Abstract: A plasma melting furnace has a melting chamber having an anode torch and a cathode torch made of graphite and having a electric conductor disposed on the bottom thereof. When the furnace is operated, the anode torch, having an inflow of electrons, which forms an unstable plasma arc is contacted with the electric conductor and is not used, while the cathode torch, having an outflow of electrons, which forms a stable plasma arc, is utilized for heating, whereby the furnace can be stably and continuously operated. Thus, since the cathode torch which is used is not heated so much and the anode torch, which is liable to be heated to a great degree, is not used, the electrode consumption rate can be greatly reduced.

Abstract: A dry sorting machine having a separating function for removing solids of more than a predetermined size from ash and a drying function for drying the ash, and a magnetic sorting machine for removing metals from the dried ash are arranged in a pretreatment route for the ash to be supplied to the furnace. Further, there is provided a drying air pipe for introducing the high-temperature air heat-recovered from exhaust gases discharged from the ash melting furnace into the dry sorting machine. Thus, by the dry sorting machine having the separating and drying functions, simplification of the ash pretreatment process and reduction of the installation space can be achieved.