JPH04272117A - Method for detecting bridging in melting scrap - Google Patents

Abstract

PURPOSE:To maintain working safety and to save energy by accurately detecting bridging in melting scrap in a converter. CONSTITUTION:Oxygen is blown into the scrap 3 in a converter 1 from an oxygen lance 5 at the rat of <=4 Nm<3>/min t to melt and refine the scrap, and the secondary combustion rate (%CO2/(%CO+%CO2)) is successively measured. When the average secondary combustion rate is controlled to <=15% throughout the period in which oxygen is supplied at 100Nm<3>/t from the lance 5, bridging is found to be present.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting so-called "shelf hanging" that occurs during melting and refining of scrap by oxygen injection in a converter or the like.

0002

BACKGROUND OF THE INVENTION In recent years, the proportion of scrap in steelmaking materials has been increasing due to its advantageous price. Traditionally, scrap has been melted in most cases using electric furnaces, but due to the high electricity costs, it is now possible to melt scrap using converter equipment, which can supply a large amount of heat from carbonaceous materials without using electricity as the heat source for melting. The dissolution technology of is now attracting attention.

[0003] Conventional scrap melting in converter
As for the refining method, for example, the applicant et al.
There is one disclosed in Japanese Patent No. 0-185192. In this scrap melting and refining method, 50 to 200 kg/t of coke is first charged into a top- and bottom-blowing combined blowing converter, and oxygen gas is blown into the bottom-blowing tuyere or top-blowing lance, or both. After igniting it to create a spark, the scrap is charged, and while the carbon material is being added, oxygen gas is blown from the bottom blowing tuyere and top blowing lance to reduce the amount of carbon in the molten steel upon completion of melting to reduce the amount of nitrogen in the product. ;2.0%
Melting proceeds to ensure the above, and after scrap melting is completed, desulfurization is performed by adjusting the slag components so that the basicity (CaO/SiO2) is 1.2 or more, and the bottom blowing tuyere By blowing in non-oxidizing gas, the slag and molten steel are stirred to reduce the total amount of Fe in the slag to less than 3%, and then, after desulfurization is completed, the slag and residual carbonaceous material are removed, and then top and bottom blowing is carried out. It decarburizes and denitrifies.

0004

In the method for melting and refining scrap in a converter, as shown in FIG. A phenomenon called "shelf hanging" 11 occurs, in which unmelted scrap 11 is bound to the wall 10 and adheres in the form of a shelf. This “shelf hanging” 11
Once formed, it deteriorates the consumption efficiency of the input energy, increasing the consumption of coke and O2 gas, which are the energy sources, and if it progresses further, it can cause problems such as the inability to operate. There were cases where it was triggered.

Furthermore, when the converter is turned over with the "shelf hangings" 11 formed, since the "shelf hangings" 11 are in a peroxidized state, the "shelf hangings" 11 and a large amount of molten steel are Contact with the converter 12 causes an abnormal reaction, which is dangerous, and a part of the "shelf hanging" 11 located above the converter 10 falls, causing the molten steel 12 to bounce back, putting workers in the vicinity at risk. There were problems such as exposure to Therefore, it is important to detect the early "shelf hanging" and eliminate it before it occurs.
There is no suitable method for detecting the occurrence of oxidation, and conventional methods include temporarily stopping the oxygen supply, overturning the converter, and visually checking.

[0006] Therefore, the main object of the present invention is to provide a method for detecting the occurrence of "shelf hanging" during melting of scrap without visual inspection, in order to ensure work safety and save energy resources. It is.

[0007]

[Means for solving the problem] The problem is to increase the average oxygen supply rate of the blown oxygen to 4 Nm3/m when blowing oxygen into the scrap in the reaction vessel to melt and refine it.
in・t or less, and the secondary combustion ratio of exhaust gas (%CO2 / (%CO + %CO2 ))
Measurement was carried out, and the total average at 100Nm3/t oxygen supply was 2.
This problem can be solved by determining that "shelf hanging" has occurred when the subsequent combustion ratio is 15% or less.

[0008]

[Operation] When a constant amount of heat is continuously applied to the scrap stored in a reaction vessel such as a converter by oxygen injection, the scrap gradually melts from the point where the O2 gas collides with the scrap. Thereafter, the unmelted portion of the scrap remains around the furnace wall and remains as a so-called "hanging shelf." While the melting of the scrap is progressing, the heat input is used for melting the scrap, so the steel bath temperature is maintained at a certain constant temperature. However, when the melting of the scrap stops and "shelf hangings" begin to form, the heat input is not used to melt the scrap, and the temperature of the molten steel begins to rise. If we consider this phenomenon in terms of exhaust gas from molten steel, CO2 +
When the reaction equation of C=2CO begins to form a "shelf suspension", it progresses to the right due to the rise in steel bath temperature, and the amount of CO in the exhaust gas composition increases significantly.

[0009] The present invention attempts to accurately detect "hanging on a shelf" by utilizing this reaction characteristic. In other words, when "shelf hanging" begins to form, the amount of CO in the exhaust gas increases, so the secondary combustion ratio (%CO2 / (
%CO+%CO2)) (hereinafter referred to as PC ratio) is significantly reduced, and by measuring this PC ratio, it is attempted to determine the presence or absence of "shelf hanging". The average oxygen delivery rate from the oxygen injection lance was set to 4 N.
m3/min・t or less is 4 Nm3/mi
This is because if it exceeds n·t, strong stirring will occur and preferential decarbonization will occur without secondary combustion occurring. Also, the PC ratio is 100Nm
3/t The total average at the time of oxygen delivery is 100
This is because if it exceeds Nm3/t, the temperature of the melted hot metal will also rise and the base of secondary combustion will fall. In addition, the judgment of the presence or absence of "shelf hanging" is based on the PC ratio of 15% or less.
This is based on test results by the inventors. In addition,
When the oxygen injection is a combined converter using top blowing and bottom blowing, the total value of the average oxygen feeding rate is 4 Nm3/mi.
n·t or less, and in this case, it is desirable that the bottom-blown O2 gas amount be at least 0.5 Nm3/min·t or more.

0010

EXAMPLES The present invention will be explained in detail below based on examples. FIG. 1 is a diagram showing the state of scrap melting in a top/bottom blowing combined converter, and the scrap 3 charged into the converter 1 is
O2 from the oxygen injection lance 5 installed above the converter 1
In addition to blowing in gas, O2 gas and N2 gas are also blown in from the bottom of the converter 1 to melt the scrap 3. Exhaust gas generated by melting is combusted by air forced into the gap between the converter 1 and the hood 4, and is recovered as steam by a waste heat boiler (not shown). When measuring %CO and %CO2 in exhaust gas, %CO2 is actually measured in the converter during melting of scrap by oxygen injection.
Continuous analysis of O and %CO2 is difficult due to operational reasons. Therefore, it is desirable to detect it in the flue of the hood 4 installed above the converter 1. Since the CO gas in the exhaust gas is oxidized by air from the gap between the opening of the converter 1 and the hood 4 to become CO2 gas, the PC ratio is determined by the method shown in Equation 1.

[0011]

[Math 1]

Note that the intrusion Air in the above equation can be specifically determined from Equation 2 based on the nitrogen balance.

[0013]

[Math 2]

(Example) In the converter 1, the top blowing oxygen rate from the oxygen blowing lance 5 was set to 3.2 Nm3/m.
in・t, the bottom blowing oxygen rate from the bottom of the converter is 0.6 N.
m3/min・t, melting and refining the scrap with the components shown in Table 1 under HMR (hot metal ratio) = 0% (all scrap), 100Nm3/t
The relationship between the PC ratio at the time of oxygen supply and the occurrence of "shelf hanging" was investigated, and the test results are shown in Figure 2.

[0015]

[Table 1]

As is clear from FIG. 2, when the PC rate is 1
If it is less than 5%, "shelf hanging" will occur,
If it exceeds 15%, no "shelf hanging" phenomenon is observed, and P
It is found that the presence or absence of "shelf hanging" can be determined at a C ratio of 15%.

[0017]

[Effects of the Invention] As described in the novel above, according to the present invention, it is possible to easily check whether "shelf hanging" has occurred without overturning the converter, thereby ensuring work safety and ensuring that its occurrence is Since it can be grasped, it is possible to save the supply heat source by removing it as appropriate.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the state of scrap melting in a converter according to the present invention.

FIG. 2 is a diagram showing test results in this example.

FIG. 3 is an explanatory diagram of the occurrence of "shelf hanging" during scrap melting in a converter.

[Explanation of symbols]

1 Converter 2 Molten steel 3 Scrap 4 Food 5 Oxygen injection lance

Claims (1)

[Claims] Claim 1: When blowing oxygen into scrap in a reaction vessel for melting and refining, the blown oxygen is fed at an average rate of 4 Nm3/min·t or less, and the exhaust gas is sequentially fed. Secondary combustion ratio (%CO2 / (
%CO+%CO2)) was measured and 100Nm3/
t. A method for detecting "shelf hanging" in scrap melting, characterized in that it is determined that "shelf hanging" has occurred when the total average secondary combustion ratio during oxygen supply is 15% or less.