Guiding into the steam from the main air inlet pipe, divided into two branches through the main air inlet valve, one is for heating, another is for steaming. Both two branches have installed steam filter and magnetic valve, heating the branch lined with the air inlet pipe of the heater, the air outlet pipe lined with the water returned pipeline. The water returned pipeline installed steam trap and bypass valve, cut stream by the steam trap, so that the condensate water could pass through.