Flow regimes in submerged gas injection |
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Authors: | E O Hoefele J K Brimacombe |
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Affiliation: | (1) Kalium Chemicals, Regina, Saskatchewan;(2) Department of Metallurgical Engineering, University of British Columbia, V6T 1W5 Vancouver, B.C., Canada |
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Abstract: | The behavior of gas discharging into a liquid has been investigated in the labora-tory and in plant. The laboratory work has
involved the injection of different gases from a submerged, horizontal tuyere into water, zinc-chloride solution, and a mercury
bath. High speed cinematography and pressure measurements in the tuyere have been carried out to characterize the flow regimes.
In the case of the mercury bath, a novel “half-tuyere” has been developed to permit visual observation of the gas. In this
way, two regimes of flow, bubbling and steady jetting, have been delineated as a function of the modified Froude number and
the ratio of gas to liquid densities. Pressure measurements at the tuyere tip have been correlated to the different stages
of bubble growth in the bubbling regime, and can be used to distinguish one flow regime from the other. The measured bubble
frequency and volume correspond reasonably well to predictions of a simple model of bubble growth under conditions of constant
flow. The forward penetration of the jet centerline from the tuyere tip has been measured and found to depend both onN
Fr′ andρg/ρl. In the industrial tests, pressure taps have been installed in the tuyeres of a nickel converter to monitor the pressure
wave of the jets under normal, low pressure blowing operations. The measurements show that the converter jets operate in the
bubbling mode with a bubble frequency of 10 to 12 s−1, similar to a gas jet in mercury. Tests involving higher pressure injection indicate that the steady jetting, or underexpanded,
regime obtains at pressures of about 340 kPa (50 psi). Based on equivalent experiments in the laboratory, it is clear that
low pressure blowing has the disadvantage of poor penetration of air into the bath so that the jets rise close to the back
wall and locally accelerate refractory wear. Moreover between the formation of successive bubbles, the bath washes against
the tuyere mouth and contributes to accretion formation. This necessitates periodic punching of the tuyeres which also contributes
to refractory wear at the tuyere line. The use of high pressure injection to achieve steady jetting conditions, as currently
practiced in the new bottom blown steelmaking processes, should be considered to solve these prob-lems, and possibly usher
in a new generation of nonferrous converters. |
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