US3314781A - Method for the control of blast refining of carbon-containing metal melts - Google Patents

Description

April 18, 1967 F. K. E. JOHANSSON ETAL 3,314,781

METHOD FOR THE CONTR OF BLAST REFINING OL OF CARBON-CONTAINING METAL MELTS Filed DeC.

INVENTORS FOLKE KE. JOHANSSON JOHN A. SMEDSTAM BY JAN L. B. UGGLA Ja/M Y- ATTORNEYS April 18, 1967 .E. JoHANssoN ETAL 3,314,781

METHOD FOR THE CONTROL OF BLAST REFINING OF CARBON-CONTAINING METAL MELTS Filed Dec. 7, 1965 2 Sheets-Sheet 2 2 POTENTIAL HEATl |N EXHAUST GAS AT MOUTH OF FURNACE PER Kg- OF CARBON OXlDlZED IN MELT HEAT |N K Cdl/Kg OFC SOOO" AVERAGE TEMPERATURE OF GAS AT MOUTHv OF FURNACE 1900 |700 |800 2000 2000 Muff JMX IOO 50 O EDEGREE OF COMBUSTION INVENTORS OF CARBON IN FOLKE K E. JOHANSSON JOHN A. SMEDSTANI BY JAN L B. UGGLA United States Patent O 3,314,781 METHOD FOR THE CONTROL OF BLAST RE- OF CARBON-CONTAINING METAL Folke Karl Evald Johansson and John Arne Smedstam, Borlange, and Jan Ludvig Bertilsson Uggla, Nykroppa,

weden assignors to Stora Ko arber s Ber sla s Aktiebolag, Falun, Sweden Pp g g g Filed Dec. 7, 1965, Ser. NO. 512,830 Claims priority, application Sweden, Mar. 20, 1962, 3,129/ 62; July 13,` 1962, 7,884/62, 7,885/ 62 12 Claims. (Cl. 7552) The present invent-ion relates to a method used in the refining of molten carbon-containing ferrous metal to part of added to the melt.

Obtaining a predetermined temperat-ure in the melt at the same time that the is essential and critical. Lf the melt is controls for taking the contents of samples. This is especially Oxygen (pneumatic high speed blast) reand analyzing true for Basic ent practice.

One of the objects of the present invention is to pro- 3,314,781 Patented pr. 18, 1967 analysis.

Another object is to control the percentage of carbon and temperature of the melt by controlling the supply of oxygen to reduce the carbon content and the supply of cooling medium to the melt in accordance with the carbon containing gases produced to simultaneously arrive at the desired composition and temperature.

A further object is to provide reliable methods of determining the ratio or degree of combustion ofthe carbon that occurs in the refining furnace These and other objects from the following :description and drawings. It is to be understood, however, that the -drawings are for the pose to the appended claims.

In the drawings:

FIGURE l is a diagrammatic View of an apparatus for carrying out the method of -the present invention; and FIGURE 2 is a chart showing the potential heat of gas, exhausted from the mouth of the furnace in relation to actual degree of carbon combustion.

The invention is particularly applicable to the manufacture of steel by Irefining molten pig iron and reference will now be made to conventional methods used in such manufacture. It is `to be understood, however, that the as nickel, to its main constituents, iron and up `to 5% by weight of carbon, also usually Icontains a relatively small percentage of silicon, manganese and phosphorus. These impurities, together with a relatively small portion of iron, are oxidized and removed from the melt as slag during refining and are herein below referred to as slag-transferable elements and after conversion to slag `constituents are referred to as slag-transferred elements. The molten pig iron is treated in a furnace, as shown in FIGURE l, having a gas space above the melt. The refining is performed -by supplying a refining gas containing free oxygen to the space above the melt and supplying solid ferrous metal, oxidic compounds thereof, slag-fonme|rs, or a combination (b) said slag-transferable a portion of said carbon Such oxidation of carbon,

elements in said metal, and (c) monoxide to carbon dioxide. slag-transferable elements and composition of pig iron, scrap iron and cooling agents initially charged to the furnace are measured. The theoretical amount of oxygen required may then be calculated from the amount of slag-transferable elements in the pig iron and the difference between the initial carbon content of the pig iron and the preselected carbon content of the steel to be produced, both of which materials must be oxidized. All carbon removed from the melt occurs as carbon monoxide and a portion of this carbon monoxide is converted to carbon ydioxide within the furnace. Thus, the initial determination of the oxygen required presupposes an assumed average degree of combustion of the carbon monoxide .formed in the refining process to carbon dioxide in the gas space of the furnace. The degree of combustion is defined as CO2 CO-l-COz i.e. the quotient obtained from the amount of the CO2 divided by the sum of the amount `of CO plus CO2 in the exhaust gas, and the quantities `of CO and CO2 are calculated as standard volumes such as moles (gram molecules). The oxygen is supplied as free oxygen injected into the gas space and metal oxides such as ore which is supplied to the melt as a cooling agent. If carbonates, supplied as iron lbearing compounds or slag-formers, are used, corresponding correction must be made of the carbon dioxide content of the exhaust gas. In order to allow large additions of iron bearing ooolants, it is advantageous to operate with a high degree of combustion, e.g. at least 70% and preferably at about 80-100% thereby producing considerable excess heat over that required to attain the preselected temperature of the final melt. By supplying ferrous metals as a coolant the quantity of ferrous metal, i.e. steel, produced at the end of the process may increase over the metal initially supplied. Some iron, it is true, is lost as oxides in the slag and as dust in the exhaust gas, and consideration must be given to such losses of iron, which are estimated by experience.

With knowledge of the heat losses from the furnace, the theoretical amounts of free oxygen and cooling agents, including metal oxides, required for obtaining the preselected temperature and carbon content can be determined by calculating heat and material (particularly oxygen) balances.

More specifically, the sensible heat content of the pig iron and cooling agents as well as refining gas charged plus the heat developed by oxidation of carbon, carbon monoxide (according to the presumed average degree of combustion) and slag-transferable elements as well as slag-forming reactions are balanced by the sensible heat content of the resulting steel and slag (at preselected temperature) and of the exhaust gas (at a measured or estimated average temperature), plus the heat required for endothermic reactions, e.g. ore reduction and decomposition of carbonates, plus heat losses from the furnace for the period `of time of a refining operation.

Similarly the amount of oxygen supplied to the furnace as free oxygen, i.e. the amount of oxygen in the refining gas plus the amount of oxygen in the air or the like entering the furnace during the feed of solids thereto, and as yoxidic oxygen, i.e. iron oxide or the like in the cooling agent, shall be balanced yby the amounts of oxygen in the exhaust gas as carbon monoxide, carbon dioxide, possibly free oxygen and iron oxide (as dust) plus the oxygen in oxides of slag-transferable elements.

It will be understood that such theoretical calculations although accurate and based on long experience cannot reliably suffice by themselves in attaining the preselected temperature and carbon content simultaneously. Therefore, the process must be interrupted for sampling, which extends the time required to process a melt, and even then does not always produce the desired carbon content and temperature because the resultsl of the analyses can only be obtained after some delay.

It has been suggested that the carbon content of the exhaust gases be utilized for determining the carbon content of the metal melt in the furnace by integrating the quantities of carbon monoxide and carbon dioxide of the exhaust gas from the beginning of the process. It is true that the reduction of the carbon content of the liquid pig iron can be closely followed, and the process can be terminated at the preselected carbon content of the melt. But, to our knowledge, in no conventional pneumatic relining process has the temperature of the melt been controlled so as in a convenient way to reach a preselected temperature simultaneously with a preselected carbon content with any degree lof accuracy.

With the method of directing the refining of a molten carbon-containing ferrous metal in a furnace in accordance with the present invention it is possible to produce a metal melt having a preselected temperature and a preselected carbon content byvcontinuously measuring the quantity of carbon monoxide and the quantity of carbon dioxide in' the exhaust gas removed from the furnace, and controlling the refining process at one or more instants during the process, and at least at one late instant near the end of the refining, by separately measuring as from the start of the refining through each one of said instants the accumulated molar amount -of'carbon monoxide and the accumulated molar amount of carbon dioxide in said exhaust gas and determining from these measurements the actual average degree of combustion up to said instant. Such actual average degree of combustion is defined as the quotient of the accumulated molar amount of carbon dioxide by the sum of the accumulated molar amounts of carbon monoxide and carbon dioxide, i.e.

(322, (Cowon as from the start of refining through said instant. The method also comprises supplying after each of said instants an amount of cooling agent that together with previously supplied amounts thereof lies within and approaches, and in case of said late instant substantially equals to, the quantity necessary for absorbing that portion of the heat developed by the oxidation at said actual average degree `of combustion of all carbon to be removed and by the oxidation and combining of said slagtransferable elements, which exceeds the heat required for attaining said preselected temperature of the final melt; and further supplying after each of said instants an amount of refining gas that' together with previously supplied amounts thereof lies within and approaches, and in case of said late instant substantially equals to, the quantity necessary for oxidizing said slag-transferable elements andv for oxidizing at said actual average degree of combustion all carbon to be removed; and thereafter terminating the refining operation, thereby obtaining refined molten metal with said preselected temperature and carbon content.

The continual measuring and separate accumulation (or integration) of the amounts of carbon monoxide and carbon dioxide from the very start of the relining is fundamental for carrying out the invention. The measuring is best carried out by automatic flow measuring and analyzing equipment as will be described more in detail hereinbelow. The values obtained may be delivered to a computing apparatus which accumulates the values and can give at any checking instant the totals of the individual values of CO2 and CO fed to it from the start (s) up to said instant (i), i.e.

i i E oo2 and E oo respectively.

The degree of combustion is denominated F. For the refining period from the start (s) to an actual checking instant (i) the average degree of combustion Fav is:

E CO2 s 1" i Z tvo-t2 oo2 combustion heat produced by oxidizing part of said carbon monoxide into carbon dioxide as determined from the average degree Iof combustion, as assumed Fav or ob tained at the checking instant Favi. The particular values to be used in this calculation are obtained from measuring the quantities and temperatures of initially charged and later added metal, slag, rnetal oxides and slagformers. Preferably, the sensible heat contents are reckoned as above room temperature, whereby the temperature of said materials need not be taken into consideration when added at about room temperature.

sensible heat. The total of all these input items constitute the heat input of the entire heat balance at a particular instant of checking Fav.

In order to determine the excess heat to be absorbed by cooling agents the total heat input is `compared with the total heat output both considered tup to the end of the process. The heat output comprises the sensible heat of the metal and slag in the furnace and emerging dust, the

obtained equals the initially charged pig iron minus the slag transferred elements and carbon nto be removed, plus iron added as coolant minus the iron refining operation. The heat losses from the furnace mainly through radiation and convection may be estimated with great accuracy from previous refining periods of the furnace and enters the calculation as a factor per unit of time.

Knowing the cooling effect per unit of the different cooling agents used, the balance between the input and able elements in the pig iron.

In making the oxygen balance the total oxygen to be supplied is that required for oxidizing the slag-transferred elements to their respective oxides and for oxidizing all the carbon to .be removed, i.e. in order to attain the preselected carbon content, into carbon monoxide, and further oxidize a portion lof said monoxide into carbon dioxide as ydetermined by the average degree of combustion Fvvvi atl the instant a heat balance is made.

amounts of coolants, supplied in air, or the like, used for feeding solids to the furnace.

The difference between the amount of free `oxygen required and the amount the process should be used. However, this value is not known, but if the successively measured Fav is used for new balances up to and near the end of the refining operation, the corresponding balances become more and more accurate so that nearly true values for the end of the process can be predicted. Thus, at the start of the process an assumed value of Fav may be used in the balances, or the process can `be started at random and after some time when a significant Fm, is obtainable, this value can be used to direct the operation toward the desired end conditions.

As the heat and oxygen balances decide the proportions of the total amounts of free oxygen and oxidic oxyleast within a minute, the determinations ought to be made frequently, process.

can be and at least near the end of the Such successive determmations project requirenear the end of the process. It will be understood that of the amounts of carbon monoxide and dioxide for obtaining the average degree of combustion, and for obtaining it without delay, it is imperative to use high speed measuring methods that are sufiiciently accurate. Therefore, the invention, according to certain aspects thereof, also comprises such methods.

In order to obtain good results when controlling a melt according to the present invention it is important that the quantity of carbon removed and the degree of combustion of this carbon to carbon dioxide in the rening chamber or furnace be determined with accuracy. The most obvious method of determining the amount of refined carbon and the degree of combustion in the furnace is, of course, to measure directly the amounts of carbon dioxide and carbon monoxide in the exhaust gas from the furnace where it leaves the furnace mouth, and to calculate the amount of carbon and the degree of combustion from the measured amounts. However, accurate measurements are not practical at the furnace mouth where dust, slag splashes and non-uniformity of the gas stream occur which make sampling difficult and jeopardize the significance of any such measurements. In accordance with the invention, a new Way has been found to determine accurately the degree of combustion of the carbon to be removed from the melt within the refining furnace when practicing the new control method.

In general the method of determining the degree of combustion comprises, collecting all exhaust gas from the furnace, supplying thereto air in excess of that required for complete oxidation of all carbon monoxide of the exhaust gas into carbon dioxide and thereby completely burning the exhaust gas to form a flue gas which contains substantially only carbon dioxide, oxygen and nitrogen. The completely burnt flue gas will have a quantity of heat in addition to the sensible heat which the exhaust gas had when leaving the furnace which is substantially equal to the combustion heat of said carbon monoxide to carbon dioxide. The accumulated molar amount of carbon dioxide in said flue gas is continuously determined by measuring the content at intervals e.g. continuously, and integrating the value against time. Any changes in the status, i.e. composition and heat content of said flue gas caused by said burning of carbon monoxide, which changes correspond to the molar amount of carbon monoxide of the exhaust gas, also are measured to obtain the actual average degree combustion. The change in status of said flue gas can be ascertained in various ways. In all these methods, however, it is necessary to measure the flow of fiue gas and the molar amount of carbon dioxide therein. Therefore, the flue gas has to be analyzed, preferably in dry state, at least with regard to carbon dioxide, and according to certain methods also with regard to oxygen.

According to one of these methods for determining the average degree of combustion based upon an oxygen balance on the gas collecting hood, the dry fiue gas is continuously analyzed to determine the molar amounts of carbon dioxide and oxygen. The remainder of the fiue gas is assumed to be nitrogen. The air used foi burning the exhaust gas contains 79% by volume of nitrogen and 21% of oxygen. Therefore, the molar amount of said nitrogen corresponds to 79/ 21 moles of oxygen admitted with the air to the exhaust gas. The difference between the molar amount of the oxygen admitted and the molar amount of oxygen found in the fiue gas is the molar amount of oxygen consumed in oxidizing the carbon monoxide of the exhaust gas into carbon dioxide. As one mole of oxygen can oxidize 2 moles of carbon monoxide (|O2{-2CO=2CO2), the said molar amount of oxygen consumed corresponds to the double molar amount of carbon monoxide in the exhaust gas. The degree of combustion at a particular instant is now obtained by dividing the difference between the molar amount of carbon dioxide found in the flue gas by analysis and fiow measurement and said molar amount of carbon monoxide determined from the oxygen removed from the air with said amount of carbon dioxide analyzed. This degree of combustion is obtained for a short moment or an arbitrarily long interval and all successive values can be integrated to obtain the average degree of combustion, the integration being made with regard to the molar amount of analyzed carbon dioxide, being equal to the molar amount of concurrently oxidized carbon removed from the metal being refined.

This method can be modified so as to :render directly the average degree of combustion at any instant, by separately integrating the molar amount of the oxygen -admitted with the combustion air (obtained from the nitrogen in the liue gas) and the molar amount of the analyzed oxygen as from the start of the refining up to the actual instant. The difference between these oxygen amounts being that consumed by the oxidation of the integrated amount of carbon monoxide of the exhaust gas. Said carbon monoxide is equal to double said difference (O2 diff-l-2COz2CO2). The integrated amount of carbon dioxide in the exhaust gas (at the outlet mouth of the furnace) is obtained as the difference between the accumulated molar amounts of carbon dioxide in the flue gas (stack) and said carbon monoxide, and the average degree of combustion is the quotient between said accumulated amounts of carbon dioxide in the exhaust gas and,` in the flue gas, respectively.

According to another method for determining the average degree of combustion the sensible heat content, in, for instance, kilo calories, of the flue gas and the amount of carbon dioxide in the flue gas are continuously measured. The heat content of the flue gas comprises two terms, the sensible heat of lthe exhaust gas supplied to the hood at the mouth of the furnace and the potential heat of cornbustion produced by burning carbon monoxide in the hood. The sensible heat of the flue gas c-annot be Vascertained directly in an easy way. Therefore, according to this invention an approximate procedure will be resorted to. Said sensible heat content may be determined from the heat absorbed by a cooling medium in theA fiue system, the heat losses Afrom said system and the remaining sensible heat in fiue gas leaving said flue system. Said losses are mainly due to radiation and convection from the fiue system. The amount of carbon dioxide may be obtained as a molar amount and then be recalculated as kilograms of carbon oxidized from the ferrous metal being refined in the furnace. From these values the heat content per kilogram of carbon removed from the metal will easily be obtained as a quotient of the accumulated amounts of kcals. and kg. of carbon. The temperature of the exhaust gas prevailing at the mouth -of the furnace can be estimated with reasonable accuracy from experience from previous similar refining operations (heats). Moreover, it is a fact that at each temperature that normally prevails in the exhaust gas the degree of combustion varies linearly with the potential heat content (in kilo calories) per kilogram of carbon refined away from the molten ferrous metal, Thus, for instance, at 1800 C. the degree of combustion increases linearly from 0% to 100% as the potential heat content per kilogram of carbon oxidized away from the metal decreases from about 6815 kcal. to about 1910 kcal., and at 1400 C. from about 6525 kcal. to about 1430 kcal. The degree of combustion for intermediate or extraneous temperatures can easily be obtained by interpolation or extrapolation, respectively. Such a relationship is illustrated in the chart in FIGURE 2 of the drawings.

According to a third method, based upon an oxygen balance on the refining furnace, of determining the :average degree of combustion up to any instant the molar `amount of carbon dioxide in the flue gas and the molar amount of free and oxidic oxygen supplied to the furnace are separately and continuously measured and accumulated from the start of the refining operation up to said instant. The oxygen so supplied to the furnace is, on the one hand, consumed therein for oxidizing carbon of the metal into carbon monoxide and Ithe slag-transferable ele- Occasionally some oxygen escapes with the exhaust gas, especially in a case where all carbon monoxide is oxidized to carbon dioxide in the furnace. Therate and amount of oxygen said amount of oxygen consumed by the carbon is equal to half of the molar amount of carbon dioxide in the ilue gas, From this consideragen stoichiometrically amount of oxygen required for 100% combustion of the carbon monoxide to carbon dioxide makes it possible ito carbon dioxide in The above described methods of measuring the degree of combustlon of the carbon scribed methods, exceeds the value 1.0 with a certain fracoxygen may be quantitatively calcuwith prevailing operating conditions.

The invention `can be carried out in different types of oxygen blast reiining furnaces, in which the refining gas can be readily injected and the exhaust gas collected The furnace may be stationary or movable by shaking, but the monoxide from the melt during the refining. The oxygen can be injected onto the or temporary degree of carbon to control the supply of oxygen Example No. l

A rotary furnace was charged with 110,250 kgs. of pig iron of the following analysis:

4.26% C, 0.77% Si, 0.70% Mn The temperature of the pig iron measured in the ladle before charging was 1280 C. After charging 5000 kgs. burnt lime, CaO, the oxygen refining process the melt was 1480 C.

Sample was taken for analysis and the determination of the percentages of C, Si and Mn and the oxygen blow-` ing was continued with nm.3 per minute under con` tinuous supply of about 325 kgs.

completely burnt with air in excess. 300 C. with a measured amount The analysis of the sample taken before the blowing period was reported after 8 minutes of blowing and was 3.65% C, 0.32% Si and 0.70% Mn. Ordered analysis after the termination of the blowing was about 0.18% C, and the steel temperature was 1620 C. In order to obtain these values and under the presumption that 65% of the carbon was burnt to CO2 in the furnace and on the basis of stoehiometric, thermodynamic and empiric data the required total oxygen demand was calculated and found to be 8970 kgs., 5790 kgs. as oxygen gas and 13,120 kgs. of ore containing 24.3% oxygen.

During the blowing period, however, the calculated average degree of combustion fell below 65 and as a consequence thereof new calculations repeated every thirty-two seconds showed lower value for the required amount of oxygen gas and ore concentrate. The supplies of gaseous oxygen and concentrate were accommodated mutually lso that the require amount of concentrate had been supplied when further 400 kgs. of oxygen gas had still to be supplied. The average degree of combustion of the carbon from the beginning of the period was then only 57% and as a consequence thereof and in accordance with the calculations based upon the analysis of the ue gas only 12,000 kgs. of concentrate and 5660 kgs. oxygen gas, or in total 8570 kgs. oxygen, were supplied during the period.

The integrated percentage of carbon calculated from the volume of ue gas showed that when the blowing period was interrupted the percentage of carbon had fallen to 0.22%.

After the blowing the temperature of the melt was found to be 1625 and a check analysis before tapping showed 0.22% C. Without the adjustment of the first calculated demand of oxygen gas and concentrate, the percentage of carbon and the temperature would have become too low for rendering the desired steel to be tapped. An additional blowing period with inferior yield of steel and an addition of carbon would then have been necessary.

Example No. 2

Steel is to be made by refining molten pig iron in a furnace.

32,500' kg. of molten pig iron containing 3.3% C, 0.3% Si, 0.80% Mn, and 1.85% P (C as Fe3C and Si as FeaSi) and having a temperature of 1275 C. is charged into the furnace and by reacting it with commercial oxygen and burnt lime as a slag former. The steel to be made is to contain 0.50% C, less than 0.01% Si, 0.20% Mn, and 0.08% P and have a temperature of 1570o C.

Ore concentrate is used as a cooling agent for absorbing excess heat. The ore concentrate had the composition of 61% Fe, 23.3% O2, and 15.7% gangue. Assuming a percentage of Fe as oxides in the slag the ore has 22.6% O2 available for refining. The cooling effect is 1230 keal./kg. of ore.

The specific demand of lime for slagging oxides of Si and P and the gangue of the ore is 7.0 kg. per kg. Si, 5.0 kg. per kg. P, and 8.0 kg. per 100 kg. of ore.

The process is performed by supplying oxygen and ore, more or less continuously, in proportions to produce the desired steel from the raw materials.

From previous heats it has been found that the following values can be used with satisfactory accuracy as starting conditions:

Average degree of combustion (assumed), (F,1

:0.75), percent 75 Average temperature of exhaust gas, C 1700 Quantity of slag at end of period, kg 7000 Fe-content of slag (FeXO=13.4% percent 10 Furnace losses, meal. (mcal.=million cal.) 300 The amount of steel obtained from the charged pig iron is equal to the weight of pig iron, 32,500 kg., less the oxidized elements, namely C, 2.80% of 32,500-1910 kg.; Si, 0.31% of 32,500=101 12 kg.; Mn (0.800.20)`% of 32,500=195 kg.; P (1.85- 0.80)% of 32,500--575 kg.; Fe to the slag 10% of 7000 :700 kg.;.Total, 2481 kg. thus steel from pig iron 32,500-2480=30,020 kg.

The ore concentrate required for cooling is estimated from the following heat balance Heat input Pig iron (1275 C.) 32,500 0.274=8905 meal..

Total input 21,468 meal.

Heal output Steel (1580 C.) 30,020 0.325=9756 meal.

Slag (1580 C.) 7000 0.455=3185 meal. Exhaust gases (1700 C.):

CO 0.25 910 1.110=253 meal. CO2 0.75 9l0 1.787=1220 meal. Furnace losses 300 meal.

Total output 14,714 meal.

The difference between input and output gives an excess heat of 6754 meal., which` shall be absorbed by the ore concentrate to be added, the cooling capacity of which is 1.23 meal. per kg. Thus,

= 5490 lig.

ore has to be supplied.

Oxygen C CO 910 1.33=1210 kg.. CO- CO2 0.75 9l0 1.33=908 kg. Si- SiO2 101 1.14=115 kg. Mn MnO 195 0.29=57 kg. PP2O5 575 1.29=742 kg. Fe- FeXO 700 0.34=238 kg.

Total oxygen demand 3270 kg. Oxygen supplied by ore 22.6% of 5490 1241 kg. Free oxygen to be supplied by lance 2029 kg.

Lime

The lime required is determined as follows:

Si 101 7.0=707 kg. P 575 5.0=2875 kg. Ore 5490 0.08=439 kg.

Total lime demand 4021 kg.

The refining process is started (prior to determination of the actual balance) in a hot furnace charged with 32,500 kg. molten pig iron and 3600 kg. cold burnt lime, by injecting kg. free oxygen per minute through the oxygen lance and supplying successively 250 kg. of ore concentrate per minute through the lance for solid additions. The deficit of lime (4020-3600=420 kg.) also is supplied through the latter lance as required.

The above information may be supplied to a computer for a standard when the refining process is to be automatically controlled and the additions and exhaust gases are measured continuously and aecumulatively, the corresponding values being supplied to the computer. Thus, the amounts of free (lance) oxygen supplied, carbon monoxide and carbon dioxide occurring in the exhaust gas are all measured individually and the measured amounts are integrated. From this information the average degree of combustion (Fav) as determined in accordance with this invention is recorded from the start s and after i seconds it is tion tends to decrease it can be the amount of ore concentrate supplied.

If the measured average degree of combustion (Fav) decreases below the assumed degree 75% (F :0.75) the supply of ore is reduced to maintain the temperature high enough at the end of the refining, i.e. when the total amount of free oxygen will have been supplied. Suppose deficiency CO to CO2. However, all this heat is not lost, because the sensible heat content per mole of CO2 is heat content per mole of CO. loss of heat is therefore:

(5.631 being reaction heat CO CO2 and 1.787 and 1.110 being sensible heats of CO2 and CO, respectively, per kilogram of carbon).

The cooling effect of 1 kg. ore being l.23 mcal. the decit heat quantity 225 mcal. -corresponds to 225;1.23=18o kg.

ore, which must deducted from previously calculated ore demand 5490 kg. The supply of ore concentrate is then stopped when 5490-180=5310 kg. ore have been supplied.

Consequently the oxygen demand decreases correspondingly, namely by 0.05 910 910 1.33 (which is the difference in oxygen in CO2 and CO) less 180 0.226 (which is the reduction already determined for the reoxygen) making 2O kg. The previously determined oxygen requirement of 2029 kg. is corrected and reduced to 2009 kg.

and analyzed 4and the temperature measured. The resulting steel had 0.48% C, no Si, 0.075% P, 0.18% Mn;

1575 C., which is very near the preselected values.

Instead of automatically controlling the entire refining value of Fav=0.70, which l 14 operation, the information obtained such as the degree the amounts of oxygen and coolant tent and temperature in the rened product.

An apparatus for performing the method of the present invention and as illustrated in the accompanying drawing Will now be described.

as to pass the flue in order to facilitate values obtained at gas through them relatively quickly, a rapid reproduction of measured various positions in the gas flow.

The furnace 1 is charged with molten pig iron in a conventional way, not illustrated, and cooling agents are charged through weighing bins 11 for URE 1, excess air is caused to flow exhaust gas by the action of the fan 5.

The exhaust gas leaving the furnace is Icompletely collected by hood 2 having a side conduit 36 connected to Water cooling, the through conduit 40, meter 42 and a thermometer 43 and side conduit through pipe 45, with flow meter 47 and a thermometer 48. Likewise the or, alternatively, conduit is also provided with a thermometer 75 for measuring the gas temperature. A gas analyzer 77 is connected by pipe 78 to the conduit 6 and has a gas outlet 79. The analyzer 77 can provide analysis, in the first hand, on carbon dioxide and also on oxygen. The water content of the gas can be determined or the gas can be analyzed after drying in the analyzing apparatus. The balance between the total of dry fiue gas and its contents of carbon dioxide and oxygen is considered as nitrogen.

Even though the flue gas is dirty, the gas temperature and composition may advantageously be investigated at the exit portion of the hood arrangement by the aid of thermometer 82 and analyzer 83, thereby avoiding the effect of CO2 absorption by water in i.e. a Wet cleaning system.

While a method and apparatus for carrying out the method are described herein, it will be understood that various changes may be made in the steps of the method and form of the apparatus shown without departing from the spirit or scope of the invention. Therefore, without limitation in this respect the invention is defined by the following claims.

We claim:

1. In a method of refining a melt of ferrous metal containing carbon in a furnace to produce a melt having a predetermined temperature at a predetermined carbon content comprising the steps of determining the initial temperature, amounty and carbon content of the melt, continuously contacting the melt with a stream of gas containing free oxygen to produce carbon monoxide, convert at least a portion of the carbon monoxide to carbon dioxide by combustion and generate heat suflicient to exceed the desired predetermined temperature of the final melt, measuring the average degree of combustion of carbon removed from the melt by determining the relative amounts of carbon monoxide and carbon dioxode produced in the furnace, utilizing the average degree of combustion for determining the amount of heat developed and absorbed by the melt to raise its temperature, continuing to supply oxygen for a period of time required to produce the desired carbon content of said melt by combustion of carbon, introducing a coolant into the melt during the refining operation in amounts sufiicient to absorb excess heat and approach the required temperature simultaneously with the approach of the desired carbon content in the melt, stopping said refining operation by stopping the supply of oxygen when the melt has the predetermined temperature and carbon content and then pouring the melt.

2. The method in accordance with claim 1 in which the `amount of coolant supplied is varied in accordance with the heat produced by the combustion of carbon to carbon monoxide and carbon dioxide to absorb said excess heat at a rate related to its generation to produce the required temperature when the proper carbon content is attained.

3. The method in accordance with claim 1 in which the carbon content of the melt and temperature of the rnelt are both determined by the average degree of combustion of removed carbon to carbon monoxide and carbon dioxide, measuring the average degree of combustion Aduring the refining operation, and intermittently varying the supply of coolant to simultaneously produce the desired carbon content and temperature.

4. In a method of refining a molten, carbon containing ferrous metal in a furnace having a gas space above the melt to produce a metal melt having a preselected temperature and a preselected carbon content, the improvement which comprises, directing the refining process towards said preselected temperature and carbon content at least at one instant before the end of the process by measuring from the start (s) of the refining operation the separate accumulated amounts of carbon monoxide and carbon dioxide in the exhaust gas and obtaining therefrom at said instant (i) the actual average degree I of combustion from the beginning of the refining process:

i 2Go,

Zoo +2002 utilizing the average degree of combustion for determining the amount of heat developed and absorbed by the melt up to said instant to raise its temperature, supplying after said instant an amount of cooling agent which, together with previously supplied amounts thereof, approaches the quantity necessary for absorbing that portion of the heat developed during the entire refining operation at said actual average degree of combustion which exceeds the heat required for attaining said preselected temperature of the final melt, supplying after said instant an amount of refining gas which, together with previously supplied amounts thereof, will oxidize the slagtransferable elements and approach that amount required to oxidize all carbon to be removed at said actual average degree of combustion, and terminating the refining process when the refined molten metal simultaneously has said preselected temperature and carbon content.

5. In a method of refining a molten, ferrous metal in a furnace having a gas space above the melt to produce a metal melt having a preselected temperature and a preselected carbon content, comprising, supplying into the furnace a refining gas which contains free oxygen and a solid material of the group consisting of ferrous metal, oxidic compounds thereof and slagformers and combinations thereof as cooling agent, in such programmed quantities so as to supply approximately that quantity of free and oxidic oxygen that is required for the oxidation of all the carbon to be removed by rening to carbon monoxide, oxidation of any slag-transferable elements in said ferrous metal -oxidizable during refining, and oxidation of a portion of said carbon monoxide to carbon dioxide to produce an estimated degree of combustion, comprising the ratio of the amount of carbon dioxide and the sum of said amount and the amount of carbon monoxide formed in said furnace, to generate approximately the quantity of heat required for raising the temperature of the melt, including said cooling agent, to said preselected temperature, measuring the quantities of carbon monoxide and carbon dioxide in the exhaust gas from the furnace to determine at least at one instant near the end of the refining operation the actual average degree of combustion of carbon removed from the melt, utilizing the average degree of combustion for determining the amount of heat developed and absorbed by the melt up to said instant to raise its temperature, varying the program by supplying after said instant and before terminating the refining process an amount of cooling agent which, together with previously supplied amounts thereof, substantially equals the quantity necessary for absorbing excess heat developed by oxidation at said actual average degree of combustion of all carbon to be removed and by oxidation of said slagtransfer-able elements to produce the desired temperature at the particular time when the melt has the preselected carbon content, and terminating the refining process when the preselected carbon content and temperature have been reached.

6. A method as claimed in claim 5 characterized in supplying after said instant an amount of supplementary refining gas that together with previously supplied amounts thereof is substantially equal to the quantity required for oxidizing said slag-transferable elements and for oxidizing all carbon to be removed and converted into carbon monoxide and carbon dioxide in the proportions of said actual average degree of combustion at said instant, and terminating said supply of refining gas as soon as the supplementary gas has been supplied.

7. A method in accordance with claim 1 in which the carbon containing average degree of combustion is measured by collecting all exhaust gas from the furnace, supplying air to the collected gases in an amount in excess of that required for complete oxidation of all carbon monoxide of the exhaust gas into carbon dioxide and thereby completely burning the exhaust gas to form a line gas containing substantially only carbon dioxide, oxygen, and nitrogen and a quantity of sensible heat in addition to that of the exhaust gas substantially equal to the combustion heat of said carbon monoxide, continuously measuring and integrating the amount of carbon dioxide in said flue gas, continuously measuring the change in said gas caused by said burning of carbon monoxide to carbon dioxide which change corresponds to the amount of carbon monoxide in the exhaust gas, and continuously integrating the measured amount of carbon monoxide so determined, whereby to obtain the actual average de gree of combustion.

8. A method as claimed in claim 7 comprising the steps of continuously measuring and integrating the quantity of said flue gas in dry state, continuously analyzing said flue `gas with regard to oxygen as well as carbon dioxide, the balance being considered as nitrogen, the molar amount of said nitrogen corresponding to 79/21 moles of oxygen admitted with said air to said exhaust gas, the difference between the molar amount of said oxygen admitted as determined by the molar amount of nitrogen and the molar amount of said oxygen analyzed representing the double molar amount of carbon monoxide in said exhaust gas, determining the degree of combustion m said exhaust gas from the ratio between said carbon monoxide and said analyzed carbon dioxide, and determining the actual average degree oi combustion by integrating said degree of combustion with regard lo accumulated amount of analyzed carbon dioxide.

9. A method as claimed in claim 7 comprising, the steps of continuously measuring and integrating the quantity of said flue gas in dry state, continuously analyzing said flue gas with regard to oxygen as well as carbon dioxide, the balance being considered as nitrogen, separately accumulating the molar amount of said admitted oxygen supplied as air as determined by the amount of nitrogen and the molar amount of said analyzed oxygen as from the start of the refining operation, the difference medium,

and the remaining 12. A method as tinuously measuring iiue gas in dry state, continuously measuring the accumulated molar amount of carbon dioxide in the flue gas heat content of the thus cooled gas.

' 7, comprising conmonoxide representing the molar amount of carbon dioxide in the exhaust gas, and determining the average degree of combustion as the quotient between said amount of carbon dioxide in the exhaust gas and said amount of carbon dioxide in the ilue gas.

References Cited by the Examiner UNETED STATES PATENTS l BENJAMIN HENKIN, Primary Examz'nen.

Claims (1)

1. IN A METHOD OF REFINING A MELT OF FERROUS METAL CONTAINING CARBON IN A FURNACE TO PRODUCE A MELT HAVING A PREDETERMINED TEMPERATURE AT A PREDETERMINED CARBON CONTENT COMPROSING THE STEPS TEMPERATURE, AMOUNT AND CARBON CONTENT OF THE MELT, CONTINUOUSLY CONTACTING THE MELT WITH A STREAM OF GAS CONTAINING FREE OXYGEN TO PRODUCE CARBON MONOXIDE, CONVERT AT LEST A PORTION OF THE CARBON MONOXIDE TO CARBON DIOXIDE BY COMBUSTION AND GENERATE HEAT SUFFICIENT TO EXCEED THE DESIRED PREDETERMINED TEMPERATURE OF THE FINAL MELLT, MEASURING THE AVERAGE DEGREE OF COMBUSTION OF CARBON REMOVED FROM THE MELT BY DETERMING THE RELATIVE AMOUNTS OF CARBON MONOXIDE AND CARBON DIOXODE PRODUCED IN THE FURNACE, UTILIZING THE AVERAGE DEGREE OF COMBUSTION FOR DETERMINING THE AMOUNT OF HEAT DEVELOPED AND ABSORBED BY THE MELT TORAISE ITS TEMPERATURE, CONTINUING TO SUPPLY OXYGEN FOR A PERIOD OF TIME REQUIRED TO PRODUCE THE DESIRED CARBON CONTENT OF SAID MELT BY COMBUSTION OF CARBON, INTRODUCING A COOLANT INTO THE MELT DURING THE REFINING OPERATION IN AMOUNTS SUFFICIENT TO ABSORB EXCESS HEAT AND APPROACH THE REQUIRED TEMPERATURE SIMULTANEOUSLY WITH THE APPROACH OF THE DESIRED CARBON CONTENT IN THE MELT, STOPPING SAID REFINING OPERATION BY STOPPING THE SUPPLY OF OXYGEN WHEN THE MELT HAS THE PREDETERMINED TEMPERATURE AND CARBON CONTENT AND THEN POURING THE MELT.

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