Chemical looping combustion (CLC) of coal has attracted great attention due to its advantage in low CO₂ and NO_x emissions. NO_x is both an air pollutant and a greenhouse gas. Therefore, it is of great practical significance to control the release of nitrogen pollutants in the process of coal combustion. In this paper, the CLC experiments of lignite and hematite used as oxygen carrier (OC) were carried out. Firstly, the thermodynamic behaviour of NH₃/HCN (NO_x precursors) and OCs were analysed. Fe₂O₃, NiO, CuO and Mn₂O₃ tended to oxidize the NH₃ and HCN to N₂ instead of NO_x. Secondly, the release characteristics of NH₃ and HCN with temperature were studied based on the TG-MS. The release of NH₃ was mainly in the devolatilization stage of lignite, while the release of HCN was not only in the devolatilization stage of lignite but also in the reaction stage of OC and lignite semi-coke. In addition, the release characteristics both of HCN and NH₃ had nothing to do with the mass ratio of OC to lignite. Thirdly, through fixed bed reactor, the nitrogen migration in the fuel reactor was also investigated by changing reaction temperature, OC mass, flow rate of carrier gas and type of OC (modified by K/Na/Ca/Ni/Cu/Mn). The release of HCN increased with the increasing of temperature, while the release NH₃ decreased. The increase of OC to lignite mass ratio would lead to the decrease of NH₃ and HCN. The increase of gas flow rate would increase the emission of NH₃ and HCN in the CLC process. Compared with hematite as OC, the NH₃ and HNC emission increased when hematite was modified by Na and Mn. Additionally, the OC had a good oxidation performance after modified by Ni and Cu, and it could significantly reduce the emission of NH₃ and HCN. Finally, the attempt of this paper was to achieve the way of reducing the emission of nitrogen oxides precursors in CLC process.

chemical looping combustion, lignite, hematite, NOx, HCN, NH3