Bottom gas injection

Iguchi M, Nakamura K, Tsujino R (1998) Mixing time and fluid flow phenomena in liquids of varying kinematic viscosities agitated by bottom gas injection. Metall Mater Trans B 29 569-... 

The experimental results suggest that empirical correlations of the bubble characteristics and the axial mean velocity and turbulence components of liquid flow, derived from cold model experiments, are applicable to actual reflning processes stirred by bottom gas injection when the radial distributions of gas holdup and bubble frequency follow Gaussian distributions. These distributions appear to be a result of the disintegration of rising bubbles due to highly turbulent liquid motion in the bath. 

Iguchi M, Kondoh T, Morita Z, Nakajima K, Hanazaki K, Uemura T, Yamamoto F (1995) Velocity and turbulence measurements in a cylindrical bath subject to centric bottom gas injection. Metall Mater Trans B 26 241-247... 

Iguchi M, Nakatani T, Okita K, Yamamoto F, Morita Z (1996) Turbulence in reactors agitated by bottom gas injection. ISIJ Int Suppl 36 38-41... 

Iguchi M, Tomida T, Nakajima K, Moiita Z (1993) Mass transfer from a solid body immersed in a cylindrical bath with bottom gas injection. ISU Int 33 728... 

In this section, swirl motions, i.e., tangential oscillation modes of a bubbling jet in a cylindrical bath with centric bottom gas injection are described. The oscillations are classified into two categories and empirical correlations are presented for the critical bath depths for the initiation and cessation of swirl motion and the swirl period. 

A variety of swirl motions are known to occur in a bath agitated by gas injection when the bath surface is exposed to the atmosphere, as described in Sect. 5.2.1.4 [18,23, 29-37]. In particular, two types of swirl motions typically occur in a circular cylindrical bath agitated by single-nozzle bottom gas injection, as schematically illustrated in Fig. 5.6 [29, 30] One is observed over an aspect ratio, H /D, from approximately 0.2-1.0. The other appears for H /D > 2. No swirl motion occurs when the aspect ratio falls in the range of 1.0-2.0. The former swirl motion is caused by bath surface oscillations due to quasi-periodic generation and subsequent arrival of bubbles at the bath surface. It resembles the rotary sloshing of a water bath contained in a circular cylindrical vessel [16,17,38]. The latter is caused by the Coanda effect [26], which appears when a bubbling jet approaches the side wall of the vessel [29,30,39]. 

The mixing time in a cylindrical water bath with aspect ratio between H /D 0.2-1.0 is significantly shortened when the bath is accompanied by the first kind of swirl motion [35, 37]. This motion may thus be beneficial for shortening the mixing time in real refining processes agitated by bottom gas injection. Most of these processes are operated under reduced pressure on the bath surface. However, measurements of the characteristics of the swirl motion and the relationship between the mixing time and the swirl motion in model experiments have been carried out solely under atmospheric pressure on the bath surface. 

Empirical relations for mixing time derived for water baths agitated by bottom gas injection are known to be approximately applicable to molten steel baths [46], This is because the kinematic viscosity of water is approximately equal to that of molten steel. Accordingly, (5.37) would be applicable to molten steel baths in the presence... 

Zaidi A, Sohn HY (1995) Measurement and correlation of drop-size distribution in liquid-liquid emulsions formed by high-velocity bottom gas injection. ISIJ Int 35 234-241... 

Takashima S, Iguchi M (2000) Metal droplet holdup in the thick slag layer subjected to bottom gas injection. Tetsu-to-Hagane 86 217-224... 

As is widely known, mixing in a bath is governed mainly by large-scale recirculation and turbulent motion. The former is characterized by the mean velocity components in the three directions, while the latter is characterized by the root-mean-square (rms) values of the three turbulence components and the Reynolds shear stresses. Desirable mixing condition would be realized when the two kinds of motions are produced together. Unfortunately, these motions on the mixing time in a bath subjected to surface flow control are poorly understood. This chapter discusses these effects with reference to experiments in which three types of boundary conditions are imposed on the surface of a water bath stirred by bottom gas injection. 

Simulations are then performed for gas bubbles emerging from a single nozzle with 0.4 cm I.D. at an average nozzle velocity of lOcm/s. The experimental measurements of inlet gas injection velocity in the nozzle using an FMA3306 gas flow meter reveals an inlet velocity fluctuation of 3-15% of the mean inlet velocity. A fluctuation of 10% is imposed on the gas velocity for the nozzle to represent the fluctuating nature of the inlet gas velocities. The initial velocity of the liquid is set as zero. An inflow condition and an outflow condition are assumed for the bottom wall and the top walls, respectively, with the free-slip boundary condition for the side walls. 

Another type of reactor using a simple injector is a reactor with a dome type cover.In this case, the injector is installed on the bottom plate of the reactor. Figure 11 shows the typical configuration of this type of reactor. In this case the dome is usually heated to a proper temperature by a separate heater to prevent precursor condensation on it. It is rather difficult to expect uniform deposition of a thin film from this asymmetrical gas injection geometry. However, it has actually been proved that good thickness and compositional uniformity are obtained over the 8 wafer surface for Ta O thin films. Figure 12 shows the typical variation in thickness of a Ta O thin film using this reactor. 

The influence of wake motion on bulk turbulence induced in the liquid is understood more clearly by inspecting oscillograms which show the fluctuation of local liquid velocity. Figure 43 shows such oscillograms taken by Kikuchi (K30) with a hot-wire probe. The bubble column is 8.0 cm in diameter, water-filled to a 170-cm height, with the probe 115 cm above the bottom gas distributor. In the column bubbles of constant volume (100 cc) are injected successively at constant time intervals, either at 2.1 sec (case a) or 0.50 sec (case b). Case c is an example of continuous bubbling at f/c = 6.45 cm/sec. 

Figs. 22 top) and 23 bottom). Gas-Kquid chromatograms of the trimethylsilyl derivatives of sulfur-containing amino acids. Column 05% w/w SE-30 on acid-washed, dichlorodimethylsilane-treated Chromosorb G (80-100 mesh) 1 meter X 35 mm i.d. glass initial temperature, 75°, programmed at 4.6° per minute Nj flow 40 ml per minute. Injected mixture contained ca, 5 /tg of each amino acid. Eeproduced from Shahrokhi and Gehrke (S4) with permission. 

Steam or gas injection is required at the bottom of the retort to start the fluidization. However, some or all of this gas may be first used in the ball stripping section. Vapor emitted by retorting adds greatly to the volumetric flow of fluidizing gas as it rises up through the retort. The vessel cross-section is increased accordingly to maintain constant conditions for the dense fluidized bed. 

Inasmuch as oxidized petroleum is more difficult to ignite, it had been decided not to try to inject air into the ignition well (No. 833). Instead, 18 m of crude oil was forced into the formation in order to saturate the bottomhole zone. According to calculations, this quantity of crude oil should have been sufficient to saturate the bed across its full thickness within a radius of 1.1 m from the well. The electrical heater was then lowered to the well bottom, whereupon injection of casing head gas, used as heat carrier, commenced. A control system was installed to measure periodically both the temperature and the consumption of the casinghead gas being injected. 

Gas-injection support plates (Fig. 8.3). These have separate openings for vapor and liquid. Vapor issues from the side openings, and liquid flows through the bottom openings, thus avoiding buildup of hydrostatic head (Fig. 8.26). 

STR with multichamber vertical multicompartment with axial stirring and gas injected at the bottom, cascading vertical multistage. Power 1.5 kW/m gas content 20% maximum volume 120 m. ... 

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