| At present,China requests huge energy consumption,the development of renewable energy has strong practical significance.Biomass energy is the most suitable renewable among several renewable energy.Among several paths of biomass utilization,Chemical Looping Gasification(CLG)is the most efficient way with the feature of low energy consumption and high syngas quality.The research on the CLG nowadays mainly focus on Iron-based oxygen carrier which makes the reaction temperature too high and the reaction rate is limited.In order to solve this problem,a combined metal oxygen carrier is proposed to improve the gasification efficiency by utilizing the oxygen decoupling property of this kind of oxygen carrier.The research contents and conclusions are as followed:(1)Cu-Mn and Cu-Fe oxygen carriers are prepared.Firstly,XRD analyzer is used for phase composition analysis,the results show that the active metal oxides of oxygen carrier react and produces new phases CuxMn3-xO4 and CuFe2O4.The grain sizes of oxygen carriers are calculated and the results show that the grain sizes of them are 20～30nm,the small grain sizes are propitious to gas-solid reaction.Thermogravimetric analyzer(TGA)is used to carry out the decoupling property and CLG preperty,the results show that CuMn oxygen carrier with mole ratio of 1.5:1:1 performs the best,thus CuxMn3-xO4 oxygen carrier with a mole ratio of 1.5:1:1 is chosen for further investigation.(2)The effects of different parameters on biomass pyrolysis are investigated by TGA,the results show that the addition of oxygen carriers can decrease the reaction temperature of the pyrolysis process.With the increase of the heating rates,the reaction rate increases,and the initial and termination temperature increases.With the increase of the mass ratio of oxygen carriers to biomass,the pyrolysis rates decreases and the solid conversion rate increases.Based on TGA data,kinetic model of pyrolysis process is established.The pyrolysis process conforms to F4 model when the conversion(α)is less than 0.5,and D4 model when a is greater than 0.5.(3)The effects of different parameters on biomass char gasification are investigated by TGA.The results show that the addition of oxygen carriers makes the reaction rate peaks from one to two.With the increase of heating rate,the final weight loss amount of samples decreases and the reaction rate increases.With the increase of the mass ratio of oxygen carriers to biomass char,the weight loss increases.Kinetic analysis shows that the gasification process of pine sawdust char conforms to D4 model at a of 0.25～0.4 and the F4 model at α of 0.4～0.75.The activation energy(E)of gasification is higher than that of pyrolysis,which indicates that pyrolysis is easier.The E of gasification of pine sawdust char increases gradually,indicating that the difficulty of gasification increases with the reaction.(4)Thermal experiments are carried out on a fixed-bed experimental platform.The results show that oxygen carriers promote the pyrolysis process and increase the gas yield.With the increase of heating rate,gas yield decreases.With the increase of temperature,H2 and CO’s contents increase,CO2 decreases,the gas yield and LHV increases gradually,which indicates that high temperature can promote pyrolysis and improve the quality of syngas.(5)Thermal experiments of gasification in a fixed bed shows that during the gasification process of biomass char,oxygen carrier releases oxygen as gasification medium to promote the gasification of biomass char.With the increase of the heating rate,the gas production rate decreases gradually.With the increase of oxygen carrier/biomass char mass ratio,CO content decreases,H2 and CO2 increases,CH4 basically remains unchanged,and gas production rate first increases and then decreases.With the increase of temperature,the content of H2 and CO increases,CH4 and CO2 decreases,and the gas production amount decreases.The LHV of syngas increases.(6)The physical properties of oxygen carriers before and after the reaction are characterized.XRD analysis shows that the phase composition of oxygen carriers remain unchanged after pyrolysis,indicating that oxygen carriers play a catalytic role in the pyrolysis process,and CuxMn2-xO2 is formed by the decoupling of oxygen carriers during gasification reaction.SEM analysis shows that oxygen carriers do not sinter after pyrolysis and gasification reaction.EDS analysis shows that a small amount of C element can be found on the surface of oxygen carriers. |
