Return to search

Processes that make larger crystal particles.

The particle size or crystal size distribution (PSD or CSD) of a solid product from a crystallizer is important in handling the solid. CSD related properties might be improved with larger particle size. The principle of particle size increase in continuous crystallization processes is to remove fine particles at a faster rate than large ones. Two technologies based on this principle are the Double Draw-Off (DDO) and the Fines Dissolving (FD) crystallizer configurations. Design charts were developed for the Fines Dissolving crystallizer. It was found that the particle size increase passes through a maximum value as the fines classification cut size is increased. Based on this information a design protocol was suggested for the FD crystallizer. A limited amount of data are required for this method of design. The modified DDO crystallizer configuration was developed in order to obtain particle size increase in processes with high natural slurry density for which a build-up of solid is impractical. This involved a recycle of a part of the overflow (in DDO operation) after further classification of particles to remove fines in a size range L(F1) to L(F2), thus controling the slurry density in the crystallizer. Design equations and design charts for this configuration were developed. Analysis showed that a stream with some fines in it might be more effective in decreasing the slurry density than a clear filtered liquor. Particle size increase was demonstrated for sodium chloride crystallization in caustic liquor using the FD, DDO and modified DDO crystallizers. A fines/feed flow modification as well as actual fines dissolution was used in the FD experiments. Significant size increase was observed in both cases. These experiments indicated that appreciable dissolution cost would be involved in FD operation. The DDO experiments produced large crystal particles with associated increase in slurry density. Slurry density information from large scale operations indicated that DDO operation would be possible for DDO ratios upto about 2.5. The modified DDO configuration also produced larger particles. However, size increases were less than expected. Loss of supersaturation outside the crystallizer might be the reason. Appreciable reduction of crystallizer vessel fouling was observed in the DDO and modified DDO experiments. Randolph et al. (1990) demonstrated significant particle size increase for calcium sulfite precipitation in flue gas desulfurization (FGD) liquor using a DDO crystallizer. Experimental particle sizes were appreciably larger than predicted values. A partial fines dissolving model was proposed to explain this behavior. It was shown that dissolution of particles smaller than 8 μm in only about 2.8% of the recycle stream was enough for the additional size increase.
Date January 1992
CreatorsSutradhar, Bhagya Chandra.
ContributorsRandolph, Alan D., Shadman, Farhang, Guzman, Roberto, Raghavan, Srini, Hiskey, J. Brent
PublisherThe University of Arizona.
Source SetsUniversity of Arizona
Detected LanguageEnglish
Typetext, Dissertation-Reproduction (electronic)
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.

Page generated in 0.0026 seconds