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Show LABORATORY COMBUSTOR The combustor used to evaluate the slagging and fouling potential of the coal is schematically illustrated in Figure 7, along with its supporting auxiliary equipment. The combustor is a vertical, refractory-lined furnace fired upward. The coal flow rate is 75-125 lb/h, with air flow of 800 to 1450 lb/h at 15 percent excess air. The gas velocities, direction of firing, and furnace exit temperatures were all selected to simulate the time-temperature heating of coal and ash in a full-scale furnace. Refractory lining was chosen to avoid premature quenching of the flue gases. Coal is fired through a burner designed with the capability of adjustable swirl. The burner is protected from slag by a small dam or weir about its periphery. Ignition is achieved with a North American Aardvark burner with a heat release of 106 Btu/h. The burner is capable of maintaining furnace temperatures during banked conditions if, for one reason or another, there is a substantial interruption in coal flow, and it is desirable to maintain the furnace at temperature. The furnace is designed to simulate the radiant section of a utility boiler. It is a refractory lined, cylindrical chamber measuring 18 ft. in length by 28 in. in diameter (internal dimensions). The furnace is assembled in eight main segments. Each segment contains three access ports, 8 inches apart vertically and 120° apart horizontally. Exceptions have been taken in three cases to permit diametric observation of probes inserted into the furnace. A cross-sectional diagram of the furnace is presented in Figure 8. The nominal bulk fluid velocity in the furnace mid-section is about 5.5 ft/s when firing a typical Eastern bituminous coal at 100 lb/h and 15-percent excess air, resulting in a furnace residence time of approximately 3-4 seconds. The furnace walls are made of 8-inch thick, high-alumina ruby plastic refractory, backed by 2 in. of an insulating castable refractory. The outer shell is constructed of 1/4-inch thick carbon steel. Upon leaving the furnace section, the flue gases pass into a horizontal duct and over a bank of heat exchange tubes that simulate the con-vective section of a utility boiler. The duct is rectangular, measuring 7-1/4-in. high by 11-1/4-in. wide, and is lined with a castable refractory. The flue gas continues its flow downward past two additional banks of con-vective heat-transfer surfaces. Nominal bulk fluid velocities in the 26 |
