EP0511121B1 - Desulfurisation agent for pig iron, comprising calcium carbide and an organic binder - Google Patents

Abstract

New product for desulphurising liquid pig iron, consisting essentially of calcium carbide and of an organic binder, and process for its manufacture. <??>The product consists of technical calcium carbide powder, with the optional addition of products intended to produce a gas release in the bath or to modify the composition of the slag, coated or agglomerated by means either of resins or of an organic compound with a well-established melting point and solid at room temperature. <??>The process comprises a number of stages: mixing the carbide and additives with binder, resin or the organic product, agglomeration by forming nuts, tablets, compression or extrusion, and optional remilling and screening to obtain the desired particle size distribution. <??>The product is introduced into the liquid pig iron with a lance, by gravity or in the form of cored wire. It has the advantage of good pourability, increased efficiency and reduced reactivity towards moisture. It is employed for the desulphurisation of pig iron, both in refining and in casting. <IMAGE>

Description

1 °) TECHNICAL AREA

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

Most desulphurizing agents are based on two alkaline earths: magnesium and calcium which combine easily with sulfur to give sulphides, forming slags insoluble in cast iron. The excess magnesium is eliminated due to its high vapor pressure at the treatment temperature; excess calcium compounds (lime, carbonate or carbide) are eliminated in the slag. Thus, separately or in combination, metallic magnesium, calcium carbonate, lime, lime diamide (mixture of Ca carbonate and carbon) and calcium carbide are used, optionally added with products intended to improve the flowability of the mixture or to release gases allowing a good distribution of the desulfurizer in the liquid iron.

These desulphurizers are, in fact, for refining cast irons, most often injected using a lance, suspended in an inert carrier gas. For molding irons, the grains of desulfurizer are simply poured into the ladle, into the pouring channel or into the bath.

The invention relates to a new desulphurizing product essentially containing calcium carbide and a binder as well as its manufacturing process.

2 °) STATE OF THE ART

French patent 1,194,778 (Union Carbide Corporation) describes a process for treating Ca carbide in oil before its use as a desulfurizer. Oil is sprayed onto the carbide, with a particle size between 0.074 and 1.168 mm and brought to 150 ° C. of the oil at a rate of 0.25 to 4% of the weight of carbide. The oil can be mineral (petroleum oil, petrol, kerosene), vegetable (linseed oil) or animal (fish oil). Synthetic waxes or paraffins may also be suitable.

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

European patent application EP 0 184 723 (Cyanamid Canada Inc.) describes a process for preparing a desulfurizer based on calcium carbide in which the calcium carbide previously crushed into pieces of 1 to 2 inches in diameter (25 to 50 mm) is then ground, in a ball mill by 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 can 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.

US Patent 4,533,572 (Neelameggham) describes a process in which metallic granules, in particular of magnesium and aluminum are coated by mixing by mechanical means with a polymerizable oil, are heated to polymerize the oil in varnish and finally heated to a higher temperature to transform, at least partially, the carbon varnish. The coating may contain fine particles of at least one calcium compound. These carbon coated granules are used for the desulfurization and deoxidation of steels.

3 °) PROBLEM POSED.

• La réaction de désulfuration se passe à l'interface CaC₂ solide-fonte liquide; elle est d'autant plus rapide que le solide est plus divisé. Pour favoriser la vitesse de réaction et éviter la présence dans les crasses d'un excès de carbure n'ayant pas réagi, on peut être tenté d'utiliser du carbure de calcium le plus fin possible. Ainsi, certains produits désulfurants sont-ils à base de carbure de calcium micronisé dont la taille moyenne des grains est voisine de 30 micromètres.
• Mais une granulométrie fine présente plusieurs 5 inconvénients:
  • risque d'explosion due à une réactivité accrue vis-à-vis de l'humidité,
  • manque de coulabilité,
  • et si le carbure est utilisé en mélange avec du magnésium de plus forte granulométrie,risque de ségrégation au cours du transport.

Desulfurization of cast iron with calcium carbide faces a dilemma:

• The desulfurization reaction takes place at the CaC ₂ 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 an excess of unreacted carbide, one may be tempted to use the finest possible calcium carbide. Thus, certain desulphurizing products are based on micronized calcium carbide whose average grain size is close to 30 micrometers.
• However, a fine particle size has several disadvantages:
  • risk of explosion due to increased reactivity towards humidity,
  • lack of flowability,
  • and if the carbide is used in mixture with magnesium of larger particle size, risk of segregation during transport.

Thus, it is sometimes preferred, in particular in foundry casting molding, coarse-grained carbide, from 300 μm to 10 mm, for example. The carbide reaction is then very incomplete, which results in high bets: up to 20 kg / t of pig iron instead of 3 kg / t with micronized carbide. Consequently, the use of this coarse carbide is reserved for the molding foundry where the quantities treated are lower. In the steel industry, it would lead to the slagging of slag containing large proportions of unreacted calcium carbide, which would be very harmful to the environment.

The problem posed is of the same nature for the desulfurization of refining and molding irons, but the suitable product does not have quite the same characteristics. For refining irons we need a product with a fine enough particle size so that it lends itself to pneumatic transport and does not clog the injection lances but not comprising too many ultrafine so that it has good flowability. For example, such a product can have approximately 85% and more of its grains between 25 and 300 μm. For molding irons we need a coarser grain product, 300 µm to 10 mm, for example.

4) OBJECT OF THE INVENTION.

The object of the invention is to solve this problem by proposing a desulfurizer having the effectiveness of micronized calcium carbide and the particle sizes indicated above. This result is achieved by increasing the particle size of the product by coating or agglomeration of the calcium carbide. micronized with a well-chosen organic binder which will disappear on contact with liquid iron, dispersing the carbide in the bath. The desulfurizer is thus self-dispersing.

• il protège le carbure contre l'oxydation et contre l'humidité. Le carbure est, surtout lorsqu'il est à l'état de fines particules, susceptible de provoquer des explosions au contact de l'air (explosions de poudres). En outre, sa réaction avec l'eau et l'humidité produit, comme on le sait, de l'acétylène, gaz très inflammable.
• il permet, tout en conservant à la température de la fonte liquide les propriétés réactives du carbure de calcium finement divisé, de réagglomérer les parties les plus fines ou poudres de carbure résultant du broyage.
• il permet, ayant un point de fusion franc relativement élevé, d'éviter le ramollissement progressif du produit au contact d'une température élevée qui provoquerait des colmatages dans les dispositifs de stockage,de manutention et de distribution du produit désulfurant.

This binder also has other functions:

• it protects the carbide against oxidation and against humidity. Carbide is, especially when it is in the form of fine particles, capable of causing explosions on contact with air (powder explosions). In addition, its reaction with water and humidity produces, as is known, acetylene, a highly flammable gas.
• it allows, while retaining the reactive properties of finely divided calcium carbide at the temperature of liquid iron, to re-agglomerate the finest parts or carbide powders resulting from grinding.
• it allows, having a relatively high frank melting point, to avoid the progressive softening of the product in contact with a high temperature which would cause clogging in the devices for storage, handling and distribution of the desulfurizing product.

• pour la fonte d'affinage, injecté sous sa forme la plus fine à l'aide d'une lance soit seul soit en co-injection avec un autre désulfurant tel le magnésium;
• pour la fonte de moulage, soit mis dans le chenal de coulée ou au fond de la poche avant qu'on y verse la fonte, soit versé simplement en chute dans la fonte, dans toua les cas sous sa forme la plus grossière;
• à la fois pour la fonte d'affinage et de moulage, conditionné à l'intérieur d'un tube continu métallique introduit progressivement dans la fonte.(fil fourré)

Such a product can be used for the desulfurization of cast iron under different conditions:

• for refining pig iron, injected in its finest form using a lance either alone or in co-injection with another desulfurizer such as magnesium;
• for casting iron, either placed in the pouring channel or at the bottom of the ladle before the iron is poured into it, or simply poured down into the iron, in all cases in its coarsest form;
• for both refining and molding cast iron, conditioned inside a continuous metallic tube gradually introduced into the cast iron (cored wire)

The invention also provides the process for manufacturing this desulfurizing product.

5 °) DESCRIPTION OF THE INVENTION.

The product for the desulfurization of liquid cast iron based on calcium carbide, object of the invention and more specifically of claim 1, is in the form of grains composed of calcium carbide powder coated or agglomerated using 'A binder consisting either of an organic product having a frank melting temperature between 70 ° C and 100 ° C, or a furfuryl resin whose polymerization temperature is between 40 ° C and 70 ° C.

The process for manufacturing the product of the invention is the subject of claim 14.

The implementation of the invention comprises two variants according to the envisaged application:

For the finest desulphurizers, intended for refining irons, we limit ourselves to the first step described below. The calcium carbide is simply coated, that is to say made up of grains of calcium carbide coated with a first internal layer of a solid binder at room temperature and possibly with a more or less continuous second external layer. finer grains of calcium carbide, also coated. The percentage by weight of grains between 25 and 300 μm is at least 85%.

For the coarsest desulfurizers, intended for molding irons, the process is more complex and comprises the three stages described below. The calcium carbide is agglomerated, that is to say made up of grains with a diameter greater than 0.3 mm, for example comprised between 0.3 and 10 mm, composed of micronized calcium carbide powder agglomerated at 1 using a binder. It is also possible by pushing the grinding, to obtain a particle size comparable to that of the coated carbide, but this unnecessarily complicates the process.

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

By "micronized calcium carbide" is meant carbide powder, the totality of the particles of which has a diameter of between a few micrometers and 250 micrometers.

The process for manufacturing such a desulfurizer comprises three stages: the first consists in preparing a homogeneous mixture of micronized calcium carbide and a binder consisting of either an organic product having a melting temperature between 70 ° C and 100 ° C, or a furfuryl resin whose polymerization temperature is between 40 ° C and 70 ° C; the second, to agglomerate the mixture thus obtained; the third, to regrind the agglomerated product to bring it to the desired particle size. As indicated above, the second and third steps are not always necessary and constitute a particular mode of implementing the invention.

5.1 Preparation of the carbide-binder mixture.

• des liants solides à la température ambiante dont le point de fusion, de préférence franc, soit compris entre 70°C et 100°C. Cette température est légèrement supérieure à celle à laquelle le désulfurant risque d'être exposé au cours du stockage, ce qui évite ainsi le collage des grains entre eux. Elle est de l'ordre de grandeur de celle régnant dans les appareils d'agglomération, ce qui facilite cette opération.

Several types of products can be chosen as a binder:

• solid binders at room temperature, the melting point of which, preferably frank, is between 70 ° C. and 100 ° C. This temperature is slightly higher than that to which the desulphurizer may be exposed during storage, which thus prevents the grains from sticking together. It is of the order of magnitude of that prevailing in agglomeration apparatus, which facilitates this operation.

To have a clear melting point, it is advantageous to use a product composed mainly of a single chemical species, at 80% or better at 90%, for example.

Some pitches will be used, stearic acid whose melting point is around 70 ° C or fatty esters of glycerol. A product marketed under the name of "RICIDROL" and resulting from the hydrogenation of castor oil is particularly suitable. Castor oil is more than 80% glycerol triricinoleate. Ricinoleic acid is a C ₁₈ acid comprising a double bond and an alcohol function. The hydrogenation of castor oil leads, by saturation of the double bond, to a product composed mainly of glycerol trihydroxystearate which has a clear melting point at 86 ° C. On the other hand, paraffins, mixtures of saturated carbides, cannot be suitable, their softening starting from 40 ° C.

• des résines furfuryliques dont la polymérisation se fait à température ambiante ou modérée ( de 40°C à 70°C ).

The fatty esters of glycerol and in particular glycerol trihydroxystearate are preferred for the manufacture of coated carbide.

• furfuryl resins, the polymerization of which takes place at ambient or moderate temperature (from 40 ° C. to 70 ° C.).

This resin, by polymerizing during the agglomeration treatment, hardens and prevents softening of the desulfurizing product during storage.

If binders other than resins are used (pitches, hydrogenated castor oil, stearic acid, etc.), the carbide-binder mixture can be done either beforehand in a mixer, a kneader or even in the reduction mill of the carbide which constitutes an excellent mixer, either directly in the agglomeration apparatus without pressure such as granulating drum, pelletizing plate, pelletizing cone. In both cases, the constituents of the mixture are generally brought to a temperature slightly above that of melting the binder so that it is liquid, but that, at the outlet of the agglomeration apparatus, the binder is solidified. This heating is essential when using micronized carbide. This can be avoided by the use of a cylinder press which has both a grinding and agglomeration function and which can be fed directly with coarse carbide and binder at room temperature.

If furfuryl resins are used as binders, the mixture of carbide and binder is done beforehand in a mixer, kneader or grinder, at room temperature. It is also possible to mix the resin and the carbide at the top of the mill used for micronizing the carbide and to add the polymerization catalyst to the mixer. The mixture is then introduced into the agglomerator where it can be slightly heated to accelerate the polymerization of the resin.

• ou bien à provoquer un dégagement gazeux dans le bain de fonte: produits carbonés (houille, anthracite, coke de pétrole etc...), dans une proportion de 4 à 10 % du poids de carbure, carbonate de calcium, chaux diamide, dans des proportions plus importantes,
• ou bien à modifier la composition du laitier: chaux, alumine, magnésie,
• ou bien à contrôler l'activité de l'oxygène dans la fonte: noir de fumée, aluminium, magnésium, calcium.

It is also possible, within the framework of this invention, to add to the calcium carbide other additions intended:

• or else to cause a gassing in the iron bath: carbonaceous products (coal, anthracite, petroleum coke, etc.), in a proportion of 4 to 10% by weight of carbide, calcium carbonate, lime diamide, in larger proportions,
• or else to modify the composition of the slag: lime, alumina, magnesia,
• or else to control the activity of oxygen in the cast iron: smoke black, aluminum, magnesium, calcium.

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

The amount of binder to be used is between 0.2 and 15% of the weight of carbide or carbide-additions mixture and, preferably, between 0.2 and 10%.

5.2 Agglomeration of the carbide-binder mixture.

The agglomeration operation implements classic techniques which will be chosen according to the nature of the binder and the size and mechanical characteristics of the agglomerate which it is desired to manufacture.

• a) des techniques par malaxage ou sans pression. Les appareils utilisés sont:
  • le tambour granulateur (ou de bouletage): il s'agit d'un cylindre tournant, incliné sur l'horizontale de quelques degrés et entraîné par un moteur à vitesse variable. Le produit à agglomérer est introduit à l'extrêmité haute du cylindre, le produit aggloméré est extrait à son extrêmité basse. Les dimensions du cylindre et sa vitesse de rotation conditionnent le temps de séjour du produit et, par conséquent, sa granulométrie finale. Si nécessaire, on procède, à la sortie du tambour, à un tamisage pour éliminer les particules ou trop fines ou trop grossières. Les premières et les deuxièmes, après rebroyage, sont recyclées en tête du tambour.
  • le plateau bouleteur: il s'agit d'un plateau circulaire situé dans un plan incliné de 30 à 65 ° sur l'horizontale tournant autour d'un axe perpendiculaire à ce plan. Ce plateau est muni sur sa circonférence d'un rebord. Le produit à agglomérer est alimenté vers le centre du plateau; les boulettes les plus grosses migrent vers le haut et sont évacuées par-dessus le rebord,à la partie basse du plateau. Comme précédemment, on procède à un tamisage du produit aggloméré avec recyclage des fines et des grosses particules rebroyées.
  • le cône de bouletage: le principe est assez voisin de celui du plateau bouleteur: il s'agit d'un tronc de cône d'angle d'ouverture compris entre 5 et 30°, ouvert du côté de sa grande base et tournant autour de son axe sensiblement horizontal. Le produit à agglomérer est introduit vers le fond du tronc de cône (côté de sa petite base); le produit aggloméré sort au voisinage de la génératrice inférieure du tronc de cône par sa grande base. Comme précédemment,on procède à un tamisage du produit aggloméré avec recyclage des fines et des grosses particules rebroyées.
  • d'autres appareils plus récents, tels par exemple les malaxeurs granulateurs à hélices.
• b) des techniques d'agglomération sous pression.Les appareils utilisés sont:
  • la presse à cylindres constituée de deux rouleaux d'axes horizontaux tournant en sens inverse, sensiblement tangents ou à faible distance et présentant éventuellement des cavités de formes variées, boulets, coussins, oeufs etc...Dans ce cas, on peut éviter le broyage-malaxage à chaud préalable et alimenter directement la presse avec du carbure grossier tout venant ( de 0 à 12 mm) et du liant en paillettes, la presse se comportant comme un broyeur à cylindres.
  • la pastilleuse dont il existe plusieurs versions, le principe restant le même: une cavité, de forme correspondant à celle de la pastille à fabriquer est constituée par une matrice cylindrique d'axe vertical, obturée à sa partie inférieure par un piston. La poudre est versée dans cette cavité, arasée, puis comprimée par la descente d'un piston supérieur au taux de compression souhaité. Après remontée du piston supérieur, le piston inférieur se déplace vers le haut pour éjecter la pastille.
  • l'extrudeuse dans laquelle le mélange pâteux est forcé au travers d'un orifice, la filière, par un système de vis tournant dans un fourreau qui peut être chauffé.

Two groups of techniques can be used:

• a) techniques by mixing or without pressure. The devices used are:
  • the granulating drum (or pelletizer): it is a rotating cylinder, tilted horizontally by a few degrees and driven by a variable speed motor. The product to be agglomerated is introduced at the top end of the cylinder, the agglomerated product is extracted at its bottom end. The dimensions of the cylinder and its speed of rotation condition the residence time of the product and, consequently, its final particle size. If necessary, a sieve is removed from the drum to remove particles that are too fine or too coarse. The first and second, after regrinding, are recycled at the top of the drum.
  • the pelletizer plate: it is a circular plate located in an inclined plane of 30 to 65 ° on the horizontal rotating around an axis perpendicular to this plane. This tray is provided on its circumference with a rim. The product to be agglomerated is fed towards the center of the tray; the larger dumplings migrate upwards and are discharged over the rim, at the bottom of the tray. As before, the product is sieved agglomerated with recycling of fine and large regrind particles.
  • the pelletizing cone: the principle is quite similar to that of the pelletizing plate: it is a truncated cone with an opening angle between 5 and 30 °, open on the side of its large base and rotating around its axis substantially horizontal. 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, the agglomerated product is sieved with recycling of the fine and large regrind particles.
  • other more recent devices, such as propeller granulator mixers.
• b) pressure agglomeration techniques. The devices used are:
  • the cylinder press consisting of two rollers with horizontal axes rotating in opposite directions, substantially tangent or at a short distance and possibly having cavities of various shapes, balls, cushions, eggs, etc. In this case, grinding can be avoided -mixing beforehand and directly feeding the press with coarse coarse carbide (from 0 to 12 mm) and glitter binder, the press behaving like a roller mill.
  • the pelletizer of which there are several versions, the principle remaining the same: a cavity, of shape corresponding to that of the pellet to be manufactured is constituted by a cylindrical matrix of vertical axis, closed at its lower part by a piston. The powder is poured into this cavity, leveled, then compressed by the descent of a piston greater than the desired compression rate. After rising from upper piston, the lower piston moves up to eject the pellet.
  • the extruder in which the pasty mixture is forced through an orifice, the die, by a system of screws rotating in a sheath which can be heated.

In the case of agglomeration under pressure, 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 grinder.

• au point de vue technique, les avantages sont du côté des machines d'agglomération sous pression car les produits agglomérés sous pression présentent une meilleure tenue mécanique. En outre, les presses à bouleter et les pastilleuses donnent des produits parfaitement calibrés.
• au point de vue économique, la situation est plus nuancée: Le coût d'exploitation des appareils sous pression est plus bas, mais leur coût d'investissement est sensiblement plus élevé que celui des appareils sans pression.

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 pressure agglomeration machines because the agglomerated products under pressure have better mechanical strength. In addition, pelletizing presses and pelletizers produce perfectly calibrated products.
• from an economic point of view, the situation is more nuanced: The operating cost of pressure vessels is lower, but their investment cost is significantly higher than that of non-pressure vessels.

5.3 Regrinding of the agglomerated product.

The pellets, balls, pellets or extrudates obtained during the agglomeration operation are often coarser than the particle size desired for the desulfurizer. 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 parts that are too fine are recycled to the agglomeration, the parts that are too coarse are recycled at the top of the mill.

In addition, it may be advantageous, to further improve the flowability of the desulfurizer obtained, to add the regrind and sifted desulfurizer in a very small amount, of the order of 1%, of smoke black, intimately mixed with the desulfurizer.

6 °) EXAMPLES

Examples 1, 2, 3, 4 and 5 illustrate the mixing by mixing of calcium carbide with different binders.

Example 1.

A) Two batches of calcium carbide from the same origin were ground in a bar mill and under identical operating conditions, at the same temperature of 115 ° C., one with the addition of 1% hydrogenated castor oil , the other without.

A particle size analysis was carried out on each of these two batches which gave the following results: Without hydrogenated castor With hydrogenated castor Mesh (µm) Refusal Cumulative refusal Refusal Cumulative refusal 100 11.2 11.2 5.6 5.6 75 11.6 22.8 10.1 15.7 50 19.6 42.4 24.5 40.2 25 31.7 74.1 46.4 86.7 passing 25.6 13.3

On each line of this table, successively for the batch without hydrogenated castor oil and with, we have entered, in the first column, the dimensions, in micrometers, of square mesh sieves, in the next column the fraction (in%) larger than the corresponding mesh but finer than the preceding mesh, in the next column the cumulative (in%) of the fractions larger than the corresponding mesh.

• que la granulométrie est plus resserrée avec le produit selon l'invention:il y a moins de grosses particules (supérieures à 100 micromètres), 5,6 % au lieu de 11,2 % et surtout il y a environ moitié moins de fines (inférieures à 25 micromètres): 13,3 % au lieu de 25,6 %
• que cependant, la proportion de particules de diamètre supérieur à 50 micromètres reste sensiblement identique, environ 50 %.

This table shows:

• that the particle size is tighter with the product according to the invention: there are fewer large particles (greater than 100 micrometers), 5.6% instead of 11.2% and above all there are approximately half less fines ( less than 25 micrometers): 13.3% instead of 25.6%
• that however, the proportion of particles with a diameter greater than 50 micrometers remains substantially identical, approximately 50%.

B) A summary flow test was made to compare the flowability of the two powders. This test consists in passing a powder sample through a calibrated orifice located at the bottom of a funnel whose half-angle at the top is 20 °. Under well-defined funnel filling conditions, the result is expressed by the diameter of the lowest orifice for which a flow is observed.
In the case of carbide powder without hydrogenated castor oil, the flow is observed for a diameter of 22 mm, while in the case of the ground powder with addition of hydrogenated castor oil, the flow is observed for a diameter of 18 mm.

où C est la capacité du condensateur, V, le voltage.C) The explosive thresholds of the carbide powder were measured comparatively without and with the addition of hydrogenated castor oil. The tests are carried out by bursting a spark of known energy within a cloud of dust of grain product less than 50 micrometers, suspended in a vertical cylinder traversed by an ascending current of carrier gas, oxygen or air. The sparks are produced by the discharge of capacitors previously charged under a direct voltage of 260 volts. The gas flow rate is 6 liters / minute, the quantity of powder, 2 grams. The energy of the spark is given by the formula: $${\text{E = 1/2 CV}}^{\text{2}}$$

where C is the capacitance of the capacitor, V, the voltage.

We carry out a series of 20 consecutive tests. The explosion threshold is defined as the minimum energy above which the probability of explosion is> 5% (1 explosion per series of 20 tests). The higher the explosive threshold, the less explosive the powder is.

With carbide powder without addition, the explosive threshold is 31 mJ (millijoule); with the powder according to the invention, the threshold rises to 213 mJ.

D) To assess the reactivity with respect to water, 2 g of each of the powders were introduced into 30 milliliters of water and the volume of acetylene released per second was measured. With the carbide without addition, a release of 70 ml / s is observed, whereas with the powder according to the invention, this release is only of 11 ml / s.

• un mélange (1) de l'art antérieur constitué de:
  • carbure de calcium technique : 93 %
  • produits carbonés ( houille,noir de fumée) : 7 %
• un mélange (2) selon l'invention constitué de:
  • carbure de calcium technique : 93 %
  • produits carbonés : 6 %
  • huile de ricin hydrogénée : 1 %
• un mélange (3) selon l'invention constitué de:
  • carbure de calcium technique : 99 %
  • huile de ricin hydrogénée: 1 %

E) The effectiveness, in terms of desulfurization, of three mixtures was compared:

• a mixture (1) of the prior art consisting of:
  • technical calcium carbide: 93%
  • carbonaceous products (coal, black smoke): 7%
• a mixture (2) according to the invention consisting of:
  • technical calcium carbide: 93%
  • carbon products: 6%
  • hydrogenated castor oil: 1%
• a mixture (3) according to the invention consisting of:
  • technical calcium carbide: 99%
  • hydrogenated castor oil: 1%

Three batches of the same cast iron were treated at the rate of 3 kg of desulphurizer / ton of pig iron with an initial sulfur content S _i = 0.050%. The table below indicates, for each of the desulphurizers, the final sulfur content reached, S _f and the desulphurization rate T defined as the ratio (S _i - S _f ) / Si. Mixed S _f T 1 0.018% 64% 2 0.013% 74% 3 0.012% 76%

These tests make it possible to note the improvement in the efficiency of the desulfurizing mixture according to the invention compared to the other mixtures.

Example 2.

Mixing by mixing of calcium carbide with a furfuryl resin.

We started with micronized calcium carbide supplemented with 7% by weight of hard coal, the mixture having the following particle size: Mesh (µm) Refused (%) Cumulative refusal (%) 200 10 10 100 28 38 75 7 45 50 14 59 25 16 75 passing 25

This carbide with added coal was mixed in a mixer with 10% of its weight of a furfuryl resin for 10 minutes, at room temperature first, then at 100 ° C to cause the resin to harden.

The particle size analysis on the product obtained is as follows:

It can be seen that the grain size has evolved towards coarser grain sizes since the figures in the last column are higher than in the starting product and that, in particular, fines less than 25 µm represent only 3.5% instead of 25%.

Example 3

Mixing by mixing of calcium carbide with hydrogenated castor oil (Ricidrol).

We started with micronized calcium carbide having the same particle size and the same quantity of coal as in the previous example.
Ricidrol, at a rate of 5% by weight of carbide, was introduced liquid into the mixer containing the calcium carbide heated to 100 ° C. Vigorous stirring was carried out for 10 minutes, then the mixture was cooled with continued stirring.

The particle size analysis on the product obtained is as follows: Mesh (µm) Refused (%) Cumulative refusal (%) 200 11 11 100 33 44 75 11 55 50 19 74 25 21.5 95.5 passing 4.5

The granulometry has also evolved towards coarser grain sizes and in particular, fines smaller than 25 µm represent only 4.5% instead of 25%. The particle size is however a little finer than with furfuryl resin.

Example 4

Mixing by mixing of calcium carbide added with coal with hydrogenated castor oil (Ricidrol).
The conditions for preparing the mixture are the same as in Example 3, but this time an amount of hydrogenated castor oil (Ricidrol) is used equal to 10% of the weight of carbide.

The particle size analysis on the product obtained is as follows: Mesh (µm) Refused (%) 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

In this example, the grain size has further evolved towards coarser grain sizes and, in particular, fines smaller than 25 µm represent only 1.5% instead of 25%. The particle size is in any case substantially coarser than with furfuryl resin or with only 5% Ricidrol.

Example 5

Mixing by mixing of calcium carbide with stearic acid (Stearin).

The conditions for preparing the mixture are the same as those of Example 3, but this time using stearic acid or stearin at 10% by weight of carbide.

The particle size analysis on the product obtained is as follows: Mesh (µm) Refused (%) Cumulative refusal (%) 200 44 44 100 45 89 75 5.5 94.5 50 4 98.5 25 1 99.5 passing 0.5

Here again, the grain size has evolved towards even coarser grain sizes and, in particular, fines smaller than 25 µm represent only 0.5% instead of 25%. The particle size is in any case significantly coarser than with furfuryl resin or with 5% or even 10% of Ricidrol.

The five examples described above show that a simple mixing in a mixer or a kneader of calcium carbide with an appropriate binder already makes it possible to increase the number of coarse particles and to decrease the number of fine particles. However, in the best case, that of Example 5, the product obtained has only 44% of particles with a diameter greater than 200 μm.

FIG. 1 represents in another, more synthetic form, the particle sizes of the starting product and of the mixtures corresponding to Examples 2 to 5. In this figure are plotted the ordinates the cumulative percentages of the grains smaller than the dimensions plotted on the abscissa.

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

Example 6

Agglomeration by tableting.

A mixture of calcium carbide and coal having the particle size indicated in Example 2 was added in a mixer, supplemented with 5% stearic acid. The temperature in the mixer was adjusted to approximately 100 ° C. in order to maintain the liquid stearic acid.
A product consisting of carbide coated with stearin was obtained having a particle size intermediate between that of the products of Examples 3 and 5. After cooling, this product was introduced into the feed hopper of a pelletizer whose pressure was set at 7 bars. The product was formed into small cylinders 10 mm in diameter and 6 mm in height having an approximate weight of 1 g. These pellets were then shredded in a gentle manner in a hammer mill. Grains were obtained, all less than 6 mm, of which approximately 64% were between 0.3 and 6 mm. The grains <0.3 mm were recycled in the mixer.

Example 7

Agglomeration with a roller press.

A mixture of calcium carbide having the particle size indicated in example 2 was added in a mixer, supplemented with 10% stearic acid. The temperature in the mixer was maintained at approximately 100 ° C. so that the stearic acid remained liquid. .
A product consisting of carbide coated with stearin having a particle size similar to that of the products of Example 5 was obtained. At a temperature of between 80 ° C. and 100 ° C. (since cooling is not necessary in this case ), the product was introduced into the feed hopper of a roller press. The interval between the rollers varied in different tests from 0.5 to 5 mm. The final product was thus obtained in the form of small plates of a few cm side and from 0.5 to 5 mm thick. These plates were then shredded in a gentle manner in a hammer mill. Grain was obtained of which about 60% was between 0.3 and 6 mm. The grain <0.3 mm was recycled in the mixer while the grain> 6 mm was recycled in the hammer mill.

Example 8.

Agglomeration with the ball press.

A mixture of calcium carbide having a particle size between 0 and 12 mm was added in a kneader supplemented with 5% stearic acid. The temperature in the mixer was kept at room temperature.
The mixture obtained was introduced into the feed hopper of a ball press, a press the cylinders of which bear alveoli in the form of balls. In the upper part where the two cylinders of the press come together, the press behaves like a grinder in which the carbide grains are reduced. The ground grains are, in the vicinity of the plane containing the axes of the cylinders, agglomerated using the binder in the form of balls. These balls were then shredded in a gentle manner in a hammer mill. Grain was obtained of which about 60% was between 0.3 and 10 mm. The grain <0.3 mm was recycled in the mixer while the grain> 10 mm was recycled in the hammer mill.

Example 9.

Four batches of the same cast iron were treated in parallel on the one hand with a desulfurizer according to the invention, prepared under the conditions of Example 7 and on the other hand with a desulfurizer of the prior art constituted by technical calcium carbide containing about 10% lime and coarsely ground, so that the grain size is between 0.3 and 4 mm. The amounts of desulfurizer used were 3.5 kg / tonne for the desulfurizer according to the invention (test No. 1) and 3.5, 10 and 20 kg / tonne for the desulfurizer of the prior art (tests n ° 2, 3, 4). The results obtained are shown in the table below, in which the initial sulfur contents S _i and final S _f are expressed in%, as well as the desulfurization rate T, equal to the ratio (S _i - S _f ) / S _i : Test number: 1 2 3 4 Initial sulfur: 0.05 0.05 0.05 0.05 Final sulfur: 0.013 0.032 0.02 0.012 Rate T: 74 36 60 76

It is found that the use of the desulfurizer based on agglomerated calcium carbide according to the invention has a desulfurization efficiency almost equivalent to that of a quantity of carbide in grains of 0.3 to 4 mm more than five times greater.

Claims (28)

1. Product for the desulphurizing of liquid cast iron consisting of calcium carbide, possibly of one or more products belonging to the group consisting of lime, calcium carbonate diamide lime, magnesium oxide, alumina, carbon black, aluminium, magnesium and calcium, in a quantity by weight at least equal to that of the calcium carbide, and of a binder, this product being in the form of a powder which is coated or agglomerated by means of a binder, this binder being either an organic product having a sharp transition temperature of between 70°C and 100°C or a furfuryl resin of which the polymerization temperature is between 40°C and 70°C.
2. Product for the desulphurizing of cast iron according to claim 1, characterized in that it consists of grains of calcium carbide coated with a first layer of solid binder at ambient temperature and possibly with a second more or less continuous external layer of finer grains of calcium carbide which are themselves coated.
3. Product for the desulphurizing of cast iron according to one of claims 1 or 2, characterized in that the carbide powder is micronized powder of which the grain diameter is between a few micrometres and 250 micrometres.
4. Product for the desulphurizing of cast iron according to one of claims 1 to 3, characterized in that the binder is a pitch.
5. Product for the desulphurizing of cast iron according to one of claims 1 to 3, characterized in that the binder is stearic acid.
6. Product for the desulphurizing of cast iron according to one of claims 1 to 3, characterized in that the binder is a saturated fatty ester of glycerine.
7. Product for the desulphurizing of cast irons according to claim 6, characterized in that the chemical purity of the saturated fatty ester is at least 90%.
8. Product for the desulphurizing of cast irons according to one of claims 6 or 7, characterized in that the saturated fatty ester is hydrogenated castor oil based on glycerine trihydroxystearate.
9. Product for the desulphurizing of cast irons according to one of claims 1 to 8, characterized in that the quantity of binder is between 0.2 and 10% of the weight of carbide.
10. Product for the desulphurizing of cast irons according to one of claims 1 to 9, characterized in that the calcium carbide powder has additions of carbonated product such as coal, anthracite, petrol coke, in a proportion of 4 to 10% by weight of carbide.
11. Product for the desulphurizing of cast irons according to one of claims 1 to 10, characterized in that 85% of its grains are between 25 and 300 micrometres.
12. Product for the desulphurizing of cast iron according to one of claims 1 to 10, characterized in that the grains have a diameter of between 0.3 and 10 mm.
13. Product for the desulphurizing of cast irons according to one of claims 1 to 11, characterized in that the agglomerated grains of calcium carbide are mixed with about 1% of carbon black.
14. Process for producing a product having the form of a powder which is coated or agglomerated by means of a binder for the desulphurizing of cast irons containing calcium carbide and possibly one or more additives belonging to the group consisting of lime, calcium carbonate, diamide lime, magnesium oxide, alumina, carbon black, aluminium, magnesium and calcium in a total quantity by weight at most equal to that of the calcium carbide, a process in which there is a prepared a homogeneous mixture of calcium carbide powder, said possible additives and a binder consisting either of an organic product having a sharp transition temperature between 70°C and 100°C or a furfuryl resin of which the polymerization temperature is between 40°C and 70°C.
15. Process for producing a product for the desulphurizing of cast irons according to claim 14, characterized in that a micronized calcium carbide and a binder consisting of an organic product having a sharp transition temperature between 70°C and 100°C are mixed at a temperature higher than the melting temperature of the binder.
16. Process for producing a product for the desulphurizing of cast irons according to claim 15, characterized in that the calcium carbide is mixed with the binder in the micronization grinder of the carbide at the inlet of which the binder is introduced.
17. Process for producing a product for the desulphurizing of cast irons according to one of claims 14 to 16, characterized in that the quantity of binder mixed with the carbide is between 0.2 and 10% of the weight of carbide.
18. Process for producing a product for the desulphurizing of cast irons according to one of claims 15 to 17, characterized in that the carbide mixture of calcium/binder has an addition of carbonated product in a proportion of 4 to 10% of the weight of carbide either in the grinder or at the outlet of the grinder.
19. Process for producing a product for the desulphurizing of cast irons according to one of claims 15 to 18, in which the binder used is an organic binder having a sharp transition point between 70 and 100°C, the mixing operations are carried out at a temperature higher than this melting point, characterized in that the homogeneous mixture obtained is then agglomerated and shaped by means of apparatuses either without pressure of the granulating drum, pelletizing plate or pelletizing cone type or with pressure of the pelletizing press, roller press, tablet press or extruder type.
20. Process for producing a product for the desulphurizing of cast irons according to claim 16, in which the binder used is a furfuryl resin, the mixing operations are preferably carried out at ambient temperature, characterized in that the homogeneous mixture obtained is then agglomerated and shaped by means of apparatuses either without pressure of the granulating drum, pelletizing plate or pelletizing cone type or with pressure of the pelletizing press, roller press, tablet press or extruder type and in that the resin is polymerized.
21. Process for producing a product for the desulphurizing of cast irons according to one of claims 19 to 20, characterized in that the agglomerated and shaped homogeneous mixture is then ground and screened to bring it to the desired grain size.
22. Process for producing a product for the desulphurizing of cast irons according to one of claims 14 to 19, 21, characterized in that the binder is a pitch.
23. Process for producing a product for the desulphurizing of cast irons according to one of claims 14 to 19, 21, characterized in that the binder is stearic acid.
24. Process for producing a product for the desulphurizing of cast irons according to one of claims 14 to 19, 21, characterized in that the binder is a fatty ester of glycerine.
25. Process for producing a product for the desulphurizing of cast irons according to claim 24, characterized in that the binder is hydrogenated castor oil based on glycerine trihydroxystearate.
26. Process for producing a product for the desulphurizing of cast irons according to one of claims 19, 21, 22, 23, 24, 25, characterized in that the calcium carbide, possibly carbonated product and binder are mixed in the agglomeration apparatus: granulating drum, pelletizing plate or pelletizing cone.
27. Process for producing a product for the desulphurizing of cast irons according to one of claims 14 to 25, characterized in that grinding of the calcium carbide having a grain size between 0 and 12 mm and the mixing thereof with the solid binder are carried out in a cylinder press at ambient temperature.
28. Process for producing a product for the desulphurizing of cast irons according to one of claims 14 to 27, characterized in that the re-ground screened agglomerated product is mixed with about 1% of its weight of carbon black.

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