Performance study of the electrostatic precipitator of a coal fired power plant: Aspects of fine particulate emission control

Particulate matter emission is one of the major air pollution problems of coal fired power plants. Fine particulates constitute a smaller fraction by weight of the total suspended particle matter in a typical particulate emission, but they are considered potentially hazardous to health because of the high probability of deposition in deeper parts of the respiratory tract. Electrostatic precipitators (ESP) are the most widely used devices that are capable of controlling particulate emission effectively from power plants and other process industries. Although the dust collection efficiency of the industrial precipitator is reported as about 99.5%, an anticipation of future stricter environmental protection agency (EPA) regulations have led the local power station seeking new technologies to achieve the new requirements at minimum cost and thus control their fine particulate emissions to a much greater degree than ever before.

This study aims to identify the options for controlling fine particle emission through improvement of the ESP performance efficiency. An ESP system consists of flow field, electrostatic field and particle dynamics. The performance of an ESP is significantly affected by its complex flow distribution arising as a result of its complex internal geometry, hence the aerodynamic characteristics of the flow inside an ESP always need considerable attention to improve the efficiency of an ESP. Therefore, a laboratory scale ESP model, geometrically similar to an industrial ESP, was designed and fabricated at the Thermodynamics Laboratory of CQUniversity, Australia to examine the flow behaviour inside the ESP. Particle size and shape morphology analyses were conducted to reveal the properties of the fly ash particles which were used for developing numerical models of the ESP.

Numerical simulations were carried out using Computational Fluid Dynamics (CFD) code FLUENT and comparisons were made with the experimental results. The ESP was modelled in two steps. Firstly, a novel 3D fluid (air) flow was modelled considering the detailed geometrical configuration inside the ESP. A novel boundary condition was applied at the inlet boundary of this model to overcome all previous assumptions on uniform velocity at the inlet boundary. Numerically predicted velocity profiles inside the ESP model are compared with the measured data obtained from the laboratory experiment. The model with a novel boundary condition predicted the flow distribution more accurately. In the second step, as the complete ESP system consists of an electric field and a particle phase in addition to the fluid flow field, a two dimensional ESP model was developed. The electrostatic force was applied to the flow equations using User Defined Functions (UDF). A discrete phase model was incorporated with this two dimensional model to study the effect of particle size, electric field and flue gas flow on the collection efficiency of particles inside the ESP. The simulated results revealed that the collection efficiency cannot be improved by the increased electric force only unless the flow velocity is optimized.

The CFD model was successfully applied to a prototype ESP at the power plant and used to recommend options for improving the efficiency of the ESP. The aerodynamic behaviour of the flow was improved by geometrical modifications in the existing 3D numerical model. In particular, the simulation was performed to improve and optimize the flow in order to achieve uniform flow and to increase particle collection inside the ESP. The particles injected in the improved flow condition were collected with higher efficiency after increasing the electrostatic force inside the 2D model. The approach adopted in this study to optimize flow and electrostatic field properties is a novel approach for improving the performance of an electrostatic precipitator.