OCR Text |
Show nozzle remained 2.5 cm (1 in.) from the end of the throat (the start of the conical section of the burner block). Stainless-steel pipes were used as the axial nozzles and were positioned at various points in the throat during the tests. Fuel and Air Supplies The burner was supplied with coal by a pneumatic feed system designed and fabricated at the IGT Combustion Research Facility. The feed system consists of steel piping, an air compressor, an air ejector, a hopper with a 27-ft^ capacity, and a variable-speed screw feeder (Figure 5). The fine-ground coal, which was stored in steel barrels with plastic liners, was transferred into the hopper using a barrel lifter, a special barrel lid, and a transfer tube. The variable-speed screw feeder transferred the coal from the hopper into the primary air flow at a constant rate. At the point where the screw feeder entered the primary air line, motivating air, supplied by a compressor and pumped through an ejector nozzle located just downstream of the fuel injection position, created a vacuum. The ejector nozzle was 0.4 inch in diameter and centered in a 2-inch pipe, into which the screw feeder dropped the coal. The system was open to atmospheric air upstream of the screw feeder, and a volume of air slightly greater than the volume of motivating air was drawn in by the ejector and helped suspend the coal. (See Figure 6.) Both motivating and entrained air flow rates were measured by orifices and manometer systems. One orifice measured the high-pressure motivating air; another measured the suction air. The flow rate of the primary air was obtained by adding these two flow rates. The high-pressure ejector (motivating) air was supplied by a gas compressor capable of supplying 20,000 SCF/hr at 80 psig. At a flow rate of 4500 SCF/hr, the pressure going into the ejector nozzle is 80 psig. When the entrained air is added in, the primary air system has a capability of 10,000 SCF/hr. The primary air was used to transport the coal and impart a velocity and momentum to it. Combustion air was supplied by a fan and could be preheated up to 900°F at that time. Natural gas was used to preheat the furnace through the same fuel nozzle and to assist in starting coal combustion. The furnace with the coal feed hopper and screw feeder are shown in Figure 7 in operating conditions. Figure 8 shows gas sampling using a water-cooled probe in the coal-fired furnace through one of the sampling doors. 16-12 |