煤焦与生物质焦CO_2共气化特性及分布活化能研究

Investigation on the Co-gasification of Coal Char With Biomass Char and the Distributed Activation Energy

对煤焦、秸秆焦、木屑焦3种焦样及其掺混焦样进行了CO2气氛的共气化热重试验,研究了各焦样在不同催化剂添加条件下的气化特性,并对各种样品在反应过程中的分布活化能进行了计算与分析。研究结果表明:煤焦、秸秆焦、木屑焦3种焦样中煤焦的反应性显然较差;对于煤焦和秸秆焦,Na盐的催化效果优于Ca盐;对于木屑焦,Ca盐的催化效果更显著。Na盐与Ca盐的添加均可使秸秆焦气化反应速率显著增加,但反应所需温度的下降却不显著。在木屑焦中添加Na盐与Ca盐后,气化反应所需温度的下降比秸秆焦显著。对于煤焦,添加催化剂首先使气化所需温度显著下降,反应速率并不显著增加;但进一步增加催化剂,则主要使反应速率提高,反应所需温度不再显著下降。在反应过程中,各样品的分布活化能均表现出先升后降的趋势。样品中灰分的存在有助于焦样在热天平内气化反应的充分进行。

Thermo gravimetric analyzer （TGA） experiments for gasification of sawdust char, wheat straw char and coal char and co-gasification of their mixtures in CO2 atmosphere were conducted. Characteristics of the gasification with and without catalysts were investigated. Kinetics of char gasification was studied employing distributed activation energy model （DAEM）. Experimental data indicate that coal char is apparently less active among these three kinds of char. And catalytic effect of Na salts on the gasification of coal char or straw char is greater than Ca slats while Ca salts function as better catalysts to the gasification of sawdust char. Both Na salts and Ca salts have the ability to significantly accelerate the reaction rate of straw char gasification, but none of them would significantly reduce the onset temperatures of these reactions. When Na salts or Ca salts were added into sawdust char, drop of the onset temperature is larger than that can be observed in the gasification of straw char. For coal char, the onset temperature drops when a catalyst is introduced while the speed of the reaction remains, but the effect of increasing quantity of catalysts is limited to the increase of the reaction speed and no notable further decrease of the onset temperature could be observed. During the gasification process, distributed activation energy of all samples shows the tendency to increase at first and decent later. The existent of ash in the samples has the ability to assist the gasification in a TGA.