Method for producing sponge iron from iron ore

Abstract

The present invention relates to a method for producing sponge iron from iron ore, comprising the steps of: charging iron ore into a direct reduction shaft (1); and introducing a hydrogen-rich treat gas into said direct reduction shaft (1) for reducing iron ore to produce sponge iron, the hydrogen-rich treat gas comprising a reducing gas containing at least 80% by volume of hydrogen gas from a hydrogen gas source (4, 21) through a first gas line (5) to said reduction shaft (1); and heating the reducing gas in said first gas line (5) to a first temperature T1. The method further comprises the steps of adding carbon dioxide gas to the reducing gas upstream or downstream of a point along the first gas line (5) where the reducing gas is heated, and adding oxygen gas to the heated reducing gas to form said hydrogen-rich treat gas; and introducing the hydrogen-rich treat gas into the shaft (1).

Description

[Technical field]

[0001] The present invention relates to a method for producing sponge iron from iron ore, comprising the steps of: charging iron ore into a direct reduction shaft; and introducing a hydrogen-rich treat gas into the direct reduction shaft for reducing the iron ore to produce sponge iron, the hydrogen-rich treat gas comprising: directing a reducing gas comprising at least 80% by volume of hydrogen gas from a hydrogen gas source through a first gas line into the reduction shaft; and heating the reducing gas to a first temperature in said first gas line. The hydrogen gas source may include both a pure hydrogen gas source, such as an electrolysis unit or a pure hydrogen gas reservoir, and a return flow of gas from the top of the reduction shaft.

[0002] The present invention also relates to an apparatus for producing sponge iron, comprising a direct reduction shaft having an inlet for the introduction of iron ore and an outlet for removing the produced sponge iron out of the direct reduction shaft, a hydrogen gas source, a first gas line extending from the hydrogen gas source to the reduction shaft, a carbon dioxide gas source, an oxygen gas source, and a heater disposed in the first gas line for heating the gas flowing in the first gas line. [Background technology]

[0003] In connection with the direct reduction of iron ore to sponge iron using primarily hydrogen gas as the reducing gas, a carbon-containing gas may be added to the hydrogen gas to allow some carburization of the sponge iron, thereby making it more suitable for melting in, for example, an electric arc furnace.

[0004] It has been proposed to use carbon dioxide as a carbon-containing gas. If the temperature of the process gas, consisting of the reducing gas and the added carbon dioxide, is high enough, the carbon dioxide reacts with the hydrogen, thereby forming carbon monoxide. Carburization with carbon monoxide is preferred. Therefore, temperature control of the process gas is essential to ensure that carbon monoxide is formed when carbon dioxide is added to the reducing gas. Summary of the Invention [Problem to be solved by the invention]

[0005] It is therefore an object of the present invention to propose a method and an apparatus which allows control of the process gas composition and of the process gas temperature, thereby allowing an efficient and reliable control of the carburization of sponge iron. [Means for solving the problem]

[0006] The object of the present invention is achieved by a method for producing sponge iron from iron ore, comprising the steps of: charging iron ore into a direct reduction shaft; and introducing a hydrogen-rich treat gas into the direct reduction shaft for reducing the iron ore to produce sponge iron, the hydrogen-rich treat gas comprising the steps of directing a reducing gas comprising at least 80% by volume of hydrogen gas from a hydrogen gas source through a first gas line into the reduction shaft; and heating the reducing gas in said first gas line to a first temperature, characterized in that the method further comprises the steps of adding carbon dioxide gas to the reducing gas upstream or downstream of a point along the first gas line where the reducing gas is heated, and adding oxygen gas to the heated reducing gas to form said hydrogen-rich treat gas; and introducing the hydrogen-rich treat gas into the shaft.

[0007] The addition of oxygen gas results in combustion of the reducing gas (to which carbon dioxide has been added) and an increase in temperature. If the temperature of the reducing gas is high enough to allow for a combustion reaction, the addition of oxygen will be used as a means of controlling the temperature of the reducing gas so that the carbon dioxide in the reducing gas will generally react with hydrogen to form carbon monoxide. A heater whose main role is to heat the reducing gas to a predetermined level may not respond quickly enough to respond to and compensate for sudden changes in gas temperature, such as those caused by fluctuations in the flow rate of the added carbon dioxide. On the other hand, the addition of oxygen provides an immediate and localized temperature increase, making it an efficient tool for rapid and accurate temperature control in addition to the basic heating provided by the heater. The flow rate of the added carbon dioxide gas should preferably be determined so that the carbon content in the sponge iron is at least 0.05% by weight, preferably at least 0.5% by weight, or even more preferably at least 1.0% by weight. To ensure uniformity in product quality, the carbon content of the produced sponge iron needs to have minimal fluctuations.

[0008] The hydrogen gas source includes an electrolysis unit or a hydrogen gas reservoir or a combination thereof. According to one embodiment, the hydrogen gas source also includes a return gas circuit, one end of which is connected to the top of the reduction shaft and the other end of which is connected to the first gas line. The return gas is usually referred to as the spent process gas leaving the direct reduction shaft from the top of the direct reduction shaft. The return gas may include a significant amount of hydrogen gas, which is preferably returned to the first gas line. The return gas circuit may include one or more devices for cleaning the return gas, compressors, etc., as known in the art. Thus, the reduction gas is made up of gas from both the hydrogen gas source and the return gas circuit. The apparatus also preferably includes at least one compressor provided in the first gas line to generate a suitable process gas pressure, usually in the range of 3 to 8 bar. According to one embodiment, the reduction gas includes at least 90% by volume of hydrogen gas.

[0009] According to one aspect, the aforementioned method includes a step of measuring the flow rate of the reducing gas in the first gas line and a step of controlling the flow rate of the added carbon dioxide based on the measured flow rate of the reducing gas. If the composition of the reducing gas is relatively constant or can be predicted with an acceptable accuracy, the knowledge regarding the flow rate of the reducing gas is sufficient information to enable the determination of the correct carbon dioxide gas flow rate to achieve the required ratio between hydrogen and carbon dioxide.

[0010] According to one aspect, this method includes a step of measuring the composition of the reducing gas in the first gas line and a step of controlling the flow rate of the added carbon dioxide based on the measured composition of the reducing gas. The knowledge regarding the composition of the reducing gas further improves the precise and accurate determination of the carbon dioxide gas flow rate to achieve the required ratio between hydrogen and carbon dioxide.

[0011] According to one aspect, the aforementioned method a) measuring the temperature of the hydrogen-rich process gas downstream of the point along the first gas line where carbon dioxide gas and oxygen gas are added to the reducing gas; and b) controlling the flow rate of the added oxygen gas based on the measured temperature of the hydrogen-rich process gas. Measuring the temperature downstream of the point where oxygen is added enables an efficient temperature control loop.

[0012] According to one aspect, this method includes an iterative process from step a) to b), and step b) c) increasing the flow rate of the added oxygen gas when the measured temperature of the hydrogen-rich process gas is below the first threshold value Tth1; and d) decreasing the flow rate of the added oxygen gas when the measured temperature of the hydrogen-rich process gas is above the second threshold value Tth2, where Tth1 < Tth2.

[0013] According to one aspect, Tth1>750° C. According to one embodiment, Tth1=800° C. Thereby, at least some reaction of carbon dioxide to carbon monoxide in the reducing gas is achieved.

[0014] According to one aspect, Tth1≧900° C. According to one embodiment, Tth1=900° C. Thereby, a substantial reaction of carbon dioxide in the reducing gas to carbon monoxide is achieved.

[0015] According to one aspect, Tth2≦1100° C. According to one embodiment, Tth2=1100° C. Thereby, excessive temperature conditions in the reduction shaft, which are detrimental to the reduction process, are avoided.

[0016] According to one aspect, the method includes measuring the temperature of the heated reducing gas upstream of a point along said first gas line where oxygen gas is added to the reducing gas, and adding oxygen gas only if the temperature of the heated reducing gas at said point is above 750°C. This results in ignition and combustion due to oxygen gas. According to one embodiment, oxygen gas is added to the reducing gas only if the temperature of the heated reducing gas at said point is above 800°C. Therefore, the heater used to heat the reducing gas upstream of the point where oxygen gas is added should be controlled to heat the reducing gas to at least 750°C, preferably at least 800°C.

[0017] According to one aspect, each of the carbon dioxide gas and the oxygen gas is added to the reduction gas in a first gas line proximate to the end of the first gas line where the hydrogen-rich process gas is introduced into the reduction shaft. According to one embodiment, the proximity is referred to as less than 10 meters. According to another embodiment, the proximity is referred to as less than 5 meters.

[0018] This object is also achieved by an apparatus for producing sponge iron, comprising: a direct reduction shaft having an inlet for the introduction of iron ore and an outlet for removing the produced sponge iron out of the direct reduction shaft; a hydrogen gas source; a first gas line extending from the hydrogen gas source to the reduction shaft; a carbon dioxide source; an oxygen gas source; and a heater disposed in the first gas line for heating the gas flowing in the first gas line, a second gas line extending from the carbon dioxide gas source to the first gas line and configured to add carbon dioxide gas from the carbon dioxide gas source to the reducing gas flowing in the first gas line from the hydrogen gas source directly towards the reduction shaft; and a third gas line extending from the oxygen gas source and connected to the first gas line downstream of the heater and configured to add oxygen gas from the oxygen gas source to the reducing gas flowing in the first gas line from the hydrogen gas source directly towards the reduction shaft.

[0019] The hydrogen gas source includes an electrolysis unit or a hydrogen gas reservoir or a combination thereof. According to one embodiment, the hydrogen gas source also includes a return gas circuit, one end of which is connected to the top of the reduction shaft and the other end of which is connected to the first gas line. The return gas circuit may include one or more devices for cleaning the return gas, a compressor, etc., as known in the art. Thus, the reduction gas is composed of gas from both the electrolysis cell and / or reservoir and from the return gas circuit.

[0020] The apparatus includes components arranged for enabling the method disclosed above, the advantages of which are similar to those already disclosed with reference to that method.

[0021] According to one aspect, the apparatus comprises a first flow sensor for sensing a flow rate of a reducing gas in a first gas line, a first valve device for regulating a flow rate of carbon dioxide in said second gas line, and a control unit configured to control the first valve device based on an input from the first flow sensor.

[0022] According to one aspect, the apparatus comprises: a gas composition sensor for detecting a composition of the reducing gas in the first gas line; a control unit configured to control the first valve device based on an input from the gas composition sensor; and Equipped with.

[0023] According to one embodiment, the apparatus includes a temperature sensor for sensing a temperature of gas within the first gas line downstream of a point where the second gas line and the third gas line are connected to the first gas line, a second valve device for adjusting a flow rate of added oxygen gas in the third gas line, and a control unit configured to control the flow rate of added oxygen gas in the third gas line based on an input from the temperature sensor.

[0024] According to one embodiment, the apparatus includes a second temperature sensor for sensing a temperature of the gas within the first gas line downstream of the heater and upstream of a point where the third gas line is connected to the first gas line, wherein the control unit is configured to enable a flow of the added oxygen gas in the third gas line only if the temperature measured by the second temperature sensor is above a predetermined level.

[0025] According to one embodiment, the first gas line includes an end through which a hydrogen-rich process gas formed by the reducing gas, the added carbon dioxide gas, and the added oxygen gas is introduced into the reducing shaft, wherein at least a third gas line is connected to the first gas line adjacent said end.

[0026] According to one embodiment, the second and third gas lines are connected to the first gas line at the same point along the first gas line, or the third gas line is connected to the first gas line downstream of a point along the first gas line at which the second gas line is connected to the first gas line.

[0027] Further objects and advantages will become apparent in the detailed description. [Brief description of the drawings]

[0028] [Figure 1] 1 is a schematic diagram of an apparatus according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] In the following detailed description, method embodiments of the present invention are disclosed, as well as apparatus configured to carry out the methods.

[0030] According to one embodiment of the present invention, an apparatus for producing sponge iron comprises a direct reduction shaft 1 having an inlet 2 for introducing iron ore and an outlet 3 for removing the produced sponge iron out of the direct reduction shaft 1. The apparatus further comprises a hydrogen gas source 4, 21, a first gas line 5 extending from the hydrogen gas source 4, 21 to the reduction shaft 1, a carbon dioxide gas source 6, an oxygen gas source 7, and a heater 16 disposed in the first gas line 5 for heating the gas flowing in the first gas line 5. The apparatus further comprises a second gas line 8 extending from a carbon dioxide gas source 6 to the first gas line 5 and configured to allow addition of carbon dioxide gas from the carbon dioxide gas source 6 to the reducing gas flowing in the first gas line 5 from the hydrogen gas source 4, 21 towards the direct reduction shaft 1, and a third gas line 9 extending from an oxygen gas source 7 and connected to the first gas line 5 downstream of the heater 16 and configured to allow addition of oxygen gas from the oxygen gas source 6 to the reducing gas flowing in the first gas line 5 from the hydrogen gas source 4, 21 towards the direct reduction shaft 1. A compressor (not shown) for generating a predetermined process gas pressure (typically in the range of 3-8 bar) and pressure inside the direct reduction shaft 1 is also provided in the apparatus.

[0031] The hydrogen gas source 4 comprises an electrolysis unit or a pure hydrogen gas reservoir or a combination thereof, here indicated with reference number 4. In the illustrated embodiment, the hydrogen gas source also comprises a return gas circuit 21, which extends from the top of the reduction shaft 1 and is connected to the first gas line 5. The return gas circuit may comprise one or more devices for scrubbing the return gas, compressors, etc., as is well known in the art. The reduction gas is thus composed of both gas from the electrolysis unit or reservoir 4 and from the return gas circuit 21. According to one embodiment, the reduction gas comprises at least 90% by volume of hydrogen gas.

[0032] The apparatus further comprises a first flow sensor 10 for detecting the flow rate of the reducing gas in the first gas line 5, a first valve device 11 for adjusting the flow rate of carbon dioxide in the aforementioned second gas line 8, and a control unit 12 configured to control the first valve device 11 based on an input from the first flow sensor 10.

[0033] The apparatus further includes a gas composition sensor 19 for detecting the composition of the reducing gas in the first gas line 5, wherein the control unit 12 is configured to control the first valve device 11 based on an input from the gas composition sensor 19.

[0034] A temperature sensor 13 is also provided for sensing the temperature of the gas within the first gas line 5 downstream of the point where the second gas line 8 and the third gas line 9 are connected to the first gas line 5, and a second valve device 14 for adjusting the flow rate of the added oxygen gas in the third gas line 9, and the control unit 12 is configured to control the flow rate of the added oxygen gas in the third gas line 9 based on input from the temperature sensor 13.

[0035] The apparatus further comprises a second temperature sensor 20 for sensing the temperature of the gas inside the first gas line 5 downstream of the heater 16 and upstream of the point where the third gas line 9 is connected to the first gas line 5. The control unit 12 is configured to allow the flow of added oxygen gas in the third gas line 9 only if the temperature measured by the second temperature sensor 20 is above a predetermined level, preferably 750° C.

[0036] The first gas line 5 includes an end 15 through which the hydrogen-rich process gas formed by the reducing gas, the added carbon dioxide gas, and the added oxygen gas is introduced into the reduction shaft 1. A third gas line 9 is connected to the first gas line 5 adjacent said end.

[0037] The second and third gas lines 8, 9 are connected to the first gas line 5 at the same point along the first gas line 5. Alternatively, not shown, the third gas line 9 may be connected to the first gas line 5 downstream of the point along the first gas line 5 where the second gas line 8 is connected to the first gas line 5. The second gas line 8 may be connected to the first gas line 5 upstream of the heater 16.

[0038] The apparatus is arranged to operate according to the method of the present invention, which is a method of producing sponge iron from iron ore, comprising the steps of charging iron ore into a direct reduction shaft 1 via a reduction shaft inlet 2, and introducing a hydrogen-rich treat gas into the direct reduction shaft 1 for reducing the iron ore to produce sponge iron, the hydrogen-rich treat gas comprising at least 80% by volume of hydrogen gas being conducted from a hydrogen gas source 4 through a first gas line 5 to the reduction shaft 1, and heating said reducing gas in said first gas line 5 to a first temperature T1 using a heater 16. The method also comprises the steps of adding carbon dioxide gas from a carbon dioxide source 6 to the reducing gas at a point, in this case downstream, along the first gas line 5 where the reducing gas is heated by the heater 16, and adding oxygen gas from an oxygen gas source 7 to the heated reducing gas to form said hydrogen-rich treat gas, and introducing the hydrogen-rich treat gas into the shaft 1. Carbon dioxide gas is added via a second gas line 8 and an oxygen gas source is added via a third gas line 9 .

[0039] The method further comprises measuring the flow rate of the reducing gas in the first gas line 5 using a first flow sensor 11 and controlling the flow rate of the added carbon dioxide based on the measured flow rate of the reducing gas using a control unit 12 and a first valve device 11. The addition of carbon dioxide is performed such that carburization of the produced sponge iron occurs such that the sponge iron has a carbon content of at least 1.0 wt.%.

[0040] The method further includes measuring the composition of the reducing gas in the first gas line 5 using a gas composition sensor 19 and controlling the flow rate of added carbon dioxide based on the measured composition of the reducing gas using the control unit 12 and the first valve device 11.

[0041] Furthermore, this method includes: a) measuring, using a first temperature sensor 13, the temperature of the hydrogen-rich process gas downstream of a point along a first gas line 5 where carbon dioxide gas and oxygen gas are added to the reducing gas; and b) controlling, using a control unit 12 and a second valve device 14, the flow rate of the added oxygen gas based on the measured temperature of the hydrogen-rich process gas.

[0042] This method includes an iterative process from step a) to b), and step b) includes: c) increasing, using a control unit 12 and a second valve device 14, the flow rate of the added oxygen gas when the measured temperature of the hydrogen-rich process gas (measured using the first temperature sensor 13) is below a first threshold value Tth1; d) decreasing, when the measured temperature of the hydrogen-rich process gas is above a second threshold value Tth2, where Tth1 < Tth2, the flow rate of the added oxygen gas.

[0043] According to one embodiment, Tth1 = 900 °C. That is, if the measured temperature is below 900 °C, the flow rate of the added oxygen gas is increased. The increment step for increasing the flow rate is a matter of design choice.

[0044] According to one embodiment, Tth2 = 1100 °C. That is, if the measured temperature is above 1100 °C, the flow rate of the added oxygen gas is decreased. The increment step for decreasing the flow rate is a matter of design choice.

[0045] This method also includes measuring, using a second temperature sensor 20, the temperature of the heated reducing gas upstream of a point along the aforementioned first gas line 5 where oxygen gas is added to the reducing gas, and adding oxygen gas only when the temperature of the heated reducing gas at the aforementioned point is above 800 °C. Thus, if the measured temperature is below 800 °C, the control unit 12 closes the second valve device 14, and the heater 16 serves to heat the gas until it reaches 800 °C. Next, oxygen gas is added to further increase the temperature (above 900 °C).

[0046] Carbon dioxide gas and oxygen gas are each added to the reducing gas in the first gas line 5 within 5 meters of the end of the first gas line 5 where the hydrogen-rich process gas is introduced into the reducing shaft 1 .

Claims

1. Charging iron ore into a direct reduction shaft (1); introducing a hydrogen-rich treat gas into the direct reduction shaft (1) to reduce the iron ore to produce sponge iron, conducting a reducing gas containing at least 80% by volume of hydrogen gas from a hydrogen gas source (4) through a first gas line (5) to the reducing shaft (1); and introducing a hydrogen-rich process gas, including heating the reducing gas in the first gas line (5) to a first temperature T1; 1. A method for producing sponge iron from iron ore, comprising: adding carbon dioxide gas to the reducing gas upstream or downstream of the point along the first gas line (5) where the reducing gas is heated, and adding oxygen gas to the heated reducing gas to form the hydrogen-rich treat gas; introducing the hydrogen-rich process gas into the shaft (1); A method comprising:

2. measuring the flow rate of the reducing gas in the first gas line (5); controlling the flow rate of added carbon dioxide based on the measured flow rate of the reducing gas; The method of claim 1 , comprising:

3. measuring the composition of the reducing gas in the first gas line (5); controlling the flow rate of added carbon dioxide based on the measured composition of the reducing gas. The method of claim 1 further comprising:

4. a) measuring the temperature of the hydrogen-rich treat gas downstream of a point along the first gas line (5) where the carbon dioxide gas and the oxygen gas are added to the reducing gas; b) controlling the flow rate of the added oxygen gas based on the measured temperature of the hydrogen-rich treat gas; The method of claim 1 , comprising:

5. The method comprises repeating steps a) to b), wherein step b) comprises: c) increasing the flow rate of the added oxygen gas when the measured temperature of the hydrogen-rich process gas is below a first threshold Tth1; d) decreasing the flow rate of the added oxygen gas if the measured temperature of the hydrogen-rich process gas is above a second threshold Tth2, where Tth1<Tth2; The method of claim 4, comprising:

6. The method of claim 5, wherein Tth1 > 750°C.

7. The method according to claim 5, wherein Tth1>900°C.

8. The method of claim 5, wherein Tth2<1100°C.

9. 2. The method of claim 1, further comprising measuring the temperature of the heated reducing gas upstream of a point along the first gas line where the oxygen gas is added to the reducing gas, and adding the oxygen gas only if the temperature of the heated reducing gas at the point is above 750°C.

10. 2. The method of claim 1, wherein each of the carbon dioxide gas and the oxygen gas is added to the reducing gas in the first gas line (5) proximate to an end (15) of the first gas line (5) where the hydrogen-rich process gas is introduced into the reducing shaft (1).

11. a direct reduction shaft (1) having an inlet (2) for the introduction of iron ore and an outlet (3) for the removal of the produced sponge iron from the direct reduction shaft (1); a hydrogen gas source (4); a first gas line (5) extending from the hydrogen gas source (4) to the reduction shaft (1); a carbon dioxide source (6); an oxygen gas source (7); a heater (16) disposed in the first gas line (5) for heating the gas flowing in the first gas line (5); An apparatus for producing sponge iron, comprising: a second gas line (8) extending from the carbon dioxide gas source (6) to the first gas line (5) and configured to be able to add carbon dioxide gas from the carbon dioxide gas source (6) to the reducing gas flowing in the first gas line (5) from the hydrogen gas source (4) toward the direct reduction shaft (1); a third gas line (9) extending from the oxygen gas source (7) and connected to the first gas line (5) downstream of the heater (16), and configured to add oxygen gas from the oxygen gas source (6) to the reducing gas flowing in the first gas line (5) from the hydrogen gas source (4) toward the direct reduction shaft (1).

12. a first flow sensor (10) for detecting the flow rate of the reducing gas in the first gas line (5); a first valve device (11) for adjusting the flow rate of carbon dioxide in the second gas line (8); a control unit (12) configured to control the first valve device (11) based on an input from the first flow sensor (10); The apparatus of claim 11 , comprising:

13. a gas composition sensor (19) for detecting the composition of the reducing gas in the first gas line (5); a control unit (12) configured to control the first valve device (11) based on an input from the gas composition sensor (19); The apparatus of claim 11 , comprising:

14. a temperature sensor (13) for sensing the temperature of the gas within the first gas line (5) downstream of the point where the second gas line (8) and the third gas line (9) connect to the first gas line (5); a second valve device (14) for adjusting the flow rate of the added oxygen gas in the third gas line (9); a control unit (12) configured to control the flow rate of the added oxygen gas in the third gas line (9) based on an input from the temperature sensor (13); The apparatus of claim 11 , comprising:

15. a second temperature sensor (20) for sensing the temperature of the gas inside the first gas line (5) downstream of the heater (16) and upstream of the point where the third gas line (9) connects to the first gas line (5); 15. The apparatus of claim 14, wherein the control unit (12) is configured to allow the flow of added oxygen gas in the third gas line (9) only if the temperature measured by the second temperature sensor (20) is above a predetermined level.

16. 12. The apparatus of claim 11, wherein the first gas line (5) includes an end (15) through which a hydrogen-rich process gas formed by the reducing gas, the added carbon dioxide gas, and the added oxygen gas is introduced into the reduction shaft (1), and wherein at least the third gas line (9) is connected to the first gas line (5) adjacent to the end.

17. 12. The apparatus of claim 11, wherein the second and third gas lines (8, 9) are connected to the first gas line (5) at the same point along the first gas line (5), or the third gas line (9) is connected to the first gas line (5) downstream of a point along the first gas line (5) at which the second gas line (8) is connected to the first gas line (5).

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