Trace elements removal from hot flue gases

Granular-bed filtration was investigated theoretically and experimentally with the view to its applicability to gaseous trace element removal at high temperatures. Granular-bed filters have received a great deal of attention recently as an alternative to the more conventional gas cleanup devices such as cyclones, electrostatic precipitators (ESP) and bag-filters. None of these conventional devices is capable of operating efficiently at high temperatures, (800-900 °C) typical of combined cycle power generation plants. Moreover, a sizeable proportion of the volatilised trace metals will exit from the reactor in the vapour phase and these purification devices are not generally designed to remove the gaseous species. In an atmospheric test rig, trace elements of concern were removed in a fixed granular-bed filter at 800-900 °C temperature range using sorbent particles (such as limestone) as the unbonded filter medium. Two configurations of the experimental apparatus were employed to enable an accurate determination of the removal efficiency of various sorbent particles. The results show that volatilised trace elements can be effectively removed from hot flue gases by passing them through a fixed bed of suitably selected solid sorbents. Removal efficiencies of higher than 99 % were achieved with solid sorbent particles in the 0.3-3.0 mm size range, operating at 800-900 °C.