Dichloromethane recovery system and method for rectifying extract liquor through heat pump

Abstract

The invention discloses a dichloromethane recovery system and a dichloromethane recovery method by rectifying extract liquor through a heat pump. The system comprises a rectifying tower, a heat pump, a heat pump gas-liquid separation tank, a first reboiler, a subcooler, a storage tank and a second reboiler. The rectifying tower comprises a rectifying section, a feeding area and a stripping section, and is used for separating light component dichloromethane from heavy component white oil in the extract liquor. A feeding port of the heat pump is connected with a tower top steam exhaust port of the rectifying tower, and a discharging port of the heat pump gas-liquid separation tank is connected with a heating medium inlet of the first reboiler. A feed port of the first reboiler is connected with a kettle bottom discharge port of the rectifying tower, and a discharge port is connected with a reboiler reflux port of the rectifying tower. Condensation latent heat of tower top steam is recovered through heat pump rectification and serves as a heat source of a tower bottom reboiler; the heat pump is used for replacing steam, the electric energy is used for replacing heat energy, and the clean energy is used for replacing non-renewable energy, so that the purposes of reducing cold and hot public engineering consumption and reducing carbon emission are achieved.

Description

Technical Field

[0001] The invention relates to a dichloromethane recovery system for extracting liquid through heat pump distillation, and also relates to a corresponding dichloromethane recovery method, 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, the white oil extract produced by the lithium battery wet process diaphragm production line has a dichloromethane concentration of more than 95%wt. In the diaphragm production process, white oil is evenly distributed in the molecular chain as a pore-forming agent. In the extraction process, dichloromethane is used as an extracting liquid to extract the pore-forming agent white oil, thereby separating the white oil from the diaphragm. At this time, the diaphragm forms a dense and uniform microporous structure.

[0004] In the Chinese utility model with patent number ZL 202022450019.X, a dichloromethane recovery device in the production process of wet-process lithium battery diaphragms is disclosed. The device is composed of a pressurized distillation tower, an atmospheric distillation tower, a tower top condenser, a dichloromethane stratification tank, a dichloromethane condensate pump, a dichloromethane reflux pump and a wastewater treatment device. A new energy-saving process for separation and recovery of dichloromethane from an extraction mixture was established by using double-effect distillation and condensate stratification separation technology. The top vapor enters the tower top condenser for condensation and then enters the dichloromethane stratification tank for stratification separation; the wastewater overflows and enters the wastewater treatment equipment, and the high-purity dichloromethane is discharged through the liquid level control system to achieve dichloromethane recovery and reuse.

[0005] However, in order to recover the dichloromethane in the extract by the distillation tower, the dichloromethane in the extract needs to be distilled / evaporated to the top of the distillation tower, and this process uses a large amount of steam as a heat source. Energy saving and consumption reduction have become the main research direction of diaphragm manufacturers, and traditional processes can no longer meet the needs. Summary of the invention

[0006] The primary technical problem to be solved by the present invention is to provide a dichloromethane recovery system for extracting liquid through heat pump distillation.

[0007] Another technical problem to be solved by the present invention is to provide a recovery method based on the above-mentioned dichloromethane recovery system.

[0008] In order to achieve the above technical objectives, the present invention adopts the following technical solutions: According to a first aspect of an embodiment of the present invention, there is provided a dichloromethane recovery system for extracting liquid by heat pump distillation, comprising a distillation tower, a heat pump, a heat pump gas-liquid separation tank, a first reboiler, a subcooler, a storage tank and a second reboiler; wherein: The distillation tower comprises a distillation section, a feed zone and a stripping section, and is used to separate the light component dichloromethane in the extract from the heavy component white oil; The feed inlet of the heat pump is connected to the top steam exhaust port of the distillation tower, and the discharge port of the heat pump is connected to the feed inlet of the heat pump gas-liquid separation tank; The heating medium inlet of the first reboiler is connected to the gas phase discharge port of the heat pump gas-liquid separation tank, and the heating medium outlet is connected to the feed port of the subcooler; the feed port of the first reboiler is connected to the bottom discharge port of the distillation tower, and the discharge port is connected to the reboiler reflux port of the distillation tower; The discharge port of the subcooler is connected to the feed port of the storage tank, and the cooling medium outlet and the cooling medium inlet are connected to the cooling medium pipeline of the subcooler; The gas phase discharge port of the storage tank is connected to the gas recovery unit, and the liquid phase discharge port is connected to the dichloromethane recovery unit and the top reflux port of the distillation tower; The feed port of the second reboiler is connected to the bottom discharge port of the distillation tower, the discharge port is connected to the reboiler reflux port of the distillation tower, the liquid phase recovery port is connected to the white oil refining unit, and the heating medium outlet and the heating medium inlet are connected to the heating medium pipeline of the second reboiler.

[0009] Preferably, a temperature sensor is provided near the discharge port of the first reboiler to detect the temperature at the discharge port of the first reboiler.

[0010] Preferably, the dichloromethane recovery system further comprises a heat pump condenser; wherein, The feed inlet of the heat pump condenser is connected to the liquid phase discharge port of the heat pump gas-liquid separation tank, and the discharge port is connected to the heat pump to provide cooling and lubricating liquid for the heat pump; the cooling medium outlet and cooling medium inlet of the heat pump condenser are connected to the cooling medium pipeline.

[0011] Preferably, the dichloromethane recovery system further comprises a preheater; wherein, The feed port of the preheater is connected to the tank area for inputting the extract, the discharge port is connected to the feed port of the distillation tower, and the heating medium outlet and the heating medium inlet are connected to the heating medium pipeline of the preheater.

[0012] Preferably, the heat pump can output dichloromethane at a pressure of 0.11 to 0.3 MPaG and a temperature range of 60 to 90°C.

[0013] According to a second aspect of an embodiment of the present invention, there is provided a method for recovering dichloromethane from an extract by heat pump distillation, which is implemented based on the aforementioned dichloromethane recovery system and comprises the following steps: Step S1: using a preheater, heating the extract inputted from the feed port of the preheater to a designed temperature, and inputting the extract into the distillation tower from the feed port of the distillation tower; the heat source of the preheater is waste hot water; Step S2: using a second reboiler to heat the bottom extract from the bottom discharge port of the distillation tower to obtain a high-temperature bottom extract; inputting the high-temperature bottom extract into the distillation tower from the reboiler reflux port of the distillation tower, and mixing with the bottom extract in the distillation tower, so that the bottom extract in the distillation tower is heated to 40° C. or above; the heat source of the second reboiler is steam; Step S3: using a heat pump to pressurize the low-temperature dichloromethane steam from the top exhaust port of the distillation tower, pressurize and heat it to the designed pressure and temperature to obtain high-temperature dichloromethane steam; the pressure of the high-temperature dichloromethane steam is 0.2 MPaG or above, and the temperature is 76° C. or above; Step S4: using the first reboiler, inputting the high-temperature dichloromethane vapor from the gas phase discharge port of the heat pump gas-liquid separation tank into the heating medium side pipeline of the first reboiler to form dichloromethane with a lower temperature, which is output to the subcooler; and inputting the kettle bottom extract from the kettle bottom discharge port of the distillation tower into the material side pipeline of the first reboiler to form a high-temperature kettle bottom extract, which is output to the reboiler reflux port of the distillation tower to mix with the kettle bottom extract in the distillation tower, so that the kettle bottom extract in the distillation tower is heated to 40° C. or above; using the first reboiler to fully exchange heat between the high-temperature dichloromethane vapor in the heating medium side pipeline and the kettle bottom extract in the material side pipeline, so that the high-temperature dichloromethane vapor is cooled to dichloromethane with a lower temperature, and the kettle bottom extract is heated to a high-temperature kettle bottom extract; Step S5: reducing or closing the steam flow of the second reboiler according to the temperature detected by the temperature sensor arranged near the discharge port of the first reboiler, so that the temperature of the discharge port of the first reboiler remains unchanged; Step S6: using the subcooler to cool the dichloromethane from the heating medium outlet of the first reboiler to below 39.8° C. to obtain dichloromethane condensate; inputting the dichloromethane condensate into a storage tank; the cold source of the subcooler is chilled water; Step S7: recovering gaseous dichloromethane using the gas phase discharge port of the storage tank; recovering liquid dichloromethane using the liquid phase discharge port of the storage tank; Step S8: Recovering liquid white oil using the liquid phase recovery port of the second reboiler.

[0014] Preferably, a temperature sensor is used to detect that the temperature of the first reboiler outlet reaches 55° C., and the steam flow value of the second reboiler is gradually reduced to maintain the temperature of the first reboiler outlet unchanged.

[0015] Preferably, a reflux port at the top of the distillation tower is used to reflux part of the liquid dichloromethane from the liquid phase discharge port of the storage tank as a reflux cold source at the top of the distillation tower.

[0016] Preferably, the distillation tower is an atmospheric pressure distillation tower.

[0017] Compared with the prior art, the present invention adopts a direct compression heat pump and innovatively uses the top gas as the heat pump working fluid. The specific operation process is: compress the top gas to increase its temperature, and then input it into the reboiler at the bottom of the tower. In this process, condensation and heat release cause the kettle liquid to reboil. After the condensate is reduced in pressure and cooled, part of it will be discharged as the product, and the other part will be used as reflux at the top of the distillation tower. This method of heat pump distillation of dichloromethane and white oil extract has the following characteristics: first, the required heat-carrying working fluid itself already exists and no additional addition is required; second, in the stable operation stage, only one heat exchanger (i.e., reboiler) is required, which makes the compression ratio of the compressor lower than that of the single working fluid circulation type; third, the entire system process is relatively simple, and the operation is stable and reliable; fourth, it can replace non-renewable energy with clean energy, which is more environmentally friendly and energy-saving. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The structure diagram of a dichloromethane recovery system of an extract through heat pump distillation in the first embodiment of the present invention. DETAILED DESCRIPTION

[0019] The technical content of the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] The technical concept of the embodiment of the present invention is to use the heat pump distillation technology, specifically to pressurize and heat the steam generated at the top of the distillation tower through a heat pump, so that it can be used as a heat source for the reboiler at the bottom of the tower. Simply put, it is to replace the traditional top condenser with a heat pump (compressor) to recover the latent heat of condensation contained in the top steam. In this process, the heat pump will compress the gas discharged from the top of the tower to increase its temperature, and then use the heated gas to replace the steam reboiler to heat the liquid at the bottom of the kettle. Among them, heat pump distillation, as an effective energy-saving technology, can achieve efficient use of energy.

[0021] Taking 50# white oil used in the wet lithium battery separator industry as an example, the kinematic viscosity is 50±3mm² / s and the boiling point exceeds 250℃. The boiling point of dichloromethane is relatively low, at 39.8℃. When separating dichloromethane white oil extract (referred to as extract) in the existing technology, the heating heat source generally selects 0.6MPaG saturated steam with a steam temperature of 165℃. Because the boiling point temperature of dichloromethane and white oil is greatly different, they are easy to separate and can still meet the product index requirements under the heat pump pressurization process. Therefore, the heat pump distillation process is adopted. The steam pressure of dichloromethane at the outlet of the heat pump only needs to be compressed to 0.2MPaG, and the temperature is raised to 76℃, so that the economic heat transfer temperature difference of 30℃ can be maintained with the bottom material of the kettle to save the consumption of high-quality steam. In addition, the relative volatility of dichloromethane and white oil is relatively large. After the heat pump distillation process is adopted, the separation purity of recovered dichloromethane can still be achieved to meet the process requirements.

[0022] like Figure 1 As shown, the first embodiment of the present invention provides a dichloromethane recovery system for extracting liquid through heat pump distillation, comprising a preheater, a distillation tower, a heat pump unit, a first reboiler, a second reboiler, a subcooler and a storage tank. The distillation tower is used to separate and extract the light component dichloromethane and the heavy component white oil in the extracting liquid, and the distillation tower comprises a distillation section, a feed zone and a stripping section.

[0023] The feed inlet of the distillation tower is connected to the discharge port of the preheater, the top exhaust port of the distillation tower is connected to the feed inlet of the heat pump unit, the top reflux port of the distillation tower is connected to the discharge port of the storage tank, the bottom discharge port of the distillation tower is connected to the feed inlets of the first reboiler and the second reboiler, and the reboiler reflux port of the distillation tower is connected to the discharge ports of the first reboiler and the second reboiler.

[0024] The feed port of the preheater is connected to the tank area for inputting the extract, the discharge port is connected to the feed port of the distillation tower, and the heating medium outlet and the heating medium inlet are connected to the heating medium pipeline of the preheater. Preferably, the heating medium of the preheater is hot water from the waste heat recovery system.

[0025] The feed port of the first reboiler is connected to the bottom discharge port of the distillation tower, the discharge port is connected to the reboiler reflux port of the distillation tower, the heating medium inlet is connected to the discharge port of the heat pump unit, and the heating medium outlet is connected to the feed port of the subcooler. A temperature sensor is arranged near the discharge port of the first reboiler to detect the temperature at the discharge port of the first reboiler.

[0026] The feed port of the second reboiler is connected to the bottom discharge port of the distillation tower, the discharge port is connected to the reboiler reflux port of the distillation tower, the liquid phase recovery port is connected to the white oil refining unit, and the heating medium outlet and the heating medium inlet are connected to the heating medium pipeline of the second reboiler. Preferably, the heating medium flow of the second reboiler can be adjusted. Optionally, the heating medium of the second reboiler can be switched, for example, hot water of the waste heat recovery system is used, and when the dichloromethane vapor is not separated at the initial stage of the system startup, the heating medium is steam.

[0027] The feed inlet of the subcooler is connected to the heating medium outlet of the first reboiler, the discharge port is connected to the feed inlet of the storage tank, and the cooling medium outlet and the cooling medium inlet are connected to the cooling medium pipeline of the subcooler. Optionally, the cooling medium of the subcooler is chilled water.

[0028] The feed inlet of the storage tank is connected to the discharge port of the supercooler, the gas phase discharge port is connected to the gas recovery unit, and the liquid phase discharge port is connected to the dichloromethane recovery unit and the top reflux port of the distillation tower.

[0029] The feed inlet of the heat pump unit is connected to the top exhaust port of the distillation tower, and the discharge port is connected to the heating medium inlet of the first reboiler. Preferably, the heat pump unit includes a heat pump, a heat pump gas-liquid separation tank and a heat pump condenser. Among them, the heat pump feed inlet is connected to the feed inlet of the heat pump unit, and the gas phase discharge port of the heat pump gas-liquid separation tank is connected to the discharge port of the heat pump unit. The discharge port of the heat pump is connected to the feed inlet of the heat pump gas-liquid separation tank. The feed inlet of the heat pump condenser is connected to the liquid phase discharge port of the heat pump gas-liquid separation tank to transport the dichloromethane material to be condensed. The discharge port of the heat pump condenser is connected to the heat pump, which is used to provide the condensed dichloromethane material as a coolant and lubricating liquid to the heat pump. The cooling medium outlet and the cooling medium inlet of the heat pump condenser are connected to the cooling medium pipeline of the heat pump condenser. Preferably, the heat pump provided in the embodiment of the present invention is an electrically driven direct pressurized heat pump. Optionally, the cooling medium of the heat pump condenser adopts cooling water.

[0030] The extract is input into the material side pipeline of the preheater as the material to be preheated, and is heated and heated by the heating medium of the medium side pipeline of the preheater, and is output as the preheated extract. The preheated extract enters the distillation tower from the feed port of the distillation tower, and is concentrated in the bottom of the distillation tower as the bottom extract. The bottom extract enters the second reboiler from the bottom discharge port of the distillation tower, and is heated by the steam of the second reboiler as the material to be heated, and is refluxed back to the distillation tower from the reboiler reflux port of the distillation tower as the high-temperature bottom extract, and is mixed with the bottom extract in the distillation tower to increase the temperature of the bottom extract. The vaporization temperature of dichloromethane at normal pressure is 39.8℃, so the bottom extract is heated to above 40℃, and the dichloromethane therein is vaporized and separated to form steam, which is discharged from the distillation tower from the top exhaust port of the tower and input into the heat pump unit as low-temperature dichloromethane steam.

[0031] Low-temperature dichloromethane steam is input into the heat pump unit as the material to be pressurized, and after being pressurized and heated to the preset pressure and temperature by the heat pump unit, it is input into the heating medium side pipeline of the first reboiler as high-temperature dichloromethane steam.

[0032] The bottom extract is fed into the feed port of the first reboiler from the bottom outlet, i.e., fed into the material side pipeline of the first reboiler as the material to be heated. The high-temperature dichloromethane vapor in the heating medium side pipeline of the first reboiler transfers heat to the bottom extract in the material side pipeline. The high-temperature dichloromethane vapor and the bottom extract fully exchange heat in the first reboiler, becoming dichloromethane with a lower temperature and the high-temperature bottom extract, respectively.

[0033] The dichloromethane cooled by the first reboiler is further condensed in the pipeline of the subcooler to obtain dichloromethane condensate, which is then fed into the storage tank. The heated high-temperature bottom extract enters the distillation tower through the reboiler reflux port of the distillation tower and mixes with the bottom extract in the distillation tower to heat the bottom extract.

[0034] Among them, the low-temperature dichloromethane steam is pressurized and heated by the heat pump unit to become high-temperature dichloromethane steam, and the pressure range of the high-temperature dichloromethane steam is 0.11-0.3MPaG, and the temperature range is 60-90°C. Preferably, the high-temperature dichloromethane steam pressure at the outlet of the heat pump unit is 0.2MPaG, and the temperature is 75-80°C. More preferably, the high-temperature dichloromethane steam pressure at the outlet of the heat pump unit is 0.2MPaG, and the temperature is 76°C. Preferably, the dichloromethane material discharged from the liquid phase discharge port of the heat pump gas-liquid separation tank is condensed and cooled by the heat pump condenser, and then input into the heat pump to cool and lubricate the heat pump.

[0035] It is worth noting that the boiling point of dichloromethane is 39.8℃. When the temperature of the bottom liquid (extract material) in the distillation tower reaches above 40℃, dichloromethane and white oil can be separated. Selecting a heat transfer temperature difference of more than 20℃ between the heating medium of the first reboiler and the material to be heated (the preferred heat transfer temperature difference is 28-32℃) can optimize the heat exchange efficiency. The temperatures of dichloromethane saturated vapor at different pressures are as follows: ① 100kPa, 39.7℃; ② 200kPa, 60.7℃; ③ 300kPa, 75.8℃; ④ 400kPa, 85.6℃; ⑤ 500kPa, 94.5℃; ⑥ 600kPa, 102.1℃. Considering the heat exchange economic benefits of the first reboiler and the equipment cost of the heat pump unit, the heat pump outlet operating conditions of 0.2MPaG and 76℃ can meet the distillation heat of dichloromethane in the distillation tower after heat exchange in the first reboiler, which can optimize the equipment economy of the heat pump and the first reboiler.

[0036] Taking 101.3kPa pressure as an example, the latent heat of vaporization of dichloromethane is 89.8kWh / t, methane is 142.3kWh / t, ethane is 135.4kWh / t, propane is 120kWh / t, methanol is 325.4kWh / t, ethanol is 238.1kWh / t, and water is 632.4kWh / t. Therefore, the unit latent heat of dichloromethane is low, and the use of direct pressurized heat pump technology can reduce the number of equipment and reduce equipment investment. For example, taking a double-tower distillation equipment as an example, a heat pump unit can replace the high-pressure distillation tower, simplifying it into a heat pump unit and a single atmospheric distillation tower equipment.

[0037] The gaseous component of the dichloromethane in the storage tank is transported to the gas recovery unit through the gas phase outlet. The liquid component is discharged from the liquid phase outlet, part of which is transported to the dichloromethane recovery unit, and the other part is refluxed to the top of the distillation tower through the top reflux port. The white oil product obtained after distillation is concentrated at the bottom of the distillation tower, and is input into the second reboiler through the bottom outlet, and recovered or transported to the white oil refining unit through the liquid phase recovery port of the second reboiler.

[0038] Compared with hydrocarbon alcohols, dichloromethane is highly corrosive, so the corrosion resistance of materials in contact with dichloromethane should be 316L or above.

[0039] A second embodiment of the present invention provides a dichloromethane recovery method, which at least includes the following steps.

[0040] Step S1: The dichloromethane recovery system in the first embodiment uses a preheater to heat the extract input from the feed port of the preheater to the designed temperature and inputs the extract into the distillation tower from the feed port of the distillation tower. The heat source of the preheater is waste hot water.

[0041] Step S2: using a second reboiler to heat the bottom extract from the bottom outlet of the distillation tower to obtain a high-temperature bottom extract. The high-temperature bottom extract is fed into the distillation tower from the reboiler reflux port of the distillation tower and mixed with the bottom extract in the distillation tower to raise the temperature of the bottom extract in the distillation tower to 40°C or above. The heat source of the second reboiler is steam.

[0042] The dichloromethane in the bottom extract of the distillation tower is vaporized and separated to become low-temperature dichloromethane vapor, which is discharged from the top exhaust port of the distillation tower. Because it is a normal pressure distillation tower, the pressure of the low-temperature dichloromethane vapor is about standard atmospheric pressure and the temperature is about 40°C.

[0043] Step S3: Use a heat pump to pressurize the low-temperature dichloromethane vapor from the top exhaust port of the distillation tower, pressurize and heat it to the designed pressure and temperature to obtain high-temperature dichloromethane vapor. The pressure of the high-temperature dichloromethane vapor is 0.2 MPaG or above, and the temperature is 76°C or above.

[0044] In addition, since a heat pump is used to pressurize the low-temperature dichloromethane vapor, the heat pump can maintain a stable pressure between the exhaust port at the top of the tower and the feed port of the heat pump, reducing the pressure or temperature fluctuations in the distillation tower caused by unstable pressure. In this way, the separation effect can be guaranteed not to be affected by pressure fluctuations. This is because pressure changes will change the composition of the gas-liquid equilibrium on the tower plate, and pressure increases or decreases will reduce or increase the relative volatility between components, thereby changing the separation efficiency. If the tower pressure fluctuates too much, it will also cause the temperature of the entire tower to change, resulting in changes in product quality.

[0045] Step S4: Using the first reboiler, the high-temperature dichloromethane vapor from the gas phase outlet of the heat pump gas-liquid separation tank is input into the heating medium side pipeline of the first reboiler to form dichloromethane with a lower temperature, which is output to the subcooler. In addition, the bottom extract from the bottom outlet of the distillation tower is input into the material side pipeline of the first reboiler to form a high-temperature bottom extract, which is output to the reboiler reflux port of the distillation tower and mixed with the bottom extract in the distillation tower to raise the temperature of the bottom extract in the distillation tower to 40°C or above.

[0046] Therefore, in the first reboiler, the high-temperature dichloromethane steam in the heating medium side pipeline and the kettle bottom extract in the material side pipeline fully exchange heat, so that the high-temperature dichloromethane steam is cooled to dichloromethane with a lower temperature, and the kettle bottom extract is heated to a high-temperature kettle bottom extract.

[0047] The dichloromethane in the bottom extract of the distillation tower is vaporized and separated to become low-temperature dichloromethane vapor, which is output from the top exhaust port of the distillation tower.

[0048] Step S5: according to the temperature detected by the temperature sensor arranged near the discharge port of the first reboiler, the steam flow rate of the second reboiler is reduced or closed so that the temperature of the discharge port of the first reboiler remains unchanged.

[0049] No matter the steam flow rate of the second reboiler is reduced or closed, the second reboiler is used as a pretreatment device for refining white oil products.

[0050] When the steam flow of the second reboiler is closed, only the heat pump is used as the heat source of the distillation tower.

[0051] When the amount of dichloromethane treated by the heat pump unit reaches the design value under the condition of reducing the steam flow rate, for example, the temperature sensor is used to detect that the outlet of the first reboiler reaches 55°C, and the steam flow value of the second reboiler is gradually reduced to maintain the outlet of the first reboiler at this temperature. For example, in the startup state, the steam flow of the second reboiler is 2000kg / h. After the heat pump runs smoothly, the steam flow of the second reboiler is reduced to the normal value of 200kg / h (not closed), and the outlet temperature of the first reboiler is 55°C. The power consumption of the heat pump unit is reduced to reduce the consumption of steam heat energy of the second reboiler.

[0052] When the steam flow of the second reboiler is turned off, when the amount of dichloromethane processed by the heat pump unit reaches the design value, for example, when the temperature sensor detects that the outlet of the first reboiler reaches 55°C, the steam flow value of the second reboiler is gradually reduced until the steam flow is turned off. In this step, the heat pump unit is used as the only heat source (steam is not required), and the electric energy used to compress and heat dichloromethane is the only energy consumption of the dichloromethane recovery system, so as to achieve the purpose of saving energy consumption and reducing the consumption of cold and hot utilities.

[0053] In addition, when the extract in the tank area fluctuates, such as the flow rate or component ratio of the extract, the temperature sensor can be used to detect the temperature change at the outlet of the first reboiler, and the steam flow of the second reboiler can be adjusted in time to quickly restore the temperature of the outlet of the first reboiler to the design value. In this way, it can be ensured that the economic heat transfer temperature difference can be maintained in the distillation tower under the condition of fluctuations, thereby ensuring that the separation effect is not affected by fluctuations.

[0054] Step S6: Using a subcooler to cool the dichloromethane from the outlet of the heating medium of the first reboiler to below 39.8°C, to obtain dichloromethane condensate. The dichloromethane condensate is input into a storage tank. The cold source of the subcooler is chilled water.

[0055] Step S7: Recover gaseous dichloromethane using the gas phase outlet of the storage tank. Recover liquid dichloromethane using the liquid phase outlet of the storage tank. Reflux part of the liquid dichloromethane from the liquid phase outlet of the storage tank using the top reflux port of the distillation tower as the top reflux cold source of the distillation tower.

[0056] Step S8: Recover the liquid phase white oil using the liquid phase recovery port of the second reboiler.

[0057] The dichloromethane recovery system and recovery method provided by the embodiment of the present invention fully utilize the low-temperature heat source of dichloromethane vapor at the top of the tower to heat the extract in the bottom of the tower. After the extract in the tower is heated by steam in the second reboiler, the dichloromethane vapor enters the heat pump unit through the top of the tower, and after the pressure and temperature are increased, it is fully heat-exchanged with the extract in the bottom of the tower in the first reboiler. The condensed dichloromethane enters the subcooler for further condensation and then enters the storage tank, a part of which is pumped out to the top of the tower for reflux, and a part is sent out of the boundary area as dichloromethane output.

[0058] The dichloromethane recovery system provided by the prior art requires sufficient steam as a heat source during the startup and stable operation stages to heat the extract to separate dichloromethane. The dichloromethane recovery system provided by the embodiment of the present invention only requires sufficient steam in the prior art for heating during the startup stage. After the equipment runs smoothly, the steam of the second reboiler can be turned off, and the heat pump unit can complete the heat cycle of the distillation tower itself. At the same time, the dichloromethane condensate also serves as a cold source for the dichloromethane steam at the top of the tower, greatly saving the amount of circulating water at the top of the tower.

[0059] Optionally, after the system runs smoothly, the second reboiler reduces the steam flow rate and continues to be used as a pretreatment device for white oil product refining. For example, the steam consumption is reduced from 2000 kg / h at startup to 200 kg / h during stable operation.

[0060] In summary, the embodiment of the present invention provides a dichloromethane recovery system and recovery method for extracts through heat pump distillation, which realizes the reverse Carnot cycle through heat pump distillation technology, that is, the working fluid is pressurized and heated, and the condensation latent heat of the top steam is recovered as the heat source of the bottom reboiler, so as to achieve the purpose of reducing the amount of cold and hot utilities. The heat pump distillation system uses a "pump" (compressor) to send heat from a low temperature to a high temperature. In this system, the energy consumed by the compressor is the only energy provided by the outside world. It is much less than the energy consumed by direct heating of the reboiler, generally only equivalent to 20% to 30% of the latter. In the prior art, the heat of steam comes from the combustion of fossil energy, while the electric energy can come from clean energy such as photovoltaic and wind power, so the present invention replaces non-renewable energy with clean energy, reducing carbon emissions.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] The above is a detailed description of a dichloromethane recovery system and recovery method for extracting liquid by heat pump distillation 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 dichloromethane recovery system for extracting liquid through heat pump distillation, characterized in that It includes a distillation tower, a heat pump, a heat pump gas-liquid separation tank, a first reboiler, a subcooler, a storage tank and a second reboiler; wherein, The distillation tower comprises a distillation section, a feed zone and a stripping section, and is used to separate the light component dichloromethane in the extract from the heavy component white oil; The feed inlet of the heat pump is connected to the top steam exhaust port of the distillation tower, and the discharge port of the heat pump is connected to the feed inlet of the heat pump gas-liquid separation tank; The heating medium inlet of the first reboiler is connected to the gas phase discharge port of the heat pump gas-liquid separation tank, and the heating medium outlet is connected to the feed port of the subcooler; the feed port of the first reboiler is connected to the bottom discharge port of the distillation tower, and the discharge port is connected to the reboiler reflux port of the distillation tower; The discharge port of the subcooler is connected to the feed port of the storage tank, and the cooling medium outlet and the cooling medium inlet are connected to the cooling medium pipeline of the subcooler; The gas phase discharge port of the storage tank is connected to the gas recovery unit, and the liquid phase discharge port is connected to the dichloromethane recovery unit and the top reflux port of the distillation tower; The feed port of the second reboiler is connected to the bottom discharge port of the distillation tower, the discharge port is connected to the reboiler reflux port of the distillation tower, the liquid phase recovery port is connected to the white oil refining unit, and the heating medium outlet and the heating medium inlet are connected to the heating medium pipeline of the second reboiler.

2. The dichloromethane recovery system according to claim 1, characterized in that: A temperature sensor is arranged near the discharge port of the first reboiler to detect the temperature at the discharge port of the first reboiler.

3. The dichloromethane recovery system as claimed in claim 1, characterized in that Also includes a heat pump condenser; wherein, The feed inlet of the heat pump condenser is connected to the liquid phase discharge port of the heat pump gas-liquid separation tank, and the discharge port is connected to the heat pump to provide cooling and lubricating liquid for the heat pump; the cooling medium outlet and cooling medium inlet of the heat pump condenser are connected to the cooling medium pipeline.

4. The dichloromethane recovery system as claimed in claim 1, characterized in that Also includes a preheater; wherein, The feed port of the preheater is connected to the tank area for inputting the extract, the discharge port is connected to the feed port of the distillation tower, and the heating medium outlet and the heating medium inlet are connected to the heating medium pipeline of the preheater.

5. The dichloromethane recovery system as claimed in claim 4, characterized in that: The heat pump can output dichloromethane at a pressure of 0.11-0.3 MPaG and a temperature range of 60-90°C.

6. A method for recovering dichloromethane from an extract by heat pump distillation, which is realized based on the dichloromethane recovery system according to any one of claims 1 to 5, characterized in that The following steps are involved: Step S1: using a preheater, heating the extract inputted from the feed port of the preheater to a designed temperature, and inputting the extract into the distillation tower from the feed port of the distillation tower; the heat source of the preheater is waste hot water; Step S2: using a second reboiler to heat the bottom extract from the bottom discharge port of the distillation tower to obtain a high-temperature bottom extract; inputting the high-temperature bottom extract into the distillation tower from the reboiler reflux port of the distillation tower, and mixing with the bottom extract in the distillation tower, so that the bottom extract in the distillation tower is heated to 40° C. or above; the heat source of the second reboiler is steam; Step S3: using a heat pump to pressurize the low-temperature dichloromethane steam from the top exhaust port of the distillation tower, pressurize and heat it to the designed pressure and temperature to obtain high-temperature dichloromethane steam; the pressure of the high-temperature dichloromethane steam is 0.2 MPaG or above, and the temperature is 76° C. or above; Step S4: using the first reboiler, inputting the high-temperature dichloromethane vapor from the gas phase discharge port of the heat pump gas-liquid separation tank into the heating medium side pipeline of the first reboiler to form dichloromethane with a lower temperature, which is output to the subcooler; and inputting the kettle bottom extract from the kettle bottom discharge port of the distillation tower into the material side pipeline of the first reboiler to form a high-temperature kettle bottom extract, which is output to the reboiler reflux port of the distillation tower to mix with the kettle bottom extract in the distillation tower, so that the kettle bottom extract in the distillation tower is heated to 40° C. or above; using the first reboiler to fully exchange heat between the high-temperature dichloromethane vapor in the heating medium side pipeline and the kettle bottom extract in the material side pipeline, so that the high-temperature dichloromethane vapor is cooled to dichloromethane with a lower temperature, and the kettle bottom extract is heated to a high-temperature kettle bottom extract; Step S5: reducing or closing the steam flow of the second reboiler according to the temperature detected by the temperature sensor arranged near the discharge port of the first reboiler, so that the temperature of the discharge port of the first reboiler remains unchanged; Step S6: using the subcooler to cool the dichloromethane from the heating medium outlet of the first reboiler to below 39.8° C. to obtain dichloromethane condensate; inputting the dichloromethane condensate into a storage tank; the cold source of the subcooler is chilled water; Step S7: recovering gaseous dichloromethane using the gas phase discharge port of the storage tank; recovering liquid dichloromethane using the liquid phase discharge port of the storage tank; Step S8: Recovering liquid white oil using the liquid phase recovery port of the second reboiler.

7. The method for recovering dichloromethane according to claim 6, wherein: The temperature sensor is used to detect that the temperature of the first reboiler outlet reaches 55° C., and the steam flow value of the second reboiler is gradually reduced to maintain the temperature of the first reboiler outlet unchanged.

8. The method for recovering dichloromethane as claimed in claim 7, wherein: A part of the liquid phase dichloromethane from the liquid phase discharge port of the storage tank is refluxed through the top reflux port of the distillation tower as a top reflux cold source of the distillation tower.

9. The method for recovering dichloromethane as claimed in claim 8, wherein: The distillation tower is an atmospheric pressure distillation tower.

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