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 two experimental techniques has been employed. One is two point optical probe technique, which has been developed and used to determine the phase distribution in terms of local liquid and gas velocities, holdup and there time series fluctuations , local maldistribution and back mixing behavior of phases. Two optical fiber tips are placed at distance of 1mm and principle behind to distinguish gas and liquid is total internal reflection phenomena. The other one is, the possibility of flow regimes and pattern identification and on-line monitoring using of gamma ray densitometry (GRD) was examined for the first time in scale down cold flow model upflow moving packed bed reactor. 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. This reactor is scanned by both two tip optical probe and by a gamma ray radioactive source of caesium-137 and detected by a NaI(Tl) detector. The measurements were conducted in various axial and radial positions with the superficial liquid flow rate of 0.017 cm/sec and superficial gas flow rate of 8.8cm/sec for two tip optical probe and superficial liquid flow rate in the range of 0 to 0.47 cm/s and superficial gas flow rate in the range of 0 to 8 cm/sec covering bubbly, pulse and spray flow regimes for GRD. The parameters measured using two point optical probe are local holdups and local velocities of gas and liquid at the void space inside the catalyst bed packing. This is the first time that these kind of study has been implemented on upflow moving bed hydrotreaters. Local holdups gives the phase distributions and local zero velocity of phases gives the local maldistribution at locally occupied void space inside the catalyst bed packing.  Zero velocity of phases condition is an undesirable event in which the void space is either occupied by continuous flow of gas, stagnant liquid or gas bubble deviation. All these conditions will lead to ineffective working of catalyst at that region. Measurement of negative velocities quantify the back mixing behavior characteristics of the phases at a specified local point. Negative velocity are generated when the flow of liquid or gas is in opposite direction to general flow of the phases, this occurs due to back pressure at that point and hence back mixing. In GRD experiment the focus was on to do the time series linear analysis using statistical approach in terms of variance and standard deviation of the measured time series of the received counts (Penetrated gamma ray) has been performed to identify flow regime. The time series non-linear analysis is also conducted based on chaotic approach. In this regard Kolmogorov entropies are calculated using the times series data obtained from the GRD. Comparison is done to see how closely linear and nonlinear analysis of the time series identifies different flow regimes. Implementing GRD to identify and to on-line monitor local flow regime and pattern is very beneficial as it is noninvasive and gives better results than pressure drop at the wall. The data analysis is also quite fast, as a matlab program to do the analysis has been developed. The result obtained by two tip optical probe shows that this technique can determine the local, radial, cross sectional and along the height of the bed phase distribution, local maldistribtuion and back mixing behavior profile and the GRD results shows that this technique can be used to monitor and identify flow regime transition in upflow moving packed bed reactor and other type of packed bed reactors. 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: Two Point Optical Probes, Phase distribution, Local Maldistribution, Back Mixing, Zero Velocity, Negative velocity, Gas Holdup, Liquid Holdup, Upflow packed bed reactor, Gamma Densitometry, Flow regime, linear, chaotic, Kolmogorov entropy