Insights into the catalytic effect of calcium occurrence and the anchored stability in char on steam gasification

Calcium-catalyzed steam gasification represents a clean and efficient technology for converting low-rank lignite into syngas. In previous studies, there was no consensus on the evolution characteristics of calcium-loaded lignite during char formation and the calcium occurrence at different pyrolysis temperatures. Therefore, the present work analyzes the calcium-catalyzed steam gasification process of char derived from the pyrolysis of lignite with and without acid treatment, simplifying the structure via demineralization. The results demonstrate that the calcium-loaded char samples' gasification performance at relatively low pyrolysis temperatures decreases after acid treatment. In addition, the gasification reaction temperature of acid-treated char decreases with the increase of pyrolysis temperature, but the gasification reaction temperature increases again at 900 °C, showing a trend of decreasing first and then increasing. The characterization results show that forming organic calcium in the char sample is the key feature affecting its steam gasification reaction performance. Simultaneously, the effectiveness of acid treatment for eluting calcium-containing compounds from the char samples is demonstrated to depend heavily on the pyrolysis temperature. For calcium-loaded coal without pyrolysis, almost all of the calcium was removed by acid treatment. For the calcium-loaded char prepared at 700 °C, the acid treatment has the weakest ability to elute calcium from the char, and only about 37 % calcium are removed. The results of this study are for further study of calcium-catalyzed steam gasification of lignite char. The catalytic mechanism in the reaction process and the efficient and clean utilization of lignite provide a theoretical basis.