Sponge iron manufacturing process

Abstract

The present disclosure relates to a process for producing sponge iron from iron ore using a direct reduction shaft, the process utilizing a reducing gas comprising more than 85% by volume of hydrogen gas, and 1 The first temperature T in the direct reduction shaft 1 measured measuring the temperature at a first temperature measurement location P 1 (s211) is located in the reduction zone of the direct reduction shaft; and the measured first temperature T 1 measured and (s213) controlling the process based at least on: The present disclosure further relates to a system adapted for carrying out such a process, and to a sponge iron product obtained by such a process.

Description

[Technical Field]

[0001] Technical Field The present disclosure relates to a process for producing sponge iron from iron ore using a direct reduction shaft. The disclosure further relates to a system adapted to carry out such a process, and to the sponge iron product obtained by such a process. [Background technology]

[0002] Background technology Steel is the world's most important industrial and construction material. It is difficult to find an object in the modern world that does not contain steel or that does not rely on steel for its manufacture and / or transportation. As such, steel is intricately involved in nearly every aspect of our modern lives. In 2018, total global production of crude steel was 1,810 million metric tons, far more than any other metal, and is expected to reach 2,800 million metric tons by 2050, 50% of which is expected to be derived from virgin iron sources.

[0003] Although the steelmaking process has been refined over decades and is approaching the theoretical minimum energy consumption, one fundamental problem remains: the reduction of iron ore with carbonaceous reductants produces CO2 as a by-product. On average, 1.83 metric tons of CO2 were produced per tonne of steel produced in 2018. The steel industry is one of the largest CO2-emitting industries, accounting for approximately 7% of global CO2 emissions. As long as carbonaceous reductants are used, excess CO2 production cannot be avoided within the steelmaking process.

[0004] The HYBRIT initiative was established to address this issue. The core of the HYBRIT concept is shaft-based direct reduction to produce sponge iron from virgin ore. In direct reduction, ore is reduced in a solid-state reduction process at temperatures below the melting point of iron. The shaft-based direct reduction process utilizes pelletized iron ore as the raw material and produces a porous crude iron product known as sponge iron or direct reduced iron (DRI). Instead of using a carbonaceous reductant gas such as natural gas as in current commercial direct reduction processes, HYBRIT proposes using hydrogen gas as the reductant, referred to as hydrogen direct reduction (H-DR). Hydrogen gas can be produced by electrolyzing water using primarily fossil-fuel-free and / or renewable primary energy sources. Thus, the key step of iron ore reduction can be achieved without fossil fuels as an input material and with water as a by-product instead of CO2.

[0005] Shaft-based direct reduction processes using hydrogen as the reducing agent are fundamentally different from carbon-based DR processes and have not previously been implemented on a commercially relevant scale. There remains a need for improved means of control of such shaft-based direct reduction processes utilizing hydrogen as the reducing agent. Summary of the Invention [Means for solving the problem]

[0006] Summary of the Invention The HYBRIT initiative has been operating a pilot direct reduction shaft capable of producing DRI at semi-industrial and commercially relevant scales since 2020 using either conventional fossil-fuel-based or hydrogen-based processes. Based on the process experience gained from the pilot operation, the inventors confirmed that shaft-based direct reduction using hydrogen as the reducing gas behaves fundamentally differently from direct reduction using conventional fossil reductants. The net result of these differences in behavior is that, unless the process is properly controlled, there is a significant risk of producing a product with wide variations in the properties of individual DRI pellets. Controlling the process based on product properties measured at the shaft outlet is sometimes an option. However, because direct reduction shafts can typically have a throughput of several metric tons per hour and residence times in the shaft can typically be measured in tens of hours per week, such methods risk producing a large amount of off-specification product before an optimal process window is found.

[0007] It would be advantageous to have a means of overcoming or at least mitigating at least some of the above-mentioned drawbacks. In particular, it would be desirable to have a means of controlling a hydrogen-based direct reduction shaft process so as to quickly enter the appropriate process window without producing excessive off-specification products. Such a means would be particularly useful in situations where the process is upset and not yet operating under steady-state conditions within the appropriate process window, such as during process start-up, production ramp-up, or when the properties of the iron ore input to the process change.

[0008] The object of the present invention is achieved by the process according to the attached independent claim, which is a process for producing sponge iron from iron ore using a direct reduction shaft, utilizing a reducing gas containing more than 85% by volume of hydrogen gas, comprising: - Charging speed of iron ore into the direct reduction shaft

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[0009] The temperature occurring within the reduction zone of a direct reduction shaft has been found to be a reliable determinant of whether the process is operating within the proper window to obtain a product of high and uniform quality, as measured by product metallization. The temperature prevailing in this section of the direct reduction shaft has been found to be highly sensitive to whether the process is operating within the proper process window when using hydrogen gas as the reducing agent, as opposed to traditional fossil-based reducing agents, which result in a more uniform temperature throughout the reduction zone. While not wishing to be bound by theory, it is believed that this may be due, at least in part, to the endothermic nature of iron oxide reduction and the difference in reaction rates between hydrogen and carbon monoxide as reducing agents. Furthermore, the temperature prevailing in the reduction zone of a direct reduction shaft has been found to be a stronger indicator of whether the process is operating within the proper process window than temperatures measured at other locations typically used to control the direct reduction process, such as the incoming reduction gas temperature or the furnace gas temperature.

[0010] The first temperature measured, T 1 measured The step of controlling the process based at least on - the first temperature T measured 1 measured a predetermined first lower limit temperature T 1 lim_lower and comparing with; - the first temperature T measured 1 measured is the first lower limit temperature T 1 lim_lower If the measured first temperature T is lower than 1 measured is the first lower limit temperature T 1 lim_lower until it is higher than P 1 controlling the process so that the temperature measured at may include:

[0011] It has been found that ensuring that the temperature measured at a location within the reduction zone of the direct reduction shaft exceeds the critical temperature provides a simple and reliable means of verifying that the process is operating within the appropriate process window.

[0012] Location P for measuring temperature 1 can be located near the wall of the direct reduction shaft. Measuring the temperature at or near the wall of the shaft furnace is more reliable and simpler than measuring the temperature at another location in the shaft, such as the center. Furthermore, the location P for measuring the temperature 1 can be located at a distance of about 50% to about 90% of the length of the reduction zone from the reducing gas inlet. The length of the reduction zone is defined as extending from the reducing gas inlet to the top end of the reduction zone in the direct reduction shaft, i.e., to the vertical charge height of the shaft. It has been found that temperature measurements at such intermediate locations within the reduction zone provide the greatest differentiation between satisfactory and suboptimal process conditions.

[0013] Location P for measuring temperature 1 can be located near the wall of the direct reduction shaft, below the vertical charge level of the shaft, i.e., between the vertical charge level and the reducing gas inlet. For example, at location P 1 can be located just below the vertical charge height of the shaft, for example, 95% of the length of the reduction zone from the reducing gas inlet. 1 lim_lower can be at least 550°C.

[0014] For example, location P 1 can be located at a distance of about 78% from the reducing gas inlet. 1 lim_lower can be at least 630° C., preferably at least 645° C. "At least" means that the temperature limit can be set higher.

[0015] The above process involves the following further steps: - Second temperature measurement location P 2 The second temperature T in the direct reduction shaft 2 measured measuring the second temperature measurement location P 2 is the first temperature measurement location P in the reduction zone 1 a step located higher or lower than the - the first temperature T measured 1 measured and the measured second temperature T 2 measured controlling the process based at least on It may further include:

[0016] By measuring temperature at multiple locations within the reduction zone and controlling the process accordingly, further confidence can be gained as to whether the process is operating within the proper window or whether the process parameters should be adjusted to fall within such a proper window.

[0017] location P 2 can be located near the wall of the direct reduction shaft.

[0018] location P 2 is the P at a distance of about 80% to about 99% of the length of the reduction zone from the reducing gas inlet. 1 In such a case, the measured second temperature T 2 measured the predetermined second lower limit temperature T 2 lim_lower can be compared with T 2 measured T 2 lim_lower If it is lower than the measured second temperature T 2 measured is the second lower limit temperature T 2 lim_lower until it is higher than P 2 The temperature can be controlled so that the temperature measured at

[0019] For example, location P 2 can be located at a distance of about 95% from the reducing gas inlet. 2 lim_lower can be at least 550°C.

[0020] Or, location P 2 is the P at a distance of about 25% to about 50% of the length of the reduction zone from the reducing gas inlet. 1 In such a case, the process can be performed under P 2 and P 1 Measured between T 2 measured -T 1 measured Temperature drop ΔT calculated as determined In such a case, the control can be based at least on the location P 1 can be located at a distance from the reducing gas inlet to about 50% to about 90% of the length of the reduction zone. It has been found that the temperature drop across this section of the reduction zone can be particularly indicative of whether the process is operating within an adequate window, and that an excessive temperature drop within this region indicates that the process is operating outside of the optimal window.

[0021] ΔT for the total temperature drop in the reduction zone determined As the parameter ΔT rel can be calculated. That is, ΔT rel =(T 2 measured -T 1 measured ) / (T lower end of reducing zone -T top end of reducing zone ) The parameter ΔT rel is the upper limit ΔT rel_lim_upper If it is greater than ΔT rel is ΔT rel_lim_upper Until ΔT rel The process can be controlled so that the

[0022] For example, P 1can be located at a distance of about 78% from the reducing gas inlet, and P 2 can be located at a distance of about 47% from the reducing gas inlet, and in such a case ΔT rel_lim_upper can be about 0.4 or less.

[0023] Reducing gas temperature T RG By increasing T 1 measured As T rises, 2 measured and / or ΔT rel The process can be controlled so that the

[0024] Reducing gas flow rate Q RG By increasing T 1 measured As T rises, 2 measured and / or ΔT rel The process can be controlled so that the

[0025] Discharge rate from direct reduction shaft

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[0026] According to another aspect, the object of the present invention is achieved by a system according to the attached independent claim. A system for producing sponge iron from iron ore comprises: - a direct reduction shaft including a reduction zone, the reduction zone including a reduction gas inlet arranged at its lower end; - a hydrogen gas source disposed in fluid communication with the reducing gas inlet; - Location P located within the reduction zone of the direct reduction shaft 1 a temperature measuring device for measuring temperature at the - a control device arranged to control the sponge iron production process based at least on the output of the temperature measuring device; Includes.

[0027] The temperature measurement device may include a thermocouple, such as a Type K thermocouple or a Type S thermocouple, which are cost-effective and relatively robust under mainstream process conditions.

[0028] The temperature measuring device can be positioned directly in the wall of the reduction shaft at a distance from the reduction gas inlet to about 50% to about 90% of the length of the reduction zone.

[0029] According to a further aspect, the object of the present invention is realized by a bulk sponge iron product as set forth in the attached independent claim, which comprises sponge iron pellets, which are essentially free of carbon and have an average metallization rate of 97% or more, with a standard deviation of the metallization rate of less than 1.5%.

[0030] Additional objects, advantages and novel features of the present invention will become apparent to those skilled in the art from the following detailed description.

[0031] BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of the present invention, and further objects and advantages thereof, the following detailed description should be read in conjunction with the accompanying drawings, in which like reference characters represent like items in the various views. [Brief explanation of the drawings]

[0032] [Figure 1] 1 illustrates a schematic diagram of a system for producing sponge iron according to an exemplary embodiment of the present invention. [Figure 2] 1 is a flowchart illustrating a process according to an exemplary embodiment of the present invention. [Figure 3] 1 is a graph showing the temperature profile in the shaft before quenching under various operating conditions. [Figure 4A] 1 is a contour plot showing the degree of metallization observed by excavation of a direct reduction shaft after quenching at operating condition K4. [Figure 4B] 1 is a contour plot showing the degree of metallization observed by hollowing out a direct reduction shaft after quenching at operating condition K3. [Figure 4C] 1 is a contour plot showing the degree of metallization observed by hollowing out a direct reduction shaft after quenching under operating condition K2. [Figure 5] 1 is a graph showing in-shaft temperature profiles for various process locations. DETAILED DESCRIPTION OF THE INVENTION

[0033] Detailed Description The present invention is based on unique insights into the shaft-based hydrogen direct reduction process gained during operation of the HYBRIT pilot direct reduction shaft. It has been found that, when hydrogen is used as the reducing gas, measurement of the main temperatures within the reduction zone of a direct reduction shaft provides a particularly sensitive means of determining whether the shaft is operating under adequate or suboptimal conditions. During adequate operation, a relatively smooth temperature curve is observed, whereas during poor operation, an inflection point may be discernible in the temperature curve, resulting in the temperature at a location within the reduction zone dropping below a critical value. When the shaft is operated under such poor conditions, a DRI product with widely varying degrees of metallization may be obtained. This is believed to be because pellets near the shaft wall are still nearly completely reduced, but to a much lesser extent than pellets in the center of the shaft. It has been found that temperatures measured at more conventional locations in the process, such as the furnace gas temperature and the reduction gas inlet temperature, are unreliable indicators of whether the process is operating within the adequate or suboptimal window.

[0034] The effects observed in the case of hydrogen direct reduction also contrast with the temperatures observed in the reduction zone during conventional direct reduction using fossil-based reducing gases containing carbon monoxide and hydrogen. The temperature curve along the reduction zone in the conventional process is somewhat flatter, and this process has been found to have correspondingly less risk of producing a DRI product with widely varying metallization rates.

[0035] Without wishing to be bound by theory, it is believed that such differences in process behavior are due, in part, to differences in thermodynamics and reaction kinetics between different reducing agents. The reduction reaction of iron oxide with hydrogen to ultimately yield metallic iron is largely endothermic, as shown below. 6Fe2O3+2H2→4Fe3O4+2H2O +32.7kJ / mol 2Fe3O4+2H2→6FeO+2H2O +127.6kJ / mol 6FeO+6H2→6Fe+6H2O +171.4kJ / mol 2Fe3O4+8H2→6Fe+8H2O +299.0kJ / mol

[0036] Thus, the process gas in the direct reduction shaft cools as the reduction proceeds, eventually resulting in an unfavorable reaction rate due to the drop in temperature and a weakening of the reduction reaction.

[0037] In contrast, the reduction and carburization reactions that occur with carbonaceous reductants are largely exothermic, as shown below. reduction

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[0038] Therefore, reductions using such carbonaceous reducing agents are less prone to temperature drops and weakening.

[0039] 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, but may vary within the scope of the appended claims. Furthermore, the drawings should not be considered as drawn to scale, as some features may be exaggerated to more clearly show certain features.

[0040] Direct reduction A suitable system for producing sponge iron 101 from iron ore 103 is shown in Figure 1, which comprises: - a direct reduction shaft 105 comprising a reduction zone 107 and comprising a reduction gas inlet 109 at the lower end of which the reduction zone is located; a hydrogen gas source 111 disposed in fluid communication with the reducing gas inlet 109; - location P located within the reduction zone 107 of the direct reduction shaft 1 a temperature measuring device 113 for measuring the temperature at - a control device 115 arranged to control the sponge iron production process based at least on the output of the temperature measurement device 113; Includes.

[0041] The direct reduction shaft 105 can be of any type commonly known in the column art. The shaft refers to a gas-solid countercurrent moving bed reactor in which the iron ore 103 charge is charged into an inlet 117 at the top of the reactor and falls by gravity toward an outlet 119 located at the bottom of the reactor. The height of the bottom of the inlet 117 determines the vertical charge height. Since the material flow is driven by gravity and the vertical direction of the shaft is given, the use of directional terms such as "top," "bottom," "above," and "below" in relation to the shaft is well established in the art and well understood by those skilled in the art.

[0042] Heated reducing gas 121, also known as "bustle gas," is introduced to reduce the iron ore charge. The reducing gas 121 is introduced into reducing gas inlet 109, flows primarily upward countercurrent to the charge, and exits the shaft as top gas 123 at top gas outlet 124 at the top end of the shaft. Reduction is typically carried out at an inlet temperature of about 750°C to about 1000°C. The required temperature is typically maintained by heating the reducing gas introduced into the reactor using heater 125, e.g., an electric heater. Further heating of the gas can be achieved by exothermic partial oxidation of the gas with oxygen or air (not shown) after it leaves the heater and before it is introduced into the reactor. Reduction can be carried out in the DR shaft at a pressure of about 1 Bar to about 10 Bar, preferably about 3 Bar to about 8 Bar.

[0043] The iron ore charge typically consists primarily of iron ore pellets, although some lump iron ore may also be introduced. The iron ore pellets typically contain mostly hematite, along with further additives or impurities such as gangue, fluxes, and binders. However, the pellets may contain some 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 the present process. Alternatively, the pellets may be specifically adapted for hydrogen direct reduction.

[0044] Top (spent) gas 123 from the DR shaft is at least partially recycled and may be cleaned and treated to remove by-products such as water and / or fines before being reintroduced into the DR shaft (shown as treatment equipment 127). This recycled top gas 129 may be mixed with fresh reducing gas 131, known as "make-up gas," before being reintroduced, or may be introduced separately from any fresh makeup gas supply. The reducing gas may consist essentially of reducing makeup gas and recycled top gas.

[0045] In contrast to current commercial direct reduction processes, the makeup gas 131 used for recharging the reducing gas contains little or essentially no carbonaceous material. The makeup gas can, for example, comprise, consist essentially of, or consist of hydrogen. For example, the makeup gas can comprise, consist essentially of, or consist of at least 85% by volume, preferably greater than 90% by volume, and even more preferably greater than 95% by volume hydrogen gas (volume % measured at standard conditions of 1 atm and 0° C.).

[0046] To cool the DRI after reduction and before discharge, cooling gas 133 from a cooling gas source 134 can be supplied to a cooling zone 135 of the shaft. The cooling zone 135 is typically located at the lower end of the direct reduction shaft. Suitable cooling gases can include, for example, nitrogen, hydrogen, or a combination thereof if carbon-free DRI is being produced, or natural gas (diluted as necessary) if carbon-containing DRI is being produced. Typically, the cooling gas can be supplied to an inlet 137 located at the lower end of the cooling zone and removed from the shaft via an outlet 139 located at the upper end of the cooling zone.

[0047] If the cooling gas 133 consists primarily of hydrogen, some or all of the cooling gas may proceed upwardly in the shaft into the reducing zone, where it forms some proportion of the reducing gas. In some cases, if essentially all of the cooling gas can proceed upwardly in this manner, a cooling gas outlet and / or cooling gas treatment circuit may not be necessary.

[0048] In some cases, cooling gas is not circulated within cooling zone 135; instead, the hot DRI is discharged to a separate shaft where it is cooled and optionally carbonized using circulating gas. Such a separate shaft arrangement is disclosed in WO 2021 / 225500 A1, which is incorporated herein by reference.

[0049] To enable control of the direct reduction process according to the present disclosure, a location P located within the reduction zone of the direct reduction shaft 1 A temperature measuring device 113 is mounted directly on the reduction shaft for measuring the temperature at location P 1 can be located, for example, near the wall of the direct reduction shaft at a distance of about 50% to about 90% of the length of the reduction zone from the reducing gas inlet. The length L of the reduction zone is defined as extending from the reducing gas inlet 109 to the top end of the reduction zone 107 of the direct reduction shaft. 1 can be located, for example, at a distance of about 78% from the reducing gas inlet.

[0050] location P 1 Location P located within the reduction zone of the direct reduction shaft, either above or below 2 A second temperature measuring device (not shown) may optionally be mounted on the shaft to measure the temperature at P 2 is a value obtained by dividing the P by a distance of about 80% to about 99% of the length of the reduction zone from the reduction gas inlet, for example, by a distance of about 95%. 1 Alternatively, it can be located on P 2 is a value obtained by dividing the P at a distance of about 25% to about 50% of the length of the reduction zone from the reducing gas inlet, for example, at a distance of about 45% from the reducing gas inlet. 1 Of course, the shaft can be fitted with further such temperature measuring devices, for example, the temperature can be measured at a location P 1 The measurements can be taken at locations within the reduction zone both above and below.

[0051] The temperature measuring device is located at 1 and / or P 2 The temperature measuring device may be any device that is capable of reasonably measuring the prevailing temperature at location P 1 and / or P 2 , can be arranged to measure the temperature directly at location P. In such cases, the temperature measuring device may comprise a thermocouple, for example, a Type K thermocouple or a Type S thermocouple. However, it is also possible to measure the temperature directly at location P using, for example, a probe located within the shaft refractory or outside the shaft refractory. 1 and / or P 2 Indirect measurement of temperature at is also envisaged.

[0052] Control of the direct reduction process To determine whether the hydrogen direct reduction is operating within the proper window, and in situations where the process is currently measured to be outside the proper process window, the following process can be used to modify the process parameters to reach the proper process window, as shown in FIG. 2.

[0053] Step s201 indicates the start of the process. In step s203, iron ore is fed at a rate

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[0054] Step s213 can be conceptualized as including at least two distinct sub-steps: Sub-step s213a includes measuring at least T to determine whether the process is operating within a sufficient process window. 1 measured with at least one predetermined limit. Substep s213b includes taking appropriate action to cause the process to operate within the appropriate window if the process is found to be operating outside the appropriate window.

[0055] Many variations of sub-step s213a are envisaged.

[0056] Substep s213a is T 1 measured a predetermined first lower limit temperature T 1 lim_lower It can include comparing with T 1 measured T 1 lim_lower If it is lower than T 1 measured T 1 lim_lower Until it gets higher, P 1 The process can be controlled so that the temperature measured at

[0057] Second temperature T 2 measured is the second temperature measurement location P as described above. 2 In such a case, step s213 is performed to measure the measured first temperature T 1 measured and the measured second temperature T 2 measured The method can include controlling the process based at least on the

[0058] Second temperature T 2 measured P 1 Place above P 2 If the temperature is measured at T 2 measured the predetermined second lower limit temperature T 2 lim_lower It can include comparing with T 2 measured T 2 lim_lower If lower, T 2 measured T 2 lim_lower Until it gets higher, P 2The process can be controlled so that the temperature measured at

[0059] Second temperature T 2 measured P 1 Location below P 2 If the temperature is measured at T 2 measured -T 1 measured P, calculated as 2 and P 1 The temperature drop ΔT measured between determined This allows the process to be controlled based at least on the ΔT determined The parameter ΔT is calculated as rel This includes determining ΔT rel is the upper limit ΔT rel_lim_upper If it is greater than ΔT rel is ΔT rel_lim_upper Until ΔT rel The process can be controlled so that

[0060] To ensure complete reduction over the entire cross section of the shaft, and to avoid operating the process with insufficient energy in the process gas, i.e., to avoid running the shaft too "cool", a predetermined limit T 1 lim_lower , T 2 lim_lower , and ΔT rel_lim_upper can be utilized separately or in any combination. However, to avoid operating the shaft with excessive energy in the process gas, i.e., to avoid the process running too "hot", the complementary parameters T 1 lim_upper , T 2 lim_upper , and ΔT rel_lim_uppermay also be predefined and used separately or in any combination. Such limits may be used to improve energy efficiency and / or to avoid problems typically associated with excessively high shaft temperatures, such as cluster formation and / or excessive equipment wear.

[0061] Substep s213b includes, if the process is found to be operating outside the appropriate window, taking appropriate action to bring the process into operation within the appropriate window, such as adjusting one or more incoming process parameters, such as the reducing gas temperature T RG , reduction gas flow rate Q RG , discharge rate from direct reduction shaft

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[0062] On the other hand, if a process is operated with excess energy in the process gas, T 1 measured Lowering T 2 measured and / or ΔT rel This means that it is appropriate to increase the reducing gas temperature T RG By lowering the reduction gas flow rate Q RG and / or the discharge rate from the direct reduction shaft.

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[0063] Incoming parameters other than those mentioned above can be used to control the process, for example the proportion of gas recycled or the amount of cooling gas allowed to enter the reduction zone can be appropriately controlled to bring the process within a suitable window or to keep the process within a suitable window.

[0064] DRI product Maintaining the hydrogen direct reduction process within an appropriate process window enables the production of DRI with high and uniform metallization. For example, the process can produce a bulk sponge iron (DRI) product comprising sponge iron pellets, which are essentially carbon-free and have an average metallization of 97% or greater, with a standard deviation of metallization of less than 1.5%. The average metallization may be 98% or greater, or 99% or greater. The standard deviation of metallization may be less than 1%, or less than 0.5%.

[0065] The metallization rate is determined by conventional methods in the art (Fe metallic / Fe total ) × 100. The metallization ratio was measured using X-ray diffraction (XRD), but can also be measured using other methods. When several methods are conventionally used to determine a single property, the variability of the measured property is typically within the limits of experimental error.

[0066] Another method for measuring such metallization is as follows: ISO 2597-1:2006 (Iron ores - Determination of total iron content - Part 1: Titrimetric method after tin (II) chloride reduction) in conjunction with ISO 5416:2006 (Direct reduced iron - Determination of metallic iron - Bromine-methanol titrimetric method); and Used in conjunction with ISO 10276-1:2000 (Chemical analysis of ferrous materials - Determination of oxygen in steel and iron Part 1: Sampling and preparation of steel samples for oxygen determination) and ISO 10276-2:2003 (Chemical analysis of ferrous materials - Determination of oxygen content in steel and iron - Part 2: Infrared method after fusion under inert gas).

[0067] experiment Unless otherwise noted, all DRI samples prepared and tested were produced in Lulea's Hybrit pilot direct reduction facility. Briefly, the pilot facility includes a direct reduction shaft having an overall height of approximately 9.3 meters, a maximum diameter of approximately 1.22 meters, and a total volume of approximately 7.6 cubic meters. Considering only the section of the shaft comprising the reduction zone, this zone has a height of approximately 3.1 meters from the reducing gas inlet to the vertical charge height (approximately 4 meters from the reducing gas inlet to the top flange) and a diameter of approximately 0.94 meters. The shaft is of conventional design; that is, it is a solid-gas countercurrent moving-bed reactor, in which the iron ore charge is inserted through an inlet at the top of the reactor and descends by gravity toward an outlet located at the bottom of the reactor. In all studies described herein, KPRS direct reduction pellets, commercially available from LKAB, were used as the iron ore charge. However, any suitable iron ore pellets can be used as the starting material to obtain the same or similar results as those described herein. The DR shaft contains a reduction zone, an isobaric (transition) zone, and a conical cooling zone that tapers towards the outlet of the DR shaft. The shaft has a nominal production capacity of about 1 tonne DRI / h, although this can vary, as shown in the study below. The operating pressure in the reactor can vary up to about 4 barg.

[0068] Research 1 - Hollowing Research Boring was performed to examine the pellet / DRI at various locations as it passed through the direct reduction shaft. This involved operating the DR shaft at a selected steady state for a measurement period, followed by quenching the shaft to stop reduction, and then boring to remove samples at various depths within the shaft. The pilot shaft was fitted with thermocouples at regular intervals away from the shaft wall to monitor the prevailing temperatures at various heights within the shaft. Note that the thermocouple depths are given relative to the top flange of the shaft. The vertical charge height within the shaft is approximately 0.9 m deep relative to this top flange, meaning that a thermocouple placed, for example, at a depth of approximately 1 m would be just below the vertical charge height.

[0069] Three different operating conditions were investigated: conventional natural gas (K2), hydrogen (K3) outside the optimum process window, and hydrogen (K4) within the optimum process window. The measured shaft temperature profiles for each of these operating conditions are shown in Figure 3.

[0070] As can be seen in Figure 3, the temperatures observed within the shaft during conventional fossil operation (K2) exhibit high uniformity, with a relative plateau observed between approximately 1 m and 3 m depth within the shaft. In contrast, the hydrogen direct reduction studies (K3 and K4) exhibit a relatively smooth temperature curve, with temperatures decreasing as one progresses from the reduction gas inlet to the top gas outlet. K3, operating outside the optimal process window, exhibits lower temperatures overall within the shaft than K4, but has a higher top gas temperature.

[0071] Quenching was performed using nitrogen gas under various operating conditions. After the reactor was quenched and cooled, it was corroded. Corroding consisted primarily of descending the shaft and sampling both radially and vertically along the shaft. The target bed thickness in the reduction zone was set at 150 mm, with thicker layers in the isobaric and cooling zones. Thirteen bed samples were taken at each bed. Each bed sample weighed approximately 1200 g. Contour plots showing the degree of metallization versus position in the shaft are shown in Figures 4a (K4, H2 sufficient process window), 4b (K3, H2 insufficient process window), and 4c (K2, natural gas direct reduction). Both K3 and K4 were found to have nearly complete metallization near the reactor wall. However, in K3, which was operated outside the appropriate process window, the core material in the reactor was reduced to a lesser extent, which resulted in a large variation in product quality at the reactor outlet, despite the product having a relatively high average metallization (95%). In K4, nearly complete reduction occurred across the entire shaft diameter, and the resulting product had a very high metallization rate (99%) with small deviations. The natural gas-based benchmark, K2, showed a relatively uniform metallization rate across the shaft diameter, but the metallization rate was much lower compared to the direct hydrogen reduction, which had an average metallization rate of about 89%.

[0072] From the drilling experiments, it was possible to conclude that while the operating conditions for hydrogen direct reduction appear to produce a high-quality DRI product with a high average metallization, there is a risk that the product may contain a proportion of relatively under-reduced material. It was further concluded that monitoring the temperature within the shaft can sometimes be used to distinguish between satisfactory and unsatisfactory operating conditions, but that the furnace gas temperature is an unreliable indicator. Furthermore, it was observed that conventional natural gas direct reduction has a more uniform temperature along the reduction zone and, perhaps because of this, is less susceptible to the same problem of product quality variation across the shaft diameter. However, the product obtained with the conventional process had a much lower average metallization.

[0073] Study 2 - Systematic variation of process parameters To more fully explore the process window of hydrogen direct reduction, independent process variables such as reducing gas inlet temperature, reducing gas flow rate, and production rate (charge and discharge rates) were systematically investigated. The resulting temperature profile within the direct reduction shaft is shown in Figure 5.

[0074] All of the process points PP6_1, PP6_2, and PP6_3 had the same inlet reducing gas temperature (780°C) and reducing gas flow (2900 Nm 3 / h), differing only in production rate; the charge in PP6_1 had a relative shaft residence time of 0.94, in PP6_2 a relative shaft residence time of 1.00, and in PP6_3 a relative shaft residence time of 1.09. Only PP6_3 produced a DRI product with a high and uniform degree of metallization (98%). Both PP6_1 and PP6_2 produced metallization rates below 90% with a large standard deviation.

[0075] Looking at the shaft temperature profiles for these three process points, it can be seen that the observed temperatures are very similar at the bottom of the reduction zone near the reducing gas inlet (RG → N9) and also at the top gas outlet (TG). The main differences are observed in the middle to upper reduction zone (N5 → N3), and especially in the middle reduction zone (N5, which is located at the shaft wall at approximately 78% of the distance between the reducing gas inlet and the vertical charge height of the shaft). PP6_1 has an N5 temperature of 611°C, PP6_2 has an N5 temperature of 577°C, and PP6_3 has an N5 temperature of 645°C. It can be seen that the poor process points PP6_1 and PP6_2 exhibit a relatively large temperature drop between point N9 (approximately 47% of the distance from the RG inlet) and point N5 (approximately 78% of the distance from the RG inlet) in the shaft, which creates a kink or inflection point in the temperature curve. Therefore, a further means of distinguishing between various process points is by comparing the temperature drop between the N9 and N5 positions (N9-N5) to the temperature drop across the entire reduction zone (roughly represented by N12-N3, with N12 being about 13% of the distance from the RG inlet and N3 being about 96% of the distance from the RG inlet). Thus, it can be seen that a satisfactory process point should typically have a relative temperature drop ((N9-N5) / (N12-N3)) of less than 0.4.

[0076] It can therefore be concluded that the transition from PP6_1 to PP6_3 by reducing the production rate brings the process into a full process window, and that the transition into this full window can be detected in the shaft temperature profile, particularly at the N5 position in the shaft, long before any impact on product quality becomes detectable at the shaft outlet.

[0077] Similarly, a comparison can be made between process points PP6_1 and PP7_1. Both process points have very similar production rates but differ in reducing gas inlet temperature (PP6_1: 780°C, PP7_1: 820°C) and reducing gas flow rate (PP7_1 has an RG flow rate that is approximately 95% of that of PP6_1). In contrast to PP6_1, PP7_1 produces a DRI product with a high and uniform metallization rate (average 98%). This transition from an insufficient to an adequate process point can be observed in the in-shaft temperature profile, where PP7_1 exhibits a smooth temperature curve and has an N5 temperature of 650°C. Therefore, this temperature profile, and especially the N5 temperature, indicates that the increase in reducing gas temperature from PP6_1 to PP7_1 more than compensates for the decrease in reducing gas flow rate, which is supported by the relative quality of the resulting products.

[0078] Thus, it can be seen that the temperature profile within the reduction zone, particularly temperature measurements at the N5 location, can be used to determine whether the process is operating within a sufficient process window, with process points exhibiting N5 temperatures below 630°C resulting in lower quality DRI, and process points exhibiting N5 temperatures above 630°C, particularly above 645°C, resulting in higher quality DRI (high uniform metallization). Note that the exact critical temperature will vary with respect to the measurement location and may vary with additional parameters such as shaft geometry or the nature of the incoming pellets (e.g., moisture). Therefore, the exact critical temperature may need to be measured repeatedly for each shaft.

[0079] Research 3 - Modeling research A modeling study was conducted to determine whether the results obtained at the pilot scale could be extrapolated to a full-scale direct reduction shaft. The model was calibrated using results obtained from operation and boring of the pilot shaft and then used to examine the expected performance of the full-scale shaft. A series of operating parameters were systematically varied to model a range of operating conditions, ranging from poor conditions with large variations in metallization to conditions with uniform, nearly complete metallization.

[0080] Under all modeled conditions, the material closest to the shaft wall is always nearly completely reduced, but under lower gas energy (low temperature and / or low flow rate) conditions, a central column of unreduced charge material was found to persist throughout the reduction zone and all the way to the shaft exit in a manner similar to Figure 4b. The temperature persisting at any particular location within the reduction zone was also found to correlate reasonably closely with the degree of reduction at that location, with lower temperatures correlating with less reduced material.

[0081] In terms of the features that can be used to distinguish between a sufficient and an insufficient state, it has been found that, in theory, temperature measurement at a location on the central axis of the shaft above the reducing gas inlet is optimal, since such a location is exposed to a wide range of temperatures in the transition from an insufficient to a sufficient operating state. However, placing a temperature probe at such a location is not very practical. Temperature measurement at the wall of the reduction zone midway through the shaft is a reasonable compromise in this regard, since such temperature measurement is relatively easy to perform and such a location is exposed to a relatively wide temperature range in the transition from an insufficient to a sufficient state. Temperature measurement at a lower location on the shaft wall near the reducing gas inlet, or at a location near the top of the shaft, has been found to be insufficient in this regard, since these locations are exposed to a narrower temperature range in the transition from an insufficient to a sufficient state.

[0082] This modeling study demonstrates that the means for controlling the hydrogen direct reduction process disclosed herein are applicable to full-scale direct reduction shafts.

Claims

1. 1. A process for producing sponge iron from iron ore using a direct reduction shaft, comprising: the process utilizes a reducing gas comprising greater than 85% by volume of hydrogen gas; - the charging rate of iron ore into the direct reduction shaft [Equation 1] Step (s203) of charging; a reducing gas temperature T ＲＧ and flow rate Q ＲＧ a step (s205) of introducing a reducing gas; - removing top gas from the direct reduction shaft at a top gas outlet (s207); - the discharge rate from said direct reduction shaft [Equation 2] Step (s209) of removing sponge iron; Including; - first temperature measurement location P １ A first temperature T in the direct reduction shaft １ ｍｅａｓｕｒｅｄ measuring the temperature at the first temperature measurement location P １ is located within the reduction zone of the direct reduction shaft; said measured first temperature T １ ｍｅａｓｕｒｅｄ (s213) controlling the process based at least on The process further comprises:

2. The measured first temperature T １ ｍｅａｓｕｒｅｄ controlling the process based at least on said measured first temperature T １ ｍｅａｓｕｒｅｄ is set to a predetermined first lower limit temperature T １ ｌｉｍ＿ｌｏｗｅｒ and comparing it with said measured first temperature T １ ｍｅａｓｕｒｅｄ is the first lower limit temperature T １ ｌｉｍ＿ｌｏｗｅｒ If the measured first temperature T １ ｍｅａｓｕｒｅｄ is the first lower limit temperature T １ ｌｉｍ＿ｌｏｗｅｒ Until it becomes higher than １ controlling the process so that the temperature measured at 2. The process of claim 1, comprising:

3. P １ is located at a location near the wall of the direct reduction shaft at a distance of about 50% to about 90% of the length of the reduction zone from the reducing gas inlet, the length of the reduction zone being defined as extending from the reducing gas inlet to an upper end of the reduction zone in the direct reduction shaft.

4. P １ is located at a distance of about 78% from the reducing gas inlet, and T １ ｌｉｍ＿ｌｏｗｅｒ 4. The process according to claim 2 or 3, wherein the temperature is at least 630°C, preferably at least 645°C.

5. - second temperature measurement location P ２ A second temperature T in the direct reduction shaft ２ ｍｅａｓｕｒｅｄ measuring the second temperature measurement location P ２ is the first temperature measurement location P in the reduction zone １ a step located higher or lower than the said measured first temperature T １ ｍｅａｓｕｒｅｄ and the measured second temperature T ２ ｍｅａｓｕｒｅｄ controlling the process based at least on The process of any one of claims 1 to 4, further comprising:

6. - P ２ at a distance of about 80% to about 99% of the length of the reduction zone from the reducing gas inlet １ Located on top of; said measured second temperature T ２ ｍｅａｓｕｒｅｄ is a predetermined second lower limit temperature T ２ ｌｉｍ＿ｌｏｗｅｒ compared to; the measured second temperature T ２ ｍｅａｓｕｒｅｄ is the second lower limit temperature T ２ ｌｉｍ＿ｌｏｗｅｒ If the measured second temperature T ２ ｍｅａｓｕｒｅｄ is the second lower limit temperature T ２ ｌｉｍ＿ｌｏｗｅｒ Until it becomes higher than ２ The process is controlled so that the temperature measured at The process of claim 5.

7. P ２ is located at a distance of about 95% from the reducing gas inlet, and T ２ ｌｉｍ＿ｌｏｗｅｒ 7. The process of claim 6, wherein the temperature is at least 550°C.

8. - P ２ at a distance of about 25% to about 50% of the length of the reduction zone from the reducing gas inlet １ Located below; - T ２ ｍｅａｓｕｒｅｄ -T １ ｍｅａｓｕｒｅｄ P, calculated as ２ and P １ The temperature drop ΔT measured between ｄｅｔｅｒｍｉｎｅｄ The process is controlled based at least on The process of claim 5.

9. Parameter ΔT ｒｅｌ is the upper limit ΔT ｒｅｌ＿ｌｉｍ＿ｕｐｐｅｒ If it is greater than ΔT ｒｅｌ is the upper limit value ΔT ｒｅｌ＿ｌｉｍ＿ｕｐｐｅｒ Until it is less than ΔT ｒｅｌ The process is controlled so that ΔT ｒｅｌ is the ΔT for the total temperature drop in the reduction zone ｄｅｔｅｒｍｉｎｅｄ 9. The process of claim 8, wherein the calculated

10. P １ is located at a distance of about 78% from the reducing gas inlet, and P ２ is located at a distance of about 47% from the reducing gas inlet, and ΔT ｒｅｌ＿ｌｉｍ＿ｕｐｐｅｒ 10. The process of claim 9, wherein is about 0.4 or less.

11. The reducing gas temperature T ＲＧ By increasing T １ ｍｅａｓｕｒｅｄ As T rises, ２ ｍｅａｓｕｒｅｄ and / or ΔT ｒｅｌ 11. The process of claim 1, wherein the process is controlled so that

12. The reduction gas flow rate Q ＲＧ By increasing １ ｍｅａｓｕｒｅｄ As T rises, ２ ｍｅａｓｕｒｅｄ and / or ΔT ｒｅｌ 12. The process of claim 1, wherein the process is controlled so that

13. the discharge rate from the direct reduction shaft [Equation 3] and optionally reducing the charging rate to the direct reduction shaft. [Equation 4] By lowering T １ ｍｅａｓｕｒｅｄ As T rises, ２ ｍｅａｓｕｒｅｄ and / or ΔT ｒｅｌ 13. The process of any one of claims 1 to 12, wherein the process is controlled so that

14. 1. A system for producing sponge iron from iron ore, comprising: a direct reduction shaft (105) comprising a reduction zone (107) and comprising a reduction gas inlet (109) at the lower end of which said reduction zone is located; a hydrogen gas source (111) placed in fluid communication with said reducing gas inlet (109); a location P located within the reduction zone of the direct reduction shaft; １ a temperature measuring device (113) for measuring the temperature at a control device (115) arranged to control the sponge iron manufacturing process based at least on the output of said temperature measuring device (113); Including, the system.

15. The system of claim 14 , wherein the temperature measurement device comprises a thermocouple, such as a type K thermocouple or a type S thermocouple.

16. 16. The system of claim 14 or 15, wherein the temperature measuring device is disposed in a wall of the direct reduction shaft at a distance from the reducing gas inlet to about 50% to about 90% of the length of the reduction zone.

17. 1. A bulk sponge iron product comprising sponge iron pellets, the sponge iron pellets being essentially free of carbon and having an average metallization rate of 97% or greater, with a standard deviation in metallization rate of less than 1.5%.

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