Plug flow fermenter

The general question of whether or not plug flow can be attained is discussed in Volume 3, Section 1.7. (Tubular Reactors) and the special case of Plug-Flow (Fermenters) is considered in Chapter 5, Section 5.11.3. A more detailed consideration of dispersion in packed bed reactors and those effects which enhance and invalidate plug flow is given in Chapter 3, Section 3.6.1. 

This integration relies on the fact that SA and XA are independent of the exit concentrations, there being no recycle stream in this instance. Plug-flow fermenters are, however, operated with recycle of micro-organisms and the condition is not valid for this generalised case. 

An ideal stirred fermenter is assumed to be well mixed so that the contents are uniform in composition at all times. Another ideal fermenter is the plug-flow fermenter, the analysis of which is analogous to the ideal batch fermenter. 

Fig. 6.4 Schematic diagram of (a) batch stirred-tank fermenter and plug-flow fermenter...

Toda and Dunn (1982) emphasized that a combination of a backmix and a plug flow fermenter with recycle streams provides better performance than does a single CSTR for the continuous production of a substance that depends on the maturity of growing cells (see Equ. 5.136). A typical example is shown in Fig. 6.39, and it illustrates that the productivity of cell mass (Fig. 6.39a), of... 

A specific enzyme acts as catalyst in the fermentation of reactant A. At a given enzyme concentration in the aqueous feed stream (25 liter/min) find the volume of plug flow reactor needed for 95% conversion of reactant A (Cao = 2 mol/liter). The kinetics of the fermentation at this enzyme concentration is given by... 

Figure 29.1 Behavior of batch or plug flow reactors for Monod type microbial fermentation.

Stirred-tank reactors can be used for continuous fermentation, because cells can grow in this type of fermentors without their being added to the feed medium. In contrast, if a plug flow reactor is used for continuous fermentation, then it is necessary to add the cells continuously in the feed medium, but this makes the operation more difficult. 

The continuous growth of micro-organisms, as with continuous chemical reactions, may be carried out either in tubular fermenters (plug flow) or in well-mixed... 

The term fermentation is used to describe the biological transformation of chemicals. In its most generic application, a fermentor may be batch, continuous-stirred tank (chemostat), or continuous plug flow (immobilized cell). Most industrial fermentors are batch. Several configurations exist for these batch reactors to facilitate aeration. These include sparged tanks, horizontal fermentors, and biological towers. 

Ariga et al. [48] have investigated the behavior of the monolith reactor in which Echerichia coli with P-galactosidase or Saccharomyces cerevisiae was immobilized within a thin film of K-carragcenan gel deposited on the channel wall. The effects of mass transfer resistance and axial dispersion on the conversion were studied. Those authors found that the monolith reactor behaved like the plug-flow reactor. The residence-time distribution in this reactor was comparable to four ideally mixed tanks in series. The influence of gas evolution on liquid film resistance in the monolith reactor was also investigated. It was shown that at low superficial gas velocities, the gas bubble may adhere to the wall, which decreases the effective surface area available for the reaction. The authors concluded that the reactor was very effective in the reaction systems accompanied by gas evolution, such as fermentations. 

The main purpose is to provide some plug-flow behavior, perhaps in a countercurrent operation with gas or an immiscible solvent to extract the product already during the fermentation. However, mass transfer and mixing issues are prominent, and an array of stirred tanks or bubble columns would be a more practical solution. 

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