煤灰和煤焦对气化合成气水煤气变换反应特性的影响

Effect of coal ash and coal char on gasification syngas water gas shift reaction

利用管式炉反应器,研究了气化合成气在较短停留时间(1~2 s)内较高温度下水煤气变换反应的特性。考察了煤中灰分以及1100℃热解煤焦对气化合成气变换反应的影响。研究结果表明,在900℃以下合成气水煤气变换反应较难发生,CO转化率接近于0,而1300℃时能发生一定程度的逆向变换反应,但不易达到化学平衡状态。在一定条件下煤灰对正逆向水煤气变换反应有一定的促进作用,其只加快反应速率而不影响反应方向。尽管高温下煤灰出现了一定程度的烧结现象,但较高温度下,煤灰对反应的促进作用更加明显。在实验条件下,相比于空白实验,加入煤灰介质后,合成气CO转化率在700,900,1100℃时分别增加了0.9%,0.8%,2.3%;而干燥合成气在700℃时仍检测不到反应的发生,在900和1100℃时,CO2转化率分别提高了0.9%和2.4%。煤灰提供的表面积以及其中含有的铁等金属元素的催化作用可能是促进变换反应进行的原因,然而气固接触不佳和较小的表面积使得这种促进作用效果受到限制。原煤热解焦对水煤气变换反应的影响,与煤灰的促进作用相似,不同粒径的煤焦对变换反应的作用效果有着明显的差异。煤焦粒径对变换反应的影响存在较优值:粒径过大时,表面积减小,促进作用下降;而粒径过小时,床层局部阻力较高,易导致气体分布不均,影响气固接触,致使固相介质的促进作用显著下降。实验条件下粒径为0.8~1.5 mm的热解焦促进效果最显著,700℃合成气CO转化率比空白实验提高了1.7%。

The water gas shift reaction(WGSR)of gasification syngas in short residence time(1-2 s)and high temperature was carried out in a tubular reactor.The effect of coal ash and coal char on WGSR was studied.The results indicate that when the temperature was below 900℃,the water gas shift reaction of syngas was difficult to occur,and the CO conversion rate was close to 0.However,the reverse shift reaction occurred at 1300℃,but it was not easy to reach chemical equilibrium state.Coal ash could promote the water gas shift reaction,which only accelerated the reaction rate without affecting the reaction direction.Although the coal ash had sintering phenomenon at high temperature,the promotion effect of coal ash on the reaction was more obvious at higher temperature.The CO conversion of syngas increased by 0.9%,0.8%and 2.3%at 700℃,900℃and 1100℃respectively after adding coal ash.For dry syngas,no reaction was detected at 700℃,and CO2 conversion increased by 0.9%and 2.4%at 900℃and 1100℃,respectively.The surface area provided by coal ash and the catalysis of iron and other metal elements in coal ash might be the reasons for promoting the reaction.However,poor gas-solid contact and small surface area limited the promotion effect.Coal char had a similar promoting effect on WGSR to coal ash.The effect of particle size of coal char on WGSR was significant.The influence of coal char particle size on shift reaction had a better value.The coal char particle size increased while the surface area decreased,and the promoting effect decreased.Minor particle size could also contribute to low promoting effect due to uneven gas distribution.Under the experimental conditions,the coal char with particle size of 0.8-1.5 mm had the most significant promotion effect,and the CO conversion of syngas at 700℃increased by 1.7%compared with the blank experiment.