| Syngas consisting mainly of H2and CO is applied to chemical synthesis. It can find a wide range of applications including use as feedstock for chemical elements in the petrochemical industry and as liquid fuels based on the Fischer-Tropsch process to produce high grade chemicals such as hydrogen, methanol or dimethyl ether. Now, syngas production process is based on the gasification of coal or natural gas. With the fossil energy exhausting and serious environmental problems, the development syngas production from renewable biomass would be significant for solving the shortage of fossil and environmental pollution. Biomass is aboundant, low-cost, environmental friendly. Biomass converted to high grade and high value-added chemicals by thermochemical processes will become the focus of further study.In this study, catalytic gasification of biomass feedstock with steam was used for syngas production. The main results were as follows:(1) Pine sawdust was employed as biomass feedstock. The results of ultimate and proximate analyses showed that pine sawdust was rich in volatile matter and it contained fewer contents of fixed carbon and ash. The thermalgravitic analysis (TGA) indicated three stages (dehydration, volatile release and slow pyrolysis) during the decomposition. The activation energy of pine sawdust pyrolysis was calculated to be200-258kJ/mol using iso-conversion methods. Pine sawdust was beneficial for the environment, as a common biomass, because it would produce less hazardous gases and solid residues.(2) Catalytic gasification of biomass with steam for syngas production was performed in a two-stage fixed bed gasifier. The self-manufacture gasifier had well thermal conductivity, continuous feeding and high currency. The effects of gasification temperature, solid residence time (SRT), steam to biomass ratio (S/B) and catalytic temperature on catalytic gasification were investigated. The results showed that the gas yield and syngas concentration increased with the increasing gasification temperature from750℃to900℃. The value of H2/CO also increased from1.16to1.80. Furthermore, prolonging SRT resulted in the high gas yield, syngas concentration and H2/CO value. However, the changes in gas composition would be neglected when SRT was above26s. The optimum S/B was found to be0.4-0.6for syngas production. At the optimum value, the H2+CO concentrations in gas product reached about70%and the H2/CO value was from2.0to2.5. Moreover, the optimum catalytic temperature was650℃for tar cracking and CH4reforming.(3) Syngas production from in volatile release stage and char gasification stage were studied in a lab-scale fixed bed. The results showed that high temperature was in favour of gas and syngas (H2, CO) yields in the two stages. When the reactot temperature was above750"C, gas yield and H2/CO were depended on the char gasification reaction. The thermalgravitic analysis revealed the mass loss of the sample in steam atmosphere was divided into two stages (221～351℃and740-805℃). The two stages were respectively described by second reaction model and random nucleation model. The calculated activation energy values in two stages were87.10kJ/mol and80.45kJ/mol, respectively.(4) TGA, TG-MS and GC-MS were used to study kinetic and mechanism of tar decomposition. The activation energy of tar decomposition was determined to be53-73kJ/mol at different conversions using FWO and KAS methods. The decomposition of tar was described by single order of reaction function and the reaction kinetic equation estimated by master plots method. With the prolonging pyrolysis time, the contents of compounds in the tar decreased. The temperature range of light components in gas product from tar decomposition was corresponding to the temperature range of mass loss. Main gas product released within150℃. When the temperature was above400℃, released gas product included CO, CO2, H2O and CH4. Compounds in tar increased with the prolonging reaction temperature, and then decreased. The contents of monocyclic aromatic hydrocarbons and oxy-compounds decreased, while PAHs gradually formed. After120s, the tar was converted to porous solid carbide. The main composition was PAHs more than4-ring and aliphatic hydrocarbon about C20.(5) Allothermal catalytic gasfication of biomass for syngas production using biomass micron fuel (BMF) was developed, and studies on a pilot-scale gasification system were carried out. Combustion of BMF could provide the higher temperature for gasfication reactions and the flue gas from the combustor contained less NOX and SO2. Under the optimum conditions, the gas yield reached1.31Nm3/kg with H2+CO concentrations of70.1%and H2/CO value of2.07. The energy evaluation on the pilot-scale gasification system suggested that cold gas efficiency, energy recovery and energy consumption ratio were48.57%,60.04%and2.40, respectively. The gasification process was high efficiency, low-cost and low contamination emission. |
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