A STUDY OF TRACE-ELEMENT BEHAVIOR IN 2 MODERN COAL-FIRED POWER-PLANTS- II - TRACE-ELEMENT BALANCES IN 2 PLANTS EQUIPPED WITH SEMIDRY FLUE-GAS DESULFURIZATION FACILITIES

Two Finnish coal-fired power plants were experimentally investigated w ith regard to the distribution of environmentally harmful trace elemen ts in the process. The plants were equipped with low NOx burners, an e lectrostatic precipitator and a semi-dry flue gas desulphurisation uni t consisting of a spray-dryer-type reactor and a fabric tilter. All th e in-going and out-going mass streams were analysed for As, Be, Cd, Co , Cr, Cu, Hg, Mn, Ni, Pb, Se and Tl in the first plant, and for As, Be , Cd, Cr, Hg, Mn, Ni, Pb, Tl and Zn in the other plant. Total atmosphe ric emissions of trace elements from the plants studied were very low; most of them even orders of magnitudes smaller than 10 mu g/m(3) (NTP ). The vaporous fraction of the trace elements was found to play a pre dominant role in the atmospheric emissions. However, the total atmosph eric emissions of even the strongly volatile Hg were very low, which c an be ascribed to the applied plant technology. Enrichment of the elem ents into the various ash streams-from the bottom ash up to the partic ulates downstream of the electrostatic precipitator-was found to be in satisfactory compliance with literature data. Element balances were c alculated over the whole process and over the desulphurisation unit fo r both plants: for the whole process the closure (i.e., ratio output/i nput) of element balances was within +/-30% for all elements studied, except for chromium in plant HE, and for the vast majority of elements it was even within +/-20%. The results imply that the sampling techni ques and analytical methods developed for this work can be well applie d to quantitative mass balance studies in this kind of processes. (C) 1998 Elsevier Science B.V. All rights reserved.