Investigation Of Chemical Looping Combustion Of Carbon Monoxide And Lignite With Fe₂O₃-based Combined Oxygen Carrier

CO2 is considered the largest contribution of the gas making to the greenhouse gases.How to separate efficiently and captue CO2 inexpensively has become the key issues for schloars.Different from conventional combustion, chemical-looping combustion (CLC) has the inherent property of separating the product CO2 from flue gases without any extra energy penalty and separation device.In addition, CLC can eradicate the formation of NOx and become more economical and environmental friendly.For CLC, the key point in the system performance is the oxygen carrier. Because of its low cost and environmental compatibility, Fe-based oxygen carrier is considered the main object in this paper, in spite of its weak redox characteristics, low oxygen transport capacity and easy agglomeration. Firstly, different magnitude orders of Co and Mn-doped Fe-based oxygen carriers were preparated by coprecipitation.Then, the physical and chemical properties were characterized by TGA, XRD, TEM and BET methods.Finally, experiments were respectively carried on for iron-based oxygen carrier with CO and lignite reaction.The reaction of different molar ration of Co-Fe2O3 and Mn-Fe2O3 with CO at 750℃,800℃ and 850℃ investigated that the conversion of Co0.2Fe was highest under 850℃.The Co0.2Fe converted completely within 3.18min, shortened by 49.6% than that of pure Fe2O3.The higher doping amount, the higher reduction conversion and more depth reduction degree. The conversion could be as high as 98% in 4.5min for Mn0.02Fe reacted with CO at 850℃. Then the analysis of chemical kinetics and reaction dynamics based on Co and Mn-doped Fe-based oxygen carriers reacted with CO were performed. Comprehensive comparison of the multicycle redox reactions of Co-Fe2O3 and Mn-Fe2O3, it was concluded that Coo.2Fe showed more excellent chemical stability and higher activity than Mno.o2Fe.Based on the above optimum performance of Co-doped oxygen carrier, depth study that increasing Co doping amuout and adding material support Al2O3 was carried out.The orthogonal experiment result indicated that, the Fe-based oxygen carrier of 25wt% Co-doped amuout, calcinated at 800℃ in 1.5h reacted with CO at 850℃, performed optimal. Multicycle redox reaction for 5,10 and 16 times of optimized oxygen carrier with CO cleared that Co-Fe2O3/Al2O3 has potential industrial application with excellent chemical stability and little attrition,except for slight sintering phenomenon.The investigation of lignite with oxygen carrier Co-Fe203/Al2O3 was performed.It was analyzed that Al2O3 hindered the full contact of oxygen carrier and lignite, and inhibited the conversion. The side product Fe2SiO4, Co3S4, CoS and coal ash made the reduced Co-Fe2O3/Al2O3 could not be completely regenerated.Therefore, separation of ash generated will be important to the success for CLC application of solid fuels.