The flow of particulate two-phase flow mixtures occur in several components of solid fuel combustion systems, such as the Pressurised Fluidised Bed Combustors (PFBC) and suspension fired coal bailers. A detailed understanding of the mixture characteristics in the conveying component can aid in refining and optimising its design. In this study, the flow of an isothermal, dilute two-phase particulate mixture has been examined in a high curvature duct, which can be representative of that transporting the gas-solid mixture from the hot clean-up section to the gas turbine combustor in a PFBC plant.
The numerical study has been approached by utilising the Eulerian-Lagrangian methodology for describing the characteristics of the fluid and particulate phases. By assuming that the mixture is dilute, the governing particle momentum equations have been solved with appropriately prescribed boundary conditions. The influence of the turbulence on the particle dispersion was represented by a stochastic model.
For the turbulent flow condition examined, it was observed that mixtures with small particle diameters had low inter-phase slip velocities and low impaction probability with the pipe walls. Increasing the particle diameters (> 50 um) resulted in higher inter-phase slip velocities and as expected their impaction probability with the pipe walls was significantly increased. The particle dispersion is significant for the smaller sizes whereas the larger particles are relatively insensitive to turbulence. The main particle impaction region, and location most prone to erosion damage, is estimated to be within an outer duct length of 2 to 5 times the duct diameter.