The enhancement of pulverized-coal combustion by using sound waves

Abstract

A model for the enhancement of pulverized coal combustion in high-intensity acoustic fields has been developed. In a power boiler pulverized coal particles and char are entrained in the main gas flow for a significant length of time. The slip velocity between the entrained particles and the gas is very low leading to low heat and mass transfer to and from the particles. This results in long combustion times for the particles, particularly if the combustion is diffusionally controlled. When a high-intensity acoustic field is applied to the gas flow, it superimposes high-velocity oscillations on the main flow. If the frequency and amplitude of this acoustic field is just right, the particles are not entrained in the acoustically induced flow oscillations. This creates a periodically varying slip velocity between the particles and the hot gas, leading to higher convective heat and mass transfer to and from the particles, thereby enhancing the combustion. The paper also presents the axial pressure gradient and shear stress in neighborhood of the particles placed in sound field.