Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
  • C01B3/50—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
  • C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
  • C01B3/06—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of inorganic compounds containing electro-positively bound hydrogen, e.g. water, acids, bases, ammonia, with inorganic reducing agents
  • C01B3/12—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of inorganic compounds containing electro-positively bound hydrogen, e.g. water, acids, bases, ammonia, with inorganic reducing agents by reaction of water vapour with carbon monoxide
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
  • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
  • C01B2203/0465—Composition of the impurity
  • C01B2203/0475—Composition of the impurity the impurity being carbon dioxide
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
  • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
  • C01B2203/0465—Composition of the impurity
  • C01B2203/0485—Composition of the impurity the impurity being a sulfur compound

Definitions

• the invention relates to the purification of a hydrogen-containing gas stream. More particularly, it relates to the use of a pressure swing adsorption system for the recovery of a purified hydrogen-containing produc .
• the thus-shifted gas stream is then further treated by alternative procedures to obtain the desired hydrogen product.
• the gas stream may be passed to a scrubbing unit for the removal of CO down to about 0.1%.
• the effluent therefrom can be further treated to remove additional CO. so as to reduce the residual content thereof to about 1 ppm.
• the effluent gas stream can be subjected to liquid nitrogen scrubbing or to cryogenic purification techniques to produce about a 97% hydrogen product stream, or a pure ammonia syngas stream, together with by-product fuel gas.
• the effluent from high temperature shift conversion can be subjected to low temperature shift conversion for further CO conversion, and then passed to a scrubbing unit to achieve CO- removal down to about 0.1%.
• the effluent therefrom can then be subjected to methanation to produce said 97% hydrogen product stream.
• the desired hydrogen purification can also be accomplished by means of a process and system utilizing pressure swing adsorption (PSA) for final purification.
• PSA pressure swing adsorption
• Such a PSA approach has the advantages of simplification, ease of operation and of high hydrogen product purity, i.e. 99.99+%, than is achieved by the altern approaches referred to above.
• improvements be developed to enhance the feasibility of employing the PSA approach in practical commercial operations.
• the obtaining of improvements in the recovery of purified hydrogen product is desired so that the size of the stream reformer, partial oxidation or other hydrogen- containing effluent gas stream generation unit can be optimized.
• a hydrogen-containing effluent gas stream is subjected to at least high temperature water gas shift conversion, scrubbed for removal of a major portion of its carbon dioxide content and introduced to a pressure swing adsorption system from which a purified hydrogen-containing product stream is recovered.
• the waste gas from the pressure swing adsorption system is recycled to the shift conversion operation or to the effluent gas stream generation operation.
• a portion of the waste gas can be discharged or passed to a supplemental pressure swing adsorption system to recover additional hydrogen-containing product prior to discharge of said portion of the waste gas.
• Nitrogen and/or argon in the gas stream passed to the pressure swing adsorption system can be allowed to break through into the purified gas product, if tolerable, to avoid build-up within the system.
• the countercurrent depressurization and/or purge steps of the pressure swing adsorption processing cycle can also be carried out with recycle of only that portion of the resulting effluent that is richest in hydrogen, with discharge of the portion thereof containing the principal amounts of said nitrogen and/or argon.
• the practice of the invention enables the objectives set forth above to be achieved, with high purity hydrogen-containing product being obtained at advantageously high recovery levels.
• Simplified processing procedures and apparatus features can be employed, with desirable conditions for water gas shift conversion and for carbon dioxide scrubbing contributing to the favorable overall technical- economic aspects of the invention.
• undesirable build-up of methane, nitrogen and/or argon in the system can be avoided, while the recovery of product gas is nevertheless enhanced.
• effluent gas streams useful in the practice of the invention.
• Such streams contain hydrogen desired as a product gas, together with carbon dioxide, carbon monoxide and other constituents such as methane, nitrogen, argon, water vapor and the like.
• the effluent gas stream is subjected to high temperature water gas shift conversion to convert carbon monoxide therein to additional hydrogen and carbon dioxide. Following such shift conversion, a major portion of the carbon dioxide content of the effluent gas stream is removed therefrom.
• the carbon dioxide-depleted effluent gas stream is then passed to a PSA system capable of discharging a purified, hydrogen-containing product gas therefrom as a less readily adsorbable component of said effluent stream.
• the more readily adsorbable component thereof comprises carbon dioxide and other impurities present in the effluent stream being treated.
• the more readily adsorbable component is removed from the PSA system as waste gas during the desorption steps carried out in each adsorbent bed of the system. Such waste gas is compressed and at least about 40% thereof is recycled to the shift conversion step and/or to the effluent gas generation step, as is further described below.
• the effluent gas stream obtained from a gas generation system will typically be available at a temperature of about 800°C or higher. This gas stream is cooled to on the order of about
• the shift conversion step so as to convert most of the carbon monoxide in the effluent stream to additional hydrogen and carbon dioxide by subjecting said stream to at least a high temperature catalytic water gas shift conversion.
• a high temperature catalytic water gas shift conversion for this purpose, more than about 80%, typically from about 85% to 98%, of the CO content of the effluent stream will generally be converted in the practice of the invention.
• the thus-treated effluent stream is passed to a carbon dioxide scrubbing zone where again the requirements are less stringent than pertain to the conventional approaches referred to above.
• a carbon dioxide scrubbing zone where again the requirements are less stringent than pertain to the conventional approaches referred to above.
• the carbon dioxide content of the effluent stream is removed therefrom in said scrubbing zone, but the residual CO level need not be reduced to 0.1%. or to about lppm, as is required in the practice of said conventional approaches. It is generally sufficient if more than about 70%, preferably between from about 85 to about 99.9%, by volume of the carbon dioxide content of the effluent stream, which is commonly on the order of 25%, is removed in the scrubbing step.
• the residual carbon dioxide content of the thus carbon dioxide-depleted effluent stream is thereby typically reduced to from about 2% to about 7% of the effluent stream, conveniently to from about 3% to about 5%.
• Those skilled in the art will appreciate that not being required to assure essentially complete removal of carbon dioxide from the effluent stream prior to its passage to the pressure swing adsorption system represents a highly advantageous feature of the invention vis-a-vis the conventional approaches referred to above for producing hydrogen from effluent gas streams.
• the thus carbon dioxide-depleted effluent stream is passed, in the practice of the invention. to a pressure swing adsorption system capable of discharging a purified, hydrogen-containing product gas therefrom as a less readily adsorbable component of said effluent stream.
• the more readily adsorbable component thereof comprises residual carbon dioxide and other impurities present in the effluent stream. It will be appreciated that said more readily adsorbable component is removed from the pressure swing adsorption system during the countercurrent depressurization and/or purge steps of the processing cycle in each bed of the adsorption system.
• the PSA cycle carried out in sequence in each adsorbent bed.
• the numeral 1 represents conduit means or a processing line for passing a hydrocarbon feed stream to a steam reformer, partial oxidation unit, coal gasification unit or other such hydrocarbon conversion means 2 for generating a hydrogen- containing effluent gas stream.
• steam is also added to said conversion means 2 by means of conduit 3.
• the effluent gas stream is passed from said reformer or other conversion means 2 through conduit means 4 to cooling and catalytic water gas shift conversion means 5 for converting carbon monoxide in said effluent gas stream to hydrogen and carbon dioxide.
• This thus-treated effluent stream leaving conversion means 5 at a temperature on the order of about 430°C is passed through conduit means 6, with appropriate cooling, and is introduced into liquid scrubbing means 7 capable of removing at least a major portion of the carbon dioxide from said effluent stream.
• the thus carbon dioxide-depleted effluent stream is passed from said scrubbing means 7 through conduit 8 for passage to PSA system 9, while the carbon dioxide-containing adsorber liquid or solvent is passed from said scrubbing means 7 through conduit 10 to flash tank 11.
• adsorber liquid is passed from flash tank 11 through conduit 14 to separation tank 15 from which carbon dioxide waste gas can be removed from the system through conduit 16.
• separation tank 15 from which carbon dioxide waste gas can be removed from the system through conduit 16.
• Regenerated adsorber liquid is passed from said tank 15 through conduit 17 containing solvent pump 18 for return to said scrubbing means 7.
• a purified hydrogen-containing product gas is discharged from PSA system 9 through conduit as the less readily adsorbable component of the effluent stream being treated in said PSA system.
• said product gas can readily have a high hydrogen product purity of 99.99% or more in accordance with the capability of established PSA technology.
• an impurities-containing waste gas is released from the feed end of the bed, said waste gas passing from said PSA system 9 through conduit 20 for repressurization in said recycle compressor 13.
• At least about 40% of said compressed waste gas is passed through recycle conduit 21 for passage to conduit 22 for recycle to shift conversion means 5 and/or for passage to conduit 23 for recycle to hydrocarbon conversion means 2 in the practice of the invention.
• conduit 24 is provided.
• the methane-containing waste gas is suitable for use as a fuel gas.
• the effluent gas stream contains nitrogen and/or argon
• Such diversion of methane, nitrogen and/or argon serves to prevent too high accumulation of such components in the recycle loop of the process and apparatus of the invention.
• methane-containing waste gas from the pressure swing adsorption system can be recycled at elevated pressure to said effluent gas generation step, ie., by passage through conduit 23 to conversion means 2.
• said means 2 comprises a steam reformer or partial oxidation unit
• the methane is converted to additional quantities of desired hydrogen.
• conversion means 2 is a coal gasification unit
• said portion of the recycled waste gas can be recycled to the gasification unit.
• the portion of the recycle waste stream passed to conversion means 2 instead of to shift conversion means 5 will vary depending upon the circumstances applicable to any given hydrogen production operation.
• an effluent gas stream is generated by primary steam reforming of hydrocarbons without the secondary reforming thereof, and the reformer effluent gas stream contains at least about 3 vol percent methane
• at least about 20% of the recycled waste gas from the pressure swing adsorption system is recycled to the reformer in desirable embodiments of the invention.
• from about 20% to 60% of said recycled waste gas preferably from about 30% to about 40%, is thus recycled to the reformer.
• the effluent gas stream from conversion means 2 contains very little methane
• most of the waste gas from the pressure swing adsorption system is desirably recycled directly to shift conversion means 5, as through conduit 22.
• the secondary reformer effluent gas contains less than about 1 vol percent methane, at least about 20% and generally the greater portion of the waste gas recycled from the pressure swing adsorption system, up to about 90% thereof, is advantageously recycled to shift conversion means 5.
• other amounts of methane are present in said recycled waste gas.
• the portion of the recycled waste gas recycled to said conversion means 2 and to said shift conversion means 5 can be determined for optimum hydrogen recovery and overall process performance in accordance with the particular operating circumstances applicable to such applications. In each instance, however, the effluent gas stream is generally cooled to on the order of about 350°C prior to use in the conversion step.
• a portion of a methane-containing waste gas from the pressure swing adsorption system is directed at an elevated adsorption pressure to a supplemental pressure swing adsorption system.
• this embodiment is provided for by the inclusion of optional bleed line 25 by means of which a portion of methane-containing waste gas can be directed to supplemental PSA system 26.
• the less readily adsorbable product gas discharged therefrom comprises additional purified, hydrogen-containing product that may be withdrawn through conduit 27.
• the more readily adsorbable waste gas separated from said product gas in PSA system 26 is removed therefrom through conduit 28.
• This methane- containing gas stream is suitable for use, if desired, as a fuel gas. It will be appreciated that a combination of such means described above for avoiding methane build-up can be employed in the practice of the invention.
• a portion of the methane-containing compressed recycle gas can be passed to conversion means 2, wherein the methane can be converted to form additional hydrogen, while a portion of the PSA waste gas may not be compressed, but sent to fuel by discharge through conduit 24.
• a portion of the compressed PSA waste gas in conduit 21 may be diverted through conduit 25 to supplemental PSA system 26 while a portion of the waste gas from said PSA system 9 is not compressed but is diverted from the system through conduit 24 for use as fuel or for other purposes.
• the diversion of a portion of the PSA waste gas in conduit 20 from the process and system through said conduit 24 can be employed to avoid undue build-up of nitrogen and/or argon in the recycle loop of the invention.
• the higher pressure adsorption step in PSA system 9 can be carried out so as to allow a breakthrough of nitrogen and/or argon into the purified, hydrogen-containing product gas discharged from the product end of each adsorbent bed of the system.
• This option is, of course, dependent upon the applicable product specifications pertaining to any given application. This option may also be used in combination with other processing variations for optimal performance in particular applications. •.
• the undesired build-up of nitrogen and/or argon in the recycle loop of the invention can be avoided by recycling, as in recycle conduit 21 of the drawing, only the portion of the waste gas from PSA system 9 that is richest in the hydrogen gas desired to be recovered.
• Such gas richest in hydrogen is released during the initial, higher pressure portion of the countercurrent depressurization step carried out in said PSA system 9.
• the gas released during further countercurrent depressurization to lower desorption presence, together with additional gas released upon purge, if employed, at said lower desorption pressure, is diverted from the process, as through conduit 24, in this embodiment of the invention.
• said gas released during the last portion of the purge step is relatively free of nitrogen and/or argon. It will be appreciated that such hydrogen-containing gas relatively free of nitrogen and/or argon, obtained particularly during purge under gradually increasing pressure conditions, is desirably recycled for purposes of the invention, while the gas released during the remaining portion of the countercurrent depressurization step and during the initial portion of the purge step is conveniently diverted from the process and system of the invention. It will readily be appreciated that such unique processing refinements enable the recovery of product hydrogen to be enhanced in accordance with the simplified and highly desirable processing features of the overall invention.
• the PSA process and systems employed can incorporate any desired number of adsorbent beds and any convenient, known processing cycles for recovering product hydrogen in the main PSA system and. when employed, in the supplemental PSA system 26.
• Any suitable adsorbent material having a desirable selectivity for purposes of the invention can be used in the practice of the invention.
• Suitable adsorbents include zeolitic molecular sieves, activated carbon, silica gel, activated alumina and the like.
• Zeolite molecular sieve adsorbents are generally desirable in the subject separation and purification of hydrogen from effluent gas streams.
• Information containing such zeolitic molecular sieves is contained in the Kiyonaga patent, U.S. 3,176,444 and various other patents relating to the PSA process and system as employed in its various embodiments.
• the carbon dioxide scrubbing step can be carried out using any known, commercially available scrubbing techniques and liquid scrubbing materials.
• the Benfield aqueous alkaline scrubbing process, the Shell Sulfinol and the Allied Chemical Selexol solvent extraction processes are examples of commercial techniques for removing carbon dioxide from gas streams that are useful in the practice of the invention.
• the process of the invention can be employed for the separation and purification of a mixture of hydrogen and nitrogen, useful as an ammonia synthesis gas mixture.
• the purified product gas stream will generally contain more than 99 ol percent hydrogen and nitrogen, with less than 1 mol percent of argon ' , methane or other gases.
• the effluent from a partial oxidation unit containing 0.5% methane is passed to high temperature shift conversion and CO, removal by scrubbing prior to being passed to a PSA system for hydrogen separation and purification. 80% of the PSA waste gas is recycled to the shift converter, 15% is recycled to the partial oxidation unit, and 5% is discharged from the process for use as fuel gas.
• the feed gas to said PSA system contains 2.5 mol percent methane, almost all of the carbon monoxide present in the effluent gas stream from the partial oxidation unit is converted to product hydrogen and by-product carbon dioxide, and 99% of all of the hydrogen present in said effluent gas str.eam is recovered.
• Such advantageous results are achieved without the necessity of employing low temperature shift or for assuring essentially complete removal of carbon dioxide from the effluent stream prior to its passage to the PSA system.
• the effluent gas stream obtained upon the steam reforming of natural gas is found to contain 2.5 mol percent methane on a dry basis.
• the feed gas to the PSA system is found to contain 6.7% methane.
• Two-thirds of the PSA waste gas is recycled to the shift converter, and one-third is recycled to the steam reformer.
• the effluent gas stream discharged upon the steam reforming of naphtha is found to contain 5 mol percent methane on a dry basis.
• the effluent gas stream being treated is passed to an absorption scrubbing column wherein its carbon dioxide concentration is reduced to 3.5 mol percent.
• the gas is further purified in a PSA system to produce a 99.99% pure hydrogen stream, and a PSA waste gas stream containing 51.4 mol percent hydrogen, 13.1 mol percent CO_, 12.1 mol percent CO and 23.4 mol percent methane.
• the PSA waste gas is discharged to a fuel gas system, and 50% of said waste stream is recompressed and recycled to the steam reformer unit, and 30% thereof is so recycled to the shift converter. Essentially all of the carbon monoxide in the effluent gas stream treated in accordance with the invention is converted to product hydrogen and by-product carbon dioxide that are reserved in the process. Essentially complete recovery of hydrogen is obtained thereby. It should be noted that, when coal or heavy oils are gasified by partial oxidation or other conversion processes, the effluent gas stream generally contains hydrogen sulfide in addition to carbon dioxide.
• At least a major portion of such components can be removed in the scrubbing zone, in accordance with the invention, preferably using selective solvents so that carbon dioxide essentially free of H.S and a H_S-rich gas stream are separately obtained. It is not necessary, in such embodiments of the invention, to achieve essentially complete removal of H-S in the scrubbing zone as final purification can be accomplished in the pressure swing adsorption system. In conventional processing without resort to cryogenic purification, the severity of the reforming operation, or of partial oxidation, must be maintained at a high level in order to desirably reduce the methane content of the product gas obtained. Conversion in the steam reformer is generally between 85% and 93%.
• the steam reformer can be operated at lower severity, i.e., at a lower outlet temperature level, and/or at a lower steam- to-carbon ratio, if desired, so that lower investment costs and/or lower steam requirements can be realized.
• the hydrocarbon feed to the reformer can be reduced by between 8% and 17% in the practice of the invention. This is especially important when naphtha feedstock is employed.
• the advantageous conditions pertaining to the invention also make it possible to reduce the steam added to the feed by between about 10% and about 30%, thereby reducing the fuel requirements of the process or permitting the export of steam from the process and system.
• the invention can be practiced without a requirement for employing a low temperature shift conversion step.
• the ability to employ a low cost carbon dioxide absorption process for the removal of at least a major portion of the carbon dioxide from the effluent stream being treated results in a permissibly low utilities requirement in the carbon dioxide removal step.
• the practice of the invention requires no methanation or cryogenic purification operations as in the conventional processes.
• the investment cost of- hydrogen production by the practice of the invention is estimated to be between 2% and 12% lower than the investment costs for a comparable conventional plant. Even more significantly, however, are the significant savings on fuel and feedstock costs made possible by the invention, such savings far outweighing the power cost for the recycle compressor used in the practice of the invention. As a result of all such significant advantages and benefits flowing from the process and apparatus as herein described and claimed, it is estimated that operating savings in excess of one million dollars a year can be realized for a plant producing six tons per hour of product hydrogen. For partial oxidation or coal gasification operations, the PSA approach of the invention requires less feed materials as well as less oxygen than in conventional approaches.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
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• Combustion & Propulsion (AREA)
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• Chemical Kinetics & Catalysis (AREA)
• Health & Medical Sciences (AREA)
• General Health & Medical Sciences (AREA)
• Separation Of Gases By Adsorption (AREA)
• Hydrogen, Water And Hydrids (AREA)

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• 1985
  • 1985-10-21 WO PCT/US1985/002039 patent/WO1987002347A1/en not_active Application Discontinuation
  • 1985-10-21 EP EP19850905301 patent/EP0243350A1/de not_active Withdrawn
  • 1985-10-21 JP JP50462185A patent/JPS63501791A/ja active Pending

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