| The macroscopic properties of the porous media, e.g., permeability, capillary pressure, relative permeability depend upon the microscopic structure of the porous medium. In the coal preparation plants, the filtration and dewatering rates of the fine coal filter cakes are important in determining the final moisture content. The microscopic structure of the porous coal filter cakes plays an important role in these operations. Moreover, the two phase flow through the porous medium can be explained in detail by considering its pore structure. Hence, the development of a technique for the micro-structural analysis of unconsolidated coal filter cakes is investigated in this work. The technique developed is also applicable to many consolidated porous media like sandstones, rocks, etc.;The investigation of -32 mesh Pittsburgh seam coal cakes reveals a non-uniform structure at low solid concentration of 0.33 kg coal/kg water. An increase in the solid concentration in the slurry produces a more uniform structure with an increase in the filtration and dewatering rates. It was found that coal filter cakes are incompressible over the range of 28 to 67 kPa applied vacuum. As expected, the addition of fine particles decreases the pore sizes in the filter cakes. The porosity value at different layers show a maximum at the top layer (in contact with the slurry) and porosity decreases with an increase in the particle sizes.;An important aspect of this work was to provide quantitative information about the presence of air bubbles in the coal filter cakes. These air bubbles are evolved from the aerated slurry and they reduce the filtration rates. The coal samples from industrial filter units also contained a significant amount of air bubbles.;A linear correlation between the particle and pore size distribution of -32 mesh Pittsburgh coal has been found in this work. This correlation is very valuable for the micro-structural analysis of porous media. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI.;The optical methods were utilized to study the micro-structure of fine coal cakes. For this purpose, an optical microscope with an automated image analyzer were employed with the help of techniques of quantitative stereology. The particle and pore size distributions were obtained from the section chord method. The experimental technique includes the vacuum impregnation of the porous cakes with an epoxy resin, polishing, and image analysis of cake sections. |
