JPS5854170B2 - Converter control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for accurately grasping the blowing status of a converter and dynamically controlling the blowing end point.

In the converter steelmaking process, control methods to increase the carbon concentration and molten steel humidity rate at the end of blowing, as well as to obtain stable slag formation, play an important role, and many studies have been reported.

Broadly speaking, these control methods can be divided into two methods: (1) a method that uses exhaust gas information from the converter, and (2) a method that directly measures and controls the steel bath carbon and steel bath temperature using a sublance. Other control methods are also being considered.

By the way, methods (2) and (2) both have advantages and disadvantages; for example, in the former, the conventional method is said to have a limited accuracy, and in the latter, it is necessary to skillfully resolve measurement errors due to non-uniformity within the furnace. However, the disadvantage is that it is not possible to grasp the slag formation situation.

The method for achieving points (1) and (2) is expected to yield good results if both are properly combined, and the inventors of the present invention have recently established a satisfactory control method and filed a patent application.

However, in cases where a converter without a sublance has been installed (for example, a small converter or a foreign converter), or the price of a measurement probe such as a sublance is a problem, it is necessary to obtain effective information from exhaust gas analysis and utilize it. You need to get started.

The present invention was made with attention to such circumstances, and its configuration is to grasp the blowing status of the charge from exhaust gas analysis that is continuously measured at an appropriate time just before the end of blowing. The gist lies in understanding the blowing situation based on the relational expression obtained by integrating the model equation shown by .

The meaning of each symbol in these formulas is as follows.

C: Carbon cake in steel bath Co: Lower limit of carbon concentration in steelmaking reaction, generally 0
．． It can be fixed to 02.

b: Decarburization rate index determined for each charge a:
A constant given by 12FO2 (11,2X10W), where FO2 is the oxygen flow rate (Nrrinea minute) W is the weight of the steel bath at the final stage (tons) t: Time to: Appropriate time at the final stage of blowing de ψ: Given by 111 decarburization oxygen efficiency at ■−ψ P: value given by 1ln− po: P value when t=to.
Although we are developing a theory starting from the -ntial model equation, the exponent ia shown in equation (3) below
It goes without saying that a completely similar theory can be established even if starting from the I model formula.

1 (In formula (3), α, β, and γ are a, ae in formula (1), respectively)
' is a constant corresponding to yb.

) Also, regarding the decarburization trajectory in a converter, formula (1) or (
In addition to the exponential model shown in equation 3) (all symbols in the equation have the same meanings as before), are other model equations known?If based on the idea of the present invention described above and below, (4), ( A similar theoretical development can also be made from equation 5).

That is, the decarburization oxygen efficiency at the final stage of blowing (the efficiency of oxygen consumed for decarburization tends to decrease when the carbon concentration (%C) in the steel bath decreases, especially when it becomes less than 0.3 to 0.8%). (Refer to p. 157 of the 27th and 28th Nishiyama Memorial Technology Lectures "Current Status and Future Developments of Steelmaking Technology"), and the steel bath during blowing [
%C] and the changes in the decarburization rate during that time, as well as the control equations for these, various model equations have been proposed from various viewpoints (see pages 160 to 162 of the same). 1) , (3) , (4) ,
(5) can also be regarded as an approximate expression similar to these.

Now, the model equation (1) shows the relationship between ψ and C as is clear from the equation, but the chart of the decarburization rate meter obtained from exhaust gas analysis generally shows the relationship between ψ and t.

Therefore, the present inventors considered the relationship between the two and tried to derive an expression representing the relationship between φ and t from the model equation (1).

Note that in the following expansion formula, x=c Co for convenience.

is obtained, Integrating this, we get is obtained.

However, ■ is an integral constant. Using equation (6), eliminate from equation (7) and set ψ=ψ0 when t=to, but by substituting the equation P ■−ψ In− shown earlier into equation (8), ψ By entering, equation (8) can be rewritten as .

This is the basic formula that provides the relationship between ψ and t.

If we further transform equation (9), we get or Then, the formulas φ= and t= are obtained, respectively.

These are relational expressions corresponding to the chart figures of the decarburization rate meter, and by using these relational expressions, the blowing situation can be grasped extremely accurately and easily.

When processing information from exhaust gas, it is often necessary to take into account the time delay (τ minutes) required from when a phenomenon occurs in the furnace until it is detected as an exhaust gas analysis value.

However, the effect of the time delay on the ψ-t relation does not change the shape of the decarburization curve, but only causes the curve to appear delayed by τ.

In other words, there is no need to make any changes to the derivation process of the above relational expression, and the above equations (9) 2 to αυ can be used as is, but only the value of t becomes (t+τ), and the figure changes accordingly in the time elapsed direction ( (to the left in Fig. 1).

Figure 1 is a graph of the equation 0]) for the case where the oxygen flow rate FO2 is 65ONm''7 minutes and the weight W of the final stage steel bath is 250 tons, and shows the cases where b=2, 4, 6, and 8, respectively. There is.

This graph closely resembles the pattern seen in actual decarburization rate meter charts.

Furthermore, FIG. 2 is an example of a plot of P versus t taken from an actual exhaust gas decarburization oxygen efficiency chart.

A linear relationship is well established, and the relationship of equation (9) is established.

Next, we will discuss how to obtain b from equation (9).

Now, if 1=11 and 1=12, ψ−φ1 and ψ
-ψ2, then from equation (9) ab(tl-t
2)=P1-P2(12).

Here, 11-12 is the time for the drop from ψ1 to φ2, and if this is △t, then the b value (the charge It is possible to obtain the decarburization rate index).

Then ψ−ψ.

We will explain how to obtain the time required to reach target C after passing through.

First, the following equation (14) is obtained from equation (7) as an equation showing the relationship between the passage of time and the amount of decarburization.

This formula is 1=1. This shows that the carbon ridge decreased from C1 to C2 between t and t2, and Δtτ is set as
When C1 is eliminated using decarburization oxygen efficiency ψ: 1-Jb (CI-CO) (I5), the basic formula shown is obtained.

This equation is ψ observed in the presence of the time delay mentioned earlier.
This is a basic formula that expresses the simultaneous relationship between C and C, and is an advantageous formula for controlling the converter by combining sublance information and exhaust gas information.

By transforming this equation, we obtain:

If we set τ-0 in equation (17), it certainly matches the original equation (1).

When C (target) is inserted into this equation, ψ (target) when C-C (target) is obtained can be obtained.

By substituting it into equation (8), ab(t(target)-1O)=P(target)-p.

abr-13n (eb(C(target)Co))-p.

(18) is obtained.

Therefore, by using the b value obtained from equation (13), 0
8) From the formula, ψ−ψ.

The time required to reach C (target) from the point in time is calculated.

When converter control was actually performed using the α8) formula, for example, in the case of a low coal level, the results shown in FIG. 3 were obtained.

In FIG. 3, the vertical axis Y is the calculated value, and the horizontal axis X is the actual measured value at the time of blow-off.

Therefore, if it were on the line y=x, it would be σ-0, but due to inappropriate settings, it was σ-0,016.

-y- However, the apparent relational expression x=ay+b to compensate for this
can be reduced to σ=0.00979.

This error is the general error σ−0 in case of static control.
,020.

The present invention is configured as described above, and even when sublance information cannot be obtained, it has become possible to increase the association rate of carbon φ based on exhaust gas information.

However, the effects of the present invention are not limited thereto, and it has also been found that the present invention has the advantage of increasing the steel bath temperature continuity rate during blow-stopping.

That is, in general, the higher b is, the higher the decarburization oxygen efficiency is, and the combustion reaction ratio of C becomes higher than that of Fe.

Therefore, as b increases, the temperature increase rate decreases,
If a correct b value is obtained using the formula 03), it becomes possible to improve the prediction accuracy of the temperature increase rate using it.

Also, for the same reason that the higher the value, the higher the decarburization oxygen efficiency becomes, there is also the advantage that it becomes possible to grasp the slag formation situation in the converter.

In other words, the total iron content value in the slag can be used as a representative characteristic value of the slag condition, but the greater the decarburization oxygen efficiency, that is, the higher b, the lower the total iron content value. As a result, it became possible to accurately grasp the slag formation status of the charge.

Since the present invention is configured as described above, it has become possible to predict with high precision the carbon content, steel bath temperature, slag formation, etc. at the time of blow-stopping.

Therefore, it became possible to control the blow-off point, making the converter operation even more reliable.

The inventors of the present invention previously applied for patent application No. 100849/1984.
In the issue, sublance information and exhaust gas information are related,
Furthermore, we proposed a method for controlling the converter by using the differential expression of the relational expression that takes into account the time delay τ in exhaust gas information analysis.

The relational expression at this time shows the relationship of φ-C, and the basic expression is, but it can also be expressed as, and it can be further modified in various ways as shown below.

Or, especially if C at ψ-0,5 is C0,5,'
-abτ CC□= -A'n(1+e),
(23)0.5b By using these relational expressions in combination with appropriate expressions in the main text related to the present invention, even more precise control can be achieved.

Furthermore, the invention of the earlier application clarified the relationship between ψ and C, and the present invention clarified the relationship between φ and t, but as another method starting from model formula (1), ,
There are also the following methods.

That is, in the integral form of model formula (1) [formula (7)], by determining the integral constant 1 from formula (23), or (where t O,5 is the time when ψ-0,5) etc.

These show the C-t relationship and further ensure converter operation based on sublance information.

In this way, the present inventors were able to simplify the relational expressions of ψ, C, and t, respectively, and contribute to improving the reliability of converter control.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between ψ and t, FIG. 2 is a graph showing the relationship between pt, and FIG. 3 is a graph showing an example of the effects of the present invention.

Claims (1)

[Claims] 1. In order to understand the blowing situation in the charge from exhaust gas analysis measured at an appropriate time just before the end of blowing, a relational expression ab (
t-t□) -P-PO A converter control method characterized in that the blowing situation is grasped and controlled based on t-t□)-P-PO. However, C is the carbon φ in the steel bath, Co is the lower limit of carbon concentration in the steelmaking reaction, and the decarburization rate index a determined for each charge is 12 F.
A constant given by O2/(11,2X 10W), F0
2 is the oxygen flow rate (Nu" The value ψ Po given by ln is the P value when t = to