Scale-up on Rate

Scale-Up on Rate Filtration rates calculated from bench-scale data shouldbe multiplied by a factor of 0.8 for all types of commercial units which do not employ continuous washing of the filter medium and on which there is a possibility of filter-medium bhnding. For those units which employ continuous filter-medium washing, belt-type drum and horizontal units, the scale-up fac tor maybe increased to 0.9. The use of this scale-up fac tor assumes the following ... 

Scale-up on rate Scale-up on cake discharge Scale-up on actual area... 

Scale-Up of Continuous Mixers Although scaling up on the basis oFconstant power per unit Feed rate [kWh/lcg or (hp-h)/lb] is iisii-allv a good First estimate, several other Factors rnav have to be considered, As the equipment scale is increased, geometric similarity being... 

Scale-up factors On rate = 0.8 On area = 0.8 On discharge = 0.9. (Scale-up on discharge maybe increased to 0.97 if based on previous experience or to 0.95 if the total filter area is based on the measured effective area of the disk.)... 

An example Hollander et al. (2001a) nicely demonstrated how the strong inhomogeneities in stirred-tank flow result in unpredictable scale-up behaviour and that the impact of the detailed hydrodynamics and of the non-uniform spatial particle distribution on agglomeration rate is larger and more complex than usually assumed their study once more illustrated the risks of scale-up on the basis of keeping a single non-dimensional number. Sophisticated CFD, especially on the basis of LES, offers an attractive alternative indeed. 

Critical heat production rates (i.e., heat production rates that still do not lead to a runaway), are often determined by small scale experiments. However, the effect of scale-up on these rates, as discussed in [161], must be taken into account. An indication of the effect of scaling in an unstirred system is shown in Figure 3.2. In this figure, the heat production rate (logarithmic scale) is shown as a function of the reciprocal temperature. Point A in the figure represents critical conditions (equivalent heat generation and heat removal) obtained in a 200 cm3 Dewar vessel set-up. It can be calculated from the Frank-Kamenetskii theory on heat accumulation [157, 162] that the critical conditions are lowered by a factor of about 12 for a 200 liter insulated drum. These conditions are represented by... 

Various aspects of the effect of process scale-up on the safety of batch reactors have been discussed by Gygax [7], who presents methods to assess thermal runaway. Shukla and Pushpavanam [8] present parametric sensitivy and safety results for three exothermic systems modeled using pseudohomogenous rate expressions from the literature. Caygill et al. [9] identify the common factors that cause a reduction in performance on scale-up. They present results of a survey of pharmaceutical and fine chemicals companies indicating that problems with mixing and heat transfer are commonly experienced with large-scale reactors. 

Figure 5. Effect of scale-up on maximum and average impellers zone shear rates...

Consideration should be given to the availability of small-scale equipment, which is vital for development work prior to scale-up on pilot- or production-scale machines. Equipment choice is not necessarily based on maximum throughput rate, since the subsequent processing stages (e.g., cutting, spheronization, and drying) are batch processes and are therefore, a rate-limiting factor in production. Since extrusion is a continuous process, it allows adequate production rates for most purposes with any of the above mentioned extruder types. 

Nienow, A.W. (1976). The effect of agitation and scale-up on crystal growth rates and on secondary nucleation. Trans. Inst. Chem. Eng. 54, 205. 

Nienow, A.W. (1996). The Effect of Agitation and Scale-Up on Crystal Growth Rates and on Secondary Nucleation, TransIChemE. 54, pp. 205-207. 

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