A method of and an arrangement for direct reduction of iron ore into sponge iron

Abstract

An arrangement for producing sponge iron by direct reduction of iron ore, comprising a direct reduction shaft (1), a first feeding chamber (4) for feeding iron ore to the direct reduction shaft (1) and a second feeding chamber (5) for feeding iron ore to the direct reduction shaft (1), the second feeding chamber (5) being connected in one end to the first feeding chamber (4) and in a second end to the direct reduction shaft (1), and a cooling zone or cooling chamber (9) provided downstream the reduction zone (8) as seen in a flow direction of the iron ore and sponge iron. There are provided first means (12; 13,14) for heat exchange between cooling gas removed from the cooling zone or cooling chamber (9) and the iron ore in the first feeding chamber (4), and second means (15, 16, 17; 18) for heat exchange between cooling gas removed from the cooling zone or cooling chamber and the iron ore in the second feeding chamber.

Description

[0001] A method of and an arrangement for direct reduction of iron ore into sponge iron

[0002] TECHNICAL FIELD

[0003] The present invention relates to a method of producing sponge iron by direct reduction of iron ore, comprising the steps of: introducing iron ore via a first feeding chamber into a second feeding chamber, and from the second feeding chamber to a direct reduction shaft, feeding the iron ore through the reduction shaft, introducing a reducing gas into the direct reduction shaft and permitting the reducing gas to flow through the direct reduction shaft in a direction opposite to the feeding direction of the iron ore in a reduction zone of the direct reduction shaft, introducing a sealing gas, other than reducing gas from the reduction zone, into the second feeding chamber, subjecting formed the sponge iron in a cooling zone or cooling chamber downstream the reduction zone to a cooling gas having a lower temperature than the sponge iron exiting the reduction zone, and removing used cooling gas from the cooling zone or cooling chamber.

[0004] The present invention also relates to an arrangement for producing sponge iron by direct reduction of iron ore in accordance with the teaching of the method.

[0005] BACKGROUND

[0006] It is known to produce pellets of sponge iron (DRI=Direct Reduced Iron) by reduction of pellets of iron ore (iron oxide) by means of hydrogen gas in a direct reduction shaft. The direction shaft may be a vertical shaft in which the iron ore moves downwards and the reduction gas moves upwards. The iron ore is introduced into an upper part of the direct reduction shaft via a feeding chamber. The feeding chamber may be pressurised by means of a sealing gas in order to prevent used reduction gas, off gas, from escaping through the feeding chamber. Upstream the feeding chamber, there might be one or more further chambers or rooms, in which the iron ore is transported to towards the final feeding chamber and the reduction shaft. Such further chambers may comprise a channel in which the iron ore pellets are transported on a conveyor belt or the like. Before removal of the DRI from the shaft the temperature of the DRI should be lowered to such a degree that reactions with ambient air is avoided. Some prior art teaches the use of so called regenerative cooling of DRI by means of a gas that can be used as reduction gas. Regenerative cooling means that cooling gas from a cooling chamber or a cooling zone is allowed to continue flowing through the direct reduction shaft, get mixed with an incoming flow of reduction gas, and thereby contribute to the reduction of the iron ore, which moves in a counter flow direction with regard to the reduction gas. As an alternative to regenerative cooling, the spent cooling gas may be recirculated back into the cooling chamber. However, such recirculation will require cooling of the heated, spent cooling gas, and maybe also cleaning thereof.

[0007] Regenerative cooling is advantageous from an energy efficiency point of view. However, it might be challenging to implement in practice. Removal of spent cooling gas from the direct reduction shaft and recirculation of spent cooling gas may therefore be an option. However, such a solution may be less good from an energy efficiency point of view.

[0008] THE OBJECT OF THE INVENTION

[0009] It is therefore an object of the present invention to present a method and an arrangement that results in efficient and reliable cooling of produced DRI and which is yet favourable from an energy efficiency point of view.

[0010] SUMMARY

[0011] The object of the invention is achieved by means of a method of producing sponge iron by direct reduction of iron ore, comprising the steps of:

[0012] -introducing iron ore via a first feeding chamber into a second feeding chamber, and from the second feeding chamber to a direct reduction shaft, -feeding the iron ore through the reduction shaft,

[0013] -introducing a reducing gas into the direct reduction shaft and permitting the reducing gas to flow through the direct reduction shaft in a direction opposite to the feeding direction of the iron ore in a reduction zone of the direct reduction shaft, -introducing a sealing gas, other than reducing gas from the reduction zone, into the second feeding chamber ,

[0014] - introducing a cooling gas having a lower temperature than the sponge iron into a cooling zone or cooling chamber downstream the reduction zone and subjecting sponge iron moving through said cooling zone or cooling chamber to the cooling gas, and

[0015] -removing used cooling gas from the cooling zone or cooling chamber, said method being characterised in that it comprises the steps of

[0016] -heating the iron ore in the first feeding chamber by exchanging heat between at least a part of the removed cooling gas and the iron ore in the first feeding chamber, and

[0017] -heating the iron ore in the second feeding chamber by exchanging heat between at least a part of the removed cooling gas and the iron ore in the second feeding chamber.

[0018] Thereby, the energy of the cooling gas removed from the cooling zone or cooling chamber is taken advantage of in a very good and efficient way, since it is used for preheating the iron ore pellets. The preheating of the iron ore pellets before they are introduced into the direct reduction shaft also means that there is a reduced risk of having condensation problems at the top of the shaft, and that the height of / volume of the shaft also possibly could be reduced. The sealing gas is introduced into the second feeding chamber for the purpose of preventing used reducing gas from escaping from the direct reduction shaft through the second feeding chamber and for preventing air and oxygen from flowing into the shaft through the second feeding chamber. Preferably, the pressure generated by the sealing gas in the second feeding chamber will be equal to or slightly below the pressure in the reduction shaft in connection to opening of the second feeding chamber towards the shaft. Preferably, there are provided valves upstream and downstream the second feeding chamber in the flow direction of the iron ore, in order to enable a controlled gas pressure in the second feeding chamber in connection to the opening thereof towards the shaft, when iron ore is to be moved from the second feeding chamber into the shaft. According to some embodiments, the step of exchanging heat between the removed cooling gas and the iron ore in the first feeding chamber comprises the step of introducing at least a part of the removed cooling gas into the first feeding chamber.

[0019] According to some embodiments, the step of exchanging heat between the removed cooling gas and the iron ore in the first feeding chamber comprises the step of exchanging heat between at least a part of the removed cooling gas and air of lower temperature than the removed cooling gas, and introducing the heated air into the first feeding chamber.

[0020] According to some embodiments, the step of exchanging heat between the removed cooling gas and the iron ore in the second feeding chamber comprises the step of conducting at least a part of the removed cooling gas a sealing gas to be introduced into the second feeding chamber into a heat exchanger for heat exchange between the used cooling gas and the sealing gas and then introducing the sealing gas into the second feeding chamber.

[0021] According to some embodiments, the step of exchanging heat between the removed cooling gas and the iron ore in the second feeding chamber comprises the step of conducting at least a part of the removed cooling gas into the second feeding chamber.

[0022] According to some embodiments, the cooling gas that is introduced into the cooling zone or cooling chamber consists of at least 80 mole%, preferably at least 90 mole%, hydrogen gas, H2.

[0023] According to some embodiments, the sealing gas consists of at least 80 mole% of an inert gas.

[0024] According to some embodiments, the sealing gas consists of at least 80 mole% of removed cooling gas. The object of the invention is also achieved by means of an arrangement for producing sponge iron by direct reduction of iron ore, comprising:

[0025] -a direct reduction shaft having an inlet for introduction of iron ore and an outlet for removal of sponge iron,

[0026] -a first feeding chamber for feeding iron ore to the direct reduction shaft,

[0027] -a second feeding chamber for feeding iron ore to the direct reduction shaft, the second feeding chamber being connected in one end to the first feeding chamber and in a second end to the direct reduction shaft,

[0028] - a reducing gas inlet for introduction of a reducing gas into the direct reduction shaft, -a gas outlet for removal of spent reducing gas from the direct reduction shaft, wherein a reduction zone of the direction reduction shaft is defined between a level of the reducing gas inlet and the outlet for removal of spent reducing gas,

[0029] -a sealing gas source connected to the second feeding chamber for conducting a sealing gas, other than reducing gas from the reduction zone, to the second feeding chamber,

[0030] -a cooling zone or cooling chamber provided downstream the reduction zone as seen in a flow direction of the iron ore and sponge iron,

[0031] -a cooling gas inlet for introduction of a cooling gas for cooling of sponge iron into the cooling zone or cooling chamber,

[0032] -a cooling gas outlet for removal of used cooling gas from the cooling zone or cooling chamber, said arrangement being characterised in that it comprises:

[0033] - first means for heat exchange between cooling gas removed from the cooling zone or cooling chamber and the iron ore in the first feeding chamber, and

[0034] - second means for heat exchange between cooling gas removed from the cooling zone or cooling chamber and the iron ore in the second feeding chamber.

[0035] According to some embodiments, said first means for heat exchange comprises a first line for conducting at least a part of the removed cooling gas from the cooling gas outlet into the first feeding chamber.

[0036] According to some embodiments, said first means comprises a heat exchanger for exchanging heat between removed cooling gas and air of lower temperature than the removed cooling gas, a gas line 25 for conducting removed cooling gas from the cooling gas outlet to said heat exchanger 13 and a channel for feeding heated air from the heat exchanger to the first feeding chamber.

[0037] According to some embodiments, the second means for heat exchange comprises a heat exchanger, connected to the second feeding chamber and to the sealing gas source, and a second line for conducting at least part of the cooling gas removed from the cooling gas outlet to said heat exchanger, for heat exchange between the removed cooling gas and the sealing gas to be introduced into the second feeding chamber.

[0038] According to some embodiments, the sealing gas source is at least partly comprised by cooling gas removed from the cooling zone or cooling chamber.

[0039] According to some embodiments, the cooling gas that is introduced into the cooling zone or cooling chamber consists of at least 80 mole%, preferably at least 90 mole%, hydrogen gas, H2.

[0040] According to some embodiments, the sealing gas consists of at least 80 mole% of an inert gas.

[0041] According to some embodiments, the sealing gas consists of at least 80 mole% of removed cooling gas.

[0042] BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Embodiments of the invention will now be disclosed more in detail with reference to the annexed drawing, on which:

[0044] Fig. 1 is a schematic representation of an embodiment of an arrangement according to the invention,

[0045] Fig. 2 is a schematic representation of an alternative embodiment of an arrangement according to the invention,

[0046] Fig. 3 is a schematic representation of yet an embodiment of an arrangement according to the invention, and Fig. 4 is a schematic representation of yet an embodiment of an arrangement according to the invention,

[0047] DETAILED DESCRIPTION

[0048] Fig. 1 shows an arrangement according to the invention, comprising a direct reduction shaft 1 having an inlet 2 for introduction of pellet of iron ore and an outlet 3 for removal of pellets of sponge iron.

[0049] The arrangement further comprises a first feeding chamber 4 for feeding iron ore to the direct reduction shaft 1 and a second feeding chamber 5 for feeding iron ore to the direct reduction shaft 1 , the second feeding chamber 5 being connected in one end to the first feeding chamber 4 and in a second end to the direct reduction shaft 1 .

[0050] There is also provided a reducing gas inlet 6 for introduction of a reducing gas into the direct reduction shaft 1 . A gas outlet 7 is provided for removal of spent reducing gas from the direct reduction shaft 1 , wherein a reduction zone 8 of the direct reduction shaft 1 is defined between a level of the reducing gas inlet 6 and the outlet 7 for removal of spent reducing gas.

[0051] A cooling zone or cooling chamber 9 is provided downstream the reduction zone 8 as seen in a flow direction of the iron ore and sponge iron, and a cooling gas inlet 10 is provided for introduction of a cooling gas into the cooling zone or cooling chamber 9.

[0052] A cooling gas outlet 11 is provided for removal of used cooling gas from the cooling zone or cooling chamber 9.

[0053] The arrangement further comprises first means 12 for heat exchange between cooling gas removed from the cooling zone or cooling chamber 9 and the iron ore in the first feeding chamber 4, and second means 15, 16, 17 for heat exchange between cooling gas removed from the cooling zone or cooling chamber 9 and the iron ore in the second feeding chamber 5. The first means for heat exchange comprises a first line 12 for conducting a part of the removed cooling gas from the cooling gas outlet 11 into the first feeding chamber 4.

[0054] According to alternative embodiments shown in figs. 2 and 4, said first means comprises a heat exchanger 13 for exchanging heat between removed cooling gas and air of lower temperature than the removed cooling gas, a gas line 25 for conducting removed cooling gas from the cooling gas outlet 11 to said heat exchanger 13 and a channel 14 for feeding heated air from the heat exchanger 13 to the first feeding chamber 4.

[0055] In the embodiments disclosed in figs. 1 and 2, the second means for heat exchange comprises a heat exchanger 15, connected to the second feeding chamber 5 and to a sealing gas source 16, and a second line 17 for conducting a part of the cooling gas removed from the cooling gas outlet 11 to said heat exchanger 15, for heat exchange between the removed cooling gas and the sealing gas to be introduced into the second feeding chamber 5. The sealing gas source 16 is an inert gas source. According to one embodiment, the sealing gas source 16 is a nitrogen gas source.

[0056] In the embodiments shown in figs. 3 and 4, the second means for heat exchange comprises a gas line 18 for conducting at least part of the cooling gas removed from the cooling gas outlet 11 to the second feeding chamber 5.

[0057] In addition to the components disclosed hereinabove, the arrangement also comprises a reduction gas and cooling gas source 19, which is hydrogen gas source, preferably a hydrolyser device, a gas line 20 from the reduction gas and cooling gas source 19 to the cooling gas inlet 10, and a gas line 21 from the reduction gas and cooling gas source 19 to the reduction gas inlet 6. In each of the embodiments shown in figs. 1-4, there is also provided gas lines 12b, 17b, 18b, 25b for recirculation of removed and heat exchanged cooling gas to back to the cooling gas inlet 10. There is a cleaning arrangement 27 for cleaning of such recirculated cooling gas that has been exchanging heat with the iron ore in the first and second feeding chambers 4,5. There is also provided a mixing point, indicated with 28, where removed cooling gas from the cooling gas outlet 11 is led off for the heating of the iron ore in the first and second feeding chambers 4, 5. The mixing point 28 could also comprise valves for controlling the respective flows of cooling gas to the means for heat exchange with iron ore in the respective feeding chambers. It may also comprise a heat exchanger for heat exchange with any further medium, if needed.

[0058] There is an off-gas line 22 extending from the reduction gas outlet 7 to the reduction gas inlet 6 of the direct reduction shaft 1 . There is a cleaning arrangement 23 for removing parts of the off gas from the hydrogen gas that is to be recirculated and used as reduction gas. There is also provided a heater 24 for heating recirculated off-gas from the reduction gas outlet 7. Fresh gas provided from the reduction gas and cooling gas source 19 is also to be heated by the heater 24.

[0059] As can be seen in the embodiments shown in figs. 1 and 2, there may also be a return gas line 16 for returning spent sealing gas back to the sealing gas source 16.

[0060] Needless to say, the arrangement may, of course, comprise other components, such as compressors, valves etc., that are well known to the person skilled in the art for the purpose of operating such an arrangement with regard to pressures, temperatures and flow rates in the arrangement. For example, there may be provided controllable valves, not shown, upstream and downstream the second feeding chamber in the flow direction of the iron ore. Preferably, there may also be provided valves in the gas lines upstream and downstream the first feeding chamber and the second feeding chamber, to enable control of gas flow and gas pressure in the respective feeding chamber.

[0061] By means of the disclosed arrangement, the following method is to be performed: -introducing iron ore via the first feeding chamber 4 into the second feeding chamber 5, and from the second feeding chamber 5 to the direct reduction shaft 1 , -feeding the iron ore through the reduction shaft 1 , -introducing the reducing gas into the direct reduction shaft 1 and permitting the reducing gas to flow through the direct reduction shaft 1 in a direction opposite to the feeding direction of the iron ore in the reduction zone 8 of the direct reduction shaft 1 ,

[0062] -introducing a sealing gas, other than reducing gas from the reduction zone, into the second feeding chamber 5 for the purpose of preventing used reducing gas from escaping from the direct reduction shaft 1 through the second feeding chamber 5,

[0063] - introducing a cooling gas having a lower temperature than the sponge iron into the cooling zone or cooling chamber 9 downstream the reduction zone 8 and subjecting sponge iron moving through said cooling zone or cooling chamber 9 to the cooling gas, and

[0064] -removing used cooling gas from the cooling zone or cooling chamber 9,

[0065] The method also comprises the steps of

[0066] -heating the iron ore in the first feeding chamber 4 by exchanging heat between at least a part of the removed cooling gas and the iron ore in the first feeding chamber 4, and

[0067] -heating the iron ore in the second feeding chamber 5 by exchanging heat between at least a part of the removed cooling gas and the iron ore in the second feeding chamber 5.

[0068] In the embodiments shown in figs. 1 and 3 the step of exchanging heat between the removed cooling gas and the iron ore in the first feeding chamber 4 comprises the step of introducing at least a part of the removed cooling gas into the first feeding chamber 4.

[0069] In the embodiments shown in figs. 2 and 4, the step of exchanging heat between the removed cooling gas and the iron ore in the first feeding chamber 4 comprises the step of exchanging heat between at least a part of the removed cooling gas and air of lower temperature than the removed cooling gas, and introducing the heated air into the first feeding chamber 4. In the embodiments shown in figs. 1 and 2, the step of exchanging heat between the removed cooling gas and the iron ore in the second feeding chamber 5 comprises the step of conducting at least a part of the removed cooling gas and sealing gas to be introduced into the second feeding chamber 5 into a heat exchanger 15 for heat exchange between the removed cooling gas and the sealing gas and then introducing the sealing gas into the second feeding chamber 5.

[0070] In the embodiments shown in figs. 3 and 4, the step of exchanging heat between the removed cooling gas and the iron ore in the second feeding chamber 5 comprises the step of conducting at least a part of the removed cooling gas into the second feeding chamber 5.

[0071] In the disclosed embodiments shown in figs. 1-4, the cooling gas is introduced into the cooling zone or cooling chamber consists of at least 80 mole%, preferably at least 90 mole%, hydrogen gas, H2.

[0072] In the disclosed embodiments shown in figs. 1-4, the sealing gas consists of at least 80 mole% of an inert gas, preferably nitrogen gas.

Claims

CLAIMS1 . A method of producing sponge iron by direct reduction of iron ore, comprising the steps of:-introducing iron ore via a first feeding chamber (4) into a second feeding chamber (5), and from the second feeding chamber (5) to a direct reduction shaft (1 ), -feeding the iron ore through the reduction shaft (1 ),-introducing a reducing gas into the direct reduction shaft (1 ) and permitting the reducing gas to flow through the direct reduction shaft (1 ) in a direction opposite to the feeding direction of the iron ore in a reduction zone (8) of the direct reduction shaft,-introducing a sealing gas, other than reducing gas from the reduction zone, into the second feeding chamber (5),- introducing a cooling gas having a lower temperature than the sponge iron into a cooling zone or cooling chamber (9) downstream the reduction zone (8) and subjecting sponge iron moving through said cooling zone or cooling chamber (9) to the cooling gas, and-removing used cooling gas from the cooling zone or cooling chamber (9), said method being characterised in that it comprises the steps of-heating the iron ore in the first feeding chamber (4) by exchanging heat between at least a part of the removed cooling gas and the iron ore in the first feeding chamber (4), and-heating the iron ore in the second feeding chamber (5) by exchanging heat between at least a part of the removed cooling gas and the iron ore in the second feeding chamber (5).

2. A method according to claim 1 , wherein the step of exchanging heat between the removed cooling gas and the iron ore in the first feeding chamber (4) comprises the step of introducing at least a part of the removed cooling gas into the first feeding chamber (4).

3. A method according to claim 1 , wherein the step of exchanging heat between the removed cooling gas and the iron ore in the first feeding chamber (4)comprises the step of exchanging heat between at least a part of the removed cooling gas and air of lower temperature than the removed cooling gas, and introducing the heated air into the first feeding chamber (4).

4. A method according to any one of claims 1-3, wherein the step of exchanging heat between the removed cooling gas and the iron ore in the second feeding chamber (5) comprises the step of conducting at least a part of the removed cooling gas and sealing gas to be introduced into the second feeding chamber (5) into a heat exchanger (15) for heat exchange between the removed cooling gas and the sealing gas and then introducing the sealing gas into the second feeding chamber (5).

5. A method according to any one of claims 1-3, wherein the step of exchanging heat between the removed cooling gas and the iron ore in the second feeding chamber (5) comprises the step of conducting at least a part of the removed cooling gas into the second feeding chamber (5).

6. A method according to any of claims 1-5, wherein the cooling gas is introduced into the cooling zone or cooling chamber consists of at least 80 mole%, preferably at least 90 mole%, hydrogen gas, H2.

7. A method according to any of claims 1 -6, wherein the sealing gas consists of at least 80 mole% of an inert gas.

8. A method according to any one of claims 1-6, wherein the sealing gas consists of at least 80 mole% of removed cooling gas.

9. An arrangement for producing sponge iron by direct reduction of iron ore, comprising:-a direct reduction shaft (1 ) having an inlet (2) for introduction of iron ore and an outlet (3) for removal of sponge iron,-a first feeding chamber (4) for feeding iron ore to the direct reduction shaft (1 ),-a second feeding chamber (5) for feeding iron ore to the direct reduction shaft (1 ), the second feeding chamber (5) being connected in one end to the first feeding chamber (4) and in a second end to the direct reduction shaft (1 ),- a reducing gas inlet (6) for introduction of a reducing gas into the direct reduction shaft (1 ),-a gas outlet (7) for removal of spent reducing gas from the direct reduction shaft (1 ), wherein a reduction zone (8) of the direct reduction shaft (1 ) is defined between a level of the reducing gas inlet (2) and the outlet (3) for removal of spent reducing gas,-a cooling zone or cooling chamber (9) provided downstream the reduction zone (8) as seen in a flow direction of the iron ore and sponge iron,-a cooling gas inlet (10) for introduction of a cooling gas for cooling of sponge iron into the cooling zone or cooling chamber (9),-a cooling gas outlet (11 ) for removal of used cooling gas from the cooling zone or cooling chamber (9), said arrangement being characterised in that it comprises:- first means (12; 13,14) for heat exchange between cooling gas removed from the cooling zone or cooling chamber (9) and the iron ore in the first feeding chamber (4), and- second means (15, 16, 17; 18) for heat exchange between cooling gas removed from the cooling zone or cooling chamber (9) and the iron ore in the second feeding chamber (5).

10. An arrangement according to claim 9, wherein said first means (12) for heat exchange comprises a first line (12) for conducting at least a part of the removed cooling gas from the cooling gas outlet (11 ) into the first feeding chamber (4).

11. An arrangement according to claim 9, wherein said first means comprises a heat exchanger (13) for exchanging heat between removed cooling gas and air of lower temperature than the removed cooling gas, a gas line (25) for conducting removed cooling gas from the cooling gas outlet (11 ) to said heat exchanger (13) and a channel (14) for feeding heated air from the heat exchanger (13) to the first feeding chamber (4).

12. An arrangement according to any one of claims 9-11 , wherein the second means for heat exchange comprises a heat exchanger (15), connected to the second feeding chamber (5) and to a sealing gas source (16), and -a second line (17) for conducting at least part of the cooling gas removed from the cooling gas outlet (11 ) to said heat exchanger (15), for heat exchange between the removed cooling gas and the sealing gas to be introduced into the second feeding chamber (5).

13. An arrangement according to any one of claims 9-11 , wherein the second means for heat exchange comprises a gas line (18) for conducting at least part of the cooling gas removed from the cooling gas outlet (11 ) to the second feeding chamber (5).

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