低阶煤程序升温热解过程中钠、硅和硫间的相互作用

对一种澳大利亚低阶煤中，钠、硅和硫在热解过程中的相互作用进行了研究，以便深入了解钠的固硫作用和硫对流化床燃烧和气化中颗粒团聚的影响。制备了水洗、酸洗煤样和酸洗、乙酸钠离子交换煤样，样品在马弗炉中以17．7℃／min升至1000℃进行程序升温热解。对700℃-100℃热解半焦样品的依次水洗、酸洗、SEM—EDX和X射线元素扫描分析表明，部分有机结合的钠形成水溶性Na2O和NaOH化合物，水溶性的硅酸钠，以及与半焦中的硫形成酸不溶组分。最后一点解释了为何以往研究中发现，热解过程中有机结合的钠具有固硫作用，以及固硫历程中为何未发现Na2S的生成。在硅酸钠区域边缘存在的高硫区域，在流化床燃烧和气化过程中将形成含硫黏性相，导致床料的黏结。当用于酸洗、钠离子交换煤样的乙酸钠从0．25mol／L增加到1．0mol／L，固硫率将增加10％。相应的酸不溶钠组分的增加表明，酸不溶钠／硫组分随乙酸钠浓度的增加而增加，从而导致固硫率上升。

Interactions between sodium, silica and sulphur in a low-rank coal during temperature-programmed pyrolysis

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 Char samples were withdrawn from the reactor and subjected to sequential water and acid leaching tests and SEM analysis employing Energy Dispersive X-ray and quantitative X-ray mapping.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 Na2O 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 Na2S 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.