Experimental Investigation On Characteristic Of Mn-based Oxygen Carrier In Chemical Looping With Oxygen Uncoupling

Chemical-looping combustion (CLC) is a novel CO2caputure and collectiointechniques. It’s not only high efficiency, but also low energy consumption, comparedwith traditional. CLC system includes air reactor and fuel reactor. Oxygen carrierscirculate between the two reactors to transfer oxygen. High concentration of CO2isobtained in the fuel reactor after combustion products are condensated. And chemicallooping with oxygen uncoupling (CLOU) is suitable for solid fuels. The most critical ofCLC is the need for a good performance oxygen carrier. Mn-based oxygen carriers werestudied because of it’s relatively high melting point and low price.Oxygen release characteristics of Mn2O3under different conditions wereinvestigated in the thermogravimetric analysis (TGA) firstly. Then the oxygenabsorption characteristics of Mn3O4, which is the product of Mn2O3after oxygen release,were investigated. It’s cycle stability and the effect on that by slag and fly ash wastested. Kinetic parameters of Mn-based oxygen carriers were obtained, too. Based onthe study, the effect of inert carriers on Mn-based oxygen carriers was examined, andthe effect of impregnation method and pore-forming using graphite on the oxygencarriers was also tested. Then better performance Mn75Al25and Mn2O3were selectedto test the cycle stability of CLOU with coal on fixed bed. XRD and SEM were appliedto study the phase analysis and microstructure analysis of oxygen carriers. Finally, theoxygen release characteristics and the cycle stability of composite oxygen carriersprepared by nitrate impregnation were also investigated using the same way.According to the experimental results, it’s found that the initial oxygen releasetemperature of Mn2O3is gradually increased and the activation energy is increasedsignificantly with the increasing of oxygen concentration. The time of oxygen release isdecreased with reaction temperature increasing. When the hating rate in improved, theactivation energy has a slight increase. The time of Mn3O4oxidation is improved withthe reaction temperature increasing. With decreasing of oxygen concentration, potentialdifference of oxidation required is smaller, and Mn3O4is easily oxidized. Mn3O4exhibits good stability in20circulation. Slag has some influence on it’s cycle stability,while fly ash has no effect on that.Investigation of modified Mn-based oxygen carriers by inert carriers shows that thetime of oxygen release of Mn75Al25is less than Mn2O3at the same reaction temperature. TiO2has most prominent change on equilibrium partial pressure ofMn-based oxygen carriers. Mn75Al25has the best cycle stability, and Mn75Zr25is notsuitable as oxygen carriers for CLOU. Mn75Al25prepared by impreganation has bettercharacteristic than Mn75(Al9C1)25prepared by pore-forming using graphite. Mn75Aland Mn2O3are not suitable as oxygen carriers for CLOU with coal.Experimental study of Mn-Cu composite oxygen carriers shows that oxygenrelease time of (Mn75Cu25)3Al1is less than Mn75Cu25at the same reactiontemperature. Oxygen release of them under anaerobic is more than aerobic conditions,while the particle size has no effect on oxygen release characteristics at the sametemperature. Both of them have good cycle stability. But oxygen release of(Mn75Cu25)3Al1is relatively stable with the number of cycles increasing. During theCLOU with coal, particle size of Mn75Cu25increses gradually with the number ofcycles increasing, but (Mn75Cu25)3Al1has only small changes. Cycle stability test ofoxygen carriers after CLOU with coal shows that every oxygen release of(Mn75Cu25)3Al1undulates smaller than Mn75Cu25with the number of cyclesincreasing.