Reactor Tracer Responses

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

The distribution of residence times of reactants or tracers in a flow vessel, the RTD, is a key datum for determining reactor performance, either the expected conversion or the range in which the conversion must fall. In this section it is shown how tracer tests may be used to estabhsh how nearly a particular vessel approaches some standard ideal behavior, or what its efficiency is. The most useful comparisons are with complete mixing and with plug flow. A glossary of special terms is given in Table 23-3, and major relations of tracer response functions are shown in Table 23-4. 

A distinc tion is to be drawn between situations in which (1) the flow pattern is known in detail, and (2) only the residence time distribution is known or can be calculated from tracer response data. Different networks of reactor elements can have similar RTDs, but fixing the network also fixes the RTD. Accordingly, reaction conversions in a known network will be unique for any form of rate equation, whereas conversions figured when only the RTD is known proceed uniquely only for hnear kinetics, although they can be bracketed in the general case. 

Ross (R2) measured liquid-phase holdup and residence-time distribution by a tracer-pulse technique. Experiments were carried out for cocurrent flow in model columns of 2- and 4-in. diameter with air and water as fluid media, as well as in pilot-scale and industrial-scale reactors of 2-in. and 6.5-ft diameters used for the catalytic hydrogenation of petroleum fractions. The columns were packed with commercial cylindrical catalyst pellets of -in. diameter and length. The liquid holdup was from 40 to 50% of total bed volume for nominal liquid velocities from 8 to 200 ft/hr in the model reactors, from 26 to 32% of volume for nominal liquid velocities from 6 to 10.5 ft/hr in the pilot unit, and from 20 to 27 % for nominal liquid velocities from 27.9 to 68.6 ft/hr in the industrial unit. In that work, a few sets of results of residence-time distribution experiments are reported in graphical form, as tracer-response curves. 

One method of characterising the residence time distribution is by means of the E-curve or external-age distribution function. This defines the fraction of material in the reactor exit which has spent time between t and t -i- dt in the reactor. The response to a pulse input of tracer in the inlet flow to the reactor gives rise to an outlet response in the form of an E-curve. This is shown below in Fig. 3.20. 

The forms of actual tracer response curves may be used to formulate models of the actual mixing processes in the reactor. One has, however, to be careful since the tracer response curve does not give a unique solution. It does, for example, not allow one to distinguish between early and late mixing, which may be important when used in the estimation of conversion in a particular reactor-reaction system. 

In an effort to determine the cause of low yields from a reactor, a tracer study was conducted. An amount m0 = 3.80 kg of an inert tracer A was injected into the feed port of the 1. 9-m3 reactor. The volumetric flow rate was constant at q0 = 3.1 L s-1. The following tracer-response data were acquired ... 

A step increase in the concentration of helium (tracer A), from 1.0 to 2.0 mmol L-1, was used to determine the mixing pattern in a fluidized-bed reactor. The response data were as follows ... 

The impulse tracer response curve of a pilot plant reactor has the shape of a trapezoid with the given equations. A first order reaction conducted in... 

The curve of tracer response from a reactor is triangular in shape, with the equation given following for Cg. A second order reaction with kC0 = 1.5 occurs there. Assuming segregated flow, find the conversion (a) when E(t) is represented by the given equation (b) when the Gamma E(tr) with the same variance is used. 

The tracer response curve of an impulse input to a reactor has the... 

The tracer response curve of impulse input to a reactor is a trapezoid with the given equations. For a second order reaction with kC0 = 2, find the... 

A reactor has a tracer response curve from an impulse input with the equation C = 0.5 cos(-nt/4) over the range 0 t 2. A reaction A= B=>C with k2 =... 

Tracer response of an impulse input to a reactor has the equation C = 5 t exp(-2.5t). What conversion is attained in segregated flow by a second order reaction with kC0 = 23.75 ... 

A reactor has a tracer response, C = 1 - 0.25t2. A reaction with a rate equation,... 

A reaction A = B => C is to be conducted in this vessel with Cb0 - 0. In plug flow at the residence time in this vessel conversion of A "would be 70%. What is the concentration of B at the outlet of this reactor in segregated flow Pertinent functions of the tracer response are... 

Impulse tracer response of a reactor made up of two equal stirred tanks connected by a long pipeline is represented by the equation C = 20 t2exp(-3.5t)... 

Tracer response data of pilot and commercial reactors are represented by the relations... 

Theoretical prediction of tracer responses and prediction of reactor performance... 

A first-order liquid-phase reaction takes place in a baffled stirred vessel of 2 volume under conditions when the flow rate is constant at 605 dm min and the reaction rate coefficient is 2.723 min the conversion of species A is 98%. Verify that this performance lies between that expected from either a PFR or a CSTR. Tracer impulse response tests are conducted on the reactor and the data in Table 6 recorded. Fit the tanks-in-series model to this data by (A) matching the moments, and (B) evaluating N from the time at which the maximum tracer response is observed. Give conversion predictions from the tanks-in-series model in each case. 

Hull and von Rosenberg (I960) injected a pulse of radioactive tracer into the catalyst inlet at the bottom of a reactor. The radioactive tracer concentration was then measured at various points in the reactor. The catalyst rate was 340 lb/hr and the holdup was 18.4 lb. The results of the tracer response were given as follows ... 

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