Fluidised Beds
Key Benefits Include:
- shorten cycle times by measuring reaction conditions through bed
- increase yield by measuring phase concentration and boundaries
- measure flow velocities to identify areas of good and poor contact
- development of new distributor arrangements
Introduction
In a fluidised bed a solid material is maintained in a fluid like state by passing a gas or liquid up through the bed at sufficient velocity to maintain fluid behaviour. They are often used in reactions where the solid is a catalyst or a heat transfer medium. When optimised, the advantages are excellent mixing and a well mixed temperature profile.
In operation the challenges are to maintain the bed fluidised, while ensuring the solid particles are not “carried over” due to too high a gas velocity and allowing any waste reaction products such as carbon to be removed. The largest use is the fluidised cat cracker (FCC riser) in a refinery.
Again the measurement requirement is to measure the homogeneity of the fluidised bed and the presence of any waste products that may need removing. This is very difficult from inside the vessel as any measurement system potentially disturbs the fluidity.
Considerable use has been made of process tomography in the investigation of different types of fluidised beds. This work has spanned the spectrum of highly theoretical studies to pragmatic large scale optimisation projects.
References
Wang SJ, Geldart D, Beck MS and Dyakowski, T (2000) A behaviour of a catalyst powder flowing down in a dipleg, Chemical Engineering Journal, Vol. 77, 51-56
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