PARTITIONING OF TRACE-ELEMENTS IN PRESSURIZED FLUIDIZED-BED COMBUSTION

The relative distribution of a few selected trace elements in the effluent streams of a 15 cm diameter pressurised fluidised-bed combustor is investigated. The effect of in-bed desulphurisation as well as high-temperature, high-pressure particle removal on trace element emissions is studied and some of the results are reported in this paper. An extractive sampling technique, used to measure the trace element concentrations in the vapour phase, is briefly discussed. This was designed to enable a more accurate assessment of the volatilisation of selected trace elements in the bed. The results show that a relatively small proportion of the fuel-bound trace metals investigated leaves the combustor in the vapour phase. A much greater proportion exists in the form of fine solid particles (the particulates). Samples taken from the bottom ash, the cyclone catch and the filter dust, and analysed for the trace element content, show that more than 99% of most metals studied remain in the bed or are removed with the solid particles elutriated from the bed. It seems that an efficient particulate control system will reduce the trace metal concentrations in the flue gas to very low levels. © 1990.