An aeration air inlet of the feeder 5-1 is connected with a purified nitrogen gas main pipe; a feed outlet of the feeder 5-1 is connected with a feed inlet of the bed body 5-2 through a pipeline; a gas inlet of the bed body 5-2 is connected with a gas outlet of the gas heater 5-4 through a pipeline; a gas inlet of the gas heater is connected with a gas outlet of the second cyclone separator 7-3 and a gas outlet of the gas purifier 5-5 through pipelines; a combustion air inlet of the gas heater 5-4 is connected with a compressed air main pipe; a fuel inlet of the gas heater 5-4 is connected with a fuel main pipe; a gas inlet of the gas purifier 5-5 is connected with a reducing gas main pipe; a feed outlet of the bed body 5-2 is connected with a feed inlet of the discharger 5-3 through a pipeline; an aeration air inlet of the discharger 5-3 is connected with the purified nitrogen gas main pipe; a feed outlet of the discharger 5-3 is connected with a feed inlet of the venturi cooler 7-1 through a pipeline; a gas outlet of the bed body 5-2 is connected with a gas inlet of the first cyclone separator 5-6 through a pipeline; a feed outlet of the first cyclone separator 5-6 is connected with the feed inlet of the discharger 5-3 through a pipeline; and a gas outlet of the first cyclone separator 5-6 is connected with a gas inlet of the combustion chamber 6 through a pipeline.

A combustion air inlet of the combustion chamber 6 is connected with the compressed air main pipe; and the gas outlet of the combustion chamber 6 is connected with the gas inlet of the venturi preheater through a pipeline.