| To seek a new renewable clean energy is extremely important due to the severer energy and environment problem. Biomass is an abundant, various and inexpensive renewable resource in the world. It is regarded as one of the most promising energy and used as the alternative energy sources of fossil fuels. Among the thermo-chemical conversion of biomass, pyrolysis is one of the most effective technologies transferred low value energy to high value energy. Therefore, the research of biomass pyrolysis is considerably significant in the solvents of energy problem. In this work, the spiral pyrolysis of pine sawdust and dried sewage sludge are carried out with a screw reactor to investigate the influence of pyrolysis temperature and solid residence time on the mass and energy distribution, product composition, heavy metal distribution as well as the potential ecological risk assessment. The main conclusion details as follows.(1) The thermo-gravimetric analysis of pine sawdust and dried sewage sludge pyrolysis showed that three stages existed in pyrolysis process. The detailed stages were the volatilization of water, the degradation of most organic matter and the residue degradation. The second stage was the main pyrolysis reaction stage, and in this stage, the mass loss for pine sawdust was 71.56% and for dried sewage sludge was 47.29%.(2) During the biomass pyrolysis, the mass loss was 1.4～11.8%. In the pine sawdust pyrolysis experiments, the gas yield gradually increased with the rising pyrolysis temperature, accompanying with the bio-oil yield obviously decreased. In the rising solid residence time, the maximum bio-oil yield of 51.7% was obtained at the solid residence time of 6 min. The minimum energy profit rate reached -13.83% at the pyrolysis temperature of 600℃ with solid residence time of 5 min. The main pyrolysis product was bio-char with the yield above 55% in the spiral pyrolysis of dried sewage sludge.(3) In the influence of pyrolysis temperature, the main composition for pine sawdust pyrolysis gas was CO with the yield of 45.74～47.19%, but for dried sewage sludge was CO2 and H2 with the value above 52.18%. Under different solid residence time, the main compositions for pine sawdust gas were CO and CO2, but for dried sewage sludge was H2 with the value above 30.65%.(4) The results of Fourier transform infrared spectroscopy (FTIR) analysis for pine sawdust bio-oil showed that phenols were the main components. But the dried sewage sludge bio-oil all consisted of-C≡N, C-O, C-O-C. The Gas chromatograph-mass spectrometer (GC/MS) results showed that solid residence time had a low effect on the composition of bio-oil.(5) With the increasing of pyrolysis temperature and solid residence time, the volatile matter content of pine sawdust bio-char decreased and the fixed carbon increased. The thermo-gravimetric analysis of pine sawdust bio-char presented that the activation energy was 461.10 kJ mol’1 and 108.45 kJ mol"1 in the ranges of 290～314 ℃ and 314～518℃, respectively. The FTIR analysis of dried sewage sludge bio-char indicated that solid residence time was not key factor in the functional group distribution.(6) The proportion of heavy metal in bio-char was between 57.49 and 81.91% indicating that these heavy metals have a better stability in bio-char. The value of potential ecological risk index (RI) for bio-char was 4525 indicating that the bio-char has high contamination. |
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