Doctor of Philosophy
Chemical and Biochemical Engineering
Dr. Cedric Briens and Dr. Franco Berruti
The stripper section of a Fluid CokerTM consists of a system of baffles (sheds) that enhances the removal of interstitial and adsorbed hydrocarbon vapors from the fluidized coke-particles. Most of the hydrocarbon-vapors released below a stripper shed flow up to the stripper shed, where they may crack and form coke deposits that foul the shed. Extensive fouling changes the shapes of the sheds, makes them thicker and reduces the free-space between the adjacent sheds until downward solids flow is so impaired that the Coker has to be shut down.
The Radioactive Particle Tracking (RPT) technique allows the determination of a radioactive tracer-particle location within a certain space inside a fluidized bed and has been the main tool used to study the motion of agglomerates and their interactions with internals.
The research presents an innovative use of the RPT system, as a tool to measure the growth of internals fouling in time without the need of stopping the process. Moreover, the technique was able to characterize the type of interactions the agglomerate has with the sheds. In conjunction with a mathematical drying model, it was possible to predict the flow of organic vapors reaching each shed, thus estimating the risk of shed fouling, as well as the amount of liquid lost with the agglomerate as it leaves the stripper section.
The investigation found that small agglomerates lose very quickly their liquid and therefore its ability to cause fouling. Moreover, experimental work showed that the solid recirculation rate is a very important parameter, e.g., decreasing it by half, quadruples the residence-time in all zones.
The comparison of different types of sheds and configurations concluded that the Mesh-Shed type of internals performs the best. With regular sheds, the best configuration reduces the total open area by only 30%, instead of 50% as with the current sheds.
A study of a ring-baffle that is inserted above the stripper section showed that its main advantage is that it increases the residence time of the agglomerates above the baffle, providing them with more time to dry. Adding flux-tubes to the baffle is detrimental to their performance.
Sanchez Careaga, Francisco J., "Hydrodynamics in Recirculating Fluidized Bed Mimicking the Stripper Section of the Fluid Coker" (2013). Electronic Thesis and Dissertation Repository. 1819.