Characterization Of Tobacco Stem Biochar And The Mechanical Property Of Charcoal Moulding Fuel

Tobacco stem is the biomass waste after tobacco harvesting. Nowadays, the dispose of tobacco stem is always by burning or discarding in the field, which causes environment pollution and also is a waste of renewable resource. Tobacco stem is ligneous material and it has great potential in biochar production, but now there are still few researches about the use of tobacco stem in biochar production. To investigate the potential use of tobacco stems as feedstock for biochar production, this paper focused on the effects of carbonization conditions, including carbonization temperature, retention time and heating rate, on the yield of pyrolysis products and characteristics of tobacco stem biochar. Then the properties of biochar produced under different conditions were analyzed, including primary analysis, calorific value, energy yield, ultimate analysis, specific surface area, pore size and distribution analysis.This research tried to produce tobacco stem charcoal moulding fuel by adding adhesive. Thus the effects of moulding conditions, including the ratio of adhesive and biochar, mixture keeping time and moulding pressure, on the mechanical properties of charcoal moulding fuel were analyzed.The main results were shown as the following:(1) The effect of carbonization conditions on the yield of pyrolysis products:the biochar yield decreased as carbonization temperature increased. It decreased obviously when the temperature increased from350to400℃and the decrease became litter when the temperature was higher than400℃. During the carbonization, the oil and gas yield was in negative correlation. Moderate retention time was advantage to get high bochar yield. When the retention time was3h, biochar yield was42%, higher than other levels. The oil yield decreased and gas yield increased as the retention time increased. Though the heating rate had litter influence on the biochar yield,the biochar produced under slower heating rate had better quality.(2) The effect of carbonization conditions on the property of biochar: carbonization conditions should be temperature of400-450℃, retention time of3h and heating rate of5℃/min to produce biochar with good quality used as fuel. The specific surface area (SBET) of biochar increased as carbonization temperature and retention time increased. In single-factor experiment of carbonization conditions, the biochar had the largest SBETt when temperature was600℃, retention time of4h and heating rate of15℃/min, respectively. Temperature of600℃, retention time of4h and heating rate of10℃/min was preferred to produce biochar with large accumulative pore volume.(3) The effect of moulding conditions on the mechanical properties of tobacco stem charcoal produced with modified cassava starch adhesive:when the adhesive ratio ranged from20%to40%, the broken resistance and axial compression strength of tobacco stem charcoal became stronger and then weakened. Tobacco stem charcoal with35%adhesive (mixture keeping time of18h, moulding pressure of2.5MPa) had better mechanical properties than those produced under other levels. After3times broken test, the remaining mass of it was as high as97%, and it also remained in integrity with remaining mass of75%after6times continuously broken test. Also, its axial compression strength was10.952kPa, which was obviously higher than others’. As to the keeping time of the biochar and adhesive mixture, when it ranged from6h to30h, the broken resistance and axial compression strength of tobacco stem charcoal became stronger and then weakened. Tobacco stem charcoal with keeping time of24h (adhesive ratio of30%, moulding pressure of2.5MPa) had best mechanical properties. After3times broken test, the remaining mass of it was81.7%and55.2%after6times continuously broken test. When the moulding pressure ranged from2.0MPa to3.5MPa, the charcoal produced under2.5MPa (adhesive ratio of30%, mixture keeping time of18h) had strongest broken resistance. It remained94.6%original mass after three times broken. But the axial compression strength of charcoal produced under3.0MPa was7.761kPa, a litter stronger than that produced under2.5MPa of which was6.695kPa. Thus, moulding pressure of2.5-3.0MPa was preferred for tobacco stem charcoal moulding.(4) Compared with tobacco stem biochar, the result of calorific value analysis showed that adding adhesive just caused litter change to the calorific value of tobacco stem charcoal. But the volatile content of the charcoal increased obviously, and the ash content decreased, and the changes were larger when the ratio of adhesive was larger.