Bubbling Fluidized Bed Co-Combustion of Different Sustainable Fuels: Trace Element Behaviour

With this paper the author will show interesting results of the co-combustion of coal in combination with bark and paper sludge in fluidized bed combustion. The results presented were collected during two measurement campaigns at a 30 kW electrically stabilized bubbling fluidized bed. The fluidized bed combustor was compared to large scale combustors in different campaigns before and thus gives an idea of the output of industrial plants. The main focus of the measurements was the behavior of trace elements of Ni Pb, Zn, Cr and Cu with a changing bed material. One bed material was pre-used under the exposure of combustion of a ternary fuel mixture of coal, bark and paper sludge over a long period of time resulting in a bed composition of 2/3 SiO₂ and 1/3 Al₂O₃. The second bed material utilized, which was a sand (primarily SiO₂) not used before thus not enriched in any compounds. When comparing the results of all trials three different trace metal partitioning effects were monitored. First an increase in the elemental concentration in the bed material which was primarily due to the higher input concentration with the pre-used bed material which was found for all three alternatives plus a decrease in filter and cyclone concentrations (Ni, Pb). Secondly an increase in all three ash fractions was detected for Cu. The third was a mixture of both with increasing filter concentrations but decreasing cyclone concentrations (Zn, Cr). An attempt was made to link the before primarily to the enrichment in Al-compounds and to a bed capacity of retention. The results presented indicate the need for longer periods of testing even at small scaled facilities if the comparison to large scale facilities is attempted.