水热处理对白石湖煤热解过程中钠钙迁移行为的影响

采用高压釜对富镜质组白石湖煤进行了水热处理,通过傅里叶红外光谱(FT-IR)分峰拟合方法分析了煤中含氧官能团变化。在固定床中开展分离废液和未分离废液水热处理煤样的热解实验,利用原子吸收分光光度计(AAS)测定了热解产物中钠钙含量。结果表明,白石湖煤经水热处理后水分、挥发分、氧含量以及Cl、Na和Ca等无机元素含量明显降低。水热处理过程中芳香醚水解和羧酸盐发生离子交换反应使得氢含量和H/C原子比增加,促进固定床热解焦油产率升高。300℃下水热处理脱除了部分有机形式Ca后随水废液被分离;废液中钠钙等无机元素的催化作用导致未分离废液较分离废液的样品具有更高热解气产率和更低焦油产率。白石湖原煤及其水热处理样品热解产物中Na含量和分布由高到低顺序均为:热解焦热解水焦油热解气,Ca含量和分布顺序为:热解焦焦油热解水热解气。水热处理温度越高,热解过程钠和钙释放率越低,释放的Na主要进入热解水,其次焦油;而释放的Ca则主要分布于焦油中,其次热解水。

Effect of hydrothermal treatment on Na and Ca migration behavior during pyrolysis of Baishihu coal

Vitrinite-rich Baishihu coal (BSR) was hydrothermally treated in an autoclave. FT-IR spectra peak fitting was used to investigate change of oxygen functional groups. Fixed bed was applied to pyrolysis of hydrothermal treated samples with and without separation of liquid waste, then contents of Na and Ca in these pyrolysis products were determined by atomic absorption spectrophotometer (AAS).The results show that moisture and chlorine content in Baishihu coal and Na₂O content in ash decrease significantly after hydrothermal treatment. The hydrolysis of aryl ethers of Baishihu coal and the ion exchange reaction of carboxylate lead to increase of hydrogen content and H/C atomic ratio, promoting increase of tar yield during pyrolysis. The organic Ca can be removed by hydrothermal treatment at 300℃ and is separated with the hydrothermal liquid waste. Because of catalysis of inorganic elements such as sodium and calcium in hydrothermal liquid on coal pyrolysis, the hydrothermal treated samples without separation of liquid waste has higher gas yield and lower tar yield than those with separation of liquid waste. Na content and distribution in pyrolysis products of BSR and treated samples decease as:char > water > tar > gas, while the order of Ca is:char > tar > water > gas. As the hydrothermally treated temperature increases, the released content of sodium and calcium during pyrolysis process decreases. The released Na during pyrolysis mainly distributes in water, followed by tar, while Ca is just opposite.