NOVELTY - Treating a gaseous mixture comprising hydrogen, carbon dioxide and at least one combustible gas involves separating hydrogen from the gaseous mixture; combusting the combustible gas(es) in the crude carbon dioxide gas in the presence of oxygen to produce heat and a carbon dioxide product gas; and recovering at least a portion of the heat from at least a portion of the carbon dioxide product gas by indirect heat exchange with at least a portion of the separated hydrogen gas to produce warmed hydrogen-containing gas and cooled carbon dioxide product gas.    USE - For use with coal-fired power stations used to produce power.    ADVANTAGE - An improved, lower cost high efficiency method of separating synthesis gases derived from partial oxidation or reforming of carbonaceous or hydrocarbonaceous fuels or biomass into pure H2 and pure CO2 gases, is provided. Emission of harmful components into the atmosphere is reduced or eliminated.    DETAILED DESCRIPTION - Treating a gaseous mixture comprising hydrogen (H2), carbon dioxide (CO2) and at least one combustible gas selected from hydrogen sulfide (H2S), carbon monoxide (CO) and methane (CH4), involves separating H2 from the gaseous mixture to produce a separated H2 gas and a crude CO2 gas comprising the combustible gas(es); combusting at least a portion of the combustible gas(es) in at least a portion of the crude CO2 gas in the presence of oxygen (O2) to produce heat and a CO2 product gas comprising combustion products of the combustible gas(es); and recovering at least a portion of the heat from at least a portion of the CO2 product gas by indirect heat exchange with at least a portion of the separated H2 gas or a gas derived from it to produce warmed H2-containing gas and cooled CO2 product gas. INDEPENDENT CLAIMS are also included for:    (1) method of producing power, comprising partially oxidizing or reforming a fuel selected from carbonaceous fuel, hydrocarbonaceous fuel or biomass fuel, to produce synthesis gas; reacting at least a portion of the CO in the synthesis gas with H2O in a shift conversion reaction to produce a gaseous mixture comprising H2, CO2 and at least one combustible gas selected from H2S, CO or CH4; separating H2 from the gaseous mixture; combusting at least a portion of the combustible gas(es) in an oxyfuel combustion process using an excess of oxidant gas consisting of O2 and, optionally, at least one fuel, to produce heat and a CO2 product gas comprising combustion products of the combustible gas(es); recycling a portion of the CO2 product gas as feed to the oxyfuel combustion process; recovering at least a portion of the heat from at least a portion of the CO2 product gas by indirect heat exchange with at least a portion of the separated H2 gas or a gas derived from it, to produce warmed turbine fuel gas and cooled CO2 product gas; and feeding warmed turbine fuel gas to a gas turbine for power generation;    (2) apparatus for treating a gaseous mixture comprising a separator (238, 250); a combustion reactor (210); heat exchanger (234); and conduits; and    (3) apparatus for producing power.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a method of treating gaseous mixture.    Combustion reactor (210)    Compressors (228, 244)    Heat exchanger (234)    Separators (238, 250)    Multi-bed desiccant drier (256)