| 2—Flow Rate by Peak Timing 
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Ratemeter Recorder 
+ Tracer 
injector 
integral number of counts during passage of a known num- 
ber of millicuries permits calculating the flow rate in 
barrels per second. 
Solid flow rate. Timing a burst of counts is also used 
in measuring solid flow rates in circulating-catalyst systems 
as sketched in Fig. 3 (8). In the catalytic-cracking process, 
catalyst beads accumulate coke and are reactivated in a 
furnace. In this continuous cycle, circulation speed must 
be controlled. No satisfactory instrument has been avail- 
able for gas-lift plants. Circulation speed now is measured 
Measuring Volume 
Liquid volume in a closed system may be difficult to 
calculate from container dimensions, or, because of foaming 
or a turbulent surface, calculated volume may not corre- 
spond to liquid volume. A radiotracer can be used if there 
is a mixing action, either by external circulation or by 
internal stirring. 
For example, H2SO, volume is desired in an alkylation 
plant where extensive intermixing between acid and hydro- 
carbon prevents a well-defined level from forming (7). 
Volume is found by adding a known quantity of Cs!*4 in 
H.SO,. After the tracer is mixed in, a sample is drawn 
out and counted in comparison with a standard prepared 
by dilution. From tracer concentration and total quan- 
tity added, total volume of H.SO, is found. 
Exponential method. Another method is applicable to 
tanks through which there is a known, constant flow. 
(See Fig. 4.) A tracer batch is put into the incoming line. 
Mathematical treatment, assuming complete mixing of 
the incoming stream with the vessel contents, predicts that 
tracer concentration in the tank falls off exponentially with 
a rate determined by throughput, R, and volume, V, as 
follows 
where C is the counting rate. 
The alkylation plant also has been checked by this 
method (7). Sample radioactivity at various times is 
measured and plotted on semi-log coordinates. Known 
throughput rate divided by slope of this plot gives acid- 
phase volume. 
3—Flow Rate in Catalytic Cracker 
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Recorder 
reliably in several such plants using tracer beads impreg- 
nated with Zr%*. The seal leg is surrounded by two rings 
of G-M counters. A radioactive bead passing these de- 
tectors produces two bursts of counts, about a minute 
apart. Dividing the calculated seal-leg capacity by the 
time interval gives catalyst circulation rate. This method 
does not give continuous readings because it depends on 
individual beads randomly spaced. However, two or 
three radioactive beads in a total of perhaps 20 X 10° give 
readings with satisfactory frequency. 
Make-up & —* 
Toke-off — 
gine in CLR 
a dV —>R 
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& — 4=—Volume by Attrition 
Circulating-loop volume. Volume of a circulating-loop 
system can be determined by still another method, in case 
mixing is slow compared to circulation rate. A concen- 
trated slug of tracer, quickly injected, is observed in re- 
peated cycles. Time between successive tracer-peak 
appearances, multiplied by circulation rate, gives the total 
volume of the circulating liquid. This is illustrated in the 
vacuum-distillation-column trace on Fig. 5. Part of the 
tracer was returned repeatedly through a recycle line. 
The initial peak was followed after an interval by an 
attenuated peak. After three or four circuits, the tracer 
peaks were spread out and merged into the background. 
This principle also has been applied to determining total 
quantity of catalyst in the catalytic cracker. Average 
time required for a complete circuit through the system 
multiplied by the flow rate (determined ‘from the same 
beads, as described above), gives total quantity. 
159 
