Multi-stage purification and reuse device for nitrogen-sealed VOCs (Volatile Organic Compounds)

Abstract

The invention discloses a multistage purification reuse device for nitrogen-sealed VOCs, and relates to the technical field of VOCs recovery processing, the VOCs recovery processing device comprises a plurality of condensers, the plurality of condensers at least comprise a first-section condenser and a tail-section condenser, a tube pass gas inlet of the first-section condenser is used for communicating with a VOCs inlet, and a tube pass gas outlet of the tail-section condenser is used for communicating with a tube pass gas outlet of the tail-section condenser; the shell pass gas outlet of the first-section condenser is used for being communicated with a purified gas outlet, the shell pass gas inlet of the tail-section condenser is used for being communicated with a liquid nitrogen inlet, heat exchange pipes of the multiple condensers are sequentially communicated through a pipe pass connecting pipeline, and shells of the multiple condensers are further sequentially communicated through a shell pass connecting pipeline. The multi-stage purifying and reusing device for the nitrogen-sealed VOCs solves the problems that the purifying efficiency is low and nitrogen in purified gas cannot be repeatedly utilized when low-oxygen VOCs are recycled and treated by traditional VOCs recycling and treating equipment.

Description

Technical Field

[0001] The present application relates to the technical field of VOCs recovery and treatment, and in particular to a multi-stage purification and reuse device for nitrogen-sealed VOCs. Background Art

[0002] In the production, storage, and transportation processes of petrochemicals, coal chemicals, and organic chemicals, atmospheric pressure storage of organic liquids is common. Vertical tanks, small horizontal tanks, and silos are commonly used. Due to the volatility of organic liquids, VOCs (volatile organic compounds) (VOCs) are released during storage. Therefore, breathing valves are installed on the tops of the tanks to prevent VOCs from escaping. However, as temperature and pressure fluctuate during storage, the breathing process of the tanks causes the oxygen inside to mix with the VOCs, posing a safety hazard. Furthermore, the emission of VOCs can cause environmental pollution and oil loss.

[0003] Currently, the most common explosion-proof and explosion-resistance technology for atmospheric pressure storage tanks containing organic liquids is inerting. Nitrogen blanketing systems are typically used for inerting protection of petroleum tanks. This involves injecting high-purity nitrogen to maintain a low-oxygen atmosphere (e.g., 8%), thereby suppressing combustion and improving tank safety. However, the purification of low-oxygen VOCs exhaled by nitrogen blanketing systems remains a challenge.

[0004] Currently, oil and vapor recovery equipment is primarily used to treat low-oxygen VOCs emitted from nitrogen blanketing systems before they are released. This treatment method, on the one hand, is based on concerns that leaks in containers and breathing valves can cause nitrogen purity to fall below the required nitrogen blanketing gas. Consequently, the nitrogen contained in the low-oxygen VOC gas cannot be reused, forcing the use of fresh nitrogen, which increases the operating cost and energy consumption of the nitrogen blanketing system. Furthermore, operational failures in the oil and vapor recovery equipment can lead to substandard emissions, causing environmental pollution. Furthermore, unsafe conditions such as oil and vapor leakage, deterioration of the activated carbon layer, and electrostatic discharge within the equipment itself can increase the risk of fire and explosion.

[0005] Patent CN110143378 discloses a method for safely collecting VOCs from storage tanks with zero emissions. By connecting the VOCs pipelines of storage tanks containing the same or similar materials, the VOCs discharged from multiple storage tanks are aggregated into an oil and gas main. These VOCs are then sent to a pressurized oil and gas recovery unit for treatment by controlling nitrogen generation equipment. The recovered nitrogen is then circulated using a tank pressure monitoring signal to control the opening or closing of the nitrogen sealing valve on the tank. This method achieves safe VOC collection, zero emissions, and nitrogen recycling, meeting increasingly stringent environmental standards. However, the pressurized recovery unit described in this patent utilizes a combination of two or more methods: pressurized absorption, pressurized adsorption, membrane separation, and condensation. The nitrogen recycling is shut down when the total hydrocarbon volume concentration at the outlet of the pressurized oil and gas recovery unit exceeds the VOC volume concentration limit in the circulating nitrogen. Therefore, there is also the risk of atmospheric pollution and fire and explosion caused by recovery unit failure. Furthermore, high-pressure, high-concentration oil and gas leaking into the air is more likely to cause fire and explosion accidents.

[0006] To address the problems of low VOC recovery rates, substandard tail gas emissions, and fire and explosion risks associated with conventional oil and gas recovery technologies, patent CN109550350A discloses a liquid nitrogen cryogenic condensation VOC recovery and treatment device. Volatile oil and gas are pressurized by a booster blower and then enter a cold insulated tank for three-stage condensation and heat exchange with liquid nitrogen. The condensed liquid is then recovered and processed through a pipe separator and a gas-liquid separator. Non-condensable gases are vented, and the vaporized liquid nitrogen is denitrified and sealed. Its advantages include a VOC recovery rate of up to 99.999%, reduced emissions of volatile organic compounds and ozone-depleting substances, and thorough recovery with no secondary pollution. However, this technology faces two challenges: 1) Due to the low refrigeration temperature, the equipment is prone to freezing, making defrosting difficult and preventing long-term continuous and stable operation. Two independent condensation systems are required to maintain long-term operational reliability. 2) The low-temperature non-condensable gas and low-temperature nitrogen cooling capacity generated by liquid nitrogen through heat exchange are not fully utilized, and the large amount of nitrogen in low-oxygen VOCs cannot be recycled and reused, resulting in high liquid nitrogen consumption and high energy consumption.

[0007] Therefore, how to efficiently, safely and environmentally friendly realize the recovery and recycling of low-oxygen VOCs gas in the nitrogen sealing system, improve the recovery efficiency of liquid nitrogen cryogenic purification, and solve the defrosting difficulties to maintain long-term operation of the equipment, is a technical problem that needs to be solved urgently for technical personnel in this field. Summary of the Invention

[0008] The purpose of this application is to provide a multi-stage purification and reuse device for nitrogen-sealed VOCs, which solves the problem that traditional VOCs recovery and treatment equipment has low VOCs purification efficiency and cannot reuse nitrogen in the purified gas when recovering and treating low-oxygen VOCs.

[0009] To achieve the above-mentioned objectives, the present application provides a multi-stage purification and reuse device for nitrogen-sealed VOCs, comprising a plurality of condensers, each of which is provided with a tube-side air inlet, a tube-side air outlet, a shell-side air inlet, and a shell-side air outlet. The plurality of condensers include at least a first-stage condenser and a last-stage condenser, wherein the tube-side air inlet of the first-stage condenser is used to connect to the VOCs inlet, the shell-side air outlet of the first-stage condenser is used to connect to the purified gas outlet, and the shell-side air inlet of the last-stage condenser is used to connect to the liquid nitrogen inlet;

[0010] The heat exchange tubes of the multiple condensers are sequentially connected through the tube-side connecting pipelines, and the shells of the multiple condensers are also sequentially connected through the shell-side connecting pipelines, so that: the VOCs introduced through the VOCs inlet flow from the first-stage condenser through the tube-side connecting pipeline and out of the last-stage condenser, and the liquid nitrogen introduced through the liquid nitrogen inlet enters the last-stage condenser and undergoes heat exchange in the last-stage condenser, and then undergoes multi-stage heat exchange with the VOCs flowing out of the last-stage condenser through the shell-side connecting pipeline toward the first-stage condenser and flows out from the purified gas outlet.

[0011] In some embodiments, the first-stage condenser includes a first-stage main condenser, and a second-stage main condenser and a third-stage condenser are provided between the first-stage condenser and the last-stage condenser, and the last-stage condenser is specifically a fourth-stage condenser;

[0012] The tube-side air inlet of the first-stage main condenser is connected to the VOCs inlet, the tube-side air outlet of the first-stage main condenser is connected to the tube-side air inlet of the second-stage main condenser, the tube-side air outlet of the second-stage main condenser is connected to the tube-side air inlet of the third-stage condenser, the tube-side air outlet of the third-stage condenser is connected to the tube-side air inlet of the fourth-stage condenser, the tube-side air outlet of the fourth-stage condenser is connected to the shell-side air inlet of the third-stage condenser, the shell-side air outlet of the third-stage condenser is connected to the shell-side air inlet of the second-stage main condenser, the shell-side air outlet of the second-stage main condenser is connected to the shell-side air inlet of the first-stage main condenser, and the shell-side air outlet of the first-stage main condenser is connected to the purified gas outlet.

[0013] In some embodiments, the first-stage condenser further includes a first-stage sub-condenser, and the plurality of condensers further includes a second-stage sub-condenser;

[0014] The tube-side air inlet of the first-stage secondary condenser is connected with the VOCs inlet, the tube-side air outlet of the first-stage secondary condenser is connected with the tube-side air inlet of the second-stage main condenser and the tube-side air inlet of the second-stage secondary condenser respectively, the tube-side air inlet of the second-stage secondary condenser is connected with the tube-side air outlet of the first-stage main condenser, the tube-side air outlet of the second-stage secondary condenser is connected with the tube-side air inlet of the tertiary condenser, the shell-side air outlet of the tertiary condenser is connected with the shell-side air inlet of the second-stage secondary condenser, the shell-side air outlet of the second-stage secondary condenser is connected with the shell-side air inlet of the first-stage main condenser and the shell-side air inlet of the first-stage secondary condenser, and the shell-side air outlet of the first-stage secondary condenser is connected with the purified gas outlet.

[0015] In some embodiments, the multi-stage purification reuse device for nitrogen-sealed VOCs further includes a first programmable valve, a second programmable valve, a third programmable valve, a fourth programmable valve, a fifth programmable valve, a sixth programmable valve, a seventh programmable valve, an eighth programmable valve, a ninth programmable valve, a tenth programmable valve, an eleventh programmable valve, a twelfth programmable valve, a thirteenth programmable valve, and a fourteenth programmable valve;

[0016] The air inlet of the first programmable valve is connected to the VOCs inlet, the air outlet of the first programmable valve is connected to the pipe-side air inlet of the first-stage main condenser, the air inlet of the second programmable valve is connected to the VOCs inlet, and the air outlet of the second programmable valve is connected to the pipe-side air inlet of the first-stage secondary condenser;

[0017] The air inlet of the fifth programmable valve is connected to the pipe-side air outlet of the first-level main condenser, the air outlet of the fifth programmable valve is connected to the air inlet of the seventh programmable valve and the air inlet of the eighth programmable valve, the air inlet of the sixth programmable valve is connected to the pipe-side air outlet of the first-level secondary condenser, the air outlet of the sixth programmable valve is connected to the air inlet of the seventh programmable valve and the air inlet of the eighth programmable valve, the air outlet of the seventh programmable valve is connected to the pipe-side air inlet of the second-level main condenser, and the air outlet of the eighth programmable valve is connected to the pipe-side air inlet of the second-level secondary condenser;

[0018] The air inlet of the thirteenth programmable valve is connected to the pipe-side air outlet of the secondary main condenser, the air outlet of the thirteenth programmable valve is connected to the pipe-side air inlet of the tertiary condenser, the air inlet of the fourteenth programmable valve is connected to the pipe-side air outlet of the secondary sub-condenser, and the air outlet of the fourteenth programmable valve is connected to the pipe-side air inlet of the tertiary condenser;

[0019] The air inlet of the eleventh programmable valve is connected to the shell-side air outlet of the third-stage condenser, the air outlet of the eleventh programmable valve is connected to the shell-side air inlet of the second-stage main condenser, the air inlet of the twelfth programmable valve is connected to the shell-side air outlet of the third-stage condenser, and the air outlet of the twelfth programmable valve is connected to the shell-side air inlet of the second-stage secondary condenser;

[0020] The air inlet of the tenth programmable valve is connected to the shell-side air outlet of the secondary main condenser, the air outlet of the tenth programmable valve is connected to the air inlet of the third programmable valve and the air inlet of the fourth programmable valve, the air inlet of the ninth programmable valve is connected to the shell-side air outlet of the secondary secondary condenser, the air outlet of the ninth programmable valve is connected to the air inlet of the third programmable valve and the air inlet of the fourth programmable valve, the air outlet of the fourth programmable valve is connected to the shell-side air inlet of the first main condenser, and the air outlet of the third programmable valve is connected to the shell-side air inlet of the first secondary condenser.

[0021] In some embodiments, a demister is provided below the tube-side gas outlet of the first-stage main condenser, the second-stage main condenser, the third-stage condenser, the fourth-stage condenser, the first-stage secondary condenser and the second-stage secondary condenser.

[0022] In some embodiments, the first-stage main condenser, the second-stage main condenser, the third-stage condenser, the fourth-stage condenser, the first-stage secondary condenser and the second-stage secondary condenser are all provided with drain ports, and each drain port is connected to an oil collecting tank.

[0023] In some embodiments, temperature detection instruments are provided at the pipe-side gas outlets of the first-stage main condenser, the second-stage main condenser, the third-stage condenser, the fourth-stage condenser, the first-stage sub-condenser, and the second-stage sub-condenser.

[0024] In some embodiments, a first differential pressure detector is provided on the pipeline between the air inlet of the first programmable valve and the air outlet of the fifth programmable valve, and on the pipeline between the air inlet of the second programmable valve and the air outlet of the sixth programmable valve;

[0025] A second differential pressure detector is provided on the pipeline between the air inlet of the seventh programmable valve and the air outlet of the thirteenth programmable valve, and on the pipeline between the air inlet of the eighth programmable valve and the air outlet of the fourteenth programmable valve.

[0026] In some embodiments, the condensing temperatures of the first-stage main condenser, the second-stage main condenser, the third-stage condenser and the fourth-stage condenser decrease in sequence. The condensing temperature range of the first-stage main condenser is 0~-5 degrees Celsius, the condensing temperature range of the second-stage main condenser is -35~-45 degrees Celsius, the condensing temperature range of the third-stage condenser is -75~-85 degrees Celsius, and the condensing temperature range of the fourth-stage condenser is -115~-125 degrees Celsius.

[0027] In some embodiments, the multi-stage purification and reuse device for nitrogen-sealed VOCs further comprises a blower, wherein the air inlet of the blower is connected to the VOCs inlet, and the air outlet of the blower is connected to the tube-side air inlet of the first-stage condenser;

[0028] The shell-side air inlet of the last-section condenser is connected to a liquid nitrogen flow control valve, and a VOCs concentration sensor is provided at the shell-side air outlet of the first-section condenser. The liquid nitrogen flow control valve is configured to adjust the liquid nitrogen input based on the data of the VOCs concentration sensor.

[0029] Compared with the above-mentioned background technology, the embodiment of the present application provides a multi-stage purification and reuse device for nitrogen-sealed VOCs, including multiple condensers, and the multiple condensers include a first-stage condenser and a last-stage condenser. The tube-side air inlet of the first-stage condenser is used to connect to the VOCs inlet, the shell-side air outlet of the first-stage condenser is used to connect to the purified gas outlet, and the shell-side air inlet of the last-stage condenser is used to connect to the liquid nitrogen inlet; the heat exchange tubes of the multiple condensers are connected in sequence through the tube-side connecting pipeline, and the shells of the multiple condensers are also connected in sequence through the shell-side connecting pipeline. In this way, the VOCs introduced from the VOCs inlet flow out from the first-stage condenser through the tube-side connecting pipeline and out of the last-stage condenser, and the liquid nitrogen introduced from the liquid nitrogen inlet enters the last-stage condenser and undergoes heat exchange in the last-stage condenser. Then, the VOCs flowing out of the last-stage condenser undergo multi-stage heat exchange through the shell-side connecting pipeline toward the first-stage condenser and flow out from the purified gas outlet.

[0030] It can be seen that, on the one hand, VOCs are condensed and purified in each condenser in sequence from the first condenser to the last condenser. On the other hand, liquid nitrogen enters the last condenser and undergoes heat exchange in the last condenser. It then undergoes multi-stage heat exchange with the VOCs flowing out of the last condenser through the shell-side connecting pipeline toward the first condenser, obtaining nitrogen with extremely low oxygen content, which finally flows out from the purified gas outlet.

[0031] The beneficial effects of the multi-stage purification and reuse device for nitrogen-sealed VOCs set up in this way mainly include:

[0032] After the VOCs are condensed and purified through a multi-stage condenser along the tube-side connecting pipeline, the vaporized gas is mixed with the VOCs non-condensable gas after heat exchange using liquid nitrogen, and further heat exchange is carried out through a multi-stage condenser along the shell-side connecting pipeline to obtain higher-purity nitrogen. Finally, the higher-purity nitrogen is introduced into the nitrogen blanketing system. This not only fully utilizes the cooling capacity of liquid nitrogen, effectively removes the VOCs components in low-oxygen VOCs, improves the purification efficiency of VOCs, and solves the problem of environmental pollution caused by substandard emission gases, but also improves the purity of nitrogen in the purified gas, so that the purified gas can return to the nitrogen blanketing system, realizing the recycling and reuse of nitrogen in nitrogen-sealed VOCs, saving resources, reducing costs, and ensuring the safety of the nitrogen blanketing system. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the following briefly introduces the drawings required for use in the embodiments or related technical descriptions. Obviously, the drawings described below are merely embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without any creative work.

[0034] Figure 1This is a connection diagram of the multi-stage purification and reuse device for nitrogen-sealed VOCs in an embodiment of the present application.

[0035] in:

[0036] 1- fan, 201- first program-controlled valve, 202- second program-controlled valve, 203- third program-controlled valve, 204- fourth program-controlled valve, 205- fifth program-controlled valve, 206- sixth program-controlled valve, 207- seventh program-controlled valve, 208- eighth program-controlled valve, 209- ninth program-controlled valve, 210- tenth program-controlled valve, 211- eleventh program-controlled valve, 212- twelfth program-controlled valve, 213- thirteenth program-controlled valve, 214- fourteenth program-controlled valve Program-controlled valve, 301-first-stage main condenser, 302-first-stage secondary condenser, 401-second-stage main condenser, 402-second-stage secondary condenser, 5-third-stage condenser, 6-fourth-stage condenser, 7-oil collecting tank, 8-demister, 9-temperature detection instrument, 1001-first differential pressure detector, 1002-second differential pressure detector, 1101-VOCs inlet, 1102-liquid nitrogen inlet, 1103-purified gas outlet. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0038] In order to enable those skilled in the art to better understand the present application, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0039] See also Figure 1 A multi-stage purification and reuse device for nitrogen-sealed VOCs provided in an embodiment of the present application includes multiple condensers, each condenser is provided with a tube-side air inlet, a tube-side air outlet, a shell-side air inlet and a shell-side air outlet, and the multiple condensers include at least a first-section condenser and a last-section condenser. The tube-side air inlet of the first-section condenser is used to connect to the VOCs inlet 1101, the shell-side air outlet of the first-section condenser is used to connect to the purified gas outlet 1103, and the purified gas outlet 1103 is used to be connected to the nitrogen sealing system, and the shell-side air inlet of the last-section condenser is used to connect to the liquid nitrogen inlet 1102.

[0040] Furthermore, a multi-stage purification and reuse device for nitrogen-sealed VOCs also includes a tube-side connecting pipeline and a shell-side connecting pipeline. The heat exchange tubes of multiple condensers are connected in sequence through the tube-side connecting pipeline, and the shells of multiple condensers are also connected in sequence through the shell-side connecting pipeline.

[0041] In this way, the VOCs introduced through the VOCs inlet 1101 flow out of the first-stage condenser through the tube-side connecting pipeline and out of the last-stage condenser, and the liquid nitrogen introduced through the liquid nitrogen inlet 1102 enters the last-stage condenser and undergoes heat exchange in the last-stage condenser. Then, the liquid nitrogen and the VOCs flowing out of the last-stage condenser undergo multi-stage heat exchange toward the first-stage condenser through the shell-side connecting pipeline and flow out from the purified gas outlet 1103.

[0042] It can be seen that, on the one hand, VOCs are condensed and purified in each condenser in sequence from the first condenser to the last condenser. On the other hand, liquid nitrogen enters the last condenser and undergoes heat exchange in the last condenser. It then undergoes multi-stage heat exchange with the VOCs flowing out of the last condenser through the shell-side connecting pipeline toward the first condenser, thereby obtaining nitrogen with extremely low oxygen content, which finally flows out from the purified gas outlet 1103 to the nitrogen sealing system.

[0043] The multi-stage purification and reuse device for nitrogen-sealed VOCs set up in this way condenses and purifies VOCs along the tube-side connecting pipeline through a multi-stage condenser, then uses liquid nitrogen to vaporize the gas and heat exchange with the VOCS non-condensable gas before mixing, and further heat exchange is carried out along the shell-side connecting pipeline through a multi-stage condenser to obtain higher-purity nitrogen, and finally the higher-purity nitrogen is introduced into the nitrogen sealing system, which not only realizes the full utilization of the liquid nitrogen cooling capacity, effectively removes the VOCs components in the low-oxygen VOCs, improves the purification efficiency of VOCs, and solves the problem of environmental pollution caused by substandard emission gas, but also improves the purity of nitrogen in the purified gas, so that the purified gas can return to the nitrogen sealing system, realizing the recycling and reuse of nitrogen in the nitrogen-sealed VOCs, saving resources, reducing costs, and ensuring the safety of the nitrogen sealing system.

[0044] In order to facilitate the provision of power for gas recovery and processing, the multi-stage purification and reuse device for nitrogen-sealed VOCs also includes a fan 1, the air inlet of the fan 1 is connected to the VOCs inlet 1101, and the air outlet of the fan 1 is connected to the pipe-side air inlet of the first-stage condenser.

[0045] In some embodiments, the multiple condensers are four-stage condensers. Specifically, the first-stage condenser includes a first-stage main condenser 301, and the multiple condensers also include a second-stage main condenser 401 and a third-stage condenser 5. The last-stage condenser is specifically a fourth-stage condenser 6. The second-stage main condenser 401 and the third-stage condenser 5 are arranged between the first-stage main condenser 301 and the fourth-stage condenser 6.

[0046] Among them, the tube-side air inlet N1 of the first-stage main condenser 301 is connected to the VOCs inlet 1101, the tube-side air outlet N2 of the first-stage main condenser 301 is connected to the tube-side air inlet N1 of the second-stage main condenser 401, the tube-side air outlet N2 of the second-stage main condenser 401 is connected to the tube-side air inlet N1 of the third-stage condenser 5, the tube-side air outlet N2 of the third-stage condenser 5 is connected to the tube-side air inlet N1 of the fourth-stage condenser 6, the tube-side air outlet N2 of the fourth-stage condenser 6 is connected to the shell-side air inlet N3 of the third-stage condenser 5, the shell-side air outlet N4 of the third-stage condenser 5 is connected to the shell-side air inlet N3 of the second-stage main condenser 401, the shell-side air outlet N4 of the second-stage main condenser 401 is connected to the shell-side air inlet N3 of the first-stage main condenser 301, and the shell-side air outlet N4 of the first-stage main condenser 301 is connected to the purified gas outlet 1103.

[0047] In this way, under the power of the fan 1, the VOCs introduced through the VOCs inlet 1101 can be condensed and purified in sequence along the tube-side connecting pipeline through the first-stage main condenser 301, the second-stage main condenser 401, the third-stage condenser 5 and the fourth-stage condenser 6. After the VOCs are purified by the fourth-stage condensation, the non-condensable gas is discharged from the tube-side outlet N2 of the fourth-stage condenser 6. The liquid nitrogen passes through the liquid nitrogen inlet 1102 and enters the shell-side inlet N3 of the fourth-stage condenser 6 through the pipeline to exchange heat with the VOCs and is discharged from the shell-side outlet N4 of the fourth-stage condenser 6. Afterwards, the nitrogen is combined with the VOCs non-condensable gas discharged from the tube-side outlet N2 of the fourth-stage condenser 6. The combined low-temperature mixed gas is then heat-exchanged through the third-stage condenser 5, the second-stage main condenser 401 and the first-stage main condenser 301, and then discharged from the shell-side outlet N4 of the first-stage main condenser 301 to the purified gas outlet 1103, and then transported to the nitrogen blanketing system for recycling and reuse.

[0048] It should be noted that, in this embodiment, the tube-side air inlet of the first-stage condenser is the tube-side air inlet N1 of the first-stage main condenser 301 , and the shell-side air outlet of the first-stage condenser is the shell-side air outlet N4 of the first-stage main condenser 301 .

[0049] In some embodiments, the condensing temperatures of the first-stage main condenser 301, the second-stage main condenser 401, the third-stage condenser 5 and the fourth-stage condenser 6 decrease successively. The condensing temperature range of the first-stage main condenser 301 is 0~-5 degrees Celsius, the condensing temperature range of the second-stage main condenser 401 is -35~-45 degrees Celsius, the condensing temperature range of the third-stage condenser 5 is -75~-85 degrees Celsius, and the condensing temperature range of the fourth-stage condenser 6 is -115~-125 degrees Celsius.

[0050] Furthermore, the first-stage condenser further includes a first-stage secondary condenser 302, and the plurality of condensers further includes a second-stage secondary condenser 402. The condensing temperature ranges of the first-stage secondary condenser 302 and the second-stage secondary condenser 402 can be set to be the same as the condensing temperature ranges of the first-stage main condenser 301 and the second-stage main condenser 401, respectively. Furthermore, the first-stage secondary condenser 302 and the first-stage main condenser 301 serve as backup condensers for each other, and the second-stage secondary condenser 402 and the second-stage main condenser 401 serve as backup condensers for each other.

[0051] Among them, the tube-side air inlet N1 of the first-stage secondary condenser 302 is connected to the VOCs inlet 1101, and the tube-side air outlet N2 of the first-stage secondary condenser 302 is respectively connected to the tube-side air inlet N1 of the second-stage main condenser 401 and the tube-side air inlet N1 of the second-stage secondary condenser 402. The tube-side air inlet N1 of the second-stage secondary condenser 402 is also connected to the tube-side air outlet N2 of the first-stage main condenser 301. The tube-side air outlet N2 of the second-stage secondary condenser 402 is connected to the VOCs inlet 1101. The air outlet N2 is connected to the tube-side air inlet N1 of the tertiary condenser 5, the shell-side air outlet N4 of the tertiary condenser 5 is connected to the shell-side air inlet N3 of the secondary secondary condenser 402, the shell-side air outlet N4 of the secondary secondary condenser 402 is connected to the shell-side air inlet N3 of the first main condenser 301 and the shell-side air inlet N3 of the first secondary condenser 302, and the shell-side air outlet N4 of the first secondary condenser 302 is connected to the purified gas outlet 1103.

[0052] It should be noted that, in this embodiment, the tube-side air inlet of the so-called first-section condenser includes the tube-side air inlet N1 of the first-stage main condenser 301 and the tube-side air inlet N1 of the first-stage secondary condenser 302, and the shell-side air outlet of the first-section condenser includes the shell-side air outlet N4 of the first-stage main condenser 301 and the shell-side air outlet N4 of the first-stage secondary condenser 302.

[0053] In some embodiments, a demister 8 is provided below the pipe-side air outlet N2 of the first-stage main condenser 301, the second-stage main condenser 401, the third-stage condenser 5, the fourth-stage condenser 6, the first-stage secondary condenser 302 and the second-stage secondary condenser 402; the first-stage main condenser 301, the second-stage main condenser 401, the third-stage condenser 5, the fourth-stage condenser 6, the first-stage secondary condenser 302 and the second-stage secondary condenser 402 are all provided with a drain port D, and each drain port D is connected to an oil collecting tank 7.

[0054] In addition, a multi-stage purification and reuse device for nitrogen-sealed VOCs further includes a first program-controlled valve 201, a second program-controlled valve 202, a third program-controlled valve 203, a fourth program-controlled valve 204, a fifth program-controlled valve 205, a sixth program-controlled valve 206, a seventh program-controlled valve 207, an eighth program-controlled valve 208, a ninth program-controlled valve 209, a tenth program-controlled valve 210, an eleventh program-controlled valve 211, a twelfth program-controlled valve 212, a thirteenth program-controlled valve 213, and a fourteenth program-controlled valve 214. Among them:

[0055] The air inlet of the first programmable valve 201 is connected to the air outlet of the fan 1, and the air outlet of the first programmable valve 201 is connected to the pipe-side air inlet N1 of the first-stage main condenser 301. The air inlet of the second programmable valve 202 is connected to the air outlet of the fan 1, and the air outlet of the second programmable valve 202 is connected to the pipe-side air inlet N1 of the first-stage secondary condenser 302. In this way, the air outlet of the fan 1 is connected to the pipe-side air inlet N1 of the first-stage main condenser 301 through the first programmable valve 201, and to the pipe-side air inlet N1 of the first-stage secondary condenser 302 through the second programmable valve 202. After being pressurized by the fan 1, the VOCs can enter the primary main condenser 301 and the primary secondary condenser 302 for heat exchange, thereby reducing the VOCs gas temperature to about 0~-5 degrees Celsius, thereby liquefying the water vapor in the VOCs. The gas and liquid are separated by the demister 8 arranged inside the primary main condenser 301 and the primary secondary condenser 302, and the non-condensable gas is discharged from the pipe-side outlet N2 of the primary main condenser 301 and the primary secondary condenser 302, and the condensate is discharged into the oil collecting tank 7 through the drain port D of the primary main condenser 301 and the primary secondary condenser 302.

[0056] The air inlet of the fifth programmable valve 205 is connected to the pipe-side air outlet N2 of the first-level main condenser 301, the air outlet of the fifth programmable valve 205 is connected to the air inlet of the seventh programmable valve 207 and the air inlet of the eighth programmable valve 208, the air inlet of the sixth programmable valve 206 is connected to the pipe-side air outlet N2 of the first-level secondary condenser 302, the air outlet of the sixth programmable valve 206 is connected to the air inlet of the seventh programmable valve 207 and the air inlet of the eighth programmable valve 208, the air outlet of the seventh programmable valve 207 is connected to the pipe-side air inlet N1 of the second-level main condenser 401, and the air outlet of the eighth programmable valve 208 is connected to the pipe-side air inlet N1 of the second-level secondary condenser 402. In this way, the VOCs after the first-stage condensation can enter the secondary main condenser 401 and the secondary secondary condenser 402 respectively for heat exchange, further reducing the VOCs temperature to about -40 degrees Celsius, so that some heavy component gases in the VOCs (such as butane, pentane, etc.) are liquefied, and gas-liquid separation is carried out through the demister 8 arranged inside the secondary main condenser 401 and the secondary secondary condenser 402. The non-condensable gas is discharged from the pipe-side outlet N2 of the secondary main condenser 401 and the secondary secondary condenser 402, and the condensate is discharged into the oil collecting tank 7 through the drain port D of the secondary main condenser 401 and the secondary secondary condenser 402.

[0057] The air inlet of the thirteenth programmable valve 213 is connected to the pipe-side air outlet N2 of the secondary main condenser 401, the air outlet of the thirteenth programmable valve 213 is connected to the pipe-side air inlet N1 of the tertiary condenser 5, the air inlet of the fourteenth programmable valve 214 is connected to the pipe-side air outlet N2 of the secondary sub-condenser 402, and the air outlet of the fourteenth programmable valve 214 is connected to the pipe-side air inlet N1 of the tertiary condenser 5. In this way, the VOCs treated by the secondary main condenser 401 and the secondary secondary condenser 402 can enter the tertiary condenser 5 for heat exchange, further reducing the VOC temperature to about -80 degrees Celsius, and again liquefying some of the gases in the VOCs (such as butane, propane, etc.). The gas-liquid separation is carried out by the demister 8 arranged inside the tertiary condenser 5, and the non-condensable gas is discharged from the pipe-side outlet N2 of the tertiary condenser 5, and the condensate is discharged into the oil collecting tank 7 through the drain port D of the tertiary condenser 5.

[0058] The tube-side air outlet N2 of the tertiary condenser 5 is directly connected to the tube-side air inlet N1 of the quaternary condenser 6, so that the gas purified by the tertiary condensation is again heat-exchanged with the liquid nitrogen entering through the shell-side air inlet N3 of the quaternary condenser, further reducing the VOCs temperature to about -120 degrees Celsius, thereby again liquefying and condensing more than 97% of the VOCs, and the non-condensable gas is discharged from the tube-side air outlet N2 of the quaternary condenser 6, and mixed with the partially vaporized low-temperature nitrogen discharged from the shell-side air outlet N4 of the quaternary condenser 6, and flows to the shell-side air inlet N3 of the tertiary condenser 5.

[0059] The air inlet of the eleventh programmable valve 211 is connected to the shell-side air outlet N4 of the tertiary condenser 5, the air outlet of the eleventh programmable valve 211 is connected to the shell-side air inlet N3 of the secondary main condenser 401, the air inlet of the twelfth programmable valve 212 is connected to the shell-side air outlet N4 of the tertiary condenser 5, and the air outlet of the twelfth programmable valve 212 is connected to the shell-side air inlet N3 of the secondary secondary condenser 402. In this way, the low-temperature mixed gas discharged from the fourth-stage condenser 6, after undergoing heat exchange in the third-stage condenser 5, can enter the secondary main condenser 401 or the secondary secondary condenser 402 for heat exchange, respectively.

[0060] The inlet of the tenth programmable valve 210 is connected to the shell-side outlet N4 of the secondary main condenser 401. The outlet of the tenth programmable valve 210 is connected to the inlet of the third programmable valve 203 and the inlet of the fourth programmable valve 204. The inlet of the ninth programmable valve 209 is connected to the shell-side outlet N4 of the secondary secondary condenser 402. The outlet of the ninth programmable valve 209 is connected to the inlet of the third programmable valve 203 and the inlet of the fourth programmable valve 204. The outlet of the fourth programmable valve 204 is connected to the shell-side inlet N3 of the primary main condenser 301. The outlet of the third programmable valve 203 is connected to the shell-side inlet N3 of the primary secondary condenser 302. In this way, the low-temperature mixed gas discharged from the secondary main condenser 401 or the secondary secondary condenser 402 can undergo heat exchange with the primary main condenser 301 and the primary secondary condenser 302, respectively.

[0061] The shell side gas outlet N4 of the first-stage main condenser 301 and the shell side gas outlet N4 of the first-stage secondary condenser 302 are both connected to the purified gas outlet 1103, and the nitrogen gas with extremely low oxygen content finally obtained flows from the purified gas outlet 1103 to the nitrogen blanketing system.

[0062] In some embodiments, temperature detection instruments 9 are provided at the pipe-side gas outlet N2 of the first-stage main condenser 301 , the second-stage main condenser 401 , the third-stage condenser 5 , the fourth-stage condenser 6 , the first-stage secondary condenser 302 and the second-stage secondary condenser 402 .

[0063] In some embodiments, a first differential pressure detector 1001 is provided on the pipeline between the air inlet of the first programmable valve 201 and the air outlet of the fifth programmable valve 205, and on the pipeline between the air inlet of the second programmable valve 202 and the air outlet of the sixth programmable valve 206; a second differential pressure detector 1002 is provided on the pipeline between the air inlet of the seventh programmable valve 207 and the air outlet of the thirteenth programmable valve 213, and on the pipeline between the air inlet of the eighth programmable valve 208 and the air outlet of the fourteenth programmable valve 214.

[0064] The following describes in detail the working process or usage of a multi-stage purification and reuse device for nitrogen-sealed VOCs in this application:

[0065] After VOCs enter the device, they are first pressurized by fan 1. The first programmable valve 201, the fourth programmable valve 204, the fifth programmable valve 205, the seventh programmable valve 207, the tenth programmable valve 210, the eleventh programmable valve 211 and the thirteenth programmable valve 213 are opened first. The VOCs first enter the heat exchange tube of the first-stage main condenser 301, then pass through the demister 8 of the first-stage main condenser 301 for gas-liquid separation, and are discharged from the tube-side outlet N2 (this process is hereinafter referred to as the "tube-side"). The VOCs then enter the tube-side of the second-stage main condenser 401, the tube-side of the third-stage condenser 5, and the tube-side of the fourth-stage condenser 6, respectively, to be graded condensed and purified.

[0066] After entering the device, liquid nitrogen flows to the outside of the heat exchange tubes of the fourth-stage condenser 6, exchanges heat with the VOCs, and is then discharged from the shell-side outlet N4 of the fourth-stage condenser 6 (this process is referred to as "shell side"). The purified VOCs discharged from the tube side of the fourth-stage condenser 6 are mixed with the low-temperature nitrogen discharged through the shell side. Then, they pass through the tube side of the third-stage condenser 5, the tube side of the second-stage main condenser 401, and the tube side of the first-stage main condenser 301 as cold sources to perform staged heat exchange with the VOCs, and are finally discharged into the nitrogen blanketing system through the purified gas outlet 1103, so that the nitrogen in the low-oxygen VOCs and the nitrogen after vaporization of the liquid nitrogen are recycled and reused.

[0067] If the first-stage main condenser 301 frosts during operation, it may cause blockage of the heat exchange tubes or reduce heat exchange efficiency. That is, when the first differential pressure detector 1001 or the temperature detector 9 reaches the alarm threshold, the device will automatically open the second programmable valve 202, the third programmable valve 203, and the sixth programmable valve 206, while closing the first programmable valve 201, the fourth programmable valve 204, and the fifth programmable valve 205. VOCs will enter the first-stage secondary condenser 302. At the same time, the low-temperature mixed gas returned from the second-stage condenser 402 will also enter the first-stage secondary condenser 302, and the first-stage secondary condenser 302 will perform the heat exchange condensation work. At this time, the first-stage main condenser 301 can be manually defrosted to eliminate the fault. Similarly, if the first-stage secondary condenser 302 also frosts, the device will automatically switch to the first-stage main condenser 301 for heat exchange, ensuring long-term stable operation of the equipment.

[0068] If the secondary main condenser 401 frosts during operation, it may cause blockage of the heat exchange tubes or reduce the heat exchange efficiency. That is, when the second differential pressure detector 1002 or the temperature detector 9 reaches the alarm threshold, the device will automatically open the eighth programmable valve 208, the ninth programmable valve 209, the twelfth programmable valve 212, and the fourteenth programmable valve 214, while closing the seventh programmable valve 207, the tenth programmable valve 210, the eleventh programmable valve 211, and the thirteenth programmable valve 213. VOCs gas will enter the secondary secondary condenser 402, and the low-temperature mixed gas returned from the tertiary condenser 5 will also enter the secondary secondary condenser 402, and the secondary secondary condenser 402 will perform the heat exchange condensation work. At this time, the secondary main condenser 401 can be manually defrosted to eliminate the fault. Similarly, when the secondary secondary condenser 402 also frosts, the device will automatically switch to the secondary main condenser 401 for heat exchange, ensuring the long-term stable operation of the equipment.

[0069] After VOCs are purified through the first stage of condensation at 0 to -5 degrees Celsius and the second stage of condensation at -40 degrees Celsius, there is virtually no solid particle formation in the residual gas, which could cause equipment frost failure. Therefore, the third-stage condenser 5 and the fourth-stage condenser 6 do not require pressure differential detection. The equipment's operating status is monitored solely by temperature detectors 9 located at the tube-side gas outlet N2 of the third-stage condenser and the tube-side gas outlet N2 of the fourth-stage condenser 6. If the temperature detectors 9 at the tube-side gas outlet N2 of the third-stage condenser and the tube-side gas outlet N2 of the fourth-stage condenser 6 detect that the temperature is too high or too low, the liquid nitrogen flow rate can be adjusted to ensure long-term stable operation of the equipment.

[0070] In some embodiments, the shell-side air inlet N3 of the fourth-stage condenser 6 can also be connected to a liquid nitrogen flow regulating valve, and a VOCs concentration sensor is provided at the shell-side air outlet N4 of the first-stage main condenser 301 and the shell-side air outlet N4 of the first-stage secondary condenser 302. The liquid nitrogen flow regulating valve is configured to adjust the liquid nitrogen input amount based on the data of the VOCs concentration sensor.

[0071] In this way, when the VOCs concentration sensor monitors the residual VOCs at the shell-side outlet N4 of the first-stage main condenser 301 and the shell-side outlet N4 of the first-stage secondary condenser 302 in real time, when it detects that the concentration is rising, the liquid nitrogen flow control valve automatically increases the liquid nitrogen input to enhance condensation, and vice versa, it reduces the liquid nitrogen supply. The liquid nitrogen flow control valve (such as a low-temperature proportional control valve) uses a PID algorithm, combined with temperature feedback and concentration data, to achieve fine adjustment of the liquid nitrogen flow.

[0072] Considering that excessive liquid nitrogen will cause the condenser to freeze and clog (increase resistance), while insufficient liquid nitrogen will cause incomplete condensation of VOCs, the above-mentioned dynamic adjustment method can ensure that the condensation temperature of the device is always in the optimal condensation range.

[0073] In summary, the multi-stage purification and reuse device for nitrogen-sealed VOCs provided by the present application avoids the safety and environmental risks of traditional oil and gas recovery and treatment equipment itself through a liquid nitrogen multi-stage condensation purification process, realizes the recycling and reuse of nitrogen, and also avoids the risk of high pressure and high concentration oil and gas leakage in traditional recovery and treatment equipment. Specifically, through 6 condensers and 14 programmable valves, a four-stage cold capacity distribution and redundant switching of condenser frosting are realized, which solves the problems of low cold capacity utilization, high heat exchanger failure and high liquid nitrogen consumption, high energy consumption, and high cost of redundant system caused by existing liquid nitrogen condensation recovery technology. In addition, the device also adopts a new process of mixing liquid nitrogen vaporized gas with VOCs non-condensable gas as a low-temperature cold source to enter the three-stage, two-stage and two-stage condensers for heat exchange, which not only realizes the full utilization of liquid nitrogen cold capacity, effectively removes the VOCs components in the hypoxic VOCs gas, but also improves the nitrogen purity in the purified gas, realizes the recycling and reuse of nitrogen in the hypoxic VOCs, and ensures the safety of the nitrogen-sealed system.

[0074] It should be noted that, in this specification, relational terms such as first and second are merely used to distinguish one entity from other entities, but do not necessarily require or imply any actual relationship or order between these entities.

[0075] The above is a detailed introduction to a multi-stage purification and reuse device for nitrogen-sealed VOCs provided by the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the scheme of the present application and its core idea. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present application, several improvements and modifications can be made to the present application, and these improvements and modifications also fall within the scope of protection of the present application.

Claims

1. A multi-stage purification and reuse device for nitrogen-sealed VOCs, characterized in that: The invention comprises a plurality of condensers, wherein the plurality of condensers include at least a first-stage condenser and a last-stage condenser, wherein the tube-side air inlet of the first-stage condenser is used to connect to the VOCs inlet, the shell-side air outlet of the first-stage condenser is used to connect to the purified gas outlet, and the shell-side air inlet of the last-stage condenser is used to connect to the liquid nitrogen inlet; The heat exchange tubes of the multiple condensers are sequentially connected through tube-side connecting pipelines, and the shells of the multiple condensers are also sequentially connected through shell-side connecting pipelines, so that: the VOCs introduced through the VOCs introduction port flows from the first-stage condenser through the tube-side connecting pipeline and out of the last-stage condenser, and the liquid nitrogen introduced through the liquid nitrogen introduction port enters the last-stage condenser and undergoes heat exchange in the last-stage condenser, and then undergoes multi-stage heat exchange with the VOCs flowing out of the last-stage condenser through the shell-side connecting pipeline toward the first-stage condenser and flows out of the purified gas outlet.

2. The multi-stage purification and reuse device for nitrogen-sealed VOCs according to claim 1, characterized in that: The first-stage condenser includes a first-stage main condenser, and a second-stage main condenser and a third-stage condenser are further provided between the first-stage condenser and the last-stage condenser, wherein the last-stage condenser is specifically a fourth-stage condenser; The tube-side air inlet of the first-stage main condenser is communicated with the VOCs inlet, the tube-side air outlet of the first-stage main condenser is communicated with the tube-side air inlet of the second-stage main condenser, the tube-side air outlet of the second-stage main condenser is communicated with the tube-side air inlet of the third-stage condenser, the tube-side air outlet of the third-stage condenser is communicated with the tube-side air inlet of the fourth-stage condenser, the tube-side air outlet of the fourth-stage condenser is communicated with the shell-side air inlet of the third-stage condenser, the shell-side air outlet of the third-stage condenser is communicated with the shell-side air inlet of the second-stage main condenser, the shell-side air outlet of the second-stage main condenser is communicated with the shell-side air inlet of the first-stage main condenser, and the shell-side air outlet of the first-stage main condenser is communicated with the purified gas outlet.

3. The multi-stage purification and reuse device for nitrogen-sealed VOCs according to claim 2, characterized in that: The first-stage condenser further includes a first-stage sub-condenser, and the multiple condensers further include a second-stage sub-condenser; The tube-side air inlet of the first-stage secondary condenser is communicated with the VOCs inlet, the tube-side air outlet of the first-stage secondary condenser is communicated with the tube-side air inlet of the second-stage main condenser and the tube-side air inlet of the second-stage secondary condenser respectively, the tube-side air inlet of the second-stage secondary condenser is communicated with the tube-side air outlet of the first-stage main condenser, the tube-side air outlet of the second-stage secondary condenser is communicated with the tube-side air inlet of the third-stage condenser, the shell-side air outlet of the third-stage condenser is communicated with the shell-side air inlet of the second-stage secondary condenser, the shell-side air outlet of the second-stage secondary condenser is communicated with the shell-side air inlet of the first-stage main condenser and the shell-side air inlet of the first-stage secondary condenser, and the shell-side air outlet of the first-stage secondary condenser is communicated with the purified gas outlet.

4. The multi-stage purification and reuse device for nitrogen-sealed VOCs according to claim 3, characterized in that: The multi-stage purification reuse device for nitrogen-sealed VOCs also includes a first program-controlled valve, a second program-controlled valve, a third program-controlled valve, a fourth program-controlled valve, a fifth program-controlled valve, a sixth program-controlled valve, a seventh program-controlled valve, an eighth program-controlled valve, a ninth program-controlled valve, a tenth program-controlled valve, an eleventh program-controlled valve, a twelfth program-controlled valve, a thirteenth program-controlled valve, and a fourteenth program-controlled valve; The air inlet of the first programmable valve is communicated with the VOCs inlet, the air outlet of the first programmable valve is communicated with the pipe-side air inlet of the first-stage main condenser, the air inlet of the second programmable valve is communicated with the VOCs inlet, and the air outlet of the second programmable valve is communicated with the pipe-side air inlet of the first-stage secondary condenser; The air inlet of the fifth programmable valve is communicated with the pipe-side air outlet of the first-level main condenser, the air outlet of the fifth programmable valve is communicated with the air inlet of the seventh programmable valve and the air inlet of the eighth programmable valve, the air inlet of the sixth programmable valve is communicated with the pipe-side air outlet of the first-level secondary condenser, the air outlet of the sixth programmable valve is communicated with the air inlet of the seventh programmable valve and the air inlet of the eighth programmable valve, the air outlet of the seventh programmable valve is communicated with the pipe-side air inlet of the second-level main condenser, and the air outlet of the eighth programmable valve is communicated with the pipe-side air inlet of the second-level secondary condenser; The air inlet of the thirteenth programmable valve is communicated with the pipe-side air outlet of the secondary main condenser, the air outlet of the thirteenth programmable valve is communicated with the pipe-side air inlet of the tertiary condenser, the air inlet of the fourteenth programmable valve is communicated with the pipe-side air outlet of the secondary sub-condenser, and the air outlet of the fourteenth programmable valve is communicated with the pipe-side air inlet of the tertiary condenser; The air inlet of the eleventh program-controlled valve is communicated with the shell-side air outlet of the three-stage condenser, the air outlet of the eleventh program-controlled valve is communicated with the shell-side air inlet of the secondary main condenser, the air inlet of the twelfth program-controlled valve is communicated with the shell-side air outlet of the three-stage condenser, and the air outlet of the twelfth program-controlled valve is communicated with the shell-side air inlet of the secondary secondary condenser; The air inlet of the tenth programmable valve is connected to the shell-side air outlet of the secondary main condenser, the air outlet of the tenth programmable valve is connected to the air inlet of the third programmable valve and the air inlet of the fourth programmable valve, the air inlet of the ninth programmable valve is connected to the shell-side air outlet of the secondary secondary condenser, the air outlet of the ninth programmable valve is connected to the air inlet of the third programmable valve and the air inlet of the fourth programmable valve, the air outlet of the fourth programmable valve is connected to the shell-side air inlet of the first main condenser, and the air outlet of the third programmable valve is connected to the shell-side air inlet of the first secondary condenser.

5. The multi-stage purification and reuse device for nitrogen-sealed VOCs according to claim 3, characterized in that: Demisters are provided below the tube-side gas outlets of the first-stage main condenser, the second-stage main condenser, the third-stage condenser, the fourth-stage condenser, the first-stage secondary condenser and the second-stage secondary condenser.

6. The multi-stage purification and reuse device for nitrogen-sealed VOCs according to claim 3, characterized in that: The first-stage main condenser, the second-stage main condenser, the third-stage condenser, the fourth-stage condenser, the first-stage secondary condenser and the second-stage secondary condenser are all provided with drain ports, and each of the drain ports is connected to an oil collecting tank.

7. The multi-stage purification and reuse device for nitrogen-sealed VOCs according to claim 3, characterized in that: Temperature detection instruments are provided at the pipe-side gas outlets of the first-stage main condenser, the second-stage main condenser, the third-stage condenser, the fourth-stage condenser, the first-stage secondary condenser and the second-stage secondary condenser.

8. The multi-stage purification and reuse device for nitrogen-sealed VOCs according to claim 4, characterized in that: A first differential pressure detector is provided on the pipeline between the air inlet of the first program-controlled valve and the air outlet of the fifth program-controlled valve, and on the pipeline between the air inlet of the second program-controlled valve and the air outlet of the sixth program-controlled valve; A second differential pressure detector is provided on the pipeline between the air inlet of the seventh programmable valve and the air outlet of the thirteenth programmable valve, and on the pipeline between the air inlet of the eighth programmable valve and the air outlet of the fourteenth programmable valve.

9. The multi-stage purification and reuse device for nitrogen-sealed VOCs according to claim 2, characterized in that: The condensing temperatures of the first-stage main condenser, the second-stage main condenser, the third-stage condenser and the fourth-stage condenser decrease in sequence. The condensing temperature range of the first-stage main condenser is 0~-5 degrees Celsius, the condensing temperature range of the second-stage main condenser is -35~-45 degrees Celsius, the condensing temperature range of the third-stage condenser is -75~-85 degrees Celsius, and the condensing temperature range of the fourth-stage condenser is -115~-125 degrees Celsius.

10. The multi-stage purification and reuse device for nitrogen-sealed VOCs according to any one of claims 1 to 9, characterized in that: The multi-stage purification and reuse device for nitrogen-sealed VOCs further comprises a fan, wherein the air inlet of the fan is connected to the VOCs inlet, and the air outlet of the fan is connected to the tube-side air inlet of the first-stage condenser; The shell-side air inlet of the final condenser is connected to a liquid nitrogen flow regulating valve, and a VOCs concentration sensor is provided at the shell-side air outlet of the first-stage condenser. The liquid nitrogen flow regulating valve is configured to adjust the liquid nitrogen input amount based on data from the VOCs concentration sensor.

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