生物质气化过程中碱金属和碱土金属的析出特性研究

研究了固定床上生物质及热解焦CO2气化过程中碱金属及碱土金属(AAEMs)的析出特性。利用原子吸收光谱仪,考察了不同生物质种类、不同热解制焦温度对AAEMs析出的影响。不同生物质由于其挥发分含量不同引起气化失重率的差异,焦气化活性随制焦温度升高而降低。生物质及焦气化过程中Na析出率最大,其次是K,碱土金属析出率低于碱金属,这与元素在生物质中的存在形式、金属价态有关。低温段K的析出率随热解制焦温度的提高而增加,而Na在热解与气化段总的析出率与制焦温度关系不大。生物质的种类尤其是灰中的Si含量对Ca和Mg的析出影响较大,气化效率高的生物质AAEMs析出较多。热力学计算结果显示,气化过程中Na、K多以氯化物的形式存在并析出,Ca、Mg则更倾向于形成硅酸化合物而不易析出。

Releasing behavior of alkali and alkaline earth metals during biomass gasification

The releasing characteristics of alkali and alkaline earth metals (AAEMs) during CO₂ gasification process of biomass and pyrolyzed char were explored in a fixed bed reactor. The amount of AAEMs releasing during the gasification of various feedstocks at different pyrolysis temperatures was determined by atomic absorption spectroscopy. Differences in weight loss of biomass during gasification are resulted from the diversity of volatile content in different biomass feedstocks. Along with the increasing of pyrolysis temperature, the reactivity of char gasification is decreased. It is found that the releasing amount of Na is larger than that of K, and that of alkaline earth metals is less, which is related to their existence form and metal valence. The increasing of pyrolysis temperature can improve the release of K at low temperatures, while it has little influence on the release of Na during the whole pyrolysis and gasification process. The type of biomass especially the Si content in ash has a significant impact on the migration of Ca and Mg, and higher char gasification conversion leads to a larger releasing amount of AAEMs. Results of thermodynamic calculations show that K and Na are released mostly in the form of chloride, while Ca and Mg mainly exist in the form of silicate which is hard to release.