Enhancing ESP Efficiency for High Resistivity Fly Ash by Reducing the Flue Gas Temperature

Abstract

the resistivity of fly ash after coal-fired boilers varies with the flue gas temperature. the normal esp operating temperature of around 150°C is typically near the maximum resistivity of the ash. for low sulphur coals the resistivity will sharply decrease if the flue gas temperature at the esp inlet is reduced to about 100°C or less. this will mean that a significantly smaller esp can be built for a given efficiency. already in the early 1970’s esps were built at the liddell power station in australia purposely designed to operate at low temperature to reduce the fly ash resistivity. the full-scale design at liddell was based on pilot testing at other locations in order to verify the low temperature approach. despite successful implementation at liddell the experiences did not result in much follow-up of low temperature esp operation. the concept was revived in japan in the 1990’s, resulting in several installations working at temperatures below 100°C these units have a considerably reduced esp size, and the energy recovered upstream the esp is used to re-heat the flue gas after the desulphurisation system. the low temperature esp operation is now well proven and a viable alternative when burning low sulphur coals.