Potassium chloride, KCl, formed from biomass combustion may lead to ash deposition and corrosion problems in boilers. Sulfates are effective additives for converting KCl to the less harmful K 2 SO 4 and HCl. In the present study, the rate constants for decomposition of ammonium sulfate and aluminum sulfate were obtained from experiments in a fast heating rate thermogravimetric analyzer. The yields of SO 2 and SO 3 from the decomposition were investigated in a tube reactor at 600−900°C , revealing a constant distribution of about 15% SO 2 and 85% SO 3 from aluminum sulfate decomposition and a temperaturedependent distribution of SO 2 and SO 3 from ammonium sulfate decomposition. On the basis of these data as well as earlier results, a detailed chemical kinetic model for sulfation of KCl by a range of sulfate additives was established. Modeling results were compared to biomass combustion experiments in a bubbling fluidized-bed reactor using ammonium sulfate, aluminum sulfate, and ferric sulfate as additives. The simulation results for ammonium sulfate and ferric sulfate addition compared favorably to the experiments. The predictions for aluminum sulfate addition were only partly in agreement with the experimental results, implying a need for further investigations. Predictions for the effectiveness of the sulfur-based additives indicate that ferric sulfate and ammonium sulfate have similar effectiveness at temperatures ranging from approximately 850 to 900°C, whereas ferric sulfate is more efficient at higher temperatures and ammonium sulfate is more effective at lower temperatures.

The cement industry aims to use an increased amount of alternative fuels to reduce production costs and CO 2 emissions. In this study three cement plants firing different kinds and percentages of alternative fuel were studied. A specially developed camera setup was used to monitor the flames in the three cement kilns and assess the effect of alternative fuels on the flame. It was found that co-firing with solid recovered fuel (SRF) would delay the ignition point by about 2 meters and lower the intensity and temperature of the kiln flame compared to a fossil fuel flame. This is related to a larger particle size and moisture content of the alternative fuels, which lowers the conversion rate compared to fossil fuels. The consequences can be a lower kiln temperature and cement quality. The longer conversion time may also lead to the possibility of localized reducing conditions in the cement kiln, which can have a negative impact on the clinker quality and process stability. The burner design may alleviate some of the issues encountered with SRF co-firing. At one of the test plants the burner was changed from a design with an annular channel for axial air to a jet design. This proved to be beneficial for an early ignition and improved dispersion of the fuel and led to an increase in cement quality and higher use of SRF.

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Waste derived fuels such as Solid Recovered Fuel (SRF) are increasingly being used in e.g. the cement industry as a means to reduce cost. The inhomogeneous nature of SRF makes it difficult to combust and many problems may arise within e.g. combustion control, feeding of fuel, deposit formation or accumulation of impurities. The combustion of polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), wood, and SRF were studied in a rotary drum furnace.The combustion was recorded on a camera (60 frames per second) so that any agglomeration or deposition of fuel or ash could be monitored. PE and PP pose no significant risk of forming deposits in a combustion environment (T > 800 °C) due to a rapid devolatilization, while PET may cause deposits due to a sticky char residue. The deposition tendency of the investigated SRF is low and it may be managed by a careful combustion control. The ash from SRF or wood does not pose significant risk of melting and deposits at temperatures up to 1000 °C, but the presence of glass impurities in some SRF may limit operation temperatures to 900 °C due to ash melting.

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