Horizontal Gas Jet Research Articles

Breaking agglomerates with low-velocity gas jets in a fluidized bed

Agglomerate formation is an issue in several industrial fluidized bed processes, such as fluidized coating, fluid coking, biomass combustion, biomass gasification, and silicon refining. Vigorous bubbling can help reduce agglomeration, but is not intense enough to break strong agglomerates. Moreover, increasing the fluidization velocity of the whole bed may have undesirable outcomes, such as increased elutriation. High-velocity gas jets will also attrit the bed particles. This paper focuses on using low-velocity (10–30 m/s) horizontal gas jets to break agglomerates in a fluidized bed. A gas jet cycles, and the shear from the emulsion solids displaced by the expanding jet cavity helps break agglomerates. Equipment configurations that provide a high fraction of broken agglomerates for a typical agglomerate will be effective for other agglomerates of various strengths. Agglomerate breakage can be enhanced by increasing the jet nozzle flowrate or the flow of gas bubbles into the jet cavity.

Numerical Simulation on Field Characteristics of the Horizontal Gas Jet Flow of Underwater Vehicle

Solid rocket motors are important for the propulsion of underwater vehicles, especially for rapid maneuvering. To study the characteristics of the gas jet flow field generated by the engine of the underwater vehicle, a numerical calculation model considering gravity and phase transition was established. The basic laws of formation and evolution of jet bubbles were studied, and the unsteady characteristics of the jet flow field considering phase transition and the influence of inflow velocity and attack angle on the jet were analyzed. The results show the gas bubbles successively take on “concave” and “convex” shapes, and there exist “rebound” and “nesting” phenomena after the gas is accelerated and injected into water by the nozzle; the engine considering the phase transition process can obtain larger momentum and the degree of pressure fluctuation becomes smaller, which contributes to improving the propulsion efficiency of solid rocket motors by adding the gas-liquid phase transition model; the inlet flow has an inhibitory effect on the pressure pulsations of the flow field, and the influence of the wake on the vehicle which adopts rocket assist decreases as the speed increases; the upward deflection of the gas bubbles intensifies and the rupture of gas bubbles become closer to the nozzle outlet as the attack angle increases.

CFD-DEM modeling of strongly polydisperse particulate systems

Particulate systems can be readily modeled and simulated with the discrete element method (DEM). Large ranges in grain sizes, however, pose a serious challenge: The number of particles per volume increases significantly and computational time steps need to be reduced. Especially large systems require an efficient treatment of the smallest particles present. We derive and discuss models for two limiting cases. (a) For clearly separated size distributions, we consider the smaller particles as continuous fields. This corresponds, for example, to fines transport through a coarse granular bed including their deposition and release and is validated against measurements on such a system (approx. 105 particles, fine-to-particle-diameter ratio 0.105, up to 200% increase in pressure drop). (b) For less strongly separated distributions, e.g. one broad range of sizes, we introduce effective parcels consisting of sub-scale particles with various diameters. This model is applied to numerical experiments with a horizontal gas jet penetrating packed beds with bi- and monodisperse compositions and forming cavities as found in blast furnaces. The results show a good agreement with what one would expect from the full size distribution at fractions of the actual particle number (Nbi ≈ 3 ⋅ 105, Neff ≈ 7 ⋅ 104). Finally, we discuss how these models might be generalized for the application to a wide range of particulate systems.

A mathematical approach to submerged horizontal buoyant jet trajectory and a criterion for jet flow patterns

This paper focused on the trajectory and flow patterns of submerged horizontal gas jet in stagnant ambient liquid. A rigorous mathematical model for the jet trajectory was developed based on geometric analysis, mass conservation, and momentum. Additional, multiple N2-Water experiments employing binary image processing were designed and performed. The experimental procedures and mathematical derivations are presented here in details. To assess the ability of the mathematical model to predict the jet trajectory, extensive experimental results were extracted for comparison with the mathematical results. The mathematical results were found to be in good agreement with the experimental results. Furthermore, a dimensionless jet spreading angle model was proposed and fitted to the experiment results. A flow pattern transition criterion based on the penetration depth of the buoyant jet in the water was also discussed, distinguishing the gas buoyant jet form bubbly or transitional flow patterns.

An experimental investigation on the characteristics of submerged horizontal gas jets in liquid ambient

Gas injections into liquid are prevalent in the natural environment and are essential in industrial applications, they can lead to complex flow. The flow structure and processes are essentially unsteady and turbulent. In this study, a set of experiments were carried out to investigate the behavior of horizontal round noncondensing gas jets that discharge in a stagnant water ambient, considering subsonic and sonic jet exit conditions. A flow visualization technique using a CCD camera, which allowed simultaneous measurements, was used to investigate such flows. This technique provided a direct measurement of the interfacial behavior between the gas jet and the liquid ambient. Two different methods, the summation and the statistical one were used to obtain and analyze the experimental results, and we have found that both methods yield almost identical results.The results showed that the injector diameter and the Froude number play an important role in dictating both the jet pinch-off and the jet interface unsteadiness. The maximum location before the jet pinch-off is shown to have a logarithmic relation with the Froude number for all the jet diameters. The jet penetration length was measured in the momentum and buoyant regimes respectively and it was found to be strongly influenced by the nozzle diameter and the Froude number as well as by the mass and momentum flow rates of the injected jet. Jet spreading which is indicative of liquid entrainment is also shown to increase with the Froude number and the injector diameters. Also it was found that the Froude number plays an important role in dictating the expansion jet angle and the jet half-width. These magnitudes were obtained from recorded time-averaged images and finally empirical correlations have been developed to predict these parameters.

Modelling of penetration of horizontal supersonic nozzles in high temperature fluidised beds

Supersonic nozzles have been applied in various jet-induced fluidised bed attrition processes such as jet milling and Fluid Coking. In jet-induced particle attrition, the penetration length into the bed of the jet issuing from the supersonic nozzle is a critical property that affects the attrition mechanisms. A numerical model was developed to predict the penetration length of jets issuing from a horizontal supersonic nozzle in high temperature fluidised beds, based on an Eulerian–Eulerian multiphase model and Granular kinetic theory. The predicted jet penetration lengths are in very good agreement with the experimental data and the predictions of Li's empirical correlation [Li, “Penetration of High Velocity Horizontal Gas Jets Into a Fluidized Bed at High Temperature”, in Fluidization XIII, S. D. Kim, Y. Kang, J. K. Lee, Y. C. Seo, Eds., Gyeong-ju, Korea 2010; Engineering Conferences International, Gyeong-ju, Korea 2010, pp. 893–900.]. The simulation results have also demonstrated that the fluidisation velocity and bed temperature have little influence on jet penetration length. © 2013 Canadian Society for Chemical Engineering

Horizontal gas and gas/solid jet penetration in a gas–solid fluidized bed

In this paper, the real time, dynamic phenomena of the three-dimensional horizontal gas and gas/solid mixture jetting in a 0.3 m (12 in) bubbling gas–solid fluidized bed are reported. The instantaneous properties of the shape of the jets and volumetric solids holdup are qualified and quantified using the three-dimensional electrical capacitance volume tomography (ECVT) recently developed in the authors’ group. It is found that the horizontal gas jet is almost symmetric along the horizontal axis during its penetration. As the jet width expands, the total volume of the gas jet increases. A mechanistic model is also developed to account for the experimental results obtained in this study. Comparison of jet penetration length and width between the model prediction and ECVT experiment shows that both the maximum penetration length and the maximum width of the horizontal gas jet increase with the superficial gas velocity. When the horizontal gas jet coalesces with a bubble rising from the bottom distributor, it loses its symmetric shape and can easily penetrate into the bed. For the horizontal gas/solid mixture jet penetration in the bed, the tail of the jet at the nozzle shrinks and the jet loses its jet shape immediately when the jet reaches its maximum penetration length, which are different from the characteristics exhibited by the gas jet. The solids holdup in the core region of the gas/solid mixture jet is higher than that in the gas jet. The penetration length of the horizontal gas/solid mixture jet is also larger than that of the gas jet.

Numerical simulation of single and multiple gas jets in bubbling fluidized beds

The behavior of single and multiple horizontal gas jet injections into a rectangular bubbling fluidized bed are studied with three-dimensional numerical simulations. The jet penetrations as well as the interactions between the jet and the surrounding gas, solids, bubbles, and other jets are investigated. As far as the average jet penetration length is concerned, limited influence of each jet on the others is observed in multiple jet injections until the jets start to overlap. The effect of the secondary gas injection on the flow hydrodynamics in the bed is examined for multiple jet injections with different jetting velocities and arrangements. It is found that the secondary gas injection mainly affects the hydrodynamics of the upper section above the injection level, while its effect is nearly negligible below the injection. Above the injection level, more particles are brought upward and the circulation of solids is promoted. Furthermore, the tendency of slugging inside the bed is observed at high secondary injection flow rates.

Mixing of secondary gas injection in a bubbling fluidized bed

In this work, three-dimensional numerical simulations with the aim of investigating the mixing of secondary gas in a bubbling fluidized bed are performed. Single and multiple horizontal gas jet injections into a small scale rectangular bubbling fluidized bed are studied. A tracer gas is introduced through the jet orifice to study the gas mixing in the system. Both transient and time-averaged results are analyzed. The effect of gas injection velocity and jet arrangement on the gas–solid contact is evaluated. It is found that the tracer distribution is non-uniform at the injection level. Within a short distance above the injection, the tracer becomes uniformly distributed. Gas back-mixing is observed in all simulations, which is prominent near the wall due to the downward flow of solids. For the cases studied, the gas back-mixing tends to decrease as the secondary gas flow rate increases. For the same secondary gas flow rate, it has been demonstrated that a better mixing between the tracer gas and solid particles is achieved when the secondary gas is injected through distributed jet arrangement.

The effect of distributor design on gas dispersion in a bubbling fluidized bed

In this study, the behavior of gas dispersion in a bubbling fluidized bed was investigated. Carbon dioxide was used as the tracer gas. Most of the gas jets from tuyeres are towards the same direction, parallel with the longitudinal axis. The movement of particles in the lateral direction was enhanced by the momentum of horizontal gas jets within the bed. The experimental results show that the effect of superficial gas velocity on the gas mixing depends on the distributor type. Comparing with perforated distributor, a better performance of gas mixing was observed while the bed was equipped with horizontal nozzle distributor.

Effect of a shroud on entrainment into a submerged jet within a fluidized bed

Following the discussions of Bohnet and Teifke [M. Bohnet, J. Teifke, New results on the efficiency transformation in gas solids-injectors, in: Proceedings—Reliable Flow of Particulate Solids: EFCE Publication Series, 1985, pp. 383–400] and Idelchek [I.E. Idelchek, Handbook of Hydraulic Resistance, CRC Press, Boca Raton, 1994] it was decided to investigate the effects of altering the region surrounding the jet in order to affect the method of contact between the jet and the fluidized bed. This was accomplished using several different configurations of “shrouds” that formed physical barriers either around the nozzle tip or draft tube inlet, or both. These new types of internals substantially increased the entrainment rate of fine fluidized particles into a submerged horizontal gas jet. The internals have been observed to affect both the solids flow pattern surrounding the jet and flux of entrained solids into the jet and the amount of fluidization gas entrained into the jet. Under the best conditions studied experimentally, the solids entrainment rate was increased by over 100% while the amount of fluidization gas entrained was reduced by approximately 50% as measured using a CO 2 tracer. In total, 5 different nozzle configurations were studied. Fluid coke particles (135 μm Sauter mean diameter and density 1450 kg/m 3) were used for bed material and air was used for both the motive and fluidization gas. CFD modeling has also been undertaken to characterize the behaviour of the internal and further elucidate the mechanism behind the increase in solids entrainment. Analysis of the simulation results reveals the presence of strong gas recirculation zones close to the nozzle tip and at the shroud inlet.

Numerical simulation of horizontal jet penetration in a three-dimensional fluidized bed

The introduction of reactant gas as a jet into a fluidized bed chemical reactor is often encountered in various industrial applications. Understanding the hydrodynamics of the gas and solid flow resulting from the gas jet can have considerable significance in improving the reactor design and process optimization. In this work, a three-dimensional numerical simulation of a single horizontal gas jet into a cylindrical gas–solid fluidized bed of laboratory scale is conducted. A scaled drag model is proposed and implemented into the simulation of a fluidized bed of FCC particles. The gas and particles flow in the fluidized bed is investigated by analyzing the transient simulation results. The jet penetration lengths of different jet velocities have been obtained and compared with published experimental data as well as with predictions of empirical correlations. The predictions by several empirical correlations are discussed. A good agreement between the numerical simulation and experimental results has been achieved.

Towards an ultimate fluidized bed stripper

Experiments were conducted in the geometrically- and dynamically-scaled UBC half-column to test different configurations that might significantly reduce stripper shed fouling and increase run length, while providing little or no decrease in stripping efficiency in two commercial fluid cokers. The results showed that a series of horizontal gas jets, without baffles, constrained to use no more steam than in the existing commercial operations, were unable to fully match the stripping efficiency of the strippers with shed internals. Wall baffles were also of little assistance. However, relatively large crossed-sheds, called “mega-sheds,” combined with a limited number of staggered gas jets, provide a promising geometry, with more tolerance to fouling and stripping efficiency equivalent to that of the existing commercial units.

Back-attack Phenomena of Gas Jets with Submerged Horizontally Blowing and Effects on Erosion and Wear of Refractory Lining.

Taken the refining process in an 18 t AOD vessel for example, the "back-attack" phenomena of the horizontal rotating and non-rotating gas jets and their effects on the erosion and wear of the refractory lining were investigated in a water model. For this refining process, the two-tuyere (lance with constant cross-sectional area) blowing of gas is operated using the annular-tube type tuyere. The geometric similarity ratio of the model unit (including the tuyere) with its prototype was 1/3. The relations of the gas blowing rate, blowing pressure, angular separation between the two tuyeres, type of tuyere and other operation parameters with the back-attack action of the gas jet and the refractory lining erosion and wear were examined under the different operating modes. The appropriate back-attack frequencies and pressures were continuously monitored and measured by means of a dynamic resistance strain-meter of YD-21 type with an anti-water pressure sensor made specially. A light-beam oscilloscope of SC16A type recorded simultaneously the back-attack waves. Also, the modeling experiment on the erosion and wear of the refractory lining was carried out. The results indicated that the back-attack phenomena of the horizontal rotating and non-rotating gas jets have respectively the different features from that in a bottom blowing. On the back-attack phenomena of these two kinds of jets, the gas streams of the inner tubes (main-tuyeres) have all a governing bearing, and the annular slit pipe (sub-tuyere) streams show an evident alleviation and suppression effect. The circulative motion of the liquid in the bath would be another important reason to bring about the back-attack phenomenon of a submerged gas jet. The buoyancy force gives a considerable influence; it is able not only to increase the back-attack intensity of a horizontal gas jet, but also to enlarge the locally eroded and worn zone of the refractory lining. The influence of the tuyere position (the angle included between the two tuyeres) is not so remarkable in the conditions of the present work. The rotating motion of a horizontal gas jet may decrease the frequency and intensity of the back-attack action and reduce the eroded and worn rate and area of the refractory lining under a same blowing pressure. The annular-spiral tube type tuyere with a reasonable structure may be expected to have a good latent using power and composite effectiveness.

Author index

The behavior of single and multiple horizontal gas jet injections into a rectangular bubbling fluidized bed are studied with three-dimensional numerical simulations. The jet penetrations as well as the interactions between the jet and the surrounding gas, solids, bubbles, and other jets are investigated. As far as the average jet penetration length is concerned, limited influence of each jet on the others is observed in multiple jet injections until the jets start to overlap. The effect of the secondary gas injection on the flow hydrodynamics in the bed is examined for multiple jet injections with different jetting velocities and arrangements. It is found that the secondary gas injection mainly affects the hydrodynamics of the upper section above the injection level, while its effect is nearly negligible below the injection. Above the injection level, more particles are brought upward and the circulation of solids is promoted. Furthermore, the tendency of slugging inside the bed is observed at high secondary injection flow rates.