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) with a reducing gas inlet (4) and a reducing gas outlet (5), a heat exchanger (10) provided for heat exchange between used reducing gas in a first gas line (8) and cleaned reducing gas in a second gas line (9), a cooling zone or cooling chamber (11) provided downstream the reduction zone (6) having a cooling gas inlet (12) and a cooling gas outlet (13). The arrangement comprises a third gas line (14) for conducting used cooling gas from the cooling gas outlet (13) to the first gas line (8) and mixing the used cooling gas with the used reducing gas at a mixing point (15) in the first gas line (8), the mixing point (15) being located upstream the heat exchanger (10) as seen in the flow direction of the reducing gas in the first gas line (8).

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 into a direct reduction shaft, feeding the iron ore through the direct reduction shaft, introducing a reducing gas comprising hydrogen gas into the direct reduction shaft through a reducing gas inlet 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, removing used reducing gas from the reduction shaft through a reducing gas outlet, cleaning the used reducing gas removed from the reduction shaft and conducting a part thereof comprising hydrogen gas to the reducing gas inlet, exchanging heat, in a heat exchanger, between the used reducing gas before cleaning thereof and used reducing gas that has been subjected to said cleaning, subjecting the sponge iron in a cooling zone or cooling chamber downstream the reduction zone of the direct reduction shaft to a cooling gas comprising hydrogen gas and having a lower temperature than the sponge iron exiting the reduction zone, and removing used cooling gas from the cooling zone or cooling chamber and from the reduction shaft.

[0004] BACKGROUND

[0005] 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.

[0006] 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 zone or 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 zone or 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 into a direct reduction shaft,

[0013] -feeding the iron ore through the direct reduction shaft,

[0014] -introducing a reducing gas comprising hydrogen gas into the direct reduction shaft through a reducing gas inlet 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,

[0015] -removing used reducing gas from the reduction shaft through a reducing gas outlet, -cleaning the used reducing gas removed from the reduction shaft and conducting a part thereof comprising hydrogen gas to the reducing gas inlet,

[0016] -exchanging heat, in a heat exchanger, between the used reducing gas before cleaning thereof and used reducing gas that has been subjected to said cleaning, -subjecting the sponge iron in a cooling zone or cooling chamber downstream the reduction zone of the direct reduction shaft to a cooling gas comprising hydrogen gas and having a lower temperature than the sponge iron exiting the reduction zone, -removing used cooling gas from the cooling zone or cooling chamber and from the reduction shaft, said method being characterised in that it comprises the steps of

[0017] -mixing used cooling gas removed from the cooling zone or cooling chamber and from the reduction shaft with used reducing gas removed from the reduction shaft through the reducing gas outlet at a mixing point located upstream said heat exchanger as seen in a flow direction of the used reducing gas.

[0018] According to some embodiments, the cooling gas comprises at least 80 mole% hydrogen gas.

[0019] According to some embodiments, the cooling gas comprises at least 90 mole% hydrogen gas.

[0020] According to some embodiments, at least 80 mole% of the reduction gas is comprised by used reducing gas removed from the reduction shaft and used cooling gas removed from the cooling zone or cooling chamber.

[0021] According to some embodiments, substantially all the reduction gas is comprised by used reducing gas removed from the reduction shaft and used cooling gas removed from the cooling zone or cooling chamber.

[0022] The object of the invention is also achieved by means of an arrangement for producing sponge iron by direct reduction of iron ore, comprising:

[0023] -a direct reduction shaft having an inlet for introduction of iron ore and an outlet for removal of sponge iron,

[0024] - a reducing gas inlet for introduction of a reducing gas into the direct reduction shaft, -a reducing gas outlet for removal of used 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 reducing gas outlet, -a cleaning arrangement for cleaning used reducing gas, said cleaning arrangement being connected to the reducing gas outlet via a first gas line,

[0025] -a second gas line extending from the cleaning arrangement to the reducing gas inlet for conducting cleaned reducing gas comprising hydrogen gas to the reducing gas inlet,

[0026] -a heat exchanger provided for heat exchange between used reducing gas in the first gas line and cleaned reducing gas in the second gas line,

[0027] -a cooling zone or cooling chamber provided downstream the reduction zone as seen in a flow direction of the iron ore and sponge iron,

[0028] -a cooling gas inlet for introduction of a cooling gas for cooling of sponge iron into the cooling zone or cooling chamber,

[0029] -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:

[0030] -a third gas line for conducting used cooling gas from the cooling gas outlet to the first gas line and mixing the used cooling gas with the used reducing gas at a mixing point in the first gas line, the mixing point being located upstream the heat exchanger as seen in the flow direction of the reducing gas in the first gas line.

[0031] According to some embodiments, the arrangement comprises a hydrogen gas source and a gas line for conducting hydrogen gas from the hydrogen gas source to the cooling gas inlet of the cooling zone or cooling chamber.

[0032] According to some embodiments, the cooling zone or cooling chamber is defined by a cone-shaped lower part of the direct reduction shaft.

[0033] The direct reduction shaft is a vertical shaft, wherein the inlet for introduction of iron ore pellets is located at the top thereof and the outlet for removal of sponge iron pellets is located at the bottom thereof. The reduction process is a dry process with essentially no melting phases present in the shaft.

[0034] BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be disclosed in detail with reference to the only figure, which is a schematic representation of an embodiment of an arrangement according to the invention.

[0035] DETAILED DESCRIPTION

[0036] Fig. 1 discloses an arrangement for producing sponge iron by direct reduction of iron ore. The arrangement comprises a direct reduction shaft 1 having an inlet 2 for introduction of iron ore and an outlet 3 for removal of sponge iron, a reducing gas inlet 4 for introduction of a reducing gas into the direct reduction shaft 1 , and a reducing gas outlet 5 for removal of used reducing gas from the direct reduction shaft 1 . A reduction zone 6 of the direction reduction shaft is defined between a level of the reducing gas inlet 4 and the reducing gas outlet 5.

[0037] The arrangement also comprises a cleaning arrangement 7 for cleaning used reducing gas, said cleaning arrangement being connected to the reducing gas outlet 5 via a first gas line 8 and a second gas line 9 extending from the cleaning arrangement 7 to the reducing gas inlet 4 for conducting cleaned reducing gas comprising hydrogen gas to the reducing gas inlet 4.

[0038] Furthermore, there is provided a heat exchanger 10 provided for heat exchange between used reducing gas in the first gas line 8 and cleaned reducing gas in the second gas line 9.

[0039] The arrangement further comprises a cooling zone or cooling chamber 11 provided downstream the reduction zone 6 as seen in a flow direction of the iron ore and sponge iron, a cooling gas inlet 12 for introduction of a cooling gas for cooling of sponge iron into the cooling zone or cooling chamber 11 , and a cooling gas outlet 13 for removal of used cooling gas from the cooling zone or cooling chamber 11 .

[0040] Furthermore, there is provided a third gas line 14 for conducting used cooling gas from the cooling gas outlet 13 to the first gas line 8 and mixing the used cooling gas with the used reducing gas at a mixing point 15 in the first gas line 8. The mixing point 15 is located upstream the heat exchanger 10 as seen in the flow direction of the reducing gas in the first gas line 8.

[0041] The arrangement also comprises a hydrogen gas source 16 and a gas line 17 for conducting hydrogen gas from the hydrogen gas source to the cooling gas inlet 12 of the cooling zone or cooling chamber 11 . The cooling zone or cooling chamber 11 is defined by a cone-shaped lower part of the direct reduction shaft 1 .

[0042] A heater 18 is provided in the second gas line downstream the heat exchanger 10 as seen a flow direction of the reducing gas in the second gas line 9.

[0043] The direct reduction shaft 1 is a vertical shaft, wherein the inlet 2 for introduction of iron ore pellets is located at the top thereof and the outlet 3 for removal of sponge iron pellets is located at the bottom thereof. The reduction process is a dry process with essentially no melting phases present in the shaft 1 .

[0044] Needless to say, the arrangement may, of course, comprise other components that are well known to the person skilled in the art for the purpose of operating such an arrangement.

[0045] By means of the disclosed arrangement, the following method is to be performed: -introducing iron ore into a direct reduction shaft 1 ,

[0046] -feeding the iron ore through the direct reduction shaft 1 ,

[0047] -introducing a reducing gas comprising hydrogen gas into the direct reduction shaft 1 through a reducing gas inlet 4 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 6 of the direct reduction shaft 1 ,

[0048] -removing used reducing gas from the reduction shaft 1 through a reducing gas outlet 5,

[0049] -cleaning the used reducing gas removed from the reduction shaft 1 and conducting a part thereof comprising hydrogen gas to the reducing gas inlet 4,

[0050] -exchanging heat, in a heat exchanger 10, between the used reducing gas before cleaning thereof and used reducing gas that has been subjected to said cleaning, -subjecting the sponge iron in a cooling zone or cooling chamber 11 downstream the reduction zone 6 of the direct reduction shaft 1 to a cooling gas comprising hydrogen gas and having a lower temperature than the sponge iron exiting the reduction zone 6, -removing used cooling gas from the cooling zone or cooling chamber 11 and from the reduction shaft 1 , and

[0051] -mixing used cooling gas removed from the cooling zone or cooling chamber 11 and from the reduction shaft 1 with used reducing gas removed from the reduction shaft 1 through the reducing gas outlet 5 at a mixing point 15 located upstream said heat exchanger 10 as seen in a flow direction of the used reducing gas.

[0052] The cooling gas, i.e. the gas cooling gas delivered to the cooling zone or cooling chamber 11 , comprises at least 90 mole% hydrogen gas. Substantially all the reduction gas is comprised by used reducing gas removed from the reduction shaft 1 and used cooling gas removed from the cooling zone or cooling chamber 11 .

Claims

CLAIMS1 . A method of producing sponge iron by direct reduction of iron ore, comprising the steps of:-introducing iron ore into a direct reduction shaft (1 ),-feeding the iron ore through the direct reduction shaft (1 ),-introducing a reducing gas comprising hydrogen gas into the direct reduction shaft (1 ) through a reducing gas inlet (4) 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 (6) of the direct reduction shaft (1 ),-removing used reducing gas from the reduction shaft (1 ) through a reducing gas outlet (5),-cleaning the used reducing gas removed from the reduction shaft (1 ) and conducting a part thereof comprising hydrogen gas to the reducing gas inlet (4), -exchanging heat, in a heat exchanger (10), between the used reducing gas before cleaning thereof and used reducing gas that has been subjected to said cleaning, -subjecting the sponge iron in a cooling zone or cooling chamber (11 ) downstream the reduction zone (6) of the direct reduction shaft (1 ) to a cooling gas comprising hydrogen gas and having a lower temperature than the sponge iron exiting the reduction zone (6),-removing used cooling gas from the cooling zone or cooling chamber (11 ) and from the reduction shaft (1 ), said method being characterised in that it comprises the steps of-mixing used cooling gas removed from the cooling zone or cooling chamber (11 ) and from the reduction shaft (1 ) with used reducing gas removed from the reduction shaft (1 ) through the reducing gas outlet (5) at a mixing point (15) located upstream said heat exchanger (10) as seen in a flow direction of the used reducing gas.

2. A method according to claim 1 , wherein the cooling gas comprises at least 80 mole% hydrogen gas.

3. A method according to claim 1 , wherein the cooling gas comprises at least 90 mole% hydrogen gas.

4. A method according to any one of claims 1 -3, wherein at least 80 mole% of the reduction gas is comprised by used reducing gas removed from the reduction shaft (1 ) and used cooling gas removed from the cooling zone or cooling chamber (11 ).

5. A method according to any one of claims 1 -4, wherein substantially all the reduction gas is comprised by used reducing gas removed from the reduction shaft (1 ) and used cooling gas removed from the cooling zone or cooling chamber (11 ).

6. 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 reducing gas inlet (4) for introduction of a reducing gas into the direct reduction shaft (1 ),-a reducing gas outlet (5) for removal of used reducing gas from the direct reduction shaft (1 ), wherein a reduction zone (6) of the direction reduction shaft is defined between a level of the reducing gas inlet (4) and the reducing gas outlet (5),-a cleaning arrangement (7) for cleaning used reducing gas, said cleaning arrangement being connected to the reducing gas outlet (5) via a first gas line (8), -a second gas line (9) extending from the cleaning arrangement (7) to the reducing gas inlet (4) for conducting cleaned reducing gas comprising hydrogen gas to the reducing gas inlet (4),-a heat exchanger (10) provided for heat exchange between used reducing gas in the first gas line (8) and cleaned reducing gas in the second gas line (9),-a cooling zone or cooling chamber (11 ) provided downstream the reduction zone (6) as seen in a flow direction of the iron ore and sponge iron,-a cooling gas inlet (12) for introduction of a cooling gas for cooling of sponge iron into the cooling zone or cooling chamber (11 ),-a cooling gas outlet (13) for removal of used cooling gas from the cooling zone or cooling chamber (11 ), said arrangement being characterised in that it comprises:-a third gas line (14) for conducting used cooling gas from the cooling gas outlet (13) to the first gas line (8) and mixing the used cooling gas with the used reducing gas at a mixing point (15) in the first gas line (8), the mixing point (15) being located upstream the heat exchanger (10) as seen in the flow direction of the reducing gas in the first gas line (8).

7. An arrangement according to claim 6, comprising a hydrogen gas source (16) and a gas line (17) for conducting hydrogen gas from the hydrogen gas source to the cooling gas inlet (12) of the cooling zone or cooling chamber (11 ).

8. An arrangement according to claim 6 or 7, wherein the cooling zone or cooling chamber (11 ) is defined by a cone-shaped lower part of the direct reduction shaft (1 ).

9. An arrangement according to any one of claims 6-8, comprising a heater (18) provided in the second gas line downstream the heat exchanger (10) as seen a flow direction of the reducing gas in the second gas line (9).

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