GB1597058A

GB1597058A - Steelmaking process and converter

Info

Publication number: GB1597058A
Application number: GB17506/78A
Authority: GB
Original assignee: Eisenwerke Gesellschaf Maximilianshuette mbH
Current assignee: Eisenwerke Gesellschaf Maximilianshuette mbH
Priority date: 1977-05-04
Filing date: 1978-05-03
Publication date: 1981-09-03
Also published as: LU79574A1; AT381955B; AU524543B2; PL206480A1; HU178526B; CA1115962A; FR2389677B1; DD137728A5; CZ286478A3; FR2389677A1; JPS541220A; BR7802772A; BE866644A; NL177610B; PL124494B1; JPS5651207B2; AR218488A1; NL177610C; NL7804802A; AU3572178A

Description

(54) STEELMAKING PROCESS AND CONVERTER (71) We, EISENWERK-GESELL SCHAFT MAXIMILIANSHUTTE MBH, a German Company of Postfach 1180, 8458 Sulzbach-Rosenberg, West Germany, do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a process for making steel from a charge comprising solid iron, in particular scrap, in a converter, wherein oxygen or other oxidizing gas surrounded by a protective medium is blown by means of tuyeres through refractory brickwork of the converter. It also relates to converters for carrying out such processes.

A number of converter steel making processes are known in which pig iron is refined by top or through blowing. Appreciable heat is generated from the oxidation of the oxidisable elements present in the pig iron and this heat is used for melting cold scrap added to the converter. For instance, when making one ton of steel, 800 kg of a conventional pig iron containing 4.2% carbon, 1.0 O,o silicon an 0.8b manganese, and 300 kg of scrap are loaded into the converter. Since scrap is generally available in large amounts and at favourable prices, while the production of pig iron in a blast furnace is expensive and relatively costly, as much scrap as possible is used when making steel. A higher proportion of scrap is more economical and avoids a corresponding enlargement of blast furnace capacity.

In addition to scrap, suitable solid sources of iron applicable to converter processes and available at fairly favourable prices include pre-reduced pellets, sponge iron, or solid pig iron. Their use, as is true for scrap, leads to increasing the steelmaking capacity without entailing an enlargement of the blast furnace capacity at the site of the converter.

The upper limit of the proportion of scrap which can be used is limited by the exothermal oxidation of the elements present in the pig iron, that is, by the heat released by the burning of the silicon, carbon and other oxidizable elements usually present in the pig iron. To use more scrap, the attempt has been made for instance to melt the scrap using a burner with a saucer-like flame in a special scrap melting apparatus, and subsequently to refine the melt in a converter together with liquid pig iron to obtain steel.

This process, however, is complicated because it requires a special scrap melting apparatus and because much time is required to melt the scrap using the saucer-like burner flame.

Furthermore, there is some risk in loading the molten scrap even when already partly pre-refined, into a pig iron melt already present in the converter, considering the high potential of oxidation of molten scrap of low carbon content in the presence of a pig iron melt with a high carbon content.

Again, the preheating of scrap in a converter using a natural gas or oil/oxygen lance burner is resorted to only occasionally because the thermal efficiency, of approximately 30two, of the fuels is low and because of the appreciable wear suffered in the refractory lining due to the relatively long preheating time, the converter furthermore being unavailable for refining during this preheating period. If there is a ratio of preheating time to refining time of 2:3, the preheating of the scrap is then at the cost of converter output.

A process of making steel in a converter from a charge containing solid iron such as scrap, in which the charge is both melted and then refined in the converter is disclosed in British Specification No. 1,027,552 and the aim of this invention is to improve such a process, providing for example a higher thermal efficiency together with a relatively low temperature of the exhaust gases and therefore an improved life of the refractory brickwork of the converter. Depending on the economics a charge in the converter of even 100or. scrap may be used.

To this end, according to the present invention we provide a process for making steel from a charge comprising solid iron in a converter having tuyeres extending through a refractory lining of the converter, each tuyere comprising two concentric pipes, wherein the solid iron is charged into the converter, an oxidising gas consisting of oxygen, air, or a mixture thereof is blown through the inner pipes of the tuyeres which are in the lower part of the converter below the level of the iron charge, a carbon carrier is introduced into the converter and is burnt in the oxidising gas and the resulting combustion gases flow upwardly through the iron charge, the oxidising gas and the carbon carrier being introduced in proportions providing a stoichiometric combustion of the carbon carrier to preheat the solid iron, further carbon carrier, which is solid and is introduced into the converter together with or after the charge, then being burnt by an increase in the proportion of oxidising gas so that the converter exhaust gases then contain carbon monoxide and the charge being substantially entirely melted, and finally the melt is refined in the converter by blowing oxygen into the melt through the inner pipes of the tuyeres, the oxygen being surrounded during refining by a sheath of protective medium introduced through the outer pipes of the tuyeres.

The process of the invention offers high thermal efficiency and makes possible a very brief time of preheating because the hot combustion gases flow through the charge of the solid iron and transfer an appreciable part of their heat due to the intimate contact and the large surfaces of contact between the gases and the iron. The exhaust gas temperature in the upper part of the converter is relatively low and therefore the wear in the refractory lining is also slight. The use of several tuyeres in the. converter bottom or in the lower part of the side wall of the converter as burners for the combustion of carbon, as is preferred, furthermore provides a very uniform distribution of the hot combustion gases across the charge of the solid iron.

The process of the invention may be divided to some extent into three phases: a first phase, hereafter designated as the preheating phase, in which the solid iron is heated to an average temperature of from 10000C to 12000C without there being a substantial formation of molten iron, and in which oxidizing combustion gases are predominantly present; a second phase, denoted as the pre-refining phase, in which the entire charge or substantially the entire charge of the solid iron is melted and in which the composition of the exhaust gases becomes much less oxidizing than the composition of the exhaust gases during the preheating phase; and finally the refining phase, in which the amount of carbon and other elements present in the melt is decreased by means of oxidation in the known manner.

Gaseous or liquid carbon carriers such as natural gas or methane, propane, butane, benzol, crude oil, fuel oil, crude tar or refinery residues are especially suitable for preheating.

These materials are preferably fed through the outer pipes of the tuyeres while the oxidizing gas, such as air, oxygen or a mixture thereof is blown into the converter through the inner or innermost pipes. In this case the proportion of oxidizing gas to the gaseous or liquid carbon carrier, which also acts as a protective sheath around the oxidizing gas, may be changed in successive phases of the process of the invention. During the preheating phase, liquid or gaseous carbon carriers are introduced in proportions required for the substantially stoichiometric combustion with the oxidizing gases to form CO.

and H20, while in the refining phase hydrocarbons are introduced only in such amounts as are needed to protect the tuyeres, that is in an amount of less than 10% by weight of the oxygen fed through the tuyeres. It may be appropriate to switch once or more often from liquid to gaseous carbon carriers.

In addition to being introduced through the tuyeres which serve for the introduction of the refining gas, the gaseous or liquid carbon carriers may be introduced also through special supply systems, for instance extending through a pipe in a taphole of the converter. Liquid carbon carriers such as petroleum, fuel oil or light oil then flow down along the converter wall to burn with the oxygen issuing from the tuyeres in the converter bottom or in the lower part of the converter wall.

It is important in all cases that the combustion of the carbon carrier should take place as close to the converter bottom as possible and below the bottom of the solid iron charge, so that the hot combustion gases when flowing upward follow a relatively long path through the solid iron.

One important preferred feature of the invention consists in using the described, short-term preheating of the solid iron, in particular scrap, for the increase of the scrap proportion in the conventional converter refining processes. The OBM/Q-BOP converters, which are described for example in United States Patent No. 3,706,549 and which comprise tuyeres for introducing oxygen surrounded by a protective medium below the surface of the melt in the converter have been found to be particularly suitable for use in the process in accordance with the invention.

Preferably a liquid carbon carrier is introduced into the converter through the annular spaces in the multiple pipe tuyeres during preheating, and a gaseous carbon carrier, for instance 1 .. by volume of propane or 5-10 yc, by volume of natural gas referred to the oxygen, is introduced into the converter through the annular spaces during refining.

The switch over from the liquid to gaseous carbon carrier takes place during the prerefining phase, or at the beginning of the refining phase.

A liquid carbon carrier, for example oil, may be fed through the annular spaces of the tuyeres into the converter at a rate of from 1 to 10 litres per minute per ton of solid iron. Simultaneously an oxidizing gas flows through the inside pipe of the tuyere at a rate of from 1.5 to 2.5 Nm of oxygen per litre of liquid carbon carrier. The tuyeres may operate as burners during the preheating phase. One advantageous tuyere construc tion useful in the invention is a conventional tuyere consisting of concentric round pipes, the tuyere annular space being ordinarily 1 mm wide. Alternatively, tuyeres consisting of individual channels of approximately square cross section with the sides 2 to 3 mm long may be used.Gaseous protective media are passed through the annular space after the preheating phase and during the pre-refining of the solid iron and the subsequent refining of the melt, for instance 1% by volume of propane, referred to the oxygen. In practical operation, the protective media were found to be problem free and very reliable for the refin;ng phase.

During the refining phase, from 50 to 400 Nm", preferably from 100 to 250 Nm"/ minute of oxygen may be supplied through the inner pipes of ten tuyeres of a 50 ton converter, that is from 1 to 8 Nm3 and pre ferably from 2 to 5 Nml per minute per ton of steel and simultaneouslv about 5 Nm per minute of propane is blown through the annular spaces of these tuyeres. A switch over from a liquid to a gaseous medium in the tuyere annular space and vice-versa may take place at any selected time, without interrupting the converter process.

Again, when a liquid hydrocarbon is used as the tuyere protective medium during the pre-refining and the refining phases, for in stance when the rates in the above converter of 60 tons capacity are about 1000 litres per hour of fuel oil for an oxygen supply rate of about 16,000 Nm" per hour, the tuyeres may be supplied with nitrogen or an inert gas in the inside pipe and in the annular space at least during tilting and swinging upright of the converter.

The proportion of scrap, defined as the weight ratio of cold scrap to liquid steel, may be increased by about 10t," for instance from about 30"., to 40'", when the solid iron in the converter is heated in the process in accordance with the invention.

When using a gaseous carbon carrier, mostly natural gas, for the preheating, no changes in the construction of the tuyeres of these converters are required. It is advantageous however to use liquid carbon carriers during the preheating period and to switch subsequently to a gaseous tuyere protective medium.

The preheating phase can be carried out in less than ten minutes and is preferably performed in from 2 to 5 minutes; it allows the increase of solid iron in steelmaking by up ot 10% and ordinarily up to a scrap proportion of about 400,0 without appreciable losses in production time. This gives rise to appreciable economic advantages.

A further increase in the proportion of solid iron, especially scrap, exceeding an increase in scrap of 10 C) is possible, since steelmaking from scrap without using any liquid pig iron can be accomplished by melting of the solid iron. The solid carbon carrier which is preferably coke, graphite, coal such as anthracite or a mixture thereof, is charged into the converter after the preheating phase and just before the pre-refining phase. After this time the proportion of CO in the converter exhaust gas also increases. The amount of solid carbon carrier is preferably from 10 to 150 kg per ton of solid iron.

The gaseous and liquid carbon carriers supplied through the annular spaces of the tuyeres may be diminished to the proportion of less than 10% by weight, referred to the oxygen, which is required to protect the tuyeres.

The solid carbon carrier may alternatively be charged into the converter together with the solid iron. However, it is particularly ad vantageous to introduce the solid carbon carriers, followir.g the preheating phase, on to the preheated solid iron in the converter.

It is advantageous for the purpose of increasing thermal efficiency to preheat the solid carbon carriers, for instance coke, before charging them.

The amount of solid carbon carrier charged into the converter increases in the process of the invention in direct relation as the amount of solid iron and the length of the preheating phase increase. Thus 20 kg, of coke per ton of scrap suffice to increase the scrap proportion by another 10% beyond the increase in scrap proportion in the total charge achieved by preheating alone, for instance from 40% to 50% scrap. To increase the scrap proportion by another 60%, that is, for a steel melt of 1000%,) scrap, the amount of solid carbon carrier increases approximately linearly to 120 kg of coke per ton of scrap.

When at least some coke is initially charged with the solid iron, the consumption of solid carbon carrier is negligible in the preheating phase because the coke reacts differently with the exhaust gases, usually consisting of carbon dioxide and water vapour and sometimes of nitrogen also, than with free oxygen gas. Thus the coke essentially is merely heated during the preheating phase, while in the pre-refining phase, during which the proportion of oxygen to fluid carbon carrier increases, the coke reacts with free oxygen or oxygen bound to oxides in an overall exathermic reaction to become CO. Thus the exhaust gas in the region of the converter above the charge of solid iron contains CO only in the prerefining phase, and from this time the melting heat is obtained principally from the combustion of solid carbon carriers, e.g. coke, or anthracite.Therefore it is not necessary to introduce the solid carbon carriers until that time. A small body of molten charge is present in the converter by this time so that part of the carbon will be dissolved in the melt and later refined out of the liquid iron.

As soon as a melt has been formed, solid carbon carriers may also be blown through the tuyeres into the converter in the form of powders with carrier gases, for instance nitrogen or argon, during the pre-refining phase. This allows particularly rapid combustion and an extremely effective heat transfer to the iron which remains in part solid and is already in part liquid.

Other solids, especially slag forming agents, for instance lime dust, are preferably blown in during the refining phase entrained in the oxidizing gas, as described in United States Patent No. 3,771,998.

Carbon carriers in powder form and other powders, and combustible or inert gases also may be fed to the stream of oxidizing gas, for instance by a special feed pipe located inside of the oxidizing gas supply pipe. It is also practical to use several concentric pipes and an annular space as the oxygen supply duct. Tuyeres as shown in German Patent No. 2 438 142 have also been found suitable for carrying out the process of the invention.

The process of the invention additionally may include the blowing of oxygen surrounded by hydrocarbons through tuyeres comprising concentric pipes and located above the surface of the melt in the converter, below the pivot axis of the converter and passing through the refractory lining of the converter. The ratio of hydrocarbon to oxygen during the refining phase is preferably less than 10 Ó and for instance may be from 0.5 to 5 5"., by weight, preferably from 1 to 2, by weight. This oxygen is used primarily to burn the carbon monoxide generated in increasing amounts frn the beginning of the pre-refining phase as it leaves the solid iron or the melt so as to form at least partly carbon dioxide.The oxygen may be blown in during the preheating phase as air, and during the pre-refining phase as industrially pure oxygen. In some instances, it may be found to be desirable to feed more than 10 by weight of hydrocarbons during the preheating phase.

This group of tuyeres may be mounted at the height of the pivot axis of the converter, for instance at a height of about 1 to 1Q metres, preferably 1.2 metres above the bottom for a newly prepared converter. The height of these tuyeres allows continuation of the operation of the tuyeres as burners beyond the time that the refining tuyeres, which are mounted in the converter bottom or slightly above the converter bottom, for example from 20 to 80 cm, preferably about 50 cm above the converter bottom, in the side wall of the converter are switched over to pure refining operation, that is, to a proportion of hydrocarbons less than 10% with respect to the oxygen.In this manner, it is possible to extend operation of the tuyeres mounted above the surface of the melt as burners up to the beginning of the refining phase. Only then is the amount of oxygen raised with respect to that of the hydrocarbons to obtain as extensive as possible combustion of the carbon monoxide above the melt The duration of the preheating and prerefining phases of the solid iron depends on the particular amount of scrap charged into the converter vessel and varies from 2 to 20 minutes. Following preheating, unless a 100 h scrap charge is involved, molten pig iron is charged into the converter. The molten pig iron together with the melt obtained from the scrap upon further heat from the refining action ensures rapid melting of the remaining solid scrap.Thus for instance up to 800 kg of scrap per ton of steel may be preheated and pre-refined and subsequently at least 300 kg of molten pig iron per ton of steel may be charged into the same converter.

In this case the preheating period lasts five minutes, the pre-refining period fifteen minutes, and the refining time is only four minutes. For smaller proportions of scrap per ton of steel and greater amounts of pig iron, the preheating and pre-refining periods are correspondingly shortened and the refining time for instance is prolonged to eight to ten minutes.

For small proportions of pig iron of 20ú to 300 kg per ton of steel, there would be a danger of explosive reactions due to the large difference in oxidation potential between the melt obtained from the scrap and the subsequently charged pig iron. However this danger does not arise in the process of the present invention because the melt obtained from melting the scrap continuously absorbs carbon from the solid carbon carriers which are present.

The process of the invention is carried out in a converter with tuyeres comprising two concentric pipes installed in the refractory lining of the converter. These tuyeres may be mounted in the converter bottom, e.g. as shown in United States Patent No. 3,706,549, or as shown in U.S. Patent No. 4,047,707 they may be mounted in the side wall of the converter below and optionally also above the melt surface, and also in the region of the converter hood. The tuyeres mounted below the melt surface may consists of four concentric pipes, whereby they form three annular spaces between the pipes. A gaseous protective medium, for instance, propane, may be blown in through the outermost annular space while liquid carbon carriers such as oils of different viscosities and preheating temperatures are supplied through the other annular spaces.The oxygen required for heating and refining is supplied through the central pipe. During the preheating phase, air or oxygen-enriched air is blown through the central pipe. During the pre-refining and refining phases it is preferred that oxygen is blown in, the oxygen being at least part of the time loaded with lime dust and other slag forming agents.

It is desirable that the tuyeres be connected outside the converter through switch over valves to at least two individual lines, one for gaseous and the other for liquid protective media or carbon carriers, so as to be able to switch from one medium to the other as a function of the individual phases of the process, for instance from inert gas, carbon dioxide, or steam to oil and back again to nitrogen and then to propane for the refining phase.

The switching from one fluid medium to another preferably takes place using a three way valve directly mounted on an assembly flange of the tuyere, the exhaust aperture of the valve being connected to the annular space of the tuyere, while one of the two intake orifices communicates with a feed line for a liquid carbon carrier or a liquid protective medium, the other input orifice communicates with a feed line for a gaseous carbon carrier or a gaseous protective medium.

By means of this device rapid switch over from one medium to another may be obtained. Individual tuyeres also may be supplied entirely with fluid carbon carriers during the preheating and/or pre-refining phases, when the converter is in a vertical position.

The invention also consists, according to another of its aspects, in a converter when used in the method in accordance with the invention, the converter comprising a refractory lined vessel, tuyeres each comprising two concentric pipes in the lower part of the lining and preferably also in the upper part of the lining.

Some examples of processes and an example of an apparatus in accordance with the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a schematic vertical longitudinal section through an OBM converter equipped with several sets of tuyeres; and, Figure 2 is an axial section to a larger scale through one of the bottom tuyeres of the converter with a switch over valve for the supply of fluid to annular spaces between the concentric pies of the tuyeres.

As shown in Figure 1, a converter 1 comprises a refractory lining 2 with side wall tuyeres 4' and an exchangeable bottom 3 with bottom tuyeres 4. Each tuyere is connected to a feed line 5 for an oxidizing gas which may be charged with powder. The charging is effected by a powder distributor 12. An annular space 6 of each tuyere 4, which has a width of about 1 mm, is connected by an assembly piece 7 both to a gas supply line 8 and to a liquid supply line 9. The lines 8, 9 pass through a multiple swivel joint 10 installed in a converter trunnion 11 and are connected with supply lines in which are mounted control valves (not shown).

A feed tube 14 for liquid carbon carriers projects through tap hole 13. Additional tuyeres 4" are located in a side wall of the converter above the surface of the melt in the converter. Oxygen, preferably surrounded by a protective medium for the after burning of carbon monoxide, is blown into the converter through the tuyeres 4".

Each bottom tuyere 4 is fixed to a converter bottom plate 15 (Figure 2) by means of a welded guide plate 16. The tuyeres 4 project through a bore 17 in the bottom plate 15 and extend through a bore 18 in converter bottom 19. The tuyere 4 is clamped between a tuyere flange 20 and a mating flange 21 on the guide piece 16 by means of bolts 22 and seals 23. An innermost pipe 24 of the tuyere 4 is connected to a feed line 25 for a refining gas or for a suspension of powder in a refining gas. The annular space 6 is connected by means of a switch over valve 26 selectively to either the feed line 8 for a gaseous medium such as argon, nitrogen and/or gaseous hydrocarbons or to a feed line 9 for a liquid medium such as oil.A valve body 27 in the switch over valve 26 connects an exhaust orifice 28 and hence the annular gap 6 of the tuyere 4 to either the liquid medium supplied through the line 9 or to the gaseous medium supplied through the line 8.

The side wall tuyeres 4' and 4" are similarly secured to the steel casing of the converter and are connected to feed lines, there being no connection to the powder distributor 12 for the tuyeres 4" which are located in the side wall above the surface of the melt.

Some samples of processes in accordance with the invention were carried out in a 60 ton converter of the kind shown in Figures 1 and 2 and of approximately circular section equipped with ten bottom tuyeres and having a volume of 0.8 Nm3 per ton of steel.

In all cases a two slag operation was followed, which is preferred when refining phosphorus rich pig iron. In such a case the entire slag, on the average about 7 tons, remains at the end of refining, for the following charge in the converter. The cold scrap then loaded into the slag was heated by the slag to a temperature of 7000C and subsequently preheated to 1 1000C. When refining without changing the slag, the additional scrap may be raised to 25 tons, which corresponds to an increase in the scrap proportion from 26% in conventional refining in an OBM converter to 41 < , that is, an increase of 15%. This further increase in scrap proportion is predicted on cold scrap being raised in temperature with higher thermal efficiency than scrap preheated by the final slag remaining in the converter.

In a comparative example using a conventional process, 19 tons of scrap and 47 tons of pig iron containing 3.5 sÓ carbon, 1.0% silicon, 1.0% manganese and 2% phosphorus were first charged into the 60 ton converter of Figures 1 and 2 and then conventionally refined by means of the bottom tuyeres 4, using oxygen surrounded with propane, the latter being present at 3 es by volume with respect to the oxygen, for ten minutes, corresponding to a total heat time of thirty-five minutes, into 60 tons of steel containing 0.03 ., carbon, 0.10'. manganese and 0.0250. phosphorus.

When operating the same converter by the process in accordance with the present invention it was possible to load 33 tons of scrap and 1.6 tons of coke as a solid carbon carrier into the converter and to preheat these for six minutes with an oil consumption of 600 litres and an oxygen consumption of 3000 Nm3. After preheating the cold charge, 33 tons of molten pig iron containing 3.59. carbon, 1.0 .. silicon, 1.0'9U manganese and 2 0f, phosphorus were charged into the converter and the coke was burnt in a prerefining phase and the melt was terminally refined for a total heat time of forty-one minutes under the same conditions. The advantage obtained was in using 33 tons of scrap in lieu of 19 tons.

For a heat made without liquid pig iron in the 60 ton converter with ten bottom tuyeres, a total of 40 tons of scrap of varying nature and with an iron content of 93 iu, corresponding to 38 tons of iron, was charged into the converter together with 6 tons of blast furnace coke. The tuyeres were supplied with nitrogen during the tilting of the converter to an upright position, whereafter the tuyere supply was switched over to 10,000 Nm3 per hour of oxygen and 30 by volume of propane. When the converter was in the upright position, a pipe 14 projecting through the tap hole 13 was fed with 150 litres of light fuel oil and at a flow rate of 50 kg a minute, for the purpose of increasing the supply of carbon carriers.The oxygen supply rate during the preheating of the scrap and coke was that required for stoichiometric burning of the fuel oil.

The oxygen was then gradually increased to 15,000 Nms/hr. in a pre-refining phase.

After a total consumption of oxygen of 7000 Nm3, the generation of gases dropped markedly, indicating the complete combustion of the coke. After a total of 20 minutes, the melt temperature was 16200C and the melt analysis showed 0.10'. carbon, 0.10"i, manganese, 0.03'" phosphorus and 0.15",, sulphur. Thereupon an after blowing was conducted for 14 minutes with 300 Nm of oxygen loaded with a total of 2000 kg of lime and the previous amount (3 O,ó by volume) of propane.The final analysis of the steel showed 0.02' c. carbon, 0.05y; manganese, 0.10"" phosphorus and 0.04% sulphur for a refining time of forty minutes and a quantity of steel of 35 tons and a temperature of 1640 C.

In another batch with the same input materials but lacking coke, a total of 750 litres of oil at a flow rate of 75 litres per minute was fed into the converter following its rotation to an upright blowing position; and the tuyeres were simultaneously supplied with a stoichiometric amount of oxygen of about 150 Nm" per minute. After ten minutes the scrap temperature was 11000C and 3.5 tons of coke were charged into the converter.

During another twenty minutes of blowing at a rate of about 200 Nm; of oxygen per minute and with 2". by volume of propane to protect the tuyeres in a pre-refining phase, the coke was burnt and the entire charge was liquefied. The charge could be tapped after a total time of blowing of thirty-eight minutes to obtain 36 tons of steel of the previously stated analysis.

Another heat was made without pig iron, as follows: 66 tons of scrap and 6.5 tons of blast furnace coke were loaded into the 60 ton converter. During the preheating phase of twelve minutes, 220 Nm per minute of oxygen were passed through the inside pipes of the ten bottom tuyeres and 100 litres per minute of oil were passed through the annular spaces. Subsequently the oxygen rate was raised to 340 Nm" per minute and the oil rate lowered to 20 litres per minute during a pre-refining phase. After another eighteen minutes, the scrap had completely melted, the melt temperature was 16000C and the steel analysis was 0.05 ",. carbon, 0.5 '" manganese, 0.03 % phosphorus and 0.09,., sulphur. The steel was tapped and desulphurized conventionally in a ladle.For a ferrous oxide content of the slag of 7% the yield was a very good 91%.

In another heat in a converter in which there were two additional tuyeres in the side wall of the converter located over the trunnions and 50 cm above the converter bottom, the additional tuyeres each consisting of one central pipe 50 mm in diameter for oxygen and a surrounding concentric pipe 54 mm in diameter. The same amount of scrap as in the previous example but only 4 tons of coke were charged into the converter and 300 Nm" per minute of oxygen were fed through the inside pipes of the tuyeres and 100 litres of oil per minute through the annular spaces during a fifteen minute long preheating period.

Subsequently in a pre-refining phase to burn the coke and in a refining phase, the oxygen rate was raised to 340 Nm3 per minute and the oil flow rate lowered to 20 litres per minute. These phases lasted for twelve minutes. Thereupon a steel of similar ana lysis and temperature was tapped.

A further heat was refined in a similar manner, except that no coke was charged initially with the cold scrap; instead 3 tons of coke preheated to 9000C were charged after ten minutes of preheating, that is, at approximately the end of the scrap preheating phase. After the charging of the hot coke, the charge was pre-refined to burn the coke and was terminally refined for ten minutes and resulted in a steel of approximately the same analysis as in the two previous examples.

If pig iron is charged into the converter in the process of the invention after preheating the sources of solid iron, then an increase of 10 (1" in the proportion of scrap results, giving a proportion of scrap of about 40%.

This involves practically no extension of the heat sequence time (tap-to-tap). The additional amount of scrap which is utilized therefore results in higher productivity. This is a particularly advantageous application of the process of the invention.

The further increase in the scrap propor tion which can be used is achieved by the preheating being followed by the pre-refining phase with the burning of the solid carbon carriers. This may be prior to the addition of the pig iron. This procedure makes it possible to increase the scrap proportion arbitrarily, for instance to 50 to 60to. Therefore the process of the invention can replace the open hearth process, since it can utilize the same proportions of scrap and consequently open hearth plants may be converted to the more economical oxygen blow through converters (OBM or Q-BOP converters) without requiring any increase of pig iron capacity.If it should happen, that due to an operational breakdown of the blast furnace, no liquid pig iron at all is available for a time, then the process of the invention may be carried out entirely with sources of solid iron, in particular scrap.

In all the variations of the process of the invention, the intensive motion of the melt and the consequently possible good heat transfer between the melt and scrap contribute significantly to problem free and rapid liquefaction of the sources of solid iron.

The symbol Nm' represents cubic metres at normal temperature (2730K) and pressure 760 mm Hg).

WHAT WE CLAIM IS:- 1. A process for making steel from a charge comprising solid iron in a converter having tuyeres extending through a refractory lining of the converter, each tuyere comprising two concentric pipes, wherein the solid iron is charged into the converter, an oxidising gas consisting of oxygen, air, or a mixture thereof is blown through the inner pipes of the tuyeres which are in the lower part of the converter below the level of the iron charge, a carbon carrier is introduced into the converter and is burnt in the oxidising gas and the resulting combustion gases flow upwardly through the iron charge, the oxidising gas and the carbon carrier being introduced in proportions providing a stoichiometric combustion of the carbon carrier to preheat the solid iron, further carbon carrier, which is solid and is introduced into the converter together with or after the charge, then being burnt by an increase in the proportion of oxidising gas so that the converter exhaust gases then contain carbon monoxide and the charge being substantially entirely melted, and finally the melt is refined in the converter by blowing oxygen into the melt through the inner pipes of the tuyeres, the oxygen being surrounded during refining by a sheath of protective medium introduced through the outer pipes of the tuyeres.

2. A process according to Claim 1, in which the carbon carrier which is stoichiometrically burnt is liquid or gaseous.

3. A process according to Claim 2, in which the carbon carrier which is stoichiometrically burnt is fuel oil or other liquid petroleum product, such as refinery residues from crude oil distillation, crude tar or mixtures thereof.

4. A process according to Claim 1 or Claim 2, in which the carbon carrier which is stoichiometrically burnt is methane, natural gas, propane, butane or other energy rich gas which is introduced through the outer pipes of the tuyeres into the converter.

5. A process according to Claim 2, in which the carbon carrier which is stochio

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. eighteen minutes, the scrap had completely melted, the melt temperature was 16000C and the steel analysis was 0.05 ",. carbon, 0.5 '" manganese, 0.03 % phosphorus and 0.09,., sulphur. The steel was tapped and desulphurized conventionally in a ladle. For a ferrous oxide content of the slag of 7% the yield was a very good 91%. In another heat in a converter in which there were two additional tuyeres in the side wall of the converter located over the trunnions and 50 cm above the converter bottom, the additional tuyeres each consisting of one central pipe 50 mm in diameter for oxygen and a surrounding concentric pipe 54 mm in diameter. The same amount of scrap as in the previous example but only 4 tons of coke were charged into the converter and 300 Nm" per minute of oxygen were fed through the inside pipes of the tuyeres and 100 litres of oil per minute through the annular spaces during a fifteen minute long preheating period. Subsequently in a pre-refining phase to burn the coke and in a refining phase, the oxygen rate was raised to 340 Nm3 per minute and the oil flow rate lowered to 20 litres per minute. These phases lasted for twelve minutes. Thereupon a steel of similar ana lysis and temperature was tapped. A further heat was refined in a similar manner, except that no coke was charged initially with the cold scrap; instead 3 tons of coke preheated to 9000C were charged after ten minutes of preheating, that is, at approximately the end of the scrap preheating phase. After the charging of the hot coke, the charge was pre-refined to burn the coke and was terminally refined for ten minutes and resulted in a steel of approximately the same analysis as in the two previous examples. If pig iron is charged into the converter in the process of the invention after preheating the sources of solid iron, then an increase of 10 (1" in the proportion of scrap results, giving a proportion of scrap of about 40%. This involves practically no extension of the heat sequence time (tap-to-tap). The additional amount of scrap which is utilized therefore results in higher productivity. This is a particularly advantageous application of the process of the invention. The further increase in the scrap propor tion which can be used is achieved by the preheating being followed by the pre-refining phase with the burning of the solid carbon carriers. This may be prior to the addition of the pig iron. This procedure makes it possible to increase the scrap proportion arbitrarily, for instance to 50 to 60to. Therefore the process of the invention can replace the open hearth process, since it can utilize the same proportions of scrap and consequently open hearth plants may be converted to the more economical oxygen blow through converters (OBM or Q-BOP converters) without requiring any increase of pig iron capacity.If it should happen, that due to an operational breakdown of the blast furnace, no liquid pig iron at all is available for a time, then the process of the invention may be carried out entirely with sources of solid iron, in particular scrap. In all the variations of the process of the invention, the intensive motion of the melt and the consequently possible good heat transfer between the melt and scrap contribute significantly to problem free and rapid liquefaction of the sources of solid iron. The symbol Nm' represents cubic metres at normal temperature (2730K) and pressure 760 mm Hg). WHAT WE CLAIM IS:-

1. A process for making steel from a charge comprising solid iron in a converter having tuyeres extending through a refractory lining of the converter, each tuyere comprising two concentric pipes, wherein the solid iron is charged into the converter, an oxidising gas consisting of oxygen, air, or a mixture thereof is blown through the inner pipes of the tuyeres which are in the lower part of the converter below the level of the iron charge, a carbon carrier is introduced into the converter and is burnt in the oxidising gas and the resulting combustion gases flow upwardly through the iron charge, the oxidising gas and the carbon carrier being introduced in proportions providing a stoichiometric combustion of the carbon carrier to preheat the solid iron, further carbon carrier, which is solid and is introduced into the converter together with or after the charge, then being burnt by an increase in the proportion of oxidising gas so that the converter exhaust gases then contain carbon monoxide and the charge being substantially entirely melted, and finally the melt is refined in the converter by blowing oxygen into the melt through the inner pipes of the tuyeres, the oxygen being surrounded during refining by a sheath of protective medium introduced through the outer pipes of the tuyeres.

5. A process according to Claim 2, in which the carbon carrier which is stochio

metrically burnt is a liquid hydrocarbon which introduced through the outer pipes of the tuyeres.

6. A process according to any one of Claims 1 to 5, wherein the solid iron is preheated to an average temperature of from 10000C to 12000C.

7. A process according to Claim 2, wherein the carbon carrier which is stoichiometrically burnt is a liquid hydrocarbon which is supplied at a rate of from 1 litre to 10 litres per minute per ton of solid iron.

8. A process according to Claim 7, in which the oxidizing gas is introduced through the tuyeres into the converter at a rate of from 1.5 to 2.5 Nm3 of oxygen per litre of hydrocarbon to burn the hydrocarbon.

9. A process according to any one of Claims 1 to 8, which includes charging liquid pig iron into the converter following the preheating and melting of the solid iron.

10. A process according to any one of the preceding Claims, in which the further solid carbon carrier is coke, graphite, coal, such as anthracite, or a mixture thereof.

11. A process according to any one of the preceding Claims, wherein the amount of the further solid carbon carrier charged into the converter is directly related to the amount of solid iron and the length of the period of preheating of the solid iron.

12. A process according to Claim 11, in which the amount of the further solid carbon carrier is from 10 to 150 kg per ton of solid iron.

13. A process according to any one of Claims 9 to 12, in which the further solid carbon carrier is preheated before it is introduced into the converter.

14. A process according to Claim 4 or Claim 5, in which the rate of supply of the gaseous or liquid carbon carrier which is fed through the outer pipes of the tuyeres is decreased, after the solid iron has been preheated and melted, to the proportion required to protect the tuyeres, that is to less than 10% by weight of the oxygen fed through the tuyeres.

15. A process according to Claim 14, in which the carbon carrier which protects the tuyeres is changed from a liquid to gaseous medium during the refining.

16. A process according to Claim 1, in which a liquid carbon carrier is blown through the tuyeres into the converter during preheating of the solid iron and a gaseous carbon carrier is blown through the tuyeres during melting of the solid iron and during refining.

17. A process according to Claim 1, in which the carbon carrier which is stoichiometrically burnt is a powdered solid carbon carrier blown into the converter by means of a carrier gas.

18. A process according to any one of the preceding Claims, in which oxygen surrounded by a protective medium is blown through said tuyeres below the surface of the melt in the converter during the burning of the further solid carbon carrier as well as during refining.

19. A process according to any one of the preceding Claims, in which the oxidizing gas is oxygen and is blown through the tuyeres into the converter at a rate of from 1 to 8 Nm3 per minute per ton of steel during refining.

20. A process according to Claim 19, in which the rate is from 2 to 5 Nms per minute per ton of steel.

21. A process according to any one of the preceding Claims, in which the oxidizing gas is oxygen and is loaded with a powdered solid during refining.

22. A process according to Claim 1, wherein the protective medium is inert gas, carbon dioxide, steam or a hydrocarbon.

23. A process according to Claim 1, in which a powdered carbon carrier and sub sequently a combustible or inert gas is blown into the converter through the outer pipes of the tuyeres and the oxidising gas is oxygen blown through the inner pipes of the tuyeres.

24. A process according to any one of the preceding Claims, in which oxygen is blown into the converter through further tuyeres above the surface of the charge in the converter after the charge has melted.

25. A process according to Claim 24, in which the oxygen blown through the further tuyeres is surrounded by a protective medium.

26. A process according to Claim 24 or Claim 25, which includes the step of burning carbon monoxide above the surface of the melt in the converter by means of the oxygen blown through the further tuyeres.

27. A process according to any one of the preceding Claims, wherein the solid iron comprises scrap, solid pig iron, iron pellets, or sponge iron.

28. A process according to any one of the preceding Claims, in which the solid iron is scrap and forms at least 40 " of the total iron charged into the converter.

29. A process according to any one of the preceding Claims, in which the whole of the iron charged to the converter is charged in a solid state.

30. A converter when used in the process of any one of the preceding Claims, the converter including a refractory lined vessel and tuyeres each comprising two concentric pipes mounted in the refractory lining of the lower part of the converter.

31. A converter according to Claim 30, wherein some tuyeres are mounted in the bottom of the lining and other tuyeres are in the upper part of the lining.

32. A converter according to Claim 31, wherein further tuyeres are mounted in the lower part of the side wall of the lining.

33. A converter according to any one of Claims 30 to 32, including feed pipes for carbon carriers mounted in the upper part of the converter.

34. A converter according to Claim 33, wherein at least one of said feed pipes passes through a tap hole of the converter.

35. A converter according to any one of Claims 30 to 34, including individual lines outside the converter connecting the tuyeres selectively to supplies of fluid media under the control of switch-over valves.

36. A method according to Claim 1, substantially as described with reference to the accompanying drawings and any one of the examples described herein.