Refrigeration – Cryogenic treatment of gas or gas mixture – Separation of gas mixture
Reexamination Certificate
2000-06-02
2001-08-07
Capossela, Ronald (Department: 3744)
Refrigeration
Cryogenic treatment of gas or gas mixture
Separation of gas mixture
C062S920000, C062S931000
Reexamination Certificate
active
06269657
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to a process and apparatus for separation of hydrogen and carbon monoxide from gaseous mixtures thereof. It has particular, but not exclusive, application to the recovery of hydrogen and carbon monoxide from synthesis gas.
BACKGROUND OF THE INVENTION
Carbon monoxide is usually obtained by separation from synthesis gas produced by catalytic conversion or partial oxidation of natural gas, oils or other hydrocarbon feedstock. Synthesis gas consists primarily of hydrogen and carbon monoxide and, depending on the level of purity, typically also contains small amounts of inter alia methane and nitrogen. It is well known to separate carbon monoxide from synthesis gas by a cryogenic separation process in which carbon monoxide is removed by a low temperature scrubbing step using liquid methane in a wash column to provide a CO-loaded methane liquid containing some, typically 2 to 4%, hydrogen. Residual hydrogen is removed from the CO-loaded methane liquid in, for example, a stripping column or flash separator to meet the required carbon monoxide product specification and the resultant hydrogen-stripped CO-loaded methane liquid is separated into a gaseous carbon monoxide product and liquid methane in a separation column. The bulk of the liquid methane is recycled to provide the methane wash liquid and a portion of the carbon monoxide product can be recycled to provide a heat pump stream.
The CO-loaded methane liquid can be withdrawn entirely from the sump of the methane wash column, in which case it is admixed with condensate from the feed gas.
However, the condensate usually has a much higher CO concentration (typically 60 to 70% CO) than the CO-loaded methane (typically 20 to 30% CO), which higher concentration is diluted by admixture with the CO-loaded methane thereby decreasing the efficiency of the subsequent separation of CO from methane. In order to mitigate this reduction in potential efficiency, the CO-loaded methane can be separately withdrawn from a location above the synthesis gas feed and fed to a stripping column at a higher location than the feed gas condensate.
European Patent Publication No. 0895961A discloses the separation of synthesis gas, or other gaseous mixtures of hydrogen and carbon monoxide, by a process in which the CO-loaded methane and feed gas condensate are separately fed from the methane wash column to vertically spaced locations of a stripping column. The stripping column is refluxed with a methane-rich scrubbing liquid withdrawn from an intermediate location of the methane wash column. Preferably, the hydrogen-stripped CO-loaded methane liquid is split into two substreams. One substream is subcooled and the subcooled liquid introduced into the separation column. The other substream is at least partially vaporized and introduced into the separation column at a location below that of the subcooled substream.
U.S. Pat. No. 5133793 discloses the separation of synthesis gas, or other gaseous mixtures of hydrogen and carbon monoxide, by a process in which feed gas condensate is separated from the feed prior to the methane wash column. Only the vapor portion from that separation is fed to the wash column. The condensate is vaporized and fed to the stripping column at a location below that of the sump liquid from the wash column. The hydrogen-stripped CO-loaded methane liquid is subcooled and split into three substreams. One substream is introduced, at about its bulb temperature, at upper location of the separation column. Another substream is vaporized and introduced, at about its dew point, at a lower location of the separation column. The third substream is vaporized and introduced, at a temperature intermediate that of the other two substreams, at an intermediate location of the separation column.
Although the feeding of feed gas condensate to a stripping column separately from the CO-loaded methane does increase the efficiency with which hydrogen is removed in that column, it does not obviate the loss in potential efficiency in reduction of the CO concentration of the condensate on admixture with the CO-loaded methane. However, the necessity of this loss has been accepted in the art.
It is an object of the present invention to improve the efficiency of separation of carbon monoxide from a mixture with hydrogen. This is achieved by reducing the extent to which the CO concentration in the feed gas condensate is diluted prior to the separation of CO and methane.
SUMMARY OF THE INVENTION
The present invention provides an improvement in a process for separating hydrogen and carbon monoxide from a condensate-containing gaseous mixture thereof in which the gaseous mixture, or a vapor portion from phase separation thereof, is scrubbed with a liquid methane wash stream in a methane wash column to provide a gaseous hydrogen product stream and a liquid CO-loaded methane stream. This CO-loaded methane stream is separated into a gaseous hydrogen-rich stream and a liquid CO/methane stream in a first stripping column and the resulting CO/methane stream is separated into a gaseous carbon monoxide stream and a liquid methane stream in a separation column. The improvement consists in that feed gas condensate from the methane wash column, or from the phase separation, is separated into a second gaseous hydrogen-enriched stream and another (“second”) liquid CO/methane stream in a second stripping column or a flash separator; the second gaseous hydrogen-enriched stream is fed to the first stripping column; and the second liquid CO/methane stream is fed to the separation column.
The invention also provides an improved apparatus for separating hydrogen and carbon monoxide from a condensate-containing gaseous mixture. The apparatus comprises a methane wash column; means for feeding the gaseous mixture to the methane wash column and optionally including phase separation means for removing a feed gas condensate from the gaseous mixture; a first stripping column; a carbon monoxide/methane separation column; means for feeding CO-loaded methane from the methane wash column to the stripping column; means for feeding liquid CO/methane from the stripping column to the separation column; and means for recycling liquid methane from the separation column to the methane wash column. The improvement consists in that the apparatus further comprises second stripping column or a flash separator; means for feeding feed gas condensate from the methane wash column, or from the phase separation means, to the second stripping column or flash separator;
means for feeding a second gaseous hydrogen-enriched stream from the second stripping column or flash separator to the first stripping column; and means for feeding a second liquid CO/methane stream from the second stripping column or flash separator to the separation column.
REFERENCES:
patent: 4478621 (1984-10-01), Fabian
patent: 4888035 (1989-12-01), Bauer
patent: 5133793 (1992-07-01), Billy
patent: 5295356 (1994-03-01), Billy
patent: 0895961 (1999-02-01), None
Air Products and Chemicals Inc.
Capossela Ronald
Chase Geoffrey L.
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