Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Reexamination Certificate
2002-07-16
2003-10-28
King, Roy (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C075S537000, C075S560000, C266S221000, C266S267000, C266S047000
Reexamination Certificate
active
06638337
ABSTRACT:
The present invention relates to a method of introducing additives during steelmaking, either to molten iron in a ladle or the like, or to molten iron while the latter is being poured.
Conditioning of steel at various stages in steelmaking processes often requires the introduction at relevant process stages of various additives (such additives are often known as conditioning agents because they “condition”, or change the properties and/or the composition of, the resulting steel). In conventional arrangements, such additives may be introduced by gravity feed (by flow of the additive from a hopper or the like placed above the molten metal), or by direct injection into molten metal or slag, using, for example, a lance arranged vertically above the hot metal (the latter being typically in a runner for directing molten pig iron tapped from a blast furnace into a hot metal ladle).
U.S. Pat. No. 4,601,749 discloses a method of the latter type, in which a lance is arranged vertically above such a hot metal runner. The method disclosed is relatively inflexible in its operation, and requires the injection lance to be arranged in the very aggressive environment of just above the surface of the molten metal in the hot metal runner. An improved arrangement has now been devised.
According to a first aspect of the present invention, there is provided a method of introducing at least one additive into molten iron in a steelmaking process, in which the additive in particulate solid form is conveyed pneumatically to impinge upon the molten iron and mix therewith, the additive being pneumatically conveyed in a divergent stream from a pneumatic conveying outlet (or gun) spaced above a surface of molten iron present in a receptacle (such as a ladle), the conveying outlet being such that the pneumatically conveyed stream including the additive has a central axis which is either horizontal or at an acute angle to the horizontal.
It is preferred that the axis is adjustable from a first angle to a second angle inclined to the horizontal. Such an adjustable outlet enables the pneumatically conveyed stream to be accurately targeted to, for example, impinge upon a pouring stream or to substantially cover a surface of molten iron in a receptacle.
When the pneumatically conveyed stream is to substantially cover a surface of molten iron in a receptacle, the outlet is above, and preferably outwardly spaced from an outer edge of the receptacle. The term “iron” as used herein encompasses any predominantly ferrous metal or alloy (which may contain incidental ingredients or impurities) suitable for use in a steelmaking process. It specifically includes the material being poured from a converter vessel in the course of a steelmaking process.
The use of a pneumatically conveyed stream provides several benefits, including lower cost, and enhanced dispersal of the additive in the molten iron. In terms of cost, there is no requirement for a specially designed treatment station, because the relevant outlet nozzles (“guns”) can be readily added to an existing plant structure, and an expensive and short-lived lance is not needed.
The central axis of the stream is one about which the stream diverges, to form a substantially divergent conical stream of pneumatically conveyed particulate additive, which impinges upon the molten iron in the form of projectiles.
The first angle may be substantially horizontal or at an acute angle to the horizontal; it should not be vertical.
It is particularly preferred in the method according to the invention that the pneumatic conveying outlet can be adjusted such that the angle of the axis of the stream can be optimised, depending on the application and the location of the surface of the molten iron.
When the pneumatically conveyed stream which includes the additive has a central axis which is substantially horizontal, the additive is preferably added to flowing molten iron during pouring of the latter (typically during pouring into a ladle or the like, the latter therefore including the surface of the molten iron referred to above). In this embodiment, the kinetic energy of the poured iron can assist in the dispersion of the additive directed thereto in a pneumatically conveyed stream. Such a method in which the additive is directed to molten iron being poured into a ladle or the like is described in more detail below.
When the central axis is at an acute angle to the horizontal, the additive may be added to the flowing molten iron during pouring, or (in a preferred embodiment of the invention) the additive may be directed towards the surface of molten iron in the receptacle.
When the stream including the additive is directed towards the surface of the molten iron in the receptacle, the additive is preferably conveyed to reach below the aforesaid surface, penetrating through slag or other surface covering thereon. It is particularly preferred in this embodiment of the invention that the stream is directed so as to substantially cover the entire surface of the molten iron in the receptacle, and impinge at least in part on sidewalls of the receptacle. This is contrary to the teachings of the abovementioned U.S. Pat. No. 4,601,749, where the added stream is directed vertically downwards to the surface of the molten iron with very little divergence of the stream.
According to the invention, however, the “footprint” of the conveyed additive preferably covers the entire surface of the molten iron in the receptacle. This can ensure, for example, that the total surface of molten iron in a ladle may be covered without the requirement to physically move either the conveying outlet or the conveyed stream so as to scan the entire molten iron surface. It is, however, possible to arrange for the stream to scan the surface, or to provide a plurality of such conveying outlets.
In further embodiments, different nozzles can be used for different applications, so that a widely divergent stream can be provided in some embodiments and a stream with little divergence can be formed in other circumstances.
In most applications of the present invention, it is preferred that the conveying gas will be air, although inert conveying gasses (such as nitrogen) may be preferred in some instances.
The additive may be in any suitable particulate form, such as tablets, pellets, briquettes or powder. The density and composition of such tablets, pellets, briquettes and the like may be tailored in order to penetrate to predetermined depths in the molten iron at a predetermined rate. This enables the additive to be tailored to perform specific reaction requirements at specific depths and times. For example, the specific density and composition of tablets introduced into molten iron may be selected to break down quickly when in the presence of hot slag, but to react with the specific chemical components in the molten iron which are targeted for neutralisation or alteration.
The predetermined specific density of the particulate additive can ensure that the particles penetrate into, and remain in, the slag (rather than descending into the liquid iron below) but resist flaring off on the surface.
Significant upward thermal currents exist above the surface of molten iron, which would hinder the deployment of additive by gravity feed. The use of the conveying gas delivery arrangement in the method according to the invention can ensure that the effect of the upward thermal air currents above the molten iron can be compensated for.
The delivery pressure and velocity of the conveying gas can therefore be tailored, depending upon the ‘sinkage’ requirements of the additive being delivered and the upward thermal currents encountered above the molten iron in the relevant process stage. Typically, the dispensing pressure of the conveying gas will preferably be substantially in the range of 7 bars plus or minus 20%. The discharge rate of dispensed material is preferably substantially in the range 0.5 to 15 m
3
per hour.
Preferably, the conveying outlet comprises a nozzle, preferably a diverging nozzle arranged to induce a diverging outlet
Bray Stephen David
Harris Keith
Bacon & Thomas
King Roy
Qual-Chem Limited
Wessman Andrew
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