The influence of cations on the pyrolysis behaviour of brown coals under flash heating conditions was investigated by means of a small fluidized-bed pyrolyser. A stream of coal particles in nitrogen was injected at rates of l-3 g coal/h directly into a heated bed of sand fluidized by nitrogen. Yields of tar, Cl-C3 hydrocarbons and total volatile matter from four Gelliondale brown coals and a Montana lignite were determined as a function of pyrolysis temperature. With all coals the maximum tar yield was obtained at 600ยฐC. Removal of cations present in the coals markedly increased the yields of tar and total volatile matter, with little effect on the yields of hydrocarbon gases. The converse was also observed in that the addition of Cap+ to a cation-free coal decreased the yields of tar and total volatile matter. The extent of the reduction in tar yield at 600ยฐC in the presence of cations was found to be similar for all coals. After acid washing, tar yields appear to correlate with the atomic H/C ratios of the coals in a manner similar to that observed previously with bituminous coals.
Preparation of acid-and calcium-form coals
Acid-form (cation-free) coals were prepared from the raw coals by extraction with 2N HCl at room temperature. Coals with a range of calcium contents were