A superheater in a power plant that superheats steam to operation conditions exceeding an operating limit of an associated steam-producing boiler. The superheater combusts oxygen and fuel with cooled recycled combustion gas to produce a CO2-rich combustion product gas stream at a fixed temperature. The combustion gas is used as the heat transfer fluid in the superheater's heat exchanger. The CO2-rich flue gas stream allows for efficient capture of substantially pure CO2. The superheater may be retrofitted to an existing power plant as a separate component, external to the boiler. The plant may thus have its electrical power output increased, while its overall CO2 emissions per nit of generated power is decreased, even when inexpensive, readily-available fossil fuels are used as the primary fuel for filing the boiler and/or the superheater.