Effect of entrapped air bubbles on fine coal dewatering via filtration

An experimental study was conducted to obtain detailed information concerning entrapped air bubbles in fine coal filter cakes and their effects on filtration and the dewatering process. Four size fractions of coal samples (?80 mesh, ?42 mesh, ?82 mesh and ?100 +200 mesh) were investigated. An image analyzer with the aid of quantitative stereology was used to measure the entrapped air bubbles in relation to the microstructure of the filter cake (i.e., the particle and pore size distribution in the filter cake).The results show that the size and number of air bubbles entrapped in the filter cake can be controlled by the degree of aeration/deaeration of the coal slurry prior to filtration. Both the rate of filtration and the extent of dewatering are adversely affected by the presence of air bubbles in the filter cake. These adverse effects can best be understood in terms of the alteration of cake structure caused by air bubbles. Specifically, the reduction in connectedness of pores within the cake matrix tends to impede the flow of filtrate through the filter cake.