The Ideal Stirred Tank

Vc = volume of holdup in the tank n = number of crystals per unit volume L = length of the crystal G = linear growth rate of the crystal t = time 

H° = zero side nuclei concentration, also called zero size population density B° = nucleation rate 

TABLE 16.3. Mean Overall Growth Rates of Crystals (m/sec) at Each Face8 

The case being considered is that in which the feed contains no 

Seed crystals with this size distribution are charged to a batch crystallizer. 

Deductions from a Differential Distribution Obtained at a Known Residence Time 

The peak of the differential distribution obtained with a residence time of 7 = 2hr corresponds to Lp, = 1.2 mm. Assuming ideal mixing, Lp jGi = X.ljlG = T , and G = 0.2mm/h. With this knowledge of G, crystal size distributions could be found at other residence times. 

Growth rates of crystals also must be measured in the laboratory or pilot plant, although the suitable condition may be expressed simply as a residence time. Table 16.3 gives some growth rate data at several temperatures and several extents of supersaturation for each substance. In most instances the recommended supersaturation measured as the ratio of operating to saturation concentrations is less than 1.1. It may be noted that at a typical rate of increase of diameter of 10 m/sec, the units used in this table, the time required for an increase of 1 mm is 2.8 hr. 

When R is specified, AZ. is found by trial, and then the size distribution is evaluated. Example 16.5 does this. 

Some common substances for which crystallization data are reported in the literature and in patents are listed in Table 16.4. 

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Continuous flow stirred tank reactors are normally just what the name implies—tanks into which reactants flow and from which a product stream is removed on a continuous basis. CFSTR, CSTR, C-star, and back-mix reactor are only a few of the names applied to the idealized stirred tank flow reactor. We will use the letters CSTR as a shorthand notation in this textbook. The virtues of a stirred tank reactor lie in its simplicity of construction and the relative ease with which it may be controlled. These reactors are used primarily for carrying out liquid phase reactions in the organic chemicals... 

The other ideal steady-state flow reactor is called the mixed reactor, the backmix reactor, the ideal stirred tank reactor, the C " (meaning C-star), CSTR, or the CFSTR (constant flow stirred tank reactor), and, as its names suggest, it is a reactor in which the contents are well stirred and uniform throughout. Thus, the exit stream from this reactor has the same composition as the fluid within the reactor. We refer to this type of flow as mixed flow, and the corresponding reactor the mixed flow reactor, or MFR. 

The Ideal Stirred Tank 533 Multiple Stirred Tanks in Series 536 Applicability of the CSTC Model 536... 

The ideal stirred-tank reactor operates isothermally and hence at a constant rate. However, an energy balance is needed to predict the constant temperature when the heat of reaction is sufficient (or the heat exchange between the surroundings and reactor is insufficient) to cause a difference between... 

In a batch reactor, there is no inflow or outflow of reactants. It is a commonly used apparatus in the fine and pharmaceutical industry as well as in laboratories because of its flexibility and multifunctionality. The ideal stirred tank reactor is characterized by complete mixing down to the molecular level. Therefore, no concentration or temperature gradients exist. The system volume (Figure 2.1) corresponds to the volume occupied by the reaction mixture as indicated in Figure 2.3. As reactants are neither added nor removed during the reaction time (batch time), the mass balance Equation 2.1 simplifies to... 

The ideally stirred tank reactor is perfectly uniform with regard to concentration and temperature. The general mass balance for such an ideally mixed reactor (either operated batchwise or in continuous mode) reads as ... 

Large-scale bioreactors can be described, as discussed above, in terms of aggregates of model reactors like the ideal stirred-tank and the ideal plug-flow reactor. These are low-dimensional compartment models that are easy to use, but they... 

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