US3920447A

US3920447A - Steel production method

Info

Publication number: US3920447A
Authority: US
Inventors: David L Schroeder; Jai K Pearce; Eberhard G Schempp
Original assignee: Pennsylvania Engineering Corp
Current assignee: Pennsylvania Engineering Corp
Priority date: 1972-02-28
Filing date: 1972-02-28
Publication date: 1975-11-18
Anticipated expiration: 1992-11-18
Also published as: AU5268173A; GB1423752A; GB1423754A; ZA731351B; GB1423753A; CA989646A; GB1423751A

Abstract

Gases, fluxes and other materials are injected through the bottom of a vessel which converts a mixture of hot metal and scrap to steel. All solid materials are in powdered form when they are injected. Additional gases are injected through the side of the vessel to oxidize unburned combustible gases. Various data and parameters of the conversion system and affiliated steelmaking equipment are sensed prior to and during the course of the conversion. This information is processed by a computer which may dynamically control the flow of the materials so that the final molten product has the temperature and metallurgical composition which is prescribed by the order the computer has selected for the heat.

Description

United States Patent [191 Schroeder et al.

[ Nov. 18, 1975 STEEL PRODUCTION METHOD [75] Inventors! David L. Schroeder; Jai K. Pearce; Exammer p.eter Roseptierg Eberhard G. Schempp, a" of Attorney, Agent, or Firm-Fred Wrvrott Pittsburgh, Pa. [73] Assignee: Pennsylvania Engineering [57] ABSTRACT v C ti Pi b h, P Gases, fluxes and other materials are injected through the bottom of a vessel which converts a mixture of hot .[22] 9 metal and scrap to steel. All solid materials are in [21] App], No,; 229,958 powdered form when they are injected. Additional gases are injected through the side of the vessel to oxidize unburned combustible gases. Various data and :J-tS-CCII parameters of the Conversion System and aflrlliated [58] Fl! id 021C Steel making q p t are sensed prior to and during le are 59 the course of the conversion This information is p cessed by a computer which may dynamically control [5 6] References the flow of the materials so that the final molten prod- UNITED STATES PATENTS uct has the temperature and metallurgical composition 3,533,778 /1970 Nilles.... 75/60 which is prescribed by the order the computer has se- 3,594.l55 7/1971 Ramachandran.. 75/60 'lected for the heat.

3,619,174 ll/l97l Fujii 75/60 3,706,549 12/1972 Knuppelr; 75/60 9 Clalms, 8 Drawmg Figures cAs rmg 33M MA HIN 93 3o iii! 29 COMPUTER l ROLLING 4 MILL 2e 32 22 fi Q 44 20 a a a AL 7 glr I i7 34' I]? 4o 41' c.'. Hm 22 l0 l9 46 53 52 BI 67 62 9| iggfg L48 XE; 5o 49 so 66 90 HOT 72 66 54 55 12s 56 127 69 59 e 4 I 123 124 A 7 U.S. Patent Nov. 18, 1975 Sheet 2 of4 3,920,447

START I DATA SPECTROMETER READ OPENING CHEMISTRY BLAST I FURNACE SLECT ORDER TO SCRAP BE PROCESSED STATION I OPERATOR COMPUTE INITIAL A' HOT METAL CHARGE STATION ADDITIvE COMPUTE GAS, FLUX STATION & OTHER ADDITIvES CONVERTER SET GAS VALVES READY POSITION DISCHARGE vALvES INDICATOR MIxER RATE INSERT INSERT THERMOCOUPLE S'GNAL VALVES &

, ISTART BLOW II V F SIGNAL THERMO- TEMP READ FLUE GAS COUPLE RATIO M ADJUST GAS ANALYZER READ TEMPERATURE FEEDLBLOW RATES vvITHDRAvv SIGNAL REACTION POINT REACHED STOP BLOW & vvITHDRAvv THERMOCOUPLE I FIGS LOAD WEIGHT READ STORAGE CELLS SIGNAL BIN STATUS i RELOAD BINS CONTINUE Sheet 4 of 4 3,920,447

U.S. Patent Nov. 18, 1975 w w B F O D N E G N m IKV w D M VIT H M a m M I F N W A% m0 MG EF AL EA D MB RL 1N vAn u HR W W U L D W M N I D 0 B R A C F I a Ib m EONE I QZ OO W FIG.7

EN D OF BLOW I I I OXYGEN PARTITION FACTOR VERSUS BLOWING TIME MAIN BLOW 105i zoEE 59x0 BLOWING TIME DESULPHURIZATION PREHE Ms L AND OR SLAG FORMATION END POINT CONTROL OF CARBON AND TEMPERATURE FIG.8

BATH TEM PERATURE STE EL PRODUCTION METHOD BACKGROUND OF THE INVENTION.

In recent years, the basic oxygen method of converting hot metal to steelhas become widely accepted. In this method, impure hot metal and scrap are introduced into a refractory lined vessel. When the vessel is so charged, an oxygen lance is projected through its substantially open top and oxygen is blown onto the melt for reducing the sulfur, carbon, phosphorous, silicon and other impurities. Concurrently with the oxygen-blowing process, various fluxes are introduced to remove the components other than carbon in the form of molten slag or in gaseous form. The reaction between carbon and oxygen, in particular, is exothermic,

non-equilibrium to exist during the blow. Because the process continuously tries to revert to an equilibrium condition, unpredictable and unstable operation results, such as the discharge of metal and slag from vessels open top. For this reason, the measurement of bath temperature and evolved gas analysis cannot be consistently related to the bath temperature and chemistry.

Further, the true temperature of the melt and the chemical composition of the gases which are evolved from the melt are essential for automating the steel conversion process. It was impossible, however, to ob tain a temperature and/or bath carbon measurement which is truly representative of the melt with the topblown basic oxygen process because the temperature probe had to be introduced into the melt in the region of the oxygen reaction where the melt was in violent agitation and the highest temperature prevailed. Because of the high temperature gradient from this region to any other point in the melt, it was impossible to insert sensors for measuring temperature, oxygen or carbon levels at a place which would yield a value that was .truly representative of the temperature of the entire melt. Moreover, temperature sensors which were located in the walls of the vessel itself did not yield representative temperatures because the vessel developed hot spots at various places due to intensive heating by radiation from the very hot regions where the oxygen reaction was primarily taking place.

It was also dificult to obtain a continuous and accurate analysis of evolved gases in the top-blown basic oxygen method because the evolved gases were mixed with air and burned at the mouth of the vessel. The products of combustion, of course, could not be precisely related to the constituents of the melt, particularly carbon, which is the primary purpose for gas anal- .ysrs.

The prior top-blown basic oxygen process essentially involves making a heat, analyzing it, taking corrective measures such as adding more ore, lime, limestone or fluorspar and then reblowing to try to get the heat within specifications. This procedure had to be repeated several times usually in order to arrive at the final desired metallurgical specifications. The inability to produceinformation on the dynamic state of the melt precluded dynamic control. Moreover, the conversion process had to belooked upon as an isolated entity in the overall process of converting raw hot metal to finished metal products. However, the rate at which refined metal is produced and the quality thereof are not isolated incidents in the entire process of making finished steel products and those skilled in the art have been aware for a long time that to produce steel of the highest quality at lowest cost all operations of the entire plant should be taken into consideration and their interactions and relationship should be dealt with as an entity although no one has heretofore been able to do this. It is evident, therefore, that steel production by prior art methods was still as much an art as it was a science.

- SUMMARY OF THE INVENTION A general object of this invention is to produce finished steel at the lowest cost, with a maximum yield and highest production rate.

A further object of the invention is to provide a converter vessel having means for completely oxidizing the combustible gases evolving from the molten metal bath to provide an inert gas plug at the vessel discharge mouth.

Another object of the invention is to provide means for monitoring the gas discharging from the vessel and for controlling the rate of oxygen supplied above the molten metal to insure complete combustion prior to discharge in the vessel.

A still further object of the invention is to provide a new and improved dynamic control method and apparatus for automatically and continuously controlling the bottom blown converter vessel to obtain a final end point temperature and carbon level.

Another object of this invention is to expedite the steel conversion process by continuously analyzing the evolved gases for controlling the variable input rates, volumes and cycles of gas and solid material introduced to the melt whereby the product will meet specifications regardless of variations in the composition of the raw hot metal and the other materials which are introduced.

A further object of the invention is to provide computer analysis of a steel conversion process for automatically adjusting various steps in the process to bring about a short conversion time or more effective use of the materials.

How the foregoing and other more specific objects are achievedwill appear from time to time throughout the course of the more detailed description of a preferred embodiment of the invention which will be set forth hereinafter.

The new steel making process is characterized by use of a process control computer in conjunction with a converter vessel having provision for both above and below bath blowing. The characteristics of different types of scrap, hot metal and fluxes which maybe used for making various types of steel are stored in the computer, along with other data relating to the process. Based on input data, the computer selects the type and quantity of steel which is to be made and a preliminary calculation of the proper proportions of gases, hot metal, scrap and flux which are required for that type of batch. The calculation also takes into consideration the availability of raw materials and the desired production rate for subsequent processes. The approximate charge weights of scrap, hot metal, ore, etc. are measured out at appropriate stations. Prior to charging the converter vessel, the temperature of the hot metal and a fast spectrometric chemical analysis of it is made. This data is inserted into the computer and it makes a final calculation which dictates how the weights of the scrap, ore and/or hot metal should be trimmed and it also recalculates the amount of fluxes and other materials and gases such as oxygen which are to be bottomblown into the vessel. The vessel is then charged. Depending on the availability of various raw materials and the desired production rate, the scrap charge will be preheated in the vessel by the injection of fuel and oxygen through the vessels tuyere system. This will be in an amount based on a calculated BTU input on the basis of charge design calculation. The fuel to oxygen containing gas ratio will be monitored and controlled to assure optimum preheating conditions. After a preheat cycle, oxygen and other gases and materials are automatically introduced in quantities and over a time period established by the computer and based upon the analysis of the gases evolved from the vessel which are continuously fed into the computer. The computer is programmed for using this data to make appropriate adjustments in the rates and quantities of blown gases and other materials so as to bring about the desired final metallurgical composition of the melt in the shortest possible time. The computer may also be programmed to control gas input to insure the complete oxidation of combustible gases prior to discharge from the vessel. The computer constantly scans or periodi cally checks the status of input data and makes adjustments in the process which optimize the results.

An illustrative embodiment of the invention will now be described in conjunction with the drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of part of a steel making plant which utilizes the invention;

FIG. 2 is a fragmentary sectional view of the converter vessel shown in FIG. 1;

FIG. 3 is an event-sequence chart which is useful for describing the invention;

FIG. 4 is a schematic diagram of the flow of information linking individual functions into an operating system; and

FIG. 5 is a graph illustrating how the feed rate of one of the bottom-blown gases or materials may vary in re spect to time during blow-down periods.

FIG. 6 is a plot of the evolution of hydrogen and carbon monoxide during a typical operating cycle in the bottom blown converter vessel illustrated in FIG. 1;

FIG. 7 is a plot of the oxygen partition factor during a typical operating cycle of the bottom blown converter vessel of FIG. 1; and

FIG. 8 is a plot illustrating the adjustment of the temperature and carbon level at the end of a typical operating cycle of the apparatus illustrated in FIG. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT FIG. 1 schematically illustrates the present invention to include a refractory-lined bottom blown converter vessel which is generally designated by the reference numeral 10. Vessel 10 is mounted in a trunnion ring 11 from which diametrically opposite trunnion shafts 12 extend and these, in turn, are mounted on conventional columns (not shown) whereby vessel 10 may be tilted through an angle of 360 about the axis of trunnion shaft 12. A pouring spout 13 extends from the side of vessel 10 so that the molten contents of the vessel may be poured out as desired when the vessel is tilted. Slag is removed from the vessel by inverting it.

A first tuyere system 14 is provided at the bottom of vessel 10 so that gases and powdered materials may be blown from the bottom through the gap 115 in the vessel 10. The tuyere system 14 includes a metallic housing 15 secured to the bottom of the vessel 10 and a plurality of spaced apart passages 16 which extend through the refractory in the lower end of vessel 10 and open into chamber 15. A first pipe 17 extends into chamber 15 and has a plurality of smaller pipes 18 extending upwardly therefrom and in a concentric relation through passages 16. A-second pipe 19 coaxial with pipe 17 is also coupled to chamber 15 and in a surrounding relation relative to pipe 17.

As those skilled in the art will appreciate, the first pipe 17 and the pipes 19 are provided to deliver gases and powdered material through the bottom of vessel 10 and into the bath 115. As those skilled in the art will also appreciate, when oxygen or an oxygen containing gas is delivered through pipes 18, a hydrocarbon gas such as propane is preferably delivered through the outer pipe 19 and the passages 16 to substantially prolong the life of the refractory lining of vessel 10. Initially, if the vessel 10 contains scrap, the hydrocarbon gas is burned to preheat this material.

A second tuyere system 114 may be provided at the side of the vessel 10 for introducing gases above the level of molten metal 115. The second tuyere system 114 includes a pipe 116 which surrounds vessel 10 and a plurality of pipe sections 118 extending downwardly from pipe 116 and through suitable openings 119 formed in vessel 10. Pipe 118 is suitably coupled to a suitable gas source through conduit 120 whereby an oxygen containing gas and other gases may be introduced above the level of the bath 115. For example, a valve 121 which is controlled by computer 99, meters the ratio of oxygen, air and/or hydrocarbon gas to conduit 120. Initially air and fuel mixture may be introduced through tuyere system 114 to preheat scrap. Fuel and an oxygen containing gas may also be introduced during the initial portion of the blowing operation to maintain the bath 115 and the vessel 10 at the desired temperature. During subsequent portions of the blowing cycle, an oxygen containing gas is introduced through tuyere system 114 to insure complete combustion of the evolved gases in vessel 10.

Extending through the side of vessel 10 and at an angle with respect to its vertical axis, is a thermocouple lance 20 whose lower end may include means for sensing temperature and oxygen and extends beneath the surface of the melt contained in the vessel during operation. Lance 20 is supported on a carriage 21 which facilitates withdrawal of the thermocouple lance when it is desired to tilt vessel 10 and for other purposes. The position of the thermocouple lance 20 may be sensed by a position sensor 32 which provides a signal to module 33 for feeding data signals which are fimctionally related to thermocouple position into computer 99. The computer, on the other hand, may also provide signals at appropriate times for advancing and retracting thermocouple lance 20 in and out of vessel 10. The control system for the thermocouple lance 20 is not shown.

The top mouth of vessel is covered by a hood 22 which may be constructed and arranged in a manner well known in the art for being slightly elevated or shifted laterally to allow vessel 10 to be tilted. The fit between hood 22 and vessel 10 is such that there is substantially no leakage of evolved gases to the atmosphere nor is there significant leakage of atmospheric air into the interior of the hood. There is no combustion of the evolved gases in the region of the hood.

Gases collected by hood 22 pass through a duct 23 to any well-known type of gas scrubber such as the Baumco type which includes a venturi and uses water to capture solids. Gases from which the solids have been removed are delivered by an exhaust fan 25 to a stack 26.

Inside of hood 22 is a gas pickup device 28 which delivers gas through a tube 29 to an oxygen partial pres sure analyzer 30 which is connected in series with an infrared sensor 31 for carbon monoxide, carbon dioxide and water vapor. It is desirable for the oxygen partial pressure analyzer to have a response time of less than one second so as to sense rapid changes in vessel conditions. Toward this end, the oxygen partial pressure analyzer 30 may be of any well known type such as the Oxysensor sold by the General Electric Company. In this device, an electrical potential is developed between two electrodes immersed into media having different oxygen partial pressures and which are separated by an oxygen-ion conducting calcium stabilized zirconium oxide electrolyte. With a preset temperature and a known reference gas oxygen partial pressure, the open cell voltage between the two gases can be used to calculate the oxygen partial pressure of the gas to be measured in accordance with the Nernst equation.

The infrared sensor which is connected in series with the oxygen partial pressure analyzer indicates the percessed in the module 31 and delivered to the computer The gas partial pressure analyzer, which employs a solid electrolyte, brings the gas mixture flowing through it to equilibrium. Because the gas temperature is also known, the ratios of carbon monoxide to carbon dioxide and hydrogen to water vapor can be determined by the use of the oxygen partial pressure factor. These gas ratios are related to the oxygen partial pressure at a given temperature by a known proportionality constant. In this manner, a redundancy check may be obtained for purposes of calibration.

Vessel 10 or its associated trunnion ring 11 may also be equipped with an angle position sensor 34 which delivers electric signals that are processed in a module 35 and inserted as vessel angular position data in computer 99. At appropriate times the computer may produce signals to operate the mechanism, not shown, for tilting vessel 10.

When a heat is in process in vessel 10, various gases, primarily oxygen, are delivered to the bath through tuyere system 14 and powdered materials such as burnt lime, limestone, iron oxide, desulfurizing agents, fluor spar and even additives are entrained in the gases and injected in the melt in accordance with the flowing se quence. Only two

pressure vessels

40 and 41 which contain powdered material are shown but it will be understood that there will be as many pressure vessels as there are types of powdered materials which are to be injected into the molten metal within vessel 10. At least sufficient powdered materials will be stored in the

vessels

40 and 41 as determined by the computer 99. A measured quantity of powdered material may be delivered to pressure reservoir 41 through conduit 42 which is fed from a larger bin 43. Bin 43 may be large enough to store sufficient powdered material for all the heats that may be run in a predetermined period and may in turn be supplied through a conduit 44, from a still larger bin (not shown) which may be outside of the building if desired. The status of all of the storage bins is converted by means of suitable sensors, such as load cells, (not shown), to data signals which are fed into computer 99. The computer is programmed to produce suitable output signals or alarm signals which dictate replenishing powdered materials in the various containers by manual or automatic means. This eliminates the possibility of there not being adequate powdered material of any type available for a particular blow of the vessel 10. Data signals indicative of the amount of powdered material delivered to a pressure vessel such as 41 from larger bin 43 may be produced and delivered to computer 99 as symbolized by line 45 which projects from bin 43.

Similar symbols

46 and 47 are indicative of data signals delivered to the computer 99 which give the status of

vessels

40 and 41, respectively.

Powdered materials are delivered consecutively or concurrently under the control of computer 99 through a header pipe 48 which connects with pipe 17 for furnishing the powdered materials to tuyere system 14 at the bottom of vessel 10 as described above. The powdered materials are, of course, entrained in whatever gas or gases that are being blown into vessel 10 at a particular time as dictated by computer 99. It is necessary to mix the powdered material from a vessel such as 41 with entraining gas in definite proportion. For this purpose, the bottom of a vessel 41, for instance, is provided with a mixing device 49, the details of which are not shown, but are well known in the art. For example, the device 49 may be of the type which withdraws powdered material from vessel 41 and injects it into the gas stream. The device 49 may be operated by motive means 50 with a controller 51. The controller is responsive to input signals from computer 99 as symbolized by the short arrowhead line 52. The controller also produces mixing device status signals which are delivered to computer 99 as symbolized by line 53. Thus computer 99 can determine dynamically the rate and quantity of powdered material that is delivered to vessel 10 during a blow and the rate, schedule and quantity of powdered materials delivered is controlled by computer 99.

The mixing devices 49 are connected to as many sources of gases as might be blown in a particular installation. Thus, from a source of oxygen which is labeled 0 oxygen may be delivered from a header 58 through a branch pipe 59, a remotely controllable valve 60 and a pipe 61 to mixing device 49. Short arrows extending from valve 60 symbolize that the valve may deliver position signals to a suitable signal converter, not shown, from whence they are delivered to computer 99. These are in the nature of feed-back signals which keep the computer updated as to valve condition. An arrow such as 62 also symbolizes that valve 60 receives signals originating in computer 99 for throttling or turning off the flow of oxygen to mixing device 49 and, hence, to vessel 10.

Other control valves may also be interposed between mixing device 49 and the sources of other gases. However, only the aforementioned controllable valve 60, connected between an air source and mixing device 49, is shown for the sake of brevity. For example, there may be additional valves interposed between air, argon, and nitrogen and gas sources which are respectively marked AIR, Ar and N The other pressure vessels such as 40, containing powdered materials may also be supplied with these various gases through suitable pipes and valves, not shown. Data signals indicative of the condition of valves such as 60 and 66 are fed into computer 99 so that the flow program of all of the solid materials and gases may be controlled by the computer.

The various vases may also be fed selectively into vessel 10 directly without entraining solid material if desired. The oxygen line, for instance, connects through remotely controlled valve 71 to gas header 58 which feeds through remotely controllable valve 72 to input pipe 17 and to tuyere system 14 at the bottom of vessel 10.

Remote valves

68 and 69 for preventing reverse flow are also provided and there are several valves 54-57 for variously directing and regulating gas flow. Similarly, remote controllable valve 72' and directional regulating valves 54'57' are provided to regulate and control the flow of various gases to the input pipe 19 of the second tuyere system 114. Extending from each of the remote controlled valves are a pair of arrows which symbolize, as in respect to the previously discussed valves, that they are subject to computer control and that their condition constitutes input data to the computer 99. The conductors connecting the various valves to the computer or to its peripheral equipment are not shown, except in the case of the oxygen valve 71 which is shown for exemplary purposes to be connected to computer 99 by means of

conductors

77 and 78. Conductors 79 and 80 between computer 99 and a mixing device controller 81 are also shown as exemplary of the various mixing device connections.

The operating mode of the converter system will now be considered in greater detail. The first steps in producing a finished heat of molten metal are undertaken during a charge preparation period. Information on the chemical composition of various types of scrap which may be used and on the metallurgical composition of various types of steel is stored in the computer along with the chemical composition of the fluxes. Based on the availability of raw materials and prescribed production rates, tradeoffs in raw materials usage and blowing practice are logically set up for charge preparation. During the charge preparation period, the amount of hot metal, iron ore, scrap and flux needed for the prospective heat are calculated and these materials are weighed out. The analysis of the scrap, iron ore, flux and hot metal are stored in the computer. The hot metal temperature, the desired carbon reduction and the temperature of the hot metal are also fed into the computer during the charge preparation period. The computer program resulting from algorithms which are representative of the reactions which occur causes the hot metal quantity, scrap quantity and flux weights to be calculated. The volume of gases to be blown are also calculated to produce the final melt with the desired specifications. These calculations produce the approximate weights for hot metal and scrap based upon an average analysis and temperature of the hot metal. The weights are typed out and displayed to an operator. The hot metal may be obtained from a blast fumace 101 and conveyed in a conventional torpedo car (not shown) to a hot metal station which is symbolized by a block denoted in FIG. 1. During the preparation period the operator weighs out an approximate quantity of hot metal in a ladle. A sample of the hot metal is then taken and sent to the laboratory for elemental analysis. This analysis data is stored in the computer. In addition, the temperature of the hot metal is measured and this data is also stored in-the computer.

Now that the computer has data on the temperature, approximate weight and chemical composition of the hot metal and on the approximate chemical composition of the scrap and the fluxes, a final hot metal calculation is made by the computer and the ordered weight of hot metal is sent to the hot metal station 90. This weight is based upon the actual temperature and analysis of the hot metal in the ladle. The hot metal is trimmed to the final weight specified by the computer usually by withdrawing more hot metal from the torpedo car. The hot metal is then moved to the furnace area for charging.

After the weight of the hot metal is trimmed, a scrap calculation is made based upon the previous data plus the actual hot metal weight. This ordered weight is sent to a scrap station 91 where the operator perceives it and trims the weight of the scrap accordingly. Trimming of a fixed scrap and/or scrap and iron ore charge with hot metal may also be calculated. Iron ore in place of part of the scrap can be preset and/or calculated. The actual scrap and/or ore weight is recorded by the computer. This material is then ready to be moved in proximity with the vessel 10 for charging.

After the final weights of scrap, iron ore and hot metal are determined, the computer responds to its program by calculating the amount of flux that is necessary to produce the final metallurgical composition of the melt which is desired. The computer also determines whether there are adequate fluxes or other material in pressure vessels such as 40 and 41 for a particular heat. If the quantities are inadequate, the computer takes action to correct this condition. With the vessel tilted so as to eliminate interference by hood 22, the charge consisting of scrap is fed into vessel 10 and it is restored to upright position under the hood. The position indicator 34 and other sensors, such as load cell 34, indicate to computer 99 that the vessel is charged and ready for preheating.

The

valve system

71, 73 and 76 are initially programmed to deliver a gaseous fuel such as propane and an oxygen containing gas through the tuyere system 14 to preheat the scrap by the addition of a predetermined btu input. The vessel 10 is agam tilted so as to eliminate interference by the hood 22 whereupon hot metal may be fed into the vessel 10. The position indicator 34 and the load cell 34 indicate to the computer 99 that the vessel is charged and ready for blowing. The vessel 10 is then returned to its upright position and blowing is commenced. The computer 99 is programmed to introduce the thermocouple 20 at the appropriate time.

' 9- The computer is programmed for minimizing the use of fluxes and other materials for producing a heat. Initrally, the computer calculates something near the stoichiometrioamounts of materials and gases which are 10 bustion canbe calculated. Appropriate signals are provided to the valve 121 by computer 99 to insure complete combustion of the gases in chamber 10 whereby an inert gas is provided to the .gas cleaning system 1. Maintaining the vessel necessary .to :produce a heat of desired metallurgical 23-28 whileat the same timecontrolling the level of composition and it establishes the flow'rates and the energy generation inthevessel and above the bath time intervals and sequences duringwhich the materi- 115. Inthis manner, explosive gas mixtures are not als and gases are to be injected into the melt. -Each mapassed to the gas cleaning system 23-28 while at the terial and gas will have its own'specific program and same time a-vcontrolled amount of heat is delivered to this will be determined by the metallurgical conditions 10 the bath 115. j which are controlled by the computer. The feed rate of In a typical processing cycle, the computer will first a material with respect to time could take the form determine thatconditions are correct for initiating the shown in the FIG. '5 plot, for instance. This plot merely blow, the appropriate valves are then opened automatidemonstrates that materialsor gases canbe blown in. cally and nitrogen. is blown, into the vessel. The first continuously or periodically over different time intersolid material to be introduced is usually a desulfurizing vals and various feed ratesanywhere within the .10 to agent which may be entrained by the nitrogen and with- 15 minutes that it takesto complete a heat. More usudrawn from a pressure vessel such as 40. The amount of ally, a gas such as oxygen will be blown in substantially nitrogen and desulfurizing agent blown and the time incontinuously from the beginningtothe end oftheheat, terval' of this blow are, of course, predetermined by the and the amount of materiaL-conveyed by the oxygen computer in the light ofall conditions which affect the may be'continuously or periodically varied in accormetallurgyv of the melt. Subsequent to desulfurizing, oxdance with'what'the computer dictates is the most deygenand fluxes, such as burnt'lime and fluorspar as necsirable feed and time relationship for producing thedeessary are blown into the melt in accordance with cysired melt. 9 f h cles that are determined by the computer as indicated Before the hood has beenlowered into position on above. In due course, all of the gasesand materials for vessel 10 so that the aspiration of air is minimized, a gas producing a heat of desired characteristics are blown mixture is metered into the tuyere system 114 through into the melt and it is finished.

valve 121 so as to completely'burn-combustibles in the It will be appreciated that the chemistry of the initial gas eminating from the bath 115. ,The burning of these charge and the final meltspecifications will determine gases provides an inert plug in the gas cleaning system the material to be supplied to the bath through the 23-28. After an inert plug is' formed, the hood is lowtuyere system 14. The computer 99 will sequence and ered into position on vessel 10. The oxygen partial monitor the

various valves

60, 66, 68, 69, 71, 72, 72, pressure gas analyzer 30 and the

infrared gas analyzer

73, 74, 75 and 76 to obtain the desired sequence of ma- 31 sense the composition of the gases passing into the terial and gas through the tuyere system 14. For exam: hood22 and the resulting signals are provided to the 35 ple, Table 1 illustrates the possible combinations of computer99. In addition a'flow meter 122 in the consuch injections during the 'various portions of a treatduit provides the computer with the gas flow rate ment cycle.

Table l Process Step Outer Tuyere 16 Inner Tuyere l9 temperature during Hydrocarbon. Air prolonged waiting periods. I '2. Rapid preheat Hydrocarbon Oxygen 3. During short waiting periods Air Air H Nitrogen Nitrogen I Air Nitrogen Air Nitrogen 4. During vessel upturn Nitrogen Nitrogen Argon Argon Hydrocarbon Oxygen 5. During desulfurization Hydrocarbon Oxygen Lime Nitrogen- Nitrogen Lime Argon Argon Lime 6. During Main Blow Hydrocarbon Oxygen Hydrocarbon Oxygen +.Lime 7. During phosphorus v removal Hydrocarbon Oxygen Lime FeO) 8. For catch carbon Hydrocarbon Oxygen top oxygen k v Ht I top FeO) v 9. For hydrogen removal I I Nitrogen Nitrogen Argon Argon "10; For decarburization Maximum Argon F Hydrocarbon Maximum Nitrogen hydrocarbon ll. For vessel tumdown Hydrocarbon Oxygen Nitrogen Nitrogen Argon Argon to the tuyere system 1 Id With information and the stack gas stoichiometry, therequired flow rates through conduit 120 inorder to achieve complete comfconcerns the analysis of the gases that are evolved from 1 l the vessel and the temperature of the bath 115 in vessel 10. The oxygen partial pressure analysis and the percentages of C0, C and H 0 in the hood 22 along with the flow rates of these gases allow the computer 99 to perform a continuous material balance on the gases evolved from the vessel and passing through the hood 22. The gases in hood 22 are preferably controlled so that the oxygen partial pressure is greater than or equal to 0.01 atmospheres. This is accomplished by regulating the valve 121 so that a gas mixture is fed through the upper tuyere system 114 such that the carbon monoxide and hydrogen generated in the process is burned to carbon dioxide and water. For example, the plot of the typically expected evolution of carbon monoxide and hydrogen during the blowing cycle is illustrated in FIG. 6.

From the oxygen partial pressure analyzer 30, the bath temperature and/or the oxygen level as measured by probe 21, and the flow rates of the various gases is measured by the flow meters 122-128, the computer can determine the process dynamic state. As an intermediate control variable, the oxygen partition factor can be used to exercise dynamic and corrective control of the materials and gases being provided to the vessel through the

tuyere systems

14 and 114. The oxygen partial pressure may be calculated from the following expression:

[ z Rair (.40 v vw where OPF Oxygen partition factor;

Rv flow rate of gas from bath;

Vco the volume fraction of CO in the gas from the bath 115;

VH o the volume fraction of water vapor in the gas from the bath 115; and

Vco the volume fraction of CO in the gas from the bath 115.

R0 the oxygen flow rate. to the vessel 10;

Rair the air flow rate to the vessel;

A0 the volume fraction oxygen in the air provided to the vessel.

Having this information, the computer determines on a substantially continuous basis whether the metallurgical qualities of the melt are converging on the desired final qualities based on the original calculations of the computer. The computer also has adaptive qualities. For example, during the course of a blow,' it may determine the rate at which the melt is converging on final conditions and make suitable adjustments in the material and gas flow rates to assure that the final product will be close to specifications.

FIG. 7 is a plot of the expected oxygen partition factor for the process cycle. During the preheat portion of the cycle, a predetermined hydrocarbon fuel to air ratio is injected into the lower tuyeres to get the predetermined heat transfer to the scrap being treated. This results in a relatively high oxygen partition factor as indicated in FIG. 7. During the desulfurization or slag formation period, the oxygen partition factor drops to a relatively low value because either no oxygen is supplied to the vessel or the oxygen that is supplied is used in slag formation during this period as indicated in Table 1. During the period of the main blow, oxygen is again used in the oxidation of carbon so that the oxygen partition factor rises initially and then drops off toward the end of the blowing cycle where the oxygen partial pressure can be correlated directly to the bath carbon concentration. If the oxygen partial pressure factor deviates from the projected trajectory shown in FIG. 7, the computer will adjust the various feed rates to obtain the desired bath conditions.

For example, if the bath carbon and temperature are not within specifications as represented by rectangle D in FIG. 8 and as sensed by the deviation of the oxygen partition factor from that established in FIG. 7, corrective action is taken either during or subsequent to the main blow. For example, if the temperature predicted at turn down is too high, as represented by the full line A-B in FIG. 8, a coolant such as iron ore or limestone is added through the tuyere system 14. This moves the predicted end point temperature along the broken line A-C as seen in FIG. 8 to bring the bath within the final specifications as represented by the area D. Also, for example, if the predicted carbon level at tumdown is below specifications, the flow rate of hydrocarbon to the vessel 10 is increased to decrease the decarburization rate. This moves the predicted carbon level along the curve E-F as shown in FIG. 8. This can be accomplished by increasing the ratio of hydrocarbon gas to oxygen through the tuyere system 14. Alternatively a carbonaceous material could be added to the bath at the end of the main blow causing a drop in temperature and an increase in carbon level as shown by the broken line E-F in FIG. 8.

As an alternative, the percent carbon in the bath 1 15 may be determined from the following expression:

where C the percent carbon in the bath; V00 the volume fraction C0 in the gas from bath Vco the volume fraction CO in the gas from bath 115; and

K is determined from the expression RTlnK=AH-TAS I where R the gas constant T the absolute temperature A H the enthalpy of the reaction of C CO 2C0; and

A S the enthropy of the reaction.

From signals provided by the temperature and the infrared analyzer 31 the computer 99 can continuously monitor the carbon level in bath 115 and adjust the same either by initiating the introduction of a carbonaceous material in powdered or gaseous form through the tuyere system 14 or adjusting the hydrocarbon-oxy gen ratio therein.

The computer 99 may also be adaptive with respect to subsequent heats. That is, it may store in its memory the experiece with one or more previous heats and make adjustments in its initial calculations tocompensate for discrepancies which militate against producing a heat with the least amount of materials and in the shortest time. For example, the computer may determine that it would be more desirable to blow a greater or lesser quantity of lime fluxing material earlier or later in the cycle in order to create conditions that 13 would result in more effective use or the use of less of another powdered material to achieve the same final desired metallurgical conditions.

The duration of the oxygen blow is approximately to 15 minutes. During this time the computer is scanning all critical analog and digital signals from the converter system for datalogging and for producing suitable alarm signals if any function gets out of a predetermined range whereby the operator can perform some manual function to thereby override computer control. In reality, practically all functions of the system are subject to being manually overridden to assure that a heat will be completed in proper condition in spite of possible component failure.

When the blow is terminated, vessel 10 is tilted, a steel sample is taken and the temperature of the bath is measured andrecorded. The sample is sent to the laboratory for analysis. The temperature and the carbon content of the melt are read by the computer and displayed for the operator.

If the melt meets specifications, the molten metal will, of course, be utilized. If on a rare occasion the melt does not meet specifications, it may be reblown as will be described below. As explained above, however, the data derived by the computer during a heat or series of heats is constantly reviewed, and the parameters are adjusted so that the likelihood of requiring reblowing is continuously diminished over a series of heats. In the bottom-blown vessel system where all materials are continuously monitored and adjusted during processing if necessary, there is a substantially lower probability of producing an unsatisfactory heat than is the case in connection with the conventional top-blown basic oxygen process wherein the total amount of oxygen which is blown is substantially the only factor that is monitored or controlled fairly accurately during processing. In the top-blown process, there is always an uncertainty as to what will result from introducing a measured quantity of flux or other material because these materials are introduced through the top of the vessel in bulk form and are not necessarily utilized with maximum efficiency as compared with the present invention where finely powdered materials are blown through the melt and intimately contact the metal constituents, resulting in equilibrium or near equilibrium conditions and minimum use of materials.

When a heat is completed or the blowing of oxygen is terminated for any reason, the computer responds to this condition by commanding the blowing of an inert gas such as nitrogen into vessel 10. This prevents molten metal within vessel 10 from doing any damage to the nozzles and tuyeres through which the powdered materials and gases are injected in the bottom of the vessel 10. Nitrogen blowing may continue until the vessel is recharged and returned to upright position preceding the next batch.

The probability of an uneconomic reblow is further minimized by the computers capability for adapting a heat to fill another order having different specifications rather than to reblow in order to obtain the original metallurgical specifications for which the computer was set. Usually, the computer will store the characteristics of other orders which could be filled and if the .final product of a heat is far from specifications, and the computer will scan to find one that coincides with the state of the melt which has been produced. This may delay completing a particular order but when time constraints permit it is obviously more economical than an extensive reblow and it does produce a useful prodcompose a given heat and by dynamically sensing factors such as the oxygen partial pressure and the percentage of C0, C0 and H 0 in the discharge gases and modulating the flow of materials during production of the heat in response to the departure of any parameter from its set point at a given time. The process is further optimized by the monitoring of oxygen containing gas and gaseous fuel and the analysis of discharge gases to preheat scrap in the vessel prior to the commencement of the main blow and the adjustment of such factors as carbon and temperature by the computer so that final specifications may be achieved.

The burning to complete combustion of the gases,

such as carbon monoxide and hydrogen which evolve from the bath by the injection of oxygen through the upper tuyere system 114, maintains the desired vessel temperature and insures that an inert plug will be provided within the gas cleaning system. This not only insures against the dangers of explosion but also minimizes the cost of the gas cleaning system itself. As a result, the inert gas plug such as nitrogen which was pumped into the hood of prior art systems is no longer required. Also, by the employment of a gas analysis system which provides an oxygen partial pressure signal and forces an equilibrium condition in the gas sample and is employed with an infrared analyzer for C0, C0 and H 0, a dynamic control of process conditions can be obtained with a redundancy check for calibration purposes.

Although an illustrative embodiment of the invention has been described it is not intended to be limited thereby, but only by the scope of the appended claims.

We claim:

1. A method of treating metal contained in a metallurgical vessel having tuyere means for delivering gases beneath the level of said metal and a gas discharge opening, said tuyere means including a first tuyere passage and a second tuyere passage surrounding said first tuyere passage, the steps of:

charging said vessel with a quantity of scrap metal while simultaneously delivering an inert gas to said vessel through said first and second tuyere passages,

terminating the delivery of said inert gas, and

simultaneously delivering to said vessel an oxygen containing gas through one of said tuyere passages and a fuel through the other to thereby produce heat for preheating said scrap metal.

2. A method of reducing fumes and pollutants emitted to the atmosphere in connection with treating metal in a vessel which has means for delivering gases beneath the level of the metal and a gas discharge opening at least one gas collecting means being associated with said vessel and said vessel being tiltable between a first position wherein its opening is relatively closely coupled with respect to said gas collecting means, and a second position wherein said opening is relatively re- 15 mote from said gas collecting means, said method comprising the steps of:

a. tilting said vessel to its second position and charging it with scrap while simultaneously delivering inert gas into said vessel to thereby reduce the quantity of fumes which would otherwise be produced, and

b. tilting said vessel to its first position and terminating the delivery of said inert gas and delivering into said vessel an oxygen containing gas and a combustible material to thereby produce heat for preheating said scrap metal and driving fume producing agents therefrom.

3. The invention set forth in claim 2 wherein:

a. said inert gas is substantially nitrogen.

4. The invention set forth in claim 2 including the step after said scrap metal preheating step of:

a. tilting said vessel to said second position while simultaneously delivering inert gas into said vessel and charging said vessel with hot metal while continuing to deliver said inert gas, and

b. then restoring said vessel to its first position to continue treating said metal.

5. The invention set forth in claim 4 wherein:

a. said last named inert gas is substantially nitrogen.

6. The invention set forth in claim 1 wherein:

a. said inert gas is substantially nitrogen.

7. The invention set forth in claim 1 and including the step of:

terminating the delivery of said oxygen containing gas and fuel, and

charging said vessel with hot metal while simultaneously delivering inert gas into said vessel.

8. The invention set forth in claim 1 including:

a. measuring the partial pressure of at least oxygen in gases evolved from said vessel opening during said scrap preheating step, and

b. adjusting the flow rate of the oxygen containing gas during preheating until the oxygen partial pressure corresponds with substantially stoichiometric conditions of combustion existing between said combustible material and said oxygen in said delivered gas.

9. The method set forth in claim 4 wherein said means for delivering gases comprises tuyere means extending through the refractory lining of the vessel and including the steps of:

terminating the delivery of fuel and oxygen containing gas to the vessel and delivering a nonreactive gas to said tuyere means,

tilting said vessel and adding a quantity of hot metal to said vessel, while continuing the delivery of said nonreactive gas,

thereafter terminating the delivery of nonreactive gas and delivering through said tuyere means oxygen and hydrocarbon shielding fluid in surrounding relation to said oxygen.

Claims

1. A METHOD OF TREATING METAL CONTAINED IN A METALLURGICAL VESSEL HAVING TUYERE MEANS FOR DELIVERING GASES BENEATH THE LEVEL OF SAID METAL AND A GAS DISCHAGE OPENING, SAID TUYERE MEANS INCLUDING A FIRST TUYERE PASSAGE AND A SECOND TUYERE PASSAGE SURROUNDING SAID FIRST TUYERE PASSAGE, THE STEPS OF: CHARGING SAID VESSEL WITH A QUANTITY OF SCRAP METAL WHILE SIMULTANEOUSLY DELIVERING AN INERT GAS TO SAID VESSEL THRUGH SAID FIRST AND SECOND TUYERE PASSAGES, TERMINATING THE DELIVERY OF SAID INERT GAS, AND SMULTANEOUSLY DELIVERING TO SAID VESSEL AN OXYGEN CONTAINING GAS THRUGH ONE OF SAID TUYERE PASSAGES AND A FUEL THROUGH THE OTHER TO THEREBY PRODUCING HEAT FOR PREHEATING SAID SCRAP METAL.

2. A method of reducing fumes and pollutants emitted to the atmosphere in connection with treating metal in a vessel which has means for delivering gases beneath the level of the metal and a gas discharge opening at least one gas collecting means being associated with said vessel and said vessel being tiltable between a first position wherein its opening is relatively closely coupled with respect to said gas collecting means, and a second position wherein said opening is relatively remote from said gas collecting means, said method comprising the steps of: a. tilting said vessel to its second position and charging it with scrap while simultaneously delivering inert gas into said vessel to thereby reduce the quantity of fumes which would otherwise be produced, and b. tilting said vessel to its first position and terminating the delivery of said inert gas and delivering into said vessel an oxygen containing gas and a combustible material to thereby produce heat for preheating said scrap metal and driving fume producing agents therefrom.

3. The invention set forth in claim 2 wherein: a. said inert gas is substantially nitrogen.

4. The invention set forth in claim 2 including the step after said scrap metal preheating step of: a. tilting said vessel to said second position while simultaneously delivering inert gas into said vessel and charging said vessel with hot metal while continuing to deliver said inert gas, and b. then restoring said vessel to its first position to continue treating said metal.

5. The invention set forth in claim 4 wherein: a. said last named inert gas is substantially nitrogen.

6. The invention set forth in claim 1 wherein: a. said inert gas is substantially nitrogen.

7. The invention set forth in claim 1 and including the step of: terminating the delivery of said oxygen containing gas and fuel, and charging said vessel with hot metal while simultaneously delivering inert gas into said vessel.

8. The invention set forth in claim 1 including: a. measuring the partial pressure of at least oxygen in gases evolved from said vessel opening during said scrap preheating step, and b. adjusting the flow rate of the oxygen containing gas during preheating until the oxygen partial pressure corresponds with substantially stoichiometric conditions of combustion existing between said combustible material and said oxygen in said delivered gas.

9. The method set forth in claim 4 wherein said means for delivering gases comprises tuyere means extending through the refractory lining of the vessel and including the steps of: terminating the delivery of fuel and oxygen containing gas to the vessel and delivering a nonreactive gas to said tuyere means, tilting said vessel and adding a quantity of hot metal to said vessel, while continuing the delivery of said nonreactive gas, thereafter terminating the delivery of nonreactive gas and delivering through said tuyere means oxygen and hydrocarbon shielding fluid in surrounding relation to said oxygen.