低阶煤程序升温热解过程中钠、硅和硫间的相互作用

Interactions of sodium, silica and sulphur in a lowrank coal during pyrolysis was investigated to understand the retention of sulphur by sodium and the role of sulphur in particle agglomeration and defluidisation in fluidizedbed combustion and gasification. Samples of water and acid washed coal, and the acidwashed coal ionexchanged with sodium acetate were prepared and subjected to temperatureprogrammed pyrolysis performed in a muffler furnace with a constant heating rate of 17.7℃/min up to 1000℃. Char samples were withdrawn from the reactor and subjected to sequential water and acid leaching tests and SEM analysis employing Energy Dispersive Xray and quantitative Xray mapping. It was revealed that for chars removed at temperatures between 700℃～1000℃, part of the organically bound sodium forms water soluble compounds such as Na2O and Na(OH), a significant proportion of water soluble sodium silicates and acid insoluble constituents with sulphur in the char. The latter explained why the presence of organically bound sodium was found to retain sulphur during pyrolysis in previous investigations and also why the formation of Na2S was not observed as the retaining mechanism. The highly concentrated regions of sulphur existing around the edges of the sodium silicate inclusion bodies were considered to be the beginning of the sticky phases of sulphur bearing compounds responsible for binding bed materials together during fluidisedbed combustion and gasification. Total sulphur retention was found to increase by 10% as the NaAc solution concentration used in the ionexchange of the acidwashedandNaexchanged coal was increased from 0.25mol/L (2% total Na) to 1.0mol/L (3.2% total Na). A corresponding increase in the acidinsoluble sodium content suggested that the amount of acidinsoluble sodium/sulphur constituents increases with acetate solution and is the reason behind the effect of total sulphur.