High-pressure high-temperature control of hydrogen sulfide, sulfur dioxide and selenium from fuel/flue gas using calcium-based sorbents

The principal aim of this research project is to gain fundamental insights into the reaction kinetics and mechanism of H₂S/Ca-sorbent interaction at elevated pressures (1–3.5 MPa) and temperatures (500–900°C) representative of IGCC power generation systems. Sulfidation experiments are conducted in a high-pressure and high-temperature differential-bed flow-through reactor. This work produced the high-pressure sulfidation kinetic data, which is free from external transport limitations and hence truly represents the in-gasifier H₂S removal. This information would lead to a greater understanding of calcination and/or sulfidation characteristics of various Ca-based sorbents at high pressures and temperatures, and optimization of sorbent structural properties for enhanced H₂S removal.; This research work also describes the sorbent/ash reactivation via novel carbonation technique to yield enhanced SO₂ removal in coal-fired combustor. A novel process has been developed for reactivation of partially utilized calcium-based sorbents for increased SO₂ removal and sorbent utilization from coal-fired boilers/combustors. Spent sorbent and combustor ash samples are treated under specific conditions to modify their internal structure and expose the under-utilized calcium for further SO₂ capture. The reactivated sorbent shows a significant improvement in utilization increasing from less than 45% to nearly 100%. Application of this novel reactivation process to ash samples obtained from a circulating fluidized bed combustor also show a marked improvement in utilization of available calcium, nearly doubling the amount of sulfur captured. This reactivation process involves carbonation of the unsulfated calcium. Better redistribution and exposure of the available calcium by the carbonation reactivation process, as compared to reactivation via hydration, is proposed as the main factor in increasing the sorbent utilization. The increased ultimate sorbent utilization obtained by this reactivation process could significantly improve the sorbent-based flue gas desulfurization technology.; In this research work, investigations are also conducted into determining the kinetics of interaction of selenium and Ca-based sorbents for removal of selenium species from hot flue gases. Ca-based sorbents are shown to capture SeO₂ via a chemical reaction leading to the formation of calcium selenite. The kinetic investigations indicated that the order of reaction with respect to SeO₂ partial pressure is 0.67 and the activation energy of reaction is 4.03 kcal/mol.