Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Reexamination Certificate
2000-06-05
2002-07-16
Kastler, Scott (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C266S044000, C266S168000, C266S171000
Reexamination Certificate
active
06419724
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to a new method for reducing iron oxides associated with the production of a liquid phase of pig iron, making it possible to produce the metal in the molten state starting with iron oxides, such as ores or recycled products, and with coal and/or gas. The invention aims to achieve several economic advantages described hereinafter and others in comparison with known methods.
The present invention also relates to installations enabling this method to be carried out.
2. Description of the background
The growth in the production of steel by electrical means has increased the need for alternative methods that make it possible to avoid the use of scrap, since scrap of adequate quality is becoming increasingly scarce.
Similarly, the competition between producers and the stagnation in sale price, together with growing ecological pressures, are encouraging steel manufacturers to develop new production methods that are less costly and less polluting.
Various methods for the reduction of iron oxide to produce what is known as direct reduced iron (DRI) have recently been developed for this purpose. DRIs are mainly obtained, for example, by gaseous reduction (HYL process, Midrex) or by reduction from carbonaceous sources as in the SL-RN, Fastmet, Inmetco or Circofer and Comet methods or by the method according to the European patent application filed by the applicant on Jan. 28, 1998 under the number 98200242.0. The majority of these methods have as a major disadvantage the fact that what is obtained is a product in the reduced state, generally described as iron sponges, of very low density and with a high specific surface area promoting a re-oxidation of the iron. This causes difficulties in storage and transport and, in most cases, makes expensive compaction necessary to allow subsequent treatment. As an example, iron sponges generally have a bulk density of 1.5 to 2 kg/dm
3
and are compacted up to a value of 5 to 5.5 kg/dm
3
.
In addition, the large amount of latent heat that is present in the reduced material before cooling is lost.
Some of the proposed reduction methods are based on the use of solid carbonaceous sources, like coal, which are added in excess amounts in order to ensure sufficient reduction. This excess of carbonaceous sources is added to other residual products containing ash that must be disposed of.
All these disadvantages can be avoided by a method for reducing and melting in stages according to the present invention. The crude pig iron produced in the molten phase may be used in all normal applications such as casting in small ingots or the refining operations in steel production, for example, in electric steel plants or in oxygen converters.
The British patent GB 1,143,527 describes a two-stage method for reducing pig iron in which iron ore is reduced in a first furnace and is transferred under gravity while hot directly into a melting furnace. The pre-reduced pieces of iron or “pellets” are propelled with such a speed that they pass through the layer of slag lying on the bath of molten pig iron. This speed is acquired by dropping the pre-reduced pieces of iron or “pellets” through a certain height into the bath. According to a particular embodiment, the pre-reduced pieces of iron or “pellets” are deposited on an inclined platform and are periodically propelled by means of a piston into a pipe in which they are accelerated sufficiently by gravitational forces to pass through the layer of slag formed on the bath of molten steel in the melting furnace. The gases from the melting furnace are led into the reducing furnace through the pipe supplying the melting furnace with reduced iron.
The U.S. Pat. No. 5,542,963 describes an installation for the two-stage production of pig iron in which the iron ore is reduced in a first furnace and is transferred under gravity while hot directly into a melting furnace. The pre-reduced pieces of iron or “pellets” are transferred by means of an Archimedean screw into the melting furnace. The gases from the melting furnace are led into the reducing furnace through a pipe separate from the pipe supplying the melting furnace with reduced iron.
One of the objects according to the present invention is to convert the reduced iron oxides directly and continuously after their production. In order to obtain the pig iron in a liquid state that are economically more advantageous and with technological equipment that is improved and more compact than existing equipment.
In particular, one of the objects according to the present invention is a continuous production of a pig iron, preferably desulphurised and separate from the slag, having a lower and more economic energy consumption through the choice of fuel and through a recovery of energy by direct recycling of the combustion gases in the installation upstream.
An apparatus for producing liquid pig iron includes a reducing furnace for reducing iron oxides and a melting furnace containing a molten phase of pig iron and slag for melting the reduced iron oxides, and units for discharging the pig iron to a pig iron refining plant and units for discharging the slag to a slag treatment plant, wherein the reducing furnace and the melting furnace are connected through one or more pipes supplying the melting furnace with a mixture of metallized iron originating from the reducing furnace by gravity transfer and one or more pipes for the discharge of combustion gases from the melting furnace to the reducing furnace, and the supply pipe or pipes are provided with regulating flap valves that make it possible to accumulate a mass of metallized mixture sufficiently large, after falling through a certain height, to penetrate the liquid pig iron forcefully after it has been poured.
A method for reducing iron oxide and melting iron according to the present invention includes at least two consecutive stages, the first of which is a standard stage of reduction until a degree of metallization is achieved of the order of 80 to 94%, and preferably of 85 to 90%, with the addition of fluxes for grading the slag to be produced in the second stage. The second stage is one that produces the pig iron and follows immediately after the first stage.
The second stage in the production of the pig iron is performed in two successive sub-stages. Firstly, the iron oxide is further reduced by virtually 100%. This may be achieved using a compact reactor with a core allowing the passage of gas or with an injection lance, and with a supply of preheated coal from above, the mixture of almost completely metallized iron, gang, fluxes and surplus coal being immediately transferred directly into a furnace containing a molten phase of pig iron, the metal and the slag then being discharged, preferably continuously, for example by overflowing.
The reduced iron oxides from the first reduction stage may result from any reduction method that may be carried out in, amongst other types of plant, a rotating-hearth furnace, a shaft furnace, a rotary furnace or a fluidized bed furnace. The implementation of the invention becomes more worthwhile economically as the temperature of the reduced product increases, i.e. contains more latent heat.
According to a first embodiment of the present invention, the energy required for the melting may be supplied by induction or possibly by means of an electric arc, a submerged arc, for example.
According to a second embodiment of the present invention, it is also possible to carry out further reduction and continuous melting in a single installation including a unit for feeding the material to be treated. Preferably, the material originates directly from the first stage at a temperature as high as possible. This feed unit emerges into one end of a rotary tubular furnace whose opposite end is open and is connected firstly to a unit, preferably funnel-shaped, for discharging the pig iron and slag, and secondly to a gas discharge unit. A burner located alongside the feed unit provides the heat required for the melting of the material
Kastler Scott
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Sidmar N.V.
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