Effect of Torrefaction on Physicochemical Properties and Steam Gasification Reactivity of Chars Produced from the Pyrolysis of Typical Food Wastes

This study compares the physicochemical properties and steam gasification reactivity of the chars produced from the pyrolysis of the raw and torrefied food wastes at 800 degrees C, including leftover rice (LR), leftover pork (LP), leftover cabbage (LC), and watermelon peel (WP). Particularly, the release and transformation of various forms of alkali and alkaline earth metallic (AAEM) species during the pyrolysis of the raw and torrefied food wastes are studied in details. Steam gasification results of the chars from the raw food wastes indicate that the LC and WP chars have much higher gasification reactivity than the LR and LP chars, mainly as a result of the higher char surface areas, higher contents of AAEM species, and less condensed carbon structures for the LC and WP chars. However, the gasification reactivity of the torrefied LR and LP chars is reduced, mainly as a result of the decreased surface areas and increased large aromatic ring (>= 6 rings) structures as well as the decreased active K content for the torrefied LP char. In contrast, the gasification reactivity of the torrefied LC and WP chars is slightly increased, most likely as a result of the less condensed carbon structures and increased contents of active AAEM species for those chars. The results demonstrate that the effect of torrefaction on char gasification strongly depends upon the type and properties of food waste, especially the contents of active AAEM species (i.e., the water- and CH3COONH4-soluble AAEM species) in food waste. For the food wastes of low contents of active AAEM species, such as LR and LP, co-torrefaction with other food wastes of high contents of active AAEM species is an important strategy to enhance the overall gasification efficiency of all food wastes.

本研究比较了在800℃下原始和烘焙食品废弃物热解所产生的焦炭的物理化学性质以及水蒸气气化反应性，这些食品废弃物包括剩饭（LR）、剩猪肉（LP）、剩卷心菜（LC）和西瓜皮（WP）。特别是，详细研究了原始和烘焙食品废弃物热解过程中各种形式的碱金属和碱土金属（AAEM）物种的释放和转化。原始食品废弃物焦炭的水蒸气气化结果表明，LC和WP焦炭的气化反应性比LR和LP焦炭高得多，这主要是因为LC和WP焦炭具有更高的表面积、更高的AAEM物种含量以及更少的缩合碳结构。然而，烘焙后的LR和LP焦炭的气化反应性降低了，这主要是因为表面积减小、大芳香环（≥6个环）结构增加以及烘焙后的LP焦炭中活性钾含量降低。相比之下，烘焙后的LC和WP焦炭的气化反应性略有提高，很可能是因为这些焦炭的缩合碳结构更少以及活性AAEM物种含量增加。结果表明，烘焙对焦炭气化的影响在很大程度上取决于食品废弃物的类型和性质，尤其是食品废弃物中活性AAEM物种（即水溶性和CH3COONH4可溶性AAEM物种）的含量。对于活性AAEM物种含量低的食品废弃物，如LR和LP，与活性AAEM物种含量高的其他食品废弃物共烘焙是提高所有食品废弃物整体气化效率的重要策略。