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

Abstract

The invention belongs to the technical field of gas recovery, and relates to a working mode switching method for VOCs recovery by an indirect heat exchange condensation method, a carrier circulating system is utilized, and the carrier circulating system comprises a first heat exchanger, a second heat exchanger, a heat-carrying agent tank, a secondary refrigerant tank and a valve assembly for controlling the flow direction of a carrier, the method includes: acquiring current states of a first heat exchanger and a second heat exchanger, and switching opening and closing states of a valve assembly according to requirements; a condensation mode is switched to a defrosting mode, so that a secondary refrigerant flows into the heat exchanger, and after flowing out, the secondary refrigerant is firstly introduced into the heat-carrying agent tank and then introduced into the secondary refrigerant tank; and when the defrosting mode is switched to the condensation mode, the heat-carrying agent flows into the heat exchanger, flows out and then is introduced into the secondary refrigerant tank, and then is introduced into the heat-carrying agent tank. According to the invention, the temperature in the secondary refrigerant tank and the heat-carrying agent tank can be prevented from greatly changing, the temperature of the secondary refrigerant and the heat-carrying agent can be kept stable in the switching process, and the condensation effect of VOCs and the defrosting effect of the heat exchanger are not influenced.

Description

Technical Field

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

[0002] VOCs (Volatile Organic Compounds) are important pollutants that affect air quality. Their emission sources are diverse, including petrochemical process exhaust, resource mining associated gas, and combustion products. With the acceleration of global industrialization, VOCs emissions have shown an increasing trend year by year, posing a serious threat to the atmospheric environment and human health.

[0003] As an effective VOCs treatment method, the condensation method reduces the temperature of each component in the VOCs gas to below its condensation point through multi-stage continuous cooling, thereby achieving the transformation from gas to liquid, which is convenient for subsequent recycling. In the condensation process, indirect heat exchange is usually adopted to improve the heat exchange efficiency and avoid the pollution problems that may be caused by direct contact between the refrigerant and the VOCs gas. That is, the refrigerant first exchanges heat with the intermediate cold (heat) carrier, and then the cold (heat) carrier exchanges heat with the VOCs gas.

[0004] However, in actual applications, the moisture in the VOCs gas will condense into frost during the condensation process. As time goes by, the frost layer gradually thickens, causing the VOCs channel of the heat exchanger to be blocked, affecting the heat exchange effect and gas circulation, and further affecting the normal operation of the VOCs recovery system. In order to solve this problem, it is necessary to add a defrost mode. However, in the process of switching between the condensation mode and the defrost mode, there are the following problems: 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 sharply, which will not only affect the defrosting effect of the heat exchanger and prolong the defrosting time, but also cause the temperature rise load of the refrigeration system to fluctuate, 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 the secondary condensing device, the refrigerant temperature in the refrigerant tank is about -35~-40℃; for the tertiary condensing device, the refrigerant temperature in the refrigerant tank is about -75~-80℃), causing the temperature in the refrigerant tank to suddenly increase significantly, 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.

[0005] 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.

[0006] It should be noted that the above information disclosed in this background technology section is only for understanding the background technology of the present inventive concept, and therefore, it may contain information that does not constitute the prior art. Summary of the invention

[0007] 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.

[0008] The technical solution provided by the present invention is as follows: a method for switching working modes for VOCs recovery by indirect heat exchange condensation method, using a carrier circulation system, the 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 direction 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; 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: first obtain the state of the valve assembly before switching, then switch the valve assembly, so that the brine flows from the brine tank into the second heat exchanger, and after flowing out, first enters the heat carrier tank for a duration of T1, and then enters the brine tank; so that the heat carrier flows from the heat carrier tank into the first heat exchanger, and after flowing out, first enters the brine tank for a duration of T2, and then enters the heat carrier tank; S2. When the first heat exchanger needs to be switched from the defrost mode to the condensation mode, and the second heat exchanger needs to be switched from the condensation mode to the defrost mode: 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 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.

[0009] 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, and 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 a large change in 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.

[0010] Based on the above technical solution, the present invention can also be improved as follows.

[0011] Further, 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.

[0012] 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.

[0013] 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 the coolant, and the heat carrier pump is arranged at the outlet of the heat carrier tank for pumping the heat carrier.

[0014] The beneficial effect of adopting the above further scheme 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.

[0015] Further, in step S1, the state before the valve assembly is switched 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: S11, opening the second coolant inlet valve and the second heat carrier outlet valve; S12, delaying for a period of time T1, closing the second heat carrier outlet valve, and opening the second coolant outlet valve; S13, closing the first coolant inlet valve and opening the first heat transfer agent inlet valve; S14, turn on the heat transfer agent pump; S15, delaying for a period of time T2, closing the first refrigerant outlet valve, and opening the first heat transfer agent outlet valve; S16, continue for a period of time TT1, and turn off the heat transfer agent pump; S17, closing the first heat carrier inlet valve and the first heat carrier outlet valve.

[0016] The beneficial effect of adopting the above further solution is that in step S1, a smooth transition from the condensation mode to the defrost mode is achieved through the opening and closing switching process of the valve assembly.

[0017] Further, in step S2, the state before the valve assembly is switched is that the second refrigerant inlet valve and the second refrigerant outlet valve are in an open state; the refrigerant pump is in an 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 a closed state, and the heat carrier pump is in a closed state. The valve assembly opening and closing switching process is as follows: S21, opening the first coolant inlet valve and the first heat carrier outlet valve; S22, delaying for a period of time T3, closing the first heat medium outlet valve, and opening the first coolant outlet valve; S23, closing the second coolant inlet valve and opening the second heat transfer agent inlet valve; S24, turn on the heat transfer agent pump; S25, delaying for a period of time T4, closing the second refrigerant outlet valve, and opening the second heat carrier outlet valve; S26, delay for a period of time TT2, and turn off the heat transfer agent pump; S27, close the second heat carrier inlet valve and the second heat carrier outlet valve.

[0018] The beneficial effect of adopting the above further scheme is that in step S2, a smooth transition from the condensing mode to the defrosting mode is achieved through the valve assembly opening and closing switching process. The present invention not only improves the overall performance of the carrier circulation system through the refrigerant pump and the heat carrier pump and the valve assembly opening and closing switching process, but also achieves a smooth transition from the condensing mode to the defrosting mode and from the defrosting mode back to the condensing mode, effectively avoiding the system load fluctuation problem caused by mode switching. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0020] Figure 1 It is a structural schematic diagram of the carrier circulation system of the present invention; In the figure, 1, the first heat exchanger; 2, the second heat exchanger; 3, the heat carrier tank; 4, the coolant tank; 5, the coolant pump; 6, the heat carrier pump; 7, the first coolant inlet valve; 8, the first coolant outlet valve; 9, the second heat carrier inlet valve; 10, the second heat carrier outlet valve; 11, the second coolant inlet valve; 12, the second coolant outlet valve; 13, the first heat carrier inlet valve; 14, the first heat carrier outlet valve. DETAILED DESCRIPTION

[0021] The serial numbers assigned to the components in this application, such as "first" and "second", are only used to distinguish the objects described, and do not imply any priority in order or specific technical meaning. In addition, the concepts of "connection" and "coupling" mentioned in this application, unless otherwise specified, are deemed to include both direct connection (coupling) and indirect connection (coupling).

[0022] When interpreting the description of this application, it is necessary to clarify that the terms such as "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc., which indicate positions or positional relationships, are based on the perspectives and layouts shown in the drawings, and are intended to facilitate explanation and simplify the description process, rather than being absolute limitations on the actual positions, construction methods, and operating modes of the devices or components. Therefore, these terms should not be understood as restrictive interpretations of the content of this application.

[0023] The principles and features of the present invention are described below in conjunction with examples. The examples are only used to explain the present invention and are not used to limit the scope of the present invention.

[0024] like Figure 1 As shown, a working mode switching method for VOCs recovery by indirect heat exchange condensation method, using 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, including the following steps: obtaining the current state of the first heat exchanger 1 and the second heat exchanger 2, and switching the opening and closing state 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, and then switch the valve assembly to allow the coolant to flow from the coolant tank 4 into the second heat exchanger 2, and then flow into the heat carrier tank 3 after flowing out, for a duration of T1, and then flow into the coolant tank 4; allow the heat carrier to flow from the heat carrier tank 3 into the first heat exchanger 1, and then flow into the coolant tank 4 after flowing out, for a duration of T2, and then flow 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, 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.

[0025] 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 refrigerant inlet valve 9, a second refrigerant outlet valve 10, a second refrigerant inlet valve 11, a second refrigerant outlet valve 12, a first refrigerant inlet valve 13 and a first refrigerant 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 refrigerant tank 3 through the first refrigerant inlet valve 13 and the first refrigerant outlet valve 14 to form a first refrigerant circulation path; the second heat exchanger 2 is connected to the refrigerant tank 3 through the second refrigerant inlet valve 9 and the second refrigerant outlet valve 10 to form a second refrigerant 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 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.

[0026] It also includes a coolant pump 5 and a heat carrier pump 6. The coolant pump 5 is arranged at the outlet of the coolant tank 4 for pumping the coolant, and the heat carrier pump 6 is arranged 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 arranging them at the outlets of the coolant tank 4 and the heat carrier tank 3, respectively, efficient and stable pumping of the coolant and the heat carrier is achieved.

[0027] In step S1, the state before the valve assembly is switched 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 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 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: S11, opening the second coolant inlet valve 11 and the second heat carrier outlet valve 10; S12, delaying for a period of time T1, closing the second heat carrier outlet valve 10, and opening the second coolant outlet valve 12; S13, close the first coolant inlet valve 7, and open the first heat transfer agent inlet valve 13; S14, turning on the heat transfer agent pump 6; S15, delay for a period of time T2, close the first refrigerant outlet valve 8, and open the first heat transfer agent outlet valve 14; S16, continue for a period of time TT1, and turn off the heat transfer agent pump 6; S17, close the first heat carrier inlet valve 13 and the first heat carrier outlet valve 14.

[0028] 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.

[0029] In step S2, the state before the valve assembly is switched 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 agent outlet valve 14; S22, delaying for a period of time T3, closing the first heat medium outlet valve 14, and opening the first coolant outlet valve 8; S23, close the second coolant inlet valve 11, and open the second heat transfer agent inlet valve 9; S24, turn 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 carrier outlet valve 10; S26, delay for a period of time TT2, and turn off the heat transfer agent pump 6; S27, close the second heat carrier inlet valve 9 and the second heat carrier outlet valve 10.

[0030] In step S2, a smooth transition from the condensing mode to the defrosting mode is achieved through the valve assembly opening and closing switching process. The present invention not only improves the overall performance of the carrier circulation system through the refrigerant pump 5 and the heat carrier pump 6 and the valve assembly opening and closing switching process, but also achieves a smooth transition from the condensing mode to the defrosting mode and from the defrosting mode back to the condensing mode, effectively avoiding the system load fluctuation problem caused by mode switching.

[0031] In this embodiment, the value range of time TT1 and time TT2 is set to 1h to 2h. At the same time, the value range of time T1, time T2, time T3 and time T4 is 30s to 180s. Of course, time T1, T2, T3, T4, TT1 and TT2 can also be set longer or shorter according to actual needs, usually based on the specific size of the first heat exchanger 1 and the second heat exchanger 2 to determine the length of time.

[0032] According to 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 4 by the heat carrier, and 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 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.

[0033] 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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for switching working modes for VOCs recovery by indirect heat exchange condensation method, using 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: Acquiring 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, the state of the valve assembly before switching is obtained, and then the valve assembly is switched, so that the coolant flows from the coolant tank (4) into the second heat exchanger (2), and after flowing out, it first flows into the heat carrier tank (3) for a duration of T1, and then flows into the coolant tank (4); the heat carrier flows from the heat carrier tank (3) into the first heat exchanger (1), and after flowing out, it 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, the state of the valve assembly before switching is obtained, and then the valve assembly is switched, so that the refrigerant flows from the refrigerant tank (4) into the first heat exchanger (1), and after flowing out, it first flows into the heat carrier tank (3) for a duration of T3, and then flows into the refrigerant tank (4); the heat carrier flows from the heat carrier tank (3) into the second heat exchanger (2), and after flowing out, it first flows into the refrigerant tank (4) for a duration of T4, and then flows into the heat carrier tank (3).

2. The working mode switching method for VOCs recovery by indirect heat exchange condensation method according to claim 1 is characterized in that: The first heat exchanger (1) and the second heat exchanger (2) are connected in parallel, and the valve assembly comprises 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) via the first refrigerant inlet valve (7) and the first refrigerant outlet valve (8), forming a first A refrigerant circulation path; the second heat exchanger (2) is connected to the refrigerant tank (4) via a second refrigerant inlet valve (11) and a second refrigerant outlet valve (12), thereby forming a second refrigerant circulation path; the first heat exchanger (1) is connected to the heat carrier tank (3) via a first heat carrier inlet valve (13) and a first heat carrier outlet valve (14), thereby forming a first heat carrier circulation path; the second heat exchanger (2) is connected to the heat carrier tank (3) via a second heat carrier inlet valve (9) and a second heat carrier outlet valve (10), thereby forming a second heat carrier circulation path.

3. The working mode switching method for VOCs recovery by indirect heat exchange condensation method according to claim 2 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).

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 S1, the valve assembly is in a state before switching, in which 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 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 a closed state; the heat carrier 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 carrier outlet valve (10); S12, delaying for a period of time T1, closing the second heat carrier 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 carrier outlet valve (14); S16, for a period of time TT1, turn off the heat transfer agent pump (6); S17, closing the first heat carrier inlet valve (13) and the first heat carrier outlet valve (14).

5. The working mode switching method for VOCs recovery by indirect heat exchange condensation method according to claim 4 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 carrier outlet valve (14); S22, delaying for a period of time T3, closing the first heat 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 carrier 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 carrier outlet valve (10); S26, delaying for a period of time TT2, and turning off the heat transfer agent pump (6); S27, closing the second heat carrier inlet valve (9) and the second heat carrier outlet valve (10).

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