Methane recovery process
AssigneeL'Air Liquide Socie
InventorsKenneth J. Wascheck, Charles L. Anderson
Life of this patent
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Abstract
A system and a process for recovering high concentrations of methane from crude natural gas and solid waste landfill exhaust gas uses a sequential combination of a pressure swing adsorber unit operation to remove volatile organic compounds from the crude feed gas mixture followed by a membrane separation unit operation. The membrane separation uses a membrane which is selectively gas permeable to reject transmission of methane and thus to produce a permeate depleted in methane relative to the feed mixture. The permeate is also free of volatile organic compounds and is recycled to the pressure swing adsorber unit operation to regenerate saturated adsorbers.
Claims13
A system for recovering methane from a feed mixture comprising methane, carbon dioxide and volatile organic compounds, the system comprising,
- a pressure swing adsorption unit having a bed of adsorbent particles and operative to adsorb volatile organic compounds from the feed mixture onto the particles so as to produce an intermediate mixture of gases having composition reduced in volatile organic compounds relative to the feed mixture, and operative to desorb the volatile organic compounds from particles into a regenerating gas,
- a primary gas separation module comprising a membrane which is selectively gas permeable to methane relative to carbon dioxide, a feed-retentate chamber within the module on a first side of the membrane, and a permeate chamber within the module on a second side of the membrane, in which the feed-retentate chamber is in fluid communication with the bed of the pressure swing adsorption unit in a manner adapted to permit transfer of the intermediate mixture into the feed-retentate chamber in contact with the first side of the membrane,
- a retentate discharge line in fluid communication with the feed-retentate chamber adapted to withdraw from the module a retentate gas having composition enriched in methane relative to the intermediate mixture,
- a permeate discharge line in fluid communication between the permeate chamber of the module and the bed of the pressure swing adsorption unit and which is operative to transfer a permeate gas having composition depleted in methane relative to the intermediate mixture and which permeate gas is adapted to receive desorbed volatile organic compounds from the particles of the bed to form a spent regenerating gas, and
- a thermal oxidizing unit in fluid communication with the pressure swing adsorption unit which is operative to destroy the volatile organic compounds in the spent regenerating gas and to produce a vent gas having composition substantially free of volatile organic compounds.
A process for separating methane from a feed mixture comprising methane, carbon dioxide and volatile organic compounds that utilizes a pressure swing adsorption unit operation to remove the volatile organic compounds from the feed mixture to form an intermediate mixture and a selectively gas permeable membrane to separate methane from the intermediate mixture and thereby produce a permeate gas having composition depleted in methane relative to the intermediate mixture, in which the improvement comprises regenerating the pressure swing adsorption units by conducting the permeate gas through the pressure swing adsorption units which have adsorbed a preselected amount of the volatile organic compounds.
A process for separating methane from a feed mixture comprising methane, carbon dioxide and volatile organic compounds comprising the steps of:
- (A) providing a plurality of pressure swing adsorption units each having a bed of adsorbent particles operative to reversibly adsorb the volatile organic compounds from the feed mixture onto the particles,
- (B) charging the feed mixture into an active pressure swing adsorption unit and contacting the feed mixture with the adsorbent particles under operating conditions including pressure and temperature to cause the volatile organic compounds to adsorb onto the particles,
- (C) withdrawing from the active pressure swing adsorption unit an intermediate mixture having composition reduced in volatile organic compounds relative to the feed mixture,
- (D) when the bed of adsorbent particles in the active pressure swing adsorbent unit has adsorbed a preselected amount of volatile organic compounds, stopping steps (B) and (C) thereby deactivating the pressure swing adsorbent unit,
- (E) providing a primary gas separation module comprising a membrane which is selectively gas permeable to methane relative to carbon dioxide, a feed-retentate chamber within the module on a first side of the membrane, and a permeate chamber within the module on a second side of the membrane,
- (F) introducing the intermediate mixture into the feed-retentate chamber of the primary module in contact with the membrane and causing the intermediate mixture to selectively permeate through the membrane into the permeate chamber,
- (G) removing from the feed-retentate chamber of the primary module a retentate gas having composition enriched in methane relative to the intermediate mixture,
- (H) removing from the permeate chamber of the primary module a permeate gas having composition reduced in concentration of methane relative to the intermediate mixture,
- (I) conducting the permeate gas through the bed of adsorbent particles in at least one of the deactivated pressure swing adsorption units under operating conditions including pressure, temperature and duration effective to desorb volatile organic compounds from the bed to form a spent regenerating gas within the deactivated pressure swing adsorption unit,
- (J) withdrawing the spent regenerating gas from the deactivated pressure swing adsorption unit,
- (K) when the bed of particles in the deactivated pressure swing adsorption unit attains a loading inventory below a pre-selected value of parts by weight volatile organic compounds per 100 parts by weight adsorbent particles, stopping steps (I) and (J) thereby activating the deactivated pressure swing adsorption unit.
Dependencies are inferred from the claim text.