JPS6137908A - Operating method of converter - Google Patents

Abstract

PURPOSE:To increase the amt. of scraps to be used in a converter and to operate the converter under the high scrap ratio by detecting the depositing conditions of an unmelted mixture to the furnace wall, and removing the deposited material in accordance with the detected results. CONSTITUTION:The amt. and composition of waste gas are continuously measured during the blowing of gaseous oxygen into a converter in the operating method of the converter wherein >=30wt% scrap is charged along with a carbonaceous source such as coke or coal and gaseous oxygen in supplied from the top or from the top and the bottom. Any one or >=2 among the amt. of C to be burnt, the amt. Os of oxygen accumulated in slag, and a change in the amt. of waste gas is obtained from said measured values, and the depositing conditions of an unmelted mixture on the furnace wall are detected from the correlation of the previously obtained amt. of C to be burnt, Os, and the change in the amt. of waste gas with the conditions of the unmelted mixture on the furnace wall. The deposit is removed in accordance with said detected results.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a converter operating method.

As is well known in the art, a converter is operated to produce molten steel by charging hot metal and scrap and then supplying O2 gas for refining.

Incidentally, in recent years, various attempts have been made to charge large quantities of scrap and iron ore in order to improve the yield of molten steel in converters. If a large amount of this scrap is charged, the heat source in the converter becomes insufficient, so a C source such as coke or coal is charged at the same time.

For example, in Japanese Patent Application Laid-open No. 57-54212, scrap,
A technology has been disclosed in which coke and hot metal are sequentially charged and oxygen blowing is performed, but this technology uses the calorific value of coke for direct reduction of iron ore and increases the amount of unburned gas. , As can be seen from the examples, the amount of scrap charged, that is, the scrap ratio [In the present invention, the scrap ratio is scrap/(hot metal + scrap)
100, expressed in weight% unless otherwise specified. ] is 9%
It was below that level.

On the other hand, in order to increase the scrap ratio, a technique for heating scrap before charging it into a converter or before charging hot metal into a converter has been proposed, for example, in Japanese Patent Laid-Open No. 56-29815. . However, this scrap heating technique requires a long time for heating, increases the energy consumption rate, and limits the scrap ratio to 30 to 35%.

Problems to be Solved by the Invention An object of the present invention is to provide a method that increases the amount of scrap used in a converter and enables stable operation at a high scrap ratio.

Means for Solving the Problems The present invention provides a converter operating method in which 30% by weight or more of scrap is charged together with a carbon source such as coke or coal, and 02 gas is supplied from the top or from the bottom. , Continuously measure the amount of exhaust gas and the components of the exhaust gas during blowing, and calculate one or more of the following: the amount of C combustion, the amount Os of accumulated oxygen in the slag, and the amount of change in the exhaust gas from the measured values. , the C combustion amount, O3, and the number of exhaust gas changes determined in advance,
The present invention relates to a converter operating method characterized in that the state of adhesion to the furnace wall is detected from the correlation between the state of adhesion of the undissolved mixture and the state of adhesion to the furnace wall, and an operation for removing adhesion is performed in accordance with the detection result.

The present inventors carried out refining using coke as a C source in a top-blown converter and gradually increasing the scrap ratio. Figure 9 shows an example of the results, with the horizontal axis representing the scrap ratio and the vertical axis representing the frequency of adhesion to the furnace wall.
The frequency of adhesion on furnace walls was expressed as a percentage of the number of times adhesion occurred relative to the total number of operations.

As can be seen from Figure 9, if the scrap ratio is about 25% or less, increasing the amount of coke added will not cause unmelted scrap and refining will continue without any problems. was completed. However, when the scrap ratio exceeds 25 to 50%, particularly 30% or more, undissolved phenomena in which the scraps are not completely dissolved frequently occur. In addition, there are many situations where stable operation is not possible due to sudden decreases in the amount of exhaust gas or abnormally large slopping occurring within the furnace.

As a result of various investigations into the cause of this problem, it was found that since the bulk density of scrap is small, when the scrap ratio is increased, the scrap 3 becomes separated and deposited on the steel bath 1 as shown in FIG. 2. For this reason, when refining is performed by supplying 02 from the blowing lance 2, cold spots are likely to occur on the furnace wall where the stirring force is relatively weak.
As shown in FIG. 3, it was found that scrap 3 and coke 4 were attached in an unmelted state. In other words, scrap 3 and coke 4 are mixed and adhere to the furnace wall, and as a result, the supply of C to the steel bath 1 is cut off, and as the steel bath 9 decreases, the reaction amount of C+1/2・02 → CO2 decreases. decreases. Therefore, as the flow rate of the exhaust gas decreases, Fa in the steel bath is oxidized, the Fen concentration in the slag increases, and a phenomenon occurs in which the amount of oxygen accumulated in the slag Os, (hereinafter simply referred to as Os) increases.

Once such a phenomenon occurs, it becomes increasingly difficult to melt the deposits on the furnace wall due to the lack of a heat source due to C combustion. Furthermore, if the scrap 3 and coke 4 adhering to the furnace wall fall into the steel bath for some reason, a reaction between C and the slag with a high FeO concentration occurs, causing abnormal slopping, which makes it impossible to continue the operation. It has been found that situations may occur where equipment is lost or various types of equipment damage occur.

In the present invention, the undissolved mixture refers to a mixture containing the scrap 3 and coke 4 as main components and deposited in an undissolved state, and hereinafter simply referred to as deposit 5.

The present invention detects the adhesion status of the deposits 5 by actively utilizing the above knowledge, performs an appropriate deposit removal operation according to the detection result, and thereby prevents the generation of deposits. This made stable operations possible.

Now, the inventors of the present invention have focused on the fact that when the deposits 5 are deposited on the furnace wall, the amount and components of the exhaust gas change as described above. We investigated and researched the correlation between

FIG. 1 shows an example of this. FIG. 1(a) shows the relationship between the furnace wall adhesion state and the exhaust gas flow rate, and FIG. 1(b) shows the relationship between O5 and the furnace wall adhesion state. This figure 1 (a) (b)
As can be seen, when deposits 5 are formed on the furnace wall, the /& amount of exhaust gas decreases rapidly, and Os also increases.

FIG. 1(c) is a diagram showing the relationship between the amount of C burnt and the condition of A/1 deposition on the furnace wall. The amount of carbon burned can be determined from the flow rate and components of the exhaust gas using the following equation (1).

We =I2/22.4 * So Vg ・(Kca
lXco2) dt-(1) However, Xco: CO concentration in exhaust gas (Nm'/NmXco2
: C□ in exhaust gas, concentration (N rn' / N m'
) This C combustion part decreases when the deposit 5 is generated,
The heat balance inside the converter is disrupted. Equation (2) below is an equation showing the heat balance in the converter, where the left side is the amount of heat input and the right side is the amount of heat output. This equation (2) can be simplified as the following equation (3) when the amount, composition, temperature, blowing point target temperature, and composition of hot metal are known.

(Hco* (1-R) +Hco2*R)*
Wc+ΣHmkaiΔMQloss
・Conflict・(2) Iro ShiHco: Heat of reaction of C-+CO (Kcal / Kg
” C) Hco2: C+C(), reaction heat (Kc
al /K g -C)R: Secondary combustion rate R=Xco
2/ (Kcal
g) Wp: Hot metal star (K g) Hsf Nisslag formation heat (Kcal /K g @Sta
g) Wsl+Slag! (Kg) Hfe-c: Heat of C dissolution in steel bath (KCaI/Kg@C
)Hst: Sensible heat of molten steel (Kcal 7Kg・5teel)
Wsc Nislag amount (K g) Hsl Nisslag sensible heat (Kcal /K g -Slag
) Cj: C in hot metal (Kg/Kg) Cf: C in molten steel (Kg/Kg) HO: Heat of iron ore decomposition (Kcal / K g * 0r
e) WO: Iron ore input (Kg) H'co: CO gas apparent (per CIKg) (Kca
l 7Kg) H'co2: Cα gas sensible heat (per CIKg) (Kcal 7Kg) Qloss: Other dissipated heat (Kcal) WSC-AI+WC1B@φ... (
3) Or ∆Wsc=As△Wc+Bes fist (3') However, A, B: const ∆Wsc Change in nickel scrap dissolving stitch (Kg)△Wc:C
Change in Burned Amount (K g) As shown in equation (3) above, a linear relationship exists between the amount of scrap melted and the amount of C burnt. This was also confirmed from the experimental results of the present inventors.

Figure 4 shows an example of the results, with hot metal in the converter and
In addition, in an experimental example in which a C source such as coke was introduced and the amount of scrap melted was increased sequentially, the horizontal axis represents the increase in the amount of C burned, and the vertical axis represents the increase in the amount of scrap melted. . As is clear from FIG. 4, there is a linear relationship between the two, and it can be seen that equation (3) or (3') is satisfied.

Therefore, the required C combustion iWc for a predetermined scrap melting amount Wsc is given by equation (3).

The solid line X in FIG. 1(c) shows the change in the C combustion amount Wc when the scrap melting is performed ideally without the occurrence of the furnace wall adhesion phenomenon. In contrast, Fig. 1 (C)
The broken line y in is the C combustion amount Wc determined from the actually measured exhaust gas amount and exhaust gas components, and the difference △Wc from the above X is the change in the scrap melting amount determined from the above (3°), that is, the amount of delay in scrap melting. Equivalent to. Therefore, the difference △
By determining Wc, the state of adhesion to the furnace wall can be detected.

Note that the slope of the solid line X in FIG.
This is because the combustion of C due to oxidation is delayed, and the latter is because the amount of late-stage steel bath 9 is reduced, the supply of C to the top blowing point becomes poor, and the amount of C burned is also reduced.

Therefore, the correlation between the furnace wall adhesion state and the above-mentioned C combustion section-1O5 and the amount of change in exhaust gas is determined in advance according to the operating conditions and equipment conditions of the converter, and the amount of exhaust gas and exhaust gas components during blowing are determined. It becomes possible to detect the state of adhesion to the furnace wall by continuously measuring the amount of C and determining the C combustion part, Os, and the amount of change in exhaust gas (ΔVg) from the measured values. In this case, it is possible to detect the furnace wall adhesion status from any one of the C combustion amount, O3, and exhaust gas change amount;
It is also possible to detect a combination of two or more.

In the experience of the present inventors, the method of calculating the amount of C burnt using equation (1) from the flow rate and components of the exhaust gas allows the furnace wall adhesion state to be expressed as a quantitative index by the amount of delay in scrap melting △Wsc. This was effective in terms of carrying out the deposit removal operation at a more appropriate timing.

In addition, to determine O5 from the exhaust gas amount and exhaust gas components, the method applied by the present applicant in Japanese Patent Application No. 54-87784, that is, the total amount of oxygen released into the exhaust gas and the total oxygen introduced into the converter. It can be calculated from the difference between the amount and the amount.

The basic formulas are shown in formulas (4) and (5) below.

dos=Fo area+Σ(αi+βi+1/2・γ+)*W
p+'-(1/2・Fco"+Fco2")
* e * (4) Os= 5”,', (do
s) dt ++ * * (5) However, Fox: Pure oxygen amount (Nrn”/sec) Fan”
: CO flow rate generated in the furnace (Ntn”/5eC) FC
02r'': CO2 flow rate generated in the furnace (Nrn''/s
ec) WFi': Decomposition reaction rate of auxiliary material of brand i introduced into the furnace (Kg/5ec) αi
: 02 generation coefficient of auxiliary material of brand i charged into the furnace
(Nm”/Kg) β
i: C02 generation coefficient of auxiliary raw material of brand i charged into the furnace (Ngo/K g) γi: H20 generation coefficient of auxiliary raw material of brand i charged into the furnace
(Nm'/Kg) Change in the amount of oxygen accumulated in the dos varnish slag (Nm"/sec) Amount of oxygen accumulated in the OS varnish slag (Nrn") Next, the method of estimating the adhesion status from O5 is Let Os be Os'', Os when it does not occur be Os', and the difference △Os and C
The following relationship exists between the combustion delay amount ΔWc. (1st
(See figure (b)).

However, △0s=Os book -〇s' R (secondary combustion rate) = Xco2 / Xco+ Xc
o2Xco (co2) : co (co2)
Determine △Wc from △O5 from concentration (a) formula, and convert this to (3
By substituting into the equation (°), the amount of scrap furnace wall material deposited ΔSc can be determined.

In addition, the method of estimating the adhesion status from the amount of change in exhaust gas ΔVg (the amount of change in flow rate between the amount of material deposited on the furnace wall [dotted line] and the time when adhesion occurs on the furnace wall [solid line] in Figure 1 (a)) is to Even if the amount of C combustion decreases due to the occurrence of adhesion, the concentration of CO and CO2 in the exhaust gas itself does not change much, so the amount of decrease in C combustion can be simply calculated as △Wc=5ΔVgdt (K is const)
, (3°), the amount ΔSc of the flap attached to the furnace wall can be estimated.

Now, when the state of adhesion to the furnace wall is detected, depending on the detection result, for example, if a preset limit value is exceeded, an operation for removing the adhesion is performed. This limit value is determined based on the converter equipment conditions, operating conditions, etc.; It may be determined by taking into consideration the aspects, etc.

Next, this deposit removal operation will be explained.

When the state of adhesion to the furnace wall is detected, the deposit 5 becomes attached to the furnace wall as shown in FIG. 3 above.

Therefore, basically, the stirring force of the steel bath near the furnace wall can be increased to eliminate cold spots and dissolve the deposits 5.

FIGS. 5 to 7 are explanatory diagrams for explaining examples of the specific operations. That is, FIG. 5 shows a normal refining 02 gas supply system 21 and 02 or 02 containing Ar, N 2 ,
This is an example using a top blowing lance 20 having two supply systems, a gas supply system 22 for removing deposits, in which an inert gas such as C02 is added and mixed. Nozzle 2 of gas supply system 22
21 is provided at a wide angle θ so as to be directed near the furnace wall where deposits 5 are formed. During normal operation, α gas for refining is supplied from the α gas supply system 21, and purge gas is supplied from the gas supply system 22 at a pressure that does not allow dust, slag, etc. in the furnace to enter the jet port 221. It's being gushed.

On the other hand, if adhesion is detected, in addition to α gas for refining,
α gas is also injected from the jet port 221 to cause secondary combustion near the furnace wall, or the inert gas is added and mixed to α to dissolve the deposits 5 attached to the furnace wall. . As a result, the deposits 5 can be efficiently dissolved in the steel bath 1 and the deposits 5 can be removed.

In Fig. 6, a bottom blowing nozzle 7 is installed near the furnace wall, and when adhesion is detected, Ar, N2
, CG or other inert gas is blown into the reactor to strengthen the stirring force near the furnace wall. .

Furthermore, FIG. 7 shows an embodiment in which, when an adhesion condition is detected, the converter body 8 is swung to remove the adhesion 5 while dissolving it.

Example 170 The present invention was carried out in the production of AQ killed steel for bars and wires in a tun converter.

The hot metal temperature and components used in this example are as shown in Table 1, the scrap ratio was 50%, 18 tons of coke having the components shown in Table 2 was charged as a C source, and the oxygen delivery rate was Blowing was performed at 30,000 Nrn'/H.

Table 1 Table 2 In this example, during blowing, the exhaust gas flow rate was continuously measured using a venturi flowmeter, and the exhaust gas components were continuously measured using a mass spectrometer. The amount of C combustion was determined based on equation (1). On the other hand, the correlation between the amount of C burnt and the state of adhesion to the furnace wall was determined in advance from past operational results.

FIG. 8 shows an example of this, in which broken lines V+ and y
2 is the normal operating state, that is, the target range.

On the other hand, the solid line X1 in the $8 chart shows the transition of the C combustion amount (hereinafter referred to as the measured C combustion amount) determined from the measured values during the blowing.

In this example, approximately 20 minutes after the start of blowing, the actually measured C combustion amount began to deviate downward from the target range, and it was detected that the furnace wall was attached. Blowing was continued for about 5 minutes, but the adhesion to the furnace wall did not resolve and instead increased, and ΔWC exceeded the allowable amount of 500 kg. A rocking operation was performed to remove deposits. As a result,
Due to the reaction between the slag width 9 and the coke in the deposit 5 that fell from the furnace wall, the C combustion amount increased and returned to within the target range. After that, the amount of C burned remained almost within the target range, and scrap melting could be carried out smoothly.

Effects of the Invention By implementing the present invention, stable operation has become possible even at a high scrap ratio of 30% or more. Therefore, by using a large amount of inexpensive scrap, the manufacturing cost could be reduced by about 5 to 10%.

[Brief explanation of drawings]

Figure 1 shows the correlation between the furnace wall adhesion status based on the present invention, and Figure 1 (a) shows the relationship between the furnace wall adhesion status and the exhaust gas flow rate, and Figure 1 (b) shows the relationship between O8 and the furnace wall. The relationship between adhesion status,
Further, FIG. 1(C) is a diagram showing the relationship between the amount of C burnt and the state of adhesion to the furnace wall. Figures 2 and 3 are explanatory diagrams for explaining the state of deposit formation on the furnace wall, Figure 4 is a diagram showing the correlation between the amount of scrap melted and the amount of C burnt, and Figures 5 to 7
The figures are explanatory diagrams for explaining different embodiments of the deposit removal operation, and Fig. 8 shows the correlation between the furnace wall deposition situation and the amount of C burnt based on the specific embodiment of the present invention, and the actual measurement. FIG. 9 is a diagram showing the change in the amount of C burned, and FIG. 9 is a diagram showing the relationship between the scrap ratio and the state of adhesion to the furnace wall. 1@...Steel bath, 2.a11 lance, 3...Scrap, 4...Coke, 5...Deposition, 7...Nozzle, 8...-furnace body, 20-@Φ lance, 21.2211・
- Gas supply system, 221... spout.

Claims (1)

[Claims] 30 scrap with C source such as coke or coal
In a converter operation method in which O_2 gas is charged from the top or the upper bottom with a charge of more than % by weight, the exhaust gas amount and exhaust gas components are continuously measured during blowing, and from the measured values, the C combustion amount,
One or more of the amount of oxygen accumulated in the slag, Os, and the amount of change in exhaust gas are determined, and the previously determined amount of C combustion, Os, and amount of change in exhaust gas are compared with the state of adhesion of the undissolved mixture to the furnace wall. Detect the furnace wall adhesion status from the correlation,
A converter operating method characterized in that a deposit removal operation is performed according to the detection result.