Method for recovering organic waste gas containing high-concentration dichloromethane

Abstract

The invention provides a method for recovering organic waste gas containing high-concentration dichloromethane. The method comprises the following steps: enabling the organic waste gas containing dichloromethane with the concentration higher than 30000 PPM to pass through a low-temperature condensation module; cooling the gas to-30 DEG C to-40 DEG C, recovering condensed dichloromethane, enabling the condensed gas phase to enter an adsorption recovery module, and recovering residual dichloromethane in the waste gas through the adsorption recovery module; the low-temperature condensation system comprises two or more condensers connected in parallel, when the interior of the condenser in a dichloromethane waste gas condensation state is iced, so that the pressure drop is increased or the waste gas cannot pass through when the waste gas passes through or the set time is reached, the condenser is switched to an ice melting state, and the temperature of the condenser is reduced. And switching to other condensers to condense the dichloromethane waste gas. The problem that ice melting of the low-temperature condensation module is difficult and not thorough is solved, the solvent recovery rate is increased, online continuous operation of the device is achieved, and operation energy consumption and investment cost are greatly reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of volatile organic solvent recovery, and particularly relates to a method for recovering organic waste gas containing high-concentration dichloromethane. Background Art

[0002] At present, the methods for treating high-concentration organic waste gas and recovering organic solvents mainly include condensation method, adsorption method, absorption method and membrane separation method. High-concentration organic waste gas is suitable for recovery by the condensation method, and low-concentration organic gas is suitable for recovery by the adsorption method.

[0003] The principle of the condensation method is to utilize the different saturated vapor pressures of gaseous pollutants at different temperatures and pressures, and lower the temperature to condense some pollutants to achieve the purpose of purification or recovery.

[0004] The selection of the condensation temperature for organic waste gas containing high-concentration dichloromethane is crucial for the condensation effect. If the condensation temperature is too high, the separation of high-concentration dichloromethane and air may be incomplete, and the inlet concentration of the subsequent adsorption device is high, the device is large, and the investment cost and the operating energy consumption of the adsorption device are high; while if the condensation temperature is too low, it will cause excessive energy consumption of the condensation device, resulting in waste, and during the use of the condensation device, the organic waste gas containing high-concentration dichloromethane usually contains water vapor, and the condensation device will produce frost blockage and ice blockage, causing the condensation device to be unable to operate continuously and normally. The selection of the condensation temperature, frost blockage and ice blockage problems are important problems that need to be faced in the practical application of the condensation technology.

[0005] The gas after condensation enters the adsorption device. The adsorption method is a technology widely used in the field of volatile organic gas treatment and organic solvent recovery. The adsorption method separates the organic components from the air components by utilizing the difference in the binding force between the components in the organic waste gas and the adsorbent. The organic components that are easily adsorbed are fixed in the adsorbent bed layer, and the air components that are not easily adsorbed are discharged into the atmosphere. The adsorbent will gradually become saturated during use, and it is necessary to regenerate the adsorbent online to restore its adsorption performance and make the adsorption device operate continuously. The regeneration process usually requires a certain amount of energy, such as steam, and the amount of steam consumed for regeneration is large, resulting in high energy consumption.

[0006] The Chinese utility model patent with the authorization announcement number CN217613860U discloses a high-concentration dichloromethane waste gas recovery and treatment system: characterized in that it includes a condensation recovery device, an adsorption system, a fan and an exhaust pipe in sequence along the flow direction of the gas, the condensation recovery device is used to condense and recover the high-concentration dichloromethane waste gas, the inlet direction of the adsorption system is connected to the outlet of the condensation recovery device, the outlet direction of the adsorption system is connected to the fan, the fan is also connected to the exhaust pipe, the adsorption system is filled with an adsorption material for adsorbing dichloromethane gas, the fan drives the waste gas flowing out of the condensation recovery device into the adsorption system, and the purified gas is discharged from the exhaust pipe. This patent solves the problem of purifying high-concentration dichloromethane waste gas, but the invention method does not solve the problem that the condensation device will produce frost and ice blockage when the high-concentration dichloromethane organic waste gas usually contains water vapor, does not solve the problem of online continuous operation of the recovery and treatment system, and does not disclose a specific implementation device.

[0007] In addition, existing technologies often condense waste gas to between -60°C and -70°C to obtain better recovery effects, which greatly increases energy consumption. High-concentration dichloromethane organic waste gas usually contains a large amount of water vapor. How to reduce the moisture content while solving the problems of frost and ice blockage in the pipeline is also an urgent problem to be solved. Summary of the invention

[0008] The purpose of the present invention is to provide a method for recovering organic waste gas containing high concentration of dichloromethane in view of the defects of the prior art, comprising the following steps:

[0009] The organic waste gas containing dichloromethane with a concentration higher than 30,000 PPM is passed through a low-temperature condensation module; the gas is cooled to between -30°C and -40°C, the condensed dichloromethane is recovered, and the condensed gas phase enters the adsorption recovery module, and the remaining dichloromethane in the waste gas is recovered through the adsorption recovery module; the low-temperature condensation system comprises 2 or more parallel condensers, when ice appears inside the condenser in the state of condensing dichloromethane waste gas, resulting in an increase in pressure drop when the waste gas passes through or the waste gas cannot pass through, or when the set time is reached, the condenser is switched to the ice melting state, and switched to other condensers to start condensing the dichloromethane waste gas.

[0010] Furthermore, the adsorption recovery module comprises two or more parallel adsorbers. When the adsorber in the state of adsorbing dichloromethane waste gas is saturated with adsorption, the adsorber is switched to the desorption regeneration state, and other adsorbers are switched to start adsorbing dichloromethane.

[0011] Further, during the condenser ice melting process, the refrigerant supply is stopped, the heat medium supply is opened, and the condenser is heated to 20°C to 40°C by the heat medium for ice melting. The liquid generated during the ice melting process is discharged through the drain port of the condenser for collection. After the ice melting is completed, the heat medium supply is stopped, the refrigerant supply is opened, and the condenser is cooled. After the condenser is cooled to below -30°C, the next condensation of dichloromethane waste gas is carried out.

[0012] Further, the condensation pressure of the low-temperature condensation module is between 0 KPa and 10 KPa (G).

[0013] Further, the refrigerant for low-temperature condensation and the heat medium for ice melting are the same medium; including ethylene glycol aqueous solution, CaCl2 solution, ethanol solution, ice river refrigerant, and Taopus refrigerant.

[0014] Further, the ice melting time range is 15 to 60 minutes.

[0015] Further, after the waste gas cooled by the low-temperature condensation module and the high-concentration organic waste gas are heat-exchanged in the energy-saving heat exchange device, they then enter the adsorption recovery module. After the energy-saving heat exchange, the temperature of the cold-side fluid is between 0°C and 10°C, and the relative humidity is between 1% and 5%; the temperature of the hot-side fluid is between 0°C and 8°C, and the relative humidity is between 95% and 100%.

[0016] Further, the adsorption material of the adsorption recovery module is one or several combinations of activated carbon, activated carbon fiber, molecular sieve, and resin.

[0017] The beneficial effects of the present invention are as follows:

[0018] 1. When icing occurs, the heat medium is introduced into the cryogenic heat exchanger to blow out the melted frost and the water generated by the melting of the frost, solving the problems of difficult and incomplete ice melting in the low-temperature condensation module;

[0019] 2. Through the first heat exchanger, not only can the temperature of the waste gas cooled by the cryogenic heat exchanger be increased, but also the temperature of the initial high-temperature waste gas can be reduced, greatly reducing the condensation load of the subsequent cryogenic heat exchanger and saving refrigerant consumption.

[0020] 3. Due to the adoption of the steam desorption method, the recovery rate of organic solvents in the waste gas is increased;

[0021] 4. Through the second heat exchanger, the steam preheat is used to heat the circulating drying air, so that little or no steam is required to heat the circulating drying air, reducing energy consumption.

[0022] 5. Since each cryogenic heat exchanger can operate independently and alternately, and be maintained in shifts, the online continuous operation of the waste gas energy-saving recovery system is realized, greatly reducing the operation energy consumption and investment cost.

[0023] 6. Through a large number of experiments, for dichloromethane organic waste gas with a concentration higher than 30,000 PPM, this application uses a low-temperature condensation module to cool the gas to between -30°C and -40°C (instead of the conventional -60°C to -70°C), which greatly saves energy consumption and at the same time greatly reduces the moisture in the waste gas (after heat exchange, up to 42% - 62% of the moisture in the high-concentration organic waste gas can be removed). Description of the Drawings

[0024] Figure 1 It is a structural block diagram of an energy-saving recovery system for waste gas containing high-concentration organic solvents.

[0025] Figure 2 It is a structural block diagram of a low-temperature condensation module.

[0026] Figure 3 It is a structural block diagram of another low-temperature condensation module.

[0027] Figure 4 It is a structural block diagram of an adsorption recovery module.

[0028] Reference Signs: 100 - Low-temperature condensation module; 200 - Adsorption recovery module; 110 - First heat exchanger; 120 - Deep cooling heat exchange device; 121 - First deep cooling waste gas channel device; 1211 - First deep cooling heat exchanger; 1212 - First refrigerant; 1213 - First heat medium; 122 - Second deep cooling waste gas channel device; 1221 - Second deep cooling heat exchanger; 1222 - Second refrigerant; 1223 - Second heat medium; 123 - Fan; 124 - Third deep cooling waste gas channel device; 1241 - Third deep cooling heat exchanger; 1242 - Third refrigerant; 1243 - Third heat medium; 125 - Fourth deep cooling waste gas channel device; 1251 - Fourth deep cooling heat exchanger; 1252 - Fourth refrigerant; 1253 - Fourth heat medium; 210 - Adsorption and desorption device; 211 - First adsorber; 212 - Second adsorber; 213 - Third adsorber; 220 - Drying fan; 230 - Second heat exchanger; 240 - Steam generation device; 250 - Solvent recovery storage tank; 260 - Exhaust pipe; 270 - Third heat exchanger

[0029] 1301 - First cryogenic heat exchanger inlet valve; 1302 - First cryogenic heat exchanger outlet valve; 1311 - Second cryogenic heat exchanger inlet valve; 1312 - Second cryogenic heat exchanger outlet valve; 1321 - Third cryogenic heat exchanger inlet valve; 1322 - Third cryogenic heat exchanger outlet valve; 1331 - Fourth cryogenic heat exchanger inlet valve; 1332 - Fourth cryogenic heat exchanger outlet valve; 1341 - First refrigerant inlet valve; 1342 - First heat medium inlet valve; 1343 - First refrigerant outlet valve; 1344 - First heat medium outlet valve; 1351 - Second refrigerant inlet valve; 1352 - Second heat medium inlet valve; 1353 - Second refrigerant outlet valve; 1354 - Second heat medium outlet valve; 1361 - Third refrigerant inlet valve; 1362 - Third heat medium inlet valve; 1363 - Third refrigerant outlet valve; 1364 - Third heat medium outlet valve; 1371 - Fourth refrigerant inlet valve; 1372 - Fourth heat medium inlet valve; 1373 - Fourth refrigerant outlet valve; 1374 - Fourth heat medium outlet valve; 1381 - Gas purge first inlet valve; 1382 - Gas purge first outlet valve; 1383 - Gas purge second inlet valve; 1384 - Gas purge second outlet valve; 2801 - First waste gas inlet valve; 2802 - Second waste gas inlet valve; 2803 - Third waste gas inlet valve; 2804 - First waste gas outlet valve; 2805 - Second waste gas outlet valve; 2806 - Third waste gas outlet valve; 2811 - First steam desorption inlet valve; 2812 - Second steam desorption inlet valve; 2813 - Third steam desorption inlet valve; 2814 - First steam desorption outlet valve; 2815 - Second steam desorption outlet valve; 2816 - Third steam desorption outlet valve; 2821 - First circulating drying air inlet valve; 2822 - Second circulating drying air inlet valve; 2823 - Third circulating drying air inlet valve; 2824 - First circulating drying air outlet valve; 2825 - Second circulating drying air outlet valve; 2826 - Third circulating drying air outlet valve. Detailed implementation mode

[0030] The present invention will be further described below through examples and comparative examples. The drugs used in the following examples are all commercially available products without special instructions, and the methods used are all conventional methods in the art without special instructions.

[0031] Example 1

[0032] As Figure 1 shown, an energy-saving recovery device for waste gas containing high-concentration methylene chloride includes a low-temperature condensation module 100 and an adsorption recovery module 200 in sequence along the gas flow direction, and the outlet of the low-temperature condensation module 100 is communicated with the inlet of the adsorption recovery module 200.

[0033] Refer to Figure 2The low-temperature condensation module 100 further includes a first heat exchanger 110 and a cryogenic heat exchange device 120. Both ends of the cryogenic heat exchange device 120 are connected to the first heat exchanger 110 through pipes. The waste gas enters the cryogenic heat exchange device 120 through the first heat exchanger 110 and then enters the first heat exchanger 110 again. The first heat exchanger 110 is used to exchange heat between the waste gas and the waste gas cooled by the cryogenic heat exchange device 120. The cryogenic heat exchange device 120 is used to cool the initial waste gas after heat exchange by the first heat exchanger 110, so that part of the water vapor and organic solvents in the waste gas condense and are discharged. Since the temperature of the initial waste gas before entering the low-temperature condensation module 100 is relatively high, and the cryogenic heat exchange device 120 can cool the high-temperature waste gas to between -30°C and -40°C. If it is directly discharged into the subsequent adsorption and recovery device, not only a large amount of cold energy is wasted, but even the adsorption material of the subsequent adsorption and recovery device freezes, resulting in system overpressure. Therefore, in the present invention, the cooled waste gas is passed through the first heat exchanger 110 again to exchange heat with the initial high-temperature waste gas entering the first heat exchanger 110 for the first time. On the one hand, this temperature range can effectively condense and recover dichloromethane with a high concentration (>30000 PPM). On the other hand, it can not only increase the temperature of the cooled waste gas, but also reduce the temperature of the initial high-temperature waste gas, greatly reducing the cooling pressure of the subsequent cryogenic heat exchange device 120 and saving the consumption of refrigerant. After heat exchange, the temperature of the waste gas cooled by the cryogenic heat exchange device 120 drops to between 0°C and 10°C, and the relative humidity is between 1% and 5%. The temperature of the initial high-temperature waste gas is between 0°C and 8°C, and the relative humidity is between 95% and 100%. After heat exchange, up to 42% to 62% of the water in the high-concentration organic waste gas can be removed, which is suitable for the condensation process of dichloromethane waste gas containing a large amount of water. By making full use of the cold energy of the cooled waste gas, the present invention reduces the operating energy consumption and ensures safety at the same time.

[0034] In this embodiment, specifically, the cryogenic heat exchange device 120 includes a first cryogenic exhaust gas channel device 121 and a second cryogenic exhaust gas channel device 122. The first heat exchanger 110 is communicated with the first cryogenic exhaust gas channel device 121 or the second cryogenic exhaust gas channel device 122. The first cryogenic exhaust gas channel device 121 includes a first cryogenic heat exchanger 1211, a first refrigerant 1212 and a first heat medium 1213. The first refrigerant 1212 and the first heat medium 1213 are respectively communicated with the first cryogenic heat exchanger 1211. The second cryogenic exhaust gas channel device 122 includes a second cryogenic heat exchanger 1221, a second refrigerant 1222 and a second heat medium 1223. The second refrigerant 1222 and the second heat medium 1223 are respectively communicated with the second cryogenic heat exchanger 1221. This embodiment includes two cryogenic heat exchangers. During the operation of the equipment, one cryogenic heat exchanger cools the exhaust gas, and the other is under maintenance. Because frost will be generated on the surface of the heat exchange pipeline during the cooling of the exhaust gas by the cryogenic heat exchanger, which will affect the continuous operation of the equipment. Therefore, the two cryogenic heat exchangers alternate to cool the exhaust gas to ensure the continuous operation of the equipment. When the cryogenic heat exchanger is under maintenance, a heat medium is introduced to raise the temperature so that the frost melts. The heat medium heats the condenser to 20°C to 40°C for ice melting. The refrigerant and the heat medium for ice melting can use the same medium, including ethylene glycol aqueous solution, CaCl2 solution, ethanol solution, ice river refrigerant, and Taopusi refrigerant.

[0035] The cryogenic heat exchange device 120 includes a fan 123. The fan 123 is in circulating communication with the first cryogenic heat exchanger 1211 or the second cryogenic heat exchanger 1221. The fan 123 is used to blow the frost and the water generated by the melting of the frost in the first cryogenic heat exchanger 1211 and the second cryogenic heat exchanger 1221, and the water flows out from the valve. Because if the water generated by the melting of the frost is not blown clean, it will refreeze during cooling. The fan 123 is used to accelerate the air flow during precooling, speed up the cooling rate of the exhaust gas, and save the consumption of refrigerant and electric energy. The ice melting time is generally more than 5 minutes, and the optimal ice melting time range is 15 to 60 minutes. If the ice melting time is too short, the ice melting will be incomplete, which will affect the normal operation of the low-temperature condensation system. After the first cryogenic heat exchanger 1211 and the second cryogenic heat exchanger 1221 in the ice melting state finish ice melting, it is necessary to precool the first cryogenic heat exchanger 1211 and the second cryogenic heat exchanger 1221. After the first cryogenic heat exchanger 1211 and the second cryogenic heat exchanger 1221 reach the set condensation temperature, the exhaust gas is then connected to the first cryogenic heat exchanger 1211 and the second cryogenic heat exchanger 1221 for cooling. This ensures the stability of the gas condensation temperature and avoids fluctuations in the inlet concentration of the exhaust gas entering the backend adsorption and recovery module due to fluctuations in the gas condensation temperature.

[0036] Reference Figure 4, the adsorption and recovery module 200 further includes a purified exhaust gas discharge pipeline, an organic solvent recovery pipeline, and a circulating drying pipeline.

[0037] The purified exhaust gas discharge pipeline includes an adsorption and desorption device 210 and an exhaust pipe 260 communicating with the adsorption and desorption device 210. The adsorption and desorption device 210 is communicated with the first heat exchanger 110. The cooled exhaust gas is directly introduced into the adsorption and desorption device 210 after heat exchange in the first heat exchanger 110. After the residual organic solvent in the cooled exhaust gas is adsorbed by the adsorption and desorption device 210, the exhaust gas reaches the emission standard and is discharged through the exhaust pipe 260. In this embodiment, the adsorption material is one or several combinations of activated carbon, activated carbon fiber, and resin.

[0038] The organic solvent recovery pipeline includes a steam generation device 240, an adsorption and desorption device 210, a second heat exchanger 230, and a solvent recovery storage tank 250 connected in sequence. Since the steam generated by the steam generation device 240 enters the adsorption and desorption device 210, the adsorbed organic solvent is desorbed and forms a vapor-liquid mixture with the steam and enters the second heat exchanger 230. In the second heat exchanger 230, heat exchange is carried out with the drying air driven by the drying fan 220 to increase the temperature of the drying air, and the temperature of the vapor-liquid mixture decreases and then forms a liquid and is collected in the solvent recovery storage tank 250.

[0039] The circulating drying pipeline includes a drying fan 220, a second heat exchanger 230, and an adsorption and desorption device 210 connected in a circulating manner in sequence. This embodiment includes three adsorbers to enhance the adsorption effect, namely a first adsorber 211, a second adsorber 212, and a third adsorber 213. The second heat exchanger 230 is used to exchange heat between the drying air driven by the drying fan 220 and the mixed gas of water vapor and organic vapor generated by the steam generation device 240. The drying air driven by the drying fan 220 removes the moisture in the adsorption and desorption device 210 to restore the adsorption capacity of the adsorption and desorption device 210. As a preferred solution, the circulating drying pipeline further includes a third heat exchanger 270. The drying fan 220, the second heat exchanger 230, the third heat exchanger 270, and the adsorption and desorption device 210 are connected in a circulating manner in sequence. The third heat exchanger 270 is also communicated with the steam generation device 240 and is used to further increase the temperature of the drying air. Generally, the drying air needs a certain temperature to ensure the realization of the drying function. The heating process of the drying air consumes energy, while the waste heat of the steam is utilized through the second heat exchanger 230, saving energy; the third heat exchanger 270 is used when the heat exchange of the second heat exchanger 230 is not sufficient to raise the drying air to the specified temperature.

[0040] The realization of the above functions depends on the opening of each valve, specifically as follows:

[0041] At Figure 2Meanwhile, open the first cryogenic heat exchanger inlet valve 1301 and the first cryogenic heat exchanger outlet valve 1302 simultaneously to activate the first cryogenic waste gas passage device 121. Open the second cryogenic heat exchanger inlet valve 1311 and the second cryogenic heat exchanger outlet valve 1312 simultaneously to activate the second cryogenic waste gas passage device 122. Open the gas purge first inlet valve 1381 and the gas purge first outlet valve 1382 simultaneously so that the fan 123 purges the water or ice frost from the first cryogenic heat exchanger 1211 and its attached pipelines. Open the gas purge second inlet valve 1383 and the gas purge second outlet valve 1384 simultaneously so that the fan 123 purges the water or ice frost from the second cryogenic heat exchanger 1221 and its attached pipelines. In Figure 4 In the waste gas discharge pipeline, open the first waste gas inlet valve 2801 and the first waste gas outlet valve 2804 simultaneously, then the first adsorber 211 activates the adsorption function. Open the second waste gas inlet valve 2802 and the second waste gas outlet valve 2805 simultaneously, then the second adsorber 212 activates the adsorption function. Open the third waste gas inlet valve 2803 and the third waste gas outlet valve 2806 simultaneously, then the third adsorber 213 activates the adsorption function; in the organic solvent recovery pipeline, open the first steam desorption inlet valve 2811 and the first steam desorption outlet valve 2814 simultaneously, then carry out the organic solvent desorption work on the first adsorber 211. Open the second steam desorption inlet valve 2812 and the second steam desorption outlet valve 2815 simultaneously, then carry out the organic solvent desorption work on the second adsorber 212. Open the third steam desorption inlet valve 2813 and the third steam desorption outlet valve 2816 simultaneously, then carry out the organic solvent desorption work on the third adsorber 213; in the circulating drying pipeline, open the first circulating drying air inlet valve 2821 and the first circulating drying air outlet valve 2824 simultaneously, then the drying air driven by the drying fan 220 dries the water adsorbed by the first adsorber 211. Open the second circulating drying air inlet valve 2822 and the second circulating drying air outlet valve 2825 simultaneously, then the drying air driven by the drying fan 220 dries the water adsorbed by the second adsorber 212. Open the third circulating drying air inlet valve 2823 and the third circulating drying air outlet valve 2826 simultaneously, then the drying air driven by the drying fan 220 dries the water adsorbed by the third adsorber 213.

[0042] Reference Figure 2 and Figure 4 , since the functions of other valves are relatively easy to understand, they will not be explained one by one here.

[0043] Embodiment 2

[0044] As Figure 3 shown, compared with Embodiment 1, the low-temperature condensation module 100 has the following differences:

[0045] The cryogenic heat exchange device 120 further includes a third cryogenic waste gas channel device 124 and a fourth cryogenic waste gas channel device 125. The first heat exchanger 110 is successively communicated with the first cryogenic waste gas channel device 121 and the third cryogenic waste gas channel device 124; or successively communicated with the first cryogenic waste gas channel device 121 and the fourth cryogenic waste gas channel device 125. The first heat exchanger 110 is successively communicated with the second cryogenic waste gas channel device 122 and the third cryogenic waste gas channel device 124, or successively communicated with the second cryogenic waste gas channel device 122 and the fourth cryogenic waste gas channel device 125.

[0046] The cryogenic heat exchange device 120 includes a fan 123. The fan 123 is successively and circularly communicated with the first cryogenic waste gas channel device 121 and the third cryogenic waste gas channel device 124, or the fan 123 is successively and circularly communicated with the first cryogenic waste gas channel device 121 and the fourth cryogenic waste gas channel device 125. The fan 123 is successively and circularly communicated with the second cryogenic waste gas channel device 122 and the third cryogenic waste gas channel device 124, or the fan 123 is successively and circularly communicated with the second cryogenic waste gas channel device 122 and the fourth cryogenic waste gas channel device 125.

[0047] The connection of the above pipelines is realized by opening each valve. Since reference Figure 3 The functions of each valve are relatively easy to understand and will not be explained one by one here.

[0048] Both the third cryogenic waste gas channel device 124 and the fourth cryogenic waste gas channel device 125 include refrigerant and heat medium, and have the same functions and structures as the first cryogenic waste gas channel device 121 or the second cryogenic waste gas channel device 122. The first cryogenic waste gas channel device 121 or the second cryogenic waste gas channel device 122 serves as a primary cryogenic heat exchange device, and the third cryogenic waste gas channel device 124 and the fourth cryogenic waste gas channel device 125 serve as secondary cryogenic heat exchange devices. By adding the secondary cryogenic heat exchange device, the high-concentration organic waste gas can be condensed in a temperature gradient, avoiding excessive load on the primary cryogenic heat exchanger. If the load is too large, the required parameter configuration will be too large, resulting in a low COP value (coefficient of performance) and low energy efficiency.

[0049] Other structures are the same as those in Embodiment 1.

[0050] Embodiment 3

[0051] An energy-saving recovery method for waste gas containing high-concentration organic solvents includes the following steps:

[0052] The dichloromethane waste gas with a concentration higher than 30000 PPM is introduced into the low-temperature condensation module 100. In the low-temperature condensation module 100, the waste gas first enters the first heat exchanger 110, and then enters the cryogenic heat exchange device 120 to cool the waste gas. The cooled waste gas enters the first heat exchanger 110 again to exchange heat with the waste gas that first enters the first heat exchanger 110. The waste gas after heat exchange enters the adsorption and recovery module 200. In the adsorption and recovery module 200, the waste gas after heat exchange enters the adsorption and desorption device 210 and is discharged from the exhaust pipe 260.

[0053] The steam generated by the steam generation device 240 is introduced into the adsorption and desorption device 210 to obtain a gas-liquid mixture of organic solvent and water vapor. The gas-liquid mixture is pushed by the steam from the adsorption and desorption device 210 into the second heat exchanger 230 to exchange heat with the drying air driven by the drying fan 220. The steam after heat exchange becomes liquid and is stored in the solvent recovery storage tank 250.

[0054] The drying air driven by the drying fan 220 is introduced into the second heat exchanger 230. In the second heat exchanger 230, the drying air exchanges heat with the gas-liquid mixture. The drying air after heat exchange sequentially passes through the adsorption and desorption device 210 and the drying fan 220 and then enters the second heat exchanger 230 for heat exchange. The drying air circulates in this way in the circulating drying pipeline. The steam generated by the steam generation device 240 is introduced into the third heat exchanger 270 to increase the temperature of the drying air after heat exchange.

[0055] The first cryogenic waste gas channel device 121 introduces the first refrigerant 1212 to cool the first cryogenic heat exchanger 1211, and then cools the waste gas passing through the first cryogenic heat exchanger 1211. The second cryogenic waste gas channel device 122 introduces the second refrigerant 1222 to cool the waste gas. If frost is generated after cooling, the first cryogenic waste gas channel device 121 introduces the first heat medium 1213 to heat up the first cryogenic heat exchanger 1211, and the second cryogenic waste gas channel device 122 introduces the second heat medium 1223 to heat up the second cryogenic heat exchanger 1221.

[0056] The fan 123 is turned on. The fan 123 is used to introduce high-speed gas simultaneously to improve the cooling efficiency when pre-cooling before introducing the waste gas into the cryogenic heat exchange device 120, and to blow the water generated by the melting of the frost in the cryogenic heat exchange device 120 when the cryogenic heat exchange device 120 is heated up.

[0057] Each cryogenic heat exchange device 120 cools down and heats up alternately to keep the cooling of the waste gas continuously carried out.

[0058] Specifically, with a wind volume of 10000 Nm 3 / h and a dichloromethane concentration of 400 g / m 3For the exhaust gas emission requirements, the comprehensive comparison between the method of this embodiment and the method of compression condensation + membrane + adsorption is as follows:

[0059]

[0060] In summary, the present invention solves the problems of difficult and incomplete ice melting in the low-temperature condensation module; realizes the improvement of the solvent recovery rate; realizes the online continuous operation of the whole device, and greatly reduces the operation energy consumption and investment cost.

[0061] The above-described embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A method for recovering organic waste gas containing high concentration of dichloromethane, characterized in that The following steps are involved: The organic waste gas containing dichloromethane with a concentration higher than 30000 PPM is passed through a low-temperature condensation module; the gas is cooled to between -30°C and -40°C, and the condensed dichloromethane is recovered. The condensed gas phase enters an adsorption recovery module, and the remaining dichloromethane in the waste gas is recovered through the adsorption recovery module; the low-temperature condensation system comprises two or more parallel condensers, and when ice appears inside the condenser in the state of condensing dichloromethane waste gas, resulting in an increase in pressure drop when the waste gas passes through or the waste gas cannot pass through, or when the set time is reached, the condenser is switched to a melting ice state, and switched to other condensers to start condensing dichloromethane waste gas; The exhaust gas cooled by the low-temperature condensation module undergoes heat exchange with the high-concentration organic exhaust gas in the energy-saving heat exchange device and then enters the adsorption recovery module. After the energy-saving heat exchange, the fluid temperature on the cold side is between 0°C and 10°C, and the relative humidity is between 1% and 5%; the fluid temperature on the hot side is between 0°C and 8°C, and the relative humidity is between 95% and 100%.

2. A method for recovering organic waste gas containing high concentration of dichloromethane according to claim 1, characterized in that: The adsorption recovery module comprises two or more parallel adsorbers. When an adsorber in the state of adsorbing dichloromethane waste gas is saturated with adsorption, the adsorber is switched to the desorption regeneration state, and other adsorbers are switched to start adsorbing dichloromethane.

3. The method for recovering organic waste gas containing high concentration of dichloromethane according to claim 1, characterized in that: During the ice melting process of the condenser, stop the refrigerant supply and turn on the heat medium supply. The condenser is heated to 20℃~40℃ by the heat medium to melt the ice. The liquid generated during the ice melting process is discharged through the drain port of the condenser for collection. After the ice melting is completed, stop the heat medium supply and turn on the refrigerant supply to cool the condenser. After the condenser is cooled to below -30℃, the next condensation of dichloromethane waste gas is carried out.

4. The method for recovering organic waste gas containing high concentration of dichloromethane according to claim 1, characterized in that: The condensation pressure of the low-temperature condensation module is between 0KPa and 10KPa (G).

5. The method for recovering organic waste gas containing high concentration of dichloromethane according to claim 1, characterized in that: The refrigerant for low-temperature condensation and the heat medium for melting ice are the same medium; including ethylene glycol aqueous solution, CaCl2 solution, ethanol solution, glacial refrigerant, and Taupes refrigerant.

6. The method for recovering organic waste gas containing high concentration of dichloromethane according to claim 1, characterized in that: The time range for ice melting is 15 to 60 minutes.

7. The method for recovering organic waste gas containing high concentration of dichloromethane according to claim 1, characterized in that: The adsorption material of the adsorption recovery module is one or a combination of activated carbon, activated carbon fiber, molecular sieve and resin.

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