JPS62243708A - Controlling method for converter blowing - Google Patents

Abstract

PURPOSE:To improve the hit rate of a molten steel temp. in the stage of blowing out by measuring the temp. increase rate of a molten metal by the secondary combustion efficiency of CO in an oxygen top blowing furnace from the result of the measurement of the CO2 concn. in a converter exhaust gas at the time of making decarburization refining of the molten iron to the molten steel in said furnace. CONSTITUTION:The exhaust gas formed by the decarburization reaction contains CO at the time of charging the molten steel into the oxygen top blowing furnace and blowing oxygen into the molten steel by a top blowing lance to oxidize and remove the C in the molten iron, thereby refining the molten iron to the molten steel. The CO is secondarily burned by the oxygen from the top blowing lance to form CO2. The molten steel is heated up by the combustion heat thereof. The decarburization reaction efficiency by O2 and the secondary combustion efficiency of the CO are nearly constant when the height of the top blowing lance is maintained constant throughout the entire decarburization efficiency and therefore, the influence to be exerted to the blowing out temp. of the molten steel is exactly estimated by measuring the concn. of CO2 in the exhaust gas as the influence that the heat by the secondary combustion of the CO exerts to the molten steel temp. is nearly constant. The hit rate of the molten steel temp. in the stage of blowing out is thus improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a converter blowing method, and more particularly to a method that can improve the accuracy of blow-stop temperature using a relatively simple dynamic control method. be.

[Prior art] Converter blowing is carried out mainly to decarburize and raise the temperature of hot metal, and the blowstop carbon has a significant effect on the quality of steel materials, and the blowstop temperature depends on the processing after blowing ( It is considered an important control item to ensure heat during component adjustment, degassing, casting, etc., and to improve operational efficiency.

For this reason, various studies have been conducted with the aim of improving the accuracy of the blow-stop carbon and blow-stop temperature during converter blowing, and recently efforts have been made to fully automate the control and operation of converter operations. Research is also actively underway.

Under these circumstances, the converter automatic operation systems currently in practical use can be roughly divided into: (1) initial conditions such as hot metal temperature and composition (especially carbon content, silicon content, etc.), oxygen injection amount, etc. (2) Various fluctuation conditions during converter operation (steel bath temperature, exhaust gas flow rate, furnace wall temperature, etc.)
It can be divided into the so-called dynamic control method, which automatically detects the temperature and incorporates these values into the initial conditions to estimate the blow-stop temperature, blow-stop carbon, etc.

The present invention relates to an operation method classified as the latter dynamic control method among these automatic operation methods, and particularly aims to provide a converter blowing control method that can improve the continuous accuracy of blow-stop temperature. It is something.

[Problems to be solved by the invention] As mentioned above, the method of increasing the accuracy of the blow-off temperature using the Dynamec control method has achieved some results, but it requires very expensive equipment and complicated management. It cannot be said that the accuracy is commensurate with the equipment cost.

In particular, promoting slag formation during blowing or T-F in slag
In cases where the height of the top blowing lance is changed in order to reduce the amount of e, the accuracy of the blow stop temperature will drop significantly, and some of the molten steel may solidify before the final ingot making process. There is also the possibility that pouring of hot water may become impossible. For this reason, conventionally, the blow-off temperature was set high to ensure heat security, but as a result, the converter refractories were significantly melted and their lifespan was shortened. In some cases, it may be necessary to re-blow one to several times after the completion of blowing to ensure the specified blow-off temperature, which can lead to problems such as complicating operations and reducing productivity. It's coming.

The present invention was made in view of these circumstances, and its purpose is to provide a method that can obtain a high level of blow-off temperature control accuracy using a relatively simple control method. .

[Means for Solving the Problems] The structure of the blowing control method of the present invention that has achieved the above-mentioned purpose is that, when carrying out converter blowing, the concentration of CO and gas in the converter exhaust gas is measured. C in the converter due to
The gist of this method is to estimate the O2 gas concentration and incorporate the molten steel temperature increase effect calculated from the CO2 gas concentration into the calculation of the blow-off temperature to control the blow-off temperature.

[Function] As mentioned above, in the conventional dynamic control system, if the height of the top blow lance is changed especially during blowing, the continuous accuracy of the blow stop temperature is significantly reduced. As we proceeded with various studies to clarify the causes of this tendency, the following facts became clear.

In other words, in conventional blowstop temperature control, although the heating effect due to the reaction of carbon in hot metal with top-blown oxygen is fully taken into consideration, the secondary combustion of carbon monoxide (CO+ 1 /202-Co2), it cannot be said that sufficient consideration has been given, at least as far as the dynamic control method is concerned. After conducting various studies, we came to the conclusion that the blow-off temperature changes significantly depending on the magnitude of the molten steel temperature rise caused by secondary combustion, and that this should be considered as one of the control items in the dynamic control system. To explain in more detail, if the height of the top blowing lance is kept constant throughout the entire blowing period, the decarburization reaction efficiency and secondary combustion efficiency are almost constant, so the heat generated by carbon combustion will affect the molten steel temperature. The effects are almost equal, so the effect on the blow-off temperature can also be estimated accurately. However, when the height of the top blowing lance is varied in the blowing process, the secondary combustion efficiency in the converter changes considerably, the amount of heat generated changes, and the temperature raising effect on the molten steel also changes.

By the way, Figure 1 shows the height of the top blow lance and the CO2 in the exhaust gas.
This is a graph showing the relationship between concentrations statistically organized, and it can be seen that as the lance height increases (as the distance between the lance and the hot water surface increases), the CO concentration in the exhaust gas clearly tends to increase. The heat generated by the reaction of carbon and oxygen is C+ 1/202- CO+ 2750Kcal/g
...(1) C+ 02 -Cow +8292
Kcal/Kg ---t2) Therefore, a change in CO3 concentration means that the generated reaction heat changes accordingly, and as a result, a part of the reaction heat affects the molten steel temperature. , the effect even appears on the blow-off temperature. However, in the conventional dynamic control method, the temperature increase effect due to the secondary combustion of CO is not added to the control element of the blowstop temperature, and therefore it is not possible to improve the accuracy of the blowstop temperature control when the lance height is varied. It is thought that the

Based on this knowledge, the present invention has developed a
The effect of increasing the temperature of molten steel brought about by the subsequent combustion is also added to the blowstop temperature control element in an attempt to improve the accuracy of the process. Specifically, by taking advantage of the fact that the amount of CO2 produced varies depending on the size of the secondary combustion efficiency, we can continuously measure the CO2 concentration in the converter exhaust gas during blowing operation, and thereby calculate the CO2 concentration in the converter. is estimated, the secondary combustion heat is determined from the estimated value, and the blow-stop temperature is controlled more accurately by taking into consideration the amount of temperature rise of the molten steel due to the secondary combustion.

For example, Figure 2 is a graph summarizing the results of investigating the CO2 concentration in the furnace, the CO2 concentration in the furnace, and the heating effect due to secondary combustion heat during generation in a blowing operation using a converter with a capacity of 85 tons. The heat transfer effect clearly increases as the CO2 concentration increases. Although there is some variation in the amount of increase, a linear linear relationship is observed.

On the other hand, the effect of increasing the temperature of molten steel due to the secondary combustion heat is as follows: Hot metal charging amount: 288 tons Hot metal [C]: 4.05% Blowing stop [C]: 0.20% Reaction: CO (1773°K) + 1/ 202 (298
) = CO2 (1773'K) HMR: 95% Specific heat of hot metal: 0.2 (al/deg-g heat transfer efficiency: 1CO%) As the CO2 concentration in the converter increases by 1%, the temperature of molten steel decreases by 1%. will rise by 9.5°C.

That is, by converting the above equations (1) and (2) into )lcal/+ol, the following equations (3) and (4) can be derived.

C+1/202-CO+33.0KCal/mol
"" (3) (+ 02 → CO2+ 99.5c
al/mol ... (4) On the other hand, the amount of hot metal treated above 28
8 tons, hot metal [C]: 4.05%, blowstop [C]: 0
．． From 20%, calculating [C] that reacts with top-blown oxygen is as follows.

880 x (4,05-0,20)/12-282.
3 Kmol From the above relationship, the calorific value in the above formulas (3) and (4) when the co gas concentration in the furnace gas is 90% and the CO2 gas concentration is 10% is as follows.

33.0xlO' x282.3xO,9+99.5
xlO" x282.3x O, 1-11, 19X
On the other hand, the CO gas concentration in the furnace gas is 89
%, when the CO2 gas concentration is 11%, the above formula (3
), the calorific value in (4) is calculated as follows.

Therefore, the increase in calorific value caused by a 1% increase in the Co2 gas concentration in the furnace is 11.38 XIO'-11,19XIO'-0,1
9X10' (in cal), and the amount of temperature rise caused by this increase in calorific value is.

In addition, under the above experimental conditions, the following relationship was obtained: [1% increase in CO concentration] = [9.5°C increase in molten steel temperature], but these relationships depend on the shape and capacity of the converter, and the top-blowing lance. Since the relationship between the CO2 concentration increase and the molten steel temperature increase is determined in advance for each converter to be applied, and the CO2 concentration in the furnace is measured during blowing operation, the relevant By converting the concentration change into the amount of temperature increase in molten steel, it is possible to accurately determine the fluctuation in molten steel temperature due to secondary combustion.

Therefore, by incorporating the amount of molten steel temperature rise caused by the change in CO2 concentration as one of the dynamic control elements for the blowstop temperature, and adding operations such as adjusting the amount of coolant according to the change, the blowstop temperature can be controlled. Accuracy can be significantly increased.

[Example] The following standard converter blowing conditions were set, and the continuous accuracy of the blow-off temperature was compared when the conventional method and the method of the present invention were combined.

Standard converter blowing conditions〉 Converter capacity: 88 Ton/C8 hot metal [C
: 4.05% Blowing stop [C] : 0.20% Top blowing oxygen amount: 350ONm'/ch Lance height: 2.2m Blowing time = 15 minutes Target blowing stop temperature: 1660℃ Close blowing temperature control method 〉 Conventional method: Static control that calculates the oxygen supply amount and coolant consumption based on initial conditions such as hot metal conditions, hot metal blending ratio, auxiliary raw material consumption, and blow-off target), blow-off by sampling during blowing, and temperature measurement. Dynamic control method that improves accuracy The method of the present invention Continuously measures the CO concentration of the two converter exhaust gas to determine the CO concentration inside the furnace, and calculates the amount of molten steel temperature rise determined from the CO concentration using the conventional dynamic control method described above. The amount of coolant (iron ore) input was adjusted.

We conducted 15 batches of blowing experiments for each of the conventional method and the method of the present invention, and determined the successive accuracy (σ) of each blow-stop temperature.
When calculated, σ = 10.3 using the conventional method was reduced to σ = 9.5 by adopting the method of the present invention.
The effect of improving accuracy for σ=0.8 was confirmed.

Next, adjust the lance height to 22CO for 10 minutes from the start of blowing.
mm, 16COml1 from 1-0 minutes until the end of blowing
When comparing the blow-stop temperature matching accuracy in the same manner as above except that the temperature was changed to A high degree of accuracy was obtained.

From these experiments, according to the method of the present invention, it was possible to obtain stable and high blow-stop temperature control accuracy not only when the lance height was kept constant, but also when the lance height was changed during blowing. In actual blowing operations, it is essential to change the lance height in order to control CaO slag formation and reduce the amount of T-Fe in the slag. The method of the present invention, which can obtain a high level of blow-off temperature consistency accuracy despite fluctuations, can be said to be very suitable for practical use.

[Effects of the Invention] The present invention is configured as described above, and by controlling the temperature including the effect of increasing the temperature of molten steel due to the secondary combustion heat of CO generated in the blowing process, it is possible to improve the continuous accuracy of the blow-off temperature. can be significantly increased. □As a result, there is no need to set the blow-off temperature to a high level, which not only suppresses converter melting and extends its life, but also eliminates the need for reblowing due to insufficient blow-off temperature. , significant benefits can be enjoyed from both the equipment and operational aspects.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between lance height and in-furnace CO concentration, and FIG. 2 is a graph showing the relationship between in-furnace CO concentration and thermal effect.

Claims (1)

[Claims] When performing converter blowing, the CO_2 gas concentration in the converter is estimated by measuring the CO_2 gas concentration in the converter exhaust gas, and the molten steel temperature increase effect calculated from the CO_2 gas concentration is used to calculate the blow-off temperature. A converter blowing control method characterized by incorporating the blow-stop temperature into a converter blowing control method.