Multiple-Reactor Systems

Consider N plug flow reactors connected in series, and let X2,.. . , be the fractional conversion of component A leaving reactor 1, 2,.. . , A. Basing the material balance on the feed rate of A to the first reactor, we find for the /th reactor from Eq. 5.18 

N plug flow reactors in series with a total volume V gives the same conversion as a single plug flow reactor of volume V. 

For the optimum hook up of plug flow reactors connected in parallel or in any parallel-series combination, we can treat the whole system as a single plug flow reactor of volume equal to the total volume of the individual units if the feed is distributed in such a manner that fluid streams that meet have the same composition. Thus, for reactors in parallel V F or r must be the same for each parallel line. Any other way of feeding is less efficient. 

EXAMPIM 6.1 OPERATING A NUMBER OF PLUG FLOW REACTORS 

The reactor setup shown in Fig. E6.1 consists of three plug flow reactors in two parallel branches. Branch D has a reactor of volume 50 liters followed by a reactor of volume 30 liters. Branch E has a reactor of volume 40 liters. What fraction of the feed should go to branch D  

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In two processes under development as of 1997, the sulfur dioxide stream reacts with reduciag gas over a proprietary catalyst to form elemental sulfur. Both processes have achieved a sulfur recovery of 96% ia a single reactor. Multiple reactor systems are expected to achieve 99+% recovery of the feed sulfur. The direct sulfur recovery process (DSRP), under development at Research Triangle Institute, operates at high temperature and pressure. A similar process being developed at Lawrence Berkeley Laboratory is expected to operate near atmospheric pressure. 

Multiple-Reactor Systems 131 Since =2 = 2Vn=i the ratio of flow rates becomes... 

The multiple reactor system could probably be eliminated. The reactor would not have to be designed for regeneration as well as reaction. 

The first multiple-reactor system we study is the reaction considered in Section 2.1, which is the irreversible reaction A —> B. The design equation for the volume of a single CSTR is given in Eq. (2.60) in terms of conversion x, specific reaction rate k, and feed flowrate F ... 

Common design problems encountered in industrial operations include size comparisons for single reactors, multiple reactor systems, and recycle reactors. 

Dynamic Modeling of Molecular Weight and Particle Size Development and Application to Optimal Multiple Reactor System Design... 

Several commercial processes have been developed for the catalytic dehydrogenation of propane to propylene as presented in Table 4. Of the seven commercial propane dehydrogenation plants in operation, six use UOP s Oleflex continuous moving-bed process. The other uses ABB Lummus Catofin cyclic multiple-reactor system. Other processes include Krupp Uhde s STAR process, as well as technologies from Linde and Snamprogetti. ... 

As a result of this effort, industrial plasma torches have been developed which can be utilized for high temperature processing of a variety of materials. EnerSoI has successfully applied plasma torches in multiple reactor systems for the gasification of materials. 

Figure 2. A tubular, packed-bed multiple reactor system...

Pollock, M. J., MacGregor, J. F., and Hamielec, A. E. (1981) Continuous poly (vinyl acetate) emulsion polymerization reactors dynamic modeling of molecular weight and particle size development and application to optimal multiple reactor system design. Computer Applications in Applied Polymer Science, (ed. T. Provder), ACS, Washington, pp. 209-20. 

For higher throughput of samples, a certain automation of solubility measurements is feasible. For example, the instrument Crystal 16 multiple reactor system (Avantium Technologies BV/Amsterdam) is capable to accommodate 16 samples (in standard HPLC glass vials of about 1 ml volume) at the same time and to simultaneously hold them at the same temperature for equilibration purposes. 

Polythermal methods have in common that a suspension containing known amounts of solvent and solute in excess is heated and the temperature where last particles dissolve is detected. For detection, visual observation (e.g., under a microscope), turbidity measurements, particle-detecting inline probes (e.g., FBRM probe (Lasentec , Mettler Toledo GmbH)), or calorimetry may be used. Since it is a dynamic method, the results depend on dissolution kinetics of the particular system. In general, polythermal measurements are easier to automate since just a temperature has to be followed and no special analytical technique is required. The above-mentioned Crystall6 multiple reactor system can also be used to perform such kind of measurements. To detect both the dissolution process for derivation of saturation temperatures (clear points) and the formation of particles (cloud points) for determination of the metastable zone width, the... 

The second objective makes the problem much more difficult than the single-reaction problems that we solved earlier, in Chapter 4. Usually, it is not possible to minimize the reactor volume and maximize the reaction selectivity simultaneously. Frequently, there is a trade-off between rate and selectivity. Ultimately, this trade-off requires an economic analysis. However, the final analysis often favors selectivity over rate because there is a large and continuing cost penalty associated with converting a valuable raw matraial into a low-value by-product There are several important questions that must be considered in designing/analyzing multiple-reactor systems ... 

Suspension polymerization of vinyl monomers is usually carried out in batch reactors. However, the feasibility of continuous suspension polymerization has been reported in some literature. A multiple-reactor system for continuous suspension polymerization of vinyl chloride is illustrated in Fig. 6 [15]. Monomer, water, initiator, and suspending agents are fed to a vertical tower reactor equipped with a multistage stirrer. The reaction mixture of about 10% conversion is then transferred to the second and third reactors, which contain blade stirrers. Each reactor is jacketed for heat removal. Plug flow of the polymerization mixture is maintained in the reaction zones. 

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