Digital X-ray Imaging Technique to Study the Horizontal Injection of Gas-Liquid Jets into Fluidized Beds

Abstract

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.

Fluidized bed with a rotating distributor operated under defluidization conditions

“…Consequently, such ''incomplete'' fluidization affect the heat and mass transfer rate in fluidized beds, and might lead to local defluidization problems [6][7][8]. Namely, the larger agglomerates tend to settle down on top of the distributor after being affected by the bed hydrodynamics [9]. These particles in the grid-zone are not much influenced by bubble motion and present the so-called ''dead zones'' between the holes of the distributor [10,11].…”

Electric conductance method to study the contact of injected liquid with fluidized particles

“…1,3 In the case of vaporizable liquids, liquid-solid agglomerates may or may not be formed, depending on the operating conditions, 4,5 while they always form with nonvaporizable liquids. 6 Bruhns et al 7 investigated the interaction between vaporizable liquid jets and fluidized solids in a pilot-scale re-actor operated at 120-180 8C. Their study indicated that the liquid injected through commercial gas-atomization nozzles did not immediately vaporize upon direct contact with the bed solids.…”

“…With nonvaporizable liquids, using an X-ray imaging technique, Ariyapadi et al 6 visually observed the formation of liquid-solid agglomerates at the tip of the cavity formed by the liquid jet in a laboratory-scale fluidized bed of coke particles. The formation of agglomerates upon the contact between liquid jets and a small-scale fluidized bed was quantified by House et al 1,8 They injected a binder solution via gas-atomization nozzles into a fluidized bed of coke particles at room-temperature, and froze the formed agglomerates right after completing the liquid injection by interrupting the fluidization air.…”

A model for collisional exchange in gas/liquid/solid fluidized beds

“…In the collision model, total equilibrium cannot be attained if momentum equilibrium is achieved before total equilibrium is achieved. Table 3 Liquid jet parameters for Tests L 1 and L 3 by Ariyapadi et al (2003).…”