Ash resistivity profiling and effect of a high frequency power supply on electrostatic precipitator efficiency

Abstract

Particulate emissions of coal-fired power stations are governed by the air quality legislation as stipulated by the Department of Environmental Affairs. The legislation stipulates the amount of particulate emission a coal-fired power station is licenced to emit during operation at full load. Failure to comply with the set-out emission limits results in none compliance, which can result in a stiff fine or jail sentence for the responsible personnel. Alternatively, a power station or production unit that fails to comply with and operate within the set-out emission limits may be required to de-load, i.e. reduce production until the point where emissions are low and within legislation compliance. Air quality legislation requires existing power plants to operate with a particulate emission limit of 100 mg/Nm3 daily average per unit for the station in which tests are conducted. The Department of Environmental Affairs is set to further reduce the emission limit for existing plants to be 50 mg/Nm3 by 2020. At present, many of Eskom’s power stations are having difficulties in maintaining particulate emissions to the required emission levels and as a result, these power stations consistently operate with load losses in order to reduce their emissions and to be within the legal specifications. Eskom power stations mainly make use of electrostatic precipitators (ESPs) for particulate emissions. In recent years, the ESPs have found it difficult to maintain emission levels and within the required limits. The reason for the power stations’ ESPs’ inability to maintain low emissions is due to a variety of factors, such as coal quality deterioration, aging plants and outdated power supply technology. This project investigates ash resistivity testing and profiling in order to determine whether the resistivity profile of the collected ash is still within the required ESP operating spectrum. The deterioration of coal quality over the years may have resulted in a high resistivity ash mean captured by the ESP, which is not ideal to maintain low particulate emissions. This project is also aimed at investigating new power supply technology for the ESPs and to compare that system’s performance with the existing power supply system. An industrial project was implemented, testing the ESP performance for existing power supply technology as well as with a new power supply system, in order to quantify the reduction in emissions within the Eskom environment.