CFSTR

The type of optimum reaetor that will proeess 200 m /hr is a eon-tinuous flow stirred tank reaetor (CFSTR). This eonfiguration operates at the maximum reaetion rate. The volume V[ of the reaetor ean be determined from the design equation ... 

A continuous flow stirred tank reactor (CFSTR) differs from the batch reactor in that the feed mixture continuously enters and the outlet mixture is continuously withdrawn. There is intense mixing in the reactor to destroy any concentration and temperature differences. Heat transfer must be extremely efficient to keep the temperature of the reaction mixture equal to the temperature of the heat transfer medium. The CFSTR can either be used alone or as part of a series of battery CFSTRs as shown in Figure 4-5. If several vessels are used in series, the net effect is partial backmixing. 

The fluidized bed in Figure 4-10 is anotlier eommon type of eatalytie reaetor. The fluidized bed is analogous to the CFSTR in that its eontents though heterogeneous are well mixed, resulting in an even temperature distribution throughout the bed. 

Table 4-4 summarizes the ratings of the various reactors. The CFSTR and the recirculating transport reactor are the best choices because they are satisfactory in every category except for construction. The stirred batch and contained solid reactors are satisfactory if the catalyst under study does not decay. If the system is not limited by internal diffusion in the catalyst pellet, larger pellets could be used and the stirred-contained solids reactor is the better choice. However,... 

CFSTR operating at the maximum reaction rate followed by a plug flow section... 

CONTINUOUS FLOW STIRRED TANK REACTOR (CFSTR) ... 

The material balance for the single CFSTR in terms of for the first order irreversible reaction is... 

Equation 5-181 is useful in obtaining the maximum yield of eom-ponent B in a CFSTR. 

Consider the liquid phase seeond order irreversible reaetion of the form A -i- B —> produets in a CFSTR at eonstant density under stable eonditions. 

CFSTR. Figure 5-22 illustrates the graphieal performanee equations for CFSTRs. 

Consider the first order reaetion A—in a battery of three eontinuous flow stirred tank reaetors with volumes Vj, Vj, and V3. The material balanee for stage 1 CFSTR is... 

Consider a system of N eontinuous flow stirred tank reaetors in series as shown in Figure 5-24. Although the eoneentration is uniform from one tank to another, there is a ehange in eoneentration as the fluid traverses between the CFSTRs. This is illustrated in Figure 5-25. The drop in eoneentration implies that the larger the number of CFSTRs in series, tlie eloser tlie system would behave as plug flow. 

Fig ure 5-25. Concentration profile through an N stage CFSTR system. 

Equation 5-247 is a polynomial, and the roots (C ) are determined using a numerical method such as the Newton-Raphson as illustrated in Appendix D. For second order kinetics, the positive sign (-r) of the quadratic Equation 5-245 is chosen. Otherwise, the other root would give a negative concentration, which is physically impossible. This would also be the case for the nth order kinetics in an isothermal reactor. Therefore, for the nth order reaction in an isothermal CFSTR, there is only one physically significant root (0 < C < C g) for a given residence time f. 

For a cascade of N CFSTRs of equal volume, Vr, in which the first order forward reaction A—occurs with a throughput u, show that the system fractional conversion is... 

A sample CFSTR of volume V[ has one inlet stream rate u, eontaining A at eoneentration seeond inlet stream of rate... 

A CFSTR with two inlets Aand B is shown below. AO BO... 

For the first CFSTR the optimal seleetion of the eonversion Xj on the I/C-i a) versus X plot is sueh that the diagonal of the reetangle must possess the same slope as the tangent to the eurve at point Xj (Figure 5-26). Therefore, the first CFSTR gives... 

Adesina has shown that it is superfluous to carry out the inversion required by Equation 5-255 at every iteration of the tri-diagonal matrix J. The vector y"is readily computed from simple operations between the tri-diagonal elements of the Jacobian matrix and the vector. The methodology can be employed for any reaction kinetics. The only requirement is that the rate expression be twice differentiable with respect to the conversion. The following reviews a second order reaction and determines the intermediate conversions for a series of CFSTRs. 

Results of the intermediate conversions in a reactor train of CFSTRs involving the second order irreversible reaction kinetics A + B products... 

---