Study On The Formation Of Pahs And Carbon Deposition During Coal Chemical Loopingcombustion Of Iron-Based Oxygen Carrier

Oxygen carrier(OC)is a carrier to realize oxygen migration in CLC,which plays a vital role in in the operating efficiency of CLC.The carbon deposition on OC is an important factor restricting the development of OC.This paper studied the flow rate of CO₂ gas,coal component structure and OC cycle times on the carbon deposit precursors PAHs in the flue gas and the carbon deposit on the oxygen carrier in the coal CLC of Fe₂O₃/Al₂O₃.Then analyze its mechanism of action in order to obtain the best carbon deposition suppression methods and improve the performance of the oxygen carrier.The results show that:(1)Comparing the scanning electron microscopy(SEM)and X-ray diffraction(XRD)pattern characteristics of the fresh,after reduction reaction and reoxidation OC,it is found that the fresh OC is loose and porous,the surface pore size is uniform,and the main crystal phase is Fe₂O₃ And Al₂O₃.After the reduction reaction,the OC begins to show a slight agglomeration and sintering phenomenon.As cycles times increases,the surface pore diameter of the OC increases and the pores decrease,and the sintering phenomenon becomes more and more obvious;(2)In the study of coal CLC,as the carbon content of coal increases,the growth of char on the OC shows an increasing trend,while the total amount of PAHs generated in the flue gas and the accumulation of soot on the OC gradually decrease.The introduction of 20 ml/min CO₂ does not change the overall trend of PAHs and char formation.The coal CLC with higher carbon content produces less PAHs,but increases the total amount of PAHs generated.At the same time,the output of soot on the OC under the same conditions is reduced by 25%?68%.(3)The higher the volatile content,the higher PAHs concentration generated by coal CLC,and the amount of soot produced on the OC gradually decreases with the increase of the volatile content.(4)When CO₂ is not introduced,the PAHs generated by coal CLC are mainly low-ring aromatic hydrocarbons.After CO₂ is introduced,among the 16 types of PAHs produced by combustion,middle-ring aromatic hydrocarbons account for a relatively high proportion.(5)With the increase of the OC cycle times,the PAHs concentration in the flue gas and the production of soot and char on the OC both show an increasing trend.The amount of soot produced on the OC decreases as the carbon content of coal increases.After the introduction of CO₂,the growth of soot under the same conditions is reduced.The coal with higher volatile content still tends to produce more PAHs during the CLC process,but the amount of soot accumulated on the OC increases with the volatilization.The introduction of CO₂ does not change this trend,but significantly reduces the amount of soot and char deposited on the OC,and when the number of cycles is small,the soot and char on the OC has a better inhibitory effect.The introduction of CO₂ has a significant inhibitory effect on soot and char on the OC.In summary,the introduction of CO₂ makes the physical characteristics of the iron-based OC perform well,which is beneficial to the recycling of the oxygen carrier.At the same time,it effectively reduces the deposition of soot and char deposits on the OC,which is expected to make a certain contribution to increasing the reaction activity and life cycle of the OC.