Release and Migration Behavior of Nitrogen in Chemical-Looping Gasification Process Based on Iron-Based Oxygen Carrier

Release and migration behavior of nitrogen in chemical-looping gasification process based on iron-based oxygen carrier

LI Yankun, GUO Qingjie*, MA Jingjing, CHANG Guozhang, HU Xiude

(Ningxia University£¬State Key Laboratory of High-efficiency Coal Utilization and Green Chemical Engineering, Yinchuan,750021,China)

Abstract: The combined thermo gravimetric-infrared-mass spectrometry (TG-FTIR-MS) analysis was used to conduct chemical-looping gasification experiments of coal under Ar atmosphere, and the mass change and gas composition during the reaction were monitored in real time. The surface element analysis of the solid phase was carried out by X-ray photoelectron spectroscopy, when the change of nitrogen functional groups in the solid phase at different stages of chemical-looping gasification was investigated. The results show that the oxygen carrier has an effect on the release of nitrogen-containing gas in different stages of the chemical-looping gasification process. During the pyrolysis stage, the oxygen carrier promotes the generation of free radicals, which accelerates the release of nitrogen-containing gas in a pyrolysis stage. At high temperature, the oxygen carrier promotes the conversion of NH₃ to HCN; The addition of the oxygen carrier during the gasification stage reduces the degree of graphitization of the semi-coke and increases the release rate of the nitrogen-containing gas. For the nitrogen functional groups in the solid phase, the oxygen carrier promotes the decomposition and conversion of pyrrole nitrogen in the pyrolysis stage. At high temperature, the protonated pyridine is converted to pyrrole nitrogen and pyridyl nitrogen due to the presence of the oxygen carrier. During the pyrolysis process carried out at a high temperature, the protonated pyridine convert to pyridinium nitrogen, During the gasification process, the presence of water vapor increases the concentration of hydrogen radicals at high temperature, and the protonated pyridine is converted into pyrrole nitrogen which is more easily decomposed and converted.

Key words: Coal; chemical-looping gasification; iron-based oxygen carrier; nitrogen-containing gas; nitrogen functional groups; TG-MS-FTIR