Size of reactor

The size of an LFR for a specified fA or cA at the outlet is defined by the length L for a specified radius R (the latter may be used as a parameter, but values chosen must be consistent with the assumption of laminar flow). If the throughput q0 and R are given, one way to establish L is to use equation 16.2-12 to develop the /A(x) or cA(x) profile. For this purpose, 

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For convenience, the loading on a flow reactor is expressed as a size of reactor per unit of flow rate, say V /V, and is labeled the. space velocity. Some of the units in practical use are stated in the Introduction. How the actual residence time is calculated when the density of flowvaries is illustrated in Table 7-8. 

It is, however, advisable to conduct a harmonic study of the system to select a more appropriate size of reactor, panicularly where the installation is expected to experience high harmonic disorders. 

Determining the size of reactor Consider a three-phase bus system as shown in Figure 28.27. If and X are the inductive reactances of each phase on account of skin and proximity effects respectively, then the impedances of each of the three phases can be expressed as... 

Assuming an average density of 800 kg-m-3, estimate the size of reactor that will give the maximum yield of B for ... 

V (a) Calculate the size of reactor that maximizes the yield of the intermediate, ANT. 

The performance of a reactor for a fluid (A) + solid (B) reaction may be characterized by /B obtained for a given feed rate (FBo) and size of reactor the latter is related to the holdup (WB) of solid in the reactor, whether the process is continuous or batch (fixed... 

The size of reactor is chosen to accommodate this holdup. The diameter is determined from the gas flow rate, q, together with, for example, an allowable superficial linear gas velocity, u (in lieu of an allowable (- AP)) D = (4qhru)m for a cylindrical vessel. The volume could be determined from an appropriate bed density, together with an overhead space for disengagement of solid and gas phases (we assume no carryover of solid in the gas exit stream). 

B = 0.80, t, which is a measure of the size of reactor, is about 1.7 min for ash-layer control, 9.5 min for reaction control, and 14.5 min for gas-film control. The relatively favorable behavior for ash-layer diffusion control in this example reflects primarily the low value of (1.67 min versus 6.67 min for the other two cases) imposed. 

A figure such as Figure 22.4 can also be used in general to determine the size of reactor for a given throughput, and specified conversion, /B, in terms of solid holdup, since from equation 22.2-8. The determination of t for a given value of /B... 

The best quality to be found may be a temperature, a temperature program or profile, a concentration, a conversion, a yield of preferred product, kind of reactor, size of reactor, daily production, profit or cost — a maximum or minimum of some of these factors. Examples of some of these cases are in this group of problems. When mathematical equations can be formulated, peaks or valleys are found by elementary mathematics or graphically. With several independent variables quite sophisticated mathematical procedures are available to find optima. Here a case of two variables occurs in problem P4.12.ll that is solved graphically. The application of Lagrange Multipliers for finding constrained optima is made in problem P4.ll.19. 

Since the reaction is very fast, equilibrium may be assumed attained in any size of reactor. 

Total acid phase, 4 kg/hr, 2.395 liters/hr Find the size of reactor and the residence time for 90% conversion of the toluene assuming it all goes to the mononitro compound. 

From this kinetic information, find the size of reactor needed to achieve 75% conversion of a feed stream of i = 1 liter/sec and C o = 0.8 mol/liter. In the reactor the fluid follows... 

Note which scheme (a) or (b) or (c) gives the smallest size of reactors. 

The size of reactor required for a given duty and for a given temperature progression is found as follows ... 

The size of reactor needed for a given duty is found as follows. For plug flow tabulate the rate for various Xp along this adiabatic operating line, prepare the y -rp) versus Xp plot and integrate. For mixed flow simply use the rate at the conditions within the reactor. Figure 9.8 illustrates this procedure. 

For the mixed flow reactor system of Example 9.5, we wish to get 70% conversion in the smallest size of reactor. Sketch your recommended system and on it indicate the temperature of the flowing stream entering and leaving the reactor as well as r, the space time needed. 

We wish to run the reaction of Example 9.4 in a mixed flow reactor to 95% conversion for a feed concentration AO = 10 mol/liter and feed rate of i = 100 liter/min. What size of reactor would we need ... 

So far we have treated two flow patterns, plug flow and mixed flow. These can give very different behavior (size of reactor, distribution of products). We like these flow patterns and in most cases we try to design equipment to approach one or the other because... 

Since the rate of reaction r and the volumetric flow rate V at each position depend on T, P, and local molal flow rate n of the key component of the reacting mixture, finding the true residence time is an involved process requiring many data. The easily evaluated apparent residence time usually is taken as adequate for rating sizes of reactors and for making comparisons. 

Relative sizes of reactors based on the two models are given in Figure 17.2 for second- and half-order reactions at several conversions. For first order reactions the ratio is unity. At small values of the parameter n and high conversions, the spread in reactor sizes is very large. In many packed bed operations, however, with proper initial distribution and redistribution the value of the parameter n is of the order of 20 or so, and the corresponding spread in reactor sizes is modest near conversions of about 90%. In such cases the larger predicted vessel size can be selected without undue economic hardship. 

For size of reactor, use great Wilhelm s factor for hard computation,... 

As the styrene process shows, it is not generally feasible to operate a reactor with a conversion per pass equal to the equilibrium conversion. The rate of a chemical reaction decreases as equilibrium is approached, so that the equilibrium conversion can only be attained if either the reactor is very large or the reaction unusually fast. The size of reactor required to give any particular conversion, which of course cannot exceed the maximum conversion predicted from the equilibrium constant, is calculated from the kinetics of the reaction. For this purpose we need quantitative data on the rate of reaction, and the rate equations which describe the kinetics are considered in the following section. 

If there are two or more reactants involved in the reaction, both can be converted completely in a single pass only if they are fed to the reactor in the stoichiometric proportion. In many cases, the stoichiometric ratio of reactants may be the best, but in some instances, where one reactant (especially water or air) is very much cheaper than the other, it may be economically advantageous to use it in excess. For a given size of reactor, the object is to increase the conversion of the more costly reactant, possibly at the expense of a substantial decrease in the fraction of the cheaper reactant converted. Examination of the kinetics of the reaction is required to determine whether this can be achieved, and to calculate quantitatively the effects of varying the reactant ratio. Another and perhaps more common reason for departing from the stoichiometric proportions of reactants is to minimise the amount of byproducts formed. This question is discussed further in Section 1.10.4. 

Whatever the nature of the reaction and whether the vessel chosen for the operation be a packed tubular reactor or a fluidised bed, the essence of the design problem is to estimate the size of reactor required. This is achieved by solving the transport and chemical rate equations appropriate to the system. Prior to this however, the operating conditions, such as initial temperature, pressure and reactant concentrations, must be chosen and a decision made concerning the type of... 

The reaction path in the T, Y plane could be plotted by solving the above set of equations with the appropriate boundary conditions. A reaction path similar to the curve ABC in Fig. 3.20 would be obtained. The size of reactor necessary to achieve a specified conversion could be assessed by tabulating points at which the reaction path crosses the constant rate contours, hence giving values of kYT which could be used to integrate the mass balance equation 3.87. The reaction path would be suitable provided the maximum temperature attained was not deleterious to the catalyst activity. 

Commercial WGS catalysts have been optimised for more than 50 years for the massive H2 production in petrochemical plants. However, on-board production requires new catalytic properties such as short response in a dynamic regime, sulfur tolerance, low toxicity and safety (commercial catalysts generally contain Cr and are pyrophoric) and above all a higher efficiency to minimize the size of reactors. Imme-... 

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