WO2008122095A1

WO2008122095A1 - Metallurgical conversion method

Info

Publication number: WO2008122095A1
Application number: PCT/BE2008/000025
Authority: WO
Inventors: Philippe Dumont
Original assignee: Lime Technology Consulting Sprl
Priority date: 2007-04-06
Filing date: 2008-04-04
Publication date: 2008-10-16
Also published as: BE1017542A5

Abstract

The invention relates to a method for converting liquid cast-iron into liquid steel in a converter, that comprises adding pieces of lime, wherein the lime supply hopper of the converter is loaded with lime from a mobile essentially sealed metal container adapted for providing a concentration of rocks and lime-pieces of more than 7 mm higher than 95 % and a water content, in the form calcium and/or magnesium hydroxide of less than 0.5 % despite a transport of more than 100 km in an atmosphere having a relative humidity of more than 80 %.

Description

Metallurgical conversion process

The present invention relates to a process for converting molten iron or a molten mass of scrap into liquid steel in a converter.

In a conversion operation of liquid iron or a molten mass of scrap in liquid steel (which can be operated, for example, in a conversion steel mill or in an electric steel mill), the role of lime is multiple.

The lime, poured into the liquid iron or the scrap melt, ensures the formation of a basic slag at the beginning of refining, fixing the acidic compounds resulting from the oxidation of silicon and phosphorus contained in the iron liquid or in the melt of scrap metal, in order to protect magnesium refractories. During this refining operation, it allows the removal of phosphorus, silica and possibly other elements, such as sulfur.

Refining is a very fast and high productivity operation. Therefore, the quality of the lime is an essential factor to the operation.

Immediate dissolution of the lime will allow to quickly obtain a slag of adequate viscosity above the metal bath and a reduction of projections and losses of iron.

In recent years, the use of high reactivity and well-calibrated lime has contributed to the improvement of steel quality, reduction of refining time and consumption of lime per ton of steel. These high reactivity lime have a high porosity and a large surface area. As a result, they are very hygroscopic and have a low impact resistance. Despite the precautions taken during the storage and transport of lime rock or pieces, the multiple manipulations of the lime between the lime kiln and the converter cause a significant increase in the content of particles less than 7 mm, as well as the content in water due to the absorption of moisture from the air. This absorption of moisture from the air will increase the low impact resistance of lime to rocks or pieces. Indeed, the hydration reaction and the conversion of calcium oxide to calcium hydroxide are accompanied by a very significant increase in the molar volume. This expansion has the effect of reducing the resistance of the lime rock or rock, resulting in an accelerated formation of fines.

Briquettes of fine particles of compacted lime are by their high density and low cohesion, particularly sensitive to this phenomenon.

This alteration of lime, which is very detrimental to its use in the iron and steel industry, depends on many factors, including the reactivity of lime, calcination and cooling processes, crushing and screening used in the production of lime in pieces or in pieces. rocks, transport time, seasonal air humidity, mode of transport, number of loading, unloading and storage operations.

This alteration of the lime by a hydration on the surface is a cause of decrease of the reactivity of the lime in rock. This alteration of the lime creates the formation at least on the surface of calcium hydroxide at least partially blocking the surface porosity of the rock lime.

According to E. Schiele / LW Berens-KaIk (1972), during lime-rock transport taking one to two days for a distance of 150km, the average annual water content of lime increases by about 50%. . For a quicklime of low reactivity, the average water content (expressed in the form of calcium hydroxide and magnesium) is of the order of 0.82% at the outlet of the baking oven, while it is the order of 1.22% after the transport of 150km. The amounts of fines formed during transport in a hopper car over a distance of 300km for straight furnace quicklime (12-50mm) and rotary kiln (10-40mm) are respectively 6.9% and 6.1%.

According to the knowledge of those skilled in the art relating to steelmaking lime, the amounts of fines less than 5 mm are 0.5% at the loading of the lime plant, 4.5% after unloading at the same time. steel mill and 12% to the converter, even by not taking into account a long lime transport between the lime plant and the steel plant.

This hydration of lime and the formation of fines create problems for steelmakers as to the quality of the steel produced, a lower reactivity of rock lime and a reduction in the performance of the refining process, which do not hesitate to demand penalties for lime producers in the case of water contents above a predetermined value and / or in the case of a fines content higher than a predetermined content.

The loss of reactivity of hydrated rock lime on the surface is also due to the formation of a nascent calcium oxide at the surface, when surface hydrated rock lime is contacted with molten iron. This nascent calcium oxide has an ability to sinter and form a skin that is able to prevent the slag from entering the lime block and reacting with the lime inside the lime block.

For steelmakers, lime fines (generally particles smaller than 7mm) are carried by the gases leaving the converter and therefore constitute a loss of production, a loss of lime, but especially dusting problems to the filters which are more quickly clogged, resulting in significant costs for disposal and treatment of filter waste. The combined water in the form of calcium hydroxide precipitated in the converter at a temperature well above the dissociation temperature (580 ° C) of the calcium hydroxide to calcium oxide causes an abrupt emission of a volume of vapor very important water. It is considered that a combined percentage of water in lime corresponds to a gas evolution equal to 30 times the volume of steel, a gas which unlike oxygen is released instantly. This volume of gas is even greater if the water reacts with carbon to form two volumes of gas in the form of hydrogen and carbon monoxide. These last two gases are very explosive, especially at high temperature, and constitute a significant risk of explosion and therefore danger.

In addition, the formation of hydrogen is not desired because hydrogen is a poison for many steels.

This sudden formation of gas is a kind of explosion carrying a large amount of iron, iron carried away constituting a loss of material useful for the converter, but also problems in filtration or dust removal installations.

In addition, the presence of water in the lime and its transformation into steam require a significant amount of energy, given the endothermicity of the transformations and reactions.

Water is also, like sulfur, a contaminant for steel by a supply of hydrogen. 9 grams of water per ton of steel is enough to raise the hydrogen content in lppm steel.

In order to try to remedy these drawbacks, it has been proposed to produce quicklime in the vicinity of the converter itself, in order to avoid deterioration of the lime during its transport. For this production, it is necessary to build a lime kiln on the steel complex and bring the limestone to the site. The major disadvantage of this solution is the transport of limestone whose weight is double that of lime. For one ton of lime, about two tons of limestone are transported. This solution was used to prepare lime in very distant countries where limestone is not found. In addition, this solution is only conceivable if the iron and steel plant is very large. The proper functioning of the steel complex will depend more on the smooth operation of the lime kiln, any stop lime kiln can create the stop at least a portion of the entire steel for lack of lime.

It has also been proposed to coat the lime with a composition intended to form a superficial crust. The crust thus formed is composed of iron oxide or alumina and silica. This crust is a contamination of lime and therefore a kind of contamination of steel.

This crust, however, remains permeable to water vapor and the improvement of the resilience is only very limited, or even zero.

It is also known to cause a slight overcooking on the surface of the lime, in order to form a surface layer of reduced porosity lime.

However, even this lime remains sensitive to the humidity of the air. In addition, the surface layer will substantially reduce the reactivity of the lime and thus the refining process. This lime is therefore not appreciated by steelmakers.

According to yet another proposal (see US4.205.994), a carbonate crust is formed on the surface of the lime by contacting the lime with carbon dioxide. In spite of the high carbonation rate which decreases the available CaO content, the carbonate layer remains permeable to water vapor, so that the hydration process is only slowed down.

Thus, for a steelmaker who does not have his own lime production plant on his own site, the hydration of lime and the formation of fines remain problematic for the conversion of cast iron or molten metal into steel.

The present invention aims to overcome these disadvantages, by ensuring that despite long-distance transport, particularly in a humid atmosphere, the lime has a low hydration, lime has a good reactivity, more lime introduced into the converter has a low fines, the metallurgical conversion process is improved.

The invention also makes it possible to ensure better control of the quality of the lime used, a better regularity of the lime used in quality and granulometry, etc., which will also allow easier and more regular control of the conversion process, and therefore the production of steel of better defined quality.

Document US 4 122 761 discloses a sealed container for transporting dangerous liquids in drums, said container being provided with a continuous ventilation device for continuously extracting air from the container, and an opening for allow fresh air to enter the container. This document does not teach the bulk transport of rock lime in a container filled to more than 80% by volume, nor the advantages of such use for a metallurgical conversion process.

The subject of the invention is therefore a process for converting liquid iron or a molten mass of scrap into liquid steel in a converter, in which lime is added in pieces or rocks to form at least one slag containing oxides. and supernatant above the liquid steel, said lime having a significant proportion of rocks or pieces larger than 7mm and a water content in the form of calcium hydroxide and / or magnesium of less than 1% by weight. weight, said lime from a feed hopper of the converter receiving lime prepared beforehand in a baking oven and fed to the feed hopper at least by road, rail and / or maritime transport, wherein said lime from of a baking oven after at least one screening step and possibly after a passage through a hopper has a rock content or pieces of more than 7 mm of more than 95% by weight and a content of e in the form of calcium hydroxide and / or magnesium of less than 0.5% by weight. According to the invention, the lime feed hopper of the converter is fed directly or via a conveyor belt by means of a lime resulting from a substantially sealed mobile metal container having a substantially parallelepiped shape with an interior volume receiving chamber. at least 5m ³ , preferably at least 10m ³ , and at least one aperture adapted to be closed by one or more movable walls, preferably guillotines. Said container has a substantially horizontal base or bottom in the transport position of said container. Filling with a filling rate of more than 80% by volume the receiving chamber of the container with lime from a baking oven has a rock content or pieces of more than 7mm more than 95% by weight and a water content in the form of calcium hydroxide and / or magnesium of less than 0.5% by weight.

Said filling operation of the container is at least partially effected by said opening, and at least partially in an inclined position of the base or base relative to a horizontal plane so as to ensure a movement of lime rock or pieces to a opposite side to said opening.

Said container is thus adapted to ensure a content of rocks and pieces of lime of more than 7 mm of more than 95% and a water content in the form of calcium hydroxide and / or magnesium of less than 0.5% by weight in spite of a transport over more than 100km, advantageously more than 150km, preferably more than 300km, more specifically more than 1000km (in particular more than 1000km of transport by sea), or even several thousand km in an atmosphere having a relative humidity more than 50%, especially more than 80% or more than 90%.

The problems to be solved by the invention are therefore: to avoid the formation of too much calcium hydroxide on the surface of the rock lime, - avoid the formation of a large amount of fines during the transport of lime rock,

- avoid the formation of too much fines during loading or unloading, and - improve the metallurgical conversion process, reducing the dust content, filtration problems, the hydrogen content formed, the risk of explosion , losses, residues, etc.

The invention also makes it possible to improve the energy balance of the metallurgical conversion process and / or increase the productivity of the converter and / or the quality of the steel, despite a lower consumption of lime.

It has been noted that these problems can be solved by using a guillotine container whose interior volume is more than 80% by volume, in particular more than 85%, preferably more than 90%, more specifically 95% or more. The filling rate of the container expressed in% volume is calculated as the volume of the receiving chamber of the container occupied by rock lime (including the volume of the voids situated between the grains of rock) divided by the total volume of the container. capable of receiving rock lime, multiplied by 100. The total volume of the container able to receive rock lime can be reduced, for example after a filling operation by one or inflatable balloons located inside the container . In this case, the filling ratio is determined with respect to the total volume of the container receiving chamber minus the volume of the inflated balloon (s).

It has been noted that such a filling level of the container could be achieved by at least partial filling of the container in an inclined position relative to its horizontal position.

The person skilled in the art could not have expected that by filling a container with lime at more than 80% by volume, it would be possible to improve the metallurgical conversion process, even if the rock lime is produced more than 100km from the converter. In this memoir,

- "lime" means quicklime or calcium oxide (CaO), calcined dolomite or double calcium and magnesium oxide (CaO.MgO), and mixtures thereof; and

"Lime in pieces or rocks" means a lime having mainly a granulometric fraction greater than 7 mm, said lime being for example obtained by calcination of limestone or dolomite, followed by sieving just after the firing step with a view to remove fines, especially particles smaller than 5 mm, or by a pulverulent lime compaction process to form briquettes.

Advantageously, the container is adapted to ensure a content of rocks and pieces of lime of more than 7 mm of more than 95%, preferably of more than 97% by weight, and a water content in the form of calcium hydroxide and / or magnesium of less than 0.5% by weight, preferably less than 0.3% by weight despite transport over 100km, advantageously more than 150km, preferably more than 300km, more specifically more 500km, in particular more than 1000km or more than several thousand km (ie at least two) (said transport being advantageously at least partially operated, preferably mainly by sea or by boat) and a stay at least one week, in an atmosphere having a relative humidity of more than 50%, in particular more than 80%, more specifically more than 90%.

According to a preferred embodiment of the process, the filling is filled with more than 90% by volume, preferably more than 95% by volume, the container using lime from a baking oven having a content in rocks or pieces of more than 7 mm by more than 95% by weight and a water content in the form of calcium hydroxide and / or magnesium of less than 0.5% by weight, said filling operation of the container being operated at least by said opening and at least partially in an inclined position of the base or bottom with respect to a horizontal plane so as to ensure a movement of the lime towards a face of the container opposite to said opening.

Preferably, the inclination of the container during the filling operation is progressively increased, continuously or not, preferably to a substantially vertical position of the container with the opening facing upwards. For example, the filling operation is started with an inclination of at least 15 °, advantageously at least 25 °, preferably at least about 30 °, while the filling operation is completed with an inclination of about 90 °, the container then being in a substantially vertical position.

According to one embodiment of the method, the receiving chamber has:

a first portion of cross section perpendicular to the substantially constant bottom or base and to the longitudinal axis of said first portion, and

a second portion extending between said first portion and said aperture adapted to be closed by one or guillotines, said second portion having a cross section perpendicular to the bottom or to the base and to the longitudinal axis of the container or the first portion, which narrows substantially continuously toward said opening.

Advantageously, the second portion has a cross section in the vicinity of said opening which has a passage section equal to less than 70%, advantageously less than 60%, preferably less than 50% of the substantially constant cross section of said first portion. For example, the cross section in the vicinity of the second opening is between 30 and 50% of the substantially constant cross section of the first portion.

According to an advantageous detail, the second portion extends over a length of at least 1m, advantageously at least 1.5m, preferably over a length of between 2 and 3m. In particular, the container is provided with at least one communication valve and / or a valve and / or a conduit for balancing the internal pressure of the container with respect to the external pressure.

According to one embodiment, the container has at least one base (advantageously two opposite bases) of at least 10 m ² , two longitudinal walls and two side walls, at least one of said side walls having an opening capable of being closed by a or walls movable substantially sealingly.

According to a detail of another embodiment, the container has a bottom and a gate remote from the bottom to define between the grid and the bottom at least one chamber adapted to receive lime passing through the gate and having a particle size less than 1 mm, advantageously less than 2 mm, preferably less than 3 mm.

According to another advantageous detail of an embodiment, the container has a bottom and a gate remote from the bottom to define between the grid and the bottom at least one chamber adapted to receive lime passing through the gate and having a particle size less than 4 mm, preferably less than 5 mm, preferably less than 7 mm.

Advantageously, the chamber defined between the grid and the bottom is adapted to retain the lime passing through the gate during the opening of the door or doors for the passage of lime rocks or pieces out of the container and or is associated with a means for retaining the lime passing through the gate during the opening of the door or doors for the passage of lime rocks or pieces out of the container. Preferably, the chamber defined between the grid and the bottom comprises a receiving drawer or is formed by a removable assembly relative to the container. According to another advantageous detail, the chamber defined between the grid and the bottom has a volume corresponding to less than 15% of the total internal volume of the container, advantageously less than 10%, preferably from 2% to 6% of the total internal volume. of the container.

According to an advantageous feature of one embodiment, the wall or walls is / are one or more sliding walls, the wall or walls being adapted to cooperate with one or more seals when the wall or walls are in the closed position. 'opening. Preferably, the seal comprises at least one bead of flexible material.

According to a particular detail, the container has a volume of between 10m ³ and 100m ³ , in particular between 15m ³ and 75m ³ , the height of said container being less than 3m, advantageously between Im and 2.5m.

According to a particular detail of a particularly advantageous form, the container comprises or is associated with a cartridge containing at least one drying agent, for example anhydrous calcium sulphate, magnesium oxide, aluminum oxide, silica gel, but especially calcium oxide

(allowing to dry the air up to a moisture content of about 0.2 mg of water per liter of air).

According to yet another particular detail, the container comprises a means, in particular a valve, for at least partially balancing the pressure inside the chamber with respect to atmospheric pressure and / or means for admitting at least one gas ( for example air), but advantageously chosen from oxygen and argon in the container.

Advantageously, the valve is associated with a desiccant cartridge capable of desiccating at least some of the gases entering the container. According to yet another advantageous detail, the container is filled with lime into rocks or pieces having a temperature greater than 50 ° C., and a gas that is poor in moisture or free of moisture is used for cooling the lime of the container. . Preferably, the container has a first closable passage capable of being associated with a delivery of a cooling gas, said first passage being adjacent to the bottom of the container, and a second passage for discharging the cooling gas out of the container. container, said second passage being adjacent to the upper wall of the container or being mounted on this upper wall. According to one feature, the first passage is adapted to bring the cooling air into the chamber located between the grid and the bottom of the container, said chamber then serving as a cooling air distribution chamber in the rock lime or in the parts. According to yet another particularity, the distribution chamber is charged with a desiccant, preferably quicklime, preferably in the form of grains having a mean particle size by weight of less than 5 mm, advantageously less than 3 mm.

According always to a detail of an advantageous embodiment of the process according to the invention, the chamber of the container is preheated by means of air or a gas at a temperature greater than 20 ° C., advantageously greater than 30 ° C. C, preferably above 40 ° C before filling the container. In particular, the container, its interior walls or the air contained in the container is preheated to a temperature equal to or greater than the temperature of the lime rock or pieces introduced into the container. This preheating of the container and the air present in the container, before the filling step, makes it possible to drive away the moisture present in the container and to reduce the degree of relative humidity of the air present in the receiving chamber lime in rocks or pieces. According to another detail of one embodiment, the container is subjected to a dehydration step, for example by means of dry air or a dry gas, before filling the container with rock lime or parts. The subject of the invention is also a container for carrying out a process according to the invention, said container having one or more characteristics as defined in any method according to the invention or any of its embodiments.

Features and details of preferred embodiments will become apparent from the following detailed description, in which reference is made to the accompanying drawings.

In these drawings:

Figure 1 is a perspective view of a container used for the implementation of a method according to the invention;

FIG. 2 is a view of the container placed on a feed hopper, FIG. 3 is a sectional view showing an advantageous detail of the container of FIG. 1,

FIG. 4 is a sectional view of another container for carrying out a method according to the invention,

FIG. 5 is a sectional view of another container for carrying out the method according to the invention, FIG. 6 is a view of the lateral face with the guillotine in the closed position,

FIG. 7 is a view of the lateral face of FIG. 6 with the guillotine in the open position,

Fig. 8 is a view of a detail of the guillotine (cut along the line VIII-VIII in Fig. 6), and Figs. 9A-9F are views showing steps of the method according to the invention.

The container of FIG. 1 is a substantially parallelepipedal container of interior volume of approximately 35 to 40 m ³ , said container having a base B of length L of approximately 6 m and width 1 of approximately 2.5 m, and a height H about 2.5m. The container has a lateral opening 1 capable of being closed by a guillotine 2 sliding along two opposite rails 3 between an open position and a closed position. Outer bars 4 extend along the lateral opening and serve as support for the guillotine 1, in particular when the container is filled with lime. Advantageously, inner bars 5 are placed opposite outer bars 4 so that bars 4.5 also form guides for guillotine 2.

The container has at its base hooking means or gripping means 6 (for example tenons) for fixing the container on a trailer of a truck, on the platform of a wagon or on a surface or the deck of 'a ship, or on another container.

On its upper face, the container has means or sockets for easy attachment to a lifting means, such means are for example openings or recesses adapted to receive a fixed part.

The opening of the guillotine 2 operates advantageously between the bottom and the upper face of the container. In one possible embodiment, the opening of the guillotine is effected by a movement of the guillotine between the longitudinal lateral walls of the container.

The guillotine 1 advantageously has a means or catch 6 for attaching a device for generating a movement of the guillotine relative to the container.

Along the edges of the opening 1 extend rubber seals 7 able to seal the container with the guillotine in the closed position.

For loading the lime container into rocks or pieces, the container is placed in a vertical position, but preferably in a variable inclined position, with the opening 1 facing upwards. For example, when filling the container, the inclination of the container increases relative to the horizontal plane. The container advantageously has a sidewall with guillotine of a size adapted to be fixed on a hopper T feeding a BT conveyor belt bringing the lime to the converter C. Once the container placed in position above the hopper T substantially tightly, the guillotine 2 is opened to allow the lime to go down into the hopper. The container plays the role of reservoir of the hopper T.

The side wall opposite the opening or the upper wall in the vicinity of this opposite side wall has an opening which can be closed off by a plug or capable of being connected to a supply of a gas, for example to a supply of air dry. This opening is open to allow air to enter the container when lime leaves the container to fall into the hopper.

FIG. 3 shows in section an advantageous detail of the container according to FIG. 1. The lateral wall 14 ', in the vicinity of the upper wall 12 of the container, is provided with an opening 50 protected by a (pivoting) cap 51 to prevent the passage rainwater. This opening 50 communicates with a chamber 52 defined by one or more walls (for example a cylindrical wall) in the interior volume of the container. This chamber 52 is adapted to receive a desiccant cartridge 54 and adapted to allow easy passage of outside air to the interior volume of the container and vice versa.

This cartridge advantageously comprises a porous envelope for capturing moisture from the incoming air, to make it a substantially dry air, and allowing easy replacement of the cartridge with a new cartridge.

The cartridge 54, before use, is advantageously placed in a sealed container or bag or substantially sealed.

The cartridge can contain any type of desiccant or mixture of desiccants. In particular, the cartridge contains quicklime. In one embodiment, the cartridge 54 is a receptacle removably mounted on the opening 50, said duct having at least one perforated or closed face with a lattice adapted to retain particles smaller than 1 mm. The cartridge is filled with quicklime rocks or pieces larger than 3mm, preferably greater than 5mm, preferably of the quality introduced into the container.

Figure 4 is a sectional view of another container according to the invention.

This container 10 of parallelepipedal shape has a bottom 11, an upper wall 12, two opposite longitudinal walls 13 and two opposite side walls 14,14 '.

A side wall 14 consists of a guillotine able to be moved from bottom to top (arrow X) to bring it to the open position. This guillotine 14 has sliding edges in opposite rails 15. To seal the closure of the wall 14, a rubber seal 16 capable of being crushed extends along the edges of the opening. The guillotine 14 further comprises a stop 17 to limit the opening movement of the guillotine.

In the vicinity of the bottom 11, the container is associated with a removable drawer 18 having an upper wall-shaped grid or perforated plate 19, a front side wall 20 adapted to pivot between an open position and a closed position, and a side wall rear 21 having at least one opening 22 (for example two, three or more) adapted to receive (each in the case of a multitude of openings) the end 23 of a channel 24 for supplying a gas. Maintaining the slide 18 along the bottom 11 is ensured, for the rear part, by engaging the ends of the gas supply channels in the openings 22, and for the front part of the drawer, by means of one or more movable, pivoting or removable fasteners. The bottom of the drawer advantageously has inclined dishes intended to form a kind of retaining chute. Advantageously, the grid 19 is also removable to allow easy cleaning of the drawer after use of the container.

The channel 24 extends in the vicinity of the rear side wall 14 'to open in the vicinity of the upper wall 12 or at the level of the upper wall 12.

A cap 26 extends above the opening of the channel 24, to allow the passage of gas, but to prevent the passage of particles or liquids. This cap is advantageously removable when the channel 24 is connected to a supply of a gas under pressure or from a cooling fan.

The upper wall 12 also has an opening 27 that can be sealed substantially by a plug 28.

Before filling the container with lime rocks or pieces of particle size greater than 7 mm (for example with an average particle size of 10 to 50 mm), is introduced into the drawer 18 of quicklime (powder or granule or piece advantageously very high reactivity). This lime is introduced by the side wall 20 after opening.

This drawer serves both as a means for distributing air from the channel 24 to equalize the internal pressure of the container with the atmospheric pressure, means or cartridge to dry the air entering the container (the air before entering in contact with the lime in pieces contacting the lime of the drawer), means for harvesting fines produced during transport (the vibrations of the transport then facilitating the passage of the fines in the drawer via the grid 19), and means for preventing the passage of fines when spilling lime into pieces in the feed hopper of the converter or conveyor belt feeding the converter.

The volume of the drawer is advantageously from 1 to 5% of the total volume of the container. The grid 19 is advantageously inclined with respect to a horizontal plane when the container at its base bears on a horizontal plane, the slide being higher in the vicinity of the guillotine 14 than the side wall 14 '.

When the container is filled with lime in pieces or in hot or warm rocks, once the container is filled and the guillotine in the closed position, and the container placed in a substantially horizontal position, the cap is opened to allow a passage of gas through the opening 27. The cap 26 is removed so as to connect the channel 24 to a supply of gas, for example air, in particular dry air. This air brought by the channel 24 is then distributed by the drawer 18 throughout the volume of lime. This air is then heated in contact with the lime and is evacuated through the opening 27. This allows a good cooling of the hot lime or warm.

The container is provided at the corners of tenons 32 to facilitate the handling of the container, these pins being useful for proper positioning of the container during a loading operation, but also for the positioning of the container on the feed hopper of the converter.

FIG. 5 is a sectional view of a container similar to the container of FIG. 4. The CH chamber for receiving lime in rock or in pieces has two parts, namely a first portion CH1 of substantially constant cross-section (section substantially square in a plane perpendicular to the bottom 11 of the container, section perpendicular to the longitudinal axis A of the container), and a second portion CH2 extending between the first portion and the guillotine 2. This second portion has a cross section (section in a plane perpendicular to the bottom of the container and to the axis A of the first portion CHl) which decreases continues as close as possible to the lateral opening 1. This reduction in cross section is obtained by welding a plate 60 to the bottom of the container, said plate extending in a plane forming an angle α with the plane of the bottom of the container, this angle being advantageously between 25 and 45 °, preferably about 30 ° The opening 1 has a passage section, when the guillotine 2 is in the open position, corresponding to less than half of the cross section of the first serving CHl. The passage section of the opening 1 is for example between 30% and 40% of the cross section of the portion CH1.

The guillotine 2 has edges sliding in the groove of rails 61. The guillotine comprises reinforcements 62, fingers 63 to ensure the opening of the guillotine by sliding thereof along rails 61, bolts or studs 64 to maintain at least the guillotine 2 in the closed position. The guillotine 2 has a height ha less than half the height H of the container, so that in the open position, the guillotine 2 always extends in the space of the frame 65 of the lateral face 66 of the container having the opening 1.

The edges 67 of the guillotine which are engaged in the rails 61 (more exactly in the grooves of the rails 61) are associated with L-shaped brackets 67 so as to limit the lateral movements of the guillotine 2 relative to the rails 61, and to to strengthen the guillotine.

The container of Figure 5 is advantageously provided with a grid 19 and an opening 27 closable by a plug 28 for supplying air or other gas into the receiving chamber CH or to remove for example hot air. The container also comprises an opening 68 along the bottom of the container for supplying air or another gas into the chamber CH3 located between the bottom of the container and the plate 60. This opening 68 is advantageously extended by a tube 69 advantageously provided with of an elbow 70. The plate 60 has one or more openings 71 for placing the chamber CH3 in communication with the space This container may also be provided with or associated with one or the other means of the container of FIG. 4.

Different steps of a method according to the invention will be described in FIGS. 9A to 9F.

In step 9A, the container is subjected to a drying step. For example, hot air is introduced into the container via the conduit 69, the chamber CH3 and the openings 71 of the plate 60, the hot air then opens under the gate before coming out through the opening 1 (guillotine 14 in the open or partially open position) and / or through the opening 27. The position of the guillotine 14 will be adapted according to the temperature of the air in the chamber CH and the flow of hot air introduced into the chamber CH.

When the container is sufficiently dry, in particular when the air temperature of the chamber CH is greater than 30 ° C., the container is brought to the filling station SR, for example in the form of a hopper receiving the lime. in rock leaving the calcination furnace, this lime advantageously having a temperature above 50 ° C. This filling station comprises a hopper 80 and an extensible chute 81 (whose length can be modified, for example by sliding one element relative to another or partially in another.

The filling operation of the container begins with an inclination of the bottom of the order of 30 ° relative to the horizontal plane, (FIG. 9B)

To ensure this inclination of the bottom of the container, the container is placed on a support 85 mounted to pivot (RR) on a carriage 86 movable relative to rails 87. The carriage 86 comprises a device 90 (for example by winding a chain 88 around a drum 89) for controlling the inclination β of the bottom of the container relative to a horizontal plane. This allows the lime rock to slide along the plate and then roll on the grid to the face 14 'of the container.

During loading, the inclination β of the container bottom is gradually increased to reach at the end of loading a substantially vertical position (Figure 9C). During this pivoting movement, the carriage 86 is also moved to adapt the position of the opening 1 of the container with respect to the hopper 80.

This ensures a substantially complete filling of the chamber CH. Due to the shape of the portion of chamber CH2, a filling rate of more than 95% can be easily obtained.

Then closing the opening 1 by means of the guillotine 2, while the container is still in a substantially vertical position. This closure operation may optionally be performed once the temperature of the lime present in the chamber is less than 40 ° C. (Figure 9D)

The container is then returned to the horizontal position and ready for transport, (Figure 9E)

The container is then transported by truck, train or boat to the metallurgical complex. Thanks to the high filling rate of the chamber and the low hydration during transport, few fines are produced, while the reactivity of the rock lime is preserved.

The container is then used as a hopper to feed a BT conveyor belt bringing lime rock to the metallurgical converter (Figure 9F). Example 1

A quicklime rock was screened to keep the fraction 7-50mm. The average particle size (by weight) of the lime was 30 mm. This lime produced by cooking in the vicinity of a quarry was transported by rail to a converter located at 300km, the duration of the journey being about 24 hours taking into account some stops of the convoy.

This quicklime was loaded for a first part in conventional wagons-tales, for a second part in containers of the type shown in Figure 1, and for a third part in containers of the type of Figure 3. The filling of lime containers were operated to prevent any sharp drop in lime. Thus, the container was inclined to allow the lime to slide along the wall of the container. In the ironmonger, the container was placed vertically above a hopper feeding a conveyor belt bringing the lime to the converter.

The rock lime at the hopper receiving lime from the baking oven was analyzed to determine the percentage by weight of the loss on ignition, the percentage by weight of carbon dioxide (CO ₂ ) of the residual calcium carbonate, the percentage by the weight of water contained in the lime in the form of calcium hydroxide, and the content (% by weight) of the fraction less than 7 mm (by a screening operation).

For this analysis, samples were taken in hermetically sealed containers.

Similar analyzes were carried out at the converter for different lime, depending on the type of transport used.

The results of these analyzes are given in Table 1 below. TABLE 1

During the steel refining operation, the best results were obtained by lime transported by container, these lime also making it possible to significantly reduce the amount of dust, said dusts being low in CaO compared to dust obtained by using the lime of the hopper car. The quantity of dust with lime from the hopper car was about 13 kg (dry dust) per tonne of steel produced with a CaO content of about 34% by weight, which represents a loss of about 10% of the lime poured into the converter.

Refining control was also improved with lime from the containers, the temperature of the melt being subject to more limited or controlled variations, and fewer iron particles were washed away. The steel obtained was better quality (lower hydrogen, sulfur and phosphorus content) demonstrating a better reactivity of the lime of the containers, in particular the container of figure 3. The lime of the containers was better used or used more efficiently .

With lime from containers, the amount of dry dust produced was less than 8.5kg per tonne of steel with a CaO content of less than 18% by weight.

Similar tests were carried out after storage of the containers for 1 week and 2 weeks in the open air. The results obtained with this lime after storage were similar to the results obtained after immediate use of lime containers, demonstrating that the lime retained its properties despite storage for several weeks.

Example 2

Example 1 was reproduced but with a calcined dolomite (CaO.MgO) in rocks screened between 7 and 50mm. This lime (dolomite) was transported by boat over 1800 km between the production site and the steel plant. The average outside temperature was of the order of 7 ° C with a relative humidity of more than 90%. This transport required several operations, including a loading operation at the departure port with intermediate storage in the hangar, an unloading operation at a port of arrival with intermediate storage and a transport of lime to the converter from the arrival port. .

Traditionally, lime handling has been done using grapples, conveyor belts and trucks. According to the invention, the transport has been carried out by means of containers according to FIG. 1 and according to FIG. 3, said containers being loaded in the very vicinity of the cooking oven.

As in Example 1, several parameters were measured for the quality of calcined dolomite (see Table 2).

TABLE 2

This calcined dolomite was mixed with lime rock or pieces at a rate of 10% by weight when used in the converter.

The use of calcined container dolomite has significantly reduced the dust content, the hydrogen content formed, the risks explosion, losses, residues, and improve the energy balance of the refining operation, the productivity of the converter and the quality of steel produced (better removal of the P ₅ S, H, despite a lesser consumption of lime).

It has indeed been noted that the use of the lime transported by container according to the invention makes it possible to have better control of the refining operation, and to make it possible to ensure less variation in the quality of the lime, and therefore to improve and facilitate the refining operation, allowing the obtaining of high quality steel.

Although the containers of the figures have only a single guillotine, it is possible to use a double guillotine, that is to say having two walls able to move towards one another to close an opening and to move away from each other to open said opening.

Example 3

In this example, containers A according to FIG. 5 were filled with rock lime calibrated between 10 and 50 mm, with a fine content of 0.15% by weight. The filling was performed as explained in FIGS. 9A to 9F. The filling rate of the container (in% volume) was greater than 95% of the volume available to receive the lime (CHl + CH2).

By way of comparison, a container B has been filled whose upper wall has been perforated with filling openings which can be closed by lids. The lime used was identical to that used for the containers A. The filling of the container B was operated in horizontal position of the container B under a single roof. Due to the formation of lime-to-rock cones, the filling rate of the container was less than about 70% of the total internal volume of the container (volume equivalent to the sum of CH1, CH2 and CH3 volumes). Container B lids were closed when the lime temperature was about 20 ° C. The outside temperature was of the order of 10 ° C, with a relative humidity of the air close to 100% (rainy weather).

Containers A and B were transported by truck over a distance of 325km, before being used in a converter.

The results of this example are given in Table 3 below:

TABLE 3

*: The water content is determined by calculating the difference between the% by weight of loss on ignition and the% by weight of CO2.

Claims

claims

A process for converting liquid iron or molten mass of liquid steel scrap into a converter, in which lime is added in pieces or rocks to form at least one slag containing oxides and supernatant above liquid steel, said lime having a significant proportion of rocks or pieces larger than 7 mm and a water content in the form of calcium hydroxide and / or magnesium of less than 1% by weight, said lime coming from a feed hopper of the converter receiving lime prepared beforehand in a baking oven and fed to the feed hopper at least by road, rail and / or maritime transport, wherein said lime from a baking oven after at least one screening step and optionally after passage through a hopper has a content of rocks or pieces of more than 7mm greater than 95% by weight and a water content in the form of hydroxide of c alkali and / or magnesium of less than 0.5% by weight, characterized in that the lime feed hopper of the converter is fed directly or via a conveyor belt by means of lime from a metal container substantially sealed mobile device having a substantially parallelepiped shape with a receiving chamber of internal volume of at least 5m ³ , preferably at least 10m ³ , and at least one opening capable of being closed by one or more mobile guillotines, said container having a substantially horizontal base or bottom in the transport position of said container, and in that filling with a filling rate of more than 80% by volume the container by means of lime from a baking oven having a content of rocks or pieces of more than 7 mm by more than 95% by weight and a water content in the form of calcium hydroxide and / or magnesium of less than 0.5% by weight, said filling operation of the container being o at least through said opening and at least partially in an inclined position of the base or bottom relative to a horizontal plane so as to ensure movement of the lime towards a face of the container opposite said opening.

2. Process according to claim 1, characterized in that filled with a degree of filling of more than 90% by volume, preferably of more than 95% by volume, the container by means of lime coming from a furnace of cooking having a rock or piece content of more than 7 mm by more than 95% by weight and a water content in the form of calcium and / or magnesium hydroxide of less than 0.5% by weight, said filling operation the container being operated at least by said opening and at least partially in an inclined position of the base or bottom relative to a horizontal plane so as to ensure a movement of lime to a face of the container opposite to said opening.

3. A method according to claim 1 or 2, characterized in that progressively increases, continuously or not the inclination of the container during the filling operation, preferably to a substantially vertical position of the container with the container. opening upwards.

4. Process according to any one of the preceding claims, characterized in that the receiving chamber has:

a first portion of cross section perpendicular to the bottom or to the base and to the longitudinal axis of said first portion, said cross section being substantially constant, and

- A second portion extending between said first portion and said aperture adapted to be closed by one or guillotines, said second portion having a cross section perpendicular to the bottom or base which narrows substantially continuously towards said opening.

5. Method according to claim 5, characterized in that the second portion has a cross section in the vicinity of said opening which has a passage section equal to less than 70%, preferably less than 60%, preferably less than 50% of the substantially constant cross section of said first portion.

6. A method according to claim 5, characterized in that the second portion extends over a length of at least Im, preferably at least 1.5m, preferably over a length of between 2 and 3m.

7. Process according to any one of the preceding claims, characterized in that the guillotine (s) cooperate with one or more seals when the guillotine or guillotines are in position closing the opening.

8. Method according to any one of the preceding claims, characterized in that the container is provided with at least one communication valve and / or a valve and / or a conduit for balancing the internal pressure of the container with respect to the external pressure.

9. A method according to any one of the preceding claims, characterized in that the container has a bottom and a gate remote from the bottom to define between the gate and the bottom at least one chamber adapted to receive lime passing through the grid and having a particle size less than 1 mm, preferably less than 2 mm, preferably less than 3 mm.

10. A method according to any one of the preceding claims, characterized in that the container has a bottom and a gate remote from the bottom to define between the gate and the bottom at least one chamber adapted to receive lime passing through the grid and having a particle size less than 4 mm, preferably less than 5 mm, preferably less than 7 mm.

11. A method according to any one of claims 9 and 10, characterized in that the chamber defined between the grid and the bottom is adapted to retain the lime passing through the gate when opening the door or doors for the passage of the lime rock or piece out of the container and / or is associated with a means for retaining the lime passing through the grid when opening the or doors for the passage of lime in rocks or pieces out of the container.

12. The method of claim 11, characterized in that the chamber defined between the grid and the bottom comprises a receiving drawer or is formed by a removable assembly relative to the container.

13. A method according to any one of claims 9 to 12, characterized in that the chamber defined between the grid and the bottom has a volume corresponding to less than 15% of the total internal volume of the container, preferably less than 10%, preferably from 2% to 6% of the total internal volume of the container.

14. A method according to any one of the preceding claims, characterized in that the container has a volume between 10m ³ and 100m ³ , in particular between 15 m ³ and 70m ³ , the height of said container being less than 3m, advantageously included between Im and 2,5m.

15. Process according to any one of the preceding claims, characterized in that the container comprises or is associated with a cartridge containing at least one drying agent.

16. Process according to any one of the preceding claims, characterized in that the container comprises means, in particular a valve, for at least partially balancing the pressure inside the chamber with respect to the atmospheric pressure and / or means for admitting at least one gas selected from oxygen and argon in the container.

17. A method according to the preceding claim, characterized in that the valve is associated with a desiccant cartridge capable of desiccating at least some of the gases entering the container.

18. Process according to any one of the preceding claims, characterized in that the container is filled with rock lime or pieces having a temperature greater than 50 ^° C., and in that a low-oxygen gas is used. moisture or rid of moisture for cooling the lime of the container.

19. A method according to the preceding claim, characterized in that the container has a first closable passage and adapted to be associated with a supply of a cooling gas, said first passage being adjacent to the bottom of the container, and a second passage for the discharging the cooling gas out of the container, said second passage being adjacent to or mounted on the top wall of the container.

20. Process according to the preceding claim and at least one of claims 9 to 13, characterized in that the first passage is adapted to bring the cooling air into the chamber located between the grid and the bottom of the container, said chamber then serving cooling air distribution chamber in lime rock or piece.

21. Process according to the preceding claim, characterized in that the distribution chamber is charged with a desiccant, preferably quicklime, preferably in the form of grains having a mean particle size by weight of less than 5 mm, advantageously less than 3 mm. .

22. Process according to any one of the preceding claims, characterized in that the chamber of the container is preheated by means of air or a gas at a temperature greater than 20 ^° C., advantageously greater than 30 ^° C. , preferably greater than 40 ^° C. before filling the container with rock lime or in pieces, and / or in that the chamber of the container is dehydrated, by means of air or of a dry gas, before filling the container with lime rock or pieces.