FI98221C - Desulfurizer containing cast iron calcium carbide and organic binder - Google Patents

Description

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Desulphurisation agent containing cast iron calcium carbide and an organic binder - Calcium carbide and organic binder 5

The invention relates to the desulphurisation of cast iron according to the preambles of claims 1 and 14 and to the desulphurisation of refined cast iron and spheroidal graphite cast iron for steelmaking. Due to the mechanical properties 10, in the former case, the sulfur content should be reduced to 0.005-0.010%. In the second case, the spherical shape is only possible for sulfur contents below 0.010%. In particular, the invention relates to a novel desulfurization product substantially containing calcium carbide and a binder, and to a process for its preparation.

Most desulfurizers are based on two alkaline earth alkalis, magnesium and calcium, which readily combine with sulfur to form sulphides, while forming slag insoluble in cast iron. Excess magnesium is removed due to its high vapor pressure at the treatment temperature. Excess calcium compound (lime, carbonate or carbide) is removed into the slag. Thus, metal magnesium, calcium carbonate, lime, diamide lime (a mixture of Ca carbonate and carbon) and calcium carbide are used separately or in combination, to which may be added • · ·! .. * the flowability of the mixture or the release of gases. substances which allow good distribution of the desulphurisation agent in liquid cast iron.

• · «·.: .- 30 •« · V · ’In the case of purified cast iron, desulphurisation agents are usually added as a suspension by means of a spray head to an inert carrier gas. In the case of foundry iron, the desulfurizer granules are simply poured into a ladle, downcomer or bath.

2 9822Ί FR 1,194,778 (Union Carbide Corporation) discloses a process for treating Ca carbide with oil prior to its use as a desulfurizing agent. In a carbide heated to a temperature of 0.074-1.168 mm and a temperature of 150 ° C, 0.25-4% by weight of carbide is evaporated. The oil can be mineral (petroleum oil, gasoline oil, kerosene oil), vegetable (linseed oil) or animal (fish oil). Synthetic waxes or paraffins may also be suitable for this purpose.

DE Patent 3,831,831 (SKW) discloses a desulfurization product consisting of a mixture of magnesium and calcium carbide, each coated with fine particles of a silicon-containing substance and an oily humectant. 15 The product is prepared by mixing carbide and magnesium with a grain size of 0.1 to 3 mm, 0.5% by weight of oil and 2-10% of a silicon-based product in a cylindrical or frustoconical mixer. The oil can be a vegetable stiffening oil, but also 20 silicone oil or mineral oil. The silicon-based product with a grain size of less than 0.01 mm is, for example, diatomaceous earth, bentonite or iron or calcium kiln dust.

EP Patent Application 0 184 723 (Cyanamid Canada Inc.) • · ·; : 25 discloses a process for preparing a desulfurizing agent based on calcium carbide, in which calcium carbide, which is ... Ϊ pre-crushed into pieces 1-2 cm (25-50 mm) in diameter • · ·, * ··, is then ground, for example in a ball mill, by adding before grinding or during it, an organic polar liquid of 0.001-1% and preferably 0.01-0.5% by weight of the carbide. The organic liquid may be a compound containing up to 10 carbon atoms and preferably one alcohol, ketone, ether, aldehyde or halogenated alkane.

35 U.S. Patent 4,533,572 (Neelameggham) discloses. method in which metal granules, especially magnesium and • · 5C, rv Γ) -1

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3 aluminum granules, coated by mechanically mixing the oil to be polymerized, the mixture is heated to polymerize the oil to a varnish, and finally heated to a higher temperature to convert the varnish at least partially to carbon.

5 These carbon-coated granules are used for desulfurization and deoxygenation of steels.

There is a problem with desulfurization of cast iron with calcium carbide: the 10 - desulphurisation reaction takes place at the interface between solid CaCl2 and liquid cast iron. It is faster the more solids it breaks down. In order to promote the reaction rate and to avoid unreacted carbide excess in the slag, an attempt has been made to use the finest possible calcium carbide. Thus, certain desulfurization products are based on micronized calcium carbide with an average grain size of close to 30 microns.

However, there are several disadvantages associated with the small grain size: - the risk of explosion due to the increased reactivity caused by moisture,. . - lack of fluidity, - when carbide is used in admixture with magnesium with a larger grain size of «· ·: 25, separation of the constituents during transport.

• ·· · • ·

Thus, carbide with a coarser grain size, for example 300 μm-10 mm, is sometimes preferred, especially in cast iron-30 work. The reaction of the carbide is then very incomplete,: v. leading to a high degree of scrap, up to 20 kg per tonne of cast iron instead of 3 kg / t when using micronised carbide.

• · *

Thus, coarse carbide is only used in cast iron jobs where the quantities to be processed are smaller. In ferrous metallurgy, it would result in the introduction into the slag of substances containing large amounts of unreacted calcium carbide, * · <·. which would be very harmful to the environment.

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The problem is similar for refined cast iron and cast iron, but the adapted product does not have exactly the same characteristics.

5 In the case of refined cast iron, a rather fine-grained product is needed to make it suitable for pneumatic conveying and not to clog the spray heads, but does not contain too many ultrafine granules to maintain fluidity. As an example, such a product may have about and more than 10 85% granules between 25-300 μτα. For foundry irons, a coarser product is needed, for example 300 μπ \ -10 mm.

It is an object of the invention to solve this problem by providing a desulfurizing agent having the same efficiency as micronized calcium carbide and the above-mentioned grain sizes. This result is achieved by the features defined in the characterizing parts of claims 1 and 4 by increasing the grain size of the product by coating or agglomerating 20 micronized calcium carbide with a well-selected organic binder which disappears from contact with the liquid cast iron when the carbide is dispersed in the bath. The desulfurizer is thus self-dispersible.

.25 The binder also has other functions: • * ··. ·. / - it protects the carbide from oxidation and moisture. In the form of very fine particles, carbide can cause explosions on contact with air (powder explosions).

•: * 30 In addition, its reaction with water and moisture produces ··· • · <t m * · '' known to be highly flammable acetylene.

• ♦ - while maintaining the reaction properties of finely divided calcium carbide at the temperature of liquid cast iron, it allows re-agglomeration of the finest parts or carbide powders resulting from grinding.

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- since it has a relatively high clear melting point, it avoids the gradual softening of the product from contact with high temperatures, which would cause clogging in the equipment used for storing, handling and distributing the desulphuriser.

Such a product can be used for the desulphurisation of cast iron under different conditions: - in the case of refined cast iron, it is sprayed in its finest form by means of a spray head, either separately or in combination with another desulphurisation agent such as magnesium; - in the case of foundry iron, either placed in a downcomer 15 or at the bottom of a ladle before being cast into an iron or simply poured down on a cast iron in all its coarsest form; - for both refined and foundry cast iron, the product is packed in a continuous metal tube which is introduced into gradual cast iron (filled wire).

The calcium carbide-based desulphurisation agent based on calcium carbide is in the form of granules: consisting of calcium carbide powder coated, coated or agglomerated with a binder consisting of either an organic substance having a melting point of 70- * · · 100 ° C , or a polymeric resin having a polymerization temperature of 40 to 70 ° C.

§0 The application of the invention comprises two variations depending on the intended use: • ·

For the finest desulfurizers for refined cast iron, the application is limited to the first step shown below. The calcium carbide is simply coated, i.e. formed from calcium carbide granules coated with a first layer of solid binder at room temperature, and possibly a more or less continuous second outer layer of finer, also coated, granular calcium carbide. The granules with a size of 25-300 μm have a weight content of at least 85%.

For the coarsest desulfurizers for foundry irons, the process is more complex, comprising the three steps below. The calcium carbide is agglomerated, i.e. granules of more than 0.3 mm in diameter are formed, for example between 0.3 and 10 mm, which consist of micronized calcium carbide powder agglomerated with a binder. By continuing grinding, it is also possible to obtain a grain size comparable to the grain size of the coating carbide 15, but in this case the method becomes unnecessarily complicated.

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

By "micronized calcium carbide" is meant a carbide powder having all particles between a few micrometers and 250 micrometers in diameter.

: 25 A process for preparing such a desulfurizer comprises three steps: in the first, a micronized one is prepared; . . a homogeneous mixture of calcium carbide and a binder which is either an organic substance having a melting point of 70 to 100 ° C or a polymeric resin having a polymerization temperature of 40 to 70 ° C, and • f .1: 1 30 in the second step, the mixture thus obtained is agglomerated. In the third step, the agglomerated product is re-ground. to achieve the desired grain size. As mentioned above,

• · I

the second and third steps are not always necessary and form a special embodiment of the invention.

35

Manufacture of carbide binder mixture.

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Many types of products can be selected as binders: solid binders at room temperature with a melting point, which is preferably clear, of about 70-100 ° C. This temperature is slightly higher than the temperature to which the desulfurizing agent may be exposed during storage, thus avoiding the granules sticking together. The temperature is in the same range as the temperature in the agglomeration plant, so this operation is facilitated.

10

In order to obtain a clear melting point, a substance which mainly consists of a single chemical species is preferably used, for example 80% or more preferably 90%.

15 It consists of certain pitch species, stearic acid with a melting point of about 70 ° C, or glycerol fatty esters. The product sold under the trade name RICIDROL, which is obtained from the hydrogenation of castor oil, is particularly well suited for this purpose. Castor oil consists of more than 80% glycerol tri-20 ricinoleate. Ricinoleic acid is an acid at C18 that contains a double bond and an alcohol function. Hydrogenation of castor oil results in saturation of the double bond with a compound which predominantly contains glycerol trihydroxystearate having a melting point of 86 ° C. On the other hand, paraffins, which are mixtures of saturated carbides, are not suitable because their softening begins at 40 ° C.

i i l • · · • · · · ··· Glycerol fatty esters and in particular glycerol trihydroxy- • · · »; *. f | teaate are preferred in the preparation of the coated carbide.

• · ... - resins polymerized at room temperature «« · or at a reasonable temperature, for example (40-70 ° C), • · · * · '' furfuryl, polyester, vinyl ester, epoxy resins,; ; 35 and this list is not exhaustive.

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As it polymerizes during the agglomeration treatment, this resin hardens and makes it possible to avoid softening of the desulfurizer during storage.

5 When using binders other than resins (pitch, hydrogenated castor oil, stearic acid ...), the carbide-binder mixture can be prepared either in advance in a mixer, grinder or even in a carbide grinder which forms an excellent grinder, or directly in a non-pressurized agglomerate. , such as in a granulation drum, a ball plate or a ball cone. In either case, the components of the mixture are generally heated to a temperature slightly higher than the melting temperature of the binder so that the binder remains liquid but the binder solidifies at the outlet of the agglomerator. Heating is necessary when using micronized carbide. It can be avoided by using a cylinder press which performs both grinding and agglomeration and to which coarse carbide and binder can be fed directly at room temperature.

When resins are used as binders, such as furfuryl, polyester, vinyl ester, epoxy resins, the mixture of carbide and binder is carried out in advance in a mixer or grinder at room temperature. It is also possible to mix the resin and carbide at the top of the refiner used for micronizing the carbide, and to add a polymerization coating. lyt in the mixer. The mixture is then added to an agglomeration unit where it can be heated slightly with the resin. to accelerate polymerization.

•• * 30 • · «

Within the scope of the invention, it is also possible to add calcium. other additives to carbide which are intended: • · 4 * .. ** - either to cause the release of gas in the melt bath; • · · * ·) * carbonaceous substances (coal, anthracite, petroleum coke •: 35 si, etc.) in a proportion of 4-10% by weight of carbide and calcium carbonate, diamide lime, • »• · 9Γ. O s'

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- or to change the composition of the slag: lime, alumina, magnesite, - or to control the effect of oxygen in cast iron; carbon black, aluminum, magnesium, calcium.

5 These additions, which may amount to about 100% by weight of the carbide, are made either in the refiner or in powder form at the outlet of the blender.

The amount of binder used is between 0.2 and 15% by weight of the carbide or carbide additive mixture, and preferably between 0.2 and 10%.

Agglomeration of the carbide-binder mixture.

15

The agglomeration operation uses traditional methods selected according to the nature of the binder and the size and mechanical properties of the agglomerating product to be produced.

20 Two groups of methods can be applied: (a) the mixing method or the non-pressurized method. The equipment used is:: 25 - granulation (or ball) drum. It is a rotating lap blade that tilts a few degrees with respect to the horizontal i; . and driven by a motor with variable speed. The agglomerated product is added to the upper end of the cylinder, the agglomerated product is removed from its lower part. The size of the cylinder and its rotational speed determine the retention time of the product and thus • * · also its final grain size. If necessary, drum ... at my outlet screening to remove either particles that are too small or too coarse. These particles are recycled to the top of the drum.

35 - ball plate; it is a circular plate which lies in a plane inclined 30-65 ° to the horizontal and Q Π 9 9 1 10 1 rotates about an axis perpendicular to that plane.

The perimeter of this plate has a border. The product to be agglomerated is fed to the center of the plate. The coarsest balls move upward and exit over the rim at the bottom of the plate. As above 5, screening of the agglomeration product is performed by recirculating the ground small and coarse particles.

- ball cone: the principle is quite similar to that of a ball-plate. It is a truncated cone with an opening angle of 5-30 ° 10 and which is open on its long side and rotates about its substantially horizontal axis. The product to be agglomerated is fed to the bottom (short side) of the truncated cone. The agglomerated product exits in the vicinity of the lower base line of the long side of the truncated cone. As above, screening of the agglomerated product is performed by recirculating the ground small and coarse particles.

- other newer equipment, such as propeller gran mixers.

20 b) Pressurized agglomeration methods. The equipment used is: - a cylinder press consisting of two rollers with 25 horizontal axes rotating in opposite directions. The cylinders are substantially lateral or at a short distance; i of which, and may have different shapes of cavity, ·· «· balls, pads, eggs, etc. In this case, in advance 4 · · ·. : All types of coarse carbide (0- • · · * 12 mm) and flaky binder can be fed directly from the hot grinding / mixing and press to the press «/••.130, as the press works like a cylinder mill.

• «« • 4 • · ··· * 1 1 - kneader, of which there are several variations. The principle is the same: a cavity with a shape corresponding to the shape of the ball to be made is formed by a cylindrical matrix with a vertical axis, the lower end of which is blocked by «· · * · 11 π π o n ί LL ·! piston. The powder is poured into this cavity, it is leveled and then compacted to the desired compression ratio as the upper piston moves downwards. When the upper piston is raised, the lower piston moves up to push the ball out.

5 - an extruder in which the paste-like mixture is forced through the opening, the feeder by means of a screw system which rotates in the jacket to be heated.

10 In the case of pressurized agglomeration, regardless of the nature of the binder, the binder-carbide mixture must be prepared before it is added to the agglomerator, mixer or grinder.

15 The choice between the two groups of agglomeration methods is determined by both technical and economic considerations: - from a technical point of view, the advantages are on the side of pressurized agglomeration machines, as pressurized agglomeration products have better mechanical strength. In addition, ball presses and kneading equipment produce fully calibrated products.

25 - from an economic point of view, the situation is more complex: i (·! The operating costs of pressurized equipment are lower, but their investment costs are clearly higher than those of non-pressurized equipment.

«III» · f I (V «« ·, '</ 30 Re-grinding of the agglomerated product • · 4 ». The spheres, spheres,» · · * 4 <· * or extruded products obtained during the agglomeration operation are often coarser than • · * * <* * required for the desulfurizer to have the desired grain size, in which case a re-grinding must be performed, which is usually superficial, followed by screening to achieve the desired grain size.After the screening, too small parts are recycled «·« · • ·

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12 to be agglomerated and excessively coarse parts are recycled to the top of the grinder.

To further improve the flowability of the resulting desulfurizer, it may be advantageous to add a very small amount, about 1% carbon black, to the refined and screened desulfurizer, which is well mixed with the desulfurizer.

Examples 10

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

Example 1 A) In a rod grinder, two batches of calcium carbide from the same source were ground under similar operating conditions and at the same temperature of 115 ° C, one of which was treated with 1% hydrogenated castor oil and the other not.

20 Grain size analysis was performed on both batches and gave the following results:

Without hydrogenated castor with the addition of hydrogenated castor 25 Mesh size Residual Accumulating Residual Accumulating ·. residue residue • · • · ·: · γ 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 30 25 31.7 74.1 46.4 86.7 • · · • · · • * .. * through 25.6 13.3 • · · • · · • · 9 η nr ·) 1 ulI i

For each successive row of the table, for the batch without hydrogenated castor oil and the batch containing it, the first column shows the size of the square mesh in micrometers, the next column a fraction (%) 5 larger than the corresponding mesh but smaller than the previous mesh, and the next column the larger mesh %).

The table shows: 10 - that the grain size is smaller when using the product according to the invention. There are fewer coarse particles (more than 100 micrometers), 5.6% instead of 11.2%, and in particular there are about half as few small particles (less than 25 micrometers): 13.3% instead of 25.6%.

- however, that the proportion of particles larger than 50 micrometres in diameter remains essentially the same, ie about 50%.

B) an approximate flow test was performed to compare the flowability of the two powders. In the test, a sample of powder is passed through a calibrated opening in the bottom of a funnel with a half angle at the tip of 20 °. Under certain funnel filling conditions, the result is expressed as the smallest diameter of the orifice for which flow is observed.

• · · • · · • · ·

Carbide powder without hydrogenated castor oil *. flow is observed for 22 mm diameter, while • · «.1. / 30 a flow is observed for powdered powder containing hydrogenated castor oil.

· ·: V C) Explosion thresholds of carbide powder were measured comparatively • ·: with and without the addition of hydrogenated castor oil. The experiments were performed by detonating a known energy spark. in a cloud of product mist with a product grain size of less than 50 micrometers, in suspension in a vertical cylinder through which an ascending carrier gas flow, oxygen or air passed. Sparks were generated by the discharge of capacitors preloaded with 260 volts direct current. The gas flow is 6 liters per minute, and the amount of powder is 2 grams. The energy of the spark is given by the formula: E = 1/2 CV2 where C is the capacitor capacity and V is the voltage.

10

Perform 20 consecutive experiments. The explosion threshold is defined as the minimum energy above which the probability of explosion is> 5% (1 explosion per set of 20 experiments).

The higher the explosion threshold, the less explosive al-15 is powder.

For carbide powder without addition, the explosion threshold is 31 mJ (millijoules). For the powder according to the invention, the threshold is 213 mJ.

D) To evaluate the reactivity with respect to water, 2 g of each powder was added to 30 ml of water and the volume of acetylene released per second was measured. For the carbide without addition, a release of 70 ml / s is observed, while for the powder according to the invention the release is 11 ml / s.

• · • ♦ ♦ * · ♦ E) The desulfurization efficiency of three alloys was compared: • · · • · · «• t • ·% '· 30 - prior art alloy 1 consisting of: ··« • 1 · V technical calcium carbide: 93 % of carbonaceous substances (coal, carbon black): 7% • · · • V - mixture 2 according to the invention consisting of: *** 'technical calcium carbide: 93% t _ 35 of carbonaceous substances: 6% of hydrogenated castor oil: 1% 15 90221 - mixture 3 according to the invention consisting of: technical calcium carbide: 99% hydrogenated castor oil: 1% 5 Three batches of the same cast iron with an initial sulfur content of β — Ο, ΟδΟ% were treated in a ratio of 3 kg of desulfurizing agent per ton of cast iron. The following table shows the final sulfur content Sf achieved for each desulphurisation agent and the desulphurisation ratio T, defined as the ratio (Sj ^ to SfJ / S ^

Seos Sf T

1 0.018% 64% 2 0.013% 74% 15 3 0.012% 76% These experiments make it possible to determine the effectiveness of the desulfurization mixture according to the invention in comparison with other mixtures.

20 Example 2

A mixture obtained by mixing calcium carbide with furfuryl meat resin.

Starting with micronized calcium carbide to which was added 25% by weight of coal. The grain size distribution of the mixture was as follows: • · • · · * ”· Eye (μm) Residue (%) Accumulating residue (%) 30 200 10 10 • ·» V 100 28 38 75 7 45 50 14 45 • · 50 14 59 35 25 16 75 through 25 4 II 1 • «· 16 Noor) λ> ϋΙΙ!

The carbide to which coal had been added was mixed in a mixer with furfuryl resin in a ratio of 10% by weight at room temperature first, and then at 100 ° C to cure the resin.

5

The grain size analysis of the obtained product is as follows:

Eye (μm) Residue (%) Accumulating ice residue (%) 10 200 12 12 100 34 46 75 12 58 50 22 80 25 16.5 96.5 15 through 3.5

It was found that grain size develops towards coarser grain sizes because the figures in the last column are higher than for the starting product and especially because particles below 25 represent only 3.5% instead of 25%.

Example 3

Calcium carbide was mixed with hydrogenated castor oil (Ricidrol).

25 The starting product was micronized calcium carbide with the same grain size and carbon content as in the previous example.

Ricidrol, which was 5% by weight of carbide, was poured in liquid form into a mixer containing calcium carbide heated to 100 ° C. The mixture was stirred vigorously for 10 minutes, after which the mixture was cooled by continuing stirring.

35

The grain size analysis of the product obtained is as follows:

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Eye (μm) Residue (%) Accumulating residue (%) 200 11 11 100 33 44 75 11 55 5 50 19 74 25 21.5 95.5 through 4.5

It was found that the grain size developed towards coarser grain sizes and 10 particles especially below 25 μm represent only 4.5% instead of 25%. However, the grain size is slightly smaller than in the case of furfuryl resin.

Example 4 Calcium carbide was mixed with coal and hydrogenated castor oil (Ricidrol).

The preparation conditions of the mixture are the same as in Example 3, but this time an amount of hydrogenated castor oil 20 (Ricidrol) corresponding to 10% by weight of the carbide is used.

The grain size analysis of the obtained product is as follows:

Eye (μm) Residue (%) Accumulating residue (%). 25 200 38.5 38.5 100 29 67.5 i ·; 'V 75 9 76.5 ···' · 50 14 90.5 25 8 98.5 • i V '* 30 through 1.5 * # · · 4 • * · In this example, the grain size distribution has evolved towards even coarser grain sizes, and especially particles smaller than 25 μm represent only 1.5% instead of 25%. In any case, the particle size distribution 35 is substantially coarser than when using furfuryl resin or 5% Ricidrol alone.

1β 98221

Example 5

Calcium carbide was mixed with stearic acid (Stearin).

The preparation conditions of the mixture are the same as in Example 3, but this time stearic acid or stearin is used in a ratio of 10% of the amount of carbide.

The grain size analysis of the product obtained is as follows:

Eye (μm) Residue Accumulating residue (%) 200 44 44 100 45 89 75 5.5 94.5 15 50 4 98.5 25 1 99.5 through 0.5 In this case, too, the grain size distribution has evolved towards 20 much coarser grain sizes, and especially particles smaller than 25 μm now represent only 0.5% instead of 25%. In any case, the grain size distribution is substantially coarser than when using furfuryl resin or 5% or even 10% Ricidrol.

; 25

The five examples above show that simply mixing calcium carbide in a mixer with a suitable binder can increase the amount of coarse particles and reduce the amount of small particles. However, in the best case • · · "30, i.e. in Example 5, the product obtained has only * 1 r V 1 44% particles with a diameter of more than 200 μm.

·· · • 1.! Figure 1 shows, in another, more synthetic form, the grain size distributions of the initial product f1-2 and the mixtures corresponding to Examples 2-5. The figure shows the percentages of cumulative granules along the coordinate that are smaller than the sizes reported along the abscissa.

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The following examples show that a combination of a mixing operation and an agglomeration operation can significantly increase the grain size.

5 Example 6

Agglomeration in a grinder

A mixture of calcium carbide and coal was prepared in a mixer with the same grain size distribution as in Examples 2 and 10 to which 5% stearic acid was added. The stirrer temperature was adjusted to about 100 ° C to keep the stearic acid liquid.

A product consisting of stearin-coated carbide with a grain size distribution between Examples 3 and 5 was obtained. After cooling, the product was placed in a ball hopper with a pressure of 7 bar. The product was formed into small cylinders with a diameter of 10 mm and a height of 6 mm and a weight of about 1 g. The balls of powder-20 were then gently reassembled in a hammer mill. All granules obtained were less than 6 mm and 64% of them ranged from 0.3 to 6 mm. Granules <0.3 mm were recycled to the mixer.

. . Example 7 25 Agglomeration in a cylinder press.

i.i i A mixture of calcium carbide having the grain size distribution indicated in Example 2 was prepared in a mixer, to which 10% stearic acid was added. The stirrer temperature was maintained at about 100 ° C to keep the stearic acid liquid.

• · · • · t • · • ·

A product consisting of a stearin-coated carbide having a grain size distribution similar to that of the products of Example 5 was obtained. At a temperature between 80-100 ° C (since cooling is not necessary in this case), the product was added to the hopper of the cylinder press. During various experiments * 9 n <~ i o -ί

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the spacing between the cylinders ranged from 0.5 to 5 mm. Thus, the final product was obtained in the form of small flakes with a side of a few millimeters and a thickness of 0.5-5 mm. These flakes were then carefully re-ground in a hammer mill. Granules were obtained, of which about 60% ranged from 0.3 to 6 mm. Granules <0.3 mm were recycled to the mixer, while granules> 6 mm were recycled to the hammer mill.

Example 8 10 Agglomeration in a ball press.

A mixture of calcium carbide with a grain size distribution of 0-12 mm was prepared in a mixer to which 5% stearic acid was added. The stirrer temperature was maintained at room temperature.

The resulting mixture was added to a ball mill hopper having ball-shaped cavities in the cylinders. In the upper part, where the two cylinders of the press converge, the press-20 behaves like a refiner, in which the carbide granules are reduced. The ground granules agglomerated into a ball shape in the vicinity of the plane containing the cylindrical shafts by means of a binder. These balls were then re-ground •, ·, carefully in a hammer mill. Granules were obtained, of which about 60% were between 0.3 and 10 mm. Granules <0.3 mm were recycled to the mixer, while granules> 10 mm were recycled to the hammer mill.

• ♦ ♦ • · · · • ·:. ** i Example 9 ♦ · «V '30 Four batches of the same cast iron were treated in parallel with a desulfurizing agent according to the invention prepared under the conditions of Example 7, and on the other hand, with a prior art desulfurizing agent consisting of technical calcium carbide containing about 10% of lime and coarsely ground so that the grain size was between 0.3 and 4 mm. The amounts of desulphurizer used were 3.5 kg / tonne for the desulphuriser according to the invention (test ««

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21 Q Ο r \ o ^ yo II i 1) and 3.5, 10 and 20 kg / ton for the desulfurizing agent according to the prior art (experiments no. 2, 3, 4). The results obtained are shown in the following table, in which the initial Si and final Sf sulfur contents are expressed in%, as well as the desulphurisation ratio T corresponding to the ratio (Sj ^ - Sf) / Sj_:

Test number 1234

Original 0.05 0.05 0.05 0.05 sulfur 10 Final 0.013 0.032 0.02 0.012 sulfur

Ratio T 74 36 60 76

It is found that the use of the desulphurisation agent based on agglomerated calcium carbide according to the invention gives almost the same desulphurisation efficiency as using a five times larger amount of carbide with granules between 0.3 and 4 mm.

20 • · · · • · · · · • · · · · · · · · · · • * * 4 • · · • · 1 · ·

Claims (27)

A product for the desulphurisation of molten cast iron, which product comprises calcium carbide, optionally one or more of the following substances: lime, calcium carbonate, diamond lime, magnesium oxide, alumina, soot, aluminum, magnesium and calcium in an amount equal to or greater than calcium carbide; and a binder, characterized in that the product is in the form of a powder coated with a binder or agglomerated with a binder, this binder being either an organic material with a clear melting point between 70 ° C and 100 ° C. Cast iron desulphurizer according to Claim 1, characterized in that it consists of calcium carbide granules 15 coated at room temperature with a first layer of solid binder and optionally a second, more or less continuous layer consisting of finer, in turn coated smaller calcium carbide granules. 20 A desulfurizer according to claim 1 or 2; they, characterized in that the carbide powder is a micronized powder having a grain diameter of between a few micro-; meters and 250 micrometers. 25 (I I I Desulfurizing agent according to one of Claims 1 to 3, characterized in that the binder is pitch. Desulfurizing agent according to one of Claims 1 to 3, characterized in that the binder is stearic acid. • f t Desulfurizing agent according to one of Claims 1 to 3, characterized in that the binder is a saturated Gly-serol fatty ester. Desulphurisation agent according to Claim 6, characterized in that the chemical purity of the saturated fatty ester is at least 90%. ; g isi e anti i ;: t -im - 35 n C- O C \, 1 | Desulphurisation agent according to Claim 6 or 7, characterized in that the saturated fatty ester is a hydrogenated castor oil based on glycerol trihydroxystearate. 5 Cast iron desulphurizer according to one of Claims 1 to 8, characterized in that the amount of binder is between 0.2% and 10% by weight of the carbide. Cast iron desulphurisation agent according to one of Claims 1 to 9, characterized in that a carbonaceous substance, such as coal, anthracite, crude oil coke, is added to the calcium carbide powder in a proportion of 4% to 10% by weight of the carbide. 15 Cast iron desulphurisation agent according to one of Claims 1 to 10, characterized in that 85% of its granules are between 25 and 300 micrometers. Cast iron desulphurisation agent according to one of Claims 1 to 10, characterized in that the diameter of the granules is between 0.3 mm and 10 mm. Cast iron desulfurizer according to one of Claims 1 to 11, characterized in that the agglomerated calcium carbide granules are mixed with about 1% of carbon black. . I * · f 14. A process for the preparation of f ft i ‘* ί’ * 30 products for the desulphurisation of cast iron in the form of a powder coated with a binder or agglomerated with a binder ·. · ..! and containing calcium carbide and optionally one or more of the following additives: lime, calcium carbonate, diamide lime, magnesium oxide, alumina, carbon black, aluminum, magnesium and calcium in an amount equal to or greater than calcium carbide, characterized in that the process produces a homogeneous mixture of said calcium Ο Γί is ί yozz s additives and a binder consisting of an organic material with a clear melting point between 70 ° C and 100 ° C. A process for preparing a cast iron desulfurizer according to claim 14, characterized in that the micronized calcium carbide and the binder consisting of an organic material having a clear melting point between 70 ° C and 100 ° C are mixed at a temperature above the melting point of the binder. A method for producing a cast iron desulfurizing agent according to claim 15, characterized in that the calcium carbide and the binder are mixed in a carbide micronization mill to which a binder is added. Process for preparing a cast iron desulfurizing agent according to one of Claims 15 to 17, characterized in that the amount of binder 20 to be mixed with the carbide is between 0.2% and 10% by weight of the carbide. Process for preparing a cast iron desulfurizing agent according to one of Claims 15 to 17, characterized in that a carbonaceous substance is added to the mixture of calcium carbide and binder in a proportion of 4% to 10% by weight of the carbide, either. in the refiner or at the outlet of the refiner. • · • · · • · · A process for preparing a cast iron desulfurizing agent according to any one of claims 15 to 18, wherein the binder used is an organic binder having a clear melting point between 70 ° C and 100 ° C and mixing operations. carried out at a temperature above this melting point, characterized in that the homogeneous mixture obtained is then agglomerated and formed in equipment either without: .35 pressure, such as in a granulation drum, pelletizing plate, '1' / pelletizing cone, or under pressure, such as in a pelletizing press, with a cylinder press, tablet machine or extruder pr <·> rj ^ 1? UZ / i 25 A process for preparing a desulfurizing agent according to claim 19, characterized in that the agglomerated and shaped homogenized mixture is ground and then screened to achieve the desired grain size distribution. Process for preparing a cast iron desulfurizing agent according to one of Claims 14 to 19, characterized in that the binder is pitch. 10 Process for preparing a cast iron desulfurizing agent according to one of Claims 14 to 19, characterized in that the binder is stearic acid. Process for preparing a cast iron desulfurizing agent according to one of Claims 14 to 19, characterized in that the binder is a glycerol fatty ester. A process for preparing a cast iron desulfurizer according to claim 23, characterized in that the binder is based on glycerol trihydroxystearate. . hydrogenated castor oil. Process according to one of Claims 19 to 24 for the preparation of a cast iron desulphurisation agent, characterized in that the calcium carbide, optionally a carbonaceous substance and the binder are mixed in an agglomeration device, such as a granulation drum, a pelletizing plate or a pellet. -tointikartiolla. . .SO • «· • · ♦ Process for producing a cast iron desulphurizer according to one of Claims 14 to 24, characterized in that the calcium carbide having a grain size distribution of between 0 mm and 12 mm is ground and mixed with a solid binder in a cylinder press at room temperature. . ···, lassa. Π f '/ ο. Λ ', ^ Process for preparing a cast iron desulphurizer according to one of Claims 14 to 26, characterized in that the agglomerated, re-ground and screened product is mixed with an amount of carbon black of about 1% by weight.