Controlling crystal size distribution (CSD) is important to downstream processing and to product quality. The distribution can be characterized by a mean or dominant size and the spread about the mean or dominant size. The development of tools leading to the control of the distribution in a batch crystallizer is the main topic of the present study. An experimentally based control scheme was implemented for batch cooling crystallization of paracetamol from ethanol solutions. Estimates of the CSD in the batch crystallizer were obtained by applying a model of the octahedral paracetamol crystals to a chord length distribution (CLD) obtained from focused beam reflectance measurement (FBRM) and Lasentec software. The model estimates showed reasonably good agreement with results obtained from sieve analyses performed at the end of the runs.

Utilization of Focused Beam Reflectance Measurement in the Control of Crystal Size Distribution in a Batch Cooled Crystallizer

Application of Internal Seeding and Temperature Cycling for Reduction of Liquid Inclusion in the Crystallization of RDX

The design of industrial crystallizers requires detailed information about the fine structure of turbulence in vessels of complex geometry. The currently available methods (e.g., empirical correlations, experimentation, simple theories, computations based on the Reynolds- averaged Navier -Stokes equations) cannot provide the required information at an adequate level of accuracy for crystallizers of non-standard design. This paper assesses the feasibility of using a computationally efficient large-eddy simulation (LES) technique to quantify the fine scale turbulent structure in an industrial crystallizer. LESs of the single-phase flow in a baffled, industrial crystallizer with a draft tube were performed at three values of the Reynolds number (Re ¼ 14 000, Re ¼ 82 000 and Re ¼ 350 000). The flow was driven by a standard Rushton turbine. A much weaker secondary flow was generated by a throughput stream that entered through a nozzle at the bottom and exited through the sidewall. The effects of the spatial resol- ution and the sub-grid scale model were investigated. The mixing performance of the tank was evaluated by means of particle tracking. It was found that the simulations adequately resolved the highly anisotropic fine-scale turbulence generated by the strong interaction between the impeller, the various other internals and the vessel wall at least at the low Reynolds number. The potential significance of the computed flow structures for crystallization performance is briefly noted.

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Large-eddy simulation of single-phase flow dynamics and mixing in an industrial crystallizer

A new process of drowning-out combined with fines dissolution and cooling crystallization (the DFC process) was proposed to recover 1,3,5-trinitro-1,3,5-triazinane (RDX) from RDX/γ-butyrolactone solution with relatively large crystal size and high yield. In this process, fine crystals induced by drowning-out are dissolved into the solution by heating so that the dissolved solute can contribute to grow seed crystals by cooling. The DFC process is repeated to reach the desired yield. Estimation of the amount of antisolvent for drowning-out is made by a simple mass balance model in which the mass of fine particles produced by drowning-out equals to that dissolved. Considering dissolution of seeds at the fines dissolution stage, an empirical parameter α which is smaller than 1 was employed for the estimation of the optimum amount of antisolvent added. α = 1 indicates that effect of dissolution of seeds is negligible. In the present work, initial seeds were prepared by rapid injection of 15 g of water into a s...

Crystallization of RDX by Drowning-Out Combined with Fines Dissolution and Cooling Process

iii ACKNOWLEDGEMENTS I first would like to acknowledge the importance of the funds provided through the Cecil J. "Pete" Silas Endowed Chair that allowed the completion of this research. I wish also to give my sincere thanks to my thesis advisor, Dr Ronald W. Rousseau, for his knowledge, his helpful advice and time he offered throughout this project. I am grateful to the committee members for all the useful suggestions and remarks made: Dr Amyn Teja, and Dr Martha Gallivan. I also want to thank past and present members of this research group for their precious help, friendship and support: I give my thanks to all the professors and staff I met at Georgia Tech for being so willingly helpful and sharing part of their knowledge with me. And last but not least, I would like to express my thankfulness to all my friends and my family for their kindness and support. They shaped the person I am today.

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Utilization of FBRM in the Control of CSD in a Batch Cooled Crystallizer

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 FD 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. Particle size increase was demonstrated in the laboratory for sodium chloride crystallization in caustic liquor using an FD crystallizer. 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 indicate that appreciable dissolution cost would be involved in FD operation. Experimental results were in good agreement with values predicted from design charts

Bhagya C. Sutradhar

Papers

Design charts for the fines-dissolving crystallizer

Double Draw-Off Crystallizer: Major Player in the Acid Rain Game?

Selectivity behaviour of non-uniform catalysts for the consecutive reactions A → B → C

"Modeling of a Venturi scrubber for the control of gaseous pollutants." Comments