A waste heat recovery system in which hot waste fluids, such as flue gasses, pass through a fluid heat exchanger configured to transfer energy in the form of heat to a heat transfer liquid, preferably molten salt. The energy in the molten salt is used to generate useable power such as electrical energy. The waste gas heat recovery system is especially adapted for use with batch processes, such as steelmaking and copper converting, and allows continuous or substantially continuous power production.