Abstract
Pyrolysis gas jets out from the surface of a solid fuel particle when heated. This study experimentally observes the occurrence of gas jets from heated solid fuel particles. Results reveal a local gas jet occurs from the particle’s surface when its temperature reaches the point at which a pyrolysis reaction occurs. To investigate the influence of the gas jet on particle motion, a numerical simulation of the uniform flow around a spherical particle with a nonuniform outflow or high surface temperature is conducted, and the drag force acting on the spherical particle is estimated. In the numerical study, the magnitude of the outflow velocity, direction of outflow, and Rayleigh number, i.e., particle surface temperature, are altered, and outflow velocities and the Rayleigh number are set based on the experiment. The drag coefficient is found to decrease when an outflow occurs in the direction against the mainstream; this drag coefficient at a higher Rayleigh number is slightly higher than that at a Rayleigh number of zero.
Highlights
Pulverized coal is mixed with air and burned in pulverized coal combustion devices in power plants and ironworks
To investigate the influence of the gas jet on particle motion, a numerical simulation of the uniform flow around a spherical particle with a nonuniform outflow or high surface temperature is conducted, and the drag force acting on the spherical particle is estimated
Katoshevski et al experimentally investigated the relation between particle temperature and drag forces; the results showed that the drag force acting on a heated particle increased due to free convection around the particle [14]
Summary
Pulverized coal is mixed with air and burned in pulverized coal combustion devices in power plants and ironworks. When a solid fuel particle such as coal is heated, the flammable gas generated by the pyrolysis reaction jets out from a part of the surface, and combustible components that are not gasified burn at the surface. An equation of the drag coefficient is important to accurately estimate particle trajectories, and many studies have been conducted on drag forces acting on a particle in a flow field. Haider and Levenspiel proposed equations for the drag coefficient of spherical and nonspherical particles [9], and numerical simulations have been conducted to investigate the drag forces acting on a nonspherical particle [10] [11]. Katoshevski et al experimentally investigated the relation between particle temperature and drag forces; the results showed that the drag force acting on a heated particle increased due to free convection around the particle [14]
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