Behavior of coal-chlorine in chemical looping combustion

Abstract

This work focuses on two aspects: (i) the behavior of coal-derived chlorine in chemical looping combustion (CLC); (ii) the potential adverse impacts of primary gaseous chlorine (i.e., HCl) 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 the outlet tube and Cl in solid phase is 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 adsorbed by Al2O3. Unconverted HCl is 15.63 ± 0.20%, which could result in corrosion of the CO2 transportation line and compression equipment. What's more, the coal ash exhibits a dechlorination function by forming KCl and CaCl2. The CO2 atmosphere and high temperature in fuel reactor show a promotion on the conversion of coal-Cl to HCl. Then, the corrosion of various OC components is evaluated by a mixture gas with 400 ppm HCl, i.e., Cu-Al (whole OC), CuO (active phase) and Al2O3 (inert support phase). It is found that a part of HCl is converted to Cl2 via the Deacon reaction (4HCl + O2 = 2H2O + 2Cl2) and oxidized by CuO (2CuO + 4HCl = 2CuCl + Cl2 + 2H2O). At the high concentration of HCl (400 ppm) atmosphere, CuO is partially lost from the OC, producing the gaseous copper chlorides, i.e., CuCl and (CuCl)3, which are found to be condensed in the outlet tube. 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.