Development and experimental testing of a porous ceramic wall to improve the thermal performance of steel billet reheating furnaces

This paper describes the development and subsequent experimental testing of a porous ceramic wall which was employed to enhance radiative heat transfer in a gas fired, billet reheating furnace. The system was fired by a recuperative burner and the porous wall, which was constructed from zirconia panels, was located in the end wall of the furnace upstream of this burner. The passage of the flue gases results in the transfer of sensible heat energy to the porous ceramic and a substantial proportion of this recovered energy is reradiated back into the furnace chamber and hence to the load or charge. The size and positioning of the porous wall was carefully selected using mathematical models and small scale laboratory tests in order to ensure high levels of radiation enhancement, low resistance to flow and acceptable flow uniformity through the wall. Furnace tests demonstrated that the porous wall can provide effective heat recovery from the exhaust gases. This has resulted in significant enhancement in thermal radiation to the test billets and consequent energy savings of up to 22%. The time to heat the billets from cold to a specified temperature was reduced and the temperature uniformity of the heated billets was improved.