Rheology, ignition, and combustion performance of coal-water slurries: Influence of sequence and methods of mixing

This paper presents the results obtained from a comprehensive study of how the conditions and methods of preparing three-component fuel slurries affect their ignition, combustion, emissions, as well as viscosity and static stability. The data obtained for slurry fuels based on bituminous coal and water with added waste hydrocarbon oil and wood biomass as well as a slurry based on coal slime. A tubular muffle furnace was used for combustion at 700–900 °C. The influence of the mixing conditions of the components on the ignition and combustion behavior was moderate. It was established that surfactants should not be added to composite slurry fuels at the final stage of component mixing. To provide more uniform burnout of a blend with wood biomass, the latter should first be mixed with water and then the coal component should be added. Iterative mixing can provide a 10–15% improvement of ignition and burnout characteristics. To obtain a more homogeneous and stable blend, it is advisable to use a cavitator (colloid mill) rather than a homogenizer or a magnetic stirrer. Based on a set of parameters (viscosity, stability, cost, ignition and combustion characteristics), a dimensionless efficiency indicator was calculated using Weighted Sum Method. The calculated values of the relative efficiency indicator of the fuel blends based on coal dust ranged from 0.67 to 0.73. The relative efficiency of a slurry was found to increase by 25–30% when coal dust is replaced by coal slime due to the economic parameter.