A recovery system and temperature position selection method for recovering dichloromethane using waste heat

Abstract

The present invention discloses a recovery system and a temperature position selection method for recovering dichloromethane using waste heat. The recovery system includes core components such as an extract evaporator, a waste heat heat exchanger, a flash tank and a hot water tank. By reasonably connecting various devices, the effective collection and integration of waste heat from the entire plant is achieved. Hot water is used as a heat exchange medium to recover the heat of the desorbed gas in the tail gas VOC recovery device and the waste heat in the steam condensate, and the heat recovery process is accurately controlled by a temperature position selection method to ensure that the temperature of the heat exchange medium in the hot water tank is stable and meet the process requirements of the extract evaporator. The recovery system effectively reduces dependence on traditional steam heat sources and reduces carbon emissions. At the same time, it optimizes heat exchange efficiency, reduces equipment investment costs, simplifies the design and operation of the waste heat recovery system for the entire plant, has significant energy-saving and consumption-reducing effects and environmental benefits, and is suitable for dichloromethane recovery processes in industries such as lithium battery diaphragm production.

Description

Technical Field

[0001] The invention relates to a recovery system for recovering dichloromethane by utilizing waste heat, and also relates to a temperature position selection method based on the recovery system, belonging to the technical field of extraction recovery. Background Art

[0002] As a commonly used organic solvent, dichloromethane is widely used in the fields of medicine, film, industrial refrigeration, industrial extraction, etc. Conventional dichloromethane tail gas recovery technologies mainly include condensation method, adsorption method and solvent absorption method.

[0003] At present, in the production process of lithium battery wet-process diaphragms, an extract containing a mixture of dichloromethane and white oil is produced. The dichloromethane and white oil in the extract discharged from the workshop can be separated by processes such as distillation / evaporation / multiple-effect evaporation or rectification / multiple-effect rectification. The separated dichloromethane is recovered by cooling, and the white oil is recovered or treated by further processing.

[0004] In the Chinese patent application with application number 202010599255.X, a separation process of a mixture of dichloromethane and white oil is disclosed. The process comprises the following steps: ① Steam is introduced into the steam chamber, and the steam flows from the top to the bottom; ② The mixture of dichloromethane and white oil is added from a liquid inlet pipe to the evaporation pipe below; ③ The mixture is heated by steam to separate the gas phase dichloromethane and the liquid phase white oil, wherein the gas phase dichloromethane flows to the gas-liquid separator for gas-liquid separation; the liquid phase white oil flows out of the distillation tower from the liquid outlet pipe; ④ The distilled white oil flowing out of the distillation tower flows back to another liquid inlet pipe at the top, and steps ② and ③ are repeated to realize the secondary distillation of the distilled white oil, or after the secondary distillation of the distilled white oil is completed, the above secondary distillation process is repeated to realize multiple distillations of the distilled white oil.

[0005] However, the existing process consumes a lot of heat during evaporation and distillation, and steam is usually selected as the heat source, which is usually obtained by burning fossil energy. Therefore, the extract recovery device consumes a lot of energy and has high carbon emissions. With the advancement of carbon neutrality and carbon peak work, energy conservation and consumption reduction have become the main research direction of diaphragm manufacturers. Summary of the invention

[0006] The primary technical problem to be solved by the present invention is to provide a recovery system for recovering dichloromethane using waste heat.

[0007] Another technical problem to be solved by the present invention is to provide a temperature level selection method based on the above recovery system.

[0008] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0009] According to a first aspect of an embodiment of the present invention, there is provided a recovery system for recovering dichloromethane using waste heat, comprising an extract evaporator, a waste heat exchanger and a flash tank; wherein:

[0010] The heat exchange medium outlet of the extract evaporator is connected to the heat exchange medium inlet of the waste heat exchanger, and the heat exchange medium inlet is connected to the heat exchange medium outlet of the waste heat exchanger;

[0011] The input port of the flash tank is connected to an upstream steam condensate source, and the liquid phase outlet is connected to a heat exchange medium inlet of the extract evaporator.

[0012] Preferably, the recovery system further comprises a hot water tank; wherein,

[0013] The liquid phase inlet of the hot water tank is connected to the heat exchange medium outlet of the waste heat exchanger and the liquid phase outlet of the flash tank, the output port is connected to the heat exchange medium inlet of the extract evaporator, and the gas phase inlet is connected to the gas phase outlet of the flash tank and the steam source of the plant area;

[0014] The hot water tank is internally provided with a steam jet heater, which can introduce steam from a gas phase inlet to heat the material in the hot water tank.

[0015] Preferably, the recovery system further comprises a fifth valve; wherein,

[0016] One end of the fifth valve is connected to the gas phase outlet of the flash tank and the steam source in the plant area, and the other end is connected to the gas phase inlet of the hot water tank.

[0017] Preferably, the recovery system further comprises a steam condensation device; wherein,

[0018] The output port of the steam condensation device is connected to the input port of the flash tank to provide steam condensation for the flash tank.

[0019] Preferably, there are multiple flash tanks, and the steam condensation device provides steam condensation of various pressures for the flash tanks.

[0020] Preferably, the recovery system further comprises a first valve, a second valve and a third valve; wherein,

[0021] One end of the first valve is connected to the heat exchange medium outlet of the waste heat exchanger, and the other end is connected to the liquid phase inlet of the hot water tank; one end of the second valve is connected to the heat exchange medium outlet of the extract evaporator, and the other end is connected to the heat exchange medium inlet of the waste heat exchanger;

[0022] The first end of the third valve is connected to the heat exchange medium outlet of the extract liquid evaporator, and the second end is connected to the liquid phase inlet of the hot water tank; the first end of the third valve is located between the heat exchange medium outlet of the extract liquid evaporator and the second valve, and the second end is located between the heat exchange medium inlet of the waste heat exchanger and the first valve.

[0023] Preferably, the recovery system further comprises an exhaust gas recovery device; wherein,

[0024] The tail gas recovery device comprises an adsorption box and a steam desorption device; the steam desorption device is used to input steam into the adsorption box to desorb and form desorbed gas;

[0025] The material inlet of the waste heat exchanger is connected to the desorption outlet of the adsorption box, and the material outlet is connected to the downstream pipeline.

[0026] Preferably, the recovery system further comprises a fourth valve; wherein,

[0027] One end of the fourth valve is connected to the heat exchange medium outlet of the extract evaporator.

[0028] Preferably, the recovery system further comprises an extract recovery device; wherein,

[0029] The extract recovery device comprises a preheater and a circulating water system; the preheater is used to preheat the extract, and the preheated extract is input into the extract evaporator for further evaporation and extraction;

[0030] The heat exchange medium inlet of the preheater is connected to one end of the fourth valve, and the other end of the fourth valve is connected to the heat exchange medium outlet of the extract evaporator; the heat exchange medium outlet of the preheater is connected to the circulating water system.

[0031] According to a second aspect of an embodiment of the present invention, a method for selecting a temperature level based on the above recovery system is provided, comprising the following steps:

[0032] Step S1: Obtain the material temperature at the material inlet of the waste heat exchanger and compare it with the preset heat exchange temperature; when the material temperature is less than the preset heat exchange temperature, jump to step S2; when the material temperature is greater than or equal to the preset heat exchange temperature, jump to step S3;

[0033] Step S2: close the first valve and the second valve, open the third valve, and connect the heat exchange medium outlet of the extract evaporator to the liquid phase inlet of the hot water tank; jump to step S4;

[0034] Step S3: Open the first valve and the second valve, and close the third valve, so that the heat exchange medium outlet of the extract evaporator is connected to the heat exchange medium inlet of the waste heat exchanger, and the heat exchange medium outlet of the waste heat exchanger is connected to the liquid phase inlet of the hot water tank; jump to step S4;

[0035] Step S4: Obtain the liquid level of the heat exchange medium in the hot water tank and compare it with the preset liquid level; when the liquid level of the heat exchange medium is less than the preset liquid level, jump to step S5; when the liquid level of the heat exchange medium is greater than or equal to the preset liquid level, jump to step S6;

[0036] Step S5: close the fourth valve to prevent the heat exchange medium outlet of the extract evaporator from being connected to the heat exchange medium inlet of the preheater; jump to step S7;

[0037] Step S6: Open the fourth valve to connect the heat exchange medium outlet of the extract evaporator to the heat exchange medium inlet of the preheater; jump to step S7;

[0038] Step S7: Obtain the temperature of the heat exchange medium in the hot water tank and compare it with the preset heating temperature; when the temperature of the heat exchange medium is lower than the preset heating temperature, jump to step S8; when the temperature of the heat exchange medium is higher than or equal to the preset heating temperature, jump to step S9;

[0039] Step S8: Open the fifth valve to connect the gas phase outlet of the flash tank to the gas phase inlet of the hot water tank; jump to step S1;

[0040] Step S9: close the fifth valve to prevent the gas phase outlet of the flash tank from being connected to the gas phase inlet of the hot water tank; jump to step S1.

[0041] Compared with the prior art, the present invention has the following technical effects: First, the recovery system can effectively collect the heat of desorbed gas and steam condensate in the whole plant area, integrate and utilize the waste heat that might have been wasted, thereby providing a heat source for the evaporation and separation of dichloromethane in the extract, significantly reducing the dependence on high-energy heat sources such as traditional steam, and reducing carbon emissions. Secondly, by setting up key equipment such as hot water tanks, waste heat exchangers and flash tanks, and accurately controlling heat recovery through temperature selection methods, the recovery system can flexibly adjust heat distribution according to different working conditions, optimize heat exchange efficiency, ensure that the temperature of the heat exchange medium in the hot water tank is stable, and meet the process requirements of the extract evaporator. In addition, the use of hot water as a heat exchange medium not only reduces the investment cost of pipeline equipment, but also simplifies the design and operation of the waste heat recovery system of the whole plant. In summary, the present invention has achieved remarkable results in energy saving and consumption reduction, reducing production costs, improving resource utilization efficiency, and reducing environmental pollution, providing strong support for the sustainable development of industries such as lithium battery diaphragm production. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a schematic structural diagram of a recovery system for recovering dichloromethane using waste heat in the first embodiment of the present invention;

[0043] Figure 2 This is a schematic structural diagram of another recovery system for recovering dichloromethane using waste heat in the second embodiment of the present invention. DETAILED DESCRIPTION

[0044] The technical content of the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] The technical concept in the embodiment of the present invention is: comprehensively collect the waste heat of the entire plant area for separation and recovery of dichloromethane and white oil extract. Specifically, the desorption heat of the adsorption box is collected by a waste heat exchanger, the steam condensate is collected by a flash tank, and the recovered waste heat is used to heat the extract evaporator to separate dichloromethane and white oil. Among them, the exhaust gas discharged from the workshop contains dichloromethane, the activated carbon adsorption device adsorbs the dichloromethane in the exhaust gas, and the desorption steam desorbs and analyzes the adsorption saturated adsorption material. After the steam desorption gas carrying dichloromethane is cooled by cooling water, the dichloromethane vapor is condensed into liquid dichloromethane, and is stratified with water in a stratification tank. The stratified dichloromethane is recovered to the dichloromethane recovery tank in the tank area. Among them, during steam desorption, a large amount of desorbed gas close to 100°C will enter the condenser and be directly cooled by cooling water, resulting in heat waste. The boiling point of dichloromethane at atmospheric pressure is 39.8℃, which is relatively low and suitable for heat sources with relatively low temperatures. Therefore, the waste heat of the desorbed gas can be used to separate and recover dichloromethane and white oil, and water can be used as the heat exchange medium. In the chemical environment, water comes from a wide range of sources, such as the steam condensate discharged from each process section, which can be used to obtain hot water after the pressure is reduced to atmospheric pressure. The boiling point of water at atmospheric pressure is 100℃, and the heat transferred can heat the dichloromethane solution to 39.8℃ or above, so that the dichloromethane in the solution can be evaporated and separated.

[0046] First embodiment

[0047] like Figure 1 As shown, the first embodiment of the present invention provides a recovery system for dichloromethane using waste heat, which at least includes a hot water tank, an extract evaporator, a waste heat exchanger and a flash tank.

[0048] The hot water tank is a storage and heating device for heat exchange medium. The liquid phase inlet of the hot water tank is connected to the heat exchange medium outlet of the waste heat exchanger and the liquid phase outlet of the flash tank, the output port is connected to the heat exchange medium inlet of the extract evaporator, and the gas phase inlet is connected to the gas phase outlet of the flash tank and the steam source in the plant area. The hot water tank is equipped with a steam jet heater, and steam is introduced from the gas phase inlet to heat the material in the hot water tank (heat exchange medium of the recovery system). Preferably, the hot water tank includes a liquid level sensor and a temperature sensor, which can measure the liquid level and temperature of the heat exchange medium in the hot water tank.

[0049] The extract evaporator is an evaporation and separation device for the extract. The heat exchange medium outlet of the extract evaporator is connected to the heat exchange medium inlet of the waste heat exchanger, and the heat exchange medium inlet is connected to the output port of the hot water tank. In the extract evaporator, the input and output of materials such as the extract are existing technologies and will not be described in detail.

[0050] The waste heat exchanger is a waste heat recovery device. The heat exchange medium inlet of the waste heat exchanger is connected to the heat exchange medium outlet of the extract evaporator, the heat exchange medium outlet is connected to the liquid phase inlet of the hot water tank, the material inlet is connected to the upstream material source, and the material outlet is connected to the downstream material processing equipment. Preferably, the waste heat exchanger includes a temperature sensor that can measure the material temperature at the material inlet. The material input to the waste heat exchanger is the desorption steam output by the upstream desorption equipment. After condensation by the waste heat exchanger, the output material is the desorption condensate.

[0051] The flash tank is a steam flash equipment. The input port of the flash tank is connected to the upstream steam condensate source, the liquid phase outlet is connected to the liquid phase inlet of the hot water tank, and the gas phase outlet is connected to the gas phase inlet of the hot water tank.

[0052] The waste heat exchanger receives the medium-temperature heat exchange medium from the extract evaporator through the heat exchange medium inlet, and after heat exchange with the material, outputs the high-temperature heat exchange medium to the hot water tank through the heat exchange medium outlet. At the same time, a single or multiple flash tanks are connected to the upstream steam source, and steam condenses, which are flashed into normal-pressure hot water and then input into the hot water tank. Heat exchange media of different temperatures are mixed in the hot water tank, and steam is introduced from the gas phase inlet of the hot water tank for heating and insulation, so as to maintain the temperature of the heat exchange medium at the design temperature. Steam is introduced into the hot water tank from the gas phase inlet of the hot water tank, and the steam source is the normal-pressure steam of the flash tank and the steam from the plant area.

[0053] The heat exchange medium in the hot water tank is transported from the liquid phase outlet to the extract evaporator to heat the extract. The heat exchange medium cooled by the extract evaporator is transported to the waste heat exchanger as a medium-temperature heat exchange medium. In this way, the heat recovered by the waste heat exchanger and the flash tank is used to heat the extract.

[0054] Optionally, the heat exchange medium outlet of the extract evaporator is connected to the heat exchange medium inlet of the waste heat exchanger, and the heat exchange medium inlet is connected to the heat exchange medium outlet of the waste heat exchanger and the liquid phase outlet of the flash tank. The input port of the flash tank is connected to the upstream steam condensate source. The heat recovered by the waste heat exchanger and the flash tank is directly transferred to the extract evaporator through the heat exchange medium.

[0055] Second embodiment

[0056] Different from the above-mentioned embodiment, the recovery system provided in the second embodiment of the present invention further includes a tail gas recovery device, a steam condensation device and an extraction liquid recovery device.

[0057] The tail gas recovery device includes an adsorption box and a steam desorption device. The adsorption box is used to adsorb dichloromethane in the tail gas. The steam desorption device inputs steam into the adsorption box to desorb and form steam desorption gas carrying dichloromethane. The material inlet of the waste heat exchanger is connected to the desorption outlet of the adsorption box, and the material outlet is connected to the downstream pipeline. The waste heat exchanger heats the heat exchange medium with the input desorption gas, and raises the temperature of the medium-temperature heat exchange medium to a high-temperature heat exchange medium. It is worth noting that the desorption outlet of the adsorption box is the output port of the tail gas recovery device. In other words, the material inlet of the waste heat exchanger is connected to the output port of the tail gas recovery device.

[0058] The output port of the steam condensate device is connected to the input port of multiple flash tanks to provide the flash tanks with steam condensate of various pressures, such as 2MPaG, 1MPaG and 0.6MPaG steam condensate. There are steam condensates of different pressure levels in the plant area. These steam condensates have undergone heat exchange and become unstable sources of waste heat. In order to make full and reasonable use of the waste heat in the plant area, steam condensates of different pressure levels are flashed in the flash tank. After flashing, hot water that meets the pressure level (0.1MPaG, adjustable) enters the hot water tank and is mixed as a heat exchange medium. After the flashed steam is conditioned, the amount of steam input to the gas phase inlet of the hot water tank is controlled by a regulating valve to heat the heat exchange medium in the hot water tank.

[0059] The extract recovery device includes a preheater and a circulating water system. The heat exchange medium inlet of the preheater is connected to the heat exchange medium outlet of the extract evaporator, and the heat exchange medium outlet is connected to the circulating water system. The preheater is used to preheat the extract, and the preheated extract is input into the extract evaporator for further evaporation and extraction. It is worth noting that the heat exchange medium inlet of the preheater is the heat exchange medium inlet of the extract recovery device. In other words, the heat exchange medium outlet of the extract evaporator is connected to the heat exchange medium inlet of the extract recovery device.

[0060] In the tail gas recovery device, the desorbed steam from the adsorption box recovers heat through the waste heat exchanger, and the medium-temperature heat exchange medium is heated to a high-temperature heat exchange medium. The steam condensation device inputs steam condensate of various pressures into a flash tank, flashes into normal pressure hot water, and then inputs it into a hot water tank to recover the water and heat in the steam condensate.

[0061] The hot water tank will recover the heat and hot water and input it into the extract evaporator as heat exchange medium to evaporate and separate the gas phase components in the extract. After cooling, part of the heat exchange medium is input into the waste heat exchanger to be heated and then sent back to the hot water tank. The other part is input into the preheater of the extract recovery device to preheat the extract, and then discharged into the circulating water system to control the liquid level of the hot water tank.

[0062] In one embodiment of the present invention, the tail gas recovery device is used to recover dichloromethane from the tail gas, and the extract recovery device and the extract evaporator are used to recover dichloromethane from the dichloromethane white oil extract. The heat exchange medium is water. Since the boiling point of dichloromethane at normal pressure is 39.8°C, the hot water recovered from the steam condensate can be used as the heat exchange medium and heat source for the evaporation of dichloromethane, and the waste heat of the desorbed gas can be used for the separation and recovery of dichloromethane and white oil.

[0063] like Figure 2 As shown, the extract evaporator is a distillation tower and a reboiler provided by the prior art, the output end of the hot water tank is connected to the heat exchange medium inlet of the reboiler, the heat exchange medium outlet of the reboiler is connected to the heat exchange medium inlet of the preheater, and the heat exchange medium outlet of the preheater is connected to the circulating water system. The liquid phase inlet of the hot water tank is connected to the heat exchange medium outlet of the waste heat exchanger and the liquid phase outlet of the flash tank.

[0064] The material inlet of the preheater is connected to the tank area for inputting the extract, and the material outlet is connected to the feeding port of the distillation tower. After the dichloromethane white oil extract is preheated by the preheater, it is input into the extract evaporator for heating and evaporation to separate dichloromethane vapor and white oil. The heat exchange medium of the preheater and the extract evaporator comes from the hot water provided by the hot water tank, and the heat comes from the heat recovered by the preheating heat exchanger and the flash tank.

[0065] Third embodiment

[0066] Different from the above-mentioned embodiment, the recovery system provided in the third embodiment of the present invention further includes a first valve, a second valve, a third valve, a fourth valve and a fifth valve.

[0067] One end of the first valve is connected to the heat exchange medium outlet of the waste heat exchanger, and the other end is connected to the liquid phase inlet of the hot water tank. One end of the second valve is connected to the heat exchange medium outlet of the extract evaporator, and the other end is connected to the heat exchange medium inlet of the waste heat exchanger. The first end of the third valve is connected to the heat exchange medium outlet of the extract evaporator, and the second end is connected to the liquid phase inlet of the hot water tank. In addition, the first end of the third valve is located between the heat exchange medium outlet of the extract evaporator and the second valve, and the second end is located between the heat exchange medium inlet of the waste heat exchanger and the first valve.

[0068] One end of the fourth valve is connected to the heat exchange medium outlet of the extract evaporator, and the other end is connected to the heat exchange medium inlet of the extract recovery device. One end of the fifth valve is connected to the gas phase outlet of the flash tank and the steam source of the plant area, and the other end is connected to the gas phase inlet of the hot water tank.

[0069] When the temperature of the material (desorbed gas) at the material inlet of the waste heat exchanger is lower than the preset heat exchange temperature, the first valve and the second valve are closed, and the third valve is opened. The medium-temperature hot water output from the heat exchange medium outlet of the extract evaporator flows back to the hot water tank through the third valve for storage and heating. The preset heat exchange temperature is set according to design requirements, for example, 40 to 80°C. Preferably, the preset heat exchange temperature is 60°C, and the temperature of the heat exchange medium (medium-temperature hot water) discharged from the extract evaporator is about 50°C.

[0070] It is worth noting that the boiling point of dichloromethane is 39.8°C. Selecting a heat exchange temperature difference of more than 20°C, that is, selecting a desorbed gas at a temperature of 60°C or above for heat exchange, can optimize the heat exchange efficiency. From the perspective of the economic benefits of the heat exchange equipment, if the temperature of the recovered desorbed gas is too low, the heat exchange equipment needs a larger capacity. A heat exchange temperature difference of more than 20°C can optimize the equipment economy of the waste heat exchanger and the hot water tank.

[0071] When the temperature of the material (desorbed gas) at the material inlet of the waste heat exchanger is greater than or equal to the preset heat exchange temperature, the first valve and the second valve are opened, and the third valve is closed. The medium-temperature hot water output from the heat exchange medium outlet of the extract evaporator is input into the waste heat exchanger through the second valve, and flows back to the hot water tank through the first valve for storage and heat preservation.

[0072] When the liquid level of the heat exchange medium (hot water) in the hot water tank exceeds the preset liquid level, the fourth valve is opened. After the medium-temperature hot water from the extract evaporator is fully exchanged, part of it enters the preheater through the fourth valve. After sufficient heat exchange with the feed in the preheater, the low-temperature water is discharged to the low-temperature condensate collection tank in the plant area and used as water for the circulating water system.

[0073] When the temperature of the heat exchange medium (hot water) in the hot water tank is lower than the preset heating temperature, the fifth valve is opened to allow steam to enter the hot water tank to heat the heat exchange medium. When the heat exchange medium is higher than or equal to the preset heating temperature, the fifth valve is closed. The preset heating temperature is set according to design requirements, for example, 60 to 95°C. Preferably, the preset heating temperature is 80°C.

[0074] It should be noted that the preset heating temperature is set by comprehensively considering the heat exchange efficiency and equipment cost of the hot water tank and the extract evaporator.

[0075] The hot water tank stores the hot water from the flash tank, and the hot water temperature is maintained at the preset heating temperature through the steam jet heater. The hot water is input into the extract evaporator as the heat exchange medium to evaporate and separate the dichloromethane. The heat exchange medium (hot water) after heat exchange and cooling is cooled to about 50°C, input into the waste heat exchanger for heat exchange and heating, and then input into the hot water tank to continue the heat exchange cycle. Because the temperature of the heat exchange medium after heat exchange and cooling in the extract evaporator is about 50°C (related to the heat exchange efficiency of the extract evaporator), the waste heat exchanger only takes the preset heat exchange temperature (60°C) and above the temperature section to pass the heat exchange medium for heat recovery.

[0076] Fourth embodiment

[0077] Based on the recovery systems provided in the above embodiments, a fourth embodiment of the present invention provides a temperature level selection method, which at least includes the following steps.

[0078] Step S1: Obtain the material temperature at the material inlet of the waste heat exchanger and compare it with the preset heat exchange temperature; when the material temperature is lower than the preset heat exchange temperature, jump to step S2; when the material temperature is greater than or equal to the preset heat exchange temperature, jump to step S3.

[0079] The preset heat exchange temperature is set according to design requirements, for example, 40 to 80° C. Preferably, the preset heat exchange temperature is 60° C.

[0080] Step S2: close the first valve and the second valve, open the third valve, and connect the heat exchange medium outlet of the extract evaporator to the liquid phase inlet of the hot water tank; jump to step S4.

[0081] Step S3: Open the first valve and the second valve, close the third valve, connect the heat exchange medium outlet of the extract evaporator with the heat exchange medium inlet of the waste heat exchanger, and connect the heat exchange medium outlet of the waste heat exchanger with the liquid phase inlet of the hot water tank; jump to step S4.

[0082] Step S4: Obtain the heat exchange medium level in the hot water tank and compare it with the preset level; when the heat exchange medium level is less than the preset level, jump to step S5; when the heat exchange medium level is greater than or equal to the preset level, jump to step S6.

[0083] Step S5: close the fourth valve to prevent the heat exchange medium outlet of the extract evaporator from being connected to the heat exchange medium inlet of the preheater; jump to step S7.

[0084] Step S6: Open the fourth valve to connect the heat exchange medium outlet of the extract evaporator with the heat exchange medium inlet of the preheater; jump to step S7.

[0085] Step S7: Obtain the temperature of the heat exchange medium in the hot water tank and compare it with the preset heating temperature; when the temperature of the heat exchange medium is lower than the preset heating temperature, jump to step S8; when the temperature of the heat exchange medium is greater than or equal to the preset heating temperature, jump to step S9.

[0086] The preset heating temperature is set according to the design requirements, for example, 60 to 95° C. Preferably, the preset heating temperature is 80° C. It is worth noting that the boiling point of dichloromethane is 39.8° C., and the temperature of the heat exchange medium in the hot water tank and the extract evaporator is 80° C., which can meet the optimization requirements of the heat exchange efficiency and equipment cost of the extract evaporator.

[0087] Step S8: Open the fifth valve to connect the gas phase outlet of the flash tank to the gas phase inlet of the hot water tank; jump to step S1.

[0088] Step S9: close the fifth valve to prevent the gas phase outlet of the flash tank from being connected to the gas phase inlet of the hot water tank; jump to step S1.

[0089] During the desorption process of the dichloromethane adsorption box of the tail gas VOC recovery device, the temperature of the desorbed gas is not always constant. In the early stage of desorption, the temperature of the desorbed gas is very low due to the low temperature of the adsorption box and a large amount of dichloromethane in it. As the temperature of the adsorption box rises and the residual amount of dichloromethane in the adsorption box becomes smaller and smaller, the temperature of the desorbed gas gradually rises to 101°C. If a desorption cycle is taken as 490s, the desorption gas temperature can only rise to 60°C when the desorption time reaches 180s (the specific data varies according to the processing capacity and fiber capacity of the VOC recovery device and other working conditions). Considering the heat exchange temperature difference, the first 36% of the heat of a desorption cycle does not need to be recovered, and even recovery will cause side effects. Therefore, in the heat recovery design provided in the embodiment of the present invention, it is necessary to design a temperature position selection heat recovery system. When the desorbed gas temperature rises to the preset recovery temperature, the valve is switched to change the hot water passage to achieve the purpose of maximizing the recovery of available heat.

[0090] Due to the unstable desorption temperature, the circulating hot water temperature is unstable. In order to ensure the constant temperature of the hot water in the extract recovery device, a hot water tank temperature control system is set. The hot water tank is designed to stay for a time that meets the requirements, such as 15 minutes, to ensure that hot water at different temperatures is fully mixed in the hot water tank. In addition, a constant temperature is set for the hot water entering the extract recovery device. When the hot water temperature is lower than the set temperature, the fifth valve is opened to heat it with steam until the set temperature is reached.

[0091] In order to make full and reasonable use of the waste heat in the plant, the steam condensates at different pressure levels in the plant, and after flash evaporation, the hot water that meets the pressure level (0.1MPaG, adjustable) enters the hot water tank. After the flash steam is conditioned, the amount of steam entering the hot water tank is controlled by a regulating valve.

[0092] In summary, the embodiments of the present invention provide a recovery system and a temperature position selection method for recovering dichloromethane using waste heat, which are interconnected through the heat integration of the tail gas VOC recovery device, the whole plant waste heat and the extract recovery device, relying on the intermediate circulating heat exchange medium hot water. After the hot water is heated by the waste heat heat exchanger of the tail gas VOC recovery device, the temperature of the hot water rises and is sent to the waste heat evaporator of the extract recovery device for preheating and evaporation of the extract. The hot water after the temperature drops is circulated and sent to the VOC recovery device to extract heat from the desorbed gas. A hot water buffer tank (hot water tank) is set in the middle of the hot water circulation section. In addition, steam condensate from other locations in the plant, including steam pipe drains and workshop steam condensate, can be collected in the hot water buffer tank, in order to maximize the benefits of the integrated utilization of the whole plant's waste heat.

[0093] In various embodiments of the present invention, the reasons for using hot water as the heat exchange medium are as follows: ① The boiling point of dichloromethane at normal pressure is 39.8°C, so the hot water recovered from the steam condensate can be used as the heat exchange medium for dichloromethane evaporation; ② The comprehensive utilization of heat between devices or between plants will cause a large pressure drop due to the long pipeline length, and the temperature of waste heat from multiple sources is not uniform, which will cause process fluctuations on the heat-using side, so the system for unified recovery of waste heat from steam condensate in the whole plant is simpler; ③ Dichloromethane is highly corrosive, and the material of the pipeline equipment needs to be 316L or above, which requires a large fixed investment. Using hot water as the heat exchange medium can reduce the investment in pipeline equipment.

[0094] It should be noted that the above embodiments are only examples, and the technical solutions of the various embodiments can be combined, all within the protection scope of the present invention.

[0095] The order of steps of the present invention can be changed according to actual needs, the order of the steps can be changed, and the serial processing can also be changed to parallel processing, which is not limited to the order of steps listed in the embodiments.

[0096] The orientation or positional relationship indicated by the terms "upper", "lower", "top", "bottom", etc. is based on the orientation or positional relationship shown in the drawings and is only for the convenience of describing the present invention and simplifying the description. It does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, it should not be understood as a limitation on the present invention.

[0097] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0098] The above is a detailed description of the recovery system and temperature selection method for recovering dichloromethane using waste heat provided by the present invention. For a person skilled in the art, any obvious changes made to it without departing from the essence of the present invention will constitute an infringement of the patent right of the present invention and will bear the corresponding legal liability.

Claims

1. A recovery system for recovering dichloromethane using waste heat, characterized in that It includes an extract evaporator, a waste heat exchanger, a flash tank, a hot water tank, an extract recovery device, a first valve, a second valve, a third valve, a fourth valve and a fifth valve; wherein, The input port of the flash tank is connected to an upstream steam condensate source; The heat exchange medium outlet of the extract evaporator is connected to one end of the second valve, and the other end of the second valve is connected to the heat exchange medium inlet of the waste heat exchanger; the waste heat exchanger includes a temperature sensor; The liquid phase inlet of the hot water tank is connected to the liquid phase outlet of the flash tank and one end of the first valve, the other end of the first valve is connected to the heat exchange medium outlet of the waste heat exchanger, and the output port of the hot water tank is connected to the heat exchange medium inlet of the extract evaporator; the hot water tank is equipped with a steam jet heater, which can introduce steam from the gas phase inlet to heat the material in the hot water tank; the hot water tank includes a liquid level sensor and a temperature sensor; One end of the third valve is connected to the heat exchange medium outlet of the extract evaporator, and the other end is connected to the liquid phase inlet of the hot water tank; One end of the fifth valve is connected to the gas phase outlet of the flash tank and the plant steam source, and the other end is connected to the gas phase inlet of the hot water tank; The extract recovery device comprises a preheater and a circulating water system; the preheater is used to preheat the extract, and the preheated extract is input into the extract evaporator for further evaporation and extraction; The heat exchange medium inlet of the preheater is connected to one end of the fourth valve, and the other end of the fourth valve is connected to the heat exchange medium outlet of the extract evaporator; the heat exchange medium outlet of the preheater is connected to the circulating water system.

2. The recovery system according to claim 1, characterized in that It also includes a steam condensation device; wherein, The output port of the steam condensation device is connected to the input port of the flash tank to provide steam condensation for the flash tank.

3. The recycling system according to claim 2, characterized in that: There are multiple flash tanks, and the steam condensation device provides steam condensation at multiple pressures for the flash tanks.

4. The recovery system according to claim 1, characterized in that It also includes an exhaust gas recovery device; wherein, The tail gas recovery device comprises an adsorption box and a steam desorption device; the steam desorption device is used to input steam into the adsorption box to desorb and form desorbed gas; The material inlet of the waste heat exchanger is connected to the desorption outlet of the adsorption box, and the material outlet is connected to the downstream pipeline.

5. A method for selecting a temperature level, implemented based on the recovery system according to any one of claims 1 to 4, characterized in that The following steps are involved: Step S1: Obtain the material temperature at the material inlet of the waste heat exchanger and compare it with the preset heat exchange temperature; when the material temperature is less than the preset heat exchange temperature, jump to step S2; when the material temperature is greater than or equal to the preset heat exchange temperature, jump to step S3; Step S2: close the first valve and the second valve, open the third valve, and connect the heat exchange medium outlet of the extract evaporator to the liquid phase inlet of the hot water tank; jump to step S4; Step S3: Open the first valve and the second valve, and close the third valve, so that the heat exchange medium outlet of the extract evaporator is connected to the heat exchange medium inlet of the waste heat exchanger, and the heat exchange medium outlet of the waste heat exchanger is connected to the liquid phase inlet of the hot water tank; jump to step S4; Step S4: Obtain the liquid level of the heat exchange medium in the hot water tank and compare it with the preset liquid level; when the liquid level of the heat exchange medium is less than the preset liquid level, jump to step S5; when the liquid level of the heat exchange medium is greater than or equal to the preset liquid level, jump to step S6; Step S5: closing the fourth valve so that the heat exchange medium outlet of the extract evaporator is not connected to the heat exchange medium inlet of the preheater; Jump to step S7; Step S6: Open the fourth valve to connect the heat exchange medium outlet of the extract evaporator to the heat exchange medium inlet of the preheater; Jump to step S7; Step S7: Obtain the temperature of the heat exchange medium in the hot water tank and compare it with the preset heating temperature; when the temperature of the heat exchange medium is lower than the preset heating temperature, jump to step S8; when the temperature of the heat exchange medium is higher than or equal to the preset heating temperature, jump to step S9; Step S8: Open the fifth valve to connect the gas phase outlet of the flash tank to the gas phase inlet of the hot water tank; Jump to step S1; Step S9: closing the fifth valve so that the gas phase outlet of the flash tank is not connected to the gas phase inlet of the hot water tank; Jump to step S1.

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