Characteristics And Simulation Study On Biomass Chemical Looping Gasification Base On Iron Oxygen Carrier

Biomass chemical looping gasification is one of the current efficient utilization technologies of biomass energy.Oxygen carrier provides lattice oxygen in the gasification process,and biomass is converted into combustible gas,so as to avoid the low heating value caused by the addition of large amount of N₂ or high cost caused by oxygen separation.In CLG,the steam flow,temperature and content of oxygen carrier have a great impact on the composition yield of syngas,and the cycle characteristics of the oxygen carrier is also the key factors for chemical looping gasification.Alkali metal has double effects on gasification.It can catalyze gasification reaction and promote oxygen carrier to release lattice oxygen,but its melting characteristics easily caused oxygen carrier to be deactivated.Nowadays,chemical looping gasification is still in initial stage,and these problems are not fully studied.Therefore,this study researched about the characteristics of CLG,as well as the influence of alkali metal.Then Aspen Plus software was used to simulate the system of CLG.The CLG was studied to obtain the characteristics of gasification in fixed-bed reactor,and the effect of steam flow,OC content and temperature was analyzed.The results show that the addition of steam can increase the yield of syngas,and significantly H₂ yield;but excessive steam will cause the decrease of CO yield and gasification efficiency.When the pump speed n=1.2r/min,higher gasification efficiency and carbon conversion rate can be obtained.Oxygen carrier can promote the gasification reaction of tar,but excessive OC can oxidize syngas deeply,which resulted in the decrease of gasification efficiency and carbon conversion rate.The optimized molar ratio of Fe₂O₃/C is 0.25.In addition,higher temperature is conducive to the reaction among pyrolysis product and oxygen carrier,but it tends to cause the sintering of oxide carrier.In the gasification reaction process,oxide carrier was reduced to Fe O and Fe without steam;after adding appropriate steam,Fe₂O₃ was completely converted into Fe₃O₄.After multiple cycles of reaction,the reaction performance of oxygen carrier decreased;compared with pure Fe₂O₃,hematite showed better stability during the cycle of gasification.Based on the previous research,the effect of hematite loaded with different alkali metal on the gasification reaction was studied.In TG-FTIR analysis,it showed that the addition of K₂CO₃ can catalyze the gasification of biomass and shorten the reaction time.At the same time,the weight loss rate increases at high temperature.Compared with pure hematite,the addition of KCl salt can catalyze the oxygen carrier to release oxygen at high temperature,and the reaction time is advanced.In the late reaction stage,C reacted with CO₂ to generate CO,resulting in the delay of CO release.Under the condition of steam,adding appropriate alkali metal can improve the gasification efficiency and carbon conversion rate of biomass.Excessive alkali metal will cause the surface sintering of oxygen carrier.Therefore,the optimal addition is 2%K₂CO₃.Aspen Plus software was used to simulate the gasification system,and the effect of Fe₂O₃/C ratio,S/B ratio and other factors on the gasification reaction was studied in the self-heating reactor.With the increase of Fe₂O₃/C molar ratio,the gasification temperature increases,but the gasification efficiency gradually decreases.Therefore,the high Fe₂O₃/C mole ratio is not good for the syngas yield.However,due to the demand of self-heating and the demand of oxygen supply temperature of chemical looping,the optimal mole ration of Fe₂O₃/C is 0.5-0.6.With the increase of S/B ratio,the gasification temperature continuously decreases,and the gasification efficiency first increases and then decreases.For different biomass,due to the higher carbon content and volatile content of pine sawdust,its gasification efficiency and gasification temperature were higher.