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Show IMPROVED COMBUSTION/THERMAL EFFICIENCY WITH COMPACT RECUPERATOR DESIGN Shyam N. Singh, Steven Yokosh, Tom Briselden, Shiw S. Singh WB Combustion, Inc. Milwaukee, Wisconsin, USA ABSTRACT Thermal efficiency of the radiant tube combustion system is improved by utilizing advanced recuperative equipments. These equipments are self recuperative single ended radiant tube and plug-in type recuperators. In order to increase their applicabilities, advanced ceramic materials are being used to manufacture the critical components exposed to higher flue gas temperature i.e. 2000 degrees F. + or 1079 degrees C. Preliminary design methods to manufacture these equipments indicate that ceramic recuperators can compete against conventional single ended and plug-in recuperators. Preliminary test results indicate that a higher preheat temperature from the ceramic recuperator is possible when the plug-in design is used. BAOFJGROUND A number of heat treatment processes require controlled atmospheres in which heat must be indirectly transferred to the load being processed. This is accomplished by two basic methods, either by using muffle furnaces or by using radiant tubes. Radiant tubes, however, are preferred over muffles, since they are less prone to leakage and more easily zoned. Radiant tubes are internally fired and become so hot that heat transfer occurs entirely by radiation (1). Quite often, radiated heat is recirculated throughout the furnace by an external fan to maintain 71 uniform heat. Most of the radiant tube gas fired combustion system operates at less than 40% thermal efficiency when there is no heat recovery device used (1). With modern heat recovery devices, this efficiency could go as high as 65% particularly when a plug-in recuperator is used against an external type recuperator (2). Under the GRI program, a recent development of a regenerative system for radiant tube of "U", "W" and Trident application has shown a fuel savings of 60%, against the 50% normally observed (3). This concept, however, cannot be applied to a single vertical radiant tube unless a major modification in the tube's shape, size and placement is made. This could result in an increased capital investment in a retrofit application (2). To overcome such a problem, an approach is made to design a ceramic single ended recuperative radiant combustion system, which could result in a thermal efficiency of 75% or higher. INDIRECT FIRED HIGH TEMPERATURE heat treating furnaces require higher heat fluxes. The equipment currently available, which has the ability to process at temperatures in excess of 1800 degrees F., are vacuum furnaces or conventional electric equipment. Vacuum furnaces are batch type with low load capacities, therefore, limit any increase in productivity, even though the high temperatures are available. Other limitations are high initial capital cost and high skills |