Method for producing carburized sponge iron
By controlling carburizing gas flow and content within the direct reduction shaft using sensors and control units, the method achieves stable and efficient carburizing of sponge iron, addressing the inefficiencies in existing carburizing processes.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-03-07
- Publication Date
- 2026-03-11
AI Technical Summary
Existing methods for producing carburized sponge iron face challenges in achieving stable and efficient carburizing without burning excess carburizing gas, particularly when using a separate carburizing shaft.
A method involving controlled introduction and regulation of carburizing gas flow through a carburizing shaft, using sensors and control units to maintain a predetermined gas content range at specific levels within the direct reduction shaft, preventing excess gas from entering the reduction zone.
This approach ensures efficient carburizing of sponge iron with minimal gas waste, optimizing carbon content and reducing the need for excess gas combustion, thereby enhancing production efficiency.
Smart Images
Figure 2026508565000001_ABST
Abstract
Description
[Technical Field]
[0001] The present invention provides a method for producing carburized sponge iron, comprising the steps of: - introducing the granulated iron ore into an iron ore inlet at the top of a vertically disposed direct reduction shaft, and allowing the granulated iron ore to flow downward through the direct reduction shaft toward a bottom outlet; - introducing a reducing gas at a predetermined first level of the direct reduction shaft, thereby generating a flow of reducing gas in a direction opposite to the flow direction of the granulated iron ore, thereby reducing the iron ore to sponge iron before it reaches the bottom outlet of the direct reduction shaft; - removing the spent reduction gas through a gas outlet provided at the top of the direct reduction shaft; - transferring sponge iron from the bottom outlet of the direct reduction shaft to the carburizing shaft via a material feed conduit, the material feed conduit allowing the passage of solids and gases between the direct reduction shaft and the carburizing shaft; - introducing carburizing gas into the carburizing shaft through a gas inlet located remote from the material supply conduit; removing the carburizing gas from the carburizing shaft through a gas outlet located adjacent to the material supply conduit. The present invention relates to a method comprising:
[0002] The invention also relates to a corresponding arrangement for producing carburized sponge iron. [Background technology]
[0003] For the production of sponge iron by a process in which hydrogen gas is primarily used as the reducing gas, the carbon content of the sponge iron is extremely low. A low carbon content may make the sponge iron more reactive and may also be less favorable for subsequent melting processes, for example, in an electric arc furnace, where carbon may contribute to better melting conditions, such as lower melting temperatures. Therefore, it has been proposed to expose the sponge iron to carburizing gases in order to increase the carbon content in the sponge iron.
[0004] The use of a separate carburizing shaft connected to the reduction shaft via a material supply conduit can be advantageous because it allows for greater versatility in controlling the flow of carburizing gas and preventing it from slipping into the reduction zone, but also allows for greater design versatility. The carburizing shaft can also be used as a cooling shaft to produce cooled direct reduced iron (DRI) pellets. A line parallel to the carburizing shaft can be installed to feed hot DRI pellets from the bottom outlet of the reduction shaft to a molding machine, which then compacts them into hot molded reduced iron, also known as HBI. Therefore, a valve arrangement can be installed to allow for such line modifications. Summary of the Invention [Problem to be solved by the invention]
[0005] The problem faced when applying a separate carburizing shaft is how to achieve as stable and efficient carburizing as possible, preferably without burning excess carburizing gas in the carburizing gas loop generated by the carburizing shaft. [Means for solving the problem]
[0006] The object of the present invention is to provide a method for producing carburized sponge iron, comprising the steps of: - introducing the granulated iron ore into an iron ore inlet at the top of a vertically disposed direct reduction shaft, and allowing the granulated iron ore to flow downward through the direct reduction shaft toward a bottom outlet; - introducing a reducing gas at a predetermined first level of the direct reduction shaft, thereby generating a flow of reducing gas in a direction opposite to the flow direction of the granulated iron ore, thereby reducing the iron ore to sponge iron before it reaches the bottom outlet of the direct reduction shaft; - removing the spent reduction gas through a gas outlet provided at the top of the direct reduction shaft; - transferring sponge iron from the bottom outlet of the direct reduction shaft to the carburizing shaft via a material feed conduit, the material feed conduit allowing the passage of solids and gases between the direct reduction shaft and the carburizing shaft; - introducing carburizing gas into the carburizing shaft through a gas inlet located remote from the material supply conduit; removing the carburizing gas from the carburizing shaft through a gas outlet located adjacent to the material supply conduit. A method comprising: - determining the content of carburizing gas at the second level of the direct reduction shaft; - controlling the flow rate of the carburizing gas introduced into the carburizing shaft based on the content of the carburizing gas determined at the second level, such that the content of the carburizing gas at the second level is within a predetermined range. This is achieved by a method comprising:
[0007] The present invention allows the lower portion of the reduction shaft to be intentionally used for carburizing purposes. The intentional and controlled slip of carburizing gas from the carburizing shaft to the reduction shaft promotes efficient carburizing. The controlled slip of carburizing gas to the reduction shaft may also contribute to less need to burn excess carburizing gas from the carburizing loop within the carburizing shaft.
[0008] According to one embodiment, the carburizing gas introduced into the carburizing shaft includes gas extracted from the carburizing shaft and additional fresh gas, and the flow rate of the additional fresh gas is controlled so that the content of carburizing gas at the second level is within the predetermined range.
[0009] According to one embodiment, the chemical composition of the gas removed from the carburized shaft is measured and the composition of the additional fresh gas is controlled based on the measured chemical composition of the gas removed from the carburized shaft.
[0010] According to one embodiment, the CO and CH4 contents in the gas removed from the carburizing shaft are measured, and the CO and CH4 contents in the additional fresh gas are controlled so that the CO and CH4 contents in the carburizing gas introduced into the carburizing shaft are within predetermined ranges.
[0011] According to one embodiment, the content of CO and H2 in the gas introduced into the carburized shaft is CO / H2<1:3 (molar ratio).
[0012] According to one embodiment, the carburizing gas introduced into the carburizing shaft through the gas inlet has the following composition (in mole %): H2: 30-65% CO: 0-10% H2O: 0-1.5% CO2: 0-1.5% N2: 0-10% CH4: 20~50% C2H6: 0-3% It has.
[0013] According to one embodiment, the carburizing gas introduced into the carburizing shaft through the gas inlet has the following composition (in mole %): H2: 50-65% CO: 0-5% H2O: 0-1.5% CO2: 0-1.5% N2: 0-10% CH4: 20-35% C2H6: 0-3% It has.
[0014] According to one embodiment, the direct reduction shaft has an internal volume V1 defined by its inner wall, a predetermined first level through which the reducing gas is introduced, and a bottom outlet, with at least 50% of the volume V1 located below the second level. The carburizing gas should be prevented from slipping down to and above the first level. Therefore, the second level should not be too far from the first level to allow for good observation of the carbon content at the first level based on measurements at the second level. According to one embodiment, at least 75% of the volume V1 is located below the second level. The carburizing gas content may vary radially along the reduction shaft, typically being higher at its center. When using a gas analysis sensor to measure the carburizing gas content at the second level, the sensor's location and the results obtained therefrom should be combined with knowledge of the radial variation of the carburizing gas content (and possibly also the temperature within the reduction shaft) to determine the reduction zone, i.e., the predetermined range obtained at the second level such that slip above the first level is prevented. Preferably, a prediction of the carburizing gas distribution in the reduction shaft based on previous detailed measurements of the carburizing gas content in the reduction shaft and, possibly, the excavation results of the stop process in which the carburizing gas distribution was studied can be used to establish a predicted carburizing gas distribution based on the determination of the carburizing gas content at the second level.
[0015] According to one embodiment, the second level is below or at the same level as the first level.
[0016] According to one embodiment, at least 10% of the volume V1 is above the second level. Measurements too close to the first level will inevitably be affected by the large reducing gas flow and therefore will be less accurate. Therefore, measuring and determining the carburizing gas flow slightly below the first level improves accuracy.
[0017] According to one embodiment, the lower limit of the predetermined range is higher than 0%. If the lower limit is too low, the measurement will tell us nothing about the content below the second level. If the content is zero at the second level, it may be zero all the way to the carburized shaft. Therefore, the lower limit must be higher than zero, indicating that carburization has occurred at least up to the second level.
[0018] According to one embodiment, the direct reduction shaft has an internal volume V1 defined by its inner wall, a predetermined first level into which reducing gas is introduced and a bottom outlet, the lower limit of said predetermined range being a content of carburizing gas such that carburization of the sponge iron occurs in at least 50%, preferably at least 60%, more preferably at least 75% of said volume V. It is preferable to use as much of volume V1 as possible for carburizing purposes, but without significant slippage of the carburizing gas into the reduction zone, i.e. above the first level.
[0019] According to one embodiment, the upper limit of the predetermined range is the content of carburizing gas that will be consumed by carburizing before essentially all of the carburizing gas reaches the first predetermined level. In other words, the flow rate of the added carburizing gas is controlled based on the content of carburizing gas determined at the second level, so that essentially no carburizing gas is allowed to slip from the carburizing shaft into the reduction zone.
[0020] According to one embodiment, the determination of the content of carburizing gas at the second level is carried out by measuring said content at said second level using a sensor located directly in the reduction shaft. According to one embodiment, the measurement is carried out at the inner circumference of the reduction shaft. However, the measurement can alternatively be carried out at a position close to or at the longitudinal centerline of the reduction shaft, where the concentration of carburizing gas is expected to be higher or highest.
[0021] According to one embodiment, the method includes determining the carburizing gas content at a third level within the direct reduction shaft, the third level being below the second level, and controlling the flow rate of the carburizing gas introduced into the carburizing shaft based on the carburizing gas content determined at the second level and based on the carburizing gas content determined at the third level. Measuring at more levels than just the second level is preferable because it improves the accuracy of the possible predictions. Alternatively, the third level may be above the first level. In such a case, the flow rate of the carburizing gas introduced into the carburizing shaft should be controlled so that the carbon content at the third level is zero.
[0022] According to one embodiment, the inner wall of the direct reduction shaft defines a truncated cone from said predetermined first level to its bottom outlet, the diameter of the truncated cone decreasing towards the bottom outlet.
[0023] According to one embodiment, the direct reduction shaft has an internal volume V1 defined by its internal wall, a predetermined first level at which the reducing gas is introduced and a bottom outlet, and the carburizing shaft has an internal volume V2 defined by its internal wall, a level of the gas inlet for introducing the carburizing gas and a level of the gas outlet for removing the carburizing gas from the carburizing shaft, where 0.5 <V1 / V2<2である。
[0024] According to one embodiment, the carburizing gas introduced into the carburizing shaft through the gas inlet has the following composition (in mole %): H2: 30-65% CO: 0-10% H2O: 0-1.5% CO2: 0-1.5% N2: 0-10% CH4: 20~50% C2H6: 0-3% It has.
[0025] According to one embodiment, the carburizing gas introduced into the carburizing shaft through the gas inlet has the following composition (in mole %): H2: 50-65% CO: 0-5% H2O: 0-1.5% CO2: 0-1.5% N2: 0-10% CH4: 20-35% C2H6: 0-3% It has.
[0026] According to one embodiment, the reducing gas introduced into the direct reduction shaft at said first predetermined level comprises at least 96 mol % H2.
[0027] The object of the present invention is also to provide an arrangement for producing sponge iron by direct reduction of iron ore, comprising: a vertically disposed direct reduction shaft including an iron ore inlet at the top of the reduction shaft and a bottom outlet for removing the sponge iron produced; a reducing gas source, - a reduction gas inlet provided on the first level of the direct reduction shaft; a gas outlet at the top of the direct reduction shaft for removing exhaust gases from the direct reduction shaft; - Carburized shaft, a material supply conduit extending from the bottom outlet of the direct reduction shaft to the carburizing shaft, the material supply conduit allowing the passage of solids and gases between the direct reduction shaft (1) and the carburizing shaft; a carburizing shaft having a carburizing gas inlet located remote from the material supply conduit and a gas outlet located adjacent to the material supply conduit; a carburizing gas source connected to said gas inlet; - a valve for controlling the flow of carburizing gas from the carburizing gas source through the carburizing gas inlet to the carburizing shaft In an arrangement including a gas sensor provided at a second level of the direct reduction shaft, the gas sensor being configured to measure the content of carburizing gases in the direct reduction shaft; a control unit configured to control the flow rate of the carburizing gas introduced into the carburizing shaft based on the content of the carburizing gas determined at the second level by controlling the valve such that the content of the carburizing gas at the second level is within a predetermined range. This is achieved by an arrangement comprising:
[0028] According to one embodiment, the arrangement includes a sensor for sensing the composition of the gas removed from the carburizing shaft via a gas outlet located adjacent to the material supply conduit, and means for influencing the composition of the gas from the carburizing gas source, and the control unit is configured to control the means for influencing the composition of the gas from the carburizing gas source based on information from the sensor for sensing the composition of the gas removed from the carburizing shaft via the gas outlet located adjacent to the material supply conduit.
[0029] According to one embodiment, the arrangement includes a gas conduit extending from a gas outlet located adjacent the material supply conduit to said carburizing gas inlet.
[0030] According to one embodiment, the arrangement includes a second gas sensor provided at a third level of the direct reduction shaft, the sensor configured to measure the content of carburizing gas in the direct reduction shaft, the third level being below the second level, and the control unit configured to control the flow rate of carburizing gas introduced into the carburizing shaft based on the content of carburizing gas determined at the second level and based on the content of carburizing gas determined at the third level. [Brief explanation of the drawings]
[0031] [Figure 1] 1 shows an embodiment of an arrangement according to the invention for producing carburized sponge iron; DETAILED DESCRIPTION OF THE INVENTION
[0032] 1 shows an arrangement for producing sponge iron by direct reduction of iron ore. The arrangement includes a vertically arranged direct reduction shaft 1 having an iron ore inlet 2 at the top of the reduction shaft 1 and a bottom outlet 3 for removing the sponge iron produced. The arrangement further includes a reducing gas source 4, a reducing gas inlet 5 at a first level L1 of the direct reduction shaft 1, and a top gas outlet 6 at the top of the direct reduction shaft 1 for removing exhaust gas from the direct reduction shaft 1.
[0033] The inner wall of the direct reduction shaft 1 defines a truncated cone from said predetermined first level L1 to its bottom outlet 3, the diameter of the truncated cone decreasing towards the bottom outlet 3.
[0034] A main reducing gas conduit 22 extends from the reducing gas source 4 to the reducing gas inlet 5, and a top gas conduit 23 extends from the top gas outlet 6 to the main reducing gas conduit 22. A gas scrubber 24 forms part of the top gas conduit 23, and a heater 25 forms part of the main reducing gas conduit 22, for the purpose of heating both the gas recycled via the top gas conduit 23 and the fresh reducing gas delivered by the reducing gas source 4.
[0035] The arrangement also includes a carburizing shaft 7 and a material supply conduit 8 extending from the bottom outlet 3 of the direct reduction shaft 1 to the carburizing shaft 7. The material supply conduit 8 allows for the passage of solids and gases between the direct reduction shaft 1 and the carburizing shaft 7. The carburizing shaft 7 has a carburizing gas inlet 9 located remote from the material supply conduit 8 and a gas outlet 10 located adjacent to (closer than) the material supply conduit 8. A carburizing gas source 11 is connected to the gas inlet 9. A valve 12 is also provided for controlling the flow of carburizing gas from the carburizing gas source 11 through the carburizing gas inlet 9 to the carburizing shaft 7.
[0036] The arrangement further includes a gas sensor 13 provided at a second level L2 of the direct reduction shaft 1, the sensor 13 configured to measure the content of carburizing gas in the direct reduction shaft 1. A control unit 14 is also provided, configured to control the flow rate of carburizing gas introduced into the carburizing shaft 1 based on the content of carburizing gas determined at the second level L2 by controlling the valve 12 such that the content of carburizing gas at the second level L2 is within a predetermined range.
[0037] The direct reduction shaft 1 has an internal volume V1 defined by the inner wall of the shaft, which is only a portion of the total volume of the direct reduction shaft 1, a predetermined first level L1 into which the reducing gas is introduced, and a level of the bottom outlet 3, with at least 50% of said volume V1 being located below a second level L2.
[0038] In the embodiment shown, the second level L2 is below the first level L1. In the embodiment shown, about 25% of the volume V1 is above the second level.
[0039] The carburizing shaft has a volume V2 defined by its inner wall, at the level of a gas inlet 9 for introducing carburizing gas and at the level of a gas outlet 10 for removing the carburizing gas from the carburizing shaft. According to the exemplary embodiment disclosed herein, V1 / V2=1.
[0040] The arrangement further includes a sensor 15 for sensing the composition of the gas removed from the carburizing shaft 7 via a gas outlet 10 located adjacent the material supply conduit 8. Means 16-19 for influencing the composition of the gas from the carburizing gas source 11 are also provided, and the control unit 14 is configured to control the means 16-19 for influencing the composition of the gas from the carburizing gas source 11 based on information from the sensor 15 for sensing the composition of the gas removed from the carburizing shaft 7 via the gas outlet 10 located adjacent the material supply conduit 8. The means 16-18 for influencing the composition of the gas include a carbon monoxide (CO) source 16 and a methane (CH4) source 17, as well as valves 18, 19 for controlling the addition of CO and CH4 to the carburizing gas from the gas source 11.
[0041] A gas conduit 20 extends from a gas outlet 10 located adjacent the material supply conduit to the carburizing gas inlet 9. A carburizing gas source 11 and a means 16 for influencing the composition of the gas from the carburizing gas source 11 are connected to the gas conduit 19. A carburizing gas loop is thereby defined, in which carburizing gas supplemented with fresh gas from the gas source 11 and the means 16 circulates through the carburizing shaft 7 and the gas conduit 9.
[0042] The arrangement further includes a second gas sensor 21 provided at a third level L3 of the direct reduction shaft 1. The second gas sensor 21 is configured to measure the content of carburizing gas in the direct reduction shaft, the third level L3 being below the second level L2, and the control unit 14 is configured to control the flow rate of the carburizing gas introduced into the carburizing shaft 7 based on the content of the carburizing gas determined at the second level L2 and based on the content of the carburizing gas determined at the third level L3.
[0043] This arrangement is particularly configured such that the control unit 14, in combination with and in conjunction with the above-mentioned sensors, controls the composition and flow rate of the carburizing gas introduced into the carburizing shaft 7 according to an embodiment of the method of the present invention to be disclosed below.
[0044] This method is - introducing granulated iron ore into the iron ore inlet 2 and allowing the granulated iron ore to flow downwards through the direct reduction shaft towards the bottom outlet 3; - introducing a reducing gas at the first level L1, thereby generating a flow of reducing gas in a direction opposite to the flow direction of the granulated iron ore, so that the iron ore is reduced to sponge iron before reaching the bottom outlet 3 of the direct reduction shaft 1; - removing the spent reducing gas through the top gas outlet 6, - transferring the sponge iron from the bottom outlet 3 of the direct reduction shaft 1 to the carburization shaft 7 via a material feed conduit 8; - introducing carburizing gas into the carburizing shaft 7 via a gas inlet 9 located remote from the material supply conduit 8; removing the gas from the carburizing shaft 7 via a gas outlet 10 located adjacent the material supply conduit 8 and returning the gas through a gas conduit 20 to the gas inlet 9; Includes.
[0045] This method is - determining the content of carburizing gas at a second level L2; - controlling the flow rate of the carburizing gas introduced into the carburizing shaft 7 based on the content of the carburizing gas determined at the second level L2 so that the content of the carburizing gas at the second level L2 is within a predetermined range. Further includes:
[0046] The carburizing gas introduced into the carburizing shaft 7 comprises gas removed from the carburizing shaft 7 and additional fresh gas from the carburizing gas source 11 and possibly from means 16-19 for influencing the gas composition. The flow rate of the additional fresh gas (including the contribution from means 16-19) is controlled so that the carburizing gas content at said second level is within said predetermined range.
[0047] The chemical composition of the gas removed from the carburized shaft is measured and the composition of the additional fresh gas is controlled using the control unit 14 and means 16 based on the measured chemical composition of the gas removed from the carburized shaft 7.
[0048] The contents of CO and CH4 in the gas removed from the carburizing shaft are measured, and the contents of CO and CH4 in the additional fresh gas are controlled by addition from means 16 so that the contents of CO and CH4 in the carburizing gas introduced into the carburizing shaft 7 are within a predetermined range.
[0049] The content of CO and H2 in the gas introduced into the carburized shaft 7 is CO / H2<1:3 (molar ratio). According to the exemplary embodiment disclosed herein, CO / H2=3:63.
[0050] According to one embodiment, the carburizing gas introduced into the carburizing shaft through the gas inlet has the following composition (in mole %): H2:63% CO:3% H2O:1% CO2: 1% N2:5% CH4: 27% C2H6:2% It has.
[0051] The lower limit of the predetermined range is greater than 0%. According to an exemplary embodiment disclosed herein, the lower limit is 2%.
[0052] The lower limit of the predetermined range is the carburizing gas content at which carburization of sponge iron occurs in at least 50%, preferably at least 60%, and more preferably at least 75% of volume V1. Based on previous data on the correlation between the carburizing gas content at the second level and the extent to which carburization occurs within the volume, the upper limit of the predetermined range can be selected to maximize carburization within volume V1 without allowing the carburizing gas to slip into the reduction zone above the first level L1. Because the gas content may vary radially along the shaft, it may not be possible to use 100% of volume V1 for carburization. Typically, the gas content is higher in volume V1 toward the longitudinal centerline of shaft 1, meaning that using the upper periphery of volume V1 for carburization purposes may be impossible without simultaneously allowing the gas to slip into the reduction zone, i.e., above the first level L1.
[0053] The upper limit of the predetermined range is the content of carburizing gas that is consumed by carburizing before essentially all of the carburizing gas reaches the predetermined first level L1.
[0054] The method also includes determining the carburizing gas content at a third level (L3) and controlling the flow rate of the carburizing gas introduced into the carburizing shaft based on the carburizing gas content determined at the second level (L2) and based on the carburizing gas content determined at the third level (L3). This can be achieved by controlling the flow rate of the carburizing gas introduced into the carburizing shaft based on the carburizing gas content determined at the third level (L3) so that the carburizing gas content at the second level (L2) is within a predetermined range. The predetermined range for the measurement at the third level (L3) can be determined based on previous data relating to the correlation between the carburizing gas content at the third level (L3) and the degree of carburization occurring within the volume (V1). Still, the upper limit must be low enough to prevent localized, typically central, slippage of the carburizing gas into the reduction zone, i.e., above the first level (L1).
[0055] According to an exemplary embodiment disclosed herein, the reducing gas introduced into the direct reduction shaft at the first predetermined level comprises 99 mol % H2.
Claims
1. 1. A method for producing carburized sponge iron, comprising: - introducing granulated iron ore into an iron ore inlet (2) at the top of a vertically disposed direct reduction shaft (1) so that the granulated iron ore flows downward through the direct reduction shaft (1) towards a bottom outlet (3); - introducing a reducing gas at a predetermined first level (L1) of the direct reduction shaft, thereby generating a flow of reducing gas in a direction opposite to the flow direction of the granulated iron ore, reducing the iron ore to sponge iron before it reaches the bottom outlet (3) of the direct reduction shaft (1); - removing the spent reducing gas through a gas outlet (6) located at the top of the direct reduction shaft (1); - transferring sponge iron from the bottom outlet (3) of the direct reduction shaft (1) to the carburizing shaft (7) through a material feed conduit, the material feed conduit (8) allowing the passage of solids and gases between the direct reduction shaft (1) and the carburizing shaft (7); - introducing carburizing gas into the carburizing shaft through a gas inlet (9) located remote from the material supply conduit (8); - removing the carburizing gas from the carburizing shaft (1) through a gas outlet (10) located adjacent to the material supply conduit (8); A method comprising: - determining the content of carburizing gas at the second level (L2) of the direct reduction shaft; - controlling the flow rate of the carburizing gas introduced into the carburizing shaft (7) based on the content of the carburizing gas determined at said second level (L2) so that the content of the carburizing gas at said second level (L2) is within a predetermined range. A method comprising:
2. 2. The method according to claim 1, wherein the carburizing gas introduced into the carburizing shaft (7) includes gas extracted from the carburizing shaft (7) and additional fresh gas, and the flow rate of the additional fresh gas is controlled so that the content of the carburizing gas at the second level (L2) is within the predetermined range.
3. 3. The method according to claim 1 or 2, wherein the chemical composition of the gas extracted from the carburized shaft (7) is measured and the composition of the additional fresh gas is controlled based on the measured chemical composition of the gas extracted from the carburized shaft (7).
4. 4. The method according to claim 3, wherein the CO and CH contents in the gas removed from the carburizing shaft are measured and the CO and CH contents in the additional fresh gas are controlled so that the CO and CH contents in the carburizing gas introduced into the carburizing shaft (7) are within predetermined ranges.
5. 5. The method according to claim 3 or 4, wherein the content of CO and H2 in the gas introduced into the carburizing shaft (7) is CO / H2<1:3 (molar ratio).
6. The carburizing gas introduced into the carburizing shaft (7) through the gas inlet (9) has the following composition (mol %): H2: 30-65% CO: 0 to 10% H2O: 0-1.5% CO2: 0-1.5% N2: 0-10% CH4: 20-50% C2H6: 0-3% 6. The method according to claim 1, wherein the
7. 7. The method according to claim 1, wherein the direct reduction shaft has an internal volume (V1) defined by its inner wall, a predetermined first level (L1) through which the reducing gas is introduced, and a bottom outlet (3), and at least 50% of said volume (V1) is located below a second level (L2).
8. 8. The method according to any one of claims 1 to 7, wherein the second level (L2) is below or at the same level as the first level (L1).
9. 9. The method according to any one of claims 1 to 8, wherein at least 10% of the volume (V1) is above the second level (L2).
10. The method of claim 1 , wherein the lower limit of the predetermined range is greater than 0%.
11. 11. The method according to any one of claims 1 to 10, wherein the determination of the content of carburizing gases at the second level (L2) is carried out by measuring said content at said second level (L2) using a sensor (13) located at said second level (L2) in the direct reduction shaft (1).
12. 12. The method according to any one of claims 1 to 11, comprising the steps of: determining a content of carburizing gas at a third level (L3) in the direct reduction shaft (1), the third level (L3) being below the second level (L2); and controlling the flow rate of the carburizing gas introduced into the carburizing shaft (7) based on the content of carburizing gas determined at the second level (L2) and based on the content of carburizing gas determined at the third level (L3).
13. 13. The method according to any one of claims 1 to 12, wherein the inner wall of the direct reduction shaft (1) defines a truncated cone from the predetermined first level (L1) to its bottom outlet (3), the diameter of the truncated cone decreasing towards the bottom outlet (3).
14. 14. The method according to any one of claims 1 to 13, wherein the direct reduction shaft has an internal volume (V1) defined by its internal wall, a predetermined first level (L1) at which the reducing gas is introduced and a bottom outlet (3), and the carburizing shaft (7) has an internal volume (V2) defined by its internal wall, the level of a gas inlet for introducing the carburizing gas and the level of a gas outlet for removing the carburizing gas from the carburizing shaft (7), wherein 0.5<V1 / V2<2.
15. The carburizing gas introduced into the carburizing shaft (7) through the gas inlet has the following composition (mol %): H2: 30-65%, CO: 0-10%, H2O: 0-1.5%, CO2: 0-1.5%, N2: 0-10%, CH4: 20-50%, C2H6: 0-3%, 15. The method of any one of claims 1 to 14, comprising:
16. 16. The method according to any one of claims 1 to 15, wherein the reducing gas introduced into the direct reduction shaft at the first predetermined level (L1) comprises at least 96 mol% H2.
17. 1. An arrangement for producing sponge iron by direct reduction of iron ore, comprising: a vertically arranged direct reduction shaft (1) comprising an iron ore inlet (2) at the top of the reduction shaft (1) and a bottom outlet (3) for removing the sponge iron produced; a reducing gas source (4), a reducing gas inlet (5) located on the first level (L1) of the direct reduction shaft (1); a gas outlet (6) at the top of the direct reduction shaft (1) for removing exhaust gases from the direct reduction shaft (1); - carburized shaft (7), a material supply conduit (8) extending from the bottom outlet (3) of the direct reduction shaft (1) to the carburizing shaft (7), allowing the passage of solids and gases between the direct reduction shaft (1) and the carburizing shaft (7); a carburizing shaft (7) having a carburizing gas inlet (9) located remote from the material supply conduit and a gas outlet (10) located adjacent to the material supply conduit (8); a carburizing gas supply (11) connected to said gas inlet (9); - a valve (12) for controlling the flow of carburizing gas from the carburizing gas source (11) through the carburizing gas inlet (9) to the carburizing shaft (7); In an arrangement including a gas sensor (13) located on the second level (L2) of the direct reduction shaft, the gas sensor (13) being adapted to measure the content of carburizing gases in the direct reduction shaft (1); a control unit (14) configured to control the flow rate of the carburizing gas introduced into the carburizing shaft (7) based on the content of the carburizing gas determined at said second level (L2) by controlling said valve (12) so that the content of the carburizing gas at said second level (L2) is within a predetermined range; 10. An arrangement comprising:
18. 18. The arrangement according to claim 17, comprising a sensor (15) for sensing the composition of gas removed from the carburizing shaft (7) through a gas outlet (10) located adjacent to the material supply conduit (8) and means (16-19) for influencing the composition of gas from the carburizing gas source (11), wherein the control unit (14) is configured to control the means (16-19) for influencing the composition of gas from the carburizing gas source (11) based on information from the sensor (15) for sensing the composition of gas removed from the carburizing shaft (7) through the gas outlet (10) located adjacent to the material supply conduit (8).
19. 19. An arrangement according to claim 17 or 18, including a gas conduit (20) extending from a gas outlet (10) located adjacent the material supply conduit (8) to the carburizing gas inlet (9).
20. 20. The arrangement according to any one of claims 17 to 19, further comprising a second gas sensor (21) provided at a third level (L3) of the direct reduction shaft (1), said sensor (21) being configured to measure the content of carburizing gas in the direct reduction shaft (1), said third level (L3) being below the second level (L2), and said control unit (14) being configured to control the flow rate of carburizing gas introduced into the carburizing shaft (7) based on the content of carburizing gas determined at the second level (L2) and based on the content of carburizing gas determined at the third level (L3).