JPS6318014A - Method for controlling flow rate of bottom blowing gas for metallurgical refining furnace - Google Patents

Abstract

PURPOSE:To execute refining to control the content of C in a product molten steel to a target value with high accuracy by determining the balance of the gaseous oxygen in a converter in a converter operation from the kind of the steel to be produced and the raw materials to be used, stopping the refining by oxygen top blowing and blowing an inert gas from furnace bottom tuyeres to stir the molten steel when the amt. of the oxygen to be blown coincides with the determined value. CONSTITUTION:The molten iron is subjected to decarburization refining by the oxygen blown from an oxygen top blowing lance 2 in a converter having the lance 2 and the furnace bottom tuyeres 6. The total O0 of the amt. O1 of the oxygen necessary for decarburization, the amt. O2 of the oxygen required for oxidation of Si, Mn, P, etc., the amts. O3, O4, O5 of the oxygen generated in the reduction stage of Mn ore, iron ore and scale, and the amt. O6 of the oxygen required for oxidation of a carbonaceous material O0=O1+O2-O3-O4-O5+O6 is measured by an integrating flow meter 5 provided to a gaseous O2 supply pipe 4. The oxygen blowing is stopped and the inert gas such as Ar is blown from the furnace bottom tuyeres 6 into the converter to stir the molten steel 3 when the measured amt. coincides with the amt. of the oxygen set in an oxygen flow rate input pattern device 11 according to the steel kinds. The molten steel approximated to the target C grade with high accuracy by the final decarburization by the FeO in the molten steel is thus produced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to flow control of bottom-blown gas that is blown into a metallurgical refining furnace such as a converter from a gas inlet provided at the bottom to stir molten steel. Regarding the method.

[Prior Art] In converter blowing, the reaction situation in the first half is rate-limiting by oxygen supply, which shows the highest decarburization rate, and the reaction situation in the second half is rate-limiting by carbon transfer. That is, as the converter blowing progresses, the reaction situation in the furnace changes from oxygen supply rate-limiting to carbon transfer rate-limiting, with the decarburization transition point CT as the boundary. In the latter half of converter blowing,
Since the amount of top-blown oxygen gas blown into the molten steel from the oxygen lance decreases, the stirring power of the molten steel in the furnace decreases, and the oxidation of the iron content of the molten steel becomes significant. To prevent this iron from oxidizing,
Conventionally, in the latter half of blowing, the amount of top-blown oxygen gas was reduced, and bottom-blowing holes (for example,
This increases the amount of gas that is blown into the molten steel through the porous plug (porous plug), thereby strengthening the stirring power of the molten steel by the bottom blowing gas. This replenishes the molten steel stirring power at the final stage of blowing, and prevents oxidation of beneficial components such as iron and manganese.

[Problem to be Solved by the Invention 1] However, in this conventional control method, the operator estimates the carbon concentration of molten steel empirically based on the elapsed time after the start of blowing, and the bottom blowing is determined by the operator's judgment. Switching the gas flow rate. In order to make the effect of stirring effective, it is preferable to increase the amount of bottom blowing gas just before the decarburization transition point. If the amount of bottom-blown gas rises too quickly, the amount of gas used will increase and refining costs will increase.On the other hand, if the amount of bottom-blown gas rises too slowly, the start of stirring will be delayed and carbon There is a problem that the supply rate of iron decreases and the iron content oxidizes. However, in the past, as mentioned above, the bottom-blowing gas style was switched based on the operator's empirical judgment, so the carbon concentration at the timing of switching the bottom-blowing gas member varied widely, and the oxidation loss of iron in the molten steel, etc. cannot be effectively prevented.

This invention was made in view of such circumstances, and
The purpose of the present invention is to provide a method for controlling the flow rate of bottom blowing gas in a metallurgical refining furnace, which can estimate the carbon concentration of molten steel with high accuracy and always switch the bottom blowing gas at an appropriate timing. shall be.

Means for Solving Problem E] The method for controlling the flow rate of bottom blowing gas in a metallurgical refining furnace according to the present invention reduces the amount of MjliI required for decarburization and, if applicable, The total amount of oxygen required for oxidation, lIO2, the amount of oxygen generated by the reduction of manganese ore, 03, the amount of oxygen generated by the reduction of iron ore, 04, the amount of oxygen generated by reduction of scale, 05, and the amount of oxygen required for oxidation of carbonaceous material, 06, is calculated using the following formula. Based on the oxygen cloud On, this is the total amount of oxygen blown into the molten steel! It is characterized in that the flow rate of the gas injected into the molten steel from the gas inlet provided at the bottom of the refining furnace is changed when it matches a predetermined value determined based on the I elementary amount Oo.

On =01+02-03-04-O5+Os...(
1) [Function] In addition to the oxygen amount O1 used for decarburization, the above formula (1) also includes, if applicable, the oxygen amount O2 required for the oxidation of silicon, iron, manganese, and phosphorus, and the reduction of manganese ore. The amount of oxygen produced by the reduction of iron ore is 0.
4. The amount of oxygen produced by reduction of scale 05 and the amount of oxygen required for oxidation of carbon material 06 are taken into consideration, and the carbon concentration is estimated excluding ml involved in these.

Therefore, the carbon concentration can be estimated with high accuracy regardless of differences in blowing conditions or reaction conditions. Therefore, by changing the amount of bottom blowing gas based on this estimated carbon concentration, the bottom blowing gas l can always be switched at an appropriate timing.

[Embodiment] FIG. 1 shows an apparatus for carrying out a bottom-blown gas profit control method according to an embodiment of the present invention. An oxygen lance 2 is inserted into the converter 1, and a pipe 4 connected to an oxygen gas supply m (not shown) is connected to the lance 2. Therefore, oxygen gas is supplied to the oxygen lance 2 via this pipe 4, and II elementary gas is discharged from the discharge port at the lower end toward the molten steel 3 in the converter.

A flow meter and a flow control valve (not shown) are interposed in the middle of the pipe 4. The detection output of this flowmeter is input to a controller (not shown), and the controller adjusts the flow rate control valve so that this oxygen gas flow rate matches the flow rate set in the controller.

An integrating flow meter 5 is also interposed in the pipe 4, and the output of this integrating flow meter 5 is input to a bottom blowing gas amount control device 10. In addition, the amount of the main raw material,
The amount of auxiliary raw materials and hot metal analysis values are input, and different oxygen flow patterns are set for each steel type in the pattern input device 11, and a predetermined oxygen flow rate is set manually or by a signal from a process computer, etc. A pattern is selected and input into the control device 10.

A plurality of tuyeres 6 (for example, porous plugs) for blowing gas are provided at the bottom of the converter 1. These tuyeres 6 are used to supply stirring gas (for example, Ar gas). A pipe 7 connected to a source (not shown) is connected. This pipe 7 is equipped with a flow meter 8-〇- and a freezing control valve 9, and the *a meter 8 detects the flow rate of Ar gas flowing through the pipe 7 and sends the detected output to the controller. The valve 9 receives a drive signal from the controller 12 and adjusts the flow rate of the gas flowing through the pipe 7.

The controller 12 adjusts the opening degree of the valve 9 based on the detection signal from the flow meter 8 so as to match the Ar gas flow rate set value inputted from the control device 10 .

The control device 10 estimates the carbon concentration [C] in the molten steel based on the total amount of oxygen 01 blown into the converter as follows. The total oxygen amount O1 introduced into the converter self-molten steel is as follows (
1) Expressed by the formula.

0@-(h +02-Os -04-01+06...
- (1) However, Os: II2 Amount of oxygen required for coal, 02: Amount of oxygen required for oxidizing silicon, manganese and phosphorus, 03 = Oxygen l generated by reduction of manganese ore.

04: Oxygen generated by reduction of iron ore -1os; Amount of oxygen generated by reduction of scale OI; Amount of oxygen required for oxidation of carbon material.

The oxygen gas introduced into the converter through the oxygen lance is 01
．． 02,Os while 03.04,O
Oxygen gas is generated as s. Therefore, the total oxygen amount is 0+
From the cabinet's income and expenditure balance with 0t-06, the above (1)
The formula holds true.

The amount of oxygen consumed for decarburization 01 is expressed by the following equation (2) when the carbon concentration [C] is higher than the vt carbon transition point [C]@, and [C] is expressed as [C]@ If it is lower than below (
3) Expressed by the formula.

Os − (Wc − Wt [C]/100)/Bs・
...(2) 01- (Wc -V? [C]s /100+Wt
([C]a -EC] )/100-1oa([CI@
-[C10)/([01-[C10))/Bl
(3) In this case, Wc is the amount of carbon in the hot metal, and is determined by the following formula (4).

Wc - W2 [C]t / 100... (4) However, Wt: 1L of steel W2: ■ amount of pig iron, [C1: Target carbon of bottom-blown gas flow rate switching timing or bottom-blown gas type switching timing Concentration, [C]s: Carbon concentration at the decarburization transition point, [C]t
; initial carbon concentration, [C10; carbon concentration at decarburization limit point, B error: maximum S
Decarburization rate.

The amount of oxygen o1 consumed by the 12 coal is determined by the above (2) in the stage transition where the blow casting stage is before the decarburization transition point and the oxygen supply rate is limited.
The switching target carbon concentration [C
By substituting .

On the other hand, when blowing progresses and the carbon concentration [C] of the molten steel exceeds the decarburization transition point, the amount of oxygen consumed by M coal becomes 0.
1 is expressed by the above equation (3), and by substituting the bottom blowing gas flow rate or bottom blowing gas type switching target carbon concentration [C] into this equation (3), the amount of oxygen that should have been consumed by that time can be calculated. 0
! is found.

Regarding silicon S1, manganese Mn, and phosphorus P in hot metal, the limit value "0" is based on the component analysis value of hot metal charged to the converter (81, from the difference between Mn and pH value and the target value for converter blowing). ,
Calculate the oxygen-02 consumed in their oxidation. Further, the oxygen required for oxidizing iron is calculated based on the target end point slag (FEIO) value given from the converter blowing target [C].

On the other hand, as for Mn ore, iron ore, and scale introduced into the converter, aS is generated by their reduction. The amount of oxygen generated, Os, 04, and Os, has been determined empirically in relation to the amount of Mn ore, iron ore, and scale input into the converter, and the amount of oxygen generated in each charge is determined by the amount of Mn ore, etc. Calculated based on

Furthermore, in the case of converter blowing of pretreated hot metal, the amount of heat in the converter may be insufficient. .

Since the II cable is consumed for saponification of this wire, the m control device 1
0 calculates the consumption amount 06 from the input amount of carbon material.

The control device 10 substitutes the oxygen amounts 01 to 06 calculated in this way into the above equation (1), and switches the bottom blowing gas flow rate to correspond to the target carbon concentration (for example, the carbon concentration immediately before the decarburization transition point). Calculate the total oxygen amount 0++ @. And III
The II device 10 changes the set value of the controller 12 when the total oxygen amount detected by the product a weighing scale 5 matches the calculated total oxygen amount 00.

Next, the operation of this embodiment will be explained. Control device 1
0, first, the setting value of the controller 12 is set to a predetermined bottom blowing gas flow rate at the start of blowing, and oxygen blowing is started. The control device 10 calculates the total oxygen amount Oo, which serves as a reference for switching the bottom blowing gas flow rate, from equations (1) to (4) above, based on the main raw material, the auxiliary raw material, and the hot metal analysis value. The total amount of oxygen blown into the converter is detected by an integrated flowmeter 5, and III
III Ii device 10 is configured so that the total oxygen amount detected by this integrated flowmeter 5 is equal to the total oxygen amount calculated from equation (1).
When the value matches the value, the set value of the controller 12 is changed to the bottom blowing gas flow rate of the clothing.

The control device 10 sequentially switches the bottom blowing gas flow (2) based on the total amount of oxygen blown into the converter in this manner. This switching of the bottom blowing gas flow rate is based on the estimated value of the carbon concentration obtained based on the total Ion of oxygen gas, which takes into account various blowing conditions that differ for each batch. Regardless of the situation, the bottom blowing gas flow rate can always be switched at the optimal timing. Therefore, according to this invention, the decrease in the steel bath stirring power at the final stage of converter blowing can be compensated for with the minimum amount of gas,
At low cost, it is possible to prevent the oxidation of iron and manganese in molten steel, and to maintain Fe01 degrees, etc. in slag at a low value.

FIG. 2 is a graph showing the effects of this invention, in which the horizontal axis is the carbon concentration of molten steel at the end point of converter blowing, and the vertical axis is the total iron in the slag at the end point! (T, Fe). In the figure, the hatched area shows the relationship between the end point [C] and (T, Fe) in conventional converter blowing, and each plot shows the relationship between the end point [C] and (T, Fe) when the bottom blowing gas flow rate is changed according to the present invention. The relationship with (T, Fe) is shown. According to this figure, conventional (T, Fe) has a variation in the range of 12 to 20%, especially when decarburizing to a low carbon concentration, (T, Fe)
There has been a significant increase in On the other hand, in the case of this invention (
T, Fe) are about 10%, which is lower than conventional ones, and the increase in (T, Fe) is suppressed to a relatively low carbon concentration (0.05%).

FIG. 3 is a graph showing the relationship between (T, Fe) and manganese yield in molten steel in less slag blowing in which no slag-forming agent is substantially introduced into the converter.

The amount of manganese ore put into the molten steel in the converter is molten steel 1
It is 15 to 20 ko per ton, and the molten steel temperature at the end point of the converter is 1630 to 1670°C. As is clear from this figure, as (T, Fe) increases, the amount of manganese transferred to the slag increases and the manganese yield in the molten steel decreases. Conventionally, when (T, Fe) is 12 to 20%, the manganese yield is about 50%, but as in this invention, when (T, Fe) is 10%, the manganese yield is about 50%. , the manganese yield is as high as 65 to 70%.

Furthermore, FIG. 4 is a graph showing the transition of the decarburization rate in converter blowing, with the horizontal axis representing the carbon concentration [C] and the vertical axis representing the decarburization rate dC/do. In the figure, white circles indicate the decarburization rate in conventional converter blowing, and black circles indicate the decarburization rate in the case of the present invention.

Moreover, the solid line shows the transition of the decarburization rate when the decarburization reaction progresses ideally. As is clear from this figure, conventionally,
While the decarburization rate decreases from a relatively high carbon concentration state, in this invention, the decarburization rate starts to decrease near the decarburization transition point and decreases along the solid line. ing. This shows that in this invention, the steel bath was sufficiently stirred even at the final stage of converter blowing.

In the above example, the carbon concentration of molten steel is estimated from the total oxygen amount, and when this carbon concentration reaches a predetermined value,
The bottom blow oxygen flow rate is changed. However, the present invention is not limited to this, and the total oxygen amount determined at a predetermined carbon concentration can be used as information for determining the timing for changing the type of bottom blowing gas (for example, Ar gas, oxygen gas, nitrogen gas, etc.). You can also use

[Effects of the Invention] According to the present invention, the carbon concentration in molten steel is estimated based on the total oxygen amount in equation (1), which is determined by taking into account various refining conditions that differ for each individual operation. Carbon concentration can always be estimated with high accuracy even though the reaction conditions differ for each individual batch operation. Therefore, in converter blowing, the bottom blowing gas flow can be changed at the optimal timing, reducing refining costs and preventing loss of iron in molten steel.
The FeO concentration in the slag can be maintained at a low value.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the state of implementation of this invention, Fig. 2 is a graph showing the relationship between end point carbon concentration and (T, Fe), and Fig. 3 is a graph showing the relationship between (T, Fe) and Mn yield. FIG. 4 is a graph showing the effects of the present invention, and FIG. 5 is a graph showing changes in decarburization rate. 1: Converter, 2: Lance, 3: Molten steel, 5: Total flow meter, 6
; tuyere, 8: flow meter, 9: valve, 10: control device, 1
1: Input device, 12: Controller applicant patent attorney
Takehiko Suzue & [C] Figure 2 (T, Fe) ('10) Carbon LLc] <0m) Figure 4

Claims (1)

[Claims] The amount of oxygen O_1 required for decarburization, and if applicable,
Amount of oxygen required for oxidation of silicon, iron, manganese and phosphorus O_2, amount of oxygen generated by reduction of manganese ore O_3
, the total oxygen amount O obtained from the following formula using the oxygen amount O_4 generated by the reduction of iron ore, the oxygen amount O_5 generated due to scale reduction, and the oxygen amount O_6 required for oxidation of carbonaceous material.
When the amount of oxygen injected into the molten steel matches a predetermined value determined based on the total oxygen amount O_0, the gas is injected into the molten steel from the gas injection port provided at the bottom of the refining furnace. A method for controlling the flow rate of bottom-blown gas in a metallurgical refining furnace, the method comprising changing the flow rate of the gas. O_0=O_1+O_2-O_3-O_4-O_5+O
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