Ash and chlorine deposition during co-combustion of lignite and a chlorine-rich Canadian peat in a fluidized bed – Effects of blending ratio, moisture content and sulfur addition

A Canadian chlorine-rich peat was co-fired with lignite in a bubbling fluidized bed combustor (FBC) in this study. With an air-cooled probe installed in the freeboard of the riser, effects of portion of peat, moisture content and addition of sulfur on ash and chlorine deposition during combustion/co-combustion of lignite–peat blends were investigated. The results indicated that the contents of chlorine element, alkali/alkaline earth metals and SiO2 and Al2O3 of the feed played a key role in the ash deposition in all tests. A higher chlorine concentration in the feed would generally result in a higher tendency of ash deposition. For instance, combustion of 100% peat pellet showed a much higher tendency of ash deposition than combustion of the lignite alone. Nevertheless, co-firing of the lignite–peat blends with 20% or 50% peat resulted in lower relative ash deposition rates (RDA). Combustion of relatively wet solid fuels produced a decreased RDA value and reduced chlorine deposition. Adding sulfur into the fuel of coal or peat could effectively decrease the chloride deposition in the ash deposits via sulfation. The sulfur addition could also reduce the ash deposition rate for the combustion of lignite, while it slightly increased the ash deposition rate for the peat fuel. The deposited Ca, Mg, Al and Si elements were present mostly in the forms of calcium and magnesium sulfates, aluminates and silicates that have relatively lower melting points.