多孔氧化钙孔结构特征的数学描述与分析

CaCO3是燃煤锅炉干法脱硫常用的脱硫剂。它在炉内煅烧后形成的多孔氧化钙(CaO)内部孔的形状为圆柱形,其孔结构特征可用孔径大小、孔径分布、孔长度、比表面积及孔容积等参数来描述。文中假设孔径分布是连续的,孔长度随孔径变化,建立了以孔径分布密度函数和孔长随半径变化函数为基础的孔结构数学模型。利用该模型计算了多孔CaO试样内部孔的比表面积和孔容积,计算值与实测值基本吻合。分析表明:不同孔径的孔分布密度不同,比表面积越大,孔径分布越窄,小孔径的微孔越多,平均孔径越小,800以上的孔分布密度接近于零;而比表面积越大,孔长度越大,最大孔长对应的孔半径越小。0~50、50~200和>200 3个孔径范围的孔的分布密度及各自的比表面积对总比表面积的贡献率互不相同,并且随比表面积的增大而变化。最佳比表面积为40~50m2/g。

THE MATHEMATICAL DESCRIPTION AND ANALYSIS ON THE CHARACTERISTICS OF PORE STRUCTURE OF POROUS CALCIUM OXIDE

CaCO3 is a sort of SO2 sorbent used often for dry desulfurization in coal-fired boiler. The shape of pore inside porous CaO formed from calcining CaCO3 in furnace is cylindrical, and pore structure characteristics can be described using pore size, distribution density (DD) of pore size, pore length, specific surface area(SSA) and pore volume.In this paper, it is supposed that the pore size distribution is continuous and pore length changes with pore size, and the mathematical models for describing pore structure are developed on the basis of the function of DD of pore-size and the function of pore length with changing pore size. The SSA and volume of pore inside porous CaO examples are calculated using the models and the calculated values are in a good greement with the experimental values. The results calculated and analyzed on the basis of the models show that the pores are different from one another in DD of pore-size and the higher SSA can cause the narrower pore-size distribution, the more micro-pores and the smaller mean pore-size, and that the higher the SSA is, the longer the pore length is, and the smaller the pore-radius corresponding to the maxmium pore length is. The pores in three pore-size ranges, 0~50,50~200 and>200, are different from one another in the DD and the contribution rates of each SSA to total SSA, and the DD and the contribution rate change with the increasement of the total SSA. The optimum SSA is 40~50m2/g.