KR950001905B1 - Desulphurigation - Google Patents

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Description

Particulate Desulfurizer for Iron Melt

The present invention relates to a desulfurizing agent, a desulfurizing agent production method and the use of an iron melt desulfurizing agent outside a furnace. Iron lysates are chosen here to mean pig iron and cast iron melts.

Desulfurization of pig iron in torpedo or open ladles outside the furnace is now part of the present technical situation. Mixtures based on calcium carbide have become widespread as preferred desulfurization agents, because these mixtures result in a rapid economic desulfurization of pig iron, resulting in a low sulfur content. Particularly preferred desulfurization agents are represented by a mixture comprising 20 to 90% of industrial calcium carbonate and calcium carbonate, preferably 2 to 20% of carbon, by weight dispersed therein and preferably particulate calcium carbonate The / carbon mixture is known under the name diamide lime (German Patent No. 1,758,250).

The Federal Republic of Germany Specification No. 2,531,047 describes a pig iron desulfurization process wherein calcium carbide, calcium cyanide or lime containing 0.5 to 3.5% by weight of aluminum or magnesium powder by weight relative to the calcium component is used as the desulfurization agent.

U.S. Patent No. 3,998,625 describes a desulfurization agent consisting of a combination of another composition with magnesium and lime, and the use of lime and non-oxidized carrier gases with carbon-containing materials is described in U.S. Patent No. 4,266,969. It is described in

A disadvantage of known desulfurization agents is that large amounts of slag, which are obtained especially in closed ladles and even in open ladles and which cause undesirable deposits and scales, air wrap a significant amount of iron resulting in significant iron loss.

Instead of calcium carbonate it has already been proposed to add to the carbon carbide an additive which generates hydrogen at iron dissolution temperatures (Patent No. 2,252,796). However, such desulfurization agents have not been proved in practice because the evolution of hydrogen does not occur clearly in a form in which sufficient dispersion in the iron melt of calcium carbide can be achieved.

: animal charcoal), 레더 차콜(leather charcoal) 형태의 탄소와 함께 탈황제로서 사용될 수 있다는 것이 또한 기술 됐지만 ,제안된 형태의 석탄은 실제로 휘발성 성분들을 함유하지 않는다(독일연방공화국 특허 제1,758,250호에 기술된 기술의 상태를 보라.Calcium carbide is used during the processing of cast iron melts, for example, pitch coke, animal charcoal (

It has also been described that it can be used as a desulfurizer with carbon in the form of animal charcoal, leather charcoal, but the proposed form of coal does not actually contain volatile components (see German Federal Patent No. 1,758,250). See the state of the art.

The object of the present invention is therefore based on the basis of calcium carbide which, on the one hand, does not inject another slag forming component into the iron melt and on the other hand releases a large amount of gas immediately upon injection into the molten iron, if possible. Developed desulfurization agents, which are suitable for the dispersion of calcium carbide. Furthermore advantageous consumption, short treatment times and final low sulfur content are achieved.

The present invention has been accomplished by a particulate desulphurizer, which is injected into the iron melt in a fluidized form by gas, comprising a mixture of industrial calcium carbide and dried coal, the dried coal containing 15% of volatile components by weight. Immediately after passing through the molten iron, at least 80 standard liters of gas are released with 1 kg of coal.

It is taken to mean a product containing 65 to 85% CaC ₂ by weight of industrial calcium carbide and the remainder mainly containing lime. The proportion of industrial calcium carbide can vary within the range of the desulfurizing agent according to the invention. Therefore, the proportion of coal can also change. The mixture preferably comprises 50 to 98% calcium carbide by weight and 50 to 2% coal by weight. Particularly preferred mixtures preferably comprise 80 to 96% of industrial calcium carbide by weight and 20 to 4% of dried coal by weight.

The mixture may also contain magnesium.

Preference is given to mixtures having from 47.5 to 95.5% by weight of industrial calcium carbide and from 50 to 2% by weight of dried coal and from 2 to 40% by weight.

As a dried product, it is particularly preferred that about 90% of the volatile components by weight are released within 60 seconds during feed into the iron melt at pneumatic pressure at a heating rate of 10 ³ to 10 ⁶ oc / sec. However, the coals are preferably used to release about 90% of the volatiles within 40 seconds. It is particularly preferable that the volatile component be released within 60 seconds at the iron dissolution temperature.

The higher the proportion of volatile compositions in coal, the generally higher the desulfurization effect. Therefore, coals are used that contain at least 25% of volatile composition by weight.

However, it is preferred that coal is used as a dried form which immediately releases at least 150 standard liters / kg of optimum gas immediately after passing into the molten iron. Coal that meets these conditions is in particular lignite, flame coal gas flame coal, gas and coking coal. They are shown in the following table.

TABLE 1

The volatile components specified in the table above for various types of coal were extracted from Rompps Chemie-Rexikon, Vol. 8, Volume 3, page 2142, published in 1983.

The amount of gas released (1 / KG) is the amount of gas that escapes from heating of very good coal to the temperature of pig iron.

The volatile component of diamide lime is taken to mean the amount of CO ₂ liberated during carbonic acid decomposition.

Gas release time is the time taken for about 90% of the total amount of gas released.

If advantageous, it can be used as a mixture of two or more grades of coal resulting from a high content of volatile compositions.

The moisture content of the dried coal is preferably less than 0.5% by weight in order to prevent it from reacting with calcium carbide to form acetylene. Such drying levels are achieved with drying devices such as commercially available helical dryers, fluidized bed dryers or grinding dryers, which are dried in a vacuum in a simple device and the material to be dried is simply moved or flipped over.

The magnesium to be used must have a particle size of less than 1 mm. It is preferred to use magnesium ground to less than 500 μm, with magnesium having a particle size of less than 350 μm being particularly preferred.

It may be advantageous to add a mixture of 1-10% fluorspar by weight to improve the properties of the slag that occurs during desulfurization. It is preferable that the mixture contains 2 to 6% of fluorospa by weight. Fluorospa may be replaced with aluminum impurities such as alumina or aluminum impurities containing 30% metallic aluminum.

The composition of the desulfurization agent according to the invention is ground except for magnesium and thoroughly mixed, at least 90% by weight of the mixture having a particle size of less than 200 μm, preferably 90% by weight of particle size of less than 100 mm. And 40 to 65% by weight is pulverized to a particle size of less than 50 μm.

To produce the desulfurization agent according to the invention, the dried coal is added to the calcium carbide at a controlled rate where the calcium carbide can be pre-milled and the mixture is generally transferred to a mill such as a tubular mill of the required particle size. It may be advantageous to work with the overall application of inert gases to ensure that the small amounts of acetylene formed are immediately removed from the mixing and grinding apparatus.

In one preferred embodiment of the invention, magnesium is added in such a way to a desulfurization agent consisting of calcium carbide and dried coal, which is fed into the melt in a uniform mixture by pneumatic pressure. Preferably, the content of industrial calcium carbide is adjusted to 47.5 to 95.5% by weight, particularly preferably 66 to 86% by weight, and the content of dried coal is 47.5 to 95.5% by weight, particularly preferably weight To 66 to 86%, the content of dried coal is adjusted to 50 to 20% by weight, particularly preferably to 20 to 4% by weight, and the content of particulate magnesium is 2.5 to 40% by weight, in particular Preferably, the weight is adjusted to 10 to 30%. On the other hand, it has often been useful to store separately from magnesium after the carbide / coal mixture has been prepared and to mix the two compositions in a conveying line or lance after separate fluidization and inject them together into the melt. Separation, fluidization and co-injection of the carbide / coal mixture has the advantage that the magnesium ratio in the mixture can be changed during the injection and coarser magnesium can be used.

The desulfurization agent according to the invention is also injected in fluidized form as deep as possible within the dissolved iron at a carrier gas flow rate of 3 to 30 liters per 1 kg of desulfurization agent. The supply flow rate of the desulfurization agent is in an amount of 10 to 100 kg / min, and preferably 30 to 80 kg / min of desulfurization agent is used.

The carrier gas used for the desulfurization agent is preferably a non-oxidizing gas such as heated argon or nitrogen alone or a mixture or dry air.

With regard to the process according to the invention, the desulfurization agent according to the invention has significant advantages over the known desulfurization agents so far. Therefore, except for the small amount of ash contained, coal does not actually inject any other slag forming composition into the dissolved iron. Therefore, when the desulfurizing agent according to the present invention is used, a significantly smaller amount of slag is obtained than when calcium carbonate or calcium hydroxide is used as the gas releasing additive.

Compared with known additives that release hydrogen and carbon dioxide, coal has the advantage that a sufficient amount of gas is released immediately after it is passed into the molten iron and complete dispersion in the molten iron of particulate calcium carbide and magnesium is achieved. Have As a result, the desulfurization effect of the desulfurization agent according to the invention is superior to known desulfurization mixtures based on calcium carbide.

Compared with known desulfurization mixtures having at least 50% magnesium, the mixtures according to the invention have the surprising advantage that the treatment of iron melts can be significantly shortened. The shortening is more than expected from the reactivity of magnesium and calcium carbide.

In connection with the injection method described above, the open ladle of the desulfurizing agent according to the invention is suitable for pig iron desulfurization in closed ladles. In addition, the need for a particularly low injection lath is advantageous, as the composition of the desulfurizing agent ensures sufficient dispensing so that high desulfurizing agent use is achieved.

The use of the desulfurization agent according to the invention requires a significantly reduced amount of desulfurization agent to allow for a significant increase in the degree of desulfurization or to achieve the same desulfurization effect.

The use of the desulfurizing agent according to the invention allows for a short treatment time of the iron melt, and in addition, only slight cooling of the melt occurs. Since the resulting amount of slag is small, there is little loss of iron in slag removal.

The following examples are intended to explain the invention in more detail.

EXAMPLE

The results obtained in the open ladle with conventional desulfurization agents based on calcium carbide and diamide lime are shown in figures 1 and 2 of Table 2, with a mixture of 50% Mg and 50% (Al ₂ O ₃ and Al). The results obtained are shown in numeral 10. The results obtained with the desulfurization agent according to the invention are shown in 3-9 and 11-13.

It is shown that the desulfurization agent according to the invention is remarkably superior to conventional desulfurization agents.

Explanation of Abbreviations Used in Table 2 and Table 3

kg Ds Desulfurizer Amount of desulfurizer injected per pig iron

t PI

kg DS Desulfurizer kg number of desulfurizers supplied per minute

min

S ₁ Initial sulfur content of dissolved pig iron

Final sulfur content of dissolved pig iron after S _E treatment

Factor for the Effect of α-Value Desulfurization Agent

(Injected amount of desulfurization agent in the initial and

Final yellow tea divided by 100)

Carbide industrial calcium carbide

Mg magnesium

Desulfurization agent consisting of 85% industrial carbide by weight CaD 8515 and 15% diamide lime by weight

% Weight percent

TABLE 2

Desulfurization in the open ladle

1) co-injection 3) test 12 average

2) Test 500 average 4) Test 20 average

TABLE 3

Desulfurization in Closed Ladles

Claims (6)

A fine particle desulfurization agent for iron melt, which is mainly composed of calcium carbide and injected into the iron melt by gas, comprising at least 15% by weight of volatiles and a volume of at least 80 standard liters / kg at the iron melting temperature. 50 to 2% by weight of dry coal and 50 to 98% by weight of industrial carbon carbide, wherein at least 90% by weight of the mixture of dry coal and calcium carbide has a particle size of less than 200 μm. Desulfurization agent for iron melt, characterized in that. The desulfurization agent according to claim 1, which further contains magnesium. The desulfurization agent of claim 2 comprising 47.5 to 95.5 wt% calcium carbide, 50 to 3 wt% dry coal and 2.5 to 40 wt% magnesium. In the iron melt desulfurization method, the desulfurization agent in the fluidized form according to any one of claims 1, 2 and 3 is supplied with a carrier gas of 10 to 100 kg / min by a carrier gas selected from the group consisting of nitrogen, argon natural gas or propane. Desulfurization method of the iron melt, characterized in that the injection into the molten iron by desulfurization. The desulfurization process of claim 4 wherein the fine magnesium and carbide / coal mixtures are stored separately, fluidized and mixed in a conveyor line or lance. 6. The desulfurization process according to claim 5, wherein the magnesium content in the final mixed mixture is changed while injecting the molten iron.