Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Patent
1993-11-22
1996-04-09
Andrews, Melvyn
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
75655, 266 44, 266225, C21C 532
Patent
active
055057624
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a lance for immersion in a pyrometallurgical bath and a method involving the lance.
In carrying out a bath smelting operation, it is necessary to inject fuel with air or oxygen enriched air below the surface of the bath to achieve both heating of the bath and mixing by means of the turbulence created by the passage of gas bubbles through the bath. Injection of the gas and fuel may be achieved by three main methods, namely: slag fuming furnace, injector type, or of the tip of the lance.
In the Mitsubishi process a steel lance is located at the surface of the slag bath and is allowed to burn away at a slow rate while it is fed into the bath from above and rotated to ensure even wear.
The above described prior art processes are "submerged combustion" processes. As an alternative to submerged combustion, a water cooled lance may be located above the level of the bath, and air or oxygen (with or without fuel) may be blown at supersonic velocity into the bath as in the LD oxygen steel making process.
One form of submerged combustion lance is described in U.S. Pat. No. 4,251,271. This employs cooling by means of the air used for combustion of the fuel. In this case the dimensions of the lance are arranged so that the gas flow rate and the velocity of flow through the lance tube cause a layer of slag to solidify on the outer surface of the lance and protect it from attack by the bath. In this type of lance a swirler is used to increase the gas velocity and enhance the heat transfer through the wall to the flowing gas. The swirler also serves the purpose of improving the mixing between the air and the fuel which is delivered through a central pipe. While this type of lance has been used successfully in a number of bath smelting applications, it suffers from a number of disadvantages.
Thus, to achieve the required heat transfer near the tip of the lance, the gases are accelerated up to velocities approaching Mach 1. When attempts are made to force the air to flow at a higher rate the spiral passages in the swirler behave as choked ducts. A very large increase in pressure is then necessary to compress the gas and achieve higher mass flow rate. Flexibility and turndown with this lance is limited by the necessity to maintain a minimum flow down the lance to ensure adequate cooling. Again, because the combustion air is the coolant for this lance, it is not possible to enrich this air with oxygen much above 35% oxygen, since with higher oxygen contents the tip of the lance may burn away.
Broadly speaking, in the present invention these limitations are at least lessened by using an annular duct through which cooling air flows at sufficiently high mass flow rate and velocity to cool an outer lance tubular member.
According to one aspect of the present invention there is provided a lance for submerged injection of materials into a liquid pyrometallurgical bath, comprising an outer end portion to be submersed in the bath, an outer lengthwise extending tubular member, an inner lengthwise extending tubular member positioned within the outer tubular member, an annular duct being thereby defined between the outer and inner tubular members for conveying a gas containing oxygen to an open outer end thereof, a conduit positioned within and extending lengthwise of the inner tubular member for conveying further gas consisting of or containing oxygen to the outer end portion of the lance, a lengthwise passage being thereby defined between the inner tubular member and the conduit for conveying combustible fluid to the outer end portion of the lace, at least one port providing communication between the passage and the annular duct and at least one exit passageway providing communication bet-ween the conduit and the outer end portion of the outer tubular member at a location downstream of the port or ports, for directing the further gas flowing from the conduit into the outer end portion of the lance.
According to another aspect of the invention, there is provided a method for submerged injection of materials in
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Denholm William T.
Taylor Robert N.
Andrews Melvyn
Commonwealth Scientific and Industrial Research Organisation
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