PFRs in Series

The overall conversion of two PRFs in series is (he same as one PRF with (he same total volume. 

Example 2-6 Sizing Plug-Flow Reactors in Series 

In addition to graphical integration, we could have used numerical methods to size the plug-flow reactors. In this example, wc shall use Simp-son s rule (see Appendix A.4) to evaluate the integrals. 

Note This is the same volume we calculated for a single PFR to achieve 80% cot 

The conversions and flow rates for PFRs in series are defined as specified in the previous section. With these definitions, the design equations for the two PFRs are 

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Real reactors deviate more or less from these ideal behaviors. Deviations may be detected with re.sidence time distributions (RTD) obtained with the aid of tracer tests. In other cases a mechanism may be postulated and its parameters checked against test data. The commonest models are combinations of CSTRs and PFRs in series and/or parallel. Thus, a stirred tank may be assumed completely mixed in the vicinity of the impeller and in plug flow near the outlet. 

Develop the E(t) profile for a 10-m laminar-flow reactor which has a maximum flow velocity of 0.40 m min-1. Consider t = 0.5 to 80 min. Compare the resulting profile with that for a reactor system consisting of a CSTR followed by a PFR in series, where the CSTR has the same mean residence time as the LFR and the PFR has a residence time of 25 min. Include in the comparison a plot of the two profiles on the same graph. 

Some multiple-vessel configurations and consequences for design and performance are discussed previously in Section 14.4 (CSTRs in series) and in Section 15.4 (PFRs in series and in parallel). Here, we consider some additional configurations, and the residence-time distribution (RTD) for multiple-vessel configurations. 

Comparison of parts (a) and (b) shows that splitting the feed of B equally among three PFRs in series with the same total volume as a single PFR results in an increase in outlet... 

The reactor is believed equivalent to a PFR in series with a CSTR. A second... 

P5.01,32CSTR WITH BYPASS AND A PFR IN SERIES. FREQUENCY RESPONSE... 

The reactor is believed equivalent to a PFR in series with a CSTR. A second order reaction with kC0 =2.5 is to be processed there. Find (a) the residence time in each element (b) conversion in segregated flow (c) ideal conversion with the PFR first in series (d) ideal conversion with the CSTR first in series. 

If the size of each reactor is fixed, a different final conversion, X2, will be achieved, depending on whether the CSTR, or the plug-flow reactor is placed first If the intermediate and exit conversions are specified, the reactor volumes as well as their sums can be different for different sequencing. Figure 2-7 shows an actual system of two CSTRs and a PFR in series. 

Figure 13-11 Real reactor modeled as a CSTK and PFR in series.

The order of a CSTR and PFR in series is investigated for a third-order reaction. [2nd ed. PI3-10]... 

For two PFRs in series in either order, the value of the integral is fixed, so the result is independent of the arrangement. The only variable left is Cgiucose/ and this is read from the abcissa of the graph on the following page for the ordinate equal to 0.968. 

Fig. 11 shows an example of the calculated reduction rate after burnout assuming plug flow in the burnout zone (isothermal PFR at 1300 C, 2 s mean residence time). The two curves in the figure represent two different reburn models, once PFR only and once PSR plus PFR in series. The figure shows that the maximum reduction predicted varies between 82 % and 95 %, depending on the model for the reburn zone. However, the calculated reduction rates or higher than the measured. 

Figure 13-19 Real reaclor modeled as a CSTR and PFR in series.

C) Using the two preceding simulations, link them to form a new reactor consisting of a CSTR and PFR in series. To integrate the PFR equation initial conditions are needed at the inlet. Let each initial condition needed for the PFR concentrations be given as the exit concentrations from the CSTR. 

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