Recovery of methane from land fill gas
AssigneeAir Products and Chemicals, Inc.
InventorsShivaji Sircar, Ravi Kumar, William R. Koch, John VanSloun
Life of this patent
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Abstract
High purity methane and carbon dioxide are recovered from landfill gas in an integrated multi-column adsorption system having a temperature swing adsorption section (TSA) for pretreatment of the crude landfill gas to remove trace impurities therefrom, the thus cleaned gas being fed to a pressure swing adsorption section (PSA) for bulk separation of CO.sub.2 from methane. Regeneration of the impurity-laden adsorbent bed of the TSA section is carried out using part of the CO.sub.2 product gas recovered from the PSA section which gas is heated to thermal regeneration temperature.
Claims38
In the process for purification and recovery of methane from landfill gas by subjecting such gas to pretreatment for removal of trace impurities therefrom followed by bulk separation of CO.sub.2 from CH.sub.4 from the pretreated gas by selective adsorption, the improvement which comprises;
- effecting such pretreatment in a multi-column temperature swing adsorption section integrated with a subsequent multi-column pressure swing adsorption section in which the separation of CO.sub.2 from CH.sub.4 is carried out, wherein a portion of the separated CO.sub.2 product recovered from the pressure swing adsorption section is employed in regeneration of adsorbent in the temperature swing adsorption section, wherein the time cycle of adsorption and regeneration in said temperature swing adsorption section is independent of that employed in said pressure swing adsorption section, and wherein the pretreatment of the landfill gas comprises the sequence of steps:
- (a) selective adsorption of contained impurities therefrom in an adsorbent bed at super ambient pressure during a predetermined time period while discharging an unadsorbed effluent consisting essentially of CO.sub.2 and CH.sub.4,
- (b) thereafter depressuring said bed to ambient pressure level and at said ambient pressure level,
- (c) thermally regenerating the impurity-laden bed with hot gas obtained by heating a portion of the CO.sub.2 product gas from said pressure swing adsorption section, followed by,
- (d) cooling the bed, and
- (e) restoring the bed to super-ambient adsorption pressure;
- and wherein said bulk separation effected in said pressure swing adsorption section comprises at least the sequence of steps:
- (1) selective adsorption of CO.sub.2 at super-ambient pressure during a predetermined time period while discharging unadsorbed high purity CH.sub.4 effluent as a product,
- (2) depressuring of the column to near-ambient pressure potentially as a CO.sub.2 product, followed by,
- (3) evacuation of said column to sub-atmospheric pressure level thereby removing sorbed CO.sub.2 from said column as a CO.sub.2 product, and
- (4) restoring the column to super ambient pressure by introduction therein of part of the CH.sub.4 produced in step (1).
In the process for purification and recovery of methane from landfill gas by subjecting such gas to pretreatment for removal of trace impurities therefrom followed by bulk separation of CO.sub.2 from CH.sub.4 from the pretreated gas by selective adsorption, the improvement which comprises;
- effecting such pretreatment in a multi-column temperature swing adsorption section integrated with a subsequent multi-column pressure swing adsorption section in which the separation of CO.sub.2 from CH.sub.4 is carried out, wherein a portion of the separated CO.sub.2 product recovered from the pressure swing adsorption section is employed in regeneration of adsorbent in the temperature swing adsorption section, wherein the time cycle of adsorption and regeneration in said temperature swing adsorption section is independent of that employed in said pressure swing adsorption section, and wherein the pretreatment of the landfill gas comprises the sequence of steps:
- (a) selective adsorption of contained impurities therefrom in an adsorbent bed at super ambient pressure during a predetermined time period while discharging an unadsorbed effluent consisting essentially of CO.sub.2 and CH.sub.4,
- (b) thereafter depressuring said bed to ambient pressure level and at said ambient pressure level,
- (c) thermally regenerating the impurity-laden bed with hot gas obtained by heating a portion of the CO.sub.2 product gas from said pressure swing adsorption section, followed by,
- (d) cooling the bed, and
- (e) restoring the bed to super ambient adsorption pressure;
- and wherein said bulk separation effected in said pressure swing adsorption section comprises the sequence of steps:
- (1) selective adsorption of CO.sub.2 at super ambient pressure during a predetermined time period while discharging unadsorbed high purity CH.sub.4 effluent as a product,
- (2) co-current rinsing of the CO.sub.2 /CH.sub.4 -laden column with CO.sub.2 product gas at near feed pressure,
- (3) countercurrent depressuring of the rinsed column to near ambient pressure, followed by,
- (4) evacuation of said column to sub-atmospheric pressure level thereby removing sorbed CO.sub.2 from said column as a high purity CO.sub.2 product, and
- (5) restoring the column to super ambient pressure by countercurrent introduction therein of part of the CH.sub.4 produced in step (1).
In the process for purification and recovery of methane from landfill gas by subjecting such gas to pretreatment for removal of trace impurities therefrom followed by bulk separation of CO.sub.2 from CH.sub.4 from the pretreated gas by selective adsorption, the improvement which comprises;
- effecting such pretreatment in a multi-column temperature swing adsorption section integrated with a subsequent multi-column pressure swing adsorption section in which the separation of CO.sub.2 from CH.sub.4 is carried out, wherein at least a portion of the separated methane-containing CO.sub.2 product recovered from the pressure swing adsorption section is employed in regeneration of adsorbent in the temperature swing adsorption section, wherein the time cycle of adsorption and regeneration in said temperature swing adsorption section is independent of that employed in said pressure swing adsorption section, and wherein the pretreatment of the landfill gas comprises the sequence of steps:
- (a) selective adsorption of contained impurities therefrom in an adsorbent bed at super ambient pressure during a predetermined time period while discharging an unadsorbed effluent consisting essentially of CO.sub.2 and CH.sub.4,
- (b) thereafter depressuring said bed to ambient pressure level and at said ambient pressure level,
- (c) thermally regenerating the impurity-laden bed with hot gas by heating a portion of the methane-containing CO.sub.2 product gas from said pressure swing adsorption section, followed by,
- (d) cooling the bed, and
- (e) restoring the bed to super ambient adsorption pressure;
- and wherein said bulk separation effected in said pressure swing adsorption section comprises the sequence of steps:
- (1) selective adsorption of CO.sub.2 at super ambient pressure during a predetermined time period while discharging unadsorbed high purity CH.sub.4 effluent as a product,
- (2) depressuring of the column to near ambient pressure potentially as a methane-containing CO.sub.2 product, followed by,
- (3) compressing at least a portion of the depressurization gas of step (2) to feed pressure and mixing it with feed to step (1) adsorption,
- (4) evacuation of said column to sub-atmospheric pressure level thereby removing sorbed CO.sub.2 from said column as a methane-containing CO.sub.2 product, and
- (5) restoring the column to super ambient pressure by countercurrent introduction therein of part of the CH.sub.4 produced in step (1).
Dependencies are inferred from the claim text.