Gas Mixing Behavior Studies in Upflow Moving Packed Bed Hydrotreating Reactor Using Developed Gas Tracer Technique for Multiphase systems
Yuan Zhou1 Hamza Al-Bazzaz2and Muthanna Al-Dahhan*
1,*Chemical Engineering and Biochemical Engineering Department
Missouri University of Science and Technology, Rolla, MO 65409-1230. USA
2,Kuwait Institute of Scientific Research, P.O Box 24885, 13109 Kuwait
Upflow moving packed bed hydrotreating reactors have been used to process feeds with higher level of contaminants including heavier feeds, to increase catalyst cycle and life of the downstream reactors by providing better protection from fouling metals of the feedstock and to improve in general the downstream reactors product quality. In these reactors spent catalyst are replaced periodically by adding fresh catalyst at the top and removing spent catalyst from the bottom, while the catalyst move downwards periodically, gas and liquid phase move upwards. The problem associated with these reactors is maldistribution, which causes hotspots, sintered carbon deposition and reduces expected conversions. To address such problems, detailed studies to enhance the understanding of the hydrodynamics in the upflow moving packed bed reactor are still required. In this work a gas tracer technique has been developed and used to determine gas phase mixing characteristics. Gas Tracer Technique are usually employed single phase gas system but it has been developed for three phase system using appropriate gas-liquid separator. Various injection and sampling point are placed in the reactor to deconvolute the exact signals for the gas movement through bed. The experimental work was carried out in 11 inch (ID) Plexiglas column for an air-water system flowing over a packed bed of extrudate catalyst 3mm in diameter. The measurements were conducted with the superficial liquid flow rate of 0.017 cm/sec and superficial gas flow rate of 1.27 cm/sec to 8.8cm/sec. The parameter measured are residence time distribution and the extent of gas phase back mixing inside the bed by determining axial dispersion coefficient. This is the first time that these kind of study has been implemented on upflow moving bed hydrotreaters. These kind of information are very essential at industrial scale, to improve the performance of the real plant reactor. In this presentation results and findings are discussed.
Keyword: Multiphase flow, Moving bed reactor, Gas tracer technique, Residence time distribution, axial dispersion coefficient
See more of this Group/Topical: Catalysis and Reaction Engineering Division