JPS58130211A - Distributing method for bottom blowing gas - Google Patents

Abstract

PURPOSE:To decrease the erosion of bottom blowing tuyeres and to increase the withstanding times of the tuyeres in a converter provided with the bottom blowing tuyeres, by providing regulating devices for the sections of gas flow passages to the gas branch pipes communicating with the respective tuyeres and maintaining the pressures and flow rates of the gases in the prespective tuyeres always at the prescribed values during the operation of the converter. CONSTITUTION:In the stage of decarburising, smelting and refining by oxygen blowing in bottom blown converters, top and bottom blown converters, etc., the oxygen to be supplied to bottom blowing tuyeres and gases for cooling the tuyeres such as propane are conducted with common pipelines to the neiborhood of the converter and are supplied from the piplines further to the tuyeres with branch pipes. In such a case, the orifices of regulating devices for the section of gas flow passages that provide opening parts for gas flow passages of 20-50% restricting ratio with respect to the section of the tuyeres are provided to the respective branch pipes and when part of the tuyeres are closed with higher degrees, the orifices of said devices are operated to control the pressures and flow rates of the gases in the respective tuyeres uniform, whereby the stoppage of the operations on account of closing of part of the tuyeres is prevented and the life of the tuyeres is prolonged.

Description

[Detailed Description of the Invention] In steelmaking methods such as bottom-blowing converters, top-bottom blowing converters, and AOD furnaces in which oxygen, inert gas, or carbon dioxide gas is blown into the bottom surface of a steel bath. This relates to the method of distributing blown gas.

Various types of bottom blowing gas blowing devices are used in these various steel manufacturing methods depending on the type of gas used.

Various types of double pipe siding, small diameter pipe tuyeres made of very thin metal pipes, and even the use of refractory joints have been developed and put into practical use. (Hereinafter, these are collectively referred to as tuyeres.) Generally, when blowing gas for bottom blowing from two or more tuyeres installed at the bottom of the furnace, it goes without saying that the bottom blowing gas blown from each tuyere It is very important that the gas amount should be controlled to substantially the same flow rate from the viewpoint of achieving the metallurgical effect by bottom blowing gas and maintaining the life of the tuyere. In particular, the flow rate per tuyere, which is determined by the tuyere dimensions, or the discharge pressure are very important factors in maintaining the life of the tuyere and preventing tuyere accidents. Always maintaining a predetermined value is an essential condition for actual operation.

The most reliable method for achieving the above conditions is to make each pipe line independent of each other and to control the flow rate individually. However, with this method, there are many pipe lines and control valves, and the structure of the so-called rotary joint that connects both the rotating furnace body side and the fixed non-furnace body side is complicated. At the same time, it is difficult to install in a limited space, so it is rarely used in reality. To overcome these equipment constraints, the generally adopted method is to guide the blown gas controlled by a single control valve to the bottom of the furnace through a single pipe, and connect each gas from a header pipe at the bottom of the furnace. The method of branching out through each branch pipe is adopted. In this method of distributing bottom-blown gas, how to evenly distribute it to each tuyere, that is, how to achieve equal distribution, depends on the stability of the blowing tuyere, as mentioned earlier. extremely important.

In distributing the gas flow from the header pipe to the branch pipes as described above, a commonly used and convenient method is to install an orifice in each branch pipe.

Approximately applying the theory of a tapered nozzle to the flow characteristics of gas passing through an orifice installed in this branch pipe, the pressure in front of the orifice (upstream side) is P. (KVctyt), orifice outlet discharge pressure is P, (KVc, ri, orifice rear branch pipe pressure is P2 (K~), the pressure drop due to the orifice is large as the flow velocity of compressed gas passing through the orifice reaches the sonic speed. Sometimes the following formula holds.

PI/Po= P'/P = (±) −/(k−”
-0,528 +1 Here, Pc is critical pressure, k is specific heat ratio (=0p/Cv)
In the case of air, oxygen, etc., k = 1.4. Further, pC/po is called the critical pressure ratio.

The gas flow through the orifice is controlled by the orifice front pressure P
. and the orifice post-pressure P2, P2/P, is completely different depending on whether or not the ratio P2/P is larger than the above-mentioned critical pressure ratio. For example, when the flowing gas is air or oxygen having the above value, when P2/P>0.528, that is, when the pressure drop due to Olycester is small and the pressure ratio is larger than the critical pressure ratio. is Pl-P2, and the orifice outlet discharge pressure is always the same as the orifice downstream side branch pipe pressure.
In this case, the flow velocity of the gas passing through the orifice has not reached the sonic velocity, and the gas flow rate is equal to the pressure P on the upstream side of the orifice. Even if is constant, it will be affected by fluctuations in the pressure of the branch pipe after the orifice.

On the other hand, when P2/P < 0.528, the pressure loss due to the baffle and orifice is large, the pressure ratio is smaller than the critical pressure ratio, and the flow velocity of the gas passing through the orifice has reached the sonic velocity, PI'' :2P2, and the orifice outlet discharge pressure P1 is not affected by the orifice back pressure P2. Therefore, the flow rate of gas passing through the orifice does not change depending on the change in the orifice back branch pipe pressure, and the orifice upstream pressure, It will be determined by the orifice cross-sectional area.

As can be understood from the flow characteristics of this orifice, the principle of equal distribution using an orifice is
” 10.528 mm pressure difference is created between the upstream and downstream sides of the orifice. This method itself is a very simple and reliable method for evenly distributing gas, and there are actually several methods based on this method. , as a method for equally distributing hydrocarbon coolant to each side of the outer tube of the double front side for bottom blowing,
No. 5527 (public notice: September 27, 1978) has been proposed. As proposed above, this method is fine when the target gas is not the main bottom-blown gas but a relatively small amount such as a protective gas for siding cooling, but when the main bottom-blown gas is the main bottom-blown gas, this method can be applied to a portion of the bottom-blown gas. It is necessary to increase the pressure excessively by the large orifice pressure drop as mentioned above, which leads to various problems such as excessive equipment costs due to the high pressure of the gas generator and pipelines, and equipment maintenance and accident prevention due to the high pressure. I have it,
There are obstacles to practical implementation.

Therefore, the present inventors conducted detailed study and research on a method of distributing gas from a header pipe to each tuyere, and succeeded in putting into practical use a very simple and effective method.

What we found through this research is that the most difficult problem with this type of technology is that when various gases are injected directly into the molten steel through the slats at the bottom of the furnace, the tips of the sidings are affected by the complex effects of the molten steel and exhibit extremely complex behavior. It is to show. For example, metal may adhere to the tips of the siding, or porous metal, so-called pine shrooms, may grow on the gas passage side, affecting the gas flow.
Furthermore, metal may enter the inside of the gas injection pipe, and the tip of the tuyere may become extremely unstable9, which may have a large effect on the relationship between flow rate and pressure at the tip of the tuyere. It is.

Therefore, in order to solve the problems of the present invention, it is necessary to investigate the above-mentioned complicated behavior of the blade tip and find a gas control method that can overcome this. For example, when determining the blockage rate at the tip of the siding during actual operation from the relationship between the flow rate and pressure of the double-pipe siding for oxygen bottom blowing, it is found that the method that does not apply the technology of the present invention results in an increase of 30% to 30% occlusion under normal conditions. rate, sometimes 40~
It was found that the occlusion rate reached 50%, and in some cases, it was found that the occlusion was almost completely closed.

In other words, such a greatly fluctuating blockage rate is essentially related to the distribution of gas to each tuyere, and the gas distribution method must be designed to prevent the extremely large blockage rate as described above. It turns out that it is necessary to solve the problems at the same time.

First, in order to investigate the effect of the blockage rate of the siding tips on the gas flow characteristics, we conducted an off-line experiment by artificially blocking the siding tips with a diameter of 22 mm with various blocking plates and blowing air into them. The pressure and flow characteristics for each blockage rate were measured as shown in Figure 1. As can be seen from this figure, even if the immediate pressure is a certain constant value, the flow rate changes depending on the blockage rate.

Next, a similar measurement was carried out by installing an oriice with an inner diameter of 18.4 mm in the upper flow of the slats, and the results are shown in Fig. 2-3. Figure 3 shows the relationship between the blockage rate at the tip of the blade and the amount of workmanship.What is interesting here is that the flow rate changes first until the blockage rate at the tip of the blade becomes equal to the aperture ratio of the orifice to the diameter of the blade. This is a huge improvement compared to Figure 1.

Based on the knowledge obtained from the above basic experiments, we conducted a model experiment of gas distribution using multiple lines.

In order to confirm the effect of Oriswiss under various conditions of blockage rate between the tuyeres, which is a problem in actual operation, the model is constructed by branching into two tuyeres from a single ladder pipe, and for a tuyere with an inner diameter of 22 + w + φ. The blockage rate of A tuyere is always fixed at 30, and B
The tuyere has a variable blockage rate, and 30% for the tuyere cross section and for the case without orifice to the branch pipe to each tuyere.
For both cases when the cross section was narrowed down, a negative flow of air t 1400× was used as the blown gas. At this time, the blockage rate of the B tuyere, the flow rate distribution situation of both tuyeres, and the discharge pressure P at the tip of the tuyere. The relationship is shown in Figure 4.

From the blockage rate of the B tuyere and the distribution of flow rates of the A and B tuyeres in Figure 4, the effect of the orifice is that the blockage rate of the B tuyere is 30 times the blockage rate of the A tuyere and the restriction rate of the orifice. The distribution situation is greatly improved compared to the state without an orifice. However, it can be seen that in the flow rate distribution situation shown in FIG. 4, the flow rate is not completely evenly distributed between both shoulders. However, looking at the relationship between the blockage rate of tuyere B and the discharge pressure at the tip of the tuyere in Fig. 4, we find that in the absence of oriace, the discharge pressures of tuyere A and B, which have different blockage rates, are the same. , if it has an orifice, the blockage rate of the B tuyere is 3.
Below 0%, the discharge pressure of the B tuyere with a small blockage rate is smaller than the discharge pressure of the A tuyere with a high blockage rate. According to a detailed study of the behavior of the slats by the present inventors, there is a close relationship between the obstruction status between multiple slats and the discharge pressure at the tip of the slats, and in general, the lower the discharge pressure, the more the siding is blocked. It has been found that the higher the discharge pressure is, the more the slats tend to open. By using this knowledge and the difference in discharge pressure between tuyeres with different blockage rates shown in Figure 4, we can identify cases where the blockage rates are significantly different between tuyeres, which would be a problem in actual operation, or where the blockage of a certain tuyere is It has been found that it is possible to completely prevent problems that would lead to accidents such as extreme progress or complete blockage.

In other words, the relationship shown in Figure 4 can be expressed as follows:

As a result of measuring various types of orifice throttling ratios, we found that by setting the orifice throttling ratio to a cross-sectional ratio of the slats that is approximately the same as the maximum possible blockage rate of the slats, Therefore, a tuyere with a relatively high occlusion rate has a relatively high discharge pressure and the tuyere tends to open, and conversely, a tuyere with a low occlusion rate has a tendency to open. found that the discharge pressure was relatively low and the slats tended to become clogged, and that a self-adjustment function worked to always maintain the same occlusion rate between the slats.

Therefore, in the method of the present invention, the metallurgical reaction While allowing a relatively small uneven distribution between the tuyeres for stabilization of the tuyere, however, due to the relationship between the discharge pressure at the tip of the tuyere due to orifice installation and the tuyere blockage rate, each tuyere acting on the tuyere itself The aim is to make the characteristics of the tuyere functional in order to equalize the blockage rate of the tuyeres. By providing such a function, the maximum blockage rate of the lining is stabilized at a much smaller value than that of conventional methods. However, we confirmed that it was significantly improved to below 40 to 50 inches. In other words, according to measurements in numerous actual furnaces, although it varies depending on the type of steel being melted and the type of gas,
The orifice according to the present invention is fully effective when the throttling rate relative to the cross-sectional area of the tuyere is 20-50%.

As described above, by applying the orifice of the present invention, the blockage rate of the lining is stabilized and improved to a smaller value than before, and for example, the critical pressure which is the concept of the conventional orifice is improved. Compared to the case where the orifice has a pressure drop greater than the ratio, the source pressure of the gas generation or supply device increases relatively little, and this can be achieved by installing an extremely simple orifice.
The furnace bottom piping and the piping leading to it are in the low pressure area (10KVcf
I or less), which has a great practical effect.

Next, examples based on the present invention will be described.

At the bottom of the 320-ton converter, four double-pipe blades were installed, and the inner pipe with an inner pipe diameter of 25+lIlφ was used to supply a total of 4,0 OON/hour of oxygen, and the outer pipe was supplied with 2.91 Nd/hour of propane. Continuous operation was performed without using a sink or orifice. As a result, an accident occurred at the 123rd charge and subsequent operations were suspended. This siding accident occurred when one siding became extremely clogged, causing the gas flow rate in the siding pipe to drop abnormally, causing the cooling propane gas in the outer pipe to flow backwards upstream from the siding, resulting in a mixture of oxygen and propane. The piping became red hot due to combustion, and abnormal erosion of the lining progressed during this process, and the average erosion coefficient of the 123 charge reached 5.6 Wa/f yardage. The average erosion coefficient for other linings is 3.3 from 1.81 charge.
The size of the tuyere was as large as 515 mm, and it was a big problem in terms of safety and lifespan of the tuyere.

Next, based on the method of the present invention, an orifice with a diameter of 21 mm was provided in the branch pipe leading to each tuyere, and the operation was carried out under the same conditions as in the above example, with the reduction ratio of the tuyere cross-sectional area being approximately 30%. I did it. The average erosion coefficient at this time is at least 0.55
- With a charge of up to 080 rMn/-t yardage, an extremely stable and long life of 1250 cycles was achieved. Furthermore, there were no tuyere accidents or abnormal tuyere melting phenomena that were observed in the examples with this groove. Comparing the two examples, there is a noticeable difference in the phenomenon.In the conventional method, the pressure of the gas sent to the blade fluctuated greatly from 5Kg/cd to 7.5K, whereas in the above example according to the present invention, 7 (-~ 7
．． It is extremely stable at 5Kg/cr/I.

This clearly shows how effective the method according to the invention is in stabilizing the blockage rate of the slat tips to a low level.

Although the above embodiment mainly describes the case of using a double pipe siding that blows oxygen from the bottom, the embodiments of the present invention are not limited to this, and include a multi-pipe siding that blows various gases, a single pipe siding that blows various gases, etc. It is also applied when various gases are injected into molten steel through tuyeres, clusters of microtubes, joints between bricks, or gaps between bricks and casing.

[Brief explanation of the drawing]

Figure 1 shows the relationship between gas pressure and air flow rate when the orifice is not in use (
Fig. 2 is a graph showing the relationship between gas pressure and air flow rate when the orifice is present (blade diameter φ22, orifice diameter φ19), Fig. 3 is the graph showing the tuyere blockage rate and actual flow rate/theoretical flow rate. FIG. 4 is a graph for explaining the orifice effect (the blade diameter φn, the orifice diameter φ184) on the fluctuation of the lining blockage rate. Patent applicant Representative patent attorney Tomoyuki Yafuki (and 1 other person)

Claims (1)

[Claims] When bottom-blowing gas into the steel bath through multiple tuyeres provided under the four sides of the steel bath, the bottom-blowing gas is guided to the vicinity of the furnace side using a common pipe line that communicates with each panel. After that, the reduction ratio with respect to the cross-sectional area of the tuyere provided in each of the branch pipes communicating from the common pipe to each of the tuyeres is increased by ~50.
A method for distributing bottom-blown gas, characterized in that it is distributed and supplied to each panel through a gas flow path cross-section regulating device that serves as a gas flow path opening.