Hydrogen gas recycling in direct reduction processes
The hydrogen recycling system addresses inefficiencies in direct reduction processes by recycling unreacted hydrogen gas, enhancing energy efficiency and reducing environmental emissions in sponge iron production.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- ハイブリット ディベロップメント アーベー
- Filing Date
- 2022-06-20
- Publication Date
- 2026-07-07
AI Technical Summary
The challenge of producing sponge iron using hydrogen as a reducing agent in direct reduction processes is the inefficient recycling of unreacted hydrogen gas, leading to energy inefficiency and environmental hazards such as NOx emissions from flaring.
A process and system for recycling unreacted hydrogen gas from the reduction shaft by conducting it through a secondary circuit, mixing it with the reducing gas, and controlling pressure to prevent flaring, thereby reducing operating costs and environmental impact.
The system effectively recycles hydrogen gas, reducing energy consumption and minimizing NOx emissions, while maintaining efficient production of sponge iron.
Smart Images
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Abstract
Description
Technical Field
[0001] Technical Field 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] Background Art Steel is the world's most important civil engineering material. It is difficult to find any object in the modern world that does not contain steel or does not depend on steel for its manufacture and / or transportation. Thus, steel is intricately involved in almost all aspects of our modern life.
[0003] In 2018, the worldwide production of crude steel was 1,810,000,000 tons, far exceeding any other metal. It is expected to reach 2,800,000,000 tons by 2050, with 50% of that expected to be derived from virgin iron sources. Steel is also the world's most recycled material with a very high recycling grade due to its performance as a metal that can be used many times after remelting using electricity as a primary energy source.
[0004] Thus, steel is the cornerstone of modern society that will play an even greater role in the future.
[0005] Steel is mainly produced via three routes, namely i) Integrated production using virgin 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 blowing oxygen into a basic oxygen furnace (BOF) and then refining to produce steel. This process is also commonly referred to as "oxygen steelmaking". ii) The creation of a scrap base using recycled steel, which is melted in an electric arc furnace (EAF) that uses electricity as the primary energy source. This process is also commonly known as "electric steelmaking." iii) Direct reduction production based on virgin iron ore, where virgin iron ore is reduced in a direct reduction (DR) process with carbonaceous reduction gas to produce sponge iron. The sponge iron is then melted together with scrap in an EAF to produce steel.
[0006] The term crude iron is used herein to refer to all iron produced for further processing into steel, whether obtained from a blast furnace (i.e., pig iron) or a direct reduction shaft (i.e., spongy iron).
[0007] The processes mentioned above have been refined over decades and are approaching theoretically the lowest energy consumption, but one fundamental challenge remains unresolved: the reduction of iron ore using carbonaceous reducing agents generates CO2 as a byproduct. In 2018, an average of 1.83 tons of CO2 were generated per ton of steel produced. The steel industry is one of the largest emitters of CO2, accounting for about 7% of global CO2 emissions. Excessive CO2 emissions are unavoidable in the steelmaking process as long as carbonaceous reducing agents are used.
[0008] The HYBRIT initiative was established to address this challenge. HYBRIT (Hydrogen Breakthrough Ironmaking Technology), a groundbreaking hydrogen-based ironmaking technology, is a joint venture between SSAB, LKAB, and Vattenfall, with partial funding from the Swedish Energy Agency, aiming to reduce CO2 emissions and decarbonize the steel industry.
[0009] The core concept of HYBRIT is the production of spongy iron through the direct reduction of virgin iron ore. However, instead of using carbonaceous reductant gases such as natural gas, as in current commercial direct reduction processes, HYBRIT proposes using hydrogen gas as the reducing agent, a process called hydrogen direct reduction (H-DR). Hydrogen gas can be produced by the electrolysis of water, primarily using fossil-free and / or renewable primary energy sources, as in the case of electricity production in Sweden. Thus, the crucial step of reducing the iron ore can be achieved without the need for fossil fuel input and with water as a byproduct instead of CO2.
[0010] Prior art uses reducing gas, which is mostly composed of natural gas. Direct reduction plants typically include a shaft in which reduction occurs. 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 the reducing gas into the shaft, and at least one outlet at the top of the shaft for the outlet of the top gas. The majority of the top gas consists of unreacted reducing gas and is probably mixed with an inert gas used to seal the inlets and outlets for the iron ore pellets and sponge iron, respectively. The conventional method of handling the top gas is flaring of the latter.
[0011] However, when hydrogen is used primarily, or exclusively, as the reducing gas, flaring 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 contains nitrogen gas (usually used as a sealing gas), flaring can lead to NO reduction. X It also releases these substances, which is undesirable from an environmental standpoint. [Overview of the Initiative] [Problems that the invention aims to solve]
[0012] Therefore, one object of the present invention is to present a process and system for the direct reduction of iron ore into sponge iron, which uses hydrogen gas primarily or exclusively as the reducing gas, and to provide a means for efficiently recycling unreacted hydrogen gas that exits directly from the reduction shaft as part of the furnace top gas. [Means for solving the problem]
[0013] Summary of the Invention The object of the present invention is achieved by a process for producing sponge iron from iron ore, and the process is The steps include loading iron ore directly into the reduction shaft, The steps include: reducing iron ore and producing sponge iron by directly introducing hydrogen-rich reducing gas from a reducing gas source into the reducing shaft; A step of removing top gas from a direct reduction shaft, wherein the top gas contains unreacted hydrogen gas, The steps include: conducting at least a portion of the removed top furnace gas into a primary circuit; mixing the portion with the reducing gas from the reducing gas source at a point downstream of a first compressor provided in a gas line leading directly from the reducing gas source to the reducing shaft; and introducing the mixture directly into the reducing shaft. The process includes the steps of removing a portion of the gas that has been conducted into the primary circuit, conducting the portion of the gas through the secondary circuit while reducing the pressure of the portion of the gas, and mixing the portion of the gas with the reducing gas from the reducing gas source at a point in the gas line upstream of the first compressor.
[0014] The removal of some of the gas into the secondary circuit is typically done in response to the pressure in the primary circuit exceeding a predetermined level. Instead of hydrogen being lost or wasted, for example, as heating fuel, most of the bled-off hydrogen is recovered and reused as a reducing gas. This reduces the operating cost of such a process. Furthermore, since most of the bled-off hydrogen no longer burns, excess NO is eliminated.X The risk of release is significantly reduced or completely avoided. In other words, the secondary circuit can control the pressure in the primary circuit without flaring the system with excess top gas containing high levels of hydrogen gas. The secondary circuit acts as a buffer, making it possible to reduce the amount of reducing gas introduced from the reducing gas source into the gas line. According to one embodiment, under dry conditions, the reducing gas introduced directly into the reduction shaft contains more than 70 vol% hydrogen. According to one embodiment, the reducing gas introduced into the shaft contains more than 80 vol% hydrogen, and according to another embodiment, the reducing gas contains more than 90 vol% hydrogen.
[0015] If the amount of top gas increases during operation, thereby increasing the pressure in the primary circuit, the excess hydrogen gas in the primary circuit is removed into the secondary circuit. Accordingly, the pressure in the primary circuit is controlled so as not to be too high relative to the pressure downstream of the first compressor. The excess hydrogen gas in the primary circuit is thus returned by being conducted through the secondary circuit to the reduction gas line, thus preventing exhaustion or flaring of the excess hydrogen gas in the primary circuit. The reduction of the pressure in the secondary circuit is preferably achieved using appropriate valves such as expansion valves or pressure reducing valves. If a pressure reducing valve is applied, power is preferably generated from the movement of the pressure reducing valve and is preferably used to generate hydrogen gas.
[0016] According to one embodiment, the first compressor is the final compressor stage in the gas line, and it brings the pressure of the reducing gas from the reducing gas source in the gas line to its final pressure before it directly enters the reducing shaft.
[0017] According to one embodiment, the gas flow rate through the gas line and into the direct reduction shaft is measured, and the reducing gas flow from the reducing gas source into the gas line is controlled based on the gas flow rate measured in the gas line. The total flow rate of reducing gas through the gas line and into the direct reduction shaft depends on the amount of iron ore introduced into and present in the shaft. If the reducing gas flow rate is too low, complete reduction of the iron ore in the direct reduction shaft is not achieved, and the temperature inside the shaft decreases. If the flow rate is too high, excess pressure appears inside the direct reduction shaft. According to one embodiment, the temperature inside the shaft is measured, and the direct reducing gas flow rate entering the shaft (including gas from the primary circuit, secondary circuit, and reducing gas source) is controlled based on it. According to one embodiment, the pressure inside the direct reduction shaft or in the primary circuit is measured, and the reducing gas flow rate entering the direct reduction shaft is controlled based on it. According to one embodiment, the reducing gas source includes at least one electrolytic device for generating hydrogen gas. According to one embodiment, the output of the electrolytic device is controlled as a means for controlling the reducing gas flow rate based on the temperature and pressure inside the direct reduction shaft.
[0018] According to one embodiment, the removal of a portion of the gas entering the secondary circuit from the primary circuit depends on the gas pressure in the primary circuit.
[0019] According to one embodiment, the process further includes the steps of measuring the gas pressure in a primary circuit and, in response to the measured pressure being above a predetermined first level, conducting the portion of the gas from the primary circuit into a secondary circuit. A pressure sensor, a controllable valve, and a control unit for controlling the controllable valve based on information from the pressure sensor are thus used. In an alternative embodiment, a relief valve is used to bleed off the portion of the furnace top gas into the secondary circuit in response to the pressure in the primary circuit exceeding a predetermined first level. A permanent bleed-off of the furnace top gas into the secondary circuit may be provided, independent of the pressure in the primary circuit.
[0020] According to one embodiment, the pressure in the primary circuit is adjusted by removing said part of the gas to the secondary circuit so as not to exceed the predetermined first level. As soon as the pressure level reaches the predetermined level, the control valve that controls the gas flow from the primary circuit into the secondary circuit by that amount is opened so that the pressure in the primary circuit does not rise further.
[0021] According to one embodiment, the primary circuit includes a second compressor provided downstream of a point along the primary circuit where said part of the gas is removed to the secondary circuit, and said measurement of the gas pressure is made upstream of the second compressor. The second compressor is necessary to increase the gas pressure to a level exceeding the level downstream of the first compressor so that the gas in the primary circuit can flow into the gas line and mix with the reducing gas in the gas line.
[0022] According to one embodiment, the gas pressure in the secondary circuit is reduced to a predetermined second level that exceeds the gas pressure level in the gas line upstream of the first compressor. The predetermined second level should be slightly higher than the pressure in the gas line upstream of the first compressor. An expansion valve or a pressure reducing valve may be used to reduce the pressure in the secondary circuit. According to one embodiment, said means is a pressure reducing valve, and the pressure reducing valve includes a turbine and means for converting the generated motion of the turbine into electric power. A vent valve may be provided in the secondary circuit for further need to reduce the pressure in the secondary circuit. According to one embodiment, such a vent valve is provided upstream of the expansion valve or the pressure reducing valve used to reduce the pressure, and upstream of the control valve that controls the gas flow from the primary circuit into the secondary circuit. The vent valve may be a relief valve or an operable valve controlled by a control unit.
[0023] According to one embodiment, the top gas undergoes a gas treatment step at a point along the first primary circuit between the point where the top gas is removed directly from the direct reduction shaft and the point where said part of the gas is conducted into the secondary circuit.
[0024] According to one embodiment, the processing step includes separating an inert gas from a part of the top gas conducted through the primary circuit. The separation unit used for separation may be a cryogenic separation unit, a membrane separation unit, a pressure swing adsorption unit, or an amine CO2 scrubber. A number of well-established gas separation means may be suitable for separating hydrogen from an inert gas (e.g., nitrogen and / or carbon dioxide). For example, cryogenic separation may be appropriate due to the large difference in boiling points between nitrogen (-195.8 °C) and hydrogen (-252.9 °C).
[0025] According to one embodiment, the processing step includes separating water from a part of the top gas conducted through the primary circuit. Preferably, the processing step also includes removing dust from the top gas.
[0026] According to one embodiment, the processing step includes reducing the temperature of the top gas in a heat exchanger and using the heat from the top gas to heat another gas used in the process.
[0027] According to one embodiment, the other gas is a reducing gas introduced directly into the direct reduction shaft through the gas line.
[0028] The object of the present invention is also achieved using a system for producing sponge iron, the system comprising 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, a second outlet for removing top gas from the shaft, and a direct reduction shaft, a reducing gas source connected to the reducing gas inlet through a gas line, a first compressor provided in the gas line, A primary circuit for conducting at least a portion of the top gas of the furnace, the primary circuit being connected at one end to a second outlet and at the other end to the gas line downstream of the first compressor, A secondary circuit for conducting at least a portion of the gas removed from the gas conducted through the primary circuit, wherein the secondary circuit is connected at one end to the primary circuit and at the other end to the gas line upstream of the first compressor, and includes means therein for reducing the pressure of the portion of the gas conducted through the secondary circuit, It includes a first valve for controlling the flow of the portion of the gas entering the secondary circuit.
[0029] According to one embodiment, the means for reducing pressure includes an expansion valve or a pressure reducing valve. According to one embodiment, the means is a pressure reducing valve, which includes a turbine and means for converting the motion generated by the turbine into electricity.
[0030] According to one embodiment, the system includes a control device for controlling the flow of reducing gas from a reducing gas source into the gas line based on the gas flow rate in the gas line. The measured gas flow rate in the gas line is the sum of the reducing gas from the reducing gas source (which may also be called makeup gas) and the gas added to it from the primary and secondary circuits. Thus, the measurement may consist of a single measurement downstream of the point where the primary circuit is connected to the gas line, or a combination of gas flow measurements in the gas line, primary circuit, and secondary circuit.
[0031] According to one embodiment, the control device includes a second valve for controlling the flow of reducing gas from a reducing gas source into a gas line, a gas flow meter for measuring the gas flow through the gas line, and a control unit configured to control the second valve based on input from the gas flow meter.
[0032] According to one embodiment, the first valve is configured to open in response to the gas pressure in the primary circuit exceeding a predetermined level, in order to allow gas to pass into the secondary circuit.
[0033] According to one embodiment, the first valve is a controllable valve, and the system further includes a pressure sensor located in a primary circuit, and a control unit configured to control the controllable first valve based on inputs received from the pressure sensor.
[0034] According to one embodiment, the primary circuit includes a second compressor provided downstream of a point along the primary circuit, to which the secondary circuit is connected, and a pressure sensor is located upstream of the second compressor.
[0035] According to one embodiment, the primary circuit includes a device for processing the furnace top gas, the device including a device for separating an inert gas from the portion of the furnace top gas conducted through the primary circuit.
[0036] According to one embodiment, the primary circuit includes a device for processing the top gas, the device including a device for separating water from the portion of the top gas conducted through the primary circuit. The device for processing the top gas preferably also includes a device for removing the top gas from the top gas.
[0037] According to one embodiment, the primary circuit includes a device for processing the top gas of the furnace, the device including a heat exchanger.
[0038] According to one embodiment, the heat exchanger is also connected to the gas line and configured to transfer heat from the top gas of the furnace to the reducing gas that is directly introduced into the reduction shaft.
[0039] According to one embodiment, the reducing gas source includes a water electrolysis unit.
[0040] Further objectives, advantages, and novel features of the present invention will become apparent to those skilled in the art from the following detailed description.
[0041] Brief explanation of the drawing To fully understand the present invention and its further objectives and advantages, the details presented below should be read in conjunction with the accompanying drawings, and the same reference numerals indicate similar items in various figures. [Brief explanation of the drawing]
[0042] [Figure 1] This outlines the iron ore-based steelmaking value chain based on the HYBRIT concept. [Figure 2] As disclosed herein, exemplary embodiments of systems suitable for performing the process are schematically illustrated. [Modes for carrying out the invention]
[0043] Detailed explanation definition The reducing gas is a gas capable of reducing iron ore to metallic iron. While the reducing components in conventional direct reduction processes are typically hydrogen and carbon monoxide, in the process of this disclosure, the reducing component is primarily or exclusively hydrogen. The reducing gas is introduced at a point below the iron ore inlet of the direct reduction shaft and flows upward opposite the moving layer of iron ore to reduce the iron ore.
[0044] The top gas is a process gas removed directly from the upper end of the reduction shaft near the iron ore inlet. The top gas typically consists of a mixture of spent reducing gas, including oxidation products of reducing components (e.g., H2O), and an inert component introduced into the process gas, such as Sealgal. After processing, the top gas may be recycled by returning it directly to the reduction shaft as a component of the reducing gas.
[0045] To prevent the accumulation of inert components in the carburization process gas, the bleed-off flow removed from the spent carburized gas is called the carburizing bleed-off flow.
[0046] The gas from the reducing gas source is sometimes called the makeup gas. In the context of this application, the makeup gas is added to the recycled top gas before being directly reintroduced into the reducing shaft. Thus, the reducing gas typically includes the makeup gas along with the recycled top gas.
[0047] The sealing gas is the gas that enters the direct reduction (DR) shaft directly from the ore packing unit at the inlet of the direct reduction shaft. The outlet end of the direct reduction shaft may also be sealed with the sealing gas, and therefore the sealing gas may enter the DR shaft from the discharge unit 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 potentially form flammable or explosive mixtures with either air or process gas, i.e., a gas that may not act as an oxidizer or fuel in combustion reactions under conditions common in the process. The sealing gas may basically consist of nitrogen and / or carbon dioxide. Although carbon dioxide is referred to as an inert gas herein, it should be noted that under conditions common in the system, it may react with hydrogen in a water-gas shift reaction to provide carbon monoxide and water vapor.
[0048] reduction A direct reduction shaft may consist of any type commonly known in the art. A shaft refers to a solid-gas countercurrent moving bed reactor, through which the iron ore charge is introduced at an inlet at the top of the reactor and descends by gravity toward an outlet located at the bottom of the reactor. A reducing gas is introduced below the reactor inlet and flows upward opposite the moving bed of ore to reduce the ore to metallized iron. Reduction typically takes place at temperatures of about 900°C to about 1100°C. The desired temperature is maintained by preheating the process gas, typically introduced into the reactor, using a preheater, such as an electric preheater. Further heating of the gas may be achieved after it has left the preheater and before it is introduced into the reactor by exothermic partial oxidation of the gas by oxygen or air. Reduction may take place in the DR shaft at a pressure 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 located at the bottom so that the sponge iron can be cooled before it is discharged from the outlet.
[0049] The iron ore charge typically consists mainly of iron ore pellets, although some chunks of iron ore may also be introduced. The iron ore pellets typically contain most hematite, along with further additives or impurities, such as gangue, flux, and binders. However, the pellets may also contain some other metals and other ores, such as magnetite. Iron ore pellets designated for direct reduction processes are commercially available, and such pellets may be used in this process. Alternatively, pellets may be specifically adapted for hydrogen-rich reduction steps, as in this process.
[0050] The reducing gas is hydrogen-rich. The reducing gas refers to the sum of the fresh makeup gas and the recycled portion of the top gas introduced directly into the reduction shaft. Hydrogen-rich means that the reducing gas entering the reduction shaft directly may consist of more than 70 vol% hydrogen gas, for example, more than 80 vol% hydrogen gas, or more than 90 vol% hydrogen gas (vol%) determined at standard conditions of 1 atm and 0°C. Preferably, reduction is carried out as a separate step. That is, carburizing is not performed at all, or if carburizing is performed, it is performed separately from reduction, i.e., in a separate reactor or in a separate, distinct region of the direct reduction shaft. This greatly simplifies the treatment of the top gas by avoiding the need to remove carbonaceous components and the expenses associated with such removal. In such cases, the makeup gas may consist of essentially hydrogen gas or solely hydrogen gas. Note that even if the makeup gas is exclusively hydrogen, some amount of carbon-containing gas may be present in the reducing gas. For example, if the outlet of the sponge iron in a direct reduction shaft is connected to the inlet of a carburizing reactor, a relatively small amount of carbon-containing gas may unintentionally permeate from the carburizing reactor into the direct reduction shaft. Another example is that carbon salts present in iron ore pellets may volatilize and appear as CO2 in the top gas of the DR shaft, and a large amount of CO2 may be recycled back into the DR shaft. Due to the overwhelming presence of hydrogen gas in the reduction gas circuit, any CO2 present may be converted to CO by a reverse water-gas shift reaction.
[0051] In some cases, it is desirable to achieve some degree of carburization in conjunction with reduction as a single step. In such cases, the reducing gas may contain up to approximately 30 vol% carbon-containing gas, for example, up to approximately 20 vol%, or up to approximately 10 vol% (determined under standard conditions of 1 atm and 0°C). Suitable carbon-containing gases are disclosed below as carburizing gases.
[0052] Hydrogen gas may preferably be obtained in part by electrolysis of water. The electrolysis of water is carried out using renewable energy, which then provides a reducing gas from a renewable source. The electrolyzed hydrogen may be transported directly from the electrolyzer to the DR shaft by a conduit, or the hydrogen may be stored at the time of production and transported to the DR shaft as needed.
[0053] When the top gas exits directly from the reduction shaft, it typically contains unreacted hydrogen, water (an oxidation product of hydrogen), and an inert gas. If carburizing is performed along with reduction, the top gas may also contain some carbonaceous components, such as methane, carbon monoxide, and carbon dioxide. When the top gas exits directly from the reduction shaft, it may first undergo dedusting to remove any impurities, and / or heat exchange to cool the top gas and heat the reducing gas. During heat exchange, water may be concentrated from the top gas. Preferably, the top gas at this stage consists essentially of hydrogen, an inert gas, and residual water. However, if carbonaceous components are present in the top gas, such carbonaceous components may also be removed from the top gas, for example, by reforming and / or CO2 absorption.
[0054] Sponge Iron The sponge iron product of the processes described herein is typically called direct reduced iron (DRI). Depending on the process parameters, it may be supplied as high-temperature (HDRI) or low-temperature (CDRI). Low-temperature DRI is sometimes also known as type (B) DRI. DRI may be prone to re-oxidation and, in some cases, spontaneously combustible. However, there are numerous known means of passivating DRI. One such passivation method commonly used to facilitate the overseas transport of the product is to press high-temperature DRI into a briquette. Such briquettes are commonly called hot briquetted iron (HBI) and are sometimes also known as type (A) DRI.
[0055] The sponge iron products obtained by the processes described herein may be essentially fully metallized sponge iron, i.e., sponge iron having a degree of reduction (DoR) greater than about 90%, for example, greater than about 94%, or greater than about 96%. The degree of reduction 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. Due to reaction kinetics, obtaining sponge iron with a DoR greater than about 96% is often commercially undesirable, but such sponge iron may be produced if necessary.
[0056] If carburizing is performed, sponge iron having any desired carbon content may be produced by the process described herein in an amount of about 0 to about 7 wt%. However, for further processing, it is typically desirable for the sponge iron to have a carbon content of about 0.5 to about 5 wt%, preferably about 1 to about 4 wt%, for example, about 3 wt%, although this may depend on the ratio of sponge iron to scrap used in the next EAF processing step.
[0057] 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, the drawings should not be considered to be drawn to a fixed scale, as some features may be exaggerated to more clearly illustrate certain features.
[0058] Figure 1 schematically illustrates an iron ore-based steelmaking value chain according to the HYBRIT concept. The iron ore-based steelmaking value chain begins at an iron ore mine 101. After mining, the iron ore 103 is concentrated and processed at a pellet manufacturing plant 105 to produce iron ore pellets 107. These pellets, along with any lump ore used in the process, are converted to spongy iron 109 by reduction in a direct reduction shaft 111, using hydrogen gas 115 as the primary reducing agent and producing water 117a as the primary byproduct. The spongy iron 109 may optionally be carburized either in the direct reduction shaft 111 or in a separate carburizing reactor (not shown). The hydrogen gas 115 is produced by the electrolysis of water 117b in an electrolytic unit 119, preferably using electricity 121 drawn mainly from fossil-free or renewable resources 122. The hydrogen gas 115 may be stored in a hydrogen reservoir 120 before being introduced into the direct reduction shaft 111. Sponge iron 109 is melted using an electric arc furnace 123, along with a certain percentage of optionally selected scrap iron 125 or other iron sources, to produce a molten metal 127. The molten metal 127 then undergoes a further downstream secondary metallurgical process 129 to produce steel 131. The entire value chain from ore to steel is intended to be fossil-free and have minimal or zero carbon emissions.
[0059] Figure 2 schematically illustrates an exemplary embodiment of a system suitable for performing the process as disclosed herein.
[0060] 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 spongy iron from the DR shaft. The DR shaft 201 further includes a number 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 204, but for simplicity, only one is shown in the figure.
[0061] The system further includes a reducing gas source 206 connected to a reducing gas inlet 204 via a gas line 207. The reducing gas source 206 may include a hydrogen production unit, typically a water electrolysis unit. The reducing gas from the reducing gas source may therefore consist almost entirely of hydrogen gas. The reducing gas from the reducing gas source 206 has a relatively low pressure of about 1.25 bar and needs to be compressed before being introduced into the DR shaft 201. The pressure in the DR shaft will be in the range of 8 to 10 bar during the operation of the DR shaft. The system therefore further includes a first compressor 208 provided in the gas line 207, configured to increase the pressure of the reducing gas to about 8 bar. For simplicity, only one compressor 208 is shown in the drawing. However, it should be understood that the compressor may consist of multiple compressors in a row if it is deemed advantageous.
[0062] The system further includes a primary circuit 209 for conducting at least a portion of the furnace top gas through it. The primary circuit 209 is connected at one end to a second gas outlet 205 and at the other end to the gas line 207 downstream of the first compressor 208.
[0063] A secondary circuit 210 is also provided for conducting at least a portion of the gas removed from the gas conducted through the primary circuit 209. The secondary circuit 210 is connected at one end to the primary circuit 209 and at the other end to the gas line 207 upstream of the first compressor 208. The secondary circuit 210 further includes means 211 for reducing the pressure of the portion of the gas conducted through the secondary circuit 210, and a first valve 212 for controlling the flow of the portion of the gas entering the secondary circuit 210. In the shown embodiment, means 211 for reducing the pressure in the secondary circuit 210 includes a pressure reducing valve, from which energy is transferred from the gas to motion and further to power, which may be recycled in the system for purposes such as operating an electrolytic device in the hydrogen gas source 206. A vent valve 221 is also provided in the secondary circuit 210, which is preferably a relief valve used to vent gas in emergency situations, for example, when the pressure reducing valve has stopped functioning and there is a rise in pressure in the secondary circuit 210. Further controllable valves (not shown) may also be provided to control the venting of the secondary circuit 210.
[0064] The secondary circuit 210 enables control of the pressure in the primary circuit 209 without flaring the excess top gas containing high-value hydrogen gas from the system. The secondary circuit 210 also functions as a buffer, reducing the amount of reducing gas supplied from the reducing gas source into the gas line 207.
[0065] The system further includes a control device for controlling the flow of reducing gas from the reducing gas source into the gas line 207. If the reducing gas source 206 includes a hydrohydrylic electrolyzer, such a control system includes a control unit 215 configured to control the output of the hydrohydrylic electrolyzer. If the reducing gas source 206 includes a hydrogen gas storage or a hydrogen gas pipeline from which hydrogen gas is drawn, the control device includes a second valve 213 for controlling the flow of reducing gas from the reducing gas source 206 into the gas line 207. In either case, the system should include a gas flow meter 214 for measuring the gas flow through the gas line 207, and a control unit 215 configured to control the hydrohydrylic electrolyzer or to control the second valve 213 based on input from the gas flow meter 214. The gas flow meter 214 is located downstream of the point where the primary circuit 209 connects to the gas line 207. If control is performed only to control the output of the hydrohydrylic electrolyzer, the second valve 213 may be omitted.
[0066] The control device also includes a temperature sensor 216 for measuring the temperature indicating the temperature inside or outside the DR shaft 201. The temperature inside the DR shaft indicates how the reduction of the iron ore is progressing. Accordingly, incomplete reduction due to the absence of reducing gas will cause the temperature inside the DR shaft to drop, thereby revealing such a deficiency, which is then used as input to the control unit 215. Based on the temperature input, the control unit 215 is configured to control the gas flow rate thus entering the gas line 207 from the hydrogen gas source, and to increase the flow rate in response to temperatures below a predetermined level.
[0067] The temperature sensor 216 may be located inside the DR shaft, or for example, inside the gas outlet 205, in which case it can be inferred that the top gas coming out of the DR shaft has a temperature that indicates the temperature inside the DR shaft 201.
[0068] The first valve 212 is a controllable valve, and the system further includes a pressure sensor 217 located in the primary circuit 209. A control unit 215 is configured to control the controllable first valve 212 based on input received from the pressure sensor 217. The primary circuit 209 includes a second compressor 218 provided at a point along the primary circuit 209, to which a secondary circuit 210 is connected, and the pressure sensor 217 is located upstream of the second compressor 218. The control unit 215 is configured to open the first valve 212 in response to the pressure in the primary circuit 209 exceeding a predetermined level. Alternatively, the first valve may be a relief valve set to open automatically when the pressure in the primary circuit 209 exceeds the predetermined level. The means 211 for reducing the gas pressure in the secondary circuit is designed to reduce the pressure to a level slightly above the gas pressure in the gas line 207 upstream of the first compressor 208, for example, to a pressure of about 1.5 bar.
[0069] The primary circuit 209 further includes a device 219 for processing the top gas, the device 219 including a device (not shown in detail) for separating inert gas from a portion of the top gas conducted through the primary circuit 209. The processing device 219 also includes a device (not shown in detail) for separating water and dust from the portion of the top gas conducted through the primary circuit 209. The processing device 219 also includes a heat exchanger (not shown in detail) for heat exchange between the top gas and the reducing gas flowing through the gas line 207. One or more separate heaters 220 for heating the reducing gas in the gas line 207 may also be provided.
[0070] Referring to Figure 2, the system described above can recycle hydrogen gas instead of flaring it when the pressure rises in the primary circuit. The control unit 215 is configured to control the flow of reducing gas from the reducing gas source 206 into the gas line 207 based on input from the disclosed sensors. If the reducing gas source 206 is a water electrolyzer, the control unit 215 may be configured to control the output of the electrolyzer based on input from the sensors and to effectively take advantage of the benefits of recycling the reducing gas through the secondary circuit 210.
Claims
1. A process for producing sponge iron from iron ore, The steps include loading iron ore directly into the reduction shaft (201), The steps include: reducing the iron ore and producing sponge iron by introducing hydrogen-rich reducing gas from a reducing gas source (206) into the direct reducing shaft (201); A step of removing top gas from the direct reduction shaft (201), wherein the top gas includes unreacted hydrogen gas, The steps include: conducting at least a portion of the removed top gas into the primary circuit (209); mixing the portion with the reducing gas from the reducing gas source (206) at a point downstream of the first compressor (208) provided in the gas line (207) leading from the reducing gas source (206) to the direct reduction shaft (201); and introducing the mixture into the direct reduction shaft (201). The steps include removing a portion of the gas that has been conducted into the primary circuit (209), conducting the portion of the gas through the secondary circuit (210), reducing the pressure of the portion of the gas, and mixing the reducing gas from the reducing gas source (206) with the portion of the gas at a point in the gas line (207) upstream of the first compressor (208). A process comprising the steps of measuring the gas pressure in the primary circuit (209), and, in response to the measured pressure being above a predetermined first level, conducting the portion of the gas from the primary circuit (209) into the secondary circuit (210).
2. The process according to claim 1, wherein the gas flow rate through the gas line (207) into the direct reduction shaft (201) is measured, and the reducing gas flow from the reducing gas source (206) into the gas line (207) is controlled based on the gas flow rate measured in the gas line (207).
3. The process according to claim 1 or 2, wherein the pressure in the primary circuit (209) is regulated by removing a portion of the gas into the secondary circuit (210) so as not to exceed the predetermined first level.
4. The process according to claim 1 or 2, wherein the primary circuit (209) includes a second compressor (218) provided downstream of a point along the primary circuit (209) from which the portion of the gas is removed to the secondary circuit (210), and the measurement of the gas pressure is performed upstream of the second compressor (218).
5. The process according to claim 1 or 2, wherein the gas pressure in the secondary circuit (210) is reduced to a predetermined second level that exceeds the gas pressure level in the gas line (207) upstream of the first compressor (208).
6. The process according to claim 1 or 2, wherein the furnace top gas undergoes a gas treatment step at a point along the primary circuit (209) between the point where the furnace top gas is removed from the direct reduction shaft (201) and the point where a portion of the gas is conducted into the secondary circuit (210).
7. The process according to claim 6, wherein the processing step includes separating an inert gas from the portion of the furnace top gas that is conducted through the primary circuit (209).
8. The process according to claim 6, wherein the processing step includes separating water from the portion of the furnace top gas that is conducted through the primary circuit (209).
9. The process according to claim 6, wherein the processing step includes reducing the temperature of the top gas in the heat exchanger and using the heat from the top gas to heat another gas used in the process.
10. The process according to claim 9, wherein the other gas is a reducing gas introduced into the direct reduction shaft (201) via the gas line (207).
11. A system for producing sponge iron, A direct reduction shaft (201), A first inlet (202) for introducing iron ore into the shaft (201), A first outlet (203) for removing sponge iron from the shaft (201), A second inlet (204) for introducing reducing gas into the shaft (201), A direct reduction shaft (201) includes a second outlet (205) for removing top gas from the shaft (201), A reducing gas source (206) connected to the reducing gas inlet (204) via a gas line (207), A first compressor (208) provided within the aforementioned gas line (207), A primary circuit (209) for conducting at least a portion of the furnace top gas through it, wherein the primary circuit (209) is connected at one end to the second outlet (205) and at the other end to the gas line (207) downstream of the first compressor (208), A secondary circuit (210) for conducting at least a portion of the gas removed from the gas conducted through the primary circuit (209), wherein the secondary circuit (210) is connected at one end to the primary circuit (209) and at the other end to the gas line (207) upstream of the first compressor (208), and includes means (211) therein for reducing the pressure of the portion of the gas conducted through the secondary circuit (210), A system comprising a first valve (212) for controlling the flow of the portion of the gas entering the secondary circuit (210), the first valve being configured to open in response to the gas pressure in the primary circuit (209) exceeding a predetermined level to allow the gas to pass into the secondary circuit (210).
12. The system according to claim 11, further comprising a control device for controlling the flow of reducing gas from the reducing gas source (206) into the gas line (207) based on the gas flow rate in the gas line (207).
13. The system according to claim 12, wherein the control device includes a second valve (213) for controlling the flow of reducing gas from the reducing gas source (206) into the gas line (207), a gas flow meter (214) for measuring the gas flow through the gas line (207), and a control unit (215) configured to control the second valve (213) based on input from the gas flow meter (214).
14. The system according to claim 11 or 12, wherein the first valve (212) is a controllable valve, and the system further includes a pressure sensor (217) located in the primary circuit (209), and a control unit (215) configured to control the controllable first valve (212) based on an input received from the pressure sensor (217).
15. The system according to claim 14, wherein the primary circuit (209) includes a second compressor (218) provided downstream of a point along the primary circuit (209) to which the secondary circuit (210) is connected to the primary circuit (209), and the pressure sensor (217) is located upstream of the second compressor (218).
16. The system according to claim 11 or 12, wherein the primary circuit (209) includes a device (219) for processing the furnace top gas, and the device (219) includes a device for separating an inert gas from the portion of the furnace top gas conducted through the primary circuit (209).
17. The system according to claim 11 or 12, wherein the primary circuit (209) includes a device (219) for processing the furnace top gas, the device including a device for separating water from the portion of the furnace top gas conducted through the primary circuit (209).
18. The system according to claim 11 or 12, wherein the primary circuit (209) includes a device (219) for processing the furnace top gas, and the device (219) includes a heat exchanger.
19. The system according to claim 18, wherein the heat exchanger is also connected to the gas line (207) and configured to transfer heat from the furnace top gas to the reducing gas introduced into the direct reduction shaft (201).
20. The system according to claim 11 or 12, wherein the reducing gas source (206) includes a water electrolysis unit.