High reactivity Ca-based sorbents for SO(2) and As(2)O(3) removal at elevated temperatures: Experimental and modeling

A high reactivity calcium carbonate sorbent with an open initial pore structure is prepared and its calcination, sintering and sulfation characteristics are investigated in an entrained flow reactor system at high temperatures (900-{dollar}1100spcirc{dollar}C) and short residence times (20-600 ms) using small particle sizes ({dollar}<{dollar}5 {dollar}mu{dollar}m). The high reactivity carbonate (HRC) shows 70-75% sulfation conversion within 0.5 s, which is substantially higher than any other calcium based sorbents ever reported in the literature. The high initial surface area combined with its open pore structure and pore size distribution of its calcine contribute to its high reactivity. The calcined HRC possesses a significant portion of its pore volume in the 50-200 A range. This pore size range represents an optimum pore size for sulfation since it provides a reasonably high surface area and is less susceptible than {dollar}<{dollar}50 A pore sizes to pore filling, or pore mouth plugging due to formation of high molar volume CaSO{dollar}sb4.{dollar} Furthermore, HRC is shown to be resistive to sintering and is able to maintain the favorable pore structure even under extreme conditions favorable for thermal sintering.; Overall sulfation behavior of the calcium sorbent is simulated using a structural model based on grain-micrograin concept. This modified grain model incorporates the structural changes due to thermal and chemical induced sintering of CaO and due to various reactions. The uniqueness of the model lies in its ability to simulate overall sulfation phenomena of calcination, sintering and sulfation and incorporate actual mechanism of sulfation involving ionic diffusion in its formulation.; In this research work, investigations are also conducted into determining the effectiveness of some commonly used mineral sorbents for removal of arsenic species from hot flue gases. Experimental investigations indicate Ca(OH){dollar}sb2{dollar} to be the most effective sorbent and presence of a chemical interaction mechanism between hydrated lime and As{dollar}rmsb2Osb3.{dollar} Calcium arsenate is confirmed as the reaction product. Sorption of arsenic on fly ash is found to be reversible and physical in nature.