JPS5825412A - Desulfurizing and dephosphorizing method for molten iron - Google Patents

Abstract

PURPOSE:To desulfurize anbd dephosphorize molten iron continuously witout intermediate slag discharge by desulfurizing the low Si molten iron in a mixer car by addition of a desulfurizing agent thereto then adding a dephosphorizing agent to the iron and blowing oxygen thereto. CONSTITUTION:Low Si molten iron of <=0.3% content of Si is put in a mixer car, and first a desulfurizing agent consisting essentially of CaC2 and CaO is blown thereto to convert the S contained therein to CaS and to remove the same as slag. In succession, a dephosphorizing agent consisting of a flux such as CaO, iron oxide, fluorite or the like and a reaction acceelerator of alkeli metal compds. such as sodium carbonate, sodium borate, cryolite or the like is blown into the molten iron and further gaseous oxygen is top blown to create an oxidizing atmoshere to remove P as P2O5 together with CaO in a stable form in slag, whereby the molten iron is dephosphorized. The molten iron is desulfurized and dephosphorized continuously with high heat efficiency without intermediate slag discharge and without decrease in productivity.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for desulfurizing and dephosphorizing hot metal, and more particularly to a method for efficiently and continuously desulfurizing and dephosphorizing hot metal in a pig iron mixing car.

The mainstream method for desulfurization and dephosphorization of hot metal is to perform it in a pretreatment furnace, but in order to shorten the series of treatment times and simplify the treatment process, there is a method in which desulfurization and dephosphorization are carried out in a pig iron mixing car. is also attracting attention. This method is a method in which desulfurization flux or dephosphorization flux is blown into hot metal in a pig iron mixing car together with a carrier gas, and satisfactory values have been obtained for the individual efficiencies of desulfurization and dephosphorization.

On the other hand, there is a method in which desulfurization and dephosphorization are performed continuously in a pig iron mixing car, but for the following reasons, it is necessary to remove slag generated during the treatment process, and various problems have been pointed out.

That is, desulfurization is a method in which a desulfurization flux such as CmCm or CaO is blown into the hot metal together with an inert gas, and S is fixed as Cm8 through the reaction of CaC dew + S -Cali and removed as slag. This reaction is a reduction process. It progresses in a sexual atmosphere. On the other hand, theoretical phosphorus is produced by blowing a CaO-iron oxide monosolvent system or a desulfurization slack such as NagCOs together with a carrier gas into the hot metal, and at the same time blowing oxygen gas upward.
→ 2PPO5 mcsiO+mPxOsi -e ncaO-mixe
This method fixes P to the slag by the reaction of s, and this reaction proceeds in an oxidizing atmosphere. In this way, the desulfurization reaction and the dephosphorization reaction proceed under contradictory reaction conditions, and the composition of the produced slag is also strikingly different. When a dephosphorization or desulfurization reaction is performed, resulfurization or rephosphorization occurs. Therefore, after desulfurization or dephosphorization is completed, the produced slag must be removed (intermediate slag), which makes the work complicated and reduces work efficiency, as well as causing various losses such as hot metal loss and heat loss caused by intermediate slag. The problem arises.

The inventors of the present invention focused on the above-mentioned circumstances, and conducted research with the aim of developing a method that would enable continuous desulfurization and dephosphorization of hot metal without intermediate removal of slag in a pig iron mixing car. It's here. The present invention was completed as a result of such research, and
The structure is that a desulfurization flux containing CmC1 or CaO as a main component is blown into the hot metal with a low 81 content together with an inert gas in the hot metal mixing car, and then C is added to the hot metal without removing the generated slag. @b, The gist is that a dephosphorizing flux consisting of iron oxide and a solvent or a reaction accelerator and these is blown in together with an inert gas, and at the same time oxygen gas is blown over.

The present invention is based on the premise that hot metal with a low Si content is targeted. This is because if hot metal contains a large amount of Si, it cannot be desulfurized sufficiently even if a large amount of desulfurization flux is used in the desulfurization process, and a large amount of desulfurization slag is produced. A large amount of Slog in the phosphorus process
This is because, as a result, resulfurization is likely to occur. However, when hot metal with a low 5i content is used, although a slight decrease in desulfurization ability is observed, it is not at a problematic level, and resulfurization does not occur even if dephosphorization is performed continuously without intermediate removal of the generated slag. Almost never happens. Although it is difficult to determine the critical upper limit of the Si content, in order to effectively exhibit the above effects, it is best to use hot metal with an S1 content of 0.3% or less, which satisfies this condition. It is necessary to use hot metal that has been desiliconized in advance.

Desulfurization treatment is performed by blowing a desulfurization flux together with an inert gas (Wl mixed, argon, etc.) into the hot metal in the pig iron mixing car. NazCO as a desulfurization flux
s, CmO or CaCt are known as main components, but in the present invention, only those containing Ci+O or CmCt as main components are used. However, NBCol has recently attracted particular attention as the most excellent hot metal desulfurization agent.
This is a strongly alkaline substance and has the problem of severely dissolving the fireproof walls of pig iron mixers, so it cannot be used as a desulfurization agent in the present invention. However, CaO or CaCt
The main component is that which produces desulfurization slag with a high softening point.
Even when dephosphorization treatment is performed without performing intermediate slag, resulfurization hardly occurs, and the final desulfurization rate can be sufficiently increased. Moreover, CaO and CmC2 replace refractories with Na
Since zCO@ does not melt or damage, there is no risk of shortening the life of the mixed pig iron car. Note that CaO and CaCg may be used alone or mixed in appropriate amounts, but usually C1
The desulfurization rate can be increased by lowering the melting point by using a small amount of a solvent such as silica. The amount of desulfurization flux used is also not particularly limited, but the most preferable amount confirmed through experiments was 1.5 to 2.0 flux per ton of hot metal.

The desulfurization flux described above is blown into the hot metal together with a carrier gas, but considering that the desulfurization reaction proceeds in a reducing atmosphere, it was decided to use an inert gas as the carrier gas.

After performing the desulfurization treatment in this manner, the dephosphorization treatment is continued without removing the desulfurization slag. For the dephosphorization treatment, a method is adopted in which a dephosphorization flux consisting of Cab, iron oxide, and a solvent or a reaction accelerator and a carrier gas is blown into the desulfurized hot metal, while oxygen gas is blown upward.

First, CaO generates low melting point slag with 510g produced in the dephosphorization process, and P! It is an essential component for fixing in the slag as 06. There are no particular restrictions on the amount of CmO added, especially since hot metal with a low S1 content is used in the present invention, 8! Since the amount of Os is small, sufficient dephosphorization efficiency can be obtained even with the addition of a relatively small amount. However, if the basicity (Ca07540g) of the dephosphorization slag is low, the dephosphorization efficiency will decrease, and the fluidity of the slag will increase, so resulfurization tends to be significant when it comes into contact with the desulfurization slag. It is desirable to ensure that the amount of carbon added is sufficient to maintain the basicity of the slag at a high level. In other words, most of the 3i in hot metal is oxidized during the dephosphorization process and becomes 5
ins and migrates into the slag, so the St in the hot metal
The content rate may be calculated in advance, and a necessary and sufficient amount of CaO may be added according to this amount. It has been confirmed through experiments that when the Si content in hot metal is 1%, if more than 0000 is added per ton of hot metal, high dephosphorization efficiency can be obtained and the resulfurization phenomenon can be minimized. It was confirmed that it was possible to suppress the For reference, the basicity of the generated slag when this CaO addition amount is adopted is 1.
45 or more.

However, if the amount of CaO added is too large, the cost of auxiliary raw materials will increase and it will be uneconomical, and the amount of slag will increase and the yield of iron will decrease, so it is preferable to limit the amount to about 50 x (k) or less.

Next, iron oxide is an essential component that lowers the melting point of the flux to promote the flux-metal reaction, and also increases the oxygen potential of the flux to promote the dephosphorization reaction. It is effective when added at a level of 1 or more per portion. However, if the amount is too high, the temperature of the hot metal will be lowered due to its decomposition, and the oxidation loss of C and - will become significant, so it is preferable to limit the degree of instant kneading to 30 or less per ton of hot metal. Mill scale, iron ore, etc. are used as iron oxide.

As a solvent, CmFt or fluorite containing CmFt as a main component is used, which has one effect of lowering the melting point of the flux and increasing its reactivity with hot metal, as well as promoting the dephosphorization reaction itself. These effects can be effectively exhibited by adding about 1O- or more per ton of hot metal, but if it is too much, the refractory will be more prone to melting and damage, leading to a shortened lifespan of the mixed pig iron car.
It is best to keep it below 1i degrees. Although it is considered most practical to determine the amount of solvent added based on the total amount of dephosphorization generated slag, experimental results show that it is in the range of 1/6 to 1/3 of the amount of CaO added. It was confirmed that the best effect was achieved when the setting was set to .

In addition, the reaction accelerator is not essential in the present invention, but is an effective component for promoting the dephosphorization reaction, and is in the range of 1 to 10% per ton of hot metal, or 174 to 1/2 of the amount of CaO added. It is possible to increase the processing efficiency by adding it.

However, if the amount is too high, the raw material cost of the dephosphorizing flux will increase, and the internal refractory wall of the pig iron mixer car will suffer significant erosion. The most common reaction accelerators are alkali metal compounds such as sodium carbonate, sodium borate, and cryolite.

The dephosphorization flux containing the above components is blown into the desulfurized hot metal together with a carrier gas such as air or nitrogen, and the dephosphorization reaction progresses due to the oxidizing action of iron oxide while floating in the hot metal together with the carrier gas.

However, the dephosphorization reaction caused by the injection of CaO-based flux is extremely dependent on the presence of oxygen gas, and in order to obtain the target dephosphorization rate, it is necessary to top-blow oxygen gas at the same time. In this case, if the top blowing of oxygen gas is aimed at the position where the dephosphorization flux and carrier gas rise to the surface of the hot metal, the oxygen gas will concentrate on the dephosphorization flux immediately after it rises to the surface of the hot metal. Since this is supplied, the dephosphorization reaction proceeds efficiently in this part. Moreover, the desulfurization slag is pushed toward the wall of the pig iron mixer by the upward flow of oxygen, and contact with the dephosphorization flux immediately after floating is suppressed, which has the advantage of suppressing resulfurization. The top blowing rate of oxygen gas is preferably in the range of 2 to 118 m/min per ton of hot metal; if it is less than 2 NII/min, it is difficult to obtain a sufficient dephosphorization rate, while if it exceeds 11 Nd/min, oxidation losses such as CJpMn will occur. The dephosphorization rate will not be improved any further.

FIG. 1 is a schematic process explanatory diagram showing an embodiment of the present invention, in which hot metal A that has been charged into the pig iron mixer 1 and has undergone preliminary desiliconization treatment is desulfurized
Up to 11 copies are transported. A flux injection lance 2 for desulfurization is installed in the desulfurization processing section so that it can be moved up and down.
The desulfurization flux sent through the Cs (or Ca0) hopper 3, quantitative rotary feeder 4, metering tank 5, and variable rotary feeder 6 is collected into hot metal A together with inert gas B, and desulfurization treatment is performed. After completing the predetermined desulfurization treatment, the desulfurization slag is transported to the dephosphorization treatment section without being intermediately discharged. In the dephosphorization processing section, a dephosphorization flux injection lance 7 and an oxygen gas upper collecting lance 8 are installed so as to be able to move up and down, respectively, and the lance 7 includes a dephosphorization flux raw material supply hopper 91.9b and a quantitative rotary feeder. 10m, 10b.

Metering tank 11. llb and variable rotary fee 11
A dephosphorization flux supply line consisting of 2m, 12b, etc. is connected to a carrier gas C feed pipe, and as shown in the figure, a lance 7 is inserted into the desulfurization hot metal to blow oxygen gas upward while blowing in dephosphorization flux. Dephosphorization is carried out by Through this series of steps, 3 and P in the hot metal are efficiently removed.

As is clear from the above description, the present invention employs a procedure in which desulfurization is first performed and then dephosphorization is performed, which is a procedure that cannot be taken lightly. That is, as is clear from the experimental examples described later, if a procedure of dephosphorization followed by desulfurization is adopted, the desulfurization rate cannot be sufficiently increased, and the object of the present invention cannot be achieved. This is because the P content level of normal hot metal is considerably higher than that of 3, so it is necessary to use a larger amount of dephosphorization flux, and the large amount of dephosphorization slag that is generated inhibits the desulfurization reaction. it is conceivable that. Moreover, when CaCs is used as a desulfurization agent, C reduces PzOi captured in the dephosphorization slag to cause rephosphorization, which may also reduce the dephosphorization rate. On the other hand, if the procedure of desulfurization followed by dephosphorization is adopted, the amount of desulfurization slag produced is small, so the dephosphorization reaction is not inhibited, and Ca
Since the carbon source originating from Cs is separated on the surface of the hot metal as high melting point desulfurization slag, the resulfurization phenomenon that occurs in the subsequent dephosphorization process can also be minimized.

The present invention has a general structure as described above, and its effects can be summarized as follows.

(2) Desulfurization and dephosphorization can be performed continuously without intermediate waste removal, which simplifies the treatment process and improves productivity. In addition, the outflow loss and heat loss of metal due to intermediate slag are eliminated, and operation management of the pig iron mixing vehicle is also simplified.

■In the method of desulfurization and dephosphorization during the transport process using a mixed pig iron truck, the preparatory furnace for desulfurization and dephosphorization is omitted, which shortens the time needed to complete the entire island, as well as the loss of hot metal due to transfer, etc. It also disappears.

Next, control examples and experimental examples will be shown.

Control Example Experimental data on the desulfurization and dephosphorization rates of hot metal pots in which desulfurization and dephosphorization treatments were carried out separately are shown below.

[Desulfurization treatment]

Flux for desulfurization...C@C! :Cl0=5 :
1 (weight%) 1.84/1 ton of hot metal carrier gas...N! , 0.4-0.5Nd/hot metal 1
Change in ton/min component...Table 1 (Weight 4) As is clear from Table 1, dephosphorization does not proceed at all in the polishing treatment using only desulfurization flux.

[Dephosphorization treatment]

Flux for dephosphorization ^...C@O:Cal:Fe0=
43%: 14*: 43% (weight), 30 instant/1 ton hot metal dephosphorization flux...CaO: CaF*: F・0
:NmtCO field = 39*: 11%: 39% = 11% (weight), 17-/1 ton of hot metal Top-blown oxygen...6Nd/1 ton of hot metal/Change in composition ・
... Shown in Table 2.

Table 11I2 (Fi amount %) As is clear from Table 2, if a dephosphorizing flux is used, desiliconization and desulfurization will occur along with dephosphorization, but the desulfurization efficiency is insufficient and a separate desulfurization treatment is required. There is.

Experimental Example Using the desulfurization or dephosphorization flux shown in Table 3, perform intermediate slag according to the method shown in Figure 1 (or a method in which the desulfurization and dephosphorization procedures are reversed)k. Continuous desulfurization and dephosphorization treatment was performed without any problems. Table 4 shows the changes in the composition of the hot metal and the final desulfurization and dephosphorization rates.

As is clear from Table 4, in the case where dephosphorization was first performed and then desulfurization was performed (Experiments 1 and 2: Comparative Examples), the desulfurization reaction was inhibited by the dephosphorization slag and a high desulfurization rate was obtained. Furthermore, rephosphorization occurs during the desulfurization process and the final dephosphorization rate also decreases.

On the other hand, those that adopted the method of the present invention (Experiments 3 and 4)
In the dephosphorization step after desulfurization, the dephosphorization reaction progresses efficiently and the desulfurization reaction also progresses further, resulting in high values for both the final desulfurization and dephosphorization rates.

[Brief explanation of drawings]

FIG. 1 is a schematic process diagram showing an embodiment of the present invention. 1... Pig mixing car, 2... Flux injection lance for desulfurization, 7... Flux injection lance for dephosphorization, 8.
...Oxygen gas top-blown lance Applicant: Kobe Steel, Ltd.

Claims (1)

[Claims] (1) In the pig iron mixing car, Cm is added to hot metal with low S1 content.
A desulfurization flux containing Cs or CaO as a main component is blown into the hot metal together with an inert gas, and then, without removing the generated slag, a dephosphorization process consisting of Cl01 iron oxide and a solvent or a reaction accelerator with these is added to the hot metal without removing the generated slag. A method for desulfurizing and dephosphorizing hot metal, which is characterized by blowing in flux together with a carrier gas and top-blowing oxygen gas.