METHOD FOR OPERATING A BLAST FURNACE INSTALLATION

Abstract

A method for operating a blast furnace for producing of pig iron, includes the following steps heating a first stream of steam in a first heater, before or after having been mixed with an oxygen source selected from oxygen and oxygen-enriched air, to provide a first heated stream of oxygen-enriched steam; heating a first stream of blast furnace gas from the blast furnace and a first stream of natural gas in a second heater, before or after being mixed together, to provide a heated carbon feed stream; feeding the first heated stream of oxygen-enriched steam and the heated carbon feed stream either as a combined stream or separately to a catalytic partial oxidation reactor to produce a stream of syngas; and feeding the stream of syngas to the shaft of the blast furnace.

Claims

1. A method for operating a blast furnace for producing pig iron, the method including the following steps of: (a) heating a first stream of steam in a first heater, before or after having been mixed with an oxygen source selected from oxygen and oxygen-enriched air, to provide a first heated stream of oxygen-enriched steam, (b) heating a first stream of blast furnace gas from the blast furnace and a first stream of natural gas in a second heater, before or after being mixed together, to provide a heated carbon feed stream, (c) feeding the first heated stream of oxygen-enriched steam and the heated carbon feed stream either as a combined stream or separately to a catalytic partial oxidation reactor to produce a stream of syngas, and (d) feeding said stream of syngas to the shaft of the blast furnace.

2. The method as claimed in claim 1, wherein the oxygen source is oxygen and the catalytic partial oxidation reactor is a Short Contact Time Catalytic Partial Oxidation reactor.

3. The method as claimed in claim 1, wherein the first stream of blast furnace gas is further subjected to a gas cleaning step, before being mixed with the first stream of natural gas.

4. The method as claimed in claim 1, wherein the heated carbon feed stream of step (b) is further heated within a third heater before step (c).

5. The method as claimed in claim 4, wherein a second stream of blast furnace gas is burned in a burner within the first and/or the second heater and/or, if applicable, the third heater to provide the heat within said heaters.

6. The method as claimed in claim 5, wherein the first heater, the second heater, and the third heater are heated by a same burner.

7. The method as claimed in claim 5, wherein off-gas produced by the burner(s) is fed to the first stream of blast furnace gas coming from the blast furnace, which is fed to the first stream of natural gas or to the heated carbon feed stream.

8. The method as claimed in claim 1, wherein the first stream of blast furnace gas and/or the first stream of natural gas and/or the heated carbon feed stream is/are subjected to a desulphurization step.

9. The method as claimed in claim 1, wherein the temperature of the combined stream in step (c) is from 200 to 500° C.

10. The method as claimed in claim 1, wherein the oxygen source for enriching the first heated stream of steam is heated to a temperature differing by no more than 100° C., from the temperature of said first heated stream of steam before oxygen enrichment.

11. The method as claimed in claim 1, wherein first heated stream of oxygen-enriched steam, the stream of natural gas and the stream of blast furnace gas are fed in amounts such that the stream of syngas of step (d) has a chemical composition fulfilling the following constraints of CH4<5% vol, H2O<8% vol and (CO+H2)/(H2O+CO.sub.2)>7.

12. The method as claimed in claim 1, wherein a stream of H2, preferably a stream of renewable H2, is added to the stream of syngas before step (d), said stream of H2 having been heated.

13. A blast furnace installation for producing pig iron comprising a blast furnace provided with gas inlets in the shaft arranged for feeding a stream of syngas to the blast furnace, said blast furnace installation further comprising a first heater in fluidic downstream connection with a stream of steam and in fluidic downstream or upstream connection with an oxygen source providing oxygen or oxygen-enriched air, said first heater being arranged for heating said stream of steam to provide a first heated stream of oxygen-enriched steam; a second heater in fluidic connection with the top of the blast furnace arranged for conveying a first stream of blast furnace gas and with a source of a first stream of natural gas, said second heater being arranged for heating said first stream of blast furnace gas and said first stream of natural gas either separately or mixed to provide a heated carbon feed stream; said first and second heater being in fluidic downstream connection with one or more reactor inlets of a catalytic partial oxidation reactor arranged for producing a stream of syngas, either directly for feeding the first heated stream of oxygen-enriched steam and the heated carbon feed stream separately to said one or more reactor inlets or through a mixing unit arranged for first joining the first heated stream of oxygen-enriched steam with the heated carbon feed stream to provide a combined stream and for feeding said combined stream to said one or more reactor inlets; said catalytic partial oxidation reactor being in fluidic downstream connection with the gas inlets in the shaft of the blast furnace.

14. The blast furnace installation as claimed in claim 13, wherein the blast furnace installation is configured for implementing the method for operating a blast furnace for producing of pig iron including the following steps: (a) heating a first stream of steam in a first heater, before or after having been mixed with an oxygen source selected from oxygen and oxygen-enriched air, to provide a first heated stream of oxygen-enriched steam, (b) heating a first stream of blast furnace gas from the blast furnace and a first stream of natural gas in a second heater, before or after being mixed together, to provide a heated carbon feed stream, (c) feeding the first heated stream of oxygen-enriched steam and the heated carbon feed stream either as a combined stream or separately to a catalytic partial oxidation reactor to produce a stream of syngas, and (d) feeding said stream of syngas to the shaft of the blast furnace.

15. The blast furnace installation as claimed in claim 13, wherein the oxygen source is oxygen gas and the catalytic partial oxidation reactor is a Short Contact Time Catalytic Partial Oxidation reactor.

16. The blast furnace installation as claimed in claim 13, wherein fluidic connection conveying the first stream of blast furnace gas from the blast furnace comprises a gas cleaning plant.

17. The blast furnace installation as claimed in claim 13, wherein said second heater is in fluidic downstream connection with a third heater arranged for further heating the carbon feed stream upstream of mixing unit.

18. The blast furnace installation as claimed claim 17, wherein a burner within the first and/or the second heater and/or, if applicable, the third heater, is in fluidic connection with the top of the blast furnace for conveying and burning a second stream of blast furnace gas to provide the heat within said heaters.

19. The blast furnace installation as claimed in claim 18, wherein the first heater, the second heater, and the third heaters are heated by a same burner.

20. The blast furnace installation as claimed in claim 18, wherein the burner or each burner comprises an off-gas collection device which is arranged for feeding said off-gas to the first stream of blast furnace gas from the blast furnace, to the first stream of natural gas or to the heated carbon feed stream.

21. The blast furnace installation as claimed in claim 13, further comprising a desulphurization unit arranged within the fluidic connection of the first stream of blast furnace gas and/or the first stream of natural gas and/or the heated carbon feed stream.

22. The blast furnace installation as claimed in claim 13, wherein the first heater, the second heater and, if applicable the third heater, are controlled such that a temperature of the combined stream is from 200 to 500° C.

23. The blast furnace installation as claimed in claim 13, wherein the first heater is in fluidic upstream connection with a source of oxygen, further comprising a fourth heater configured for heating oxygen for enriching the first heated stream of steam downstream of the first heater to a temperature differing by no more than 100° C. from the temperature of said first heated stream of steam before oxygen enrichment.

24. The blast furnace installation as claimed in claims 13 to 23, wherein the fluidic connection between the catalytic partial oxidation reactor and the gas inlets in the shaft of the blast furnace is provided with a fluidic connection to a source of a stream of H2, is provided with a further heater for heating said stream of H2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Preferred embodiments of the disclosure will now be described, by way of example, with reference to the accompanying drawings in which:

[0048] FIG. 1 is a schematic flowsheet diagram of an embodiment of a blast furnace installation according to the disclosure and allowing for implementing the method of the disclosure.

[0049] Further details and advantages of the present disclosure will be apparent from the following detailed description of several not limiting embodiments with reference to the attached drawing.

DETAILED DESCRIPTION OF THE DRAWINGS

[0050] The requirements for the syngas and its utilization in the blast furnace are different to the applications already used today:

[0051] Reduction degree and temperature level of the syngas:

[0052] In other industries normally the syngas is produced and then cooled to separate the excess of steam from the syngas. Thereby only cooled gas is used in the downstream processes. In existing industrial applications beside the steel industry, a high reduction degree is not important. In steel industry however a high reduction degree, preferably above 7, is preferable, whereas the reduction degree is defined by the following molar ratio:(cCO+cH.sub.2)/(cH.sub.2O+cCO.sub.2).

[0053] Furthermore, high temperatures of syngas are favored compatible to the temperature level required for shaft injection in order to allow maximum thermal efficiency. Thus the temperature should be in the order of 900 to 1100° C. to allow its injection in the shaft of a blast furnace.

[0054] Ratio H.sub.2/CO

[0055] In the other industries, beside steel industry, the syngas is used for specific applications, such as pure hydrogen production, ammonia or the production of other chemical components. Thereby a specific ratio of hydrogen to CO is generally required.

[0056] In comparison, an advantage by using syngas in the blast furnace is reduction of ore, which is achieved with both reducing components, CO and hydrogen. While there is a difference between the reduction of ore with CO or hydrogen, this difference is relatively marginal considering that syngas is only part of the reducing gas used within the blast furnace.

[0057] CO.sub.2 Emissions

[0058] Coke is the main energy input in the blast furnace iron making. From the economic and CO.sub.2 point of view, this is the less favorable energy source. Substitution of coke by other energy sources, mostly injected at tuyere level, is widely employed. Due to cost reasons mostly pulverized coal is injected, however in countries with low natural gas price, this energy is used. Often residues like waste plastics are also injected in the blast furnace.

[0059] These auxiliary fuels may have a positive impact on the CO.sub.2 emissions from the blast furnace steel making, meanwhile their utilization is limited to process reasons and very often these limits are already attained today. The blast furnace produces blast furnace gas (BFG), which contains up to approximately 40% of the energy input to the blast furnace. This gas is generally used for internal heat requirements in the steel plant, but also for electric energy production. For the advantage of reducing the CO.sub.2 footprint of a blast furnace based steel production, one important strategy is thus to use this BFG for metallurgical reasons and apply other CO.sub.2 lean energies such as green electric energy for the remaining energy requirement of the steel plant.

[0060] Hence, the synthesis gas production should, beside the utilization of a CO.sub.2 lean hydrocarbon, also integrate blast furnace gas as much as possible in order to improve the CO.sub.2 emission reduction potential from the blast furnace iron making.

[0061] Impurities

[0062] Due to the utilization of coal and coke as well as often cheap secondary fuels as waste plastics or tar being used in the blast furnace, the typical and detrimental chemical components, such as chlorine and sulfur containing molecules, are part of the blast furnace gas. When using this gas for the production of syngas, these components may lead to quick poisoning of the reforming catalyst if not properly and pre-treated.

[0063] Pressure

[0064] Reforming reactions are favored by low pressure due to the Le Chatelier principle. However because compression of syngas downstream the reformer is costly (due to the increased flow rate) and smaller dimensions of equipment and catalyst bed, common syngas processes are operated at high pressure. In case of blast furnace application, low pressure levels are required only. Therefore, the syngas is injected in the shaft of the blast furnace, with a pressure typically between 1 and 4 barg.

[0065] Reforming and auxiliary technologies for syngas production: [0066] Reforming reactions [0067] Natural gas reforming can principally be performed by following reactions: [0068] Partial oxidation in the presence of oxygen: CH.sub.4+½ O.sub.2=CO+H.sub.2 [0069] This reaction is the dominant reaction in CPO and is strongly exothermic thereby releasing high amounts of energy. [0070] Steam reforming in the presence of steam: CH.sub.4+H.sub.2O═CO+3H.sub.2 [0071] Dry reforming in the presence of CO.sub.2: CR.sub.4+CO.sub.2═2CO+2H.sub.2

[0072] These two last reactions are strongly endothermic and require a lot of heat.

[0073] Reforming technologies and its adaptation to blast furnace shaft injection

[0074] The thermodynamic equilibrium at the desired best reduction potential of the gas, leads to a temperature of the syngas, which is still too low for its injection in the shaft. In fact, increasing the temperature further result in higher requirement of higher oxygen and decreased reduction potential of the syngas, which is not favorable for the intended use.

[0075] Pre-Heating of the Feed Gases

[0076] The inventors found that to improve the situation a pre-heating of the feed gases could be applied to a CPO. In fact, with such a pre-heating, not only the reduction potential of the syngas can be increased, but the desired syngas temperature of about 1000° C. can also be obtained.

[0077] FIG. 1 illustrates an embodiment of a preferred method for operating a blast furnace installation comprising the shaft injection of a stream of syngas at temperatures of about 1000° C. and at a pressure of 1 to 4 barg.

[0078] FIG. 1 identifies the following main streams which will be further explained below: [0079] [1]—First stream of NG fed to the second heater after mixing with a first stream of BFG. [0080] [2]—First stream of BFG that will be mixed with the first stream of NG and then fed to the second heater and CPO reactor. This first stream of BFG stream should be properly treated before (metals and HCl removal). [0081] [2*]—Second stream of BFG fed to the burner to heat the first, second and third heaters. [0082] [3]—Heated carbon feed stream composed of heated BFG-NG to be fed to the CPO reactor. [0083] [4]—Heated stream of steam (to be enriched with oxygen) and fed to the CPO reactor. [0084] [5]—Heated oxygen stream (to be mixed with steam) and fed to the CPO reactor (6.). [0085] [6]—First heated stream of oxygen-enriched steam to be fed to the CPO reactor. [0086] [7]—First heated stream of oxygen-enriched steam and heated carbon feed stream as a combined stream in the CPO reactor (flowing from static mixer towards reactor). [0087] [8]—Stream of syngas (to be injected in the shaft of the blast furnace) optionally with added hydrogen, preferably renewable hydrogen.

[0088] In FIG. 1, a first stream of blast furnace gas [2] is collected from the top of the blast furnace and if necessary cleaned, e.g. by removing dust, metals, HCl, etc. This stream of cleaned blast furnace gas and a first stream of natural gas [1] are heated in a second and a third heater, before or after being mixed together, to obtain a heated carbon feed stream [3] for the downstream catalytic partial oxidation reactor. If deemed necessary or useful, the first stream of natural gas [1], the first stream of blast furnace gas [2] or the carbon feed stream [3] may be further cleaned, such as by submitting them to a desulfurization step (desulfurization filter).

[0089] Concurrently, a first stream of steam [4] is heated in a first heater, before or after having been mixed with an oxygen source, selected from oxygen (oxygen gas 02) and oxygen-enriched air, to obtain a first heated stream of oxygen-enriched steam [6]. Preferably the oxygen source is first heated in an oxygen heater, e.g. a heat exchanger heated by a second stream of steam to obtain a heated oxygen stream [5], condensed water resulting from the heat exchange of this second stream of steam being thereafter discharged from the heat exchanger (condensation discharge). The heated oxygen stream [5] is preferably heated in a fourth heater (oxygen heater) to temperatures approaching/closely matching those of the heated carbon feed stream [4] (i.e. temperatures differing e.g. by no more than 100° C., preferably by no more than 50° C., from the temperatures of the heated carbon feed stream).

[0090] The first, second and third heaters are advantageously heat exchangers, preferably within the same enclosure (Fired heater), more preferably heated by one common burner. Said burner is preferably operated by burning a second stream of blast furnace gas in the presence of air, oxygen-enriched air or even oxygen. In some embodiments, the exhaust gas resulting from the combustion of the second stream of blast furnace gas in the presence of air, oxygen-enriched air or oxygen can be added to the first stream of blast furnace gas [2] or to the first stream of natural gas [1] or to the carbon feed stream [3], preferably to the first stream of blast furnace gas [2] upstream of the above-mentioned cleaning step(s).

[0091] If useful or necessary, a stream of nitrogen from a nitrogen source can be added to the heated carbon feed stream [4], to the heated oxygen stream [5] or to the combined stream [6], preferably after having been heated in a further (nitrogen) heater to temperatures approaching/closely matching those of the stream to which it is added (i.e. temperatures differing e.g. by no more than 100° C., preferably by no more than 50° C., from the temperatures of the stream to which it is added).

[0092] The first heated stream of steam [4] is then mixed to the heated oxygen source stream [5] to obtain a first heated stream of oxygen-enriched steam [6] which will be fed to the CPO reactor through one or more CPO reactor inlets.

[0093] The heated carbon feed stream is also fed to the CPO reactor through one or more reactor inlets. The combined stream of first heated stream of oxygen-enriched steam and carbon feed [7], optionally after having been mixed in a mixer, e.g. a CPO static mixer, is then allowed to react on the catalyst surface within the CPO reactor to form a stream of syngas [8] having temperatures in the range of 900 to 1100° C.

[0094] If desired or beneficial a stream of hydrogen, preferably renewable or so-called “green” hydrogen, can be added to the stream of syngas [8], if necessary after having preheated in an appropriate heater (hydrogen heater).

[0095] The (optionally further compressed) stream of syngas [8], optionally with added hydrogen, preferably renewable hydrogen, is thereafter fed to gas inlets within the shaft of the blast furnace, i.e. above the bosh, preferably within the gas solid reduction zone of ferrous oxide above the cohesive zone.