CFD and experimental studies on capture of fine particles by liquid droplets in open spray towers

A computational fluid dynamics (CFD) model to predict the capture of particles by liquid droplets in spray towers has been developed and tested against experiments made in a semi-scale test rig and in a full-scale spray tower used for wet flue gas desulphurization (WFGD) in one operating coal fired power plant. Each of the dispersed phases, i.e., the particles and the droplets, is modeled using the Lagrangian approach. Correlations for the two main capture mechanisms (inertial impaction and Brownian diffusion) are used to predict the capture efficiency. For isothermal conditions, the predicted capture efficiencies by CFD in the semi-scale test rig are in good agreement with the experimentally measured efficiencies in all tests made at various nozzles' design- and operating-configurations. However, the model under-predicts the collection efficiency for the full-scale spray tower, especial in the sub-micron region, which implies there may be other capture mechanisms in the real WFGD spray tower that result in a better removal, such as the size-growth of sub-micron particles by vapor and SO3 condensation during and after the sudden cooling of the flue gas at the inlet of the spray tower. Keywords: CFD, Multiphase flow, Particle capture by droplet, Wet scrubbe