Pyrolysis of biomass or coal, if operated at temperature high enough to complete tar evolution, is expected to give resulting char a tar-free nature. Use of such tar-free char instead of the original fuel in gasification would reduce or even completely eliminate the need for use of complex devices/mechanisms for tar/soot removal. Increasing pyrolysis temperature may not only decrease the content of residual tar in the char but also reduce its reactivity in the gasification. There is thus a range of optimum pyrolysis temperatures depending on the original fuel and type/mode of gasification, which yields char of suitable quality. In this work, a variety of char samples were prepared by pyrolysis (first pyrolysis) of three different woody biomass feedstock and a Victorian lignite with heating rate and peak temperature of 10 C/min and 450-750 C, respectively, and were further subjected to flash pyrolysis (second pyrolysis) at 920 C. A gas-chromatography/ mass-spectrometry (GC/MS) detected more than 200 compounds in the volatile products from the second pyrolysis and quantified 58 aromatic compounds over a range from benzene to coronene, which accounted for more than 85% of the compounds detected based on peak area on the total ion chromatogram. Total emission of tar, defined as the aromatics except monoaromatic hydrocarbons, from the biomass chars was 0.03-0.08 wt %-char even at the first pyrolysis temperature of 450 C and further decreased to a level around 0.01 wt % by raising the temperature to 600 C. It was also found that despite containing as much as 20-27 wt % of residual volatile matter, chars produced by pyrolysis at 500 C contained less than 0.1 wt % of residual tar.
All Science Journal Classification (ASJC) codes
- Chemical Engineering(all)
- Fuel Technology
- Energy Engineering and Power Technology