NOVELTY - Producing purified synthesis gas stream from feed synthesis gas stream comprising hydrogen sulfide (H2S), hydrogen cyanide (HCN) and/or carbonyl sulfide (COS) involves removing HCN and/or COS by contacting the stream with a catalyst in a HCN/COS reactor (2) in the presence of steam/water; converting H2S to elemental sulfur, by contacting the stream with aqueous reactant solution containing solubilized iron (Fe)(III) chelate of organic acid at a temperature below melting point of sulfur and at sufficient solution to gas ratio; and removing carbon dioxide from the stream.    USE - For producing a purified synthesis gas stream useful for producing electricity; in catalytic processes selected from Fischer-Tropsch synthesis, methanol synthesis, dimethyl ether synthesis, acetic acid synthesis, ammonia synthesis, methanation to make substitute natural gas (SNG) and processes involving carbonylation or hydroformylation reactions (claimed); as a fuel, in gas turbines; in catalytical chemical conversions; and in an integrated gasification combined cycle.    ADVANTAGE - The process enables removal of hydrogen sulfide, carbonyl sulfide and/or hydrogen cyanide to low levels. The purified synthesis gas, because of its low level of contaminants, is suitable for use as fuel, suitably in gas turbines, or for use in catalytical chemical conversions. The purified synthesis gas is especially suitable for use in an integrated gasification combined cycle (IGCC). The process is economical because H2S in the synthesis gas stream is converted directly into elemental sulfur. The synthesis gas stream depleted in H2S has very low concentrations of H2S, enabling the use of an inexpensive non-selective acid gas removal unit to remove remaining H2S as well as CO2. Moreover, the process reduces or even eliminates the need for a separate source of hydrogen, from an external supply. Thus, the carbonaceous fuel feedstock is able to provide a further reactant required in the overall process of biomass or coal to liquid products conversion, increasing the self- sufficiency of the overall process. The process is a very selective process that does not require any tail gas treatment, and it requires only one reactor. The pressurized gas stream enriched in carbon dioxide is suitable for enhanced oil recovery with less compression equipment needed.    DETAILED DESCRIPTION - Producing a purified synthesis gas stream from a feed synthesis gas stream comprising besides the main constituents carbon monoxide and hydrogen also hydrogen sulfide (H2S), hydrogen cyanide (HCN) and/or carbonyl sulfide (COS), involves: a) removing HCN and/or COS by contacting the feed synthesis gas stream with a catalyst in a HCN/COS reactor (2) in the presence of steam/water, to obtain a synthesis gas stream depleted in HCN and/or in COS; b) converting hydrogen sulfide in the synthesis gas stream depleted in HCN and/or in COS to elemental sulfur, by contacting the synthesis gas stream with an aqueous reactant solution containing solubilized Fe(III) chelate of an organic acid, at a temperature below the melting point of sulfur, and at a sufficient solution to gas ratio and conditions effective to convert H2S to sulfur and inhibit sulfur deposition, to obtain a synthesis gas stream depleted in hydrogen sulfide; and c) removing carbon dioxide from the synthesis gas stream depleted in hydrogen sulfide, to obtain the purified synthesis gas stream and a gas stream enriched in carbon dioxide (CO2).    DESCRIPTION OF DRAWING(S) - The figure shows a view of the process for producing the purified synthesis gas stream.    Gasification unit (1)    Shift unit (2)    Sulfur recovery unit (3)    Acid gas removal unit (4)