Abstract: A method of heating process streams fed to a boiler incorporating an oxygen transport membrane device that includes an oxygen-containing stream and a boiler feed water stream. The membrane device separates oxygen to support combustion of a fuel and generate heat to raise the steam. Heat is recovered and process streams are heated by separately heating portions of the oxygen-containing stream and the boiler feed water stream with a retentate stream produced from the oxygen separation and a flue gas stream generated from the combustion. The flow rate of the portion of the oxygen-containing stream heated by the retentate stream is greater than that heated by the flue gas stream to help minimize heat transfer area and thus, fabrication costs. Also, water is condensed from the flue gas stream during the heat exchange involved in the heat recovery to increase thermodynamic efficiency.