NOVELTY - The process comprises subjecting a part of gas stream comprising a syngas to a treatment, where the hydrogen content of the syngas is increased, subjecting a part of the syngas to a water gas shift reaction in which carbon monoxide and steam react to form carbon dioxide and hydrogen, subjecting a part of the gas mixture to a treatment for removing hydrogen sulfide to obtain a hydrogen sulfide-depleted gas mixture, and subjecting all or a part of the syngas to a hydrolysis treatment for removing contaminants including hydrogen cyanide and carbonyl sulfide.    USE - The process is useful for removing contaminants including sulfur compounds from a gas stream, which is useful in a synthesis process for preparing hydrogen, a hydrocarbon product or a chemical product (claimed) and useful for generating electricity via a gas turbine fired on the synthesis gas.    ADVANTAGE - The process is capable of energy-efficiently, simply and economically removing the contaminants from the gas stream in an environmental friendly manner.    DETAILED DESCRIPTION - The process comprises subjecting a part of gas stream comprising a syngas to a treatment, where the hydrogen content of the syngas is increased, subjecting a part of the syngas to a water gas shift reaction in which carbon monoxide and steam react to form carbon dioxide and hydrogen, subjecting a part of the gas mixture to a treatment for removing hydrogen sulfide to obtain a hydrogen sulfide-depleted gas mixture, subjecting all or a part of the syngas to a hydrolysis treatment for removing contaminants including hydrogen cyanide and carbonyl sulfide to obtain a contaminants-depleted syngas, contacting a part of the hydrogen sulfide-depleted gas mixture and the contaminants-depleted syngas with an absorption liquid that absorbs sulfur compounds to obtain a sulfur compounds-enriched absorption liquid and a sulfur compounds-depleted gas stream, passing a part of the sulfur compounds-depleted gas streams through a bed of a solid adsorbent for adsorbing contaminants including metal carbonyls to obtain a metal carbonyls-depleted gas stream, and passing a part of the metal carbonyls-depleted gas stream through a bed of a solid adsorbent comprising copper and zinc oxide for the further removal of sulfur compounds and to obtain a sulfur compounds-depleted gas stream. The water gas shift reaction is carried out at a temperature of 200-600 degrees C and a pressure of 15-100 bar, where the steam/carbon monoxide molar ratio is 0.6-3. The absorption liquid comprises water, a physical solvent and an amine. The hydrolysis treatment is carried out in the presence of a steam-resistant hydrolysis catalyst at a temperature of 150-250 degrees C and a pressure of 15-100 bar. An INDEPENDENT CLAIM is included for a synthesis process for preparing hydrogen, a hydrocarbon product or a chemical product.    DESCRIPTION OF DRAWING(S) - The figure shows a flow chart of a process for removing contaminants from a gas stream.    Via line (1, 3, 4, 6, 8, 9, 11, 12, 13, 15, 17)    Water quenching unit. (2, 5, 7, 10, 14, 16)