The invention relates to a process for removal of unwanted, in particular acidic gas constituents, for example carbon dioxide and hydrogen sulfide, from a crude synthesis gas by gas scrubbing with a scrubbing medium. According to the invention the flash gases obtained during the decompression of the laden scrubbing medium are supplied to a recompressor in order to recycle these to the crude synthesis gas and thus utilize them materially after the recompression. Alternatively or in addition the flash gases may also be supplied to a decompression turbine to recover refrigeration and mechanical work. If the recompressor and/or the decompression turbine are/is designed to have multiple stages, the flash gases obtained at different pressure levels are preferably supplied to a corresponding pressure level of the recompressor and/or of the decompression turbine.

A method of producing syngas comprising receiving raw syngas from a gasification unit; introducing the raw syngas and water to a syngas scrubber to produce unshifted syngas; introducing a first portion of unshifted syngas to a first cooling unit to produce cooled unshifted syngas and a first aqueous condensate comprising cyanide in an amount of 5-200 ppmw; recycling the first aqueous condensate to the syngas scrubber; introducing a second portion of unshifted syngas to a water gas shift unit to produce shifted syngas; introducing the shifted syngas to a second cooling unit to produce cooled shifted syngas and a second aqueous condensate comprising cyanide in an amount of less than 2.5 ppmw; contacting the cooled shifted syngas with the cooled unshifted syngas to produce modified syngas; and introducing the second aqueous condensate to a sour water stripper to produce stripped water and an acid gas comprising H.sub.2S, CO.sub.2, and ammonia.

A method of producing syngas comprising receiving raw syngas from a gasification unit; introducing the raw syngas and water to a syngas scrubber to produce unshifted syngas; introducing a first portion of unshifted syngas to a first cooling unit to produce cooled unshifted syngas and a first aqueous condensate comprising cyanide in an amount of 5-200 ppmw; recycling the first aqueous condensate to the syngas scrubber; introducing a second portion of unshifted syngas to a water gas shift unit to produce shifted syngas; introducing the shifted syngas to a second cooling unit to produce cooled shifted syngas and a second aqueous condensate comprising cyanide in an amount of less than 2.5 ppmw; contacting the cooled shifted syngas with the cooled unshifted syngas to produce modified syngas; and introducing the second aqueous condensate to a sour water stripper to produce stripped water and an acid gas comprising H.sub.2S, CO.sub.2, and ammonia.

A method of forming a syngas for producing liquid hydrocarbons, the method comprising: providing a feed gas comprising carbon dioxide, hydrogen and compounds of sulfur; providing a carbon-monoxide-enriched feed gas by passing the feed gas to a reverse-water-gas-shift reaction chamber to convert a portion of the carbon dioxide and a portion of the hydrogen to carbon monoxide and water, and to convert at least a portion of the compounds of sulfur to hydrogen sulfide; passing the carbon-monoxide-enriched feed gas to a carbon-dioxide-removal unit to provide the syngas and a carbon-dioxide-enriched stream, the carbon-dioxide-enriched stream comprising carbon dioxide and hydrogen sulfide; providing a purified carbon-dioxide stream by passing the carbon-dioxide-enriched stream to a hydrogen-sulfide-removal unit to remove hydrogen sulfide from the carbon-dioxide-enriched stream; and recycling the purified carbon-dioxide stream into the feed gas.