JPS61291910A - Method for controlling flow rate of gas to be blown to refining furnace - Google Patents

Abstract

PURPOSE:To improve the transient responsiveness for the gas flow rate change in a refining process by measuring the flow rates of the gases to be blown to a gas blown furnace such as converter, feeding the measured values back to gas flow rate control valves and controlling the gas flow rates to set values. CONSTITUTION:The values measured by flowmeters 14A, 14B for a gas A and gas B are fed as feedback signals to flow rate control valves 22A, 22B for controlling the constant flow rates of flow rate control valves 16A, 16B for both gases in the stage of changing the gas flow rate in the process for refining the molten iron, etc. in the converter 10 by blowing the tuyere cooling gases such as oxygen A and propane B from tuyeres 12 to the converter. The tuyere back pressure signal measured with a pressure gauge 20 near the tuyere is fed as a feedback signal. The control signals from a pressure controller 24 for controlling the constant pressure of the flow rate control valves 16A, 16B, the flow rate control valves 22A, 22B and the pressure controller 24 are selected and are changed over by change-over circuits 26A, 26B, by which the flow rates of both gases are changed with the fast responsiveness.

Description

[Detailed description of the invention]

[Industrial Field of Application] 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, and in particular, the present invention relates to a method for controlling the flow rate of blown gas in a refining furnace. The gas is blown into the smelting furnace from the tuyere using constant flow key control, which is suitable for use in equipment that blows gas into the tuyere and controls the gas flow rate to the set flow rate by feeding back the measured gas flow rate to the yJr valve. The present invention relates to a method for controlling the flow rate of blown gas in a refining furnace. [Prior Art] Generally, as shown in FIG. 6, equipment for injecting different gases A and B into a molten metal refining furnace 1 such as a converter through a tuyere 2 immersed in high-temperature molten metal via piping is used. , flowmeter 3A, 3B
, the gas supply lines LA and LB including the flow rate adjustment valves 4A and 4B, and the cutoff valve 5A and 15B, and the gas flow rate measured by the flowmeters 3A and 3B are used as feedback signals to adjust the flow rate wr.
Flow IT controller 6 that controls each of the IT valves 4A and 4B
It is equipped with A16B. Conventional gas flow rate control and power switching control in such equipment generally employs the method shown in the time chart of FIG. 7. That is, when switching from gas A to gas B during blowing in the refining furnace 1, a drive command to open the cutoff valve 5B of the gas B supply line LB is issued at the switching trigger timing set by a timer, for example, and the cutoff valve is After confirming that 5B is open, open the shutoff valve 5A of the gas supply line LA for the preceding gas A.
close. At this time, the operation of the flow rate control valves 4A and 4B of both gas supply lines LA and LB is controlled by the corresponding cutoff valves 5A and 5.
When B is open, the flow rate feedback control is
Further, when the shutoff valves 5A and 5B are in a closed state, a preset opening degree is maintained. At this time, it is common to change the ijl setting value when switching to a different type of gas, since the properties of the gas are different. Incidentally, each of the gases A and B reaches the tuyere 2 through considerable lengths of piping and headers after the shutoff valves 5A and 5B, and is blown into the molten metal of the m-drilling 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 like an am, making it possible to switch between different gases in a relatively stable state. I have to. Also, T! ! If you simply want to change the flow rate setting without switching between the four types of gases, change the flow rate! Only the set values of the one-section meters 6A and 6B were changed, and therefore, the response of the gas flow control system itself was left to the adjusted PID parameters and valve time constants. [Problems to be Solved by the Invention] Generally, in the bottom-blown process gas control system of a bottom-blown smelting furnace, the pressure loss at the tuyeres has a large proportion to the total pressure loss. is the turning point in the control of the gas flow rate/switching control system. This tuyere pressure 111
The 1\Ff property (Tuyere chart) can be calculated theoretically using the basic principle of compressible fluid mechanics. In other words, if the inner diameter of the tuyere is large and the heat balance until the gas is blown into the molten metal is negligible, for example, a double tuyere where 02 gas is blown from the inner tube and a cooling gas such as propane gas is blown from the outer tube. 1 tube tuyere or a single tube with an inner diameter of about 5 mm
In the case of several tuyeres arranged at the bottom of the furnace to blow inert gas, due to the critical condition in isentropic flow, the
uyere chart can be obtained. In addition, when the inner diameter of the tuyere is small and the heat balance of the gas flowing in the tuyere tube becomes dominant, for example, in the case of a tuyere in which 10 thin tubes with an inner diameter of 1 to 2n are arranged, Raylei
By assuming a gh flow, the tuyere
Chart can be obtained. 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,
Flow rate is a function of pressure, resulting in a generally linear relationship as pressure increases above a certain determined value. When tuyeres with such characteristics are used to configure a gas flow rate/switching side system as shown in Fig. 6, the shutoff valve 5A
The dark buffer volume between , 5B and tuyere 2 actually inhibits the rapid response of the gas flow rate injected into the molten metal!
This has the problem that it results in F. That is, from the viewpoint of metallurgical reactions, it is ideal to obtain a flow rate response as shown in actual mA in FIG. 8. Further, the response of the gas flow rate control system supplied to the buffer volume becomes a waveform shown at one point 111i1B when the PID parameter of the flow rate 11-section meter 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 buffer volume, the larger the tuyere volume.
The smaller the slope of the flow rate/pressure in the chart, the worse the rapid response 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 in a blowing gas flow rate control system in a refining furnace, when the set value of the gas blowing flow rate is significantly changed in steps, and when the type of blowing gas is changed. A method for controlling the flow rate of blown gas in a smelting furnace, which can significantly improve transient response characteristics by speeding up the rise or fall of the flow rate of gas actually blown into molten metal from the tuyere when switching the flow rate. The purpose is to provide

[Means to solve the problem]

The present invention provides a blowing gas for a refining furnace that controls the gas flow rate blown 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 the control valve. In the flow rate control method, as shown in Fig. 1, when changing the set value of the gas blowing flow rate in steps or changing the type of gas,
First, the constant flow rate control is switched to constant pressure control in which the measured tuyere back pressure is fed back to the control valve to control the gas pressure, and then the tuyere back pressure is adjusted based on the flow rate pressure characteristic curve. The above object is achieved by returning from constant pressure control based on the tuyere back pressure to constant flow control when a pressure set value determined in relation to the changed flow rate set value is reached. [Effect] As mentioned above, isentropic flow or Rayl
By assuming eight flow, the flow rate of gas blown into the furnace from the tuyere is expressed as a function of the tuyere backpressure. Therefore, it is possible to calculate the blown gas flow rate arithmetically from the tuyere pressure. The present invention has been made with attention to this point, and by measuring the tuyere back pressure and using that value as an index to switch the control mode of the flow ram control valve, it is possible to actually move the tuyere into the smelting furnace. The transient response characteristics of the gas flow rate blown into the molten metal are significantly improved. That is, in the present invention, the gas flow rate blown into the refining furnace from the tuyere is controlled by constant flow II amount control, which controls the gas flow rate so that the measured gas flow rate is fed back to the control valve to reach the set flow rate. When changing the gas blowing flow rate set value in steps or changing the type of gas, first feed back the measured tuyere back pressure from the constant flow rate -1111 to the control valve to adjust the gas pressure. Then, the tuyere back pressure is changed to i! based on the flow rate pressure characteristic curve. When a pressure set value determined in relation to the set value is reached, the constant pressure control based on the tuyere back pressure is changed to the constant flow rate control. Therefore, the influence of the pressure loss at the tuyere and the buffer volume from the valve deck to the tuyere, which occurs when the gas blowing flow II constant value is changed stepwise or when the type of blowing gas is changed, etc. Due to
It is possible to eliminate the inconvenience of interfering with the coordination of the actual injection weight to the molten metal in the smelting furnace. That is, the responsiveness of the flow rate of gas blown from the tuyere can be significantly improved. [Embodiment 1] Hereinafter, an embodiment of a bottom-blown gas flow rate control device for a converter to which the present invention is adopted will be described in detail with reference to the drawings. In this embodiment, as shown in FIG.
, gas supply lines LA and LB that supply gases A and B into the converter 10 through the tuyere 12 and are equipped with flow rate control valves 16A and 16B and cutoff valves 18A and 18B; The gas flow rate measured by the pressure gauge 20 installed near the tuyere 12 of the N-building furnace 10 and the flow meters 14A, 74B is used as a feedback signal to control the flow rate control valve 1.
Flow rate controller 22 that controls each of 6A and 116B at a constant flow rate
A, 22B and the tuyere back pressure signal measured by the pressure gauge 20 as a feedback signal, the flow 1 regulating valve 16A11
6B and a pressure regulator 24 that controls the flow I11 at a constant pressure.
It is comprised of signal switching circuits 26A, 26B that selectively switch control signals from the moderators 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, 268k
myo-)r, the output of the flow meter 22A, 22B is transmitted to the flow rate control valves 16A, 16B. In addition, in a transient state when switching gases or greatly changing the flow Il set value, the signal switching circuits 26A and 26B are switched off until the tuyere back pressure reaches a predetermined pressure set value. The output of the pressure regulator 24 is then transmitted to the flow I regulating valves 16A and 16B. 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) can be expressed by the function f −F (P), as shown in Fig. 3, and when the flow rate is given, the inverse function F
−1(f) can be used to calculate the pressure P. Therefore, using the flow rate settings S1, Sz and the relational expression f-F(P) obtained from the pressure flow characteristics of the tuyere, the pressure setting 1i
T! P is determined from the relational expression of P-F'(S). In this case, consider the time constant of the control system and set p raax-σ to the threshold value (
The pressure setting is 1i1). However, σ is a minute pressure value. Note that, depending on the case, this threshold value may be equal to the pressure setting value P-
It may be set as F-1(S). 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 82. Figure 4 shows flow @ set value from low level S to high level S.
118 when the flow rate is significantly changed in 2 steps
11 shows the movement of the flit system and the flow rate and pressure transition. First, in FIG. 2, in the gas supply line LA for gas A, the shutoff valve 18A is open, and the flow control valve 16A is open. The flow rate setting value S1 set by the flow rate controller 22A is set by the controller 22A. The opening degree is adjusted by feeding back the measured flow rate from the flow meter 14A. Therefore, 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 I)-F-
It is stable at a value very close to '(S+). During such constant flow rate 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 while adjusting the flow rate to be constant S1. The opening degree of the valve 16A is controlled. Next, at time t1 in FIG. 4, the flow rate is set to 1ff.
An operation to significantly increase the value from is1 to Sz is performed by the following procedure. "The expected pressure at the tuyere 12 when the flow rate of gas A reaches the i stage setting asz is the Tuyere pressure shown in FIG.
Since it can be found as F-1 (Sz) using the chart, (F-1 (Sz) - σ) is determined as the threshold value of the tuyere back pressure. Note that F'(Sz) itself can also be determined as the threshold value, but here, taking into account the time constant of the control system and considering safety, the threshold value of the tuyere backpressure is determined as (F'(Sz) −σ
). The flow rate setting value of gas A after switching is Sz, but the signal switching circuit 26A is switched by the switching command at time [1] as the trigger timing, and the flow rate of gas A is set to 2! lI control is from constant flow control by flow rate controller 22A to pressure controller 2.
Switches to constant pressure control using 4A. In this way, the pressure y4 meter 24A sets the pressure measured by the pressure gauge 20A to the flow I with (F'(Sz)-σ) as the tuyere back pressure range value.
Constant pressure control is entered with feedback to the I control valve 16A. As a result, the tuyere back pressure increases from F''1 (S+) to (F-' (Sz) - σ) due to the pressure transition shown in Figure 4. The flow rate of gas A increases rapidly, as shown in Figure 4 (a). During this pressure increase process, the 5! , On the other hand, the tuyere back pressure reaches the threshold value (F'(Sz) - σ). This means that the buffer volume between the flow ff11 node valve 16A and the tuyere 12 is filled with gas A. This rising period t, ~[2
When the pressure rise curve DE of , is smaller than the target flow rate set value S2, but compared to conventional flow rate control, the rise of the blowing flow rate is much faster.The tuyere back pressure increases and ktlI (F-' (32)-σ
) is detected by the pressure gauge 20, the signal switching circuit 26A is switched, and the flow rate controller 22A returns to constant flow rate control with the flow rate setting value set at 82. In this way, the flow control valve 16A feeds back the measured value of the flowmeter 14A and is controlled to have a constant flow rate so that the flow rate becomes the set value $2. Along with this, the tuyere back pressure is also stabilized near F-1 (Sz), and thereafter, gas A is continuously blown out from the tuyere at the set value S2. Above, we have explained the case where the gas A is greatly layered in a stepwise manner, but even when it is significantly reduced in a stepwise manner, the pressure range value at a low flow rate level determined from the pressure flow rate characteristics of the tuyere, It can be applied using similar operations. Next, the case of switching from gas A to gas B will be explained. Gas A is passed through the flow rate control valve 16A by the flow rate controller 22A.
Constant flow rate control is achieved by controlling . 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 opened.
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 signal switching circuit 26B
In response to this command, the flow rate control valve 16B is switched to constant flow rate control based on the set flow rate value after switching by the flow rate controller 22B. 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 will be explained when inert gas was blown through the tuyere to stir the molten steel in the converter No. 180. Figure 5 shows N2 gas? This figure shows the change in the gas flow gutter actually blown from the tuyere when the IL amount setting value is changed from N m3 to 20 N m3. Broken line F in the diagram
shows the results of the conventional method, and solid line G shows the results when the present invention is applied. In addition, the buffer volume is 0°233 m''. Also, the threshold value is 1
9 N n+'/Win. 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, about 1/1 second of the time is required for the flow rate to reach 95% of the set value. 95 in 13.5 seconds of 3
%, and it can be seen that the actual blowing flow rate rises quickly. In addition, although the above embodiment was adopted for the converter 10,
The present invention is not limited thereto, and may be applied to refining furnaces other than converters. 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 gases other than bottom-blowing. [Effects of the Invention] As explained above, according to the present invention, the blowing gas flow rate subsystem can be used to significantly change the set value of the gas blowing flow m in steps or to switch the type of blowing gas. In some cases, it has the excellent effect of significantly modifying the transient response characteristics of the gas flow rate actually blown into the furnace from the tuyere.

[Brief explanation of drawings]

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. A front view and a cross-sectional view including a partial block diagram showing the structure, and FIG.
Fig. 4 is a diagram showing an example of the flow rate transition and pressure transition in the above example, and Fig. 5 is a diagram showing an example of the implementation result of the above example with the conventional method. The diagram shown in Fig. 6 shows the bottom blowing gas flow rate control W of a conventional converter.
A front view and a cross-sectional view including a partial block diagram showing the overall configuration of the J device, FIG. 7 is a diagram showing a gas switching time chart, and FIG. 8 is a diagram showing the flow rate transient characteristics. FIG. 10... Converter, 12... Tuyere, 14A, 14B... Flow meter, 16A116B... Flow rate ￥A control valve, 18A118B... Shutoff valve, 20... Pressure gauge, 22A, 22B ...Flow rate regulator, 24...Pressure regulator, 26A...26B...Signal switching circuit.

Claims (1)

[Claims] (1) Smelting furnace blowing that controls the gas flow rate blown into the smelting furnace from the tuyere by constant flow control, which controls the gas flow rate to the set flow rate by feeding back the measured gas flow rate to the control valve. In the gas flow rate control method, 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 fed back to the control valve. Then, when 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, the tuyere A blowing gas flow rate control method for a refining furnace, characterized in that the constant pressure control based on mouth back pressure is returned to the constant flow rate control.