Production Of Synthesis Gas By Pressurized Gasification Of Pine Sawdust With CaO As Catalyst

With the depletion of coal resource, more and more countries attaches importance to the technology of liquid fuel synthesis using the syngas from biomass gasification. A suitable H2/CO and pressure of syngas are extremely important for Fischer-Tropsch synthesis. Among the technologies, pressurized gasification undoubtedly has some irreplaceable advantages. In this thesis, the researches on pyrolysis kinetics of pine sawdust are carried out and the process of steam gasification is developed in a fixed bed. The main contents and results are as follows:First of all, a pressurized thermo-gravimetric research is conducted and the results show that there are great effects of the pressure and CaO on the pyrolysis. Increasing reaction pressure leads to a lower weight loss rate. According to the analysis of dynamics, the reaction activation energy is reduced when increasing the pressure, which is beneficial to the pyrolysis reaction. However, an opposite trend takes on when pressure exceeded0.7MPa. With addictive amount of CaO additive increased, the final weight loss rate is increased from73.80%to89.54%. DTG curve presents four weight lose peaks and they are water loss peak, volatile matter release peak, Ca(OH)2and CaCO3decomposition peak, respectively.Secondly, effects of the temperature and pressure on gasification are researched in a fixed bed and the results show that high temperature and pressure have positive roles on hydrogen-rich syngas preparation. A limited reaction time (30min) promotes an increasing concentration of H2and CO but a decrease of CO2and CH4. The dry gas production increases with the rising temperature, but the increasing amplitude slows down gradually. The value of H2/CO increases at first and then decreases, acquiring the maximum H2/CO ratio(4.2) at850℃. With the increase of temperature in the complete gasification reaction, the concentration of CO and CH4are increased while CO2is decreased, and H2has a small change. Dry gas production increases first and then decreases, the maximum value is1.97Nm3/kg-1at850℃.The value of H2/CO is decreased constantly and the maximum ratio is5.4.When the pressure is increased, concentration of H2, CO2is ballooned while CO decreased and CH4has a slight reduction. In addition, the dry gas production and the value of H2/CO are improved. The value of H2/CO ranges from2.0to9.0when the water flow is excessive. Generally speaking, tar amount in syngas would be reduced when the pressure increased within a certain range. The analysis of GC/MS shows that increasing reaction pressure lead to a significant decrease of tar species and an increase of the compounds which include the benzene ring structure with fewer branches, such as benzene, naphthalene, phenanthrene, fluoranthen and pyrene and so on.At last, the results proved that adding CaO into the pine sawdust has great influence on gas composition. At the condition of800℃,0.5MPa and0.5Ca/C ratio, the H2concentration is increased from50.27%to59.35%, CO2concentration is decreased by50%at least and the gas calorific value is increased from10.97Nm3/kg to12.97Nm3/kg. At900℃,0.5MPa, with the Ca/C ratio increasing, tar content in the gas is reduced gradually, obtaining the minimum value of2.48g/Nm3when Ca/C ratio is1.0. The kinds of component in tar are changed slightly when the CaO is added into pine sawdust. However, the compounds which contain aromatic ring structures are become stable.A catalytic steam gasification of pine sawdust is conducted in this study. The H2concentration in syngas is more than60%, H2/CO ratio ranges from2.0to9.0and the total proportion of H2and CO is more than70%. In addition, the tar content in the syngas can be decrease to1.99g/Nm3.