A Study on the Cavity Ratio in NaCl Crystals Made by Oslo Type Crystallizer
1996 Volume 50 Issue 2 Pages 77-82
Details
1996 Volume 50 Issue 2 Pages 77-82
One of four crystallizeres in our salt plant is the Oslo type producing large particle size and the others are the slurry circulation type producing middle or small particle size. In these particles, there are small cavities filled with mother liquor. The cavity ratio of product produced by the Oslo-type crystallizer is much higher than that of other products. As the first step in determining the reason for this, we studied the relation between the cavity ratio of products and operating conditions, which are epresented by growth rate and particle size. Using the Oslo-type crystallizer, test runs were done in two type of operations, stationary and nonstationary. The cavity ratio of the resulting products obviously showed particle size dependency, so we called it the “average cavity ratio” and gave the name of “cavity ratio” to the differential quotient of average cavity ratio by particle size, which corresponds to the cavity ratio of the thin surface layer of the particle. In the nonstationary mode, particle size distribution (PSD) was very sharp so that the growth rate of each size of particle (G(L)) could appear to be the same as the average growth rate (Gav). But in the stationary operation, PSD was wide and G(L) could not be determined from Gav. Therefore, as a temporary parameter in this case, Gav was substituted for G(L). In each mode, the cavity ratio data were expressed as a function of particle size and growth rate. For both types of operations trends were similar but not identical. Under the assumption that this difference in trends can be fully explained by the substitution of Gav for G(L), the relation between G(L) and Gavin the stationary mode was derived from the difference in trends of the cavity ratio. In both modes, each one cavity ratio corresponds to the smallest particle size sample was deviated from the trend of the other data. These deviations are considered to be affected too much by the carier of growth in the circulating slurry.
