ABSTRACT:This work focuses on the behavior of coal-derived chlorine in chemical looping combustion (CLC) and the potential adverse impacts of primary gaseous chlorine on Cu-based oxygen carrier (OC). The inactivation mechanism of the sol-gel-derived CuO/Al₂O₃ OC is investigated. Systematic experiments are conducted in a batch fluidized reactor. First, in CLC of coal, chlorine distribution including HCl, Cl₂, Cl adsorbed in tube and Cl in solid phase are studied under various bed inventories, temperatures and gas atmospheres. The main gaseous Cl from coal is HCl, which shows a high reactivity towards CuO and is partially physically absorbed by Al₂O₃. Unconverted HCl is 15.63±0.20%, which could result in corrosion of the CO₂ transportation line and compression equipment. Then, a mixture gas with 400 ppm HCl are fed to evaluate the corrosion of various OC components, i.e., Cu-Al (whole OC), CuO (active phase) and Al₂O₃ (inert support phase). It is found that part of HCl is converted to Cl2 via the Deacon reaction (4HCl + O₂ = 2H₂O + 2Cl₂) and oxidized by CuO (CuO + HCl = CuCl + Cl₂ + H₂O). The coal ash exhibits a dichlorination function, forming KCl and CaCl₂. The CO₂ atmosphere and high temperature in fuel reactor show a promotion on the conversion of coal-Cl to HCl. Under a high concentration of HCl, the active phase CuO of the OC is partially lost, producing the gaseous copper chlorides, i.e., CuCl and (CuCl)₃. Besides, the solid-phase copper chlorides also degrade the oxygen donation capacity of the OC. Finally, the migration path of coal-chlorine during CLC is summarized. This work will contribute to the development of Cl-resistance OCs and control approaches for Cl emission.
 

chemical looping combustion; coal; chlorine; oxygen carrier