Partitioning behaviour of some toxic trace elements during coal combustion—the influence of events occurring during the deposition stage

The distribution of trace elements in a sub-bituminous coal seam and a peat dome both located in the Waikato/Hauraki region of the central North Island of New Zealand is controlled by the presence or absence of inorganic layers. One of these is a volcanic ash fall layer (tephra) containing high titanium and low calcium levels compared to inorganic phases in other regions of the seam. When coal samples taken from the centre of the seam and including the tephra derived parting were combusted in an underfeed stoker, the partitioning behaviour of the toxic class II volatile boron was found to be significantly different than for samples of coal from other parts of the seam not including the tephra derived parting. Reasons for the different behaviour are identified.