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 pusher mechanism mounted to and extending through a second one of the casing sides opposite from the first one side. The pusher mechanism is operable to engage and transport residue of materials received on the upper surface of said refractory mass and being pyrolyzed in the chamber across the upper surface of the refractory mass toward the collection cavity. Also, an arrangement for monitoring the position of the pusher mechanism is included in the apparatus.