Trace Element Distribution in and Around the Recovery Boiler, 2004 International Chemical Recovery Conference

The amounts and concentrations of six trace elements, arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), manganese (Mn), and nickel (Ni) were studied in and around the recovery boiler of a large kraft pulp mill. All together over 100 samples were collected from streams within the pulp mill. In this paper the results are presented for the whole mill and for the streams into and out from the recovery boiler, including the black liquor after the evaporators, the fired black liquor, the fly ash, the flue gases, the particulate matter in the flue gases, and the smelt. The samples were analyzed with various analytical methods including Inductively Coupled Plasma emission Mass Spectrometry (ICP-MS) with enhanced sensitivity. The mass balance could be satisfactorily closed for some of the trace elements studied, while for others the difference between ingoing and outgoing amounts were fairly big. The observed distribution of the elements between flue gas and smelt can to a great extent be explained by their different volatility. A predictive model for the trace element chemistry in the recovery boiler is developed and the first preliminary results are presented.