Abstract: A multiple pressure boiler is disclosed having a plurality of boiler sections, each section operating at a successively lower temperature and lower pressure than the preceding section. The intake air for the firebox is heated by the flue gases, then superheated by the steam, to provide heated air for combustion, and the steam from the highest pressure section is superheated by the flue gases prior to its being used in a steam turbine or other steam engine. The fuel for the firebox is heated initially by being used as the coolant for a steam condenser, and is superheated by superheated steam from the heat exchanger. It is contemplated that a sufficient quantity of heat will be removed from the flue gases that the solids will precipitate out, and the gas will be substantially at ambient temperature.