JPS6233710A - Method for heating molten steel in converter - Google Patents

Abstract

PURPOSE:To improve the heating up efficiency of a molten steel to the max. extent by specifying the distance between the apertures of oxygen supply nozzles for secondary combustion provided to the side wall of a main lance for blowing and molten metal surface and specifying the oxygen supply conditions thereof. CONSTITUTION:The plural oxygen nozzles 2 for blowing are opened to the top end of a top blowing lance and plural pieces of the secondary oxygen nozzles 3 for combustion of CO are provided to the upper side part thereof. The nozzles are set at about 25-45 angle of inclination theta. The oxygen supply line of the secondary line for the oxygen nozzles 2 for blowing. The distance between the apertures of the secondary oxygen nozzles 3 and the molten steel surface is so set as to be made about 150-250 times the diameter of the nozzles 3. The secondary combustion oxygen of >=15% of the amt. of the oxygen to be blown from the top end of the main lance is blown at a velocity of 0.5-1.5 Mach. The combustion efficiency is thereby improved and the molten steel temp. is increased, by which the introduction of scrap, etc., is made possible.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a method for heating up molten steel in a converter, and in particular, to secondary combustion of co2 generated during blowing, the combustion efficiency is improved. In order to improve the temperature of the molten steel, the temperature of the molten steel is increased to compensate for the heat in the subsequent treatment process, and as a result of this heat compensation, it is possible to reduce the inconvenience caused by charging a large amount of cold material such as scrap or iron ore. This relates to technology that enables the input of large amounts of scrap, etc., while reducing the amount of waste.

[Prior art] As is well known, the main purposes of blowing in a converter are: (1) to remove a large amount of carbon contained in the hot metal by combustion with oxygen, and (1) to raise the temperature of the molten steel to A along with the combustion. In order to effectively achieve the latter objective, "secondary combustion of CO generated by primary combustion" plays a large role.

For this reason, in converter blowing, it is considered advantageous to supply, in addition to blowing oxygen, secondary combustion oxygen for secondary combustion of the CO produced by the blowing reaction. Various studies have been proposed along these lines.6 For example, (1) JP-A No. 102205/1986 not only provides a blowing brewer supply nozzle at the tip of the main lance, but also A method has been proposed in which a sub-nozzle for supplying oxygen for subsequent combustion is opened and oxygen supplied from the same oxygen source is separately blown into the combustion chamber. As another method, (2) JP-A No. 58-221214 proposes a method in which blowing oxygen and secondary combustion oxygen are supplied from independent nozzles, respectively. In this case, various considerations have been made regarding the injection position (distance # from the lance head) of secondary combustion oxygen and the injection angle relative to the main lance axis.

[Problems to be Solved by the Invention] However, in the method (1) above, it is extremely difficult to control the oxygen discharge position for secondary combustion, which has a large effect on secondary combustion efficiency, and it is difficult to obtain a sufficient heating effect. It has been confirmed that the secondary combustion efficiency increases as the distance between the lance and the hot water surface increases, and the first step to increasing the secondary combustion efficiency is to raise the main lance position. However, if blowing is carried out with such a lance arrangement, problems such as slopping will occur due to soft blowing, which will significantly impede blowing operability.

In addition, in method (2) above, consideration is given to the distance between the secondary combustion oxygen nozzle and the surface, as well as the flow rate and flow velocity of secondary combustion oxygen, which are considered to have the greatest influence on secondary combustion efficiency. There is no possibility that the 'tl thermal effect of secondary combustion is being fully utilized.

As described above, at the current state of the art, it has only been conceptually confirmed that ``the secondary combustion efficiency of CO has a large effect on the degree of rise in molten steel temperature.'' As far as the specific conditions under which secondary combustion oxygen should be supplied, it cannot be said that sufficient research has been carried out.The present invention is concerned with this situation, and This paper aims to clarify the oxygen supply conditions for secondary combustion that can effectively increase the secondary combustion efficiency, and to provide a technology that can obtain the best heating effect with the minimum amount of oxygen supplied.

[Means for Solving the Problems] The molten steel heating method of the present invention that has achieved the above-mentioned objects is based on at least one secondary combustion oxygen provided on the side wall of the main lance for blowing. In the method of blowing oxygen for secondary combustion from the supply nozzle toward the hot metal surface to burn the converter exhaust gas and raise the temperature of the molten steel, the space between the opening of the secondary combustion oxygen supply nozzle and the hot metal surface as described in 1iii. The distance is set to be 150 to 250 times the nozzle diameter, and the main lance sprays secondary combustion oxygen of 15% or more based on the amount of oxygen at a speed of Matsuha 0.5 to 1.5. The gist lies in the way it is sprayed.

[Function] The present inventors conducted research toward the ultimate goal of accelerating the heating of molten steel by improving secondary combustion efficiency, and found that (1) the scene and secondary combustion oxygen (hereinafter referred to as secondary oxygen) ) The distance between the nozzle openings is set to 150 to 250 times the nozzle diameter, (2) The amount of secondary oxygen supplied is 15% or more of the amount of # element for blowing (hereinafter referred to as primary oxygen). and (3)2.
(3) Set the flow rate of oxygen to 0.5 to 1.5.
The detailed basis for each setting will be clarified in the examples below, but the outline is as follows.

(The distance between the hot water surface and the opening of the secondary oxygen supply nozzle is set to 150 to 250 times the nozzle diameter.) It is best to ensure that the tip of the flame formed by the injection is near just above the molten metal surface (details will be described later). In order to maintain the tip of the flame at such a suitable position.

It is necessary to set the above-mentioned interval in a range of 150 to 250 times the diameter of the secondary oxygen supply nozzle. However, the distance between the levers is 15
If it is less than 0 times, a part of the secondary oxygen will be consumed in the deoxidizing reaction, and the purpose of temperature increase will not be fully achieved. On the other hand, if it is more than 250 times, CO combustion will occur at a high position far away from the hot water surface. As a result, heat transfer to the molten steel cannot be expected, resulting in insufficient heat rise.

(2) The point where the secondary oxygen supply rate is 15% or more of the primary oxygen.The combustion of CO gas caused by the injection of primary oxygen is determined by the oxygen concentration in the internal atmosphere of the blowing furnace, that is, the injected 2
Influenced by the amount of secondary oxygen, if this amount is insufficient, the CO combustion rate cannot be sufficiently increased, and in order to achieve the goal, 1
15% or more, more preferably 20% based on the amount of oxygen
or more secondary oxygen must be supplied.

(3) The flow rate of secondary oxygen is set at 0.5 to 1.5. This flow rate refers to the flow rate immediately after the outlet of the secondary oxygen supply nozzle, and if the flow rate exceeds 1.5, The flame that should be formed by the supply of secondary oxygen is blown away by the secondary oxygen itself, and no substantial flame is formed.

As a result, the combustion efficiency of CO becomes extremely low, and the effect of heating up the molten steel cannot be sufficiently exhibited. On the other hand, if the flow rate is less than 0.5, the flame formed by the injection of secondary oxygen will be too short and will not reach the hot water surface.
The molten steel heating action will no longer be effective.

Requirements (1) to (3) above are indispensable requirements individually in order to increase the reaction efficiency between CO and secondary oxygen present near the molten metal surface and to effectively heat up the molten steel. However, these effects mutually influence each other, and even if one of these requirements is missing, the object of the present invention cannot be achieved, and if these three requirements are mutually favorable. As a result, even with a relatively small amount of secondary oxygen, heating of molten steel can be achieved with high efficiency.

Figure 1.2 illustrates the top blowing lance 1 used in the present invention, Figure 1 is a schematic vertical sectional view of the tip, and Figure 2 is a schematic bottom view. The lance l has one or more (five in the figure) oxygen nozzles 2 for blowing opened at its tip, and has a plurality of secondary oxygen nozzles 3 for co combustion on the upper side thereof (five in the figure). 8) are opened, and this nozzle 3 has an inclination angle of 0 with respect to the axis P of the lance l.
It is most preferable to set the temperature in the range of 25 to 40 degrees, and the oxygen supply system is set up as a separate line from the oxygen supply system for blowing, and the speed is controlled to be the most suitable for the secondary combustion of CO. configured to obtain.

Then, this lance 1 is inserted into the converter 4 as shown in FIG. 3 (a schematic longitudinal sectional view), and blowing is performed by blowing oxygen toward the surface of the molten metal. In this example, the converter 1 is shown as having a bottom blowing nozzle 5 attached to the bottom, but the bottom blowing nozzle 5 does not necessarily need to be provided, and the shape of the lance 1 is not limited to that shown in the figure. However, the number and shape of the blowing oxygen nozzles 2 and the secondary oxygen nozzles 3, the distance between the two nozzles 2.3 in the height direction, etc. can be changed arbitrarily as necessary.

[Example] The present inventors have determined that the secondary combustion efficiency of CO depends on a number of conditions such as (1) the flow rate and flow velocity of secondary oxygen, and (2) the distance between the secondary oxygen discharge level and the hot water surface. In order to grasp these relationships indefinitely, we constructed a small combustion test furnace as shown in Figure 4 (6 in the figure is the combustion chamber, 7 is the oxygen injection nozzle, and 8 is the oxygen injection nozzle). Exhaust hole, 9 is the primary rectifier plate, 10 is 2
(shown below), LDG (Co: 70
%, CO2 = 15%, N2: 15%) An oxygen gas blowing test was conducted using various nozzles in an atmosphere.

As a result, the combustion of CO gas in the combustion chamber 6 is
The concentration of 02 in the air is significantly affected by the amount of secondary combustion oxygen injected from the nozzle 8. In order to ensure a high level of secondary combustion efficiency, the ratio of the amount of secondary oxygen to the amount of primary oxygen must be adjusted. It has become clear that it should be at least 15%, more preferably 20% or more.

By the way, Figure 5 is a graph showing the results of examining the quality of CO combustibility when the ratio of the secondary oxygen flow rate to the primary oxygen flow rate and the flow rate were varied, and there are slight differences depending on the blowing flow rate. However, it can be seen that if the ratio is set to 15% or more, preferably 20% or more, CO combustion can be efficiently promoted. However, as can be easily understood from this figure, when the flow rate of secondary oxygen exceeds Matsuha 1.5, the flame itself is no longer formed, and the secondary oxygen does not contribute much to the combustion of CO gas in the furnace and the molten steel will be consumed for decarburization. However, the flow velocity is Matsuha 0.5
If the temperature is less than 100 m, the flame is too short and the reaction between secondary oxygen and CO occurs at a position far from the molten metal surface, so it does not contribute much to the heat rise of the molten steel.

That is, the flame formed by the injection of secondary oxygen has a shape as schematically shown in FIG. 6 ([Secondary oxygen/Primary oxygen) x 100 = 20%], flow rate: Mach 1.0.2 Oxygen nozzle diameter: Dmm)

Although the thermal effect on the molten metal changes depending on the position of the flame relative to the molten metal surface, the inventors have confirmed through experiments that the flame end point in Fig. 6 is slightly below the molten metal surface.
The best heating effect can be achieved by setting the position of the nozzle so that it is in the L direction. By the way, the position of ■ in the diagram is
Area where flame is not formed and secondary oxygen is not burned,■
At position t, although a flame is formed, a considerable amount of unburned oxygen remains and the secondary combustion efficiency is low, and even if there is a hot water level around this area, no heating effect on the molten steel can be expected. On the other hand, position (3) is an area where secondary combustion is sufficiently carried out and combustion heat is efficiently transferred to raise the temperature of molten steel, so it is effective to have a molten metal level around this area. . However, at the position (■), since the secondary combustion has already been completed, the amount of heat generated is small, and if the hot water level is at that position, the heating efficiency is insufficient.

To summarize these considerations, the secondary combustion efficiency and molten steel)
When L thermal efficiency is considered, the most preferable hot water surface position (or more correctly expressed, the flame position relative to the hot water surface) is considered to be the area indicated by X in Figure 6.

Fig. 7 is a graph showing the relationship between the flow velocity of secondary oxygen immediately after the nozzle exit and the flame position [(secondary oxygen Fi, amount/primary oxygen flow rate) The formation position is determined by the flow velocity and its nozzle diameter; if the nozzle diameter is held constant, as the flow velocity increases, the distance the flame is blown away increases and the flame end point moves away from the nozzle.

Furthermore, in Fig. 8 (A) to (C), a secondary oxygen nozzle with a diameter of 11.9 + s layer is used, and the flow rate is set to 1/\0.4゜1.
．． This is a graph showing the temperature distribution of the flame when the setting is set to It is thought that this could make a contribution.

Based on the preliminary experimental data described above, an actual blowing experiment was conducted using a 250-ton converter. The main lance used had the basic structure shown in Figure 1.2.

First, Figure 9 shows [Secondary Oxygen iA-
This is a graph showing the results of CO combustion efficiency determined as the rate of increase in CO2 in the furnace when the ratio of [Amount of primary oxygen] was varied drastically.

(Experimental conditions) Alternating layers between the lance tip and the scene: 2,200m layer primary (
Blowing) Oxygen nozzle diameter (D): 44 m Secondary oxygen nozzle diameter: 201 Same Incline angle ((J): 30 degrees Secondary oxygen flow rate (
1.2 Distance between nozzle head and secondary oxygen nozzle: 1.500+s As is clear from Figure 9, in order to increase the secondary combustion efficiency of CO, [secondary oxygen/primary oxygen] Flow rate ratio of 15% or more,
More preferably, it needs to be 20% or more.

Next, in Figure 10, the [secondary oxygen/primary oxygen] flow rate ratio is 20.
%, and the flow rate of secondary oxygen was varied in various ways.

From the results in Figure 10, it is clear that the higher the flow rate of secondary oxygen is, the lower the C0zh rise rate becomes.In order to increase the CO combustion efficiency, the flow rate should be lower than Matsuha 1.5, more preferably 1.25. It can be seen that it should be kept below.

However, if the flow rate becomes too low, even if combustion is promoted, the combustion heat will not be effectively transferred to the hot water surface, resulting in only an increase in the exhaust gas temperature, so the lower limit of the flow rate was set at 0.5.

Furthermore, as explained in Fig. 7 above, the position of the flame formed by secondary oxygen varies depending on the diameter of the secondary oxygen nozzle and the flow rate of secondary oxygen, but under the most standard converter blowing conditions ( C when the distance between the lance head and the opening end of the secondary oxygen nozzle, 1 (L), is changed under (as shown below)
When the relationship between O combustion efficiency (C○2 increase rate) was investigated, the results shown in FIG. 11 were obtained.

(Experimental conditions) Distance between the lance tip and the hot water surface f11 + 2,200 m Primary (blowing oxygen nozzle diameter (1)) + 44 weight Secondary oxygen nozzle diameter: 20 m Inclination angle (0)
: 30 degrees Secondary oxygen flow rate (Matsuha) : 1.2 (Secondary oxygen/
Primary oxygen): 20% As is clear from Figure 11, there is a suitable range for the distance between the secondary oxygen nozzle and the hot water surface, and if it is outside this range, a satisfactory CO reaction rate may not be achieved. The preferred range is 150D to 250D (
More preferably, it is in the range of 180D to 240D).

From the above results, the best blowing conditions (secondary oxygen/1
Secondary oxygen) flow rate ratio: 20%, lance height: 2.200 layers, secondary oxygen flow rate: Mach 1.2. Distance between secondary oxygen nozzle and lance head @:l, 500 mm, respectively. We conducted a number of experiments and compared the secondary combustion rate of CO and the degree of heating of molten steel with the conventional method, as shown in Figure 12.According to Shukan I91, the secondary combustion rate was about 10%, It was confirmed that the degree of heating can be improved by about 4% in terms of scrap ratio.

Figure 13 shows an example of a secondary blowing pattern using a secondary oxygen independent control nozzle. The aim is to increase the supply amount of molten steel and improve the heating effect of molten steel. In this example, hot metal that has not been subjected to preliminary deP or S is used for blowing, but when using hot metal that has already been deP or S, there is no deP or S phase. Remove C immediately
Therefore, it is preferable to increase the secondary butyric flow rate a little earlier.

[Effects of the Invention] The present invention is configured as described above, but the point is that by specifying the distance between the secondary oxygen supply nozzle and the hot water surface, the supply amount and flow rate of secondary oxygen The combustion efficiency of CO by oxygen and the heating efficiency of molten steel related to the combustion can be maximized, and an increase in the scrubbing ratio can enjoy benefits such as an increase in blowstop temperature. .

[Brief explanation of drawings]

Figures 1.2 illustrate the lance used in the present invention; Figure 1 is a schematic vertical sectional view of the tip, Figure 2 is a bottom view, Figure 3 is an explanatory diagram showing the blowing situation, Figure 4 is a schematic vertical cross-sectional view showing the test furnace used in the preliminary experiment, and Figure 5 is a graph showing the influence of the flow rate of secondary oxygen and the flow rate ratio (secondary oxygen/primary oxygen) on the combustibility of co. Figure 6 is a model diagram of the flame generated during secondary combustion of CO, Figure 7 is a graph showing the relationship between the secondary oxygen flow rate and the distance between the secondary oxygen nozzle and the melt surface on the flame during secondary combustion, and Figure 8. is a graph showing the relationship between the distance from the opening end of the secondary oxygen nozzle and the flame temperature, and Figure 9 is a graph showing the relationship between the distance from the opening end of the secondary oxygen nozzle and the flame temperature.
Figure 10 is a graph showing the effect of the primary oxygen) flow rate ratio on the CO2 rise rate (CO reaction rate) in the furnace.
The figure is a graph showing the influence of the distance between the lance and the secondary oxygen nozzle (and the distance between the lance head and the secondary oxygen nozzle) on the 002 increase rate. Figure 12 shows the secondary combustion efficiency and the degree of heating up of molten steel (scrap ratio) FIG. 13 is an explanatory diagram illustrating the 2 o'clock oxygen supply pattern when implementing the present invention. l...Lance

Claims (1)

[Claims] When performing converter blowing, oxygen for secondary combustion is sprayed toward the hot water surface from at least one oxygen supply nozzle for secondary combustion provided on the side wall of the main lance for blowing, and the exhaust gas of the converter is combusted. In the method of increasing the molten steel temperature by
The distance between the opening of the oxygen supply nozzle for secondary combustion and the melt surface is set to be 150 to 250 times the diameter of the nozzle, and the secondary combustion is 15% or more of the amount of oxygen blown from the tip of the main lance. 1. A method for heating up molten steel in a converter, characterized by spraying commercial oxygen at a speed of Mach 0.5 to 1.5.