The use of a hot cyclone for separation of heavy metals during combustion, evaluation by chemical equilibrium calculations

This degree-project is a part of a project financed by the European Communities non Nuclear energy program. The aim of the project is to reach a sustainable use of biofuels as energy source. A requirement for sustainable use of biomass fuel in combustion and gasification plants is that the ash produced can be recycled back to the forest and farmlands in a safe and controlled way. Recycling is important because most of the nutrients (Ca, Mg, P, Na and K) are ending up in the ash. However, the ashes also contain heavy metals and organic pollutants that should not be recycled. To solve this problem, a new technique for separation of the heavy metals during combustion is under development. This technique builds on evaporation of heavy metals and particle separation with a hot cyclone. The idea is that the heavy metal will pass the cyclone as gas species while the nutrients will be separated in the cyclone from the flue gas. The heavy metals are then collected in the more efficient cleaning device downstream in the process. In the present study, the technique has been evaluated by chemical equilibrium calculations and the results were compared with some previously performed full-scale experiments. The results show that by this technique a separation of Cd and Pb will be possible. Concerning the elements As, Cu and Cr, it may be possible to separate them to some extent while the element Ni and V will not be separated. At least 60-70% of Na and K and 90% of Ca, Mg and P will be separated in the cyclone 21 refs, 12 figs, 2 tabs