METHOD FOR OPERATING A BLAST FURNACE

Abstract

A method for operating a blast furnace, including collecting a blast furnace gas from the blast furnace, the blast furnace gas being a CO.sub.2 containing gas, combining the blast furnace gas with a fuel gas to obtain a gas mixture, the fuel gas being a hydrocarbon containing gas, subjecting the gas mixture to a reforming process, thereby producing a synthesis gas containing CO and H.sub.2; and feeding at least a portion of the synthesis gas and an oxygen-rich gas into the blast furnace, where the blast furnace gas is combined with the fuel gas while containing substantially the same amount of CO.sub.2 as when exiting the blast furnace and wherein the blast furnace gas is combined with the fuel gas in an over-stoichiometric ratio, so that the synthesis gas contains a surplus portion of the blast furnace gas.

Claims

1. A method for operating a blast furnace, the method comprising: collecting a blast furnace gas from the blast furnace, said blast furnace gas being a CO.sub.2 containing gas; combining the blast furnace gas with a fuel gas to obtain a gas mixture, said fuel gas being a hydrocarbon containing gas; subjecting said gas mixture to a reforming process, thereby producing a synthesis gas containing CO and H.sub.2; and feeding at least a portion of the synthesis gas and an oxygen-rich gas into the blast furnace; wherein the blast furnace gas is combined with the fuel gas while not having been submitted to a preliminary decarbonating after exiting the blast furnace; and wherein the blast furnace gas is combined with the fuel gas in an over-stoichiometric ratio, so that the synthesis gas contains a surplus portion of the blast furnace gas.

2. A method according to claim 1, wherein the blast furnace gas is combined with the fuel gas in an over-stoichiometric ratio before the reforming process.

3. A method according to claim 1, wherein the blast furnace gas is combined with the fuel gas in a stoichiometric ratio before the reforming process, while additional blast furnace gas is combined with the synthesis gas after the reforming process.

4. A method according to claim 1, wherein the oxygen-rich gas contains at least 60% of O.sub.2.

5. A method according to claim 1, wherein the oxygen-rich gas has a temperature below 100° C.

6. A method according to claim 1, wherein the synthesis gas is fed into the blast furnace at a tuyere level and/or lower shaft level having a temperature of at least 800° C.

7. A method according to claim 1, wherein the over-stoichiometric ratio is adjusted to control a top gas temperature of the blast furnace.

8. A method according to claim 1, wherein the over-stoichiometric ratio is adjusted to control a flame temperature of the blast furnace.

9. A method according to claim 1, wherein in addition to the synthesis gas and the oxygen-rich gas, an auxiliary fuel is fed into the blast furnace.

10. A method according to claim 1, wherein a portion of the blast furnace gas is burned with oxygen to create a waste gas.

11. A method according to claim 10, wherein the waste gas is condensated and cooled.

12. A method according to claim 1, wherein a portion of the blast furnace gas is burned in a heating device.

13. A method according to claim 1, wherein the heating device is used for heating the blast furnace gas, the fuel gas, the gas mixture and/or the synthesis gas.

14. A method according to claim 10, wherein at least a portion of the waste gas is used for carbon capture and storage and/or carbon capture and utilization.

15. A method according to claim 10, wherein at least a portion of the waste gas is used for synthesis gas production.

16. A method according to claim 1, wherein the oxygen-rich gas contains at least 80% of O.sub.2.

17. A method according to claim 1, wherein the oxygen-rich gas contains at least 90% of O.sub.2.

18. A method according to claim 1, wherein the synthesis gas is fed into the blast furnace at a tuyere level and/or lower shaft level having a temperature of at least 1000° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Preferred embodiments of the disclosure will now be described, by way of example, with reference to the accompanying drawings, in which:

[0031] FIG. 1 is a schematic view of a blast furnace installation for carrying out the method for operating a blast furnace according to the present disclosure.

DETAILED DESCRIPTION

[0032] FIG. 1 shows a blast furnace installation 10 comprising a blast furnace 12. The top end 16 of the blast furnace 12 generally receives a charge of coke 18 and a charge of ore 20, while the bottom end 22 of the blast furnace 12 generally receives pulverized coal 24 and an oxygen-rich gas 26. For example, the oxygen-rich gas may have an O.sub.2 concentration of 95% and an N.sub.2 concentration of 5%. At the bottom end 22, pig iron 28 and slag 30 are extracted from the blast furnace 12. The operation of the blast furnace itself is well known and will not be further described herein.

[0033] The blast furnace installation 10 further comprises gas recovery tubes 40 for recovering blast furnace gas from the blast furnace 12. By way of example, the recovered blast furnace gas may have a N.sub.2 concentration below 5%, a CO and CO.sub.2 concentration of about 40% each and about 15% of H.sub.2. More generally, the blast furnace gas may have an N.sub.2 concentration of 0-50%, a CO and CO.sub.2 concentration of 20-50% each and a H.sub.2 concentration of 2-25%. It is fed to gas recovery piping 42 comprising a distribution valve 44. The blast furnace installation 10 may comprise a gas cleaning plant 43 arranged between the gas recovery tubes 40 and the distribution valve 44 for cleaning the gas recovered from the blast furnace 12, mostly for removing particulate matter from the gas and possibly condensing a part of the vapor contained in the blast furnace gas. It should be noted that the above concentrations are for a dry composition of blast furnace gas. However, the blast furnace gas may also be wet, i.e. it may contain moisture.

[0034] At the distribution valve 44, at least a portion of the recovered blast furnace gas is directed through a first feed pipe 46 to a mixing chamber 48. The mixing chamber 48 is provided with a second feed pipe 50 for feeding a hydrocarbon containing gas, for example coke oven gas and/or natural gas and/or biogas, into the mixing chamber 48. Within the mixing chamber 48, the blast furnace gas and the hydrocarbon containing gas are mixed together to form a gas mixture. This gas mixture is then fed through a third feed pipe 52, which may comprise a blower 54, into a reactor 56. Energy 53 may be added to the reactor 56 in order to sustain the reaction and to heat the gas mixture. The energy 53 can be supplied directly or indirectly to the reactor. The energy can be any kind of energy, as for example electric energy using an electric arc, a plasma torch or an electric resistance but can advantageously result from a burning process of a fuel gas in the burner 57. The gas mixture is normally compressed. Alternatively, both gases can be compressed individually and be mixed afterwards. In the reactor 56, the gas mixture is heated to a high temperature, thereby subjecting the gas mixture to a reforming process, which in this case is mainly a dry reforming process according to the following reaction: CO.sub.2+CH.sub.4.fwdarw.2H.sub.2+2CO. In this example, the dry reforming process is carried out at a temperature between 800° C. and 1500° C. within the reactor 56 without the need of a catalyst. Alternatively, a catalyst could be used, e.g. by providing the reactor 56 with a catalyst.

[0035] The produced synthesis gas is then fed via a fourth feed pipe 58 as reducing gas back into the blast furnace 12, either at a tuyere level or at a lower shaft level.

[0036] In case of injection of the synthesis gas at the tuyere level, the synthesis gas is injected along with the auxiliary fuel 24 and the oxygen-rich gas 26. While the synthesis gas is fed at a temperature of at least 800° C., the oxygen-rich gas 26 typically has ambient temperature, although it may also have a higher temperature.

[0037] While the use of the oxygen-rich gas 26 increase the productivity of the blast furnace 12, it could potentially lead to difficulties. On the one hand, it could lead to an increased flame temperature in the raceway of the blast furnace 12, because the flame is not cooled by nitrogen, on the other hand, the top gas temperature could decrease because heat transport by nitrogen, and thus the heating of the cold furnace burden, is greatly decreased. To counter these problems, a flow control valve 47 is disposed in the first feed pipe 46, by which the ratio of the blast furnace gas and the fuel gas can be adjusted. In general, an over-stoichiometric ratio is applied, so that the synthesis gas may contain unreacted blast furnace gas. In particular, the CO.sub.2 concentration and/or the H.sub.2O concentration of the synthesis gas is increased. On the one hand, this additional blast furnace gas brings additional latent heat into the blast furnace 12, which helps to increase the top gas temperature. On the other hand, the CO.sub.2 and/or H.sub.2O contained in the synthesis gas may react with C in the blast furnace 12 to produce CO and/or H.sub.2 in an endothermic reaction, which lowers the flame temperature. In particular, the top gas temperature and/or the flame temperature may be monitored and the ratio may be adjusted to control at least one of these temperatures and keep it within a desired range. At the distribution valve 44, at least a portion of the recovered blast furnace gas may be directed through a fifth feed pipe 60 to the burner 57 of the reactor 56 to supply the energy 53 required to heat up the gas mixture and sustain the reforming reaction. Alternatively or additionally, it could also be used for a burner for heating the blast furnace gas in the first feed pipe 46, the coke oven gas in the second feed pipe 50 or the synthesis gas in the fourth feed pipe 58. In the burner 57, the blast furnace gas is burned preferably with oxygen 64, thereby producing a high CO.sub.2 containing waste gas 66. The waste gas 66 may have a composition of e.g. 80% CO.sub.2, 15% H.sub.2O and 5% N.sub.2. It can be collected and supplied to a cooler 68, where it is condensated and cooled, whereby the CO.sub.2 concentration can be increased further, e.g. up to 95%. Therefore, it can be used for carbon capture and storage (CCS) in a storage site 70 or it can be used, e.g. in a chemical plant 72, for synthesis gas production.

[0038] Another portion of the blast furnace gas is provided through a sixth feed pipe 62 to an external plant 74 that is not part of or directly associated with the blast furnace. It can be some other device in a steel plant or even outside the steel plant. In this external plant 74, the blast furnace gas may be used e.g. as burner fuel or for other chemical purposes.