Distribution Study - Reactor
A TRACERCO Diagnostics™ Distribution Study is a means of identifying
liquid or vapor distribution characteristics in a Fixed Bed Reactor. A
suitable injection point is located upstream of the reactor such as a
sample valve and liquid or gaseous tracer injected. External
detectors are positioned at the inlet and outlet as well as specific vertical
positions around the catalyst bed. As the radiotracer passes each detector
a response is shown. Analysis of each response allows the residence time
and flow distribution to be measured.
In some cases a reactor is constructed with very heavy walls or operates
under conditions that do not easily allow distribution to be measured
using inert radiotracer material and external detectors. In this case
a different technique is employed. A liquid radiotracer (less than 1 gram
of material) is injected with a suitable solvent into the reactor at a
suitable upstream location. The tracer distributes with the flow of liquid
into the reactor. Once in the catalyst bed the tracer is absorbed into
the catalyst. A number of TRU-SCAN®’s can then be performed
around the circumference of the catalyst bed and the responses compared.
Even distribution will show an identical signal at the detector around
the bed. Any maldistribution will be seen by differences in the detector
response. In many cases the tracer moves slowly through the catalyst bed.
Over time the scans can be performed starting at the Reactor’s top
tangent and continue through the Distributor and bed elevations down to
a point in the bed where the radiation readings are consistent with background.
This allows both distributor performance and reactor bed flow to be determined.
 Plug Flow
Reactor
Typically flow through fixed catalyst beds is designed to be plug flow.
Ideally, this flow will move through the bed as a wave front. To measure
residence time and mixing characteristics in a fixed bed two tracer detectors
can be located with one at the inlet and the other at the exit point.
A suitable radiotracer is injected upstream of the inlet to the reactor.
The inlet and outlet detector responses are recorded and the Method of
Moments technique is used to calculate the Inverse Peclet Number (IPN),
which is a measure of plug flow. The closer the IPN is to zero, the closer
the vessel is to perfect plug flow.
 Stirred
Tank Reactor
In contrast to plug flow, ideal well-mixed flow occurs when the reaction
fluids enter a vessel and immediately mix in the total volume of the vessel.
A suitable radiotracer can be injected into a mixing vessel and an external
detector located on the exit line. Good mixing of the fluids is characterized
by an immediate and strong response from the radiotracer on the outlet
detector immediately after the inlet response. This initial response is
followed by a long gradual decline. Analysis of the detector response
recorded uses the Method of Moments technique to calculate the Stirred
Tank Equivalent (STE) value. The STE is a measure of mixing, where 1 stirred
tank is the best mixing that can be achieved.
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