Improved utilization of off-gases in an iron-ore reduction process and apparatus therefor

Abstract

This invention relates to a method for reducing the CO2 emissions produced in the reduction process of iron ore and to improved utilization of off-gases in such an iron-ore reduction process and to an apparatus therefor.

Description

[0001] IMPROVED UTILIZATION OF OFF-GASES IN AN IRON-ORE REDUCTION PROCESS AND APPARATUS THEREFOR

[0002] Field of the invention

[0003] This invention relates to a method for reducing the CO2 emissions produced in the reduction process of iron ore and to improved utilization of off-gases in such an iron- ore reduction process and to an apparatus therefor.

[0004] Background of the invention

[0005] In the energy transition large efforts are being made to move away from traditional carbon based steelmaking practices such as the conventional blast furnace route as these are significant contributors to carbon dioxide emissions in the atmosphere.

[0006] The reduction of CO2 in the steel industry via Carbon Capture and Storage (CCS) is energy intensive due to the regeneration of the alkanolamines used as a sorbent and the compression energy to store the CO2. All this reduces the efficiency of the steel making process. Other technologies, such as dry reforming, require high energy inputs due to the high endothermic nature of the reaction (CH4 + CO2 <— > 2CO + 2H2 AH = 247 kJ / kmol CH4) and the use of natural gas, thereby reducing the CO2 conversions. On top of that, the gas (syngas or synthesis gas) produced cannot be easily stored. Fermentation of CO and CO2 has also been used (Lanzatech process) in the steel industry but in practice, the conversion is limited to CO rich feed streams since the CO2 conversion is minor. There is also the challenge of scaling-up the reactors. Syngas, or synthesis gas, is a mixture of hydrogen and carbon monoxide, in various ratios. The gas may contain also some carbon dioxide and methane. Syngas is combustible and can be used as a fuel or as a reductor to directly reduce iron ore.

[0007] Several alternative carbon based iron-making processes have been proposed that generate less carbon dioxide per ton of iron. The HIsarna® process, as developed by Tata Steel, is a process which makes efficient use of carbon and is able to achieve a 50% reduction in carbon use compared to blast furnaces (BF). Nowadays attention is also directed towards production of iron by using (green) H2 as a reductor rather than carbon to produce direct reduced iron.

[0008] Direct reduced iron (DRI) is produced from the direct reduction of iron ore conglomerates (mainly hematite, Fe2Os) in the form of lumps, pellets, or fines into solid iron by a reducing gas. Due to its structure with a very high specific surface area, direct- reduced iron is also referred to as sponge iron. Direct reduction refers to a solid-state process which reduce iron oxides to metallic iron at temperatures below the melting point of iron. There are several processes for producing DRI known to the person skilled in the art. Known examples of direct-reduction processes include the Midrex process, Tenova's HYL process, Tenova's HYL I and the HYL II and the HYL III process, Posco's HyREX process, and the Hybrit process. A known process relates to a direct reduction plant (DRP) or DRI reactor comprising a direct reduction shaft furnace having a reduction zone and a lower discharge zone from which direct reduced iron in solid form is discharged at a regulated rate by means of a suitable discharge mechanism.

[0009] Iron oxide conglomerates in the form of agglomerates, pellets, lumps or mixtures thereof are fed to the reduction furnace and descend by gravity through the reduction zone were DRI is formed by reaction of said iron oxides with a reducing gas stream at high temperature that is mainly composed of H2 and contains also CO, carbon dioxide, methane, and nitrogen in those embodiments wherein a hydrocarbon such as natural gas or a syngas derived from coal is used as the source of the reducing gas.

[0010] The reduction of iron oxides is carried out through the following net reactions:

[0011] The DRI in solid form is further processed directly on exit from the discharge zone, and optionally also after being compacted into briquettes, in a melt shop typically comprising one or more electric-arc furnaces (EAF) or submerged-arc furnaces (SAF), in the art also known as a reducing electrical furnace (REF).

[0012] In the majority of these known direct- reduction processes, natural gas is reformed in a catalyst bed with steam and / or gaseous reduction products evacuated from the iron-reduction reactor to produce a reducing gas which is supplied to the iron production reactor where it reacts with the iron oxides in the iron ore to generate reduced metallic iron. Partial oxidation processes which gasify liquid hydrocarbons, heavy residuals or coal have also been proposed for the production of the reducing gas. In both cases, a reducing gas containing CO and H2is obtained. Direct-reduction processes have thus far been of particular interest in regions which have access to suitable iron ores and inexpensive natural gas, non-coking coals and / or renewable energy sources, such as hydroelectric power. It is expected that non-coal based direct-reduction processes will gain in importance as the drive to reduce CO2emissions in the global iron- and steelindustry gains further momentum.

[0013] However, since the availability of green H2(hydrogen from renewable sources) is limited, and is expected to remain limited in the near future, there is a need to further reduce the CO2emissions of iron production.

[0014] Objectives of the invention

[0015] It is an object of the invention to provide a method to reduce the CO2emissions of the reduction of iron ore to iron.

[0016] It is also an object of the invention to provide a method to reduce the CO2emissions of the direct reduction of iron ore process. It is also an object of the invention to provide a method to reduce the CO2 emissions of the HIsarna® iron making process.

[0017] It is also an object of the invention to provide a method to make the direct- reduction iron making processes more circular.

[0018] It is also an object of the invention to provide a method to store excess H2 safely.

[0019] Description of the invention

[0020] One or more of the objects is reached by a method for reducing CO2 emissions from an iron ore reduction process in an iron production reactor 1 comprising the following steps: a) producing iron from iron ore in an iron production reactor 1 direct thereby producing reduced iron ore and a top-gas 2 comprising one, more or all of CO2, CO, H2, H2O, NOx, SOx, CH4, and dust particles; b) removing, if present in the top-gas 2, dust particles, NOx and SOx from the top-gas 2 in a gas cleaning unit 13; c) dividing the top-gas into a first gas stream 3 and a second gas stream 4; d) wherein the first gas stream 3 comprises CO2, CO, H2 and H2O and converting it into syngas 15 in a syngas production unit 5 by increasing the CO and / or H2 content and by reducing the CO2 content and returning the syngas into the iron production reactor; e) compressing the second gas stream 4 comprising CO2, CO, H2 and H2O in a compression unit 6, and subsequently removing H2O from the compressed second gas stream, after which H2 will be optionally added to the dehydrated second gas stream 4a; f) sending the dehydrated second gas stream 4a for processing to a dimethyl ether production unit 7 to produce gaseous dimethyl ether 8 and a returning gas stream 10 and separating the dimethyl ether 8 from the returning gas stream 10; g) optionally refining the separated dimethyl ether 8 to a higher purity in a refining unit 9, collecting the dimethyl ether and optionally returning the remaining gas stream 14 that is stripped of dimethyl ether to the iron production reactor 1 to reduce iron ore; h) optionally returning the returning gas stream 10 and the remaining gas stream 14 into the iron production reactor to reduce iron ore; i) optionally heating the returning gas stream 10 and / or the remaining gas stream 14 prior to re-introducing the gas stream(s) 10, 14 into the iron production reactor 1.

[0021] Preferably these steps are performed continuously. Preferably these steps are performed consecutively. The top gases 2 (off-gas) arising from the iron production reactor 1 contains CO2 that are used to produce dimethyl ether by making them react with H2 produced that is preferably sourced from renewable sources. This way the CCh-emissions of the iron production process is reduced and made more circular.

[0022] These steps are motivated by the following. The top-gas is cleaned from particles and sulphur compounds. This is important as these particles and compounds potentially may disturb the subsequent steps. Preferably there is as little as possible nitrogen in the top gas. The inert nature of nitrogen means that its presence is undesired from a heat management perspective. The amount of nitrogen in the top gas can be reduced by using industrially pure oxygen instead of air or oxygen enriched air in the process.

[0023] The cleaned gas is then split into 2 streams, a first gas stream 3 that goes to a syngas production unit 5 to enrich the gas to have higher CO and H2 concentration that can subsequently be used in the iron production reactor 1. The second gas stream 4 is sent to a compression unit 6 where it will be compressed to a pressure at a value between 10 to 50 bar. Water is removed from the compressed top gas after subsequent compression steps in condensation units. The removal of the water is preferred because too much water in the compressed top gas will quickly saturate any sorbent in the subsequent dimethyl ether (DME) production unit. This removal of water is achieved preferably by condensation of H2O in a condenser after each compression step by cooling the compressed top gas, preferably to a temperature between 30 and 80°C. The dehydrated compressed second gas stream will be further processed in a DME production unit 7 adapted to produce gaseous dimethyl ether 8 and a by-product gas mixture comprising one or more of CO, H2, MeOH, CO2 which will be referred to as returning gas stream 10.

[0024] The DME 8 produced this way will be separated from the by-product gas mixture coming out of the dimethyl ether production unit 7, so that DME 8 and a returning gas stream 10 comprising H2 and CO may be obtained. The returning gas stream 10 can be used as fuel or be heated and reintroduced into the iron production reactor 1 together with the syngas 15 produced from the first gas stream 3. The DME 8 that is produced by the dimethyl ether production unit 7 is not 100% pure DME and it can be further refined in a refining unit 9 to increase the purity of the DME. Preferably this is done by a distillation process. Within the context of this invention a higher purity is intended to mean a higher purity level of DME. Purity levels between 75 and 99.9 mol.% can be reached. The DME purification can also be achieved by using membranes, absorption processes or cryogenic distillation. After purification the remaining gas stream 14, which is now stripped of DME, comprises one or more of methanol (MeOH), CO and H2 which can be directed towards the heater 11 and introduced into the iron production reactor 1. This gas stream can also directly be introduced into the iron production reactor 1 without heating.

[0025] The division of the gas stream in step c) of the process according to the invention offers the possibility to produce more or less DME in the process and adjust the amount of that is sent to the syngas production unit 5. In case the iron ore production reactor 1 is idling or running at a low production rate, then more or all gas can be used for DME production, making the most efficient use of H2 in such a situation and storing it as DME safely for future use.

[0026] By using a dimethyl ether production unit 7 there is no need to concentrate CO2 in the top-gas 2. After the aforementioned cleaning in the gas cleaning unit 13 the topgas 2 can be used as is.

[0027] In a preferred embodiment the dimethyl ether production unit 7 is a Sorption- Enhanced (or Separation-Enhanced) DME Synthesis reactor (SEDMES). An example of such a SEDMES reactor is disclosed in EP3402746-A1 which is hereby incorporated herein by reference.

[0028] The desulphurization of the top-gas 2 is important for the SEDMES unit. Sulphur compounds poison the catalyst in such a unit. The concentration of sulphur compounds in the gas stream must be low and should preferably be below 1 ppm. The SEDMES unit requires higher pressures that the ones found in the steel industry. For this reason the pressure must be raised to a value of between 10 to 50 bar. During the compression steps, water can be removed from the system to avoid saturating the sorbent of the SEDMES unit with water. Preferably the water content should be lower than 5 mol %. The SEDMES unit operates as a semi-continuous system where several columns are operated in different steps (reaction occurring, regeneration of the sorbent and pressurization of the column). Depending on the conversion of CO2 and the purity of DME required (this depends on the final use), the downstream processing can be different. For the downstream processing, an option is to have a compression unit plus a condensation unit where DME and a rich H2 stream with CO are obtained. Another type of technology can also be used such as membranes, absorption or cryogenic distillation. The DME can be further refined by distillation to increase the purity to the desired level. Purity levels between 75 and 99.9 mol.% can be reached. Alternatively the DME can be directly used for heating purposes (purity preferably at least 75 mol.%), for instance in the fire heater 11.

[0029] The returning gas stream 10 after the SEDMES process consists mainly of H2 (from 50 - 90 mol.%) and CO (from 10 - 50 mol.%). All gas percentages are in mol.%, unless otherwise indicated. This gas stream 10 can be used as reducing gas in the iron production reactor 1. For this purpose it may have to be heated, e.g. to temperature of about 1100°C. The heating can be indirectly done in a fired heater 11. Alternatively, by injecting substoichiometric amounts of oxygen plus natural gas into a partial oxidation reactor along with the returning gas stream 10 a reducing gas is obtained at temperatures between 900 and 1300°C. The returning gas stream 10 may have to be enriched with H2 and / or CO before using it for the iron ore reduction. This may be provided by the output of the first gas stream treatment, or by directly injecting more H2 from an electrolyser or biomass gasification unit into the gas stream, or by directly injecting H2 directly into the iron production reactor 1.

[0030] Dimethyl ether (DME) is a valuable compound which is useful in the chemical industry, e.g. as a precursor for dimethyl sulphate, acetic acid or for olefin production. It is an important research chemical and is used as refrigerant and propellant. It is a colourless and non-toxic chemical. Moreover, DME may find more widespread use in the future, as it is being developed as a novel fuel, e.g. as replacement for or additive to propane in LPG, and as replacement for diesel fuel. DME has a melting point of 132 K and a boiling point of 249 K and is a gas at ambient temperatures.

[0031] Conventionally DME is produced by dehydration of methanol, where the methanol may be obtained from synthesis gas (syngas) consisting mainly of CO and H2:

[0032] To force the reaction (4) towards the production of DME the water needs to be removed. This can be done by using an adsorbent which selectively binds water. Using a selective water adsorbent in the synthesis of DME is referred to as sorption enhanced DME synthesis (SEDMES) or separation enhanced DME synthesis (SEDMES).

[0033] Flexibility is very important in complicated production processes such as the blast furnace process, the direct iron ore reduction process or the HIsarna® process. The process according to the invention allows re-use of the top-gas emerging from the iron reduction process in two ways: by converting it into syngas in a syngas production unit 5 by increasing the CO and / or H2 content and reducing the CO2 content or by leading it towards a reactor 7 to produce gaseous dimethyl ether 8 therein.

[0034] The top gases 2 (off-gas) arising from the direct reduction process or from the HIsarna process contains CO2 that can be used to produce dimethyl ether by making them react with H2 produced that is preferably sourced from renewable sources. The top gas contains CO2 in ranging from 10 to 90 vol.% and CO from 5 - 35 vol. %, depending on the source of the top gas. HIsarna top gas is very rich in CO2 (50 - 95 mol.%), whereas DRP top gas is less rich (typically about 15 mol.% CO2 and about 25 mol.% CO). BF top gas top typically contains about 15 - 25 mol% CO2 and about 15 - 25 mol% CO.

[0035] The DME can be used for heating purposes in the iron and steel industry or it can be sold to the market where it can be used e.g. as a diesel replacement, as a LPG replacement, as an intermediate chemical product for monomers or aromatic compounds or even as aerosol propellent. In this way, excess H2 produced from renewable energies can be converted into DME and at the same time reduce CO2 emissions. The DME can also be stored for later use much more easily and safely than excess H2-gas.

[0036] In an embodiment of the invention the method is used to "store" excess H2 in the form of DME. DME can be considered an h -precursor in this respect. If desired, the H2 can be released again by steam reforming of DME:

[0037] CH3OCH3+ 3 H2O -► 6 H2+ 2 CO2

[0038] A unit like the SEDMES unit can be integrated in the direct iron ore reduction process as demonstrated in the following non-limiting drawings.

[0039] Brief description of the drawings

[0040] The invention will now be explained by means of the following, non-limiting drawings.

[0041] Figure 1 shows an example of the process flow of an embodiment of the invention. The gas compositions that are shown are examples and not intended to be limiting.

[0042] Figure 2 shows the DME reactor integrated in a schematic iron production route using an iron production reactor 1 DRI-unit according to the invention.

[0043] Figure 3 shows a DRI iron production reactor 1 integrated in a schematic iron production route. The symbol ® depicts a valve or switch to steer the gas stream into one direction or split the gas stream into two gas streams according to the invention.

[0044] Figure 4 shows a HIsarna iron production reactor 1 integrated in a schematic iron production route according to the invention.

[0045] Figure 3 and 4 show the same basic process flow as figure 2, but here an additional heat regeneration cycle is shown where a hot and clean top gas stream 2a is led to a heat exchanger 12 to heat the returning gas stream 10 and optionally also the remaining gas stream 14 and the syngas stream produced in syngas production unit 5, after which the cooled gas 2b is led back to the main stream.

[0046] List of reference numbers

[0047] 1. iron production reactor

[0048] 2. top-gas

[0049] 3. first gas stream

[0050] 4. second gas stream

[0051] 5. syngas production unit

[0052] 6. compression unit (including H2O separation unit)

[0053] 7. dimethylether (DME) production unit 8. dimethylether

[0054] 9. refining unit for refining DME 8 to a higher purity

[0055] 10. returning gas stream

[0056] 11. indirect fired heater 12. heat exchanger

[0057] 13. gas cleaning unit

[0058] 14. remaining gas stream

[0059] 15. syngas

[0060] 16. separation unit to separate DME 8 from remaining gas stream 14

Claims

CLAIMS1. Method for reducing CO2 emissions from an iron ore reduction process in an iron production reactor (1) comprising the following steps: a) producing iron from iron ore in an iron production reactor (1) direct thereby producing reduced iron ore and a top-gas (2) comprising one, more or all of CO2, CO, H2, H2O, NOx, SOx, CH4, and dust particles; b) removing, if present in the top-gas (2), dust particles, NOx and SOx from the top-gas (2) in a gas cleaning unit (13); c) dividing the top-gas into a first gas stream (3) and a second gas stream (4); d) wherein the first gas stream (3) comprises CO2, CO, H2 and H2O and converting it into syngas (15) in a syngas production unit (5) by increasing the CO and / or H2 content and by reducing the CO2 content and returning the syngas into the iron production reactor; e) compressing the second gas stream (4) comprising CO2, CO, H2 and H2O in a compression unit (6), and subsequently removing H2O from the compressed second gas stream, after which H2 will be optionally added to the dehydrated second gas stream (4a); f) sending the dehydrated second gas stream (4a) for processing to a dimethyl ether production unit (7) to produce gaseous dimethyl ether (8) and a returning gas stream (10); g) separating the dimethyl ether (8) from the returning gas stream (10); h) optionally refining the separated dimethyl ether (8) to a higher purity in a refining unit (9), collecting the dimethyl ether and optionally returning the remaining gas stream (14) that is stripped of dimethyl ether to the iron production reactor (1); i) optionally returning the returning gas stream (10) and the remaining gas stream (14) into the iron production reactor (1); j) optionally heating the returning gas stream (10) and / or the remaining gas stream (14) prior to re-introducing the gas stream(s) (10, 14) into the iron production reactor (1).

2. Method according to claim 1 wherein the iron production reactor (1) is a blast furnace, BF.

3. Method according to claim 1 wherein the iron production reactor (1) is a direct reduction plant, DRP.

4. Method according to claim 1 wherein the iron production reactor (1) is a HIsarna plant.

5. Method according to any one of claims 1 to 4 wherein the H2O is removed from the second gas stream (4) in the compression unit (6) by compressing the second gas stream (4) to a pressure of between 10 and 50 bar, followed by condensation of the H2O in a condenser by cooling the compressed gas, preferably by cooling the compressed gas to a temperature between 30°C and 80°C.

6. Method according to any one of claims 1 to 5 wherein the division of the top-gas (2) into the first gas stream (3) and the second gas stream (4) is variable, and wherein the ratio of the flow rates of the first (3) and second gas stream (4) is determined by the demand of the iron production reactor (1) for syngas from the syngas production unit (5), and wherein the other part of the top-gas (2) becomes the second gas stream (4).

7. Method according to any one of claims 1 to 6 wherein the sensible heat of the top gas (2) is used to heat the returning gas stream (10) by leading at least part of the top gas (2a) through a heat exchanger (12) through which the returning gas stream (10) passes, and subsequently leading the top gas (2b) exiting the heat exchanger (12) back to re-join the top gas stream (2).

8. Method according to any one of claims 1 to 7 wherein the separated dimethyl ether (8) is refined to a higher purity, preferably to a purity level between 75 and 99.9 mol.%, preferably by means of a distillation step in the refining unit (9).

9. Method according to any one of claims 1 to 8 wherein the dimethyl ether production unit (7) adapted to produce gaseous dimethyl ether is a sorption enhanced dimethyl ether synthesis reactor.

10. Method according to any one of claims 1 to 9 wherein the dimethyl ether (8) is converted into syngas (15) to be used in the iron production reactor (1).

11. Apparatus for producing iron from iron ore comprising : a) An iron production reactor (1) for producing iron from iron ore and a top-gas (2) comprising one, more or all of CO2, CO, H2, H2O, NOx, SOx, CH4, and dust particles; b) A gas cleaning unit (13) to remove, if present, dust particles, NOx and SOx, from the top-gas (2);c) Dividing means for dividing the top-gas (2) into a first gas stream (3) and a second gas stream (4); d) A syngas production unit (5) to convert the gaseous components in the first gas stream (3) into syngas by adapting the CO and / or H2 content and by reducing the CO2 content for use as syngas (15) in the iron production reactor (1) to reduce iron ore; e) A compression unit (6) for compressing the second gas stream (4) comprising CO2, CO, H2 and H2O for removing H2O from the compressed second gas stream (4) by condensation, and optionally adding H2 to the compressed second gas stream (4); f) A dimethyl ether production unit (7) adapted to produce gaseous dimethyl ether (8) from the dehydrated second gas stream (4) and for separating the dimethyl ether (8) from the returning gas stream (10); g) An optional refining unit (9) for refining the separated dimethyl ether to a higher purity, collecting the dimethyl ether and for optionally returning the remaining gas stream (14) that is stripped of dimethyl ether to the iron production reactor (1) to reduce iron ore; h) Transport means for returning the returning gas stream (10) into the iron production reactor (1) to reduce iron ore; i) Optionally transport means for returning the returning gas stream (14) into the iron production reactor (1) to reduce iron ore; j) Optionally heating means (11), optionally operated by burning dimethyl ether (8), for heating the returning gas stream (10) and / or the remaining gas stream (14) prior to re-introducing the gas stream(s) (10, 14) into the iron production reactor (1).

12. Apparatus according to claim 11 wherein the dimethyl ether production unit (7) adapted to produce gaseous dimethyl ether is a sorption enhanced dimethyl ether synthesis reactor.

13. Apparatus according to any one of claims 11 or 12 provided with a heat exchanger (12) for using the sensible heat of the top gas (2) to heat the returning gas stream (10) by leading at least part of the top gas (2a) through the heat exchanger (12) through which, in use, the returning gas stream (10) and / or the remaining gas stream (14) passes, and for subsequently leading the top gas (2b) exiting the heat exchanger (12) back to re-join the top gas stream (2).

14. Apparatus according to any one of claims 11 to 13 wherein the iron production reactor (1) is a blast furnace, or a direct reduction plant, or a HIsarna plant.

15. Apparatus according to any one of claims 11 to 13 wherein the iron production reactor (1) is a direct reduction plant.

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