METHOD AND CORRESPONDING APPARATUS FOR PRODUCING IRON FROM DIRECT REDUCTION OF IRON ORE

Abstract

A method for producing direct reduced iron is provided. The method includes circulating a first stream of spent reducing gas exiting a reactor in a reducing gas circuit through at least one carbon dioxide removal unit and a reducing gas heater and the reactor. The method also includes mixing the first stream with reducing gas containing heavier hydrocarbons than methane.

Claims

1. A method for producing DRI in a direct reduction process using a reducing gas chosen among a natural gas having a high content of total hydrocarbons heavier than methane, or coke oven gas (COG) having complex carbon compounds (BTX) or other synthetic gases coming from any source with high content of CH.sub.4 and heavy hydrocarbons, said method comprising circulating a first stream (F1) of reducing gas exiting a reactor (10) in a reducing gas circuit (20) through at least one carbon dioxide removal unit (38), a reducing gas heater (42) and said reactor (10); and feeding, into said reducing gas circuit (20), between said reducing gas heater (42) and said reduction reactor (10), a stream (F2) of fresh reducing gas which amounts to more than 20% of the overall quantity of fresh reducing gas sent to the reduction reactor (10).

2. The method as in claim 1, wherein said gas stream (F2) is pre-heated to a temperature lower than 650° C.

3. The method as in claim 2, wherein said stream (F2) is pre-heated in a convective zone (43) of said reducing gas heater (42).

4. The method as in claim 2, wherein said stream (F2) is pre-heated in a heat exchanger or fired heater separated from said reducing gas heater (42).

5. The method as in claim 1, wherein said stream (F2) is injected into the circuit (20) without being pre-heated.

6. The method as in claim 1, the method further comprising feeding at least one further fresh stream (F3, F4) of said fresh reducing gas which amounts to the portion of fresh reducing gas not injected into the reducing gas circuit (20) by the stream (F2).

7. The method as in claim 6, wherein said stream (F3) is injected in correspondence with any portion whatsoever of the reducing gas circuit (20) located between said carbon dioxide removal unit (38) and said reducing gas heater (42).

8. The method as in claim 6, wherein it feeds said stream (F4) directly into the reactor (10).

9. The method as in claim 6, the method comprising feeding a combination of said fresh reducing gas which amounts to the portion of fresh reducing gas not injected by the stream (F2), formed by the stream (F3) injected in correspondence with any portion whatsoever of the circuit (20) located between said carbon dioxide removal unit (38) and said reducing gas heater (42), and by the stream (F4) injected directly into the reactor (10).

10. The method as in claim 1, wherein at least the stream (F2) is controlled by at least one control unit (68) configured to regulate flow rate and therefore the percentage of said fresh reducing gas injected into the circuit (20).

11. The method according to claim 10, wherein said control unit (68) regulates the flow rate of said gas stream (F2) in response to a signal emitted by a flow rate sensor (69, 70) measuring the flow rate of gas stream (F3) and/or (F4).

12. The method as in claim 10, wherein said control unit (68) additionally to regulating the flow rate of said gas stream (F2) also regulates the flow rate of gas stream (F3) and/or (F4).

13. The method as in claim 10, wherein said control unit (68) regulates at least the flow rate of the stream (F3) so as to maintain the sum of the heat provided by stream (F2) plus the heat provided by stream (F3) within a predetermined range of values so as to maintain the operating conditions of the reduction zone (12) of the reactor (10) to produce DRI at a predetermined production rate.

14. The method as in claim 10, wherein said control unit (68) also regulates a flow rate of oxygen (52) with the aim of compensating the loss of energy caused by the fact that gas stream (F2) bypassing the fired heater (42) will not have in any case the same temperature of the pipe (28) after heating in same fired heater (42).

15. The method as in claim 1, wherein said method does not comprise any step of removal of the fraction of heavier hydrocarbons from the reducing gas, in particular it does not comprise any reforming step.

16. An apparatus for producing DRI from direct reduction of iron ore using a reducing gas having a high content of hydrocarbons heavier than methane, chosen among a natural gas having a high content of hydrocarbons heavier than methane, or coke oven gas (COG) having complex carbon compounds (BTX) or other synthetic gases coming from any source with high content of CH.sub.4 and heavy hydrocarbons, said apparatus comprising a reduction reactor (10), a carbon dioxide removal unit (38) and a heater (42), a reducing gas circuit (20) being provided which passes through said carbon dioxide removal unit (38) and said heater (42) and said reactor (10), said apparatus comprising a first injection means (49a) configured to feed, into said reducing gas circuit (20) between said reducing gas heater (42) and said reduction reactor (10), a stream (F2) of fresh reducing gas which amounts to more than 20% of the quantity of reducing sent to the reduction reactor (10).

17. The apparatus as in claim 16, wherein the apparatus comprises further injection means (49b, 49c) configured to inject into the reducing gas circuit (20) at least one fresh stream (F3, F4) of said reducing gas which amounts to the portion of reducing gas not injected into the reducing gas circuit (20) by the stream (F2).

18. The apparatus as in claim 17, wherein said injection means (49b) are configured to inject said stream (F3) in correspondence with any portion whatsoever of the reducing gas circuit (20) located between said carbon dioxide removal unit (38) and said reducing gas heater (42).

19. The apparatus as in claim 17, wherein said injection means (49c) are configured to feed said stream (F4) directly into the reactor (10).

20. The apparatus as in claim 16, wherein the apparatus comprises at least one control unit (68) connected to at least one of valves (56, 58, 60, 62) and configured to regulate the respective streams (F2, F3, F4).

21. The apparatus as in claim 20, wherein the at least one control unit (68) is connected to the source (52) of oxygen and configured to regulate its flowrate.

22. The apparatus as in claim 16, wherein said apparatus does not comprise any means or device for removal of the fraction of heavier hydrocarbons from the reducing gas, in particular it does not include any reformer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] These and other characteristics of the present invention will become apparent from the following description of some embodiments, given as a non-restrictive example with reference to the attached drawings wherein:

[0044] FIG. 1 is a schematic representation of an apparatus for implementing a method according to the embodiments described here.

[0045] To facilitate comprehension, the same reference numbers have been used, where possible, to identify identical common elements in the drawings. It is understood that elements and characteristics of one embodiment can conveniently be incorporated into other embodiments without further clarifications.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

[0046] We will now refer in detail to the various embodiments of the present invention, of which one or more examples are shown in the attached drawings. Each example is supplied by way of illustration of the invention and shall not be understood as a limitation thereof. For example, the characteristics shown or described insomuch as they are part of one embodiment can be adopted on, or in association with, other embodiments to produce another embodiment. It is understood that the present invention shall include all such modifications and variants.

[0047] Before describing these embodiments, we must also clarify that the present description is not limited in its application to details of the construction and disposition of the components as described in the following description using the attached drawings. The present description can provide other embodiments and can be obtained or executed in various other ways. We must also clarify that the phraseology and terminology used here is for the purposes of description only, and cannot be considered as limitative.

[0048] Embodiments described here concern a method for producing DRI in a direct reduction process using a reducing gas chosen among a natural gas having a high content of total hydrocarbons heavier than methane (>4%), or coke oven gas (COG) having complex carbon compounds (BTX) or other synthetic gases coming from any source with high content of CH.sub.4 and heavy hydrocarbons. It is understood that by hydrocarbons heavier than methane we mean the sum off all hydrocarbons with two or more carbon atoms (C2+). Possible examples are ethane (C.sub.2H.sub.6), propane (C.sub.3H.sub.8), butane (C.sub.4H.sub.10) or higher. Thus, the expression “high content of total hydrocarbons heavier than methane” as used in the embodiments described herein means that the sum off all hydrocarbons with two or more carbon atoms (C2+) is more than 4%.

[0049] The method can be favourably implemented by means of an apparatus 100 for example as shown in FIG. 1.

[0050] The method according to the present description comprises circulating a first stream F1 of reducing gas exiting from a reduction reactor 10 in a reducing gas circuit 20 through at least one carbon dioxide removal unit 38 and a reducing gas heater 42 and a reactor 10.

[0051] According to one aspect of the invention, the method provides to feed, into the reducing gas circuit 20 between the reducing gas heater 42 and the reduction reactor 10, a stream F2 of fresh reducing gas which amounts to more than 20% of the overall quantity of reducing gas sent to the reactor 10 and thus needed to operate the direct reduction process.

[0052] In possible implementations, the stream F2 of said reducing gas amounts to more than 25%, or 30%, or 35%, or 40%, or 45%, or 50%, or 55%, or 60%, or 65%, or 70%, or 75%, or 80%, or 85%, or 90%, or 95%, of the quantity of the reducing gas needed to operate the direct reduction process.

[0053] In accordance with some embodiments, the method can provide that the stream F2 of gas is pre-heated to a temperature below 650° C.

[0054] According to some embodiments, the pre-heating of the stream F2 can occur in a convective zone 43 of the reducing gas heater 42.

[0055] In other embodiments, the stream F2 can be pre-heated in a heat exchanger or fired heater separate from the reducing gas heater 42.

[0056] In further embodiments, the stream F2 can be injected into the reducing gas circuit 20 without being pre-heated.

[0057] According to some embodiments, the method can provide to feed at least one other streams F3, F4 of fresh reducing gas, which amounts to the portion of reducing gas not injected into the reducing gas circuit 20 by the stream F2.

[0058] In a possible embodiment, the stream F3 can be injected in correspondence with any portion whatsoever of the reducing gas circuit 20 located between the carbon dioxide removal unit 38 and the reducing gas heater 42.

[0059] In another possible embodiment, the stream F4 can be injected directly into the reactor 10.

[0060] In another possible embodiment, it is conceivable to perform a combined feed of reducing gas which amounts to the portion of reducing gas not injected into the reducing gas circuit 20 by the stream F2, formed by the stream F3 injected in correspondence with any portion whatsoever of the reducing gas circuit 20, located between the carbon dioxide removal unit 38 and the reducing gas heater 42, and by the stream F4 injected directly into the reactor 10.

[0061] Some embodiments can also provide that at least the second stream F2, and possibly one and/or the other of the streams F3, F4, are controlled by at least one control unit 68 of the apparatus 100, configured to regulate the flow rate and therefore the percentage of reducing gas injected into the reducing gas circuit 20.

[0062] According to embodiments, the control unit 68 may regulate the flow rate of the gas stream F2 in response to a signal emitted by a flow rate sensor 69 and/or 70 measuring the flow rate of gas stream F3 and/or F4.

[0063] In other embodiments, control unit 68 additionally to regulating the flow rate of gas stream F2 also may regulate the flow rate of gas stream F3 and/or F4.

[0064] In other embodiments, not shown here, each stream F2, F3, F4 can be controlled by a respective and dedicated control unit, which can be connected to each other.

[0065] In some embodiments the control unit 68 may also regulate a flow rate of oxygen 52 with the aim of compensating the loss of energy caused by the fact that gas stream F2 bypassing the fired heater 42 will not have in any case the same temperature of the pipe 28 after heating in same fired heater 42.

[0066] FIG. 1 is used to describe embodiments of an apparatus 100 for producing iron from direct reduction of iron ore using reducing gas having a high content of total hydrocarbons heavier than methane (>4%), chosen among a natural gas having a high content of hydrocarbons heavier than methane, or coke oven gas (COG) having complex carbon compounds (BTX) or other synthetic gases coming from any source with high content of CH.sub.4 and heavy hydrocarbons.

[0067] According to one embodiment, the apparatus 100 comprises a reduction reactor 10, the carbon dioxide removal unit 38 and the heater 42. The apparatus 100 comprises the reducing gas circuit 20 which passes through the carbon dioxide removal unit 38 and the heater 42 and the reactor 10. According to one embodiment, the apparatus 100 comprises first injection means 49a configured to feed, into the reducing gas circuit 20 between the reducing gas heater 42 and the reduction reactor 10, the stream F2 of fresh reducing gas which amounts to more than 20% of the quantity of reducing gas needed to operate the direct reduction process.

[0068] In possible implementations, the first injection means 49a are configured to feed the stream F2 of fresh reducing gas which amounts to more than 25%, or 30%, or 35%, or 40%, or 45%, or 50%, or 55%, or 60%, or 65%, or 70%, or 75%, or 80%, or 85%, or 90%, or 95%, of the amount of reducing gas needed to operate the direct reduction process.

[0069] In some embodiments, the apparatus 100, as indicated above, can include a control unit 68 to control the first injection means 49a for the stream F2, and possibly one and/or the other of other injection means 49b, 49c provided for the streams F3, F4 as described in detail below. The control unit 68 regulates at least the flow rate of the fresh reducing gas stream F3 so as to maintain the sum of the heat provided by stream F2 plus the heat provided by stream F3 within a predetermined range of values so as to maintain the operating conditions of the reduction zone 12 of the reactor 10 to produce DRI at a predetermined production rate. In some embodiments, the control unit 68 additionally to regulating the flow rate of fresh reducing gas stream F2 also regulates the flow rate of fresh reducing gas stream F4.

[0070] In some embodiments, the first injection means 49a are connected at exit from the heater 42. The heater 42 receives the stream F2 from an entry pipe 29 associated with a source 46 of reducing gas. A by-pass branch 60a is advantageously associated with the pipe 29 and with the first injection means 49a, in order to allow to by-pass at least the feed of a part of the second stream F2 of fresh reducing gas to the heater 42 and inject it, instead, directly into the first injection means 49a.

[0071] In a possible embodiment, the apparatus 100 comprises, as mentioned above, other one or more injection means 49b, 49c configured to inject into the reducing gas circuit 20 at least the stream F3, F4 of fresh reducing gas which amounts to the portion of reducing gas not injected into the reducing gas circuit 20 by the second stream F2.

[0072] In a possible embodiment, injection means 49b are provided configured to inject the stream F3 in correspondence with any portion whatsoever of the reducing gas circuit 20 located between the carbon dioxide removal unit 38 and the reducing gas heater 42. According to some embodiments, a source 44 of reducing gas, associated with the injection means 49b, can be provided to supply the stream F3 of fresh reducing gas.

[0073] In another possible embodiment, injection means 49c are provided configured to feed the stream F4 directly into the reactor 10. According to some embodiments, a source 48 of reducing gas, associated with the injection means 49c, can be provided to supply the stream F4 of fresh reducing gas.

[0074] In further embodiments, it can be provided that both the injection means 49b and also the injection means 49c are present, in order to feed a combination of reducing gas which amounts to the portion of reducing gas not injected by the stream F2, formed by the stream F3 injected in correspondence with any portion whatsoever of the reducing gas circuit 20 located between the carbon dioxide removal unit 38 and the reducing gas heater 42, and by the stream F4 injected directly into the reactor 10.

[0075] In one embodiment, the reduction reactor 10 is of the gravitational type.

[0076] In one embodiment, the reduction reactor 10 comprises a reduction zone 12, inside which the iron ore reduction processes occur, feeding means 16 to feed iron ore 15 into the reactor 10, an aperture 13 to extract spent reducing gas and a discharge zone 14 to discharge reduced iron 18.

[0077] In one embodiment, the reducing gas circuit 20 is configured to regenerate the spent reducing gas exiting the reactor 10 and re-inject it into the reactor 10 once it has been regenerated.

[0078] In one embodiment, the apparatus 100 comprises:

[0079] devices 32, 34, 36, 40 for regenerating the spent reducing gas,

[0080] the source 44 of reducing gas connected to the reducing gas circuit 20 before the heater 42,

[0081] a suitable source 52 of oxygen connected to the reducing gas circuit 20 between the heater 42 and the reactor 10,

[0082] the source 46 of reducing gas connected between the heater 42 and the source 52 of oxygen,

[0083] the source 48 of reducing gas connected directly to the reactor 10;

[0084] a valve 56 disposed on the injection means 49b, a valve 58 disposed on the entry pipe 29, a valve 60 disposed on the by-pass branch 60a, and a valve 62 disposed on the injection means 49c;

[0085] the at least one control unit 68, which can be connected to at least one of the valves 56, 58, 60, 62 and configured to regulate the respective streams F2, F3, F4 in response to signals emitted by the flowrate sensors 69, 70.

[0086] In other embodiments (not shown), the at least one control unit 68 may be connected to the source 52 of oxygen and configured to regulate its flowrate.

[0087] According to some embodiments, the stream F1 of spent reducing gas exiting the reactor 10 can be injected into the reducing gas circuit 20 by means of an aperture 13 connected to the reducing gas circuit 20.

[0088] In particular, the stream F1 of spent reducing gas reaches, by means of a pipe 21, a heat exchanger 32 suitable to reduce the temperature of the gas.

[0089] The cooled reducing gas can be sent to a cooling tower 34 by means of a pipe 22. In the cooling tower 34, the gas is further cooled and is substantially deprived of the water component.

[0090] The water extracted from the gas by the cooling tower 34 can be conveyed in a pipe 25, by means of pumping means 66, in order to be reused in subsequent gas treatments described below, in particular to be transferred to a humidifier 40 described below.

[0091] Possible inert gases present in the spent reducing gas, and therefore not useful for the reduction processes, can be extracted from the reducing gas circuit 20 through a pipe 23 on which a vent valve 54 is disposed, to control the pressure of the circuit.

[0092] According to some embodiments, the inert gases exiting the vent valve 54 can possibly be reinjected into the reducing gas circuit 20 to participate in other functions as described below.

[0093] The reducing gas which remains inside the reducing gas circuit 20, which is not extracted through the vent valve 54, is directly fed through a pipe 24 connected to the pipe 23, to a pumping means 64.

[0094] The gas exiting from the pumping means through the pipe 24 is sent to a cooler 36, configured to decrease the temperature of the gas.

[0095] In some embodiments, the reducing gas circuit 20 of the reduction apparatus 100 described here comprises at least the carbon dioxide removal unit 38 configured to remove CO.sub.2 from the reducing gas.

[0096] According to some embodiments, the carbon dioxide removal unit 38 is located downstream of the cooler 36 and connected to it by means of a pipe 26.

[0097] According to some embodiments, the carbon dioxide removal unit 38 can be of the chemical absorption type where the CO.sub.2 is absorbed by a solvent, for example, amines or potassium carbonate.

[0098] According to other embodiments, the carbon dioxide removal unit 38 can be of the physical adsorption type where the CO.sub.2 is adsorbed by a solid substrate.

[0099] In preferred embodiments, the carbon dioxide removal unit 38 can be disposed at a point of the reducing gas circuit 20 so that it receives the reducing gas which has been treated by the treatment devices 32, 34, 36.

[0100] In accordance with further embodiments, the carbon dioxide removal unit 38 can be disposed before the spent reducing gas is mixed with fresh reducing gas.

[0101] The reducing gas purified of the CO.sub.2, or process gas, exits from the device 38 through a pipe 27 to reach the humidifier 40.

[0102] Some embodiments provide that in correspondence with the pipe 27, the source 44 of reducing gas suitable to inject the stream F3 of fresh reducing gas into the circuit can be connected through the injection means 49b.

[0103] The possible injection of fresh reducing gas of the stream F3 and its volume can be controlled by the valve 56 which controls the flowrate toward the pipe 27.

[0104] The process gas exiting from the carbon dioxide removal unit 38, possibly mixed with reducing gas coming from the stream F3, can reach the humidifier 40 in which the percentage of water in the gas can be increased up to a desired value by means of the direct contact of the gas with hot water.

[0105] According to some embodiments, the humidifier 40 can use, for its function, the water extracted by the cooling tower 34, which is connected to the humidifier 40 by means of a pipe 25 provided with the pumping means 66.

[0106] The humidified gas reaches, by means of a pipe 28, the heater 42 in which it is heated, for example up to a temperature comprised between 800° C. and 1000° C.

[0107] The heater 42 functions by burning a suitable fuel introduced into the heater 42 by a supply source 50.

[0108] According to some embodiments, the suitable fuel can be fresh reducing gas, reducing gas extracted by the vent valve 54 or a combination thereof.

[0109] According to some embodiments, the vent valve 54 can then be connected to the fuel supply source 50.

[0110] Some embodiments provide that the source 46 of fresh reducing gas is connected to a convective zone 43 of the heater 42 through the entry pipe 29. According to some embodiments, the pipe 29 can divide following a path external to the convective zone of the heater 42 by means of the by-pass branch 60a.

[0111] In accordance with some embodiments, the source 46 of fresh reducing gas or heavy hydrocarbon gases is connected to the reducing gas circuit 20 between the heater 42 and the reactor 10 by the injection means 49a.

[0112] Some embodiments can provide that the valve 58 and/or the valve 60 are able to direct and control the second stream F2 toward the heater 42, in particular the respective convective zone 43.

[0113] In particular, the valve 58 is used to control the overall stream F2, while the valve 60, disposed on the by-pass branch 60a, is used to vary the quantity of reducing gas that is injected into the heater 42.

[0114] Advantageously, the pre-heating allows to inject into the reducing gas circuit 20 reducing gas that is sufficiently hot for the subsequent steps, so as to minimize the temperature drop resulting from the mixing of the fresh reducing gas with the reducing gas coming from the heater 42.

[0115] According to some embodiments, between the injection means 49a and the reactor 10, the source 52 of oxygen can be provided, configured to inject oxygen so as to increase the temperature of the incoming gas up to a temperature level comprised between 950° C. and 1150° C. This injection of oxygen also allows to compensate for the temperature loss caused by mixing the fresh reducing gas, cold or pre-heated, with the reducing gas coming from the heater 42.

[0116] The regenerated gas can then be injected into the reactor 10.

[0117] It is clear that modifications and/or additions of parts or steps may be made to the apparatus for the direct reduction and its corresponding method as described heretofore, without departing from the field and scope of the present invention.

[0118] It is also clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms of plants for direct reduction, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.

[0119] In the following claims, the sole purpose of the references in brackets is to facilitate reading: they must not be considered as restrictive factors with regard to the field of protection claimed in the specific claims.