Comparison of the Forest Fertilizer Properties of the Ash Fraction from the Co-Firing of Peat and Forest Residues at a Large-Sized (246 MW) Combustion Plant of a Pulp and Paper Mill Complex
H. NURMESNIEMI1, R. POYKIO2, K. MANSKINEN3 and R. L. KEISKI4
1 Stora Enso Oyj,
Veitsiluoto Mill, FI - 94800 Kemi (Finland)
hannu.nurmesniemi@storaenso.com
2 City of Kemi,
Valtakatu 26, FI - 94100 Kemi (Finland)
risto.poykio@kemi.fi
3 Stora Enso Oyj,
Heinola Fluting Mill, FI - 18101 Heinola (Finland)
kati.manskinen@storaenso.com
4 University of Oulu, Mass and Heat Transfer Laboratory, Department of Process and Environmental Engineering,
University of Oulu 4300, 90014 Oulu (Finland)
riitta.keiski@oulu.fi
Keywords: Ash, fertilizer, fluidized bed boiler, forest residue, waste
Pages: 197–204
Abstract
The bottom ash and fly ash investigated in this study originated from the bubbling fluidized bed boiler at the large-sized (246 MW) combustion plant of a pulp and paper mill complex. Approximately 40 % of the energy produced by the boiler originated from the incineration of commercial peat fuel, and approximately 60 % from the incineration of clean forest residues (i.e. bark, woodchip and sawdust). Due to the low heavy metal concentrations (As, Cd, Cr, Cu, Hg, Pb, Ni and Zn) in the bottom ash and fly ash, these residues are potential forest fertilizers as such. However, additional Ca is needed for the bottom ash, because its Ca concentration of 5.8 % (d.w.) was lower than the statutory Finnish minimum limit value of 6.0 % (d.w.) for Ca in forest fertilizers. Except for potassium, nutrients and heavy metals were enriched in the fly ash. Compared to the total phosphorous content, which was 0.2 % (d.w.) in the bottom ash and 1.3 % (d.w.) in the fly ash, the water soluble phosphorous content in both ashes was negligible (<0.01 %; d.w.). This finding is discussed on the basis of the minerals observed in the XRD data for the ashes, as well as on the grounds of findings reported by other researchers.
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