Fly ash characteristics and potential utilization in construction applications from wood co-firing and pure combustion in an industrial scale pulverized fuel boiler

摘要

The objective of this work was to evaluate the potential utilization of fly ash, in industrial practiced construction applications, obtained from a high thermal share of co-fired wood dust biomass and pure wood dust biomass combustion in an industrial scale pulverized fuel facility. The methods used include the analyses of the fly ashes by XRD analyses, SEM-EDX analyses, particle size distribution analyses, reactivity index determinations, mechanical strength development, initial setting time determinations, soundness testing evaluations, and ICP-OES analyses of the bulk fly ashes. In addition, evaluations were conducted of the different particle sizes entering the ESP by ICP-OES analyses. The results of the analyses were compared with standards used in industry for fly ash applications in construction practices. Results show that despite the increased free calcium oxide content in the fly ashes, above usually accepted limit values, the fly ashes were still sound without any expansion. The strength gain and activity indexes of pure wood dust combustion without the use of primary NOx reduction measures were comparable to pure cement testing. Employing primary NOx reduction measures, such as implementation of low NOx burnes lead to a reduction in reactive phases in the ashes due to an increase in unburned carbon, i.e. LOI. The fly ash from the 50% thermal share met the requirements of the EU EN 450-1 standard, giving it a very high value market end use, despite the high thermal share of the biomass that have significantly different chemical compositions as coals. This is attributed to the high quality wood pellets trade in accordance with the IWPB association requirements and the low ash content of the wood pellets. As there is not enough date from long-term performance testing involving fly ashes generated from biomass combustion in pulverized fuel facilities, current conclusions are that pure biomass fly ashes still have good reactivity characteristics, good reactive mineral phases present, and with an increased free CaO content, which can contribute to strength gain in fly ashes through carbonation, the ashes are very suitable for low strength requirement uses, such as mortars, rendering systems, bricks, road construction, low-tech building materials, or may even be considered in niche applications such as chemical binders, blended cements, or geopolymers. The practice of utilization of fly ashes generated from pure biomass combustion or a very high thermal share of co-fired biomass in a pulverized fuel industrial facility is not common or widely reported. The implication of the findings are expanding the scientific's community knowledge about fly ashes generated from biomass combustion in pulverized fuel facilities, which can impact decisions by policy makers, power plant personnel, fly ash management organizational personnel, the construction industry, and researches.