An arrangement for and a method of producing sponge iron from iron ore

Abstract

An arrangement for producing sponge iron from iron ore, wherein the arrangement comprises a vertical reduction shaft (1), a first heat exchanger (13) arranged to exchange heat between a reduction gas in a first gas line (4) and top gas obtained from the reduction shaft (1). A second heat exchanger (14) is arranged to exchange heat between the reduction gas in the first gas line (4) and a cooling gas for cooling of reduced pellets, the second heat exchanger (14) being provided upstream the first heat exchanger (13) in the first gas line (4) as seen in the flow direction of the reduction gas from the reduction gas source (3) to the direct reduction shaft (1), and the first heat exchanger (13) is a counter-current heat exchanger.

Description

[0001] An arrangement for and a method of producing sponge iron from iron ore

[0002] TECHNICAL FIELD

[0003] The present invention relates to an arrangement for producing sponge iron from iron ore, wherein the arrangement comprises a vertical reduction shaft having an inlet at an upper part of the reduction shaft for receiving a plurality of iron ore pellets, a reduction gas source, a first gas line extending from the reduction gas source to the reduction shaft, at least one reduction gas inlet for introduction of reduction gas into the reduction shaft, a reduction gas outlet for removal of top gas from the reduction shaft, a heater for heating the reduction gas in the first gas line, a cooling chamber provided downstream a reduction zone of the reduction shaft and arranged to receive reduced iron ore pellets from the reduction zone, a cooling gas inlet into said chamber, a cooling gas outlet from said chamber, provided upstream the cooling gas inlet as seen in the flow direction of the reduced iron ore pellets in said chamber, a second gas line extending outside said chamber from the cooling gas outlet of said chamber to the cooling gas inlet of said chamber, and a first heat exchanger arranged to exchange heat between the reduction gas in the first gas line and top gas obtained from the reduction shaft through the reduction gas outlet, said first heat exchanger, being arranged upstream the gas heater in the first gas line as seen in the flow direction of the reduction gas from the reduction gas source to the direct reduction shaft.

[0004] BACKGROUND

[0005] Prior art arrangements like the one disclosed hereinabove normally use a so- called co-current heat exchanger, or recuperator, for the heat exchange between the top gas and the reduction gas, although co-current heat exchangers are less efficient than counter-current ones given the same set of fluid temperatures and flows and exchange area. The reason for this is the fact that there is a high risk for clogging when using a counter current tubes-and-shell heat recuperator in the top gas outlet of the reduction shaft. In a counter current configuration, the exit side of the tubes, where gas temperature is lower, meets the ingoing cold reduction gas that is in the shell side. In plant conditions where top gas temperature is low, there is significant risk of condensation on the inside of the tubes given the high moisture of the top gas. Since this gas also carries dust particles, condensation would favor dust accumulation and clogging, leading to lower heat exchanger efficiency and eventually damage to the tubes. This problem is solved by applying a co-current heat exchanger, in spite of its lower efficiency.

[0006] It is an object of the present invention to present a solution which improves the efficiency in the arrangement defined hereinabove, preferably by enabling the use of a counter-current heat-exchanger for heat exchange between the top gas and the reduction gas in said first heat exchanger.

[0007] SUMMARY

[0008] The object of the invention is achieved by means of an arrangement for producing sponge iron from iron ore, wherein the arrangement comprises:

[0009] -a vertical reduction shaft having an inlet at an upper part of the reduction shaft for receiving a plurality of iron ore pellets;

[0010] -a reduction gas source,

[0011] -a first gas line extending from the reduction gas source to the reduction shaft, -at least one reduction gas inlet for introduction of reduction gas into the reduction shaft,

[0012] -a reduction gas outlet for removal of top gas from the reduction shaft, -a heater for heating the reduction gas in the first gas line;

[0013] -a cooling chamber provided downstream a reduction zone of the reduction shaft and arranged to receive reduced iron ore pellets from the reduction zone,

[0014] - a cooling gas inlet into said chamber;

[0015] -a cooling gas outlet from said chamber, provided upstream the cooling gas inlet as seen in the flow direction of the reduced iron ore pellets in said chamber, -a second gas line extending outside said chamber from the cooling gas outlet of said chamber to the cooling gas inlet of said chamber, and -a first heat exchanger arranged to exchange heat between the reduction gas in the first gas line and top gas obtained from the reduction shaft through the reduction gas outlet, said first heat exchanger, being arranged upstream the gas heater in the first gas line as seen in the flow direction of the reduction gas from the reduction gas source to the direct reduction shaft; said arrangement being characterized in that it comprises

[0016] -a second heat exchanger arranged to exchange heat between the reduction gas in the first gas line and gas in said second gas line, the second heat exchanger being provided upstream the first heat exchanger in the first gas line as seen in the flow direction of the reduction gas from the reduction gas source to the direct reduction shaft; and in that the first heat exchanger is a counter-current heat exchanger.

[0017] The provision of the second heat exchanger will result in a preheating of the reduction gas that will enable the use of a counter-current heat exchanger as the first heat exchanger. Thereby, improved efficiency is obtained compared to prior art, while clogging and condensation of top gas is still prevented. Energy from the cooling circuit, which has been transferred from the reduced iron ore pellets to the cooling gas, is also taken advantage of.

[0018] According to some embodiments, the second heat exchanger is a co-current heat exchanger. Thereby, clogging and condensation of the cooling gas in the second gas line is prevented.

[0019] According to some embodiments, the reduction gas source comprises a hydrogen gas source.

[0020] According to some embodiments, the reduction gas source comprises an electric hydrolyzer for producing hydrogen gas from water.

[0021] According to some embodiments, the arrangement comprises a third gas line for conducting top gas from the reduction gas outlet to the first gas line, said third gas line being connected to the first gas line at a point upstream the second heat exchanger as seen in the flow direction of the reduction gas in the first gas line.

[0022] According to some embodiments, the first heat exchanger comprises a shell-and- tube heat exchanger. A tube and shell heat exchanger is a device that transfers heat from one fluid to another fluid without them touching each other directly. It consists of a shell (a large pressure vessel) and a tube bundle. One fluid flows inside the tubes and the other fluid flows over the tubes. The tubes and the shell are made of thermally conductive metals that allow easy heat transfer. The temperature difference between the two fluids is the driving force for heat exchange.

[0023] According to some embodiments, the first gas line is defined by a shell side of the first heat exchanger, and the top gas is conducted through the tube side of the first heat exchanger.

[0024] According to some embodiments, the second heat exchanger comprises a shell- and-tube heat exchanger.

[0025] According to some embodiments, the first gas line is defined by the shell side of the second heat exchanger and the second gas line is defined by the tube side of the second heat exchanger.

[0026] According to some embodiments, there is provided a gas cleaning arrangement in the third gas line for separating dust and water of the top gas from hydrogen gas of the top gas and removing the separated dust and water from the third gas line, and wherein said cleaning arrangement is provided downstream the first heat exchanger as seen in the flow direction of the top gas in the third gas line.

[0027] The object of the invention is also achieved by means of a method of producing sponge iron from iron ore, said method comprising the steps of: -introducing iron ore pellets into a vertical reduction shaft, -conducting a reduction gas from a reduction gas source to the reduction shaft through a first gas line,

[0028] -heating the reduction gas by means of a heater in the first gas line, -introducing the heated reduction gas into to reduction shaft,

[0029] -removing top gas from the reduction shaft through a reduction gas outlet, -forwarding reduced iron ore pellets from a reduction zone in the reduction shaft to a chamber,

[0030] -introducing a cooling gas in the chamber through a cooling gas inlet, permitting the cooling gas to flow through the chamber, thereby cooling the reduced iron ore pellets in said chamber,

[0031] -removing cooling gas from the chamber through a cooling gas outlet,

[0032] -conducting the cooling gas from the cooling gas outlet to the cooling gas inlet through a second gas line outside said chamber,

[0033] -exchanging heat between top gas removed from the reduction shaft and the reduction gas in the first gas line in a first heat exchanger, the first heat exchanger being located upstream the heater as seen in the flow direction of the reduction gas in the first gas line, said method being characterized in that it comprises the step of

[0034] -exchanging heat between the reduction gas in the first gas line and the cooling gas in the second gas line in a second heat exchanger, and in that

[0035] -the flow directions of the reduction gas and the top gas through the first heat exchanger are opposite to each other.

[0036] According to some embodiments, the flow directions of the reduction gas and the cooling gas in the second heat exchanger are the same. In other words, according to some embodiments, the second heat exchanger is a co-current type of heat exchanger.

[0037] According to some embodiments, the flow rate of the cooling gas in the second gas line is controlled such that the temperature of the reduction gas leaving the second heat exchanger is high enough to result in the temperature of the top gas in the first heat exchanger not going below the dew point of the top gas due to the heat exchange with the reduction gas in the first heat exchanger. The flow rate of the cooling gas through the cooling zone in said chamber, and thus the flow rate of the cooling gas in the second gas line, is controlled such that a predetermined pellets temperature at a pellets outlet from the chamber is achieved. The pellets temperature should be below a predetermined level to avoid reactions between the pellets and the surrounding atmosphere. The flow rate in the second gas line is thus dependent on the set outlet temperature of the pellets. However, how much of the gas in the second gas that is actually conducted through the second heat exchanger could be regulated. Preferably, the flow rate in the second gas line is controlled such that the reduction gas gets a sufficiently high temperature before reaching the first heat exchanger, to prevent condensation of top gas in the latter.

[0038] According to some embodiments, the reduction gas from the reduction gas source comprises at least 80 mole% hydrogen, preferably at least 90 mole% hydrogen.

[0039] According to some embodiments, the method comprises the step of conducting top gas from the reduction gas outlet of the reduction shaft to the first gas line through a third gas line, said third gas line being connected to the first gas line at a point upstream the second heat exchanger as seen in the flow direction of the reduction gas in the first gas line.

[0040] According to some embodiments, the cooling gas comprises at least 80 mole% hydrogen, preferably at least 90 mole% hydrogen.

[0041] BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The invention will now be described in detail with reference to the annexed drawing, on which:

[0043] Fig.1 is a schematic representation of an arrangement according to the invention.

[0044] DETAILED DESCRIPTION Fig. 1 shows an embodiment of an arrangement for producing sponge iron from iron ore according to the present invention. The iron ore comprises iron ore pellets comprising iron oxide.

[0045] The arrangement comprises a vertical reduction shaft 1 having an inlet 2 at an upper part of the reduction shaft for receiving a plurality of iron ore pellets. The arrangement further comprises a reduction gas source 3, a first gas line 4 extending from the reduction gas source 3 to the reduction shaft 1 , and a reduction gas inlet 5 for introduction of reduction gas into the reduction shaft 1 .

[0046] The arrangement further comprises a reduction gas outlet 6 for removal of top gas from the reduction shaft 1 and a heater 7 for heating the reduction gas in the first gas line 4.

[0047] There is also provided a cooling chamber 8 provided downstream a reduction zone 9 of the reduction shaft 1 and arranged to receive reduced iron ore pellets from the reduction zone 9. In the disclosed embodiment, the chamber 8 is defined by a lower part of the reduction shaft 1 , just below the reduction zone 9. Alternative embodiments may comprise a chamber which is more or less separated from the reduction shaft. According to another embodiment, not shown, the chamber is separated from the reduction shaft.

[0048] A cooling gas inlet 10 is provided for the introduction of a cooling gas into the chamber 8, and a cooling gas outlet 11 is provided for removal of cooling gas from the chamber 8. The cooling gas outlet 11 is provided upstream the cooling gas inlet 10 as seen in the flow direction of the reduced iron ore pellets in said chamber 8.

[0049] There is provided a second gas line 12 extending outside said chamber 8 from the cooling gas outlet 11 of said chamber to the cooling gas inlet 10 of said chamber 8. A first heat exchanger 13 is arranged to exchange heat between the reduction gas in the first gas line 4 and top gas obtained from the reduction shaft 1 through the reduction gas outlet 6. The first heat exchanger 13 is arranged upstream the gas heater 7 in the first gas line 4 as seen in the flow direction of the reduction gas from the reduction gas source 3 to the direct reduction shaft 1 .

[0050] The arrangement further comprises a second heat exchanger 14 arranged to exchange heat between the reduction gas in the first gas line 4 and gas in said second gas line 12, the second heat exchanger 14 being provided upstream the first heat exchanger 13 in the first gas line 4 as seen in the flow direction of the reduction gas from the reduction gas source 3 to the direct reduction shaft 1.

[0051] The first heat exchanger 13 is a counter-current heat exchanger, and the second heat exchanger 14 is co-current heat exchanger.

[0052] The reduction gas source 3 comprises a hydrogen gas source. In the disclosed embodiment, the reduction gas source 3 comprises an electric hydrolyzer for producing hydrogen gas from water. In the disclosed embodiment, there is also provided a fourth gas line 15 from the reduction gas source 3 to the second gas line 12. The fourth gas line 15 is connected to the second gas line 12 downstream the second heat exchanger 14 as seen in the flow direction of the cooling gas in the second gas line 14 during operation of the arrangement.

[0053] The arrangement further comprises a third gas line 16 for conducting top gas from the reduction gas outlet 6 of the reduction shaft 1 to the first gas line 4, said third gas line 16 being connected to the first gas line 4 at a point upstream the second heat exchanger 14 as seen in the flow direction of the reduction gas in the first gas line 4.

[0054] The first heat exchanger 13 comprises a shell-and-tube heat exchanger. A tube and shell heat exchanger is a device that transfers heat from one fluid to another fluid without them touching each other directly. It consists of a shell (a large pressure vessel) and a tube bundle. One fluid flows inside the tubes and the other fluid flows over the tubes. The tubes and the shell are made of thermally conductive metals that allow easy heat transfer. The temperature difference between the two fluids is the driving force for heat exchange.

[0055] The first gas line 4 is defined by a shell side of the first heat exchanger 13, and the top gas is conducted through the tube side of the first heat exchanger 13. The third gas line 16 thereby defines, i.e. is formed by, the tube side of the first heat exchanger 13.

[0056] The second heat exchanger 14 also comprises a shell-and-tube heat exchanger. The first gas line 4 is defined by the shell side of the second heat exchanger and the second gas line 12 is defined by the tube side of the second heat exchanger 14.

[0057] There is provided a gas cleaning arrangement 17 in the third gas line 16 for separating dust and water of the top gas from hydrogen gas of the top gas and removing the separated dust and water from the third gas line 16. The cleaning arrangement 17 is provided downstream the first heat exchanger 13 as seen in the flow direction of the top gas in the third gas line 16. There is provided a compressor 18 in the third gas line 16 downstream the cleaning arrangement 17.

[0058] There is also provided a second gas cleaning arrangement 19 in the second gas line 12 for separating dust and water of the cooling gas from hydrogen gas of the cooling gas and removing the separated dust and water from the second gas line 12. The second cleaning arrangement 19 is provided downstream the second heat exchanger 14 as seen in the flow direction of the cooling gas in the second gas line 12. There is also provided a second compressor 20 in the second gas line 12 downstream the second cleaning arrangement 19.

[0059] The operation of the disclosed embodiment of the arrangement comprises the steps of

[0060] -introducing iron ore pellets into the vertical reduction shaft 1 , -conducting a reduction gas from the reduction gas source 3 to the reduction shaft 1 through a first gas line 4,

[0061] -heating the reduction gas by means of the heater 3 in the first gas line 4, -introducing the heated reduction gas into the reduction shaft 1 ,

[0062] -removing top gas from the reduction shaft 1 through the reduction gas outlet 6, -forwarding reduced iron ore pellets from the reduction zone 9 in the reduction shaft 1 to a chamber 8,

[0063] -introducing a cooling gas in the chamber 8 through a cooling gas inlet 10, permitting the cooling gas to flow through the chamber 8, thereby cooling the reduced iron ore pellets in said chamber 8,

[0064] -removing cooling gas from the chamber 8 through the cooling gas outlet 11 , -conducting the cooling gas from the cooling gas outlet 11 to the cooling gas inlet 10 through a second gas line 12 outside said chamber 8,

[0065] -exchanging heat between top gas removed from the reduction shaft 1 and the reduction gas in the first gas line 4 in the first heat exchanger 13, -exchanging heat between the reduction gas in the first gas line 4 and the cooling gas in the second gas line 12 in the first heat exchanger 13

[0066] The flow rate of the cooling gas in the second gas line 12 is controlled such that the temperature of the reduction gas leaving the second heat exchanger 14 is high enough to result in the temperature of the top gas in the first heat exchanger 13 not going below the dew point of the top gas due to the heat exchange with the reduction gas in the first heat exchanger 13.

[0067] The reduction gas from the reduction gas source comprises 100% hydrogen gas.

[0068] The operation also comprises the step of conducting top gas from the reduction gas outlet 6 of the reduction shaft 1 to the first gas line 4 through the third gas line 16. Fresh cooling gas, comprising approximately 100% hydrogen gas, is conducted to the second gas line 12 from the reduction gas source 3 via the fourth gas line 15.

Claims

CLAIMS1 . An arrangement for producing sponge iron from iron ore, wherein the arrangement comprises:-a vertical reduction shaft (1 ) having an inlet (2) at an upper part of the reduction shaft (1 ) for receiving a plurality of iron ore pellets;-a reduction gas source (3),-a first gas line (4) extending from the reduction gas source (3) to the reduction shaft (1 ),-at least one reduction gas inlet (5) for introduction of reduction gas into the reduction shaft (1 ),-a reduction gas outlet (6) for removal of top gas from the reduction shaft (1 ),-a heater (7) for heating the reduction gas in the first gas line (4);-a cooling chamber (8) provided downstream a reduction zone (9) of the reduction shaft (1 ) and arranged to receive reduced iron ore pellets from the reduction zone (9),- a cooling gas inlet (10) into said chamber (8);-a cooling gas outlet (11 ) from said chamber (8), provided upstream the cooling gas inlet (10) as seen in the flow direction of the reduced iron ore pellets in said chamber (8),-a second gas line (12) extending outside said chamber (8) from the cooling gas outlet (11 ) of said chamber (8) to the cooling gas inlet (10) of said chamber (8), and-a first heat exchanger (13) arranged to exchange heat between the reduction gas in the first gas line (4) and top gas obtained from the reduction shaft (1 ) through the reduction gas outlet (6), said first heat exchanger (13), being arranged upstream the gas heater (7) in the first gas line (4) as seen in the flow direction of the reduction gas from the reduction gas source (3) to the direct reduction shaft (1 ); said arrangement being characterized in that it comprises-a second heat exchanger (14) arranged to exchange heat between the reduction gas in the first gas line (4) and gas in said second gas line (12), the second heat exchanger (14) being provided upstream the first heat exchanger (13) in the firstgas line (4) as seen in the flow direction of the reduction gas from the reduction gas source (3) to the direct reduction shaft (1 ), and in that the first heat exchanger (13) is a counter-current heat exchanger.

2. An arrangement according to claim 1 , wherein the second heat exchanger (14) is a co-current heat exchanger.

3. An arrangement according to claim 1 or 2, wherein the reduction gas source (3) comprises a hydrogen gas source (3).

4. An arrangement according to any one of claims 1 -3, wherein the reduction gas source (3) comprises an electric hydrolyzer for producing hydrogen gas from water.

5. An arrangement according to any one of claims 1 -4, comprising a third gas line (16) for conducting top gas from the reduction gas outlet (6) to the first gas line (4), said third gas line (16) being connected to the first gas line (4) at a point upstream the second heat exchanger (14) as seen in the flow direction of the reduction gas in the first gas line (4).

6. An arrangement according to any one of claim 1 -5, wherein the first heat exchanger (13) comprises a shell-and-tube heat exchanger.

7. An arrangement according to claim 6, wherein the first gas line (4) is defined by a shell side of the first heat exchanger (13), and the top gas is conducted through the tube side of the first heat exchanger (13).

8. An arrangement according to any one of claims 1 -7, wherein the second heat exchanger (14) comprises a shell-and-tube heat exchanger.

9. An arrangement according to claim 8, wherein the first gas line (4) is defined by the shell side of the second heat exchanger (14) and the second gas line (12) is defined by the tube side of the second heat exchanger (14).

10. An arrangement according to claim 5, wherein, in the third gas line (16), there is provided a gas cleaning arrangement (17) for separating dust and water of the top gas from hydrogen gas of the top gas and removing the separated dust and water from the third gas line (16), and that said cleaning arrangement (17) is provided downstream the first heat exchanger (13) as seen in the flow direction of the top gas in the third gas line (16).

11. A method of producing sponge iron from iron ore, said method comprising the steps of:-introducing iron ore pellets into a vertical reduction shaft (1 ), -conducting a reduction gas from a reduction gas source (3) to the reduction shaft (1 ) through a first gas line (4),-heating the reduction gas by means of a heater (7) in the first gas line (4), -introducing the heated reduction gas into to reduction shaft,-removing top gas from the reduction shaft through a reduction gas outlet (6), -forwarding reduced iron ore pellets from a reduction zone (9) in the reduction shaft (1 ) to a chamber (8),-introducing a cooling gas in the chamber (8) through a cooling gas inlet (10), permitting the cooling gas to flow through the chamber (8), thereby cooling the reduced iron ore pellets in said chamber (8),-removing cooling gas from the chamber (8) through a cooling gas outlet (11 ), -conducting the cooling gas from the cooling gas outlet (11 ) to the cooling gas inlet (10) through a second gas line (12) outside said chamber (8),-exchanging heat between top gas removed from the reduction shaft (1 ) and the reduction gas in the first gas line (4) in a first heat exchanger (13), the first heat exchanger (13) being located upstream the heater (7) as seen in the flow direction of the reduction gas in the first gas line (4), said method being characterized in that it comprises the step of-exchanging heat between the reduction gas in the first gas line (4) and the cooling gas in the second gas line (12) in a second heat exchanger (14), and in that -the flow directions of the reduction gas and the top gas through the first heat exchanger (13) are opposite to each other.

12. A method according to claim 11 , wherein the flow directions of the reduction gas and the cooling gas in the second heat exchanger (14) are the same.

13. A method according to claim 11 or 12, wherein the flow rate of the cooling gas in the second gas line (12) is controlled such that the temperature of the reduction gas leaving the second heat exchanger (14) is high enough to result in the temperature of the top gas in the first heat exchanger (13) not going below the dew point of the top gas due to the heat exchange with the reduction gas in the first heat exchanger (13).

14. A method according to any one of claims 11-13, wherein the reduction gas from the reduction gas source (3) comprises at least 80 mole% hydrogen, preferably at least 90 mole% hydrogen.

15. A method according to any one of claims 11-14, comprising the step of conducting top gas from the reduction gas outlet (6) of the reduction shaft (1 ) to the first gas line (4) through a third gas line (16), said third gas line (16) being connected to the first gas line (4) at a point upstream the second heat exchanger (14) as seen in the flow direction of the reduction gas in the first gas line (4).

16. A method according to an one of claims 11-15, wherein the cooling gas comprises at least 80 mole% hydrogen, preferably at least 90 mole% hydrogen.

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