A device and method for treating low-temperature methanol-washed hydrocarbon-containing exhaust gas

Abstract

The invention discloses a device and method for treating low-temperature methanol washing hydrocarbon-containing exhaust gas, which relates to the technical field of coal chemical industry and low-temperature methanol washing. It includes a coke oven gas absorption tower, a shift gas absorption tower, a flash tower, a carbon dioxide product tower, a hydrogen sulfide concentration tower, a nitrogen stripping tower, a thermal regeneration tower, an acid gas separator, a tail gas water washing tower, and a buffer tank; the upper part of the flash tower is a coke oven gas treatment section, and the lower part is a shift gas treatment section; the lower part of the coke oven gas absorption tower is connected to the upper part of the flash tower, and the coke oven gas treatment section is connected to the nitrogen stripping tower; the lower part of the shift gas absorption tower is connected to the lower part of the flash tower, and the shift gas treatment section is connected to the carbon dioxide product tower, the hydrogen sulfide concentration tower, and the nitrogen stripping tower in sequence; the nitrogen stripping tower is connected to the thermal regeneration tower, and the thermal regeneration tower is connected to the acid gas separator and the buffer tank respectively. The present invention can enrich and recycle the hydrocarbon-containing flash gas in the coke oven gas process, realize the reuse of waste gas, and reduce equipment investment and operating costs.

Description

Technical Field

[0001] The invention relates to the technical field of coal chemical industry, and in particular to a device and method for treating hydrocarbon-containing exhaust gas from low-temperature methanol washing. Background Art

[0002] The low-temperature methanol washing unit processes two streams of raw gas, one is the raw gas produced by coal gasification, the converted gas after CO conversion, and the other is coke oven gas. The low-temperature methanol washing process of the raw gas produced by coal gasification is as follows: first, a small stream of methanol is injected into the raw gas conversion gas to reduce the dew point of the conversion gas, and then enters the conversion gas cooler to exchange heat with multiple streams, and enters the conversion gas absorption tower to pass through the desulfurization section and decarbonization section in turn. In the tower, sulfides and CO2 are removed by low-temperature lean methanol, and it comes out from the top of the conversion gas absorption tower and is sent to the methanol synthesis unit after heat exchange; among them, the -22℃ methanol rich liquid after the absorption of CO2 in the decarbonization section of the absorption tower, most of it enters the medium-pressure flash tower, and a small part enters the desulfurization section of the absorption tower to absorb H2S and then enters the medium-pressure flash tower, and is flashed under reduced pressure respectively. When the two solutions are flashed, most of the effective gases (CO, H2) are desorbed. The two flash gas streams merge in the tower, exchange heat and send to the flash gas compressor to return to the system for recycling; before the coke oven gas enters the low-temperature methanol washing device, it exchanges heat with the purified coke oven gas, and then enters the coke oven gas absorption tower for washing. A large amount of lean methanol is sprayed from the top, and the acidic gas components and other sulfides in the coke oven gas are absorbed at the same time. The rich methanol coming out from the bottom enters the medium-pressure flash tower, and the CO and H2 dissolved in the methanol are recovered by flash evaporation and returned to the compression for recycling. The rich methanol after flash evaporation enters the hydrogen sulfide concentration tower, and is mixed with the rich methanol from the upper section of the hydrogen sulfide concentration tower after absorbing the acidic gas in the water gas, and washes the gas stripping gas from the top of the nitrogen stripping tower and the pre-washing flash gas from the top of the extractor. However, since the CO2 emission gas generated by the water gas and coke oven gas regeneration process is sent to the exhaust gas after washing in the tail gas water washing tower, due to the high content of hydrocarbon substances, there is currently no feasible treatment technology to make the hydrocarbon substances in the exhaust gas meet the latest environmental emission standards.

[0003] Therefore, finding a method and device that can effectively recycle and utilize hydrocarbon substances in exhaust gas to solve the problem that low-temperature methanol washing of hydrocarbon-containing exhaust gas does not meet the standards is a technical problem that needs to be solved urgently in this field. Summary of the invention

[0004] The object of the present invention is to provide a device for treating low-temperature methanol-washed hydrocarbon-containing exhaust gas.

[0005] Another object of the present invention is to provide a method for treating low temperature methanol-washed hydrocarbon-containing exhaust gas.

[0006] The present invention is achieved through the following technical solutions:

[0007] A device for treating low-temperature methanol-washed hydrocarbon-containing exhaust gas comprises a coke oven gas absorption tower, a shift gas absorption tower, a flash tower, a carbon dioxide product tower, a hydrogen sulfide concentration tower, a nitrogen stripping tower, a thermal regeneration tower, an acid gas separator, a tail gas water washing tower, and a buffer tank; the flash tower is divided into four sections from top to bottom, the upper two sections are coke oven gas treatment sections, and the lower two sections are shift gas treatment sections; the lower drain pipe of the coke oven gas absorption tower is connected to the upper coke oven gas treatment section of the flash tower, and the coke oven gas treatment section is connected to the nitrogen stripping tower; the lower drain pipe of the shift gas absorption tower is connected to the lower shift gas treatment section of the flash tower, and the shift gas treatment section is connected to the carbon dioxide product tower, the hydrogen sulfide concentration tower, and the nitrogen stripping tower in sequence; the nitrogen stripping tower is connected to the thermal regeneration tower, and the thermal regeneration tower is respectively connected to the acid gas separator and the buffer tank; the exhaust ports of the carbon dioxide product tower and the hydrogen sulfide concentration tower are respectively connected to the tail gas water washing tower.

[0008] Furthermore, the drainage pipe at the bottom of the coke oven gas absorption tower is connected to the first section of the flash tower, and the first section at the top of the flash tower is connected to the second section of the flash tower through a pipeline.

[0009] The lower part of the conversion gas absorption tower is a desulfurization section, and the upper part is a decarbonization section. The desulfurization section drain pipe is connected to the fourth section at the bottom of the flash tower, and the decarbonization section drain pipe is connected to the third section of the flash tower.

[0010] A filter is arranged at the bottom of the coke oven gas absorption tower.

[0011] Furthermore, the present invention also discloses a method for treating low-temperature methanol-washed hydrocarbon-containing exhaust gas using the above device, the steps of which are:

[0012] 1) Cool the coke oven gas to -23℃~-27℃, spray low-temperature methanol liquid, and enter the bottom of the coke oven gas absorption tower under the first tower plate of the pre-wash section for washing. Spray -50℃~-55℃ methanol liquid from the top of the upper main wash section. The pre-wash methanol solution from the bottom of the pre-wash section is sent to the extractor, and the methanol liquid from the bottom of the main wash section enters the first stage of the flash tower for reduced pressure flash evaporation;

[0013] 2) The shift gas is injected with methanol and fed into the bottom of the shift gas absorption tower after heat exchange. The sulfide and carbon dioxide are removed by low-temperature methanol at -50℃~-55℃, and the methanol-rich liquid is fed into the third and fourth sections at the bottom of the flash tower;

[0014] 3) The -30℃~-36℃ rich methanol liquid sent from the bottom of the first stage of the flash tower enters the second stage, and the hydrocarbon-containing methanol sent from the bottom of the second stage enters the nitrogen stripping tower for stripping. The gas from the top of the nitrogen stripping tower is input to the bottom of the second stage of the medium-pressure flash tower to further strip the rich methanol from the bottom of the first stage, and is washed by the rich methanol to form a cycle;

[0015] 4) After the methanol-rich liquid in the shift gas absorption tower is flashed in the third and fourth sections of the flash tower, the methanol liquid is processed in the carbon dioxide product tower and the hydrogen sulfide concentration tower in turn, and the gas enters the tail gas water scrubber for treatment, and the liquid enters the nitrogen stripping tower;

[0016] 5) After the methanol liquid is treated in the nitrogen stripping tower, it is successively treated in the thermal regeneration tower, the gas is treated in the acid gas separator, and the liquid is treated in the filter.

[0017] The present invention processes coke oven gas and water gas separately, that is, low-temperature methanol washing and absorption of coke oven gas, low-pressure flash evaporation of rich methanol after medium-pressure flash evaporation, and nitrogen stripping gas recovery are designed as one line, and low-temperature methanol washing and absorption of water gas, methanol solution after flash evaporation is successively introduced into a carbon dioxide absorption tower and a hydrogen sulfide concentration tower, and stripping recovery is designed as one line; in specific operation, before the coke oven gas enters the methanol washing device, it is heat-exchanged and cooled to -27°C to -23°C with the purified coke oven gas purified gas after purification, and in order to prevent the coke oven gas from being cooled to below the dew point and freezing, a small amount of methanol is sprayed into the coke oven gas before it enters the coke oven gas cooler to reduce the coke oven gas content. The dew point of the coke oven gas is reduced, and then it enters the lower part of the first tower plate of the coke oven gas absorption tower for washing. The coke oven gas absorption tower is set up in two sections, the lower section is the pre-wash section, and the upper section is the main washing section. The pre-wash section first washes the coke oven gas, and the pre-wash methanol solution at about -24°C coming out of the bottom is filtered and sent to the extractor to recover flash gas and naphtha. A large amount of lean methanol at about -52°C is sprayed above the upper tower plate of the main washing section to absorb the acidic gas components H2S, CO2 and other sulfides in the coke oven gas at the same time, so that the total sulfur of the coke oven gas purified gas is less than 0.1PPm, CO2≤20PPm, and the temperature is 25°C, which meets the requirements of LNG deep Air intake requirements for the cold separation unit: The rich methanol from the lower plate of the main wash section of the coke oven gas absorption tower enters the medium-pressure flash tower at the top of the first section upper packing for reduced pressure flash evaporation to desorb the absorbed effective gas, and the flash gas at about -33°C sent from the top of the medium-pressure flash tower is reheated to 30°C and sent to the compression cycle for recycling; the rich methanol at about -33°C sent from the bottom of the first section after medium-pressure flash evaporation enters the medium-pressure flash tower above the upper packing for low-pressure flash evaporation, and the flashed hydrocarbon-containing methanol sent from the bottom of the second section enters the nitrogen stripping tower for stripping after pressurization and heat exchange by the hydrocarbon-containing methanol pump, and the nitrogen steam is used for steam stripping. The nitrogen stripping gas coming out of the top of the stripping tower enters the bottom of the second section of the medium-pressure flash tower, and further strips the rich methanol from the bottom of the first section. At the same time, the rich methanol further washes the nitrogen stripping gas and flashes in the second section. The flash gas is sent out from the top of the second section and mixed with the pre-wash flash gas from the top of the extractor to be recycled as hydrocarbon-containing exhaust gas. After stripping, the methanol at the bottom of the first section enters the water gas nitrogen stripping tower and is incorporated into the regeneration post-process; thereby, the hydrocarbon substances in the CO2 exhaust gas generated by the low-temperature methanol washing of coke oven gas are recovered and can be used as fuel gas, so that the CO2 exhaust gas of the low-temperature methanol washing device contains almost no hydrocarbon substances.

[0018] The present invention has a simple structure, can ensure that CO2 emission gas meets emission standards, enrich and recover hydrocarbon-containing flash gas in the coke oven gas process, realize the reuse of waste gas, and greatly reduce equipment investment cost and operation cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of the present invention;

[0020] In the figure: 1-coke oven gas absorption tower, 2-flash tower, 3-carbon dioxide product tower, 4-hydrogen sulfide concentration tower, 5-nitrogen stripping tower, 6-thermal regeneration tower, 7-acid gas separator, 8-tail gas washing tower, 9-buffer tank, 10-filter, 11-conversion gas absorption tower. DETAILED DESCRIPTION

[0021] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0022] like Figure 1 The device shown in the figure for treating low-temperature methanol-washed hydrocarbon-containing exhaust gas comprises a coke oven gas absorption tower 1, a shift gas absorption tower 11, a flash tower 2, a carbon dioxide product tower 3, a hydrogen sulfide concentration tower 4, a nitrogen stripping tower 5, a thermal regeneration tower 6, an acid gas separator 7, a tail gas water washing tower 8, and a buffer tank 9; the flash tower 2 is divided into four sections from top to bottom, the upper two sections are coke oven gas treatment sections, and the lower two sections are shift gas treatment sections; the lower discharge pipe of the coke oven gas absorption tower 1 and the upper coke oven gas treatment section of the flash tower 2 are connected to each other; The coke oven gas treatment section is connected to the nitrogen stripping tower 5; the lower drain pipe of the conversion gas absorption tower 44 is connected to the conversion gas treatment section at the lower part of the flash tower 2, and the conversion gas treatment section is connected to the carbon dioxide product tower 3, the hydrogen sulfide concentration tower 4, and the nitrogen stripping tower 5 in sequence; the nitrogen stripping tower 5 is connected to the thermal regeneration tower 6, and the thermal regeneration tower 6 is respectively connected to the acid gas separator 7 and the buffer tank 9; the exhaust ports of the carbon dioxide product tower 3 and the hydrogen sulfide concentration tower 4 are respectively connected to the tail gas water washing tower 8.

[0023] The drain pipe at the bottom of the coke oven gas absorption tower 1 is connected to the first section of the flash tower 2, and the first section at the top of the flash tower 2 is connected to the second section of the flash tower 2 through a pipeline; the lower part of the conversion gas absorption tower 11 is a desulfurization section, and the upper part is a decarbonization section. The drain pipe of the desulfurization section is connected to the fourth section at the bottom of the flash tower 2, and the drain pipe of the decarbonization section is connected to the third section of the flash tower; a filter 10 is provided at the bottom of the coke oven gas absorption tower 1.

[0024] The operating steps are as follows: 1) A small stream of methanol is injected into the coke oven gas to reduce the dew point of the coke oven gas, and then the gas enters the bottom of the first tower plate at the bottom of the lower pre-wash section of the coke oven gas absorber for washing. The pre-wash section first washes the coke oven gas, and the pre-wash methanol solution at about -24°C from the bottom is filtered through a filter and sent to the extractor to recover flash gas and naphtha. A large amount of lean methanol at about -52°C is sprayed above the upper tower plate of the upper main washing section to absorb H2S, CO2 and other sulfides in the coke oven gas, so that the total sulfur of the coke oven gas purified gas is less than 0.1PPm, CO2≤20PPm, and the temperature is 25°C, which meets the air intake requirements of the LNG deep cold separation unit. The rich methanol from the lower tower plate of the main washing section of the coke oven gas absorber enters the upper packing of the first section at the top of the medium-pressure flash tower for reduced pressure flash evaporation to desorb the absorbed effective gas. The flash gas at about -33°C sent from the top of the medium-pressure flash tower is reheated to 30°C and sent to the compressor. Circular recycling; 2) Methanol is injected into the conversion gas, and after heat exchange, it is input into the bottom of the conversion gas absorption tower, and the sulfide and carbon dioxide are removed by low-temperature methanol at -50℃~-55℃, and the methanol-rich liquid is input into the third and fourth sections of the flash tower; 3) The -30℃~-36℃ rich methanol liquid sent out from the bottom of the first section of the flash tower enters the second section, and the hydrocarbon-containing methanol sent out from the bottom of the second section enters the nitrogen stripping tower for stripping. The gas coming out from the top of the nitrogen stripping tower is input into the bottom of the second section of the medium-pressure flash tower, and the rich methanol from the bottom of the first section is further stripped, and washed with rich methanol to form a cycle; 4) After the methanol-rich liquid of the conversion gas absorption tower is flashed in the third and fourth sections of the flash tower, the methanol liquid is successively treated by the carbon dioxide product tower and the hydrogen sulfide concentration tower, and the gas enters the tail gas water washing tower for treatment, and the liquid enters the nitrogen stripping tower; 5) After the methanol liquid is treated in the nitrogen stripping tower, it is successively treated in the thermal regeneration tower, and the gas is treated by the acid gas separator and the liquid is treated by the filter.

Claims

1. A device for treating low-temperature methanol-washed hydrocarbon-containing exhaust gas, characterized in that: It includes a coke oven gas absorption tower, a conversion gas absorption tower, a flash tower, a carbon dioxide product tower, a hydrogen sulfide concentration tower, a nitrogen stripping tower, a thermal regeneration tower, an acid gas separator, a tail gas water washing tower, and a buffer tank; the flash tower is divided into four sections from top to bottom, the upper two sections are coke oven gas treatment sections, and the lower two sections are conversion gas treatment sections; the drainage pipe at the bottom of the coke oven gas absorption tower is connected to the first section at the top of the flash tower, and the first section at the top of the flash tower is connected to the second section of the flash tower through a pipeline; the coke oven gas treatment section is connected to the nitrogen stripping tower; the conversion gas treatment section of the flash tower The gas treatment section is connected with the carbon dioxide product tower, the hydrogen sulfide concentration tower and the nitrogen stripping tower in sequence; the lower part of the conversion gas absorption tower is the desulfurization section, and the upper part is the decarbonization section. The desulfurization section drain pipe is connected with the fourth section at the bottom of the flash tower, and the decarbonization section drain pipe is connected with the third section of the flash tower; the nitrogen stripping tower is connected with the thermal regeneration tower, and the thermal regeneration tower is respectively connected with the acid gas separator and the buffer tank; the exhaust ports of the carbon dioxide product tower and the hydrogen sulfide concentration tower are respectively connected with the tail gas water washing tower; a filter is arranged at the bottom of the coke oven gas absorption tower.

2. A method for treating low-temperature methanol-washed hydrocarbon-containing exhaust gas using the device of claim 1, characterized in that: The steps are: 1) Cool the coke oven gas to -23℃~-27℃, spray low-temperature methanol liquid, and enter the bottom of the coke oven gas absorption tower under the first tower plate of the pre-wash section for washing. Spray -50℃~-55℃ methanol liquid from the top of the upper main wash section. The pre-wash methanol solution from the bottom of the pre-wash section is sent to the extractor, and the methanol liquid from the bottom of the main wash section enters the first stage of the flash tower for reduced pressure flash evaporation; 2) Methanol is injected into the shift gas, which is then fed into the bottom of the shift gas absorption tower after heat exchange. The sulfide and carbon dioxide are removed by low-temperature methanol at -50℃ to -55℃, and the methanol-rich liquid is fed into the third and fourth sections of the lower part of the flash tower; 3) The -30℃~-36℃ rich methanol liquid sent from the bottom of the first stage of the flash tower enters the second stage, and the hydrocarbon-containing methanol sent from the bottom of the second stage enters the nitrogen stripping tower for stripping. The gas from the top of the nitrogen stripping tower is input to the bottom of the second stage of the medium-pressure flash tower to further strip the rich methanol from the bottom of the first stage, and is washed by the rich methanol to form a cycle; 4) After the methanol-rich liquid in the shift gas absorption tower is flashed in the third and fourth sections of the flash tower, the methanol liquid is processed in the carbon dioxide product tower and the hydrogen sulfide concentration tower in turn, and the gas enters the tail gas water scrubber for treatment, and the liquid enters the nitrogen stripping tower; 5) After the methanol liquid is treated in the nitrogen stripping tower, it is successively treated in the thermal regeneration tower, the gas is treated in the acid gas separator, and the liquid is treated in the filter.

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