Gas Injection Velocity Research Articles

Influence of solids outlets and the gas inlet design on the generation of a gas-solids rotating fluidized bed in a vortex chamber for different types of particles

Two design aspects of vortex chambers for the generation of gas-solids rotating fluidized beds are experimentally studied for different types of particles: the solids outlet(s) and the gas inlets. Efficient solids retention and minimal solids losses via the chimney are aimed at so that the gas and solids residence times can be controlled independently. The importance of a strong vortex in the central particle bed freeboard region is demonstrated. It is shown that separate, well-dimensioned and -positioned solids outlets prevent a significant presence of particles in the freeboard region, increasing the vortex strength in this region. This is found to be particularly important when fluidizing small/light particles. The ratio centrifugal force-to-radial gas-solid drag force that is generated by the gas injection is shown to also have an important impact. Theoretically it is shown that this ratio strongly depends on the particle characteristics and to what extent it can be increased by increasing the gas injection velocity, preferentially by reducing the gas inlet slot size and otherwise the number of gas inlet slots. Experiments with different vortex chambers and particles qualitatively confirm the theoretical expectations, but show that limitations are encountered. A very high gas injection velocity prevents efficient penetration of especially fine/light particles in the gas inlet jets which is detrimental for the transfer of tangential momentum between the gas and the particle bed. Slots smaller than the particle size are also shown to be inefficient, as they generate rotational motion of the particles around their own center of gravity.

Mechanism and influencing factors of EOR by N2 injection in fractured-vuggy carbonate reservoirs

Multi-scale fractures and karst caves are the main reservoir bodies in fractured-vuggy carbonate reservoirs, and there are still various types of remaining oil after water flooding. Oilfield development practices demonstrate that the method of N2 injection can enhance oil recovery effectively. However, the development effect of a single well with gas injection is highly different, and the mechanism and influencing factors of gas injection for enhanced oil recovery are not clear. To reveal the mechanism and influencing factors of enhanced oil recovery through physical experiments and numerical simulation, we have produced a series of physical models of fracture and cave combinations based on the characteristics of this type of reservoir, established a visual physical simulation experimental apparatus and process, and analyzed the main factors affecting the production efficiency of gas injection wells in combination with the actual development of oilfields. The research results demonstrate that the primary types of remaining oil after water flooding in fractured-vuggy carbonate reservoirs are oil at the top of karst caves, oil shielded from high flow channels and oil not swept by the wells. The mechanism of gas injection-enhanced oil recovery is primarily composed of three aspects. First, the injected gas forms a secondary gas cap because of the effect of gravitational differentiation, and the gas cap can displace the remaining oil on top of the karst cave that the injected water cannot drive; Then, injected gas can change the pressure field distribution and the direction of fluid flow after water injection, driving the remaining oil that is shielded by high flow diversion channels; in addition, the injected gas has a certain effect on the reservoir energy supply. The geological conditions, such as the remaining reserves of injecting gas wells, filling level, well-reservoir position relationship and bottom water energy, have great influence on the development effect. The starting time of gas injection has an optimal point, and injecting too early or late will affect the oil recovery. The cyclic gas injection quantity and gas injection velocity are the primary injection production parameters that influence the production effect of a gas injection well. Finally, the principle of selecting a well for gas injection according to the research results is discussed, which can provide reference for selecting gas injection wells and injection methods of fractured-vuggy reservoirs in Tahe Oilfield.

Bubble formation regimes during gas injection into a liquid cross flow in a conduit

AbstractA study was performed to characterize the different bubble formation regimes that occur during the process of gas jet injection into a liquid cross flow in a conduit. Air was injected perpendicularly into a turbulent, fully developed water flow circulating through a 12.7 mm square channel. Three different gas injectors, with diameters of 0.27 mm, 0.52 mm, and 1.59 mm were used. The bulk water velocity values ranged between 1.1 and 4.3 m/s. The effects that the gas injection velocity, liquid mean velocity, and injection gas injection diameter have on the process of bubble generation were investigated. A high‐speed visualization technique was used to determine the regimes near the gas inlet region. Four distinct regimes were identified: Single Bubbling (SB), Pulse (P), Elongated Jetting (EJ), and Atomizing Jetting (AJ). It was observed that the shift between regimes occurs gradually, producing the need to identify transitional regions: SBP and PTJ. Sets of independent dimensionless variables were used to categorize the proposed regimes using bubble formation maps. It was determined that the injection diameter plays a primary role in jet formation: as the injection diameter increased, the observable number of regimes decreased, indicating a more stable and continuous process of bubble generation. Empirical correlations that delimit the boundaries between ordered and chaotic bubble generation are presented.

Effect of microbubble generator operating parameters on oxygen transfer efficiency in water

This study utilized multistage orifice microbubble generator to investigate dissolved oxygen (DO) formation characteristics and to increase its efficiency, by considering saturator pressure, water supply, and gas flow rates as the main operating factors. The effect of changing the parameters was described in terms of dissolution performance using volumetric mass transfer rate, which is very important element for aerator design and scale-up. Pressure values from 1 to 6 atm were taken for the analysis. To improve the oxygen transfer efficiency of the multistage orifice, the internal supply line was controlled to circulate the bubbles water up to 300% cycling. The volumetric mass transfer coefficient was limited below 0.01 per min for air; however, the value varied from 0.10 to 0.13 per min for oxygen at 4.5 L/min flow rate, showing increasing pattern with pressure. The transfer characteristic was doubled, with circulating ratio applied, because circulation could multiply the number of microbubbles. Examining the various operating conditions within the range set for the cost to generate 1 kg of DO, under gas injection velocity of 1.27 m/s, higher liquid pressurization showed lower cost per production in case of oxygen than air. Thus, natural water bottom area environment can be economically improved using oxygen microbubbles, considering the excessive dissolution.

VOC decomposition by a plasma-cavity combustor

Volatile organic compounds (VOCs) are hydrocarbon gases produced from processes including painting and drying. The diluted VOCs have low calorific heat and their stable combustion cannot be ensured by direct combustion.A novel plasma-cavity combustor (NPCC) was proposed to remove the VOCs with higher destruction and lower energy. The NPCC is a combined technology, consisting of a plasma burner, a 3D matrix burner, and a cavity combustor.The characteristics of representative VOC removal were examined according to selected parameters that serve as important factors for the VOC decomposition. Measurements obtained confirmed that the NPCC made VOC destruction possible with the following optimal operating conditions; when the VOC injector was placed inside and a 3D matrix was installed at a gas injection velocity of 4.17m/s and electric input power of 100W. Said conditions generated VOC decomposition efficiency of 99%, while energy efficiency was 447 g(kWh)−1.

Particles mixing induced by bubbles in a gas‐solid fluidized bed

The effect of bubble injection characteristics on the mixing behavior of a gas‐solid fluidized bed is investigated using a discrete particle model. The effect of different parameters including gas injection time, velocity, and mode are studied. Simulation results show that injecting gas at a constant gas flow rate in the form of small bubbles results in a better overall particle mixing. It was also found that the injection velocities have limited effect on particle mixing behavior for the same total gas volume injected into the bed. Moreover, the mixing index (MI) of continuous gas jet bubbling regime is compared with the MI obtained in uniform gas injection regime and the results revealed that the MI of continuous jet bubbling regime has a larger value than that of uniform gas injection regime at the fixed total gas flow rate. In both regimes, z‐direction MI is larger than x‐direction index. The differences between two direction indices are more noticeable in continuous jet bubbling in comparison with the uniform gas injection regime. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1430–1438, 2016

A new empirical model for self-leveling behavior of cylindrical particle beds

ABSTRACTDuring the material relocation phase of core disruptive accidents in sodium-cooled fast reactors, the rapid quenching and fragmentation of molten materials discharged from the reactor core into the lower plenum region can lead to the formation of debris beds. Coolant boiling may lead to leveling of the mound-shaped beds, which changes both the beds' coolability with decay heat in the fuel and the neutronic characteristics. In this study, a series of experiments using simulant materials were performed to develop an experimental database of self-leveling processes of particle beds in a cylindrical system. To simulate the coolant boiling in the beds in the experiments, a gas injection method was used to percolate nitrogen gas uniformly through the base of a bed with a conical-shaped mound. Time variations in bed height during the self-leveling process were measured for different particle sizes, densities and sphericities, and gas injection velocities. Using a dimensional analysis approach, a new model was proposed. This model correlates the experimental data on transient bed height with an empirical equation using a characteristic time for self-leveling development and an equilibrium bed height. The proposed model reasonably predicts the self-leveling development of particle beds.

A three-dimensional refined modeling for the effects of SF6 release in ionosphere

The traditional simulation model of sulfur hexafluoride ionosphere release is a simple point-source model and the simulation precision is not high. The three-dimensional refined simulation model of rocket SF6 release is established in this paper, in which the rocket pose and velocity, gas injection velocity and flow, and wind velocity are all taken into account in the diffusion equation. Meanwhile, the influences of geomagnetic inclination and the field diffusion on artificial disturbance form are considered in the plasma diffusion equation, and the two-dimensional plasma diffusion equation is extended to three-dimensional case. The ray tracing method is used to study the influence of ionospheric artificial disturbance on the short wave propagation path. The research results of the ionosphere kinetics process, ionospheric uneven body generation mechanism and evolution are of great significance.

Radial pressure profiles in a cold-flow gas-solid vortex reactor.

A unique normalized radial pressure profile characterizes the bed of a gas‐solid vortex reactor over a range of particle densities and sizes, solid capacities, and gas flow rates: 950–1240 kg/m3, 1–2 mm, 2 kg to maximum solids capacity, and 0.4–0.8 Nm3/s (corresponding to gas injection velocities of 55–110 m/s), respectively. The combined momentum conservation equations of both gas and solid phases predict this pressure profile when accounting for the corresponding measured particle velocities. The pressure profiles for a given type of particles and a given solids loading but for different gas injection velocities merge into a single curve when normalizing the pressures with the pressure value downstream of the bed. The normalized—with respect to the overall pressure drop—pressure profiles for different gas injection velocities in particle‐free flow merge in a unique profile. © 2015 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 61: 4114–4125, 2015

Enhanced foam stability by adding comb polymer gel for in-depth profile control in high temperature reservoirs

Abstract A long-term stability of gel enhanced foam as an in-depth profile control agent in high temperature reservoirs was successfully prepared by adding comb polymer gel. The increased viscosity of gel brings a negative effect on surface tension which reduces the gel enhanced foam volume. In turn, the increased viscosity could enhance the thickness and strength of foam film which increases foam stability and plugging capacity in porous media. The morphology results show that the gel enhanced foam has a thicker bubble film which enhances its foam stability. The effect of injection mode, gas–liquid ratio, gas injection velocity and formation permeability on the plugging capacity was investigated by single sand-pack experiments. When the gas–liquid ratio and gas injection velocity were respectively set at 1:1 and 0.5 ml/min, co-injection of gel enhanced foaming solution and gas could obtain a better plugging capacity in high permeability sand-packs. Parallel sand-pack experiments show that the profile improvement capacity of high formation permeability ratio is much better than that of low formation permeability ratio. The visual simulation experiment was also conducted to illustrate the flowing behavior of gel enhanced foam. By Jiamin effect or Jamin superimposed effect, directly plugging and bridging in the large pore space, the gel enhanced foam can effectively reduce the permeability of porous media in high permeability zones and divert fluid into low permeability zones, thus increases the swept volume. The treatment has been successfully used in Henan oilfield of China which provides a reference to water production control in other similar high temperature oilfields.

Solids velocity fields in a cold-flow Gas–Solid Vortex Reactor

In a Gas–Solid Vortex Reactor (GSVR), also referred to as a Rotating Fluidized Bed in Static Geometry, a fluidized bed is generated in a centrifugal field by introducing the gas via tangential inlet slots to the reactor chamber. Better heat and mass transfer are observed, making this a promising reactor type for Process Intensification. Developing GSVRs on industrial scale requires, amongst other, a good insight and understanding of the hydrodynamics of the granular flow. In the present work experiments are performed over a wide range of operating conditions in a cold flow pilot-scale set-up. The set-up has a diameter of 0.54m, a length of 0.1m and 36 tangential inlet slots of 2mm. Different materials with solids density between 950–1800kg/m3 and particle diameters of 1–2mm, at varying gas injection velocities from 55 to 110m/s are tested between minimum and maximum solids capacities. All these operating conditions are used to follow the change of granular flow by performing PIV. The rotating fluidized bed can change from a smoothly rotating, densely fluidized bed to a highly bubbling rotating fluidized bed depending on the operating conditions. Bubbling diminishes with increasing solids density and particle diameter. Experimental measurements of azimuthal particle velocity fields in a GSVR are for the first time reported. Azimuthal solids velocity is found to decrease with higher solids density and larger particle diameter. The critical minimum fluidization velocity, that is the minimum velocity at which the complete bed is fluidized, is calculated and the centrifugal bed behavior is mapped in terms of a dimensionless radial gas velocity and a dimensionless particle diameter, as conventionally done for gravitational beds.

Numerical study of particle segregation in a coal beneficiation fluidized bed by a TFM–DEM hybrid model: Influence of coal particle size and density

Abstract Particle segregation behavior in a coal beneficiation fluidized bed (CBFB) is numerically studied using a TFM–DEM hybrid model, in which the gas and the dense solid phases are modeled using a Eulerian–Eulerian or two fluid model (TFM), while the beneficiated coal particles are modeled as a dilute phase by the discrete element method (DEM). For validation purpose, the numerical model was setup using geometric and operating conditions similar to a laboratory experimental model with the bed thickness set to one particle diameter to save computational cost. For a fixed gas injection velocity, the influence of particle size and density of the beneficiated samples was studied. It was found that the particles would segregate along the bed height due to the density differences with the degree of segregation being strongly influenced by particle size. Obvious segregation occurs for the coarse samples (6.7 mm and 4.3 mm) and little segregation occurs for the particles smaller than 3 mm. The flow patterns and segregation kinetics were qualitatively comparable with those observed in physical experiments conducted under similar conditions. On this basis, the underlying mechanisms governing particle segregation have been explained in terms of the hydrodynamic forces acting on individual particles. It was demonstrated that the segregation of coarse particles was mainly controlled by the balance between gravity and the local pressure force, while fine particles were more strongly affected by the direct drag forces from the gas phase and the continuum solid phase, thus making them difficult to separate.

Development of a gliding arc plasma reactor for CO2 destruction

A gliding arc plasma reactor was designed to destruct carbon dioxide (CO2), which is a major greenhouse gas. To increase the CO2 destruction rate with a high processing gas volume, an orifice baffle for gathering the gas flow at the centre of the electrodes was installed in the gliding arc plasma reactor. The CO2 inflows with methane (CH4) and steam (H2O) improve the CO2 destruction. The parametric studies have been made of the change of CH4 addition, gas injection velocity of the centre nozzle, change of CO2 gas flow rate, and orifice baffle configuration. The produced gases were measured, and the data analysis has been achieved in determining the CO2 destruction rate, CH4 conversion rate, destruction energy efficiency, and selectivity for CO2 and H2. The highest CO2 destruction rate for each parameter has been shown as follows: the CH4/CO2 ratio is 1 as 40%, and the injection gas velocity is 69.5 m/s as 35.7%, the CO2 flow rate is 5 L/min as 42.6%, and the orifice baffle is Type 1, which had the smallest internal area, as 35.7%.

Numerical Study of Effect of Injection Parameters on Combustion and Emission Performance of a Direct Injection Diesel-Natural Gas Engine

By using AVL FIRE code, three-dimensional numerical simulations of the diesel-natural gas injection characteristics in a direct injection diesel-natural gas engine were conducted. The effects of the start of injection (SOI) of the pilot diesel and natural gas injection velocity on combustion and emission performance were investigated. The results showed that diesel-natural gas injection characteristics have an important influence on the subsequent combustion and emission. NO and Soot emission performance is better when the SOI was 36°BTDC (Before Top Dead Center), and a larger natural gas injection velocity usually leads to a lower engine economical efficiency.

Bed stability and maximum solids capacity in a Gas–Solid Vortex Reactor: Experimental study

A Gas–Solid Vortex Reactor (GSVR), in literature also referred to as Rotating Fluidized Bed in Static Geometry (RFB-SG), is a promising reactor type for Process Intensification (PI) with respect to reactor volume reduction. Although replacing gravitational by centrifugal force has been considered since the seventies, the hydrodynamics of the reactor flow and the bed behavior remain largely unknown. In the present work experiments have been carried out in a cold flow GSVR with diameter of 0.54m, length of 0.1m and 36 inlet slots of 2mm. Gas injection velocities of 55–111m/s and particles with densities of 950–1800kg/m3 and diameters of 1–2mm have been applied. Depending on solids density, particle diameter and gas injection velocity the bed behavior can be considered as stable, semi-stable or unstable. For semi-stable and stable flow regimes the effect of the above process conditions on the maximum solids capacity was investigated. With increasing solids density, the bed stability considerably decreases, while the maximum solids capacity increases. By increasing the gas injection velocity, both the bed stability and the maximum solids capacity increase. Once bed stability is accomplished, a further increase of the gas injection velocity does not affect the maximum solids capacity. With increasing particle diameter, the bed stability decreases while the maximum solids capacity increases.

Raceway formation in laterally gas-driven particle beds

The formation of a circulating region of particles or ‘raceway’ occurs in many processes when gas is laterally injected into a bed of particles. The granular dynamics occurring during raceway formation is still, however, not fully understood as there are significant technical difficulties to experimentally gathering data within an active particle bed. We use a coupled Discrete Element and Navier–Stokes numerical solver to simulate these systems in order to investigate the dependency of raceway formation and dynamics on gas injection velocity, particle shape and bed pressure. Lateral gas injection into a particle bed is found to give a transition from static to circulating particle flow at a specific gas inflow velocity. A theoretical model is presented, based on a force balance at the gas inlet location, giving an expression for this gas inflow velocity. This model gives good agreement with numerical simulations, showing that raceway formation is governed by the balance between lateral bed loading and the drag forces on particles around the gas inlet. Furthermore, we find that non-spherical particles can form raceways at lower gas inflow velocities than spherical particles. Highly aligned, packed, regions are also observed in simulations of non-spherical particles, closely corresponding to the location of high-density regions found in experimental measurements.

Effect of refractory properties on initial bubble formation in continuous-casting nozzles

A water model has been applied to investigate initial bubble behavior using specially-coated samples of porous MgO refractory to simulate the high-contact angle of steel-argon refractory systems with different permeabilities. Air is injected through the porous refractory and travels through many inter-connected pores to exit the surface through “active sites”. An active site is a pore where bubbles exit from the surface of the porous refractory. The effect of refractory properties has been investigated in both stagnant and downward-flowing water. The number of active sites increases with increasing gas injection flow rate, permeability, and velocity of the downward-flowing water, and lower contact angle.

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.

Aerodynamics of a slender axisymmetric Bunsen flame with large gas expansion

The flow around a stationary axisymmetric premixed flame attached to a plug flow Bunsen burner and propagating with a constant burning velocity relative to the fresh gas is analyzed for large values of the ratio of fresh gas injection velocity to flame burning velocity and small values of the burnt-to-fresh gas density ratio. The shape of the flame is close to a cone of small semiangle, and its presence induces only a small perturbation in the fresh gas. The velocity of the burnt gas is the superposition of a uniform axial velocity and the velocity induced by a line of sources on the axis of the burner. The pressure of the burnt gas on the flame is the sum of a uniform part that does not change the velocity of the fresh gas and a small variable part that causes a vertical acceleration of this gas and a slight deformation of the flame. Only a weak vorticity is generated at the flame. The analysis breaks down in small regions around the tip and the base of the flame where the assumption of a constant burning velocity is not valid.

String Corrosion and String Protection During Constructing and Operating Gas Storage Facility in Bedded Salt Deposit

Summary With more and more salt cavern gas storage under construction, the corrosion problems of leaching string, production string, and production casing require more attention by experts on gas storage. This paper introduces several corrosion phenomena that are encountered during the operation of leaching salt caverns and during natural-gas injection and withdrawal. The main corrosion factors are discussed such as brine, air, microbes, components of natural gas, gas injection velocity, operating status, and others. The corrosion mechanisms are also analyzed. To prevent the corrosion effects, a series of measures are successfully applied during different construction phases of the gas storage facility in the Yangtze River Delta, such as oxygen scavenger and biocide, coating protection, annulus protection liquid, and cathodic protection.