OCR Text |
Show plot indicates that carbon carry over decreases with increasing temperature. The data point which deviates from the trend, at a bed temperature of 1650°F, is due to the low air rate used in the test (3 percent below stoichiometric). The correlation of carbon carry over and excess air failed to produce reliable trends in data. Discussion The objectives of the study were to determine the unique combustion, emission, and operational characteristics of Occidental char. The independent variables for the experiment were fuel and air feed rates and bed temperature. These particular independent variables were considered to have a dominant effect upon combustion efficiency and NO emissions, the dependent variables of technical interest in the study. To reiterate, the behavior of the char, its characteristics are dependent on the parent coal and the formation process. The Occidental char exhibited excellent ignition and flame stability despite low volatile content. This was probably due to the high porosity leading to a relatively high surface area of the char particles. It was not within the scope of this experiment to determine the controlling mechanism of the reaction. Also worth noting was the char's excellent emission characteristic, in part due to low sulfur and nitrogen content of the char and to reactions occurring in the freeboard to be discussed later. The only operational problem encountered in the study was a direct result of the small particle size of the char. The char would tend to compact under its own weight in the feed hoppers, resulting in bridging in the hopper and ultimately intermittent feed to the combustor. The bridging was overcome by replacing the feed hopper with a larger diameter hopper and inducing an air stream at the throat of the hopper. However, the Occidental char's small particle size must be considered in the design of a materials handling system for the combustor. The elevated combustion zones observed in the study were assumed to be a direct result of the char's small particle size. The high ratio of 22-15 |