Recycle ratio in FBC Boiler
For a given test condition and a narrow range of limestone to coal feed rate, one expects the total available mole of calcium to each mole of coal sulfur to increase as the recycle ratio (recycle rate/coal rate) increases.
The total available calcium oxide is defined as the combined calcium oxide from the limestone feed and the unreacted calcium oxide in the recycle stream;
it is designated as (CaO)R + (CaO)L. the limestone feed rate or the recycle ratio.
The expected trend of the effect of recycle ratio on sulfur capture for two different Ca/S feed ratios. Ideally, for a given set of conditions, sulfur capture should increase with increasing recycle ratio due to an increase in the total available calcium to sulfur ratio. The rate of increase in sulfur capture (slope of the curve) will gradually diminish as the reactivity of the recycled lime decreases due to higher calcium utilization.