CN-117241874-B - Method for regenerating a prepurification vessel

Abstract

A system and method for regenerating a prepurification vessel is provided that is particularly suitable for prepurification of a feed air stream in a cryogenic air separation plant that uses an oxygen-enriched purge gas stream to regenerate the prepurification plant. The disclosed prepurification systems and methods are configured to remove substantially all of the water, carbon dioxide, and other impurities, optionally including hydrogen and carbon monoxide impurities, from the feed air stream. The method of regenerating the prepurification vessel preferably includes regenerating the prepurification vessel with an oxygen-enriched purge gas after depressurizing the vessel, then partially repressurizing the prepurification vessel with an auxiliary purge gas to dilute the oxygen concentration of the gas contained in the prepurification vessel, and optionally depressurizing the partially repressurized vessel.

Inventors

• J.R. Handley
• R. C. Siganovich
• C.E. Selik
• B.S. Powell
• D. A. Dashani

Assignees

• 普莱克斯技术有限公司

Dates

Publication Date

20260505

Application Date

20211012

Priority Date

20210419

Claims (17)

1. 1. A method of regenerating a prepurification vessel, the method comprising the steps of: (i) Depressurizing a prepurification vessel having one or more layers of adsorbent and/or catalyst disposed therein to a regeneration pressure; (ii) Heating the one or more layers of adsorbent material and/or the one or more layers of catalyst material disposed within the prepurification vessel with a hot oxygen-enriched purge gas to desorb water and carbon dioxide from the one or more layers; (iii) Cooling the one or more adsorbent and/or the catalyst layer within the prepurification vessel with a cold oxygen-enriched purge gas to a temperature suitable for the prepurification process; (iv) After the cooling step, partially repressurizing the prepurification vessel with an auxiliary purge gas to dilute the oxygen concentration of the gas contained in the prepurification vessel; (v) The prepurification vessel is fully repressurized to a working pressure at which prepurification of the feed gas is performed, wherein the oxygen concentration of the gas in the repressurized prepurification vessel is less than or equal to 30 mole percent.
2. 2. The method of claim 1, wherein the oxygen concentration of the gas in the pre-purification vessel after repressurization is less than or equal to 26 mole percent.
3. 3. The method of claim 1, wherein the step of partially repressurizing the prepurification vessel with an auxiliary purge gas further comprises partially repressurizing the prepurification vessel with an auxiliary purge gas to an intermediate pressure, then depressurizing the prepurification vessel and releasing the auxiliary purge gas and any oxygen-enriched purge gas remaining within the prepurification vessel.
4. 4. The method of claim 1, wherein the step of partially repressurizing the prepurification vessel with an auxiliary purge gas further comprises partially repressurizing the prepurification vessel with a nitrogen-rich gas having a nitrogen concentration greater than 85 mole percent to an intermediate pressure to dilute the oxygen concentration of the gas remaining in the prepurification vessel.
5. 5. The method of claim 1, wherein the temperature of the hot oxygen-enriched purge gas is at least 150 ℃.
6. 6. The method of claim 1, wherein the temperature of the cold oxygen-enriched purge gas is less than or equal to 50 ℃.
7. 7. The method of claim 1, wherein the prepurification vessel is coupled to an air separation device and the feed gas is air, wherein the one or more layers of adsorbent within the prepurification vessel comprises activated alumina, silica gel, zeolite-based molecular sieve, zeolite X, or a combination thereof, and is configured to remove impurities in the feed gas, including water, carbon dioxide, and other contaminants.
8. 8. The method of claim 7, wherein the one or more layers of catalyst within the prepurification vessel comprises a hopcalite catalyst or a noble metal catalyst and is configured to remove impurities, including hydrogen and carbon monoxide.
9. 9. The method of claim 1, wherein the prepurification vessel is coupled to an air separation device and the hot oxygen-enriched purge gas and the cold oxygen-enriched purge gas are taken from an oxygen-enriched stream of a distillation column system of the air separation device.
10. 10. The method of claim 9, wherein the step of heating the one or more layers of adsorbent material and/or the one or more layers of catalyst material with the hot oxygen-enriched purge gas further comprises heating the oxygen-enriched stream using an electric heater, a gas heater, or a steam heater.
11. 11. The method of claim 1, wherein the prepurification vessel is coupled to an air separation unit that produces argon, and the hot oxygen-enriched purge gas and the cold oxygen-enriched purge gas are oxygen-enriched streams taken from an argon condenser associated with the air separation unit.
12. 12. The method of claim 3, wherein the regeneration pressure is less than 6.0 bar, the operating pressure is greater than or equal to 6.0 bar, and the intermediate pressure is between the regeneration pressure and the operating pressure.
13. 13. The method of claim 3, wherein the prepurification vessel is coupled to an air separation device and the auxiliary purge gas further comprises a dry air stream taken from a location downstream of a prepurifier device associated with the air separation device, or a split portion of feed air taken from a location upstream of the prepurifier device associated with the air separation device, or a synthetic air stream taken from the air separation device.
14. 14. A method according to claim 3, wherein an auxiliary purge gas is introduced to the prepurification vessel at or near the outlet via an auxiliary purification control valve and during depressurization, the auxiliary purge gas and any retained gas in the prepurification vessel are released at or near the outlet via a partial depressurization control valve or the depressurization control valve.
15. 15. The method of claim 4, wherein the prepurification vessel is coupled to an air separation plant and the nitrogen-rich gas is taken from the air separation plant or a nitrogen storage tank.
16. 16. The method of claim 4, wherein nitrogen-rich gas is introduced into the prepurification vessel at or near the outlet via an auxiliary purge gas control valve.
17. 17. The method of claim 4, wherein the regeneration pressure is less than 6.0 bar, the operating pressure is greater than or equal to 6.0 bar, and the intermediate pressure is between the regeneration pressure and the operating pressure.

Description

Method for regenerating a prepurification vessel Technical Field The present invention relates to a system and method for regenerating a prepurification vessel and, more particularly, to a method and system for regenerating a prepurification vessel of an air separation plant wherein the regeneration purge gas is an oxygen-enriched purge gas. Background Adsorption is a well-known technique for purifying gases and treating fluid waste streams. Purification and separation of atmospheric air constitutes one of the main areas of widely used adsorption processes. New and improved prepurification systems and methods are continually being developed to increase their efficiency. One of the areas of intense commercial and technical interest represents the pre-purification of air prior to its cryogenic distillation. Conventional air separation units for the production of nitrogen (N 2) and oxygen (O 2) and argon (Ar) by cryogenic separation of air consist essentially of two or at least three integrated distillation columns, respectively, operating at very low temperatures. Because of these low temperatures, water vapor (H 2 O) and carbon dioxide (CO 2) must be removed from the compressed air fed to the air separation unit. If not removed, the water and carbon dioxide present in the feed air will freeze and clog the heat exchanger used to cool the feed air prior to distillation in the cryogenic distillation tower. Preferably, to avoid freezing, the water content in the compressed and pre-purified air feed stream must be less than 0.1ppm (parts per million) while the carbon dioxide content in the compressed and pre-purified air feed stream must be less than 1.0ppm. Removal of hydrocarbons and nitrous oxide is often required to ensure safe operation of such cryogenic distillation systems, which typically involve treatment of an oxygen-enriched gas stream. Current commercial processes for pre-purifying feed air include temperature swing adsorption units employing a layer of adsorbent material in conjunction with optional catalytic pre-purification techniques. Prepurification devices upstream of cryogenic distillation systems are typically used that include a front-end adsorbent layer to remove water, carbon dioxide, and hydrocarbons and other contaminants, including nitrogen oxides. Such prepurification devices may also optionally include one or more catalysts for removing one or more contaminants, followed by a final adsorbent layer downstream of the optional catalyst for removing contaminants produced by the catalytic process. For example, some cryogenic air separation applications in the electronics industry and other industries selected require removal of hydrogen and/or carbon monoxide from a feed air stream prior to processing the feed air stream in a cryogenic distillation system to produce high purity or ultra high purity nitrogen products. The thermal regeneration process applied to such temperature swing adsorption prepurification devices associated with the air separation device is used to desorb water, carbon dioxide and selected other contaminants such as hydrocarbons and nitrous oxide from the various layers in the prepurifier device. Conventional thermal regeneration is preferably performed using a multi-step process involving at least four general steps, namely, (i) depressurizing the prepurification vessel to a lower pressure suitable for the regeneration process, (ii) heating the layers within the prepurification vessel with a heated purge gas to desorb water, carbon dioxide and other contaminants from the individual adsorption layers and clean the catalyst layers, (iii) cooling the layers within the prepurification vessel with a cooler purge gas (commonly referred to as a cold purge gas) to a temperature suitable for the prepurification process, and (iv) repressurizing the prepurification vessel back to the higher operating pressure required for the prepurification process. In conventional thermal regeneration of the prepurification vessel, the hot purge gas and cold purge gas typically comprise a stream of air or a waste nitrogen-rich air stream. However, the use of oxygen-enriched streams as hot and cold purge gases has also been previously employed, but safety considerations have been particularly required. The safe operation of the air separation plant is critical. Thus, when using an oxygen-enriched purge gas to regenerate a prepurifier unit associated with an air separation unit, if such components are exposed to a gas stream having a high oxygen concentration, it may be necessary to subject some of the piping, vessels, valves and other equipment to special cleaning treatments or to employ special materials to ensure safe operation. It is therefore desirable to minimize special cleaning/handling and special material requirements (and associated costs) by ensuring that the oxygen content of the gas remaining in the prepurifier vessel is diluted after regeneration is performed, thereby ensuring that