FR2679256A1 - Desulphuriser for liquid pig iron based on agglomerated calcium carbide - Google Patents

Abstract

Self-dispersing product for the desulphurisation of pig iron and process for its manufacture. The product is made up of technical calcium carbide powder to which are optionally added products intended to cause a gas release in the bath or to modify the composition of the slag, and agglomerated by means either of resins or of an organic compound with a definite melting point. The process includes a number of stages: mixing the carbide and the additives with the resin or the organic product, agglomeration by forming spheroids, pelleting, compression or extrusion, and optional regrinding and screening to obtain the desired particle size. The product is employed for desulphurising pig iron, both for refining and casting. It has the advantage of combining the effectiveness of the fine powders and the easy flow of the coarser particles.

Description

DESULFURANT FOR CAST IRON
OF AGGLOMERATED CALCIUM CARBIDE.

 1) TECHNICAL FIELD OF THE INVENTION

The technical field of the invention is that of the desulphurization of cast irons, whether they are for refining, that is to say intended for the manufacture of steel, or for molding, intended in particular for the manufacture of graphite cast irons. spheroidal. In the first case, for reasons of mechanical characteristics, the sulfur content must be lowered to 0.005 -0.010%; in the second case, spheridisation is only possible for sulfur contents of less than 0.010%.

Most desulphurizing agents are based on two alkaline earths: magnesium and calcium, which combine easily with sulfur to form sulphides, forming insoluble slag in the iron. Excess magnesium is removed because of its high vapor pressure at the processing temperature; Excess calcium compounds (lime, carbonate or carbide) are removed in the slag. Thus, magnesium metal, calcium carbonate, lime, lime diamide (mixture of Ca and carbon carbonate) and calcium carbide, optionally with products intended to improve, are used, separately or in combination. flowability of the mixture or to release gases allowing a good distribution of the desulphurizer in the molten iron.

These desulfurants are, in fact, most often, injected with a lance, suspended in an inert carrier gas.

The invention relates to a novel desulphurizing product containing mainly calcium carbide and its manufacturing process.

2 ") STATE OF THE ART
French Patent 1,194,778 (Union Carbide Corporation) describes a method of treating the oil Ca carbide prior to its use as a desulphurizer. It is sprayed on the carbide, with a particle size of between 0.074 and 1.168 mm and brought to 1500C of the oil at a rate of 0.25 to 4% of the weight of carbide. The oil can be a mineral oil (petroleum oil, gasoline, kerosene), vegetable oil (linseed oil) or animal oil (fish oil). Synthetic waxes or paraffins may also be suitable.

German Patent DE 3,831,831 (SKI) discloses a desulfurizing product composed of a mixture of magnesium and calcium carbide both coated with fine particles of a silica-containing substance and an oily wetting means. . The product is produced by mixing in a frustoconical drum or mixer, carbide and magnesium, with a particle size of between 0.1 and 3 mm with 0.5% of the total weight of oil and from 2 to 10% of the product. Silica base.The oil can be a high viscosity oil of vegetable origin, but also silicone or mineral oil. The silica product with a particle size of less than 0.01 mm is, for example, diatomaceous earth, bentonite or dust from ferro or calcio-silicon furnaces.

European Patent Application EP 0 184 723 (Cyanamid Canada
Inc.) discloses a process for preparing a calcium carbide desulfurizer in which the calcium carbide previously crushed into pieces 1 to 2 inches in diameter (25 to 50 mm) is then ground in a ball mill. for example, with addition before or during the grinding of a polar organic liquid at a rate of 0.001 to 1% and preferably from 0.01 to 0.5% of the weight of carbide. The organic liquid may be a compound containing up to 10 carbon atoms and preferably an alcohol, an ester, a ketone, an ether, an aldehyde or a halogenated alkane.

 3) PROBLEM POSE.

The desulfurization of calcium carbide cast iron faces a dilemma:
The desulphurization reaction occurs at the CaC2 solid-liquid iron interface; it is all the more rapid as the solid is more divided. To promote the reaction rate and avoid the presence in the dross of excess unreacted carbide, it may be tempting to use the finest possible calcium carbide. Thus, some desulphurizing products are based on micronized calcium carbide whose average grain size is close to 30 microns.

-But a fine grain size has several disadvantages:
- risk of explosion due to increased reactivity to moisture,
- lack of flowability,
and if the carbide is used in a mixture with magnesium of larger particle size, risk of segregation during transport.

Thus, it is sometimes preferred, particularly in foundry casting cast iron, coarser grain carbide, 300 to 4000 micrometers, for example. The reaction of the carbide is then very incomplete, which results in high readings: up to 20 kg / t of cast iron instead of 3 kg / t with micronized carbide. Therefore, the use of this coarse carbide is reserved for the casting foundry where the quantities treated are lower. In the iron and steel industry, it would lead to slagging of slag containing high proportions of unreacted calcium carbide, which is very harmful to the environment.

 4) OBJECT OF THE INVENTION

The object of the invention is to solve this problem by providing a self-dispersing desulphurizer having the efficiency of micronized calcium carbide and the chemical inertness and flow properties of coarse-grain carbide.

The invention also provides methods for making this autodisperse desulfurizer.

 5) DESCRIPTION OF THE INVENTION

The self-dispersing desulphurizer, object of the invention is in the form of grains with a diameter greater than 0.3 mm, for example between 0.3 and 6 mm, composed of micronized calcium carbide powder agglomerated with using a binder.

By "calcium carbide" is meant also technical calcium carbide which may contain from 10 to 15% or more impurities, especially lime.

By "micronized calcium carbide" is meant carbide powder whose total particles have a diameter of between a few micrometers and 250 micrometers.

The method of manufacturing such a desulphurizer comprises three steps: the first consists in preparing the carbureliant mixture; the second, to agglomerate the mixture thus obtained; the third, not always necessary, to regrind the agglomerated product to bring it to the desired particle size.

5.1 Preparation of the carbide-binder mixture.

Several types of products can be selected as binder:
solid-state binders having a melting point, preferably a free melting point, of from 70 ° C to 100 ° C. This temperature is slightly higher than that at which the desulphurizer may be exposed during storage, which thus prevents the gluing of the grains between them.

It is of the order of magnitude of that prevailing in the agglomeration apparatus, which facilitates this operation.

For example, some pitches, stearic acid whose melting point is about 70 C or fatty esters of glycerol, will be used. A product marketed under the name "RICIDROL" and resulting from the hydrogenation of castor oil is particularly suitable. Castor oil is more than 80% glycerol triricinoleate.

Ricinoleic acid is a C18 acid comprising a double bond and an alcohol function. The hydrogenation of the castor oil thus leads, by saturation of the double bond, to a product composed for the most part of glycerol trihydroxystearate which has a free melting point at 86 ° C. On the other hand, paraffins, carbide mixtures saturated can not be suitable, their softening starting from 40 C.

 resins whose polymerization is carried out at ambient or moderate temperature (from 40 ° C. to 70 ° C.), for example, furfuryl resins, polyesters, vinyl ester resins, epoxy resins, this list not being limiting.

If binders other than resins (pitches, Ricidrol, stearic acid, etc.) are used, the carbide-binder mixture can be prepared either beforehand in a mixer, a kneader or even in the carbide reduction mill which constitutes an excellent mixer, either directly in the agglomerator without pressure such as granulator drum, bouleteur tray, pelletizing cone. In both cases, the constituents of the mixture are brought to a temperature slightly higher than that of the binder fusion so that it is liquid, but that, at the outlet of the agglomeration apparatus, the binder is solidified .

If binders are used, for example, furfuryl, polyester, vinyl ester or epoxy resins. the mixture of carbide and binder is first made in a mixer, kneader or mill at room temperature. It is also possible to mix the resin and the carbide at the top of the grinder used for carbide micronization and to add the polymerization catalyst to the mixer. The mixture is then introduced into the agglomeration apparatus where it can be slightly heated to accelerate the polymerization of the resin.

 It is also possible, in the context of this invention, to add to the calcium carbide other additions intended: or to cause gas evolution in the melt bath: carbonaceous products (coal, anthracite, petroleum coke, etc. ...), in a proportion of 4 to 10% of the weight of carbide, calcium carbonate, lime diamide, in greater proportions, or to modify the composition of the slag: lime, alumina, magnesia.

These additions, the total of which may be of the order of 100% of the weight of carbide, are either in the mill or in the form of a powder in a mixer at the outlet of the mill.

5.2 Agglomeration of the carbide-binder mixture.

The agglomeration operation uses conventional techniques which will be chosen according to the nature of the binder and the size and mechanical characteristics of the agglomerate that is to be manufactured.

Two groups of techniques can be used:
a) techniques by mixing or without pressure. The apparatuses used are:
- The granulator drum (or pelletizing): it is a rotating cylinder, inclined to the horizontal of a few degrees and driven by a variable speed motor. The product to be agglomerated is introduced at the upper end of the cylinder, the agglomerated product is extracted at its low end. The dimensions of the cylinder and its rotational speed condition the residence time of the product and, consequently, its final particle size. If necessary, is carried out at the exit of the drum, sieving to remove particles or too fine or too coarse. The first and the second, after regrinding, are recycled at the head of the drum.

the bouleteur plateau: it is a circular plateau located in a plane inclined from 30 to 65 on the horizontal rotating about an axis perpendicular to this plane. This plate is provided on its circumference with a rim. The product to be agglomerated is fed towards the center of the plate; the larger pellets migrate upwards and are evacuated over the rim at the lower part of the plateau.

As before, sieving of the agglomerated product is carried out with recycling of fines and coarse particles.

-the pelletizing cone: the principle is quite similar to that of the bouleteur plateau: it is a truncated cone of opening angle between 5 and 30, open on the side of its large base and rotating around its substantially horizontal axis. The product to be agglomerated is introduced towards the bottom of the truncated cone (side of its small base); the agglomerated product leaves in the vicinity of the lower generatrix of the truncated cone by its large base. As before, sieving of the agglomerated product is carried out with recycling of fines and coarse particles.

- other more recent devices, such as for example propellant granulator mixers.

(b) pressure agglomeration techniques.The apparatus used is:
-the pelletizing machine consisting of two axis rollers
horizontally rotating in the opposite direction, substantially tangent
and having cavities of various shapes,
balls, cushions, eggs etc ...

-the roller press next to the previous one but in
which rollers are smooth and separated from each other
by a space.There is then a continuous strip of
the thickness of the space, which must then be crushed for
obtain the desired particle size.

the pelletizer of which there are several versions, the
principle remaining the same: a cavity, of corresponding shape
to that of the pellet to be manufactured is constituted by a
cylindrical matrix of vertical axis, closed at its part
lower by a piston. The powder is poured into this
cavity, leveled, then compressed by the descent of a piston
greater than the desired compression ratio. After recovery from
upper piston, the lower piston moves upwards
to eject the pellet.

the extruder in which the pasty mixture is forced to
through a hole, the die, by a screw system
turning in a sheath that can be heated.

In the case of pressurized agglomeration, and whatever the nature of the binder used, the binder-carbide mixture must be prepared prior to its introduction into the agglomeration apparatus, in a mixer, kneader or mill.

The choice between the two groups of agglomeration techniques is guided by both technical and economic considerations:
- From the technical point of view, the advantages are on the side of the machines of agglomeration under pressure:
The agglomerated products under pressure have a better mechanical strength.

The pellet presses and the pelletizers give perfectly calibrated products which therefore have excellent flowability.

- from an economic point of view, the situation is more nuanced:
The operating cost of pressure vessels is lower because the amount of binder to be used is generally lower: 2 to 5% against 10 to 15% for non-pressure appliances. But binders are relatively expensive products, compared to the price of carbide.

Non-pressure agglomerators, ball and roller presses have an hourly output several tens of times higher than the pelletizers.

On the other hand, investment costs for all pressure agglomerators are significantly higher than those for non-pressure equipment.

5.3 Regrinding of the agglomerated product.

The pellets, pellets, pellets or extrudates obtained during the agglomeration process are often coarser than the desired particle size for the desulphurizer. It is therefore necessary to carry out a regrinding, generally summary, followed by sieving, to bring them to this particle size. At the end of this sieving, the too fine parts are recycles to the agglomeration, the parts too coarse ones are recycled at the top of the crusher.

In addition, it may be advantageous, to further improve the flowability of the desulphurizer obtained, to add the desulfurant regrind and sieved a very small amount, of the order of 1%, carbon black, intimately mixed with the desulphurizer.

 6) EXAMPLES

Examples 1, 2, 3, 4 illustrate the kneading mixture of calcium carbide with various binders.

Example 1

Mixing by blending calcium carbide with a furfuryl resin.

Micronized calcium carbide was added with 7% by weight of coal, the mixture having the following particle size:
Mesh () Refusal (%) Accumulated refusal (%) 200 10 10 100 28 38 75 7 45 50 14 59 25 16 75 passing 25
This carbide added with coal was mixed in a kneader with 10% of its weight of a furfuryl resin for 10 m, at room temperature first and then at 100 ° C to cause curing of the resin.

The granulometric analysis on the product obtained is as follows:
Mesh (p) Refusal (%) Cumulative refusal (%) 200 12 12 100 34 46 75 12 58 50 22 80 25 16.5 96.5 passing 3,5
It is noted that the particle size has changed to coarser grain sizes since the figures in the last column are higher than in the starting product and that, in particular, the fines below 25 p are only 3.5%. instead of 25%.

Example 2
Mixing by blending calcium carbide with hydrogenated castor oil (Ricidrol).

Micronized calcium carbide having the same particle size and the same amount of coal as in the previous example was started.

Ricidrol, at a rate of 5% of the weight of carbide, was introduced liquid into the mixer containing the calcium carbide heated to 100 C. An energetic stirring was carried out for 10 m then the mixture was cooled with further stirring.

The granulometric analysis on the product obtained is as follows:
Mesh (u) Refusal (%) Cumulative refusal (%) 200 11 11 100 33 44 75 11 55 50 19 74 25 21.5 95.5 passing 4.5
It is found that the particle size has evolved to coarser grain sizes since the figures in the last column are higher than in the starting material and that, in particular, the fines below 25 p are only 4.5%. instead of 25%. The particle size is however a little thinner than with the furfuryl resin.

Example 3
Blend of calcium carbide mixed with coal with hydrogenated castor oil (Ricidrol).

The conditions of preparation of the mixture are the same as those of Example 2, but this time an amount of hydrogenated castor oil (Ricidrol) equal to 10% of the weight of carbide is used.

The granulometric analysis on the product obtained is as follows:
Mesh () Refusal (%) Cumulative refusal (%) 200 38.5 38.5 100 29 67.5 75 9 76.5 50 14 90.5 25 8 98.5 passing 1,5
It is found that the particle size has changed to coarser grain sizes since the figures in the last column are higher than in the starting product and that, in particular, the fines below 25 p are only 1.5%. instead of 25%. The particle size is in any case substantially coarser than with the furfuryl resin or with only 5% of Ricidrol.

Example 4
Mixing by blending calcium carbide with stearic acid (stearin).

The conditions of preparation of the mixture are the same as those of Example 2 but this time using stearic acid or stearin at 10% by weight of carbide.

The granulometric analysis on the product obtained is as follows:
Mesh (p) Refusal (%) Cumulative refusal (%) 200 44 44 100 45 89 75 5.5 94.5 50 4 98.5 25 1 99.5 passing 0.5
It can be seen that the particle size has evolved towards grain sizes that are still much coarser since the figures in the last column are higher than in the starting product and that, in particular, fines smaller than 25 p only represent 0, 5% instead of 25%. The particle size is in any case substantially coarser than with the furfuryl resin or with 5% or even 10% of Ricidrol.

The four examples described above show that a simple mixing in a calcium carbide mixer or kneader with a suitable binder already makes it possible to increase the number of coarse particles and to reduce the number of fine particles. However, in the best case, that of Example 4, the product obtained has only 44% of particles of diameter greater than 200 p.

FIG. 1 shows, in another more synthetic form, the particle sizes of the starting material and the mixtures corresponding to Examples 1 to 4. In this figure, the cumulative percentages of the grains smaller than the dimensions on the abscissa are plotted on the ordinate.

The following examples show that a combination of a mixing and agglomerating operation makes it possible to significantly increase the particle size.

Example 5
Pastillage agglomeration.

A mixture of calcium carbide and hard coal having the particle size indicated in Example 1 supplemented with 5% stearic acid was prepared in a kneader. The temperature in the kneader was set at about 100 ° C. in order to maintain the temperature. liquid stearic acid.

A product consisting of stearin-coated carbide having a particle size intermediate between that of the products of Examples 2 and 4 was obtained. After cooling, this product was introduced into the feed hopper of a pelletizer whose pressure was set at 7 ° C. The product was shaped into small cylinders 10 mm in diameter and 6 mm in height with an approximate weight of 1 g. These pellets were then milled in a hammer mill. Grains, all smaller than 6 mm, of which about 64% were between 0.3 and 6 mm, were obtained. The grains <0.3 mm were recycled to the kneader.

Example 6
Agglomeration with roller press.

A mixture of calcium carbide having the particle size indicated in Example 1 supplemented with 10% stearic acid was prepared in a kneader. The temperature in the kneader was maintained at about 100 ° C. so that the stearic acid remained liquid. .

A product consisting of stearin-coated carbide having a particle size similar to that of the products of Example 4 was obtained. At a temperature between 80 ° C. and 100 ° C. (because cooling is not necessary in this case) the product was introduced into the feed hopper of a roller press, the gap between the rolls varied in different tests from 0.5 to 5 mm, thus obtaining the final product in the form of small wafers a few cm square and 0.5 to 5 mm thick, these plates were then milled in a hammer mill, giving grains about 60% of which were between 0.3 and 6 mm.The grains <0.3 mm were recycled in the mixer while the grains> 6 mm were recycled in the hammer mill.

Example 7

Four batches of the same cast iron were treated in parallel with a desulphurizer according to the invention, prepared under the conditions of Example 6, and on the other hand with a desulfurant of the prior art consisting of by technical calcium carbide containing about 10% lime and coarsely ground, so that the grain size is between 0.3 and 4 mm. The quantities of desulphurizer used were 3.5 kg / ton for the desulphurizer according to the invention (test No. 1) and 3.5, 10 and 20 kg / ton for the desulphurizer of the prior art (tests no. "2, 3, 4). The results obtained are given in the table below, in which the initial sulfur contents Si and final Sf are expressed in *, as well as the desulphurization rate T, equal to the ratio (Si - Sf) / Si: N "of the test: 1 2 3 4
Initial sulfur: 0.05 0.05 0.05 0.05
Final sulfur: 0.013 0.032 0.02 0.012
T rate: 74 36 60 76
It is found that the use of the agglomerated calcium carbide based desulphurizer according to the invention has a desulphurization efficiency almost equivalent to that of a grain carbide amount of 0.3 to 4 mm more than five times higher.

Claims (20)

1 Self-dispersing desulphurizer for liquid iron based on calcium carbide in the form of grains composed of calcium carbide powder agglomerated with a binder consisting of an organic product having a melting point of between 70 ° C. C and 1000 is a resin that polymerizes at a temperature between 40 ° C and 70 ° C. Self-dispersing disulfide according to Claim 1, characterized in that the grains have a diameter of between 0.3 and 6 mm. Self-dispersing disulfide according to one of claims 1 or 2, characterized in that the carbide powder is micronized powder whose grain diameter is between a few micrometers and 250 micrometers. Self-dispersing desulphurizer according to one of claims 1 to 3, characterized in that the binder is a pitch. Self-dispersing desulfurant according to one of Claims 1 to 3, characterized in that the binder is stearic acid. Self-dispersing disulfide according to one of claims 1 to 3, characterized in that the binder is a fatty ester of glycerol. Self-dispersing disulfide according to claim 6, characterized in that the binder is hydrogenated castor oil. Self-dispersing disulfide according to one of claims 1 to 3, characterized in that the binder belongs to the group of furfuryl resins, polyesters, vinyl-ester, epoxy. Self-dispersing disulfide according to one of claims 1 to 8, characterized in that the calcium carbide powder is added with carbonaceous product such as coal, anthracite, petroleum coke, in a proportion of 4 to 10% of carbide weight. Self-dispersing disulfide according to one of claims 1 to 9, characterized in that the calcium carbide powder is added with one or more products belonging to the group consisting of lime, calcium carbonate, lime diamide, magnesia alumina, in a total proportion of up to 100% by weight of carbide. Self-dispersing disulfide according to one of claims 1 to 10, characterized in that the agglomerated calcium carbide grains are mixed with about 1% carbon black. 12 A method of manufacturing a self-dispersing desulfurizer  prepare a homogeneous mixture of micronized calcium carbide, optionally carbonaceous product and binder,  -Gglomerate and shape this homogeneous mixture with the aid of apparatus or without pressure of the granulator drum type, bouleteur platter, pelletizing machine, or with pressure of the pellet press type, roller press, pelletizer, extruder,  grinding, if necessary, and sieving the agglomerated product to bring it to the desired particle size, characterized in that the binder used is an organic binder with a melting point greater than or equal to 70 ° C., the mixing operations being carried out preferably at a temperature above this melting point. 13 Process for manufacturing a self-dispersing desulfurizer consisting of  prepare a homogeneous mixture of micronized calcium carbide, optionally carbonaceous product and binder,  agglomerating and shaping this homogeneous mixture by means of apparatus or without pressure of the type of granulator drum, bouleter platter, pelletization cone, or with pressure of the pellet press type, roller press, pelletizer, extruder,  grinding, if necessary, and sieving the agglomerated product to bring it to the desired particle size, characterized in that the binder used is a polymerizable organic resin at room temperature or moderate, 40 "C to 70" C. Process for manufacturing a self-dispersing desulphurizer according to claim 12, characterized in that the binder is a pitch. A method of manufacturing a self-dispersing desulfurizer according to claim 12 characterized in that the binder is stearic acid. Process for the production of a self-dispersing desulphurizer according to claim 12, characterized in that the binder is a fatty ester of glycerol. Process for the production of a self-dispersing desulphurizer according to claim 16, characterized in that the binder is hydrogenated castor oil. 18 A method of manufacturing a self-dispersing desulfurant according to claim 13 characterized in that the binder is a resin belonging to the group formed by furfuryl resins, polyesters, vinylester, epoxy. 19 Process for manufacturing a self-dispersing desulphurizer according to one of claims 12, 14, 15, 16, 17, characterized in that the mixture of calcium carbide, optionally of carbon product and of binder is made in the apparatus of Agglomeration: granulator drum, bouler tray or pelletizing cone. A method of manufacturing a self-dispersing desulfurant according to one of claims 12 to 19, characterized in that the agglomerated, regrind, sieved product is mixed with about 1% of its weight of carbon black.