Advances in rigid porous high temperature filters

The development of de-dusting hot gases is of increasing importance and growing interest, especially in advanced power generation systems and (petro-)chemical processes. High temperature de-dusting has advantages of exceeding dew points, enhancing energy recovery at higher temperatures, protecting the downstream heat recovery equipment from fouling or erosion, and potentially simplifying the overall process. Additional benefits are a reduced power consumption and the possibility to simultaneously capture gaseous pollutants (SO2, HCl) by the gas-solid reaction with injected alkali or by integrating catalysts to abate NOx, VOC (volatile organic compounds) and PCDD/F (polychlorinated dioxins and furans). Both porous ceramic and porous metal fiber filters have been proposed, with a growing preference for the rigid metal fibre filters. Either surface or depth filters are applied. The operation parameters of hot gas de-dusting by rigid fibre filters include the applied face velocity, the porosity of the filter fleece, its construction and the pulse jet cleaning performance. These parameters will be integrated into design equations to determine the operational pressure drop and filtration efficiency for a given gas flow rate, operating temperature, dust characteristics and pulse-jet cleaning mode. The broad range of potential applications of the filters prior to an energy recovery stage will be illustrated for petrochemical/chemical processes and for combustion and gasification. The expected durability and long-term successful operation necessitate a proper design of the filter media (porosity, pore size, thermal, mechanical and corrosion resistance). The appropriate fabrication materials will be evaluated, with stainless steel or high grade metal alloys recommended for use in the extreme conditions at high temperatures and pressures. Finally prospects and challenges are summarized.