from the arc heaters merge and project into the housing application_number US 60357975 A description in fig1 a polyphase arc heater system is generally indicated at 5 and it comprises a housing 7 a plurality such as three of arc heaters 9 and a reactor 11 the housing 7 is preferably a cylindrical member forming a plenum chamber 13 and consisting of double walls 15 17 forming a water coolant compartment 19 therebetween the upper end of the housing 7 includes an inlet 21 through which solid particulate material 23 may be introduced into the chamber 13 for example where the arm heater system is used for the reduction of an ore to the elemental metal such as fe 2 o 3 to iron the solid particulate material 23 comprises iron ore the lower end of the housing 7 is open and communicates with the interior of the reactor 11 although three arc heaters 9 are disclosed it is understood that two or more arc heaters may be employed for the purpose of this invention the arc heaters 9 are similar in construction and operation to that disclosed in u s pat no 3 705 975 entitled 34 self stabilizing arc heater apparatus 34 of which the inventors are charles b wolf and maurice g fey because of the full disclosure in that patent the description of the arc heaters 9 is limited herein to the basic structure and operation each of the arc heaters 9 is a single phase self stabilizing ac device capable of power levels of up to about 3500 kilowatts or up to 10 000 kilowatts for a three phase plant installation for the practice of this invention it is preferred that three arc heaters be provided one for.