Method for liquefying and recovering dimethyl ether in mixed gas

Abstract

The invention provides a method for liquefying and recovering dimethyl ether in mixed gas, which comprises the following steps: feeding raw material gas containing 3-9% of gaseous dimethyl ether into a washing tower, washing the dimethyl ether in the raw material gas until the content of the dimethyl ether in the raw material gas is below 1%, cooling dimethyl ether liquid for washing to keep the circulating temperature of the dimethyl ether liquid below 40 DEG C, the method comprises the following steps of: washing raw material gas, feeding the washed raw material gas into a first-stage temperature swing adsorption tower group consisting of two or more towers to finally obtain product gas in which the total content of dimethyl ether, methyl acetate and methanol is less than 100ppm, and carrying out isobaric back flushing operation on the adsorption towers by using the raw material gas heated to 140-160 DEG C as regenerated gas to achieve the purpose of recovering dimethyl ether. And after the regeneration of the adsorption tower is finished, the adsorption tower is cooled to enter the next cycle. According to the method, the dimethyl ether can be efficiently recycled, and the economic and environment-friendly requirements are met.

Description

Technical Field

[0001] The invention mainly relates to the technical field related to dimethyl ether recovery, and specifically is a method for liquefying and recovering dimethyl ether in a mixed gas. Background Art

[0002] In the process of producing ethanol and dimethyl ether from coal-to-syngas, the tail gas of dimethyl ether production contains 3%-9% dimethyl ether. It is necessary to recover the dimethyl ether in the tail gas through reasonable means to ensure environmental protection requirements and increase benefits.

[0003] The previous process is to use temperature swing adsorption to recover 85%-90% of the effective gas hydrogen and carbon monoxide, and then burn the remaining gas in the flare. This not only wastes the produced dimethyl ether, but also increases the carbon emissions of the flare. At the same time, this process will lose 10%-15% of the effective hydrogen and carbon monoxide, which is not economical and environmentally friendly. Therefore, it is necessary to design a method that can meet environmental protection requirements and achieve efficient recovery of dimethyl ether to solve the shortcomings of the existing technology. Summary of the invention

[0004] In order to solve the shortcomings of the current technology, the present invention combines the existing technology and provides a method for liquefying and recovering dimethyl ether in a mixed gas from the perspective of practical application, which can achieve efficient recovery of dimethyl ether and meet economic and environmental protection requirements.

[0005] The technical solution of the present invention is as follows: A method for liquefying and recovering dimethyl ether in a mixed gas, the method comprising: (A) The raw gas containing 3%-9% gaseous dimethyl ether is sent to the scrubber, where the dimethyl ether liquid at room temperature is circulated for scrubbing and absorption, and the wire mesh demister absorbs the dimethyl ether droplets, so that the dimethyl ether content in the raw gas is washed to less than 1%; (B) The dimethyl ether liquid for washing is circulated by a circulating pump, and the circulating dimethyl ether liquid is cooled so that its circulation temperature is maintained below 40 degrees; (C) The raw gas after washing is sent to a first-stage temperature swing adsorption tower group consisting of two or more towers. The first-stage temperature swing adsorption tower group controls the dimethyl ether content in the raw gas to less than 0.3%, and then sends the intermediate gas to a second-stage temperature swing adsorption tower group consisting of two or more towers for further adsorption operation, and finally obtains a product gas with a total content of dimethyl ether, methyl acetate and methanol below 100 ppm; (D) For the adsorption towers with saturated adsorption in the first-stage temperature swing adsorption tower group and the second-stage temperature swing adsorption tower group, the raw gas heated to 140-160 degrees is used as the regeneration gas for isobaric backblowing operation, and the dimethyl ether gas-liquid mixture in the adsorbent is blown out of the adsorption tower, cooled by the cooler, and then washed with dimethyl ether liquid at room temperature in the washing tower and liquefied, so as to achieve the purpose of recovering dimethyl ether. At the same time, the adsorbent is regenerated. After the regeneration of the adsorption tower is completed, the temperature is reduced and cooled to enter the next cycle.

[0006] The present invention uses a washing tower to liquefy dimethyl ether gas and absorb it into dimethyl ether liquid. At the same time, in this process, the temperature of the circulating dimethyl ether liquid will gradually increase due to the liquefaction of the dimethyl ether gas. The temperature of the dimethyl ether liquid is reduced by a circulating pump and cooling method to complete the circulating washing of the dimethyl ether liquid and ensure the washing and absorption effect of the dimethyl ether liquid. The gas absorbed by the dimethyl ether liquid enters the first-stage temperature swing adsorption tower group composed of two or more towers, and the gas dimethyl ether is absorbed by the adsorbent in the bed layer of the regenerated adsorption tower. The dimethyl ether in the gas is absorbed by the adsorbent, and the dimethyl ether partial pressure in the adsorbent gradually reaches the liquefaction partial pressure, forming a gas-liquid mixture of dimethyl ether inside the adsorbent. The gas with a dimethyl ether content within the design index from the first-stage temperature swing adsorption tower group goes to the second-stage temperature swing adsorption tower group composed of two or more towers for further adsorption operation, and finally obtains a product gas with a total content of dimethyl ether, methyl acetate and methanol below the design standard. The adsorption tower with saturated adsorption uses heated raw gas for isobaric back-blowing operation, and the high-concentration dimethyl ether gas-liquid mixture in the adsorbent is blown out of the adsorption tower from top to bottom. After being cooled by the cooler, it is washed by dimethyl ether liquid at room temperature in the scrubbing tower and liquefied to achieve the purpose of recovering dimethyl ether. At the same time, the adsorbent is regenerated. After the regeneration of the adsorption tower is completed, it is cooled down and enters the next cycle. Using raw gas as the regeneration gas source for the adsorption bed avoids the factors of product gas pollution caused by using other gases for regeneration. At the same time, the regenerated gas returns to the scrubbing tower without external discharge loss.

[0007] Furthermore, method (A) uses a two-stage scrubber for scrubbing, wherein the first-stage scrubber scrubs the dimethyl ether content in the raw gas to less than 1.5%, and the second-stage scrubber scrubs the dimethyl ether content in the raw gas to less than 1%.

[0008] Furthermore, both the first-stage washing tower and the second-stage washing tower adopt a circulating pump followed by a cooler to reduce the temperature of the liquid dimethyl ether to below 40 degrees.

[0009] Furthermore, in method (D), the raw gas after the first-stage washing tower is divided into two gases with a pressure difference, of which 15-25% of the high-pressure part is used as the regeneration gas, and the rest is sent to the second-stage washing tower after decompression. The dimethyl ether gas-liquid mixture desorbed by the regeneration gas in the adsorption tower is cooled by a cooler and then sent to the second-stage washing tower.

[0010] The two-stage scrubber is used. The first-stage scrubber can wash the dimethyl ether content in the raw gas to below 1.5%. After this treatment, the degree of pollution of the adsorption bed when the raw gas is used as regeneration gas is reduced. After the second-stage scrubbing, the dimethyl ether in the raw gas is reduced to below 1%, reducing the amount of adsorbent used in the later stage.

[0011] The raw gas pressure reducing regulating valve and the regeneration gas flow regulating valve are used to divide the raw gas into two gases with a pressure difference. 15-25% of the high-pressure part is used as the regeneration gas, and the rest is decompressed to go to the main process to remove and recover dimethyl ether. After the pressure difference is formed by the raw gas pressure reducing regulating valve, the regeneration gas is guaranteed to work and be recovered normally. The system pressure drop is less than 0.2Mpa, which can fully meet the pressure requirements of the subsequent work section.

[0012] Furthermore, in method (C), the adsorbent is selected from one or more of activated carbon, 5A molecular sieve and silica gel.

[0013] Furthermore, in method (C), dimethyl ether is adsorbed by the adsorbent, and after the dimethyl ether concentration inside the adsorbent reaches a liquefied concentration, a dimethyl ether gas-liquid mixture is formed inside the adsorbent bed.

[0014] Furthermore, the first-stage temperature swing adsorption tower group is composed of two towers, adsorption tower A and adsorption tower B. When adsorption tower A or adsorption tower B is saturated and the content of dimethyl ether at the outlet reaches the design index of 0.3%, the adsorption is switched to another adsorption tower. The saturated adsorption tower enters the regeneration process, and the intermediate gas is sent to the second-stage temperature swing adsorption tower group. After the desorption of the high-temperature regeneration gas in adsorption tower A or adsorption tower B is completed, the intermediate gas from another adsorption tower is used to cool the temperature, and the cooled intermediate gas is sent to the second-stage temperature-swing adsorption tower group.

[0015] The two-stage adsorption tower is operated alternately, and the adsorption tower can use the intermediate gas of another adsorption tower for cooling when cooling down.

[0016] Furthermore, the second-stage temperature-swing adsorption tower group consists of three towers: adsorption tower C, adsorption tower D, and adsorption tower E. The intermediate gas containing 0.3% dimethyl ether enters the adsorption tower C or the adsorption tower D. When the total content of dimethyl ether, methyl acetate and methanol at the upper outlet of the adsorption tower reaches the designed value of 100ppm, the tower is cut off, and the adsorption tower C or the adsorption tower D enters the regeneration process, and the product gas is sent to the product gas pipeline.

[0017] Furthermore, in the second-stage temperature-swing adsorption tower group, after the desorption of the high-temperature regeneration gas in the adsorption tower C or the adsorption tower D is completed, the raw gas without heating is first used to pass through the adsorption tower E to replace and cool the adsorption tower C or the adsorption tower D that needs to be cooled, and the replacement gas is sent to the washing tower, and the product gas of another adsorption tower is used for cooling, and the cooled product gas is sent to the product gas pipeline.

[0018] Furthermore, after the adsorption tower E has been running for a certain period, the raw gas heated to 140-160 degrees is used as the regeneration gas to regenerate the adsorbent and recover dimethyl ether. After the desorption of the adsorption tower E by the high-temperature regeneration gas is completed, the product gas of the adsorption tower C or the adsorption tower D is used to cool down, and the cooled product gas is sent to the product gas pipeline.

[0019] After the regeneration gas from adsorption tower C or adsorption tower D is heated, the regeneration gas that has passed through adsorption tower E without heating can be used to cool and replace the adsorption tower that needs to be cooled, so as to replace the high concentration of dimethyl ether brought by the regeneration gas main pipeline.

[0020] According to another aspect of the present invention, there is also provided a recovery system for implementing the above recovery method, comprising: a washing tower group, a first-stage temperature swing adsorption tower group, and a second-stage temperature swing adsorption tower group; The raw gas pipeline is connected to the washing tower group, and the washing tower group is equipped with a dimethyl ether liquid circulation pipeline and a regeneration gas pipeline main pipe. The dimethyl ether liquid circulation pipeline is provided with a dimethyl ether liquid circulation pump and a dimethyl ether liquid cooler; The first stage temperature swing adsorption tower group is connected to the outlet of the washing tower group and the main regeneration gas pipeline through pipelines and valves; The second stage temperature swing adsorption tower group is connected to the outlet of the first stage temperature swing adsorption tower group and the regeneration gas pipeline main through pipelines and valves, and the second stage temperature swing adsorption tower group is equipped with a product gas pipeline; The first-stage temperature-swing adsorption tower group and the second-stage temperature-swing adsorption tower group are both connected to the inlet of the washing tower group through a desorption gas pipeline and a valve, and a desorption gas cooler is arranged on the desorption gas pipeline.

[0021] Furthermore, the washing tower group includes a washing tower A and a washing tower B, the regeneration gas pipeline main is arranged between the washing tower A and the washing tower B, a raw gas pressure reducing regulating valve is arranged on the pipeline connecting the washing tower A and the washing tower B, a regeneration gas flow regulating valve is arranged on the regeneration gas pipeline, and the desorption gas pipeline is connected to the washing tower B.

[0022] Furthermore, the dimethyl ether liquid circulation pipelines of the washing tower A and the washing tower B are connected to the liquid product dimethyl ether pipeline through pipelines and dimethyl ether liquid level regulating valves.

[0023] Furthermore, the first-stage temperature-swing adsorption tower group includes an adsorption tower A and an adsorption tower B, which are arranged in parallel, and the adsorption tower A and the adsorption tower B are connected to the second-stage temperature-swing adsorption tower group through an intermediate gas pipeline.

[0024] Furthermore, the adsorption tower A and the adsorption tower B are interconnected through pipelines and valves, and are both connected to the intermediate gas cooling pipeline. An intermediate gas cooler is arranged on the intermediate gas cooling pipeline, and the intermediate gas cooling pipeline is connected to the intermediate gas pipeline.

[0025] Furthermore, the second-stage temperature-variable adsorption tower group includes an adsorption tower C, an adsorption tower D and an adsorption tower E. The adsorption tower C and the adsorption tower D are arranged in parallel. The inlets of the adsorption tower C and the adsorption tower D are connected to the intermediate gas pipeline, and the outlets are connected to the product gas pipeline.

[0026] Furthermore, the adsorption tower C, the adsorption tower D, and the adsorption tower E are connected to each other through pipelines and valves.

[0027] Furthermore, the regeneration gas pipeline main has three branches, the first branch pipeline is connected to adsorption tower A and adsorption tower B, the second branch pipeline is connected to adsorption tower C, adsorption tower D and adsorption tower E, and the third branch pipeline is connected to adsorption tower E.

[0028] Furthermore, a regeneration gas heater is provided on the first branch pipeline and the second branch pipeline of the regeneration gas pipeline main pipeline.

[0029] Furthermore, all valves on the pipeline are remote-controlled valves to facilitate automated control of the system.

[0030] Beneficial effects of the present invention: 1. The method of the present invention efficiently recovers and liquefies dimethyl ether in tail gas, and there is no effective gas loss in the whole process. The total content of dimethyl ether, methyl acetate and methanol in the product gas is guaranteed to be below the design index, which has obvious economic benefits and environmental protection value.

[0031] 2. The method of the present invention has no external gas outlet in the entire operation process, so full recovery is achieved, reducing the gas loss of decompression and venting in the traditional process. The power system only has a dimethyl ether circulation pump, the pressure of the recovered dimethyl ether liquid is the system pressure, the power load is low, and the recovery cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Attached Figure 1 This is a schematic diagram of the system of the present invention.

[0033] Numbers shown in the figure: 1-raw gas pipeline; 2-washing tower A; 3-washed raw gas pipeline; 4-regeneration gas flow control valve; 5-raw gas pressure reduction control valve; 6-dimethyl ether liquid level control valve A; 7-dimethyl ether liquid circulation pump; 8-liquid product dimethyl ether pipeline; 9-dimethyl ether liquid cooler; 10-dimethyl ether liquid level control valve B; 11-washing tower B; 12-dimethyl ether liquid circulation pipeline; 13-regeneration gas pipeline main; 14-adsorption tower A; 15-adsorption tower B; 16-regeneration gas heater; 17-first program-controlled valve; 18-second program-controlled valve; 19-third program-controlled valve; 20-fourth program-controlled valve; 21-fifth program-controlled valve; 22-regeneration gas cooling pipeline ; 23-regeneration gas heating pipeline; 24-regeneration gas pipeline; 25-regeneration gas regeneration pipeline; 26-regeneration gas inlet program-controlled valve; 27-intermediate gas cooling pipeline; 28-adsorption tower E regeneration program-controlled valve; 29-product gas pipeline; 30-desorption gas pipeline; 31-desorption gas cooler; 32-reflux pipeline; 33-cooling program-controlled valve; 34-adsorption tower C; 35-adsorption tower D; 36-adsorption tower E; 37-intermediate gas pipeline; 38-adsorption tower E regeneration gas outlet program-controlled valve; 39-adsorption tower E cooling program-controlled valve A; 40-adsorption tower C, adsorption tower D cooling program-controlled valve; 41-adsorption tower E cooling program-controlled valve B; 42-intermediate gas cooler. DETAILED DESCRIPTION

[0034] The present invention will be further described with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope limited by the application. Example

[0035] This embodiment provides a system for liquefying and recovering dimethyl ether in a mixed gas. The system schematic diagram is as follows: Figure 1 shown.

[0036] The recovery system of this embodiment is mainly composed of a washing tower group, a first-stage temperature swing adsorption tower group, a second-stage temperature swing adsorption tower group, pipelines and corresponding valves.

[0037] like Figure 1 As shown, the washing tower group mainly includes washing tower A2 and washing tower B11. The raw gas pipeline 1 is connected to the washing tower A2, and the washing tower A2 is equipped with a dimethyl ether liquid circulation pipeline 12. The dimethyl ether liquid circulation pump 7 and the dimethyl ether liquid cooler are arranged on the dimethyl ether liquid circulation pipeline 12, and the dimethyl ether liquid circulation pipeline 12 is connected to the liquid product dimethyl ether pipeline 8 through the dimethyl ether liquid level regulating valve A6.

[0038] The top outlet of the washing tower A2 is connected to the washed raw gas pipeline 3, and the washed raw gas pipeline 3 has two branches, one of which is connected to the regeneration gas pipeline main 13 through the regeneration gas flow regulating valve 4, and the other branch is connected to the washing tower B11 through the raw gas pressure reducing regulating valve 5. The washing tower B11 is equipped with a dimethyl ether liquid circulation pipeline 12, on which a dimethyl ether liquid circulation pump 7 and a dimethyl ether liquid cooler 9 are arranged, and the dimethyl ether liquid circulation pipeline 12 is connected to the liquid product dimethyl ether pipeline 8 through a dimethyl ether liquid level regulating valve B10.

[0039] The first-stage temperature-variable adsorption tower group mainly includes an adsorption tower A14 and an adsorption tower B15. The adsorption tower A14 and the adsorption tower B15 are arranged in parallel, and the upper pipelines are provided with a first program-controlled valve 17 and a second program-controlled valve 18 (the program-controlled valve referred to in this application is a remote control valve). The intermediate gas pipeline 37 is connected through the first program-controlled valve 17, and the first branch pipeline of the regeneration gas pipeline main 13 is connected through the second program-controlled valve 18.

[0040] The lower pipelines of adsorption tower A14 and adsorption tower B15 are both equipped with a third program-controlled valve 19, a fourth program-controlled valve 20 and a fifth program-controlled valve 21, which are connected to the outlet of washing tower B11 through the third program-controlled valve 19, connected to washing tower B11 through the third program-controlled valve 19, connected to the desorption gas pipeline 30 through the fourth program-controlled valve 20, and connected to the intermediate gas cooling pipeline 27 through the fifth program-controlled valve 21. The intermediate gas cooling pipeline 27 is connected to the intermediate gas pipeline 37, and an intermediate gas cooler 42 is arranged on the intermediate gas cooling pipeline 27, and a desorption gas cooler 31 is arranged on the desorption gas pipeline 30.

[0041] The second stage temperature swing adsorption tower group mainly includes adsorption tower C34, adsorption tower D35 and adsorption tower E36. Adsorption tower C34 and adsorption tower E35 are arranged in parallel, and the upper pipelines are provided with a first program-controlled valve 17 and a second program-controlled valve 18, which are connected to the product gas pipeline 29 through the first program-controlled valve 17 and connected to the upper pipeline of the adsorption tower E36 through the second program-controlled valve 18. The lower pipelines of adsorption tower C34 and adsorption tower D35 are equipped with a third program-controlled valve 19, a fourth program-controlled valve 20 and a fifth program-controlled valve 21, which are connected to the intermediate gas pipeline 37 through the third program-controlled valve 19, connected to the desorption gas pipeline 30 through the fourth program-controlled valve 20, connected to the bottom of adsorption tower E36 through the fifth program-controlled valve 21 and the program-controlled valve A39 for cooling adsorption tower E, and connected to the product gas pipeline 29 through the program-controlled valve 40 for cooling adsorption tower C and adsorption tower D, and the upper part of adsorption tower E36 is connected to the product gas pipeline 29 through the program-controlled valve B41 for cooling adsorption tower E.

[0042] The upper part of the adsorption tower E36 is connected to the second branch of the regeneration gas main pipeline 13, namely the regeneration gas pipeline 24. The pipeline has two branches, the regeneration gas cooling pipeline 22 and the regeneration gas heating pipeline 23. A valve is set at each pipeline. The regeneration gas cooling pipeline 22 and the regeneration gas heating pipeline 23 are connected in parallel, and the adsorption tower E regeneration program-controlled valve 28 is set between them. The third branch regeneration gas regeneration pipeline 25 is connected to the lower part of the adsorption tower E36, and is connected to the reflux pipeline connection 32 through the adsorption tower E regeneration gas outlet program-controlled valve 38. The reflux pipeline 32 is connected to the desorption gas pipeline 30.

[0043] The regeneration gas pipeline main 13 has three branches. The first branch pipeline is provided with a regeneration gas inlet programmable valve 26 and a regeneration gas heater 16 and is connected to the first-stage temperature-swing adsorption tower group. The second branch pipeline is provided with a regeneration gas heater 16 and is connected to the second-stage temperature-swing adsorption tower group. The third branch pipeline is provided with a regeneration gas inlet programmable valve 26, but no regeneration gas heater 16 is provided. The third branch pipeline is connected to the adsorption tower E36. Example 1

[0044] This embodiment provides a specific dimethyl ether recovery method and recovery process.

[0045] During the implementation of the method, the raw gas with a pressure of 2.2-5.2Mpa and containing 3%-9% of gaseous dimethyl ether is first sent to the washing tower A2 through the raw gas pipeline 1, and the dimethyl ether content in the raw gas is reduced from 3%-9% to below 1.5% by washing and absorbing with liquid dimethyl ether and absorbing dimethyl ether droplets with a wire mesh demister. Then, the gas is divided by a regeneration gas flow regulating valve 4, wherein the regeneration gas accounts for 15-25% of the raw gas, and the remaining gas is decompressed by the raw gas pressure reducing regulating valve 5 and sent to the washing tower B11. The washing tower B11 washes the dimethyl ether content in the raw gas to below 1%, and then sends it to the adsorption tower A14 or the adsorption tower B15. When the dimethyl ether content at the upper outlet of the adsorption tower A14 or the adsorption tower B15 reaches the design index of 0.3%, it is switched to another adsorption tower for adsorption, and the intermediate gas is sent to the second-stage temperature-swing adsorption tower group through the intermediate gas pipeline 37.

[0046] In the above washing process, the temperature of the circulating dimethyl ether liquid will gradually increase due to the liquefaction of dimethyl ether gas. The dimethyl ether liquid circulation pump 7 plus the dimethyl ether liquid cooler 9 is used to reduce the temperature of the liquid dimethyl ether to below 40 degrees to ensure the effect of dimethyl ether liquid washing and absorption. The temperature of the liquid dimethyl ether at the bottom of the washing tower A2 and the washing tower B11 should be controlled below 40°C after the dimethyl ether liquid cooler 9. In this way, the dimethyl ether content in the outlet gas at the top of the washing tower A2 and the washing tower B11 is easy to control below the design index. After the secondary washing, the dimethyl ether in the raw gas is reduced to less than 1%, reducing the amount of adsorbent used in the later stage.

[0047] In order to ensure the regeneration effect of adsorption tower A14 and adsorption tower B15, the temperature range of the regeneration gas after heating by the regeneration gas heater 16 is 140℃-160℃, which effectively ensures that the dimethyl ether content in the intermediate gas is lower than the design index of 0.3%. The raw gas pressure reducing regulating valve 5 and the regeneration gas flow regulating valve 4 are used to divide the raw gas into two gases with pressure difference, of which 15-25% of the high-pressure part is used as the regeneration gas, and the remaining part is removed and recovered by the main process after pressure reduction. After the pressure difference is formed by the raw gas pressure reducing regulating valve 5, it is guaranteed that the regeneration gas can work normally and be recovered, and the system pressure drop is less than 0.2Mpa, which can fully meet the pressure requirements of the subsequent stage. The first-stage washing tower washes the dimethyl ether content in the raw gas to less than 1.5%. After such treatment, the degree of pollution of the adsorption bed when the raw gas is used as the regeneration gas is reduced.

[0048] When adsorption tower A14 or adsorption tower B15 reaches adsorption saturation and the outlet dimethyl ether content reaches 0.3%, the tower is switched off and the adsorption tower enters the regeneration process, and the generated intermediate gas is sent to the second-stage temperature-swing adsorption tower group.

[0049] The regenerated gas is heated to 140-160 degrees through the regenerated gas inlet programmable valve 26 and the regenerated gas heater 16, and then goes to the top of the adsorption tower A14 or the adsorption tower B15 through the second programmable valve 18. Under the action of the high-temperature gas, the dimethyl ether adsorbed in the adsorbent is gradually desorbed in the form of a gas-liquid mixture, passes through the fourth programmable valve 20, enters the desorption gas cooler 31, and finally enters the bottom of the washing tower B11, thus completing the process of dimethyl ether liquefaction.

[0050] The adsorbent in the adsorption tower is selected from one or more of activated carbon, 5A molecular sieve and silica gel. After the dimethyl ether concentration inside the adsorbent reaches the liquefied concentration, a dimethyl ether gas-liquid mixture is formed inside the adsorbent bed. The mixed gas containing 1% dimethyl ether is reduced to less than 0.3% in the first stage temperature swing adsorption tower group composed of adsorption tower A14 and adsorption tower B15, and then enters the second stage adsorption tower group composed of adsorption tower C34, adsorption tower D35 and adsorption tower E36. The total content of dimethyl ether, methyl acetate and methanol in the final product gas can be controlled below 100ppm. The dimethyl ether gas-liquid mixture in the adsorbent is subjected to isobaric backblowing operation using raw gas heated to 140-160 degrees to desorb the high-concentration dimethyl ether gas-liquid mixture in the adsorbent. After being cooled in a cooler, it is washed with dimethyl ether liquid in a washing tower and then liquefied to achieve the purpose of recovering dimethyl ether. The adsorbent is regenerated and the raw gas is used as the regeneration gas source for the adsorption bed, thereby avoiding the use of other gases for regeneration and causing product gas pollution. At the same time, the regenerated gas is returned to the washing tower B11 without external discharge loss.

[0051] After the adsorption tower A14 or the adsorption tower B15 is desorbed by the high-temperature regeneration gas, the intermediate gas of the other adsorption tower is used for cooling. If the desorption of the regeneration gas of the adsorption tower A14 is completed, the intermediate gas of the adsorption tower B15 enters the adsorption tower A14 through the first program-controlled valve 17, goes to the intermediate gas cooling pipeline 27 through the fifth program-controlled valve 21, and then goes to the adsorption tower C34 and the adsorption tower D35 through the intermediate gas pipeline 37. After the cooling of the adsorption tower is completed, it enters the adsorption stage, and the adsorption tower B15 enters the temperature rise regeneration stage, and the two adsorption towers adsorb alternately.

[0052] The intermediate gas containing 0.3% dimethyl ether enters the adsorption tower C34, and the product gas after dimethyl ether adsorption directly enters the product gas pipeline 29. When the total content of dimethyl ether, methyl acetate and methanol at the upper outlet of the adsorption tower C34 reaches the designed value of 100ppm, it is switched to the adsorption tower D35 for operation, and the adsorption tower C34 enters the regeneration process, and the adsorption towers C34 and D35 adsorb alternately.

[0053] The regenerated gas is heated through the regenerated gas pipeline and the regenerated gas heater 16 to 140-160 degrees and then goes to the adsorption tower C34 or the adsorption tower D35. In the regenerated adsorption tower, under the action of the high-temperature gas, the dimethyl ether adsorbed in the adsorbent is gradually desorbed in the form of a gas-liquid mixture, passes through the fourth programmable valve 20, enters the desorption gas cooler 31, and finally enters the bottom of the washing tower B11, thus completing the whole process of dimethyl ether liquefaction.

[0054] After the regeneration gas is heated up and the adsorbent is regenerated, the regeneration gas from the third branch of the regeneration gas pipeline main pipe 13 is first used, and the regeneration gas enters the adsorption tower C34 or adsorption tower E35 that needs to be cooled through the regeneration gas inlet programmable valve 26, the regeneration gas regeneration pipeline 25, the adsorption tower E36 and the temperature reduction programmable valve 33, and is used to cool the adsorption tower C34 or adsorption tower D35 that needs to be cooled and replaced for no less than 5 minutes. The replaced gas returns to the bottom of the washing tower B11 through the fourth programmable valve 20. Afterwards, the adsorption tower C34 or adsorption tower D35 that needs to be cooled and cooled is cooled by the product gas of another adsorption tower, and the product gas of another adsorption tower passes through the first programmable valve 17, the adsorption tower that needs to be cooled, the fifth programmable valve 21, and finally goes to the product gas pipeline 29 to further cool the adsorption tower. After the temperature reduction is completed, it enters the adsorption stage, and the other adsorption tower enters the temperature increase regeneration stage.

[0055] After the adsorption tower E36 has run for five cycles (after replacing the adsorption tower C34 or the adsorption tower D35 five times), it is regenerated by using the regeneration gas through the regeneration gas pipeline 24, the regeneration gas heater 16, and the adsorption tower E regeneration programmable valve 28. The desorbed gas from the adsorption tower E36 is sent to the washing tower B11 through the reflux pipeline 32 to recover dimethyl ether. After the regeneration of the adsorption tower E36 is completed by heating, the product gas cooled by the adsorption tower C34 or the adsorption tower D35 is sent to the product gas pipeline 29 through the adsorption tower E cooling programmable valve A39, the adsorption tower E36, and the adsorption tower E cooling programmable valve B41 for cooling.

[0056] After the regeneration gas of adsorption tower C34 or adsorption tower D35 is heated, the regeneration gas passing through the regeneration gas regeneration pipeline 25, the regeneration gas inlet program-controlled valve 26, the adsorption tower E36 and the temperature-lowering program-controlled valve 33 is used to cool and replace the adsorption tower that needs to be cooled for no less than 5 minutes, so that the dimethyl ether with a high concentration brought by the regeneration gas main pipeline 13 can be replaced. Only after the replacement is completed can the product gas be used for cooling, so that the total content of dimethyl ether, methyl acetate and methanol in the product gas can be effectively guaranteed to be below 100ppm. Example 2

[0057] This embodiment provides a specific implementation method based on the above dimethyl ether recovery system and recovery method. The following Table 1 shows the raw gas conditions during implementation.

[0058] Table 1 Raw gas conditions .

[0059] The key points of the process implementation in this embodiment are as follows: The key to the implementation of this process is first, washing of liquid dimethyl ether; second, absorption by adsorbent; and third, regeneration and liquefaction.

[0060] The main purpose of washing is to use the liquid dimethyl ether liquefied at the top and flowing downward to directly absorb part of the dimethyl ether in the raw gas, which can reduce the dimethyl ether entering the adsorbent and reduce the amount of special adsorbent used.

[0061] The main purpose of adsorbent absorption is: the adsorbent adsorbs dimethyl ether, and after the dimethyl ether concentration inside the adsorbent reaches the liquefied concentration, a dimethyl ether gas-liquid mixture is formed inside the adsorbent.

[0062] The main purpose of regeneration liquefaction is to completely desorb the dimethyl ether gas-liquid mixture in the adsorbent by heating, absorb it by dimethyl ether liquid, and obtain product liquid dimethyl ether. At the same time, the adsorbent is regenerated and enters the next cycle.

[0063] Table 2 below shows the implementation results.

[0064] Table 2 Implementation effect .

[0065] According to statistics, the recovery of dimethyl ether is: (254Nm3 / h-0.2034Nm3 / h) = 253.7966Nm3 / h, 521.6Kg / h, and the annual recovery of dimethyl ether is: 417.28 tons, with a value of 13.77 million yuan. (Calculated at 3,300 yuan / ton).

[0066] Example 4 This embodiment provides a specific implementation method based on the above dimethyl ether recovery system and recovery method. The following Table 3 shows the raw gas conditions during implementation.

[0067] Table 3 Raw gas conditions .

[0068] The key points of the process implementation in this embodiment are as follows: The key to the implementation of this process is first, washing of liquid dimethyl ether; second, absorption by adsorbent; and third, regeneration and liquefaction.

[0069] The main purpose of washing is to use the liquid dimethyl ether liquefied at the top and flowing downward to directly absorb part of the dimethyl ether in the raw gas, which can reduce the dimethyl ether entering the adsorbent and reduce the amount of special adsorbent used.

[0070] The main purpose of adsorbent absorption is: the adsorbent adsorbs dimethyl ether, and after the dimethyl ether concentration inside the adsorbent reaches the liquefied concentration, a dimethyl ether gas-liquid mixture is formed inside the adsorbent.

[0071] The main purpose of regeneration liquefaction is to completely desorb the dimethyl ether gas-liquid mixture in the adsorbent by heating, absorb it by dimethyl ether liquid, and obtain product liquid dimethyl ether. At the same time, the adsorbent is regenerated and enters the next cycle.

[0072] Table 4 below shows the implementation results.

[0073] Table 4 Implementation effect .

[0074] According to statistics, the dimethyl ether recovery rate is 1123.82 kg / h, and the annual recovery rate is 8990.56 tons, with a value of RMB 29.6688 million.

Claims

1. A method for liquefying and recovering dimethyl ether in a mixed gas, characterized in that: include: (A) The raw gas containing 3%-9% gaseous dimethyl ether is sent to the scrubber, where the dimethyl ether liquid at room temperature is circulated for scrubbing and absorption, and the wire mesh demister absorbs the dimethyl ether droplets, so that the dimethyl ether content in the raw gas is washed to less than 1%; (B) The dimethyl ether liquid for washing is circulated by a circulating pump, and the circulating dimethyl ether liquid is cooled so that its circulation temperature is maintained below 40 degrees; (C) The raw gas after washing is sent to a first-stage temperature swing adsorption tower group consisting of two or more towers. The first-stage temperature swing adsorption tower group controls the dimethyl ether content in the raw gas to less than 0.3%, and then sends the intermediate gas to a second-stage temperature swing adsorption tower group consisting of two or more towers for further adsorption operation, and finally obtains a product gas with a total content of dimethyl ether, methyl acetate and methanol below 100 ppm; (D) For the adsorption towers with saturated adsorption in the first-stage temperature swing adsorption tower group and the second-stage temperature swing adsorption tower group, the raw gas heated to 140-160 degrees is used as the regeneration gas for isobaric backblowing operation, and the dimethyl ether gas-liquid mixture in the adsorbent is blown out of the adsorption tower, cooled by the cooler, and then washed with dimethyl ether liquid at room temperature in the washing tower and liquefied, so as to achieve the purpose of recovering dimethyl ether. At the same time, the adsorbent is regenerated. After the regeneration of the adsorption tower is completed, the temperature is reduced and cooled to enter the next cycle.

2. The method for liquefying and recovering dimethyl ether in a mixed gas according to claim 1, characterized in that: Method (A) uses a two-stage scrubber for scrubbing. The first-stage scrubber scrubs the dimethyl ether content in the raw gas to less than 1.5%, and the second-stage scrubber scrubs the dimethyl ether content in the raw gas to less than 1%.

3. The method for liquefying and recovering dimethyl ether in a mixed gas according to claim 2, characterized in that: Both the first-stage washing tower and the second-stage washing tower use a circulating pump followed by a cooler to reduce the temperature of the liquid dimethyl ether to below 40 degrees.

4. The method for liquefying and recovering dimethyl ether in a mixed gas according to claim 2, characterized in that: In method (D), the raw gas after the first-stage scrubbing tower is divided into two gases with a pressure difference, of which 15-25% of the high-pressure part is used as the regeneration gas, and the rest is sent to the second-stage scrubbing tower after decompression. The dimethyl ether gas-liquid mixture desorbed by the regeneration gas in the adsorption tower is cooled by a cooler and then sent to the second-stage scrubbing tower.

5. The method for liquefying and recovering dimethyl ether in a mixed gas according to claim 1, characterized in that: In method (C), the adsorbent is selected from one or more of activated carbon, 5A molecular sieve and silica gel.

6. The method for liquefying and recovering dimethyl ether in a mixed gas according to claim 1, characterized in that: In method (C), dimethyl ether is adsorbed by an adsorbent, and after the dimethyl ether concentration inside the adsorbent reaches a liquefied concentration, a dimethyl ether gas-liquid mixture is formed inside the adsorbent bed.

7. The method for liquefying and recovering dimethyl ether in a mixed gas according to claim 1, characterized in that: The first stage temperature swing adsorption tower group consists of two towers, adsorption tower A and adsorption tower B. When adsorption tower A or adsorption tower B is saturated and the content of dimethyl ether at the outlet reaches the design index of 0.3%, it switches to another adsorption tower for adsorption. The saturated adsorption tower enters the regeneration process, and the intermediate gas is sent to the second stage temperature swing adsorption tower group; After the desorption of the high-temperature regeneration gas in adsorption tower A or adsorption tower B is completed, the intermediate gas from another adsorption tower is used to cool the temperature, and the cooled intermediate gas is sent to the second-stage temperature-swing adsorption tower group.

8. The method for liquefying and recovering dimethyl ether in a mixed gas according to claim 1, characterized in that: The second-stage temperature-swing adsorption tower group consists of three towers: adsorption tower C, adsorption tower D, and adsorption tower E. The intermediate gas containing 0.3% dimethyl ether enters adsorption tower C or adsorption tower D. When the total content of dimethyl ether, methyl acetate and methanol at the upper outlet of the adsorption tower reaches the designed value of 100ppm, the tower is cut off and adsorption tower C or adsorption tower D enters the regeneration process, and the product gas is sent to the product gas pipeline.

9. The method for liquefying and recovering dimethyl ether in a mixed gas according to claim 8, characterized in that: In the second-stage temperature-swing adsorption tower group, after the desorption of the high-temperature regeneration gas in the adsorption tower C or the adsorption tower D is completed, the raw gas without heating is first used to pass through the adsorption tower E to replace and cool the adsorption tower C or the adsorption tower D that needs to be cooled. The replacement gas is sent to the washing tower, and the product gas of another adsorption tower is used for cooling. The cooled product gas is sent to the product gas pipeline.

10. The method for liquefying and recovering dimethyl ether in a mixed gas according to claim 9, characterized in that: After the adsorption tower E has been running for a certain period, the raw gas heated to 140-160 degrees is used as the regeneration gas to regenerate the adsorbent and recover dimethyl ether. After the desorption of the high-temperature regeneration gas in the adsorption tower E is completed, the product gas from the adsorption tower C or the adsorption tower D is used to cool down the temperature, and the cooled product gas is sent to the product gas pipeline.

Images