Method for producing hydrogen and renewable carbon from methane catalytic pyrolysis for the steel industry

Abstract

Method for the production of hydrogen and renewable carbon from catalytic pyrolysis of methane for the steel industry including the steps of: - receive a gas stream including methane - receive an amount of amorphous carbon catalyst - at a controlled temperature in a reactor, perform a methane cracking reaction using the amorphous carbon catalyst generating a mixture of hydrogen and an additional gas, preferably methane; and an amorphous coke carbon comprising the catalyst carbon and carbon deposited during cracking.

Description

[0001] METHOD FOR PRODUCING HYDROGEN AND RENEWABLE CARBON

[0002] FROM METHANE CATALYTIC PYROLYSIS FOR THE STEEL INDUSTRY

[0003] DESCRIPTION

[0004] TECHNICAL FIELD

[0005] The present invention refers to a method for the production of renewable hydrogen and carbon from catalytic pyrolysis of methane for the steel industry, based on environmentally sustainable and economical processes e.g. the supply of energy carriers and the direct reduction of iron oxides.

[0006] BACKGROUND ART

[0007] In accordance with the EU environmental policy, Fit-For-55, the steel industry must reduce CO2 emissions. In fact, globally, the steel sector is responsible for about 8% of total CO2 emissions and its decarbonization is crucial to achieving climate goals. An important step in this direction would be the use of modern steelmaking methods for energy consumption and for direct reduction reactions (DR) of iron oxides, allowing a significant reduction in the use of hard coal in favor of the use of sustainable and renewable reducing agents such as hydrogen, biomethane and renewable biocarbons. The production of hydrogen and carbon is of particular interest for the present invention.

[0008] Currently, 96% of the world's H2 production is carried out by reforming processes, which use fossil fuels and produce large quantities of CO2 (approximately 9.5t of CO2 per It of H2). However, there are emerging solutions for the production of low-CO2 hydrogen, with different technological maturity: electrolysis coupled with renewable resources, methane reforming with carbon capture and storage, liquid phase reforming, and pyrolysis or methane cracking.

[0009] Among the various emerging technologies, the one of interest is the pyrolysis or cracking of methane, CH4, as it has several advantages over other technologies. In particular, methane reforming using water vapor, traditionally employed, is a highly exothermic reaction that releases carbon as CO2 and requires the use of carbon capture and storage (CCS) to be carbon neutral; this technique can be carbon negative if, in addition to CSS systems, bioCH4 is used; the electrolysis of water requires a large amount of electricity, which must necessarily be renewable if a green process is to be obtained; Liquid phase reforming is a process that attracts a lot of attention but is still in its infancy. Finally, methane pyrolysis is an endothermic reaction, it releases carbon in the form of solid carbon and is carbon negative if bioCH4 is used. Considering that this technology makes it possible to produce hydrogen and coal without CO2 emissions in a single step, its use in the steel industry is of great interest.

[0010] AIMS AND SUMMARY OF THE INVENTION

[0011] The purpose of the present invention is achieved by means of a method of direct reduction of iron oxides to obtain Iron including the phases of: receiving a flow of gas preferably methane e.g. a mixture of methane and nitrogen, natural gas etc.; receive an amount of carbon-based amorphous carbon catalyst; at a controlled temperature in a reactor, perform a methane cracking reaction using the amorphous carbon catalyst generating a mixture of hydrogen and the unconverted gaseous reactant; and an anthracitic carbonaceous solid comprising the catalyst carbon and the carbon deposited during cracking; use the hydrogen mixture in the direct reduction of iron oxides; use the carbonaceous solid as a fuel, or biogenic reducing agent in the production of steel and other alloys.

[0012] Hydrogen produced by methane cracking using catalyst carbon has characteristics suitable for use in the direct iron reduction process. This is particularly advantageous when the catalyst carbon and / or methane come from waste which, through their respective thermochemical decomposition processes, produce materials with a high carbon content such as methane and coal. In addition, the catalyst carbon, enriched by the carbon generated during methane cracking, can in turn be used in further steel processes as a fuelizer, foaming agent and reducing agent.

[0013] According to one aspect of the present invention, amorphous coke carbon is periodically replaced to maintain a predefined percentage of hydrogen in the mixture for direct reduction.

[0014] Since the catalyst can be used in subsequent processes, the percentage of hydrogen generated can be adjusted by substitution at controlled time intervals. According to a preferred form of implementation of the present invention, there is a direct connection between the reactor and a steelworks in which the direct reduction of iron oxides is carried out in order to send the said mixture, e.g. a pipe between the reactor and the furnace.

[0015] An important aspect of the invention is the high usability e.g. by providing only the filtration from particulate matter or other mechanical / physical operation, of the mixture with hydrogen or direct i.e. of the gas mixture as obtained inside the cracking reactor and, in any case, without the need to apply further chemical or electrochemical processes to the mixture e.g. to separate the hydrogen from the methane. In addition, a relative concentration of hydrogen and methane can be achieved to the advantage of hydrogen, e.g. 60% v / v hydrogen and 40% v / v methane, or even higher than hydrogen. This hydrogen mixture is, in an industrialized process, sent in a continuous flow to the furnace. Alternatively, intermittent delivery is also possible.

[0016] According to one aspect of the present invention, a residence period of catalyst carbon is greater than an intermittency time of the replacement of amorphous coke carbon with new catalyst amorphous carbon.

[0017] For example, the catalyst carbon replacement period in the reactor during cracking is less than 30 minutes, preferably less than 15 minutes, and the residence time of the gas mixture comprising methane is less than 10 seconds, preferably less than 5 seconds. In addition, both residence time and intermittency time are periodic during the cracking process or may vary during the cracking process.

[0018] According to one aspect of the present invention, the amorphous catalyst carbon is a biocarbon, i.e. obtained through the following steps:

[0019] - receive an organic sludge or biomass containing carbonaceous matrices and compounds of Calcium and / or Phosphorus and / or Magnesium and / or aluminates and / or silicates and / or Potassium

[0020] - thermo-chemically decompose organic sludge or biomass to produce a carbonaceous matrix biochar

[0021] - leach the biochar with mono and diprotic acids to bring the aforementioned compounds and / or aluminates and / or silicates into solution, separating them from the carbonaceous matrix - dry the matrix obtaining the amorphous carbon catalyst.

[0022] The invention also concerns an integrated steel plant comprising a methane cracking reactor, appropriate piping and an iron oxide furnace, configured to perform the direct reduction method as previously identified.

[0023] Preferably the steel plant comprises a furnace cooling circuit and the reactor and / or a gas inlet line including methane are connected in heat exchange with an outlet of the cooling circuit.

[0024] In this way, it is possible to recover at least part of the waste heat from the iron oxide reduction process.

[0025] In addition, it is possible to retrofit a furnace of an existing steel plant, by connecting a methane cracking reactor to the furnace so that the gas mixture produced during cracking flows to the furnace intermittently.

[0026] BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The invention will now be described in an illustrative and non-limiting way through the attached figure which schematically illustrates a steel plant equipped with a reactor that implements the method of the present invention.

[0028] DESCRIZIONE DETTAGLIATA DELLTNVENZIONE

[0029] The present invention concerns, for a steel use of iron production by direct reduction, a combined method for the production of hydrogen from methane and bio anthracite, i.e. a coal with high quantities of amorphous carbon and usable in a steel plant, e.g. for the production of iron and carbon alloys. Bioanthracite derives from the use of an innovative catalyst based on amorphous carbon, preferably from organic waste, and enriched with particulate carbon that is deposited on the catalyst and deriving from the cracking of the methane itself; This biontracite, therefore, comes out of the cracking process with a high carbon content for the steel industry, and is obtained through the thermochemical decomposition phases e.g. pyrolysis of waste raw materials with predominantly biogenic matrices, leaching of the carbonization product (biochar) to obtain a catalyst based on amorphous coal, i.e. biocoal, and methane cracking / pyrolysis reaction to produce bioanthracite and hydrogen; the latter is sent to the furnace of a steel plant for the direct reduction of iron oxides. Waste raw materials are e.g. biomass and / or industrial or municipal sludge. Industrial and urban sludge contains compounds of aluminized Calcium and / or Phosphorus and / or Magnesium and / or Aluminum, e.g. and / or Silicon, e.g. silicates and / or Potassium.

[0030] The pyrolysis process optionally starts with a preliminary drying step to reduce the moisture of the raw materials from predominantly biogenic matrices.

[0031] Subsequently, pyrolysis of biomass and / or organic waste on an industrial scale preferably takes place in a single reactor with temperatures between 450°C and 650°C, preferably 500°C, although higher temperatures can be used, and a residence time between 30 and 120 minutes, preferably between 30 and 60 minutes to obtain a dry carbonaceous material without organic compounds and having other impurities e.g. one or more of the compounds mentioned above.

[0032] The biochar is cooled and removed from the reactor.

[0033] Preferably biochar is shredded below 500 microns, preferably below 250 microns.

[0034] The biochar is placed in a mixing chamber, with water.

[0035] Biochar is mixed with preferably demineralized water, forming a mixture with water:biochar ratio in a range of 4:1 to 20:1 to obtain an aqueous solution. Mixing is done in a temperature range between 50 and 90°C.

[0036] The water-biochar mixture is subjected to a leaching step, preferably with monoprotic and / or diprotic acids. In this step, different acids and optionally bases can be used to extract components of interest, i.e. that damage the subsequent process of treating ferrous oxides to obtain iron or steel.

[0037] In a preferred form of construction, leaching includes the steps of:

[0038] - treat the mixture with a first acid reagent, e.g. nitric acid, for the removal of calcium-based compounds from the biochar, the same treatment could be done using sulphuric acid;

[0039] - optionally the mixture can undergo a second acid treatment with a second acid reagent, e.g. hydrochloric acid.

[0040] The leaching process of the water-biochar mixture takes place in a time interval of 60 to 120 minutes, and at a temperature in the range of 50-90°C, the amount of reagents used in leaching by weight are in a range of 40% to 70%, and the ratio by weight of dry solid phase, e.g. biochar leached i.e. ennobled, and liquid, e.g. inorganic solution, is in a range of 1:5 and 1:20. Downstream of the reactor used for leaching, the leaching mixture is subjected to separation of the solid phase, e.g. leached biochar, from the liquid phase, e.g. inorganic solution. For example, a plate separator filter or centrifugal separator or any other system useful for solid / liquid separation is used.

[0041] The liquid phase is treated with a basic reagent, e.g. CaO, Ca(OH)2, NaOH and KOH obtaining the inorganic material of interest i.e. P, Ca, Mg, Al. The inorganic material of interest is not limited to the elements P, Ca, Mg, Al, K, but depends on the initial inorganic composition of the raw materials from predominantly organic matrices.

[0042] The filtered solid phase of leached biochar is washed with water at a temperature in the range of 25-60°C and then dried to obtain a charcoal pure enough to act as a catalyst for the methane cracking reaction. The purity of the catalyst is such that it does not have a significant impact on the treatment of iron oxides.

[0043] The catalyst for the methane is then loaded into the reactor, preferably a counterflow reactor, for cracking the methane or natural gas.

[0044] The methane or natural gas is flushed into the reactor, possibly together with nitrogen in a ratio, e.g. CH4:N2, in the range of 1:1-1:9.

[0045] The reactor has a minimum operating temperature of approximately 900°C which is reached before the catalyst and reagents enter the reactor. The temperature previously stated is not restrictive, and higher temperatures can be used. The catalyst from the waste is chemically stable at the cracking temperature.

[0046] Optionally, a gas detector can be interfaced with the reactor to monitor the development of gases during the reaction so that the composition of the outgoing gas mixture can be verified.

[0047] During the cracking reaction, explained in more detail below, the chemical bonds of methane are broken forming molecular hydrogen and carbon particles that are deposited on the catalyst. The conversion of methane to hydrogen depends, when the pyrolysis temperature is constant as in this case, on factors such as the degree of catalyst saturation or, in other words, catalyst replacement time and residence time of methane in the reactor. Once a desired conversion level has been reached, even in the presence of methane and possibly one or more other gases, the gaseous mixture generated during pyrolysis flows e.g. via a pipeline from the cracking reactor to the furnace of the direct reduction steel plant.

[0048] The catalyst has a residence time in the reactor in the order of minutes, e.g. less than 30 minutes, preferably in the time interval 5-10. At the end of the residence time, the catalyst added with carbon from the deposited methane is extracted and is suitable for the steel industry, e.g. for the process of iron oxides and to obtain steel.

[0049] The gaseous mixture, preferably methane or natural gas, is heated to the previously defined reaction temperature before being flushed into the reactor at an hourly spatial velocity of the volume e.g. 3 L / grams*hour.

[0050] The inlet gaseous mixture has a residence time in the cracking reactor in the order of seconds, preferably in the time interval of 10 seconds, generally less than 5 seconds. At the end of the residence time, the gaseous mixture enriched with the hydrogen produced in the molecular cracking process is extracted and is suitable for the steel industry without further chemical or electrochemical treatments.

[0051] The cracking process in the reactor is continuous, so at the end of the residence time of the gaseous mixture and catalyst they are replaced by a new load of gaseous mixture and catalyst and the process starts again.

[0052] In a schematic description, the cracking reaction includes the following steps: adsorbing methane on the surface of the catalyst, breaking the carbon-hydrogen bonds, releasing hydrogen from the surface while the carbon remains adsorbed. The cracking reaction occurs numerous times leading to a progressive increase of carbon from the methane adsorbed on the surface of the catalyst. This mechanism is also the reason behind the residence time of the catalyst in the reactor.

[0053] According to the present invention, a process of direct reduction is carried out using the gaseous product, i.e. gaseous mixture with hydrogen added, and the solid product, i.e. catalyst with the addition of carbon deriving from the methane deposited on the surface, a metal oxide, preferably iron oxide, including the phases of: loading iron oxide into the reactor, a gas mixture containing at least 25% hydrogen, a carbonaceous material that is not completely oxidized, i.e. non-CO2, convert iron oxide, i.e. hematite, into an iron oxide in which iron has a lower oxidation number, i.e. magnetite, convert magnetite into an iron oxide in which iron has a smaller oxidation number, I.e.. FeO producing water and carbon dioxide at each pass, extracting a gaseous phase, i.e. a gaseous mixture including carbon dioxide and water, and extracting a solid phase, i.e. metallic iron.

[0054] In the Figure, a diagram of a plant for the finishing A of biowaste, e.g. biomass or waste water and an integrated steel plant B, is shown. The finishing plant is dedicated to anaerobic digestion and / or wastewater treatment to obtain melamine biochar and biomethane; The integrated steel plant is dedicated to the production of hydrogen and biocoal and is fluidically connected directly with an iron or steel production group, in particular connected with a furnace of the production group.

[0055] Plant A includes a reactor for anaerobic digestion of biowaste, a reactor for slow pyrolysis and a reactor for chemical leaching. The anaerobic digestion reactor receives biowaste as input and has digestate and biomethane as a product of interest, and carbon dioxide and other gases as a waste product. The slow thermochemical decomposition reactor e.g. pyrolysis receives the digestate as input and has biochar as a product of interest and pyrogas as a waste product. The chemical leaching reactor receives biochar, nitric acid and water as input and has ennobled biochar and inorganic compounds as a product of interest, and water as a waste product.

[0056] Plant B is directly connected with a steel production plant and includes a reactor for methane pyrolysis. The methane pyrolysis reactor receives biomethane, melamine biochar and heat as input, the latter being waste heat supplied by the steel production plant. Plant B has unconverted biomethane, hydrogen and biocoal as a product of interest.

[0057] The steel production plant connected directly to plant B receives unconverted biomethane, hydrogen and biocoal as input.

[0058] Preferably but not limited to, an iron oxide reduction furnace cooling system includes an exhaust connected in heat exchange with the cracking reactor and / or with the supply of the methane gas or natural gas mixture in order to contribute to the heating of the latter by recovering the waste heat of the reduction furnace.

Claims

CLAIMS1. Method for the production of hydrogen and renewable carbon from catalytic pyrolysis of methane for the steel industry including the steps of:- receive a gas stream including methane- receive an amount of amorphous carbon catalyst- at a controlled temperature in a reactor, perform a methane pyrolysis reaction using the amorphous catalyst carbon, generating a mixture of hydrogen and methane; and an amorphous anthracitic carbon comprising catalyst carbon and carbon deposited during pyrolysis.

2. Method according to claim 1, including the phase of carrying out the direct reduction of iron oxides by means of the mixture of hydrogen and methane.

3. Method according to claim 1 or 2, including the step of periodically replacing anthracite carbon to maintain a percentage of hydrogen in the hydrogen and methane mixture for direct reduction above a predefined minimum threshold.

4. Method according to any of the foregoing claims, where a residence period of catalyst carbon is greater than an intermittency time of replacing anthracitic carbon with new catalyst amorphous carbon.

5. Method according to any of the foregoing claims, where the mixture intended for direct reduction comprises 50% or more hydrogen than methane.

6. Method according to any of the foregoing claims, in which the hydrogen of the mixture is not separated from the methane.

7. Method according to any of the foregoing claims, for the production of anthracite carbon in an additional furnace for the production of steel and / or other alloys.

8. Method according to any of the foregoing claims, including the following additional steps for the realization of the said amorphous carbon catalyst:- receive an organic sludge or biomass containing carbonaceous matrices and compounds of Calcium and / or Phosphorus and / or Magnesium and / or aluminates and / or silicates and / or Potassium- thermochemically decompose organic sludge or biomass to produce a carbonaceous matrix biochar- leach the biochar with mono and diprotic acids and basic solutions to bring the said compounds and / or aluminates and / or silicates into solution, separating them from the carbonaceous matrix- dry the matrix obtaining the amorphous carbon catalyst.

9. Steel plant including:- a furnace for the direct reduction of iron oxides- a reactor having a first inlet to receive a gas stream including methane and a second inlet to receive an amount of amorphous catalyst carbon, in which the reactor is configured to, at a controlled temperature, perform a methane pyrolysis reaction via the catalyst amorphous carbon generating a mixture of hydrogen and an additional gas, preferably methane; and an amorphous anthracitic carbon comprising catalyst carbon and carbon deposited during pyrolysis;- a pipe between the reactor and the furnace to send the said mixture of hydrogen and methane to the furnace and allow the direct reduction of iron oxides.

10. A steel plant according to claim 9, comprising a furnace cooling circuit and in which the reactor and / or a gas inlet line including methane are connected in heat exchange with an outlet of the cooling circuit.

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