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The increasing use of biomasses in the production of electricity and heat results in an increased amount of burning residue, fly ash which disposal is becoming more and more restricted and expensive. Therefore, there is a great interest in utilizing fly ashes instead of just disposing of it. This study aimed to establish whether the utilization of fly ash from the fluidized bed combustion of peat, wood, and forest residues can be improved by electrostatic precipitator separation of sulfate, chloride, and some detrimental metals. Classification selectivity calculations of electrostatic precipitators for three different fuel mixtures from two different power plants were performed by using Nelson's and Karnis's selectivity indices. Results showed that all fly ashes behaved similarly in the electrostatic separation process SiO resulted in coarse fractions with Nelson's selectivity of 0.2 or more, while sulfate, chloride, and the studied detrimental metals (arsenic, cadmium, and lead) enriched into fine fractions with varying selectivity from 0.2 to 0.65. Overall, the results of this study suggest that it is possible to improve the utilization potential of fly ashes from fluidized bed combustion in concrete, fertilizer, and earth construction applications by using electrostatic precipitators for the fractionating of fly ashes in addition to their initial function of collecting fly ash particles from flue gases. The separation of the finer fractions (ESP 2 and 3) from ESP 1 field fly ash is recommended.

Five different fly ashes originating from fluidized bed combustion of peat, wood and different type of wastes was studied by their chemical and physical characteristic to find out how they fulfill the requirements for concrete set by European EN 450-1 standard. Fly ash originating mostly from peat combustion is the only fly ash fulfilling all requirements for concrete without any treatments. For other studied fly ashes some chemical and physical characteristics are exceeded: most probably free CaO, sulfate, chloride, and fineness. Also the sum of main components (SiO2, Al2O3, Fe2O3) failed for other ashes than the one originating from mostly peat combustion. However, it should be kept in mind that requirements set by European standard is more restrictive than similar in America and some mechanical treatments are possible way to increase their utilization potential.