A device for recovering dichloromethane and liquid nitrogen by deep cooling

Abstract

The utility model relates to exhaust treatment technical field, concretely is a kind of methylene chloride liquid nitrogen deep cooling recovery device.The device includes three-stage condensing unit, nitrogen supply unit, condensate collection unit and automatic control unit;The three-stage condensing unit is connected in series by first-stage spiral plate condenser, second-stage tube condenser, third-stage liquid nitrogen vaporizer, realizes the gradient condensation of waste gas;Nitrogen supply unit provides cold energy by glycol refrigerant, low-temperature nitrogen and liquid nitrogen grading, and recycled nitrogen after vaporization is used in workshop nitrogen seal;Condensate collection unit collects each stage condensate by liquid seal pipe, and uncondensed gas is recycled to front end of system and processed again;Automatic control unit is interlocked by temperature, pressure, differential pressure sensor and PLC control, realizes the intelligent regulation and control of liquid nitrogen flow, valve switching and thawing operation.The utility model solves the problem of high-concentration methylene chloride waste gas, low-temperature ice blocking and cold energy waste, has the advantages of efficient recovery and stable operation, and is suitable for comprehensive treatment of methylene chloride waste gas in pharmaceutical and chemical industry.

Description

Technical Field

[0001] This utility model belongs to the field of waste gas treatment technology, specifically relating to a dichloromethane liquid nitrogen cryogenic recovery device. Background Technology

[0002] Currently, conventional industrial treatment technologies for dichloromethane (DCM) waste gas mainly include membrane separation and activated carbon adsorption. While membrane separation can partially recover DCM, the concentration of DCM in the treated waste gas remains as high as 4000 mg / m³. 3 The above points are relevant; activated carbon adsorption has problems such as limited adsorption capacity, high regeneration energy consumption, and susceptibility to water vapor interference, making it difficult to achieve stable emission standards.

[0003] For the deep treatment of low-boiling-point organic compounds, liquid nitrogen cryogenic technology can significantly improve the condensation efficiency of dichloromethane because it can provide a low-temperature environment below -90℃. However, the application of liquid nitrogen cryogenic technology needs to solve two key problems: first, the utilization efficiency of liquid nitrogen cold energy is too low; second, dichloromethane waste gas contains trace amounts of moisture in a low-temperature environment, which is prone to freezing and clogging pipes or condensers at low temperatures.

[0004] Chinese Patent CN119733337A discloses an integrated liquid nitrogen cryogenic waste gas treatment and solvent recovery system, relating to the field of waste gas treatment technology. The system includes a waste gas input pressurization unit, a liquid nitrogen condensation and recovery unit, a tail gas treatment optimization unit, and a solvent storage unit. The tail gas treatment optimization unit includes a cold energy recovery heat exchanger and a demister. The top and bottom of the demister are the exhaust end and intake end, respectively, and the demister's interior is equipped with a curved plate demister mechanism and an active cleaning mechanism. This invention organically combines the waste gas input pressurization unit, liquid nitrogen condensation and recovery unit, tail gas treatment optimization unit, and solvent storage unit, realizing an integrated process from waste gas input to solvent recovery and tail gas treatment. The system is rationally designed, compact in structure, and improves overall operating efficiency and stability, possessing high social value and application prospects. The aforementioned device lacks a specifically designed multi-stage low-temperature gradient, which may result in the exhaust gas concentration remaining higher than the subsequent treatment requirements after condensation. While a demister is installed in the exhaust gas treatment optimization unit to remove liquid water, no active defreezing measures are designed for ice blockage scenarios. In actual operation, ice blockage can lead to increased pressure differential, decreased treatment efficiency, and even shutdown, failing to meet the requirements for continuous and stable operation. Therefore, those skilled in the art urgently need to solve the aforementioned technical problems. Utility Model Content

[0005] The present invention aims to solve the above-mentioned prior art, effectively reduce the concentration of exhaust gas, and improve the operational stability of equipment.

[0006] The technical solution adopted by this utility model is:

[0007] A cryogenic liquid nitrogen recovery device for treating dichloromethane waste gas includes a three-stage condensation unit, a nitrogen supply unit, a condensate collection unit, and an automatic control unit.

[0008] The three-stage condensation unit includes a first-stage condenser, a second-stage condenser, and a third-stage vaporizer arranged in series.

[0009] The nitrogen supply unit includes a liquid nitrogen tank, a workshop nitrogen storage tank, an ethylene glycol refrigerant supply pipeline, and a steam supply pipeline;

[0010] The condensate collection unit includes a receiving tank and a liquid seal pipe;

[0011] The automatic control unit includes a PLC control cabinet and sensors;

[0012] The nitrogen supply unit is connected to the refrigerant side of the three-stage condensation unit;

[0013] The condensate collection unit is connected to the liquid phase outlet of the three-stage condensation unit via a liquid seal pipe;

[0014] The three-stage condensation unit is connected to the nitrogen supply unit and the condensate collection unit via pipelines, and the sensors of the automatic control unit are installed in the three-stage condensation unit, the nitrogen supply unit, and the condensate collection unit.

[0015] The dichloromethane waste gas is cooled and recovered in stages through the series connection of the three-stage condensation units.

[0016] By adopting the above technical solution, the series design of the three-stage condensation unit allows dichloromethane exhaust gas to pass through three stages sequentially: pre-cooling (first stage), intermediate cooling (second stage), and deep cooling (third stage). Through step-by-step temperature reduction precisely matching the condensation characteristics of dichloromethane (from -5℃ to -35℃ and then to -90℃), the condensation efficiency of high-concentration exhaust gas is significantly improved, ensuring a substantial reduction in exhaust gas concentration. The nitrogen supply unit is connected to the refrigerant side of the three-stage condensation unit, utilizing ethylene glycol refrigerant for initial cooling (reducing liquid nitrogen consumption) and providing intermediate and ultra-low temperature cooling energy through low-temperature nitrogen and liquid nitrogen, thus realizing the cooling energy... The gradient utilization avoids the waste of a single cold source; the condensate collection unit is connected to the liquid phase outlet of the three-stage condensation unit through a liquid seal pipe, which not only prevents gas phase leakage during condensate collection, but also recycles uncondensed waste gas back to the front end of the system through the connection between the gas phase outlet of the receiving tank and the waste gas collection end, thereby improving the overall recovery rate of dichloromethane; the sensors of the automatic control unit are installed at key nodes of each unit, and in conjunction with the signal connection of the PLC automatic control cabinet, real-time monitoring and intelligent control of parameters such as cold energy supply, condensation temperature, and equipment differential pressure are realized, effectively preventing faults such as ice blockage and overpressure, and ensuring continuous and stable operation of the equipment.

[0017] Furthermore, the first-stage condenser consists of two spiral plate heat exchangers connected in parallel;

[0018] The shell-side inlet of the first-stage condenser is connected to the dichloromethane exhaust gas collection fan, and the shell-side outlet is connected to the shell-side inlet of the second-stage condenser.

[0019] The tube-side inlet of the first-stage condenser is connected to the ethylene glycol refrigerant supply line of the nitrogen supply unit, and the tube-side outlet is connected to the ethylene glycol refrigerant return line.

[0020] The outer shell of the first-stage condenser is equipped with a steam tracing coil. The inlet of the steam tracing coil is connected to the steam supply pipeline of the nitrogen supply unit, and the outlet is connected to the steam trap assembly.

[0021] By adopting the above technical solution, the "one in use, one standby" design of the two parallel spiral plate heat exchangers, combined with the connection between the shell-side inlet and the exhaust gas collection fan, and the shell-side outlet and the second-stage condenser, ensures seamless switching to the other condenser when the differential pressure increases due to ice blockage or scaling in one condenser. This avoids system downtime caused by equipment maintenance and significantly improves the continuous processing capacity of the unit. The connection between the tube-side inlet and the ethylene glycol refrigerant supply pipeline utilizes conventional low-temperature ethylene glycol to pre-cool the exhaust gas to -5°C, achieving both pre-condensation of moisture and reducing the direct consumption of liquid nitrogen. This system enables the graded utilization of cold energy, reducing operating costs. The connection between the outer shell steam heating coil and the steam supply pipeline and drain valve group allows for rapid thawing of the condenser when it is blocked by ice. Combined with the one-in-use and one-out-of-use switching logic, it avoids equipment failure or frequent manual cleaning caused by ice blockage, ensuring reliable operation under low-temperature conditions. The shell-side inlet is connected in series with the exhaust fan, and the outlet is connected in series with the second-stage condenser, allowing the exhaust gas to directly enter the next stage after pre-cooling in the first stage. This reduces pipeline redundancy and pressure loss, improving the overall efficiency of exhaust gas treatment.

[0022] Furthermore, the second-stage condenser is a shell-and-tube heat exchanger;

[0023] The shell-side inlet of the second-stage condenser is connected to the shell-side outlet of the first-stage condenser, and the shell-side outlet is connected to the shell-side inlet of the third-stage vaporizer.

[0024] The tube-side inlet of the second-stage condenser is connected to the low-temperature nitrogen outlet of the nitrogen supply unit, and the tube-side outlet is connected to the workshop nitrogen storage tank of the nitrogen supply unit.

[0025] By adopting the above technical solution, the shell-side inlet is connected in series with the outlet of the first-stage condenser and with the inlet of the third-stage vaporizer. This allows the exhaust gas to seamlessly enter the second stage after pre-cooling at -5°C, further cooling it to -35°C, forming a gradient condensation process. This precisely matches the condensation characteristics of dichloromethane at different temperatures, significantly improving the overall recovery efficiency of high-concentration exhaust gas. The tube-side inlet is connected to the low-temperature nitrogen outlet of the nitrogen supply unit, utilizing the low-temperature nitrogen that has not yet fully heated after liquid nitrogen vaporization as a refrigerant. This cools the exhaust gas to -35°C by releasing the cold energy of the nitrogen. The nitrogen gas, after releasing its cooling energy, is then connected to the nitrogen storage tank in the workshop via the tube outlet. This allows for the reuse of the nitrogen in processes such as nitrogen sealing in the workshop, achieving multi-stage utilization of liquid nitrogen cooling energy, avoiding energy waste, and reducing liquid nitrogen consumption. A shell-and-tube heat exchanger is used as the second-stage condenser. Its shell-and-tube structure is highly adaptable to medium and low temperature conditions and is more resistant to pressure fluctuations than a spiral plate heat exchanger. Furthermore, it is less likely to form ice bridges between the tubes due to trace amounts of residual moisture, reducing the risk of ice blockage. At the same time, the modular design of the shell-and-tube heat exchanger facilitates inspection and maintenance, ensuring the long-term stable operation of the intermediate cooling system.

[0026] Furthermore, the third-stage vaporizer consists of two vaporizers connected in parallel;

[0027] The shell side of the third-stage vaporizer is a waste gas passage with waste gas entering from the bottom and exiting from the top. The shell side inlet is connected to the shell side outlet of the second-stage condenser, and the shell side outlet is connected to the tail gas main pipe of the adsorption-desorption device.

[0028] The third-stage vaporizer also includes a workshop vaporizer. The tube side of the workshop vaporizer is a liquid nitrogen channel with liquid nitrogen entering and exiting from the bottom. The tube side inlet is connected to the liquid nitrogen main pipeline of the liquid nitrogen tank of the nitrogen supply unit, and the tube side outlet is connected to the workshop nitrogen storage tank of the nitrogen supply unit.

[0029] A hot compressed air coil is provided between the shell side and the outer shell of the third-stage vaporizer, and the inlet of the hot compressed air coil is connected to the compressed air outlet of the steam heat exchanger.

[0030] By adopting the above technical solution, the design of two parallel vaporizers, combined with the connection between the shell-side inlet and the outlet of the second-stage condenser, and the connection between the shell-side outlet and the adsorption-desorption device, ensures that when one vaporizer needs to be thawed due to ice blockage or frost, the other can seamlessly take over the cryogenic task, avoiding system downtime due to equipment maintenance, ensuring the continuity of the -90℃ deep condensation process, and significantly improving the final recovery efficiency of dichloromethane. The connection between the tube-side liquid nitrogen channel and the liquid nitrogen tank and the workshop gas storage tank allows liquid nitrogen to directly release ultra-low temperature cold energy within the vaporizer, cooling the exhaust gas from -35℃ to... -90℃; the vaporized nitrogen is returned to the workshop nitrogen storage tank through the tube outlet, which not only completes the cryogenic task, but also realizes the full-chain utilization of liquid nitrogen cold energy, avoiding cold energy waste. The connection between the shell side and the outer shell of the hot compressed air coil and the steam heat exchanger heats the compressed air to 60℃ through steam. When the vaporizer is blocked by ice due to residual moisture, the hot compressed air circulates to heat the outer shell and quickly thaws the ice blockage in the shell side. With the switching logic of one in use and one in standby, the equipment failure or frequent manual intervention caused by ice blockage at deep low temperature is avoided, ensuring the reliability of the cryogenic process.

[0031] Furthermore, the condensate collection unit has two receiving tanks;

[0032] The shell-side liquid outlet of the first-stage condenser is connected to the inlet of one of the receiving tanks via a liquid seal pipe, and the shell-side liquid outlets of the second-stage condenser and the third-stage vaporizer are connected to the inlet of another receiving tank via liquid seal pipes.

[0033] The top gas phase outlet of the receiving tank is connected to the inlet pipe of the dichloromethane waste gas collection fan.

[0034] Furthermore, the automatic control unit includes a temperature sensor, a pressure sensor, and a differential pressure sensor;

[0035] The temperature sensor is located at the shell-side outlet of the third-stage vaporizer, the pressure sensor is located in the workshop nitrogen storage tank of the nitrogen supply unit, and the differential pressure sensor is located before and after the first-stage condenser.

[0036] The PLC control cabinet is electrically connected to the temperature sensor, pressure sensor, and differential pressure sensor, respectively.

[0037] The beneficial effects of this utility model are as follows:

[0038] 1. This utility model, through the series design of three-stage condensation units, allows dichloromethane waste gas to pass through three stages in sequence: pre-cooling, intermediate cooling, and deep cooling. This precisely matches the condensation characteristics of dichloromethane at different temperatures, significantly improving the condensation efficiency of high-concentration waste gas and ensuring a substantial reduction in waste gas concentration. This lays the foundation for subsequent connection to the adsorption-desorption device to achieve emission standards.

[0039] 2. This utility model connects the nitrogen supply unit to the refrigerant side of the three-stage condensation unit, and uses ethylene glycol refrigerant, low-temperature nitrogen and liquid nitrogen to form a gradient cold energy supply, which not only reduces the direct consumption of liquid nitrogen, but also realizes the multi-stage utilization of cold energy through the secondary reuse of nitrogen cold energy, effectively reducing the operating cost of the device.

[0040] 3. This utility model solves the problem of ice blockage of equipment by trace amounts of moisture in exhaust gas at low temperatures by using the steam heating coil of the first-stage condenser and the hot compressed air coil of the third-stage vaporizer, combined with the "one for use and one for standby" switching logic. This avoids downtime or frequent manual cleaning caused by ice blockage and ensures the continuous and stable operation of the device under low temperature conditions.

[0041] 4. This utility model achieves real-time monitoring and intelligent control of key parameters such as condensation temperature, nitrogen pressure, and condenser differential pressure by electrically connecting the sensor of the automatic control unit to the PLC automatic control cabinet, effectively preventing faults such as overpressure and ice blockage, and significantly improving the reliability and automation level of the device operation. Attached Figure Description

[0042] The above and / or additional aspects and advantages of this utility model will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, in which:

[0043] Figure 1 This is a schematic diagram of the structure of this utility model;

[0044] Figure 2 for Figure 1 Enlarged diagram of section A in the middle;

[0045] Figure 3 for Figure 1 Enlarged diagram of section B in the middle;

[0046] Figure 4 for Figure 1 Enlarged diagram of section C.

[0047] Among them, 10-three-stage condensation unit; 11-first-stage condenser; 12-second-stage condenser; 13-third-stage vaporizer; 131-workshop vaporizer;

[0048] 20 - Nitrogen supply unit; 21 - Liquid nitrogen tank; 22 - Workshop nitrogen storage tank;

[0049] 30 - Condensate collection unit; 31 - Receiving tank; 32 - Liquid seal pipe;

[0050] 40 - Exhaust gas collection fan. Detailed Implementation

[0051] The embodiments of this utility model are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this utility model, and should not be construed as limiting this utility model.

[0052] The dichloromethane liquid nitrogen cryogenic recovery device of this utility model embodiment is described below with reference to the accompanying drawings.

[0053] like Figure 1 , Figure 2 and Figure 3 As shown in the embodiment of this utility model, the three-stage condensation unit 10 is the core processing module of the dichloromethane liquid nitrogen cryogenic recovery device. It consists of a first-stage condenser 11, a second-stage condenser 12, and a third-stage vaporizer 13 connected in series. All components are connected end-to-end through an exhaust gas pipeline to achieve a gradient cooling of the exhaust gas from -5℃ to -35℃ and then to -90℃. The first-stage condenser 11 consists of two spiral plate heat exchangers connected in parallel, one in use and one on standby. The shell-side inlet of the first-stage condenser 11 is connected to the outlet of the dichloromethane exhaust gas collection fan 40 through an exhaust gas pipeline. The exhaust gas enters the shell side from the exhaust gas collection fan 40. The shell-side outlet of the first-stage condenser 11 is connected to the second-stage condenser 12 through a pipeline. The shell-side inlet is connected to the pre-cooled exhaust gas entering the second-stage condenser 12. The tube-side inlet of the first-stage condenser 11 is connected to the ethylene glycol refrigerant supply pipeline of the nitrogen supply unit 20. The low-temperature ethylene glycol refrigerant enters the tube side to provide -5℃ cooling energy. The tube-side outlet of the first-stage condenser 11 is connected to the ethylene glycol refrigerant return pipeline. After heat exchange, the refrigerant returns to the circulation system. A steam tracing coil is welded to the outer shell of the condenser unit 10 and spirally wraps around the outer wall of the shell side. The coil inlet is connected to the steam supply pipeline of the nitrogen supply unit 20 through a steam pipe. The coil outlet is connected to a steam trap group through a pipe to discharge steam condensate and connect to the steam heating shell to thaw ice blockage in the shell side.

[0054] The second-stage condenser 12 is a shell-and-tube heat exchanger. The shell-side inlet of the second-stage condenser 12 is connected to the shell-side outlet of the first-stage condenser 11 via a pipeline to receive pre-cooled waste gas at -5℃. The shell-side outlet of the second-stage condenser 12 is connected to the shell-side inlet of the third-stage vaporizer 13 via a pipeline. The intercooled waste gas at -35℃ enters the third-stage vaporizer 13. The tube-side inlet of the second-stage condenser 12 is connected to the low-temperature nitrogen gas after liquid nitrogen vaporization from the low-temperature nitrogen outlet of the nitrogen supply unit 20 via a nitrogen pipeline. The nitrogen gas enters the tube side to provide intercooling energy. The tube-side outlet of the second-stage condenser 12 is connected to the workshop nitrogen storage tank 22 via a pipeline. The nitrogen gas after releasing the cooling energy is recycled for workshop nitrogen sealing.

[0055] The third-stage vaporizer 13 consists of two parallel workshop vaporizers 131. The shell side of the third-stage vaporizer 13 has a vertical exhaust gas channel with bottom inlet and top outlet. Its inlet is connected to the shell-side outlet of the second-stage condenser 12 via a pipe to receive -35℃ intercooled exhaust gas. The shell-side outlet of the third-stage vaporizer 13 is connected to the exhaust gas main pipe of the adsorption-desorption unit via a pipe, allowing the -90℃ cryogenic exhaust gas to enter the adsorption treatment. The tube side of the third-stage vaporizer 13 has a vertical liquid nitrogen channel with bottom inlet and bottom outlet. Its inlet is connected to the nitrogen supply via a liquid nitrogen pipeline. The liquid nitrogen main pipeline of the liquid nitrogen tank 21 in unit 20 connects to the storage tank, allowing liquid nitrogen to enter the tube side and release -195℃ ultra-low temperature cold energy; the tube side outlet is connected to the workshop nitrogen storage tank 22 through a nitrogen pipeline, and the vaporized nitrogen is recycled to the workshop. A spiral hot compressed air coil is provided between the shell side and the outer shell of the third-stage vaporizer 13, which is surrounded by the outer wall of the shell side. The coil inlet is connected to the compressed air outlet of the steam heat exchanger through a pipeline and heated to 60℃; the coil outlet is directly discharged into the atmosphere, where the hot compressed air heats the outer shell and thaws the ice blockage in the shell side.

[0056] Nitrogen supply unit 20 is the core source of cooling energy, providing gradient cooling energy to the three-stage condensing unit through multiple pipelines and recovering vaporized nitrogen. Liquid nitrogen tank 21 is connected to the tube-side inlet of the third-stage vaporizer 13 via a liquid nitrogen pipeline to directly supply liquid nitrogen. At the same time, a branch of the main liquid nitrogen pipeline goes to the workshop vaporizer 131 for conventional nitrogen sealing. The tube-side outlet is connected to the workshop nitrogen storage tank 22 via a pipeline to store the vaporized liquid nitrogen. The workshop nitrogen storage tank 22 is connected to the tube-side inlet of the second-stage condenser 12 via a nitrogen pipeline to supply low-temperature nitrogen as an intercooling refrigerant. A pressure sensor self-control unit is installed on the top of the storage tank to monitor the pressure and interlock the liquid nitrogen shut-off valve. The ethylene glycol refrigerant supply pipeline is connected to the tube-side inlet of the first-stage condenser 11 via a pipeline to supply -15℃ ethylene glycol as a precooling refrigerant. The return pipeline returns to the refrigerant unit for recycling. The steam supply pipeline is connected to the inlet of the steam tracing coil of the first-stage condenser 11 via a pipeline to supply 0.3MPa steam for defrosting, and the outlet of the steam trap group is connected to the condensate recovery system via a pipeline.

[0057] The condensate collection unit 30 connects to the liquid phase outlet of the three-stage condensation unit via a liquid seal pipe 32, achieving centralized collection of dichloromethane liquid and circulation of uncondensed gas. The receiving tanks 31 consist of two φ800×1000mm, 0.5m³ insulated storage tanks. The inlet of the first receiving tank 31 is connected to the shell-side liquid phase outlet of the first-stage condenser 11 via a 500mm liquid seal pipe 32 to collect the dichloromethane liquid generated during pre-cooling at -5℃. The top gas phase outlet is connected to the inlet pipe of the dichloromethane exhaust gas collection fan 40 via a pipeline, circulating the uncondensed gas back to the condensate collection unit. At the system front end, the inlet of the second receiving tank 31 is connected to the shell-side liquid outlet of the second-stage condenser 12 and the shell-side liquid outlet of the third-stage vaporizer 13 via a 500mm liquid seal pipe 32 to collect dichloromethane liquid generated by the -35℃ intermediate cooling and -90℃ deep cooling. The top gas phase outlet is also connected to the inlet of the waste gas collection fan 40 via a pipe for the recycling of uncondensed gas. All liquid seal pipes 32 are made of stainless steel and have a vertical height of 500mm to prevent gas phase leakage through the liquid phase outlet. The bottom is welded and fixed to the inlet of the receiving tank 31.

[0058] In one embodiment, the automatic control unit monitors key parameters in real time through sensors and implements intelligent interlock control via a PLC control cabinet. Three temperature sensors are installed on the shell-side outlet pipe of the third-stage vaporizer 13 to monitor the temperature of the cryogenic exhaust gas, with a target of -90°C. The signal is transmitted via a shielded cable to the PLC control cabinet to interlock and control the opening of the liquid nitrogen regulating valve. Two pressure sensors are installed: one is installed on the top of the nitrogen storage tank 22 in the workshop to monitor nitrogen pressure, with a target of 0.15–0.25 MPa; the other is installed on the shell-side inlet pipe of the first-stage condenser 11 to monitor exhaust gas pressure to prevent overpressure. The signal is transmitted to the PLC to interlock and control the liquid nitrogen shut-off valve.

[0059] Two differential pressure sensors are installed on the inlet and outlet pipes of the shell side of the first-stage condenser 11 to monitor the pressure difference before and after. The target is ≤1kPa. When the differential pressure exceeds the limit, the signal is transmitted to the PLC and the switching logic of the first-stage condenser is triggered, the standby condenser is started and the steam tracing defrosting is started.

[0060] The PLC control cabinet is integrated in the equipment control room. It is electrically connected to all sensors via a 485 bus and outputs signals to control actuators such as liquid nitrogen regulating valves, nitrogen pneumatic valves, and steam pneumatic valves to achieve closed-loop control of temperature, pressure, and differential pressure.

[0061] Working Principle: Dichloromethane exhaust gas is fed into the first-stage condenser 11 by the exhaust gas collection fan 40, where it is pre-cooled to -5°C using ethylene glycol refrigerant to remove trace amounts of moisture. After pre-cooling, the exhaust gas enters the second-stage condenser 12, where it is further cooled to -35°C using low-temperature nitrogen gas obtained from liquid nitrogen vaporization. After intercooling, the exhaust gas enters the third-stage vaporizer 13, where it is directly cooled to -90°C by releasing ultra-low temperature cold energy directly from liquid nitrogen. Through three-stage gradient condensation, the condensation characteristics of dichloromethane are precisely matched, condensing the dichloromethane in the exhaust gas into a liquid. Simultaneously, the nitrogen supply unit works in synergy with multiple cold energy sources. The first-stage condenser 11 uses conventional ethylene glycol refrigerant to reduce liquid nitrogen consumption. The second-stage condenser 12 utilizes the low-temperature nitrogen gas that has not fully heated after liquid nitrogen vaporization for secondary cold energy utilization. The third-stage condenser 13 directly uses liquid nitrogen to provide ultra-low temperature cold energy. The vaporized nitrogen gas is ultimately recycled for nitrogen sealing in the workshop, effectively reducing operating costs. In addition, the dichloromethane liquid from each condensation stage is collected into two receiving tanks 31 via 500mm liquid seal pipes. The uncondensed gas at the top of the receiving tanks 31 is circulated back to the front end of the waste gas collection fan through pipelines and re-enters the system for condensation to improve the overall recovery rate. To address the issue of water freezing at low temperatures, the first-stage condenser 11 adopts a one-in-one-outstand and steam-heated coil defrosting scheme, while the third-stage vaporizer 13 adopts a one-in-one-defrosting and hot compressed air coil defrosting scheme. The automatic control unit monitors key parameters in real time through temperature, pressure, and differential pressure sensors, and the PLC control cabinet interlocks and controls the liquid nitrogen flow, valve switching, and defrosting operation to ensure continuous and stable operation of the equipment.

[0062] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A dichloromethane liquid nitrogen cryogenic recovery device, characterized in that: It includes a three-stage condensation unit (10), a nitrogen supply unit (20), a condensate collection unit (30), and an automatic control unit; The three-stage condensation unit (10) includes a first-stage condenser (11), a second-stage condenser (12) and a third-stage vaporizer (13) arranged in series along the direction of the waste gas flow. The first stage condenser (11) consists of two spiral plate heat exchangers connected in parallel. The shell-side inlet of the first stage condenser (11) is connected to the dichloromethane exhaust gas collection fan (40), the shell-side outlet is connected to the shell-side inlet of the second stage condenser (12), and the tube-side inlet is connected to the ethylene glycol refrigerant supply pipeline of the nitrogen supply unit (20). The second-stage condenser (12) is a shell-and-tube heat exchanger. The shell-side inlet of the second-stage condenser (12) is connected to the shell-side outlet of the first-stage condenser (11), the shell-side outlet is connected to the shell-side inlet of the third-stage vaporizer (13), the tube-side inlet is connected to the low-temperature nitrogen outlet of the nitrogen supply unit (20), and the tube-side outlet is connected to the workshop nitrogen storage tank (22) of the nitrogen supply unit (20). The third-stage vaporizer (13) consists of two vaporizers connected in parallel. The shell side of the third-stage vaporizer (13) is a waste gas passage with waste gas entering from the bottom and exiting from the top. The shell side inlet is connected to the shell side outlet of the second-stage condenser (12), and the shell side outlet is connected to the tail gas main pipe of the adsorption and desorption device. The pipe side inlet is connected to the liquid nitrogen main pipeline of the liquid nitrogen tank (21) of the nitrogen supply unit (20), and the pipe side outlet is connected to the workshop nitrogen storage tank (22). The condensate collection unit (30) includes a receiving tank (31) and a liquid seal pipe (32), which is connected to the liquid phase outlet of the three-stage condensation unit (10). The automatic control unit includes a PLC control cabinet, a temperature sensor, a pressure sensor, and a differential pressure sensor. The temperature sensor is located at the shell-side outlet of the third-stage vaporizer (13), the pressure sensor is located at the nitrogen storage tank (22) in the workshop, and the differential pressure sensor is located before and after the first-stage condenser (11). The PLC control cabinet is electrically connected to the temperature sensor, the pressure sensor, the differential pressure sensor, the liquid nitrogen regulating valve, the liquid nitrogen shut-off valve, the nitrogen pneumatic valve, and the steam pneumatic valve, respectively.

2. The dichloromethane liquid nitrogen cryogenic recovery device according to claim 1, characterized in that: The tube outlet of the first stage condenser (11) is connected to the ethylene glycol refrigerant return pipeline. The outer shell of the first stage condenser (11) is equipped with a steam tracing coil. The inlet of the steam tracing coil is connected to the steam supply pipeline of the nitrogen supply unit (20), and the outlet is connected to the steam trap valve group.

3. The dichloromethane liquid nitrogen cryogenic recovery device according to claim 1, characterized in that: The tube-side inlet of the second-stage condenser (12) is connected to the outlet of the low-temperature nitrogen gas after liquid nitrogen vaporization, so that the low-temperature nitrogen gas is used as the refrigerant of the second-stage condenser (12). The tube-side outlet of the second-stage condenser (12) is connected to the workshop nitrogen storage tank (22), so that the nitrogen gas after releasing the cold energy enters the workshop nitrogen storage tank (22).

4. The dichloromethane liquid nitrogen cryogenic recovery device according to claim 1, characterized in that: The third-stage vaporizer (13) also includes a workshop vaporizer (131). The tube side of the workshop vaporizer (131) is a liquid nitrogen channel with liquid nitrogen entering and exiting from the bottom. The tube side inlet of the workshop vaporizer (131) is connected to the liquid nitrogen main pipeline of the liquid nitrogen tank (21), and the tube side outlet is connected to the workshop nitrogen storage tank (22).

5. The dichloromethane liquid nitrogen cryogenic recovery device according to claim 1, characterized in that: A hot compressed air coil is provided between the shell side and the outer shell of the third-stage vaporizer (13), and the inlet of the hot compressed air coil is connected to the compressed air outlet of the steam heat exchanger.

6. The dichloromethane liquid nitrogen cryogenic recovery device according to claim 1, characterized in that: There are two receiving tanks (31). The shell-side liquid outlet of the first-stage condenser (11) is connected to the inlet of one of the receiving tanks (31) through a liquid seal pipe (32). The shell-side liquid outlets of the second-stage condenser (12) and the third-stage vaporizer (13) are connected to the inlet of the other receiving tank (31) through a liquid seal pipe (32).

7. The dichloromethane liquid nitrogen cryogenic recovery device according to claim 6, characterized in that: The top gas phase outlet of the receiving tank (31) is connected to the inlet pipe of the dichloromethane waste gas collection fan (40).

8. The dichloromethane liquid nitrogen cryogenic recovery device according to claim 1, characterized in that: The PLC control cabinet is used to control the opening of the liquid nitrogen regulating valve according to the temperature signal of the shell outlet of the third-stage vaporizer (13), to control the liquid nitrogen shut-off valve according to the pressure signal of the workshop nitrogen storage tank (22), and to control the operation switching of the two first-stage condensers (11) and the opening of the steam pneumatic valve according to the pressure difference signal before and after the first-stage condenser (11).

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