Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Hill, Priscilla J.

Committee Member

Toghiani, Rebecca

Committee Member

Walters, Keisha B.

Committee Member

Schneider, Judy

Date of Degree

4-30-2011

Document Type

Dissertation - Open Access

Major

Chemical Engineering

Degree Name

Doctor of Philosophy (Ph.D)

College

James Worth Bagley College of Engineering

Department

Dave C. Swalm School of Chemical Engineering

Abstract

Particle breakage can be significant in stirred vessels such as crystallizers. During crystallization, particle breakage can occur due to particle contact with other particles, the impeller, the suspension fluid, and/or the vessel. Such breakage produces fines and can cause filter plugging downstream. Although research has been conducted with respect to particle breakage, a comprehensive study is still needed to quantify the breakage occurring in stirred vessels. The overall goal of this research is to model the particle breakage occurring in a stirred vessel by analyzing the particle size and shape distributions that result from breakage. Breakage experiments are based on collision influences that affect the two dominant collisions types, crystal-to-crystal and crystal-to-impeller collisions. Results showed that the quantity of fines produced are affected by the solids concentration or magma density and suspension fluid utilized. Additionally, aqueous saturated solutions produced particle size distributions that differ from those obtained using a nonsolvent. Similar particle size distributions for two different materials (NaCl and KCl) are achieved in the same nonsolvent (acetonitrile) by adjusting the agitation rate using the Zwietering correlation to account for property differences; moreover, the same agitation rate adjustment produced similar distributions for KCl in acetone and acetonitrile which were both nonsolvents. However, modifications to the Zwietering correlation, such as changing the significance of the initial particle size, are proposed before this method of adjustment is deemed accurate. Number-based population modeling of particle breakage is achieved within 1-5% error for NaCl at each agitation rate investigated. Breakage modeling using a discretized population balance equation with Austin's equation for attrition and the power law form of the product function for fragmentation is a viable approach; however, more work is needed to increase the accuracy of this model.

URI

https://hdl.handle.net/11668/19337

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