413 are exposed to the high temperature conditions existing in the primary oxidation chamber 400 it is possible to utilize conventional low temperature steel pipe to form such flutes 413 by providing a blower or other means not shown to circulate a coolant such as air or water through the pipes when the primary oxidation chamber 400 is operational to thereby avoid the need for using expensive special high temperature alloys in the construction of such flutes 413 the gaseous effluent leaving the primary oxidation chamber 400 through the insulated exit duct 412 passes into the secondary oxidation chamber 600 the secondary oxidation chamber 600 is defined by an insulated wall 601 and in the preferred embodiment the insulated wall 601 is arranged to define a secondary oxidation chamber which is in the form of a cylinder whose longitudinal axis is coextensive with the longitudinal axis of the insulated exit duct 412 of the primary oxidation chamber 400 a secondary oxidant is added to the secondary oxidation chamber 600 to burn or completely oxidize gaseous materials flowing into the secondary oxidation chamber through the insulated exit duct 412 from the primary oxidation chamber 400 again ambient air is satisfactory for use as the secondary oxidant and may be provided to the secondary oxidation chamber 600 by means of a.