A condensation and refrigeration device for VOCs tail gas

Abstract

The present application discloses a condensation and freezing device for VOCs tail gas, including a condenser, a freezer, a nitrogen feed main pipe and a tail gas feed main pipe. Both the condenser and the freezer adopt a heat exchanger structure; the inlet of the liquid nitrogen feed main pipe is connected to the liquid nitrogen system, and the outlet of the liquid nitrogen feed main pipe is divided into two ways to discharge liquid nitrogen, which are respectively sent to the condenser tube and the freezer tube for heat exchange; the low-temperature nitrogen generated in the condenser tube and the low-temperature nitrogen generated in the freezer tube are collected into the low-temperature nitrogen main pipe, and the outlet of the low-temperature nitrogen main pipe is connected to the nitrogen downstream system; the inlet of the tail gas feed main pipe is introduced into the VOCs tail gas, and the outlet of the tail gas feed main pipe is connected to the lower inlet of the condenser shell, and the upper outlet of the condenser shell is connected to the inlet of the freezer shell through a pipeline, and the purified tail gas discharged from the freezer shell outlet is sent to the tail gas downstream system. The device of the present application can effectively reduce the VOC in the tail gas S content, while recovering VOCs components, reducing the load of the post-processing device, and having high safety and environmental protection performance.

Description

Technical Field

[0001] The present application relates to a condensation and refrigeration device for VOCs tail gas. Background Art

[0002] Currently, in the field of VOCs treatment, condensation is an effective treatment method for VOCs tail gas with high concentration and low freezing point. However, in the actual production process, its operating status and recovery efficiency are greatly affected by the cooling temperature, cold utilization efficiency and temperature control accuracy of the coolant. If the cooling temperature of the coolant is low, the actual recovery efficiency is low. If the cold utilization efficiency of the overall solution is low, the economic efficiency of the device is poor. If the temperature control accuracy is poor, the composition of the outlet VOCS fluctuates greatly, affecting the treatment of downstream devices and resulting in excessive tail gas emissions. Summary of the Invention

[0003] The purpose of this application is to provide a condensation and refrigeration device for VOCs tail gas to address the process defects of existing condensation and freezing recovery treatment. The device of this application recovers and treats the VOCs components of the tail gas and is suitable for related enterprises with high-concentration VOCs tail gas emissions with low freezing points.

[0004] The condensation and refrigeration device for VOCs tail gas is characterized by comprising a condenser, a freezer, a liquid nitrogen feed main pipe and a tail gas feed main pipe, wherein the condenser and the freezer both adopt a shell-and-tube heat exchanger structure; the inlet of the liquid nitrogen feed main pipe is connected to the liquid nitrogen system, and the outlet of the liquid nitrogen feed main pipe is divided into two ways to discharge liquid nitrogen, one way of feeding the liquid nitrogen into the condenser tube side for heat exchange through the sixth pipeline, and the other way of feeding the liquid nitrogen into the freezer tube side for heat exchange through the seventh pipeline; the low-temperature nitrogen generated by heat exchange in the condenser tube side is collected through the eighth pipeline and the low-temperature nitrogen generated by heat exchange in the freezer tube side is collected through the ninth pipeline to the low-temperature nitrogen main pipe, and the outlet of the low-temperature nitrogen main pipe is connected to the nitrogen downstream system;

[0005] VOCs tail gas is introduced into the tail gas feed main inlet, and the tail gas feed main outlet is connected to the lower inlet of the condenser shell side, and the upper outlet of the condenser shell side is connected to the freezer shell side inlet through a pipeline. The purified tail gas discharged from the freezer shell side outlet is sent to the tail gas downstream system through the fourth pipeline.

[0006] The VOCs tail gas condensation and freezing device is characterized by further comprising a recovery liquid storage tank, a liquid outlet is provided at the bottom of the condenser shell, and the generated VOCs condensate is sent to the recovery liquid storage tank through the fourteenth pipeline.

[0007] The condensation and refrigeration device for VOCs tail gas is characterized in that a liquid outlet is provided at the bottom of the freezer shell, which is connected to the recovery liquid storage tank through the sixteenth pipeline; the lower part of the freezer shell is also connected to the eleventh pipeline for introducing hot gas.

[0008] The condensation and refrigeration device for VOCs tail gas is characterized by further comprising a demister, a heat exchange jacket being provided on the outside of the demister, a twelfth pipeline being connected to the low-temperature nitrogen main pipe, the other end of the twelfth pipeline being connected to the heat exchange jacket on the outside of the demister so as to allow low-temperature nitrogen to be passed to the outside of the demister to cool and keep the demister as a whole cold, and a thirteenth pipeline for discharging nitrogen being connected to the heat exchange jacket on the outside of the demister;

[0009] The cooled tail gas discharged from the shell side outlet of the condenser is sent to the demister through the second pipeline for defoaming. The liquid intercepted in the demister is sent to the recovery liquid storage tank through the fifteenth pipeline. The defoamed tail gas discharged from the demister is sent to the shell side of the freezer through the third pipeline.

[0010] The VOCs tail gas condensing and freezing device is characterized in that a first thermometer and a second regulating valve are provided on the eighth pipeline, and a first regulating valve is correspondingly provided on the sixth pipeline, and the first thermometer is connected to the first regulating valve signal through a PLC control system; when the nitrogen temperature detected by the first thermometer is higher or lower than the set value, the PLC control system is used to feedback and control the increase or decrease of the opening of the first regulating valve;

[0011] A second thermometer is provided on the second pipeline, and the second thermometer is connected to the first regulating valve and the second regulating valve signal through the PLC control system;

[0012] When the condenser condenses the VOCs exhaust gas normally, the second thermometer performs independent feedback control on the second regulating valve through the PLC control system. When the exhaust temperature detected by the second thermometer is lower or higher than the set value, the PLC control system provides feedback and controls the opening of the second regulating valve to be lowered or raised, so that the exhaust temperature detected by the second thermometer is within the set value range.

[0013] When the condenser over-condenses the VOCs exhaust gas so that the exhaust gas temperature detected by the second thermometer is lower than the critical abnormal value of condensation, the second thermometer transmits the abnormal signal to the PLC control system, and the PLC control system feedbacks and controls the lowering of the opening of the first regulating valve and the second regulating valve until the exhaust gas temperature detected by the second thermometer rises to within the set value range, and then restores the separate feedback control of the first regulating valve by the first thermometer through the PLC control system, and restores the separate feedback control of the second regulating valve by the second thermometer through the PLC control system; wherein, the first regulating valve and the second regulating valve preferentially respond to the signal sent from the second thermometer through the PLC control system.

[0014] The VOCs tail gas condensing and freezing device is characterized in that a third thermometer and a fourth regulating valve are provided on the ninth pipeline, and a third regulating valve is correspondingly provided on the seventh pipeline, and the third thermometer is connected to the third regulating valve signal through a PLC control system; when the nitrogen temperature detected by the third thermometer is higher or lower than the set value, the PLC control system is used to feedback and control the increase or decrease of the opening of the third regulating valve;

[0015] A fourth thermometer is provided on the fourth pipeline, and the fourth thermometer is connected to the third regulating valve and the fourth regulating valve through a PLC control system;

[0016] When the freezer is performing normal freezing on the exhaust gas after defoaming, the fourth thermometer performs independent feedback control on the fourth regulating valve through the PLC control system. When the exhaust temperature detected by the fourth thermometer is lower or higher than the set value, the PLC control system provides feedback and controls the opening of the fourth regulating valve to be lowered or raised so that the exhaust temperature detected by the fourth thermometer is within the set value range.

[0017] When the freezer over-freezes the exhaust gas after defoaming so that the exhaust gas temperature detected by the fourth thermometer is lower than the freezing critical abnormal value, the fourth thermometer transmits the abnormal signal to the PLC control system, which feeds back and controls the opening of the third regulating valve and the fourth regulating valve through the PLC control system until the exhaust gas temperature detected by the fourth thermometer rises to within the set value range, and then restores the independent feedback control of the third regulating valve by the third thermometer through the PLC control system, and restores the independent feedback control of the fourth regulating valve by the fourth thermometer through the PLC control system; wherein, the third regulating valve and the fourth regulating valve preferentially respond to the signal sent from the fourth thermometer through the PLC control system.

[0018] Compared with the prior art, the beneficial effects achieved by this application are:

[0019] This application can effectively treat VOCs components in tail gas, especially for high-concentration low-freezing point exhaust gas. The device of this application can not only effectively recover VOCs, greatly reduce the concentration of VOCs in the tail gas, and reduce the processing load of subsequent devices. At the same time, it can also greatly reduce the investment in subsequent VOCs treatment solutions. The treatment efficiency of this set of devices for VOCs components in tail gas is above 98%. Taking the subsequent activated carbon adsorption as an example, the effective recovery of VOCs by the device of this application can greatly reduce the consumption of activated carbon, reducing the consumption of activated carbon to 1 / 50 of the original. It can improve the economic benefits of enterprises and reduce the emission of environmental pollutants. It is especially suitable for related enterprises with high-concentration VOCs tail gas emissions containing low freezing points. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1This is a schematic diagram of the structure of the condensation and refrigeration device for VOCs tail gas in this application. DETAILED DESCRIPTION

[0021] The present invention will be further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto.

[0022] Example: Control Figure 1

[0023] A condensation and freezing device for VOCs tail gas comprises a condenser I, a demister II, a freezer III, a liquid nitrogen feed main pipe 5, and a tail gas feed main pipe 1. The condenser I and the freezer III both adopt a shell-and-tube heat exchanger structure. The inlet of the liquid nitrogen feed main pipe 5 is connected to a liquid nitrogen system, and the outlet of the liquid nitrogen feed main pipe 5 is divided into two paths for discharging liquid nitrogen. One path feeds the liquid nitrogen into the tube side of the condenser I through a sixth pipeline 6 for heat exchange, and the other path feeds the liquid nitrogen into the freezer III through a seventh pipeline 7 for heat exchange. In actual operation, the flow rate of liquid nitrogen introduced into the tube side of the condenser I is relatively large, while the flow rate of liquid nitrogen introduced into the tube side of the freezer III is relatively small. Since the VOCs components in the VOCs tail gas have more condensation phase variables in the shell side of condenser I, and the heat exchange with the liquid nitrogen introduced into the tube side of condenser I is large, when the process control is relatively stable, even if the flow rate of liquid nitrogen introduced into the tube side of condenser I is relatively large, the VOCs components in the VOCs tail gas will not be frozen in the shell side of condenser I.

[0024] The low-temperature nitrogen generated by heat exchange in the condenser I tube pass is collected through the eighth pipeline 8 and the low-temperature nitrogen generated by heat exchange in the freezer III tube pass is collected through the ninth pipeline 9 to the low-temperature nitrogen main pipe 10, and the outlet of the low-temperature nitrogen main pipe 10 is connected to the nitrogen downstream system.

[0025] VOCs tail gas is introduced into the tail gas feed main pipe 1 inlet, and the tail gas feed main pipe 1 outlet is connected to the lower inlet of the condenser I shell side, and the upper outlet of the condenser I shell side is then connected to the shell side inlet of the freezer III through a pipeline. The purified tail gas discharged from the shell side outlet of the freezer III is sent to the tail gas downstream system through the fourth pipeline 4.

[0026] Furthermore, the apparatus of the present application includes a recovery liquid storage tank IV. A liquid outlet is provided at the bottom of the shell side of condenser I, and the generated VOC condensate is delivered to recovery liquid storage tank IV via a fourteenth pipeline 14. The cryogenic nitrogen generated by the vaporization of liquid nitrogen in the tube side of condenser I is delivered to a cryogenic nitrogen main 10 via an eighth pipeline 8.

[0027] A liquid outlet is located at the bottom of the shell side of freezer III, connected to the recovery liquid storage tank IV via the sixteenth pipeline 16. The lower portion of freezer III is also connected to the eleventh pipeline 11 for introducing hot gas. Normally, the liquid outlet at the bottom of freezer III does not discharge liquid. The exhaust gas is cooled to its freezing point, causing the VOCs in the gas to solidify within the shell side of freezer III. Consequently, the pressure differential as the exhaust gas enters freezer III gradually increases. When the pressure differential as the exhaust gas enters freezer III exceeds 2 kPa (adjustable as needed), the liquid nitrogen feed to freezer III is shut off, and hot gas is introduced into the lower portion of freezer III via the eleventh pipeline 11 to melt the solid VOCs. The condensed VOCs are then transferred to the recovery liquid storage tank IV via the sixteenth pipeline 16. After the two-step condensation and freezing process, the purified exhaust gas is delivered to the downstream exhaust system via the fourth pipeline 4. This downstream exhaust system can further adsorb the purified exhaust gas using an activated carbon adsorption device to achieve emission standards.

[0028] Furthermore, the device of the present application also includes a demister II, a heat exchange jacket is provided on the outside of the demister II, and a twelfth pipeline 12 is also connected to the low-temperature nitrogen main pipe 10, and the other end of the twelfth pipeline 12 is connected to the heat exchange jacket on the outside of the demister II so as to introduce low-temperature nitrogen into the outside of the demister II to cool and keep the demister II as a whole cold. A thirteenth pipeline 13 for discharging nitrogen is also connected to the heat exchange jacket on the outside of the demister II.

[0029] The cooled tail gas discharged from the shell side outlet of condenser I is sent to the demister II through the second pipeline 2 for defoaming. The liquid intercepted in the demister II is sent to the recovery liquid storage tank IV through the fifteenth pipeline 15. The defoamed tail gas discharged from the demister II is sent to the shell side of the freezer III through the third pipeline 3.

[0030] When the VOCs tail gas is treated by the device of the present application: the tail gas first passes through the condenser and is cooled by the coolant liquid nitrogen. More than 95% of the VOCs components in the tail gas are condensed into liquid and flow into the recovery liquid storage tank by gravity. The tail gas then passes through the demister to remove the entrained droplets. The gas after defoaming is sent to the freezer, and the liquid intercepted by the demister is sent to the recovery liquid storage tank. The small amount of VOCs remaining in the tail gas is reduced to below the freezing point by liquid nitrogen in the freezer and adsorbed in the freezer. The purified tail gas is discharged to the post-processing section. The coolant liquid nitrogen used in the device of the present application controls the flow of liquid nitrogen entering the condenser and freezer under the action of the supporting control system, and efficiently distributes the cooling capacity to cool the tail gas to within the set value range.

[0031] The process of controlling the flow of liquid nitrogen into the condenser and the freezer by the device of the present application is as follows:

[0032] The eighth pipeline 8 is provided with a first thermometer T1 and a second regulating valve, and the sixth pipeline 6 is correspondingly provided with a first regulating valve. The first thermometer T1 is connected to the first regulating valve signal through a PLC control system; when the nitrogen temperature detected by the first thermometer T1 is higher or lower than the set value, the PLC control system is used to feedback and control the increase or decrease of the opening of the first regulating valve.

[0033] A second thermometer T2 is provided on the second pipeline 2, and the second thermometer T2 is connected to the first regulating valve and the second regulating valve signal through the PLC control system;

[0034] When the condenser 1 is condensing the VOCs tail gas normally, the second thermometer T2 performs independent feedback control on the second regulating valve through the PLC control system. When the tail gas temperature detected by the second thermometer T2 is lower or higher than the set value, the PLC control system provides feedback and controls the opening of the second regulating valve to be lowered or raised, so that the tail gas temperature detected by the second thermometer T2 is within the set value range;

[0035] When the condenser I over-condenses the VOCs exhaust gas so that the exhaust gas temperature detected by the second thermometer T2 is lower than the critical abnormal value of condensation, the second thermometer T2 transmits the abnormal signal to the PLC control system, and the PLC control system feedbacks and controls the opening of the first regulating valve and the second regulating valve to be lowered until the exhaust gas temperature detected by the second thermometer T2 rises to within the set value range, and then the first thermometer T1 and the second thermometer T2 are restored to the separate feedback control of the first regulating valve through the PLC control system, and the second thermometer T2 and the second regulating valve are restored to the separate feedback control; wherein, the first regulating valve and the second regulating valve preferentially respond to the signal sent from the second thermometer T2 through the PLC control system.

[0036] The ninth pipeline 9 is provided with a third thermometer T3 and a fourth regulating valve, and the seventh pipeline 7 is correspondingly provided with a third regulating valve. The third thermometer T3 is connected to the third regulating valve through a PLC control system. When the nitrogen temperature detected by the third thermometer T3 is higher or lower than the set value, the PLC control system provides feedback and controls the increase or decrease of the opening of the third regulating valve.

[0037] A fourth thermometer T4 is provided on the fourth pipeline 4, and the fourth thermometer T4 is connected to the third regulating valve and the fourth regulating valve through a PLC control system;

[0038] When the freezer III is performing normal freezing of the defoamed exhaust gas, the fourth thermometer T4 performs independent feedback control on the fourth regulating valve through the PLC control system. When the exhaust gas temperature detected by the fourth thermometer T4 is lower than or higher than the set value, the PLC control system provides feedback and controls the opening of the fourth regulating valve to be lowered or raised, so that the exhaust gas temperature detected by the fourth thermometer T4 is within the set value range.

[0039] When the freezer III over-freezes the exhaust gas after defoaming so that the exhaust gas temperature detected by the fourth thermometer T4 is lower than the freezing critical abnormal value, the fourth thermometer T4 transmits the abnormal signal to the PLC control system, and the PLC control system feedbacks and controls the opening of the third regulating valve and the fourth regulating valve to be lowered or raised until the exhaust gas temperature detected by the fourth thermometer T4 rises to within the set value range, and then the third thermometer T3 and the fourth thermometer T4 are restored to their separate feedback control over the third regulating valve through the PLC control system, and the fourth thermometer T4 and the fourth regulating valve are restored to their separate feedback control through the PLC control system; wherein, the third regulating valve and the fourth regulating valve preferentially respond to the signal sent from the fourth thermometer T4 through the PLC control system.

[0040] The condensing and freezing device of the present application is suitable for treating high-concentration VOCs exhaust gas in which the freezing points of all main components differ slightly. For example, if the freezing points of all main components in the high-concentration VOCs exhaust gas differ by only 30°C, the use of the condensing and freezing device of the present application can achieve better technical effects.

[0041] In high-concentration VOCs exhaust gas, the lowest value of the freezing points of all main components is recorded as the lowest freezing temperature. Then, when the condensation refrigeration device of this application treats high-concentration VOCs exhaust gas:

[0042] The set value range for the second thermometer T2 can be 10-30°C above the minimum freezing temperature. During the control and adjustment process, if the actual exhaust gas temperature detected by the second thermometer T2 is 1-2°C lower or higher than the set value, it should be assumed that Condenser I is condensing the VOC exhaust gas normally, and the control process stability is good. However, if Condenser I over-condenses the VOC exhaust gas, the temperature of the cooled exhaust gas discharged from the shell-side outlet of Condenser I will drop too much, which is not conducive to process control. A critical condensation abnormality value can be set to further control the situation. This critical condensation abnormality value can be 5-20°C lower than the set value of the second thermometer T2.

[0043] The set value range for the fourth thermometer T4 can be 1 to 30°C below the minimum freezing temperature. During the control and adjustment process, if the actual exhaust gas temperature detected by the fourth thermometer T4 is 1 to 2°C lower or higher than the set value, it should be assumed that the freezer III is performing normal freezing treatment on the defoamed exhaust gas, and the control process stability is good. However, if the freezer III overfreezes the defoamed exhaust gas, the temperature of the cooled exhaust gas discharged by the freezer III will drop too much, which is not conducive to process control. A critical freezing abnormality value can be set. This critical freezing abnormality value can be 5 to 20°C lower than the set value of the fourth thermometer T4.

[0044] For example, when the condensing refrigeration device of the present application processes tail gas containing saturated piperylene:

[0045] The set value range of the second thermometer T2 can be -60 to -90°C, and the critical condensation abnormal value can be 5 to 20°C lower than the set value of the second thermometer T2. For example, if the set value of the second thermometer T2 is -70°C, the critical condensation abnormal value is -80°C.

[0046] The set value range of the fourth thermometer T4 can be -95 to -120°C, and the critical freezing abnormal value can be 5 to 20°C lower than the set value of the fourth thermometer T4. For example, the set value of the fourth thermometer T4 is -110°C, and the critical freezing abnormal value is -120°C.

[0047] When using the condensation and refrigeration device of this application to treat tail gas containing saturated piperylene, the VOC recovery rate in the tail gas can reach over 98%. The tail gas treated by the condensation and refrigeration device of this application can be sent to a downstream tail gas system, where an activated carbon adsorption device can be used to further adsorb and treat the purified tail gas before it meets emission standards.

[0048] The contents described in this specification are merely an enumeration of implementation forms of the inventive concept, and the protection scope of the present invention should not be considered as being limited to the specific forms described in the embodiments.

Claims

1. A condensation and refrigeration device for VOCs tail gas, characterized in that The invention comprises a condenser (I), a freezer (III), a liquid nitrogen feed main pipe (5) and a tail gas feed main pipe (1), wherein the condenser (I) and the freezer (III) both adopt a shell-and-tube heat exchanger structure; the inlet of the liquid nitrogen feed main pipe (5) is connected to the liquid nitrogen system, and the outlet of the liquid nitrogen feed main pipe (5) is divided into two ways to discharge liquid nitrogen, one way is to send the liquid nitrogen into the condenser (I) tube pass through the sixth pipeline (6) for heat exchange, and the other way is to send the liquid nitrogen into the freezer (III) tube pass through the seventh pipeline (7) for heat exchange; the low-temperature nitrogen generated by heat exchange in the condenser (I) tube pass is collected through the eighth pipeline (8) and the low-temperature nitrogen generated by heat exchange in the freezer (III) tube pass is collected through the ninth pipeline (9) to the low-temperature nitrogen main pipe (10), and the outlet of the low-temperature nitrogen main pipe (10) is connected to the nitrogen downstream system; The VOCs tail gas is introduced into the tail gas feed main pipe (1) inlet, the tail gas feed main pipe (1) outlet is connected to the lower shell side inlet of the condenser (I), the upper shell side outlet of the condenser (I) is further connected to the shell side inlet of the chiller (III) through a pipeline, and the purified tail gas discharged from the shell side outlet of the chiller (III) is sent to the tail gas downstream system through the fourth pipeline (4); The lower part of the shell side of the freezer (III) is also connected to an eleventh pipeline (11) for introducing hot gas; The apparatus further comprises a demister (II), wherein a heat exchange jacket is provided on the outside of the demister (II), a twelfth pipeline (12) is connected to the low-temperature nitrogen main pipe (10), and the other end of the twelfth pipeline (12) is connected to the heat exchange jacket on the outside of the demister (II) so as to allow low-temperature nitrogen to be introduced to the outside of the demister (II) to cool and keep the demister (II) as a whole. A thirteenth pipeline (13) for discharging nitrogen is also connected to the heat exchange jacket on the outside of the demister (II); The cooled tail gas discharged from the shell side outlet of the condenser (I) is sent to the demister (II) through the second pipeline (2) for defoaming. The liquid intercepted in the demister (II) is sent to the recovery liquid storage tank (IV) through the fifteenth pipeline (15). The defoamed tail gas discharged from the demister (II) is sent to the shell side of the freezer (III) through the third pipeline (3). The small amount of VOCs remaining in the exhaust gas is reduced to below the freezing point by liquid nitrogen in the freezer.

2. A condensation and refrigeration device for VOCs tail gas according to claim 1, characterized in that It also includes a recovery liquid storage tank (IV). A liquid outlet is provided at the bottom of the shell side of the condenser (I), and the generated VOCs condensate is sent to the recovery liquid storage tank (IV) through the fourteenth pipeline (14).

3. A condensation and refrigeration device for VOCs tail gas according to claim 2, characterized in that A liquid outlet is provided at the bottom of the shell side of the freezer (III), which is connected to the recovery liquid storage tank (IV) through the sixteenth pipeline (16).

4. A condensation and refrigeration device for VOCs tail gas according to claim 1, characterized in that The eighth pipeline (8) is provided with a first thermometer (T1) and a second regulating valve, and the sixth pipeline (6) is correspondingly provided with a first regulating valve. The first thermometer (T1) is connected to the first regulating valve signal through a PLC control system. When the nitrogen temperature detected by the first thermometer (T1) is higher or lower than a set value, the PLC control system is used to feedback and control the opening of the first regulating valve to be increased or decreased. A second thermometer (T2) is provided on the second pipeline (2), and the second thermometer (T2) is connected to the first regulating valve and the second regulating valve signal through a PLC control system; When the condenser (I) condenses the VOCs tail gas normally, the second thermometer (T2) performs independent feedback control on the second regulating valve through the PLC control system. When the tail gas temperature detected by the second thermometer (T2) is lower than or higher than the set value, the PLC control system provides feedback and controls the opening of the second regulating valve to be lowered or raised, so that the tail gas temperature detected by the second thermometer (T2) is within the set value range. When the condenser (I) over-condenses the VOCs exhaust gas so that the exhaust gas temperature detected by the second thermometer (T2) is lower than the critical abnormal value of condensation, the second thermometer (T2) transmits an abnormal signal to the PLC control system, and the PLC control system feedbacks and controls the opening of the first regulating valve and the second regulating valve to be lowered until the exhaust gas temperature detected by the second thermometer (T2) rises to within the set value range, and then the first thermometer (T1) is restored to independently feedback control of the first regulating valve through the PLC control system, and the second thermometer (T2) is restored to independently feedback control of the second regulating valve through the PLC control system; wherein, the first regulating valve and the second regulating valve preferentially respond to the signal sent from the second thermometer (T2) through the PLC control system.

5. A condensation and refrigeration device for VOCs tail gas according to claim 1, characterized in that The ninth pipeline (9) is provided with a third thermometer (T3) and a fourth regulating valve, and the seventh pipeline (7) is correspondingly provided with a third regulating valve. The third thermometer (T3) is connected to the third regulating valve signal through a PLC control system. When the nitrogen temperature detected by the third thermometer (T3) is higher or lower than the set value, the PLC control system is used to feedback and control the third regulating valve to increase or decrease the opening. A fourth thermometer (T4) is provided on the fourth pipeline (4), and the fourth thermometer (T4) is connected to the third regulating valve and the fourth regulating valve via a PLC control system; When the freezer (III) is performing normal freezing on the exhaust gas after defoaming, the fourth thermometer (T4) performs independent feedback control on the fourth regulating valve through the PLC control system. When the exhaust gas temperature detected by the fourth thermometer (T4) is lower than or higher than a set value, the PLC control system provides feedback and controls the opening of the fourth regulating valve to be lowered or raised, so that the exhaust gas temperature detected by the fourth thermometer (T4) is within the set value range. When the freezer (III) overfreezes the exhaust gas after defoaming so that the exhaust gas temperature detected by the fourth thermometer (T4) is lower than the freezing critical abnormal value, the fourth thermometer (T4) transmits an abnormal signal to the PLC control system, and the PLC control system feedbacks and controls the opening of the third regulating valve and the fourth regulating valve to be lowered or raised until the exhaust gas temperature detected by the fourth thermometer (T4) rises to within the set value range, and then the third thermometer (T3) is restored to independently feedback control of the third regulating valve through the PLC control system, and the fourth thermometer (T4) is restored to independently feedback control of the fourth regulating valve through the PLC control system; wherein, the third regulating valve and the fourth regulating valve preferentially respond to the signal sent from the fourth thermometer (T4) through the PLC control system.

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