Fate of Sulfur during Entrained-Flow Gasification of Pittsburgh No. 8 Coal: Influence of Particle Size, Sulfur Forms, and Temperature

Sulfur release behavior and gas-phase sulfur emissions during gasification of Pittsburgh no. 8 coal were examined using an entrained-flow gasifier at atmospheric pressure. To study the fate of sulfur forms, the coal was separated into specific gravity fractions that were rich in organic sulfur (SG1), organic and inorganic sulfur (SG2), and inorganic sulfur (SG3). Two particle sizes in each specific gravity fraction, finer (75–106 μm) and coarser (212–425 μm), were examined to determine the influence of particle size at three different temperatures (1573, 1673, and 1773 K). The results showed that the initial coal particle size affected (finer > coarser) the sulfur release behavior of SG2 fractions rich in both organic and inorganic sulfur and SG3 fractions rich in inorganic (predominantly pyritic) sulfur, indicating that mass transfer resistance to sulfur release increases with inorganic sulfur and mineral matter in the feed. The percent sulfur released into the gas phase was highest for organic-sulfur-rich fractions and lowest for inorganic-sulfur-rich fractions. The sulfur released from SG2 fractions was similar or slightly lower than that released from SG1 fractions because of increased fragmentation and a possible synergistic effect between organic matrix and inorganic sulfur. The percent sulfur released reached a plateau for all particle classes beyond 1573 K, indicating that most of the sulfur was released before the middle stage of gasification. With respect to gas-phase emissions, a large percentage of sulfur was released as H2S, followed by COS, CS2, and SO2. Decomposition and oxidation of inorganic sulfur and interaction of pyritic sulfur with organic matrix appear to be the paths for the release of SO2 and CS2, respectively.