Characterization Of Chemical Looping Gasification Of Bituminite Based On NiFe₂O₄ Oxygen Carrier

Chemical looping gasification（CLG）is a new,clean and efficient energy utilisation technology.In this study,the influence of different process conditions on the gasification process and product distribution was investigated based on the treatment of bituminite by chemical looping gasification with Ni Fe₂O₄ as the oxygen carrier.The reaction characteristics and component orientation control method of chemical looping gasification of coal under complex atmosphere were obtained,and finally the high quality syngas was achieved.At the same time,the changes of oxygen carrier phase,elemental valence,microstructure and the migration and transformation of lattice oxygen during the gasification and cyclic reactions were studied at the microscopic level by various characterization methods.In addition,the effect of the addition of alkali metals on the modification of oxygen carriers and the gasification process was investigated in more depth.It was found that increasing the temperature was beneficial to promote the gasification reaction of bituminite,but the promoting effect is no longer significant after 950℃.A high or low O/B value（oxygen carrier mass/bituminite mass）is not conducive to the acquisition of high quality syngas;the addition of a suitable amount of steam can significantly promote the conversion of bituminite and the improvement of syngas quality;Zr O₂ doping can have a further modifying effect on the oxygen carrier.Under the reaction temperature of 950°C,O/B value of7/3,steam of 0.08 m L/min and Zr O₂ doping ratio of 30%,the final carbon conversion of bituminite was 94.64%and the gas production efficiency was 86.23%.Under the optimum reaction conditions,the carbon conversion of bituminite was maintained at over 90%and the gas production efficiency was maintained at about 80%for 20 cycles,thus achieving a high quality syngas.During the gasification process,the Fe and Ni elements of the oxygen carrier underwent the changes of Ni²⁺→Ni,Fe³⁺→Fe^8/3+→Fe²⁺→Fe,accompanied by the migration and transformation of lattice oxygen.After long-term cycling,the oxygen carrier pore structure remained good,but the particle size increased slightly and slight sintering and agglomeration occurred;the oxygen carrier phase changed,part of Ni Fe₂O₄ did not get regenerated and gradually existed in the form of Fe₂O₃,Ni O,etc.;the alkali metal Ca in the bituminite ash gradually accumulated on the surface of the oxygen carrier,which played a certain role in promoting the whole gasification reaction.It is proved that Ni Fe₂O₄ has good reaction performance,strong anti-sintering ability and stable cycling performance after doping with Zr O₂,which is suitable for chemical chain gasification of bituminite.The addition of appropriate amounts of alkali metals can promote the bituminite CLG process and improve the bituminite carbon conversion rate and syngas yield.The addition of alkali metal plays a further modifying role on the oxygen carrier,optimising the pore structure of the oxygen carrier,weakening the Fe-O metal ion bond,making the Fe³⁺in the oxygen carrier more inclined to convert to the lower valence Fe,Fe²⁺and no longer Fe^8/3+,and also increasing the oxygen carrier reactivity.The modifying effect of alkali woody ash is better than that of K₂CO₃ and also allows for the reuse of disposable catalyst alkali lignin.However,the addition of excess alkali metals can also cause problems with oxygen carrier pore blockage,sintering and agglomeration.The above research provides a theoretical basis for opening up new avenues for the efficient use of coal resources and for achieving clean and efficient use of coal resources.