Stirred tank draft tubes

Figure 8.11 Types of reactors for gas-liquid precipitation, (a) bubbling stirred tank, (b) fiat interface stirred tank, draft-tube bubble column, (d) spray column after Wachi and Jones, 1994)...

A basic stirred tank design is shown in Fig. 23-30. Height to diameter ratio is H/D = 2 to 3. Heat transfer may be provided through a jacket or internal coils. Baffles prevent movement of the mass as a whole. A draft tube enhances vertical circulation. The vapor space is about 20 percent of the total volume. A hollow shaft and impeller increase gas circulation (as in Fig. 23-31). A splasher can be attached to the shaft at the hquid surface to improve entrainment of gas. A variety of impellers is in use. The pitched propeller moves the liquid axially, the flat blade moves it radially, and inclined blades move it both axially and radially. The anchor and some other designs are suited to viscous hquids. 

FIG. 23-30a A basic stirred tank design, not to scale, showing a lower radial impeller and an upper axial impeller boused in a draft tube. Four equally spaced baffles are standard. H = beigbt of liquid level, Dj = tank diameter, d = impeller diameter. For radial impellers, 0.3 < d/Dt < 0.6. 

Aiba (A3), Fox and Gex (F8), Kramers, Baars and Knoll (K15), Metzner and Taylor (MIO), Norwood and Metzner (N3), Van de Vusse (V5) and Wood et al. (W12) have studied flow patterns and mixing times. In addition, Brothman et al. (B22), Gutoff (G9), Sinclair (S16) and Weber (W3) analyzed flow in a stirred tank in terms of the recycle flow model of Fig. 23F. This model corresponds to the draft-tube reactor, and with sufficiently large recycle rate the performance prediction of this model approximates backmix flow. 

A loop fermenter is a tank or column fermenter with a liquid circulation loop, which can be a central draft tube or external loop. Depending on how the liquid circulation is induced, it can be classified into three different types air-lift, stirred loop, and jet loop (Figure 6.22). 

Flower [25], Panda et al. [26], Doran [27]. and Payne et al. [28]. Several kinds of bioreactors, such as the stirred tank bioreactor with hollow paddle and flat blade impellers, the bubble column, the airlift bioreactor with internal and external loops, the rotating drum bioreactor, the stirred-tank with a draft tube, and the mist bioreactor have been attempted for plant cell, tissue and organ cultures (Fig. 1). 

Much more information is available on the product ky a than on kl and a separately. For low solids concentrations it may be assumed that the solids do not affect the value of A a, so that the existing relations for two-phase gas-liquid reactors can be applied. For reviews on these relationships, see Lee and Foster [76], for draft tube slurry reactors Goto et al. [77], for bubble columns Deckwer and Schumpe [78] and Deckwer [79], and for stirred tank reactors Mann [80] and Schluter and Deckwer [81]. Despite of much research published on the influence of solids on k a there is still no universally applicable relation describing the influence of all types of particles in any weight fraction in any liquid. 

A common form of stirred-tank reactor has an impeller and a draft tube, which together cause the contents to circulate in a toroidal loop without much mixing except in the region of the feed. This is a simple case of a more general description suggested by van de Vusse (2). Such a reactor can be represented as a loop, described by the differential equation... 

Tanaka, M., Izumi, T., Application of stirred tank reactor equipped with draft tube to suspension polymerization of styrene, J. Chem. Eng. Jpn. 18 (1985) 345. 

Stirred tank design, 287,288 baffles, 287 draft tubes, 287... 

FIGURE 10.1 Types of stirred tank reactor, (a) Multiphase stirred reactor. I impeller, 2 baffles, 3 cooling coils, 4 gas sparger, (b) Stirred reactor with gas-inducing impeller (dead-end type), (c) Stirred reactor with helical ribbon impeller (used with or without a draft tube). 

Fig. 5 Draft-tube-impeller stirred tank fermenter. (View this art in color at www.dekker.com.)...

For high-viscosity applications, lack of turbulence adjacent to the bubble, and the general difficulty in pumping around the draft tube (riser), prevent the use of simple pneumatically agitated airlift fermenters. Stirred tank fermenters are typically used for media with a viscosity exceeding 100 cP. As noted before, an... 

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