A method for recovering high-pressure tail gas from an acetic acid plant

Abstract

The invention discloses a method for recovering high-pressure tail gas from an acetic acid device. The method comprises the following steps: opening a first shut-off valve, a fifth plug valve, an eighth plug valve, a second ball valve, a second plug valve, a second regulating valve, and a fifth regulating valve, starting a diaphragm compressor, closing the fifth regulating valve, opening the third regulating valve, closing the fourth regulating valve, and closing the fourth regulating valve. After a methanol device has a condition for recovering high-pressure tail gas, the twelfth plug valve, the ninth regulating valve, and the third regulating valve are opened, and the value of the seventh pressure transmitter is kept stable until the third regulating valve is closed, and the high-pressure tail gas is recovered to the methanol device. When the methanol device does not have a condition for recovering high-pressure tail gas, the first regulating valve is opened, the fifth regulating valve is closed, and the high-pressure tail gas is sent to a fuel gas pipeline network for use. The invention vents and recovers the high-pressure tail gas from the acetic acid device to the methanol device or the fuel gas pipeline network, effectively solving the problems of energy waste and environmental pollution, and reducing the production cost of the acetic acid device.

Description

Technical Field

[0001] The present invention relates to the technical field of tail gas recovery, and more specifically to a method for recovering high-pressure tail gas from an acetic acid device. Background Art

[0002] Acetic acid is an important organic chemical product, mainly used in the production of vinyl acetate (VAM), acetate, acetic anhydride, terephthalic acid (PTA), chloroacetic acid, diketene and other products. It is an important raw material for synthetic fibers, adhesives, medicines, dyes, medicines, dyes and pesticides. In addition, it is also an excellent organic solvent and has a wide range of uses in the chemical, textile, plastic, pharmaceutical, rubber and dye industries.

[0003] The methanol carbonylation method for producing acetic acid is currently the mainstream method for producing acetic acid products in the acetic acid industry. The raw materials for the reaction are methanol and carbon monoxide. During the reaction, the precipitation of the rhodium catalyst is not prevented, and the reaction system is controlled to emit carbon monoxide to the flare system for combustion, which not only causes high consumption of raw material carbon monoxide and increases production costs, but also causes energy waste and environmental pollution. Therefore, the exhaust gas needs to be recycled. Summary of the invention

[0004] In order to solve the problem of venting and recycling the high-pressure tail gas of the current acetic acid device, the present invention proposes a method for recovering the high-pressure tail gas of the acetic acid device, one process is incorporated into the plant area fuel gas pipeline network for use as the hot blast furnace fuel gas, and one process is pressurized by a diaphragm compressor and sent to a methanol device for treatment and recycling. In order to avoid the high-pressure tail gas from being vented when the methanol device does not have the recovery conditions or the diaphragm compressor is under maintenance, the high-pressure tail gas can be incorporated into the fuel gas pipeline network for use as the hot blast furnace fuel gas, thereby improving the tail gas recovery efficiency, reducing production costs, saving energy consumption, and avoiding environmental pollution.

[0005] The objectives of the present invention are achieved through the following technical solutions.

[0006] The high-pressure tail gas recovery method of an acetic acid device comprises the following processes: opening a first shut-off valve, a fifth plug valve, an eighth plug valve, a second ball valve, a second plug valve, a second regulating valve and a fifth regulating valve in a high-pressure tail gas recovery system of the acetic acid device, starting a diaphragm compressor, slowly closing the fifth regulating valve until the value of a seventh pressure transmitter meets the requirement after the diaphragm compressor runs stably, slowly opening the third regulating valve, closing the fourth regulating valve, during which the value of the seventh pressure transmitter is kept stable, until the fourth regulating valve is completely closed, when a methanol device has the conditions for recovering the high-pressure tail gas, opening the twelfth plug valve, slowly opening the ninth regulating valve, and closing the third regulating valve at the same time, during which the value of the seventh pressure transmitter is kept stable, until the third regulating valve is completely closed, and the high-pressure tail gas is recovered to the methanol device; when the methanol device does not have the conditions for recovering the high-pressure tail gas, opening the first regulating valve, closing the fifth regulating valve, and sending the high-pressure tail gas to a fuel gas pipeline network for use.

[0007] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0008] The present invention connects a combustion pipeline and a first regulating valve to a fuel gas pipeline network at the top port of a high-pressure liquid separator tank, and arranges a first shut-off valve, a second regulating valve, a third gas-liquid separator, a fourth flow meter, a fifth plug valve, a sixth diaphragm compressor, an eighth plug valve, a ninth regulating valve, a tenth flow meter, and a twelfth plug valve from a venting pipeline of the high-pressure liquid separator tank to a conversion gas pipeline, which are connected in series with pipelines according to the flow direction of a process medium, and a reflux pipeline, a venting pipeline and a first regulating valve, a second plug valve, a third regulating valve, and a fourth ball valve are arranged at an outlet of the diaphragm compressor, so that the high-pressure tail gas is sent to a fuel gas pipeline network or to a methanol ammonia washing tower after being pressurized by a diaphragm compressor, thereby achieving the purpose of tail gas recovery, reducing energy consumption, and avoiding environmental pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a schematic diagram of the original high-pressure tail gas venting process;

[0010] Figure 2 It is a schematic diagram of the high-pressure tail gas recovery method of the acetic acid device of the present invention.

[0011] Figure numerals: 1-first regulating valve, 2-fourth regulating valve, 3-fuel gas pipeline network, 4-first shut-off valve, 5-venting pipeline, 6-gas-liquid separator, 7-second regulating valve, 8-fifth plug valve, 9-diaphragm compressor, 10-eighth plug valve, 11-recovery pipeline, 1101-first pipeline, 1102-second pipeline, 1103-third pipeline, 12-third regulating valve, 13-conversion gas pipeline, 14 -The fourteenth pressure transmitter, 15-the fourth flow meter, 16-the ninth regulating valve, 17-the high-pressure liquid separation tank, 18-the seventh pressure transmitter, 19-the tenth flow meter, 20-the rich liquid methanol tank, 21-the high-pressure absorption tower, 22-the high-pressure tail gas cooler, 23-the ammonia washing tower, 24-the coil heat exchanger, 25-the second plug valve, 26-the second ball valve, 27-the fifth regulating valve, 28-the twelfth plug valve, 29-the combustion pipeline. DETAILED DESCRIPTION

[0012] The present invention will be further described below in conjunction with the accompanying drawings.

[0013] The layout and principle of the high-pressure tail gas process in the original process, such as Figure 1 As shown. It mainly includes a high-pressure absorption tower 21, a high-pressure tail gas cooler 22, a rich liquid methanol tank 20, and a high-pressure liquid separator tank 17. The lower part of the high-pressure absorption tower 21 is connected to the tail gas pipeline of the acetic acid synthesis process, and the upper part is connected to the methanol pipeline. The bottom of the high-pressure absorption tower 21 is connected to the rich liquid methanol tank 20 through a pipeline, and the bottom of the rich liquid methanol tank 20 is connected to the acetic acid synthesis process through a pipeline. The top outlet of the high-pressure absorption tower 21 is connected to the top inlet of the high-pressure liquid separator tank 17 through a pipeline after condensation by the high-pressure tail gas cooler 22, and the top outlet of the high-pressure liquid separator tank 17 is connected to the venting pipeline 5 to the flare venting, and the venting pipeline 5 is provided with a fourth regulating valve 2.

[0014] Original process workflow: the exhaust gas from the synthesis process enters the high-pressure absorption tower 21. After methanol absorbs organic matter such as methyl iodide and acetic acid, the rich liquid methanol in the bottom of the tower is sent to the rich liquid methanol tank 20 and returned to the synthesis process. The non-condensable gases such as carbon monoxide, hydrogen, and carbon dioxide at the top of the tower are cooled by the high-pressure exhaust gas cooler 22 and sent to the high-pressure liquid separator 17. After further gas and liquid separation in the high-pressure liquid separator 17, they are sent to the flare for venting and combustion treatment.

[0015] The high-pressure tail gas recovery system of the acetic acid device of the present invention is improved on the basis of the original high-pressure tail gas venting process. Figure 2 As shown, the process from the high-pressure liquid separator 17 to the fuel gas pipeline network 3 is added, and the original venting pipeline of the high-pressure liquid separator 17 is connected to the conversion gas pipeline 13 of the methanol unit conversion process to the ammonia washing tower 23 process. Specific improvements:

[0016] The top outlet of the high-pressure liquid separator 17 is connected to the combustion pipeline 29 to the fuel gas pipeline network 3, and the pipeline is provided with a first regulating valve 1. The venting pipeline 5 is connected to the recovery pipeline 11, and the recovery pipeline 11 is provided with a first shut-off valve 4, a second regulating valve 7, a gas-liquid separator 6, a fourth flowmeter 15, a fifth plug valve 8, a diaphragm compressor 9, a seventh pressure transmitter 18, and an eighth plug valve 10 in sequence from the inlet end to the outlet end. The inlet end of the recovery pipeline 11 is connected to the venting pipeline 5 connected to the inlet of the fourth regulating valve 2, and the outlet end of the recovery pipeline 11 is divided into three routes. The first pipeline 1101 (i.e., the reflux pipeline) is connected to the top inlet of the high-pressure liquid separator 17, the second pipeline 1102 is connected to the venting pipeline 5 connected to the outlet of the fourth regulating valve 2 and sent to the flare for venting along the gas direction, the third pipeline 1103 is connected to the conversion gas pipeline 13 of the methanol unit conversion process and sent to the ammonia washing tower 23 of the methanol unit along the gas direction, the top outlet of the ammonia washing tower 23 is connected to the coil heat exchanger 24 through a pipeline and sent to the methanol acid removal process, and the bottom of the ammonia washing tower 23 is connected to the condensate pipeline to the tail gas washing system of the coal gasification unit to recover the condensate. Among them, the fifth regulating valve 27 and the second stopcock 25 are arranged along the gas direction on the first pipeline 1101 at the outlet end of the recovery pipeline 11, the third regulating valve 12 and the second ball valve 26 are arranged along the gas direction on the second pipeline 1102, and the ninth regulating valve 16, the tenth flow meter 19, the fourteenth pressure transmitter 14 and the twelfth stopcock 28 are arranged in sequence along the gas direction on the third pipeline 1103.

[0017] The high-pressure tail gas is discharged to the flare through the fourth regulating valve 2, switched to the fuel gas pipeline network 3 through the first regulating valve 1 for use as hot blast furnace fuel, or pressurized through the first shut-off valve 4, the gas-liquid separator 6, the second regulating valve 7, the diaphragm compressor 9, and the ninth regulating valve 16, and then sent to the conversion gas pipeline 13 of the methanol unit conversion process, and sent to the ammonia washing tower 23 along the material direction, thereby achieving the purpose of high-pressure tail gas recovery.

[0018] The method for recovering high-pressure tail gas from an acetic acid device of the present invention comprises the following steps:

[0019] 1) The newly added combustion pipeline 29, recovery pipeline 11, first pipeline 1101, second pipeline 1102, and third pipeline 1103 are purged, airtight, and replaced as qualified.

[0020] 2) New instrument control valves, transmitters, flow meters, etc. have been debugged and put into use after passing the test.

[0021] 3) Check that the oil circuit, gas circuit and other instrument accessories of the diaphragm compressor are in good condition and put into use, and confirm that the conditions for starting the machine are met.

[0022] 4) Open the first shut-off valve 4, the fifth plug valve 8, the eighth plug valve 10, the second ball valve 26, the second plug valve 25, the second regulating valve 7, and the fifth regulating valve 27, start the diaphragm compressor 9, and after the diaphragm compressor 9 runs stably, slowly close the fifth regulating valve 27 until the value of the seventh pressure transmitter 18 meets the requirement, slowly open the third regulating valve 12, close the fourth regulating valve 2, and keep the value of the seventh pressure transmitter 18 stable during this period until the fourth regulating valve 2 is completely closed. When the methanol unit has the conditions for high-pressure tail gas recovery, open the twelfth plug valve 28, slowly open the ninth regulating valve 16, and at the same time close the third regulating valve 12. During this period, the value of the seventh pressure transmitter 18 must always be kept stable until the third regulating valve 12 is completely closed, and the high-pressure tail gas is recovered to the methanol unit; when the methanol unit does not have the conditions for high-pressure tail gas recovery, open the first regulating valve 1, close the fifth regulating valve 27, and the high-pressure tail gas is sent to the fuel gas pipeline network 3 for use.

[0023] Although the functions and working processes of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific functions and working processes. The above-mentioned specific implementation methods are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the purpose of the present invention and the claims, which are all within the protection of the present invention.

Claims

1. A method for recovering high-pressure tail gas from an acetic acid plant, characterized in that: The high-pressure absorption tower (21) mainly comprises a high-pressure tail gas cooler (22), a rich liquid methanol tank (20), and a high-pressure liquid separator tank (17). The lower part of the high-pressure absorption tower (21) is connected to the tail gas pipeline of the acetic acid synthesis process, and the upper part is connected to the methanol pipeline. The bottom of the high-pressure absorption tower (21) is connected to the rich liquid methanol tank (20) through a pipeline, and the bottom of the rich liquid methanol tank (20) is connected to the pipeline to the acetic acid synthesis process; the top outlet of the high-pressure absorption tower (21) is connected to the top inlet of the high-pressure liquid separator tank (17) through a pipeline after condensation by the high-pressure tail gas cooler (22), and the top outlet of the high-pressure liquid separator tank (17) is connected to the venting pipeline (5) to the flare venting, and the venting pipeline (5) is provided with a fourth regulating valve (2); The top outlet of the high-pressure liquid separator (17) is connected to the combustion pipeline (29) to the fuel gas pipeline network (3), and a first regulating valve (1) is arranged on the pipeline; the venting pipeline (5) is connected to the recovery pipeline (11), and the recovery pipeline (11) is provided with a first shut-off valve (4), a second regulating valve (7), a gas-liquid separator (6), a fourth flow meter (15), a fifth stopcock (8), a diaphragm compressor (9), a seventh pressure transmitter (18), and an eighth stopcock (10) in sequence from the inlet end to the outlet end; the inlet end of the recovery pipeline (11) is connected to the venting pipeline (5) connected to the inlet of the fourth regulating valve (2), and the outlet end of the recovery pipeline (11) is divided into three routes, the first route (1101) is connected to the top inlet of the high-pressure liquid separator (17), and the second route (1102) is connected to the gas flow rate of the venting pipeline (5) connected to the outlet of the fourth regulating valve (2). The gas is sent to the flare for venting, the third pipeline (1103) is connected to the conversion gas pipeline (13) of the methanol unit conversion process and sent to the ammonia washing tower (23) of the methanol unit along the gas direction, the top outlet of the ammonia washing tower (23) is connected to the coil heat exchanger (24) through a pipeline and sent to the methanol acid removal process, the bottom of the ammonia washing tower (23) is connected to the condensate pipeline to the tail gas washing system of the coal gasification unit to recover the condensate; wherein, the first pipeline (1101) at the outlet end of the recovery pipeline (11) is provided with a fifth regulating valve (27) and a second plug valve (25) along the gas direction, the second pipeline (1102) is provided with a third regulating valve (12) and a second ball valve (26) along the gas direction, and the third pipeline (1103) is provided with a ninth regulating valve (16), a tenth flow meter (19), a fourteenth pressure transmitter (14), and a twelfth plug valve (28) in sequence along the gas direction; The high-pressure tail gas recovery method comprises the following steps: opening a first shut-off valve (4), a fifth plug valve (8), an eighth plug valve (10), a second ball valve (26), a second plug valve (25), a second regulating valve (7), and a fifth regulating valve (27) in a high-pressure tail gas recovery system of an acetic acid device, starting a diaphragm compressor (9), and after the diaphragm compressor (9) runs stably, slowly closing the fifth regulating valve (27) until the value of a seventh pressure transmitter (18) meets the requirement, slowly opening the third regulating valve (12), and closing the fourth regulating valve (2), during which the seventh pressure transmitter (18) is kept at a constant value. The value of the seventh pressure transmitter (18) is kept stable until the fourth regulating valve (2) is completely closed. When the methanol unit meets the conditions for recovering the high-pressure tail gas, the twelfth stopcock (28) is opened, the ninth regulating valve (16) is slowly opened, and the third regulating valve (12) is closed at the same time. During this period, the value of the seventh pressure transmitter (18) must always be kept stable until the third regulating valve (12) is completely closed and the high-pressure tail gas is recovered to the methanol unit. When the methanol unit does not meet the conditions for recovering the high-pressure tail gas, the first regulating valve (1) is opened, the fifth regulating valve (27) is closed, and the high-pressure tail gas is sent to the fuel gas pipeline network (3) for use.

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