Method and plant for continuous production of sponge iron from iron ore

Abstract

The invention discloses equipment for producing sponge iron. Comprising a direct reduction shaft furnace (1), means (2) for charging iron ore into the direct reduction shaft furnace (1), means (3) for removing sponge iron from the direct reduction shaft furnace (1), a source of hydrogen-rich reducing gas (4), a reducing gas line (5) extending from the source of hydrogen-rich reducing gas (4) to the direct reduction shaft furnace (1), and a heater (6) for heating the hydrogen-rich reducing gas in the reducing gas line (5). The apparatus comprises: a flow meter (7) configured to measure a flow rate of a hydrogen-rich reducing gas in a reducing gas line (5); and a control unit (8) configured to control the means (2) for charging iron ore into the direct reduction shaft furnace (1) and the means (3) for removing sponge iron from the direct reduction shaft furnace (1) on the basis of the input from the flow meter (7), the flow of the iron ore and the flow of the sponge iron are proportional to the measured flow of the hydrogen-rich reducing gas.

Description

Technical Field

[0001] The present invention relates to the continuous production of sponge iron from iron ore, comprising the following steps: charging the iron ore into a direct reduction shaft furnace; providing a hydrogen-rich reducing gas; heating the hydrogen-rich reducing gas to a predetermined temperature; introducing the heated hydrogen-rich reducing gas into the direct reduction shaft furnace to reduce the iron ore to produce sponge iron; and taking out the produced sponge iron from the direct reduction shaft furnace.

[0002] The present invention also relates to an apparatus for producing sponge iron, comprising: a direct reduction shaft furnace; a device for charging iron ore into the direct reduction shaft furnace; a device for removing sponge iron from the direct reduction shaft furnace; a source of hydrogen-rich reducing gas; a reducing gas pipeline extending from the device for providing hydrogen-rich reducing gas to the direct reduction shaft furnace; and a heater for heating the hydrogen-rich reducing gas. Background Art

[0003] The continuous production of sponge iron by direct reduction of iron ore in a direct reduction shaft furnace is known. Thus, hydrogen can be used primarily as reducing gas, whereby carbon dioxide emissions from the shaft furnace are significantly reduced compared to technologies that primarily use carbon-containing gases (such as natural gas) as reducing gas.

[0004] Hydrogen is usually produced in a so-called electrolyser by a process driven by electricity. The availability of electricity required for the electrolyser may vary over time and / or the price of available electricity may fluctuate. As a result, the flow from the electrolyser to the direct reduction shaft furnace may fluctuate. The prior art suggests adding an additional reducing gas (e.g. natural gas) to the hydrogen flow in order to compensate for the latter's fluctuations. However, such compensation would lead to an increased emission of carbon dioxide emissions.

[0005] Purpose of the Invention

[0006] An object of the present invention is to propose a method and an apparatus for producing sponge iron by direct reduction of iron ore by means of a hydrogen-rich reducing gas, said method and apparatus compensating for flow fluctuations of the hydrogen-rich reducing gas, with reduced emissions of carbon dioxide from the direct reduction compared to solutions in which natural gas is used for compensation, or with no increase in carbon dioxide emissions at all.

[0007] Fluctuations in the flow rate of the hydrogen-rich gas may be due to deliberate control of the flow rate, for example caused by fluctuations in the price of electricity required to produce the hydrogen used in the process, or to unintentional fluctuations, for example caused by fluctuating availability of electricity for producing the hydrogen used in the process. In the case where hydrogen is taken from the top gas of the direct reduction shaft furnace and added to the hydrogen used as reducing gas, fluctuations may also be caused by fluctuating conditions in the direct reduction shaft furnace causing fluctuations in the flow rate of hydrogen taken from the top gas. The fluctuations may be of great magnitude and may be of considerable duration. Summary of the invention

[0008] The objects of the present invention are achieved by a method for continuously producing sponge iron from iron ore, the method comprising the following steps:

[0009] - charging the iron ore into the direct reduction shaft furnace,

[0010] -Provide hydrogen-rich reducing gas,

[0011] - heating the hydrogen-rich reducing gas to a predetermined temperature,

[0012] - introducing heated hydrogen-rich reducing gas into a direct reduction shaft furnace to reduce iron ore to produce sponge iron, and

[0013] - removing the produced sponge iron from the direct reduction shaft furnace,

[0014] - The method is characterized in that it comprises the following steps:

[0015] - measuring the flow rate of the hydrogen-rich gas, and

[0016] - controlling the flow of iron ore into the direct reduction shaft furnace based on the measured flow of hydrogen-rich gas, and

[0017] - controlling the flow rate of sponge iron taken out of the direct reduction shaft furnace based on the measured flow rate of hydrogen-rich gas, wherein

[0018] - The flow rates of iron ore and sponge iron are controlled so that they are proportional to the measured flow rate of hydrogen-rich reducing gas.

[0019] According to one embodiment, the method comprises the further step of measuring the composition of the hydrogen-rich reducing gas, wherein the flow of iron ore entering the shaft furnace and the flow of sponge iron withdrawn from the direct reduction shaft furnace are controlled based on the measured flow of the hydrogen-rich reducing gas and based on the measured composition of the hydrogen-rich reducing gas.

[0020] According to one embodiment, the composition of the hydrogen-rich reducing gas is evaluated according to its content of reducing agent that will cause direct reduction of iron ore, wherein the content of reducing agent and the flow rate of the hydrogen-rich reducing gas are multiplied with each other to produce an input value, based on which the flow rates of iron ore and sponge iron are controlled.

[0021] According to one embodiment, the flow rate of iron ore and the flow rate of sponge iron are controlled so that they correspond to each other and so that the combined level of iron ore and sponge iron in the direct reduction shaft furnace is maintained at a constant level.

[0022] According to one embodiment, the flow rate of the hydrogen-rich reducing gas has a predetermined nominal value applicable during predetermined nominal operating conditions of the direct reduction shaft furnace, and wherein a predetermined initial decrease in the flow rate of the hydrogen-rich gas from said nominal value to a threshold value is compensated by adding methane gas to the hydrogen-rich gas without a corresponding decrease in the flow rates of iron ore and sponge iron, and when the flow rate of the hydrogen-rich gas further decreases below said threshold value, the flow rates of iron ore and sponge iron are controlled based on the measured flow rates of hydrogen.

[0023] According to one embodiment, the method comprises the step of measuring the pressure in the direct reduction shaft furnace, wherein the addition of the methane gas is controlled such that the nominal operating pressure is maintained in the direct reduction shaft furnace when the flow rate of the hydrogen-rich reducing gas is reduced from the nominal value to the threshold value.

[0024] According to one embodiment, the hydrogen rich gas comprises at least 80 wt% hydrogen.

[0025] According to one embodiment, the hydrogen rich gas comprises at least 90 wt% hydrogen.

[0026] According to one embodiment, the hydrogen rich gas comprises at least 95 wt. % hydrogen.

[0027] According to one embodiment, the hydrogen-rich reducing gas comprises hydrogen produced in the electrolyser and hydrogen obtained from off-gas withdrawn from the direct reduction shaft furnace.

[0028] According to one embodiment, the step of measuring the flow rate of hydrogen-rich gas comprises measuring the flow rate of hydrogen carried by the exhaust gas or measuring the flow rate of hydrogen obtained from the exhaust gas. Preferably, the method comprises the step of mixing hydrogen from the electrolyser with hydrogen obtained from the exhaust gas, wherein the measurement is performed upstream of the point at which the hydrogen is mixed, as seen in the flow direction of the respective hydrogen. The flow rate of hydrogen in the exhaust gas is a good indicator of whether reduction has been carried out with sufficient hydrogen to produce sponge iron having a predetermined minimum metallization level, preferably above 90% by weight, or even more preferably above 92.5% by weight of iron. By controlling the flow rate of iron ore entering the direct reduction shaft furnace based on the measured flow rate of hydrogen in or obtained from the exhaust gas, and controlling the flow rate of sponge iron removed from the direct reduction shaft furnace based on the measured flow rate of hydrogen in or obtained from the exhaust gas, the flow rate of hydrogen carried by the exhaust gas can be controlled within a predetermined range for producing sponge iron having at least the predetermined minimum metallization level. The object of the present invention is also achieved by an apparatus for producing sponge iron, the apparatus comprising:

[0029] - Direct reduction shaft furnace,

[0030] - an apparatus for charging iron ore into a direct reduction shaft furnace,

[0031] - an apparatus for removing sponge iron from a direct reduction shaft furnace,

[0032] - a source of hydrogen-rich reducing gas,

[0033] - a reducing gas line extending from a hydrogen-rich reducing gas source to a direct reduction shaft furnace,

[0034] - A heater for heating the hydrogen-rich reducing gas in the reducing gas pipeline, the device being characterized in that it comprises

[0035] - a flow meter configured to measure the flow rate of the hydrogen-rich reducing gas in the reducing gas pipeline, and

[0036] a control unit configured to control the means for charging iron ore into the direct reduction shaft furnace and the means for withdrawing sponge iron from the direct reduction shaft furnace based on input from the flow meter, such that the flow rates of the iron ore and the sponge iron are proportional to the measured flow rate of the hydrogen-rich reducing gas.

[0037] According to one embodiment, the apparatus comprises a sensor for measuring the composition of the hydrogen-rich reducing gas, and wherein the control unit is configured to control the means for charging iron ore into the direct reduction shaft furnace and the means for removing sponge iron from the direct reduction shaft furnace based on input from the sensor.

[0038] According to one embodiment, the control unit is configured to evaluate the composition of the hydrogen-rich reducing gas according to its content of the reducing agent that will cause direct reduction of the iron ore, and to multiply the content of the reducing agent and the flow rate of the hydrogen-rich reducing gas by each other and generate an input value, based on which the device for charging iron ore and the device for removing sponge iron are controlled.

[0039] According to one embodiment, the control unit is configured to control the device for charging iron ore into the direct reduction shaft furnace and the device for removing sponge iron from the direct reduction shaft furnace so that the flow rates of iron ore and sponge iron correspond to each other and so that the combined level of iron ore and sponge iron in the direct reduction shaft furnace is maintained at a constant level.

[0040] According to one embodiment, the apparatus comprises a methane gas source and means for controlling the flow of methane gas from the methane gas source into the reducing gas pipeline, and wherein the flow rate of the hydrogen-rich reducing gas has a predetermined nominal value applied during predetermined nominal operating conditions of the direct reduction shaft furnace, and wherein, in response to a predetermined initial decrease in the measured flow rate of the hydrogen-rich gas from the nominal value to a threshold value, the control unit is configured to compensate for the decrease by controlling the addition of methane gas from the methane gas source to the hydrogen-rich reducing gas without a corresponding decrease in the flow rate of iron ore and the flow rate of sponge iron, and the control unit is configured to control the flow rate of iron ore and the flow rate of sponge iron by controlling the means for charging iron ore and the means for withdrawing sponge iron based on the measured flow rate of the hydrogen-rich reducing gas when the flow rate of the hydrogen-rich reducing gas further decreases below the threshold value.

[0041] According to one embodiment, the apparatus comprises a sensor for measuring the pressure in the direct reduction shaft furnace, and wherein the control unit is configured to control the addition of said methane gas in such a way that a nominal operating pressure is maintained in the direct reduction shaft furnace when the flow rate of hydrogen-rich reducing gas decreases from said nominal value to said threshold value.

[0042] According to one embodiment, the source of hydrogen-rich reducing gas comprises an electrolyzer and an off-gas recovery line for recovering off-gas taken from a direct reduction shaft furnace.

[0043] According to some embodiments, the apparatus further comprises a flow meter configured to measure the flow of hydrogen in the exhaust gas recovery line, wherein the control unit is configured to control the device for charging iron ore into the direct reduction shaft furnace and the device for removing sponge iron from the direct reduction shaft furnace based on input from the flow meter. The control unit is configured to control the device so that the flow of iron ore and the flow of sponge iron are proportional to the measured flow of the flow of hydrogen carried by the exhaust gas. In the disclosed embodiment, the flow meter is positioned upstream of the exhaust gas cleaning device provided in the exhaust gas recovery line. However, as long as the exhaust gas cleaning device is efficient in terms of the percentage of hydrogen it can extract, the flow meter can also be located downstream of the exhaust gas cleaning device. The control is performed based on previous data related to the relationship between the quality of sponge iron (mainly defined by the degree of metallization) and the hydrogen content in the exhaust gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 is a schematic illustration of a device according to one embodiment of the invention to which the method according to the invention is applied, and

[0045] Figure 2 A second embodiment of the present invention is shown. DETAILED DESCRIPTION

[0046] In the following detailed description, embodiments of the methods of the present invention will be disclosed, as well as devices configured to implement the methods.

[0047] The apparatus for producing sponge iron comprises: a direct reduction shaft furnace 1, a device 2 for charging iron ore into the direct reduction shaft furnace 1, a device 3 for removing sponge iron from the direct reduction shaft furnace 1, a source of hydrogen-rich reducing gas 4, 13, and a reducing gas pipeline 5 extending from the hydrogen-rich reducing gas source 4, 13 to the direct reduction shaft furnace 1. The hydrogen-rich gas contains at least 95% by weight of hydrogen. A heater 6 for heating the hydrogen-rich reducing gas in the reducing gas pipeline 5 is also provided. According to one embodiment, the heater 6 is an electric heater that uses a resistance element to heat the gas passing through the heater. The direct reduction shaft furnace 1 is a vertical shaft furnace, in which iron ore is charged through an inlet at the top of the shaft furnace and removed through the bottom of the shaft furnace. The device 2 for charging iron ore includes valve means suitable for this purpose, and the device 3 for removing sponge iron includes valve means suitable for this purpose. The source of hydrogen-rich reducing gas includes an electrolyzer 4 and an exhaust gas recovery pipeline 13 for recovering exhaust gas removed from the direct reduction shaft furnace 1. The heater 6 is a heater for heating the reducing gas to a temperature within a range of 750°C to 1100°C.

[0048] The apparatus further comprises: a flow meter 7 configured to measure the flow rate of the hydrogen-rich reducing gas in the reducing gas pipeline 5; and a control unit 8 configured to control the device 2 for charging the iron ore into the direct reduction shaft furnace 1 and the device 3 for taking out the sponge iron from the direct reduction shaft furnace 1 based on the input from the flow meter 7. The control unit 8 is configured to control the devices 2 and 3 so that the flow rates of the iron ore and the sponge iron are proportional to the measured flow rate of the hydrogen-rich reducing gas. The control unit 8 may be any suitable combination of hardware and software, by which the operation of the apparatus is controlled.

[0049] The apparatus further comprises a sensor 9 for measuring the composition of the hydrogen-rich reducing gas. The control unit 8 is configured to control the device 2 for charging the iron ore into the direct reduction shaft furnace 1 and the device 3 for removing the sponge iron from the direct reduction shaft furnace 1 based on the input from the sensor 9. More precisely, the control unit 8 is configured to evaluate the measured composition of the hydrogen-rich reducing gas according to its content of the reducing agent that will cause direct reduction of the iron ore, and to multiply the content of the reducing agent and the flow rate of the hydrogen-rich reducing gas by each other and generate an input value, based on which the device 2 for charging the iron ore and the device 3 for removing the sponge iron are controlled.

[0050] Furthermore, the control unit 8 is configured to control the device 2 for charging iron ore and the device 3 for removing sponge iron so that the flows of iron ore and sponge iron correspond to each other and the combined level of iron ore and sponge iron in the direct reduction shaft furnace 1 is maintained at a constant level.

[0051] The apparatus comprises a methane gas source 10 and a valve device 11 for controlling the flow of methane gas from said methane gas source 10 into a reducing gas pipeline 5. The flow rate of the hydrogen-rich reducing gas has a predetermined nominal value applied during predetermined nominal operating conditions of the direct reduction shaft furnace 1, and further, in response to a predetermined initial decrease in the measured flow rate of the hydrogen-rich gas from said nominal value to a threshold value, a control unit 8 is configured to compensate for said decrease by controlling the addition of methane gas from the methane gas source to the hydrogen-rich reducing gas without correspondingly decreasing the flow rates of iron ore and sponge iron. The control unit 8 is configured to control the flow rates of iron ore and sponge iron by controlling the device for charging iron ore 2 and the device for removing sponge iron 3 based on the measured flow rate of the hydrogen-rich reducing gas when the flow rate of the hydrogen-rich reducing gas further decreases below said threshold value.

[0052] The apparatus further comprises a sensor 12 for measuring the pressure in the direct reduction shaft furnace 1. The output from the pressure sensor 12 is used as an input to a control unit 8. The control unit 8 is configured to control the addition of said methane gas so that the nominal operating pressure is maintained in the direct reduction shaft furnace 1 when the flow rate of the hydrogen-rich reducing gas is reduced from said nominal value to said threshold value.

[0053] It goes without saying that the apparatus is also provided with further devices known to those skilled in the art for achieving functions such as pressurization, exhaust gas cleaning, etc. Therefore, the apparatus also includes an exhaust gas cleaning device 14, an exhaust gas recovery line 13 and a compressor device 15 arranged in the reducing gas line 5. If necessary, further compressors and cleaning steps can also be provided.

[0054] Therefore, the device is configured to perform the method of the present invention. The method comprises the following steps:

[0055] - charging iron ore into the direct reduction shaft furnace 1;

[0056] -Provide hydrogen-rich reducing gas;

[0057] - heating the hydrogen-rich reducing gas to a predetermined temperature;

[0058] - introducing heated hydrogen-rich reducing gas into the direct reduction shaft furnace 1 to reduce the iron ore to produce sponge iron; and

[0059] - The produced sponge iron is taken out from the direct reduction shaft furnace 1.

[0060] The method further comprises the following steps:

[0061] -Measure the flow rate of hydrogen-rich gas, and

[0062] - controlling the flow of iron ore into the direct reduction shaft furnace 1 based on the measured flow of hydrogen-rich gas, and

[0063] - controlling the flow rate of sponge iron taken out of the direct reduction shaft furnace 1 based on the measured flow rate of hydrogen-rich gas, wherein

[0064] - The flow rates of iron ore and sponge iron are controlled so that they are proportional to the measured flow rate of hydrogen-rich reducing gas.

[0065] The method further comprises the step of measuring the composition of the hydrogen-rich reducing gas, wherein the flow of iron ore entering the shaft furnace 1 and the flow of sponge iron withdrawn from the direct reduction shaft furnace 1 are controlled based on the measured flow of the hydrogen-rich reducing gas and based on the measured composition of the hydrogen-rich reducing gas.

[0066] The composition of the hydrogen-rich reducing gas is evaluated according to its content of reducing agent that will cause direct reduction of iron ore, and the content of reducing agent and the flow rate of the hydrogen-rich reducing gas are multiplied with each other to produce input values, based on which the flow rates of iron ore and sponge iron are controlled.

[0067] The flow rate of iron ore and the flow rate of sponge iron are controlled so that they correspond to each other and so that the combined level of iron ore and sponge iron in the direct reduction shaft furnace 1 is maintained at a constant level.

[0068] The flow rate of the hydrogen-rich reducing gas has a predetermined nominal value applied during predetermined nominal operating conditions of the direct reduction shaft furnace 1, and wherein a predetermined initial decrease in the flow rate of the hydrogen-rich gas from said nominal value to a threshold value is compensated by adding methane gas to the hydrogen-rich gas without a corresponding decrease in the flow rates of iron ore and sponge iron, and wherein when the flow rate of the hydrogen-rich gas further decreases below said threshold value, the flow rates of iron ore and sponge iron are controlled based on the measured flow rates of hydrogen. Adding methane gas is an optional embodiment. As an alternative embodiment, compensation of fluctuations in the flow rate of the hydrogen-rich reducing gas is accomplished by controlling only the flow rates of iron ore entering the shaft furnace and the flow rate of sponge iron leaving the shaft furnace.

[0069] The method further comprises the step of measuring the pressure in the direct reduction shaft furnace 1 , wherein the addition of the methane gas is controlled such that the nominal operating pressure is maintained in the direct reduction shaft furnace 1 when the flow rate of the hydrogen-rich reducing gas is reduced from the nominal value to the threshold value.

[0070] Figure 2 The second embodiment disclosed in Figure 1The embodiment shown in differs in that the step of measuring the flow of hydrogen-rich gas comprises measuring the flow of hydrogen carried by the exhaust gas or measuring the flow of hydrogen obtained from the exhaust gas. Preferably, the method comprises the step of mixing hydrogen from the electrolyser with hydrogen obtained from the exhaust gas, wherein the measurement is made upstream of the point at which the hydrogen is mixed, as seen in the flow direction of the respective hydrogen gases. The flow of hydrogen in the exhaust gas is a good indicator of whether sufficient hydrogen has been used for reduction to produce sponge iron having a predetermined minimum metallization level, preferably above 90 wt. %, or even more preferably above 92.5 wt. % iron. By controlling the flow of iron ore into the direct reduction shaft furnace based on the measured flow of hydrogen in or obtained from the exhaust gas and controlling the flow of sponge iron removed from the direct reduction shaft furnace based on the measured flow of hydrogen in or obtained from the exhaust gas, the flow of hydrogen carried by the exhaust gas can be controlled within a predetermined range for producing sponge iron having at least the predetermined minimum metallization level.

[0071] according to Figure 2 The device comprises a flow meter 16 configured to measure the flow of hydrogen in the exhaust gas recovery line 13, wherein the control unit 8 is configured to control the device 2 for charging iron ore into the direct reduction shaft furnace 1 and the device 3 for removing sponge iron from the direct reduction shaft furnace 1 based on the input from the flow meter 16. The control unit 8 is configured to control the devices 2, 3 so that the flow of iron ore and the flow of sponge iron are proportional to the measured flow of hydrogen carried by the exhaust gas. In the disclosed embodiment, the flow meter 16 is located upstream of the exhaust gas cleaning device 14. However, as long as the exhaust gas cleaning device 14 is efficient in terms of the percentage of hydrogen it can extract, the flow meter 16 can also be located downstream of the exhaust gas cleaning device 14.

[0072] The control unit 8 is preferably configured so as to give priority to the input from the flow meter 16 in the exhaust gas recovery line rather than the input from the flow meter 7 in the reducing gas line 5. Therefore, the input from the flow meter in the exhaust gas recovery line 13 will be decisive for the control of the devices 2, 3 so that the flow of iron ore and the flow of sponge iron are proportional to the measured flow of hydrogen carried by the exhaust gas in case the input from different meters produces different suggestions for the output from the control unit 8.

Claims

1. A method for continuously producing sponge iron from iron ore, comprising the steps of: - charging the iron ore into a direct reduction shaft furnace (1), -Provide hydrogen-rich reducing gas, - heating the hydrogen-rich reducing gas to a predetermined temperature, - introducing heated hydrogen-rich reducing gas into the direct reduction shaft furnace (1) to reduce the iron ore to produce sponge iron, and - removing the produced sponge iron from the direct reduction shaft furnace (1), - The method is characterized in that it comprises the following steps: - measuring the flow rate of said hydrogen-rich gas, and - controlling the flow of iron ore into the direct reduction shaft furnace (1) based on the measured flow of the hydrogen-rich gas, and - controlling the flow rate of the sponge iron taken out of the direct reduction shaft furnace (1) based on the measured flow rate of the hydrogen-rich gas, wherein - The flow rate of the iron ore and the flow rate of the sponge iron are controlled so that they are proportional to the measured flow rate of the hydrogen-rich reducing gas.

2. The method according to claim 1 , comprising the further step of measuring the composition of the hydrogen-rich reducing gas, wherein the flow rate of the iron ore entering the shaft furnace (1) and the flow rate of the sponge iron withdrawn from the direct reduction shaft furnace (1) are controlled based on the measured flow rate of the hydrogen-rich reducing gas and based on the measured composition of the hydrogen-rich reducing gas.

3. The method according to claim 2, wherein the composition of the hydrogen-rich reducing gas is evaluated according to its content of a reducing agent that will cause direct reduction of the iron ore, and wherein the content of the reducing agent and the flow rate of the hydrogen-rich reducing gas are multiplied with each other to produce an input value, based on which the flow rates of the iron ore and the sponge iron are controlled.

4. The method according to any one of claims 1 to 3, wherein the flow rate of the iron ore and the flow rate of the sponge iron are controlled so that they correspond to each other and so that the combined level of iron ore and sponge iron in the direct reduction shaft furnace (1) is maintained at a constant level.

5. A method according to any one of claims 1 to 4, wherein the flow rate of the hydrogen-rich reducing gas has a predetermined nominal value which applies during predetermined nominal operating conditions of the direct reduction shaft furnace (1), and wherein a predetermined initial decrease in the flow rate of the hydrogen-rich gas from the nominal value to a threshold value is compensated by adding methane gas to the hydrogen-rich gas without a corresponding decrease in the flow rates of the iron ore and the sponge iron, and wherein when the flow rate of the hydrogen-rich gas further decreases below the threshold value, the flow rates of the iron ore and the sponge iron are controlled based on the measured flow rate of hydrogen.

6. The method according to claim 5, comprising the step of measuring the pressure in the direct reduction shaft furnace (1), wherein the addition of the methane gas is controlled so that the nominal operating pressure is maintained in the direct reduction shaft furnace (1) when the flow rate of the hydrogen-rich reducing gas decreases from the nominal value to the threshold value.

7. The method of any one of claims 1 to 6, wherein the hydrogen-rich gas comprises at least 80 wt% hydrogen.

8. The method of any one of claims 1 to 6, wherein the hydrogen-rich gas comprises at least 90 wt% hydrogen.

9. The method of any one of claims 1 to 6, wherein the hydrogen-rich gas comprises at least 95 wt. % hydrogen.

10. The method according to any one of claims 1 to 9, wherein the hydrogen-rich reducing gas comprises hydrogen produced in an electrolyser and hydrogen obtained from exhaust gas withdrawn from the direct reduction shaft furnace (1).

11. A method according to claim 10 and any one of claims 1 to 9, wherein the step of measuring the flow rate of the hydrogen-rich gas comprises measuring the flow rate of hydrogen carried by the exhaust gas or measuring the flow rate of hydrogen obtained from the exhaust gas; preferably, the method comprises the step of mixing hydrogen from an electrolyzer with hydrogen obtained from the exhaust gas, wherein the measurement is performed upstream of the point where the hydrogen is mixed, as seen in the flow direction of the respective hydrogen.

12. An apparatus for producing sponge iron, comprising: - a direct reduction shaft furnace (1), - a device (2) for charging iron ore into the direct reduction shaft furnace (1), - a device (3) for removing sponge iron from the direct reduction shaft furnace (1), - a source of hydrogen-rich reducing gas (4), - a reducing gas line (5) extending from the hydrogen-rich reducing gas source (4, 13) to the direct reduction shaft furnace (1), - a heater (6) for heating the hydrogen-rich reducing gas in the reducing gas pipeline (5), the device being characterized in that the device comprises - a flow meter (7) configured to measure the flow rate of the hydrogen-rich reducing gas in the reducing gas pipeline (5), and - a control unit (8) configured to control the device (2) for charging iron ore into the direct reduction shaft furnace (1) and the device (3) for removing sponge iron from the direct reduction shaft furnace (1) based on input from the flow meter (7), so that the flow rates of the iron ore and the sponge iron are proportional to the measured flow rate of the hydrogen-rich reducing gas.

13. Apparatus according to claim 12, wherein the apparatus comprises a sensor (9) for measuring the composition of the hydrogen-rich reducing gas, and wherein the control unit (8) is configured to control the means (2) for charging iron ore into the direct reduction shaft furnace (1) and the means (3) for removing sponge iron from the direct reduction shaft furnace (1) based on input from the sensor (9).

14. The apparatus according to claim 13, wherein the control unit (8) is configured to evaluate the composition of the hydrogen-rich reducing gas according to its content of reducing agent that will cause direct reduction of the iron ore, and to multiply the content of the reducing agent and the flow rate of the hydrogen-rich reducing gas by each other and generate an input value, based on which the device (2) for charging iron ore and the device (3) for removing sponge iron are controlled.

15. The apparatus according to any one of claims 12 to 14, wherein the control unit (8) is configured to control the device (2) for charging iron ore into the direct reduction shaft furnace (1) and the device (3) for removing sponge iron from the direct reduction shaft furnace (1) so that the flow rates of iron ore and sponge iron correspond to each other and so that the combined level of iron ore and sponge iron in the direct reduction shaft furnace (1) is maintained at a constant level.

16. The apparatus according to any one of claims 12 to 15, wherein the apparatus comprises a methane gas source (10) and valve means (11) for controlling the flow of methane gas from the methane gas source (10) into the reducing gas pipeline (5), and wherein the flow rate of the hydrogen-rich reducing gas has a predetermined nominal value which applies during predetermined nominal operating conditions of the direct reduction shaft furnace (1), and wherein, In response to a predetermined initial decrease in the measured flow rate of the hydrogen-rich gas from the nominal value to a threshold value, the control unit (8) is configured to compensate for the decrease by controlling the addition of methane gas from the methane gas source to the hydrogen-rich reducing gas without correspondingly reducing the flow rates of the iron ore and the sponge iron, and wherein the control unit (8) is configured to control the flow rates of the iron ore and the sponge iron by controlling the device (2) for charging iron ore and the device (3) for removing sponge iron based on the measured flow rates of the hydrogen-rich reducing gas when the flow rate of the hydrogen-rich reducing gas further decreases below the threshold value.

17. The apparatus according to claim 16, wherein the apparatus comprises a sensor (12) for measuring the pressure in the direct reduction shaft furnace (1), and wherein the control unit (8) is configured to control the addition of the methane gas so that the nominal operating pressure is maintained in the direct reduction shaft furnace (1) when the flow rate of the hydrogen-rich reducing gas decreases from the nominal value to the threshold value.

18. The apparatus according to any one of claims 12 to 17, wherein the hydrogen-rich reducing gas source comprises an electrolyser (4) and an exhaust gas recovery line (13) for recovering exhaust gas taken from the direct reduction shaft furnace (1).

19. The apparatus according to claim 18 and any one of claims 12 to 17, comprising a flow meter (16) configured to measure the flow rate of hydrogen in the off-gas recovery line (13), wherein the control unit (8) is configured to control the device (2) for charging iron ore into the direct reduction shaft furnace (1) and the device (3) for removing sponge iron from the direct reduction shaft furnace (1) based on input from the flow meter (16).

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