Stage Continuous Flow Stirred Tank Reactor

MULTI-STAGE CONTINUOUS FLOW STIRRED TANK REACTOR  

Consider the first order reaetion A—in a battery of three eontinuous flow stiired tank reaetors, where 

Vp = volume of fluid in eaeh stage (-r j) = rate of reaetion per unit volume in stage i. This ehanges witli i. 

Fig ure 5-23. Battery of continuous flow stirred tank reactors. 

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 

Rearranging Equation 5-207 with the mean residence time t = V,/u gives 

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An endothermic reaction A — R is performed in three-stage, continuous flow stirred tank reactors (CFSTRs). An overall conversion of 95% of A is required, and the desired production rate is 0.95 x 10 3 kmol/sec of R. All three reactors, which must be of equal volume, are operated at 50°C. The reaction is first order, and the value of the rate constant at 50°C is 4 x 10-3 sec-1. The concentration of A in the feed is 1 kmol/m3 and the feed is available at 75°C. The contents of all three reactors are heated by steam condensing at 100°C inside the coils. The overall heat transfer coefficient for the heat-exchange system is 1,500 J/m2 sec °C, and the heat of reaction is +1.5 x 108 J/kmol of A reacted. 

Continuous flow stirred tank reactors are widely used in the chemical process industry. Although individual reactors may be used, it is usually preferable to employ a battery of such reactors connected in series. The effectiveness of such batteries depends on the number of reactors used, the sizes of the component reactors, and the efficiency of mixing within each stage. 

Three-stage nitration to mono-, di-, and trinitrotoluene was formerly used, but continuous-flow stirred-tank reactors and tubular units using the countercurrent flow of strong acids and toluene permit better yields and reaction control. 

When dispersion is complete and uniform, the contents of the vessel are perfectly mixed with respect to both phases. In that case, the concentration of the solute in each of the two phases in the vessel is uniform and equal to the concentrations in the two-phase emulsion leaving the mixing tank. This is called the ideal CFSTR (continuous-flow-stirred-tank-reactor) model, sometimes called the perfectly mixed model. Next we develop an equation to estimate the Murphree-stage efficiency for liquid-liquid extraction in a perfectly mixed vessel. 

Figure 8.2 Types of continuous-flow stirred-tank reactors (a) three-stage cascade of stirred-tank reactors (b) vertically staged cascade of three stirred tanks. Compartmented versions of a battery of stirred tanks in a single horizontal shell may also be employed. (Adapted from J. R. Couper, W. R. Penney, J. R. Fair, and S. M. Walas. Chemical Process Equipment Selection and Design. Copyright 2010. Used with permission of Elsevier.)...

In this chapter, we develop the basis for design and performance analysis for a CSTR (continuous stirred-tank reactor). The general features of a CSTR are outlined in Section 2.3.1, and are illustrated schematically in Figure 2.3 for both a single-stage CSTR and a two-stage CSTR. The essential features, as applied to complete dispersion at the microscopic level, i.e., nonsegregated flow, are recapitulated as follows ... 

Sulfonation of p-nitrotoluene (PNT) is performed in a cascade of Continuous Stirred Tank Reactors (CSTR). The process is started by placing a quantity of converted mass in the first stage of the cascade, a 400-liter reactor, and heating to 85 °C with jacket steam (150°C). PNT melt and Oleum are then dosed in simultaneously (exothermal reaction). When 110°C is reached, cooling is switched on automatically. On the day of the accident, a rapid increase in pressure took place at 102 °C. The lid of the reactor burst open and the reaction mass, which was decomposing, flowed out like lava, causing considerable damage. 

Classical chemical reaction engineering provides mathematical concepts to describe the ideal (and real) mass balances and reaction kinetics of commonly used reactor types that include discontinuous batch, mixed flow, plug flow, batch recirculation systems and staged or cascade reactor configurations (Levenspiel, 1996). Mixed flow reactors are sometimes referred to as continuously stirred tank reactors (CSTRs). The different reactor types are shown schematically in Fig. 8-1. All these reactor types and configurations are amenable to photochemical reaction engineering. 

The sulfur dioxide-rich citrate solution in the bottom of the absorber is fed by level control through a steam-heated exchanger to a three-stage continuous stirred tank reactor system countercurrent to a flow of hydrogen sulfide gas. For this installation the gas source is a tank of liquid hydrogen sulfide. 

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