Study On The Lean Iron Ore As The Oxygen Carrier In Chemical Looping Combustion

Chemical looping combustion(CLC)can achieve oxygen transportation through the circulation of oxygen carrier between the fuel and air,which can improve the CO2 capture efficiency and reduce the energy consumption of CO2 capture.The performance of the oxygen carrier is the key to the CLC system.The lean iron ore which is inexpensive and environmental friendly,has wide raw material sources.The activity of the lean iron ore is moderate,which is a suitable choice for oxygen carrier.The small particle size of oxygen carrier has a strong oxygen carrying capacity,and the residence time in the fuel reactor is in the range of several seconds to tens of seconds.In the previous experiments,the scholars focused on the study of the oxygen carrier redox reaction characteristics,in which the residence time mostly in a dozen or even tens of minutes.The CO was selected as the reducing gas.The CO residence time was less than 60 seconds in order to make the redox reactions process of the lean iron ore more realistic.Consecutive reduction-oxidation cycles were carried out in the thermogravimetric analyzer(TGA)and the fixed bed to study the activity of the lean iron ore and the modified iron ore.The experimental results of the lean iron ore in the TGA,in which residence time was 60s,indicates that the reduction reactivity of lean iron ore remains stable in the 15 cycles.The available conversion rate of lean iron ore increases with the increasing temperature and the CO concentration.In the short-time reduction reaction,the lean iron ore shows the comparable the reduction of reactive activity to hematite and ilmenite ore.The residence time was changed in the experiments of the lean iron ore in fixed bed.The CO2 concentration at the outlet of the reactor decreases as the residence time decreases.The cyclical stability of lean iron ore is gradually strengthened with the decrease of residence time.When the residence time is shortened from 60s to 40s,the CO2 concentration at the outlet of the reactor decreases relatively from 11.14%to 3.41%.The analysis of SEM shows that the shorter the residence time is,the smaller the structure of the surface of the lean iron ore changes.There was no serious sintering on the surface.The lean iron ore with the longer residence time has the larger pores.The paper used the plant-ash aqueous water to modify the lean iron ore.The test of the modified iron ore was carried out in the TGA.The reduction condition and the chemical reaction rate of the modified oxygen carrier were better than those of the lean iron ore.The cyclic stability of the modified oxygen carrier remains well in the 100 cycles.The oxygen carrier has a small amount of mass loss.K+ reduces the effect of the temperature changes on the reaction activity.When the reaction time is 600 s,the chemical reaction rate constant of the modified iron ore is up to 11.82 times of that of the natural iron ore at 800?.When the reaction time is shortened to 20s,the chemical reaction rate constant of the modified oxygen carrier can reach 4 times of that of the modified oxygen carrier at 800?.The load ratio of K+was changed to study the effect of load ratio of K+ on the iron ore.The results of experiments in the fixed bed indicate that three modified iron ores show strong cyclic stability in 100 cycles.The analysis of the XRD and SEM experiments shows K+ will diffuse from the surface of the modified iron ores,which has a higher concentration of K+,to the centre of the particle.This can lead the formation of pores,which can cause the powdering of modified iron ore.The phenomenon of powdering is likely to cause the loss of oxygen carrier.