SULFUR CAPTURE DURING PARTIAL COAL COMBUSTION

A coal-water slurry is an econonical substitute for premium liquid fuels, but the amount of sulfur in coal is usually higher than in petroleum liquids. Lime has been used to capture sulfur in fluidized coal combustion as CaSO₄, but the latter decomposes above 1273 K. We report here on the possible capture of sulfur in the ash as CaS, which has higher thermal stability than CaSO₄. This can be accomplished using a fuel-rich first stage in a coal-water slurry combustor, or under the conditions normally encountered in some coal gasifiers. Thermodynamic calculations and some preliminary experiments suggest that the concept is promising for effective sulfur removal and, by extension, for NO_x, control.