TECHNICAL FIELD

The present disclosure relates to a method for producing steel according to claim 1 and to a system for producing steel according to claim 13.

BACKGROUND ART

The conventional way of producing steel from iron ore requires a large amount of carbon rich coke to melt, reduce and carburize the steel. The steel industry is therefore one of the largest CO2 polluters in the world. It is therefore of utmost importance to reduce the CO2 pollution from steel production. To this fact it has been suggested to instead of using coke, it is possible to use hydrogen. See for example the document GB2112019A discussing such a method where the iron is reduced out from the iron ore.

SUMMARY OF THE INVENTION

There is a need to provide steel out of the reduced iron ore.

An object of the present disclosure is to provide a method for producing steel wherein some of the problems with prior art technologies are mitigated or at least alleviated.

The disclosure proposes a method for producing steel. The method comprises the steps of: providing a predetermined amount of iron ore to a vessel, reducing the iron ore to a predetermined amount of Fe and carburizing the predetermined amount of Fe in order to produce steel. The steps of reducing and carburizing is performed using a main stream of CO and H ₂ being divided into at least two streams. In a first stream, H2 is removed from the stream and is fed to the vessel for reducing the iron ore. A second stream comprising CO is fed to the vessel for carburizing the predetermined amount of Fe for producing steel with a predetermined content of C.

The advantage of the method is that the carbon content in the resulting steel is controlled in an accurate and reliable way by controlling the amount of CO and H ₂ in the first and second stream, respectively to a vessel to which iron ore is fed. No coke or methane is used upon reduction and carburization of the steel. Thus, the method provides for an environmentally friendly way of producing steel (so-called green steel) since very small amounts of CO2 is formed in the vessel. Much less CO2 is formed upon production of the steel according to the present method as compared to the conventional steel production process. In the conventional process, more than 800 kg CO2/ton iron ore is produced to be compared with about 450 kg CO2 per 1000 kg iron ore of the present method. In addition, the CO2 formed in the present process is not formed in the vessel, instead it is formed in the process where it is collected thereby preventing CO2 emission to the atmosphere. Thus, the proposed method is environmental friendly as compared with conventional steel production.

According to a further development, the amount of the second stream being fed to the vessel is controlled such that all carbon atoms from CO of the second stream are bonded to Fe atoms when carburizing the predetermined amount of Fe.

The advantage is that a reliable and accurate way of producing steel with a predetermined content of C is provided.

According to a further development, the predetermined amount of Fe is carburized according the following formula,

3 Fe + CO + H ₂ => Fe ₃ C + H ₂ O.

The carbon content in the steel is in the range of 0.0002 % to 10 %, preferably in the range of 0.002 % to 6.5 %, most preferably in the range of 0.02 to 2.5 %.

The advantage is that the carbon content of the steel is controlled.

According to a further development, the main stream of CO and H2 originates from syngas.

The advantage is that by using syngas upon producing steel according the present method very small amounts of CO2 is formed in the vessel as compared to conventional steel production where coke for reducing and carburizing. By using syngas, the predetermined content of C in the steel is reliably and accurately controlled.

According to a further development, the syngas is extracted from waste, such as auto shredder residue, ASR, carbon fibre reinforced plastics, glass fibre reinforced plastics, sewage sludge, and/or municipal solid waste, MSW.

The advantage is that the energy bound in the waste is recovered. Furthermore, landfill which typically is the endpoint of many types of waste is reduced. Materials, such as metals, from the waste may be separated and recycled after formation of the syngas. By using waste for extraction of syngas, the method is very cost efficient.

According to a further development, the syngas is formed by allowing the waste to be heated to a temperature of at least 3000 °C. The advantage is that syngas may be extracted from waste without the need of separating different parts of the waste, such as cabling and car upholstery of auto shredder residue, prior to recycling the different parts.

According to a further development, heat generated at the formation of syngas is used upon the steps of reducing and carburizing, such as for heating the vessel prior to or upon reducing the iron ore and/or carburizing of the Fe.

The advantage is that heat generated upon the formation of the syngas may be recovered upon production of the steel, such as for heating the vessel. The heat may also be recovered and used for heating other arrangements, such as buildings.

According to a further development, the syngas is subject to at least one cleaning step prior to forming the main stream of CO and H2.

The advantage is that by cleaning the syngas, syngas having a high purity is formed. Thereby, the control of the predetermined amount of C in the steel becomes very reliable and accurate.

According to a further development, the step of reducing the iron ore to a predetermined amount of Fe, takes place according to the following formulas,

3Fe20s ⁺ H2 ^=> 2FesO4 ⁺ H2O,

FesO4 + H2 => 3FeO + H2O, and

FeO + H ₂ => Fe + H ₂ O.

The advantage by using H2 for reducing of the iron ore is that only Fe and H2O is formed. Thus, the proposed method is very environmentally friendly as compared to conventional methods for producing steel in which a large amount of CO2 is formed upon reduction of the iron ore.

According to a further development, in the first stream the H2 is removed from the stream according to the following formula,

CO + H ₂ O => H ₂ + CO ₂ .

The advantage is that a high yield of H2 is removed from the first stream of H2 and CO in a very efficient way.

According to a further development, the method further comprises a step of separating the CO2 and H2 and collecting the CO2 in a sealed container. This provides for improved handling of the CO2 formed by the proposed method as compared to conventional production of steel where CO2 is formed in the vessel. The advantage is that CO2 formed upon removing of H2 in the first stream, is collected in a sealed container thereby preventing emission of CO2 to the atmosphere. The separated CO2 may be subject to carbon capture and utilization, CCU, where the CO2 is recycled.

According to a further development, in the step of providing a predetermined amount of iron ore to a vessel also a predetermined amount of scrap iron is provided to the vessel.

This provides for that scrap iron is recycled and is used in the process for producing steel. By the use of scrap iron, a smaller amount of iron ore is used, thereby the process becomes more energy efficient and cost efficient.

The disclosure further proposes a system for producing steel according to the method. The system comprises at least one vessel. The vessel comprises an inlet for iron ore, an inlet for H ₂ and one inlet for CO + H2 and an outlet for produced steel with a predetermined carbon content.

The system is able to produce steel according to the proposed method. Thus, the system provides for production of steel having all the above-mentioned advantages. In addition, the system may be modular comprising a number of units, thus the system may be designed and redesigned depending on the needs of the steel producer.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 schematically illustrates an example of a system for producing steel according to the method of the present disclosure.

Fig. 2 illustrates the method according to the present disclosure.

DETAILED DESCRIPTION

The present disclosure relates to a method for producing steel.

Fig. 1 schematically illustrates an example of a system 100 for producing steel according to the method of the present disclosure. The system 100 may be modular and comprises a number of different units which will be described more in detail below. The modularity of the system 100 may facilitate design and redesign of the system 100. The system 100 may be tailor-made for example depending on type and size of a feedstock being fed into the system. Standard conduits for liquids and gases may be used for connecting the different units of the system 100 to each other.

The system 100 comprises at least one vessel 9 comprising an inlet 15 for iron ore, an inlet 17 for H2 and one inlet 18 for CO + H2 and an outlet 16 for produced steel with a predetermined carbon content.

The system 100 may further comprise a water-gas-shift unit 7, a pressure swing adsorption (PSA) unit 8, at least one valve 14a, 14b and a control unit 10. The system may further comprise a cleaning unit 6, a heat recovery unit 4, a container for inorganic material 5, a gasification unit 2, a container for slug collection 3, an oxygen generator 12, a chopper/shredder unit 1 , a container for collecting CO2 11 , and/or a pump system 13.

As illustrated in Fig. 1 , the system may comprise a chopper/shredder unit 1 to which a feedstock, i.e. a raw material, is provided. The chopper/shredder unit 1 is arranged for chopping/shredding the feedstock into a desired size. The system may comprise a plurality of chopper/shredder units 1 . The size and type of the chopper/shredder unit 1 chosen may depend on the size and type of feedstock the system is arranged to process. In a further example, the feedstock is provided in a desired size and/or shape prior to entering the system 100 and a chopper/shredder unit 1 is not needed. In such case, the feedstock may be directly fed into a gasification unit 2, which will be described in detail below.

The feedstock may comprise waste, such as auto shredder residue, ASR, carbon fibre reinforced plastics, glass fibre reinforced plastics, sewage sludge and/or municipal solid waste, MSW. The feedstock may comprise other types of organic materials and/or inorganic materials, such as metals. Typically, the feedstock comprises a mix of organic and inorganic materials. In one example, the feedstock comprises very large objects, such as wind blades from wind turbines and hulls from plastic boats. In another example, the feedstock comprises parts from car interiors, such as car upholstery, car dashboards and cablings. The system may comprise a gasification unit 2. The system 100 may further comprise a feeding unit (not shown) for feeding the feedstock into a gasification unit 2. The feeding unit may for example be a screw arrangement.

The gasification unit 2 may comprise a pyrolysis zone and a plasma zone. The pyrolysis zone may be arranged for combusting of the feedstock in presence of a predetermined amount of oxygen. The oxygen may be provided from an oxygen generator 12. The oxygen generator 12 may comprise a pressure swing adsorption (PSA) unit and a compressor. The amount of oxygen provided may be controlled manually or automatically by means of a valve (not shown). The amount of oxygen provided and the temperature upon combustion may depend on the desired degree of combustion of the feedstock. The temperature upon combustion of the feedstock, i.e. in the pyrolysis zone, may be in the range of about 600 to 900 °C. The combusted feedstock, i.e. ash, may then be provided to the plasma zone of the gasification unit 2. The plasma zone of the gasification unit 2 may be heated to a temperature of at least 3000 °C. The plasma zone may comprise a light arc in which the formation into plasma of the combusted feedstock takes place. Due to the very high temperature, the chemical bonds of the compounds of the combusted feedstock are broken and the compounds may be decomposed into a plasma. Oxygen may be provided by the oxygen generator to the plasma zone in order to form CO of carbon being released upon the formation of plasma. The plasma formed in the gasification unit 2 comprises syngas. By providing pure oxygen instead of air, it is avoided that the resulting syngas comprises unnecessarily high amounts nitrogen or nitrogen compounds.

Syngas, also known as synthesis gas, is a gas mixture comprising primarily of H2 and CO. Depending on the process in which the syngas is formed, such as the material of the feedstock and temperatures in the pyrolysis zone and the plasma zones of the gasification unit 2. The syngas may also comprise small amounts of other gases, such as H ₂ O, CO2, N2 and CH4. As an example, cooled syngas may comprise about 5 % N2 and about 5 % CO2. Before being cooled, the syngas may also comprise up to 25 % of H ₂ O.

Upon formation of the syngas, there may also be some residual materials formed in the gasification unit 2, such as inorganic materials, which is condensed before the gas is leaving the plasma zone or is not fully decomposed into plasma. These materials may be collected in a slag collection unit 3. The materials collected in the slag collection unit 3 are typically materials having a relatively high boiling point. Examples of such materials are metals, such as copper (Cu), and silicon (Si). The materials collected in the slag collection unit 3 may be recycled and reused in manufacturing industry.

The system 100 may comprise more than one gasification unit 2 in order to ensure a high utilization of material of the feedstock.

The system 100 may further comprise a heat recovery unit 4. The heat recovery unit 4 is arranged to cool the syngas being formed in the gasification unit 2.

In the heat recovery unit 4, the syngas may be cooled by a working fluid, such as water. The working fluid may be arranged to circulate in a closed system 19 by means of a pump system 13. The heating fluid may be circulated to different units of the system 100, thereby heating and/or cooling different units of the system 100. In one example (shown in Fig. 1 ), the closed system may be arranged to circulate the working liquid from the heat recovery unit 4 to a water-gas-shift unit 7, to a vessel 9 and back to the heat recovery unit 4. Typically, heat is generated in the recovery unit 4 and/or in the water-gas-shift unit 7.

As will be discussed more in detail below, heat generated in the heat recovery unit 4 and/or in the water-gas-shift unit 7 may be used to heat the vessel 9 upon reducing and carburizing. For example, the heat may be used for pre-heating of the iron ore in the vessel 9. Alternatively, the heat generated in the recovery unit 4 and/or in the water-gas-shift unit 7 may be used for heating other arrangements.

Upon cooling of the syngas, condensed inorganic materials may be collected in a container 5. The materials collected in the container 5 is typically materials having a boiling point which is lower than the boiling point of the materials being collected in the slag collection unit 3. Examples of materials being collected in the container 5 is aluminum and cadmium. The materials collected in the container 5 may be recycled and reused in manufacturing industry.

The system may further comprise a cleaning unit 6. The cleaning unit 6 is arranged for cleaning and purifying of the syngas. In one example, the syngas may be led from the heat recovery unit 4 to the cleaning unit 6 by means of a fan device (not shown).

The cleaning unit 6 may comprise filters and/or a cleaning liquid which is circulated in the cleaning unit 6 by means of a pump system. In one example, the syngas is firstly led through one or more filters in order to purify the syngas from undesired compounds. Secondly, the syngas is “showered” by the cleaning liquid. The cleaning liquid may typically be water. In this step, H2O and water-soluble compounds may be separated from the syngas. The syngas may be repeatedly circulated within the cleaning unit 6 until the syngas has reached a desired purity.

The system 100 may comprise a plurality of cleaning units 6 arranged after one another. In one example, the plurality of cleaning units 6 may comprise different types of filters and/or cleaning liquids. The syngas resulting from the cleaning unit 6 typically comprises H2 and CO in the ratio of 1 :1 . In addition, the syngas may comprise small amounts of CO ₂ , N ₂ and traces of CH ₄ .

The syngas resulting from the cleaning unit 6 may, but need not, be compressed by a compressor (not shown).

The system 100 may further comprise at least one valve 14a, 14b. In one example, the at least one valve 14a may be arranged for controlling the amount of H ₂ and CO being divided into the first stream and at least one valve 14b is arranged for controlling the amount of H ₂ and CO being divided into the second stream.

In one example, the at least one valve 14a, 14b is manually controlled by an operator.

In yet an example, the system may comprise a control unit 10 which may be arranged to control the at least one valve 14a, 14b automatically.

The control unit 10 may be arranged to control the at least one valve based on a predetermined carbon content of the steel. In one example, the control unit 10 may be arranged to divide the main stream into 30 % to the second stream and the remaining 70 % to the first stream.

The main stream of syngas may have been formed in the gasification unit 2 and may, as described above, have been subject to cooling in the heat recovery unit 4 and/or cleaning in the cleaning unit 6. In a first stream, H ₂ is removed from the stream and is fed to the vessel (9) for reducing said iron ore. The second stream comprising of CO and H ₂ is fed to the vessel 9 for carburizing the predetermined mount of Fe.

The system 100 may further comprise a water-gas-shift unit 7, to which the first stream of CO and H ₂ (syngas) is fed. The water-gas-shift unit 7 is arranged for removing CO from the first stream. In the water-gas-shift unit 7, water steam is provided, wherein CO from the syngas reacts with water, thereby forming CO ₂ and H ₂ . The water-gas-shift unit 7 may be a commercial available water-gas-shift unit. As discussed above, the water-gas-shift unit 7 may generate heat which may be arranged to heat the working liquid in the closed loop 19. The system 100 may further comprise a pressure swing adsorption, PSA, unit 8. Pressure swing adsorption is a well-known technique used to separate some gas species from a mixture of gases. In the system 100, the pressure swing adsorption unit 8 is arranged for separating CO2 and H2. The resulting H2 being separated by the swing adsorption unit 8 has a high purity, typically in the range of 99.999 %.

The CO2 being separated in the PSA unit 8 may preferably be liquefied and be stored in a sealed container 11 . The separated CO ₂ may be subject to carbon capture and utilization, CCU. CCU is a process where carbon dioxide is captured and is recycled for further usage. The aim of CCU is to convert the captured carbon dioxide into e.g. plastics, concrete or biofuel in a controlled way, thereby preventing the CO2 from reaching the atmosphere. Alternatively, the CO2 may be subject to carbon capture and storage, CCS, wherein the CO2 may be permanently stored in an underground geological formation, thereby preventing the CO2 from reaching the atmosphere.

The system further comprises at least one vessel 9. The vessel 9 comprises an inlet for iron ore 15, an inlet for H2 17, and one inlet for CO + H2 18 and an outlet for produced steel 16 with a predetermined carbon content.

The vessel 9 is arranged for reducing iron ore (iron oxides) and for carburization of iron into steel. The vessel 9 may be a commercial available MIDREX® shaft furnace. Iron ore is provided to an inlet 15, which typically is arranged at the top of the vessel 9. The iron ore descends downwards in the vessel 9 due to gravity wherein the iron ore is reduced to a predetermined amount of Fe and a predetermined amount of Fe is carburized in order to produce steel.

As mentioned above, the resulting H2 being removed from the first stream is fed into the vessel 9 for reducing the iron ore. The H ₂ is fed to the vessel via the inlet 17. A second stream comprising CO and H ₂ is fed to the vessel 9 for carburizing the predetermined mount of Fe. The second stream is fed to the vessel via inlet 18. Upon reducing the iron ore and carburizing the predetermined amount of Fe, the vessel 9 may be heated to a temperature of about 1500 °C. Details regarding the reduction of iron ore and carburization of Fe are discussed in detail with reference to the method below. As shown in Fig. 1 , the resulting steel is output from the outlet 16, which typically is arranged at the lower end of the vessel 9.

As mentioned above, and being illustrated in Fig. 1 , the heat circulating in a closed loop 19 from the heat recovery unit 4 and/or the water-gas-shift unit 7 may be used for heating the vessel 9, upon the steps of reducing and carburizing. In one example, the working liquid in the closed loop 19 may be used for heating the vessel 9 prior to or upon reducing the iron ore and/or carburizing of the Fe.

The system described above may be used for the method of producing steel according to the present disclosure.

Fig. 2 schematically illustrated the method according to the present disclosure.

The method for producing steel comprises a step of providing a predetermined amount of iron ore to a vessel 9. Iron ores comprises rocks and minerals from which metallic iron may be extracted. The iron ore typically comprises different types of iron oxides, such as magnetite (FesC^), hematite (Fe ₂ Os) and FeO (wustite). By “predetermined amount” is meant the amount of iron ore from which it is desired to extract iron. In the step of providing a predetermined amount of iron ore to a vessel also a predetermined amount of scrap iron may be provided to the vessel 9. By scrap iron is meant for example parts of steel from scrapped vehicles.

The method further comprises a step of reducing said iron ore to a predetermined amount of Fe. In the step of reducing the iron ore, oxygen is removed from the iron ore. By reduction is meant the gain of electrons or decrease in the oxidation state of an atom, an ion or of certain atoms in a molecule. As will be discussed more in detail below, H ₂ is used for reducing the iron ore in the method of the present disclosure. By “predetermined amount” is meant the amount of iron which is desired to be carburized in order to produce steel.

The method further comprises a step of carburizing said predetermined amount of Fe in order to produce steel. By carburizing is meant that Fe or steel absorbs carbon while the Fe is heated in the presence of a high carbon content material. The reason for carburizing the iron is to provide steel with desired properties, such as a desired hardness of the steel. Thus, by controlling the carbon content in the resulting steel, the hardness of the resulting steel is controlled.

The steps of reducing and carburizing is performed using a main stream of CO and H ₂ . The main stream of CO and H ₂ may be syngas.

The syngas may be extracted from waste, such as auto shredder residue, ASR, carbon fibre reinforced plastics, glass fibre reinforced plastics, sewage sludge, and/or municipal solid waste, MSW. The formation of syngas from waste was discussed in detail above with reference to the system. The main stream of CO and H ₂ is divided into at least two streams. In a first stream, H ₂ is removed from the stream and is fed to the vessel 9 for reducing said iron ore. A second stream is fed to the vessel 9 for carburizing the predetermined amount of Fe for producing steel with a predetermined amount of C. The ratio of CO to H ₂ is typically 1 :1 in the main stream as well as in the first and second streams.

As described with reference to the system above, the amount of the main stream of CO and H ₂ being divided into the at least two streams is controlled by the control unit 10. Alternatively, the amount of the main stream of CO and H ₂ being divided into the at least two streams is manually controlled by at least one valve 14a, 14b. The ratio of the first and the second stream is controlled based on the amount of carbon from the CO needed in order to produce steel with a predetermined content of C.

The amount of the second stream being fed to the vessel may be controlled such that all carbon atoms from CO of the second stream are bonded to Fe atoms when carburizing the predetermined amount of Fe. If there is an excess of CO and/or carbon atoms in the second stream not all of the carbon atoms may be bonded to Fe. Thus, an excess of CO may result in an undesired high carbon content of the steel and/or formation of undesired CO2 in the vessel.

The amount of compressed H ₂ and CO (syngas) needed for reducing and carburizing 1000 kg of iron ore (Fe ₂ Os) is in the range of 10-50 kg, depending on the amount of the desired carbon content in the resulting steel. In one example, 25 kg H ₂ and CO (syngas) results in a carbon content in the steel of about 1 %.

The remaining portion of the main stream may then be provided into the first stream. Alternatively, also the amount of the main stream being divided into the second stream is controlled. The amount of H ₂ and CO (syngas) in the first stream needs to be high enough to produce an amount of resulting H ₂ needed to reduce the carbon ore into a predetermined amount of Fe in the vessel. However, an excess of H ₂ in the vessel upon reducing of the iron ore as well as upon carburization does not affect the carbon content in the steel. Thus, an excess of H ₂ in the vessel does not adversely affect the production of the steel.

In a first stream, H ₂ is removed from the stream and is fed to the vessel 9 for reducing said iron ore. The H ₂ may be removed from the stream by means of a water-gas-shift unit as described with reference to the system above. The H ₂ may be removed according to the following formula,

CO + H ₂ O => H ₂ + CO ₂ . As described above, the CO2 may be separated from the H2 by means of a pressure swing adsorption unit, PSA unit, and may be collected in a sealed container.

The step of reducing the iron ore to a predetermined amount of Fe may take place according to the following formulas,

3Fe20s + H2 => 2FesO4 + H2O Exothermic reaction

FesO4 + H2 => 3FeO + H2O, and Endothermic reaction

FeO + H ₂ => Fe + H ₂ O Endothermic reaction

Thus, upon the step of reducing the iron ore, a predetermined amount of Fe is formed. As will be described more in detail below, the resulting predetermined amount of Fe is carburized in order to produce steel. As noted above, H ₂ O formed during the reducing of iron ore. The H2O vaporizes due to the high temperature in the vessel. Typically the vaporized H ₂ O is may be led out via a chimney (not shown) which is arranged on the vessel. The heat from the vaporized H ₂ O may also be recovered and used for heating purposes.

The second stream is fed to the vessel for carburizing said predetermined amount of Fe for producing steel with a predetermined content of C.

The amount of the second stream being fed to the vessel is controlled such that all carbon atoms from CO of the second stream are bonded to Fe atoms when carburizing said predetermined amount of Fe. As described above with reference to the system, the control of the amount of the main stream being divided into the first stream and the second stream may be performed by the control unit. An excess of CO may result in an undesired high C content in the steel and/or undesired formation of CO2 in the vessel.

The predetermined amount of Fe may be carburized according the following formula,

3Fe + CO + H ₂ => Fe ₃ C + H ₂ O.

The carbon content in the steel may be in the range of 0.0002 % to 10 %, preferably in the range of 0.002 % to 6.5 %, most preferably in the range of 0.02 to 2.5 %.

The amount of H2 and CO of the first and second stream, respectively, is determined depending on the desired properties of the resulting steel, such as the desired hardness of the resulting steel. The properties of the steel depends on the amount of carbon bonded to the Fe atoms in the steel. An increased amount of CO provided to the predetermined amount of Fe, thus results in an increased percentage of carbon in the steel. Typically, the amount of CO and H ₂ that is needed for the desired carbon content in the steel is provided for the carburizing (second stream) and then the remaining amount of CO and H ₂ is divided into the first stream in which the H ₂ is removed from the stream and fed to the vessel. The amount of CO needed in order to carburize the iron depends on the amount of iron ore provided to the vessel. In one example, 70 % of the CO and H ₂ is provided in the first stream and 30 % of the CO and H ₂ is provided in the second stream. By this method, all carbon atoms in the steel originates from CO.

Conventional method for production of steel for comparison

Production of steel typically results in formation of large amounts of carbon dioxide. The conventional reduction process of iron ore (iron oxides) typically takes place by carbon monoxide from coke according to the following chemical reactions below:

3Fe ₂ O ₃ + CO => 2Fe ₃ O4 + CO ₂ Exothermic reaction

Fe ₃ O4 + CO => 3FeO + CO ₂ Endothermic reaction

FeO + CO => Fe + CO ₂ Exothermic reaction

Further, conventional carburization of iron takes place according to the following reaction:

3Fe + 2CO => Fe ₃ C + CO ₂ Exothermic reaction

As seen above, carbon dioxide is formed during both the reduction and carburization steps upon the conventional method for producing steel.