The Experimental Study on Pyrolysis and Combustion Characteristics of Bio-oil

Bio-oil is the liquid product from fast pyrolysis of biomass. Compared with biomass, bio-oil has a higher energy density and is cheaper to transport and store. Many researches have been done on its applications and further treatments. Using bio-oil as fuel for boilers,furnaces,diseal engines and gas turbines has been proved feasible, gasification of bio-oil for synthesis gas has also attracted considerable attention recently. To deal with the problems occurred during the combustion and pyrolysis process of bio-oil better and supply necessary data required for designing of combustion and pyrolysis equipments, the physicochemical properties analysis of bio-oil produced from wood powder by self-heating biomass fast pyrolysis facility was carried out. Then TG, TG-FTIR and tube furnace were employed to investigate the pyrolysis and combustion characteristics of bio-oil. The thermogravimetric analysis of bio-oil was carried out in high purify O2 and N2 under different heating rates(5℃/min～20℃/min) to a maximum temperature of 1000℃. The results indicated that bio-oil pyrolysis occurs in 2 steps. The first concerns the evaporation of low-boiling point compounds, then followed by the cracking of heavy fractions. Bio-oil combustion starts with evaporation followed by cracking, at last combustion of char formed during the previous steps takes place. In N2, with increases of heating rate, the starting temperature of weight loss, the maximum velocity of weight loss and temperature corresponding to it all rise, and less residue form at high heating rate. The ignition temperature of bio-oil rise with increase of heating rate, final weight loss does not change. The evolving volatile products during the pyrolysis process were analyzed by FTIR. On the basis of TG data, the kinetic fittings of each reaction period during pyrolysis and combustion were carried out. The pyrolysis process of bio-oil can be described by two first-order reactions, the combustion process can be described by three first-order reactions. Pyrolysis of bio-oil in tube furnace was carried out over a temperature range of 700～1100℃ under inert atmosphere. The composition and yield of the derived gases and distribution of the pyrolyzed product were determined. It is found that with increasing temperature the gas yield goes up. The gaseous product mainly consists of H2, CO, CO2 and hydrocarbons such as CH4,C2H4,C2H6. Its heating value is in the range of 16.9～19.1MJ/Nm3. The product distribution ratio of gas, tar and char is about 30:6:64 at 900℃. The char yield of bio-oil pyrolysis is lower than that of wood powder under the same condition, but the tar yield is higher.