KR20000045516A - Method and device for predicting concentration of carbon in molten metal in electric furnace work - Google Patents

Abstract

PURPOSE: A method and a device are provided to improve precision of prediction of carbon concentration using exhaust gas data after measuring a sub-lance. CONSTITUTION: A first calibration for renewing the concentration of carbon in molten steel(1) is performed by measured data of a sub-lance(6) measured at the final stage of gas blowing while predicting the concentration of carbon in molten steel using exhaust gas data. A secondary calibration is performed by setting up the ratio of predicted decarbonization amount to the real decarbonization amount accumulated to a sub-lance measurement time from the starting of gas blowing by using a calibration parameter able to reduce measurement error of an exhaust gas model. Thereby the precision of prediction of the concentration of carbon is improved.

Description

Method and apparatus for predicting carbon concentration in molten steel in converter operation

The present invention relates to a method and apparatus for predicting carbon concentration in molten steel in converter operations.

The converter blow related to the present invention is a process of refining molten steel by injecting supersonic gas oxygen into the upper part of the molten iron using a lance to oxidize and remove impurities such as carbon, and predicting the carbon concentration in the molten steel at the end of the drilling in terms of quality and cost. very important. However, within the converter, the reaction proceeds for a very short time of less than 20 minutes, while the control factors are so numerous that advanced techniques are needed to predict the endpoint carbon concentration.

Conventional carbon concentration control methods include static control and dynamic control.

Static control is a method of determining basic operating conditions such as the amount of oxygen taken up and the amount of coolant input from the temperature and composition of the main raw materials such as molten iron and scrap metal measured before blowing.The control degree of carbon concentration in molten steel at the end of blowing is extremely low. It is rarely used alone, and often uses dynamic control together.

Dynamic control is a method of controlling the carbon concentration and temperature in molten steel by determining the injection oxygen and coolant input amount from the point of sublance measurement to the end of the blowing using the carbon concentration and temperature information of the molten steel measured by immersing the sub lance in the molten steel during the drilling. to be. In the dynamic control method using the sub lance, the calculation is performed by substituting the carbon concentration measurement value and the target carbon concentration into a decarburization formula model which is set in advance at the time of the sub lance measurement. However, the equation used in the dynamic control model is often derived from the operation experience. Therefore, when the steel grade changes, the blowing conditions change, or the input conditions of the sub-material or coolant changes, the mathematical model does not respond to this change sensitively, the degree of control is lowered. In the case of molten steel with a carbon concentration of 1.0% or less, the solidification temperature of the molten steel is closely related to the carbon concentration in the molten steel, so the carbon concentration information obtained by measuring the solidification temperature of the molten steel sample collected by the seabranes at the end of the drilling is very accurate. Do. However, because of the cost and time constraints of the probe, only one sub-lance measurement is allowed at a point in time at the end of the blow.

Among the recent dynamic control methods, there is a method of controlling the carbon concentration at the end point of the blowdown by using information on the off-gas generated during the blow, that is, the exhaust gas composition and the off-gas flow rate, in addition to the above-described sub-lance measuring method. This method is a method for estimating the carbon concentration in molten steel decarburized in a way to obtain the total amount by integrating with respect to the decarburization rate and calculate the decarburization speed by measuring the CO, CO ₂ concentration and flue gas flow in the exhaust gas to the blow time. This method has the advantage that the carbon concentration forecast is updated rapidly and continuously by the actual information for each cycle in which flue gas information is obtained, while also having the problem that the flue gas flow rate information used in the decarburization rate calculation is inaccurate. In the case of a 100 ton capacity converter, the flue-gas flow rate ranges from 70,000 to 200,000 Nm ³ / hr, which is very wide. Since the total amount of exhaust gas generated at this time reaches 40,000 Nm ³ , even if the flowmeter error is assumed to be only 0.5%, the error of carbon concentration in molten steel is ± 0.04%. It is impossible to do. In order to correct the flowmeter error, a method of statistically obtaining and applying a flow rate correction factor from the operation results has been attempted. However, the calculation method of the correction coefficient is very complicated, and even if the correction factor is calculated, it is not suitable for practical operation. It is very difficult to do.

In FIG. 1, the end point carbon concentration predicted using only the exhaust gas information is compared with the actually measured value. It can be seen that the standard deviation of the residual between the performance value and the calculated value reaches 0.035%, and the hit ratio of ± 0.02% is only about 35%.

The present invention has been studied to solve the above conventional problems, it is measured continuously at a predetermined time interval from the start of the drilling, but using a low-accuracy exhaust gas information to predict the carbon concentration in the molten steel is measured exactly at the end of the drilling The primary correction is performed to update the carbon concentration in the molten steel according to the sub lance measurement information, and the error ratio between the estimated decarburized gas and the actual decarburized gas that has been accumulated and managed from the time point of the blow time to the sublance measurement is reduced. It is an object of the present invention to provide a method and apparatus for improving the prediction degree of carbon concentration using exhaust gas information after measurement of sub lances by performing secondary correction by setting the correction parameters that can be made.

1 is a graph comparing end point carbon performance and calculated values when only exhaust gas information is used;

2 is a block diagram of the blowdown terminal carbon concentration prediction device of the present invention;

Figure 3 is a graph of the change in flue gas CO, CO ₂ concentration and flue gas flow rate during blowing,

4 is a conceptual diagram of a process of performing only the first correction and a process of simultaneously performing the first and second corrections when R _Dev >1;

5 is a conceptual diagram of a process in which only the first correction is performed when R _Dev <1 and a process in which the first and second corrections are performed simultaneously;

Fig. 6 is a table of the frequency distribution of the performance value and the calculated value residual when the first correction is performed only and the first and second corrections are performed simultaneously.

Explanation of symbols on the main parts of the drawings

1: molten steel 2: converter 3: lance 4: flue gas analyzer

5: flue gas flow meter 6: sub lance 7: flue gas hood

20: carbon concentration prediction means 21: decarburization rate and carbon concentration calculation unit from the start of the sub-lance measurement to the measurement point 22: carbon concentration update and correction parameter calculation unit

23: decarburization rate and carbon concentration calculation unit from the time of sub lance measurement to the end of blowing

24: Carbon Concentration Monitoring Screen

Hereinafter, with reference to the accompanying drawings, the present invention for achieving the above object will be described in more detail.

2 is a schematic view of the apparatus for predicting the blowing carbon concentration of the present invention. The converter facility in which the apparatus of the present invention is implemented includes a converter 2 for blowing molten steel 1, a lance 3 for injecting supersonic gas oxygen, and an exhaust gas analyzer 4 for continuously measuring exhaust gas composition every constant cycle. , Exhaust gas flow meter (5) for measuring the flow rate of the exhaust gas in the same cycle as the exhaust gas analyzer (4), sub-lance (6) for providing accurate carbon concentration information at the end of the blow, exhaust gas serving as a passage for recovering the exhaust gas to a predetermined place It is configured to include a hood (7). 2 to 20 show the prediction means of the present invention. The prediction means 20 is a decarburization rate and carbon concentration calculation unit 21 from the start of the blow to the sub lance measurement time, and the carbon concentration update and correction at the sub lance measurement time. The parameter calculation part 22, the decarburization speed, the carbon concentration calculation part 23, and the carbon concentration monitoring screen 24 from the time point of sub lance measurement to the completion | finish of blown-up are comprised.

The carbon concentration prediction method of the present invention using the above apparatus is as follows.

3 is a graph showing changes in CO and CO ₂ concentrations and flue gas flow rates in flue gas during converter blowdown. Since carbon is removed by gas in converter refining, the decarburization rate from the start of blowing to the time before the measurement of the sub lance can be expressed by the following equation.

Where t _PRE: elapsed time from blow start to the time of sub lance measurement,

: decarburization rate at t _PRE ,

W _ST (t _PRE ): molten steel weight at t _PRE ,

CO (t _PRE ), CO ₂ (t _PRE ): CO, CO ₂ concentration at t _PRE ,

k: unit conversion factor,

Q _off (t _PRE ): Flue gas flow at t _PRE .

Since the decarburization speed represented by the above formula (1) is an instantaneous value for one cycle, the decarburization speed is integrated with the refining time, and thus the total decarburization amount from the start of blowing to the present can be obtained.

Here, ΔC (t _PRE ): total decarburization amount expressed in% from the start of blowing to t _PRE .

Therefore, by subtracting the predicted decarburization amount from the exhaust gas information from the carbon concentration in the molten iron at the beginning of the converter operation, the carbon concentration represented by the following formula is derived.

C (t _PRE ) _off = C _inl -ΔC (t _PRE ) -------------------- (3)

Where C (t _PRE ) _off : the carbon concentration at t _PRE predicted from the flue gas information,

C _inl : Carbon concentration at the beginning of the converter operation.

The carbon concentration is estimated by the above equation (3) until the time before the sub lance measurement, and the carbon concentration information is obtained at the time of the sub lance measurement. The instantaneous carbon concentration prediction value is updated to the following equation (4).

C (t _SL ) _off = C _SL -------------------------- (4)

Where t _SL : sub lance measurement time,

C _SL : Sub-Lance Measured Carbon Concentration.

The actual decarburization amount from the sub lance carbon concentration from the start of blowing to the measurement point of the sub lance is represented by the following equation (5).

_{ΔC act = W C.inl -W eT (} t SL) · C SL / 100 ---------------- (5)

Here, ΔC _act : actual decarburization amount from the start of blowing to the time point of sub lance measurement,

W _C.inl : Total carbon weight at the beginning of blowing.

As can be seen from the curve (1) of FIG. 4 and the curve (1) of FIG. 5, the error of the carbon concentration prediction value is maintained until the end point of the blowing. Therefore, even if accurate information is obtained at any moment, the previous error is not included in the subsequent calculation. It continues to include. With this in mind, by comparing the actual decarburization amount with the exhaust gas decarburization amount, a correction parameter which can grasp how far the exhaust gas decarburization amount is from the actual value can be defined as in the following equation (6).

Where R _Dev : flue gas decarburization correction parameter.

If R _Dev > 1, the exhaust gas predicted decarburization amount is less than the actual decarburization amount. If R _Dev <1, the exhaust gas predicted decarburization amount is overcalculated than the actual decarburization amount. Since the error as much as the correction parameter R _Dev is maintained even after the sub lance measurement, the exhaust gas predicted decarburization amount after the sub lance measurement has a form similar to the equation (2).

Where: _POST : elapsed time from the sublance measurement to the end of the blow.

Likewise, the carbon concentration at any refining time t _POST after the sublance measurement takes the form similar to Eq. (3).

C (t _POST ) _off = C _SL -ΔC (t _POST ) ------------------- (8)

Where C (t _POST ) _off : the carbon concentration at t _POST predicted from the gas information.

In the present invention, the process of performing only the first correction based on the sub-lance measured carbon concentration and the process of simultaneously performing the second correction based on the ratio of the actual decarburization amount and the exhaust gas decarburization amount after the first correction are performed. Large and small cases are shown in Figs. 4 and 5, respectively. In addition, the accuracy of the carbon concentration prediction according to the present invention was evaluated for the 300 ton converter. A total of 97 hits of operating data were analyzed to perform only the first correction based on the sub-lance carbon concentration, and the second correction based on the ratio of the actual decarburization and the exhaust gas decarburization after the first correction. The operation results are shown in FIG. 6 as a frequency distribution table. The standard deviation of the residual, which is the difference between the performance value and the calculated value, has been greatly improved from 0.018% when performing the first correction only to 0.012% when performing the first and second corrections simultaneously, and the hit ratio of ± 0.02% at 67%. Significantly improved to 89%. In addition, the effect of reducing the carbonization agent by improving the carbon concentration hit rate, the improvement of the tapping error rate by the prevention of overdose is expected.

Claims (2)

Predicting carbon concentration in molten steel by performing sub-measurement information measured at the end of the blowing, using the flue gas information continuously measured at regular time intervals from the start of blowing, and performing the first correction, From the sub lance measurement to the sub lance measurement point by setting the ratio of the estimated decarburization amount and the actual decarburization amount to the correction parameter that can reduce the prediction error of the exhaust gas model, and performing the secondary correction to predict the end point after the sub lance measurement. A method for predicting carbon concentration in molten steel in converter operations, characterized by improving accuracy. A converter 2 for blowing molten steel, a lance 3 for injecting supersonic gas oxygen, an exhaust gas analyzer 4 for continuously measuring exhaust gas composition every fixed cycle, and a flow rate of exhaust gas are the same as the exhaust gas analyzer 4 In the converter facility comprising a flue gas flow meter (5) measured by the cycle, a sub lance (6) providing carbon concentration information in the molten steel at the end of the blow, and a flue gas hood (7) serving as a passage for recovering the flue gas to a predetermined place. In Decarburization rate and carbon concentration calculation unit 21 from the start of the blow to the sub lance measurement time, the carbon concentration update and correction parameter calculation unit 22 at the time of the sub lance measurement, and from the time of the sub lance measurement until the end of the blow An apparatus for predicting carbon concentration in molten steel in a converter operation, comprising: a carbon concentration predicting unit (20) including a decarburization rate and carbon concentration calculating unit (23) and a carbon concentration monitoring screen (24).