Flammability Characteristics of Treated Coals

The effects of two processes used to treat coal on the flammability characteristics of the coal are presented. Experiments were conducted on an Entrained Dust Flow Facility which supports a stationary premixed coal dust and air flame. The facility is designed to provide access for thermocouples so that detailed axial and radial temperature profiles of the coal flames can be used to investigate the flame structure. Flame speeds of the coal and air mixtures were determined based on the inlet velocity of the flow and the temperature maps. Flame speed increases of over 35 percent were observed as a direct result of an aggregate flotation process which reduced the ash content and the average size of the coal and increased the volatile content and heating value. Partially devolatilized chars were burned to simulate the use of a low-volatile solid by-product of a gasification process. Under most conditions either methane addition or inlet air heating was required to establish a flame. Both methane addition and inlet air heating with the low-volatile chars resulted in improved flame stability and higher flame speeds. Relatively modest amounts (2.2 percent by volume) of methane addition with the parent coal increased the flame speed by a factor of 2 to 3.