Theoretical and experimental demonstration of lignite chemical looping gasification of phosphogypsum oxygen carrier for syngas generation

•Phosphogypsum was used as oxygen carrier in CLG process for syngas.•Lignite was used as solid fuel in this paper.•Syngas generation is via solid-solid reaction and gas-solid reaction.•Optimizing operation condition has been obtained.•Contrasted experiment and theory analysis.

Phosphogypsum (PG) is a by-product in the phosphate fertilizer industry, and low rank coal-lignite has high moisture which seriously influence its direct use. As a promising raw material for chemical industry, syngas can be obtained through a properly designed lignite Chemical Looping Gasification (CLG) of PG oxygen carrier. The understanding of the reaction mechanism has been developed, while optimal conditions have been investigated. The study found that the product of syngas mainly comes from the solid-solid and gas-solid reactions, while the consumption of syngas mainly takes place via gas-solid reaction. Additionally, the effects of several reaction conditions on the production of syngas have also been analyzed. The optimum values of these reaction conditions are found to be as follows: the PG/lignite molar ratio (X) should be about 0.2; reaction temperature should be over 1123 K; 40-140 mesh size particles should be used. Meanwhile, the crystallization and properties of used phosphogypsum have been studied using X-ray diffraction and Scanning Electron Microscopy. The results suggested that calcium sulfate was almost completely converted to CaS at a temperature higher than 1123 K, while the sintering of used PG particles can take place for 140 mesh and 200 mesh sizes.