US3779744A

US3779744A - Modification and improvement to dynamic bof control

Info

Publication number: US3779744A
Application number: US00241416A
Authority: US
Inventors: L Matteson; N Carlson
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1972-04-05
Filing date: 1972-04-05
Publication date: 1973-12-18
Anticipated expiration: 1990-12-18

Abstract

A method is disclosed for dynamically controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas to provide a desired final carbon level utilizing instantaneous values of carbon-oxidation rate to determine the end of the blow.

Description

United States Patent Matteson et al.

[ Dec. 18, 1973 MODIFICATION AND IMPROVEMENT TO DYNAMIC BOF CONTROL Inventors: Lucius G. Matteson, Pittsburgh;

Norman R. Carlson, Export, both of Pa. 1 Assignees Westinghouse Electric Corporation,

Pittsburgh, Pa.

Filed: Apr. 5, 1972 Appl. No.: 241,416

Related US. Application Data Continuation of Ser. No. 855,596, Sept. 5, 1969, abandoned.

US. Cl. 75/60, 75/59 Int. Cl. C2lc 5/30 Field of Search '75/59, 60

Primary Examiner-L. Dewayne Rutledge Assistant Examiner-Peter D. Rosenberg Att0rrzey-F. H. Henson et al.

[57] ABSTRACT A method is disclosed for dynamically controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas to provide a desired final carbon level utilizing instantaneous values of carbonoxidation rate to determine the end of the blow.

13 Claims, 4 Drawing Figures CONTROLS FOR .1

OXYGEN FLOW DISPLAY OXYGEN LANCE 3,? 140 AND COOLANT ADDITION DIGITAL COMPUTER SYSTEM T 22\ J34 OXYGEN FLOW, PRESSUREJEMPERATURE,

CHARGE WEIGHT, BATH BLOWING CONDITIONS, GAs TEMPERATURE TARGETHNAL TEMP." FLOW DETECTOR AND C (FeO) etc. L

ACTUAL CONDITIONS FROM 32 PREVIOUS HEATS 25 23 30 {3 r r as C02 H20 0 co BASIC OXYGEN FURNACE MODIFICATION AND IMPROVEMENT TO DYNAMIC BOF CONTROL This is a continuation, of application Ser. No. 855,596 filed Sept. 5, 1969.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to steel-making processes and more particularly to improved methods for dynamic control of the carbon content and temperature of the steel bath in a top blown oxygen steelmaking converter such as the basic oxygen furnace (BOF).

2. Description of the Prior Art It may be explained that in the basic oxygen steelmaking process, a lance is controllably positioned to feed a controlled amount of oxygen into the basic oxygen vessel principally for the purpose of heating and decarburizing the metal bath. Since carbon level significantly effects the properties of steel product, it is necessary that the carbon level of steel made in the BOF be controlled as in the case of other types of steelmaking furnaces and further that the carbon control be compatible with other BOF controls such as endpoint temperature control placed on the bath. By the term carbon level, it is meant herein to refer to the weight percentage of carbon in a quantity of steel. By the term carbon content, it is meant herein to refer to the weight of carbon in a quantity of steel. When the weight of a quantity of steel is known, the carbon content can readily be determined from the carbon level and vice versa.

In commercial practice, it is desirable that carbon level and temperature control be effective during the BOP steelmaking process to produce specified carbon level steel at the desired temperature at the process endpoint. By the terminology process endpoint, it is herein intended to refer to a point in time just prior to vessel turndown usually about 25 to 30 minutes after oxygen blowing begins.

Various methods have been developed in an attempt to effect carbon level and temperature control during the BOP steelmaking process. One recently developed process is disclosed in US. Pat. No. 3,377,158 entitled Converter Control Systems and Methods. As the present invention is an improvement of the methods disclosed in that patent, said patent is hereby incorporated by reference herein.

Briefly and with reference to FIG. 3 of the drawings, the method of control disclosed in said patent generally involves determination, preferably by a computer, of values of carbon-oxidation rate d) for the heat being controlled through the flat portion of the illustrated decarburization rate versus carbon level curve. There is a basic assumption that at low levels of remaining bath carbon there is an exponential relationship between the value of carbon-oxidation rate, as calculated by a computer, and the remaining bath carbon content. The carhon-oxidation rate continues to be determined into the dynamic fall-off region of the curve until the instantaneous value of carbon-oxidation rate descends to approximately eight or nine tenths of the value of the horizontal asymptote, i.e., at point t,

The computer then uses determined carbonoxidation rate values and curve-fitting techniques to project a carbon endpoint curve, that is the remaining end portion of the carbon-oxidation rate curve. The computer then calculates from the projected curve end portion the amount of additional oxygen needed to reduce the present bath carbon level to the desired endpoint or target value C Next the computer predictively calculates the increase in bath temperature that will result from blowing the amount of oxygen predicted for reducing the carbon level to the target value C At this time, the bath temperature is recorded by an immersion thermocouple and this temperature plus the rise in temperature predicted from the additional oxygen to be blown is the predicted bath endpoint temperature when endpoint carbon C is reached. if this projected endpoint temperature is acceptable the blow continues as scheduled; if, however, the predicted endpoint temperature is off-target, the computer recommends corrective actions. If, for example, the molten steel is expected to be colder than desired when the endpoint carbon content is reached, the computer advises blowing additional oxygen to generate additional heat, and it calculates the quantity of additional oxygen needed to reach target temperature. If, on the other hand, the predicted endpoint temperature at endpoint carbon C is too high, the computer calculates not only the additional amount of oxygen required to reduce the endpoint carbon level to C, but also the amount of coolant needed to reduce the temperature to the target temperature. The coolant, usually limestone, is added to the BOP during the remainder of the blow.

The dynamic control method just described estimates oxygen volume to blow down to the target carbon C from an estimate of current carbon level in the bath which is made at a relatively high carbonoxidation rate value, i.e., at 1,. The accuracy with which the endpoint carbon level can be controlled is accordingly materially limited by the extent to which the actual end portion of the carbon-oxidation rate curve deviates from the end curve portion predicted from the relatively high carhon-oxidation rate value.

SUMMARY OF THE INVENTION The present invention provides a method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas comprising the steps of determining the content of carbon and oxygen compounds in the waste gases per unit of time throughout the blow and flow of waste gases, determining the amount of oxygen blown per unit of time throughout the blow, determining from the preceding two determinations successive values of carbon-oxidation rate over a predetermined portion of the blow after carbonoxidation rate fall-off, determining successive values of bath carbon level from the successive values of carbonoxidation rate, and terminating the blow of oxygen containing gas at the point in time at which it is determined from the carbon-oxidation rate values that the carbon level of the bath has fallen to the desired value unless predetermined conditions direct otherwise.

Preferably, the final temperature may be fixed by making a temperature reading of the bath at a preselected point in the blow, calculating the bath endpoint temperature on the basis of the temperature reading and the carbon level in the bath as the carbon level is determined, and when required, adjusting the point of termination of the blow and supplying a coolant to control the endpoint temperature to the desired level, said coolant preferably being free of material that would otherwise supply carbon to the bath.

The present invention, therefore, provides a method utilizing successive values of carbon-oxidation rate to determine successively better predictions for the end of the oxygen blow. Practice of the invention tightens the limits within which carbon level can be controlled in an accurate and efficient manner which is compatible with other BOF process controls such as endpoint temperature control placed on the bath.

BRIEF DESCRIPTION OF THE DRAWINGS A complete understanding of the invention may be obtained from the foregoing and the following description thereof, taken together with the appended drawings, in which:

FIG. 1 shows a basic oxygen furnace with an oxygen lance;

FIG. 2 shows BOF control apparatus for carrying out the invention;

FIG. 3 shows a curve of decarburization rate versus carbon; and

FIG. 4 shows a curve of carbon oxidation rate versus carbon level, illustrating the diminishing effect of 4; value noise on carbon level as the carbon level diminishes.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings wherein like reference numerals refer to like parts throughout the several views, there is illustrated in FIG. 1 a basic oxygen furnace of conventional design provided with a hood l2, ducting 14 leading to stacks (not shown), a vertically movable lance l6 and a coolant supply hopper 18. As shown in FIG. 2, a gas flow meter is provided, usually on the stacks, to determine by measurement the rate of waste gas flow. This rate is fed by line 22 to a programmed digital computer system 24.

Gas analyzers

26, 28, 30 and 31 are used for determining the C0, C0 H 0 and 0 content of the waste gases. The results of the analysis are fed to the computer 24.

A bath temperature or a continuous series of bath temperature readings can be made by a bath temperature detector 32. The detector 32 may, for example, be a device known in the trade as a bomb thermocouple when only one temperature reading is to be made or it can be a sheathed protected thermocouple when a series of temperature readings are to be made. Readings from the detector 32 are fed by line 34 to the computer 24.

Conventional instrumentation shown as block 36 is provided for automatically determining and feeding to the computer 24 the oxygen flow rate, pressure and temperature and for manually or automatically feeding the determined blowing conditions such as target temperature and target carbon. The computer 24 is programmed to supply the final data to display and printout iinstruments as indicated at 38 and 40, respectively. If desired, coolant source controls and oxygen lance positioning controls and oxygen flow controls can be computer operated as indicated by the reference character 41. Those skilled in the art will understand that the apparatus thus far described is conventional.

A brief outline of the manner heretofore utilized in operating such equipment will aid in the understanding of the present invention and the manner in which the present invention, departs from the prior art, and more specifically the manner in which the invention departs from the above-mentioned U.S. patent.

Outline of Prior Art Practice The required data generated in real time for the heat which it is desired to control and which is fed ,to the computer is essentially that data required to calculate the carbon-oxidation rate In order to calculate the carbon-oxidation rate (11 measurements are made of (l) the content of carbon and oxygen compounds in the waste gas for a given period of time and (2) the amount of oxygen blown during the same period of time. By dividing the measured carbon content of the waste gas per unit of time by the amount of oxygen blown per unit of time, the carbon-oxidation rate 4) is determined. As is known, the functional relationship between the carbon-oxidation rate d) and the carbon content of the bath is as shown in Equation (1):

where:

4) is the carbon-oxidation rate in points carbon /1 ,000

SCF of oxygen;

0:, B and 'y are parameters; and

C is the carbon level in the bath.

The graph shown in FIG. 3 is a typical example of a member of a family of curves of carbon-oxidation rate to carbon level of the bath for a furnace. The parameters a, B and 'y have unique values for any particular curve. To implement computer control it is necessary to determine which carbon-oxidation carbon content curve is being followed during the progress of refining. Once this is done, a measured value of da can then be used by the computer to calculate a corresponding value for C and the volume of oxygen to move from the calculated carbon level to the desired endpoint carbon level.

A number of techniques have been developed to forecast, in real time, values of a B and y for the heat under control. Briefly, one technique relies on the facts that the decarburization curve intercepts the carbon axis at a relatively fixed value, and that a the asymptotic value of the curve, can be determined during actual refining. The value of the variable 'y can then be determined at time t from the ratio of the first derivative to the second derivative of the equation of the curve. This briefly outlined technique is more fully set forth in the above-mentioned U.S. patent.

Having determined at I, the values of a B and y for the heat it is desired to control, the computer uses Equation (1) and measured (b at t, to calculate C at 1,. Integrating the relation between bath carbon and carhon-oxidation rate (Equation 1) over the limits from the determined value of bath carbon level at t, to the desired final value (C produces the volume of oxygen which must be blown in order to arrive at the desired final carbon concentration. Under prior art practice, this volume of oxygen is then blown unless temperature corrective control action is required.

The dynamic control method just described is commercially effective but it is characterized with deficiencies including the following:

I. The single determination at time t, of the carbonoxidation curve (for the heat it is desired to control) is inaccurate, because not enough of the fall-off portion of the curve has been observed, with the result that determination of the parameter at I, is imprecise. From Equation (1 it is evident that imprecision in 'y generally causes imprecision in the calculation of C from measured d) and in particular this is so at time t,. Equation (2) illustrates the error in C at t, which is causedby an error in estimating at z,

where:

A C is the error in carbon level in weight percent; A y is the error in estimating the true value of y y is the true value of 'y for heat being followed; a is the true value of a for heat being followed; and 4) I is the value of d) at t, Since 4) at t is approximately 0.85 a and y at-this point typically is approximately 4.5, it follows that:

A C/A 'y l/(4.5) ln(0.l5) l.9/20.25 0.0938

Thus, a percent error in 'y (A 'y 0.45) causes an error in C of 0.042 weight percent at time t,

2. Having determined the values of 'y and C at time t the described method thereupon proceeds to estimate the volume of oxygen necessary to move from the carbon level at t, to the target level C Inaccuracy in determining 'y at t also affects the estimate of oxygen volume required to reach C as shown by Equation (3):

the symbol A preceding a character indicates the error in estimating its value and those characters not preceded by the A symbol are true values for the heat being followed;

C is the intercept of the carbon-oxidation rate curve with the carbon level axis.

A set of typical values which are seen in daily operation of the BOP process are as follows:

Substituting these values in Equation (3) gives the following:

Am/A 10 101728 17, 230.

' any), no utilization is made of (11 values which occur between t and endpoint. Thus, the method ignores those 4) values which otherwise would contribute to more accurate estimates of the y parameter as well as more precise determinations of current bath carbon level. Greater precision in the determinations of current bath carbon level result from the fact that d) noise causes less carbon estimation inaccuracy as carbon level decreases as is illustrated in FIG. 4. It can be seen from FIG. 4, that with incertainty in d) determinations caused by noise, bath carbon levels are more accurately calculated as the bath carbon level diminishes.

4. Utilization of any carbon-bearing coolant such as limestone during the blow affects the measured values, thereby rendering them useless for indicating more accurately the carbon-oxidation curve for the current heat or for indicating the current bath carbon level. In this sense the method is self-defeating, as it destroys the very information which otherwise would improve the control of target carbon level and temperature.

DESCRIPTION OF THE METHOD IN ACCORDANCE WITH THE INVENTION In the present invention the computer 24 is programmed to calculate d) values from process measurements in the manner previously described. More beneficially, however, calculation and storage of (b is performed at the end of each of successive data sampling intervals, preferably every 5 seconds through the blow. At time t,, the 'y parameter is estimated (the a parameter is determined by averaging values of (I) previously observed for the heat it is desired to control, and the B parameter is established by the fixed intercept of the d) curve with the carbon axis). Having made an initial estimate of 'y the computer estimates the volume of oxy' gen to endpoint, and the temperature at endpoint, and recommends an amount, perhaps zero, of substantially non-carbon-bearing coolant such as scrap or iron ore.

Because non-carbon-bearing coolant is used, values of (b which are calculated after 2, and preferably throughout the remaining part of the blow period, continue to provide valid process information particularly regarding -y and bath carbon level. Each new value of d) after time t is used in conjunction with those already recorded to provide an increasingly more precise determination of 'y and thus an increasingly more precise indication of bath carbon level. Thus, it is preferred as already indicated that ii; calculations and carbon level estimations be made throughout the blow, although such calculations and estimations can be terminated at a point in time between t and the end of the blow. If the last carbon level estimate occurs between 1 and the end of the blow, the remaining oxygen volume calculation associated with the last carbon estimate would ordinarily be used to define the point in time at which the blow is ended for predicted attainment of target carbon level.

In order to implement the redetermination of upon receipt of each new qS value, let:

(I) t observed value of (b at time 1,;

qb, first observed value of (b one sampling interval after t 4) n nth observed value of 5 n sampling intervals after t, Then from Equation (1):

11) t a [38 m 4), a Be +pe n. Consider d) t, and 5, where da is the value of d: observed m sampling intervals after t but before (1) hence:

In(zbt z, 1 mo:)=-y(C, C,,,). 4

In Equation (4), 1 and (11, are observed by the computer, and a is known for the heat it is desired to control by averaging observed values of 5 prior to the falloff region of the curve. Equation (4) indicates that each time a new value of (b is observed, a new updated estimate of -y is available provided that the difference in carbon levels (C, C,,,) is known. Because the computer records waste gas flow and content of carbon compounds (C0, C0 it is therefore programmable to calculate the difference in bath carbon level between any two points of time by calculating the amount of carbon removed in the waste gas between the same two points of time. The computer forms in its memory a table of observed d) values and corresponding bath carbon level differences as follows:

(1) t, no entry An entry is made in this table at the end of each sampling interval. The computer makes entries until the heat reaches endpoint.

Although each pair of values in the table provides an estimate of'y through Equation (4), a more meaningful estimate can be made by means of the least squares method, which uses all value pairs from t to the most recent entry. Thus, if the most recent entry in the table is the Kth, then 'y is given by Equation (5);

At the end of each sampling period, the computer enters a new pair of values in the table, advancing K by one unit, following which it employs Equation (5) and all value pairs to date (up to and including the Kth) to redetermine y Then the carbon-oxidation curve and the new observations of da are used to calculate both the current bath carbon level and the oxygen volume to target carbon. These values are displayed to operating personnel. When the calculated oxygen volume to target carbon reaches zero or when the calculated bath carbon level reaches the target value, the oxygen blow is terminated in accordance with the preferred practice of the invention.

An important feature of the invention is that the carbon-oxidation curve parameter 7 is redetermined at the end of successive sampling intervals from I to a subsequent time point in the blow and preferably to the end of the blow, with the result that each redetermination considers yet another value in the fall-off portion of the carbon-oxideation curve, yielding estimates of y of ever increasing accuracy, and sharply contrasting with the prior art practice which estimates 7 only at time 2,. Utilization of 11 values, observed in the dynamic fall-off portion of the carbon-oxidation curve after t, for determination of y values of ever increasing accuracy illustrates that the method of the invention enables computer control of the BOP without reference to past vessel history as is the practice of the prior art. Because the current bath carbon level is estimated at the end of successive sampling intervals the estimates become increasingly more accurate due to the increasing accuracy ofy and due to the lower sensitivity of bath carbon level to (b value noise as the carbon level diminishes as pointed out above with reference to H6. 4. Therefore, endpoint chemistry and particularly endpoint carbon level is made more accurately controllable.

At the end of each sampling interval after time 1,, the newly determined carbon-oxidation curve yields a new and more accurate estimate of the time of the forthcoming end of the blow. Therefore, it is useful and desirable to display, after each redetermination of 'y for operating personnel not only the current bath carbon level and volume of oxygen to target, but also the forecast temperature when target carbon level is reached, basing said temperature forecast on a single temperature measurement made at a preselected time (prior to t,), on the cooling effect of the non-carbon bearing coolant recommended at t,, the size and makeup of the bath and on the volume of oxygen elapsing between the time of the preselected temperature measurement and the time of the newly forecast endpoint. Displays of current carbon level, oxygen volume to target and temperature at target, are updated each time a new (i) value is observed after t,, so that operating personnel are cognizant of the most accurate indicators of the state of the metal bath. If a new temperature prediction based on the current carbon endpoint prediction shows that coolant or added heat is needed to reach the target temperature, a new temperature corrective action is preferably determined by the computer and it is taken during the remaining part of the blow or, if desired in the case of a coolant addition action which takes about 15 to 20 seconds to perform and about 1 /2 minutes for coolant dispersion, after the termination of the blow and prior to actual bath temperature measurement after the blow. In many cases, temperature corrective action involving an extended oxygen blow would take precedence over target carbon requirements, i.e., the heat would be accepted at target temperature with low but correctable carbon level. r

With regard to endpoint temperature control it is also possible in accordance with the invention to make more than one discrete bath temperature measurement, or to measure the bath temperature continuously, by means of a sheathed thermocouple, for example. In either case, the temperature forecasting for target carbon level is based on the most recent measurement of bath temperature and on the elapsed oxygen volume between the time of said most recent temperature measurement and the time of the newly predicted carbon endpoint. Accuracy of predicted temperature at target carbon is substantially increased by making temperature measurements at preselected points between t, and endpoint, as opposed to the single preselected point before It is within the spirit of the invention to measure the bath temperature endpoint by means of a bombthermocouple, thermocouple lance, or any other temperature measuring device which is capable of measuring bath temperature with the vessel upright. This eliminates the loss of production time involved in rotating the vessel to enable insertion of the standard dip-type immersion thermocouple customarily used in the iron and steelmaking industry. It is also within the spirit of the invention to enter the measured endpoint temperature into the computer either automatically or mechanically, after which the computer calculates additional oxygen if the bath temperature is low, or additional coolant if the temperature is high. Control of'oxygen or collant addition may be under operator command or it may be under computer control as indicated bythe reference character 41.

It has been determined that practice of the dynamic control method of the above-mentioned US. patent has improved the process control in a BOF by more than two to one; that is twice as many heats reach the desired endpoint temperature and carbon content'without reblowing. By the use of the method of the present invention, even higher efficiency and productivity can be expected since successive instantaneous values of carbon-oxidation rate are utilized during the fall off of the carbon oxidation rate to make successive projections of the end of the oxygen blow with increasing accuracy. This contrasts with the prior art method of estimating the required oxygen volume to blow down to the desired endpoint carbon level from an estimate of bath carbon which is determined from a carbon oxidation rate value made at a relatively early process time point.

The foregoing description has been presented only to illustrate the principles of the invention. Accordingly, it is desired that the invention not be limited by the embodiment described, but rather, that it be accorded an interpretation consistent with the scope and spirit of its broad principles. What is claimed is:

1. A method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas, said method including the steps of:

measuring the content of carbon and oxygen compounds in the waste gases per unit of time during the blow;

measuring the amount of oxygen blown per unit of time during the blow;

determining from said content of carbon and oxygen compounds and said amount of oxygen a plurality of successive values of carbon oxidation rate over at least a predetermined period after carbon oxidation rate fall off and substantially up to the termina- 4 tion of the blow;

determining a plurality of successive values of bath carbon level difference respectively corresponding to said successive values of carbon oxidation rate;

determining from said plurality of carbon oxidation rate values and said plurality of carbon level difference values at least one value of carbon level of said bath; and

controlling the blow of oxygen containing gas to terminate when said value of carbon level of the bath has a predetermined relationship to a desired target carbon level.

2. A method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas as set forth in claim 1, wherein:

the plurality of successive carbon oxidation rate values are determined as a sampled data series of values over at least a substantial part of the carbon oxidation rate fall off period substantially up to the termination of the blow;

the plurality of successive carbon level values are determined as a sampled data series of values respectively corresponding in relation to time to the carbon oxidation rate values; and

said blow is terminated at a point in time when the carbon level value of said bath substantially equals a desired target carbon level value.

3. A method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gases set forth in claim 1, wherein said method further includes the steps of:

measuring at least one temperature value of the bath;

determining at least one bath endpoint temperature on the basis of the measured temperature value and at least one bath carbon level value; and

making any desired temperature corrective action in response to the determined bath endpoint temperature before the desired process endpoint.

4. A method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas as set forth in claim 1 wherein said method additionally includes the step of determining at least one value of oxygen volume required to reach the desired target carbon level.

5. A method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas as set forth in claim 2, wherein said method additionally includes the step of determining a respectively corresponding plurality of oxygen volume values required to reach the desired target carbon level from the determined carbon level values and carbon oxidation rate values.

6. A method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas as set forth in claim 1, wherein said method further includes the steps of:

measuring the temperature value of the bath at least at one preselected point in the blow;

calculating the bath endpoint temperature on the basis of the measured temperature value, and, making at least one bath temperature corrective action selected from predetennined actions including adjusting the carbon determined point of termination of the blow of oxygen containing gas and supplying a coolant substantially free of material that would otherwise supply carbon to the bath.

7. A method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas as set forth in claim 1, wherein said method further includes the steps of:

measuring at least one actual bath temperature during the blow;

calculating the bath endpoint temperature on the basis of said measured temperature and thecorresponding bath carbon level value; and

making a desired temperature corrective action in response to said bath endpoint temperature before the process endpoint.

8. A method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas as set forth in claim 1, wherein said method further includes the steps of:

measuring at least one actual bath temperature during the blow;

calculating the bath endpoint temperature in relation to at least said one temperature and the corresponding carbon level difference value, and making at least one bath temperature corrective action in relation to said endpoint temperature and selected from adjusting the carbon determined point of termination of the blow of oxygen containing gas and supplying a coolant to the bath.

9. A method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas as set forth in claim 1, wherein:

the carbon oxidation rate values are determined as a sampled data series of values over at least a selected part of the carbon oxidation rate fall off period and substantially up to the termination of the blow;

The carbon level difference values are determined as a sampled data series of values respectively corresponding to said rate value series; and

the blow is controlled to terminate when the carbon level of the bath substantially equals the desired target carbon level.

10. A method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas as set forth in claim 1, wherein:

the carbon level difference values are determined as a sampled data series of values respectively corresponding to the rate value series; and

the blow is controlled in response to said carbon oxidation rate values and said carbon level difference values to terminate when the carbon level of the LII bath substantially equals the target carbon level.

11. A method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas as set forth in claim 1, wherein:

the carbon oxidation rate values are used to make successively more accurate approximations of the carbon oxidation rate versus carbon content curve defined by the equation d) a B e 7 where d) is the carbon oxidation rate, a is the curve asymptote value, C is the bath carbon content, and y and B are unknown parameters and the successive curve approximations include determining a series of updated values respectively corresponding to the series of carbon oxidation rate values.

12. A method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas as set forth in claim 1], wherein the updated values of 7 are derived from equation:

4),, carbon oxidation rate value at time a.

d) 5 carbon oxidation rate value at later time n.

C carbon level value at time a.

C, carbon level value at later time n.

13. A method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas as set forth in claim 11, wherein each updated value ofy is a weighted combination of the present and all previous 7 values determined for the same heat with the use of the said equation.

Claims

2. A method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas as set forth in claim 1, wherein: the plurality of successive carbon oxidation rate values are determined as a sampled data series of values over at least a substantial part of the carbon oxidation rate fall off period substantially up to the termination of the blow; the plurality of successive carbon level values are determined as a sampled data series of values respectively corresponding in relation to time to the carbon oxidation rate values; and said blow is terminated at a point in time when the carbon level value of said bath substantially equals a desired target carbon level value.
3. A method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gases sEt forth in claim 1, wherein said method further includes the steps of: measuring at least one temperature value of the bath; determining at least one bath endpoint temperature on the basis of the measured temperature value and at least one bath carbon level value; and making any desired temperature corrective action in response to the determined bath endpoint temperature before the desired process endpoint.
4. A method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas as set forth in claim 1 wherein said method additionally includes the step of determining at least one value of oxygen volume required to reach the desired target carbon level.
5. A method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas as set forth in claim 2, wherein said method additionally includes the step of determining a respectively corresponding plurality of oxygen volume values required to reach the desired target carbon level from the determined carbon level values and carbon oxidation rate values.
6. A method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas as set forth in claim 1, wherein said method further includes the steps of: measuring the temperature value of the bath at least at one preselected point in the blow; calculating the bath endpoint temperature on the basis of the measured temperature value, and, making at least one bath temperature corrective action selected from predetermined actions including adjusting the carbon determined point of termination of the blow of oxygen containing gas and supplying a coolant substantially free of material that would otherwise supply carbon to the bath.
7. A method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas as set forth in claim 1, wherein said method further includes the steps of: measuring at least one actual bath temperature during the blow; calculating the bath endpoint temperature on the basis of said measured temperature and the corresponding bath carbon level value; and making a desired temperature corrective action in response to said bath endpoint temperature before the process endpoint.
8. A method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas as set forth in claim 1, wherein said method further includes the steps of: measuring at least one actual bath temperature during the blow; calculating the bath endpoint temperature in relation to at least said one temperature and the corresponding carbon level difference value, and making at least one bath temperature corrective action in relation to said endpoint temperature and selected from adjusting the carbon determined point of termination of the blow of oxygen containing gas and supplying a coolant to the bath.
9. A method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas as set forth in claim 1, wherein: the carbon oxidation rate values are determined as a sampled data series of values over at least a selected part of the carbon oxidation rate fall off period and substantially up to the termination of the blow; The carbon level difference values are determined as a sampled data series of values respectively corresponding to said rate value series; and the blow is controlled to terminate when the carbon level of the bath substantially equals the desired target carbon level.
10. A method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas as set forth in claim 1, wherein: the carbon oxidation rate values are determined as a sampled data series of values over at least a selected part of the carbon oxidation rate fall off period and substantially up to the termination of the blow; the carbon level differencE values are determined as a sampled data series of values respectively corresponding to the rate value series; and the blow is controlled in response to said carbon oxidation rate values and said carbon level difference values to terminate when the carbon level of the bath substantially equals the target carbon level.
11. A method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas as set forth in claim 1, wherein: the carbon oxidation rate values are used to make successively more accurate approximations of the carbon oxidation rate versus carbon content curve defined by the equation phi Alpha + Beta e C, where phi is the carbon oxidation rate, Alpha is the curve asymptote value, C is the bath carbon content, and gamma and Beta are unknown parameters and the successive curve approximations include determining a series of updated values respectively corresponding to the series of carbon oxidation rate values.
12. A method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas as set forth in claim 11, wherein the updated values of gamma are derived from equation: ln ( phi a - Alpha )/ phi n - Alpha -> gamma (Ca - Cn) where: phi a carbon oxidation rate value at time a. phi n carbon oxidation rate value at later time n. Ca carbon level value at time a. Cn carbon level value at later time n.
13. A method of controlling the refining of a bath of iron of known weight by blowing it with oxygen containing gas as set forth in claim 11, wherein each updated value of gamma is a weighted combination of the present and all previous gamma values determined for the same heat with the use of the said equation.