Chiang Mai Journal of Science

In the present study, the effects of  moisture in coal briquettes on mechanical strength, ignition time, and combustion characteristics of cylindrical, honey-comb cross-sectional coal briquettes were investigated. Each coal briquette was ~1.0 kg, ~10 cm diameter, ~10-12 cm high, with sixteen ~1 cm diameter axial holes. The moisture contents in the coal briquettes were in the range of 10-30 wt%. The mechanical strength of the coal briquettes was examined as a compressive strength by a compression machine in both vertical and horizontal directions. The ignition time was investigated using a muffle furnace at the temperatures of 700, 800, and 900 oC. For the combustion tests, the already ignited coal briquettes, with an initial temperature of 800 oC, were placed in a Thai traditional cooking stove. During each combustion test, mass loss history and the temperature of the coal briquette surface were monitored. It was found that the compressive strengths in the vertical and horizontal directions were in the ranges of 360.8-1,052.0 and 37.6-70.0 kN/m² , respectively. When moisture content in the coal briquettes increased, their compressive strength decreased. Ignition times for the temperatures of 700, 800, and 900 ^oC ranged from 14-37, 8-16, and 5-10 minutes, respectively. The ignition time decreased as the ignition temperature increased. On the contrary, the ignition time increased with moisture content. A decrease in mass of the coal briquettes with higher moisture contents was slower than that with lower moisture contents. The combustion of  the coal briquettes was found to be first order for all moisture contents. The rate constants (k) were 0.0402, 0.0439, and, 0.0508 min^-1  for the coal briquettes with moisture contents of 10, 20, and 30 wt%, respectively