Process and system for producing sponge iron from iron ore.

Abstract

A system for producing sponge iron, the system comprising: a direct reduction shaft (201), a reducing gas source (206), a reducing gas vessel (209), a primary circuit (210) for guiding at least a portion of the top gas, a secondary circuit (211) for guiding at least a portion of the gas removed from the gas guided through the primary circuit (210), the secondary circuit (211) being connected at one end to the primary circuit (210) and at the other end to the reducing gas vessel (209), a second gas line (212) connecting the reducing gas source (206) to the reducing gas vessel (209), and a third gas line (213) connecting the reducing gas vessel (209) to the first gas line (207). A control unit (214) is configured to control the flow of reducing gas from the reducing gas source (206) to the first gas line (207) and to control the flow of reducing gas through a third gas line (213) from a reducing gas container (209) to the first gas line (207), the control unit (214) being configured to correspondingly reduce the flow rate of reducing gas from the reducing gas source (206) to the first gas line (207) while allowing the flow of reducing gas from the reducing gas container (209) to said first gas line (207).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a process for producing sponge iron from iron ore. The present disclosure further relates to a system for producing sponge iron.

BACKGROUND ART

[0002] Steel is the most important engineering and construction material in the world. In the modern world, it is difficult to find an object that does not contain steel or does not depend on steel for its manufacture and / or transportation. As such, steel is intricately involved in almost every aspect of modern life.

[0003] In 2018, the total global crude steel production reached 1.81 billion tonnes, far exceeding all other metals, and is expected to reach 2.8 billion tonnes by 2050, of which 50% is expected to come from unused iron sources. Steel is also the most recycled material in the world, and it is a metal that can be used over and over again after remelting using electricity as the primary energy source, so its degree of recyclability is extremely high.

[0004] Therefore, steel is the cornerstone of modern society, and its role to play in the future will be even more prominent.

[0005] Steel is mainly produced by three methods. i) Integrated production using unused iron ore in a blast furnace (BF), where iron oxide in the ore is reduced by carbon to produce iron. The iron is further processed in a steel plant by oxygen blowing and refining in a basic oxygen furnace (BOF) to produce steel. This process is also commonly referred to as "basic oxygen steelmaking". ii) Scrap-based production using recycled steel, where the recycled steel is melted in an electric arc furnace (EAF) using electricity as the primary energy source. This process is also commonly referred to as "electric steelmaking". iii) Direct reduction production based on unused iron ore, in which unused iron ore is reduced by carbonaceous reducing gas in a direct reduction (DR) process to produce sponge iron. Then, the sponge iron is melted together with scrap iron in an EAF to produce steel.

[0006] In this specification, the term crude iron is used to refer to all iron produced for further processing into steel, whether obtained from a blast furnace (i.e., pig iron) or directly from a reducing shaft (i.e., sponge iron).

[0007] While the processes described above have been refined over decades and are theoretically approaching minimal energy consumption, one fundamental problem remains unresolved: the reduction of iron ore using carbonaceous reducing agents produces CO2 as a byproduct. In 2018, an average of 1.83 tons of CO2 were produced per ton of steel produced. The steel industry is one of the largest emitters of CO2, accounting for approximately 7% of global CO2 emissions. As long as carbonaceous reducing agents are used, it is impossible to avoid excessive CO2 production in the steel production process.

[0008] The HYBRIT initiative was established to address this issue. HYBRIT, short for Hydrogen Breakthrough Ironmaking Technology, is a joint venture between SSAB, LKAB, and Vattenfall, partly funded by the Swedish Energy Agency, and aims to reduce CO2 emissions and decarbonize the steel industry.

[0009] At the core of the HYBRIT concept is the production of sponge iron from unused iron ore based on direct reduction. However, instead of using carbonaceous reducing gases such as natural gas as the direct reduction process currently industrialized, HYBRIT proposes using hydrogen gas as the reducing agent, which is called hydrogen direct reduction (H-DR). Hydrogen gas can be produced by the electrolysis of water using primary energy sources that do not primarily use fossil fuels and / or are renewable, as in the case of electricity production in Sweden. Therefore, it is possible to realize an important process of reducing iron ore without the need to input fossil fuels and with water as a byproduct instead of CO2.

[0010] Conventional technology uses reducing gas, which is mostly natural gas. Direct reduction plants typically have a shaft in which reduction takes place. The shaft has an inlet at the top into which iron ore pellets are introduced and an outlet at the bottom from which sponge iron is removed from the shaft. There is also at least one inlet at the bottom of the shaft for introducing reducing gas into the shaft, and at least one outlet at the top of the shaft for releasing the top gas. The top gas consists mostly of unreacted reducing gas, which is sometimes mixed with an inert gas used to seal the inlets and outlets for the iron ore pellets and sponge iron, respectively. Conventional methods for processing the top gas are by burning it.

[0011] However, when hydrogen is used primarily or alone as a reducing gas, combustion is not a very attractive option from an energy efficiency standpoint, as hydrogen gas production requires a considerable amount of energy compared to natural gas. Furthermore, if the top gas of the furnace contains nitrogen gas (usually used as a sealing gas), combustion may result in the release of NOx, which is undesirable from an environmental perspective.

[0012] Hydrogen gas is typically produced by a water electrolytic cell, which requires a considerable amount of electricity. Depending on the power source used to generate the electricity, the availability of electricity can fluctuate over time. Therefore, energy-efficient and cost-effective control of the reduction process includes optimizing the process in relation to electricity availability. [Overview of the project] [Problems that the invention aims to solve]

[0013] Therefore, an object of the present invention is to present a process and system for the direct reduction of iron ore into sponge iron, using primarily or exclusively hydrogen gas as the reducing gas, and to provide means for controlling the pressure in the direct reduction shaft by efficiently reusing unreacted hydrogen gas exiting the direct reduction shaft as part of the furnace top gas.

[0014] Furthermore, an object of the present invention is to present a process and system that enables energy-efficient and cost-effective control of the reduction process, and therefore includes process optimization related to the availability of electricity. [Means for solving the problem]

[0015] The object of the present invention is realized by a process for producing sponge iron from iron ore, and this process is - The process of directly loading iron ore into the reduction shaft, - A process to reduce iron ore to produce sponge iron, in which a hydrogen-rich reducing gas is directly introduced into the reduction shaft from a reducing gas source via a first gas line, - A step of directly extracting top gas from the reduction shaft, wherein the top gas contains unreacted hydrogen gas, and the extraction step is as follows: - A step of guiding at least a portion of the extracted furnace top gas into the primary circuit and directly reintroducing the said portion of the furnace top gas into the reduction shaft, - A step of taking a portion of the gas guided into the primary circuit out of the primary circuit and guiding the gas portion through the secondary circuit to a reducing gas container, - A step of guiding the reducing gas from the reducing gas source to the reducing gas container, and forming a gas mixture in the reducing gas container together with the gas from the secondary circuit, - The process includes guiding the gas mixture from the reducing gas container to the first gas line, and correspondingly reducing the flow rate of the reducing gas from the reducing gas source to the first gas line.

[0016] The reducing gas container can be made to have a large capacity. According to one embodiment, the reducing gas container constitutes a lined rock storage tank.

[0017] According to one embodiment, the step of guiding the gas mixture from the reducing gas container to the first gas line is performed in response to the gas pressure in the reducing gas container exceeding a predetermined level.

[0018] According to one embodiment, the reducing gas source comprises an electrolytic cell driven by power associated with fluctuating access-related parameters, the process comprising the steps of continuously registering fluctuations in the access-related parameters and guiding a gas mixture from the reducing gas container to the first gas line in response to the access-related parameters falling below a predetermined first level.

[0019] According to one embodiment, the access-related parameters include either the level of electricity stored in the power storage unit or the access level to means for generating electricity, such as solar, wind, or hydroelectric power. When access to electricity is reduced, for example at night in the case of solar power generation, the reducing gas is obtained from a reducing gas container rather than from a reducing gas source and delivered into the shaft via a first gas line.

[0020] According to one embodiment, the reducing gas source comprises an electrolytic cell driven by electric power provided via a public electricity network, and the process comprises the step of guiding a gas mixture from the reducing gas container to the gas line in response to the load on the public network exceeding a predetermined level.

[0021] According to one embodiment, the reducing gas is guided from the reducing gas source to the reducing gas container in response to the access-related parameter exceeding a predetermined second level.

[0022] According to one embodiment, said extraction of said gas portion from the primary circuit to the secondary circuit is performed in response to the pressure in the primary circuit exceeding a predetermined level.

[0023] According to one embodiment, the gas delivered via the secondary circuit and the reducing gas delivered from the reducing gas source to the reducing gas container are compressed in a compressor step before entering the reducing gas container. The pressure in the reducing gas container can be at a level significantly higher than the pressure in the rest of the system. For example, the pressure in the direct reduction shaft can be on the order of 10 bar, and the pressure in the reducing gas container can be on the order of 100 bar.

[0024] The object of the present invention is also achieved by a system for producing sponge iron, which system comprises: - a direct reduction shaft, - a first inlet for introducing iron ore into the shaft, - a first outlet for removing sponge iron from the shaft, - a second inlet for introducing reducing gas into the shaft, and - a direct reduction shaft provided with a second outlet for withdrawing top gas from the shaft, - a reducing gas source connected to the reducing gas inlet via a gas line, - a reducing gas container, - A primary circuit for guiding at least a portion of the top gas of the furnace, the primary circuit being connected to a second outlet at one end and to the first gas line at the other end, - A secondary circuit for guiding at least a portion of the gas extracted from the gas guided through the primary circuit, the secondary circuit being connected to the primary circuit at one end and to the reducing gas container at the other end, - A second gas line connecting the reducing gas source to the reducing gas container, - A third gas line connecting the reducing gas container to the first gas line, - A control unit configured to control the flow of reducing gas from a reducing gas source to a first gas line, and to control the flow of reducing gas from a reducing gas container to a third gas line to the first gas line, and further comprising a control unit configured to allow the flow of reducing gas from the reducing gas container to the first gas line, while correspondingly reducing the flow rate of reducing gas from the reducing gas source to the first gas line.

[0025] According to one embodiment, the system includes means for enabling the flow of reducing gas from the reducing gas container to the first gas line in response to the gas pressure in the reducing gas container exceeding a predetermined level. According to one embodiment, a pressure reducer is provided in the third gas line. According to one embodiment, the predetermined pressure in the reducing gas container induces a gas flow in the third gas line and is substantially higher than the pressure in the first gas line. The pressure reducer is configured to convert the higher energy of the gas passing through the pressure reducer into electricity (for example, by equipping it with a turbine), which is used to generate hydrogen gas, preferably in the reducing gas source.

[0026] According to one embodiment, the reducing gas source comprises an electrolytic cell driven by power associated with fluctuating access-related parameters, the system comprises means for continuously registering fluctuations in the access-related parameters, and the control unit is configured to enable the flow of reducing gas from the reducing gas container to the gas line in response to the access-related parameters falling below a predetermined first level.

[0027] According to one embodiment, the access-related parameters include either the level of electricity stored in the power storage unit, or the access level to means for generating electricity such as solar power, wind power, or hydropower.

[0028] According to one embodiment, the reducing gas source comprises an electrolytic cell driven by electricity provided via a public electricity network, the system comprises means for registering the load on the public electricity network, and the control unit is configured to allow the flow of a gas mixture from the reducing gas container to the gas line in response to the load on the public network exceeding a predetermined level. Therefore, when the load on the public network is high and as a result electricity prices are high, especially when the reducing gas source comprises an electrolytic cell, more reducing gas to the reducing shaft is obtained from the reducing gas container than from the reducing gas source.

[0029] According to one embodiment, the control unit is configured to reduce the output of the reducing gas source in response to enabling the reducing gas flow from the reducing gas container to the first gas line, provided that the required reducing gas flow in the first gas line is realized.

[0030] According to one embodiment, the control unit is configured to enable the flow of reducing gas from the reducing gas source to the reducing gas container in response to access-related parameters exceeding a predetermined second level. When access to power allows the reducing gas source to generate reducing gas at a faster rate required for the shaft, the control unit controls the generation and delivery of reducing gas so that any excess reducing gas generated by the reducing gas source is delivered to the reducing gas container. The compressor is preferably located in the second gas line to generate a high pressure within the reducing gas container.

[0031] According to one embodiment, the system includes means configured to enable the extraction of the gas portion from the primary circuit to the secondary circuit in response to the pressure in the primary circuit exceeding a predetermined level. The system also, or alternatively, includes means configured to provide continuous extraction of top gas from the primary circuit to the secondary circuit.

[0032] According to one embodiment, the system includes a compressor arrangement for compressing the gas portion delivered via a secondary circuit and the reducing gas delivered from a reducing gas source through the second gas line before entering a reducing gas container. The compressor arrangement may include the compressor located within the second gas line.

[0033] According to one embodiment, the system comprises at least one first sensor for measuring the flow rate of reducing gas in a first gas line, at least one second sensor for measuring the temperature in a direct reduction shaft, and at least one third sensor for measuring the pressure indicating the pressure in the direct reduction shaft, and the control unit is configured to determine the required flow rate of reducing gas into the direct reduction shaft in the first gas line based on inputs received from the first, second, and third sensors.

[0034] According to one embodiment, the direct reduction shaft has a nominal rate of sponge iron production per hour, and the storage capacity of the reduction gas container corresponds to the amount of hydrogen gas required to enable reduction at the nominal reduction rate for at least 1 hour, preferably at least 3 hours, and more preferably at least 6 hours.

[0035] For a more complete understanding of the present invention and its further objectives and advantages, the detailed description below should be read in conjunction with the accompanying drawings, where the same reference numerals in the various figures refer to similar articles. [Brief explanation of the drawing]

[0036] [Figure 1] This diagram schematically illustrates the steelmaking value chain based on iron ore, according to the Hybrid concept. [Figure 2] This figure schematically illustrates an exemplary embodiment of a system suitable for performing the processes disclosed herein. [Modes for carrying out the invention]

[0037] definition A reducing gas is a gas capable of reducing iron ore to metallic iron. In conventional direct reduction processes, the reducing components are typically hydrogen and carbon monoxide, but in the process disclosed herein, the reducing component is primarily or exclusively hydrogen. The reducing gas is introduced from a point lower than the iron ore inlet of the direct reduction shaft and flows upward opposite to the moving bed of iron ore to reduce the ore.

[0038] The top gas is a process gas extracted directly from the upper end of the reduction shaft near the ore inlet. Typically, the top gas consists of a mixture of partially spent reducing gas containing oxidation products of reducing components (e.g., H2O) and an inert component introduced into the process gas, such as a sealing gas. After treatment, the top gas can be recycled directly back into the reduction shaft as a component of the reducing gas.

[0039] The extract stream removed from used carburizing gas to prevent the accumulation of inert components in the carburizing process gas is called the carburizing extract stream.

[0040] The gas from the reducing gas source can be called the supplement gas. In the context of this application, the supplement gas is added to the recycled top gas before being directly reintroduced into the reducing shaft. Therefore, the reducing gas typically includes the supplement gas along with the recycled top gas.

[0041] The sealing gas is the gas that enters the direct reduction (DR) shaft from the ore loading configuration at the inlet of the DR shaft. The outlet end of the direct reduction shaft can also be sealed using the sealing gas, and therefore the sealing gas can enter the DR shaft from the discharge configuration at the outlet of the direct reduction shaft. The sealing gas is typically an inert gas to prevent the formation of explosive gas mixtures at the shaft inlet and outlet. An inert gas is a gas that does not form a potentially flammable or explosive mixture, including air or process gases, i.e., gases that do not act as oxidizers or fuels in combustion reactions under the conditions prevailing in this process. The sealing gas can essentially consist of nitrogen and / or carbon dioxide. Herein, carbon dioxide is referred to as the inert gas, but it should be noted that under the conditions prevailing in this system, carbon dioxide can react with hydrogen in the water-gas shift reaction to provide carbon monoxide and vapor.

[0042] reduction A direct reduction shaft can be any type commonly known in the art. A shaft refers to a solid-gas counter-flow moving-bed reactor through which iron ore charges are introduced from an inlet at the top of the reactor and descend by gravity to an outlet located at the bottom of the reactor. A reducing gas is introduced from a point lower than the reactor inlet and flows upward, opposite to the moving bed of ore, reducing the ore to metallic iron. Reduction is typically carried out at temperatures of about 900°C to about 1100°C. The required temperature is typically maintained by preheating the process gases introduced into the reactor, typically using a preheater, such as an electric preheater. Further heating of the gases can be achieved by exothermic partial oxidation of these gases with oxygen or air after they have left the preheater and before they are introduced into the reactor. Reduction can be carried out in a DR shaft at pressures of about 1 bar to about 10 bar, preferably about 3 bar to about 8 bar. The reactor may have a cooling and discharge cone positioned at the bottom to allow the sponge iron to be cooled and discharged from the outlet.

[0043] The iron ore charge typically consists mainly of iron ore pellets, but lump iron ore may also be introduced. Iron ore pellets typically contain mainly hematite and further additives or impurities such as gangue, flux, and binders. However, the pellets may also contain other metals and other ores such as magnetite. Iron ore pellets designated for direct reduction processes are commercially available and such pellets can be used in this process. Alternatively, the pellets may be specially adapted for hydrogen-rich reduction processes, similar to this process.

[0044] The reducing gas is hydrogen-rich. The reducing gas refers to the combination of the new supplemental gas and the reused portion of the top gas introduced directly into the reduction shaft. A hydrogen-rich gas means that the reducing gas entering the direct reduction shaft can consist of more than 70 vol% hydrogen gas, for example, more than 80 vol% hydrogen gas, or more than 90 vol% hydrogen gas (volume percentage is determined under normal conditions of 1 atm and 0°C). Preferably, reduction is carried out as a separate step. That is, carburizing is not carried out at all, or if carburizing is to be carried out, it is carried out separately from reduction, i.e., in a separate reactor or in a separate, separate section of the direct reduction shaft. This greatly simplifies the treatment of the top gas by avoiding the need to remove carbonaceous components and the costs associated with such removal. In such cases, the supplemental gas can consist essentially of hydrogen gas, or may consist solely of hydrogen gas. Note that even when the supplemental gas is exclusively hydrogen, some amount of carbon-containing gas may be present in the reducing gas. For example, if the sponge iron outlet of a direct reduction shaft is coupled to the inlet of a carburizing reactor, a relatively small amount of carbon-containing gas may unintentionally permeate directly from the carburizing reactor into the reduction shaft. Another example is that carbonates present in iron ore pellets may volatilize and appear as CO2 in the top gas of the DR shaft, resulting in a certain amount of CO2 being recirculated into the DR shaft. Since hydrogen gas is overwhelmingly abundant in the reduction gas circuit, even if CO2 is present, it can be converted to CO by the reverse water-gas shift reaction.

[0045] In some cases, it is desirable to perform reduction and obtain some degree of carburization as a single step. In such cases, the reducing gas may contain up to approximately 30 vol% of a carbon-containing gas, for example, up to approximately 20 vol% or up to approximately 10 vol% (determined under normal conditions of 1 atm and 0°C). Suitable carbon-containing gases are disclosed below as carburizing gases.

[0046] Hydrogen gas can preferably be obtained by at least partly the electrolysis of water. If the electrolysis of water is carried out using renewable energy, this makes it possible to provide reducing gas from renewable resources. Electrolyzed hydrogen can be transported directly from the electrolytic cell to the DR shaft by conduits, or the hydrogen can be stored during production and transported to the DR shaft as needed.

[0047] The top gas as it exits the direct reduction shaft typically contains unreacted hydrogen, water (an oxidation product of hydrogen), and inert gases. If carburizing is performed along with reduction, the top gas may also contain some carbonaceous components such as methane, carbon monoxide, and carbon dioxide. The top gas as it exits the direct reduction shaft can first be subjected to adjustments such as deduplication to remove any entrained solids and / or heat exchange to cool the top gas and heat the reducing gas. During heat exchange, water from the top gas can be condensed. Preferably, at this stage, the top gas consists essentially of hydrogen, inert gases, and residual water. However, if carbonaceous components are present in the top gas, such carbonaceous components can also be removed from the top gas, for example, by reforming and / or CO2 absorption.

[0048] Sponge iron The sponge iron products of the processes described herein are typically called directly reduced iron (DRI). DRI can be supplied at high temperatures (HDRI) or low temperatures (CDRI), depending on the process parameters. Low-temperature DRI is sometimes also known as type (B) DRI. DRI can undergo re-oxidation and may be spontaneously combustible. However, several means of inactivating DRI are known. One such inactivation method, commonly used to facilitate the transport of the product overseas, is to pressurize high-temperature DRI into briquettes. Such briquettes are commonly called hot briquette iron (HBI) and are sometimes also known as type (A) DRI.

[0049] The sponge iron products obtained by the processes described herein can be essentially fully metallized sponge iron, i.e., sponge iron with a reduction degree (DoR) greater than about 90%, for example, greater than about 94%, or greater than about 96%. The reduction degree is defined as the amount of oxygen removed from the iron oxide and is expressed as a percentage of the initial amount of oxygen present in the iron oxide. Obtaining sponge iron with a DoR greater than about 96% is often not commercially desirable from a reaction kinetic standpoint, but such sponge iron can be produced if desired.

[0050] If carburizing is performed, the process described herein can produce sponge iron having any desired carbon content of about 0 to about 7 weight percent. Typically, however, for further processing, it is desirable that the sponge iron has a carbon content of about 0.5 to about 5 weight percent, preferably about 1 to about 4 weight percent, for example, about 3 weight percent, although this may depend on the ratio of sponge iron to scrap used in the later EAF processing step.

[0051] Embodiment The present invention will now be described in more detail with reference to certain exemplary embodiments and drawings. However, the present invention is not limited to the exemplary embodiments discussed herein and / or shown in the drawings, and may be modified within the scope of the appended claims. Furthermore, these drawings are not to be considered to be drawn to actual size, and some features may be exaggerated to more clearly show certain features.

[0052] Figure 1 schematically illustrates the iron ore-based steelmaking value chain according to the Hybrid concept. The iron ore-based steelmaking value chain begins at the iron ore mine 101. After mining, the iron ore 103 is concentrated and processed at the pelletizing plant 105 to produce iron ore pellets 107. These pellets, along with any lump ore used in this process, are converted to sponge iron 109 by reduction using hydrogen gas 115 as the main reducing agent in the direct reduction shaft 111, producing water 117a as the main byproduct. The sponge iron 109 can optionally be carburized in the direct reduction shaft 111 or in a separate carburizing reactor (not shown). The hydrogen gas 115 is produced in the electrolytic cell 119 by the electrolysis of water 117b using electricity 121, which is preferably derived from a power source 122 that does not primarily use fossil fuels or is renewable. Hydrogen gas 115 can be stored in the hydrogen storage unit 120 before being directly introduced into the reduction shaft 111. Sponge iron 109 is melted using an electric arc furnace 123 along with an optional proportion of scrap iron 125 or other iron sources to provide a molten material 127. The molten material 127 is then subjected to a downstream secondary metallurgical process 129 to produce steel 131. The entire value chain from ore to steel is intended to be fossil fuel-free and to have minimal or zero carbon emissions.

[0053] Figure 2 schematically shows an exemplary embodiment of a system suitable for performing the processes disclosed herein.

[0054] The system shown in Figure 2 includes a direct reduction (DR) shaft 201. The DR shaft includes a first inlet 202 for introducing iron ore into the DR shaft and a first outlet 203 for removing sponge iron from the DR shaft. The DR shaft further includes a plurality of second inlets 204 for introducing reducing gas into the shaft and at least one second outlet 205 for removing top gas from the DR shaft. There may be many second inlets, but for simplicity, only one is shown in this figure.

[0055] The system further comprises a reducing gas source 206 connected to a reducing gas inlet 204 through a first gas line 207. The reducing gas source may include a hydrogen generation unit. In the embodiment presented, the reducing gas source includes a water electrolytic cell unit. The reducing gas from the reducing gas source 206 has a fairly low pressure of about 1 bar and needs to be compressed before being introduced into the DR shaft. Therefore, the system further comprises a first compressor 208 located in the first gas line 207, the first compressor 208 configured to increase the pressure of the reducing gas to about 8 bar.

[0056] The system further comprises a reducing gas container 209. In the embodiment presented, the reducing gas container 209 constitutes a lined rock storage tank. The direct reduction shaft 201 has a nominal rate of production of sponge iron per hour, and the storage capacity of the reducing gas container 209 corresponds to the amount of hydrogen gas required to enable reduction at the nominal reduction rate for at least 6 hours.

[0057] The system further comprises a primary circuit 210 for guiding at least a portion of the top gas of the furnace, the primary circuit being connected at one end to a second outlet 205 and at the other end to the first gas line 207.

[0058] A secondary circuit 211 is provided to guide at least a portion of the gas extracted from the gas guided through the primary circuit 210. The secondary circuit 211 is connected to the primary circuit 210 at one end and to the reducing gas container 209 at the other end. The secondary circuit 211 is used to control the pressure within the primary circuit 210, and thereby within the DRI shaft.

[0059] The system further comprises a second gas line 212 connecting a reducing gas source 206 to a reducing gas container 209, and a third gas line 213 connecting the reducing gas container 209 to a first gas line 207. In the embodiment shown in Figure 2, the second gas line 212 is connected to the reducing gas source 206 via the first gas line 207 and a fourth gas line 216 extending from the first gas line to the second gas line 212. The third gas line 213 is connected to the first gas line 207 via the fourth gas line 216. The fourth gas line 216 is connected to the first gas line 207 downstream of the first compressor 208. Alternative embodiments are also possible in which the fourth gas line is omitted and the second gas line 212 and the third gas line 213 do not share a common gas to be connected to the first gas line, but extend separately to the first gas line.

[0060] The control unit 214 is configured to control the flow of reducing gas from the reducing gas source 206 through the first gas line 207 by controlling an operable valve 224 located in the first gas line 207. The control unit 214 is also configured to control the flow of reducing gas from the reducing gas container 209 through the third gas line 213 to the first gas line 207 by controlling an operable valve 220 located in the third gas line 213. The control unit 214 is configured to enable the flow of reducing gas from the reducing gas container 209 to the first gas line 207 and, in correspondence, reduce the flow rate of reducing gas from the reducing gas source 206 to the first gas line 207. The control unit 214 is also configured to control the flow of reducing gas to the second gas line 212 by controlling an operable valve 225 located in the fourth gas line 212. An operable valve 225 in the fourth gas line 216 is also used to control the gas flow from the reducing gas container 209 to the first gas line 207. Preferably, each of the controllable valves is a proportional valve, thereby allowing control of the flow rate and pressure in each gas line.

[0061] The system includes means for enabling the flow of reducing gas from the reducing gas container 209 to the first gas line 207 in response to the gas pressure in the reducing gas container 209 exceeding a predetermined level. The means include a pressure sensor 215 located in the third gas line and an operable control valve 220 located in the third gas line 213 and controlled by a control unit 214. A pressure reducer may also be provided in the third gas line 213, although this is not shown. According to one embodiment, the predetermined pressure in the reducing gas container 209 induces a gas flow in the third gas line 213, which is substantially higher than the pressure in the first gas line 207. The pressure reducer, where applicable, should be configured to convert the higher energy of the gas passing through the pressure reducer into electricity (for example, by equipping it with a turbine), which is used to generate hydrogen gas, preferably in the reducing gas source.

[0062] The reducing gas source 206 comprises an electrolytic cell driven by power from a power source 217. In one embodiment, the power source 217 constitutes a renewable energy source such as a solar power plant or a wind power plant. Since the power generated by such a power plant may fluctuate over time, the control unit 214 is configured to allow the flow of reducing gas from the reducing gas container 209 to the first gas line 207 in response to the power being generated falling below a predetermined first level.

[0063] Power supply 217 can also constitute a public electricity network, and the system includes means for registering the load on the public electricity network. In this case, control unit 214 can be configured to allow the flow of a gas mixture from the reducing gas container 209 to the first gas line 207 in response to a load on the public network, thereby causing the price of electricity to exceed a predetermined level. Thus, when the load on the public network is high and as a result the price of electricity is high, especially when the reducing gas source 206 includes an electrolytic cell, the reducing gas to the reducing shaft 201 can be delivered mainly from the reducing gas container 209 rather than from the reducing gas source 206.

[0064] The control unit 214 is configured to reduce the output of the reducing gas source 206 in response to enabling the reducing gas flow from the reducing gas container 209 to the first gas line 207, provided that the required reducing gas flow into the DR shaft in the first gas line 207 is realized.

[0065] The control unit 214 is configured to enable the flow of reducing gas from the reducing gas source 206 to the reducing gas container 209 in response to access to power exceeding a predetermined second level. When access to power allows the reducing gas source 206 to generate reducing gas at a faster rate required for the DR shaft, the control unit 214 controls the generation and delivery of reducing gas so that any excess reducing gas generated by the reducing gas source 206 is delivered to the reducing gas container 209.

[0066] The system comprises a pressure sensor 218, an operable valve 219, and a control unit 214, thereby controlling the valve 219 to extract the gas portion from the primary circuit 210 to the secondary circuit 211 in response to the pressure in the primary circuit 210 exceeding a predetermined level, based on input from the sensor 218. The system may also, or alternatively, include means configured to provide continuous extraction of top gas from the primary circuit 210 to the secondary circuit 211.

[0067] The system further comprises compressor arrangements 220, 221 for compressing the gas portion delivered via the secondary circuit 211 before entering the reducing gas container 209, and the reducing gas delivered from the reducing gas source 206 through the second gas line 212.

[0068] The system comprises at least one first sensor 222 for measuring the reductive gas flow rate in the first gas line 207, at least one second sensor 223 for measuring a temperature indicating the temperature inside or at the outlet of the direct reduction shaft 201 or inside or at the outlet of the DR shaft 201, and at least one third sensor, in this case a pressure sensor 218 in the primary circuit, for measuring a pressure indicating the pressure inside the DR shaft. The control unit 214 is configured to determine the required reductive gas flow rate into the DR shaft in the first gas line 207 based on inputs received from the first sensor 222, the second sensor 223, and the third sensor 218.

[0069] The primary circuit 210 further comprises a device 226 for treating the top gas, the device 226 comprising a device (not shown in detail) for separating inert gas from the portion of the top gas to be guided through the primary circuit 210. The treatment device 226 also comprises a device (not shown in detail) for separating water and dust / particulate matter from the portion of the top gas to be guided through the primary circuit 210. The treatment device 226 also comprises a heat exchanger (not shown in detail) for heat exchange between the top gas and the reducing gas flowing through the gas line 207. A separate heater 227 is also provided for heating the reducing gas in the first gas line 207, i.e., for heating the reducing gas coming from the reducing gas source 206 and / or reducing gas container 209 and the primary circuit 210.

Claims

1. A process for producing sponge iron from iron ore, - A process of directly loading iron ore into the reduction shaft (201), - A step of introducing a hydrogen-rich reducing gas into the direct reduction shaft (201) from a reducing gas source (206) via a first gas line in order to reduce the iron ore and produce sponge iron, - A step of extracting top gas from the direct reduction shaft (201), wherein the top gas contains unreacted hydrogen gas, - A step of guiding at least a portion of the extracted furnace top gas into the primary circuit (210), and reintroducing the portion of the furnace top gas into the direct reduction shaft (201), - The primary circuit (210) is connected to a second outlet at one end and to a first gas line at the other end, and the process involves taking out a portion of the gas guided into the primary circuit (210) from the primary circuit (210) and guiding the gas portion through the secondary circuit (211) to the reducing gas container (209), - A step of guiding the reducing gas from the reducing gas source (206) to the reducing gas container (209) and forming a gas mixture in the reducing gas container (209) together with the gas from the secondary circuit (211), - The process includes the step of guiding the gas mixture from the reducing gas container (209) to the first gas line (207), and correspondingly reducing the flow rate of the reducing gas from the reducing gas source (206) to the first gas line (207), - The gas delivered via the secondary circuit (211) and the reducing gas delivered from the reducing gas source (206) to the reducing gas container (209) are compressed in a compressor step before entering the reducing gas container (209). process.

2. The process according to claim 1, further comprising the step of guiding the gas mixture from the reducing gas container (209) to the first gas line (207) in response to the gas pressure in the reducing gas container (209) exceeding a predetermined level.

3. The process according to claim 1 or 2, wherein the reducing gas source (206) comprises an electrolytic cell driven by power associated with fluctuating access-related parameters, and the process includes the steps of continuously registering fluctuations in the access-related parameters and guiding the gas mixture from the reducing gas container (209) to the gas line in response to the access-related parameters falling below a predetermined first level.

4. The process according to claim 3, wherein the access-related parameters include either the level of electricity stored in the power storage unit, or the access level of means for generating the electricity, such as solar power, wind power, or hydropower.

5. The process according to claim 1 or 2, wherein the reducing gas source (206) comprises an electrolytic cell driven by power provided via a public electrical network, and the process includes the step of guiding the gas mixture from the reducing gas container (209) to the first gas line (207) in response to the load on the public network exceeding a predetermined level.

6. The process according to claim 3, wherein, in response to the access-related parameter exceeding a predetermined second level, a reducing gas is guided from the reducing gas source (206) to the reducing gas container (209).

7. The process according to claim 1 or 2, wherein the extraction of the gas portion from the primary circuit (210) to the secondary circuit (211) is performed in response to the pressure in the primary circuit (210) exceeding a predetermined level.

8. A system for producing sponge iron, - Direct reduction shaft (201), A first inlet (202) for introducing iron ore into the shaft (201), A first outlet (203) for removing the sponge iron from the shaft (201), A second inlet (204) for introducing reducing gas into the shaft (201), and A direct reduction shaft (201) is provided with a second outlet (205) for extracting top gas from the shaft (201), - A reducing gas source (206) connected to the reducing gas inlet (204) via the first gas line (207), - Reducing gas container (209), - A primary circuit (210) for guiding at least a portion of the furnace top gas, the primary circuit (210) is connected at one end to the second outlet (205) and at the other end to the first gas line (207), - A secondary circuit (211) for guiding at least a portion of the gas extracted from the gas guided through the primary circuit (210), the secondary circuit (211) being connected to the primary circuit (210) at one end and to the reducing gas container (209) at the other end, - A second gas line (212) connecting the reducing gas source (206) to the reducing gas container (209), - A third gas line (213) that connects the reducing gas container (209) to the first gas line (207), - A control unit (214) configured to control the flow of reducing gas from the reducing gas source (206) to the first gas line (207), and to control the flow of reducing gas from the reducing gas container (209) to the first gas line (207) through the third gas line (213), wherein the control unit (214) is configured to allow the flow of reducing gas from the reducing gas container (209) to the first gas line (207) while correspondingly reducing the flow rate of reducing gas from the reducing gas source (206) to the first gas line (207), The system includes a compressor arrangement (220) for compressing the gas portion delivered via the secondary circuit (211) and the reducing gas delivered from the reducing gas source (206) through the second gas line (212) before entering the reducing gas container (209), system.

9. The system according to claim 8, further comprising means (214, 215, 220, 225) for enabling the flow of reducing gas from the reducing gas container (209) to the first gas line (207) in response to the gas pressure in the reducing gas container (209) exceeding a predetermined level.

10. The system according to claim 8 or 9, wherein the reducing gas source (206) comprises an electrolytic cell driven by power associated with fluctuating access-related parameters, the system comprises means for continuously registering fluctuations of the access-related parameters, and the control unit (214) is configured to enable the flow of reducing gas from the reducing gas container (209) to the first gas line (207) in response to the access-related parameters falling below a predetermined first level.

11. The system according to claim 10, wherein the access-related parameters include either the level of electricity stored in the power storage unit, or the access level of means for generating the electricity, such as solar power, wind power, or hydropower.

12. The system according to claim 8 or 9, wherein the reducing gas source (206) comprises an electrolytic cell driven by power provided via a public electricity network, the system comprises means for registering the load on the public electricity network, and the control unit (214) is configured to enable the flow of a gas mixture from the reducing gas container (209) to the gas line in response to the load on the public network exceeding a predetermined level.

13. The system according to claim 8 or 9, wherein the control unit (214) is configured to reduce the output of the reducing gas source (206) in response to enabling a reducing gas flow from the reducing gas container (209) to the first gas line (207), provided that the required reducing gas flow in the first gas line (207) is realized.

14. The system according to claim 11, wherein the control unit (214) is configured to enable the flow of reducing gas from the reducing gas source (206) to the reducing gas container (209) in response to the access-related parameter exceeding a predetermined second level.

15. The system according to claim 8 or 9, wherein the system comprises means configured to enable the extraction of the gas portion from the primary circuit (210) to the secondary circuit (211) in response to the pressure in the primary circuit (210) exceeding a predetermined level.

16. The system according to claim 8 or 9, comprising at least one first sensor (222) for measuring the flow rate of reducing gas in the first gas line (207), at least one second sensor (223) for measuring the temperature in the direct reduction shaft (201), and at least one third sensor (218) for measuring a pressure indicating the pressure in the direct reduction shaft (201), wherein the control unit (214) is configured to determine the required flow rate of reducing gas into the direct reduction shaft (201) in the first gas line (207) based on inputs received from the first sensor (222), the second sensor (223), and the third sensor (218).

17. The system according to claim 8 or 9, wherein the direct reduction shaft (201) has a nominal rate of production of sponge iron per hour, and the storage capacity of the reduction gas container (209) corresponds to the amount of hydrogen gas required to enable reduction at the nominal rate of production for at least one hour.

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