Chemical behavior of fluorine and phosphorus in chemical looping gasification using phosphogypsum as an oxygen carrier

Abstract

In China, the amount of phosphogypsum (PG) has exceeded 250 million tons with more than 55 million tons of growth rates each year. As the micro constituent, fluorine and phosphorus restrict the resourceful disposal of PG. This paper focused on chemical looping gasification (CLG) which used PG as an oxygen carrier, systematically investigated the gasification performance and chemical behavior of fluorine and phosphorus contained in PG during CLG process. Main conclusions are as follows. The main pollutant of chemical looping gasification process was HF, which was transformed from NaF. Phosphorus transformed from water-soluble phosphorus (Ca(H2PO4)2, Ca(HPO4)) into insoluble Ca3(PO4)2.20 reducing-oxidizing cycles were investigated, and a less and less fluorine content in oxygen carrier was found because its phase transformation from solid NaF to gaseous HF, and the phosphorus content in oxygen carrier changed slightly under the current conditions. The Ca3(PO4)2 particle layers existed in both the middle of the reduced solid particles and the middle of the cycled oxygen carrier particles, confirmed to actually act as a glue between the particles. Furthermore, transformation routes of fluorine and phosphorus during the CLG process were discussed and the generation of syngas in CLG process needed to be purified.