When increasing the utilisation of waste fuels, the operational impact of ash-related problems are generally becoming more severe. Pulp and paper industry is a good example of this development due to paper recycling and higher degree of mill closure. When sludge streams from de-inking and water treatment plants increase, combustion often turns out as the most cost-efficient way to handle these waste materials. Paper mill sludge has typically high ash content because its main chemicals are kaolin clay (Al_2Si_2O_5(OH)_4), calcium carbonate (CaCO_3) and talc (Mg_3Si_4O_(10)(OH)_2). Due to heavy loading with paper mill sludge the fluidised bed boilers of this study faced heavy fouling and leakages of evaporator and superheater tubes. Firing plastics and wood-based waste together with paper mill sludge meant that the boilers inevitably faced chlorine-induced corrosion. This paper describes ash-related problems which generated malfunctions and leakages and thus increased forced stops and maintenance hours for repairs. Principally the ash-related problems can be divided into three categories: - Erosion, - Fouling, and - Corrosion. With respect to these ash-related problems, the inorganic fuel components and reactions related to this paper are described below.
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