Hydrogen-rich Syngas Production From Steam Gasification Of Biomass In Molten Salt

Syngas?H₂+CO?is an important industrial raw material,which can be used for heat generation and high-value fuel production.The traditional syngas production process using fossil fuels such as coal and petroleum as raw materials causes environmental pollution.Biomass,which is characterized by renewability,low pollution,abundant resources and wide distribution,has become an alternative raw material for syngas production.In biomass utilization technology,pyrolysis and gasification are the core methods of thermochemical transformation,which are widely used in commercial applications.In this thesis,fir sawdust and its three components were used as raw materials,molten salt of Li₂CO₃-Na₂CO₃-K₂CO₃?LNK?was used as the thermal medium and catalyst,and steam was used as gasification agent to gasify biomass to produce hydrogen-rich syngas in a tank reactor.The main research contents and results are listed as follows:1.The gasification of main biomass components?cellulose,hemicellulose and lignin?and synthetic biomass in molten salt were investigated.A predictive model for hydrogen-rich syngas production from biomass gasification in molten salt was established and tested.The result of lignin gasification for H₂ was better than those of cellulose and hemicellulose under the same experimental conditions.The amount of tar components from three-component gasification followed the order:lignin<cellulose<hemicellulose.In the process of biomass gasification,there are obvious interactions between the three components of synthetic biomass and between the volatiles obtained from gasification process.The established predictive model can well describe the relationship between the contents of hemicellulose,cellulose and lignin in biomass and the yields of H₂ and syngas.2.Molten salt catalyzed gasification of fir sawdust to hydrogen-rich syngas was studied.The effects of temperature,molten salt,mass ratio of steam to biomass?S/B?,carrier gas flow,biomass shape and size on biomass gasification were investigated.It was found that higher temperature was beneficial to the production of syngas and H₂.When the gasification temperature was 750?,the syngas yield reached 911.61 m L/g biomass,and the content and yield of H₂ reached 55.5 vol.%and 681.77 m L/g biomass,respectively.Molten salt could effectively reduce the yield of tar,promote tar gasification and improve the yield of gas products.The introduction of steam could improve the yield of H₂ and H₂/CO in gas products,but the excessive steam would increase the energy consumption of the reaction system,and hence it was found that the appropriate S/B was 1?2.The carrier gas flow had an indistinctive effect on the gas products composition and yield for the flake biomass gasification.As a whole,the results of flake biomass gasification were better than those of powdered biomass.By pressing and shaping the raw materials,the loss of raw materials in the feeding process could be effectively avoided,which was conducive to the contact between raw materials and molten salt ions,and could also improve the unit handling capacity of the equipment and save molten salt.Within the scope of the experimental design,the optimal condition of the raw material was 0.25 g/tablet,with the yield of H₂ and syngas reaching 807.53 and 1119.82 m L/g biomass,respectively.3.The steam gasification of biomass co-catalyzed by molten salt-absorbent or nickel-based catalyst to produce hydrogen-rich syngas was studied.In the experiments,Ca O and dolomite were selected as the absorbent,and Ni O/Al₂O₃ and Ni/Al₂O₃catalysts were prepared to improve the yield of syngas and H₂/CO by improving the water-gas shift reaction,tar catalytic cracking and reforming reactions,respectively.It was found that the absorbent added into molten salt could enhance the water-gas shift reaction to a certain extent and increased the content of H₂ in the product gas.However,the powder solid absorbent had a certain inhibitory effect on the catalysis and heat transfer rate of molten salt.The additive nickel-based catalyst could improve the total gas yield.During the gasification process,Ni/Al₂O₃ could promote the cracking and reforming of tar and improve the yield of H₂ in syngas.In this study,a predictive model for biomass gasification in molten salt was established,and hydrogen-rich syngas with high yield was produced from steam gasification of fir sawdust in molten salt.The co-catalytic effects of molten salt-absorbent and nickel-based catalyst on biomass gasification were investigated.These results can provide reference for the application of biomass catalytic cracking,gasification and steam reforming to produce hydrogen-rich syngas,and also provide reference for the energy utilization of agricultural and forestry wastes and the production of syngas.