Cryogenic production of ammonia synthesis gas
AssigneeExxon Research & Engineering Co.
InventorDaniel Traficante
Life of this patent
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Abstract
An improved cryogenic separation process is provided for forming a substantially CO-free and lower hydrocarbon-free hydrogen-rich gas, suitable for use in producing an ammonia synthesis gas, from a hydrogen-containing gas stream also containing carbon monoxide and lower hydrocarbon impurities, wherein the hydrogen containing gas is subject to a two-stage autorefrigerated cryogenic flash treatment to remove concentrated methane-containing and carbon monoxide-containing streams, and the thus-purified hydrogen gas is passed to a nitrogen wash tower in counter-current contact with liquid nitrogen to form the desired hydrogen-rich product streams as an overheads from the wash tower.
Claims18
A process for producing a hydrogen-rich gas substantially free of carbon monoxide and methane which comprises:
- (a) cooling a hydrogen-containing raw gas stream, containing hydrogen as a main constituent together with carbon monoxide and methane, in a first heat exchange zone to condense at least a major portion of said methane;
- (b) recovering and expanding said methane-containing condensate and returning the resulting cooled methane-containing vapor and liquid to said first heat exchange zone to cool additional quantities of said raw gas stream;
- (c) further cooling said cooled raw gas stream, now depleted in methane, in a second heat exchange zone to condense at least a major portion of said carbon monoxide therefrom and to form a treated hydrogen gas stream containing low levels of carbon monoxide and methane;
- (d) recovering and expanding said carbon monoxide-containing condensate and serially passing the resulting cooled carbon monoxide gas and liquid to said second heat exchange zone and thence to said first heat exchange zone to provide at least a portion of the cooling medium passed to said zones;
- (e) contacting said treated hydrogen gas stream in a nitrogen wash tower with liquid nitrogen to remove essentially all of said remaining carbon monoxide and methane therefrom, thereby forming a liquid bottoms product containing nitrogen and said removed carbon monoxide and methane impurities, and an overhead product comprising said hydrogen-rich gas containing hydrogen and nitrogen and substantially free of carbon monoxide and methane;
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- (f) expanding said liquids bottoms product and passing the resulting cooled vapor and liquid as cooling medium to a third heat exchange zone to which is also fed a nitrogen gas feedstream, wherein said nitrogen in said feedstream is liquefied to form said liquid nitrogen for use as feed to said nitrogen wash tower.
A process for producing an ammonia synthesis gas substantially free of carbon monoxide and methane which comprises:
- (a) cooling a hydrogen-containing raw gas stream, containing from about 50 to 70 volume percent hydrogen, together with from about 15 to 30 volume percent carbon monoxide and from about 1 to 25 volume percent methane, in a first heat exchange zone to condense at least a major portion of said methane;
- (b) recovering and expanding said methane-containing condensate and returning the resulting cooled methane-containing vapor and liquid to said first heat exchange zone to cool additional quantities of said raw gas stream;
- (c) further cooling said cooled raw gas stream, now depleted in methane, in a second heat exchange zone to condense at least a major portion of said carbon monoxide therefrom and to form a treated hydrogen gas stream containing low levels of carbon monoxide and methane;
- (d) recovering and expanding said carbon monoxide-containing condensate and serially passing the resulting cooled carbon monoxide gas and liquid to said second heat exchange zone and thence to said first heat exchange zone to provide at least a portion of the cooling medium passed to said zone;
- (e) contacting said treated hydrogen gas stream in a nitrogen wash tower with liquid nitrogen to remove essentially all of said remaining carbon monoxide and methane therefrom, thereby forming a liquid bottoms product containing nitrogen and said removed carbon monoxide and methane impurities, and an overhead product comprising a hydrogen-rich gas containing hydrogen and nitrogen and substantially free of carbon monoxide and methane;
- (f) expanding said liquids bottoms product and passing the resulting cooled vapor and liquid as cooling medium to a third heat exchange zone to which is also fed a nitrogen gas feedstream, wherein said nitrogen in said feedstream is liquefied to form said liquid nitrogen for use as feed to said nitrogen wash tower;
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- (g) admixing said hydrogen-rich gas product withdrawn from step (e) with additional quantities of nitrogen gas to form said ammonia synthesis gas.
Dependencies are inferred from the claim text.