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Show EXPERIMENTAL STUDY The purpose of the experimental study performed by IGT was to evaluate a bench-scale combustor-heater for concept proof. Specifically, the surface combustor-heater should be capable of high combustion efficiency and intensity, high heat-transfer rates, low emissions, low pressure drop, and high turndown ratio. The bench-scale surface combustor-heater system flow diagram, the measuring devices used to evaluate the concept, and the unit setup are shown in Figures 3 and 4. The system consists of a 6-inch by 6-inch burner, a heat exchanger using water as the working fluid, and the measuring system. The combustor-heater unit consists of six parts connected together by flanges - • Natural gas/combustion air mixture plenum • Cooled distribution grate • Combustion, heat-exchange, and sampling chamber • Exhaust plenum • Exhaust stack • Support frame with legs. The mixture of natural gas and combustion air is brought into the unit by a 1-1/4 inch pipe and mixture plenum. The distribution of the mixture is provided by the water-cooled grate equipped with the 16 specially designed distribution nozzles. Each nozzle contains 6 semicircular- shaped openings through which the mixture is delivered into the combustion chamber. The cooling water is channeled through the double-wall grate in such a way that the body of each nozzle is evenly cooled. In addition, each nozzle contains a cooling rod that is attached to the cap of the nozzle on one side and exposed to the cooling water on the other side. This arrangement assures additional cooling of the caps of the nozzles. The grate assembly is attached to the support frame so that it can be adjusted to a height relative to the position of the cooling tubes (the distance between the first row of cooling tubes and the top of the distribution nozzles). The chamber is lined with 6-inch-thick, high-temperature insulating block o minimize the heat losses. The inner surface of the block is coated with a zirconia-bond coating to harden the surface of the block and add to its heat-resistance capability. The exhaust plenum is also lined with high-temperature insulating block and coated with the 8 INSTITUTE o F GAS TEe H N 0 LOG Y |