Plug-flow reactors sequencing

This is the equation for a plug flow reactor. It can be derived directly from the rate equations with the aid of Laplace transforms. The sequences of second-order reactions of Figs. 7-5n and 7-5c required numerical integrations. 

The reactor system may consist of a number of reactors which can be continuous stirred tank reactors, plug flow reactors, or any representation between the two above extremes, and they may operate isothermally, adiabatically or nonisothermally. The separation system depending on the reactor system effluent may involve only liquid separation, only vapor separation or both liquid and vapor separation schemes. The liquid separation scheme may include flash units, distillation columns or trains of distillation columns, extraction units, or crystallization units. If distillation is employed, then we may have simple sharp columns, nonsharp columns, or even single complex distillation columns and complex column sequences. Also, depending on the reactor effluent characteristics, extractive distillation, azeotropic distillation, or reactive distillation may be employed. The vapor separation scheme may involve absorption columns, adsorption units,... 

Figure 4.1 Plug-flow reactor represented as sequence of small batch reactors.

The final sequence we shall consider is a CSTR and plug-flow reactor in series. There are two ways in wlricb this sequence can be arranged (Figure... 

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. 

The monomer feed is converted into Polyamide-6 by polycondensation and polyaddition reactions [930]. This reaction step can be realized by a complex reactor which can be modeled as a sequence of stirred tank and plug-flow reactors. An exemplary model flowsheet comprising two reactors (CSTR) with an intermediate water separation (Split) is shown in Fig. 5.20. Such a model of the reaction section can be analyzed by means of Polymers Plus, an extension of Aspen Plus for handling polymer materials [513]. 

The difficulty in this is the awkward form of equation (6-140) with respect to 7). One likes to compute in sequence through the series of cells, but here we face the implicit form of Ti as a function of r, i. This is the same basic difficulty that limits the utility of the CSTR sequence as an analytical model for nonisothermal reactors. For the case here though, where we employ a relatively large value of the index n in approximation of a plug-flow reactor, and where the solution will be via numerical methods anyway, we will strong-arm the problem with the approximation T,- r,- ] in the exponentials, so that... 

Using temperature T z) as a control function at constant pressure, formulate the problem of the plug flow reactor in Section 1.3.2 (p. 6) to maximize the concentration of the intermediate product B in the following sequence of elementary first order reactions... 

There are three main types of digesters—covered lagoons, complete mix, plug flow and also anaerobic sequencing batch reactors, and fixed... 

Thus, in the idealised tubular reactor all elements of fluid take the same time to pass through the reactor and experience the same sequence of temperature, pressure and composition changes. In calculating the size of such a reactor, we are concerned with its volume only its shape does not affect the reaction so long as plug flow occurs. 

In reactions with parallel steps of different reaction orders or with sequential steps, selectivities depend on the reactor type. Batch and plug-flow tubular reactors give higher selectivities to the product formed by the parallel step of higher order, or to the first product in a step sequence, than do continuous stirred-tank reactors. 

Sketch the RTD curves for the sequence of plug flow and continuous stirred tank reactors given in Figure 8.3.1. 

Using either the data in Table 3-2 or Figure 2-5, calculate the reactor volumes U, and Vj for the plug-flow sequence shown in Figure 2-4 when the intermediate ctu -version is 40% and the final conversion is 80%. The entering molar flow rate is ltie same as in the previous examples, 0.867 moJ/s. 

The dilemma can be summarized as follows. Plug-flow mass and thermal energy balances in a packed catalytic tubular reactor are written in terms of gas-phase concentrations and temperature of the bulk fluid phase. However, the volumetrically averaged rate of reactant consumption within catalytic pellets is calculated via concentrations and temperature on the external surface of the pellets. When external transport resistances are negligible, design of these reactors is simplified by equating bulk gas-phase conditions to those on the external catalytic surface. In this chapter, we address the dilemma when bulk gas-phase conditions are different from those on the external surface of the pellet. The logical sequence of calculations is as follows ... 

The simplest flow-sheet for the reaction Aj o Aj is the RD column sequence with an external recycling loop shown in Fig. 5.1. The system as a whole is fed with pure Aj. According to the assumed relative volatility of the two components a > 1, the reaction product A2 is enriched in the column distillate product whereas the bottom product contains non-converted reactant Aj, which is recycled back to the reactor (continuous stirred tank reactor, CSTR, or plug flow tube reactor, PFTR). The process has two important operational variables the recycling ratio cp = B/F, that is the ratio of recycling flow B to feed flow rate F, and the reflux ratio of the distillation column R = L/D. At steady-state conditions, D = F since the total number of moles is assumed to be constant for the reaction Aj A2. As principal design variables, the Damkohler number. 

F to 500°F in a 1-2 parallel-counterflow heat exchanger with a mean overall heat transfer coefficient of 75 Btu/hr ft T.lt is converted to C by the exothermic reaction, A -(- B C, in an adiabatic plug-flow tubular reactor (Figure 4.30). For a process simulator, prepare a simulation flowsheet and show the calcula-1 tion sequence to determine ... 

---