Abstract: A dual fuel gasification-combustion system (44)with multi-stage fluidised bed gasifier (32)for complete carbon conversion of the input fuel using single or combineable oxidants and sulphur sorbents to produce a clean fuel gas and combustion gas at any pressure for use with boilers gas turbines,or, combined cycle gas-steam turbines.The application (44) for combined cycle power includes a multi-stage gasifier (32)with design number of stages to maximise carbon conversion of input liquid or solid fuels being connected to a gas turbine (53)via gas cleaners (45),(47)and afterburner (46)to produce a clean combustion gas entering the gas turbine. The system has coolant conduits (6) in the gasifier and in the afterburner at (50) and generated steam from the boiler (54) for the steam turbine (51).