GRIMETHORPE FILTER ELEMENT PERFORMANCE - THE FINAL ANALYSIS

A demonstration hot gas filter, funded by the Electric Power Research Institute and installed in a pressurised fluidised bed combustor at Gr imethorpe, South Yorkshire, UK was operated for a second period in 199 1-92 for the Grimethorpe Topping Cycle Project (GTCP). This project wa s aimed at assessing the feasibility of running a gas turbine on coal- derived gas as part of the development programme for the Air Blown Gas ification Cycle (formerly known as the British Coal Topping Cycle). As in previous studies operation of the filter led to progressive change s to the mechanical properties of the tubular clay-bonded silicon carb ide filter elements. In order to explain the mechanisms behind these c hanges and thus determine operating conditions which influence element properties and performance detailed element characterisation and micr ostructural studies have been carried out. It has been found that slow bond devitrification and the development of a bond-grit interlayer of cristobalite led to changes in the integrity of the interface, with l oss of strength and elastic modulus and a decrease in ultrasonic pulse velocity through the material. Microstructural studies suggest that t he combination of the upper temperature of operation (approximate to 8 30 degrees C) and the thermal cycling during reverse pulse cleaning to remove the dust cake results in microcracking. While the strength los ses experienced did not result in in-plant element failures, the relia bility of the elements would be improved if operation can be limited t o a temperature at which devitrification of the element's bond materia l is minimised.