Reaction Mechanism for Syngas Preparation by Lignite Chemical Looping Gasification Using Phosphogypsum Oxygen Carrier

In this study, syngas preparation by chemical looping gasification (CLG) process is investigated through theory and experiment. The starting materials for the syngas are low quality lignite, which cannot be used for other applications, and phosphogypsum (PG), the byproduct of wet phosphoric acid. The results show that the CO production is mainly due to the following reaction: (CaSO4 + 4C -> CaS + 4CO) and (C + CO2 -> 2CO), while the main reactions of H-2 generation are (CO2 + H2O(g) + 2CH(4) -> 3CO + 5H(2)) and (C -> H2O(g) -> CO + H-2). The analysis results indicate that high temperature and water vapor content are detrimental for phosphogypsum recycling. Furthermore, after three times recycling of phosphogypsum, some sintering is observed. The composition of syngas is very important for the corresponding applications. Therefore, the relationships between reaction factors and products are also investigated. The results of Analysis of Variance (ANOVA) show that H-2 and CH4 generation are strongly dependent on water vapor content. The influence of the different factors on CO yield is in the following order: PG/lignite's molar ratio > temperature > water vapor. Among the three factors, reaction temperature effect on CO2 generation is less than that of the other factors. Moreover, the reaction temperature and the PG/lignite's molar ratio have a great influence on lignite decomposition. The results of this work can provide some guidance for preparing syngas with the desired composition by the CLG process.