US3207596A

US3207596A - Production of steel

Info

Publication number: US3207596A
Application number: US137879A
Authority: US
Inventors: Pinches Elwyn
Original assignee: Richard Thomas and Baldwins Ltd
Current assignee: Richard Thomas and Baldwins Ltd
Priority date: 1960-09-21
Filing date: 1961-09-13
Publication date: 1965-09-21
Anticipated expiration: 1982-09-21
Also published as: CH397744A; DE1249900C2; GB930388A; ES270491A1; DE1249900B; BE608399A

Description

Sept. 2l, 1965 E. PlNcHEs O 3,207,596

A PRODUCTION OF STEEL Filed Sept. 13, 1961 6 Sheets-Sheet l z/'/' /4 f6 :j

Inventor ELM/YN PlNCHES Sept. 21, 1965 E. PlNcHr-:s 3,207,595

PRODUCTION 0F STEEL Filed sept. 1s. 1961 e .sheets-sheet 2 Inventor ELwYN PmcHE-s Wed, aowu, Sewf fwadfe,

A ttorneys Sept. 21, 1965 E. PlNcHEs PRODUCTION OF STEEL 6 Sheets-Sheet 5 Filed Sept. 15, 1961 Inventor LwyN PINCHES y wu @L wma/ Ww, J6 l S f Aflornefeys Sept. 2l, 1965 E. PINCHEs 3,207,596

PRODUCTION OF STEEL Filed Sept. 13, 1961 6 Sheets-Sheet 4 Inventor ELWYN PINCHS Sept. 21, 1965 E. PINCHEs 3,207,596

PRODUCTION OF STEEL Filed Sept. l5, 1961 6 Sheets-Sheet 5 m D y V 1 /9 /9 f 1 U U 6/ r f 62 52 60 60 Inventar ELW YN PI NCH E5 y Waard, 640W, ScW-@Jmfs Sept. 21, 1965 E. PlNcHEs 3,207,596

PRODUCTION 0F STEEL Filed Sept. 15, 1961 6 Sheets-Sheet 6 Inventor ELWYN PINCHE'S Attorneys United States Patent O 3,207,596 PRODUCTIUN OF STEEL Elwyn Pinches, Bridgend, Glamorganshire, Wales, assignor to Richard Thomas & Baldwins Limited Filed Sept. 13, 1961, Ser. No. 137,879 Claims priority, application Great Britain, Sept. 20, 1960,

32,442/60; Aug. 18, 1961, 29,925/61 8 Claims. (Cl. 75-11) The processes used for many years in the manufacture of steel from iron ore have always been two-stage processes. In the rst stage iron ore is reduced to iron, generally in a blast furnace, whilst in the second stage iron is converted into steel by various methods, for example in an open hearth furnace or a Bessemer converter,

There are a number of disadvantages in the use of a blast furnace for reducing iron ore. Firstly, for efficiency, a blast furnace should be large and have a high capacity. The installation of such a furnace thus involves considerably capital expenditure. Furthermore, blast furnaces require both high-quality ores and coke, so that it is expensive to operate these furnaces where there is no abundant supply o-f good coking coal or high-quality ore. The consumption of coke in a blast furnace is generally from 700 to 1000 kg. of coke per 1000 kg. of iron produced. It is recognised that about 400 kg. of this coke is consumed in the chemical reduction of iron oxides, and that the remainder provides heat for the process by combustion.

Iron ore may also be reduced in an electric arc furnace. In such a furnace the heat requirements of the reduction process are met by electrical power, so that the consumption of carbon (in the form of coke or other carbon-bearing materials) is limited to that required by the chemical process of reduction. However, for this process to be economically attractive it is necessary to have a cheap supply of electricity.

In recent years numerous modifications in the methods of reducing iron ores to iron have been proposed. These processes (including the beneciation of ores and sintering) can in some cases make use of poorer iron ores and other sources of carbon, such as lignite. All these processes yield iron in some form, eg. pig iron and sponge iron, and this iron must subsequently be processed into steel.

In the invention iron ore is reduced to iron, and this iron is converted into a low-carbon iron, of which steel is an example, in a single furnace. This is done according to the invention, by electrically heating7 the ore with carbon and limestone in an arc furnace to produce molten metal, which collects at the bottom of the furnace, and injecting oxygen into the pool of molten metal with the production of hot reducing gases, which pass through and reduce further ore within the furnace. The ore may be used in its raw state or in the form of sinter or of a mixture of the two.

The oxygen, as in the Bessemer converter, oxidises the impurities in the molten iron and this oxidation is accompanied by a considerable evolution of heat. In the Bessemer converter the heat is largely wasted, but in the present process it is utilised in heating the unreduced ore above the molten iron. Furthermore, because of their content of carbon monoxide, the hot gases passing out of the layer of molten iron have reducing properties, which are also utilised in the reduction of the iron ore. Once the conversion of the molten iron into steel has commenced, the supply of electrical power can be reduced as the heat evolved by the refining of the molten iron increases, thus making possible a considerable reduction in power consumption. Conversely, as the amount of molten iron present increases, so is the rate of flow of oxygen iincreased. The process may be carried on in 3,207,596 Patented Sept. 21, 1965 ICC batch fashion, as in a Bessemer converter. Then, when all the iron ore has been reduced to iron and the molten iron has been suiciently treated to remove impurities, the slag formed is removed and the usual additions of alloys to the steel can be made. Alternatively the process may be carried on continuously, as in known smelting furnaces having stacks into which the charge is introduced to move down into the furnace vessel proper.

The carbon which is mixed with the ore for the reduction thereof can be coke as in conventional processes, but one of the advantages of this process is that substantially any convenient source of carbon may be used. Thus materials such as lignite, charcoal and even sawdust may be used to provide the carbon in the burden.

Similarly, the process of the invention may be used to reduce iron ores unsuitable for reduction in a blast furnace. Thus, for example, titaniferous magnetite, large deposits of which exist in numerous countries, is considered not very suitable for reduction in a blast furnace, but this ore has been processed by electric arc smelting, and is likewise suitable for processing in accordance with the present invention with steel. Vanadium-containing ores may also be used in this process.

As mentioned above, the gases evolved from the molten iron pass through the unreduced ore above it and in so doing both help to heat the ore and to reduce it. However, the gases may still have a high content of carbon monoxide when they have passed through the bed of ore, and it is a feature of the invention that at least part of this carbo-n monoxide should be recovered and returned to the furnace.

The limestone is used to aid slag formation, and is mixed with the iron ore charge. However, during the rening of the motlen iron it may be necessary to introduce more lime to react with excess silica and thus aid the removal of phosphorus from the melt. This is conveniently effected by blowing powdered lime into the melt with, for example, the oxygen or with recycled carbon monoxide. A deficiency of carbon in the melt can be met by blowing in powered carbon in a similar manner. This may be necessary when there is no longer any carbon in the melt in order to increase the rate at which molten iron is produced from the iron ore and to prevent burning of the iron of the melt.

The process may be carried out in various forms of furnace, which are themselves a part of the invention, and all of which comprise the combination of an arc furnace and means for introducing oxygen into metal in the bottom of the furnace.

Some furnaces according to the invention are illustrated in the accompanying drawings, in which;

FIGURE 1 is a front view, partially in section, of one furnace;

FIGURE 2 is a side view, partly in section on the line II-II in FIGURE l;

FIGURE 3 is a plan view of the furnace shown in FIGURE 1;

FIGURE 4 is a view similar to FIGURE 1 showing a second furnace;

FIGURE 5 is a side view of the furnace shown in FIGURE 4;

FIGURE 6 is a front view of another furnace;

FIGURE 7 is a front view, partially in section, of a fourth furnace; and

FIGURE 8 is a plan view of the furnace shown in FIGURE 7.

In the furnace shown in FIGURES l, 2 and 3 there is a vessel 1 composed of a steel shell 3 and a refractory lining 4, which externally somewhat resembles a Bessemer converter and will be referred to as the converter. Three vertical electrodes 2 pass through the mouth of this converter into the burden inside it. One feature of the invention is the special shape of the lining 4, provided to help in supporting the weight of the burden in the converter. The lower part 5 of the converter, where molten metal collects, has a smaller diameter than the upper part 6, and where the converter widens out between these parts there is an inclined portion 7 which helps to support the weight of the burden 8 in the upper part. The shell 3 of the converter may be shaped in a similar manner, but, as illustrated, it is preferred that the shape f be obtained by varying the thickness of the brickwork 4 in a shell of conventional shape. the inside of the converter in this way is to provide a wider upper section in the converter in order to present as much unreduced ore as possible to the gases rising from the lower part of the furnace, and hence increase the eliiciency both of the heat-exchange between the gases and solids and of the chemical action of the gases on the ore. The sloped section 7 supports part of the weight of the burden and serves to direct this into the narrower lower section of the furnace, where the ends of the electrodes 2 are situated. In this way the electrical heating is distributed more evenly through the burden.

The converter is supported on trunnions 9 and 10 by a trunnion belt 11 which surrounds it. The trunnion belt 11 incorporates a guide 12 for a lance 13 at each trunnion, so that a lance can be projected into the converter from above each trunnion at an angle of about 35 to the horizontal. This angle will vary widely in the different furnaces, since it depends very largely on the rel-ative dimensions of the converter. The opening 14 for the lances on the inside of the lining should be just above the maximum level 15 reached by molten metal in the converter during production. Unless the openings 14 are arranged in this way, above the highest level of molten metal 15 and in or near the vertical plane through the axis of the trunnions 9 and 10, hot liquid metal may enter and damage the passages through the brick lining 4 for the lances when the converter is tilted. It is an important feature of this construction that the openings 14 are at all times and in all positions of the converter clear of molten metal.

The trunnions 9 and 10 are carried in bearings 16 supported on pillars 17. A motor 18 is connected to the trunnion'10 to tilt the converter 1.

The lances 13 are water-cooled, water and oxygen being supplied from water and oxygen supply service pipes 20 and through iiexible pipes 21. The lances are advanced or retracted through the guides 12 and the wall of the converter by means of an endless wire rope haulage device 22 fixed to each lance. Asthe lances move in and out of the converter slack in the exible pipes 21 is taken up by weighted pulleys 23. In the position of use indicated by the dotted lines 24 the lances 13 project obliquely downwards almost to the bottom of the converter. Powdered materials such as carbon and lime are stored in bins 19, and these materials may be drawn into the lances through flexible pipes 35. Y

The three vertical electrodes 2 are of conventional design and are arranged symmetrically at the apices of an equilateral triangle. They are carried by lifting gear 2S so that they can be lifted clear of the converter 1 for pouring, and are supplied with electrical power from a transformer 37. The electrodes pass through a fixed hood 26 which is cooled by water flowing through annular electrode guides 36. The hood 26 is supported by steel girders 27. The purposes of the hood is to collect the eiiiuent gases from the converter so that these may be utilised further, eg., by recycling, and to this end a pipe 28 for the gases is provided. There is sufficient clearance between the base of the hood 26 and the mouth 29 of the converter to allow the latter to be turned into the pouring position, andthe gap created in this way is closed during operation by a movable gas seal 30. This comprises a steel ring which fits onto the mouth of the converter and closely surrounds the base of the hood, and is carried by a The effect of shaping l lifting mechanism (not shown) to lift it above the base of the hood when pouring is to take place. A bunker 31 is provided for charging the furnace with raw materials. The converter is fed from this bunker through pipes 32, the supply of raw materials being cut olf by rneans` of gates 33 operated by pneumatic rams 34.

When the process according to the invention is carried out in this furnacethe converter is first charged with a mixture of iron ore, limestone, and carbon, the electrodes already being in their lowered position, and the current is switched on. During this stage of the process the power consumption is similar to that in a conventional electric smelting furnace, since all the heat for the reduction must be provided by electrical power. A pool of molten iron forms gradually at the bottom of the converter, and when this pool has become suiiiciently large oxygen is injected into the molten iron. Although oxygen injection could begin as soon as there is molten iron present, in practice it may be desirable to wait until an appreciable amount has collected, for example about 1 ton in a converter of a nominal capacity of 100 tons. As soon as the oxygen contacts the molten iron there is a rapid rise in temperature caused by chemical reactions, and carbon monoxide gas is evolved. Much of the heat of these reactions is transferred to the unreduced ore by the gas which passes up through the converter, and, in addition, the carbon monoxide in *this gas contributes to the reductionyof the ore. Because of this heat transference less electrical power is required, and the current intensity and supply may be automatically reduced in a manner similar to conventional electric smelting furnace techniques. During operation the lances 13 maybe retracted as the level of molten metal in the converter rises.

The lances may actually dip into the molten metal, or alternatively may be above the metal and direct a jet or oxygen at its surface. When oxygen is -injected under pressure into liquid metal in the bottom of the converter in either of these ways there is a violent chemical reaction and a tendency for the metal to rise upwards in the centre of the converter away from the lining. This action is different from that in conventional top-blown processes in which a jet of oxygen under pressure impinges vertically downwards onto the surface of liquid metal, and in which the metal may swirl outwards and scour the face of the brickwork lining of the converter, thus causing considerable wea-r of the lining.

The gases which are evolved and pass out of the converter through the gas-collecting hood 26 contain a high proportion of carbon monoxide, and this may be used vagain in the process, for example to cool the inside upper surface of the converter lining, to act as a conveying medium for solid materials such as carbon or lime which it may be desired to inject into the molten metal, and to increase the chemical eiiiciency of the process by being recycled through the converter. The etlluent gases may be cleaned in a conventional electrostatic precipitator or by a wet-washing process and recycled by means of a booster fan. Excess carbon monoxide may be used elsewhere in the steelworks.

The nal stages of the reduction of ore can generally be carried out without electrical power. The current may be cut off either manually or automatically, and then the electrodes are lifted out of the converter. This permits visual inspection of the molten metal, so that the operator may judge when it is ready for pouring. During these final stages of the process, alloying additions may also be made.

To pour the steel from the converter, the lances and electrodes are first completely withdrawn and the movable gas seal is raised. On tipping the converter, the slag lirst runs off, and then the steel is poured into suitable ladles or other containers. The position of the converter during pouring is indicated by the dotted lines 35 in FIGURE 2.

In the furnace shown in FIGURES 4 and 5, the three vertical electrodes are replaced by a pair of horizontal electrodes 40. These electrodes project through the centre of trunnions 41 of modified construction and through the side wall of the converter, and are supported outside the converter on trolleys 42. The trunnions 41 are of a disc-like construction, the central part 43 of the disc being integral with a conventional trunnion belt 44, and hollow at its centre to allow an electrode to pass freely through it. The rim 45 of each disc forms the bearing surface of each trunnion. Between the rim 45 and the central part 43 there is a thinner intermediate portion 46, which is provided with reinforcing ribs 47. Each trunnion bearing surface is supported on four smaller wheels 48 arranged below it. These wheels are mounted in pairs in brackets 49 which themselves can pivot in fixed mountings 50.

In this construction four lances 13 are provided, the details of their construction being the same as in the furnace of FIGURES 1-3. One lance 13 enters the converter on each side of each electrode 40 through guides 51. The converter itself has a smaller mouth 52 than the converter in FIGURES 1-3, and the hood 53 and gas seal 54 are of a correspondingly simpler arrangement. The lining of the converter is essentially the same as in the first construction, except that it projects further inwards in the neighbourhood of the electrodes at 55 to afford the sides of these some protection.

The bunker 31 is similar to that in FIGURES 1-3, but the pipe 56 leading from it is not mounted in the hood 53, and simply directs a stream of the raw materials into the converter when the movable seal 54 is raised.

A feature of this furnace is that it uses an indirect arc and a single-phase power supply, and this may be advantageous for local power supplies in some areas.

In another modified furnace, shown in FIGURE 6, metal-lined brick tuyeres 60 replace the lances 13 of FIG- URES 1-3. The tuyeres must be placed in the same positions as those occupied by the openings for the lances, that is to say above the maximum level of molten metal in the converter 1, so that for the gas injected through the tuyeres to reach the molten metal, particularly in the early stages of the process, higher pressures are necessary in order to penetrate the intervening burden and make contact with the molten metal. The tuyeres may be Watercooled and gas is permitted through pipes 62 to the tuyeres. The containers 19 supply powdered materials to nozzle boxes 61, and these materials may then be drawn into the tuyeres by the gases flowing through the pipes 62. In all other respects this furnace is identical with that ilillustrated in FIGURES l-3, except that the trunnions 63 are proportioned somewhat differently.

The use of such tuyeres has the advantage that complex water-cooling is unnecessary, and the attendant pipes and flexible connections are eliminated. The tuyeres will burn away like the lining brickwork, and may be replaced when the converter is re-lined.

The furnace shown in FIGURES 7 and 8 somewhat resembles one type of conventional electric smelting furnace, and is adapted for what may be regarded as continuous production of steel. There is a short stack 70 above the furnace 71 itself, and the electrodes 72 are arranged vertically, thereby simplifying the arrangement of the electrodes and the attendant lifting gear 73. As the furnace stack 70 is kept filled with burden during production, greater utilisation of the heat of the effluent gases is possible compared with the modified Bessemer converters described above. At the top of the stack 70 there is a conventional charging bell 74 for charging the furnace. This is fed by an endless belt 75.

The stack 70 is surrounded vby six vertical electrodes 72, which enter the furnace 71 through the upper part of the furnace casing 76. As in the modified Bessemer converter, the interior of the furnace has a smaller diameter at its base, where molten metal and slag collect. Openings for lances 77 are again provided above the maximum level of molten metal 78, and above these openings the wall of the furnace slopes outwards at an angle of about 60. Since the furnace is fixed, it is not necessary to limit the positioning of lances around it, and in the construction shown there are four lances arranged on the lines 79 in FIGURE 8. More lances may be provided if desired around the perimeter of the furnace. A notch 80 is provided on one side of the furnace for tapping the slag and another notch 81 on the other side for tapping the molten steel periodically in a conventional manner. The efiiuent gases are removed from the furnace rstack through a pipe 82.

In this furnace also the metal-lined tuyeres described above with reference to FIGURE 6 may replace the Watercooled lances.

I claim:

1. A process rfor the production of low carbon iron by smelting and refining iron in a single process from a charge of iron ore, coke and limestone, which comprises charging an electric arc furnace with the charge, electrically heating the charge to smelt the iron ore and to produce molten pig iron, collecting the molten pig iron as a pool at the bottom of the furnace, and injecting essentially pure oxygen into the pool of molten pig iron to purify it and produce reducing gases whereby an iron of the desired carbon content is produced and heat is generated, the hot reducing gases passing up through the charge to assist in the heating and smelting of the charge.

2.. A process according to claim 1 in which powdered lime is blown into the molten iron at the time the oxygen is injected.

3. A process according to claim 1 in which powdered carbon i-s blown into the molten iron at the time the oxygen is injected.

`4. A process according to claim 1 in which carbon monoxide-containing -gases leaving the furnace are returned and blown into the molten iron.

5. A process according to claim 1 in which carbonmonoxide-containing gases leaving the furnace are recovered and returned to the furnace.

6. A process according to claim 2 in which the powdered lime is blown into the molten iron by means of the oxygen.

7. A process according to claim 2 in which the powdered lime is -blown into the molten iron by means of recycled carbon monoxide-containing gases.

8. A process according to claim 3 in which the powdered carbon is blown into the molten iron by means of recycled carbon monoxide-containing gases.

References Cited by the Examiner UNITED STATES PATENTS 1,034,784 8/12 Greene 75-11 X 1,513,735 A11/24 Bigge 75--11 11,920,376 8/33 Greene 75-11 2,066,665 1/37 Baily 75-11 2,207,746 7/ 40 Maier 13-9 2,448,886 9/48 Hopkins 13-9 3,058,823 10/ 62 Churcher 75-52 3,079,249 2/ 63 De Moustier 75-52 DAVID L. RECK, Primary Examiner.

MARCUS U. LYONS, WINSTON A. DOUGLAS,

Examiners.

Claims

1. A PROCESS FOR THE PRODUCTION OF LOW CARBON IRON BY SMELTING AND REFINING IRON IN A SINGLE PROCESS FROM A CHARGE OF IRON ORE, COKE AND LIMESTONE, WHICH COMPRISES CHARGING AN ELECTRIC ARC FURNACE WITH THE CHARGE, ELECTRICALLY HEATING THE CHARGE TO SMELT THE IRON ORE AND TO PRODUCE MOLTEN PIG IRON, COLLECTING THE MOLTEN PIG IRON AS A POOL AT THE BOTTOM OF THE FURNACE, AND INJECTING ESSENTIALY PURE OXYGEN INTO THE POOL OF MOLTEN PIG IRON TO PURIFY IT AND PRODUCE REDUCING GASES WHEREBY AN IRON OF THE DESIRED CARBON CONTENT IS PRODUCED AND HEAT IS GENERATED, THE HOT REDUCING GASES PASSING UP THROUGH THE CHARGE TO ASSIT IN THE HEATING AND SMELTING OF THE CHARGE.