JPS6136051B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to a metal smelting furnace (hereinafter referred to as a converter equipped with a gas bottom blowing tuyere) having a tuyere through which all or part of the refining gas is blown from below the surface of the molten metal in the smelting furnace. (described as an example) relates to a method of switching the type of refining gas blown into the tuyere.

Generally, in a converter equipped with a gas bottom blowing tuyere, blowing from the tuyere is used to prevent molten metal (hereinafter, molten steel will be described as an example) from entering the tuyere and clogging or melting the tuyere. It is well known that the gas flow rate must be maintained above a certain minimum flow rate determined by the tuyere diameter and the static pressure of the molten steel located above the tuyere.

The minimum flow rate to prevent molten steel from entering the tuyere is determined by the tuyere diameter and molten steel static pressure (=molten steel depth x molten steel density). However, as a result of the tuyere tip being extremely cooled by the sensible heat and decomposition endotherm of the injected refining gas, the molten steel 7 adheres to the tip of the tuyere 5 as shown in Fig. 2, and the metal 6 (generally called a pine room) ) grows.

While the refining gas is being blown into the pine room 6 through the tuyere 1, the pine room 6 exhibits subtle changes and behavior due to the exothermic or endothermic reactions caused by the blown gas and the intense flow of the molten steel. In other words, phenomena such as rapid growth, shrinkage, or even momentary shedding of the pine room occur. Therefore, there is a need for a method for controlling the supply pressure and flow rate of the blown gas, a method for switching the type of blown gas, etc. that can withstand such behavior of the pine room and also enable stable operation.

Now, we will examine how the properties of the pine room mentioned above affect the relationship between the behavior of the pine room at the tip of the tuyere, the blown gas pressure, and the flow rate when refining oxygen gas is blown into the inner tube of a double-pipe tuyere. will be explained in detail using an example.

For example, when blowing oxygen gas into a certain depth of molten steel through a tuyere with a double pipe tuyere inner diameter of 30 mmφ, the minimum flow rate is the minimum flow rate to prevent molten steel from entering the tuyere when there is no pine loom attached to the tip of the tuyere. 1000N
Let m ³ /Hr. At this time, the pressure after the flow control valve of the gas supply equipment (so-called secondary pressure with respect to the gas supply source pressure) was 3.5 Kg/cm ² in gauge pressure.
However, if gas injection is continued, a pine room is generated at the tip of the tuyere, and the effective diameter d of the opening at the tip of the tuyere becomes smaller (see FIG. 2).

At this time, if the minimum flow rate is always maintained so that molten steel does not enter into the 30mmφ tuyere where the pine room is not attached, the secondary pressure of the blown gas will be the effective diameter of the opening at the tip of the tuyere (actually not a perfect circle, but similar to a circle). The diameter of the cross-sectional area varies as shown by curve a in Figure 3.
However, strictly speaking, the relationship of curve a in FIG. 3 differs depending on the characteristics such as piping resistance of the gas supply equipment, pressure loss due to valves, and pressure loss within the tuyere.

On the other hand, when refining gas is injected into molten steel through a tuyere for a certain purpose, the amount of gas required for that refining purpose is generally determined by adjusting the secondary pressure, which varies depending on the formation status of the pine room shown in curve a in Figure 3. Despite this behavior, it is necessary to maintain it during the targeted refining period.

Furthermore, in terms of preventing the intrusion of molten steel into the tuyere as mentioned above, it is likely that the required minimum flow rate can be reduced as the effective diameter of the tuyere tip opening becomes smaller due to the pine room.
The behavior of pine looms, that is, the phenomenon in which large pine looms momentarily fall off and rapidly return to their original tuyere diameter, is often observed in actual operations.

This change corresponds to the effective diameter of the tuyere tip opening, which has become smaller due to the growth of the pine loom, and if the flow rate is reduced to the minimum required to prevent the intrusion of molten steel, the rate of pine loom shedding will decrease. The tuyere diameter suddenly increased due to the fall of the pine loom faster than the operating speed of the flow control valve.
Due to the delay in securing the minimum flow rate of the blowing gas necessary to prevent the intrusion of molten steel,
Molten steel may enter the tuyere and cause tuyere blockage and tuyere damage.

From this, even for purposes other than refining,
In other words, even just for the purpose of preventing molten steel from entering the tuyere, the blown gas flow rate must always be maintained at the minimum gas flow rate to prevent molten steel from entering the tuyere at the tuyere diameter when there is no pine room. is necessary.

This is curve a in Figure 3, assuming that the effective diameter of the tuyere tip opening becomes 20 mmφ due to the growth of the pine room.
The secondary pressure is required to be up to about 6 kg/cm ² , which means that the source pressure supply pressure and piping must be able to withstand this pressure.

The above also applies to cases where the purpose of gas injection is different and the blown gas is changed midway through.

In particular, in the case of gas switching, for example, two blown gas lines are involved, and even in the event of an abnormality in the operation of all valves in these two lines or in the gas source pressure, etc., as mentioned earlier,
It is necessary to ensure and maintain the required minimum flow rate to prevent molten steel from entering the tuyere.

In addition, generally in steel refining work, there is the work of putting scrap iron and hot metal into a steelmaking furnace (hereinafter referred to as charging work),
Work is divided into work that involves refining using pure oxygen gas (hereinafter referred to as blowing work) and work that removes rust from refined molten steel. It is important to use the type of refining gas that matches the purpose of each operation. That is, for example, inert gas is generally used in charging operations to prevent the generation and dissipation of red smoke.

In blowing operations, pure oxygen or an oxidizing gas whose main component is oxygen is generally used to refine hot metal into steel, but gases such as nitrogen and argon may also be used depending on the purpose of refining. Ru.

When tilting the converter equipped with bottom blowing tuyere after blowing work is completed, inert gas is generally used for the same reason as charging work and to prevent fluctuations in the molten steel composition due to continued oxidation of the molten steel. are using.

In rust removal steel work where a converter equipped with a bottom blowing tuyere is tilted so that the tuyere is positioned above the molten steel, the main purpose is to prevent slag flowing on the furnace wall and gas from entering the tuyere. , relatively inexpensive air/nitrogen gas that does not react in any way with hot metal or molten steel is used.

Figure 1 is a schematic diagram of the types of bottom-blown gases in a 300-ton, bottom-blown converter. The tuyere 2 has a double pipe configuration, and oxygen, argon, nitrogen, or air can be blown into the inner pipe. In addition, either hydrocarbon, argon, or nitrogen can be blown from the outer tube, and the flow rate of each blown gas is controlled by valve 3 to flow the gas type and gas flow rate that are suitable for each work content. There is. 4 is a lance for top-blowing acid.

As described above, there is an optimal type of gas for each task, and it is extremely important to smoothly switch the gas that matches the purpose.

As described in Japanese Unexamined Patent Publication No. 49-66518, this gas switching method is such that while the flow rate of the leading gas A is maintained at the minimum flow rate at which molten steel does not enter the tuyere, the flow rate of the trailing gas B is maintained so that the molten steel does not enter the tuyere. There is a method of switching the gas by stopping the flow of the preceding gas A after adding or adding the minimum flow rate that does not cause intrusion.
figure).

The advantage of this method is that even if there is an abnormality in either the leading gas or the trailing gas, such as valve operation or a drop in source pressure, the gas flow rate will be the minimum flow rate that will not allow molten steel to enter the tuyeres. (This method is hereinafter referred to as the flow rate control gas switching method).

However, the disadvantage of this method is that during the gas switching process, it is necessary to ensure a minimum flow rate for each of the leading and trailing gases to prevent molten steel from entering the tuyere. is twice the minimum flow rate at which molten steel does not enter the tuyere (accurately it varies depending on the properties of the gas type, but in actual operation it can be approximated to about twice) and depends on the condition of the pine room at the tip of the tuyere. As shown in curve b in Figure 3, the secondary pressure of the leading gas and trailing gas is a maximum of 12 kg/kg in this equipment.
It became cm ² . In other words, due to gas switching, the supply source pressure (primary pressure) of various gases and the secondary pressure after flow rate control are significantly increased.

Therefore, when designing actual equipment using this gas switching method, the abnormal growth of the pine room (in Figure 3, the effective diameter of the tuyere tip opening due to the pine room is 20
mmφ or less), the secondary pressure must be 10Kg/cm ² or more, and is therefore subject to the High Pressure Gas Control Law.

For this reason, maintenance of the equipment becomes complicated, and the source pressure of the blown gas has to be increased, resulting in major drawbacks such as the gas supply equipment becoming large-scale.

The present invention is the result of various studies on the characteristics of the above-mentioned pine room and the characteristics of the flow rate regulating valve, and as a result, a completely ideal blowing gas switching method has been invented, which is described in the above-mentioned Japanese Patent Application Laid-Open No. 49-66518. This completely eliminates the drawbacks of the flow rate control gas switching system.

That is, in the present invention, there is no need to increase the primary and secondary pressures of various gases to switch gases, and these gas pressures are not required to perform normal blowing operations except when switching gases. The maximum pressure applied is sufficient. Furthermore, since the total gas flow rate when switching the blown gas is relatively small, there are great advantages such as less scattering of molten steel and a higher yield.

This gas switching method can also be applied to the outer tube of a double tube.

Hereinafter, an embodiment of gas switching according to the present invention will be described in detail based on FIG.

Horizontal axis (time axis) o, e, f, g, h, i, j,
k represents the valve actuation timing. First, in FIG. 5 [ ], the preceding gas A is controlled at a constant flow rate until time e. In order to switch to the succeeding gas B, at f, the valve for the leading gas A is narrowed down to an opening that ensures a gas flow rate that will prevent molten steel from entering the tuyere even if the pine room falls off (hereinafter referred to as the specified opening), and the valve opening is measured. Confirm this by etc.

Then, in actual operation, since the pine room is growing, the gas flow rate decreases as shown in [ ] and becomes the gas flow rate corresponding to the specified opening degree. At the same time or after a certain amount of time has elapsed, when the valve for the following gas B is set to the specified opening (this also includes setting the valve for the following gas to the specified opening in advance and opening the shutoff valve), at time h, the As shown, each gas flow rate is approximately the same, and the total flow rate reaches a peak as shown in [ ]. This flow rate depends on the size of the pine room and is not constant. Similarly, the secondary pressure of the gas was 5.5 Kg/cm ² in the example shown in FIG.

Next, after the valve for the trailing gas B reaches the specified opening degree, the valve for the leading gas A is closed at time i, and at time j, the flow rate of the leading gas A becomes O as shown in [ ], but as the flow rate of the trailing gas B increases Since the valve is maintained at the specified opening, the flow rate of the subsequent gas B is equivalent to the specified opening. At time k, the subsequent gas is controlled to a flow rate that meets the purpose of the blowing operation after gas switching, and this completes the gas switching (hereinafter, this method will be referred to as the specified opening gas switching method).

The significant difference between the specified opening degree gas switching method of the present invention and the flow rate control gas switching method described above will be explained in more detail below.

In the flow rate control gas switching method, as mentioned above, in the gas switching process, in order to prevent molten steel from entering the tuyere even if the pine room suddenly falls off, the minimum gas flow rate necessary to prevent this is set to the preceding gas flow rate. and subsequent gas,
It has the characteristic that the gas supply source pressure and secondary pressure are significantly high.

On the other hand, in the specified opening gas switching system of the present invention, the opening degrees of the control valves for the leading gas and the trailing gas are respectively set to a virtual state where there is no pine room at the tuyere tip, that is, a state where the pressure drop at the tuyere tip is minimal ( Gas switching is performed by setting the valve opening to obtain the lowest flow rate at which molten steel does not enter the tuyere (secondary pressure is at its minimum). In other words, in this method, gas switching is performed at the gas supply source pressure (primary pressure) sufficient to obtain the minimum flow rate of gas that does not allow molten steel to enter the tuyere in a state where there is no pine room at the tip of the tuyere and the secondary pressure is minimal. It is in.

In actual operation using this method, as mentioned above, the pine room at the tip of the tuyere always undergoes slight changes, and rapid shedding phenomena are often observed.

When the pine room grows large and the pressure drop at the tip of the tuyere becomes large, the primary pressure is constant in the method of the present invention, so the gas flow rate decreases by an amount corresponding to the increased pressure loss. The effective diameter of the opening at the tip of the tuyere is small, completely preventing molten steel from entering.

The pine tree grows to a certain size again,
When the pine room suddenly falls off under a corresponding gas flow rate, the effective diameter of the tuyere tip opening increases instantaneously, but in this case, with the method of the present invention, the valve is always maintained at the specified opening. Since there is no need to operate the tuyere, the gas flow rate can be increased instantaneously by increasing the effective diameter of the tuyere.

As mentioned above, the present invention has been developed by studying the complex behavior of the tip of a gas injection tuyere, and completely preventing tuyere accidents caused by molten steel entering the tuyere due to valve malfunctions involved in gas switching, and The present invention provides an excellent gas switching method that enables this while minimizing the source pressure (primary pressure) and secondary pressure of the various gases involved, so it will greatly benefit the industry. be.

[Brief explanation of the drawing]

Figure 1 is a conceptual diagram of the blown gas flow in a bottom-blowing converter.
Figure 2 is a conceptual diagram of the pine loom attached to the tip of the double pipe tuyere, Figure 3 is ^a diagram of the relationship between the effective diameter of the opening at the tip of the tuyere and secondary pressure.
b is a relationship diagram when the gas flow rate is 2000Nm ³ /H, Figure 4 is a schematic diagram of the gas switching method, gas flow rate, and gas pressure described in JP-A-49-66518, and Figure 5 is a diagram of the gas flow rate according to the present invention. A schematic diagram of the switching method, gas flow rate, and gas pressure is shown. 1: Bottom blowing converter, 2: Double pipe tuyere, 3: Gas flow rate control valve, 4: Top blowing acid lance (Figure 1), 5:
Tuyere, 6: Pine room, 7: Molten steel (second
figure).

Claims (1)

[Claims] 1. In a metal refining method using a refining furnace equipped with a gas bottom blowing tuyere, when switching the bottom blowing gas to the desired gas according to the refining process, the valve opening of the valve for the gas pipe to be switched is adjusted to the tip of the tuyere. After setting the opening to ensure the minimum gas flow rate that can prevent tuyere clogging in a hypothetical state where there is no deposited metal, or at the same time, adjust the valve opening of the switching gas pipe valve. In a hypothetical state where there is no metal attached to the tip of the tuyere, the opening is set to the minimum gas flow rate that can prevent tuyere clogging, and then the passage of the gas to be switched is stopped, and the switching is performed thereafter. A bottom-blown gas switching control method in a metal smelting furnace, characterized by controlling gas to a desired flow rate necessary for smelting work.