Characterization of tar from sawdust gasified in the pressurized fluidized bed

The paper investigated the features of tar releasing from sawdust gasification in a new designed pressurized fluidized bed. Gel permeation chromatography (GPC) was used to determine the average molecular weight and the molecular weight distribution of sawdust gasified tar, also a photodiode array (PDA) detector was used in parallel to analyze the Ultraviolet (UV) spectra from 210 to 380 nm. At the pressure of 0.5–2.0 MPa and 800 °C, tar had the similar molecular weight distribution and the average molecular weight, the UV spectra absorbed at 254 nm revealed tar of sawdust air gasification at different pressures had aromatic character which increased with the increment of the pressure. By increasing the temperature from 700 to 900 °C, the relative amount of different molecular weight distribution fractions showed that tar contained higher fractions of small molecular weight components. It so gave an indication that tar progressively broke down with the increment of temperature under gasification conditions. The results from the UV absorbed in 254 nm showed a similar aromatic characteristic between 700 and 900 °C, which expressed the presence of larger polynuclear aromatic ring systems, unsaturated conjugated long chain alkyl, heterocyclic structures and alkyl of heteroatom substitutions.