褐煤原位气化半焦的反应性及微观结构的演化行为

在自制两段新型固定床反应器上进行了褐煤热解及"热"半焦的原位气化反应的研究。在高纯氩气、400/600/800 ℃的条件下,对褐煤热解5 s后,立刻将反应器移到气化段,同时切换气氛为15%水蒸气对"热"半焦进行原位气化反应(900 ℃、2~30 min),制得原位气化半焦。利用TGA和Raman光谱仪,对原位气化半焦进行反应性和微观结构表征。结果表明,原位气化半焦产率及反应性在气化10 min内降低幅度相对较大,10~30 min降低相对缓慢。大部分的含氧官能团在气化2 min内被释放,气化2 min后含氧官能团变得非常少。半焦中小的芳环与大环体系之比在气化2 min内急剧降低,2~30 min降低较为缓慢。半焦的微观结构对其反应性有一定的影响,随着气化反应的不断进行,半焦中无定形结构、小的缩合芳环等活性基团逐渐减少,反应性相应降低。

Evolution behavior of reactivity and microstructure of lignite char during in-situ gasification with steam

The pyrolysis of brown coal and the in-situ gasification of "hot" char were carried out in a newly-designed two-stage fixed-bed reactor. Firstly, the brown coal was pyrolyzed in ultrapure argon for 5 s under the temperature of 400 ℃, 600 ℃, and 800 ℃ at the pyrolysis stage. Then the reactor was shifted to the "gasification stage" immediately and the "hot char" obtained at the pyrolysis stage was gasified in-situ for 2~30 min at 900 ℃ with a 15%H₂O balanced with argon to obtain a so-called in-situ gasification char. TGA and Raman spectroscope were used to characterize the reactivity and microstructure of char, respectively. Results show that the yields of in-situ gasification char decrease significantly within the initial 10 min, and then decrease slowly with prolonging the holding time further (10~30 min). Plenty of O-containing functional groups are released in the first 2 min during gasification. The ratio of small aromatic ring systems to big aromatic ring systems decreases dramatically within 2 min, and then decreases slowly from 2 min to 30 min. Microstructure of char has an effect on its reactivity. With the char gasification, the amorphous carbon as well as small aromatic ring systems with high activity decreases, leading to the char reactivity decreaseing consequently.