PURPOSE: To supply superheated steam with a high-thermal efficiency by a method wherein an intermittent flow of saturated steam generated from a boiler is turned into a continuous flow of saturated steam, which fluctuates in flow rate and pressure, through an accumulator, and the saturated steam is converted to superheated steam by a gas turbine waste heat recovery heat exchanger.

CONSTITUTION: A high-temperature gas intermittently discharged from a metal processing furnace 1 is sent to a waste gas treatment apparatus 2 where saturated steam is generated, and the saturated steam enters an accumulator 5 after passing through a steam drum 3. When the valve-lift of an inlet pressure regulating valve of a steam turbine 12 is kept constant, the steam discharged from the accumulator 5 enters a gas turbine waste heat recovery heat exchanger 6 with its flow rate fluctuating in proportion to the internal pressure of the accumulator 5, and is turned in to superheated steam which drives the steam turbine 12 to generate power. Thus, as the waste heat of the gas turbine 7 is utilized, the thermal efficiency is improved.