Combustion of spent mushroom compost and coal tailing pellets in a fluidised-bed

Abstract

Previous investigations found that fluidised-bed combustion of spent mushroom compost–coal tailing pellets was preferred for these high ash content fuels. This paper considers the combustion tests carried out on these wastes in a laboratory-scale fluidised-bed, where parameters, including the pellet feedrate, primary/fluidising air flowrate and bed depth, were investigated. Based on the minimum air ratio of 2.5 required to achieve high combustion efficiencies of around 97%, the optimum operating conditions for the combustor employed were a pellet feedrate of 3.25 kg/h (180 kg/m 2h) and a total air flowrate of 650 kg/m 2h. A lower sand bed depth of 0.22 m was also deemed beneficial, as deeper beds resulted in slugging and noticeable reductions in combustion efficiency. Acid gas emissions (NO x , SO x and HCl) were found in limited concentrations, as species remained primarily as inorganic compounds in the flyash. Some N 2O is thought to have formed, as fluidised-bed combustors are particularly prone to this. The alkali index of the ash suggests probable fouling/slagging in the system. For industrial-scale combustion of these wastes, the combustion efficiency could be improved by the presence of secondary air jets to aid turbulent mixing.