Batch mixing uniformity variation

However, at the start of a production run the machinery is cold so it is necessary to heat the mass of metal of the machinery. With a two-roll mill this is normally done by starting to mix with the cooling water supply turned off, thus allowing the metal of the rolls to be heated. This mix will, of course, be different from the next batches as the temperature at which the rubber is processed is different. The amount of energy put into the mix will vary because of this and it can show up in final uniformity variations. 

The third time constraint depends on whether the product can be extracted from seeds or fruits. This uncouples protein expression and purification. Large batches of seeds containing the recombinant protein can be produced and stored at low costs. Provided the protein remains stable in the stored seeds, purification can be carried out on demand or shifted according to free capacities. The advantage of one large harvest, with seeds mixed to uniformity, is that this allows production on demand. In contrast, mammalian cell culture is prone to minor batch-to-batch variations in... 

An ideal stirred bioreactor is assumed to be well mixed so that the contents are uniform in composition at all times. The plug-flow bioreactor (PFB) is an ideal tubular-flow bioreactor without radial concentration variations. The nutrient concentration of an ideal batch bioreactor after time t will be the same as that of a steady-state PFB at the longitudinal location of the residence time. Therefore, the following analysis applies for both the ideal batch bioreactor and the steady-state PFB. 

Piston flow is a convenient approximation of a real tubular reactor. The design equations for piston flow are relatively simple and are identical in mathematical form to the design equations for well-mixed batch reactors. The key to their mathematical simplicity is the assumed absence of any radial or tangential variations within the reactor. The dependent variables a, b,. .. T, P change in the axial, down-tube direction but are completely uniform across the tube. This allows the reactor design problem to be formulated as a set of ODEs in a single independent variable z. As shown in previous chapters, such problems are readily solvable given the initial values... 

As with conventional CLC, two continuously operated and interconnected fluidized beds are a well-suited reactor configuration for CLPO due to the excellent gas-solid contacting pattern, and several studies have been conducted with this set-up [92,117,119,120]. Additionally, the back-mixing inherent in this reactor configuration results in a uniform oxygen availability as opposed to the temporal variation in the previously discussed batch-fluidized beds (which constitute integral reactors in which the lattice oxygen decreases with time). 

For a larger size non-uniformity, for example, variation within the batch of internal mixers may appear as a pressure oscillation observed by a pressure-tap at the chamber wall of a mixer [13]. It may also appear as an oscillation of the mixing torque (see Table 3.1 [24]). However, before using these oscillations as a measure of degree of nonuniformity, an independent check by actual sampling of the contents must be done, because the oscillation is also related to the way in which the compound is moved around the mixer. For the batch-to-batch variation, previously mentioned two-point measurements of moduli may be used. If the requirement is not very critical, even a one-point measurement may be adequate. 

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