Effect of circulating ash on sulfur conversion characteristics in the coal polygeneration process

Abstract Sulfur transformation in the polygeneration process of Xinzhou high-sulfur coal employing a circulating ash heat carrier was studied using a fixed bed reactor. Circulating ash was effective in capturing the gaseous sulfur, along with ~ 80% of H 2 S, 59% of COS, 55% of CS 2 , and 48% of SO 2 . Sulfur mass balance calculations revealed that 30.88% of the total sulfur content was retained in the circulating ash at 600 °C. The sulfur retention capacity of the ash was promoted by an increase in temperature, an increase in the ash to coal mass ratio, and a decrease in ash particle size. Sulfur captured in the circulating ash released lower quantities of SO 2 than the sulfur remaining in the char during combustion. Furthermore, CaO and Fe 2 O 3 played a dominant role in the sulfur retention of the circulating ash, and the sulfur retention capacity of Fe 2 O 3 was superior to that of CaO during pyrolysis. X-ray diffraction results indicated that the sulfur captured by CaO and Fe 2 O 3 was converted into CaS and FeS. However, FeS was easily oxidized to Fe 2 O 3 , accompanied by the emission of SO 2 , while CaS tended to be oxidized to CaSO 4 during combustion.