Christoph Maschowski1, Peter Kruspan2, Patxi Garra3, Ali Talib Arif4,5, Gwenaëlle Trouvé3, Reto Gieré6. 1. Institute of Earth and Environmental Sciences-Geochemistry, University of Freiburg, D-79104 Freiburg, Germany. 2. LafargeHolcim Ltd, Zürcherstrasse 156, 8645 Jona, Switzerland. 3. Laboratoire Gestion des Risques et Environnement (LGRE), Université de Haute-Alsace, F-68093 Mulhouse Cedex, France. 4. Institute for Infection Prevention and Hospital Epidemiology, University Medical Center Freiburg, University of Freiburg, Faculty of Medicine, University of Freiburg, D-79106 Freiburg, Germany. 5. Kurdistan Institution for Strategic Studies and Scientific Research (KISSR), Qirga, Sulaimani, Iraq. 6. Department of Earth and Environmental Science and Center of Excellence in Environmental Toxicology, University of Pennsylvania, Philadelphia, PA 19104-6316, USA.
Abstract
Bottom and fly ash samples from six biomass power plants with different power scales and various flue gas treatment strategies were collected and analyzed in regard to their mineralogical composition, and their bulk major and trace element contents, all of which are of concern for regulations on biomass ash for further utilization. Furthermore, individual ash particles were investigated by scanning electron microscopy to characterize their physicochemical microstructures. Thermal behavior of wood-pellet ash, i.e. decomposition processes and mineral transformations during combustion, was indicated by thermogravimetric analysis and X-ray diffraction. Results reveal extensive variation of physicochemical features across the different ash types: wood-chip fly ash from electrostatic precipitators mainly consisted of water-soluble salts, whereas wood-chip fly ash from cyclones contained predominantly cenospheres (hollow spherical fly ash particles) and higher heavy metal concentrations. In addition, the fuel type and admixture had influences on ash compositions; some fuels like Miscanthus straw require a liming agent such as calcium hydroxide to be admixed to prevent fouling, which is then predominantly found in the ash. Furthermore, boiler size had an influence on fly ash composition. Cadmium concentrations were elevated in some fly ash samples at levels of concern for further utilization, whereas concentrations of troublesome Cr(VI) were below the detection limit for all investigated ash samples. Other contaminating elements such as Ni, Pb and Zn were variable but below limit values. Results clearly show that the nature of biomass ash calls for careful analyses prior to further application as, e.g., cement clinker replacement material.
Bottom and fly ash samples from pan class="Chemical">six biomass power plants with different power scales and various flue gas treatment strategies were collected and analyzed in regard to their mineralogicalcomposition, and their bulk major and trace element contents, all of which are of concern for regulations on biomass ash for further utilization. Furthermore, individualash particles were investigated by scanning electron microscopy to characterize their physicochemical microstructures. Thermal behavior of wood-pellet ash, i.e. decomposition processes and mineral transformations during combustion, was indicated by thermogravimetric analysis and X-ray diffraction. Results reveal extensive variation of physicochemicalfeatures across the different ash types: wood-chip fly ash from electrostatic precipitators mainly consisted of water-soluble salts, whereas wood-chip fly ash from cyclones contained predominantly cenospheres (hollow spherical fly ash particles) and higher heavy metalconcentrations. In addition, the fuel type and admixture had influences on ash compositions; some fuels like Miscanthus straw require a liming agent such ascalcium hydroxide to be admixed to prevent fouling, which is then predominantly found in the ash. Furthermore, boiler size had an influence on fly ash composition. Cadmiumconcentrations were elevated in some fly ash samples at levels of concern for further utilization, whereasconcentrations of troublesome Cr(VI) were below the detection limit for all investigated ash samples. Other contaminating elements such as Ni, Pb and Zn were variable but below limit values. Results clearly show that the nature of biomass ash calls for careful analyses prior to further application as, e.g., cement clinker replacement material.