| In promoting social development,fossil energies also brought about many issues such as environmental pollution and energy crisis,which prompts people to seek alternative energies that is environmental friendly and renewable.Biomass energy is such an ideal alternative with the advantages of little impact on environment,renewable,large reserves,etc.In the use of biomass,hydrogen production from gasification is an effective way to convert biomass energy into high-grade energy,thus is gaining increasing attention now.One of the major difficulties in biomass utilization is the wide varieties and different nature of biomass.But fortunately,almost all kinds of biomass are composed by three main components:cellulose,hemicellulose and lignin.Extra effort will be saved and the understanding of biomass gasification mechanism will be promoted if biomass gasification characteristics can be explained by the three components.The biomass steam gasification experiments were carried out on an updraft fixed-bed reactor in the temperature ranges of 9201220?,using the three components cellulose,hemicellulose and lignin and three kinds of real biomass.The effects of temperature and biochemical components on hydrogen production were studied,as well as a simulation by Aspen Plus.The results show that in the temperature ranges of 920-1220?,the gasification characteristics of cellulose and hemicellulose are similar,but are significantly different with that of lignin.During gasification of cellulose and hemicellulose,the gas release rate is greater and more H2,CO2 and less CO,CH4 is produced compared with lignin gasification.And with temperature increases,H2 content rises and CO content declines first and then increases.The gasification characteristics of three kinds of actual biomass are between lignin and cellulose,hemicellulose,basically satisfying the qualitative rule:biomass with large lignin coefficient has similar gasification characteristics with lignin,and biomass with large hemicellulose coefficient has similar gasification characteristics with hemicellulose.The maximum hydrogen production rate was 1.09 Nm3/kg at1020?by lignin among all the feedstock,and 0.67 Nm3/kg at 1220?by poplar leaves among the actual biomass.Component coefficients were used to fit syngas composition of the actual biomass.The fitting result has a certain linear correlation with the experimental results,which can be used as a reference for estimating the syngas composition of a certain kind of biomass.Biomass with higher lignin coefficient may have greater hydrogen production and higher H2 volume fraction,thus is more suitable for hydrogen production by gasification.Simulation study by Aspen Plus shows that lignin has the most hydrogen production rate among the three components,and the hydrogen production rate of the actual biomass is between lignin and hemicellulose,which is same as experiment results.The experiment results of lignin is the closest to thermodynamic equilibrium.The effects of temperature and biochemical composition on hydrogen production characteristics during biomass steam gasification was studied by experiments and simulations of three components and three kinds of real biomass.The results can be used as a reference to estimate hydrogen yield from biomass gasification and select gasification materials. |
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