Abstract
Although fluidized bed in situ desulphurization from coal combustion has been widely studied, there are aspects that remain under investigation. Additionally, few publications address Brazilian coal desulphurization via fluidized beds. This study used a 250 kWth bubbling fluidized bed pilot plant to analyze different aspects of the dolomite desulphurization of two Brazilian coals. Superficial velocities of 0.38 and 0.46 m/s, flue gas recycling, Ca/S molar ratios and elutriation were assessed. Results confirmed the influence of the Ca/S molar ratio and superficial velocity - SO2 conversion up to 60.5% was achieved for one coal type, and 70.9% was achieved for the other type. A recycling ratio of 54.6% could increase SO2 conversion up to 86.1%. Elutriation and collection of ashes and Ca-containing products did not present the same behavior because a lower wt. % of CaO was collected by the gas controlled mechanism compared to the ash.
Highlights
Fluidized bed coal combustion has the advantage of creating SO2 treatment through a sulphation reaction from the in situ injection of dolomite or limestone
Coal A and Coal B are from two different Brazilian federative states, Rio Grande do Sul and Santa Catarina, respectively
The steady state conditions to obtain desulphurization data were considered to occur after the SO2 concentration of the flue gases and the bed temperatures, T04 and T05, were stabilized
Summary
Fluidized bed coal combustion has the advantage of creating SO2 treatment through a sulphation reaction from the in situ injection of dolomite or limestone. This procedure has been widely explored; some details and local behaviors based on coal characteristics are still under investigation. Only a conversion of 30–40% of CaO is obtained. This relatively low utilization of limestone is one of the major limitations of the technology (Anthony and Granatstein, 2001). The presence of SO2 affects limestone particle size because it generates a hard sulphate shell around the unreacted CaO core of the particle, which reduces its fragmentation (Scala et al, 2011). Substantial changes in the sorbents’ particle size distribution can be achieved from particle attrition and fragmentation
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