Sulfur retention in an oxy-fuel bubbling fluidized bed combustor: Effect of coal rank, type of sorbent and O2/CO2 ratio

• The optimum temperature for sulfur retention in oxy-fuel fluidized beds is 900–925 °C.
• The sulfur retentions with the dolomite are higher than with the limestones.
• Sulfur retention depends on sulfur content of the coal.
• O2/CO2 ratio hardly affects sulfur retention.
• A decrease in the sorbent particle size produces an increase in sulfur retention.

In this work, SO2 retention via calcium-based sorbents added in a continuous bubbling fluidized bed combustor (∼3 kWth) operating in oxy-fuel combustion mode is analyzed. Tests were performed at different operating temperatures with three sorbents, two limestones and one dolomite, and with three coals, ranging from lignite to anthracite, to analyze the influence of coal rank, type of sorbent, sorbent particle size, and O2/CO2 feeding ratio on the sulfation process.It was found that the combustor temperature had a strong influence on the limestones sulfur retention with a maximum at 900–925 °C. The behavior of the limestones was qualitatively similar with the three coals, attaining the highest sulfur retention values working with the lignite and the lowest working with the bituminous coal. On the contrary, with the dolomite the sulfur retention was hardly affected by the combustion temperature and the sulfur retentions attained were higher than with the limestones. The sulfur retention increased with diminishing the Ca-based sorbent particle size, and it was hardly affected by the O2/CO2 ratio fed into the combustor.