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1.
There has never been any fundamental explanation presented for the transition from the bubbling regime to the jetting regime
when gas is injected into liquid at high velocity through submerged tuyeres. This is an important issue in metallurgical processes,
since the flow regime is known to influence refining rates, refractory erosion, and the penetration of the liquid into the
tuyere. Based on the observation that many small droplets of liquid and gas bubbles are formed to create the jets, a combined
Kelvin-Helmholtz and Rayleigh-Taylor instability analysis has been applied to bubbles forming at submerged tuyeres. For particular
wavelengths of disturbances, the interface will be unstable and create bubbles and droplets. The critical injection velocity
for instability depends on surface tension, tuyere diameter, and the gas-to-liquid density ratio, which can be summarized
by We = 10.5(ρ*)−1/2, where We is the Weber number based on the gas velocity and density and tuyere diameter, and ρ* is the gas-to-liquid density
ratio. The importance of surface tension had not been appreciated previously for this regime of gas injection. There is considerable
controversy in the literature concerning the measurement of the transition from bubbling to jetting. The 70 pct “linking”
point, proposed by Ozawa and Mori, describes the situation where 70 pct of the bubbles link with the preceding bubbles and
produce a reasonably steady jet. The theoretical correlation developed above predicts the velocity to reach this point ±20
pct (95 pct confidence level) in a variety of systems from six different groups of workers. The theoretical analysis demonstrates
that the instabilities are primarily capillary in nature, not gravity waves, which explains the observation that orientation
has little effect on the jetting transition. 相似文献
2.
A. A. Bustos G. G. Richards N. B. Gray J. K. Brimacombe 《Metallurgical and Materials Transactions B》1984,15(1):77-89
Injection phenomena in a Peirce-Smith copper converter and a slag fuming furnace have been investigated during blowing. A
tuyerescope attached to the back of a given tuyere has been employed to observe the build-up, and to obtain samples, of accretions
while a piezoelectric transducer has been used to measure pressure fluctuations in the tuyere. It has been found that in both
processes the accretions grow upward by a freezing mechanism from the bottom of the horizontal tuyere. Probing the shape of
an accretion in the fuming furnace, without coal injection, showed that the accretion grew into the bath 30 to 40 mm from
the tuyere tip. A study of the shape and frequency of the pressure pulses as well as the duration of intervals of low pressure
in the tuyere has revealed that the closely spaced tuyeres may operate independently or may interact. Tuyeres in a full slag
fuming furnace act independently of one another, and the air discharges in the classical bubbling regime at 5 to 6 bubbles
per second. In the copper converter there is more tuyere interaction as bubbles growing at adjacent tuyeres coalesce to form
a horizontal unstable gas envelope. In both processes if the tuyeres are shallowly submerged the gas may channel directly
to the surface without forming bubbles. The influence of bath viscosity, the extent of wall erosion at the tuyere line, and
tuyere submergence on these injection phenomena have been elucidated qualitatively.
G.G. RICHARDS, formerly Graduate Student 相似文献
3.
The mathematical model developed for the molten steel flow in the combined side and top blowing AOD refining process of stainless steel has been used to compute and analyze the flow fields of the liquid phases in the baths of the 120 t AOD converter and its water model unit with a 1/4 linear scale. The influence of the side tuyere number and the angle between each tuyere on the flows has been examined. The results demonstrate that the mathematical model can quite reliably and well model and predict the fluid flow in an AOD bath with the combined blowing. The liquid flow in an AOD converter bath with the combined blowing is resulted from the gas side blowing streams under the influence of a gas top blowing jet. The streams play a governing role on it; and the liquid in the whole bath is in active agitation and circulatory motion during the gas blowing process. The gas jet from the top lance does not change the essential features of the gas stirring and liquid flow in the bath, but can make the local flow pattern of the bath liquid obviously vary and its turbulent kinetic energy enhance. The changes in the tuyere position and number have similarly not altered the basic characteristics and patterns of the gas agitation and liquid flow and turbulent kinetic energy distribution in the bath. At a given tuyere number and gas side blowing rate or a given angular separation between each tuyere and gas side blowing rate, however, the variation of the angle between each tuyere or the tuyere number can locally change them. Using 6 tuyeres with 27° can reach the more uniform flow field and turbulent energy distribution of the liquid in the bath than taking 7 tuyeres with 18° or 22.5° and 6 tuyeres with 22.5°. 相似文献
4.
The mass transfer characteristics in a steel bath during the AOD refining process with the conditions of combined side and top blowing were investigated. The experiments were conducted on a water model unit of 1/4 linear scale for a 120‐t combined side and top blowing AOD converter. Sodium chloride powder of analytical purity was employed as the flux for blowing, and the mass transfer coefficient of solute (NaCI) in the bath was determined under the conditions of the AOD process. The effects of the gas flow rates of side and top blowing processes, the position arrangement and number of side tuyeres, the powdered flux particle (bubble) size and others on the characteristics were examined. The results indicated that, under the conditions of the present work, the mass transfer coefficient of solute in the bath liquid is in the range of (7.31×10?5‐3.84×10?4) m/s. The coefficient increases non‐linearly with increasing angle between each tuyere, for the simple side blowing process at a given side tuyere number and gas side blowing rate. The gas flow rate of the main tuyere has a governing influence on the characteristics, and the gas jet from the top lance decreases the mass transfer rate, the relevant coefficient being smaller than that for a simple side blowing. Also, in the range of particle (bubble) size used in the present work and with all other factors being constant, raising particle (bubble) size increases the coefficient. Excessively fine powder particle (bubble) sizes are not advantageous to strengthening the mass transfer. With the oxygen top blowing rate practiced in the industrial technology, the side tuyere arrangements of 7 and 6 tuyeres with an angular separation of 22.5° and 27° between each tuyere, as well as 5 tuyeres with an angle of 22.5° between each tuyere can provide a larger mass transfer rate in the bath. Considering the relative velocity of the particles to the liquid, the energy dissipation caused by the fluctuation in the velocity of the liquid in turbulent flow and regarding the mass transfer as that between a rigid bubble and molten steel, the related dimensionless relationships for the coefficient were obtained. 相似文献
5.
The fluid flow in a bath in combined top and bottom blowing vacuum‐oxygen decarburization (VOD) refining process of stainless steel has numerically been simulated. The three‐dimensional mathematical model used is essentially based on that proposed in our previous work for the flow in combined side and top blowing argon‐oxygen decarburization (AOD) process, but considering the influence of reduced ambient pressure. Applying it to the flow in the bath of a 120 t VOD vessel under the refining conditions, the results present that the model can fairly well simulate and estimate the flow phenomena. The flow pattern of molten steel in the bath with the combined blowing is a composite result under the common action of the jets from a three‐hole Laval top lance and gas bottom blowing streams. The jets have a leading role on it; the molten steel in the whole bath is in vigorous stirring and circulatory motion during the blowing process. The streams do not alter the basic features of the gas agitation and liquid flow, but can evidently change the local flow pattern of the liquid and increase its turbulent kinetic energy to a certain extent. The flow field and turbulent kinetic energy distribution in the combined blowing with three tuyeres are more uniform than those in the blowing with double tuyeres. Increasing properly the tuyere eccentricities is of advantage for improving the velocity and turbulent kinetic energy distributions, the stirring and mixing result in the practical VOD refining process. 相似文献
6.
A mathematical model of accretion growth on single-pipe injectors has been used to analyze the process of accretion growth
during copper converting and inert gas stirring of steel. A sen-sitivity analysis of the model developed in Part I of this
article revealed that the critical unknown factor controlling the growth process is the local bath velocity. It is likely
that the asymmetric forms seen in accretions are due primarily to nonuniformity in bath flow around the accretion. The important
factors controlling the size of accretions in copper converting are bath superheat, gas flow rate, and oxygen content. Blockage
of the tuyeres in the converter is a function of wall and bath superheat and likely is a result of the freezing of matte in
the pipe. The effect of gas-flow rate on accretion size is clearly shown in the case of inert gas injection into steel. The
transition between the different accretion types found on single-pipe tuyeres, pipes, porous pipes, and hemispheres, depends
on events at the tuyere-pipe tip. Conditions of high back-attack frequency, low superheat, and small tuyere diameters tend
to lead to accretions forming over the tip. If this takes place at high injection pressures and with a relatively ductile
material, a “porous plug” will form, on which a hemisphere will grow. Under other conditions, it may result in a blockage.
The presence of accretions at a tuyere has a strong influence on the thermal profile in the surrounding refractory and tuyere
pipe. Steep thermal gradients near the tip in both regions will likely lead to refractory deterioration and pipe distortion.
Formerly Associate Professor, University of British Columbia, Vancouver. 相似文献
7.
Ji‐He Wei Hong‐Li Zhu Sen‐Long Yan Xin‐Chao Wang Jin‐Chang Ma Guo‐Min Shi Qing‐Yan Jiang He‐Bing Chi Li‐Bing Che Kai Zhang 《国际钢铁研究》2005,76(5):362-371
The fluid mixing characteristics in the bath during the side and top combined blowing AOD (argon‐oxygen decarburization) refining process of stainless steel were preliminarily investigated on a water model unit of a 120 t AOD converter. The geometric similarity ratio between the model and its prototype (including the side tuyeres and the top lances) was 1:4. On the basis of the theoretical calculations for the parameters of the gas streams in the side tuyeres and the top lances, the gas blowing rates used for the model were more reasonably determined. The influence of the tuyere number and position arrangement, and the gas flow rates for side and top blowing on the characteristics was examined. The results demonstrated that the liquid in the bath underwent vigorous circulatory motion during gas blowing, without obvious dead zone in the bath, resulting in a high mixing effectiveness. The gas flow rate of the main tuyere had a governing role on the characteristics, a suitable increase in the gas flow rate of the subtuyere could improve mixing efficiency, and the gas jet from the top lance made the mixing time prolong. Corresponding to the oxygen top blowing rate specified by the technology, a roughly equivalent and good mixing effectiveness could be reached by using six side tuyeres with an angle of 27 degrees between each tuyere, and five side tuyeres with an angular separation of 22.5 or 27 degrees between each tuyere. The relationships of the mixing time with the gas blowing rates of main‐tuyeres and sub‐tuyeres and top lance, the angle between each tuyere, and the tuyere number were evaluated. 相似文献
8.
Investigations were carried out in a water model of bottom-blown oxygen steelmaking processes like OBM/Q-BOP to understand
certain aspects of the dynamics of these processes. Wall shear stress along the bottom of a cylindrical plexiglass model vessel
was measured as a function of process parameters, using the electro-chemical technique. Experiments were conducted with one,
three, six and twelve tuyeres in various geometrical configurations. Air was used to simulate the gases blown into the bottom-blown
converters. In single-tuyere experiments, two concentric pipes were employed and air was distributed between the inner pipe
and the annular region to simulate oxygen and the shrouding gas respectively. It was found that the wall shear stress (τ)
decreased drastically with increasing distance from the tuyere. The rms value of the fluctuations (τ′) in shear stress were
directly proportional to the time-averaged value (τ). Percentage air in the annulus and the length of tuyere protrusion into
the bath had significant effect on t only at points close to the tuyere. Dimensionless correlations have been attempted for
these variables at the point closest to the tuyere at which measurements have been made. Results of visual observations and
photogaphy are also reported. Multiple-tuyere experiments were conducted with the tuyeres in symmetric and asymmetric arrangements.
It was observed that for any tuyere configuration rms value of τ′ was proportional to t. There seem to be an optimum number
of tuyeres for minimizing shear stress along the bottom. Asymmetric arrangement of tuyeres resulted in higher level of shear
stress. An attempt has been made to relate the observations of the study to the wear of the bottom ref actory lining.
N.B. Ballal formerly a graduate student at Indian Institute of Technology, Kanpur 相似文献
9.
The behavior of gas discharging into melts at high velocities but still in the bubbling regime has been investigated in a
laboratory modeling study for constant flow conditions. Air or helium was injected through a vertical tuyere into water, zinc-chloride,
and aqueous glycerol solutions. High speed cinematography and pressure measurements in the tuyere have been carried out simultaneously.
Pressure fluctuations at the injection point were monitored and correlated to the mode of bubble formation. The effects of
high gas flow rates and high liquid viscosities have been examined in particular. Flow rates were employed up to 10-3 m3/s and viscosity to 0.5 Ns/m2. In order to attain a high gas momentum, the tuyere diameter was only 3 x 10-3 m. The experimental conditions and modeling liquids were chosen with special reference to the established practice of submerged
gas injection to treat nonferrous slags. Such slags can be highly viscous. Bubble volume is smaller than that calculated from
existing models such as those given by Davidson and Schüler10,11 due to the effect of gas momentum elongating the bubbles.
On the other hand, viscosity tends to retard the bubble rise velocity, thus increasing volumes. To take elongation into account,
a mathematical model is presented that assumes a prolate ellipsoidal shape of the bubbles. The unsteady potential flow equations
for the liquid are solved for this case. Viscous effects are taken into account by noting that flow deviates from irrotational
motion only in a thin boundary layer along the surface of the bubble. Thus, drag on the bubble can be obtained by calculating
the viscous energy dissipation for potential flow past an ellipse. The time-dependent inertia coefficient for the ellipsoid
is found by equating the vertical pressure increase inside and outside the bubble. This pressure change in the bubble is obtained
by assuming that gas enters as a homogeneous jet and then calculating the stagnation pressure at the apex of the bubble. 相似文献
10.
A unified approach to bubbling-jetting phenomena in powder injection into iron and steel 总被引:1,自引:0,他引:1
The injection of powder into liquids has been investigated by physical modeling and by multi-phase fluid dynamic modeling.
The transition from gas-particle jets which penetrate deeply into the liquid and a gas bubbling regime was found to depend
on the coupling between gas and particle phases in the conveying line; fine particles at high loading couple well and form
jets, whereas coarse particles separate from the gas during bubble formation. The measured penetration depths of submerged
jets in water and lead and top jets in water were very well described by equations balancing the momentum of the jet and its
buoyancy. A regime of particle-liquid jets that forms in conjunction with bubbling also appears to depend on coupling, between
the particle and liquid phases. The effect of surface tension on the particle penetration through a bubble interface was modeled
for the single particle and multi-phase cases and compared with the work of others. On the basis of this modeling, the expected
regime of flow for many powder injection conditions can be predicted. The flow regimes of existing processes are discussed,
and guidelines for the design of processes employing various types of reactions are presented.
Formerly with McMaster University during the course of this work, 相似文献
11.
Factors affecting bubble overlap (interaction) in multipoint (multituyere/lance) gas-injection systems such as the Pierce-Smith
converter and the zinc-fuming furnace have been investigated in laboratory room-temperature modeling experiments and at the
industrial scale. Pressure changes have been recorded simultaneously from adjacent tuyeres both in the laboratory and in plant
trials. It has been found that the factors which influence bubble overlap include the tuyere separation to tuyere diameter
ratio, gas injection velocity, gas and liquid properties, and position and orientation of the tuyeres. 相似文献
12.
A room temperature model of a submerged gas-particle jet was used to investigate the hydrodynamics and gas-liquid mass transfer
in such systems. Air or CO2 was used to inject particles of silica sand into water. In some cases, the sand was coated with resin to produce a hydrophobic
surface. The flow regimes of behavior were observed: In the bubbling flow regime large bubbles of gas are formed and penetrated
by a stream of particles which did not entrain gas, and in the steady jet flow regime the gas and particles travel together
in a narrow cone. The second flow regime is favored by a high gas velocity, a small particle size, and a high ratio of particles
to gas in the jet. The surface characteristics of the injected particles do not appear to affect this transition. A CO2-NaOH solution model was used to determine the effects of inert particle injection of the rate of mass transfer from gas to
liquid. The rate of mass transfer was higher in steady cone jets, because under these conditions, the gas is dispersed into
finer bubbles and carried deeper in the bath.
Formerly Graduate Student in the Department of Civil Engineering, Mechanics, and Metallurgy, University of Illinois at Chicago 相似文献
13.
Model study of mixing and mass transfer rates of slag-metal in top and bottom blown converters 总被引:2,自引:0,他引:2
Water model experiments have been conducted to clarify mixing rates of molten steel and mass transfer rates between slag and
metal in LD and Q-BOP furnaces using six different circular tuyere arrangements. Splashing and ‘spitting’ were also examined
with a view to finding a quiet bath with minimum mixing time and maximum mass transfer rate. Froude’s similarity criterion
was fulfilled to determine gas flow rate and bath depth. Complete mixing time of water determined by tracer technique had
been 0.9 second to 1.8 seconds for Q-BOP as compared to 6 seconds to 13 seconds for LD. This shows that the stirring intensity
in Q-BOP is remarkably larger than that of LD. A simple relationship τ = 5.9(Q/N)
−0.49 was obtained with gas flow rateQ and number of tuyereN. This indicates that flow rate of gas per tuyere should be intensified to realize better mixing. Mass transfer coefficient
KBa for bottom blowing was found to be almost double that for top blowing. Of all the tuyere configurations studied for Q-BOP’s,
a half circular tuyere arrangement was found to be the best considering all aspects of mixing, mass transfer, and bath agitation. 相似文献
14.
15.
16.
Measurement of the velocities of bubbles and liquid with a two-element electroresistivity probe and laser-Doppler velocimeter,
respectively, during bottom injection of air into a water bath, has confirmed the existence of a critical gas-injection rate.
Above the critical flow rate, the change of axial bubble velocity in the air jet, and of liquid velocity with increasing volume
flow rate, diminishes markedly. The existence of the critical flow rate is explicable from high-speed motion pictures of the
vertical gas jets, which reveal four zones of gas dispersion axially distributed above the orifice: primary bubble at the
orifice, free bubble, plume consisting of disintegrated bubbles, and spout at the bath surface. With increasing gas-injection
rate, the free-bubble zone expands such that the point of bubble disintegration rises closer to the bath surface. Above the
critical flow rate, the free bubbles rise with minimal breakup and erupt from the bath surface with maximum energy discharge.
The combined Kelvin-Helmholtz, Rayleigh-Taylor instability theory has been applied to analyze the bubble breakup in the bath
and the critical gas-injection rate in a gas-stirred ladle. The criterion for the critical diameter of bubble breakup has
been found to depend primarily on the surface tension and density of the liquid. In the analysis, the propagation time of
a disturbance on a bubble surface at the “most unstable” wave number has been compared with the bubble rising time in the
bath in order to determine the critical gas-flow rate. The predicted critical values are in close agreement with the measured
results.
M. ZHOU formerly was Post Doctoral Fellow with the Centre for Metallurgical Process Engineering, University of British Columbia,
Vancouver, BC, Canada V6T 1Z4
J.K. BRIMACOMBE holds the Alcan Chair in Materials Process Engineering 相似文献
17.
The gas fraction and bubble frequency distributions in a submerged air jet, injected horizontally into mercury, have been
measured under isothermal, nonreactive conditions for nozzle diameters of 0.325 and 0.476 cm and jet Froude numbers ranging
from 20.5 to 288. The measurements reveal that the jets expand extremely rapidly upon discharge from the nozzle with an initial
expansion angle of 150 to 155 deg. This value, which is over seven times greater than is found with air jets in water, indicates
that the physical properties of the liquid exert considerable influence on the jet behavior. In conjunction with the rapid
expansion, the air jets in mercury were also found to penetrate extensively behind the nozzle, and in many respects resembled
a vertically injected jet. The extent of backward penetration of the jets was constant for all blowing conditions studied
while the forward penetration increased with both increasing jet Froude number and nozzle diameter. The measured jet penetration
in both the forward and backward directions were considerably larger than expected from model predictions. The core of the
jets consists of a high concentration of gas bubbles. Both the gas volume fraction and bubble frequency in the core increase
with increasing jet Froude number and nozzle diameter. The gas concentration and bubble frequency decrease with increasing
distance along the jet trajectory due presumably to entrainment of liquid metal and bubble coalescence. On the basis of these
findings, it is likely that process jets, such as are injected into copper converters, also expand rapidly and penetrate only
a short distance into the bath. Thus rather than reacting in the middle of the bath, the jets may be impinging on the backwall
refractory and contributing to the erosion observed there. 相似文献
18.
合理调整风口对大型高炉吹透中心、活跃炉缸十分重要。目前,实际操作常常认为增加风口长度、增加风口回旋区深度、缩小风口面积能提高风速,进而提高鼓风动能,以利于吹透中心。建立了调整风口参数的数学模型,并以某厂3 200 m3高炉为例,给出了在总风量不变的条件下,增加1个风口长度、减小1个风口面积以及多个风口尺寸调整时,各风口风量、风速和鼓风动能的变化。发现增加部分风口的长度时,对应风口风量、风速、鼓风动能降低。缩小少数风口的面积,会降低对应风口的风量;只有在缩小多数风口的面积时,已调整的风口风速和鼓风动能才可能提高,而未调整的风口风量、风速和鼓风动能提高幅度更大。根据该数学模型,定量化给出该高炉调整风口的相关参数,可用于调整炉缸煤气流的均匀性,维持高炉稳定、顺行。 相似文献
19.
High speed cinematography and a pressure trace technique have been used to investigate the fluid dynamics of inert gas jets
injected vertically upward into water, molten tin, lead-tin alloy, and iron. Two flow regimes of jet behavior were observed:
one in which unstable bubbles were produced at the jet nozzle, and one in which a steady cone of gas emerged from the nozzle
and broke up continuously into small bubbles. The transition between bubbling and continuous jet flow was controlled by the
mass flow of gas per unit area of the jet and occurred at a flow rate of approximately 40 g/cm2 s in all of the systems studied. 相似文献
20.
A three‐dimensional mathematical model has been developed to predict growth and removal of inclusions during gas stirring through eccentric tuyeres in a ladle. In the model, the efficiency of inclusion removal is investigated under three different collision mechanisms: Brownian, turbulent and Stokes collision. The Importance of the three approaches of wall adhesion, Stokes flotation and bubble adhesion on inclusion removal is analysed and the efficiency of inclusion removal through three types of tuyeres in central, eccentric and multi‐tuyere form is studied. The results indicate that inclusion growth resulting from turbulent collision is most important and the effect of Stokes collision is remarkable with increased inclusion size, while inclusion growth resulting from Brownian collision is negligible. Removal by Stokes flotation is the main mechanism for large inclusions, while inclusion removal by wall adhesion is negligible. The smaller the bubbles are, the higher the efficiency of inclusion removal is. The type of tuyere arrangement has a great effect on inclusion removal. Inclusion removal in a 135t ladle with one eccentric tuyere is more efficient than in a ladle with central tuyere or multi‐tuyere design. 相似文献