Modeling Of Dust Loaded Electrical Characteristics And Collection Efficiency Of Industrial Electrostatic Precipitators

Abstract

With the increase in population and industrial growth, the need for power has increased manifold. A major share of India’s power generation is coal-based generation. Thermal power generation through coal combustion produces minute particles of ash that causes serious environmental problems. Most of the thermal power stations in India use bituminous coal and produce large quantities of fly ash. Fly ash is produced primarily by thermal power plants and, to a lesser extent, by cement and steel plants and railways. This poses problems in the form of land use, health hazards, and environmental dangers. Today the fly ash from thermal power plants is utilized to make cement. Cement industry needs fly ash with more fine particles. If these fine particles (of diameter in micro-meter range) are left out to atmosphere, it will be easily breathed into lungs, creating health hazard to human as well as animal life. If properly collected, it forms a valuable by product. Hence collecting fly ash is important to reduce pollution and also to increase revenue. Even though there are many devices like cyclones, fabric filters etc. the Electrostatic Precipitator (ESP) is the most efficient device to capture the fly ash. It is at this juncture a need for such a simple ESP model was felt to facilitate prediction of the V-I characteristics of dust loaded precipitators, be it cement dust or fly ash. Given the fact that 99% of Indian ESPs are operated under DC energization and most of them are running inefficiently due to lack of proper diagnostic tools and also due to lack of interest to invest on an ESP. In such circumstances, the free availability of a simple model that combines the V-I curves with collection efficiency serves to improve the ESP performance in our Indian industries. In an ESP Voltage-Current (V-I) characteristics are used to diagnose any electrical problems occurring in it. Mathematical model of V-I characteristics under clean air and dust laden conditions will be helpful in diagnosing the ESP problems as well as in designing the ESP. The model will also indirectly reflect upon the collection efficiency of the ESP. The collection efficiency should be as high as possible not only to prevent pollution but also to collect maximum fly ash which is a valuable by-product. The modeling of collection efficiency will help the industries to design a new precipitator as well as to improve the performance the collection efficiency to meet the changing restrictions set by the government to reduce pollution. In this thesis a mathematical model of ESP based on Finite Difference Method is developed. The modeling is done in three sections. 1. Simulation of clean air V-I characteristics. 2. Simulation of dust laden V-I characteristics. 3. Simulation of collection efficiency. Simulation of clean air V-I characteristics is done by iteratively solving the Poisson’s equation and current continuity equation, using FDM in one quarter region of the ESP. Just by introducing the effect of particle charge into this solution the dust laden V-I characteristics are simulated. Finally, the collection efficiency is calculated using average charge density at the plates obtained from the above solution. The developed model is validated at first against published experimental and simulated data and then, with the data obtained through conduction of experiments, by the author, on commercial precipitators situated at a thermal power station and a cement plant, in India. The thesis discusses in detail these theoretical and experimental studies.