(653d) Oxy-Combustion of Low-Volatility Fuel With High Water Content

High water content fuels, such as coal fine, microalgae and bioethanol, are abundant in nature. Fundamental study is necessary to investigate the novel idea of direct combustion of high water content fuels, which avoids the energy intensive dewatering process. Our previous research investigated the flame stability for high-volatility fuels, including ethanol, 1-propanol and t-butanol. In this study, we continue the study and focus on low-volatility fuel and glycerol is chosen as the candidate. It is found that self-sustained flame can only be obtained for glycerol solution with concentration higher than 50 wt%, when it is burned in pure O₂. However, the flame is lifted far away from the nozzle, which is not typical for a swirl stabilized burner. Knowing ethanol having strong preferential vaporization over water from previous study, ethanol was added as additive to enhance the flame stability. Experiment showed that anchored flame can be obtained by burning the mixture of 10 wt% ethanol, 30 wt% glycerol and 60 wt% water under oxy-fired condition. The flame stability for this mixture was characterized under 100% and 85% swirl flow conditions. It is found in our previous research that t-butanol shows even stronger preferential vaporization behavior than ethanol. The flame stability for the mixture of 8.3 wt% t-butanol, 30 wt% glycerol and 61.7 wt% water, which has the same energy content as the mixture of 10 wt% ethanol, 30 wt% glycerol and 60 wt% water, was characterized under the same flow conditions as ethanol case. Under 100% swirl flow condition, the blow-off limits are approximately the same for both cases. Under 85% swirl flow condition, the blow-off limits for t-butanol case are much lower in the low flow rate region. Additionally, the lift-off limits for t-butanol case are shifted to the left compared to the ethanol case, which means the flame stability for t-butanol case is better. Further, flame structure was characterized. Contours of temperature across the chamber’s centerline were obtained for flame burning 10 wt% ethanol, 30 wt% glycerol and 60 wt% water under three different running conditions, including 100% O₂ and 100% swirl, 100% O₂ and 85% swirl, 80% O₂ and 100% swirl. It is found the anchored flame becomes narrower as the swirl intensity decreases and the peak temperature zone shifts downstream as the O₂ concentration decreases.