Autothermal combustion of mechanically-activated micronized coal in a 5 MW pilot-scale combustor

We report on the first successful realization of self-sustained (autothermal) combustion of mechanically activated micronized coal in a pilot-scale installation of a nominal capacity of 5 MW. The thermogravimetric analysis (TGA) of the thermal decomposition of coal milled in several types of mills showed that a new rotating impact disintegrator (DIS) decreases the overall coal activation threshold by a factor of two or more compared to the parent coal from a conventional power-plant mill. The combustion experiments confirmed that such mechanically disintegrated coal of average particle size ≈40 μm can burn without any gas or oil support, whilst its flame characteristics resemble closely those of heavy oil. In contrast, coal of almost equal size distribution microground in a vibrocentrifugal mill (VCM) burns as coal from a conventional power-plant mill, with a longer flame and visible trajectories of burning particles. The TGA test of the VCM coal confirmed that grinding in this mill brought no notable change in coal reactivity. The BET and deBoer nitrogen adsorption analyses of the particles texture showed only 15% increase in the surface-to-volume ratio of the DIS sample compared to VCM, confirming that the main effect of high impact disintegration is on the change of the kinetic coal reactivity. Easier ignition, more stable combustion and lower NOx emission achieved with micronized activated coal open prospects for improvement of combustion in diverse installations, more efficient coal gasification as well as for replacing liquid fuels in various applications.