WO2024254680A1

WO2024254680A1 - Process, system, and method for cycling carbon in an integrated electric steelmaking plant

Info

Publication number: WO2024254680A1
Application number: PCT/CA2024/050780
Authority: WO
Inventors: Ian Archibald Cameron; Takshi SACHDEVA; Richard Samuel Barr ELLIOTT; Paul Smit Baumann; Nicholas AUBRY; Daysi Josefina PEREZ
Original assignee: Hatch Ltd
Current assignee: Hatch Ltd
Priority date: 2023-06-11
Filing date: 2024-06-11
Publication date: 2024-12-19
Anticipated expiration: 2025-12-11

Abstract

A process, system, and method for cycling carbon in an integrated electric steelmaking plant. The process and method comprise receiving an off-gas comprising nitrogen and carbon-containing gases from the plant, methanation of the off-gas, separating nitrogen from the carbon-containing gases, and recycling the carbon-containing gases within the plant. The system comprises an electric steel-making plant comprising a shafter furnace for producing direct reduced iron, an electric smelting furnace, an off-gas recycling unit comprising a methanation unit, a nitrogen separation unit downstream of the methanation unit, and a conduit for receiving from the nitrogen separation unit and providing to the electric steel-making plant carbon containing off-gases.

Description

PROCESS. SYSTEM. AND METHOD FOR CYCLING CARBON IN AN INTEGRATED ELECTRIC STEELMAKING PLANT

FIELD

[0001] The present invention relates to integrated electric steelmaking processes and more specifically to an integrated steelmaking process comprising an electric smelting furnace.

BACKGROUND

[0002] Many steel producers are currently replacing blast furnaces with direct reduced ironmaking (DRI) process as a greenhouse gas reduction strategy. Two strategies have emerged: melting DRI with an electric arc furnace (EAF) to produce steel directly; and smelting DRI in a fixed electric smelting furnace (ESF) to produce hot metal that is refined into steel in basic oxygen furnaces (BOF). Sustainability drivers for the DRI-ESF-BOF process route include the ability to use blast furnace grade iron ore, slag valorization for cement manufacturing, and to avoid stranding existing BOF steelmaking assets. However, the DRI-ESF-BOF process still produces CO and CO2 emissions as part of its off-gasses. As the steelmaking industry is moving towards lower CO/CO2 emissions for making steel, there is an ongoing need for an integrated steel making process that has reduced CO/CO2 emissions, or can achieve near zero CO/CO2 emissions.

BRIEF DESCRIPTION OF THE FIGURES

[0003] FIG. 1A shows a flowsheet for a direct reduce iron, electric smelting furnace, and basic oxygen furnace in accordance with an embodiment of the present disclosure.

[0004] FIG. 1B shows a flowsheet for a direct reduce iron (DRA), electric smelting furnace (ESF), and basic oxygen furnace (BOF) (collectively, a DRI-ESF-BOF in accordance with an embodiment of the present disclosure.

[0005] FIG. 2 shows a carbon balance for a DRI-ESF-BOF using blast furnace quality iron ore pellets in accordance with an embodiment of the present disclosure.

[0006] FIG. 3 shows a flowsheet of a CO-rich off-gas being recycled from the ESF and BOF for use as a heating fuel in the process gas heater in the DRI plant in accordance with an embodiment of the present disclosure. [0007] FIG. 4 shows an example mass balance calculation for reduced CO2 emissions when ESF and BOF off gas is used to offset natural gas use at the process gas heater.

[0008] FIG. 5 shows a flowsheet for the methanation treatment of ESF and BOF offgases in accordance with an embodiment of the present disclosure.

[0009] FIG. 6 shows a flowsheet a process comprising recycling ESF and/or BOF offgas in a DRI plant comprising a shaft furnace in accordance with an embodiment of the present disclosure.

[0010] FIG. 7 shows a methanation process in accordance with an embodiment of the present disclosure.

[0011] FIG. 8 shows a comparison of CO2 emissions including for embodiments of the present disclosure.

[0012] FIGS. 9 to 20 show flowsheets for various embodiments of the present disclosure.

DETAILED DESCRIPTION

[0013] Integrated Steel Works providers (comprising a coke-based blast furnace and basic oxygen furnace) have recently been considering replacement of the blast furnace with a shaft-based direct reduced iron production process to help reduce greenhouse gas emissions in the making of steel. Blast furnaces are a significant contributor to GHG emissions. Replacement of the blast furnace may help eliminate sintering, coking, and blast furnace operations. An emerging flowsheet is to smelt the direct reduced iron (DRI) in an Electric Smelting Furnace (ESF) producing carbon containing hot metal that can be converted into liquid steel using existing BOF steelmaking facilities and their related refining and casting equipment (FIG. 1A & 1 B).

[0014] In accordance with an invention described herein, hydrogen is produced and/or carbon is captured from the off-gases of the DRI, ESF and/or BOF plants. The offgases comprise CO and/or CO2. The off-gases may be CO-rich. For example, the off-gases of a DRI, ESF, and BOF may comprise predominantly CO rather than CO2. The ratio of CO to CO2 in the off-gases from a ESF may be equal to or greater than 6-to-1 by volume. The ratio of CO to CO2 in the off-gases from a BOF may be equal to or greater than 2-to-1 by volume. The captured carbon-containing off-gas streams with the available hydrogen may be used to produce a CO-rich stream (with potentially some residual amount of CO2) for use in the steelmaking process to provide needed carbon. An embodiment of this invention may be an alternative to carbon capture and storage (CCS).

[0015] FIGS. 1A and 1 B show flowsheets for a direct reduce iron, electric smelting furnace, and basic oxygen furnace in accordance with an embodiment of the present disclosure.

[0016] Most producers have selected the shaft-furnace DRI process for its potential to start on a natural gas-based operation and then transition to greater amounts of green hydrogen as this becomes available. However, the emerging DRI-ESF-BOF process route - where high gangue DRI is smelted into molten iron in a fixed ESF and processed into liquid steel using existing BOF assets - produces high CO I CO2 1 green house gas emissions. An object of the invention as disclosed herein is to utilize off gases and/or hydrogen in the DRI- ESF-BOF process to reduce greenhouse gas emissions. In an embodiment of the invention, the CO-rich and/or CO2-rich off-gases generated from the ESF and BOF, when all three plants are co-located, may be re-used in the steelmaking process. In another embodiment of the invention, the CO-rich and/or CO2-rich off-gases recycling process can be employed in connection with a DRI and ESF process, only; a BOF and ESF as a standalone process, or a combination of DRP to ESF with no BOF downstream such that ESF is directly producing steel

[0017] Embodiments of the invention as disclosed herein provide a recycle and/or reuse of the CO-rich and/or CO2-rich off-gases generated from the ESF and BOF. In an example, the CO-rich off gases may be used as fuel in the DRI Plant process gas heater. This may reduce CO2 emissions, for example, CO2 emissions may be reduced by 53 kg CO2 11 liquid steel compared to each sub-plant operating in isolation. In another example, methanation and recycling of the ESF and BOF off-gases to the DRI Plant may be used to allow for re-use of carbon in the plant in a circular fashion. This may allow for continued operation of the DRI Plant using the well-known natural gas-based practices while using green hydrogen instead: CO and/or CO2 in the waste off-gasses is used to make methane (including in the form of SNG) which is used as a replacement for natural gas within the shaft furnace reactor. According to embodiments as described herein, CO2 emissions may be reduced, for example, by up to about 240 kg CO2/ 1 liquid steel compared to all three plants operating in isolation.

[0018] The collection and methanation of the ESF and BOF off-gas may offer an opportunity to use carbon in a circular manner in the broader steelmaking flowsheet / process to reduce emissions. There is need for additional carbon in the process in any event. This may also be an alternative to using hydrogen directly in the DRI shaft furnace which can help reduce risks by avoiding unknown operational aspects that arise when natural gas is completely replaced with hydrogen. The off-gas may be treated with methanation, reverse water gas shift, and/or pyrolysis. With methanation applied, carbon capture of the remaining CO2 may be simplified and could potentially allow the DRI-ESF-BOF/DRI-ESF steel plant to reach near zero CO/CO2 emission rates.

[0019] Typically, the shaft-based DRI process is either combined with a standard EAF or operates on a stand-alone basis. The fixed ESF is new to the steel industry. The inventors have found that ESFs differ from the EAF regarding off-gas quality and re-use potential. The ESF operates continuously and is sealed to minimize air ingress. A CO-rich off-gas with -25% N2 may be produced by the ESF that has significant energy potential. [0020] The DRI-ESF-BOF steel works requires carbon to make the BOF process viable. Furthermore, even as hydrogen usage increases, natural gas usage at the DRI plant will still be needed to efficiently carburize the ESF hot metal.

[0021] The inventors examined the impact on CO2 emissions in a DRI-ESF-BOF steelworks that results from processing the DRI-ESF-BOF off-gases to re-use carbon and the related chemical energy in accordance with an embodiment of the invention. Modeling was completed based on ™ direct reduction process technology. Strategies examined include fossil fuel replacement at the DRI Plant’s process gas heater, methanation of the off-gases to produce synthetic natural gas (SNG) and producing CO-H2 syngas for iron ore reduction from captured CO2.

Using Off-gases as a Fuel for the DRI Plant Process Gas Heater

[0022] FIG. 2 shows the carbon balance for the base case using blast furnace grade iron ore pellets and natural gas-based direct reduction in accordance with an embodiment of the present disclosure. [0023] FIG. 3 shows a flowsheet of a CO-rich off-gas being recycled from the ESF and BOF for use as a heating fuel in the process gas heater in the DRI plant in accordance with an embodiment of the present disclosure. This process may reduce overall natural gas consumption.

[0024] FIG 4. shows an example mass balance calculation where plant-wide direct CO2 emissions were reduced by 8%, or 53 kg CO2 1 t-LS, when the CO-rich process offgases replaced natural gas used by the process gas heater in accordance with an embodiment of the present disclosure.

[0025] However, not all ESF and BOF gas is consumed to meet the PGH heating demands. For example, about 16% of these off-gases may still be burnt or flared somewhere in the steel works. All CO2 emissions from the integrated plant are emitted at the Direct reduction plant (DRP) which facilitates capture and storage. In an example, capture and storage of this CO2 could further reduce DRI plant CO2 emissions.

Further Reducing GHG Emissions in the DRI-ESF-BOF Integrated Steel Works

[0026] In embodiments as described herein, methanation of ESF and BOF off-gases is employed. Additionally, or alternatively, embodiments as described herein further provide conversion of process generated CO2 into a CO-H2 syngas. Additionally or alternatively, pyrolysis may be employed to treat the ESF and/or BOF off-gasses.

Methanation of the ESF-BOF Off-gases

[0027] In an embodiment, methanation of the CO-rich off-gases from the ESF and BOF plants may be employed. Methanation is the conversion of carbon monoxide (CO) and/or carbon dioxide (CO2) to methane through hydrogenation. The off gases of the ESF and BOF plants contain a mixture of CO I CO2 and N2. N2 cannot be permitted to remain with the CO/CO2 for it to be re-cycled in accordance with one or more embodiments of the invention. This is because the elements of an electrical steel-making plant that are capable of utilizing the CO-rich off-gas (i.e. , the DRP) are sensitive to N2 and may function less effectively if the amount of N2 in the off-gas is too great. Among other things, N2 increases the volume of gas circulating which increases equipment size and corresponding capital costs. Elevated nitrogen circulating in the DRP will also detrimentally affect the process kinetics. Preferably N2 levels are below 2% of the total gas in a gas circuit. Accordingly, the N2 and the CO/CO2 need to be separated from one-another. [0028] Separation of CChfrom N2 is relatively common. CO2 and N2 have different boiling points and molecular weights from one-another. Accordingly, cryogenic distillation and pressure swing adsorption may be used. Furthermore, CO2 may be scrubbed from N₂ by using a solvent to bind the CO2 to remove from the off-gasses. Although separation of CO from other gases is industrially common, the separation of N₂from CO, however, is challenging. CO and N₂ have the same molecular weight and their boiling point is within about 5 degrees Celsius of one another preventing the use of separation methods such as cryogenic distillation. Since the carbon containing off-gasses from a DRI, ESF, or BOF can comprise predominantly CO rather than CO2, it is important to be able to remove N2 from CO in the off-gasses.

[0029] In accordance with an embodiment of this invention, N2 is removed from the off-gases after methanation of the carbon-containing gases comprising CO. In an embodiment, methanation may allow for the effective removal of N2 from carbon-containing gases, making the reuse of carbon-containing gases for non-heating applications possible and practical. In an embodiment, some of the carbon-containing gases may also be incidentally removed while removing the N2 from the majority of the CO. The ESF and/or BOF off gases containing CO (and optionally CO2) may be combined, cleaned, cooled, and/or compressed. The off gases are sent to the methanation synthesis to produce a methanated off-gas. The methanated off-gas comprises CH4. The CH4 may be in the form of synthetic natural gas (SNG). SNG is a fuel with higher heating value. The N2 is then separated from the carbon containing gases of the methanated off-gas. N₂ may be removed from the methanated off-gas by, for example, pressure swing adsorption or cryogenic distillation. The methanated off-gas with N2 removed may then be used in the DRI process. [0030] H₂ generated from electrolysis may be used in the methanation synthesis. Syngas may also be produced from CO₂ and H₂ via Reverse Water Gas Shift (RWGS).

[0031] Methanation of the off-gasses may be used to produce, for example, CH4-rich gas, CH4-lean gas, and/or superheated steam. In an example, CH4-rich gas may be used as a chemical input into the shaft furnace direct reduction process. CH4-lean gas, which may result from the imperfect separation of CH4 and N2, may be used as fuel in the integrated electric steel-making plant for heating. Superheated steam may be a by-product of the exothermic methanation reaction and may be used or exported elsewhere in the steel plant. [0032] In an example, methanation may be used to produce SNG (for example, approximately 94-98 vol% CH4) from ESF and BOF off-gases that may be recycled back into the shaft furnace. This process may reduce external natural gas usage by instead using SNG. The inclusion of methanation may improve the subsequent separation of N2 from CO which is otherwise technically challenging. By first methanating the off-gases containing CO, subsequent N2 removal becomes more viable. In another example, methanation of the offgases may be used in order to use hydrogen while still maintaining the required amount of carbon in DRI that is needed for the ESF-BOF operations. Methanation may be used as a lower risk approach to using hydrogen compared to direct H2 injection into the shaft furnace for the DRI-ESF-BOF flowsheet.

[0033] FIG. 5 shows a simplified flowsheet for the methanation treatment of ESF and BOF off-gases in accordance with an embodiment of the present disclosure.

[0034] FIG. 6 shows a flowsheet a process comprising recycling ESF and/or BOF offgas in a DRI plant comprising a shaft furnace in accordance with an embodiment of the present disclosure. The ESF and BOF off-gases may be blended and processed together or treated separately. The process may comprise directing ESF and/or BOF off-gas to the combustion-based heating system of a DRI plant. For example, the off-gas from ESF and/or BOF may be used as a heating fuel for the process gas heater or reformer. The off-gases may be additionally or alternatively directed to a reverse water gas shift reactor to convert CO2 to CO rich gas. CO rich gas may be directed to a methanation unit or recycled back to the shaft furnace for DRI production. The CO rich gas from the reverse water gas shift reactor and/or the off-gases from the ESF and BOF may be directed to a methanation unit. The methanation unit may convert CO and CO2 to methane through hydrogenation. An electrolyzer fed with water may be used to produce hydrogen (H2) by electrolysis for use in the methanation unit. The H2 from electrolysis may also be used for combination with the CO rich gas and off-gases in the reverse water gas shift reactor. The mixture may be compressed before being directed to the methanation unit. The methanation unit may produce CH4 lean gas, CH4 rich gas, and superheated steam. The superheated steam may be used to generate electrical power and offset compression energy demands. The CH4 lean gas may be directed to the PGH as heating fuel. A portion of the CH4 rich gas may be directed to the shaft furnace for use in DRI production. A portion of the CH4 rich gas may be directed to a pyrolysis unit for production of hygrogen and solid carbon (syncarbon). Syngas (CO and H2) may be produced from CO2 and H2 via the reverse water gas shift reactor. The syn carbon may be recycled to the ESF for use in hot metal carburization.

[0035] An integrated steel plant as described herein may include a flowsheet comprising a shaft furnace, ESF, and BOF. The ESF may be positioned downstream of the shaft furnace. The BOF may be positioned further downstream of the ESF. Each of the ESF and BOF comprises an off-gas output that may be connected to a methanation unit. The methanation unit may comprise an output for superheated steam which may be recycled to the plant. The methanation unit may also comprises CH4 rich gas and CH4 lean gas output. In an example, the CH4 rich gas output may be connected to one or more of a downstream pyrolysis unit or the upstream shaft furnace. In an example the CH4 lean gas output may be connected to a process gas heater or reformer for the DRI plant. The methanation unit may be connected to an electrolyzer or pyrolysis unit for providing H2 to the methanation unit. A reverse water gas shift reactor may also be present in the integrated steel plant flowsheet. The reverse water gas shift reactor converts CO2 to CO by reaction with H2. H2O by-product from the reverse water gas shift reactor may be easily separated from the gases to produce a high quality syngas, for example a CO/H2 mix. Syngas may be used directly in the direct reduction shaft furnace as a chemical reagent, which may assist in minimizing natural gas consumption. The reverse water gas shift reactor may be upstream of the methanation unit. The off-gas outputs of the ESF and the BOF may be connected to the reverse water gas shift reactor. The electrolysis unit may be configured to provide H2 to the reverse water gas shift reactor. The reverse water gas shift reactor may output CO rich gas to the methanation unit and/or recycle CO rich gas back to the upstream shaft furnace. An amine system may be provided upstream of the methanation step. The amine system may be used to remove CO2 from the ESF and BOF off-gases. The removal of CO2 upstream of the methanation unit may help to reduce H2 consumption per unit of CH4 produced by the methanation system. In an example, the CO2 from the off-gases can be separately treated in a reverse water gas shift reactor to produce CO for direct use in the shaft furnace. Removed CO2 can optionally (additionally or alternatively) be sent for sequestration (CCLI/S). In an example, the resulting CO rich gas may be sent to the methanation unit. In another example, the whole off-gas stream may be sent to the methanation unit, eliminating the need for the amine system and the reverse water gas shift reactor, if desired. The pyrolysis unit downstream of the methanation unit may be configured to recycle H2 back to the reverse water gas shift reactor. The pyrolysis unit may also comprise a recycle stream connected to the ESF for return syngas, for example syn carbon, back to the ESF for use in hot metal carburization. The solid carbon (syn carbon) may be used, for example, in the ESF to replace coals which may allow looping of the carbon from the off-gases back into the process. H₂ from pyrolysis can be sent to the methanation step and/or reverse water gas shift reactor to displace H₂ produced by electrolysis, which may help to minimize system electrical demand. If there is an excess of carbon, the excess carbon may be exported from the site as a valuable by-product or used as a solid sequestration option.

[0036] FIG. 7 shows a methanation process in accordance with an embodiment of the present disclosure. The methanation process technology produces SNG compatible with pipeline specifications, addresses heat recovery by producing high-pressure superheated steam, and uses a catalyst able to operate in the temperature range from 250-700°C. In another example, a reverse water gas shift (RWGS) unit may be used prior to the methanation step. The RWGS unit may promote the CO2 conversion into more CO prior to the methanation step.

[0037] After ESF off-gas and BOF off-gas methanation, nitrogen may be removed using gas separation membranes providing SNG with -96% CH4. 4.2 GJ 11 DRI of SNG can be recycled to the DRI plant, reducing direct CO2 emission by 240 kg CO2 /t-LS; a 36% reduction compared to the conventional process (Table 1). Alternatively, a variation of other techniques well established in the oil and gas industry may be used to remove nitrogen from the off-gas methanation.

[0038]

[0039] Prior to methanation, ESF off-gas and BOF off-gas may be mixed with hydrogen and then compressed to 25 barg pressure. Six stages of compression may be used. Six stages of compression may require up to 36 MW of power. After mixing with hydrogen, and optionally compressing, the gas mixture may be fed to the reactors, for example, the three reactors shown in FIG. 6. The Topsoe methanation process generates superheated steam (100 barg 1540°C) that can generate electrical power to offset compression energy demands. Typical steam production is 3.0-3.5 kg steam I Nm³ SNG and only a minor amount of the energy is removed by water cooling.

[0040] Running the superheated steam through a turbogenerator can generate 34 MW of power that can significantly off set the net compression power demand, reducing this from 36 to 2 MW. The use of steam powered compressors may further reduce the need for purchased power for off-gas compression.

Methanation versus Direct H2 use in the DRI-ESF-BOF Steel Works

[0041] For the DRI-ESF-BOF operation, carbon in the DRI produced is needed to carburize the hot metal and melt scrap in the BOF. In an example where methanation is used, 410 Nm3 of H2 / 1 DRI was used to methanate all ESF and BOF off gas produced. The carbon content of the resulting DRI was 4.0% C and the ESF hot metal was 3.8% C.

[0042] When adding the same 410 Nm3 of H2 / 1 DRI (4.4 GJ 11 DRI) directly into the DRI Shaft Furnace, with the balance of the energy being supplied by natural gas, the carbon in the DRI was reduced to 2.0% C and the resulting hot metal contained 2.9% C. In this mode of operation, ESF off-gas, BOF off-gas and natural gas were used to fire the process gas heater.

[0043] With reduced carbon in hot metal when adding H2 directly to the DRI Plant, the hot metal demand increases to produce liquid steel. The resulting CO2 emissions for each case can be compared in Table 2 and FIG. 8.

[0044] While direct use of H2 in the DRI Plant does result in the lowest direct CO2 emissions, methanating the ESF off-gas and BOF off-gas can provide important advantages when considering the DRI-ESF-BOF flowsheet. For example, (i) the operation of the DRI Plant remains based on well-known CH4 as an energy source. This eliminates concerns regarding the shaft furnace energy balance with 100% H2, decreased DRI carbon content and related stability with reduced Fe3C and potential increase in fines generation; (ii) with methanation, all carbon bearing off-gases in the DRI-ESF-BOF steel works report to two discharge points at the DRI Plant, (iii) the CO2 in these streams can be extracted using amine, PSA, and/or cryogenic technologies, facilitating CCLI/S options, (iv) facilities are eliminated to capture carbon from ESF and BOF off-gas needed to reach near zero emissions, (v) hot metal carburization is simplified by maintaining a high carbon content in the DRI produced, (vi) the BOF operates in a familiar envelope compared to processing lower carbon containing hot metal, (vii) BOF scrap consumption is higher when methanation is used as the hot metal contains more carbon, enhancing circular steelmaking strategies, and (vii) H2 usage per tonne of steel decreases when methanation is deployed. [0045] Integrating the DRI-ESF-BOF plants and methanating the ESF-BOF off-gases may offer operational advantages, reducing risk while reducing CO2 emission rates to 431 kg C02/t LS. With the application of CCLI/S to the DRI plant off-gas streams, a near zero emission steel operation is possible.

Utilizing CO2 as a Reducing Gas Feedstock

[0046] Considering the availability of lower cost renewable power and the continued need for renewable carbon for industrial use, the technology trajectory of Power-to-X (PtX) may gain momentum. PtX involves the generation of hydrogen via electrolysis and the production of carbon monoxide (CO) via the reverse water gas shift reaction from CO2, with the resultant combined syngas stream (CO + H2), serving as the reagents for processes that require carbon such as steelmaking, chemicals and/or liquid fuels production.

[0047] A conventional DRI process may require the addition of a carbon source in the form of natural gas to the shaft burners and furnace as well as anthracite in the ESF smelter. Some advantages that may be realized over the conventional process according to embodiments of the invention as disclosed herein may include: (i) natural gas and anthracite consumption reduction by converting carbon contained in the off gases to methane by methanation process and recycle back to the DRI process; (ii) converting CO2 to CO required for DRI using an RWGS unit and benefit from the exothermic reaction on iron reduction FeO + CO Fe + CO2, and may further reduce the overall energy consumption; (iii) producing syncarbon (which is synthetic solid carbon produced from pyrolysis) and hydrogen gas which can be in the steel plant. Possible uses of the syncarbon include carburization and manufacturing of electrodes used in the ESF smelter. Any excess carbon may be inherently sequestered.

[0048] The invention as disclosed herein may allow for a novel way to recycle the carbon in the off gases from ESF and BOF back into the steel plant. This integrated flowsheet of DRI-ESF-BOF with methanation, reverse water gas shift and pyrolysis as described herein may help lower the total natural gas consumption and the plant-wide CO2 emissions. Methanation in the process may be used to capture carbon in the off-gas streams from ESF and BOF, which can then be recycled to the DRI plant. RWGS processes may also use the carbon rich off gas streams and produce a CO rich stream which can serve as the reductant in the DRI plant. Pyrolysis, if included in the process, may utilize the natural gas to produce syn-carbon which can then be recycled to the ESF smelter. The hydrogen produced from pyrolysis can also be used in the reverse water gas shift, methanation or the DRI shaft directly as a reductant (with makeup natural gas). Additional example embodiments of an invention as disclosed herein shown as block flow diagrams are provided below. Some examples of flowsheet options according to an invention as disclosed herein include: (i) ESF and BOF off-gases collected and exported as fuels used elsewhere on site, (ii) Integrated heating fuel: ESF and BOF off-gases collected and used as fuel in the DRP heating system, displacing natural gas, (iii) Methanation of off-gases only; (iv) Methanation of off-gases plus pyrolysis as an option to produce solid carbon for the ESF, (v) Methanation of off-gases plus amine CCS, (vi) Methanation of off-gases plus amine CCS plus pyrolysis, (vii) Methanation of off-gases plus amine & RWGS, and (viii) Methanation of off-gases plus amine & RWGS PLUS pyrolysis.

[0049] FIGS. 9 to 20 show flowsheets for various embodiments of the present disclosure.

[0050] FIG. 9 shows a flowsheet for a DRP-ESF-BOF process where the off-gases of the ESF and BOF are collected and exported as fuel gases.

[0051] FIG. 10 shows a flowsheet for an embodiment of the present disclosure in which off-gases from the ESF and BOF are collected and provided to the DRP for use as fuel in the DRP gas heating system.

[0052] FIG. 11 shows a flowsheet for an embodiment of the present disclosure in which off-gases from the ESF and BOF are collected and provided directly to methanation. The CH4-lean gas is then sent to the DRP gas heating system while the CH4-rich gas is blended into the process gas feed to the shaft furnace reactor.

[0053] FIG. 12 shows a flowsheet for an embodiment of the present disclosure in which off-gases from the ESF and BOF are collected and sent directly to methanation. The CH4-lean gas from methanation is then sent to the DRP gas heating system, while part of the CH4-rich gas is blended into the process gas feed to the shaft furnace reactor, and another part of the CH4-rich gas is sent to pyrolysis to produce solid carbon for use in the ESF.

[0054] FIG. 13 shows a flowsheet for an embodiment of the present disclosure in which off-gases from the ESF and BOF are collected and treated using an amine system to produce a CO2-lean gas that is sent to methanation. The CH4-lean gas is then sent to the DRP gas heating system while the CH4-rich gas is blended into the process gas feed to the shaft furnace reactor.

[0055] FIG. 14 shows a flowsheet for an embodiment of the present disclosure in which off-gases from the ESF and BOF are collected and treated using an amine system to produce a CO2-lean gas that is sent to methanation. The CH4-lean gas is then sent to the DRP gas heating system, while part of the CH4-rich gas is blended into the process gas feed to the shaft furnace reactor, and another part of the CH4-rich gas is sent to pyrolysis to produce solid carbon for use in the ESF.

[0056] FIG. 15 shows a flowsheet for an embodiment of the present disclosure in which off-gases from the ESF and BOF are collected and treated using an amine system to produce a 002-lean gas that is sent to methanation. The CO2-rich gas is treated by reverse water-gas-shift to produce a CO-rich gas steam, that is also sent to methanation. The Chilean gas is then sent to the DRP gas heating system while the CH4-rich gas is blended into the process gas feed to the shaft furnace reactor.

[0057] FIG. 16 shows a flowsheet for an embodiment of the present disclosure in which off-gases from the ESF and BOF are collected and treated using an amine system to produce a CO2-lean gas that is sent to methanation. The CO2-rich gas is treated by reverse water-gas-shift to produce a CO-rich gas steam; a part of this CO-rich gas is sent to methanation and another part is sent to the shaft furnace reactor. The CH4-lean gas is then sent to the DRP gas heating system, while part of the CH4-rich gas is blended into the process gas feed to the shaft furnace reactor, and another part of the CH4-rich gas is sent to pyrolysis to produce solid carbon for use in the ESF.

[0058] FIG. 17 shows a flowsheet for an embodiment of the present disclosure in which off-gases from the ESF and BOF are collected and treated using an amine system to produce a CO2-lean gas that is sent to methanation. The CO2-rich gas is treated by reverse water-gas-shift to produce a CO-rich gas steam, that is sent to the shaft furnace reactor. The CH4-lean gas is then sent to the DRP gas heating system while the CH4-rich gas is blended into the process gas feed to the shaft furnace reactor.

[0059] FIG 18 shows a flowsheet for an embodiment of the present disclosure that is substantially similar to the flowsheet of FIG. 17, but without an amine system for receiving the ESF and BOF Off-gases.

[0060] FIG. 19 shows a flowsheet for an embodiment of the present disclosure that is substantially similar to the flowsheet of FIG 17, with the options for direct methanation of ESF and BOF gases similar to the embodiment shown in FIG 11.

[0061] FIG. 20 shows a flowsheet for an embodiment of the present disclosure comprising two CO-rich gas streams from a reverse water gas shift, one of the two CO-rich gas streams is provided to the amine system.

Claims

CLAIMS: We claim:

1. A process comprising, a) receiving an off-gas of an integrated electrical steel-making plant comprising a

Direct Reduced Iron plant (DRP) plant, the off-gas comprising nitrogen and carbon containing gases, wherein at least a portion of the off-gas is received from an Electric Steelmaking Furnace (ESF) plant of the integrated electrical steel-making plant, b) methanation of the off-gas to produce a methanated off-gas; c) separating nitrogen from the carbon containing gases of the methanated offgas downstream of the methanation of the off-gas step; and, d) recycling the carbon containing methanated off-gas within the integrated electrical steel-making plant.

2. The process according to claim 1, wherein the methanation produces one or more of a CH4 rich gas and a CH4 lean gas from the carbon containing off-gas.

3. The process according to claim 1 or 2, further comprising receiving at least a portion of the off-gas from a Basic Oxygen Furnace (BOF) of the integrated electrical steel-making plant.

4. The process according to any one of claims 1 to 3, further comprising receiving at least a portion of the off-gas from the DRP.

5. The process according to any one of claims 1 to 4, wherein the recycling comprises providing the carbon-containing methanated off-gas to the DRP.

6. The process according to claim 2 wherein the recycling comprises directing to and using within a combustion heating system of the DRP at least a portion of the CH4 lean gas.

7. The process according to any one of claims 1 to 6, further comprising, prior to the methanation step, directing at least a portion of the off-gas to a reverse water gas shift reactor to produce a CO-rich gas upstream of the methanation step.

8. The process according to claim 7, further comprising returning to and using within a shaft furnace of the DRP at least a portion of the CO-rich gas.

9. The process according to claim 7 or 8, comprising methanation of at least a portion of the CO-rich gas.

10. The process according to any one of claims 7 to 9 wherein one or more of the off-gas and the CO-rich gas is mixed with hydrogen, and optionally compressed, prior to methanation.

11. The process according to any one of claims 2 to 10 comprising directing to and using within the shaft furnace of the DRP at least a portion of CH4 rich gas resulting from the methanation.

12. The process according to claim 11, further comprising directing at least a portion of the CH4 rich gas to a methane pyrolysis step.

13. The process according to claim 12, wherein H₂ produced from the pyrolysis step is directed back to a reverse water gas shift unit upstream of the methanation.

14. The process according to claim 12 or 13 further comprising production of syn carbon in the pyrolysis step and returning the syn carbon to the ESF for use in hot metal carburization.

15. The process according to any one of claims 1 to 14, wherein a superheated steam is produced in the methanation step.

16. The process according to claim 15, wherein the superheated steam is used to generate electrical power and offset compression energy demands.

17. The process of any one of claims 1 to 16, wherein receiving the off-gas of the integrated electrical steel-making plant comprises receiving more CO than CO2.

18. The process of claim 17, wherein the ratio of CO to CO2 in the off-gas received from the ESF is equal to or in excess of a ratio of about six-to-one by volume.

19. The process of claim 1, wherein methanation of the off-gas comprises methanation of a CO-rich off-gas.

20. The process of claim 5, further comprising increasing the carbon content of DRI produced by the DRP, the carbon for helping carburize the hot metal produced by the ESF.

21. The process of claim 11, further comprising using CH4 rich gas as reducing agent in the shaft furnace of the DRP.

22. The process of any one of claims 1 to 21 , further comprising removing CO2 from the off-gas prior to methanation.

23. The process of claim 22, wherein the CO2 is removed from the off-gas with an amine system.

24. An integrated electric steel-making plant comprising: a shaft furnace for production of direct reduced iron (DRI); an electric smelting furnace (ESF) downstream of the shaft furnace and comprising an off-gas output; an off-gas recycling unit comprising a methanation unit in communication with the off-gas output of the ESF for recycling carbon-containing off-gas of the ESF within the integrated electric steel-making plant and producing a methanated offgas; and, a nitrogen separation unit downstream of the methanation unit for separating nitrogen from carbon containing gases of the methanated off-gas; and a conduit for providing the carbon containing methanated off-gas to the electric steel-making plant.

25. The integrated electric steel-making plant of claim 24, further comprising a basic oxygen furnace (BOF) downstream of the ESF and comprising a BOF off-gas output, the off-gas recycling unit connected to the BOF off-gas output for receiving from the BOF and recycling carbon-containing off-gas of the BOF within the integrated electric steel-making furnace plant.

26. The integrated electric steel-making plant of claim 24 or 25, wherein the off-gas recycling unit comprises a reverse water gas shift reactor to produce CO rich gas from the off-gas received by the off-gas recycling unit.

27. The integrated electric steel-making plant of any one of claims 24 to 26, wherein the off-gas recycling unit comprises a methane pyrolysis unit downstream of the methanation unit.

28. The integrated electric steel-making plant of claim 27, wherein the methane pyrolysis unit comprises a recycle stream for returning syn carbon produced by the pyrolysis unit back to the ESF.

29. The integrated electric steel-making plant of claim 27 or 28, wherein the methane pyrolysis unit returns produced hydrogen to the methanation unit or the reverse water gas shift reactor.