Method for operating a metallurgical furnace

Abstract

A method for operating a metallurgical furnace and a simplified way of providing synthesis gas for a metallurgical furnace, includes the following steps performing a combustion process outside the metallurgical furnace by combusting a carbon-containing material with an oxygen-rich gas to produce an offgas, which offgas is a CO.sub.2 containing gas; and combining the offgas, while having an elevated combustion-induced temperature due to the combustion process, with a hydrocarbon-containing fuel gas to obtain a first gas mixture having a temperature above a reforming temperature necessary for a reforming process, preferably a dry reforming process; the first gas mixture undergoing the reforming process, thereby producing a synthesis gas containing CO and H.sub.2, the reforming process being performed non-catalytically; and feeding the synthesis gas into the metallurgical furnace.

Claims

1. A method for operating a metallurgical furnace, the method including the following steps: performing a combustion process outside the metallurgical furnace by combusting a carbon-containing material with an oxygen-rich gas having a O.sub.2 concentration significantly higher than air to produce an offgas, which offgas is a CO.sub.2 containing gas, combining the offgas, while having an elevated combustion-induced temperature above 1000° C. due to the combustion process, with a hydrocarbon-containing fuel gas to obtain a first gas mixture having a temperature above a reforming temperature necessary for a reforming process, the first gas mixture undergoing the reforming process, thereby producing a synthesis gas containing CO and H.sub.2, the reforming process being performed non-catalytically and being a dry reforming process and/or a wet reforming process; and feeding the synthesis gas into the metallurgical furnace.

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

3. The method according to claim 1, wherein the offgas, when being combined with the hydrocarbon-containing fuel gas, has a combustion-induced temperature above 1500° C.

4. The method according to claim 1, wherein the hydrocarbon-containing fuel gas, when being combined with the offgas, has a temperature below 100° C.

5. The method according to claim 1, wherein the offgas and the hydrocarbon-containing fuel gas are combined with a supplemental gas, which is a CO.sub.2 containing gas, to obtain the first gas mixture.

6. The method according to claim 1, wherein the carbon-containing material comprises tar, coke breeze, charcoal, coal and/or heavy fuel oil.

7. The method according to claim 1, wherein the hydrocarbon-containing fuel gas comprises natural gas, coke oven gas and/or biogas.

8. The method according to claim 1, wherein the synthesis gas immediately after the reforming process has a post-reforming temperature above 1000° C.

9. The method according to claim 1, wherein the metallurgical furnace is a shaft furnace.

10. The method according to claim 1, wherein the metallurgical furnace is a blast furnace.

11. The method according to claim 10, wherein the synthesis gas is fed into the blast furnace at a tuyere level.

12. The method according to claim 10, wherein the synthesis gas is fed into the blast furnace at a shaft level above a tuyere level.

13. The method according to claim 1, wherein the synthesis gas is fed into the metallurgical furnace along with an additive gas having a temperature lower than a post-reforming temperature of the synthesis gas, which additive gas is a CO and/or H.sub.2 containing gas.

14. The method according to claim 13, wherein the synthesis gas is mixed with the additive gas to form a second gas mixture before it is fed into the metallurgical furnace.

15. The method according to claim 14, wherein the second gas mixture has a temperature between 700° C. and 1200° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred embodiments of the disclosure will now be described, by way of example, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic view of a blast furnace installation for carrying out an embodiment of the inventive method; and

(3) FIG. 2 is a schematic view of a part of the blast furnace installation from FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

(4) FIG. 1 schematically shows a blast furnace installation 1 comprising a blast furnace 10. At its top end, blast furnace 10 generally receives coke 12 and ore 13 from a stock house 15. At the bottom end of the blast furnace 10, pig iron and slag are extracted (which is not shown for sake of simplicity). The operation of the blast furnace 10 itself is well known and will not be further described herein. At the top end, blast furnace gas 14 is recovered from the blast furnace 10. The recovered blast furnace gas 14, which e.g. may have a N.sub.2 concentration below 40%, a CO and CO.sub.2 concentration of about 25-40% each and about 5-15% of H.sub.2, may be treated in a gas cleaning plant 20, mostly for removing particulate matter from the blast furnace gas 14 and possibly condensing a part of the vapour contained in the blast furnace gas 14. The recovered and cleaned blast furnace gas 14 may be used for various purposes which are not discussed here in detail. After cleaning the blast furnace gas 14, its CO.sub.2 content may be reduced in a carbon capture device 21. Here, a portion of the blast furnace gas is separated as a carbon capture gas 22, which is a gas having a high concentration of CO.sub.2, e.g. more than 50% or more than 70%. This carbon capture gas 22, or part thereof, may be used as supplemental gas 48.

(5) In the lower part of the blast furnace 10, namely at a tuyere level 10.1, the blast furnace 10 receives pulverised coal 26 and hot blast 27 provided from a hot stove plant 25 comprising a plurality of cowpers. The hot blast 27 may comprise air or an oxygen-rich gas. Alternatively, at the tuyere level, the blast furnace may receive a cold oxygen containing gas with a concentration typically of 95%, thereby largely or completely replacing the hot blast. Another option is that a synthesis gas 45 comprising CO and/or H.sub.2 is injected together with the hot blast and/or cold oxygen containing gas and the pulverised coal.

(6) At a shaft level 10.2, which is located above the tuyere level 10.1, the blast furnace 10 receives a mixture 47 of a synthesis gas 45 and an additive gas 46. The synthesis gas 45 is prepared in a syngas reactor 30, which is schematically shown in FIG. 2. The syngas reactor 30 comprises a burner 31 that is supplied with an oxygen-rich gas 40 and a carbon-containing material 41. The oxygen-rich gas 40 may contain least 90% of O.sub.2, while the carbon-containing material 41 may e.g. comprise tar, coke breeze, charcoal, coal and/or heavy fuel oil. The carbon-containing material 41 is burned with the oxygen-rich gas 40 in a combustion process in the burner 31, whereby an offgas 42 is produced, which by way of example may have a composition of e.g. 80% CO.sub.2, 15% H.sub.2O and 5% N.sub.2. Due to the strong exothermic combustion process, the flame temperature may be above 3000° C. The offgas 42 and a fuel gas 43 are injected into a mixing section 32 where they are mixed. The fuel gas 43 is a hydrocarbon-containing gas, e.g. coke oven gas, natural gas and/or biogas. When the offgas 42 is combined with the fuel gas 43, it has a combustion-induced temperature of at least 2000° C., while the fuel gas 43 may have a temperature below 100° C., e.g. ambient temperature. The fuel gas 43 and the offgas 42 form a first gas mixture 44 having a temperature above a reforming temperature that is necessary for a reforming process, preferably a dry reforming process. The reforming temperature should be above 800° C. and may preferably be between 900° C. and 1600° C. Due to the high temperature of the first gas mixture 44, which in turn is largely due to the combustion-induced temperature of the offgas 42, the reforming process starts without the need of additional heating or application of a catalyst. As an option, a supplemental gas 48 may be added to the fuel gas 43 and the offgas 42 to form the first gas mixture 44, Such supplemental gas 48 may e.g. be blast furnace gas and/or basic oxygen furnace gas and/or the carbon capture gas 22 (or at least a portion thereof), as indicated by the dashed arrow in FIGS. 1 and 2. Since the carbon capture gas 22 like the offgas 42 has a high CO.sub.2 content, it may be used as a supplemental gas 48. However, since the temperature of the carbon capture gas 22 is significantly lower than the temperature of the offgas 42, the ratio of the carbon capture gas 22 is adjusted in order to keep the temperature of the first gas mixture above the reforming temperature. In FIG. 2, a reaction section 33 is shown next to the mixing section 32, but these need not be two different, distinguishable sections, since the reforming process begins as the fuel gas is mixed with the offgas.

(7) The dry reforming process occurs according to the following reaction: CO.sub.2+CH.sub.4.fwdarw.2H.sub.2+2CO. It may be supported by an increased pressure inside the mixing section 32 and/or the reaction section 33. To some extent, a wet reforming may also occur according to the following reaction: H.sub.2O+CH.sub.4.fwdarw.3H.sub.2+CO. After undergoing the dry reforming process (and/or the wet reforming process), the offgas 42 and the fuel gas 43 and, if applicable, supplemental gas 48 are mainly converted into a synthesis gas 45, which comprises CO and H.sub.2. Although the reforming process is an endothermic reaction which lowers the temperature of the synthesis gas 45 with respect to the gas mixture, a post reforming temperature of the synthesis gas 45 may still be above 1200° C. Since the synthesis gas 45 is intended for injection into the blast furnace 10 at the shaft level 10.2, the post-reforming temperature is incompatible with the temperature distribution inside the blast furnace 10. Therefore, an additive gas 46, which comprises CO and H.sub.2, is introduced into the blast furnace 10 together with the synthesis gas 45. The additive gas 46 has the temperature that is significantly lower than the post-reforming temperature, for instance it could have ambient temperature. Preferably, the synthesis gas 45 and the additive gas 46 are mixed before they are introduced into the blast furnace 10, so that a resulting second gas mixture 47 has a temperature lower than the post-reforming temperature. In particular, the ratio of the two gases can be adjusted so that the mixture 47 has a temperature corresponding to the temperatures inside the blast furnace at the shaft level 10.2.

(8) The introduction of the synthesis gas 45 and the additive gas 46 at the shaft level 10.2 helps prevent the top gas temperature of the blast furnace 10 from dropping below a certain level even if the gas flow through the blast furnace 10 is reduced. Reducing the gas flow is beneficial in that it reduces the likelihood of irregularities like flooding or hanging and slipping.

(9) Alternatively or additionally to introducing the synthesis gas 45 into the blast furnace 10 at the shaft level 10.2, it could be introduced at the tuyere level 10.1, as indicated by the dashed arrow in FIG. 1. In this case, the post-reforming temperature is compatible with the temperatures inside the blast furnace 10 at the tuyere level 10.1. Therefore, there is no need to mix the synthesis gas 45 with any additive gas 46, i.e. the synthesis gas 45 can be fed into the blast furnace 10 as it is.