| Bench-scale differential reactor experimental studies on the low-temperature removal of SO2 and HCl using calcium-based sorbents, have been performed. For the reactions of limestone with HCl only or SO2 only, the effects of relative humidity, acid gas concentration, and limestone type and particle size, have been defined. For the simultaneous reaction of limestone with both SO2 and HCl, the interaction between SO 2 and HCl has been investigated and quantified.; It has been shown that relative humidity has a substantial effect on both reaction rate and final sorbent conversion. Under low-temperature and humidified conditions, complete limestone conversion has been achieved for either HCl or SO2; in addition, initial reaction rates increase exponentially with the increase of relative humidity. Smaller particle size and larger BET surface area benefit the reactions of HCl or SO2 removal, and the initial reaction rate is proportional to the reciprocal of the particle diameter, and to sorbent BET surface area. The effect of acid gas concentration is closely related to relative humidity. Higher acid gas concentration results in a higher initial reaction rate, however, this effect is insignificant under low relative humidity conditions.; For the simultaneous reaction of limestone with SO2 and HCl, the interaction between SO2 and HCl is very complicated, and is directly related to relative humidity. Over the whole relative humidity range, the interaction may be best defined as the combination of competitive and synergistic effects.; Rate-limiting steps have been determined using the shrinking unreacted core model. It has been demonstrated that the rate-controlling step changes with the progress of the reaction when relative humidity is high. At the beginning of the reaction, the reaction rate is controlled by chemical reaction. As the reaction progresses, more product is produced, therefore, the product-layer diffusion effect gradually becomes significant, and finally, overtakes chemical reaction as the rate-limiting step. |
