(389c) Industrial Reactor Evaluation with Uncertainties In Mixing Performance and Reaction Kinetics

Frequently the Fluid Mechanics & Mixing Discipline of The Dow
Chemical Company (Dow) is asked to assess the mixing-sensitivity of industrial chemistries. 
The chemistries may be undergoing scale-up or are in some way experiencing process
difficulties.  Sometimes the aim is to minimize impurities of any sort.  In
other, perhaps more challenging, cases the aim is to maintain a constant
distribution of by-products to ensure that the product performance is
unchanged.  Most desirably, we have access to a detailed intrinsic kinetic rate
model and detailed knowledge of the fluid dynamics, so that the pertinent time
scales can be calculated and a Damkohler analysis completed for mixing
sensitivity.  Reality is frequently quite different. 

Generally, we have the following scenarios with respect to kinetics:

-         
A kinetic model exists or can be derived from the correct type of
existing lab or process data.

-         
A kinetic model does not exist, but a reactor mole balance & product
distribution is available or can be derived from process data.  Reactor
sampling may be impossible, meaning the engineer must resort to approximations
based on plant feed and product flows, compositions, tank level changes, etc.  Calorimetric
data may exist.  If resources allow, a kinetic model can be derived from molecular
modeling and thermochemical kinetics, then validated with product data.

-         
No intrinsic kinetic data exist.  Previous process data was taken with a
transport limitation.

And generally
we have these scenarios for flow field:

-         
Vessel geometry is known precisely and the flow field is
well-characterized.

-         
Vessel geometry is known but flow characteristics are not known.  If the
reaction is localized, process instrumentation such as thermowells help
understand some spatial reaction characteristics.

-         
Studies in lab glassware, such as a round-bottomed flask, have given
satisfactory performance.  Blending is inherently rapid.  No significant changes
to the flow field have been studied.

Furthermore,
there can of course be large interactions between the turbulence and reactions. 

The next
scale often must fit in to an already-existing reactor somewhere.  In this
case, the stakeholders need assurance that the existing reactor can work, and whether
any changes must be made to the agitation, feed introduction, etc. to ensure
success.  Sometimes the reactor is yet to be built, so that many degrees of
freedom for design are available.

This talk
will focus on real examples of recent industrial problems encountered and the
methodologies used to address them.