PORE-STRUCTURE OPTIMIZATION OF CALCIUM-CARBONATE FOR ENHANCED SULFATION

A modified CaCO3 sorbent with an open internal pore structure is prepa red and its sulfation characteristics are investigated in an entrained flow reactor at high temperatures (900-1,100 degrees C) and short con tact times (20-600 ms) using small particle sizes (< 5 mu m). The most distinguishing feature of this modified carbonate (MC) is its 70-75% sulfation conversion within 0.5 s, which is substantially higher than any other sorbents published. The MC is prepared by carbonation-precip itation from a calcium hydroxide suspension by optimizing the operatin g parameters to generate carbonate particles of the desired pore struc tural properties. The high initial surface area combined with its open pore structure and pore-size distribution of its calcine contribute t o its high reactivity. The calcined MC possesses a significant portion of its pore volume in the 50-200 Angstrom range. This size range repr esents an optimum pore size for sulfation since it provides a reasonab ly high surface area and is less susceptible than < 50 Angstrom pore s izes, to pore filling, or pore-mouth plugging due to the formation of higher molar volume CaSO4. Investigation with other carbonates reveals that a much higher portion of their calcines' porosity lies in the sm aller pores, which leads to premature termination of sulfation. Result s show the impact of internal pore structure on initial reactivity and ultimate sorbent conversion.