Modelling of gas flow and liquid spray in wet type electrostatic precipitators

Wet Electrostatic Precipitator (ESP) can effectively remove fine particular matters from many industry emission sources. The wet ESP normally applies water spray, or running water on the collecting electrode. Particularly, a falling water film is created on the collecting plate, so that the dust collected can be washed into the hopper without rapping. Introduction of liquid spray also changes the gas flow condition (temperature and humidity) which affects the electric field and particle charging. The particle collection efficiency depends strongly on the gas flow, the behaviours of spray droplets, and the distribution of liquid film. Based on Computational Fluid Dynamics (CFD), the present paper simulated the liquid spray generation, gas-droplet flow in electric field. Firstly, the electric field intensity and ion charge density are solved locally around a typical corona emitter, which are then applied to the entire ESP using periodic conditions. Secondly, the LISA breakup equations originally for a flat liquid sheet is extended to conical sprays, in order to calculate the initial particle conditions after atomization: particle size, locations and velocities. Next, the Euler-Lagrange method is used for gas-droplet flow. Liquid droplets are tracked statistically along their trajectories, together with evaporation and particle charging. Finally the deposition density on the plate provides inputs for the future simulation of the falling liquid film. The numerical simulations in terms of flows, heat and mass transfers provided the process details. Main findings: The extended Linearized Instability Sheet Atomization (LISA) model predicts the mean droplet size accurately. Electric field has strong effect on the droplet trajectories. Some droplets may escape by passing the non-charge regions. Hollow cone spray is compared with solid cone spray.