant inlet valve 7, and open the first heat transfer agent inlet valve 13;

[0051] S14, turning on the heat transfer agent pump 6;

[0052] S15, delaying for a period of time T2, closing the first refrigerant outlet valve 8, and opening the first heat transfer outlet valve 14;

[0053] S16, for a period of time TT1, turn off the heat transfer agent pump 6;

[0054] S17 , close the first heat carrier inlet valve 13 and the first heat carrier outlet valve 14 .

[0055] In step S1, a smooth transition from the condensing mode to the defrosting mode is achieved through the opening and closing switching process of the valve assembly.

[0056] In step S2, the valve assembly is in the state before switching, that is, the second refrigerant inlet valve 11 and the second refrigerant outlet valve 12 are in the open state; the refrigerant pump 5 is in the open state; the first refrigerant inlet valve 7, the first refrigerant outlet valve 8, the second heat carrier inlet valve 9, the second heat carrier outlet valve 10, the first heat carrier inlet valve 13 and the first heat carrier outlet valve 14 are in the closed state, and the heat carrier pump 6 is in the closed state. The valve assembly opening and closing switching process is as follows:

[0057] S21, opening the first coolant inlet valve 7 and the first heat transfer outlet valve 14;

[0058] S22, delaying for a period of time T3, closing the first heat transfer medium outlet valve 14, and opening the first coolant outlet valve 8;

[0059] S23, close the second coolant inlet valve 11, and open the second heat transfer agent inlet valve 9;

[0060] S24, turning on the heat transfer agent pump 6;

[0061] S25, delaying for a period of time T4, closing the second refrigerant outlet valve 12, and opening the second heat transfer outlet valve 10;

[0062] S26, delay for a period of time TT2, and turn off the heat transfer agent pump 6;

[0063] S27 , close the second heat carrier inlet valve 9 and the second heat carrier outlet valve 10 .

[0064] In step S2, a smooth transition from condensing mode to defrost mode is achieved through the valve assembly opening and closing switching process. The present invention, through the refrigerant pump 5 and the heat transfer pump 6, and the valve assembly opening and closing switching process, not only improves the overall performance of the carrier circulation system, but also achieves a smooth transition from condensing mode to defrost mode and back again, effectively avoiding system load fluctuations caused by mode switching.

[0065] In this embodiment, the time TT1 and time TT2 are set to a range of 1 hour to 2 hours. Meanwhile, the time T1, time T2, time T3, and time T4 are all set to a range of 30 seconds to 180 seconds. Of course, the time T1, T2, T3, T4, TT1, and TT2 can also be set longer or shorter based on actual needs, and are generally determined based on the specific dimensions of the first heat exchanger 1 and the second heat exchanger 2.

[0066] The working mode switching method of the present invention is that when the condensing mode is switched to the defrosting mode, the refrigerant with a lower temperature originally in the heat exchanger is first pushed into the refrigerant tank 4 by the heat carrier; when the defrosting mode is switched to the condensing mode, the heat carrier with a higher temperature originally in the heat exchanger is first pushed into the heat carrier tank 3 by the refrigerant, thereby avoiding a large change in the temperature in the refrigerant tank 4 and the heat carrier tank 3, ensuring that the temperatures of the refrigerant and the heat carrier remain stable during the switching process, not affecting the condensation effect of VOCs and the defrosting effect of the heat exchanger, and avoiding fluctuations in the heating and cooling loads of the refrigeration system.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for switching working modes for VOCs recovery using an indirect heat exchange condensation method, utilizing a carrier circulation system, wherein the carrier circulation system comprises a first heat exchanger (1), a second heat exchanger (2), a heat carrier tank (3), a coolant tank (4), and a valve assembly for controlling the flow direction of the carrier, characterized in that: The following steps are involved: Obtaining the current status of the first heat exchanger (1) and the second heat exchanger (2), and switching the opening and closing status of the valve assembly according to demand; S1. When the first heat exchanger (1) needs to be switched from the condensing mode to the defrosting mode, and the second heat exchanger (2) needs to be switched from the defrosting mode to the condensing mode: first, obtain the state of the valve assembly before switching, then switch the valve assembly, so that the coolant flows from the coolant tank (4) into the second heat exchanger (2), and after flowing out, first flows into the heat carrier tank (3), for a duration of T1, and then flows into the coolant tank (4); so that the heat carrier flows from the heat carrier tank (3) into the first heat exchanger (1), and after flowing out, first flows into the coolant tank (4), for a duration of T2, and then flows into the heat carrier tank (3); S2, when the first heat exchanger (1) needs to be switched from the defrost mode to the condensation mode, and the second heat exchanger (2) needs to be switched from the condensation mode to the defrost mode: first, obtain the state of the valve assembly before switching, then switch the valve assembly, so that the coolant flows from the coolant tank (4) into the first heat exchanger (1), and after flowing out, first flows into the heat carrier tank (3), for a duration of T3, and then flows into the coolant tank (4); so that the heat carrier flows from the heat carrier tank (3) into the second heat exchanger (2), and after flowing out, first flows into the coolant tank (4), for a duration of T4, and then flows into the heat carrier tank (3); The first heat exchanger (1) and the second heat exchanger (2) are connected in parallel, and the valve assembly includes a first coolant inlet valve (7), a first coolant outlet valve (8), a second heat carrier inlet valve (9), a second heat carrier outlet valve (10), a second coolant inlet valve (11), a second coolant outlet valve (12), a first heat carrier inlet valve (13) and a first heat carrier outlet valve (14). The first heat exchanger (1) is connected to the coolant tank (4) through the first coolant inlet valve (7) and the first coolant outlet valve (8), forming a first A refrigerant circulation path; the second heat exchanger (2) is connected to the refrigerant tank (4) through a second refrigerant inlet valve (11) and a second refrigerant outlet valve (12), forming a second refrigerant circulation path; the first heat exchanger (1) is connected to the heat carrier tank (3) through a first heat carrier inlet valve (13) and a first heat carrier outlet valve (14), forming a first heat carrier circulation path; the second heat exchanger (2) is connected to the heat carrier tank (3) through a second heat carrier inlet valve (9) and a second heat carrier outlet valve (10), forming a second heat carrier circulation path.

2. The working mode switching method for VOCs recovery by indirect heat exchange condensation according to claim 1 is characterized in that: It also includes a coolant pump (5) and a heat carrier pump (6), wherein the coolant pump (5) is arranged at the outlet of the coolant tank (4), and the heat carrier pump (6) is arranged at the outlet of the heat carrier tank (3).

3. The working mode switching method for VOCs recovery by indirect heat exchange condensation method according to claim 2 is characterized in that: In step S1, the state of the valve assembly before switching is that the first refrigerant inlet valve (7) and the first refrigerant outlet valve (8) are in an open state; the refrigerant pump (5) is in an open state; the second refrigerant inlet valve (11), the second refrigerant outlet valve (12), the first heat transfer agent inlet valve (13), the first heat transfer agent outlet valve (14), the second heat transfer agent inlet valve (9) and the second heat transfer agent outlet valve (10) are in a closed state, and the heat transfer agent pump (6) is in a closed state. The valve assembly opening and closing switching process is as follows: S11, opening the second coolant inlet valve (11) and the second heat transfer agent outlet valve (10); S12, delaying for a period of time T1, closing the second heat transfer medium outlet valve (10), and opening the second coolant outlet valve (12); S13, closing the first coolant inlet valve (7) and opening the first heat transfer agent inlet valve (13); S14, turning on the heat transfer agent pump (6); S15, delaying for a period of time T2, closing the first refrigerant outlet valve (8), and opening the first heat transfer outlet valve (14); S16, for a period of time TT1, turning off the heat transfer agent pump (6); S17, closing the first heat transfer agent inlet valve (13) and the first heat transfer agent outlet valve (14).

4. The working mode switching method for VOCs recovery by indirect heat exchange condensation method according to claim 3 is characterized in that: In step S2, the state of the valve assembly before switching is that the second refrigerant inlet valve (11) and the second refrigerant outlet valve (12) are in an open state; the refrigerant pump (5) is in an open state; the first refrigerant inlet valve (7), the first refrigerant outlet valve (8), the second heat carrier inlet valve (9), the second heat carrier outlet valve (10), the first heat carrier inlet valve (13) and the first heat carrier outlet valve (14) are in a closed state, and the heat carrier pump (6) is in a closed state. The valve assembly opening and closing switching process is as follows: S21, opening the first coolant inlet valve (7) and the first heat transfer outlet valve (14); S22, delaying for a period of time T3, closing the first heat transfer medium outlet valve (14), and opening the first coolant outlet valve (8); S23, closing the second coolant inlet valve (11) and opening the second heat transfer agent inlet valve (9); S24, turning on the heat transfer agent pump (6); S25, delaying for a period of time T4, closing the second refrigerant outlet valve (12), and opening the second heat transfer outlet valve (10); S26, delaying for a period of time TT2 and turning off the heat transfer agent pump (6); S27, close the second heat transfer agent inlet valve (9) and the second heat transfer agent outlet valve (10).

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