Increasing the utilization potential of fly ashes from fluidized bed combustion by mechanical treatments

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.