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Show CATALYTIC RADIANT TUBE FOR INDUSTRIAL PROCESS HEATING APPLICATIONS John L. Lannutti, Richard J. Schreiber Alzeta Corporation Santa Clara, California, USA ABSTRACT This paper describes research on an innovative industrial process heating concept using catalytic radiant tubes. The gas-fired radiant tube concept employs a combustion catalyst applied to the inside surface of a ceramic tube. A preheated, combustible mixture of gas and air passing through the tube burns catalytically on the tube surface. Some of the heat generated conducts through the wall and is transmitted by radiation from the outside surface to the heat sink. Advantages over existing gasfired radiant tubes include more uniform tube heating and low NOx emissions. During this project, silicon carbide tubes were catalyzed with platinum and metal oxide catalysts and operated in a laboratory combustion test apparatus. The results were encouraging. A tube temperature of 11000C was achie~ed, and heat flux (47.3 to 94.6 kW/m ) was comparable to that of electric elements. NOx concentration was negligible. The tube material did not experience thermal shock. Catalyst stability was the limiting factor. Future work will concentrate on developing a better catalyst and catalyst coating method which will then lead to stable combustion operation. Following the identification of a reliable catalyst, a prototype furnace using the radiant catalytic tubes will be built and tested. When commercialized, this concept could be used in place of the currently popular electric resistance elements. 29 Michael A. Lukasiewicz Gas Research Institute Chicago, Illinois, USA MANY INDUSTRIAL PROCESS HEATING FURNACES employ electric resistance elements as sources of radiant heat. These elements provide the user with many desirable operating characteristics, including indirect heating (that is, the workpiece is not exposed to combustion products), high temperatures (1IOOoC and above) and precise temperature control. Currently, a gas-fired indirect heating system with all of the above attributes does not exist. The need for such a system is evident, because competing gas-fired equipment will protect existing gas markets -- primarily heat treating -- and open up new areas for natural gas utilization in processes operating above 11000C (20000F). The radiant tube concept described in this paper has the potential for meeting these system needs. DESCRIPTION OF CONCEPT This gas-fired radiant tube concept employs high temperature heterogeneous catalytic combustion. In this process, combustion is promoted by a catalyst-coated surface. The combustion reaction occurs on or near this surface without a suspended flame. Heat transfer occurs by radiation directly from the hot surface and by convection from the combustion products that leave the surface. Relatively intensive fundamental and applied research on the catalytic combustion of natural gas has been conducted during the past decade (References 1, 2, 3, 4, and 5). This research has demonstrated that the |