A material processing apparatus includes a casing having a top and bottom and a plurality of sides defining a pyrolysis chamber for receiving and pyrolyzing feed materials therein into fluid materials and a mass of refractory material disposed upon the bottom of the casing and spaced below the top thereof and extending between its sides. The refractory mass includes an upper surface defining a bottom of the pyrolysis chamber and having an end spaced from a first one of the casing sides to define an ash residue collection cavity therebetween. The apparatus also includes a system of tunnels defined within the refractory mass being spaced below the upper surface thereof. The system of tunnels includes an inlet defined in the refractory mass at the end thereof and below the upper surface thereof and in communication with the cavity for receiving a flow of materials from the pyrolysis chamber into the system of tunnels and an outlet defined in a second one of the sides of the casing for discharging the flow of materials from the system of tunnels. The apparatus also includes elongated heater units mounted to sides of the casing and extending into and axially along selected ones of the tunnels in the system thereof.