Residence-time distribution normalized response

Bypassing the reactor showed that the broadening of the pulse caused by the feed and effluent lines was negligible. Hence, the normalized pulse response is the residence time distribution (RTD) of the recycle reactor. 

In the method known as pulse, an amount of tracer is injected into the feed entering the reactor over a period of time approaching zero. The discharge concentration (or equivalent) is then measured as a function of time. Typical concentration curves at the outlet of the reactor can take the form of any of the residence time distribution plots discussed earlier. The most usual response takes the form similar of that in Figure 14.13. Generally, the response approaches a normal or log-normal distribution curve. 

Extensions of residence time distributions to systems with multiple inlets and outlets have been described (27-29). If the system contains M inlets and N outlets one can define a conditional density function E. (t) as the normalized tracer impulse response in outlet j to input in inlet i as shown schematically in Figure 2. 

The conductivity probe technique can also be used to measure the residence time distribution of continuous flow systems by installing probes at the inlet and outlet of the mixing vessel. The probe response can be normalized and interpreted as ouUined by Levenspiel (1972) or as discussed in Chapter 1 of this book. Care should be taken to ensure that the data are collected over a sufficiently long time, because the tail can have a large effect on the measured mean residence time and the derived variance. 

If the tail is truncated, then the tracer impulse response should be normalized based on the area under the curve to obtain a proper density function that approximately describes the distribution of residence times in regions through which there is active flow. 

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