Study On Performance Evaluation And Reaction Mechanism Of Calcium-based Sorbent

SO2 is one of the major air pollutants from coal-fired electric power plants, leading to serious environmental pollution. There are two approaches can be used to meliorate SO2 removal efficiency by reforming the desulphurization technic used now or improving sorbent performance. There has been well recognized that different kind of sorbent vary considerably in their ability to capture SO2. It becomes more important to select sorbent species with high reactivity using in SO2 removal technology. The aim of current work is to go deep into studying the reactity of SO2 sorbents systemically through experiments integrated theoretical analysis.In this paper, three types limestone and two types sea shell were chosed as SO2 sorbents. The physical and chemical properties of sorbents such as chemical composition, pore volume, pore size distribution, surface configuration before and after sulphation and so on were measured by methods of ICP, SEM and mercury porosimeter. And also, an experiment set-up of bench-scale fluidized bed reactor was designed and established. Series of thermal desulphurization experiments were carried out on the reactor. It can be seen from the results that sorbent reactivity is related with various factors which associate with each other. Consequently, we chose two kinds parameters, the chemical composition and pore structure characteristics, as basic indexes, establishing an evaluation standard and system based on principle component analysis comprehensive evaluation method. And also we obtained the relation between CaO conversion of sorbent and principle component. Factors which effect the sorbent reactivity were analyzed which can provide theoretical guidance for sorbent performance optimization and selection.The structure of calcined sorbents is a porous system with self-similarity characteristic. According to the mercury porosimetry experiments and Menger manifold, a model based fractal geometry was proposed to simulate the porous structure of calcined sorbent, and fractal dimension was calculated on the basis of experimentally obtained pore size distribution. By simulating the processes of fractal construction, the relationship among porosity, specific surface area and permeability was described. It shows that the model is capable of reflecting pore information full-scaled.According to the mercury porosimetry experiments, the pore size distribution of calcimined sorbent shows following Gaussian function form. The cylindrical geometry have been used to define the pore structure of calcium oxide derived from different calcium-based sorbents and the sulphation is described by a pore size distribution model. The calculations made agree well with experiments carried out on five different sorbents in fluidized bedreactor. The pore size distribution model explains the effects of particle size, pore size distribution and concentration of SO2, suggesting these factors to be important for CaO conversion.At last, the reaction mechanism of lime/limestone wet flue gas desulphurization was discussed and the effects of additives on sorbent reactivity were investigated experimentally. The results show that different additives chosed in this paper can improve the SO2 absorption ability. As to the same additive, the improvement effectiveness differs with different concentration. For the magnesium hydroxide additive, experiment results here suggested that dissolved sulfur dioxide reacts mainly with the magnesium sulfite ion pair, which is responsible for the increased absorption rate of SO2.