Refining and recycling method of hydrogen chloride tail gas

Abstract

The invention discloses a method for refining and recovering tail gas of hydrogen chloride. The method comprises the following steps: 1) compressing the tail gas to a high-pressure state through a compressor; (2) introducing the high-pressure gas obtained in the step (1) into a refining tower for separation, obtaining non-condensable gas containing HCl at the tower top, extracting a high-purity hydrogen chloride product from the tower, and obtaining a liquid phase containing organic matters at the tower kettle; and 3) feeding the non-condensable gas at the tower top of the refining tower to a downstream absorption unit, feeding the product hydrogen chloride in the tower to the periphery for supply, decompressing the liquid phase at the tower bottom, and returning to the upstream for recycling. The method can reduce 75% of energy consumption, finally realizes purification of hydrogen chloride gas containing non-condensable gas and organic matter impurities, reduces the amount of waste gas and the amount of byproduct hydrochloric acid, produces high-purity hydrogen chloride products with high added values, realizes efficient circulation of chlorine resources in a park, and has remarkable economic benefits and social benefits.

Description

Technical Field

[0001] The invention relates to the field of process waste gas treatment, and in particular to a method for recovering waste gas containing a large amount of non-condensable gas, organic matter and hydrogen chloride. Background Art

[0002] Hydrogen chloride is an important industrial chemical substance used to make dyes, fragrances, medicines, various chlorides, corrosion inhibitors and other chemicals. In addition, high-purity HCl gas is widely used in the electronics industry. Electronic-grade hydrogen chloride is mainly used in processes such as gas phase polishing, epitaxy and etching in the microelectronics industry. It can also be used in metal smelting, optical communications and scientific research.

[0003] The by-product hydrogen chloride tail gas in the industrial park contains a lot of organic matter and non-condensable gases such as nitrogen, which limits its application in many fields. The tail gas is generally treated by water absorption to produce hydrochloric acid. The hydrochloric acid produced by this method also contains high TOC and trace salt impurities, which also limits the application of by-product hydrochloric acid. The downstream hydrochloric acid market is becoming saturated, and there is even a risk of hydrochloric acid storage being stopped due to difficulties in selling hydrochloric acid. High-purity hydrogen chloride has a wide range of applications, such as PVC, epichlorohydrin, methyl chloride and other fields. Therefore, how to purify hydrogen chloride tail gas is an important issue.

[0004] CN110272022A discloses a tail gas recovery and treatment technology containing nitrogen and hydrogen chloride, wherein the tail gas is compressed and separated and enriched by a composite membrane, and the recovery rate of hydrogen chloride reaches 97%. The cost of preparing the membrane material and the equipment investment is high, the gap of the composite membrane is small, it is difficult to solve the problem of a small amount of solid impurities in the tail gas, and the anti-interference ability is weak.

[0005] CN116059777A discloses a method for deep separation of fluorine-containing HCl in tail gas of lithium hexafluorophosphate synthesis, wherein the tail gas is passed into a carbon nanotube adsorbent to deeply remove hydrogen fluoride and phosphorus pentafluoride in the tail gas. This method is an adsorption removal method, which cannot solve the problem of non-condensable gas in the tail gas of hydrogen chloride.

[0006] CN117105177A discloses a method for compressing, condensing and recovering acidic tail gas containing HF-HCl, which purifies the tail gas by compression and pressure swing adsorption to obtain high-purity HF, HCl and nitrogen. The tail gas can be separated and purified into three products with high product purity, but pressure swing adsorption involves repeated pressure changes, high energy consumption, large floor space and high investment cost.

[0007] CN117504324A discloses a concentrated hydrochloric acid analysis system and analysis process, which solves the problem that the circulation effect of hydrochloric acid vapor is poor, affecting the subsequent analysis and purification process. Although the hydrochloric acid analysis process can purify hydrogen chloride, the process produces a large amount of dilute acid, high energy consumption and easy corrosion, which affects its large-scale application. Summary of the invention

[0008] The purpose of the present invention is to provide a tail gas treatment and recovery method containing hydrogen chloride, non-condensable gas and organic matter, so as to overcome the defects of the above-mentioned prior art. The hydrogen chloride gas is separated from the non-condensable gas and organic matter in the tail gas under high pressure conditions, so that the hydrogen chloride gas can be recycled, thereby optimizing the process flow, increasing the added value of hydrogen chloride, reducing the amount of waste gas treatment, so as to achieve the purpose of reducing production costs, improving economic benefits, reducing by-products, and also reducing the overall operating energy consumption.

[0009] To achieve the above object, the technical solution of the present invention is as follows:

[0010] A method for refining and recovering hydrogen chloride tail gas, comprising the following steps:

[0011] 1) compressing the tail gas to a high pressure state through a compressor; preferably, compressing the hydrogen chloride tail gas to 1.0-2.0 MPaG to obtain a high pressure gas;

[0012] 2) passing the high-pressure gas from step 1) into a refining tower for separation, obtaining a non-condensable gas containing HCl at the top of the tower, extracting a high-purity hydrogen chloride product of >99wt% in the tower, and obtaining a liquid phase containing organic matter in the bottom of the tower;

[0013] 3) The non-condensable gas at the top of the refining tower is sent to the downstream absorption unit, the hydrogen chloride product in the tower is sent to the outside for supply, and the liquid phase at the bottom of the tower is depressurized and returned to the upstream for recycling.

[0014] In the present invention, the hydrogen chloride tail gas in step 1) is a byproduct gas of the device, which comprises:

[0015]

[0016] Among them, inert gases include but are not limited to nitrogen, argon, carbon monoxide, carbon dioxide, hydrogen, chlorine and other gases that do not undergo chemical reactions during compressed transportation; inert organic matter includes but is not limited to chlorobenzene, toluene, carbon tetrachloride, phosgene, alkanes, olefins, dichlorobenzene, ureas and other substances; active organic matter refers to substances that are prone to undergo chemical reactions such as polymerization and salt formation at high temperatures to generate solid blockages, including but not limited to phosgene, olefins, isocyanates, and amines.

[0017] Preferably, the compressor adopts a wet compressor, and an inert solvent can be sprayed at the inlet, including but not limited to chlorobenzene, toluene, diethyl carbonate, dichlorobenzene, carbon tetrachloride, alkanes, toluene and other organic solvents to improve the operating stability of the compressor.

[0018] In the present invention, the refining tower described in step 2) is a high-efficiency packed tower, and the feed includes gas inlet at the bottom of the tower and liquid reflux at the top of the tower. The extraction is divided into three extractions: gas phase extraction at the top of the tower, liquid phase extraction in the tower, and liquid phase extraction at the bottom of the tower. The liquid phase in the tower is extracted as a product of high-purity hydrogen chloride, and the mass proportion of hydrogen chloride is >99%. In order to recover the energy of this liquid hydrogen chloride, the material is flashed under reduced pressure, and heat is exchanged with the gas phase to be cooled at the top of the tower in the first heat exchanger E01 to achieve energy coupling, save the energy consumption of the second heat exchanger E02, and reduce the cooling energy consumption of the entire system by 75%. The flash pressure of liquid HCl is 0.3-0.8MPaG, and the determination of the flash pressure depends on the pressure demand of the downstream HCl demand end. After heat exchange in E01, the liquid HCl is completely vaporized and transported to downstream customers in gaseous state. The temperature of the HCl product after flashing is -35 to -60°C.

[0019] The gas phase (non-condensable gas containing HCl) produced from the top of the tower undergoes heat exchange in E01, with an outlet temperature ranging from -30 to -45°C. It then passes through heat exchanger E02 and is cooled to -40 to -70°C, condensing most of the HCl and refluxing it. The remaining small amount of non-condensable gas and HCl are discharged to the downstream waste gas treatment system.

[0020] The output from the refining tower is mainly liquid organic matter and a small amount of hydrogen chloride. After decompression, heating and flash evaporation are used to achieve gas-liquid separation. The liquid organic matter returns to the upstream system, and the flash gas phase is sent to the waste gas treatment system. The flash pressure is controlled at 0.1 to 0.4 MPaG and the temperature is controlled at 0 to 30°C to ensure that low-boiling impurities such as phosgene, ammonia, alkanes, isocyanates, olefins and other organic matter are not enriched in the system.

[0021] Since most of the liquid HCl is extracted from the tower, the liquid phase strength of the lower layer of the tower packing is low, the gas-liquid mass ratio ranges from 25 to 75, and the gas-liquid contact requirements are high. Therefore, a customized special liquid phase distributor is used, which is suitable for the working condition with a large gas-liquid ratio and can achieve an operating flexibility of 20%-100%. The distributor is above each section of the packing in the distillation tower to evenly disperse the reflux liquid phase to ensure sufficient gas-liquid interaction on the packing. The liquid distributor adopts a multi-stage hole design with a pore size of 1.5 to 3mm, preferably 2mm; the drop point density of the distributor is controlled at 50-100 / m 2 , ensuring sufficient liquid phase distribution and sufficient residence time. Smaller pore sizes bring the risk of clogging, so pre-filters are designed at the bottom of the upper packing and the gas inlet pipeline to prevent solid particles from moving downward and clogging, so as to ensure that the operation cycle of the entire tower is more than 2 years.

[0022] Preferably, the gas phase feed pipe of the refining tower and the liquid inlet pipe of the distributor are both equipped with filters to prevent clogging, and the filtration accuracy is 50-100 mesh.

[0023] In the present invention, the overhead exhaust gas in step 3) passes through downstream absorption units including but not limited to hydrochloric acid absorption, organic matter absorption and other systems, and the high-purity hydrogen chloride product is supplied to downstream industries including but not limited to VCM, methyl chloride, epichlorohydrin and the like;

[0024] The beneficial effects of the present invention are:

[0025] (1) After using this process, hydrogen chloride in the tail gas can be recovered and purified, with a recovery rate of >80%, and the purity of hydrogen chloride increased from 70-80% to >99%. High-purity hydrogen chloride can be sent to peripheral manufacturers, reducing the amount of waste gas treatment and increasing the added value of the product;

[0026] (2) This process has been optimized in design, with the addition of solvent spray at the inlet, and good operating stability. The tower bottom reboiler is eliminated, and the tower top economizer E01 is added to achieve energy coupling. The overall operating energy consumption is reduced by 75% compared with conventional distillation, which has a significant cost advantage.

[0027] (3) Heating and flash evaporation are designed at the bottom of the tower to remove light component impurities and ensure material balance in the system.

[0028] (4) The refining tower uses a customized liquid phase distributor to ensure operational flexibility under atmospheric liquid ratio conditions and achieve efficient separation of organic matter and gas phase. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a flow chart of HCl tail gas refining and recovery according to the present invention, wherein E01, E02, and E03 are the first, second, and third heat exchangers; and K01 is a compressor.

[0030] Figure 2 It is a schematic diagram of the structure of the liquid phase distributor, where a, liquid inlet pipe; b, connecting pipe; c, distribution plate; d, branch pipeline; e, liquid distribution nozzle; f, filter. DETAILED DESCRIPTION

[0031] Embodiments of the present invention will be described in more detail below. For those skilled in the art, different embodiments can be combined with each other as needed as long as the opposite situation is not obviously generated from the context.

[0032] The process of the present invention is as follows Figure 1 As shown: the hydrogen chloride tail gas (raw gas) is compressed by a compressor (the compressor adopts a wet type, and the inert solvent chlorobenzene is sprayed at the inlet), and then enters a refining tower. The non-condensable gas containing hydrogen chloride obtained at the top of the tower is sent to the downstream processing unit, the product hydrogen chloride obtained in the tower is sent to the periphery for supply, and the organic liquid phase obtained in the bottom of the tower is returned to the upstream for recycling.

[0033] like Figure 2As shown, the reflux liquid phase in the tower enters the connecting pipe through the liquid inlet pipe a. The connecting pipe is provided with a filter f, which can remove a small amount of solid particles to prevent solid particles from entering the packing layer and clogging it. The liquid phase enters the distribution plate c through the filter f, and after being evenly distributed, the liquid phase enters the packing and contacts with the gas phase in countercurrent.

[0034] The following examples are the results of small-scale tests and simulations. The mixed gas feed flow 1 is about 200 Nm 3 / h (about 300kg / h), the raw material contains 80wt% hydrogen chloride.

[0035] Example 1

[0036] The raw gas is compressed to 2.0MPaG by compressor K01, and then separated and refined by a refining tower (the gas phase feed pipe and the distributor liquid inlet pipe are equipped with filters to prevent blockage, and the filtration accuracy is 50 mesh). The distributor aperture is 2mm, and the drop point density of the distributor is controlled at 80 / m 2 The gas phase from the top of the tower enters the first heat exchanger E01 to exchange heat with the 200kg / h HCl product from the tower. The outlet temperature of E01 is -35℃. It enters the second heat exchanger E02. The outlet temperature of E02 is -40℃. The gas phase of E02 enters the waste gas treatment. The remaining liquid phase (HCl liquid phase) returns to the top of the tower. The 200kg / h HCl product from the tower is produced with a purity of 99.5%. There is no organic matter in the product HCl. The pressure is reduced to 0.8MPaG. After heat exchange in E01, the cooling capacity is recovered by 135KW. The bottom liquid of the tower is flashed at 0.3MPaG and 10℃ in the third heat exchanger E03. The gas phase enters the waste gas treatment, and the liquid phase returns to the upstream system. The overall system operation power consumption is 45KW, the HCl recovery rate is 83%, and the operating cost is 0.23KW / kgHCl.

[0037] Example 2

[0038] The raw gas is compressed to 1.8MPaG by compressor K01, and then separated and refined by a refining tower (the gas phase feed pipe and the distributor liquid inlet pipe are equipped with filters to prevent blockage, and the filtration accuracy is 50 mesh). The distributor aperture is 2mm, and the drop point density of the distributor is controlled at 80 / m 2 . The gas phase from the top of the tower enters the first heat exchanger E01 for heat exchange with the 210kg / h HCl product produced in the tower. The outlet temperature of E01 is -40℃. It enters the second heat exchanger E02. The outlet temperature of E02 is -50℃. The gas phase of E02 enters the waste gas treatment, and the remaining liquid phase (HCl liquid phase) returns to the top of the tower. 210kg / h HCl product is produced in the tower with a purity of 99.3%. There is no organic matter in the product HCl. The pressure is reduced to 0.6MPaG, and the heat exchange of E01 recovers 140KW of cold capacity; the bottom liquid of the tower is flashed at 0.3MPaG and 10℃, and then returned to the upstream system. The overall system operation power consumption is 42KW, the HCl recovery rate is 87%, and the operating cost is 0.20KW / kgHCl.

[0039] Example 3

[0040] The raw gas is compressed to 1.6MPaG by compressor K01, and then separated and refined by a refining tower (the gas phase feed pipe and the distributor liquid inlet pipe are equipped with filters to prevent blockage, and the filtration accuracy is 50 mesh). The distributor aperture is 2mm, and the drop point density of the distributor is controlled at 80 / m 2 . The gas phase from the top of the tower enters the first heat exchanger E01 for heat exchange with the 215kg / h HCl product produced in the tower. The outlet temperature of E01 is -45℃. It enters the second heat exchanger E02. The outlet temperature of E02 is -60℃. The gas phase of E02 enters the waste gas treatment, and the remaining liquid phase (HCl liquid phase) returns to the top of the tower. 215kg / h HCl product is produced in the tower with a purity of 99.2%. There is no organic matter in the product HCl. The pressure is reduced to 0.4MPaG, and the heat exchange of E01 recovers 144KW of cold capacity; the bottom liquid of the tower is flashed at 0.3MPaG and 10℃, and then returned to the upstream system. The overall system operation power consumption is 40KW, the HCl recovery rate is 89%, and the operating cost is 0.19KW / kgHCl.

[0041] Example 4

[0042] The raw gas is compressed to 1.8MPaG by compressor K01, and then separated and refined by a refining tower (the gas phase feed pipe and the distributor liquid inlet pipe are equipped with filters to prevent blockage, and the filtration accuracy is 50 mesh). The distributor aperture is 5mm, and the drop point density of the distributor is controlled at 150 / m 2 . The gas phase produced from the top of the tower enters the first heat exchanger E01 for heat exchange with the 190kg / h HCl product produced in the tower. The outlet temperature of E01 is -40℃. It enters the second heat exchanger E02. The outlet temperature of E02 is -50℃. The gas phase of E02 enters the waste gas treatment, and the remaining liquid phase (HCl liquid phase) returns to the top of the tower. 190kg / h HCl product is produced from the tower with a purity of 99.3%. There are trace organic matter (chlorobenzene, carbon tetrachloride) in the product HCl, which limits the application of the product. The pressure is reduced to 0.4MPaG, and the heat exchange of E01 recovers 125KW of cold capacity; the bottom liquid of the tower is flashed at 0.3MPaG and 10℃, and then returned to the upstream system. The overall system operation power consumption is 70KW, the HCl recovery rate is 79%, and the operating cost is 0.37KW / kgHCl.

[0043] Comparative Example 1

[0044] The raw gas is compressed to 2.0MPaG by compressor K01, and then separated and refined by a refining tower (the gas phase feed pipe and the distributor liquid inlet pipe are equipped with filters to prevent blockage, and the filtration accuracy is 50 mesh). The distributor aperture is 2mm, and the drop point density of the distributor is controlled at 150 / m 2, no E01 heat exchanger is set. The gas phase at the top of the tower is extracted and enters the second heat exchanger E02, the outlet temperature of E02 is -50℃, the gas phase of E02 enters the waste gas treatment, and the remaining liquid phase (HCl liquid phase) returns to the top of the tower to extract 200kg / hHCl product with a purity of 99.3%, and there is no organic matter in the product HCL; the bottom liquid is flashed at 0.3MPaG 10℃ and returned to the upstream system. The overall system has a high power consumption of 180KW, a high HCl recovery rate of 83%, and an operating cost of 0.84KW / kgHCl.

[0045] Comparative Example 2

[0046] The raw gas is compressed to 2.0MPaG by compressor K01, and then separated and refined by a refining tower (the gas phase feed pipe and the distributor liquid inlet pipe are equipped with filters to prevent blockage, and the filtration accuracy is 50 mesh). The distributor aperture is 2mm, and the drop point density of the distributor is controlled at 80 / m 2 . The extraction from the tower is cancelled, and all the liquid phase is extracted from the bottom of the tower. The feed of E01 is changed from the extraction from the tower to the bottom liquid. The gas phase extracted from the top of the tower enters the first heat exchanger E01 for heat exchange with the 190kg / h HCl product extracted from the tower. The outlet temperature of E01 is -40℃, and enters the second heat exchanger E02. The outlet temperature of E02 is -50℃. The E02 gas phase enters the waste gas treatment, and the remaining liquid phase (HCl liquid phase) returns to the top of the tower. 212kg / h HCl product is extracted from the bottom of the tower with a purity of 98.3%. There is a small amount of organic matter (chlorobenzene, carbon tetrachloride) in the product HCl, which makes the product unqualified. The pressure is reduced to 0.8MPaG, and the cooling capacity is recovered by heat exchange of E01 150KW; after heat exchange by E01, the bottom liquid is decompressed to 0.3MPaG and flashed at 10℃, and returned to the upstream system. The overall system operation power consumption is 50KW, and the HCl product contains organic matter and is unqualified.

[0047] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for refining and recovering hydrogen chloride tail gas, characterized in that the steps include: 1) Compress the exhaust gas to a high pressure state through a compressor; 2) passing the high-pressure gas from step 1) into a refining tower for separation, obtaining non-condensable gas containing HCl at the top of the tower, extracting high-purity hydrogen chloride product from the tower, and obtaining a liquid phase containing organic matter at the bottom of the tower; 3) The non-condensable gas at the top of the refining tower is sent to the downstream absorption unit, the hydrogen chloride product in the tower is sent to the outside for supply, and the liquid phase at the bottom of the tower is depressurized and returned to the upstream for recycling.

2. The recycling method according to claim 1, characterized in that: In step 1), the hydrogen chloride tail gas contains 55-85 wt% hydrogen chloride, and the remaining inert gases include but are not limited to nitrogen, argon, carbon monoxide, carbon dioxide, hydrogen, and chlorine; inert organic substances include but are not limited to chlorobenzene, toluene, carbon tetrachloride, alkanes, dichlorobenzene, and ureas; and active organic substances include but are not limited to phosgene, olefins, isocyanates, and amines.

3. The recovery method according to claim 1 or 2, characterized in that: The compressor outlet pressure is 1.0-2.0MPaG.

4. The recycling method according to any one of claims 1 to 3, characterized in that: The compressor adopts a wet type, and an inert solvent is sprayed at the inlet, preferably one or more of chlorobenzene, toluene, diethyl carbonate, dichlorobenzene, carbon tetrachloride, alkane, and toluene.

5. The recycling method according to any one of claims 1 to 4, characterized in that: Step 2) The refined HCl in the tower is taken out as liquid phase, flashed under reduced pressure to 0.3-0.8 MPaG, at a temperature range of -35 to -60°C, and heat exchanged with the non-condensable gas containing HCl taken out from the top of the tower.

6. The recycling method according to any one of claims 1 to 5, characterized in that: Step 2) The non-condensable gas containing HCl obtained at the top of the tower is heat exchanged in a primary heat exchanger and then condensed in a secondary condenser. The outlet temperature of the secondary condenser ranges from -40 to -70°C. The liquid phase is refluxed to the top of the refining tower, and the gas phase is decompressed and sent to the tail gas treatment system.

7. The recycling method according to any one of claims 1 to 6, characterized in that: Step 2) The refining tower is a packed tower, comprising a gas phase feed pipe, a packing section and a distributor; the gas phase feed pipe and the distributor liquid inlet pipe are both equipped with filters to prevent clogging, and the filtration accuracy is 50-100 mesh.

8. The recycling method according to claim 7, characterized in that: The distributor adopts a multi-stage hole design with a hole diameter of 1.5 to 3 mm, preferably 2 mm; the drop point density of the distributor is controlled at 50-100 / m 2 .

9. The recycling method according to any one of claims 1 to 8, characterized in that: The output from the bottom of the refining tower is mainly liquid organic matter and a small amount of hydrogen chloride. After decompression, heating and flash evaporation are performed to achieve gas-liquid separation. The liquid organic matter returns to the upstream system, and the flash gas phase is sent to the waste gas treatment system. Preferably, the flash pressure is controlled at 0.1 to 0.4 MPaG and the temperature is controlled at 0 to 30°C.

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