NOVELTY - The process comprises generating synthesis gas containing hydrogen, carbon monoxide and methane in a generation unit (5) supplied by a feed gas and a fuel (41), purifying the synthesis gas in a separation apparatus for producing a fluid enriched either in carbon monoxide or in hydrogen and a fluid enriched in methane, pressurizing the fluid enriched in methane after it is mixed with other fluid process and directing a portion of the mixture to the generation unit. The other fluid is hydrogen rich gas derived from separation apparatus.    USE - The process is useful for generating and purifying synthesis gas comprising hydrogen, carbon monoxide and methane.    ADVANTAGE - The process is capable of easily and effectively generating and purifying the synthesis gas with less consumption of energy.    DETAILED DESCRIPTION - The process comprises generating synthesis gas containing hydrogen, carbon monoxide and methane in a generation unit (5) supplied by a feed gas and a fuel (41), purifying the synthesis gas in a separation apparatus for producing a fluid enriched either in carbon monoxide or in hydrogen and a fluid enriched in methane, pressurizing the fluid enriched in methane after it is mixed with other fluid process and directing a portion of the mixture to the generation unit. The other fluid is hydrogen rich gas derived from separation apparatus and a carbon dioxide-rich gas derived from an acid gas removal unit for treating the synthesis gas. The process comprises: purifying the synthesis gas in a cryogenic separation apparatus (17), pressurizing the fluid enriched in methane by pumping a liquid enriched in methane from the separation apparatus and vaporizing a part of the pumped liquid and directing to the generation unit; mixing the fluid enriched in methane with other fluid derived from the apparatus in a downstream of the generation unit for producing a gaseous mixture and compressing the gaseous mixture in a compressor (53, 63) and directing the mixture to the generation unit; and mixing the fluid enriched in methane with the feed gas from the generation unit for producing the gaseous mixture and compressing the gaseous mixture in a compressor and directing the mixture to the generation unit. An INDEPENDENT CLAIM is included for an apparatus for generating and purifying the synthesis gas.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a process for generating and purifying the synthesis gas.    Generation unit (5)    Cryogenic separation apparatus (17)    Pump (21)    Fuel (41)    Compressor. (53, 63)