(174cd) Harmful Components Migration and Transformation in the Chemical Looping Gasification of Phosphogypsum As Oxygen Carrier

Jing Yang, Liping Ma*, Jie Yang, Zhiying Guo, Bounkhong Keomounlath, Wei Zhang

Faculty of Environmental Science and Engineering, Kunming University of Science and Technology, Kunming, Yunnan 650093, China

Abstract:

The phosphogypsum(PG) in Kunming, China, is one of the largest integrated phosphogypsum(PG) basin newly found. The present work concentrates on the application of chemical looping gasification (CLG) with a Kunming phosphogypsum(PG), which is characterized by many types of harmful impurities content, such as fluorine, phosphorus, potassium and sodium. In order to study the pollution behavior in the preparation of syngas by melting method using Kunming phosphogypsum (PG) as oxygen carrier, the thermodynamic equilibrium states of fluorine, phosphorus, potassium and sodium elements were calculated by Factsage7.1 software package combined with the chemical composition analyses of the Kunming phosphogypsum (PG). The transport and transformation of fluorine, phosphorus, potassium and sodium elements were explored at different temperatures. The results show that the fluorine element gradually reach up to thermodynamic equilibrium state while the phosphorus, potassium and sodium elements a higher temperature are required during the heating process in CaSO₄-C-H₂O(g) system using phosphogypsum(PG) as oxygen carrier. At 900 ° C, fluorine mainly exists as HF、KF gases and Ca₄Si₂F₂O₇(53.47%) solids; phosphorus exists as Ca₅HO₁₃P₃ solids; potassium exists as KAlSiO₄ solids; sodium exists as NaAlSiO₄ solids. After 900℃, with the temperature gradually increasing, fluorine has the transformation trend from solids Ca₄Si₂F₂O₇ into HF、KF、NaF gases; phosphorus has the transformation trend from solids Ca₅HO₁₃P₃ into solids Ca₁₀(PO₄)₆F₂; potassium has the transformation trend from solids KAlSiO₄ into KOH、KF、K gases; sodium has the transformation trend from solids NaAlSiO₄ into NaF、NaOH、Na gases. In addition, the experiments at 900 °C are conducted to verify the prediction on the transformation of fluorine and phosphorus, the results from which are well in agreement with the theorectical calculations.

The information obtained in this study could be used to evaluate the feasibility of phosphogypsum(PG) as an oxygen carrier chemical looping gasification (CLG), mitigating the pollution to the environment.