High-resistivity Ash Research Articles

Solution to the Problem of Precipitation of High-Resistivity Ashes by Electrostatic Precipitators

The innovative and highly effective Russian electrostatic precipitators of the EGAV type were created in order to solve problems associated with the reduction of ash emissions at coal power plants. The new electrostatic precipitators ensured an increase in precipitation effectiveness to 99.87% in the same overall housing sizes along with a reduction in emissions up to 16 times, with actual emissions ranging from 12.6 to 119 mg/m3 (under standard conditions). The technical solutions for intensifying electrostatic precipitation realised in EGAV precipitators increase particle drift velocity to the precipitating electrode by 65%. The application of the EGAV type electrostatic precipitators for removing high-resistivity ashes from flue gases led to the required reduction of emissions during the modernization of the acting electrostatic precipitators. The cost of reconstructing the gas-cleaning unit with the application of innovative electrostatic precipitators turned to be less than with the use of a combined electrostatic precipitator or a bag filter. The new electrical cleaning technology also formed a scientific basis for the innovative development of other promising gas-cleaning technologies.

Fly Ash Resistivity Profiling for South African Coal Fired Power Stations

Particulate emission is a major problem in industrial processes, mainly power plants that make use of coal as a primary source of energy. Stringent emissions limits, set by government organisations requires industries to conform to these limits to ensure that air quality is sustained and with minimum pollutant present. Electrostatic precipitators are typically used to filter and collect these particulate emissions. Fly ash resistivity is a primary parameter in the collection of particulate emissions, and there is a resistivity range at which electrostatic precipitator collection is most efficient and anything outside this range limits, their operation. High resistivity ash results in back-corona discharge, whilst low resistivity results in particle re-entrainment into the flue gas stream. The purpose of this paper is to investigate and obtain a fly ash resistivity profile for existing power plants in South Africa. Ash samples obtained from power plants are, tested making use of an ash-resistivity test oven, in accordance with IEEE Standard 548-1984. This paper discusses obtained experimental results, to determine the resistivity profile at which South African power plant electrostatic precipitators operate. The electrical efficiency of the electrostatic precipitator system is evaluated based on the obtained resistivity profiles.

Theoretical modelling of electrostatic precipitators performance (PRELEC code)

This paper presents a model designed to characterize the performance of plate-type electrostatic precipitators (ESP). PRELEC is a rigorously Deutschian model, completely theoretically derived, that avoids the use of empirical estimations in its calculations. In the present version, those estimations related with non-ideal effects are not considered. PRELEC calculates electric fields, based on the applied voltage wave, including the effects of ionic and particulate space charge. It is able to simulate two possible types of ESP energization: full-wave rectified current and pulse generation. It also allows the transient evolution of electrical conditions inside the ESP during the rapping intervals to be analysed, taking into account the dust build-up influence. The model predictions show good agreement with experimental measurements taken at two ESPs of Spanish Power Plants under several operational conditions, including different dust characteristics, very high resistivity ashes, operation before and after the installation of a flue gas conditioning plant, and the use of rectified current and pulse energization. PRELEC predictions are also compared with those obtained from Version 3 of EPA/SRI model.

Dust Emission, Its Quantity and Composition, Depending on Dust Collector, Coal Quality and Other Factors

Dust emission measurements have been carried through at Danish coal-fired power stations. Investigations show that modern electrostatic precipitators can meet Danish emission standards even for high resistivity ash. Modern electrostatic precipitators can reduce particulate emissions with a factor 10-20 compared to older precipitators. Trace metals that are very strongly attached to the finest particulates (As, Cd, Mo, Pb etc.) show less reduction in emission.

Design and Application of High Voltage Power Supplies in Electrostatic Precipitation

Proper electrical energization methods and equipment are the keys to successful electrostatic precipitation. The design, operation, and application of conventional high voltage power supplies in this process are reviewed. Emphasis is on requirements and methods of achieving the high performance and reliability necessary in modern air pollution control systems. Typical field data on operations and effects in various precipitator applications, including high resistivity ash, high temperature, and/or high pressure gas treatment, are discussed.