PURPOSE: To increase power energy recovery efficiency by producing a fuel gas through chemical reaction at high temperature for effecting heat exchange with a heat exchange medium after removal of dust by means of a hot filtration device, and generating power by means of a high temperature stream of the hot heat exchange medium.

CONSTITUTION: An air separation plant 2 is provided for supplying oxygen stream to a reactor (direct reduction gasification furnace) 4 for producing iron and a fuel gas from iron ore and coal. The fuel gas at a temperature below about 100°C from the reactor 4 is passed through a hot filtration device 6 at a temperature of at least 2000°C, and supplied to a heat exchanger 8 after solid particles are separated and removed from the gas to contact a heat exchange medium (nitrogen or the like) countercurrently and heat the medium to about 50°C. The medium is delivered to an expansion turbine 10 for performance of work, such as driving a downstream power generator 12 forming a part of a power station 14. The fuel gas from the heat exchanger 8 is either separated to produce a pure water gaseous product or used for electric power generation by itself.