Mechanistic studies of ultrafast sulfur dioxide and selenium removal by calcium-based sorbents

This research deals with the mechanism of interaction and kinetics of various phenomena involved in the capture of SO{dollar}sb2{dollar} and selenium from flue gas by using dry calcium-based powders. Dry sorbent injection (DSI) involves the injection of fine sorbent powders into the combustor, furnace sorbent injection (FSI), which is the main focus of this work, takes place in above-the-flame region. The temperature window in this upper-furnace region is 1150-800{dollar}rmspcirc C{dollar} and the residence time of the flue gas is about 1-2 seconds.; The Ca(OH){dollar}sb2{dollar}-SO{dollar}sb2{dollar} interaction phenomena has been investigated at very short contact times (below 50 ms) in two stages: first, the calcination and sintering alone without SO{dollar}sb2{dollar}; and second, the combined calcination, sintering and sulfation reaction in the presence of SO{dollar}sb2.{dollar} The kinetics and structural evolution of the calcine during ultrafast calcination and sintering has been successfully modeled. The investigations of transformations in the pore size distribution both in the absence and presence of SO{dollar}sb2{dollar} are carried out. The evolution of pores of various size ranges and the implications of the loss of the smallest pores is studied.; The investigation and development of improved calcium-based sorbents is conducted to improve the sorbent reactivity and utilization. Studies with the high surface area carbonate and hydrate and a critical comparison with unpromoted hydrate and carbonate have been able to correlate the pore structure and reactivity. This work has laid the foundation and background for harnessing the sorbent pore structure and tailoring it to develop sorbents with very high reactivity.; Selenium is a highly volatile trace toxic and is emitted to the atmosphere with the flue gas during fossil-fuel combustion. This study has shown that calcium-based sorbents possess high sorption capability compared with alumino-silicate sorbents. Thorough mechanistic investigations have revealed that the CaO reacts directly with SeO{dollar}sb2{dollar} to lead to the formation of calcium selenite, which does not require the presence of oxygen. Due to the high vapor pressure and decomposition characteristics of CaSeO{dollar}sb3{dollar} above {dollar}700rmspcirc C,{dollar} the most favorable temperature range lies at {dollar}600rmspcirc C{dollar} or below.