US3561743A - Use of stack gas as oxygen potential measurements to control the bof process - Google Patents

Use of stack gas as oxygen potential measurements to control the bof process Download PDF

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US3561743A
US3561743A US675877A US3561743DA US3561743A US 3561743 A US3561743 A US 3561743A US 675877 A US675877 A US 675877A US 3561743D A US3561743D A US 3561743DA US 3561743 A US3561743 A US 3561743A
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oxygen
control
heat
lance
bath
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David L Schroeder
David L Lippitt
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General Electric Co
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General Electric Co
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    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B13/00—Adaptive control systems, i.e. systems automatically adjusting themselves to have a performance which is optimum according to some preassigned criterion
    • G05B13/02—Adaptive control systems, i.e. systems automatically adjusting themselves to have a performance which is optimum according to some preassigned criterion electric
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/28—Manufacture of steel in the converter
    • C21C5/30—Regulating or controlling the blowing

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  • This invention relates to a control method and apparatus for a basic oxygen furnace steel making facility of the type having an oxygen lance for supplying oxygen to a molten metal bath within the furnace and means for moving the oxygen lance relative to the molten metal bath for controlling the partition of oxygen supplied by the lance to the molten metal bath.
  • conditions are continuously sensed which are indicative of the oxygen content of the molten bath, the oxygen lance height and the oxygen lance flow rate to provide input data relative to the partitioning of the lance oxygen within the molten bath in the BOF vessel.
  • This input data is processed by suitable computation means which derives measurements representative of the temperature, carbon content and oxygen content of the molten bath during the course of the heat, as well as corrective output signals for the lance height and/or lance oxygen flow-rate to optimize the process.
  • the output control signals thus derived are then fed back in a dynamic, closed loop to control of the furnace to thereby optimize its operation.
  • the continuously sensed condition is the oxygen potential of the gases emanating from the furnace.
  • the sensing is accomplished by a gas analyzer which is positioned ahead of any stack gas cleaning equipment located in the stack of the furnace, and which accordingly has a high response speed.
  • the gas analyzer derives output measurement signals indicative of the oxygen partitioning of the lance oxygen, and these output measurement signals are employed to automatically and continuously control the position of the lance and the flow rate of the oxygen supplied therethrough to optimize the same during a heat.
  • the invention relates to a new and improved, dynamic control method and apparatus for dynamically and continuously controlling a basic oxygen furnace during the course of a heat to optimize its operation in a manner so as to assure production of molten steel which is within desired end-point temperature, carbon content and oxygen content specifications.
  • lance is meant the tool (which is in the shape of a lance) with which oxygen is blown into the mass of molten metal within the furnace.
  • the furnace which is maintained at a high temperature level in the neighborhood of 2,200 to 3,000 F., processes the charge to produce some quantity of steel, of some analysis and at some end-point temperature, along with some slag, flue gases and losses to thereby complete a heat.
  • the speed at which a heat is conducted places an extremely severe demand on a human operator. Therefore, some type of automatic sensing and control over the furnace is required during the course of the heat in order to bring the heat in on some specified end-point temperature, carbon content and oxygen content.
  • the basic oxygen furnace (hereinafter referred to as BOF) steel making process is a selective oxidation distribution process.
  • undesirable impurities in a liquid metal charge received from a blast furnace are removed.
  • the oxidation reactions that occur generate enough heat to melt a substantial amount of scrap, and to elevate the temperature of the resultant molten bath to about 3,000 F.
  • Oxidation or reduction is involved in all of the chemical reactions taking place in the BOF vessel during the course of a heat. These oxidations occur selectively and fall into three fairly definite characteristic periods (phases) that occur during the course of a heat. These periods are the slag formation period, the carbon boil period, and the metal refine period.
  • control by charge calculation is identified as control by charge calculation.
  • the charge calculation technique is a ballistic means for using thermodynamic calculations along with past operating data to compute the weights of the various materials to be supplied to the BOF vessel and an oxygen blowing schedule. The purpose of this is to achieve the best thermodynamic charge and blowing rate for a prescribed heat. It is aimed at statistically bringing in a higher percent of heats on desired end-point specifications and can also reduce the standard deviation from a desired end-point bath carbon and temperature achieved at first turn-down. By first turn-down is meant the point at which the BOF vessel is tilted to do sampling of the molten bath.
  • Still another known control technique for the BOF process is identified as dynamic end-point control.
  • U.S. Pat. No. 3,236,630 and U.S. Pat. No. 3,181,343 are illustrative ofcontrol systems employing this technique.
  • the dynamic control of end-point carbon and temperature requires exact input temperature and carbon values upon which to base control calculations and logic.
  • input carbon and temperature data values should be obtained some time near the end of the heat. Having determined the carbon and temperature of a bath at a particular point in the course of a heat, and knowing the carbon-versustemperature trajectory that a particular heat is following, control actions can be taken in the following manner.
  • the control logic should raise the lance and increase the oxygen blowing rate. This would result in correcting the temperature and/or carbon content so that the heat at the point of turn-down would end up within end-point specifications.
  • the trajectory as initially programmed, might lead to a heat in which the carbon and/or temperature is too high at first turn-down. Under these conditions the control logic should call for the addition of a coolant such as limestone, scrap, spar, etc., to be added to the heat. The resultant new trajectory would then lower the carbon and/or temperature so that at the point of turn-down the heat is within end-point specifications.
  • the programmed trajectory would bring a specific heat in within desired end-point specifications at the point of first turn-down.
  • the technique has definite weaknesses in that the error in the measurement of the initial carbon content of the charge generally is of the same magnitude as the specified end-point carbon. Additionally, the integration of carbon loss based on stack gas analysis is itself subject to error. Further, it provides no means for preventing undesired slopping or sparking during the earlier phases of a heat with their consequent material wastages.
  • the controlled blowing of heats to specified end-point carbon content, temperature and oxygen content satisfied the primary quality requirements of BOF shops and leads to increased refractory life and minimum nitrogen and oxygen in the steel bath. It also greatly facilitates further processing (molding, rolling, etc.) by controlling oxygen content of the molten metal at the point of first turn down.
  • the present invention provides a dynamic control for the BOF process having the above-listed desirable capabilities.
  • a further object of the invention is to provide a new and improved dynamic control method and apparatus for automatically and continuously controlling a basic oxygen furnace to optimize its operation during the course of a heat in a manner so as to controllably produce molten steel having a desired end-point temperature, carbon content and oxygen content.
  • a new and improved dynamic control method and apparatus for a basic oxygen furnace steel making facility having an oxygen lance for supplying oxygen to the molten metal bath within the furnace and means for moving the oxygen lance relative to the molten metal mass for controlling the partition of oxygen supplied to the molten bath.
  • an oxygen lance for supplying oxygen to the molten metal bath within the furnace and means for moving the oxygen lance relative to the molten metal mass for controlling the partition of oxygen supplied to the molten bath.
  • output control signals are continuously derived for controlling the partitioning of the lance oxygen within the molten bath during the course of the heat. These output control signals are then supplied back to dynamically control the furnace to thereby optimize its operation.
  • the condition that is continuously sensed is the oxygen potential of the gases emanating from the furnace. This is done by analyzing the stack gases emanating from the furnace at a position ahead of any stack gas cleaning equipment located in the stack and deriving output measurement signals indicative of the oxygen partitioning of the lance oxygen. These output measurement signals are then fed back to control the position of the oxygen lance and the flow rate of oxygen supplied therethrough in order to optimize partitioning of the oxygen and hence the BOF process.
  • FIG. I is a functional schematic diagram of a basic oxygen furnace steel making facility constructed in accordance with the invention.
  • FIG. 2 is a schematic diagram indicative of the chemical reactions taking place in a BOF vessel during the course of a heat
  • FIG. 3 is an idealized trajectory plotting a factor identified as the oxygen utilization factor (O.U.F.) versus time, and illustrates the manner in which oxygen is utilized during the three readily identified, primary phases of a BOF process;
  • O.U.F. oxygen utilization factor
  • FIG. 4 is a functional block diagram of a new and improved dynamic control system constructed in accordance with the present invention, and it illustrates the manner in which the system is applied to the BOF facility shown schematically in FIG. 1;
  • FIGS. 5. 6, and 7 are graphs illustrating plots of the lance oxygen flow rate and lance height versus time, as well as oxygen utilization factor (O.U.F.) and mole fraction of carbon monoxide occurring within the BOF vessel in the course of a heat, and illustrate such plots for a nonslopping heat, a mildly slopping heat and a badly slopping heat;
  • O.U.F. oxygen utilization factor
  • FIG. 8 is a plot of the blowing time versus bath carbon level for constant carbon increments
  • FIG. 9 is a plot of three representative carbon-temperature trajectories illustrating end-point control of low carbon heats.
  • FIG. 10 is a plot showing the correlation of the oxygen content of the stack gases to the molten metal bath carbon content.
  • FIG. 1 of the drawings is a schematic functional diagram of a basic oxygen furnace steel making facility, and illustrates the several major components of such facility which are employed in conjunction with a suitable general purpose digital computer for use in practicing the present invention.
  • the facility shown in FIG. 1 is comprised by a conventional BOF closed hood vessel shown at 11 in which a charge of molten metal. scrap, etc., shown at 12 had been deposited by a suitable charging or loading apparatus illustrated schematically at 13. While a closed hood facility has been illustrated, the invention may be practiced in conjunction with an open hood system with equal ease, as will be described more fully hereinafter.
  • the hood of the BOF vessel 11 is connected with a stack 14 having a suitable gas cooling and cleaning equipment I5 disposed therein which cools and cleans the gases emanating from the furnace vessel 11 prior to discharging them into the atmosphere.
  • a suitable gas cooling and cleaning equipment I5 disposed therein which cools and cleans the gases emanating from the furnace vessel 11 prior to discharging them into the atmosphere.
  • an oxygen lance shown at 16 is moveably disposed within the vessel II when it is tilted to its upright or blowing position.
  • the oxygen lance 16 may be raised or lowered within the vessel II by a suitable height controlling mechanism shown at 17, and the flow rate of the oxygen supplied through the lance I6 is con trolled by a suitable flow rate control shown at 18,
  • instrumentation means shown broadly at 19 and 21 are provided.
  • the instrumentation means are comprised by a gas analyzer for obtaining output signals indicative of the oxygen partial pressure, the mole fraction of carbon dioxide and/or the mole fraction of carbon monoxide present in the gaseous atmosphere.
  • the instrumentation means also includes a stack gas flow rate meter 21 for measuring the flow rate of the gases.
  • means are provided shown at 22 for inserting a disposable bomb thermocouple into the furnace. Also, it may prove essential at a particular point in the course of the heat to provide to the molten metal mass 12 in the vessel l1 additives such as spar, ore, or lime shown generally at 23 by means of a suitable automatically operated conveyor and weighing hopper system shown generally at 24. These additives can act as Coolants to the molten metal mass so as to in effect lower its temperature, and bring it in at the end ofa heat on a desired end-point temperature.
  • additives such as spar, ore, or lime shown generally at 23 by means of a suitable automatically operated conveyor and weighing hopper system shown generally at 24.
  • the BOF steel making process is a selective oxidation and distribution process wherein during the process undesirable impuritiesin the liquid metal received from the blast furnace are removed.
  • the oxidation reactions that occur generate enough heat to melt a substantial amount of scrap and to elevate the temperature of the resultant molten metal bath to a high value in the neighborhood of 3,000 F.
  • the primary reactions that occur in the BOF vessel during the course ofa heat are shown in FIG. 2 of the drawings.
  • oxidation or reduction is involved in all of the chemical reactions. These chemical reactions fall into three fairly definite and readily identifiable characteristic periods (phases) which occur during the course of a heat.
  • FIG. 3 of the drawings is a plot of an idealized oxygen utilization trajectory in which an oxygen utilization factor is plotted versus time for the course of a heat conducted in a BOF process.
  • the oxygen utilization factor (O.U.F.) will be defined more fully hereinafter, as well as the manner of its derivation, but for the purpose of the instant disclosure, it can be considered to be indicative of the partitioning of the lance oxygen between the several reactions that occur in the BOF furnace in the course of a heat.
  • This oxygen utilization factor (O.U.F.) in the particular embodiment of the invention disclosed, is in effect a measurement of the partitioning of the lance oxygen between the several reactions occurring in the vessel, and can be correlated with the carbon content of the molten metal bath.
  • the partitioning of the lance oxygen between the several reactions occurring in the vessel can be selectively controlled to obtain optimum process performance.
  • the lance oxygen is primarily used to selectively form the oxides FEO SIO MNO, etc. These combine with the flux material to form a slag.
  • a properly oxidized slag one containing proper contents of FEO, SIO MNO, etc. is essential to the stability of the BOF process and its refining capability. If an excessively oxidized slag is formed, slopping (ejection of slag from the vessel) might occur. If a slag is formed that is insufficiently oxidized, the maximum elimination of phosphorus from the molten metal bath will not occur.
  • the partitioning of lance oxygen begins to change to almost entirely oxidation of carbon into the gas phase as carbon monoxide (CO) and carbon dioxide (C0).
  • CO carbon monoxide
  • C0 carbon dioxide
  • the transition from the slag formation phase to the carbon boil period lasts from 2 to 4 minutes.
  • the carbon within the metal reacts with the lance oxygen as fast as oxygen can be supplied to the molten metal bath (resulting in the violent boiling action from which this period derives its name).
  • the substantial consumption of the lance oxygen during this phase of the heat is best il- Iustrated in FIG. 3 wherein it will be seen that the oxygen utilization factor (O.U.F.) drops substantially to zero or below during the carbon boil period.
  • the limiting factor controlling decarbonization rate during this carbon boil period is the supply of oxygen to the bath. Hence, during this phase, an idealized control would maximize the supply of oxygen to the bath. Eventually, as the carbon concentration decreases below a certain level, the rate of carbon diffusion to the reaction sites with oxygen can no longer keep up with the rate at which oxygen is being supplied to the bath. At this point, carbon diffusion becomes a rate limiting phenomenon which determines the rate of decarbonization.
  • the transition from the carbon boil phase to the metal relining phase is again marked by a characteristic change in partitioning ofthe lance oxygen.
  • the portion of the oxygen used for decarbonization is decreasing. Accordingly, the oxygen utilization factor (O.U.F.) trajectory will continually increase through the metal refining period with an increasing portion of the lance oxygen going into the reaction changing CO into CO and also into the reaction forming FeO.
  • This final metal refining period generally lasts less than three minutes during which all subsequent process steps to determine end-point characteristics of the heat, must be carried out.
  • FIGS. 5, 6, and 7 are plots obtained from reduced data which illustrate the trajectories that certain measured process variables including O.U.F. tend to follow during the course of a heat in a semiclosed hood BOF vessel of the type shown schematically in FIG. 1.
  • FIG. 5 illustrates a trajectory for a nonslopping heat
  • FIG. 6 a trajectory for a mildly slopping heat
  • FIG. 7 illustrates a trajectory for a badly slopping heat.
  • FIGS. 5, 6, and 7 it will be appreciated that there is a pronounced difference between the trajectories of slopping and nonslopping heats. Large changes occur in the ratio of carbon monoxide to carbon dioxide in the gases emanating from the BOF vessel. Similarly, large changes occur in the amount of lance oxygen which goes to make carbon monoxide and carbon dioxide during the course of a heat. Accordingly, it will be appreciated that it becomes possible to make use ofthese process variables individually or in combination to dynamically control the BOF process.
  • Control Theory In order to implement a dynamic, on-line process control. some arrangement must be provided for gathering control information data for use in following process response and reac tion kinetics. Setting of the oxygen lance height and the oxygen blowing rate at preset fixed values will lead merely to the generation of random, after the fact data since the lance oxygen partition between the gas-slag-metal reactions cannot be a priori predicted from these particular parameters if they are preset.
  • a preferred means of obtaining control information is to regulate the flow at predetermined (preprogrammed) lance oxygen partition values (by appropriate adjustment of the lance oxygen height above the molten metal and the oxygen flow rate), and determining the response of the process under these preset conditions.
  • FIG. 4 of the drawings is a functional block diagram of a dynamic, on-line process control apparatus for carrying out the novel control method of the invention.
  • the BOF vessel is shown at 11 together with the molten metal bath I2 being processed during the course of a heat, the oxygen lance 16, the stack 14 for carrying away gases emanating from the vessel 11 during the process, and gas cleaning equipment 15.
  • the lance height and lance oxygen blowing rate sensing and control mechanisms are shown at l7, 18 together with an online general purpose, digital computer 25.
  • the computer 25 includes suitable analog-to-digital and digital-to-analog converters comprising a part thereof for converting analogue measurements to digital values useable by the computer, and for reconverting digital values processed by the computer into analogue signals suitable for use with a particular control in question.
  • the computer 25 has supplied thereto output measurements from the stack gas analyzer 19 (to be described more fully hereinafter), a conventional stack gas flow rate sensor 21 where a facility is not designed to operate at a constant stack gas flow rate, and the output temperature measurement of a disposable bomb thermocouple 22.
  • the computer processes the input data in a manner to be described more fully hereinafter from the array sensing instruments and derives output controlling signals for the lance height and lance oxygen blowing rate control l7, 18.
  • a coolant addition control 26 can be provided for automatically supplying additives to the molten metal bath in the vessel 11 at a desired point in a heat.
  • a turn-down control 27 may be provided for automatically turning down the vessel and pouring out the molten metal bath into suitable receptacles such as molds, ladles, etc., for receiving the processed metal.
  • an automatic charge control 28 can be included for automatically supplying a new charge to the vessel 11 in response to suitable coitrol signals supplied thereto from the computer 25.
  • V Automatic turnoff of the lance oxygen to provide a specified carbon content and turn-down of the vessel at a point in the heat when desired specified end-point conditions can be obtained.
  • the lance height and lance oxygen blowing rate sensing and control l7, 18 of FIG. 4 is provided.
  • This device may in fact comprise a lance hoist drum and shaft manufactured and sold by Kaiser Engineers of Linst, Austria together with a position-regulated adjustable voltage drive having a positioning accuracy of plus or minus one-half inch.
  • the position references of this adjustable voltage drive should be settable by the computer 25.
  • the oxygen flow rate sensor can comprise a conventional, commercially available flow meter of the type manufactured and sold by Republic Engineering Corporation.
  • the control on the flow rate of the lance oxygen maybe comprised 'by any suitable valving arrangement, but it is necessary that the oxygen flow rate reference be settable by the computer 25.
  • the stack gas flow rate sensor 21 may comprise a conventional, commercially available flow rate sensor of the type using an orifice plate and suitable means for sensing the pressure drop across this orifice plate.
  • the stack gas analyzer 19 In order to determine the oxygen potential in the stack gas, the stack gas analyzer 19 is employed.
  • the stack gas analyzer 19 comprises more than'one instrument since it in effect must provide output signals indicative not only ofthe oxygen partial pressure (P0 in the stack gas but also the percent of CO and CO in the stack gas.
  • a commercially available instrument known as the General Electric "Oxysensor" Mark I is employed in order to determine the oxygen partial pressure (Po of the stack gases.
  • the GE. Oxysensor" is an industrial instrument that continuously measures the oxygen potential of gaseous media.
  • the instruments characteristics are such that it provides: (a) a logarithmically increasing signal with linearly decreasing oxygen partial pressure; (b) extremely low drift: (0) continuous fast response; (d) ability to process corrosive and particle laden gas streams without adversely affecting the instruments sensitivity.
  • the G.E. Oxysensor operates on the principle that an electrical potential (volts) will be developed between two electrodes immersed in two gases having different oxygen partial pressures; the gases being separated by an oxygen-ion conducting calcium-stabilized zirconium oxide electrolyte.
  • the measured open cell voltage of the Oxysensor is related to the oxygen partial pressure in the two gases by the Nernst equation.
  • the temperature of the Oxysensor is preset and the oxygen partial pressure in the reference gas is known. Therefore, by measuring the open cell voltage between the two gases, the oxygen partial pressure in the gas to be measured can be calculated'by means of the'N'ernst equation. This measured oxygen partial pressure is directly related to the oxygen concentration and chemical composition of the gas being measured.
  • Oxysensor has been designed to operate on industrial gas samples with a minimum of filtering required and includes its own filters, dryers, and pump for gas movement. A needle valve and gas flow meter is also included for regulating and measuring the gas flow rate.
  • the cell temperature is maintained at 850 C plus or minus 5 C by a solid state proportional controller.
  • the cells voltage output is treated in a self-contained amplifier circuit so that it can either be read directly or outputted to subsequent processing instrumentation such as a computer or recorder.
  • the Oxysensor is manufactured and sold commercially by the Instrument Department of the General Electric Company located in Lynn, Mass. Because the Oxysensor is a commercially available instrument, a further description of its characteristics is believed unnecessary.
  • the percent CO and percent CO in the stack gas may be measured by a conventional, commercially available infrared analyzer such as that manufactured and sold by the Leeds and Northrup Company. ln particular, a Leeds and Northrup Model No. 7804-A6-A5 lnfra-Red Analyzer is quite satisfactory for measuring these parameters.
  • the oxygen potential of the gases emanating from a BOF vessel during the course of a heat is expressed in terms of the oxygen utilization factor (O.U.F.) Since the O.U.F. is a'measure of the oxygen potential of the vessel gases it in effect is indicative of the capability of these gases to react with the molten metal bath, and hence is indicative of the oxygen content formance. 2 5
  • Oxysensor unit and the CO and/or CO measured thereafter with an infrared sensor or other convenient sensors along with the measurement of the gas flow rate in the stack gas and the lance oxygen flow rate. Using these measurements, the O.U.F.
  • the flow rate balance is given by: t RA uu RA (A02)
  • the oxygen balance is given by: f R. m SW2) RA (A02) I (.%02 Eco
  • the carbon balance is given b: u: ea SIUZ) t
  • the Oxysensor measurement is processed according to:
  • FIG. 3 of the drawing shows an idealized trajectory plotting the O.U.F. versus time for a particular heat.
  • FIG. 5 of the drawing illustrates how the O.U.F. trajectory can be employed in controlling the lance height (LH) in FIG. 5. and the lance oxygen flow rate (1 in FIG. 5 to thereby control the lance oxygen partitioning and optimize the process performance.
  • O.U.F. signal can be employed to correct the lance height and/or lance oxygen flow rate at particular points in the course of a heat to optimize process performance.
  • oxygen utilization factor O.U.F.
  • the flow rate balance is given by:
  • the oxygen balance is given by:
  • FIG. 9 of the drawings is a plot of the bath temperature versus bath carbon for three different heats identified as A, B, and C.
  • the envelope shown in dotted outline form defines the endpoint tolerance allowed for the heats in question.
  • the control logic should raise the lance and increase the oxygen blowing rate so that the trajectory would be lifted to follow along the dotted line A-D. In this manner, the heat could be turned down within end-point specifications at point D.
  • the heat will be within specifications if the programmed trajectory is followed and turn-down occurs at point E.
  • the control logic should call for the addition of coolants such as limestone, scrap, etc, to be added to the heat. The new trajectory would then be along the dashed line CF, and the heat could be turned down within specifications at point F.
  • the control philosophy outlined in FIG. 8 is possible.
  • the gas analysis equipment must produce a useable signal within about 15 seconds after a change in the reaction occurring in the BOF vessel.
  • the sen sor for the stack gas analyzer I9 is located before the main gas cleaning equipment in the vessel stack as shown in FIG. 4.
  • the determination of the molten metal bath carbon content by subtraction of carbon leaving the stack from the initial carbon is demonstratably unsatisfactory.
  • the error in the measurement of the initial carbon content of the charge can be of the same magnitude as the specified end-point carbon.
  • integration of carbon loss based on stack gas analysis is itself subject to error.
  • the integration of carbon removal from the start of a heat appears to have value only in statistically improving endpoint performance on high carbon heats (carbon content greater than 0.4 percent).
  • FIG. 10 of the drawings is a graph of the percentage carbon in the bath at the time of first turn-down plotted against the oxygen percentage in the stack gas measured some 10 seconds before the lance oxygen is turned off, and is an indication of the correlation between the oxygen in the stack gas and the bath carbon content.
  • a correlation factor of 0.93 has been obtained by linearly fitting test data measurements of oxygen in the stack gas and bath carbon at the time of first turndown. Accordingly, it will be appreciated that the oxygen potential of the stack gas as measured by the stack gas analyzer provides, reliable end-point carbon datum values upon which to base control calculations and logic. The com puter processes this information and employs the same in determining the correct point of turn-off of the lance oxygen at the end of the heat.
  • a bomb thermocouple such as the Jet BOB" manufactured and sold by the Lamp Glass Department of the General Electric Company located in Willoughby, Ohio, is suitable for this purpose.
  • This device provides a means of obtaining a datum temperature value within three to five minutes before the projected end of a heat. At this point the scrap in the vessel should be completely melted. If, in fact, the scrap is melted, then the actual temperature value provided by the bomb thermocouple will compare favorably to a predicted end-point temperature based on a time integration of the input temperature of the charge and the amount of oxygen supplied to the vessel in the course of a heat.
  • the control may then take suitable measures through the coolants addition control 26 to add materials such as lime, ore, scrap, etc.. to bring the heat in on desired end-point conditions. Should it appear that the heat is coming in too low, then additional oxygen may be called for.
  • the invention makes available a dynamic, closed-loop control method and apparatus for a BOF facility wherein measurements taken of the stack gas can be used to detect the imminence of slopping and the presence of slopping before it can be seen outside the BOF vessel.
  • the dynamic process control by adjusting lance height, oxygen flow rate and possibly adding lime or other additives, can cause a proper slag to form, thus eliminating the slopping condition.
  • a bomb thermocouple dropped into the bath provides another process control input parameter.
  • the actual bath temperature information plus bath carbon datum obtained from continuing offrgas oxygen measurements are used for endpoint bath temperature and end-point bath carbon control.
  • the digital process control computer 25 in addition to its vital role in the dynamic, closed-loop control can be employed to provide indispensable services during the implementation stages in charge calculation, etc. It can also be employed in the gathering and logging of data required for control model refinement.
  • the invention attains the objective of a dynamic control which can maximize production rate and quality while simultaneously decreasing raw material and labor costs.
  • the production rate of a shop can be greatly increased.
  • the controlled blowing of heats to specified end-point carbon and end-point temperature values satisfies two of the primary quality requirements in BOF shops.
  • the optimization of the oxygen flow rate leads to increased refractory life and minimizing excess nitrogen and oxygen in the bath.
  • the control of the oxygen content of the bath at the point of turn-down is also made possible, and facilitates further processing steps and cleanliness of the resultant metal product.
  • the invention provides a new and improved dynamic control method and apparatus for automatically and continuously controlling a basic oxygen furnace to optimize its operation during the course of a heat in a manner so as to controllably produce molten steel having a desired end-point temperature, carbon content and oxygen content.
  • a control apparatus for a basic oxygen furnace steel making installation of the type having an oxygen lance for supplying oxygen to a molten metal bath within the furnace and positioning means for moving the oxygen lance relative to the molten metal mass for controlling the partition of oxygen therein, the improvement comprising:
  • sensing instrument means for deriving output measurement signals indicative of the oxygen content of the molten bath comprising: stack gas analysis means positioned ahead of any stack gas cleaning equipment located in the stack for deriving measurement signals indicative of the oxygen potential of the gaseous atmosphere in the BOF vessel and the partitioning of the lance oxygen, and further comprising: means for providing measurement signals indicative of the oxygen lance height, the lance oxygen flow rate, and the stack gas flow rate said stack gas analysis means comprising, oxygen partial pressure measuring means for measuring and providing a measurement signal representative of the oxygen partial pressure of the gaseous atmosphere emanating from the furnace, carbon dioxide measuring means for measuring and providing a measurement signal representative of the mole fraction carbon dioxide present in the gaseous atmosphere emanating from the furnace, and means for providing a measurement signal representative of the mole fraction carbon monoxide present in the gaseous atmosphere emanating from the furnace.
  • the measurement signals thus provided being indicative of the oxygen potential of the gaseous atmosphere in the furnace and therefore indicative of the oxygen content of the molten bath
  • feedback means including computation means for deriving from said measurement signals corrective output control signals for controlling partitioning of the lance oxygen,
  • computation means comprises means for solving the following equation, and deriving its output control signals in accordance therewith:
  • VCO is the mole fraction of carbon monoxide produced in the furnace gases by the lanceoxygen
  • VCO is the mole fraction of carbon dioxide produced in the furnace gases by 2.
  • a control apparatus according to claim 1 wherein the computation means further includes means for comparing an actual instantaneous measured O.U.F. signal to an initially programmed O.U.F. trajectory and for deriving therefrom corrective output control signals for adjusting the lance height and the lance oxygen flow rate to thereby dynamically and continuously control the partitioning of the lance oxygen during the course of a heat.
  • a control apparatus further including charge control means for supplying an initial charge of known ingredients under known conditions to the furnace, and means supplying a charge control signal from said computation means to said charge control means for automatically controlling the operation thereof.
  • a control apparatus further including coolant addition control means for supplying additives to the bath at a desired point in a heat, and coolant addition feedback means for supplying a coolant addition feedback control signal from the computation means to the coolant addition control means for automatically controlling the supply of additives to the bath at a desired point in a heat.
  • a control apparatus further including turn-down control means for turning down the furnace at a desired point in a heat and pouring out the molten metal into appropriate receptacles, and additional feedback means for supplying a turn-down control output signal from said computation means to said turn-down control means for automatically controlling the operation thereof.
  • a control apparatus further including charge control means for supplying an initial charge of known ingredients under known conditions to the furnace.
  • charge control means for supplying a charge control signal from said computation means to said charge control means for automatically controlling the operation thereof
  • coolant addition control means for supplying additives to the bath at a desired point in a heat
  • coolant addition feedback means for supplying a coolant addition feedback control signal from the computation means to the coolant addition control means for automatically controlling the supply of additives to the bath at a desired point in a heat
  • turn-down control means for turning down the furnace at a desired point in a heat and pouring out the molten metal into appropriate receptacles
  • additional feedback means for supplying a turn-down control output signal from said computationmeans to said turn-down control means for estsm llx na ps e Op at c thereof:
  • the computation means further includes means for producing an integrated heat output signal representative of the predicted bath temperature and based on a time integration of the initial bath temperature, the lance oxygen flow rate and the time that has elapsed from the beginning ofa heat, means for inserting a disposable bomb thermocouple in the molten metal bath at a point in time just prior to the end ofa heat. and means for supplying the actual instantaneous bath temperature signal from said bomb thermocouple to the computation means, said computation means further including means for comparing the predicted bath temperature output signal to the actual bath temperature signal supplied by the bomb thermocouple and for deriving integrated heat balance corrective output control signals for bringing the heat in on a desired end-point temperature.
  • the computation means includes means for comparing the actual O.U.F. signal to an initially programmed O.U.F. versus percent carbon content trajectory for the bath and deriving a cutoff control signal therefrom for terminating the supply of oxygen to the bath at the end ofa heat.
  • a control apparatus further including charge control means for supplying an initial charge of known ingredients under known conditions to the furnace, and means for supplying a charge control means for automati cally controlling the operation thereof.
  • a control apparatus further including coolant addition control means for supplying additives to the bath at a desired point in a heat and coolant addition feedback means responsive to an integrated heat balance corrective output feedback control signal from the computation means for automatically controlling the supply of additives to the bath at a desired point in a heat.
  • a control apparatus further including turn-down control means for turning down the furnace at a desired point in a heat and pouring out the molten metal into appropriate receptacles, and additional feedback means for supplying a turn-down control output signal from said computation means to said turn-down control means for automatically controlling the operation thereof.
  • a control apparatus further including charge control means for supplying an initial charge of known ingredients under known conditions to the furnace, means supplying a charge control signal from said computation means to said charge control means for automatically controlling the operation thereof.
  • coolant addition control means for supplying additives to the bath at a desired point in a heat
  • coolant addition feedback means responsive to a first integrated heat balance corrective output feedback control signal from the computation means for automatically controlling the supply of additives to the bath at a desired point in a heat where required
  • turndown control means for turning down the furnace at a desired point in a heat and pouring out the molten metal into appropriate receptacles
  • additional feedback means for supplying a turn-down control output signal from said computation means to said turn-down control means for automatically controlling the operation thereof.

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  • General Physics & Mathematics (AREA)
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  • Treatment Of Steel In Its Molten State (AREA)
  • Manufacture And Refinement Of Metals (AREA)
US675877A 1967-10-17 1967-10-17 Use of stack gas as oxygen potential measurements to control the bof process Expired - Lifetime US3561743A (en)

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BE (1) BE722376A (xx)
DE (1) DE1803047A1 (xx)
ES (1) ES359144A1 (xx)
FR (1) FR1594663A (xx)
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NL (1) NL6814899A (xx)

Cited By (17)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3707069A (en) * 1970-10-13 1972-12-26 Air Pollution Ind Gas collector for steel furnace
US3816720A (en) * 1971-11-01 1974-06-11 Union Carbide Corp Process for the decarburization of molten metal
US3871871A (en) * 1967-12-11 1975-03-18 Centre Nat Rech Metall Monitoring and control of pig iron refining
DE2707502A1 (de) * 1976-02-24 1977-08-25 Nippon Steel Corp Verfahren zum steuern der temperatur von geschmolzenem stahl und des kohlenstoffgehaltes in einem sauerstoffkonverter
US4133036A (en) * 1976-02-26 1979-01-02 Republic Steel Corporation Method and system for monitoring a physical condition of a medium
US4291379A (en) * 1978-11-10 1981-09-22 Renzo Cappelletto Method and an installation for regenerating molding sands
US4416691A (en) * 1980-07-03 1983-11-22 Kobe Steel, Ltd. Method for converter blow control
US4731732A (en) * 1985-08-07 1988-03-15 Aluminum Company Of America Method and apparatus for determining soluble gas content
US5610346A (en) * 1996-01-05 1997-03-11 Bethlehem Steel Corporation Apparatus for storing and dropping expendable BOF sensors
US5984998A (en) * 1997-11-14 1999-11-16 American Iron And Steel Institute Method and apparatus for off-gas composition sensing
US6171364B1 (en) 1996-03-22 2001-01-09 Steel Technology Corporation Method for stable operation of a smelter reactor
US20040006435A1 (en) * 1999-02-18 2004-01-08 Furnace Control Corp. Systems and methods for controlling the activity of carbon in heat treating atmospheres
US6693947B1 (en) 2002-09-25 2004-02-17 D. L. Schroeder & Associates Method to protect the anode bottoms in batch DC electric arc furnace steel production
CN102169326A (zh) * 2011-03-02 2011-08-31 中冶南方(武汉)威仕工业炉有限公司 基于数据挖掘的最优炉温设定值优化系统
EP2423336A1 (de) * 2010-08-25 2012-02-29 SMS Siemag AG Verfahren zur Temperaturkontrolle des Metallbades während des Blasprozesses in einem Konverter
CN107299183A (zh) * 2017-06-28 2017-10-27 河钢股份有限公司邯郸分公司 一种智能降低转炉终渣氧化性的系统及方法
US9956609B1 (en) * 2014-06-24 2018-05-01 Melt Cognition, LLC Metal sorting, melting and fabrication apparatus and methods

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2219975A1 (en) * 1973-03-01 1974-09-27 Centre Rech Metallurgique Controlling the refining of pig iron - by adjusting lance height,oxygen flow and material addns

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3184226A (en) * 1961-06-06 1965-05-18 Ajax Magnethermic Corp Automatic pouring furnace
US3372023A (en) * 1964-05-23 1968-03-05 Beteiligungs & Patentverw Gmbh Method of monitoring and controlling the oxygen blowing process
US3396580A (en) * 1966-07-25 1968-08-13 Gen Electric Storage and release apparatus for measuring devices

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3184226A (en) * 1961-06-06 1965-05-18 Ajax Magnethermic Corp Automatic pouring furnace
US3372023A (en) * 1964-05-23 1968-03-05 Beteiligungs & Patentverw Gmbh Method of monitoring and controlling the oxygen blowing process
US3396580A (en) * 1966-07-25 1968-08-13 Gen Electric Storage and release apparatus for measuring devices

Cited By (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3871871A (en) * 1967-12-11 1975-03-18 Centre Nat Rech Metall Monitoring and control of pig iron refining
US3707069A (en) * 1970-10-13 1972-12-26 Air Pollution Ind Gas collector for steel furnace
US3816720A (en) * 1971-11-01 1974-06-11 Union Carbide Corp Process for the decarburization of molten metal
DE2707502A1 (de) * 1976-02-24 1977-08-25 Nippon Steel Corp Verfahren zum steuern der temperatur von geschmolzenem stahl und des kohlenstoffgehaltes in einem sauerstoffkonverter
US4133036A (en) * 1976-02-26 1979-01-02 Republic Steel Corporation Method and system for monitoring a physical condition of a medium
US4291379A (en) * 1978-11-10 1981-09-22 Renzo Cappelletto Method and an installation for regenerating molding sands
US4416691A (en) * 1980-07-03 1983-11-22 Kobe Steel, Ltd. Method for converter blow control
US4731732A (en) * 1985-08-07 1988-03-15 Aluminum Company Of America Method and apparatus for determining soluble gas content
US5610346A (en) * 1996-01-05 1997-03-11 Bethlehem Steel Corporation Apparatus for storing and dropping expendable BOF sensors
US6171364B1 (en) 1996-03-22 2001-01-09 Steel Technology Corporation Method for stable operation of a smelter reactor
US5984998A (en) * 1997-11-14 1999-11-16 American Iron And Steel Institute Method and apparatus for off-gas composition sensing
US20040006435A1 (en) * 1999-02-18 2004-01-08 Furnace Control Corp. Systems and methods for controlling the activity of carbon in heat treating atmospheres
US6693947B1 (en) 2002-09-25 2004-02-17 D. L. Schroeder & Associates Method to protect the anode bottoms in batch DC electric arc furnace steel production
EP2423336A1 (de) * 2010-08-25 2012-02-29 SMS Siemag AG Verfahren zur Temperaturkontrolle des Metallbades während des Blasprozesses in einem Konverter
CN102169326A (zh) * 2011-03-02 2011-08-31 中冶南方(武汉)威仕工业炉有限公司 基于数据挖掘的最优炉温设定值优化系统
CN102169326B (zh) * 2011-03-02 2013-11-13 中冶南方(武汉)威仕工业炉有限公司 基于数据挖掘的最优炉温设定值优化系统
US9956609B1 (en) * 2014-06-24 2018-05-01 Melt Cognition, LLC Metal sorting, melting and fabrication apparatus and methods
CN107299183A (zh) * 2017-06-28 2017-10-27 河钢股份有限公司邯郸分公司 一种智能降低转炉终渣氧化性的系统及方法

Also Published As

Publication number Publication date
NL6814899A (xx) 1969-04-21
BE722376A (xx) 1969-04-01
FR1594663A (xx) 1970-06-08
GB1239253A (xx) 1971-07-14
DE1803047A1 (de) 1969-10-02
ES359144A1 (es) 1970-05-16

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