JPS5819424A - Controlling method for cooling of bottom tuyere of converter - Google Patents

Abstract

PURPOSE:To cool and protect the bottom bricks of the tuyeres in the bottom of a converter effectively over the entire period of converter blowing by controlling the flow rate of blowing of fluid for cooling according to the change in the cooling conditions of the tuyeres decided from the flow rate and pressure of blowing of the fluid for cooling from the bottom of the converter. CONSTITUTION:In tuyeres of double construction, for example, double-ply pipe tuyeres provided to a bottom blown converter, a porous solidified shell 2 known as a mushroom is formed along the annular flow passage 1 for fluid for cooling on the inner side of the furnace. In this invention, the state of formation of the mushroom during blowing is detected precisely from the flow rate and pressure of blowing of the fluid for cooling. The flow rate of blowing of the fluid for cooling is controlled according to the change in the shape of the mushroom, whereby the shape and size of the mushroom are maintained always in an optimum state over the entire period of blowing and the tuyeres are cooled effectively.

Description

[Detailed Description of the Invention] Jin's invention relates to a method for controlling the flow of the bottom tuyere of a converter, and in particular to a method for controlling the flow of the bottom tuyere and the bottom bricks near the bottom tuyere during the entire period of converter blowing. The aim is to achieve effective cooling protection for

- Generally, in converters equipped with a bottom blowing function, such as bottom blowing converters, top blowing converters, and bottom blowing converters, double pipe or A multiple tube such as a triple tube is used, and a cooling fluid such as a hydrocarbon gas such as propane, OO2 gas, or liquid CO□ is injected through the annular gap of the multiple tube, and an endothermic reaction due to thermal decomposition is utilized. Cooling and maintenance of the hearth bottom tuyeres is carried out.

A tuyere of this kind of structure or a triple pipe siding installed in a bottom-blown converter has an annular shape, which is a flow path for the cooling fluid inside the furnace, as shown in Fig. 1 and its cross section and plan view. A porous solidified shell called a pine mushroom is formed along the flow path 1, and this pine mushroom-〇 shape and size cools.

In other words, in order to maximize the cooling ability of the cooling fluid, it is important to make the flow of the cooling fluid uniform, but for this purpose, the mushrooms must be ideally formed in both shape and size. It is false to think that only in this way can melting damage of the tuyere and the bottom bricks near the tuyere be minimized.

Therefore, in order to achieve the above objective, it is important to accurately grasp the formation state of the pine mushroom during the entire blowing period.However, in the past, it was not possible to judge the shape of the pine mushroom during the blowing process, and the blowing process was completed. This invention had no choice but to perform visual observation after the furnace was emptied by pouring out the hot water, and therefore it was not possible to effectively cool the tuyere or to control it. This method advantageously solves the problem by accurately grasping the formation state of the pine mushroom during blowing from the blowing flow rate and pressure of the cooling fluid, and adjusting the blowing flow rate of the cooling fluid according to changes in the shape. As a result, the shape and size of the pine mushroom are always maintained in an optimal state throughout the blowing period, allowing for effective tuyere cooling.

That is, this invention blows oxidizing refining gas into the molten metal contained in the converter through multiple tube tuyeres provided at the bottom of a converter equipped with a bottom blowing rudder, and blows the tuyere into the molten metal contained in the converter through the annular gap. When injecting a cooling fluid for cooling, an ideal flow rate characteristic curve is determined in advance for the relationship between the flow rate and pressure of the cooling fluid that maximizes the tuyere cooling capacity based on past blowing results, and this ideal flow rate is determined in advance. The cooling status of the tuyere is determined from the deviation of the flow rate and pressure of the cooling fluid in actual operation with respect to the characteristic curve, and the tuyere is adjusted to reduce the deviation by adjusting the amount of cooling fluid blown in according to the deviation. This is a cooling control method for the bottom tuyere of a converter, which is characterized by increasing the cooling capacity.

This invention will be specifically explained below based on the experimental results that led to this invention. Note that the case where a cooling gas is used as the cooling fluid will be shown.

For example, in a bottom-blown converter equipped with triple-tube tuyeres, the pressures in the central passage through which the oxidizing refining gas is blown and the annular passage through which the cooling gas is blown are measured. Focusing on the pressure in the annular channel, which is closely related to the formation of , the annular channel pressure fluctuates depending on the flow rate of the cooling gas and the elapsed blowing time. The cause of this pressure fluctuation is thought to be that the shape and size of the pine mushroom change due to changes in cooling capacity, changes in steel bath temperature, and changes in solidification temperature due to decrease in carbon content in molten steel.

Therefore, the inventors focused on the pressure fluctuations in this annular flow path, and thought that by detecting the pressure in the annular flow path, it might be possible to grasp the formation state of pine mushrooms, and through visual observation after pouring the hot water, it was confirmed that pine mushrooms were the most suitable. The conditions for blowing the cooling gas in the charged charge were summarized in terms of the relationship between the blowing flow rate and the pressure.The results are plotted and shown in Figure 3.

As is clear from the figure, each measurement point was found to lie approximately on a straight line, although there was some variation.

This suggests that effective wing cooling can be achieved by controlling the blowing conditions of the cooling gas to the flow rate and pressure along the first straight line. By injecting the cooling gas at the flow rate and pressure shown by , effective protection of the tuyeres was achieved with high cooling performance.

In this specification, the straight line that provides the blowing conditions for the cooling gas that forms a pine mushroom with an ideal shape and size and provides the maximum cooling capacity is referred to as the ideal flow rate characteristic curve and is denoted by MN in this specification. Note that the blowing conditions for the cooling gas that bring about effective tuyere cooling do not need to strictly satisfy the blowing flow rate and pressure indicated by MN, but are stored within a certain range. Therefore, in this invention, as shown in Figure 1, two straight lines are drawn parallel to each other by an allowable width apart from MN, and these lines are connected to the pine mushroom under-limit curve M.
The SL pine mushroom excessive limit curve MLL is named, and the area between these two curves MSL and MLL is defined as the appropriate area.If the cooling gas injection conditions are within this appropriate area, the shape and size of the pine mushroom will be good and effective. It is determined that the tuyere cooling can be achieved.

An example of how to obtain these curves MN, MSL, and MLL will be described below.

(1) Collect a small amount of operational data when the shape of the pine mushroom is recognized as ideal.

(2) The ideal flow rate characteristic curve is approximated by a linear equation of the form y-az+b, and the pressure (xn) of each operation data.

y of point (xn, y1) with flow rate (yn) as x, y coordinates
The distance Dn with respect to -ax+b is determined.

Find the values (a1, b1) of the coefficients a and b when S expressed in (3) is made the minimum Smin, and find this y=a1x+b
Let the straight line represented by 1 be MN.

(4) Find σ (NF: degree of freedom), and calculate the above y=a1x
Draw two straight lines parallel to +b1 and separated by ±σ, and define these as MSL-MLL.

There are various ways to calculate 0, but here we will use standard deviation as one standard. The degree of freedom N is calculated as Ny-a −/ (N: number of data).

Thus, the pressure of the cooling gas measured in actual operation (x
A point (xn) where the x and y coordinates are the flow rate (yn) and the flow rate (yn).

If yn) is within the appropriate area between SL and MLL, the shape and size of the pine mushroom is determined to be good, and if it deviates from this area, it is determined that ``if it is above SL, the pine mushroom is undersized.'' If it is below ILL, it is determined that the pine mushroom is too large, and the □ pine mushroom is corrected to a favorable shape and size by adjusting the blowing flow rate of the cooling gas.

Hereinafter, with reference to FIG. Figure 5A
, B show the MN, MSL, and MLL determined for a top and bottom blowing converter with a capacity of 250 tons, respectively, and the cooling gas injection flow rate was initially 7 NM/min.

(b) First, when the size of the pine mushroom is becoming too small, that is, at the location shown in Figure 5A, the coordinate point indicated by the pressure and flow rate gradually moves away from MN and moves to the position indicated by a in the figure. However, if there is a risk of deviating from the appropriate range, the following measures will be taken.

Increase the cooling gas flow rate to 10 Nm/min.

Then, the coordinate point moves to the position shown in the figure as the pressure increases, and then as time passes, the cooling effect increases, the pine mushroom grows, and the pressure increases accordingly (arrow 0).
) Eventually the coordinate point will come to 6 points on MN. At this point, the cooling gas flow rate is reduced to the original 7 Nm/min and returned to the point.

(b) On the other hand, if the shape of the mushroom becomes too large, the following measures may be taken.

That is, at the coordinate point shown in Figure 5, a'
If there is a risk of entering the excessive mushroom area below the MLL, first lower the flow rate of the cooling gas from 7 Nm/min to 4 Nm/min. Then, the coordinate point moves to point b' with a pressure drop, but if the flow rate is maintained as it is, the pine mushroom will gradually become smaller and the pressure will decrease (arrow C'), so the coordinate point will move to point b' on the NIB. At this point, the flow rate is increased to 7 NIB/min and returned to point e'.

Thus, during the whole blowing period, the shape of the pine mushroom,
The size can be maintained appropriately, and effective blade cooling can be easily achieved with high cooling capacity.

Above, we have mainly explained the case where this invention method is applied to the cooling control of the bottom tuyere in tube top and bottom blowing converters.
Needless to say, the present invention can be applied to any converter equipped with bottom blowing, such as OD converter (-KG) and MuOD converter. Furthermore, the method of the present invention can of course be applied not only to triple-pipe tuyeres but also to triple-pipe tuyeres and any other similar type of tuyeres as long as they have cooling fluid blowing and pouring functions.

As described above, according to the present invention, the bottom blowing ridge mat-
The shape and size of the pine mushrooms produced along the annular flow path of the bottom blowing tuyere can be controlled to the ideal shape at all times during the entire blowing period in the converter equipped with the converter, by adjusting the blowing flow rate of the cooling fluid. Under the cooling capacity, melting damage of the bottom tuyeres and the bottom bricks in the vicinity thereof can be suppressed to a minimum, thus helping to extend the life of the tuyeres.

[Brief explanation of the drawing]

Figures 1 and 2 are a sectional view and a plan view showing the state of formation of a pine mushroom together with the bottom tuyere of a bottom blowing converter, respectively, and Figure 3 is a diagram showing the cooling process when an ideal pine mushroom is obtained. Figure 5 is a graph showing the relationship between the blowing flow rate and pressure of the cooling gas, Figure 5 is a diagram showing the appropriate range of flow rate characteristics to form a suitable pine mushroom, and Figures 5A and B are the graphs showing the relationship between the blowing flow rate and pressure of the cooling gas. FIG. 2 is an explanatory diagram of a procedure for controlling cooling of the bottom tuyere by adjusting the blowing flow rate. Patent applicant: Kawasaki Steel Corporation Figure 1 Figure 8 Pressure re-Icwpti Pressure inertia 4-q Figure 5 (A) Warp Afn-q Pressure leprosy-q

Claims (1)

[Claims] 1. The bottom of the converter equipped with a bottom-blowing facility is equipped with a nine-layer pipe system that blows oxidizing refining gas into the molten metal contained in the converter, and cools the tuyere through its annular gap. When injecting cooling fluid for cooling, an ideal flow rate characteristic curve is determined in advance for the relationship between the flow rate and pressure of the cooling fluid that maximizes the tuyere cooling capacity based on past blowing results, and this ideal flow rate is The cooling status of the shell tuyere is determined from the deviation of the flow rate and pressure of the cooling fluid in actual operation with respect to the characteristic curve, and the tuyeres are adjusted in the upper region of the deviation by adjusting the amount of cooling fluid blown in according to the deviation. A method for controlling the cooling of the bottom tuyere of a furnace, which is characterized by increasing the cooling capacity of the furnace.