Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Patent
1992-01-23
1993-06-01
Andrews, Melvyn J.
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
266150, C22B 1918
Patent
active
052155722
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an improved apparatus and process for absorbing zinc vapour into molten lead.
Gases containing zinc vapour are commonly generated in zinc smelting processes (for example, the Imperial Smelting Process (ISP)) in slag fuming; and in the treatment of zinc-containing dusts and residues.
Existing industrial processes for recovering zinc from gases containing zinc vapour are essentially of three kinds, of which the abovementioned ISP process is one. The ISF process uses rotors or impellers to splash lead from a molten pool into the zinc-laden gas stream. In an alternative ISP process, zinc is used as the condensing medium rather than lead. The so-called SKF process uses molten lead or molten zinc in the form of a spray or curtain as cooling metal or medium towards which the gas stream containing zinc vapour is directed.
References relevant to the processes mentioned include D Temple, "Zinc-lead blast furnace--key developments", 1980 extractive metallurgy lecture to AIME, Metallurgical Transactions B vol. 2B, pp 343-352; GB 1,010,436 (Imperial Smelting); and GB 2,122,648 (SKF).
The ISP process suffers from accretions at the mouth of the condenser and in the condenser/absorption chamber causing frequent stoppages of the furnace operation. These accretions form on surfaces that are below the temperature where solid ZnO forms by the reaction Zn+CO.sub.2 .fwdarw.ZnO+CO. This reaction is called the reversion reaction and the temperature at which it occurs the `reversion temperature`. The SKF process is free of this problem only because of the highly reduced gas entering the condenser.
Both processes suffer from shortcomings such as listed below: build and maintain zinc recoveries.
Further shortcomings of the existing process technologies and how they are overcome by the present invention will be described below.
In a principal aspect the invention provides a process for absorbing zinc vapour in molten lead characterised in that a gas containing zinc vapour is contacted with and then separated from a flowing stream of molten lead in a cyclone.
Preferably the cyclone contact stage is preceded by a stage in which the molten lead is introduced into and contacted with the stream of gas containing zinc vapour in a mixing chamber.
In a more preferred embodiment, the apparatus of the invention comprises a refractory lined crossover or off-take with an outlet at the bottom which opens into the mixing chamber that joins a cyclone.
Lead is introduced into the chamber by a lead spray directed into the gas stream. This spray produces a dispersion of lead droplets within the gas stream. Lead may be also introduced by additional sprays that completely wet the walls of both the vertical section before the cyclone and also within the cyclone itself.
The vertical chamber before the cyclone may also house one or more banks of static mixing elements. These elements not only serve to mix the lead droplets and gas together but also break up the lead droplets. This action causes a high degree of shear and a large contacting area as well as turbulence in both phases.
Mixing columns housing static mixing elements are known, and reference may be made by way of example to one such apparatus described in U.S. Pat. No. 4,744,928 to Sulzer Brothers Limited of Switzerland. The static mixing elements in that design are disposed within the chamber in a manner that deflects the flow of fluid impinging thereon and thereby promotes efficient mixing of gases and/or liquids passing through the chamber.
Provided the static mixing elements promote efficient mixing, their precise configuration is not critical to the present invention.
The molten lead now containing the absorbed zinc is passed into a system for recovery of the latter as well as for recirculation of the molten lead for renewed absorption. The off-gas is passed to a conventional gas cleaning system.
In the accompanying drawings:
FIG. 1 is a diagrammatic representation of an exemplary preferred embodiment of the process according to the invention;
FIG. 1a is a diagramma
REFERENCES:
patent: 4042379 (1977-08-01), Harris et al.
patent: 4508566 (1985-04-01), Eriksson et al.
patent: 4687513 (1987-08-01), Santen
Andrews Melvyn J.
Pasminco Australia Limited
LandOfFree
Process and apparatus for absorption of zinc vapour in molten le does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process and apparatus for absorption of zinc vapour in molten le, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process and apparatus for absorption of zinc vapour in molten le will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1811709