Method and apparatus for separating a synthesis gas

A method for separating a synthesis gas containing carbon monoxide and hydrogen wherein:

• i) compressing a synthesis gas flow originating from a synthesis gas source in a compressor;
• ii) purifying the compressed synthesis gas in a purification unit to remove water and/or carbon dioxide;
• iii) cooling the compressed purified synthesis gas flow;
• iv) separating the cooled synthesis gas flow by a separation process selected from the group consisting of scrubbing, distillation at a cryogenic temperature, adsorption in a separation unit, and combinations thereof;
• and
• v) producing at least the following three gases in the separation unit:
• a carbon monoxide-enriched gas, a hydrogen-enriched gas, a residual gas containing carbon monoxide and hydrogen which contains less carbon monoxide than the carbon monoxide-enriched gas and less hydrogen than the hydrogen-enriched gas,
• wherein only if the synthesis gas flow passed to the compressor is below a threshold or zero, at least a portion of at least two the gases selected from the group consisting of the carbon monoxide-enriched gas, the hydrogen-enriched gas, the residual gas, and combinations thereof, are introduced at a location downstream of the source and upstream of the purification unit.

An apparatus for separating a synthesis gas containing carbon monoxide and hydrogen comprising:

• a compressor configured to compress a synthesis gas flow originating from a source of synthesis gas;
• a purification unit configured to remove water and/or carbon dioxide from the compressed synthesis gas;
• means for cooling the flow of compressed purified synthesis gas;
• a unit configured to separate the cooled synthesis gas flow via a process selected from the group consisting of scrubbing, distillation at a cryogenic temperature, an adsorption unit, and combinations thereof;
• means for producing at least the following three gases from the separation unit:
• a carbon monoxide-enriched gas, a hydrogen-enriched gas, a residual gas containing carbon monoxide and hydrogen which contains less carbon monoxide than the carbon monoxide-enriched gas and less hydrogen than the hydrogen-enriched gas;
• means for measuring a flow rate of the synthesis gas passed to the compressor;
• means for passing at least a portion of at least two of the gases selected from the group consisting of the carbon monoxide-enriched gas, the hydrogen-enriched gas, the residual gas, and combinations thereof, downstream of the source and upstream of the purification unit;
• and
• means for initiating the return of at least a portion of the at least two gases as claimed in the flow of synthesis gas originating from the source upstream of the compressor.