Simultaneous Removal of SO_2 and NOx by Calcium Hydroxide at Low Temperature: Evolution of the Absorbent Surface Structure

摘要

The surface structure characteristics of the absorbent subjected to SO_2 and NO_2 for different reaction times were measured by using the N_2 adsorption method. The pore surface and structure fractal dimensions (D_1 and D_2) calculated from the N_2 adsorption isotherms data were applied to analyze the fractal characteristics of absorbent particles during reactions. On the basis of the measurement results and the reaction mechanism of SO_2 and NO_2 removal, the evolution mechanism of absorbent surface structure during reactions was discussed. The presence of reaction products on the surface of the absorbent can reshape the pore structure. With the comparison of the evolution of the surface structure in SO_2 and NO_2 single removal, the interaction of SO_2 and NO_2 on the absorbent surface has a great effect on the change of surface structure with simultaneous removal of SO_2 and NO_2. The decrement of the surface structure parameters values is lower than that in both SO_2 and NO_2 single removal. The change trend of the D_1 and D_2 can also not be well explained by their changes in SO_2 and NO_2 single removal. Because of the expansion rate discrepancy of the NO_2 removal product and SO_2 removal product, the pores from 7 to 30 nm were formed in SO_2 and NO_2 by simultaneous removal. The homogeneous reaction product and the same expansion rate make the product layer compact in both SO_2 and NO_2 single removal. On the basis of the analysis of both surface fractal dimension and structure fractal dimensions, it can be concluded that the higher surface fractal dimension as well as an appropriate pore structure fractal dimension D_2 will helping in getting higher SO_2 and NO_2 removal.