Gas-liquid jets injected into fluidized beds of particles/catalyst find applications in many industrial processes. The effective distribution and mixing of the feed droplets with the entrained bed particles is vital in improving the process efficiency. The present study utilizes a sophisticated digital X-ray imaging system to study the internal flow structure of jets injected into fluidized beds. The system is equipped with an X-ray image intensifier (XRII) and optical detectors, which convert the transmitted X-ray photons into digital images of up to 60 frames s-1. The imaging technique provides useful information such as the jet expansion angle and the penetration distance. These are functional quantities in optimizing the performance of feed nozzles, and in modeling the jet-fluidized bed interactions.In this work, the horizontal injection of gas, gas-liquid, and liquid jets into fluidized beds is investigated. The results indicate that the jet expansion (half-angle) is considerably reduced for a gas-liquid jet (5-7 degrees) when compared to that of a gas jet (10-15 degrees). The gas-liquid jet also appears to penetrate more than a gas jet with the same momentum. When a liquid feed is introduced into a fluidized bed of particles, the particles may agglomerate if they are wet-enough to form liquid bridges. Improper feed distribution may be a direct contributor to enhanced agglomeration. In this regard, radio-opaque tracers mixed with the feed liquid are injected to track the formation and the movement of agglomerates. The tracer experiments show that the agglomerates are generated at the end of the jet region, close to its maximum penetration distance. A brief discussion on the modifications required to achieve improved contrast for the acquired images, and the effect of some important X-ray parameters are also included in the present study.

A new method has been developed to predict the horizontal jet penetration of gas-liquid sprays injected into gas-solid fluidized beds. The technique involves combining a theoretical model to predict the momentum flux of two-phase sprays with the Benjelloun et al. (1995) correlation for gas jets. Following this treatment, a generalized version of the jet penetration correlation has been developed, which includes the effect of nozzle geometry. The correlation predictions are in very good agreement with the experimental data for a wide range of nozzle geometries, nozzle scales, and jet fluids.

The injection of a gas−liquid spray jet into a fluidized bed of particles is used in many applications such as fluid catalytic cracking or fluid coking. In such applications uniform contact of the liquid droplets and entrained particles is essential for high yields. The objective of this study is to measure the quality of the solid−liquid mixing when a gas−liquid jet is injected into a fluidized bed of coke particles. A quick method has been developed to determine the local quality of solid−liquid mixing on a short time scale. The measuring technique uses temperature to characterize the solid−liquid mixing. Cold ethanol is injected into the fluidized bed via a two-phase spray nozzle and is mixed with the heated fluidized coke particles. An assembly of fast response thermocouples, located downstream of the gas−liquid spray jet, provides instantaneous temperature readings over the liquid spray jet cross section at different axial positions along the length of the jet. In the case of perfect mixing, the temperature should be the same at each radial position. From the variations of the time-averaged temperature, contour plots of the liquid/solid distribution within the cross-sectional area of the jet are created. This technique is used to compare solid−liquid mixing for two cases:  when the spray is introduced as a free jet and when a draft tube is placed downstream of the gas−liquid spray. The use of a draft tube is found to improve liquid/solid mixing. The measurement technique has proven to be a reliable method to determine the liquid/solid distribution in the cross section of the jet. It shows that very good and rapid contact between sprayed droplets and particles can be achieved by using a draft tube mixer.

montrent un bon accord avec les données expérimen-tales. Le présent modèle peut servir à caractériser le comportement de jets gaz-liquide (vaporisations fines) injectés dans des lits fluidisés de particules fines.

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