DE1408188A1 - Process for desulphurization of pig iron baths - Google Patents

Description

Hoesch Aktiengesellschaft, Dortmund,

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Procedure for

It is known to use pig iron baths with soda or soda-lime grit mixtures to desulfurize, those to lower the melting point of themselves • fluorspar is partly added to the slag that forms. It is also It has been suggested that these desulphurising agents are distributed in the pig iron ladle or in a special vessel for better effectiveness Blow through the mold. Finally, the sulfur can be finely divided Remove lime. Air or, better still, non-oxidizing gas is used as the lifting gas Gases used.

In these known methods, it has been found to be a disadvantage that the air is successful because of the oxidizing conditions it creates the desulphurisation reduced. In addition, pure lime desulphurisation occurs a dry, but extremely firm cinder cake that almost contains the iron that gets into the cinder through the blowing process holds on completely because of this and because of the difficulty in pulling it off This solid slag, which first has to be crushed, and is partially immersed in the iron bath and absorbs more iron Iron losses also stood in the way of the introduction of the procedure for economic reasons. ■. . "

Attempts have also been made to use pig iron powdered lime powder has been added in a shaking pan for desulfurization and experience has already been made that low Soda additions of approx. 5% prevent the slag from sticking to the pan wall prevent and reduce the loss of iron droplets in lime powder. In these attempts, no significantly better degree of desulphurization came through " the mentioned .Soda addition within the first 5 min. of the treatment of the

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Pig iron in the shaking pan comes into its own, even if the degree of desulfurization with approx. 90% after 30 min. duration of action can be regarded as extraordinarily good. However, these attempts were made in a small pan carried out and the exposure time easily leads to excessive cooling of the pig iron. In addition, the installation is more complex Schüttelpfaimen in many cases difficulties,

The present invention has set itself the task of kachteile mentioned to avoid and concerns a desulfurization process for pig iron using lime-soda mixtures, whereby in the desulfurization vessel reducing conditions are maintained »

According to the invention, a lance is placed in the pan filled with pig iron Lime-soda mixtures blown in, with the proportion of soda in the lime-soda mixture is between 1 to 18% with the proviso that only that much carrier gas it is used that only 3 to 7 liters of carrier gas are required for 1 kg of pesticide, and that, finally, the injection pressure is kept in the pan only about 0.1 to 0.2 atmospheres higher than the pressure prevailing at the lance mouthpiece will"

As a special feature, 5 to 15% soda is added to the iron bath at a temperature of 1200 to 1400 ° C and a sulfur content of 0.10 to 0.25% sulfur in a mixture with the lime to be blown. The bath temperature is low and is below 1200 C, the SOdäzusatz is un lime to ⁰ to 5 Io over the above value is increased to be blown lime. 3

In general, the amount of lime to be blown in depends on the sulfur content of the Depending on pig iron, according to the invention, in order to achieve the desired slag constitution, the addition of soda correspondingly increasing lime aggregates from 6 kg of desulphurisation mixture per ton of pig iron to around 40 kg Entsctov. M. / to pig iron increased by 1 to 18% in the total mixture will. To illustrate this, a diagram is shown which shows the soda content of the mixture as a function of that of the pig iron represents the amount of lime to be added. *

In the case of the registered procedure, it is essential that only those t ■ - 3 - BAD ORIGINAL

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To use amounts of carrier gas that the solids are being promoted and the carrier gas itself but has no metallurgical effect on the pig iron. With the small amounts of gas in question, blowing with nitrogen is recommended to avoid all harmful side effects. Furthermore, the injection pressure is kept only slightly higher than the counter pressure at the mouth of the lance. This measure has the effect that the solids emerge from the outlet opening or openings of the lance without significant pressure. The pig iron is swirled through only weakly and the solids increase by virtue of their compared to steel. low specific weight slowly to the surface. This results on the one hand in the conversion of the lime with the sulfur or a low conversion of the lime with the silicon, especially when air is used as the carrier gas, on the other hand the carbonic acid is released. It bubbles slowly through the bath with the carrier gas and expands the slag that has formed on the surface. This process is promoted by the not yet fully degassed Na ₀ CO ₀ in the slag itself which has not yet reached the slag.

A substantial part of the lime goes through the bath unhindered. On the surface of the bath, a certain amount of the silicon is still oxidized to silica, so that a slag is obtained which contains essentially 30% CaO, 2 to 4% CaS, approx. 4% SiO ₀ and 2% Na ₀ O. The rest are iron granules or iron oxide.

This slag has a melting temperature that is 300 to 400 C above that Temperature of the pig iron is so that it is dry. At the same time surrender but due to the addition of soda during the blowing process in addition to the aforementioned 'Blowing effect also locally higher melting point depressions, so that the Slag does not form a firmly coherent cake, can be easily peeled off in a short time and cannot get stuck on the walls. The total iron content of the slag drops from 75% to 50%. ObAvohl but z. B. in the desulfurization of a 0.15% sulfur-containing pig iron in the slag even with an eight percent soda content of the lime-soda mixture It contains only about 30% less iron compared to that

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.pure CaO bubbles, the ratio of the true iron losses is from The reasons given above are even more favorable, namely at around 1: 3 for batches with added soda versus those without added soda. This is coming with 40 t pans this equates to an iron gain of approx. 1 t / batch. Simultaneously there is a gain in time.

A stronger silicon content of the pig iron does not interfere with the process, but even leads to a better degree of desulphurization, where from ■ approx. 0.9% Si content, a maximum effect is achieved. '

The method is preferably set-up that one after beginning of blowing the lance from above into the hot metal pan and the Powdered lime and the powdery soda are separated via pipes conveys into a pneumatic mixer, mixed there, and then blows in.

With a sulfur content of 0.15% in the pig iron and a soda content of the lime-soda mixture of 8%, an increase in the efficiency of the Desulphurization achieved when blowing in 20% compared to pure lime blowing. This corresponds to an equal reduction in the Lime consumption by 20%. Compared to the usual soda process also better desulphurisation. -

With the possibility of a more precise final sulfur content setting at According to the invention, there is also no need for an additional correction of the sulfur content of the insert pans in the Thomas factory.

The procedure is explained using a practical example:

42, 3; tarröhe iron with 0.144% S, 0.27% Si and 0.53% Mn were according to the invention processed in a pan. The temperature of the iron was 1223 C. Soda up to G mm grain size were filled. The containers were connected by two conveyor roller lines to a pneumatic mixer in which the mixing process was set so that IUO kg CaO 8, 7 kg soda accounted for.

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The lance, which was connected to the mixer and which could be lowered into the bath from above, hung over the bohe-iron pan. When the pan was full, the blowing process was started shortly above the surface and the lance was then lowered in one pass to a 1.20 m bath depth. The loading of the carrier gas with the lime-soda mixture per 4 liters of gas was 1 kg of solid. Within 3 minutes, 528 kg of lime-soda mixture were introduced into the pig iron using a nitrogen pressure of 1.1 atmospheres.

After the treatment, the sulfur content was 0.06%, the Si content was 0.20% and the Mn content 0 ^ 40%. The lance brought an even greater immersion depth no more efficiency improvement.

This resulted in a degradation of 0.084% for sulfur, 0.07% for silicon and 0.04% for manganese. This results in a desulfurization rate • of 57.7 % with an efficiency of lime utilization of 11.6%.

The slag was loose and could easily be removed. Whereby the iron losses only 0.61 to, so I ₅ 49%, respectively, compared with 1 ^ 80 tonnes or 4, 3% of the use upon blowing of pure lime in one, equally with 41 t RoI iron filled pan. ■ ...

Comparing rfahren in which oxygen and lime are blown by means of the lance in an iron bath, _s it should be noted that in the present process no significant metallurgical effects of the gas were intended, nor these experiments with the known Ve

. have taken place because you can manage with 4 liters of gas per kg of solid,. f ■ ..

while when fresh with the Sauerctoffverfahren amounts of Q, 4 to

3
8 kg per Nm or at least 125 liters of gas per kg of solid is used.

The prints differ just as much in the process carried out here with 1-1 atm against 4 to 20 atm in the oxygen bubble method. Other attempts at desulphurization by blowing in lime using nitrogen have been made carried out with at least 26 liters of carrier gas per kg of desulphurisation mixture (Trentini et al.).

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The description of the example shows how to carry out the procedure it has already been said that lime and soda are taken from two containers, which are connected by conveying pipelines to a pneumatic mixer. The mixture was adjusted in such a way that about the two Feed lines were fed certain weighed amounts to the mixer and then good mixing was achieved by fluidizing.

Suitable for the pneumatic mixer and the conveyance to the lance a conveyor device as described in German patent application H 37 711 XI / 8Ie. It is at this point on the content and the Drawing of this application pointed out. It describes a loosening floor for pneumatic conveyors consisting of zones of different specific Permeability is composed, the permeability in an area of at least the size of the feed nozzle inlet and of the same surface shape as this is equal to zero, while the remaining part of the loosening soil has a permeability that increases gradually or continuously with increasing distance from the nozzle, up to the edge of the Soil, the maximum permeability calculated for the task or area of responsibility of the conveyor is achieved. The permeable area of the soil has an edge protruding over the surface of the floor and is adjustable so that the permeability can be changed during operation.

But you can also work with devices as they are known per se, in which the mixing ratio varies during operation and the Amount of the powder mixture can be controlled. Such devices are e.g. B. designed so that one in the feed between the reservoirs and the pneumatic mixer installs metering screws that have a simultaneous sluice effect. In that actually. Mixer is located then only so much desulphurizing agent that by the different program-controlled dosing of the delivery from the storage tank into the mixer the mixing ratio continuously, as required is variable. This enables precise control of the pig iron treatment possible, e.g. B. in this way the first G kg of lime / t of pig iron without. Blow in soda, and only when the amount of lime increases will also

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the lime-soda ratio changed accordingly during blowing, which means that the degree of desulphurisation and the quality of the slag are favorable be influenced. The same applies to a slow start of the bubble and then desulphurizing agents increasing per unit of time. '"-" ".

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Claims (4)

Patent requests 1. Process for the desulfurization of pig iron by means of a. lime-soda mixture suspended in a carrier gas, characterized by the combination of the following Process features: 1. The use of a known lime ^ soda mixture with a content of 5 to 15% soda 2. The suspension of the desulphurisation mixture in any carrier gas at a gas / pesticide ratio of max. 5 1/1 kg. 3. Blowing in the desulphurisation mixture in a manner known per se with the help of a lance deep into the pig iron bath. 4. The use of a blowing pressure that is 0.1 to 0.2 atmospheres higher than that prevailing at the mouth of the lance ferrostatic pressure guaranteed. 2. The method according to claim 1, characterized in that the quantitative ratio of the desulfurization mixture during the Bringing within the claimed limits continuously changed, in particular the soda content increased will. New at torL. ".. ORIGINAL ■ 80980-3 / 0468 140818b 3. The method according to claims 1 and 2, characterized in that that the amount of desulfurization mixture to be introduced into the pig iron during the Bringing in is continuously increased. 809803/0468