Gas turbines for producing mechanical and electrical power without polluting the atmosphere are fueled by an improved clean fuel gas having a heat of combustion of preferably about 70-100 BTU/SCF. Fuel-gas is produced by the partial oxidation of a hydrocarbonaceous fuel in a free-flow non-catalytic fuel gas generator. Feedstock to the fuel gas generator may include high ash, high sulfur, hydrocarbonaceous fuel. Pollutants are separated from the process stream of fuel gas, and a CO.sub.2 -rich stream is recovered. Optionally, this CO.sub.2 -rich stream may be used either as a portion of the temperature moderator in the gas generator or in a noncatalytic, thermal, reverse water-gas shift reaction with hydrogen in the process fuel gas stream to increase the mole ratio (CO/H.sub.2), or both.The clean fuel gas is burned in the combustion chamber of a gas turbine with a gaseous oxidizing stream which comprises air and a portion of the exhaust flue gas from said power-developing expansion turbine. Preferably, a portion of the exhaust flue gas may be passed through a heat exchanger in indirect heat exchange with the clean flue gas on its way to the gas turbine combustor. A remaining portion of said exhaust flue gas is passed through a heat exchanger in indirect heat exchange with said compressed gaseous oxidizing stream feeding said combustor.