Abstract: Power generating plant comprising a pressurized fluidized bed combustor (PFBC) (11) in combination with a gas turbine (12,13) and associated compressor (14), is enabled to operate over an extended range of load and to respond rapidly to substantial load changes by arranging for such range and changes to be achievable while maintaining the PFBC at substantially constant temperature and varying, instead, the gas pressure in and mass flow rate through the PFBC. For effecting the required changes, the gas turbine and/or the compressor are provided with variable geometry, in the form of variable inlet or inter-stage guide vanes (34) and/or interstage bypass or blow-down valves (39,40).