GB2553342A

GB2553342A - Producing steel

Info

Publication number: GB2553342A
Application number: GB1614938.7A
Authority: GB
Inventors: Stuart Millman Maurice
Original assignee: Materials Proc Institute
Current assignee: Materials Proc Institute
Priority date: 2016-09-02
Filing date: 2016-09-02
Publication date: 2018-03-07
Also published as: GB201614938D0

Abstract

A method of producing steel comprising: melting material to form liquid steel; introducing a reactant which undergoes chemical reaction to form nitrogen including compound; and removing nitrogen containing compound. Preferably reactant is hydrogen gas which reacts to form ammonia. Preferably, dry superheated steam is injected supersonically into liquid steel to produce carbon monoxide and hydrogen, the hydrogen reacting with the nitrogen in the steel to form ammonia, which is then removed. An apparatus comprising: a furnace 201; reactant introducing devices 203,204; and an off-gas system 206. Preferably, furnace is electric arc furnace. Preferably, injectors introduce hydrogen gas or supersonic steam and perform gas burning before injection. Preferably, off-gas system comprises heat recovery system.

Description

(54) Title of the Invention: Producing steel

Abstract Title: Producing steel with reduced Nitrogen content (57) A method of producing steel comprising: melting material to form liquid steel; introducing a reactant which undergoes chemical reaction to form nitrogen including compound; and removing nitrogen containing compound. Preferably reactant is hydrogen gas which reacts to form ammonia. Preferably, dry superheated steam is injected supersonically into liquid steel to produce carbon monoxide and hydrogen, the hydrogen reacting with the nitrogen in the steel to form ammonia, which is then removed. An apparatus comprising: a furnace 201; reactant introducing devices 203,204; and an off-gas system 206. Preferably, furnace is electric arc furnace. Preferably, injectors introduce hydrogen gas or supersonic steam and perform gas burning before injection. Preferably, off-gas system comprises heat recovery system.

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Producing Steel

CROSS REFERENCE TO RELATED APPLICATIONS

This application represents the first application for a patent directed towards the invention and the subject matter.

BACKGROUND OF THE INVENTION

The present invention relates to a method of producing steel, in which a charge material is melted to form liquid steel. The present invention also relates to an apparatus for the production of steel, in which a furnace is configured to receive charge material, apply heat and produce liquid steel.

It is known in the art to produce steel from steel scrap in an electric arc furnace. It is also known that steel produced in this way tends to have a high nitrogen content, which in turn may result in a greater susceptibility to strain ageing. Furthermore, steels produced in this way tend to have a lower ductility when cold rolled, therefore their applications become somewhat limited. For example, for steels used in deep drawing applications, nitrogen levels are required to be less than fifty parts per million and in more stringent applications, such as ultra-low carbon interstitial-free steels used for exposed auto body applications, the nitrogen level is required to be below forty parts per million and is often close to twenty parts per million. Problems continue to persist in terms of producing very low nitrogen steels from an electric arc furnace, using steel scrap.

In electric arc furnace steel making, several sources of nitrogen are known. For example, scrap used as a source material may contain typically thirty parts per million to one hundred parts per million nitrogen, depending upon its source. Furthermore, added carbon may also contain high levels of nitrogen, typically between twenty-five parts per million and one hundred and twenty parts per million.

It is also known that nitrogen can be absorbed into liquid steel when the surface of the steel is exposed to surrounding air; thus, the nitrogen is absorbed from the surrounding atmosphere. To reduce the introduction of nitrogen from this source, it is known to maintain an unbroken, protective slag layer over the liquid steel surface.

Furthermore, it is also known for nitrogen to be introduced from ionised atmospheres forming part of the plasma arcs produced at the tips of the electrodes. Thus, a dissociation occurs of arc furnace nitrogen molecules, thereby introducing atomic and ionic nitrogen, that may then be introduced into the liquid bath.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided a method of producing steel, comprising the steps of melting a charge material to form liquid steel, wherein said liquid steel has nitrogen absorbed therein; introducing a reactant into said liquid steel, wherein said reactant undergoes one or more chemical reactions to form a nitrogen-including compound from said absorbed nitrogen; and removing said nitrogen-including compound from the liquid steel.

Many materials are available that can be used as a charge material. In an embodiment, the charge material comprises one or more materials selected from: steel scrap; directly reduced iron; hot briquetted iron; pig iron: and hot blast furnace iron in liquid form.

In an embodiment, the reactant is hydrogen, such that the removed nitrogen-including compound includes hydrogen. In an embodiment, the nitrogen-including compound is ammonia. In an embodiment, the hydrogen is introduced into the liquid steel as hydrogen gas.

In an alternative embodiment, the reactant comprises a first compound that includes hydrogen; said first compound undergoes a first reaction to release hydrogen; and said released hydrogen undergoes a second reaction with said absorbed nitrogen.

In an embodiment, the first reactant is steam, wherein the steam is introduced into the liquid steel; and said first reaction is a reaction between said steam and carbon monoxide, so as to perform said hydrogen releasing step.

In an embodiment, the second reaction produces ammonia; and said removing step removes said ammonia.

In an embodiment, the steam is dry superheated steam at a temperature above two hundred degrees Celsius.

In an embodiment, the steam is injected supersonically at a pressure above five atmospheres (506.62 kPa).

According to a second aspect of the present invention, there is provided an apparatus for the production of steel, comprising: a furnace configured to receive charge material, apply heat and produce liquid steel; a plurality of reactant introducing devices, configured to introduce a reactant into said liquid steel, wherein said reactant undergoes one or more chemical reactions to produce a nitrogen-including compound from nitrogen contained within said liquid steel; and an off-gas system for removing said nitrogenincluding compound.

In an embodiment, the furnace is an electrically powered furnace. The electrically powered furnace may be an electric arc furnace.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Figure 1 shows a method of producing steel;

Figure 2 shows an example of an electric arc furnace;

Figure 3 shows an alternative example of a furnace;

Figure 4 details an injector module of the type identified in Figure 3;

Figure 5 illustrates experimental results for the introduction of Hydrogen; and

Figure 6 illustrates an experimental result for the introduction of superheated steam.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1

A method of producing steel is illustrated in Figure 1, in which charge material is melted in an electric furnace 101 to form liquid steel.

In this example, the charge material may include solid steel scrap 102, directly reduced iron 103, hot briquetted iron 104, pig iron 105, liquid blast furnace iron 106 or any combination of charge materials 102 to 106.

During the melting process, chemical reactions take place within the furnace, resulting in the production of process gas that is exhausted, as illustrated by arrow 107, via an off-gas system 108. The off-gas system 108 may also include a heat recovery system, such that heat recovered may be used to preheat scrap charge material 102 or preheat other examples of solid cold charge material.

An output from the furnace may be selectively applied to secondary steel making processes, either singularly or in combination. As illustrated in Figure 1, these secondary steel making processes may include re-heating, stirring and alloying 109, de-gasing and alloying 110 and re-heating with alloying 111. When alloying processes are performed, suitable alloying agents are added and stirred into the liquid steel to derive homogeneous liquid steel at the required composition and temperature.

After the secondary processes, the liquid steel is cast, as illustrated at 112, into a solid product by ingot casting or continuous casting. After casting, shaping processes, as indicated at 114, may be performed on the solid steel product, such as rolling or forging.

For most applications, degassing process 110 is sufficient to remove hydrogen, when the presence of hydrogen is seen as being undesirable. However, for a small number of applications, it may be necessary to reduce the hydrogen concentration to very low levels, for example below one part per million. Thus, after a casting process 112 and before shaping process 114, some steels may undergo a further de-gasing operation by allowing the diffusion of hydrogen from the solid steel, as indicated by process 113, while maintained at an elevated temperature.

Figure 2

An example of an electric furnace 101 is shown in Figure 2. This may be identified as a three phase alternating current electric arc furnace, in which carbon electrodes 201 cause the creation of electric arcs, thereby introducing energy into the charge to produce liquid steel 202. During this process, gases may be introduced, as illustrated by arrow 203 and arrow 204, at the positions of purging plug 205 and purging plug 206 respectively.

It should also be understood that other examples of electric furnace may be deployed, such as direct current electric arc furnaces and electric induction furnaces etc. The further description, with respect to an electric arc furnace, is only by way of example.

Process gases are removed from the furnace, as illustrated by arrow 206, by the off-gas system 108 and electrical energy is supplied via the graphite electrodes 201. An oxidised slag is present at the end of the process and ferrous oxide levels in the slag are likely to be between ten and twenty percent; which represents an iron yield loss for the process. Conventionally, nitrogen levels in the liquid steel bath are likely to be between forty and one hundred and twenty parts per million. At the end of the melting process, performed by the apparatus illustrated in Figure 2, the liquid steel 202 is discharged from the furnace and into a ladle.

Figure 3

High nitrogen content steel can cause strain ageing and can lower the ductility of cold rolled and annealed low carbon aluminium killed (LCAK) flat rolled steel products; as used in deep drawing applications that require nitrogen levels to be less than fifty parts per million.

In more stringent applications, such as those using ultra low carbon interstitial-free steels (ULC-IF) used for exposed auto body applications, nitrogen levels are required to be below forty parts per million and often there is a requirement for nitrogen levels to be close to twenty parts per million. Typically, nitrogen levels in steels produced from a basic oxygen furnace steel making operation are less than half of those present in steels made from scrap-based electric arc furnace steel making. Thus, for many of those skilled in the art, there is a belief that electric arc furnace based steel making is not capable of producing the very low nitrogen level steels that are required for the highest quality steel strip grades, such as those required for exposed auto body parts.

Steel scrap 102 in the charge may contain typically thirty parts per million to one hundred parts per million nitrogen, depending upon its source. Nitrogen can also be absorbed into the steel when the surface of the steel is exposed to surrounding air. Possibly, nitrogen from this source can be decreased by maintaining an unbroken protective slag cover oyer the liquid steel surface. Furthermore, an ionised atmosphere in the form of a plasma is created around tips of the electrodes 201, resulting in the disassociation of gaseous nitrogen from the surrounding atmosphere. Thus, this promotes nitrogen absorption into the bath of liquid steel 202.

To limit the amount of nitrogen absorbed into the liquid steel bath, it is known to develop a deep protective foamy slag around the plasma arc, to reduce contact between ambient air and molten steel and to minimise disassociation. This may be achieved by the injection of gaseous oxygen and fine carbon into the slag that resides on the liquid steel surface, using either a side wall injection module or modules to inject the oxygen and fine carbon, or by the use of other types of pneumatic injection. The oxygen and carbon chemically react to generate a large number of small carbon monoxide gas bubbles, that assist in the development of slag foaming.

A known way of removing dissolved nitrogen from an electric arc furnace melt is to generate substantial volumes of small gas bubbles deep within the liquid steel bath. As the small gas bubbles rise up through the melt, they effectively sweep nitrogen out of the liquid metal. To achieve this, it is known to oxidise carbon dissolved in the steel bath in order to generate carbon monoxide gas bubbles. The carbon content of the liquid steel should remain above 0.3 percent by mass, or iron oxidization will occur preferentially. Consequently, the natural level of carbon in the liquid steel bath may be supplemented by external carbonaceous sources, either directly within the charge or indirectly by injecting appropriately graded carbon into the liquid steel bath.

A furnace vessel 301 is illustrated in Figure 3. This is provided with six injectors 302 to 307. These injectors may be arranged to introduce combustible gases, such as methane and propane, mixed with oxygen, in order to introduce chemical energy into the furnace; so as to assist the electric arcs when performing a melting operation. In particular, the use of burners in this way may facilitate a more even heating operation and remove the existence of cold spots. Thereafter, devices are known that may switch to an injection operation in which gases, such as oxygen gas, may be injected into the liquid steel bath at supersonic speeds, which may in turn produce considerable volumes of carbon monoxide gas in the form of small bubbles that rise up through the liquid steel bath.

It is known that it is possible to increase productivity by the injection of oxygen with a flammable gas such as methane (usually derived from natural gas), propane or butane into the electric arc furnace via an injection module or modules (such as modules 302 to 307) positioned in a water cooled furnace sidewall 308. The oxygen-gas burner modules may be mounted relatively high in the furnace sidewall 308, in order to mitigate against high thermal loads and to reduce splashing and consequent blocking of burner outlets with metal and slag.

However, the higher the injector is installed, the lower the jets momentum onto the melt. Typically, a water cooled furnace sidewall extends 0.2 metres to 0.3 metres beyond a refractory furnace bottom section 309. Consequently, the oxygen-gas burner module should be angled away from the refractory material to prevent refractory erosion. However, the shallower the injection angle, the less will be the degree of metal penetration of the oxygen jet. Thus, to facilitate penetration, sidewall mounted injectors are known that deliver oxygen at supersonic speeds using coherent jet technology.

Further techniques are known for reducing the nitrogen content of steel produced by an electric arc furnace. Thus, it is possible for furnaces to operate in a flat-bath mode, with a large hot heel size of typically up to one hundred tonnes. This works with a deep protective slag cover that shrouds the arcs and thereby prevents excessive nitrogen pick-up from the atmosphere. However, problems still exist in that, for many applications, the resulting nitrogen concentration is still too high and an aim of the present invention is to put forward techniques that ensure that the tap nitrogen content from the electric arc furnace is comparable with the tap nitrogen content from basic oxygen furnaces.

The furnace of Figure 2 and the furnace of Figure 3 both provide apparatus for the production of steel that are configured to receive charge material, apply heat and produce liquid steel. To reduce nitrogen concentration, one or more reactant introducing devices are provided, configured to introduce a reactant into the liquid steel. The reactant undergoes one or more chemical reactions with nitrogen contained within the liquid steel to produce a nitrogen-including compound from nitrogen contained within the liquid steel. This nitrogen containing compound is then removed by an off-gas system, thereby significantly reducing the amount of nitrogen retained within the liquid steel and the subsequent solidified steel.

The procedure is particularly applicable to electrically powered furnaces and the embodiments described herein show its application with respect to electric arc furnaces, although other types of electrically powered furnaces, such as electric induction furnaces, may also benefit.

Electric arc furnaces are often used for the recycling of scrap steel 102. However, as previously described, other materials, including directly reduced iron 103, hot briquetted iron 104, pig iron 105 and liquid blast furnace iron 106 may be included in order to provide a degree of flexibility to the furnace operation.

Referring to Figure 2, purging plugs 205 and 206 may provide devices for introducing the reactant at the bottom of the furnace. In an embodiment, the reactant introducing devices 205 and 206 are configured to introduce hydrogen gas. As described with respect to Figure 5, this results in a direct reaction with dissolved nitrogen in order to yield ammonia that is removed by the off-gas system 206.

In an alternative embodiment, the reactant introducing plugs 203 and 204 may be configured to receive superheated steam, which in turn undergoes a first reaction to produce hydrogen which then in turn undergoes a second reaction to produce ammonia, as described with respect to Figure

6.

Returning to Figure 3, an alternative is to use the injectors 302 to 307 as devices for introducing the reactant. Thus, the arrangement of injectors configured to inject oxygen supersonically may be deployed in a similar fashion to introduce the reactant. Again, in an embodiment, the injectors inject hydrogen, so as to implement the method described with respect to Figure 5. In an alternative embodiment, the injectors are configured to introduce super-heated steam, so as to perform the method described with respect to Figure 6.

Figure 4

Injector module 302 is detailed in Figure 4. The injector consists of a central supersonic nozzle 401 and a coaxial annular-gap nozzle 402. The reactant, possibly mixed with oxygen, is received from source 403 and supplied to the central supersonic nozzle 401. A combustion gas, possibly natural gas (methane) mixed with oxygen, is supplied to the coaxial annulargap nozzle 402 from a source 404.

In operation, both nozzles are water cooled, as indicated by pipe 405, and the device creates a shroud of hot combustion gas (from source 404) which covers a cold jet of reactant gas from source 403, thereby increasing the supersonic jet length.

Thus, in an embodiment, the hydrogen containing reactant is introduced as a gas through the furnace bottom (as illustrated in Figure 2) alternatively, the hydrogen containing reactant may be injected through a sidewall injection module or modules (as described with respect to Figure 3 and Figure 4) or by using other types of pneumatic injection system.

As an alternative, hydrogen could be a constituent of another or gas mixtures, that might be injected into the liquid steel bath by way of a sidewall injection module or modules or by using other types of pneumatic systems or by injection through the furnace bottom. Another approach could be to introduce hydrogen into the liquid steel bath by charging hydrogen-containing solids or liquids.

The injecting system described with respect to Figure 3 and Figure 4, may also be used to deploy superheated steam at supersonic speed, as an alternative to hydrogen. The superheated steam may be introduced alone, or in combination with another gas or gases or in combination with injectiongrade carbon. Steam temperatures before injection are expected to be greater than two hundred degree Celsius and possibly will fall within a range of two hundred and fifty degrees Celsius to four hundred and fifty degrees Celsius. Upstream steam pressure is expected to be in a range of between five atmospheres and fifteen atmospheres.

Figure 5

Embodiments described herein disclose a steel making method in which hydrogen is added into a liquid steel bath either directly as hydrogen gas or in compounded form. With dissolved hydrogen at around half of its saturation level in the liquid steel bath, nitrogen levels are expected to be reduced to below fifty parts per million, with the prospect of less than twenty parts per million when dissolved hydrogen is at saturation.

As illustrated in Figure 5, experiments have been performed to evaluate the effectiveness of the denitrogenation process of liquid steel at one thousand six hundred degrees Celsius (1600 °C) and an initial dissolved nitrogen level of around eighty parts per million.

Hydrogen gas 501 introduced into the steel bath breaks down to produce atoms of hydrogen 502. These atoms of hydrogen 502 then react with atoms of nitrogen 503 to produce molecules of ammonia gas 504, that is then removed by the off-gas system 108.

A graph is shown at 505, summarising and interpolating experimental results for the introduction of hydrogen. A first axis 506 identifies the total amount of hydrogen introduced for each particular experiment, defined in terms of mass of hydrogen relative to the mass of steel present within the furnace. Thus, in this example, a range of relative masses has been considered up to a maximum value of 0.005.

A second axis 507 identifies the residual amount of gas remaining in the specimen, measured in terms of parts per million. Thus, the graph represents a steady state analysis showing residual gas levels for a range of introduced hydrogen concentrations.

A first plot 508 represents the concentration of nitrogen remaining in the steel at the end of the process. Thus, by increasing the level of introduced hydrogen up to a value of 0.005 per unit mass of steel, the residual nitrogen level reduces from a value above eighty parts per million (with no introduced hydrogen) to a value of less than twenty parts per million. This does however result in residual hydrogen being left in the steel, as illustrated by a second plot 509, rising from a proportion of zero parts per million up to a saturation level of approximately twenty-three parts per million.

Thus, when the relative mass of hydrogen is increased from 0.001 to 0.005, there is a significant reduction in the amount of residual nitrogen but the amount of residual hydrogen is relatively unchanged, due to saturation.

Thus, by deploying the direct injection of hydrogen gas into the liquid steel bath, a proportion of the hydrogen gas dissolves into the liquid steel and reacts with the dissolved nitrogen to form ammonia gas, which is then extracted by the off-gas system during the process. The dissolved nitrogen level decreases from around eighty parts per million to less than twenty parts per million at hydrogen saturation.

It has also been noted that direct hydrogen injection lowers the dissolved oxygen present in the liquid steel. Furthermore, this approach also reduces the amount of iron present in the slag. Consequently, by adopting this process, there should be yield gain, due to a reduction in the amount of iron present in the slag at hydrogen saturation. It is also likely that the dissolved carbon level in the steel will also decrease.

Figure 6

In an alternative embodiment, hydrogen is introduced into the liquid steel bath by the introduction of superheated steam, possibly injected at supersonic speed into the liquid steel bath using sidewall injection modules. In this way, it is possible for the superheated steam to deeply penetrate the liquid steel.

Steam temperature before injection is expected to be greater than two hundred degree Celsius and in a preferred deployment, lies within a range between two hundred and fifty degrees Celsius and four hundred and fifty degrees Celsius. Upstream steam pressure is expected to be in a range of between five atmospheres and fifteen atmospheres. Molecules of steam 601 introduced into the steel bath break down to produce atoms of hydrogen 602 and atoms of oxygen 603. The atoms of hydrogen 602 react with atoms of nitrogen 604 to produce molecules of ammonia gas 605.

Oxygen 606 released in the process, reacts with carbon 607 to produce carbon monoxide 608. Thus, ammonia is formed from hydrogen and nitrogen dissolved in the liquid steel bath. Furthermore, the reaction is catalysed by iron and further promoted by the inclusion of calcium oxide and silicon dioxide etc. present in the slag. The reaction is relatively low yielding but the electric arc furnace is not a closed reactor vessel and the resulting ammonia gas released from the liquid steel is removed through the off-gas system. Consequently, increasing amounts of hydrogen dissolved in the liquid steel bath continue to react with decreasing amounts of dissolved nitrogen to form more ammonia; thereby ensuring the progress of the reaction up to the hydrogen saturation limit in the liquid steel bath, that is around twenty three parts per million at one thousand six hundred degrees Celsius.

A graph is shown at 608, summarising and interpolating experimental results for the introduction of superheated steam. A first axis 609 identifies the total amount of steam introduced for each particular experiment, defined in terms of the mass of steam relative to the mass of steel present within the furnace. Thus, in this example, a range of relative masses has been considered up to a maximum value of 0.05.

A second axis 610 identifies the residual amount of gas remaining in the specimen, measured in terms of parts per million. Thus, the graph represents a steady state analysis showing residual gas levels for a range of introduced superheated steam concentrations.

A first plot 611 represents the concentration of nitrogen remaining in the steel at the end of the process. Thus, by increasing the level of introduced steam by mass up to a value of 0.05 per unit mass of steel, the residual nitrogen level reduces from a value of above eighty parts per million (with no introduced hydrogen) to a value of less than twenty parts per million. Again, however, this does result in residual hydrogen being left in the steel, as illustrated by a second plot 612, rising from a proportion of zero parts per million up to a saturation level of approximately twenty-three parts per million. Thus, when the relative mass of steam is increased from 0.005 to 0.05, there is a significant reduction in the amount of residual nitrogen, with the amount of residual hydrogen remaining relatively unchanged, due to saturation.

When the liquid steel bath reacts with superheated steam, iron oxide and hydrogen will be formed. Without appropriate countering measures in place, the resulting iron oxide formation could result in excessive iron yield loss. The potential additional yield loss may be countered by maintaining the liquid steel carbon content above 0.3 percent, possibly by injecting carbon in parallel with the steam injection or by the addition of appropriate carbon containing materials.

The approach of introducing additional carbon will further promote the formation of carbon monoxide gas bubbles, which will also help in terms of reducing dissolved nitrogen by sweeping out the nitrogen from the liquid steel bath.

When dissolved hydrogen in the liquid steel bath exceeds its saturation limit, additional hydrogen gas will be present in the off-gas system that will combust downstream and consequently increase the temperature of the off-gas.

As illustrated in Figure 1, further counter measures can be deployed before attempting to cast the liquid steel to a solid product, so as to reduce the dissolved hydrogen content, which will be at or close to its saturation limit at tap. Consequently, a secondary process of degassing 110 may be deployed.

Further experimentation also suggests that steam injected in this way will oxidise carbon and phosphorous, while increasing the level of dissolved oxygen in the steel and thereby increasing the level of iron oxide present in the slag. At low steam injection levels, it is also possible to remove dissolved sulphur.

Claims

CLAIMS The invention claimed is:

1. A method of producing steel, comprising the steps of: melting a charge material to form liquid steel, wherein said liquid steel has nitrogen absorbed therein;

introducing a reactant into said liquid steel, wherein said reactant undergoes one or more chemical reactions to form a nitrogen-including compound from said absorbed nitrogen; and removing said nitrogen-including compound from the liquid steel.

2. The method of claim 1, wherein said charge material comprises one or more materials selected from: steel scrap; directly reduced iron; hot briquetted iron; pig iron and hot blast furnace iron in liquid form.

3. The method of claim 1 or claim 2, wherein said reactant is hydrogen, such that said removed nitrogen including compound includes hydrogen.

4. The method of claim 3, wherein said nitrogen including compound is ammonia.

5. The method of claim 3 or claim 4, wherein said hydrogen is introduced into the liquid steel as hydrogen gas.

6. The method of claim 1 or claim 2, wherein:

said reactant comprises a first compound that includes hydrogen; said first compound undergoes a first reaction to release hydrogen;

and said released hydrogen undergoes a second reaction with said absorbed nitrogen.

7. The method of claim 6, wherein:

said first reactant is steam, wherein said steam is introduced into the liquid steel; and said first reaction is a reaction between said steam and carbon monoxide, so as to perform said hydrogen releasing step.

8. The method of claim 6 or claim 7, wherein: said second reaction produces ammonia; and said removing step removes said ammonia.

9. The method of claim 7 or claim 8, wherein said steam is dry superheated steam at a temperature above two hundred degrees Celsius.

10. The method of any of claims 7 to 9, wherein said steam is injected supersonically at a pressure above five atmospheres (505 kPa).

11. An apparatus for the production of steel, comprising:

a furnace configured to receive charge material, apply heat and produce liquid steel;

one or more reactant introducing devices, configured to introduce a reactant into said liquid steel, wherein said reactant undergoes one or more chemical reactions with nitrogen contained within said liquid steel to produce a nitrogen-including compound from nitrogen contained within said liquid steel; and an off-gas system for removing said nitrogen-including compound.

12. The apparatus of claim 11, wherein said furnace is an electrically powered furnace.

13. The apparatus of claim 12, wherein said electrically powered furnace is an electric arc furnace.

14. The apparatus of any of claims 11 to 13, wherein said charge material is selected individually or in any combination from a list comprising: steel scrap; directly reduced iron; hot briquetted iron; pig iron; and blast furnace iron in liquid form.

15. The apparatus of any of claims 11 to 14, wherein said reactant introducing devices are injectors that are configured to supersonically inject said reactant.

16. The apparatus of any of claims 11 to 15, wherein said off-gas system includes a heat recovery sub-system.

Intellectual

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Application No: GB1614938.7

16. The apparatus of any of claims 11 to 15, wherein said reactantintroducing devices are configured to introduce hydrogen gas.

17. The apparatus of any of claims 11 to 15, wherein:

said reactant-introducing devices are configured to introduce superheated steam;

said superheated steam undergoes a first reaction to produce hydrogen;

said hydrogen undergoes a second reaction to produce ammonia; and said ammonia is removed by said off-gas system.

18. The apparatus of any of claims 15 to 17, wherein said injectors are also configured to perform a gas burning operation prior to performing said injection operation.

19. The apparatus of any of claims 11 to 18, wherein said off-gas system includes a heat recovery sub-system.

20. The apparatus of any of claims 11 to 19, further comprising one or more stages for performing hydrogen removal.

21. A method of producing steel, substantially as herein described with reference to the accompanying drawings.

5 22. An apparatus for the production of steel, substantially as herein described with reference to the accompanying drawings.

AMENDMENT TO CLAIMS ARE FILED A SFOLLOWS CLAIMS 1. A method of producing steel in an electric arc furnace, comprising the steps of: melting a charge material to form liquid steel, wherein said liquid steel 5 has nitrogen absorbed therein; supersonically injecting a reactant into said liquid steel by means of one or more injectors, wherein said reactant undergoes one or more chemical reactions to form a nitrogen-including compound from said absorbed nitrogen; and 10 removing said nitrogen-including compound from the liquid steel. • · • « * ·♦· • 2. The method of claim 1, wherein said charge material comprises one or more materials selected from: steel scrap; directly reduced iron; hot • · briquetted iron; pig iron and hot blast furnace iron in liquid form. . · 15 • · • 3. The method of claim 1 or claim 2, wherein said reactant is • • · · ··· a • hydrogen, such that said removed nitrogen including compound includes hydrogen. • > 20 4. The method of claim 3, wherein said nitrogen including compound is ammonia. 5. The method of claim 3 or claim 4, wherein said hydrogen is introduced into the liquid steel as hydrogen gas. 25 6. The method of claim 1 or claim 2, wherein: said reactant comprises a first compound that includes hydrogen; said first compound undergoes a first reaction to release hydrogen; and

said released hydrogen undergoes a second reaction with said absorbed nitrogen.

7. The method of claim 6, wherein:

said reactant is steam, wherein said steam is introduced into the liquid 5 steel; and said first reaction is the breaking down of said steam to produce hydrogen and oxygen, so as to perform said hydrogen releasing step.

8. The method of claim 6 or claim 7, wherein: said second 10 reaction produces ammonia; and said removing step removes said ammonia.

• to • · ♦ ♦ ·«

• ♦ • • to • • • to to * <«· • to • • to

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11. An apparatus for the production of steel, comprising:

an electric arc furnace configured to receive charge material, apply heat and produce liquid steel;

one or more reactant introducing devices, configured to introduce a reactant into said liquid steel, wherein said reactant undergoes one or more chemical reactions with nitrogen contained within said liquid steel to produce a nitrogen-including compound from nitrogen contained within said liquid steel; and an off-gas system for removing said nitrogen-including compound; wherein:

said reactant introducing devices are injectors that are configured to supersonically inject said reactant.

12. The apparatus of claim 11, wherein said charge material is selected individually or in any combination from a list comprising: steel scrap; directly reduced iron; hot briquetted iron; pig iron; and blast furnace iron in liquid form.

13. The apparatus of claims 11 or 12, wherein said reactantintroducing devices each include means for introducing hydrogen gas.

14. The apparatus of any of claims 11 to 13, wherein:

10 said reactant-introducing devices each include means for introducing super-heated steam;

said superheated steam undergoes a first reaction to produce ’·... hydrogen;

····· said hydrogen undergoes a second reaction to produce ammonia; and

15 said ammonia is removed by said off-gas system.

• · ·· ·· • · 15. The apparatus of claims 13 or claim 14, wherein said injectors „··. are also configured to perform a gas burning operation prior to performing ·· · M„; said injection operation.

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