A fire tube boiler system including a plurality of oxygen transport reactors that heats a working fluid. Each oxygen transport reactor has a first inner tube with an ion transport membrane that receives air from a first supply line, extracts oxygen from the air, and evacuate oxygen depleted air through a first exhaust line, a second inner tube that surrounds the first inner tube that receives the oxygen from the ion transport membrane and a mixture of fuel and carbon dioxide from a second supply line and produces a oxy-combustion, and an peripheral tube that surrounds the second inner tube and evacuates the exhaust gases produced by the oxy-combustion and transfer heat from exhaust gases to the working fluid and the ion transport membrane.