Perfect mixer characteristics

The arrangement of the loop reactor (with perfect mixer characteristics) and the post-reaction coil (approaching plug flow characteristics) will make sure that the maximum conversion of the LAB feedstock is achieved. All equipment is constructed in stainless steel 316L. 

In summary, we have considered three characteristic times associated with a CSTR /mix, ri/2, and t. Treating the CSTR as a perfect mixer is reasonable provided that /mix is substantially shorter than the other characteristic times. 

At low holdups, longitudinal dispersion due to continuous-phase velocity profiles controls the amount of mixing in the countercurrent spray column whereas at higher holdups the velocity profile flattens, and the shed-wake mechanism controls. Above holdups of 0.24, the temperature jump ratio is linearly proportional to the dispersed-to-continuous-phase flow ratio, and all mixing is caused by shed wakes into the bulk water and coalescence of drops. As column size decreases, it approaches the characteristics of a perfect mixer, and the jump ratio approaches unity (as compared with the value of zero for true countercurrent flow). It is interesting to note that changing the inlet temperature of dispersed phase by about 55°F hardly affected the jump ratio, probably due to the balancing effects of reduced viscosities and a decrease of drop diameter. 

The loop circulating reactor outlined above expresses in chemical engineering terms, the characteristics of a perfect mixer. This type of reactor presents the following characteristics required for the neutralisation step ... 

An important question for the design of continuous flow systems is When can the classic perfectly mixed assumption (ideal CSTR) be used in a continnons flow stirred tank reactor The blend time concept can be used here. If the blend time is small compared to the residence time in the reactor, the reactor can be considered to be well mixed. That is because the residence time is proportional to the characteristic chemical reaction time. A 1 10 ratio of blend time to reaction time is often used, but often, larger values result because the mixer must do other jobs, which lead to even smaller blend times. Frequently, residence time distributions are used to determine whether a reactor is well-mixed. It is usually easy to achieve well-mixed conditions in continuous flow, turbulent stirred vessels unless the reactions are very fast, such as acid-base neutralizations. Even in laminar systems the blend time can be made much less than the required residence time for the chemical reaction mainly because required residence times are so long for high viscosity reactants. For discussions of residence time distribution analysis, see Chapter 1, Levenspiel (1972), and Nauman (1982). 

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