Scale-up of Batch Mixers

Scale-Up of Batch Mixers The prime basis of scale-up of batch mixers has been equal power per unit volume, although the most desirable practical criterion is equal blending per unit time. As size is increased, mechanical-design reqmrements may hmit the larger mixer to lower agitator speeds if so, blend times will be longer in the larger... 

Scale-up of Batch Mixers While a desirable objective of scale-up might be equal blending uniformity in equal time, practicality dictates that times for blending are longer with larger batches. Scale-up of many processes and applications can be successfully done by holding constant the peripheral speed of the rotating element in the mixer. Equal peripheral speed, often called equal Up speed, essentially means mat the maximum velocity in the mixer remains constant. 

Scale-up of Continuous Mixers While geometric similarity may be practical for most batch mixers, changes in the length-to-diameter ratio or other geometry may be necessary with continuous mixers. The most common problem is heat generation by friction and heat removal by surface transfer. 

Kataoka T and Nishiki T. Dispersed mean drop sizes of (W/0)/W emulsions in a stirred tank. J Chem Eng Jpn 1986 19 408-412. Nishikawa M, Mori F, and Fujieda S. Average drop size in a liquid-liquid phase mixing vessel. J Chem Eng Jpn 1987 20 82-88. Nishikawa M, Mori F, Fujieda S, and Kayama T. Scale-up of liquid-liquid phase mixing vessel. J Chem Eng Jpn 1987 20 454—459. Berkman PD and Calabrese RV. Dispersion of viscous liquids by turbulent flow in a static mixer. AIChE J 1988 34 602-609. Chatzi EG, Gavrielides AD, and Kiparissides C. Generalized model for prediction of the steady-state drop size distributions in batch stirred vessels. Ind Eng Chem Res 1989 28 1704—1711. 

Landin, M. York, P. Cliff, M.J. Rowe, R.C. Wigmore, A. J. The effect of batch size on scale-up of pharmaceutical granulation in a fixed bowl mixer-granulator. Int. J. Pharm. 1996, 134, 243-246. 

As pointed out at the beginning of the chapter, when designing a new polymer processing operation to produce a product or to blend or compound a new material, it is often desirable or necessary to work on a smaller scale such as a laboratory extruder, internal batch mixer, stirring tank, etc. The evolving model must then be scaled up or down to the actual operation. 

Recommendations for Handling Blending Requirements for Fast Reactions. For handling fast reactions, if the power requirements are unreasonable to maintain equal blend time on scale-up, then one should consider two alternates (1) inject the semi-batch feed into a recycle loop in the inlet of a static mixer and (2) do the reaction in-line while pumping out the vessel through an in-line mixer. 

Crude oil and brine pumps may be centrifugal or positive displacement, but must be capable of providing steady flow to the mixing device because emulsion properties are highly dependent on the resulting crude-oil-brine ratio. Surfactant may be dissolved in the brine phase on a batch or continuous basis. Static mixers provide a simple method for the preparation step because they require no moving parts, are easy to scale up, and provide an mixing intensity that is suited to preparation of transport emulsions. 

Impeller tip speed corresponds to the shear rate and has been used as a scale-up parameter in fluid mixing. For processing of lactose granulations in Gral mixers, however, it was shown by Horsthuis et al. that the same tip speed did not result in the same endpoint [in terms of particle size distribution (PSD)]. These findings were contradicted by other studies with Fielder mixers indicating that for a constant tip speed, successful scale-up is possible when liquid volume is proportional to the batch size and wet massing time is related to the ratio of impeller speeds. ° ... 

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