The effect of the porous structure on sorbent sulfation under coal-fired boiler conditions

A study of the behavior of different sorbents (3 limestones, a commercial calcium carbonate and a commercial calcium hydroxide) in the sulfation process has been carried out in a drop-tube, using similar conditions to those existing in sorbent injection in pulverized-coal boilers. The main variables affecting the sulfation process have been analyzed, namely, Ca/S molar ratio, SO2 concentration, temperature, sorbent particle size and reaction time. The work concentrates on the evolution of the porous system in the sorbents and its influence on their sulfation capacity. A direct relation between chemical structure (calcium hydroxide-calcium carbonate) and sorbent reactivity was not found. Sorbents with a widespread pore size distribution with pores above 100 Angstrom showed the highest reactivity and sulfation capacity, maintaining pores of small size (under 80 Angstrom) at all times and operating conditions. In the less reactive sorbents, pores less than 80 Angstrom became blocked during sulfation, being more sensitive to the effect of the different operating variables affecting the sulfation process.