OCR Text |
Show analyzing the products of combustion for concentrations S02, NO , and CO. Sulfur dioxide emissions were easily suppressed without additional limestone. The initial bed of fresh limestone provided all the sulfur capture necessary to maintain S02 emissions below measurable limits in all tests. Due to the extremely high calcium to sulfur mole ratio and the batch type reactor operation, the sulfur capture data for the experiments will not be referenced further in the study. The data indicated that NO emissions were dependent upon excess air. A plot of NO emission versus excess air (Figure 4) shows a trend of increasing NO emissions with increasing rates of excess air. Two data points, Test Runs 13 and 14, do not follow the overall trend. Both data points are probably due to the majority of combustion occurring in the bed, reducing the potential for the NO /carbon reaction to occur in the freeboard. The high NO rate in Test Run 14 was probably due to a combination of a high bed temperature, a low fuel feed rate, and a low superficial velocity. The cause of the high NO emissions of Test Run 13 is not apparent. The overall NO emissions results compare favorably with data obtained in the pulverized fuel boiler study.2 The small particle size, the high ratio of surface area to volume, and the highly reactive nature of the char combined to produce very low levels of CO emissions, which is usually associated with good combustion efficiencies. In most tests the CO levels were below 100 ppmV**. The CO levels were similar to the levels observed in the pulverized fuel boiler study.2 Another interesting trend in the data is shown by a plot of weight percentage of carbon in the cyclone fines versus temperature (Figure 5). The carbon percentage is assumed to indicate carbon carry over. The **ppmV -- parts per million on volume basis. 22-12 |