稻秆热解过程中碱金属转化析出过程试验研究

Experimental study on alkali emission during rice straw pyrolysis

为了对高碱生物质热化学转化中碱金属问题的解决提供理论指导,定量研究了稻杆中K、Na、Cl的热解析出过程.以化学分馏法和相关检测为基本分析手段,在小型固定床热解试验台上以稻杆为原料进行了试验,得到不同形式的碱金属和Cl在热解各阶段的动态析出过程和转化特性.结果表明,稻杆中的碱金属在673 K以下随热解进行快速析出,然后转入高温慢速析出阶段.K、Na和Cl在热解中的转化模式大体类似,其中Cl在523 K以下的低温热解阶段表现出更强的挥发性.水溶性K和Na占生物质原料中碱金属含量的90%以上,是造成碱金属热解析出的主要原因.热解过程中,不同形式的K之间还存在一定程度的相互转化,而Na的行为相对单纯,除水溶性外的其他形式Na在热解中表现出较强的惰性.

To deal with the alkali problems of high-alkali biomass thermochemical utilization, the quantitative study of the release of K, Na and Cl from rice straw pyrolysis was carried out. On the basis of chemical fractionation and subsequent measurements, the transformation and emission characteristics of different forms of alkali and Cl during the whole process of rice straw pyrolysis were examined in a small-scale fixed bed pyrolysis reactor. The results show that the alkali in rice straw is released rapidly during pyrolysis under 673 K, then evolves into a high temperature slow releasing stage. K, Na and Cl have similar releasing behaviors during pyrolysis while Cl shows more volatility in low temperature pyrolysis stage under 523 K. More than 90% of alkali in rice straw is water-soluble, and this part of alkali is crucial to the alkali pyrolytic release. Different forms of K undergo reciprocal conversion during pyrolysis, but the pattern of Na releasing is simple, and most forms of Na show relatively low activity except water-soluble Na.