CLIAMS:1. A process for controlling the slag-metal-gas reactions in the steelmaking converter, adapted to hold a molten metal bath, through online maneuvering of a single parameter BETA, comprising of :
-blowing oxygen through a lance on to the metal bath to remove the impurities;
-monitoring the iron oxide content of the slag of the bath by monitoring means to maintain and manage the required FeO level in the slag and the physical condition of slag condition throughout the blow period by means of outgoing CO and CO2 level in gases;
-calculating the parameter BETA, which is the ratio of ((% CO2)/ (% CO+ %CO2)) at the mouth of vessel before air entrainment determined through analysis of exhaust gases by using a gas analysis probe and the ((%CO2)/ (%CO+ %CO2 )) inside the vessel on the basis of jet characteristics, nozzle design, lance height, slag condition, entrainment into the jet inside the vessel ;
- controlling the turbulence in advance by a controlling means, managing the said parameter BETA by controlling the process based on comparison of actual BETA calculated and standard BETA;
-determining the required change in the single parameter BETA used as an indication of the slag-metal-gas condition inside the vessel and the determining probability of an occurrence of rapid changes in turbulence inside the vessel;
-correcting the turbulence by monitoring the single parameter BETA at predetermined intervals on the basis of nozzle design, lance height, oxygen flow rate and the measured CO and CO2,resulting in the controlled slag-metal-gas reaction, smooth reaction, reduced slopping and dry slag formation.

2. A process as claimed in claim 1, wherein the FeO content in slag inside the vessel is related to the BETA. An increased FeO quantity (actually the increased chemical potential of FeO) leads to slopping and the less FeO quantity (actually the reduced chemical potential of FeO) causes dry blow resulting in poor dephosphorisation and increased loss of iron in dust.

3. A process as claimed in claim 1, wherein the monitoring means used to monitor the CO and CO2 level and the FeO content is any micro-processor based control system like Programmable Logic Controller, micro computer etc.

4. A process as claimed in claim 1, wherein the controlling means used to monitor the deviation in the BETA parameter is BETA control model which is used to determine the required changes in lance height, oxygen flow rate, flux and/or coolant addition by generating the alarm when the process is expected to go out of control.

5. A process as claimed in claim 1, wherein the actual BETA is based on the actual pattern of variation of BETA, the rate of change of BETA, cumulative BETA and the standard pattern of variation of BETA.
6. A process as claimed in claim1, wherein the standard BETA is determined independently for a given nozzle design, estimated amount of retained slag in vessel from previous heat, initial silicon content and initial temperature of metal.

7. A process as claimed in claim1 , wherein the required change in the addition of flux like lime, dolomite and coolants like iron ore, lime stone, dolomitic stone is decided on continuous basis by comparing the standard BETA and actual BETA pattern.

8. A process as claimed in claim 1, wherein in case when the actual BETA deviates positively from the desired BETA, above a specified margin, indicating the building up of foamy slag, the correction is done by lowering the lance heightand/or changing the oxygen flow rate, adding coolant, adding flux.

9. A process as claimed in claim 1, wherein when the actual BETA deviates negatively from the desired BETA, below a specified margin, indicating the drying up of slag, the correction is done by increasing the content of FeO through raising the lance height and changing oxygen flow rate.

10. A device for carrying out the process in the steel making converter adapted to hold a molten metal bath and slag through online maneuvering of a single parameter BETA, comprising of :
-a lance fitted with supersonic nozzle(s) for blowing oxygen on to the metal bath to remove the impurities from metal bath and to form a slag on surface;
-monitoring means to maintain and manage the required FeO level in the slag throughout the blow period by means of outgoing CO and CO2 level in gases.
-a method for calculating the ratio of the gas composition at the mouth of vessel before air entrainment and from jet characteristics and entrainment into jet within the vessel.
- a controller means for controlling the level of turbulence inside the vessel in advance and managing the said parameter BETA for controlling the process based on comparison of actual BETA and standard BETA,
wherein the required change is determined by the single parameter BETA being used as an indication of the slag-metal-gas condition and the probability of rapid changes in turbulence inside the metal bath, and for correcting the turbulence by monitoring the single parameter BETA at predetermined time intervals on the basis of nozzle design, lance height, oxygen flow rate and the measured and CO2 in gas at the mouth of the vessel with a gas analysis probe resulting in controlled slag-metal-gas and smooth reactions.

11. A device as claimed in claim 10, wherein the monitoring means used to monitor the CO and CO2 level and the FeO content is any micro-processor based control system like Programmable Logic Controller, microcomputer etc.

12. A device as claimed in claim 10, wherein the controlling means used to monitor the deviation in the BETA parameter is BETA control model which is used to determine the changes necessary in lance height, oxygen flow rate, flux and coolant addition(s) by generating the alarm when the process is expected to go out of control.
,TagSPECI:Field of Invention:
The present invention relates to a process for controlling the slag-metal-gas reactions in a steel making converter comprising of at least one blowing lance, fitted with supersonic nozzle(s) at its tip, which is placed above the surface of the bath at a distance whose height is controlled by a single parameter “BETA” that includes all the measured parameters of outgoing gases like concentration of CO, CO2, H2 ), waste gas flow rate and design parameters of lance used like nozzle design, lance height, oxygen supply rate.
Prior Art:
Prior to this, there was no way to assess the mass of carried over slag and of retained slag already present in the refining vessel, before the start of refining. Also there was no way to assess the condition of slag during refining, except by visual observations. As soon as the refining starts, the body of the lance begins to receive thermal radiation from surfaces of refractory lining inside the vessel, metal and also from escaping gases. The heat received from slag is affected by the physical condition, mass and temperature of slag. Due to jet impact, slag is thrown up and a part of it may become deposited on the lance surface. It is required to have some technology of using the lance surface itself as sensor and thereby as a means of estimating the mass, temperature, and condition of slag at the start of refining operation as well as during the refining operation.
The mass, temperature and composition of slag affect the composition, mass and temperature of metal and exhaust gases, and vice versa. Since the refining process is highly turbulent and sometimes becomes chaotic especially due to the condition of slag itself, an improved technology is needed to control the refining operation such that slag formation is proper and no abnormalities take place. Also, the aim temperature and composition windows should be met at the end of refining. An improved control technology is needed to meet these requirements.
A technology is also needed to decide the aim temperature and composition window themselves at the end of refining operation. This is actually related to the grade of steel to be cast, ladle condition, intermediate processing and the time it would take for the casting to actually start after the steel has been refined and delivered to the caster. Huge temperature drop takes place during tapping of steel. Temperature drop also depends upon the thermal state of the ladle in which steel is tapped and transported, and intermittent operations of secondary metallurgy. Thus, to decide the right temperature window it is necessary to bind the operations of refining with ladle condition, else the advantages of improved refining would be lost.
US Patent No.US5028258 teaches an operation of a top-blowing steelmaking converter having at least one blowing lance, the distance of the said lance from the surface of the molten metal bath is controlled as a function of the sound levels of the blowing noise measured at selected frequencies. In order to minimize the risk of slopping, the actual values of the sound levels measured at predetermined frequencies are combined to form a resultant value, the difference between said resultant value and a predetermined reference value, which is associated with a sound level and indicates that slopping is likely to occur, is determined, and the said difference is used as an indication of the probability of an occurrence of slopping and is compared with at least one predetermined probability limit, the distance of the blowing lance and also, optionally, the oxygen supply rate is corrected when the said difference exceeds the said probability limit.
Drawbacks of the conventional process:

1. Physical loss of metal and slag due to uncontrolled throwing of slag and metal resulting in lower yield.
2. Eventual disruption of the process and consequent increase in processing time leading to loss in production.
3. Required temperature not being attained in the desired range (temperature window) at the end of refining.
4. Required concentration of impurities C, Si, Mn, S, P, etc., not being attained in the desired range (composition window) at the end of refining.

Object of the Invention:
The object of the present invention is to provide a comprehensive technology to:
(a) Predict the slag condition during and at the end of refining operation by using lance body as one of the tools of assessment.
(b) Suggest and also implement necessary control actions based on slag condition.
(c) Control and steer the refining process in the right direction of achieving the desired temperature and composition windows at the end of refining, by avoiding unfavorable conditions of uncontrolled ejections and emissions from the vessel.
(d) Decide the aim temperature window at the end of refining operation on the basis of grade of steel and thermal state of the ladle in which liquid steel is to be tapped and transported.

Summary of the invention
Oxygen is blown from the top in Basic Oxygen Furnace (BOF), or converter, or its several variants to refine the hot metal containing various dissolved elements like C, Si, Mn, Ti, V, P, S, etc. While the carbon dissolved in hot metal escapes as CO and CO2 in the waste gas, the elements like Fe, Si, Mn, Ti, V and P are stored in the slag as oxides. A small amount of iron which is oxidized or vaporized from the jet impact region escapes as oxide fume. The total amount of iron lost in this manner is usually less than 10 kg/ton of steel weight for an efficiently operated process. For an inefficient process, in which slag formation is not properly controlled and slag dries up, the iron loss in the form of fumes can be as much as 25–35 kg/ton of steel. In addition to vaporization and oxidation of iron in the jet impact region, metal and slag droplets are produced due to the impact of oxygen jets on the metal bath (hot spot). Very fine droplets of metal and slag can be carried away directly from the hot spot along with the waste gasses. Under certain conditions, the slag mixture is also deposited on the mouth of the converter and on the lance. When the deposit on the lance becomes excessive then the deposit (skull) has to be removed or the lance has to be replaced by a new one. This process may consume additional production time. Similarly, the deposits on converter mouth (called mouth jam) have to be removed from time to time because they affect the pressure inside the BOF vessel and the escaping gas velocity at the mouth of the converter, and hence the dust losses which may increase with decrease in mouth diameter. Retention or capture of gas bubbles in the slag causes slag foaming. It is necessary to avoid excessive foaming of slag, else the slag foam may rise, reach up to the mouth of vessel and then flow out of vessel. This is called slopping which should be avoided completely because it leads to physical loss of material from vessel, thereby reducing yield of the process and also causing several related operational problems. It is said: “Good slag making is good steel making.” It is important to properly control slag formation and also to be able to (a) predict the possibility of slopping in advance and (b) suggest necessary measures to avoid slopping.

The progress of slag formation in a BOF can be understood, predicted, and controlled through visual observations as well as through interacting effects of several input and output blowing parameters like: waste gas flow, waste gas temperature, waste gas composition, lance height, oxygen flow rate, addition of fluxes like lime and dolomite, addition of coolants like iron ore, sinter and scrap, sound generated in vessel (audio measurements), difference of exit lance water temperature and cooling (inlet) water flow rate in the lance. The behavior of all these parameters also depends on the type and dimensions of nozzle tip, condition (life) or geometry of the vessel, oxygen flow rate, capacity of vessel, and mass of slag and metal. Thus, the process of slag formation is very complex and is dependent on many parameters. Here comes the necessity of identifying a single parameter through which all the available and vital parameters can be understood and factored for an efficient control of the process.

Detailed Description of the Invention
The present invention provides a technology of control based on a single parameter ‘BETA’ that includes interactive effects of all above stated output and input blowing parameters so as to indicate the condition of the slag throughout the process and suggest the necessary lance height corrections and adjustments in oxygen flow rate, addition of fluxes and coolants for efficient process operation. Predictions of slag condition can be made much earlier before the slag condition deteriorates, either leading to slopping or to drying up of slag. It also predicts the desired mass input materials and the final mass, temperature and composition of final products obtained.
In a well controlled and smoothly operated process, the amount of ferrous oxide (FeO) in the slag during the blow and so also the pattern of waste gas flow and composition should follow a definite pattern. The FeO formation starts almost at the start of the blow and rises rapidly to its peak level during the de-siliconization period. Thereafter it starts coming down gradually to its lowest level due to decarburization and then again rises gradually to its required level by the end of the blow when carbon level in the metal has come down.
A variety of reactions between essential elements, for example, C, Fe, Si and O take place simultaneously, in forward or backward direction, depending upon the conditions at several locations within the system:

FeO + ½ Si = Fe + 1/2SiO2 ?GFeO-1/2 Si
(CO2) + [C] = 2(CO) ?GCO2-C
(CO) + ½[Si] = ½(SiO2)+ [C] ?GCO-1/2[Si]
(CO2) + [Si] = (SiO2) + [C] ?GCO2-[Si]
(CO2) +1/2 [Si] = ½(SiO2)+ (CO) ?GCO2-1/2Si
[C] + [O] = (CO) ?G[c]-[O]
[C] + 2 [O] = (CO2) ?G[c]-2[O]
[O] + {Fe} = (FeO) ?G[O]-{Fe}
[O] + ½[Si] = ½(SiO2) ?G[O]-1/2Si

Actually the metal may contain many other elements besides C, Si, Fe and O, for which ?G values are considered.
The ?G values refer to free energy of reaction and are different for each reaction. The ?G values are dependent upon temperature and effective concentration (thermodynamic activity) of elements and products involved in each case. In addition to ?G values, the kinetics of reactions have also to be considered.
The CO and CO2 gases are formed during the entire blow. Part of the CO gas is en-trained in the oxygen jet and is converted to CO2. Conversion of CO to CO2 within the vessel volume is called post combustion. It also takes into account the CO and CO2 gas generated from decomposition of fluxes.
When the slag begins to foam due to the entrapment of gas bubbles in the slag, the slag height increases. In the period of peak foaming the re circulation patterns of gas, slag and metal within the vessel change significantly because a part or whole of the jet (depending upon foam height) can get submerged in the foam. Obviously, during this period the post combustion behavior and hence the BETA value changes.
Besides the entrapment of gases into the impinging gas jet(s), in the period of foaming the conversion of CO to CO2 is partially through the overall reaction
FeO + CO = Fe + CO2
Thus, the FeO content of slag partially controls the amount of CO2 produced. The extent of this reaction depends upon the physical condition, thermodynamic properties of slag, and the factors controlling the kinetics of reactions.
At any moment of process operation, for a given nozzle design, the most important factors which control the CO2 level in the outgoing gases are thus related to the FeO content of the slag, slag composition, temperature, the lance height, oxygen flow rate, temperature and composition of metal and the coolants added. Vessel design, volume, and height of metal and slag also affect the post-combustion.
The new parameter BETA is based on all the measured parameters of the outgoing gases (like concentration of CO, CO2, H2), waste gas flow and design parameters of lance used like nozzle design, lance height, oxygen supply rate. The composition of waste gases is measured at considerable distance from the vessel mouth, after some amount of air entrainment has already taken place. The composition of gas at the mouth of vessels is back calculated by considering air entrainment that has taken place on the basis of nitrogen content of gas. A Rough estimate of nitrogen is considered through purging operations The actual ratio [%CO2/(%CO2 + %CO)] at the mouth of vessel divided by the calculated ratio of [%CO2 /(%CO2 + %CO)] inside the vessel is called BETA. The calculated ratio [%CO2 /(%CO2 + %CO)] inside the vessel is obtained from jet characteristics, lance height, oxygen flow rate, nozzle design, pressure inside the vessel, slag volume, and the resulting entrainment of gases within the vessel into the jet. In the BOF process, the value of BETA changes dynamically with time in the process.
Exhaust gas is continuously analyzed. The single parameter BETA defined above is calculated regularly at predetermined intervals, on the basis of nozzle design, lance height, oxygen flow rate, and the CO and CO2 contents of gas at the mouth of vessel. The actual control of process is based both on the actual pattern of variation of BETA, the rate of change of BETA, lag or excess of BETA, change in cumulative BETA at predetermined intervals, with respect to values computed for standard pattern of variation of BETA. The standard pattern of variation of BETA is determined independently for a given nozzle design, estimated amount of retained slag in vessel from previous heat, initial concentration of impurities in metal, and initial temperature of metal. The control strategy is thus guided by comparison of actual BETA and standard BETA and therefrom determine the required changes in lance height, oxygen flow rate, amount of fluxes and coolants. The amount of retained slag from previous heat is estimated within first few minutes of the blow from heat transfer processes taking place to lance body inside the vessel. In this respect the lance body is being used as a sensor. The amount of retained slag affects the pattern of BETA.For a finer control of the process corrective actions are also suggested in flux and coolant additions and their timings based on continuous comparison of standard and actual BETA patterns.
Practically, the control strategy is implemented on the shop floor as follows. In a normal process, the value of BETA, rises quickly to a peak value in the initial stages of the blow and goes down gradually towards the end of decarburization. Thereafter it rises again at the end of blow.
The calculations are applied to more than 200 batches of steel produced under different conditions. The values of all heats are plotted together and a common trend is evolved. A best fit curve equation is derived for the trend. With this equation the desired BETA is calculated at regular intervals based on frequency of gas analysis. The actual value of BETA is compared dynamically with the standard or desired BETA value at required intervals of time.
If the actual BETA deviates positively from the desired value by a defined margin, then it is an indication of foaming of slag and this requires correction in lance height in predetermined lowering steps (for example, in steps of 10 cm). Similarly, if the actual BETA deviates negatively, then it indicates drying up of slag. The corrective action is to raise the lance in predetermined steps (for example 10 cm). In extreme cases of positive deviation, the oxygen flow rate is reduced in steps, for example in steps 20 m3/min, while respecting the minimum and maximum permissible limits of oxygen flow rate calculated in advance for a given nozzle design. The steps of lance height decrease or increase are dependent on dynamic changes in BETA.
Brief Description of the Drawing:
The present invention is further described with reference to the accompanying drawings, without restricting the scope of the invention, wherein:
1. A typical pattern of cumulative BETA for an actual heat is shown in Fig. 1. The flat portions of the curve indicate a steady process. When the process is steady, no changes are suggested in lance height and oxygen flow rate from the predefined patterns. Else, the suggested changes are able to control slopping or dry slag formation. Rapid increase in cumulative BETA indicates tendency for slopping. Rapid decrease in BETA indicates tendency towards dry slag formation. Both the tendencies are able to provide the control actions to be taken well in advance for bringing the process close to the desired path well in time, leading to a smooth and trouble free operation.
2. The progress of standard and actual BETA for a typical heat, marked with arrows, is shown in Fig. 2. The lance height pattern for standard BETA is decided for specific cases of initial conditions of hot metal composition and temperature. It actually amounts to automatic control of turbulence (chaos) depending upon the progress of cumulative BETA (Fig. 1) and change in actual BETA with respect to the prevailing conditions of slag-metal-gas system inside the vessel. This particular feature of chaos control is entirely new and has not been reported anywhere so far.
3. Fig:3 is a typical example of waste gas flow rate, lance height, predicted % skull on lance, and the actual difference in inlet and exit lance water temperature with time. Of special importance is also the pattern of change of lance water temperature for calculating the total heat transferred to lance at any given time.

4. Fig:4 is a system structure for on-line implementation of BETA control. The drawing is a block diagram representing an apparatus for carrying out a process of dynamically controlling the reactions of slag-metal-gas in the steel making converter.

The above description of the exemplary embodiments according to the present invention serves only for illustration purposes and not to restrict the invention. Various changes and modifications are possible within the context of the invention, without departing from the scope of the invention and its equivalents.