JPS6315324B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for controlling the flow rate of blown gas in a refining furnace, and in particular, the present invention relates to a method for controlling the flow rate of blown gas in a refining furnace. The constant flow rate control, which is suitable for use in equipment that blows gas through various types of tuyeres, feeds back the measured gas flow rate to the control valve to control the gas flow rate to the set flow rate. The present invention relates to a method for controlling the flow rate of gas blown into a refining furnace, which controls the flow rate of gas blown into the refining furnace.

[Conventional technology]

Generally, as shown in Fig. 6, different gases A and B
The equipment for blowing into a molten metal refining furnace 1 such as a converter through a tuyere 2 immersed in high-temperature molten metal via piping includes flowmeters 3A, 3B, flow rate control valves 4A, 4.
B, gas supply line LA including shutoff valves 5A and 5B,
LB, and a flow rate regulator 6A that controls each of the flow rate regulating valves 4A and 4B using the gas flow rate measured by the flow meters 3A and 3B as a feedback signal.
6B.

Conventional gas flow rate control and gas switching control in such equipment generally employs the method shown in the time chart of FIG.

That is, when switching from gas A to gas B during blowing in the refining furnace 1, for example, the supply line LB of gas B is switched at the switching trigger timing set by a timer.
A drive command to open the shutoff valve 5B is issued, and the shutoff valve 5B is opened.
After confirming that B is open, turn on the leading gas A.
Close the shutoff valve 5A of the gas supply line LA.
At this time, the operation of the flow rate control valves 4A and 4B of both gas supply lines LA and LB is such that when the corresponding cutoff valves 5A and 5B are open, flow rate feedback control is performed, and when the cutoff valves 5A and 5B are in the open state, When in the closed state, the preset opening degree is maintained. At this time, when switching to a different type of gas, it is common to change the flow rate setting value because the properties of the gas are different.

By the way, each gas A, B is connected to a cutoff valve 5A, 5B.
After passing through a considerable length of piping, header, etc., it reaches the tuyere 2 and is blown into the molten metal of the refining furnace 1. At this time, the total volume in the pipe between the shutoff valves 5A, 5B and the tuyere 6 (hereinafter referred to as buffer volume) acts as a buffer, allowing switching between different gases in a relatively stable state. making it possible.

Furthermore, when simply changing the set value of the flow rate without switching between different gases, the set value of the flow rate controllers 6A and 6B is simply changed, and therefore the response of the gas flow rate control system itself is adjusted. was left to the PID parameters and valve time constants.

[Problem that the invention seeks to solve]

Generally, in the bottom-blown process gas control system of a bottom-blown smelting furnace, the pressure loss at the tuyere has a large proportion to the total pressure loss, so the pressure loss at the tuyere is the main factor in controlling the gas flow rate and switching control system. This is the main point. The pressure flow characteristics of this tuyere (Tuyere
chart) can be calculated theoretically using the basic principles of compressible fluid mechanics.

In other words, when the inner diameter of the tuyere is large and the heat balance until _the gas is blown into the molten metal can be ignored. In the case of a heavy pipe tuyere or a tuyere in which inert gas is blown into the furnace by arranging ten or more single pipes with an inner diameter of about 5 mm at the bottom of the furnace, the Tuyere chart of the tuyere is determined from the critical conditions in isentropic flow.
can be found.

In addition, when the tuyere has a small inner diameter and the heat balance of the gas flowing inside the tuyere tube becomes dominant, for example, in the case of a tuyere with several dozen thin tubes with an inner diameter of 1 to 2 mm, Rayleigh flow is assumed. By doing so, the tuyere
You can ask for a Tuyere chart.

As mentioned above, although the method for determining the pressure-flow characteristics of a tuyere differs depending on the type of tuyere, in any case, the flow rate is a function of pressure, and when the pressure rises above a certain value, This generally results in a linear relationship.

When tuyeres with such characteristics are used to construct a gas flow rate/switching control system as shown in FIG. However, there is a problem in that the rapid response of the gas flow rate blown into the molten metal is adversely affected.

That is, from the viewpoint of metallurgical reactions, the solid line A in FIG.
It is ideal to obtain a flow rate response as shown in . Further, the response of the gas flow rate control system supplied to the buffer volume has a waveform shown by a dashed-dotted line B when the PID parameter of the flow rate controller is set to the optimum value. However, the response waveform of the gas flow rate actually blown into the molten metal from the buffer volume through the tuyere becomes as shown by the broken line C due to the influence of the buffer volume. Moreover, the larger the tuyeres, the larger the tuyeres.
The smaller the gradient of flow rate/pressure in the chart, the worse the responsiveness of the gas flow rate actually blown into the molten metal.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned conventional problems, and is used when the blowing gas flow rate control system in a refining furnace is used to significantly change the set value of the gas blowing flow rate in steps or when changing the type of blowing gas. A method for controlling the flow rate of blown gas in a smelting furnace that can significantly improve transient response characteristics by speeding up the rise or fall of the gas flow rate actually blown into the molten metal from the tuyere when switching the gas flow rate into the molten metal. The purpose is to provide.

[Means for solving problems]

The present invention provides a refining furnace that controls the gas flow rate injected into the refining furnace from the tuyere by constant flow control that controls the gas flow rate to a set flow rate by feeding back the measured gas flow rate to a control valve. In the blown gas flow rate control method, as shown in Fig. 1, when changing the set value of the gas blown flow rate in steps or changing the type of gas, first, the constant flow rate control is changed to the measurement mode. Switching to constant pressure control in which the tuyere back pressure is fed back to the control valve to control the gas pressure, and then the tuyere back pressure is
When the pressure setting value determined in relation to the changed flow rate setting value based on the flow rate pressure characteristic curve is reached, the constant pressure control using the tuyere back pressure returns to the constant flow rate control, thereby achieving the above purpose. This has been achieved.

[Effect]

As mentioned above, isentropic flow or
By assuming Rayleigh flow, the flow rate of gas blown into the furnace from the tuyere can be expressed as a function of tuyere backpressure. Therefore, it is possible to calculate the blown gas flow rate arithmetically from the tuyere pressure.

The present invention has been made focusing on this point,
By measuring the tuyere back pressure and using that value as an index to switch the control mode of the flow control valve, we have significantly improved the transient response characteristics of the gas flow rate that is actually injected from the tuyere into the molten metal in the smelting furnace. It was designed to do so.

That is, in the present invention, the gas flow rate blown into the refining furnace from the tuyere is controlled by constant flow control in which the measured gas flow rate is fed back to the control valve and the gas flow rate is controlled to a set flow rate. When significantly changing the set value of the gas blowing flow rate in steps or changing the type of gas, first, from the constant flow rate control, the measured tuyere back pressure is fed back to the control valve to adjust the gas pressure. The control switches to constant pressure control, and then the tuyere backpressure is
When the pressure setting value determined in relation to the changed flow rate setting value based on the flow rate pressure characteristic curve is reached, the constant pressure control based on the tuyere back pressure is returned to the constant flow rate control. Therefore, this problem may occur when changing the gas injection flow rate setting value step by step or changing the type of injection gas.
It is possible to eliminate the inconvenience of impeding the quick response of the actual amount of injection into the molten metal in the smelting furnace due to pressure loss at the tuyere portion and the influence of the buffer volume from the valve deck to the tuyere. That is, the responsiveness of the flow rate of gas blown from the tuyere can be significantly improved.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a bottom-blown gas flow rate control device for a converter to which the present invention is applied will be described in detail with reference to the drawings.

In this embodiment, as shown in FIG.
A, 14B, flow control valves 16A, 16B, and cutoff valves 18A, 18B, the tuyere 12 is inserted into the converter 10.
Gas supply line that supplies gas A and B through
LA, LB, a pressure gauge 20 installed near the tuyere 12 of the refining furnace 10 of the gas supply lines LA, LB, and the gas flow rate measured by the flowmeters 14A, 14B as a feedback signal to the flow rate regulating valve 16.
Flow rate regulators 22A and 22B that control constant flow rates for the flow rate regulating valves 16A and 16B, respectively, and a pressure regulator 24 that controls the flow rate regulating valves 16A and 16B at constant pressure using the tuyere back pressure signal measured by the pressure gauge 20 as a feedback signal. and signal switching circuits 26A, 26B that selectively switch control signals from the flow rate regulators 22A, 22B and the pressure regulator 24.

The signal switching circuits 26A, 26B select the signals to be output to the flow control valves 16A, 16B in the following manner. That is, in the steady control state, the signal switching circuits 26A and 26B control the flow rate controller 22.
The outputs of A and 22B are transmitted to flow control valves 16A and 16B. In addition, in a transient state when switching gases or changing the flow rate setting value significantly, the signal switching circuits 26A and 26B are switched until the tuyere back pressure reaches a predetermined pressure setting value. The output of the pressure regulator 24 is connected to the flow rate regulating valves 16A, 16.
Communicate to B. Note that the pressure set value of the tuyere back pressure and the pressure set value output by the pressure regulator 24 in this transient state are determined based on the pressure flow characteristics of the tuyere.

Specifically, the relationship between the flow rate and the tuyere pressure (pressure flow rate characteristic) is as shown in Fig. 3, f=F(P).
If the flow rate f is given, the pressure P can be calculated using the inverse function F ^-1 (f). Therefore, the relational expression f=F obtained from the flow rate set values S ₁ , S ₂ ′ and the pressure flow characteristics of the tuyere
(P) to calculate the pressure setting value P=F ^-1 (S)
It is obtained from the relational expression. In this case, Pmax-σ is set as the threshold value (pressure setting value) in consideration of the time constant of the control system. However, σ is a minute pressure value. In addition, in some cases, this threshold value may be the pressure setting value P=F ^-1 (S)
You can also set it as .

Next, the operation of this embodiment will be explained.

First, a case will be described in which the flow rate of gas A is significantly increased stepwise from the set value _S1 to _S2 .

FIG. 4 shows the movement of the control system and the flow rate pressure transition when the flow rate setting value is significantly changed stepwise from the lower level _S1 to the higher level _S2 .

First, in FIG. 2, in the gas supply line LA of gas A, the cutoff valve 18A is open, and the flow rate adjustment valve 16A is controlled by the flow rate controller 22A to the flow rate setting value S ₁ set by the flow rate controller 22A. The opening degree is adjusted by feeding back the measured flow rate from the flow meter 14A. Therefore, the gas A is blown into the refining furnace 10 from the tuyere 12 under constant flow control. At this time, the back pressure p of the tuyere 12 measured by the pressure gauge 20 is stable at a value extremely close to p=F ^-1 (S ₁ ). During such constant flow control of the gas A system, the signal switching circuit 26A is connected to the flow rate controller 22A side, and the flow meter 14A measures the flow rate of gas A so that the flow rate becomes constant _S1 . The opening degree of the control valve 16A is controlled.

Next, at time t ₁ in FIG. 4, an operation to significantly increase the flow rate from the flow rate set value S ₁ to S ₂ is performed according to the following procedure.

The expected pressure at the tuyere 12 when the flow rate of gas A reaches the set flow rate _S2 is the Tuyere pressure shown in FIG.
Using the chart, it can be found as F ^-1 (S ₂ ), so
Define {F ⁻¹ (S ₂ ) − σ} as the threshold of tuyere back pressure.
Note that F ^-1 (S ₂ ) itself can also be determined as a threshold value, but here we consider the time constant of the control system and, for safety, set the threshold value of the tuyere backpressure as {F ^-1
(S ₂ )−σ}.

The flow rate setting value of gas A after switching is _S2 , but
At time _t1 as the trigger timing, the signal switching circuit 26A is switched by the switching command, and the flow rate control of the gas A is switched from constant flow rate control by the flow rate regulator 22A to constant pressure control by the pressure regulator 24A. In this way, the pressure regulator 24A becomes {F ^-1
(S ₂ )-σ} is the tuyere back pressure range value, pressure gauge 20A
Constant pressure control is entered in which the pressure measured by is fed back to the flow control valve 16A. As a result,
Due to the pressure transition as shown in Figure 4, the tuyere back pressure is
It increases from F ^-1 (S ₁ ) to {F ^-1 (S ₂ )−σ}. Along with this, the flow rate of gas A measured by the flow meter 14A rises rapidly, as shown in FIG. 4a. In this pressure increase process, the flow rate of gas A reaches a constant value after exceeding the flow rate set value S ₂ , while the tuyere back pressure reaches the threshold value {F ^-1 (S ₂ ) -
σ} is reached. This only indicates that the buffer volume between the flow control valve 16A and the tuyere 12 is filled with gas A. The pressure rise curve DE during this rise period t ₁ to t ₂ is expressed as g
(t-t ₁ ), the flow rate of gas A actually blown into the refining furnace 10 from the tuyere 12 is F{g(t
−t ₁ )}. Although this flow rate is less than the target flow rate set value _S2 , the rise in the blowing flow rate is much faster when compared with conventional flow rate control.

When the pressure gauge 20 detects that the tuyere back pressure has increased to the threshold value {F ^-1 (S ₂ ) - σ}, the signal switching circuit 26A switches, and the flow rate controller 22A changes. Return to constant flow control with flow rate set value _S2 .

In this way, the flow rate control valve 16A is controlled by the flow meter 1.
Feedback the measured value of 4A and set the flow rate.
The constant flow rate will be controlled so that _S2 . Along with this, the tuyere backpressure stabilizes around F ^-1 (S ₂ ),
Thereafter, gas A is continuously blown out from the tuyeres at the set value _S2 .

Above, we have explained the case where gas A is significantly increased in steps, but even when it is significantly decreased in steps, the same applies based on the pressure range value at a low flow rate level determined from the pressure flow characteristics of the tuyere. It can be applied with simple operations.

Next, the case of switching from gas A to gas B will be described.

The gas A is controlled to have a constant flow rate by controlling the flow rate control valve 16A using the flow rate controller 22A. Next, at the switching trigger timing, an open drive command is output to the gas B cutoff valve 18B, and after confirming that the cutoff valve 18B is open, the preceding gas A cutoff valve 18A is closed. Switch from gas A to gas B. At this switching trigger timing, the pressure regulator 24 enters constant pressure control of the flow rate regulating valve 16B in response to a command from the signal switching circuit 26B.

Next, when the tuyere back pressure reaches the threshold value, the flow rate control valve 16B is switched to constant flow rate control according to the set flow rate value after switching by the flow rate controller 22B in response to a command from the signal switching circuit 26B.

As described above, when switching from gas A to gas B, the operation is basically the same as the operation when significantly increasing the amount of gas A described above.

Hereinafter, the results of implementing the present invention when inert gas was blown from the tuyere to stir molten steel in a 180t converter will be explained. Figure 5 shows the flow rate setting value of 5N using _N2 gas.
This figure shows the change in the gas flow rate actually blown from the tuyere when changing from ^m3 to ^20Nm3 . The broken line F in the figure shows the results of the conventional method,
A solid line G shows the result when the present invention is applied. The area of Batufu Aboruium is ^0.233m3 . Also, the threshold value is set to 19Nm ³ /min. As is clear from Fig. 5, in the case of the conventional method,
It takes 36.1 seconds for the flow rate to reach 95% of the set value, but according to the present invention, it takes about 1/3 of that time.
It reaches 95% in 13.5 seconds, which shows that the actual blowing flow rate rises quickly.

In addition, although the said Example was employ|adopted to the converter 10, this invention is not limited to this and may be made to employ|adopt to a refining furnace other than a converter.

Further, in the above embodiments, the gas is bottom blown, but the present invention is not limited to this, and can be applied to other types of gas than bottom blown.

〔Effect of the invention〕

As explained above, according to the present invention, when the blowing gas flow rate control system significantly changes the gas blowing flow rate set value stepwise or when changing the type of blowing gas, etc. This has the excellent effect of significantly improving the transient response characteristics of the gas flow rate blown into the furnace through the mouth.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing the gist of the method for controlling the flow rate of blown gas in a refining furnace according to the present invention, and FIG. 2 shows the overall configuration of an embodiment of a bottom-blown gas flow rate control device for a converter in which the present invention is adopted. 3 is a diagram showing an example of the pressure flow characteristics (Tuyere chart) of the tuyere in the above embodiment, and FIG. 4 is a front view and a sectional view including a partial block diagram. A diagram illustrating an example of a flow rate transition and a pressure transition; FIG.
Fig. 6 is a front view and a sectional view including a partial block diagram showing the overall configuration of a conventional bottom blowing gas flow rate control device for a converter, and Fig. 7 is a diagram showing a time chart of gas switching. , FIG. 8 is a diagram similarly showing flow rate transient characteristics. 10... Converter, 12... Tuyere, 14A, 14B
...Flowmeter, 16A, 16B...Flow rate control valve, 1
8A, 18B...Shutoff valve, 20...Pressure gauge, 22
A, 22B...Flow rate controller, 24A...Pressure regulator, 26A...26B...Signal switching circuit.

Claims (1)

[Claims] 1. The gas flow rate blown into the refining furnace from the tuyere is controlled by constant flow control, which controls the gas flow rate to a set flow rate by feeding back the measured gas flow rate to the control valve. In the blowing gas flow rate control method for a refining furnace, when significantly changing the gas blowing flow rate set value in steps or changing the gas type, first, from the constant flow rate control, the measured tuyere back pressure is adjusted as described above. Switching to constant pressure control in which gas pressure is controlled by feedback to the valve, and then the tuyere back pressure reaches a pressure set value determined in relation to the changed flow rate set value based on the flow rate pressure characteristic curve. A blowing gas flow rate control method for a refining furnace, characterized in that, at times, the constant pressure control using the tuyere back pressure returns to the constant flow rate control.