Effect Of Inherent Minerals On Char Gasification In Mixture Of H₂O And CO₂

The technology which partially replaces steam by CO2from rectisol as thegasification agents is an innovation in pressurized fixed bed dry bottomgasification. It can not only reduce the CO2emission, but also decrease theamount of phenolic wastewater. A few studies have reported char gasificationreactivity with H2O and CO2, but the research results can’t guide the industrialtest and production sufficiently. Therefore, to further study char gasification withmixture of H2O and CO2has the important theoretical and practical significance.Yining coal, which was chosen in the study, is the raw coal used inpressurized fixed bed dry bottom gasifier. The char gasification reactivity inmixture of H2O and CO2was analyzed by thermal gravity analysis. The effect ofthe temperature and the ratio of co-gasification agent on gasification reactivitywere investigated. It was found that there was an obvious synergistic effectduring char gasification in mixture of H2O and CO2. In order to identify thereason of synergistic effect, the inherent minerals in the raw coal were firstlyidentified by low temperature ashing and XRD. Then, char gasificationreactivities of successively demineralized coals were analyzed, it was found thatcatalysis of calcite is the reason that causes the synergistic effect. The catalyticmechanism was also discussed. L–H kinetic model was used to describe the dynamic behavior of the raw coal and the demineralized coal in co-gasification.The main conclusions are as follows:(1) With the temperature increases, the co-gasification reactivity of Yiningchar with mixture of H2O and CO2increases. However, the co-gasificationreactivity in H2O66.6%+CO233.3%at800°C is higher than that at850°C.Besides, the co-gasification reactivity is better than the single gasificationreactivity at800°C. This is considered as the synergistic effect.(2) The result shows that the catalysis of inherent minerals in the coal is thereason causing the synergistic effect. Low temperature ashing is the methodwhich can oxidize the organic matter in the coal without changing the states ofinorganic matters. The low temperature ash was analyzed by XRD. The resultshows that the inherent minerals are composed of quartz, kaolinite, kalsilite,calcite, siderite, and pyrite.(3) By comparing the gasification reactivity of successively demineralizedcoals with different mineral species, the catalysis of calcite is considered as thereason of synergistic effect. CaO from the decomposition of calcite can adsorbH2O and CO2simultaneously to the surface of the coal, then, H2O and CO2reactwith carbon in the coal. It makes the gasification reactivity in co-gasificationmuch better than that in any single gasification.(4) L–H kinetic model was used to describe the gasification reaction ofYining char and demineralized char in mixture of H2O and CO2. Theexperimental reaction rate of Yining char co-gasification is larger than the calculated reaction rate when using separate active sites and the common activesites. It is consistent with the synergistic effect in the co-gasification reaction.Besides, the common active sites assumption in L–H model fits theco-gasification reaction of demineralized Yining char well.