Retention mechanism of calcium ferrite and compositions of ash on selenium during chemical looping gasification--颗粒学报PARTICUOLOGY

Han, Z., Kang, H., Yuan, N., Guo, X., Ma, J., & Guo, Q. (2023). Retention mechanism of calcium ferrite and compositions of ash on selenium during chemical looping gasification. Particuology, 79, 143-152. https://doi.org/10.1016/j.partic.2022.11.002

Retention mechanism of calcium ferrite and compositions of ash on selenium during chemical looping gasification

Ziheng Han ^a, Huifen Kang ^a, Nini Yuan ^a, Xintong Guo ^a, Jingjing Ma ^a *, Qingjie Guo ^{a b *}

a State Key Laboratory of High-efficiency Utilization of Coal and Green Chemical Engineering, College of Chemistry and Chemical Engineering, Ningxia University, Yinchuan, 750021, China
b Key Laboratory of Clean Chemical Engineering in Universities of Shandong, College of Chemical Engineering, Qingdao University of Science & Technology, Qingdao, 266042, China

10.1016/j.partic.2022.11.002

Volume 79, August 2023, Pages 143-152

Received 21 December 2021, Revised 25 October 2022, Accepted 2 November 2022, Available online 17 November 2022, Version of Record 24 January 2023.

E-mail: majingjing@nxu.edu.cn; qjguo@qust.edu.cn

Highlights

• Increased calcium content in oxygen carrier enhances the immobilization of selenium.

• As the number of cycles increases Ca₂Fe₂O₅ is more stable for retaining selenium.

• MgO and CaO in bottom ash have obvious fixing effect on selenium.

Abstract

Selenium pollution by coal utilization is of increasing concern. Calcium-iron (Ca–Fe) oxygen carriers (OCs) and alkali metal ions have strong inhibitory effects on selenium, which can reduce the emissions of selenium vapor. The retention mechanisms of selenium by Fe₂O₃, CaFe₂O₄, Ca₂Fe₂O₅ and bottom ash are investigated during chemical looping gasification (CLG). Iron-based OC can oxidize H₂Se(g) to SeO₂(g); furthermore, lattice oxygen is released by Fe₂O₃, contributing to the formation of an Fe–O–Se structure to retain selenium and form selenite. Because calcium ferrite is poorly oxidizing, it cannot oxidize H₂Se(g), but the CaO produced when OCs are reduced can react with H₂Se(g) to form CaSe(s), and this process can be promoted by H₂S(g). The best retention rates reached 32.301% when Ca₂Fe₂O₅ was used. In the cyclic experiment, the selenium retention of the bottom ash gradually increases. Alkali metal ions in bottom ash are the main factor in retaining selenium. Ca²⁺ and Mg²⁺ do not easily vaporize due to their high melting points; therefore, their selenium retention is significantly better than that of K⁺ and Na⁺. This research provided a new idea for the removal of selenium by using OCs and bottom ash particles during CLG.

Graphical abstract

Keywords

Selenium; Chemical looping gasification; Oxygen carrier; Retention mechanism; Ash composition

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