Tracer continuous-stirred tank reactor

In Section 11.1.3.2 we considered a model of reactor performance in which the actual reactor is simulated by a cascade of equal-sized continuous stirred tank reactors operating in series. We indicated how the residence time distribution function can be used to determine the number of tanks that best model the tracer measurement data. Once this parameter has been determined, the techniques discussed in Section 8.3.2 can be used to determine the effluent conversion level. 

A system of N continuous stirred-tank reactors is used to carry out a first-order isothermal reaction. A simulated pulse tracer experiment can be made on the reactor system, and the results can be used to evaluate the steady state conversion from the residence time distribution function (E-curve). A comparison can be made between reactor performance and that calculated from the simulated tracer data. 

Two dynamic alternatives to the static approach have been used in HO calibration and measurement. In the CSTR (continuously stirred tank reactor) approach, air containing the tracer or tracers flows into the reactor to balance the bulk flow out to the HO measuring devices, and the contents are stirred by a fan or other means. The HO chemical tracer is measured in the inlet flow to obtain [T]() and in the outlet flow to obtain [T], Mass balance requires... 

The fluidised bed will be considered as a continuous stirred tank reactor in which ideal macromixing of the particles occurs. As shown in the section on mixing (Chapter 2, Section 2.1.3), in the steady state the required exit age distribution is the same as the C-curve obtained using a single shot of tracer. In fact the desired C-curve is identical with that derived in Chapter 2, Fig. 2.3, for a tank containing a liquid with ideal micromixing, but now the argument is applied to particles as follows ... 

Reactor Tracer Responses Continuous Stirred Tank Reactor (CSTR) With magnitude Cf, the unsteady material balance of tracer a step input of... 

I l urc 6. Combined effect of chemical reaction and mass transport. Single instantaneous inputs of A nd ( are made to ( ) a well-mixed closed system and (b) a continuously stirred tank reactor (CSTR). I ollutant C is conservative tracer its concentration is constant in the closed system, and decreases in i In- ( STR because of the outward flux of water. Chemical A is transformed into product B according In liisl-order kinetics. The sum [A] + [B]) is constant in the closed system, but decreases in the CSTR, Loss of A from the CSTR arises from both chemical reaction and mass transport. 

Activity. A comparison of the global rates of CO conversion on a per gram of catalyst or on a per gram of cobalt in the catalyst at 500 K shows that the activities of the chromium- and zirconium-doped catalysts were substantially higher than any of the other catalysts studied. (Specific rates on a per active catalyst site basis (13,21) are not available for these catalysts. Such measurements will be undertaken for the more promising catalysts in the near future (22). Justification for this use of the continuous stirred-tank reactor (CSTR) design equation was provided by pulse tracer experiments (20).) These are followed by the activated carbon-... 

Isothermal Reactor with Complex Reaction 265 Continuous Stirred-Tanks, Tracer Experiment 273 Deactivating Catalyst in a CSTR 268 Distribution of an Insecticide in an Aquatic Ecosystem 581... 

In Figures 3.4 and 3.5, the RTDs of ideal reactors are presented together with the RTD of a real reactor. The ideal, continuously operated stirred tank reactor (CSTR) has the broadest RTD between all reactor types. The most probable residence time for an entering volume element is t = 0. After a mean residence time t = t), 37% of the tracer injected at time t = 0 is still present in the reactor. After five mean residence times, a residue of about 1% still remains in the reactor. This means that at least five mean residence times must pass after a change in the inlet conditions before the CSTR effectively reaches its new stationary state. 

How can tracer methods help us in solving these two problems We know that reactor performance, as measured by conversion of the limiting reactant or by product selectivity, is a function of kinetics, flow pattern and mixing pattern in the reactor. The flow and mixing phenomena in various reactor geometries are complex, and we are currently unable to characterize them completely (at an economical cost). The only reactors that we know how to design, predict their performance and scale up with confidence, are those that behave as the two ideal reactor types, i.e. the plug flow (PFR) and the continuous flow stirred tank reactor (CSTR). 

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