Abstract
Co-combustion of animal waste, in waste-to-energy boilers, is considered a method to produce both heat and power and to dispose of possibly infected animal wastes. This research conducted full-scale combustion tests to identify the impact of changed fuel composition on a fluidized-bed boiler. The impact was characterized by analyzing the deposit formation rate, deposit composition, ash composition, and emissions. Two combustion tests, denoted the reference case and animal waste case, were performed based on different fuel mixes. In the reference case, a normal solid waste fuel mix was combusted in the boiler, containing sorted industry and household waste. In the animal waste case, 20 wt% animal waste was added to the reference fuel mix. The collected samples, comprising sampling probe deposits, fuel mixes, bed ash, return sand, boiler ash, cyclone ash and filter ash, were analyzed using chemical fractionation, SEM-EDX and XRD. The results indicate decreased deposit formation due to animal waste co-combustion. SEM-EDX and chemical fractionation identified higher concentrations of P, Ca, S, and Cl in the bed materials in the animal waste case. Moreover, the risk of bed agglomeration was lower in the animal waste case and also a decreased rate of NOx and SO2 emissions were observed.
Highlights
Increasing demand for sustainable heat and power production, as well as problems landfilling wastes, has prompted heat and power plants to replace fossil fuels with alternatives such as combustible municipal solid wastes (MSW) or refuse-derived fuels (RDF) [1,2]
Despite higher concentrations of Cl, alkali and S for the deposits formed in the animal waste (AW) case, there were no indications of higher corrosion
SEM-Energy Dispersive X-ray (EDX) analysis of the coatings formed on return sand and bed ash particles indicated higher concentrations of P, Ca, S, and Cl in the bed material in the AW case; this was confirmed by the chemical fractionation analysis
Summary
Increasing demand for sustainable heat and power production, as well as problems landfilling wastes, has prompted heat and power plants to replace fossil fuels with alternatives such as combustible municipal solid wastes (MSW) or refuse-derived fuels (RDF) [1,2]. Formation of bed and fly ashes, which may contain large amounts of potentially toxic metal compounds, is a problem when waste fuels are combusted. These ashes, which could harm the environment, are classified as hazardous materials and need special treatment and storage when landfilled [7]. Regardless of these problems, the combustion of waste fuels is still an interesting option, considering their often high energy content, their abundance, and the economic aspects of combusting them. The emissions of NOx in the flue gas were measured, to identify whether high nitrogen content of animal waste [11] may change NOx emissions in positive or negative way
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