Network, reactor

Significant recent approaches to chemical reactor network synthesis can be classified into two categories, viz. superstructure optimization and network targeting. In the former, a superstructure is postulated and then an optimal sub-network within it is identified to maximize performance index (Kokossis and Floudas, 1990). 

Balakrishna, S. and Biegler, L.T., 1992b. Targeting strategies for the synthesis and energy integration of non-isothermal reactor networks. Industrial and Engineering Chemistry Research, 31(9), 2152. 

Balakrisliiia, S. and Biegler, L.T., 1996. Chemical reactor network targeting and integration An optimisation approach. In Admnces in Chemical Engineering. Ed. J.L. Anderson, 23, 243. 

Hildebrandt, D. and Biegler, L.T., 1994. Synthesis of chemical reactor networks. In Foundations of Computer aided process design (FOCAPD 94), Eds. L.T. Biegler and M.F. Doherty, Snowmass CO, p. 52. 

Kokossis, A.C., Floudas, C.A., 1990. Optimization of complex reactor networks - I Isothenual operation. Chemical Engineering Science, 45(3), 595. 

Kokossis A.C and Floudas C.A (1990) Optimization of Complex Reactor Networks - I Isothermal Operation, Chem Eng Sci, 45 595. 

In order to reduce the disparities in volume or space time requirements between an individual CSTR and a plug flow reactor, batteries or cascades of stirred tank reactors ard employed. These reactor networks consist of a number of stirred tank reactors confiected in series with the effluent from one reactor serving as the input to the next. Although the concentration is uniform within any one reactor, there is a progressive decrease in reactant concentration as ohe moves from the initial tank to the final tank in the cascade. In effect one has stepwise variations in composition as he moves from onfe CSTR to another. Figure 8.9 illustrates the stepwise variations typical of reactor cascades for different numbers of CSTR s in series. In the general nonisothermal case one will also en-... 

We wish to determine the effect of using a cascade of two CSTR s that differ in size on the volume requirements for the reactor network. In Illustration 8.8 we saw that for reactors of equal size the total volume requirement was 6.72 m3. If the same feed composition and flow... 

ILLUSTRATION 8.10 USE OF THE DESIGN CHARTS FOR COMPARISON OF ALTERNATIVE REACTOR NETWORKS... 

REACTOR NETWORKS COMPOSED OF COMBINATIONS OF IDEAL CONTINUOUS STIRRED TANK REACTORS AND PLUG FLOW REACTORS... 

For optimum utilization of a given set of ideal reactors operating as ah isothermal reactor network, an examination of the 1 /( — rA) versus CA curve is a good way to find the best arrangement of units. The following general rules have been enunciated by Levenspiel (24). 

It has been suggested that the following liquid phase reaction be carried out in this reactor network. 

ILLUSTRATION 10.6 AUTOTHERMAL OPERATION OF A REACTOR NETWORK CONSISTING OF A STIRRED TANK REACTOR FOLLOWED BY A PLUG FLOW REACTOR... 

There are three general stimulus techniques commonly used in theoretical and experimental analyses of reactor networks in order to characterize their dynamic behavior. 

For linear systems the relative response to a pulse input is equal to the derivative of the relative response to a step input. Illustration 11.1 indicates how the response of a reactor network to a pulse input can be used to generate an F(t) curve. 

Different reactor networks can give rise to the same residence time distribution function. For example, a CSTR characterized by a space time Tj followed by a PFR characterized by a space time t2 has an F(t) curve that is identical to that of these two reactors operated in the reverse order. Consequently, the F(t) curve alone is not sufficient, in general, to permit one to determine the conversion in a nonideal reactor. As a result, several mathematical models of reactor performance have been developed to provide estimates of the conversion levels in nonideal reactors. These models vary in their degree of complexity and range of applicability. In this textbook we will confine the discussion to models in which a single parameter is used to characterize the nonideal flow pattern. Multiparameter models have been developed for handling more complex situations (e.g., that which prevails in a fluidized bed reactor), but these are beyond the scope of this textbook. [See Levenspiel (2) and Himmelblau and Bischoff (4).]... 

The Stirred Tanks in Series Model Another model that is frequently used to simulate the behavior of actual reactor networks is a cascade of ideal stirred tank reactors operating in series. The actual reactor is replaced by n identical stirred tank reactors whose total volume is the same as that of the actual reactor. 

The integral may be evaluated for each stage of the reactor network in turn. For the first stage, Cn 1 = Co, so that... 

Use the data of Illustration 11.1 for the response of a reactor network to a pulse input to determine the number of identical stirred tank reactors in series that gives a reasonable fit of the experimental data. Use both the slope and variance methods described above. 

The variance approach may also be used to determine n. From Illustration 11.2 the variance of the response data based on dimensionless time is 30609/(374.4)2, or 0.218. From equation 11.1.76 it is evident that n is 4.59. Thus the results of the two approaches are consistent. However, a comparison of the F(t) curves for n = 4 and n = 5 with the experimental data indicates that these approaches do not provide very good representations of the data. For the reactor network in question it is difficult to model the residence time distribution function in terms of a single parameter. This is one of the potential difficulties inherent in using such simple models of reactor behavior. For more advanced methods of modeling residence time effects, consult the review article by Levenspiel and Bischoff (3) and textbooks written by these authors (2, 4). 

You have been asked to carry out a residence time distribution study on a reactor network that has evolved over the years by adding whatever size and type of reactor was available at the moment. The feed stream presently contains 1... 

In an effort to determine the cause of low yields from a reactor network, your technicians have carried out some tracer studies in which 4.000 kg of an inert material are quickly injected at the feed port. The tracer levels leaving the reactor at various times after injection were as follows. 

A similar procedure can be used to analyze the second stage of the reactor network. In this case, equation M becomes... 

Temperature and Conversion Profiles for Packed Bed Reactor Network... 

Temperature profiles and the possibility of hot spots within a given reactor network configuration. 

Volume requirements for different reactor network configurations. 

Subash Balakrishna and Lorenz T. Biegler, Chemical Reactor Network Targeting and Integration An Optimization Approach... 

An autocatalytic reaction, A B, with(-rA) = kAcAC%, is to be conducted in a reactor network consisting of a PFR and CSTR... 

Balakrishna, S. and L. T. Biegler. Targeting Strategies for the Synthesis and Energy Integration of Nonisothermal Reactor Networks. Ind Eng Chem Res 31 2152-2164 (1992). 

Hildebrandt, D. and L. T. Biegler. Synthesis of Reactor Networks. In Foundations of Computer Aided Process Design 94, AIChE Symposium Series. L. T. Biegler M. F. Doherty eds. 91 52-68 (1995). 

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