Analysis Of Chemical-looping Gasification Reactivity Of Pine And Oxygen Carrier Fe₂O₃

With development of the economy and society, energy and environment problem has become the focus in the world. Fossil fuel is not one of renewable source, so developing renewable and recyclable new energy is necessary for us. In the serious energy situation, energy intensity of renewable energy still keeps rising. Compared with fossil fuel, biomass energy is one of renewable energy which does not emit carbon dioxide. The syngas produced from the biomass instead of fossil fuel is one of promising new energy technologies. Cost of traditional biomass gasifying technology is so expensive that some scholars have proposed chemical-looping gasification technology based on chemical looping combustion. Cost of chemical-looping gasification technology between biomass and iron-based oxygen carrier is so cheap that it has a bright study future. Because reactivity of iron-based oxygen carrier is very bad, reactivity of iron-based oxygen need to be improved.Firstly, this thesis, based on the minimization of Gibbs free energy, intended to look for the optimum conditions through thermodynamic calculations. The optimum conditions would provide a basis for experiment. At the same time, oxygen carriers were prepared with sol-gel method and mixing method; Alkali metal potassium was added to oxygen carrier for improving their reactivity. On this basis, influence of different oxygen carrier and Alkali metal potassium amount was studied on pine chemical looping by thermogravimetric analysis. For further study gasification character, influence of different factor was studied in fixed bed experiment system on pine chemical-looping gasification. Finally, oxygen carrier properties at micro scale were studied by SEM and XRD technology. The results show:① At 850°C ~900°C and 1.2 of Fe2O3/C mole ration, there was best gasification efficiency when adding steam. With increasing reaction temperature, the amount of CO increased relatively and the amount of CO2 reduced relatively. Higher reaction temperature was in favor of gasification result. Because of the physical properties of iron based oxygen carrier, higher temperature was bad for biomass chemical looping gasification when temperature was over 950°C. When amount of Fe2O3 was below turning point gasification, the carbon conversion ratio and the amount of syngas increased with increasing temperature. When amount of Fe2O3 was over gasification turning point, gasification became to burn and CO began to convert CO2. This situation was bad for biomass gasification. H2 amount gradually increased with H2O/C mole fractions increasing. Consider gasification result and reaction equilibrium, optimal values of H2O/C mole fractions would be 1.0~1.4 for chemical-looping gasification.② Oxygen carrier Fe Al3K10 which was prepared with sol-gel method showed the best reaction characteristics on experiment. The study found that reactivity of oxygen carrier Fe7Al3 by sol-gel process was better than oxygen carrier H-Fe7Al3 by mixing method. The result was consistent with SEM analysis. Compared with oxygen carrier H-Fe7Al3 by mixing method, there was higher porosity of oxygen carrier Fe7Al3 by sol-gel process. When adding Alkali metal potassium in iron based oxygen carrier, biggest weight loss change of mixture between oxygen carrier and biomass was more evident; athlete oxygen of Fe7Al3K5 and Fe Al3K10 on oxidation has risen greatly and their reactivity change became better.③ At 900°C, oxygen carrier Fe7Al3K10 showed better gasification character.The addition of steam would improve the production of hydrogen and gases quality became better than no steam. Gas composition has some change at different reaction temperature(850°C, 900°C, 950°C). The heat value and carbon conversion ratio were the highest at 900°C. Oxygen carrier obviously improved biomass gasification efficiency. Compared with oxygen carrier H-Fe7Al3 which prepared with mixing method, gasification between biomass and oxygen carrier Fe7Al3 which prepared with sol-gel process had better gasification efficiency. Alkali metal potassiumon iron based oxygen carrier would greatly promote gasification efficiency on biomass chemical-looping gasification. For different Fe7Al3/biomass mass ratio(0,3,5), the heat value and carbon conversion ratio were the highest at mass ratio 5. In X-ray diffraction patterns, diffraction peak of unreacted oxygen carrier Fe7Al3K5 was same as diffraction peak of reacted oxygen carrier Fe7Al3K5; this result illustrated reduction oxygen carrier was completely oxidized.