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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.

The increasing use of biomasses in the production of electricity and heat delivers an increased amount burning residue, fly ash that disposal is becoming more and more restricted and expensive. Therefore, there is a great interest to utilize fly ash in other means than disposal. This study aimed to determine the suitability of air jet sieving and air classification to separate detrimental elements, such as sulfate, chloride and some heavy metals, into fine fractions. Furthermore, the effect of fly ash deagglomeration on classification selectivity was studied. Experiments were conducted using two fly ash samples originated from fluidized bed combustion of peat, forest residues and wastes. The results showed that it is possible to significantly improve the utilization potential of fly ashes using air jet classification. In classification, calcium is concentrated into a fine fraction and silica and aluminum are concentrated in coarse fractions. Sulfate, chloride and studied detrimental metals (cadmium, copper, lead and zinc) enrich to the fine fraction with high selectivity. Deagglomeration had a minor effect, as it slightly improved the classification selectivity for some elements.

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