Combustion performance of oil shale and biomass fuels and their blends

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2014
Özgür, Emre
The aim of this thesis was to evaluate the co-combustion performance of different origins of oil shales (Ulukışla and Himmetoğlu regions of Turkey) and various biomass samples (hazelnut shell, wheat bran, poplar, and miscanthus) at different biomass proportions (10, 20, and 50% by weight) using thermogravimetric analyzer (TGA), differential scanning calorimeter (DSC), and thermogravimetric analyzer-mass spectrometer (TGA-MS) at different heating rates (10, 30, 50 oC/minute). The ignition temperatures of the parent fuels and blended fuels as indicators of the level of improvement in combustion performance were investigated with the addition of biomass. The effect of biomass model compounds (cellulose, hemicellulose, and lignin) on the combustion performance were also investigated to identify the components that have the most influence in a combustion system. It is noticed that the ignition temperature of Ulukışla and Himmetoğlu oil shale is 244, 296, and 302 oC and 197, 224, and 231 oC, respectively; whereas the ignition temperature of biomass fuels are in the range of 219-233, 240-255, 250-260 oC, at the same experimental conditions (at heating rates of 10, 30, 50 oC/minute, respectively). Biomass fuels were characterized as low ash content fuels in the range of 0.1-2.9% by weight. Himmetoğlu oil shale and Ulukışla oil shale were observed to have ash contents of 18.5 and 84.5% by weight, respectively. The activation energies of all oil shale and biomass samples were determined using Arrhenius, Coats-Redfern Kissenger, Ozawa-Flynn-Wall, and ASTM kinetic methods. The results of the values for oil shale combustion are in the range of 99-107 kJ/mol and 66-76 kJ/mol, respectively for Arrhenius and Coats-Redfern kinetic methods. The results for the combustion of biomass fuels are in the range of 72-85 kJ/mol for Arrhenius and Coats-Redfern kinetic methods. The results of isoconversional kinetic methods are in the range of101-284 kJ/mol by Kissenger method, 113-184 kJ/mol for ASTM method and in the range of 176-302 kJ/mol by Ozawa-Flynn-Wall method for oil shale; and in the range of 129-222 kJ/mol by Kissenger method, 139-151 kJ/mol for ASTM method and 184-198 kJ/mol by Ozawa-Flynn-Wall method for biomass fuels. It was observed that activation energies were in direct relation with the ignition temperatures. It was observed that the addition of biomass improved the combustion performance of high-ash oil shale by lowering the ignition temperature of the blends in a synergistic manner. Cellulose was the most difficult one to combust among biomass model compounds (cellulose, hemicellulose, and lignin) because of its strong structure. All results were evaluated statistically to identify possible relationships between the physical properties of the fuels and the combustion performance. It was observed that carbon content and volatile matter content are the most deterministic parameters for the ignition temperature of fuels. Carbon content and volatile matter content has a reducing effect on ignition temperature. It was also observed that as the heating rate increases, the dependence of ignition temperature on carbon content and volatile matter content increases. This is due to the better ignition conditions at higher heating rates by decreasing the loss of volatile matters in the devolatilization stage before combustion. The R2 values of 94.0, 84.1, and 76.7 were obtained between sample and combustion properties for the heating rates of 50, 30, and 10 oC/minute, respectively.

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Citation Formats
E. Özgür, “Combustion performance of oil shale and biomass fuels and their blends,” Ph.D. - Doctoral Program, Middle East Technical University, 2014.