Experimental Study on the Characteristics of Self-Desulfurization during Sugarcane Leaf Combustion in a Circulating Fluidized Bed

During biomass combustion, the SO2 emission would still be a problem in some cases, although the average sulfur content is relatively lower than that of coal and other fossil fuels. In this work, the characteristics of self-desulfurization during sugarcane leaf combustion in a circulating fluidized bed were experimentally investigated. First, a laboratory fixed-bed reactor was used to study how the char particles take part in the self-desulfurization process. It was observed that SO2 can be largely captured by char in the temperature range of 700–900 °C. Most of the captured sulfur was incorporated with organic char matrix rather than directly retained by inherent alkali and alkaline-earth matters in the form of inorganic salts. During char combustion, substantial amounts of the captured sulfur could be retained in the ash, which was mainly limited by the alkali and alkali-earth matters available. At higher temperatures (>800 °C), the sulfur retention reduced, mainly because the alkali and alkali-earth matters would give priority to form silicate compounds rather than the occurrence of sulfate reactions. Then, a pilot-scale circulating fluidized-bed experiment was performed to study SO2 emission behaviors during sugarcane leaf combustion. It showed that there was nearly no SO2 emission when the combustion temperature was controlled below 800 °C. The sulfur retention calculation based on ash balance showed that about 87% of fuel S was retained in fly ash. This was mainly attributed to the intense gas–solid contact within the combustor that could largely enhance the sulfur retention reactions.