JPS5913012A - Method for protecting tuyere of blowpipe for refining molten iron - Google Patents

Abstract

PURPOSE:To protect advantageously the tuyere of a blowpipe by recovering exhaust gas from a refining vessel without causing burning, removing N2 from the gas under specified conditions, and feeding the remaining gas to the tuyere as a flow of a covering gas. CONSTITUTION:A flow of gaseous O2 or a gas contg. O2 for refining is blown into an iron bath contained in a refining vessel from the tuyere of a blowpipe for refining molten iron through the wall of the vessel together with a flow of a covering gas which flows around the flow of the refining gas. Exhaust gas from the refining vessel is recovered without causing burning, N2 is removed from the gas in accordance with the equation, and the remaining gas is fed as the flow of the covering gas. In the equation, CN2 is the concn. (%) of N2 in the covering gas, qo is the total flow rate (Nm<3>/min) of gaseous O2 for refining, and qBo is the flow rate (Nm<3>/min) of O2 fed to the tuyere of the blowpipe.

Description

[Detailed description of the invention]

The present invention relates to a method for protecting the lining of soft pipes for smelting molten iron, and is often used for blowing a refining gas stream made of oxygen or at least a gas containing oxygen in, for example, bottom blowing or top or bottom blowing converters. This is a new proposal based on the results of many years of research and experimentation regarding the suitability of insurance fluids for soft pipe linings, such as the double pipe type that has been developed. Conventionally, OB
Hydrocarbon gases such as propane, butane or natural gas commonly used in M/Q-BOP, the oxygen bottom-blown converter process, or kerosene in a similar steelmaking process called LWS, both of which are soft Oxidizing gas for refining, especially pure oxygen gas, is injected into the bath as a fine flow of the pipe siding, and the encapsulated gas is used for cooling by this encapsulated gas. Efforts were made to extend the life of the feather. However, the conventional Class 1 protective fluid contains hydrogen atoms, which are absorbed into the iron bath and have an unfavorable effect on the quality of steel production. On the other hand, in the AOD method in stainless steel refining, a holding fluid that does not contain hydrogen atoms, such as an inert gas, especially argon or nitrogen, is used. As a result, there is no heat removal effect sufficient to sufficiently cool the tip of the soft tube lining that opens into the iron bath, and the lining life is only 850 heats at most, which is 1000 heat in OBM/Q-BOP.
G, 1m comparison is much inferior. In addition to the above-mentioned methods, it is known that carbon dioxide gas or liquid can be used.
The former is in Publication No. 8, and Rev. Metalurgie (19ri 8), p18-19
The latter are disclosed in the following, but since they do not involve a decomposition reaction, the heat removal and cooling effects are not sufficient. In other words, taking propane (0, H8) among hydrocarbons as an example, The flow rate of the encapsulated gas, which is about 4% in terms of volume percentage against the oxygen used as the operating gas, achieves sufficient insurance for the soft pipe wall, and the heat removal effect of propane is one of the reasons why Sensible heat when the temperature rises to the bath temperature (rflao. °C) is added, as well as endothermic heat when propane decomposes into 0 and H8, and calculated by setting these thermodynamic constants, the amount of heat extracted is 6. The sum is about 1'□
□8 Kdhl/nxol', whereas when carbon dioxide is a gas, it has a simple sensible temperature, oxidation rate, 160
Approximately 1 B, 4 KOal/mol while reaching 0°C
,,Also, even if heat of vaporization is added to the liquid, it will be about & 1,
5 KOal/hlo is about 1, which is not much different in both cases, and the volume percentage relative to oxygen is 17%, and it is necessary to supply a retaining fluid that is about 1 times the volume of propane. Made here - Even though hydrogen pickup, which is a quality concern, has been eliminated, there is still a difference in the amount of protective fluid used, and propane,
In addition to the disadvantage of being expensive, the heat balance inside the converter is poor (jS
Accompanied by normal blowing, the iron ore list, dosage is PI
25kg/1steel, unless the degree is reduced,
It became impossible to obtain the temperature at the end of the helmet, and as a point iron source,
This makes it virtually impossible to use cheap iron ore, leading to a decline in production and steel tapping yields = ・Furthermore,
Oxidizing moth 1. Carbon oxide, which is a carbon oxide, is a Mg070-based 65-resistant σ? 0, the lifespan of the refractory material will be reduced. , like this 1. 1. As a protective fluid for the soft tube and mouth. The use of carbon dioxide is far less economical than conventional propane, and therefore has not yet reached the first stage of industrial practical use.
Well, no. On the other hand, according to Japanese Patent Publication No. 55-48ri68, regarding the OBM process mentioned in 4 above, in addition to hydrocarbons listed in 1., rare gases, and carbon dioxide, -carbon oxides can also be used as insurance fluids. Of the things mentioned: 1. The specific application of this is limited to the propene mentioned above. Also, JP-A No. 66-98814,
The bulletin discloses 1. The use of "unburned exhaust gas recovered from bottom-blown smelting furnaces" as a cooling medium. Regarding the expansion function of carbon monoxide, which is present and accounts for most of the volume of exhaust gas, cooling by carbon monoxide is not mentioned at all, and is actually contraindicated. Such effects had not even been considered in the past.The inventors boldly went beyond the above-mentioned taboos and
- An attempt was made to investigate the protection of soft pipe tuyere using carbon oxide, and it was found that hydrocarbon-based It has been found that the present invention is comparable to the case using gas, and can be advantageously realized without any hydrogen pickup, which is its biggest drawback. By using this carbon oxide (hereinafter simply referred to as CO),
The mechanism by which the blowing tuyere significantly reduces erosion loss is thought to be as follows. In other words, due to the outflow of OO-containing encapsulated gas surrounding the jet flow of oxidizing gas into the iron bath, so-called pine mushrooms made of porous solidified iron are formed in the gap between the inner and outer tubes of the soft tube lining. is formed as before, but when the encapsulated gas flow passes through the pores, the following equation (1), 200→0 (S) + 00. −−−−− (
The reaction 1) proceeds to the right, causing the precipitation of a large amount of powdered carbon. This powdered carbon is entrained in the encapsulated gas airflow and permeates into the iron bath, while the sulfur (hereinafter simply referred to as 0.
The following formula (2), 0(S) + Fe0-+Na
+ 00 ------ (2) The endothermic reaction occurs, and the area around the tip of the soft tube slats is effectively cooled by this reaction heat. In addition, 0. When the gas was blown into the iron bath, a large amount of FeO was produced, which reacted with the refractory material around the tip of the soft tube tuyere, lowering its melting point and causing the risk of the refractory material being melted away by the high-temperature molten iron. However, the blowing of 00 is advantageous in that it reduces FeO by the reaction of the following formula (8) % formula % (8) and lowers the FeO concentration in the vicinity, and since CO is reducing, While CO8, which has already been cited as a conventional technology, is oxidizing, it is useful from the viewpoint of deterioration due to oxidation of magnesia-carbon-based or magnesia-dolomy (magnesia-dolomy) carbon-based bricks, which are particularly useful as bottom-resistant materials for bottom-blowing converters. is also advantageous. In order to enhance the weld protection effect of the siding and the surrounding refractories described above, especially by utilizing the endothermic reaction of equation (2) listed above, it is necessary to use powdered carbon based on the reaction of equation (1). It is desirable to achieve sufficient precipitation, and in this respect, the higher the 00 concentration in the encapsulated gas, the more advantageous it is. However, using a high 00 concentration, for example, pure OO gas, as the encapsulating gas increases cost, which runs counter to the current demand for cost reduction. 1 In this regard, it would be extremely advantageous in terms of cost if it were possible to use unburned exhaust gas recovered from a refining vessel such as a converter, which is easily available and contains a large amount of 00 within a steelworks. When recovering unburned waste gas, it is difficult to avoid mixing of air, and therefore, as shown in Table 1, a considerable amount of nitrogen (hereinafter simply referred to as N) is mixed in the recovered converter exhaust gas. ing. Table 1 It has been found that if converter exhaust gas containing such a relatively large amount of N is used as it is as encapsulating gas, the nitrogen concentration in the hot metal will increase and the quality of the steel will deteriorate. Therefore, the inventors collected the unburned converter exhaust gas,
Adsorbing and removing N in the exhaust gas by passing it through an N adsorption tower,
After conducting numerous experiments and studies using various N and concentrations and using these exhaust gases as the encapsulating gas, we found that the encapsulating gas flow rate required for effective protection of the lining was determined by the bottom blowing 08 gas flow rate, and the above When using a converter exhaust gas of 0.00 minutes, the bottom blows 0. Approximately 5-go% of the gas flow rate is appropriate;
It was also found that the concentration of N in molten iron depends on the concentration of N in the encapsulated gas and its flow rate.
In order to prevent a substantial increase in the concentration, the upper limit of the Ng concentration in the encapsulated gas (10) should be set to 0. It was discovered that the gas flow rate should be specified by the bottom blowing 0g gas flow rate for Gas Zenryusha, and thus it was found that the cooling and preservation of the soft pipe wall was particularly effective without causing an increase in N in the molten iron by 6 degrees. They have discovered that this can be achieved with no inferiority and advantages compared to the case of using pure gas. This invention is based on this knowledge, and it is possible to reduce the wear and tear of soft pipe linings for molten iron refining and the surrounding refractories at low cost without increasing the concentration of hydrogen or N in steel. The purpose is to reduce the To achieve the above object according to the present invention, the following configuration is the main point of the solution. Molten iron refining according to the present invention can be carried out using a so-called bottom-blown converter, as long as the above-mentioned soft pipe lining is used for blowing refining gas into the iron bath.
Top, one bottom blowing converter, electric furnace, open hearth or AO
It is mainly applied to the D-method, etc., regardless of the type of eclipse container, etc., and also for molten iron, which is mainly made of blast furnace hot metal - carbon-based (11) Hamochirun Denki. High alloys whose main raw materials are high alloy scraps, such as melted iron-carbon baths such as scraps in furnaces, etc., and high alloy scraps, which are mainly used for refining by the AOD method.
Any method such as an iron-carbon ice bath may be used. In addition, in this invention, the soft pipe surface used for molten iron refining is a conventional general concentric double pipe groove type, and a refining gas airflow consisting of oxygen or a gas containing oxygen is passed from the inner pipe. , and the outer tube, to be more specific, the li between the inner tube and the outer tube! In addition, a cooling and enveloping gas flow to the tip of the soft tube siding is applied according to the customary practice of blowing into an iron bath contained in a refining vessel. In this invention, the encapsulating gas is N, and the cleaning furnace exhaust gas with a reduced concentration has a cooling and setting effect on soft tube tuyere comparable to that of conventional propane, as described above.
The concentration of N in the encapsulated gas (ON (%)) is derived from the knowledge that it can be realized without causing the inevitable adverse effects of hydrogen pickup just before the use of propane. qo Te O for refining, total gas flow rate (Nm8/m1n), q, P Te 0. Assuming that the supply flow rate (Nm'Ainj is each increment), the following formula (4), " □
It has been confirmed that the object of the present invention is met as long as the ON statement--5, o/q(,,-(4)) is followed. I will explain about a test example in which blowing was carried out in a bottom-blowing converter with a furnace capacity of 5 tons. 6 - ・ Figure 1 shows the furnace surface of a bottom-blowing converter, and Figure 1 shows the furnace surface of a bottom-blowing converter. is that A'-A'
The arrow plane number is shown. This bottom-blown converter + has a furnace wall steel shell 1 lined with high temperature fired magnesia dolomite bricks 2, At the bottom 4- of the furnace, 4'' double-tube tuyeres 5 were arranged in a line parallel to a □-to-nion axis member (not shown). □ □ The inner pipe 6 through which the 02 gas passes through has an inner diameter of □8 and an outer diameter of 12. 7. The outer tube is made of double-metal copper tube and forms an annular gap through which the protective fluid passes. has an inner diameter of 1, . 9. q, u, outer diameter 19.0
5m5+ copper! A tube was used. Therefore, the inner tube, 6. and outer tube 7
The annular gap formed by and is 0.6 mm.
. As shown in FIGS. 2 and 8, each tube, tuyer 5, and port 6 are connected to a refining gas supply pipe 11 via an inner pipe 6, a pipe 8, a branch pipe 9, and a header lO. The outer tube 7 includes a
In this test, in particular 2
A continuous protective fluid supply pipe 14@Np4 was connected. Note that the supply pipes 11, 14 and 1.5 are
When the furnace is not blowing, such as during tilting, ←1. 1. necessary to counteract the static pressure of the dissolution bath. switchably connected to an inert gas pressure source. Blast furnace hot metal having the following composition was charged into this converter/furnace. 0:4. Town weight% (hereinafter simply expressed as %), i91!
0.88'%,)in,,: 0.41%,P,10
．． 10%, S! 0.086%. Moreover, the melting temperature and pig iron temperature were 1200°C. During this charging, each soft tube layer 6 has u, g 5 in its inner tube.
Nm/min, OJ for outer tube 7 8 Nm/min
Ns gas was supplied at a minimum of 100 mL to prevent clogging of the siding, and immediately after finishing the installation, the converter was placed in an upright position and the next blowing process was carried out. Test Example 1 One soft tube tuyere 5, 0.0 from the inner tube 6. 1.25 gas
The N gas is supplied at a rate of Nm8/min.
For the bottom blow 02 flow rate, it is equivalent to 20% of the bottom blow 02 flow rate.
84%C0-5%C02-8% at 25 Nm/min
Converter exhaust gas whose composition was adjusted to N2-3%N2, and also for group b, 0.10 Nm/min 1
While supplying propane to each tuyere, a top blowing lance was inserted into the furnace from the converter mouth, and 6Nm 7'
02 gas was sprayed onto the surface of the hot metal bath to make up for the lack of bottom blowing refining gas, and at the same time as blowing started, 150 to 9 burnt lime was added to the hot metal from the top of the furnace, and blowing was continued for about 20 minutes. I did it. Then, while pulling up the top blow lance, each soft pipe siding 5
The supply of N2 was switched to the one listed above, and the converter was then tilted toward the charging side. The temperature of the molten steel was measured and sampled, and the following blowing results were obtained. 0: 0.02%, In+0.2
4%, Si:tr. P: 0.015%, S: 0.0
21%, W1#! Flooding level: 1660°C0 Then, the steel is reversed to the tapping side and tapped into the ladle, and the furnace body is again tilted to the charging side to remove the molten slag from the furnace mouth and make the furnace empty. , and the inspection plug 1B directly under the inner pipe shown in FIGS. 2 and 8 was removed to measure the melting damage at the tip of the soft pipe siding 5. The one that applies the above 1 charge is 1.6
111i, the corrosion loss was 1.9 m, while the b group, that is, the one cooled with propane, had a loss of 9.3 sm, 2.4 m.
It was m. Note that these measured values are shown as average values at six locations on the circumference of the end face contour of the inner tube 6. The amount of encapsulated gas used in this test was 20%, but as shown in the test example below, at a usage amount of 15 to 20%, the erosion loss exceeded that of propane at the conventional general usage amount. The preventive effect has been revealed. Test Example 2 To the inner pipe 6 of the soft pipe tuyere 6, 1.25 per piece, Nu8
/min 02 gas, outer tube? Atbil [0, 19 equivalent to 15% of the bottom blow 0□ flow rate through group II]
Converter exhaust gas having the same composition as in Test Example 1 described above was supplied at 1 Jm8/mi, n, and blowing was performed only by bottom blowing. The amount of damage to the siding at this time was 1.9 to 2.1 s〆charge, and the effect of preventing erosion was equal to or higher than that of propane. However, in this case, the N concentration in the molten iron was
8 ppm, which is about 5 to 10 ppm higher than when normal propane is used. Thus, molten iron with a high N concentration requires low N.
It cannot be used for that purpose for steel types. Therefore, in order to find out the N concentration in the encapsulated gas that can achieve the same level of lining protection function as propane and satisfy the N concentration below goppm, which is considered to have no problem with the quality of normal products, various N, The relationship between the concentration of N in molten iron and the concentration of N in encapsulated gas and the amount of injection was investigated using converter exhaust gas. In the experiment, the overall 011 gas flow rate was kept constant at 1 ONm /min in both cases of bottom blowing only and top and bottom blowing in combination, and 0.000. The tests were carried out under conditions where the flow rate was changed to various ratios. Further, the flow rate of the encapsulating gas was set to be bottom blowing O and in the range of 15 to 20% of the gas amount. In addition, total 0. Bottom blow to gas flow rate 0. When the gas flow rate ratio was 0.1, 8 of the 4 soft tube slats were occluded, and only one was used. The obtained results are summarized in FIG. 4. As is clear from the results shown in the same figure, the total N concentration in the molten iron is 0. It depends on the ratio of the bottom blowing 0° gas flow rate to the gas flow rate and the concentration of N in the encapsulated gas, and to keep it below 20 ppm, which is usually considered to cause no problem in steel manufacturing quality,
The total concentration of N in the encapsulated gas is 0. 2.5 for gas flow rate
% or less, 50% bottom blowing to 5% or less, and 10% bottom blowing to 2.6% or less. Summarizing the above results, the total flow rate of O and gas for refining is q. (
When the amount of O and gas supplied from the soft pipe surface per 1m8/m1n) is expressed as q,F (Nm'/h+in), the N and concentration in the encapsulated gas necessary to effectively reduce the N8 concentration in molten iron are: , (%) is given by n. In addition, in the above-mentioned test blowing, the hydrogen concentration of the molten steel sample taken at the time of blow-stopping is 1.8 to 1.8 g, oppm according to the present invention.
and when propane is used, it is 4.5±1.2
Compared to the amount of about ppm, it can be said that virtually no hydrogen pickup occurs. By the way, in order to remove N and gas to a predetermined concentration from the converter exhaust gas recovered while it is still unburned, de-Ning is performed by pumping the exhaust gas to an adsorption tower filled with an adsorbent. Although a treatment process is required, this de-N removal is expensive. Therefore, it is not preferable from a cost standpoint to use converter exhaust gas that has been subjected to de-N removal and treatment throughout the blowing period. Therefore, in order to achieve such de-N removal and reduction of the cost required for treatment, the inventors developed a low-N, converter exhaust gas according to the present invention, which is necessary to prevent the concentration of N in molten iron from increasing. We also conducted repeated research on the period of use. In general, when the generation of 00 gas due to decarburization is active in the early stage of blowing, the degassing effect is high, so even if N and gas are blown, most of it is discharged outside the bath, so IIT is absorbed into the molten iron. Therefore, the experiment focused on the second half of blowing. The experiment was conducted in accordance with the test blowing described above, with the 0° gas flow rate for refining being 10 Nm'/min and 5 Nm'/min t.
The remaining 51 m'', 'h+in' were supplied from the upper blow lances from the t-blowpipe section. Also, the encapsulated gas flow rate was as follows:
The bottom blow was 0 and the gas flow rate was in the range of 15 to Bθ%. In this experiment, the initial stage of blowing was 00280~98%, 1o
o, s a ~ 6 la dawn; , N, !
6-9 Rakyo; , H, 寞 8-45 The converter exhaust gas having a composition of I is used as it is without de-Ning or treatment, and in the middle of blowing, N according to the present invention is used. This was done by switching to converter exhaust gas that had been de-Ned and processed to a concentration of 2 to 5% N, which satisfied the concentration range. The molten steel temperature at the time of blow-stopping is 1680 to 1090°C.

[0] Concentration was 0.02-0.85%. Figure 6 shows the amount of decarburization Δ0 (when switching to jO-encapsulated gas) during the period of blowing with low N and converter exhaust gas according to the present invention.

[0]-
stopper

[0]) and the N concentration in the molten iron at the time of blow-stopping.・As shown in the figure, the above decarburization □
amount Δ0 and N in molten iron. There is a clear relationship between the encapsulation gas and the molten iron concentration.

[0] Dark change stops blowing

At least 0.76% higher than the [0] value

It has become clear that this should be done when the [0] concentration is reached. Therefore, N in molten iron,
In order to prevent the concentration from increasing, it is not necessary to use particularly low N and converter exhaust gas from the start of blowing to the middle stage, and untreated raw converter and furnace exhaust gas can be used. It is possible to reduce the training cost. Note that this invention is not limited to mere cooling of an octet tube tuyere, but generally 0. It can also be applied when using a protective fluid ejection pipe attached to a gas ejection pipe.
As described above, according to the present invention, the erosion of the surrounding bricks, including the tips of the soft pipe slats, can be prevented by effective utilization (BO) of the unburned exhaust gas recovered from the refining vessel at low cost. It can also be achieved without hydrogen or even nitrogen pickup.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing the hearth surface of a bottom blowing converter, Figure 8 is a view from the Moum' arrow, Figure 8 is a back view of the hearth 1, and Figure 4 is the molten iron at the end of blowing. Figure 6 is a graph showing the relationship between the medium N concentration and the N concentration in the encapsulated gas, which shows the amount of decarburization Δ0 during the period of blowing with low N and converter exhaust gas according to the present invention, and the amount of decarburization in molten iron during barking. It is a graph showing the relationship between N and darkening. Patent applicant Kawasaki Steel Corporation Kinsha'=C] Figure 4

Claims (1)

[Scope of Claims] 1. A refining gas stream consisting of oxygen or a gas containing oxygen is passed through the wall of the refining vessel, together with an encapsulated gas stream flowing out around the gas stream. The exhaust gas discharged from the refining vessel and recovered unburnt as the encapsulated gas stream is blown into the soft pipe lining for molten iron refining into the bath, and the nitrogen content is expressed by the following formula % formula % where ON: Nitrogen concentration in the encapsulated gas (%) qo + total flow rate of oxygen residue for refining (Nm /hlin) qoB: consists of removing and supplying according to the oxygen supply flow ii (Nm"7mln) of the soft pipe lining, Insurance method for soft pipe lining for molten iron smelting. Nitrogen removal is at least 0.7 below the blow stop [0] value.
At the final stage of decarburization, when the concentration exceeds 6% [0], l
Method described. '& The method according to 1 or 2, wherein the soft pipe wall is made of a double pipe, and the refining gas is blown into the iron bath from the inner pipe, and the encapsulating gas is blown into the iron bath from the outer pipe. □ Table The method according to 1.2 or 8, wherein the refining operation is carried out exclusively by blowing gas through the soft pipe lining, and the nitrogen concentration in the encapsulated gas is less than 2.5%. 4. The refining operation is assisted by blowing refining gas from the top blowing lance, and the top blowing oxygen supply amount is q. 8. The method according to 1.2 or 8, wherein the concentration of nitrogen in the encapsulated gas is ON and ≦L 5 (qoB+q,'')/q.