Chemical looping gasification of lignite to syngas using phosphogypsum: Overview and prospects

Chemical looping gasification (CLG) has achieved cleaner production of coal, avoiding the production of carbon dioxide. Phosphogypsum (PG) is a by-product of phosphate fertilizer's production. Up to now, various research results have shown great potential for syngas production via CLG with PG, which can achieve "high-value coal utilization and carbon reduction". However, moving from laboratory to industrial scale faces several challenges that need to be addressed. Compared with previously published works, this paper discusses the research on CLG of PG for the generation of syngas, and includes five main aspects: gasification effects, gasification mechanism, oxygen release mechanism, elemental migration and fluidization experiments. The advantage of PG as an oxygen carrier is that the main component of CaSO4 has strong oxygen carrying capacity, whereas Al and Fe of PG can reduce the decomposition temperature. Moreover, Si of PG can improve the anti-agglomeration capability of the oxygen carrier. In order to prepare a compound oxygen carrier, the combination of PG with other metals can decrease the reaction temperature, providing a theoretical basis for PG to cooperate with other solid wastes as an oxygen carrier. Furthermore, the paper also discusses the migration changes of non-primary elements of PG, which provide a guide for controlling PG such as F and P. The study of fluidization experiments provides a guidance for industrial applications. However, the current research is restricted only to laboratory-scale and lacks large-scale studies, particularly those focusing on the cold and hot fluidized bed. There are more macro studies and fewer molecular-scale studies about the CLG of PG. In order to study the mechanism in detail, molecular-scale research is recommended. Additionally, with the goal of industrialization, the material and heat balances of CLG are essential. Additionally, economic analysis of the whole process is also needed, so as to ensure the effect of actual industrialization process. This work provides guidance for further research on the role of PG as an oxygen carrier in the CLG process for industrial construction.