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Show The ports on the gun-type nozzle were enlarged to 1.3-cm (1/2-in.) diameter. Coal was fired at 8% and 13% primary air with ambient combustion air. The puffing problem remained at 8 % primary air, but ceased when the primary air was increased to 10%. At 10% primary air, the shape of the flame remained the same, the visual length was 35-cm (14-in.), and the flame was stable. A 76% less than 200 mesh (standard) pulverized coal and natural gas were fired using 20% excess air under similar conditions as the fine-ground coal firing for comparison and baseline data. The pulverized coal was burned using 10% primary air with the 1-1/4 inch stainless-steel pipe and gun-type nozzles. In both tests, the visual flame was very long (230 cm, 190 cm) and lazy. The natural gas flame was measured when using the 1-1/4 inch stainless-steel pipe nozzle. The natural gas flame was very short, only about 10 cm long. The gun-type and 1-inch stainless-steel pipe nozzles were used with natural gas fuel, also. The concentration of carbon monoxide measured in the flue was between 85 and 100 ppm for all the tests in which it was measured. The carbon monoxide was measured on the furnace axis. (See Figure 12.) These measurements substantiate that the visual length of the flame is a relatively good indication of completeness of combustion. Fly Ash Sampling Fly ash sampling was performed on the furnace axis for fine-ground coal burned (with 20% excess air) with both the 1-1/4 inch stainless-steel axial nozzle and the gun-type nozzle (1.3 cm diameter ports) with 13% primary air. The analysis of the fly ash for hydrogen and carbon is presented in Table 8 for various distances from the burner. Because the sampling was not done isokinetically, the particle size could have had an effect on the analysis since the smaller particles could have been selectively collected at a greater rate. This effect would occur in both the pulverized and fine-ground coal samplings, and, because the pulverized coal has larger particles, the possible error in the analysis would be greater with the pulverized coal sampling. The percent of unburned carbon is plotted against the distance from the burner at which the sample was taken in Figure 13. The results show that the combustion of the fine-ground coal was more rapid with the gun-type nozzle than with 1-1/4 inch stainless-steel pipe nozzle. The solid samples were taken on the furnace axis, which may not give a complete picture of what is happening throughout the entire furnace. HoweVer a flv ash sample taken at the entrance to the flue for pulverized coal combustion showed 15.5% of the carbon unburned. (See Table 8 and Figure 13.) 16-29 |