Method for producing iron or steel and associated plant

Abstract

The present invention concerns a method and a plant complex for producing iron or steel.

Description

[0001] METHOD FOR PRODUCING IRON OR STEEL AND ASSOCIATED PLANT

[0002] The present invention concerns a method and a plant complex for producing iron or steel.

[0003] Steel production involves a first step of hot metal production such as molten iron, a second step of conversion of hot metal into liquid steel, and optionally the production of coke.

[0004] Hot metal is obtained in a blast furnace from iron ores, additives such as coke and other reducing agents such as coal, oil, gas, biomasses, recycled waste plastics or other substances containing carbon and / or hydrogen. CO, CO2, hydrogen and water vapour are inevitable products of the reduction reactions. Apart from the aforementioned constituents, a blast-furnace furnace top gas drawn off from the blast-furnace process often has a high content of nitrogen. The amount of gas and the composition of the blast-furnace top gas are dependent on the feedstock and the operating mode and are subjected to fluctuations. Typically, however, blast-furnace top gas contains 35 to 60% by volume N2, 20 to 30% by volume CO, 20 to 30% by volume CO2 and 2 to 15% by volume H2. Around 30 to 40% of the blast-furnace top gas produced in the production of hot metal is generally used for heating up the hot air for the blast-furnace process in air heaters; the remaining amount of top gas may also be used externally in other areas of the works for heating purposes or for electricity generation.

[0005] In the converter, which is arranged downstream of the blast-furnace process, hot metal is converted into liquid steel. By blowing oxygen onto hot metal, amounts of unwanted components such as carbon, silicon, sulphur and phosphorus are reduced. Since the oxidation processes are exothermic, scrap is often added in amounts of up to 25% with respect to the hot metal to increase the metal yield. Furthermore, lime is added as slag forming agent to remove unwanted impurities form the hot metal. A converter gas that has a high content of CO and also contains nitrogen, hydrogen and CO2 is drawn off from the steel converter. A typical converter gas composition has from 50 to 70% by volume of CO, from 10 to 20% by volume of N2, about 15% by volume of CO2 and about 2% by volume of H2. The converter gas is either burned off or, in the case of modern steel mills, captured and passed on to be used for energy supply.

[0006] The plant complex may be operated in combination with a coking plant. In this case, the plant complex described at the beginning additionally comprises a coke-oven plant, in which coal is converted into coke by a coking process. In the coking of coal into coke, a coke-oven gas occurs, containing high hydrogen content and considerable amounts of CH4. Typically, coke-oven gas contains 55 to 70% by volume H2, 20 to 30% by volume CH4, 5 to 10% by volume N2 and 5 to 10% by volume CO. In addition, the coke-oven gas has fractions of CO2, NH3 and H2S. In practice, the coke-oven gas is used in various areas of the steel shop for heating purposes and in the power-generating process for electricity generation. In addition, it is known to use coke-oven gas together with blast-furnace top gas or with converter gas for producing syngas.

[0007] In an integrated metallurgical plant that is operated in combination with a coking plant, approximately 40 to 50% of the raw gases that occur as blast-furnace top gas, converter gas and coke-oven gas are used for chemical or biotechnological engineering processes. Approximately 50 to 60% of the gases produced are fed to the power-generating plant and used for electricity generation. The electricity produced in the power-generating plant covers the electricity demand for the production of hot metal and liquid steel.

[0008] Ideally, the energy balance is closed, so that, apart from iron ores and carbon in the form of coal and coke as sources of energy, no further energy input is necessary and, apart from liquid steel and slag, no product leaves the plant complex.

[0009] EP3080309 discloses a plant complex for steel production comprising a blast furnace for producing hot metal, a converter for producing liquid steel, a gas-conducting system for gases that occur in at least one of the production of hot metal and liquid steel, and a biotechnological plant connected to the gas-conducting system.

[0010] This plant complex focuses on energy and cost optimization but is silent about the overall environmental impact and the management of co-products.

[0011] Thus, there is a need for a steelmaking plant complex in which the integration and the productivity of the biotechnological plant are improved, and the global environmental footprint of the process is reduced.

[0012] There is also a need for a steelmaking plant complex that produces steel with an improved cost-effectiveness and with reduced costs.

[0013] The present invention solves these needs.

[0014] The present invention relates to a method for producing iron or steel, which comprises:

[0015] - producing hot metal and a blast furnace top gas in a blast furnace,

[0016] - producing liquid steel and a converter gas in a converter, and

[0017] - producing at least one product and biomass in a biotechnological plant, wherein: a) at least a partial amount of a blast-furnace top gas and / or of the converter gas is fed to the biotechnological plant to produce the at least one product and the biomass, and b) the biomass produced in the biotechnological plant is transformed into a biogas in a transformation unit.

[0018] Thanks to the invention, it is possible to upcycle the biomass produced by the biotechnological plant, thereby reducing the impact on the environment.

[0019] The method of the invention may also comprise the following optional characteristics considered separately or according to all possible technical combinations:

[0020] - before being fed to the biotechnological plant, the at least partial amount of the blastfurnace top gas and / or converter gas is subjected to a gas-conditioning operation;

[0021] - the gas-conditioning operation is a compression and / or a pressure swing adsorption (PSA) and / or a water-gas-shift reaction (WGS) and / or a Vacuum Pressure Swing Adsorption (VPSA) and / or a steam reforming;

[0022] - the biotechnological plant comprises a fermentation broth that comprises the product and biomass, and said fermentation broth is fed to a recovery unit in which the product is recovered and separated from the biomass and from an effluent;

[0023] - the biomass is dried before being sent to the transformation unit;

[0024] - the transformation of the biomass into a biogas is chosen among a burning step, a gasification step, a pyrolysis step and an anaerobic digestion step;

[0025] - the biotechnological plant is a plant for the fermentation of the blast-furnace top gas or converter gas and allows production of at least one product, preferably chosen from alcohols such as methanol, ethanol, propanol, butanol, isobutanol or 2,3-butanediol ; acetone ; and organic acids such as acetic acid, butyric acid, isobutyric acid, propionic acid, hexanoic acid or caproic acid;

[0026] - the fermentation is carried out by one of more strains of carboxydotrophic bacteria which are preferably anaerobic ; preferably the carboxydotrophic bacterium is selected from Clostridium, Moorella and Carboxydothermus, most preferably the carboxydotrophic bacterium is Clostridium autoethanogenum such as a Clostridium autoethanogenum having the identifying characteristics of DSMZ deposit number 19630 or having the identifying characteristics of DSMZ deposit number DSMZ 10061 ;

[0027] - the biogas is used in the iron and steel production;

[0028] - the biogas is injected in the blast furnace and / or in a direct reduction plant; and / or

[0029] - it further comprises a power-generating plant that is fed with a gas stream coming from the blast-furnace top gas and / or the converter gas, and / or with a coke oven for producing coke. The present invention also relates to a plant complex for the production of iron or steel for implementing an iron or steel production method according to the invention, comprising:

[0030] - a blast furnace producing hot metal and a blast furnace top gas, and / or a converter producing liquid steel and a converter gas,

[0031] - a gas-conducting system for gases that occur in the production of hot metal and / or steel, and

[0032] - a biotechnological plant and a transformation unit both connected to the gas-conducting system, wherein: the biotechnological plant is operated with at least a partial amount of the blast-furnace top gas and / or of the converter gas, and produces at least one product and biomass, and said biomass is transformed in the transformation unit into a biogas.

[0033] Other characteristics and advantages of the invention will emerge clearly from the description of it that is given below by way of an indication, and which is in no way restrictive, with reference to the appended figure (Figure 1 ) which illustrates an embodiment of a method according to the invention.

[0034] It is noted that the figure represents mainly one embodiment of the object of the invention but other embodiments which correspond to the definition of the invention may exist. Elements in the figure are illustration and may not have been drawn to scale.

[0035] Figure 1 illustrates a plant complex to implement a steel production method according to one embodiment of the invention.

[0036] The plant complex for iron or steel production that is represented in FIG. 1 comprises a blast furnace 1 and converter 22 for producing hot metal and steel, and a biotechnological plant 11 . A gas-conducting system is also represented, but not linked to a specific number.

[0037] In the blast furnace 1 , hot metal such as molten iron 3 is obtained substantially from iron ore 30 and reducing agents 31 , in particular coke and coal. Reduction reactions cause the production of a blast-furnace top gas 7, which contains N2, CO, CO2 and H2 as the main constituents.

[0038] The converter 22 is arranged downstream of the blast-furnace 1 process, so that hot metal 3 is converted into liquid steel. By blowing oxygen onto the liquid hot metal, amount of unwanted component, in particular carbon, silicon and phosphorus, are reduced. Scrap may be added in amounts of up to 25% with respect to the amount of hot metal. Furthermore, lime is added for forming slag. At the top of the converter, a converter gas 23 that has a very high proportion of CO is drawn off.

[0039] The blast furnace top gas 7 (BFG) and the converter gas 23 (BOFG) are captured and directed to a gas conducting system. BFG 7 and BOFG 23 differ in amount, composition, calorific value and purity and are used again at various points in the plant complex. In an overall consideration, from 35 to 45%, usually approximately 45%, of the raw gas 7 and / or converter gas 23 are reused into the metallurgical process for producing hot metal 3 or producing liquid steel (not represented on FIG. 1 ).

[0040] According to the representation in FIG. 1 , a biotechnological plant 11 is provided, connected to the gas-conducting system. At least a partial amount of the blast-furnace top gas 7 and / or at least a partial amount of the converter gas 23 is used as a useful gas for operating the biotechnological plant 11. Provided upstream of the biotechnological plant 11 in the direction of flow is a cleaning device 13 for producing a cleaned gas 4 of blast-furnace top gas 7 and the converter gas 23. Typically, the cleaning device 13 for the blast-furnace top gas 7 and the converter gas 23 is a water wash cleaning device.

[0041] The cleaning device 13 aims to separate out troublesome contents, in particular tar, sulphur and sulphur compounds, aromatic hydrocarbons (BTX) and high-boiling hydrocarbons.

[0042] In the case of the plant complex represented in FIG. 1 , the blast-furnace top gas 7 and / or the converter gas 23 is fed preferably after a gas-conditioning operation in a gas conditioning unit 9 to the biotechnological plant 11. In other words, the biotechnological plant 11 is operated with at least a partial amount of the blast-furnace top gas 7 and / or the converter gas 23 after a gas-conditioning operation. Preferably, at least one gasconditioning operation unit 9 is present in the gas-conducting system between the blast furnace 1 and / or the converter 22 and the biotechnological plant 11 .

[0043] During the gas-conditioning operation, the proportion of the components CO, CO2 and H2 within the raw gas is changed. The gas-conditioning operation comprises for example a compression and / or a pressure swing adsorption (PSA) (for separating out and enriching H2) and / or a Vacuum Pressure Swing Adsorption (VPSA) and / or a water-gasshift reaction (WGS) for converting CO into H2 and / or a steam reforming for converting the CH4 fraction into CO and H2. It aims notably to reduce the CO2 concentration of the gas. Typically, the gas-conditioning unit 9 comprises a compressor and then a PSA unit. The compression allows obtaining a required pressure that may be useful for the biotechnological plant 11 . According to the representation in FIG. 1 , the cleaned gas 4 goes through the PSA unit 9 before feeding the biotechnological plant 11 . PSA 9 aims to separate out and enrich the gas in H2 and / or CO. PSA 9 may further aim to remove from the gas any of the contaminants that are deleterious to the biotechnological plant 11. Said contaminant is especially HCN. Preferably, the PSA 9 comprises at least one pressure vessel, preferably at least six pressure vessels. The pressure vessel comprises an adsorbent material. At the exit of the PSA, the gas 34 preferably comprises high CO and H2 levels.

[0044] The gas 34 feeds the biotechnological plant 11. The biotechnological plant 11 is a plant for the biochemical transformation of the blast-furnace top gas 7 and / or the converter gas 23 into a chemical product. Said chemical product may be chosen from alcohols (such as methanol, ethanol, propanol, butanol, isobutanol or 2,3-butanediol), acetone and organic acids (such as acetic acid, butyric acid, isobutyric acid, propionic acid, hexanoic acid or caproic acid).

[0045] The biotechnological plant 11 produces at least one chemical product and biomass 15, and can also produce a residual gas.

[0046] By “biomass” here, it is meant recently living - but now dead - microorganisms, as well as organic waste matter that is produced in the biotechnological plant, such as for example carbohydrates, proteins, nucleic acids and / or minerals.

[0047] Typically, the amount of biomass that is generated by the fermentation process used in the invention is around 812 kg biomass / h; this corresponds to a yield of around 105 kg biomass / ton alcohol (such as ethanol).

[0048] Said gas 34 and residual gas may be syngas.

[0049] By « syngas » or « synthesis gas », it is meant a gas comprising at least a mixture of carbon monoxide (CO) and dihydrogen (H2). The syngas may further comprise other carbon-containing gases such as carbon dioxide (CO2), methane (CH4) and optionally nitrogen (N2).

[0050] The residual gas has typically a CO content that is lower than 5% and a H2 content that is lower than 1 %. However, the specific composition of the residual gas can vary, depending on the composition of the feed gas given to the biotechnological plant.

[0051] The blast-furnace top gas 7 and the converter gas 23 may be combined in any way desired. The combination of gas streams using the bast-furnace top gas 7 and the converter gas 23 depends on the desired syngas or the product that is to be produced in the biotechnological plant 11. Preferably, the biochemical transformation is a fermentation reaction and is more preferably carried out by one of more strains of carboxydotrophic bacteria. By « carboxydotrophic bacteria », it is meant bacteria that have the ability to oxidize CO. Preferably, the carboxydotrophic bacteria are anaerobic. Preferably, the carboxydotrophic bacterium is selected from Clostridium, Moorella and Carboxydothermus.

[0052] Clostridium autothenogenum DSMZ (German Resource Centre for Biological Material) 19630, Clostridium autothenogenum DSMZ 10061 , Clostridium ragsdahlei ATCC no. BAA-622, Clostridium autoethanogenum, Moorella sp HUC22-1 , Moorella thermoaceticum, Moorella thermoautotrophica, Carboxydothermus, Clostridium formicoaceticum, Clostridium butyricum, Clostridium aceticum, Clostridium ljungdahlii, Clostridium ATCC 29797 and Clostridium carboxidivorans, in particular ATCC BAA-624.

[0053] Most preferably, the carboxydotrophic bacterium is Clostridium autoethanogenum. Preferably, the Clostridium autoethanogenum is a Clostridium autoethanogenum having the identifying characteristics of DSMZ deposit number 19630. In another embodiment, the Clostridium autoethanogenum is a Clostridium autoethanogenum having the identifying characteristics of DSMZ deposit number DSMZ 10061 .

[0054] During the fermentation, typically the feed gas 34 which enters into the biotechnological plant 11 is rich in CO and H2. Indeed, the richer the feed gas is in CO and H2, the more product can be produced in the biotechnological plant.

[0055] The fermentation may be carried out in any suitable bioreactor. The term "bioreactor" includes a fermentation device consisting of one or more vessels and / or towers or piping arrangements, which can include the Continuous Stirred Tank Reactor (CSTR), Immobilized Cell Reactor (ICR), Trickle Bed Reactor (TBR), Bubble Column, Gas Lift Fermenter, Membrane Reactor such as Hollow Fibre Membrane Bioreactor (HFMBR), Static Mixer, or other vessel or other device suitable for gas-liquid contact. In some embodiments of the invention, the bioreactor may comprise a first growth reactor in which the bacteria are cultured, and a second fermentation reactor, to which fermentation broth from the growth reactor is fed and in which most of the fermentation product is produced.

[0056] The fermentation should desirably be carried out under appropriate conditions for the desired fermentation to occur (preferably CO-to-alcohol). Reaction conditions that should be considered include pressure, temperature, gas flow rate, liquid flow rate, media pH, media redox potential, agitation rate (if using a continuous stirred tank reactor), inoculum level, maximum gas substrate concentrations to ensure that CO in the liquid phase does not become limiting, and maximum product concentrations to avoid product inhibition. The optimum reaction conditions will depend partly on the particular carboxydotrophic bacteria used. However, in general, it may be preferable that the fermentation be performed at a pressure higher than ambient pressure. Operating at increased pressures allows a significant increase in the rate of CO transfer from the gas phase to the liquid phase where it can be taken up by the carboxydotrophic bacteria as a carbon source for the production of alcohol.

[0057] The products of the fermentation reaction can be recovered using known methods. Preferably, alcohol such as ethanol may be recovered from the fermentation broth by methods such as fractional distillation or evaporation, and extractive distillation. Distillation of ethanol from a fermentation broth yields an azeotropic mixture of ethanol and water (i.e. 95% ethanol and 5% water). Anhydrous ethanol can subsequently be obtained through the use of molecular sieve ethanol dehydration technology, which is also well-known in the art. Preferably, the biotechnological plant allows production of at least one chemical product chosen from alcohols, preferably chosen from ethanol, propanol, butanol, isobutanol and 2,3-butanediol, and more preferably at least ethanol.

[0058] The biotechnological plant 11 is operated with the cleaned gas 34 submitted to PSA, and produces at least one chemical product, preferably an alcohol, and biomass in a fermentation broth 15. The broth 15 is fed to a recovery unit such as a distillation unit 5, in which the alcohol 14 is recovered and separated from the biomass 16 and from an effluent 33. A part of the effluent 33 of the recovery unit 5 is sent to a treatment unit 6 for further use (upcycling unit). For example, the treatment unit 6 is a wastewater treatment plant; this allows recycling water and ammoniac which are effluents 18 from the biotechnological plant 11. As the effluent 33 of the recovery unit 5 includes ammoniac (NH3), and as high amounts of ammoniac are needed for fermentation, ammoniac and (clean) water 18 generated in the wastewater treatment plant 6 can thus be sent back to the biotechnological plant 11 for further use.

[0059] Besides water and ammoniac, other useful products generated in the wastewater treatment plant 6 are notably phosphate products 19 (i.e. PO4). They can be valorized separately, and notably used as fertilizers for agriculture.

[0060] Biomass 16 that is separated in the distillation unit 5 is still in humid form, i.e. is in the form of a dissolved biomass 16 or sludge.

[0061] It may be first dried in a drying unit 8 to obtain a solid biomass 17.

[0062] According to the invention, at least a part of said solid biomass 17 is sent to a transformation unit 24, to obtain a biogas 25. According to an other embodiment, the outlet of the biotechnological plant 11 is directly connected to the transformation unit, preferably with a connecting line in which the biomass produced in the biotechnological plant goes to the transformation unit.

[0063] This transformation unit 24 may be chosen among a burning unit, a gasification unit, a pyrolysis unit and an anaerobic digestor. It is preferably an anaerobic digester. Anaerobic digestion is a sequence of processes by which microorganisms break down biodegradable material in the absence of oxygen. The process produces a biogas 25, consisting of methane, carbon dioxide and traces of other contaminant gases such as H2S.

[0064] The biogas 25 may comprise from 60 - 70% by volume of CO2, from 30 - 40 % by volume of CH4 and from 1000 - 3000 ppm by volume of H2S. It is preferably subjected to a desulfurization step, to reduce its content of H2S to less than 5ppm by volume before further use.

[0065] This biogas 25 can be used directly as fuel, in combined heat and power gas engines or upgraded to natural gas-quality biomethane. It may also be used in a unit of the plant complex for iron or steel production.

[0066] Preferably, the biogas 25 is sent to the blast furnace 1 and / or to a direct reduction plant (not represented). It can be used as fuel for the cowpers of the blast furnace 1 or for the heating of the reducing gas of the direct reduction plant, it may also be used as reducing gas either in the blast furnace 1 or in the direct reduction furnace or a carburizing gas for the direct reduction plant.

[0067] This allows to further reduce the overall CO2 footprint of the process as biogas is used as substitute to fossil carbon gases such as methane or natural gas.

[0068] The plant complex may also additionally comprise a power-generating plant. A powergenerating plant (not represented in FIG. 1 ) can be designed as a steam-turbine powergenerating plant (such as a traditional gasfired steamboiler and a steam turbine driven generator to generate the electrical energy) or as a gas-turbine power-generating plant or gas-turbine and steam-turbine power-generating plant and is operated with a gas that comprises at least a partial amount of the blast-furnace top gas 7 and / or converter gas 23. A gas-conducting system can be provided for carrying the gases. From 50 to 60%, usually approximately 55%, of the raw gas 7 can be used for operating a power-generating plant and the biotechnological plant 11.

[0069] Preferably, when a power-generating plant for electricity generation is present, the power-generating plant is connected to the gas-conducting system and arranged in parallel with the biotechnological plant 11 with respect to the gas supply. In other words, the powergenerating plant and the biotechnological plant 11 are preferably arranged in a parallel setup with respect to the gas supply. In such a case, preferably, the power-generating plant is fed with a first gas stream and the biotechnological plant 11 is operated with a second gas stream. Both the first and second gas streams comprise at least a partial amount of the blast-furnace top gas 7 and / or at least a partial amount of the converter top gas 23. The gas-conducting system may comprise a switchable gas diverter for dividing the streams of gas that are fed to the power-generating plant and the biotechnological plant 11 . Preferably the gas-conducting system further comprises, upstream of the switchable gas diverter in the direction flow, a mixing device for producing a mixed gas comprising blast-furnace top gas 7 and converter gas 23.

[0070] Externally obtained electricity and power-generating plant electricity, which is produced by the power-generating plant of the plant complex, are used to cover the electricity demand of the plant complex. The externally obtained electricity is preferably obtained completely or at least partially from renewable energy and originates for example from wind turbine generator plants, solar plants, hydroelectric power-generating plants and the like. To achieve operation of the plant complex that is as cost-effective as possible, electricity is bought in as external electricity at times of low electricity prices and the powergenerating process for supplying electricity is cut back. At times of high electricity prices, the partial stream of the useful gas that is used in the power-generating plant for producing electricity is increased.

[0071] According to an embodiment, the residual gas produced by the biotechnological plant 11 can be directly connected to the power-generating plant. According to another embodiment, the residual gas produced by the biotechnological plant 11 is connected to the tail gas stream produced by a gas-conditioning operation unit 9 of the blast-furnace top gas 7 or converter gas 23, such as a PSA unit.

[0072] The plant complex may also additionally comprise a coke oven. A part of the biomass 17 generated by the biotechnological plant 11 can also be loaded in the coke oven for producing coke. Said biomass 17 can be loaded with coal, together or separately, in the coke oven.

[0073] Many different arrangements of the described invention are possible without departing from the spirit and scope of the present invention. Embodiments of the present invention are described herein with the intent to be illustrative rather than restrictive. Alternative embodiments will become apparent to those skilled in the art that do not depart from its scope. A skilled artisan may develop alternative means of implementing the disclosed improvements without departing from the scope of the present invention.

[0074] Further, it will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations and are contemplated within the scope of the claims. Not all steps listed in the figure and description need to be carried out in the specific order described. The description should not be restricted to the specific described embodiments.

Claims

CLAIMS1 . Method for producing iron or steel, which comprises:- producing hot metal (3) and a blast furnace top gas (7) in a blast furnace (1 ),- producing liquid steel and a converter gas (23) in a converter (22), and- producing at least one product (14) and biomass (16,17) in a biotechnological plant (11 ), wherein: a) at least a partial amount of a blast-furnace top gas (7) and / or of the converter gas (23) is fed to the biotechnological plant (1 1) to produce the at least one product (14) and the biomass (16,17), and b) the biomass (16,17) produced in the biotechnological plant (11 ) is transformed into a biogas (25) in a transformation unit (24).

2. Method according to claim 1 , wherein, before being fed to the biotechnological plant (1 1 ), the at least partial amount of the blast-furnace top gas (7) and / or converter gas (23) is subjected to a gas-conditioning operation.

3. Method according to claim 2, wherein the gas-conditioning operation is a compression and / or a pressure swing adsorption (PSA) and / or a water-gas-shift reaction (WGS) and / or a Vacuum Pressure Swing Adsorption (VPSA) and / or a steam reforming.

4. Method according to any one of the preceding claims, wherein the biotechnological plant (11 ) comprises a fermentation broth (15) that comprises the product (14) and biomass (16,17), and said fermentation broth (15) is fed to a recovery unit (5) in which the product is recovered and separated from the biomass and from an effluent (33).

5. Method according to any one of the preceding claims, wherein the biomass (16) is dried before being sent to the transformation unit (24).

6. Method according to any one of the previous claims, wherein the transformation of the biomass (16,17) into a biogas (25) is chosen among a burning step, a gasification step, a pyrolysis step and an anaerobic digestion step.

7. Method according to any one of the preceding claims, wherein the biotechnological plant (11 ) is a plant for the fermentation of the blast-furnace top gas or converter gas and allows production of at least one product (14), preferably chosen from alcohols such as methanol,ethanol, propanol, butanol, isobutanol or 2,3-butanediol ; acetone ; and organic acids such as acetic acid, butyric acid, isobutyric acid, propionic acid, hexanoic acid or caproic acid.

8. Method according to claim 7, wherein the fermentation is carried out by one of more strains of carboxydotrophic bacteria which are preferably anaerobic ; preferably the carboxydotrophic bacterium is selected from Clostridium, Moorella and Carboxydothermus, most preferably the carboxydotrophic bacterium is Clostridium autoethanogenum such as a Clostridium autoethanogenum having the identifying characteristics of DSMZ deposit number 19630 or having the identifying characteristics of DSMZ deposit number DSMZ 10061.

9. Method according to any one of the preceding claims, wherein the biogas (25) is used in the iron and steel production.

10. Method according to claim 9, wherein the biogas (25) is injected in the blast furnace (1 ) and / or in a direct reduction plant.1 1 . Method according to any one of the preceding claims, which further comprises a powergenerating plant that is fed with a gas stream coming from the blast-furnace top gas and / or the converter gas, and / or with a coke oven for producing coke.

12. Plant complex for the production of iron or steel for implementing an iron or steel production method according to any one of claims 1 to 10, comprising:- a blast furnace (1 ) producing hot metal (3) and a blast furnace top gas (7), and / or a converter (22) producing liquid steel and a converter gas (23),- a gas-conducting system for gases that occur in the production of hot metal (3) and / or steel, and- a biotechnological plant (11 ) and a transformation unit (24) both connected to the gasconducting system, wherein: the biotechnological plant (1 1 ) is operated with at least a partial amount of the blast-furnace top gas (7) and / or of the converter gas (23), and produces at least one product (14) and biomass (16,17), and said biomass (17) is transformed in the transformation unit (24) into a biogas (25).

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