Ironmaking method and associated plant

Abstract

The invention relates to an ironmaking method wherein two gases (13,14) are injected into a blast furnace at a single level, said injection being done at the tuyere level of the blast furnace and comprises the injection of an O2-rich gas (13) comprising more than 95% in volume of O2 and of an H2-rich gas (14) comprising more than 95% of H2, without any injection of other reductant at the tuyere level.

Description

[0001] Ironmaking method and associated plant

[0002]

[0001] The present invention relates to an ironmaking method to produce hot metal in a blast furnace. The invention is also related to an associated plant.

[0003]

[0002] Currently, more than 75% of the steel in the world is produced through the blast furnaces (BF) and basic oxygen furnaces (BOF) production route which include raw material production plants, such as coke and sinter plants. Cokemaking, iron ore pelletizing and sintering generate about 20% of total CO2 emissions, and blast furnace ironmaking generates about 70%. At present, a well operating blast furnace (BF) produces around 1300kg of CO2 per tonne of hot metal (kg / thm). Kg / thm stands for kilograms per tonne of hot metal, wherein a tonne, also known as metric Ton, is equal to 1000kg.

[0004]

[0003] Technically, the steel industry could minimize its CO2 emissions by switching to the so called DRI+EAF Route wherein iron ore is reduced to iron using a Direct Reduction Process and then melted in an Electric Arc Furnace (EAF). However, worldwide certain types of iron ores into pellets are not compatible in terms of quality with the DRI+EAF route, and some steel products have specific properties which are not yet reachable with the DRI+EAF route. Therefore, there is a need to reduce the CO2 footprint of the BF-BOF route, and especially of the Blast Furnace process itself.

[0005]

[0004] One of the suggested solutions consists in capturing the top gas emitted by the blast furnace, the blast furnace gas (BFG) removing its CO2 and re-injecting it into the blast furnace. One of the problems is the accumulation of nitrogen in the gas recirculation loop. This results in a high bleed rate of the BFG and consequently reduces the CO2 savings.

[0006]

[0005] Another solution is the injection of a reducing gas at the shaft level of the blast furnace, but this requires development of new injection devices, major modifications of the blast furnace itself to integrate these new injection devices and there are still uncertainties on the impact on the burden distribution and thus on the efficiency of the blast process method linked to this new shaft gas injection.

[0007]

[0006] There is therefore a need for a method of reducing the CO2 footprint of iron production in a blast furnace that does not affect the productivity of the blast furnace and does not require major modifications to the equipment.

[0008]

[0007] For this purpose, a first object of the present invention consists in an ironmaking method wherein iron ore and a solid carbon reductant are charged into a blast furnace to produce hot metal, the method comprising the injection of two gases into the blast furnace at a single level, said injection being done at the tuyere level of the blast furnace and comprises the injection of an 02-rich gas comprising more than 95% in volume of 02 and of an H2-rich gas comprising more than 95% of H2, without any injection of other reductant at the tuyere level.

[0009]

[0008] The method according to the invention may also have the optional features listed below, considered individually or in combination: the temperature of injection of the 02-rich gas is from 25°C to 1200 °C, the temperature of injection of the H2-rich gas is from 25°C to 1200 °C. the hydrogen of the H2-rich gas is green hydrogen, the hydrogen is produced by electrolysis of water, the oxygen of the 02-rich gas is also a product of the electrolysis of water. only the H2-rich gas is heated to be injected at a temperature from 900 to 1200°C, the H2-rich and / or the 02-rich gases are heated by electrical energy, the H2-rich and / or the 02-rich gases are heated by plasma, a blast furnace top gas is emitted and captured, the captured blast furnace top gas is used in a direct reduction process of iron oxides, hydrogen is extracted from the captured blast furnace top gas and at least partly used in the H2-rich gas.

[0010]

[0009] The invention il also related to an ironmaking plant allowing to implement a method according to anyone of the previous combinations.

[0011]

[0010] 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 figures in which:

[0012] - Figure 1 illustrates a blast furnace allowing to implement a method according to the invention,

[0013] - Figure 2 illustrates an ironmaking plant allowing to implement a method according to an embodiment of the invention,

[0014] - Figure 3 is a graphic showing the emission saving rate with different temperatures of the hydrogen injected.

[0015] - Figure 4 is a graphic showing the emission saving rate with different temperatures of the oxygen injected.

[0016] - Figure 5 illustrates an ironmaking plant allowing to implement a method according to another embodiment of the invention.

[0011] First, it is noted that on the figures, the same references designate the same elements regardless of the figure on which they feature and regardless of the shape of these elements. Similarly, should elements not be specifically referenced in one of the figures, their references may be easily found by referring to another figure.

[0017]

[0012] It is also noted that the figures represent 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 figures are illustration and may not have been drawn to scale.

[0018]

[0013] Figure 1 illustrates an ironmaking plant allowing to perform a method according to one embodiment of the invention. This plant comprises at least one blast furnace 1 wherein an iron-containing charge 10 such as sintered iron ore, iron ore pellets, lump iron ore is loaded, optionally with fluxes such as limestone or dolomite, in the throat of the blast furnace 1. A first carbon-based reductant 11 is also charged, preferably independently from the other raw materials, into the throat of the blast furnace 1. This first-carbon based reductant 11 may be coke but is preferentially a non-fossil-based carbon reductant such as biochar or biocoal or waste plastics.

[0019]

[0014] By biochar or biocoal it is meant a charcoal that is produced by pyrolysis of biomass in the absence of oxygen. Biomass is renewable organic material that comes from plants and animals. Biomass sources for energy include notably wood and wood processing wastes — firewood, wood pellets, and wood chips, lumber and furniture mill sawdust and waste, and black liquor from pulp and paper mills, agricultural crops and waste materials — corn, soybeans, sugar cane, switchgrass, woody plants, and algae, and crop and food processing residues, biogenic materials in municipal solid waste, paper, cotton, and wool products, and food, yard, and wood wastes and animal manure and human sewage.

[0020]

[0015] The iron-containing charge 10 is converted to hot metal 12 by reduction of the iron oxides. In the method according to the invention this reduction is done to the injection of gases 13, 14 at a single level 2 of the blast furnace. This level 2 is the classical tuyere level wherein, in standard blast furnaces, the blast is injected. In the present invention the blast is replaced by an 02-rich gas 13 comprising more than 95% of oxygen 02 in volume, on a dry basis, and a H2-rich gas 14 comprising more than 95% of hydrogen H2 in volume, on a dry basis, in also injected at this tuyere level.

[0021]

[0016] The 02-rich gas 13 is preferably injected at a temperature from 25°C to 1200°C. This 02-rich gas aims to provide thermal energy to the iron reduction process by the combustion of coke and the production of a reducing gas mainly consisting of H2 and CO. This reducing gas then flow upwards and reduce iron oxides.

[0017] The H2-rich gas 14 is preferably injected at a temperature from 25°C to 1200°C. This H2-rich gas may play two different roles. First it is a reducing gas which allows reducing iron oxides and thus reduce the needs of carbon reductant. Then, according to its temperature of the injection it may also be a heat carrier.

[0022]

[0018] The 02-rich gas 13 is injected continuously through the tuyeres while the H2-rich gas 14 is injected through a dedicated lance, also at the tuyere level.

[0023]

[0019] Figure 3 is a graphic representing the CO2 savings of an ironmaking method according to the invention when compared to an ironmaking method according to prior art with blast injection and no top gas recycling according to the temperature of injection of the H2-rich gas which would contain 100%H2. The 02-rich gas containing 100% 02 is, in the present configuration, injected at 25°C.

[0024]

[0020] Figure 4 is a graphic representing the CO2 savings of an ironmaking method according to the invention when compared to an ironmaking method according to prior art with blast injection and no top gas recycling according to the temperature of injection of the 02-rich gas which would be 100% 02. The H2-rich gas would be 100% H2 and, in the present configuration, injected at 1100°C.

[0025]

[0021] Increasing the temperature of injection of the H2-rich gas can reduce the coke rate significantly and consequently reduce the CO2 emission. Increasing the temperature of injection of the 02-rich gas can also reduce the coke rate and the CO2 emission but to a lesser extent. In a preferred embodiment the 02-rich gas 13 is injected at ambient temperature while the H2-rich gas 14 is injected at a temperature from 900°C to 1200°C.

[0026]

[0022] The inventors have surprisingly discovered that by injecting both the 02-rich gas and the H2-rich gas at the tuyere level, it was possible to achieve the required reduction and smelting of iron ores to produce hot metal without the needs for any other additional injections such as pulverized coal injection or reducing gas injection at shaft level. It is then possible to reduce the coke consumption without a need to add a second row of injectors to the blast furnace.

[0027]

[0023] The 02-rich and H2-rich gases 13,14 are preferably heated before injection. This heating is preferably done by electrical heating, more preferably powered by CO2 neutral electricity. CO2 neutral electricity includes notably electricity from renewable sources which is defined as energy that is produced from renewable resources, which are naturally replenished on a human timescale, including sources like sunlight, wind, rain, tides, waves, and geothermal heat. In some embodiments, the use of electricity coming from nuclear sources can be used as it is not emitting CO2 to be produced.

[0028]

[0024] In a preferred embodiment the hydrogen of the H2-rich gas 14 is green hydrogen. Green hydrogen (GH or GH2) is hydrogen generated by renewable energy or from low- carbon power. This H2 stream may be provided by a dedicated H2 production plant, such as an electrolysis plant. It may be a water or steam electrolysis plant. In a preferred embodiment from 50 to 120kg / Thm of the H2-rich gas are injected into the BF.

[0029]

[0025] Another embodiment of a method according to the invention is illustrated in Figure 2. All the elements of the embodiment illustrated in figure 1 have the same reference in figure 2 and all options described in the embodiment of figure 1 may be combined with this embodiment when technically possible.

[0030]

[0001] In this embodiment, the ironmaking process emits a blast furnace top gas (BFG) 15 which is captured. The BFG preferably comprises from 14 to 36% in volume of CO, from 50 to 70% in volume of H2 and from 13 to 17% in volume of CO2.

[0031]

[0002] The BFG 15 is preferably subjected to a cleaning step, for example by going through a dust-remover 3 and / or a water remover 4. The cleaned BFG is then subjected to a H2 separation step in a H2 separation device 5 to produce an H2 rich stream 16B and a CO rich stream 16A. The H2 separation device 5 may be a Pressure Swing Adsorption device or PSA, a Vacuum Pressure Swing Adsorption device VPSA, a cryogenic unit, or a combination of those technologies. At the exit of the H2 separation device 5, the H2-rich stream 16B preferably comprises more than 85% in volume of H2.

[0032]

[0026] The H2-rich stream 16B is then mixed with an H2 make-up stream 17 before being injected into the blast furnace as the H2-rich gas 14. The mixture may first go through a heater 6 to be heated at a temperature from 900°C to 1200°C.

[0033]

[0027] The CO-rich stream 16A may be, optionally after having been subjected to a CO2 separation step, used for external valorisation or to produce H2 via a water gas shift reaction.

[0034]

[0028] This allows to almost use the CO and H2 exhausted from the blast furnace fully and thus further reduce the environmental footprint.

[0035]

[0029] Another embodiment of a method according to the invention is illustrated in Figure 5. All the elements of the embodiments illustrated in figures 1 and 2 have the same reference in figure 5 and all options described in the embodiments of figure 1 and 2 may be combined with this embodiment when technically possible.

[0030] In this embodiment the BFG 15 is captured and is preferably subjected to a cleaning step as in the embodiment of figure 2. The cleaned BFG is then subjected to a CO2 removal step in a CO2 separation device 22 to produce a reducing stream 36B and a CO2 rich stream 36A. The reducing stream 36B is a reducing gas with a high reducibility potential which can be advantageously used as reducing gas in a direct reduction process. In such a process iron ore 18 is charged in direct reduction furnace 7 and is reduced to metal iron by a reducing gas 20 flowing counter current. The resulting product is discharged from the bottom of the furnace 7 and is called a direct reduced iron product (DRI) 19. The reducing stream 36B is preferably first heated in a heater 6 and the heated stream 17 is then sent to the DRI plant where it can be either mixed with the reducing gas 20 or injected directly in the DR furnace 7.

[0036]

[0031] The top gas 21 emitted by the direct reduction process may also be captured and subjected to the same treatments’ steps as the BFG, preferably using same equipment 3, 4, 5, 6 as for the BFG so as to be recycled back as reducing gas. This would allow to almost fully used the CO and H2 exhaust from the blast furnace and thus further reduce the environmental footprint. This moreover crates a synergy between the Direct Reduction plant and the Blast Furnace plant which could ease the transition from one route to the other.

[0037]

[0032] The CO2-rich stream 36A comprises more than 80% in volume of CO2 and can be use in Carbon Capture Usage (CCU) technologies and / or Carbon Capture Storage (CCS) technologies.

[0038] Example

[0039]

[0033] CO2 savings using a process according to the 2ndembodiment of the invention (E2), with recycling a part of the BFG within the BF, and accordion to the 3rdembodiment (E3) with recycling of a part of the BFG as reducing gas in a DRI plant were calculated. The savings are based on comparison with a classical blast furnace with injection of hot blast and pulverized coal at tuyere level, charging of coke as carbon reductant in the throat of the BF.

[0040]

[0034] Calculations were done using a heat and mass balance program called MM HF, details of which can notably be found in the paper “Techniques de I’lngenieur, Haut Fourneau-Exploitation from Maurice Burteaux, published on April 10, 1992”. For the purpose of the calculation the target was to maintain a raceway adiabatic flame temperature (RAFT) of 1700 °C. The RAFT is a commonly known parameter for the person skilled in the art of blast furnace operations, definition can notably be found in Coal Handbook, volume 2 - Towards Cleaner Coal Utilization 2ndEdition.

[0035] The typical conditions of iron ores, coke, injection coal, and hot blast of a present blast furnace ironmaking are shown in the Table 1, Table 2, and Table 3 respectively.

[0041] Table 1. The Chemical Compositions of Iron Ore Pellet and Sinter

[0042] Table 2. The Chemical Compositions of Coke

[0043] Table 3. The Chemical Compositions of Pulverized coal

[0044]

[0036] Based on the given conditions of raw materials and the hot blast, Table 4 shows typical blast furnace operations and its specific CO2 emission from its top gas. The typical specific CO2 emission is 1345.6 kg per tonne of hot metal.

[0045] Table 4. Present Typical Blast Furnace Operations and Its Specific CO2 Emission

[0046] Table 5. The Specific CO2 emissions saved with methods according to the invention.

[0037] In E2A and E2B, an H2-rich stream is extracted from the BFG and then mixed with an H2 make up stream to inject it back into the BF.

[0047]

[0038] In E3A and E3B, a reducing stream is extracted from the BFG and then used as part of the reducing gas in a DRI process.

[0048]

[0039] Two series of calculations have been done with different temperatures of injection of the H2-rich gas, while the 02-rich gas was always injected at the ambient temperature of 25 °C.

[0049]

[0040] In examples A the H2-rich gas is heated to 1000 °C via an electrical furnace 6 before injection, while in examples B, a plasma heater is used to boost the H2-rich gas temperature to 1200°C.

[0050]

[0041] The CO2 savings are calculated based on the difference of specific CO2 emissions between the different embodiments of the method according to the invention (E2A, E2B, E3A, E3B) and the typical blast furnace operations illustrated in table 4.

[0051]

[0042] In E3A, with the process conditions as indicated in Table 5, the total coke rate would be of 241 .7 kg / Thm and the H2 rate of 99.3 kg / Thm. In this case, to produce one tonne of hot metal, and considering that BFG would be first subjected to treatments including dedusting, moisture removal, CO2 removal, and heating, hypothesis was taken that 5% of the total volume would leak, then 140.10 Nm3 of CO and 715.47 Nm3 of H2 can be exported to the DRI Furnace. Nm3 stands for Normal cubic meters and is a unit of measurement of the quantity of gas which corresponds to the content of a volume of one cubic meter, for a gas under normal temperature and pressure conditions (0°C and 1 atm.)

[0052]

[0043] With the complete reuse of these amounts of CO and H2 in the direct reduction process, 1442.1 kg of metallic Fe can be produced, which is equivalent to 1497.0 kg of hot metal. This amount of hot metal is considered in the overall calculation of CO2 emissions per tonne of hot metal which leads to the calculated total CO2 emission savings of 81 .8%. Same hypotheses are taken for E3B.

Claims

CLAIMS1 ) An ironmaking method wherein iron ore (10) and a solid carbon reductant (11 ) are charged into a blast furnace (1 ) to produce hot metal (12), the method comprising the injection of two gases (13, 14) into the blast furnace at a single level, said injection being done at the tuyere level (2) of the blast furnace and comprises the injection of an 02-rich gas (13) comprising more than 95% in volume of 02 and of an H2-rich gas (14) comprising more than 95% of H2, without any injection of other reductant at the tuyere level.2) A method according to claim 1 wherein the temperature of injection of the 02-rich gas is from 25°C to 1200 °C.3) A method according to any one of claims 1 or 2 wherein the temperature of injection of the H2-rich gas is from 25°C to 1200 °C.4) A method according to any one of claims 1 to 3 wherein the hydrogen of the H2-rich gas is green hydrogen.5) A method according to claim 4 wherein the hydrogen is produced by electrolysis of water.6) A method according to claim 5 wherein the oxygen of the 02-rich gas 13 is also a product of the electrolysis of water.7) A method according to anyone of the previous claims wherein only the H2- rich gas is heated to be injected at a temperature from 900 to 1200°C.8) A method according to any one of claims 1 to 6 wherein the H2-rich and / or the 02-rich gases are heated by electrical energy.9) A method according to any one of claims 1 to 6 wherein the H2-rich and / or the 02-rich gases are heated by plasma.10) A method according to any one of claims 1 to 9 wherein a blast furnace top gas (15) is emitted and captured.11 ) A method according to claim 10 wherein the captured blast furnace top gas (15) is used in a direct reduction process of iron oxides.12) A method according to claim 10 wherein hydrogen (16B) is extracted from the captured blast furnace top gas (15) and at least partly used in the H2-rich gas (14).13) An ironmaking plant to implement a method according to anyone of the previous claims.

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