Tracer plug-flow reactor

Unlike the situation in a plug flow reactor, the various fluid elements mix with one another in a CSTR. In the limit of perfect mixing, a tracer molecule that enters at the reactor inlet has equal probability of being anywhere in the vessel after an infinitesimally small time increment. Thus all fluid elements in the reactor have equal probability of leaving in the next time increment. Consequently there will be a broad distribution of residence times for various tracer molecules. The character of the distribution is discussed in Section 11.1. Because some of the... 

In the ideal plug flow reactor, the flow traverses through the reactor hke a plug, with a uniform velocity profile and no diffusion in the longitudinal direction, as illustrated in Figure 6.2. A nonreactive tracer would travel through the reactor and leave with the same concentration versus time curve, except later. The mass transport equation is... 

In Example 6.6, we saw that there is little difference between a plug flow reactor and 10 or more reactors-in-series when the constituent is undergoing a first-order reaction under steady-state conditions. This is not true for all circumstances. One example would be a conservative tracer under unsteady boundary conditions, as discussed in this section. 

For a conservative tracer with an unsteady input, a plug flow reactor simply acts as a time lag, where the input comes out of the reactor later, precisely as it went in. The examples of a pulse input and a front input at time t = 0 are given in Figure 6.7. The only difference between the inflow and the outflow are the times at which the... 

Plug Flow Reactor. The plug flow reactor model requires only a residence time tf). So, the tracer cloud is used to determine tp. 

Rivers are generally considered as a plug flow reactor with dispersion. Determination of the dispersion coefficient for rivers was covered in Chapter 6, and determination of the gas transfer coefficient is a slight addition to that process. We will be measuring the concentration of two tracers a volatile tracer that is generally a gas (termed a gas tracer, C) and a conservative tracer of concentration (Cc). The transported quantity... 

Figure 8-29. Dispersion of the tracer in a plug flow reactor.

Plug Flow Reactor The tracer material balance over a differential reactor volume dVr is... 

The basic scheme of a single plug flow reactor with recycle is shown below in Fig.4.4-1. Such a reactor may be described also as a combination of perfectly mixed reactors. Other simplified configurations are described in the following cases, 4.4-l(l) and 4.4-l(2). The states are the concentration of the tracer in the perfectly mixed reactors, i.e. SS = [Ci, C2,. ]. The residence time in the... 

Cases a and b demonstrate the effect of the residence time tp in the plug flow reactor, 0.2 and 1. As seen, in case a tp was too short for the pulse introduced in reactor 1 to reach its maximum value of unity. The effect of the recycle, R = 0 and 10 is demonstrated in cases a and c. As observed, the concentration of the tracer in reactors 2 and 3 becomes identical at tp = 0.2 the concentration are different in the absence of a recycle. The effect of Xi is demonstrated in cases a, d and e. In case a and d all ti = QiA i = are equal in case a ii = 10 (i = 1,. .., 4) and in d pi = 100 (i = 1,. .., 4). Note that a large pi indicates a smaller volume of reactor for a constant Qi. Thus, it is clearly demonstrated that the system attains faster its steady state values for p.j = 100. Case e demonstrates the effect of large p. =100 for reactors 2 and 3, by comparison to the behavior of reactors 1 and 4 for which pi = 10. It is observed that the response of reactors 2, 3 is faster than the response of reactors 1 and 4. It should be noted that if the tracer is introduced into reactor 2, the behavior is similar, however the concentration in reactor 2 remains constant and begins to change only after tp time units have passed. 

Fig.4.4-2 demonstrates a plug flow reactor containing a "dead water" element of volume Vd where the active part is of volume Vp. The system contains also two perfectly mixed reactors 1 and 2. A tracer in a form of a pulse is introduced into reactor 1 and is transferred by the flow Qi into reactor 2 where it accumulates. 

Fig.4.4-5a demonstrates the effect of p on the transient response of C2 and Cn, i.e. the first and the last perfectly mixed reactors in the upper plug flow reactor in Fig.4.4-5. The tracer was introduced into reactor 2. It is obsereved that by increasing p from 80 to 800, the number of oscillations for reaching the steady state concentration 1/22 in the system is increased. It should also be noted that for p = 800, the distance between two successive peaks corresponding to C2 and Cn is...

Plug-flow reactor with moving front of tracer.. 443... 

In order to improve the flow characteristics through the tubular reactor, 10 lengths (each 50 cm) of static mixer elements were inserted at 100 cm internals along the tube. Residence-time distribution studies using a pulse of potasiun chloride as tracer shewed that this tubular reactor had the flow characteristics equivalent to a cascade of 35 stirred tanks in series. Thus for practical purposes, this tube can be considered to have flow characteristics equivalent to those of a plug flow reactor. 

Because of the different paths taken by elements of a fluid to pass through a packed column, a residence-time distribution is generally obtained using a tracer signal at the bed input (salt, dyes), and by analysis of the output response [11]. A ical downstream signal is obtained, dependent on the kind of flow and mixing in the reactor (plug-flow reactor, mixed-flow reactor). The experimental distribution curve may be characterized in terms of mean and variance by ... 

Plug flow reactor models must be constructed with a frame of reference in mind. An observer riding along on the tracer slug would see no change in concentration over the modeled time and could infer nothing about the reactor. 

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