COMBUSTION CHARACTERIZATION OF COAL-WATER SLURRY FUEL PREPARED FROM PLANT COAL AND RECOVERED COAL FINES

In the process of coal cleaning operations, a significant amount of coal is washed away as waste into the ponds. Clearly, such a large quantity of dumped coal fines has a detrimental effect on the environment. This investigation presents in innovative approach to recover and utilize waste coal fines from the preparation plant effluent streams and tailing ponds. Due to the large moisture content of the recovered coal fines, this study is focused on the utilization of coal fines in the coal-water slurry fuel (CWSF). The CWSF consists of 53.3% weight solids with a viscosity of less than 500 centipoise and 80-90% of solids passing 200 mesh. The 53.3% weight solids constitute a blend of 15% effluent recovered coal fines and 85% clean coal. It is the authors premise that a blend of plant coal and recovered waste coal fines can be used to produce a coal-water slurry fuel with the desired combustion characteristics required by the industry. In order to evaluate these characteristics the coal-water slurry fuel is fired in a test furnace at three firing rates (834,330 Btu/hr, 669,488 Btu/hr and 508,215 Btu/hr) with three different burner settings for each firing rate. Combustion tests were conducted to determine the range of secondary air swirl required to maintain a stable combustion flame. Results obtained during the flame stability testing show no significant effect of swirl settings on Nox, SO2 and CO2 for three combustion tests (834, 330 Btu/hr, 669, 488 Btu/hr, 508 215 Btu/hr). At each of the two higher firing rates, combustion was relatively complete regardless of swirl settings, therefore, burner settings may be adjusted to provide a visually stable flame without concern for higher carbon in ash as a function of burner settings. The parameters affecting flame stability are mainly coal particle size, volatile matter, ash content and excess air. Tests conducted at three different locations (top, Middle, Bottom) revealed that the gaseous concentrations such as Nox, SO2 and CO2 were a function of residence time for each of the firing rates. Effect of swirl settings on Nox for three firing rates were investigated. It was found that the variation of Nox concentrations with respect to the change in swirl numbers was significant. But, the variation of Nox Concentration with respect to firing rates was found to be consistent with the increase in firing rates. The flame stability was accessed by the visual observation of the flame with relation to the burner quarl