JPS6366363B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a desulfurization agent for molten metals, particularly molten steel and hot metal, whose main component is a CaC ₂ -CaO crystal mixture produced from a melt, and a method for producing the same.

Desulfurization agents based on the CaC ₂ --CaO system and additionally containing fluorite are known (see German Patent No. 2037758). The molten metal can then be mixed with industrial carbides (approximately 80% by weight CaC, balance CaO) or mixtures of such carbides with additives such as lime, coke, and gas separation materials such as _{CaCO 3 ,} CaCN ₂ , Ca(OH) ₂ It is also a known technique to desulfurize with a carbon dioxide (see West German Patent No. 2252795). In order to achieve high utilization rates, the known desulfurization agents must first be ground to as fine a particle as possible, in particular using the immersion lance method. Although this desulfurization agent thereby meets the requirements, it is expensive to produce and use.
Despite fine grinding, relatively large amounts of desulfurization agent must be added to achieve the desired degree of desulfurization.

Therefore, the object of the present invention is to obtain a desulfurization agent with high utilization rate and an economical process for its preparation.

According to the invention, part of the CaO in the crystal mixture is Ca
Desulfurization agents that are hydrated to (OH) ₂ are proposed.
In this case CaO40-80% by weight (therefore _CaC220
~60 wt%), especially CaO45~80 wt% ( _CaC220
~55 wt%) or CaO40~65 wt% ( _CaC2 35
Starting from a crystal mixture containing ~60% by weight). Furthermore, according to an advantageous embodiment of the desulfurization agent according to the invention, the amount of CaO in the crystal mixture is 1 for the amount of CaC ₂ -CaO.
-6% by weight, especially 2.5-3.5% by weight of _H2O . CaO and
CaC ₂ crystallizes as a crystal mixture, in which CaC ₂
and CaO crystals exist intermixed with each other, and for a given CaC ₂ -CaO weight ratio, have a hypoeutectic composition within the eutectic range or shifted to the lime side. When water is added, a portion of the CaO in the crystal mixture reacts with the CaO crystals and the mixed CaC ₂ with almost no attack by H ₂ O, according to the formula CaO + H ₂ O → Ca(OH) ₂ .

When such a desulfurizing agent is blown into molten metal,
Ground particles consisting of a CaO-CaC ₂ crystal mixture in which a portion of the CaO crystals is hydrated are decomposed according to the formula CaC ₂ +Ca(OH) ₂ →2CaO+2C+H ₂ when a temperature of 800° C. or higher prevails. Because gas is generated at the reacting crystal interface, the ground particles separate the highly reactive lime in the nascent stage, while at the same time removing the CaO− that has entered the particles.
Split regularly while enlarging the crystal surface of CaC ₂ . In the case of a nearly eutectic crystal structure, an ideally large reaction surface results. The free gas acting on the ring elements in this case provides optimal conditions for CaO to react with the sulfur dissolved in the molten metal.

Such a desulfurization agent is particularly suitable for a desulfurization process in which the reaction time between the desulfurization agent and sulfur is very short. This method includes the immersion lance method, in which the desulfurization agent is injected into the molten metal below the surface, allowing the desulfurization agent to exit the molten metal and rise to the bath surface within a short period of time. The reaction of the agents must be as complete as possible.

It has been found that the desulfurization agent according to the present invention has a desulfurization effect superior to that of known desulfurization agents, which also have good carbide-based desulfurization effects. Because of the intercrystalline gas reactions in the milled particles, the reaction of _CaC2 to CaO and the concomitant expansion of the crystal surface area is effective, and the gas generation is e.g. It is much more uniform and loose than the known desulfurization agent according to the publication. Desulphurization therefore takes place quietly in open pans and torpedoes, with almost no metal splashing. Due to the high reactivity of the desulfurization agent of the present invention, which occurs as a result of the crystal surface area expansion when the milled particles break up in the molten metal, the material can be used in coarse grains, eliminating the need for expensive fine milling. .

Owing to the homogeneous composition of the desulphurizing agent according to the invention, the final content required in each case can be achieved with great reliability. The manufacturing cost of the desulfurizing agent of the present invention is significantly lower than that of known carbide desulfurizing agents.

Furthermore, according to the invention there is
Adding _H2O during the trituration of the _CaC2 −CaO crystal mixture;
Alternatively, a method for producing a desulfurization agent is proposed, which is characterized by partially hydrating CaO in the produced ground particles.

According to an advantageous embodiment of this process, a final product containing 20-55% by weight of calcium carbide, 45-80% by weight of calcium oxide and water chemically bound to the calcium oxide is produced in a conventional manner. Finely divided calcium oxide is added to the calcium carbide melt already present containing up to 45% by weight of calcium oxide in an excess of 3 to 15% by weight over the amount desired in the final product, and the resulting mixture is solidified while 450
℃ and pre-milling at this temperature to a particle size smaller than 150 mm, separating the particles smaller than 4 mm that inevitably occur in the process from the rest of the product;
The remaining product is heated to 100°C or less, especially 10 to 50°C, in the presence of air or nitrogen containing 5 to 20 g of moisture/ ^Nm3 .
Grind and grind to a particle size of 10 mm, especially less than 0.1 mm, at a temperature of .

This process selectively and advantageously provides that (a) the final product contains 1 to 6% by weight of water chemically bound to calcium oxide, and (b) the addition of calcium oxide, the so-called carbide depletion, (c) Calcium oxide to be added to the calcium carbide melt is heated to a temperature of up to 2000 °C and introduced into the melt at a high temperature, with a preheating temperature of 45 to 80 wt. (d) Starting from a carbide melt containing 20-45% by weight of calcium oxide, (e) From 4 mm sieved after pre-grinding. It is characterized by sending small particles back into the process.

Add calcium oxide to the melt in advance.
Preheat to a temperature of up to 2000℃, especially up to 1100℃,
By introducing into the melt at this temperature, the CaO content in the carbide can be increased up to 80% by weight, with preheating increasing the desired proportion of additionally dissolved calcium oxide from 45 to 80% by weight. You have to choose high. This allows its use in low-carbon hot metal and steel, and also increases the desulfurization rate for calcium carbide.

The particle fraction smaller than 4 mm, which is screened out after pre-grinding, consists essentially of CaO and is sent back to the process as finely divided calcium oxide, where it is used as starting product together with fresh CaO. It will be appreciated by those skilled in the art that the sieving of the particles smaller than 4 mm generated after pre-grinding separates from the product those parts which have little or no desulphurization effect, thereby significantly increasing the potency of the final product. It was impossible to predict.

The products produced according to the invention can be milled much more easily than those obtained by known methods. This is particularly important since the products often have to be used in particle sizes smaller than 0.1 mm.

The invention will now be illustrated by way of example.

Example 1 Calcium carbide is produced from lime and coke by known methods, for example electrothermal methods, and the lime-coke mixture in the charge is adjusted to a weight ratio of 100:40, corresponding to a carbide with a CaO content of approximately 40% by weight.
The molten carbide stream discharged from the furnace into the pan is filled with CaO with a particle size of 3 to 8 mm and a Ca(OH) ₂ and CaCO ₃ content of less than 1% by weight each, until the pan is filled with a total CaC ₂ :CaO weight ratio of 43: Add at a rate and amount such that 57. This is 14% CaO by weight compared to the desired 50% CaO content in the final product.
corresponds to an excess of The solidified carbide block is then cooled until the average temperature is approximately 400°C and the block is pre-milled to a size smaller than 150 mm.

The particle fraction smaller than 4 mm generated during pre-milling contains almost an excess of CaO, and the remaining product with a particle size larger than 4 mm is a crystal mixture of 50% by weight CaC ₂ and 50% by weight CaO, which is then Water 10g/
Milled in a rotary mill at 50° C. with a throughput of 500 Kg/h to a particle size smaller than 0.1 mm while introducing 1500 m ³ /h of air containing m ³ (at 15° C.). The sieved particles smaller than 4 mm are used again as starting product with fresh lime (CaO). The resulting product contains 2.5% by weight of chemically bound water.

By blowing 1500 kg of this product into 300 tons of hot metal with a sulfur content of 0.03% by weight at a temperature of 1400°C, the sulfur content of the hot metal is reduced to below 0.005% by weight.

Example 2 Example 1 is carried out except that the CaO is preheated to about 1100° C. before addition and the amount of CaO is increased to give an overall CaO content of 62.5% by weight in the pan.
This corresponds to an excess of 4% by weight relative to the desired CaO content of 60% by weight in the final product produced.

1800Kg of processed and milled product according to the invention
is used to desulfurize 300 tons of molten steel with a sulfur content of 0.02% by weight and a temperature of 1650℃. At that time, the sulfur content of the molten steel is
It decreases to 0.005% by weight or less.

Example 3 (a) 300 tons of hot metal having a composition (wt%) of 4.5% carbon, 0.8% silicon, 0.7% manganese, 0.08% phosphorus, 0.064% sulfur, balance iron (in weight %) was converted into 50% CaC ₂ by weight according to the present invention by the immersion lance method. Desulfurization is carried out in an open pot with a desulfurization agent having a composition of 50% by weight of CaO hydrated with % and about 3% by weight of H ₂ O. The blowing speed was 100 kg/min. Sulfur content is 0.009% by weight due to total desulfurization agent consumption of 4.5Kg/t
It declined to . This corresponds to a degree of desulfurization of 86%.

(b) Industrial carbide ( _CaC2 content 78% by weight) 85
% by weight and CaCO ₃ 15% by weight to achieve the same degree of desulphurization for the same starting sulfur content with the same immersion depth and blowing rate as in 3(a) 6.0 Kg/t
required.

In the case of the desulfurization agent according to the present invention, compared to the known desulfurization agent used in the comparative experiment, the absolute amount of desulfurization agent
% savings and a 45% savings is achieved for CaC ₂ minutes. Processing time is also reduced at the same rate.

Claims (1)

[Claims] 1 Crystallized from a melt consisting of CaO and CaC ₂
It consists of a _CaC2 /CaO crystal mixture, 40-80% by weight of this crystalline mixture consists of CaO, and 1-6% by weight of this crystalline mixture consists of chemically bound water, which is the hydration of CaO into the form of Ca(OH) ₂ . Desulfurization agent for molten metals consisting of H ₂ O as. 2. The desulfurization agent according to claim 1, which is produced from a crystal mixture having a CaO content of 45 to 80% by weight. 3. The desulfurization agent according to claim 1, which is produced from a crystal mixture having a CaO content of 40 to 65% by weight. 4 Exists in the form of lump material in the production of desulfurization agents for molten metals, especially molten steel and hot metal, whose main component is a CaC ₂ -CaO crystal mixture produced from a melt.
1. A method for producing a desulfurizing agent for molten metal, which comprises adding H ₂ O while grinding a CaC ₂ -CaO crystal mixture, or partially hydrating CaO in the ground particles produced. 5. Already containing up to 45% by weight of calcium oxide, prepared by conventional methods, to produce a final product containing 20-55% by weight of calcium carbide, 45-80% by weight of calcium oxide and water chemically bound to the calcium oxide. Add fine calcium oxide to the calcium carbide melt present in the final product in the desired amount
an excess of 15% by weight is added, and the resulting mixture is then cooled with solidification to a temperature of 350-450°C and pre-milled at this temperature to a particle size smaller than 150 mm, with the resultant grain size smaller than 4 mm necessarily occurring. Separate the grains from the rest of the product and reduce the remaining product to a moisture content of 5 to 20 g/N.
5. The process according to claim 4, which comprises crushing and grinding to a particle size of less than 10 mm in the presence of air or nitrogen containing m ³ at a temperature below 100°C. 6. The manufacturing method according to claim 5, wherein calcium oxide is added in the pot. 7 Calcium oxide to be added to the calcium carbide melt is preheated to a temperature of up to 2000°C and introduced into the melt at that high temperature, with the preheat temperature adjusted to the desired amount of additionally dissolved calcium oxide of 45 to 80% by weight. The manufacturing method according to claim 5, wherein the higher the ratio, the higher the ratio. 8. The production method according to claim 5, starting from a calcium carbide melt containing 20 to 45% by weight of calcium oxide. 9. The manufacturing method according to claim 5, wherein the sieved particles smaller than 4 mm after pre-pulverization are sent back to the process. 10 The remaining product is heated at a temperature of 10 to 50 °C in the presence of air or nitrogen containing 5 to 20 g of water/ ^Nm3 .
The manufacturing method according to claim 5, which comprises crushing and grinding to a particle size smaller than mm. 11. The process according to claim 5, wherein the remaining product is ground to a particle size smaller than 0.1 mm.