Power agitation

Limit agitator power input and provide proper impeller design Limit shaft speed Monitor shaft speed Provide adequate cooling system Design system to accommodate maximum expected temperature, and pressure... 

Excessive mixing Limit agitator power input and provide proper of reactants or impeller design impurities which, Return process to pilot or development to rede-promotes process to eliminate or minimize this emulsification. problem Poor phase separa- tion resulting in L it shaft speed problems in subse- Monitor shaft speed quent processing, phase separation steps or in down- stream equipment. I" " de-emulsifiers CCPS G-29 Lees 1996... 

Interlock agitator power consumption to cutoff feed of reactants or catalyst or activate emergency cooling... 

In a slurry reactor (Fig 5.4.74), the catalyst is present as finely divided particles, typically in the range 1-200 pm. A mechanical stirrer, or the gas flow itself, provides the agitation power required to keep the catalytic particles in suspension. One advantage is the high catalyst utilization not only is the diffusion distance short, it is al.so possible to obtain high mass-transfer rates by proper mixing. 

In these equations, a is the specific interfacial area for a significant degree of surface aeration (m2/m3), I is the agitator power per unit volume of vessel (W/m3), pL is the liquid density, o is the surface tension (N/m), us is the superficial gas velocity (m/s), u0 is the terminal bubble-rise velocity (m/s), N is the impeller speed (Hz), d, is the impeller diameter (m), dt is the tank diameter (m), pi is the liquid viscosity (Ns/m2) and d0 is the Sauter mean bubble diameter defined in Chapter 1, Section 1.2.4. 

These reactors employ small particles in the range 0.05 - 1.0 mm (0.0020 -0.039 in) with the minimum size being limited by filterability. Small diameters are used to provide as large an interface as possible, since the internal surface of porous pellets is poorly accessible to the liquid phase (Perry and Green, 1999). The catalyst concentration in slurry reactors is limited by the agitation power of the mechanical stirrer or by the gas flow. 

Substitution of the generalized Reynolds number (Section IIB) for the simple Newtonian Reynolds number has been shown (06) to enable approximate prediction of agitator power consumption for non-Newtonian fluids at low Reynolds numbers. The conventional Newtonian power number-Reynolds number charts which have been drawn up by Rushton et al. (R9) were shown to be applicable in the laminar region. This laminar region, however, appeared to extend to Reynolds numbers of 20 to 25, as compared with critical values of 8 to 10 for Newtonian liquids. Above Reynolds numbers of about 70 the conventional Newtonian curve again appeared to be followed. 

For a range of gas rates, the sum of gas compressor power plus agitator power becomes almost minimal [12]. 

Figure 5.3-5. Agitator rotation velocity vs. hydrogen flow and power consumption [15]. Agitator power...

In this chapter, we study various correlations for gas-liquid mass transfer, interfacial area, bubble size, gas hold-up, agitation power consumption, and volumetric mass-transfer coefficient, which are vital tools for the design and operation of fermenter systems. Criteria for the scale-up and shear sensitive mixing are also presented. First of all, let s review basic mass-transfer concepts important in understanding gas-liquid mass transfer in a fermentation system. 

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