Flame Stabilization of Low Volatile Fuels

Abstract

Abstract Four chars, an ultra fine grind anthracite and a bituminous coal were burned in a special one-dimensional furnace. With a standard grind anthracite, the flame would not stabilize. The furnace used was a reconstruction of that used 10 years ago by Howard and Essenhigh (1965, 1966, 1967, 1967a). The principal observations were: flame front location determined as ignition distance below a stabilizing water-cooled tube bank; and wall temperature profiles. Effects of particle size, fuel/air ratio, cloud velocity and influence of a hot or cold boundary at the furnace bottom were investigated. Search for particle shattering at the flame front was negative. The fuels were found to split into two groups, either of high reactivity with flame fronts 4 or 5 cm below the tube bank, or low reactivity with flame fronts 40 to 50 cm below the tube bank. The high reactivity group included the bituminous coal and two of the chars thus supporting the contention that reactivity is not conferred by volatile matter per se. Reactivity is controlled by the gasification process not the parent coal. The conclusion, supported by appropriate N2 area and porosity measurements, is that high reactivity is primarily a function of internal surface. This is further supported by the critical importance of ultra fine grinding with the anthracite at one extreme and the insensitivity of behavior to particle size of the high reactivity fuels. Ignition times of the high reactivity fuels are in good agreement with simple radiation theory, but the theory does not account properly for the factor 5 to 10 difference in ignition times between the high and low reactivity fuels. This is under investigation in a theoretical model with results to be published elsewhere in due course