Experimental And Modeling Study Of Bio-oil Gasification

Bio-oil made from fast pyrolysis of biomass is convenient for being collected, stored and transported with potential to be used as a fossil oil substitute. However, higher viscosity, higher moisture, higher acidity, lower heating value and heat instability are unbeneficial properties of bio-oil to be used in high class way. Therefore, it is one of the important approaches that changing bio-oil from the liquid into H₂, CO, CO₂, CH₄, C₂, C₃, etc. that could be used to synthesize high grand fuel such as methanol, dimethyl ether, etc. after further disposal. Form the aspects of mechanism, modeling and experiments, the gasification of bio-oil was fully investigated in this paper.Firstly, the investigations of pyrolysis and combustion of bio-oil were preformed using Thermo-gravimetric analyzer. The characteristics of pyrolysis and combustion of bio-oil were analyzed and kinetic mechanism model and parameters were obtained. The release behaviors of the products of pyrolysis were made on-line analysis by thermo-gravimetric analyzer coupled with Fourier Transform Infrared Spectroscopy.The products of pyrolysis were determined and the characteristics of release of them with temperature were studied. The results indicated that pyrolysis of bio-oil divided into two stages and combustion divided into three stages. The main products of pyrolysis are CO, CO₂, H₂O and hydrocarbons etc.Then, based on ASPEN PLUS, a bio-oil gasification model by the method of Gibbs free energy minimization was approached and representative model compounds were selected to simulate bio-oil. Analysis was made that the effects of relevant factors (such as temperature, pressure, the amount of gasification agent and reaction atmosphere) on parameters of products on the prerequisite of material balance and chemical equilibrium. The simulation results showed that the decomposition of bio-oil was more thoroughly and the concentration of H₂ and CO increased as temperature rised. The concentration of H₂ and CO was inversely proportional to the increase of pressure. It was more appropriate to choose a low amount when the gasification agent was O₂ and H₂O. It was a better choice that chooses CO₂ as gasification agent. Finally, experiments of bio-oil gasification were operated on fixed bed under various conditions (temperature, the flow of carrier gas, reaction atmosphere and adding water into bio-oil). The more optimal reaction conditions were given after simulation results were compared with experimental results. The results indicated that 800℃was the best temperature of pyrolysis under experimental conditions. The flow of N₂ of 75ml/min provided best residence time of pyrolysis. It was not appropriate that choose O₂ as gasification agent of external heated gasification system. When used for industrial application the low amount of O₂ was a better choice. When choosed CO₂ as gasification agent the concentration of H2 was almost invariant and the concentration of CO increased significantly. Therefore CO₂ was an appropriate gasification agent. The products of pyrolysis mainly formed from macromolecular organic compounds that were not soluble in water.