Process system for recovering elemental sulfur from sulfur-containing tail gas and co-producing methanol

Abstract

The invention provides a process system for recovering elemental sulfur and co-producing methanol from sulfur-containing tail gas, the process system comprises an elemental sulfur recovery system and a methanol synthesis system, the elemental sulfur recovery system comprises a membrane separation unit, a hydrogen sulfide thermal decomposition furnace, a sulfur production waste heat boiler, a waste heat boiler, a tail gas liquid separation tank, a tail gas waste heat unit, a hydrogenation reactor, an MDEA absorption tower and an MDEA hydrogen sulfide regeneration tower; the methanol synthesis system comprises a methanol reaction tower, a high-pressure separator, a low-pressure separator, a rectifying tower and a PSA adsorption tower II. According to the process system disclosed by the invention, energy conservation and consumption reduction are realized to the greatest extent, the process system is particularly more effective in matching use with a methanol production project, up-to-standard emission of sulfur-containing tail gas can be realized, and effective hydrogen and effective carbon in the tail gas can be reasonably recovered.

Description

Technical Field

[0001] The invention relates to the technical field of coal chemical industry, and in particular to a process system for recovering elemental sulfur from sulfur-containing tail gas and co-producing methanol. Background Art

[0002] The sulfur recovery device in the coal chemical plant recovers sulfur-containing elements such as hydrogen sulfide and sulfur dioxide from the tail gas, prepares sulfur products required by the industry, and burns the tail gas to meet the emission standards. At present, large chemical plants and refineries have a complete and mature set of equipment for tail gas treatment, among which the Claus process is widely used due to its simple process, mature technology, low investment and high sulfur recovery purity.

[0003] The current sulfur-containing tail gas recovery processes are mainly divided into the following categories:

[0004] 1. Claus Recovery Process

[0005] The Claus process is a relatively mature sulfur recovery process with a history of nearly 100 years and is widely used in refineries, chemical plants, fertilizer plants, etc. The efficiency of the Claus process is closely linked to the benefits of the enterprise. In recent years, the Claus process has been continuously improved and optimized, and the recovery rate has been improved by adding corresponding processes and equipment. Therefore, it is necessary to continuously move towards high quality, high environmental protection, and economical direction.

[0006] The basic principle of Claus process sulfur production is as follows, and its main reaction formula is:

[0007] H2S+3 / 2O2=SO2+H2O

[0008] 2H2S+SO2=3S+2H2O

[0009] According to the principle of the above process flow, the sulfur recovery step is a process of converting sulfur into elemental sulfur through a series of reactions. The specific reaction process is: hydrogen sulfide is input into an oxygen-rich environment for combustion, and its product sulfur dioxide can react again with the input and unreacted hydrogen sulfide. After the reaction occurs under the action of a catalyst, the sulfur element can be extracted to obtain industrial sulfur. In this process reaction, there are many impurities in the tail gas before entering the Claus process, accompanied by a variety of chemical reactions, so a variety of compounds will also be generated. There are currently three common and relatively mature Claus process methods: partial combustion method, diversion method and sulfur combustion method.

[0010] 2. Super Claus Process

[0011] The recovery rate of the traditional Claus process, which is widely used in the process, has reached about 97%. It is generally divided into the following steps: conversion of sulfides, environmental condensation, diversion, and reheating of process gas. However, this process still has some shortcomings: limited by thermodynamic equilibrium, when the water content in the reaction product increases, the content of sulfur dioxide and the like will decrease. That is, there are too many side reactions in the whole process, and the output of elemental sulfur will decrease. At the same time, the proportion of reactants in the Claus process is strictly controlled, making the whole reaction process relatively difficult to control. Therefore, in the super Claus process, a new oxidation catalyst is selected, and the reaction does not need to go through two steps to directly convert hydrogen sulfide into elemental sulfur, and the sulfur recovery rate of this process can be as high as 99.5%.

[0012] 3. Low temperature Claus process

[0013] When the reaction temperature of the Claus process is lower than the sulfur dew point, it is named the low-temperature Claus process. That is, the relatively mature cold bed adsorption method (MCRC method and CBA method) is added to the tail gas treatment, and the sulfur conversion rate is improved by controlling the temperature below the sulfur dew point.

[0014] 4. Claus Direct Oxidation Process

[0015] The Claus direct oxidation process is a new process proposed for the conventional Claus process when the hydrogen sulfide content in the acid gas is too low to sustain the reaction in the device, that is, the reaction cannot continue. It is an oxidation process. There are two methods. The first method: under the action of a special catalyst, the sulfur element in the sulfide can be replaced to directly obtain the required sulfur element; the second method: after the sulfide reaction, two reaction products, elemental sulfur and sulfur dioxide, can be obtained. After oxidation, the conventional Claus process continues.

[0016] 5. Oxygen-enriched Claus process

[0017] In the conventional Claus process, air catalyst is added to the oxidation of hydrogen sulfide in acid gas. As long as the air contains a large amount of inert gases such as nitrogen, the entire reaction can be slowed down, reducing the recovery rate of sulfur. However, if oxygen-enriched air is used as a catalyst instead of air in the entire process, the conversion efficiency can be greatly improved.

[0018] At present, the sulfur recovery and environmental protection unit mainly recovers sulfur from sulfur-containing tail gas through various sulfur recovery processes, and the tail gas is discharged in accordance with national emission standards. The effective hydrogen and effective carbon in the sulfur-containing tail gas are not effectively utilized, which wastes resources and has low returns. Summary of the invention

[0019] In order to solve the deficiencies existing in the prior art in the process of recovering sulfur-containing tail gas, the present invention provides a process system for recovering elemental sulfur and co-producing methanol.

[0020] In order to achieve the purpose of the present invention, the present invention adopts the following technical solutions:

[0021] The present invention provides a process system for recovering elemental sulfur from sulfur-containing tail gas and co-producing methanol, the process system comprising an elemental sulfur recovery system and a methanol synthesis system;

[0022] The elemental sulfur recovery system comprises a membrane separation unit, a hydrogen sulfide thermal decomposition furnace, a sulfur production waste heat boiler, a waste heat boiler, a tail gas liquid separator, a tail gas waste heat unit, a hydrogenation reactor, an MDEA absorption tower and an MDEA hydrogen sulfide regeneration tower; the sulfur-containing tail gas is separated by the membrane separation unit to obtain hydrogen sulfide gas and other gases, the hydrogen sulfide gas is decomposed in the furnace tube of the hydrogen sulfide thermal decomposition furnace, and then passes through the sulfur production waste heat boiler and the waste heat boiler in turn for heat exchange and cooling, and then is subjected to gas-liquid separation in the tail gas liquid separator, the hydrogen obtained at the top of the tail gas liquid separator is sent to the methanol synthesis system as a raw gas, and liquid sulfur is obtained at the bottom of the tank;

[0023] The other gases obtained by the membrane separation unit are burned in the furnace of the hydrogen sulfide thermal decomposition furnace to obtain sulfur dioxide and carbon dioxide, and are hydrogenated in the hydrogenation reactor to obtain hydrogen sulfide after being cooled by the tail gas waste heat unit; the hydrogen sulfide and the carbon dioxide enter the MDEA absorption tower, and the carbon dioxide at the top of the tower is sent to the methanol synthesis system as a feed gas, and the MDEA absorption liquid in the MDEA absorption tower enters the MDEA hydrogen sulfide regeneration tower for regeneration, and the regenerated hydrogen sulfide is recycled to the sulfur-containing tail gas, and the MDEA absorption liquid in the MDEA hydrogen sulfide regeneration tower is circulated back to the MDEA absorption tower;

[0024] The methanol synthesis system comprises a methanol reaction tower, a high-pressure separator, a low-pressure separator, a distillation tower and a PSA adsorption tower II; the carbon dioxide at the top of the MDEA absorption tower and the hydrogen at the top of the tail gas separator tank are used as raw gas to enter the methanol reaction tower for reaction, and the gas out of the tower is cooled and then subjected to gas-liquid separation in the high-pressure separator, and the obtained liquid phase continues to enter the low-pressure separator for further gas-liquid separation, and liquid methanol and gas phase are separated by the high-pressure separator and the low-pressure separator; the liquid methanol is distilled by the distillation tower to obtain refined methanol, and the gas phase is purified by the PSA adsorption tower II, and a part of the hydrogen obtained is recycled to the hydrogenation reactor, and the other part is incorporated into the inlet of the hydrogen compressor as the raw gas of the methanol synthesis system.

[0025] The elemental sulfur recovery system comprises a membrane separation unit, a hydrogen sulfide thermal decomposition furnace, a sulfur production waste heat boiler, a waste heat boiler, a tail gas liquid separator, a tail gas waste heat unit, a hydrogenation reactor, an MDEA absorption tower and an MDEA hydrogen sulfide regeneration tower; the sulfur-containing tail gas is separated by the membrane separation unit to obtain hydrogen sulfide gas and other gases, the hydrogen sulfide gas is decomposed in the furnace tube of the hydrogen sulfide thermal decomposition furnace, and then passes through the sulfur production waste heat boiler and the waste heat boiler in turn for heat exchange and cooling, and then is separated into gas and liquid in the tail gas liquid separator, and hydrogen is obtained at the top of the tail gas liquid separator, and liquid sulfur is obtained at the bottom of the tank;

[0026] The other gases obtained by the membrane separation unit are burned in the furnace of the hydrogen sulfide thermal decomposition furnace to obtain sulfur dioxide and carbon dioxide, and are hydrogenated in the hydrogenation reactor to obtain hydrogen sulfide after being cooled by the tail gas waste heat unit; the hydrogen sulfide and the carbon dioxide enter the MDEA absorption tower, and the carbon dioxide at the top of the tower is sent to the methanol synthesis system as a feed gas, and the MDEA absorption liquid in the MDEA absorption tower enters the MDEA hydrogen sulfide regeneration tower for regeneration, and the regenerated hydrogen sulfide is recycled to the sulfur-containing tail gas, and the MDEA absorption liquid in the MDEA hydrogen sulfide regeneration tower is circulated back to the MDEA absorption tower;

[0027] The methanol synthesis system comprises a methanol reaction tower, a high-pressure separator, a low-pressure separator, a distillation tower and a PSA adsorption tower II; the carbon dioxide at the top of the MDEA absorption tower and the hydrogen at the top of the tail gas separator tank are used as raw gas to enter the methanol reaction tower for reaction, and the gas out of the tower is cooled and then subjected to gas-liquid separation in the high-pressure separator, and the obtained liquid phase continues to enter the low-pressure separator for further gas-liquid separation, and liquid methanol and gas phase are separated by the high-pressure separator and the low-pressure separator; the liquid methanol is distilled in the distillation tower to obtain refined methanol, and the gas phase is purified by the PSA adsorption tower II to obtain hydrogen, part of which is recycled to the hydrogenation reactor, and the other part is used as the raw gas for the methanol synthesis system.

[0028] In some specific embodiments, the elemental sulfur recovery system further includes an acid gas separation tank, and the sulfur-containing tail gas enters the membrane separation unit after the liquid therein is separated and removed in the acid gas separation tank.

[0029] In the process system provided by the present invention, the membrane separation unit comprises a plurality of membrane separators connected in sequence.

[0030] In some specific embodiments, the tail gas waste heat unit includes a steam superheater, a tail gas waste heat boiler I, a tail gas waste heat boiler II and a cooler I which are connected in sequence.

[0031] In the process system provided by the present invention, the hydrogen at the top of the tail gas separator tank enters the PSA adsorption tower I to purify the obtained hydrogen and the remaining gases, the purified hydrogen enters the hydrogen compressor for pressurization and serves as the raw gas of the methanol synthesis system, and the remaining gases are sent to the hydrogen sulfide thermal decomposition furnace as fuel gas.

[0032] In some specific embodiments, the carbon dioxide at the top of the MDEA absorption tower is pressurized in a carbon dioxide compressor;

[0033] The hydrogen at the top of the tail gas separator tank is pressurized in a hydrogen compressor; the pressurized carbon dioxide and hydrogen are reacted in the methanol reaction tower after heat exchange and temperature increase in an intermediate heat exchanger.

[0034] In some specific embodiments, the outlet gas of the methanol reaction tower is cooled by heat exchange in the intermediate heat exchanger, then enters the water cooler I for cooling, and then undergoes gas-liquid separation in the high-pressure separator.

[0035] In some specific implementations, the liquid methanol separated by the low-pressure separator is pumped to a water cooler II through a crude methanol pump to cool it down, and then subjected to distillation treatment in the distillation tower.

[0036] In some specific embodiments, the top gas phase of the distillation tower is cooled by a cooler and then flash-evaporated in a separator to obtain the refined methanol.

[0037] The above technical solution has the following technical effects:

[0038] The process system of the present invention uses a hydrogen sulfide thermal decomposition furnace to efficiently thermally decompose hydrogen sulfide in sulfur-containing tail gas to produce hydrogen and liquid sulfur, and the liquid sulfur is recovered as a product. The hydrogen and carbon dioxide produced by the combustion furnace are separated, purified, and pressurized to enter a synthesis tower to undergo a methanol synthesis reaction to produce crude methanol, and the crude methanol is refined by a distillation tower to produce a qualified refined methanol product.

[0039] The process system of the present invention realizes maximum energy saving and consumption reduction, and is particularly effective for supporting projects producing methanol. It not only achieves standard emission of sulfur-containing tail gas, but also reasonably recovers effective hydrogen and effective carbon in the tail gas, turning waste into treasure, achieving clean production, and achieving the purpose of protecting the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 : An implementation method of the process system provided by the present invention;

[0041] Among them, 1. Acid gas liquid separator, 2. Membrane separator, 3. Hydrogen sulfide thermal decomposition furnace, 4. Sulfur production waste heat boiler, 5. Waste heat boiler, 6. Tail gas liquid separator, 7. Steam superheater, 8. Tail gas waste heat boiler I, 9. Tail gas waste heat boiler II, 10. Cooler I, 11. Hydrogenation reactor, 12. MDEA absorption tower, 13. MDEA hydrogen sulfide regeneration tower, 14. PSA adsorption tower I, 15. PSA adsorption tower II, 16. Carbon dioxide compressor, 17. Hydrogen compressor, 18. Intermediate heat exchanger, 19. Methanol reaction tower, 20. Water cooler I, 21. High pressure separator, 22. Low pressure separator, 23. Crude methanol pump, 24. Water cooler II, 25. Distillation tower, 26. Cooler II, 27. Liquid separator. DETAILED DESCRIPTION

[0042] In order to facilitate the understanding of the present invention, the present invention will be further described below in conjunction with examples. It should be understood that the following examples are only for a better understanding of the present invention and do not mean that the present invention is limited to the following examples.

[0043] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0044] The present invention provides a process system for recovering elemental sulfur from sulfur-containing tail gas and producing methanol. Figure 1 As shown, the process system includes an elemental sulfur recovery system and a methanol synthesis system;

[0045] The sulfur-containing tail gas is separated by multiple membrane separators 2 connected in sequence to obtain hydrogen sulfide gas and other gases (tail gas containing a small amount of hydrogen sulfide gas, carbon dioxide, carbon monoxide and other components). The hydrogen sulfide gas is decomposed in the furnace tube of the hydrogen sulfide thermal decomposition furnace 3 to produce hydrogen and sulfur, and then passes through the sulfur-making waste heat boiler 4 and the waste heat boiler 5 for heat exchange and cooling. The sulfur-making waste heat boiler 4 produces 4.1MPa saturated steam, and the waste heat boiler 5 produces 0.46MPa saturated steam. After cooling, the decomposed gas enters the tail gas separator 6 for gas-liquid separation. Liquid sulfur is obtained at the bottom of the tail gas separator 6, and hydrogen is obtained at the top of the tank. The hydrogen is recycled as raw gas to the hydrogen compressor 17 in the methanol synthesis system.

[0046] The hydrogen at the top of the tail gas separator tank 6 enters the PSA adsorption tower Ⅰ14 to purify the hydrogen and the remaining gases. The purified hydrogen enters the hydrogen compressor 17 to increase the pressure, and the remaining gases are sent to the hydrogen sulfide thermal decomposition furnace 3 as fuel gas.

[0047] The other gases obtained by the membrane separation unit are burned in the furnace of the hydrogen sulfide thermal decomposition furnace 3 to obtain sulfur dioxide and carbon dioxide. The sulfur dioxide and carbon dioxide are cooled by the tail gas waste heat boiler Ⅰ8 and the tail gas waste heat boiler Ⅱ9, and 4.1MPa saturated steam and 0.46MPa saturated steam are respectively generated. The 4.1MPa saturated steam is converted into superheated steam by the steam superheater 7 and incorporated into the 4.1MPa superheated steam network. The tail gas waste heat boiler 5 and the tail gas waste heat boiler Ⅱ9 are merged and incorporated into the 0.46MPa saturated steam network; the cooled sulfur dioxide is further cooled in the cooler Ⅰ10, and then hydrogenated in the hydrogenation reactor 11 to obtain hydrogen sulfide. Hydrogen sulfide and unreacted carbon dioxide enter the MDEA absorption tower 12, and the carbon dioxide at the top of the tower is pressurized in the carbon dioxide compressor 16 and sent to the methanol synthesis system as raw gas. In some specific embodiments, the pressurized carbon dioxide and hydrogen are reacted in the methanol reaction tower 19 after heat exchange and temperature increase in the intermediate heat exchanger 18. The MDEA absorption liquid in the MDEA absorption tower 12 enters the MDEA hydrogen sulfide regeneration tower 13 for regeneration, and the regenerated hydrogen sulfide is recycled to the sulfur-containing tail gas. The MDEA absorption liquid in the MDEA hydrogen sulfide regeneration tower 13 is circulated back to the MDEA absorption tower 12. The MDEA absorption tower 12 absorbs hydrogen sulfide and is regenerated. The regenerated hydrogen sulfide can be used as raw gas. The closed cycle of the absorption and regeneration system effectively reduces the emission of waste gas and waste liquid, and avoids environmental pollution.

[0048] The methanol synthesis system in the process system of the present invention comprises a methanol reaction tower 19, a high-pressure separator 21, a low-pressure separator 22, a distillation tower 25 and a PSA adsorption tower II 15; the carbon dioxide at the top of the MDEA absorption tower 12 and the hydrogen at the top of the tail gas separation tank 6 enter the methanol reaction tower 19 as raw gas for methanol synthesis reaction, the outlet gas of the methanol reaction tower 19 is cooled by the intermediate heat exchanger 18, enters the water cooler I 20 for cooling, and then undergoes gas-liquid separation in the high-pressure separator 21, and the liquid phase obtained by gas-liquid separation continues to enter the low-pressure separator 22 for further gas-liquid separation. Liquid methanol and gas phase are separated by the high-pressure separator 21 and the low-pressure separator 22.

[0049] Specifically, the separated gas phase is purified by PSA adsorption tower II 15, and the hydrogen obtained is recycled to the hydrogenation reactor 11, and the rest is recycled as fuel gas to the hydrogen sulfide thermal decomposition furnace 3. The liquid methanol is distilled in the distillation tower 25, and the top gas phase is cooled by cooler II 26, and then flashed and separated by the liquid separator 27 to obtain refined methanol.

[0050] In some specific embodiments, the elemental sulfur recovery system further includes an acid gas separator tank 1 , and the sulfur-containing tail gas enters the membrane separator 2 after the liquid therein is separated in the acid gas separator tank 1 .

[0051] In some specific embodiments, the liquid methanol separated by the low-pressure separator 22 is pumped to the water cooler II 24 through the crude methanol pump 23 for cooling, and then subjected to distillation treatment in the distillation tower 25 .

Claims

1. A process system for recovering elemental sulfur from sulfur-containing tail gas and co-producing methanol, characterized in that: The process system includes an elemental sulfur recovery system and a methanol synthesis system; The elemental sulfur recovery system comprises a membrane separation unit, a hydrogen sulfide thermal decomposition furnace (3), a sulfur production waste heat boiler (4), a waste heat boiler (5), a tail gas liquid separator (6), a tail gas waste heat unit, a hydrogenation reactor (11), an MDEA absorption tower (12) and an MDEA hydrogen sulfide regeneration tower (13); the sulfur-containing tail gas is separated by the membrane separation unit to obtain hydrogen sulfide gas and other gases; the hydrogen sulfide gas is decomposed in the furnace tube of the hydrogen sulfide thermal decomposition furnace (3), and then passes through the sulfur production waste heat boiler (4) and the waste heat boiler (5) in sequence for heat exchange and cooling before gas-liquid separation is performed in the tail gas liquid separator (6); hydrogen is obtained at the top of the tail gas liquid separator (6) and is sent to the methanol synthesis system as raw gas, and liquid sulfur is obtained at the bottom of the tank; The other gases obtained by the membrane separation unit are burned in the furnace of the hydrogen sulfide thermal decomposition furnace (3) to obtain sulfur dioxide and carbon dioxide, and after being cooled by the tail gas waste heat unit, they are hydrogenated in the hydrogenation reactor (11) to obtain hydrogen sulfide; the hydrogen sulfide and the carbon dioxide enter the MDEA absorption tower (12), and the carbon dioxide at the top of the tower is sent to the methanol synthesis system as a raw gas. The MDEA absorption liquid in the MDEA absorption tower (12) enters the MDEA hydrogen sulfide regeneration tower (13) for regeneration, and the regenerated hydrogen sulfide is recycled to the sulfur-containing tail gas, and the MDEA absorption liquid in the MDEA hydrogen sulfide regeneration tower (13) is circulated back to the MDEA absorption tower (12); The methanol synthesis system comprises a methanol reaction tower (19), a high-pressure separator (21), a low-pressure separator (22), a distillation tower (25) and a PSA adsorption tower II (15); the carbon dioxide at the top of the MDEA absorption tower (12) and the hydrogen at the top of the tail gas separator (6) are used as raw gas to enter the methanol reaction tower (19) for reaction, and the outlet gas is cooled and then subjected to gas-liquid separation in the high-pressure separator (21), and the obtained liquid phase is continuously fed into the low-pressure separator (22) for further gas-liquid separation, and liquid methanol and gas phase are obtained after separation by the high-pressure separator (21) and the low-pressure separator (22); the liquid methanol is distilled by the distillation tower (25) to obtain refined methanol, and the gas phase is purified by the PSA adsorption tower II (15), and a part of the hydrogen obtained is recycled to the hydrogenation reactor (11), and the other part is used as the raw gas for the methanol synthesis system.

2. The process system according to claim 1, characterized in that: The elemental sulfur recovery system further comprises an acid gas liquid separator tank (1), and the sulfur-containing tail gas enters the membrane separation unit after the liquid therein is separated and removed in the acid gas liquid separator tank (1).

3. The process system according to claim 2, characterized in that: The membrane separation unit comprises a plurality of membrane separators (2) connected in sequence.

4. The process system according to claim 3, characterized in that: The tail gas waste heat unit comprises a steam superheater (7), a tail gas waste heat boiler I (8), a tail gas waste heat boiler II (9) and a cooler I (10) which are connected in sequence.

5. The process system according to any one of claims 1 to 4, characterized in that: The hydrogen at the top of the tail gas separator tank (6) enters the PSA adsorption tower I (14) to purify the obtained hydrogen and the remaining gas. A part of the purified hydrogen enters the hydrogen compressor (17) to be pressurized as the raw gas of the methanol synthesis system, and the remaining gas is sent to the hydrogen sulfide thermal decomposition furnace (3) as fuel gas.

6. The process system according to any one of claims 1 to 5, characterized in that: The carbon dioxide at the top of the MDEA absorption tower (12) is pressurized in a carbon dioxide compressor (16).

7. The process system according to claim 6, characterized in that: The carbon dioxide and hydrogen after being pressurized are heated by the intermediate heat exchanger (18) and then reacted in the methanol reaction tower (19).

8. The process system according to any one of claims 1 to 7, characterized in that: The outlet gas of the methanol reaction tower (19) is cooled by heat exchange in the intermediate heat exchanger (18), then enters the water cooler I (20) for cooling, and then undergoes gas-liquid separation in the high-pressure separator (21).

9. The process system according to any one of claims 1 to 8, characterized in that: The liquid methanol separated by the low-pressure separator (22) is pumped to the water cooler II (24) by the crude methanol pump (23) for cooling, and then subjected to distillation treatment in the distillation tower (25).

10. The process system according to claim 9, characterized in that: The gas phase at the top of the distillation tower (25) is cooled by a cooler II (26) and then flash-evaporated and separated by a separator (27) to obtain the refined methanol.

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