METHOD FOR OPERATING A BLAST FURNACE INSTALLATION

Abstract

A method for operating a blast furnace for producing of pig iron, comprising the steps of including heating a stream of hydrocarbon gas and a stream of steam in a first heater to provide a heated stream of hydrocarbon gas and steam, feeding and partially reforming the heated stream of hydrocarbon gas and steam in a pre-reformer to provide a stream of partially reformed syngas, heating a first stream of blast furnace gas from the blast furnace and the stream of partially reformed syngas in a second heater, before or after their mixing together, to provide a heated carbon feed stream, reforming the heated carbon feed stream in a secondary reformer to provide a second stream of syngas, and feeding said second stream of syngas to the shaft of the blast furnace.

Claims

1. A method for operating a blast furnace for producing pig iron, comprising the steps of (a) heating a stream of hydrocarbon gas and a stream of steam in a first heater to provide a heated stream of hydrocarbon gas and steam, (b) feeding and partially reforming the heated stream of hydrocarbon gas and steam in a pre-reformer to provide a stream of partially reformed syngas, (c) heating a first stream of blast furnace gas from the blast furnace and the stream of partially reformed syngas in a second heater, before or after their mixing together, to provide a heated carbon feed stream, (d) reforming the heated carbon feed stream in a secondary reformer to provide a second stream of syngas, and (e) feeding said second stream of syngas to the shaft of the blast furnace.

2. The method as claimed in claim 1, wherein the temperature of the heated stream of hydrocarbon gas and steam is between 300 C. and 600 C.

3. The method as claimed in claim 1, wherein 2 to 25%, of methane contained in the hydrocarbon gas has been converted to CO and H.sub.2, at operation temperatures between 400 and 550 C. and pressures between 1 and 4 barg.

4. The method as claimed in claim 1, wherein 2 to 25%, of methane contained in the hydrocarbon gas has been converted to CO and H2 and wherein a stream of H.sub.2 is added upstream or downstream the first heater before step (b) and the operation temperature of the pre-reformer is up to 700 C., said stream of H.sub.2 having been heated.

5. The method as claimed in claim 1, wherein the first heater and the second heater are configured as heat exchangers and a heating medium from the second heater is used to heat said upstream first heater.

6. The method as claimed in claim 1, wherein the first heater and the second heater are configured as heat exchangers and the partial reforming in step (b) is effected in a heat exchanger type reformer, a heating medium from the second heater being used to heat said heat exchanger type reformer and said first heater.

7. The method as claimed in claim 1, wherein the reforming in step (d) is effected as dry reforming process.

8. The method as claimed in claim 7, wherein the temperature of the heated carbon feed stream after step (c) is between 500 C. and 800 C.

9. The method as claimed in claim 7, wherein step (d) further comprises heating the dry reformer by burning a second stream of blast furnace gas in a burner with air, oxygen-enriched air or oxygen and additionally obtaining a stream of hot exhaust gas.

10. The method as claimed in claim 9, wherein heat from the hot exhaust gas is used to heat the upstream second heater and/or the pre-reformer and/or the first heater, sequentially the upstream second heater, the pre-reformer and the first heater.

11. The method as claimed in claim 1, wherein the reforming in step (d) is effected in an autothermal reformer with the addition of oxygen.

12. The method as claimed in claim 11, wherein the temperature of the heated carbon feed stream after step (c) is between 750 C. and 950 C.

13. The method as claimed in claim 11, wherein step (d) further comprises heating the second heater by burning a second stream of blast furnace gas in a burner with air, oxygen-enriched air or oxygen and additionally obtain a stream of hot exhaust gas.

14. The method as claimed in claim 13, wherein heat from the hot exhaust gas is used to heat the upstream pre-reformer and/or the first heater.

15. The method as claimed in claim 1, wherein a stream of H.sub.2 is added to the first stream of partially reformed syngas before step (c), to the first stream of blast furnace gas before step (c) and/or to the heated carbon feed stream before step (d) and/or to the second stream of syngas before step (e), said stream(s) of H.sub.2 having been heated.

16. The method as claimed in claim 1, wherein the first stream of blast furnace gas is further subjected to a gas cooling and/or cleaning step, a vapor removal step, a dust removal step, metals removal step, HCl removal step and/or sulfurous component removal step, before being mixed with the stream of partially reformed syngas.

17. The method as claimed in claim 1, wherein a third stream of blast furnace gas is additionally fed to the pre-reformer in step (b), after said third stream of blast furnace gas has been heated in the first heater and/or subjected to a gas cooling and/or cleaning step, a vapor removal step, a dust removal step, metals removal step, HCl removal step and/or sulfurous component removal step.

18. The method as claimed in claim 1, wherein any exhaust gas produced in the method is subjected to one or more exhaust treatments before being released to the atmosphere, said exhaust treatments being selected from Carbon Capture and Utilization (CCU) and Carbon Capture and Storage (CCS), wherein the carbon capture is effected in a CO.sub.2 removal unit using Pressure Swing Adsorption (PSA), Vacuum Swing Adsorption (VSA) or Vacuum Pressure Swing Adsorption (VPSA) or amine gas treatment (amine scrubbing).

19. A blast furnace installation for producing pig iron comprising a blast furnace provided with gas inlets in a shaft arranged for feeding a second stream of syngas to the blast furnace, said blast furnace further comprising a first heater in fluidic connection with a source of a stream of hydrocarbon gas and a source of a stream of steam, said first heater being arranged for heating said stream of hydrocarbon gas and said stream of steam to provide a heated stream of hydrocarbon gas and steam, and the first heater being in fluidic downstream connection with an inlet of a pre-reformer, said pre-reformer being arranged for partially reforming the heated stream of hydrocarbon gas and steam to provide a stream of partially reformed syngas, a second heater in fluidic connection with a top of the blast furnace arranged for conveying a first stream of blast furnace gas, said second heater being arranged for heating said first stream of blast furnace gas and said stream of partially reformed syngas, either separately or mixed, to provide a heated carbon feed stream; and a secondary reformer in fluidic connection with the second heater, said secondary reformer being arranged for converting the heated carbon feed stream to a second stream of syngas and being in fluidic downstream connection with said gas inlets in the shaft of the blast furnace.

20. The blast furnace installation as claimed in claim 19, wherein the blast furnace installation is configured for implementing a method for operating a blast furnace for producing pig iron, comprising the steps of heating a stream of hydrocarbon gas and a stream of steam in a first heater to provide a heated stream of hydrocarbon gas and steam, feeding and partially reforming the heated stream of hydrocarbon gas and steam in a pre-reformer to provide a stream of partially reformed syngas, heating a first stream of blast furnace gas from the blast furnace and the stream of partially reformed syngas in a second heater, before or after their mixing together, to provide a heated carbon feed stream, reforming the heated carbon feed stream in a secondary reformer to provide a second stream of syngas, and feeding said second stream of syngas to the shaft of the blast furnace.

21. The blast furnace installation as claimed in claim 19, wherein the first heater and the second heater are configured as heat exchangers and said second heater is in fluidic heating connection with said upstream first heater.

22. The blast furnace installation as claimed in claim 19, wherein the first heater and the second heater are configured as heat exchangers and the pre-reformer is a heat exchanger type reformer, the second heater being in fluidic heating connection with said heat exchanger type reformer and said heat exchanger type reformer being in fluidic heating connection with said first heater.

23. The blast furnace installation as claimed in claim 19, wherein the first heater and/or the pre-reformer is/are in fluidic connection with a source of a stream of H.sub.2.

24. The blast furnace installation as claimed in claim 19, wherein the secondary reformer is a dry reformer.

25. The blast furnace installation as claimed in claim 24, wherein the dry reformer comprises a burner in fluidic connection with the top of the blast furnace arranged for conveying a second stream of blast furnace gas to said burner.

26. The blast furnace installation as claimed in claim 24, wherein the dry reformer is in fluidic heating connection with the upstream second heater.

27. The blast furnace installation as claimed in claim 19, wherein the secondary reformer is an autothermal reformer in fluidic connection with a source of oxygen.

28. The blast furnace installation as claimed in claim 27, wherein second heater comprises a burner in fluidic connection with the top of the blast furnace arranged for conveying a second stream of blast furnace gas to said burner.

29. The blast furnace installation as claimed in claim 19, wherein the second heater and/or the secondary reformer and/or the gas inlets in the shaft of the shaft furnace is/are in fluidic connection with a source of a stream of H.sub.2, said fluidic connection(s) comprising a fourth heater for heating said stream of H.sub.2.

30. The blast furnace installation as claimed in claim 19, wherein the fluidic connection with the top of the blast furnace arranged for conveying a first stream of blast furnace gas further comprises a gas cooling and/or cleaning plant, a vapor removal unit, a dust removal unit, metals removal unit, HCl removal unit and/or sulfurous component removal unit.

31. The blast furnace installation as claimed in claim 19, wherein the inlet of the pre-reformer is additionally in fluidic connection with the top of the blast furnace arranged for conveying a third stream of blast furnace gas to said pre-reformer, said fluidic connection for the third stream of blast furnace gas being in fluidic heating connection with the first heater.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Preferred embodiments of the disclosure will now be described, by way of example, with reference to the accompanying drawings in which:

[0066] FIG. 1 is a schematic flowsheet view of an embodiment of a first variant of a blast furnace installation configured to implement the present blast furnace operating method; and

[0067] FIG. 2 is a schematic flowsheet view of an embodiment of a second variant of a blast furnace installation configured to implement the present blast furnace operating method.

[0068] 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 drawings.

DETAILED DESCRIPTION

[0069] The requirements for the syngas for its utilization in the blast furnace are different to its requirements for applications in other industries.

[0070] The main requirements for syngas utilization in the blast furnace are:

[0071] Reduction Degree and Temperature Level of the Syngas:

[0072] 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 therefore not important. In steel industry however a high reduction degree, preferably above 7, is preferable and essential for process efficiency, whereas the reduction degree is defined as: (cCO+cH.sub.2)/(cH.sub.2O+cCO.sub.2).

[0073] 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 above the cohesive zone of a blast furnace.

[0074] Ratio H.sub.2/CO

[0075] 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.

[0076] In comparison, the objective 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 one part of the reducing gas used within the blast furnace.

[0077] Pressure Level

[0078] Whereas in other industries the pressure level of the reformers are relatively high, mostly above 20 bara or even above 40 bara, in the blast furnace application the required pressure level is 2 to 6 bara only. This has important impact on the operating conditions and limits of the reforming equipment such as carbon formation and equilibrium conversion. Whereas the lower pressure level will favor a higher methane conversion at the same temperature level, it unfortunately also favors the formation of carbon, reason for which the utilization of a pre-reformer is specifically advantageous in the syngas production for its utilization in the blast furnace.

[0079] CO.sub.2 Emissions

[0080] 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.

[0081] 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.

[0082] 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 objective 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.

[0083] 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.

[0084] Hydrogen Addition

[0085] If desired or beneficial a stream of hydrogen, preferably renewable hydrogen, can be added to the method, in particular before the pre-reformer and/or the secondary reformer reducing carbon deposition, thereby the hydrogen stream can be added before or after the first heater or before or after the second heater. Before addition, it may be beneficial to heat the stream of hydrogen, preferably using a further heat exchanger installed within the fluidic heating connections of the heat integrating conducts, such as in any one or more of locations A (if applicable), B, C or D.

[0086] Impurities

[0087] 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 pre-treated.

[0088] Reforming and Auxiliary Technologies For Syngas Production:

[0089] Reforming Reactions

[0090] Hydrocarbon gas reforming, such as natural gas reforming can principally be performed by following reactions:

[0091] Partial oxidation in the presence of oxygen: CH.sub.4+O.sub.2CO+H.sub.2

[0092] This reaction is strongly exothermic and releases a high amount of energy.

[0093] Steam reforming in the presence of steam: CH.sub.4+H.sub.2O=CO+3H.sub.2

[0094] Dry reforming in the presence of CO.sub.2: CH.sub.4+CO.sub.2=2CO+2H.sub.2

[0095] These two last reactions are strongly endothermic and require a lot of heat.

[0096] Reforming technologies and its adaptation to blast furnace shaft injection

[0097] For ATR reforming technologies, 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 oxygen requirement and decreased reduction potential of the syngas, which is not favorable for the intended use.

[0098] Pre-Heating of the Feed Gases

[0099] The inventors found that to improve the situation a preheating of the feed gases could be applied. The thermodynamic composition of the syngas at its optimum could be obtained by pre-heating the feed gases to between 400 and 550 C. Indeed, with such a pre-heating, not only the reduction potential of the syngas can be increased, but the desired syngas temperature of about 900 to 1100 C. can also be obtained.

[0100] Pre-Reforming:

[0101] When using a pre-reformed gas or partially reformed gas, which has been reformed at moderate temperatures of up to 600 C., preferably between 430 and 500 C. and most preferably between 450 and 480 C., the reduction potential of the gas from the secondary reformer can be further improved. Methane conversions of about 2 to 18% can be achieved alleviating the required work for the secondary reformer. Further advantages are the elimination of higher hydrocarbons before entering the secondary reformer and thus reduction of possible soot formation. In addition, the catalyst in the pre-reforming reactor is normally a high surface type that can bear higher poison concentrations as the catalyst being employed in the secondary reformer. Furthermore, sulfur will deposit on the catalyst of the pre-reformer thereby protecting the catalyst of the secondary reformer from poisoning by sulfur.

[0102] When using the ATR technology as secondary reformer the pre-reforming of the methane results in a considerable reduction of energy requirement for that second process step allowing to reduce the oxygen consumption. This in turn significantly increases the reduction potential of the synthesis gas produced in the secondary reformer.

[0103] Additionally, the pre-reforming will preferably be realized with indirect energy supply. The heat source may result from burning blast furnace gas in a burner further improving the CO.sub.2 balance of the process in combination with the steel production.

[0104] Heating of the Partially Reformed Gas

[0105] Higher hydrocarbons tend to thermal reactions leading to non-saturated components and carbon. This might lead to carbon deposit in heat exchangers if unreformed gas is heated up to relatively high temperatures, typically between 700 and 1000 C. Using the pre-reformed gas in which the higher hydrocarbons are converted allows heating up to high temperatures.

[0106] When using the ATR technology as a secondary reformer the high inlet temperature of pre-reformed gas results in a considerable reduction of energy requirement for that process step, which allows a significantly reduction of oxygen consumption.

[0107] Additionally, this helps to increase the reduction potential of the synthesis gas produced in the secondary reformer significantly.

[0108] In addition, the pre-heating will preferably be realized with indirect heating. The heat source may result from the burning of blast furnace gas which leads to further improvement of the CO.sub.2 balance regarding the process in combination with the steel production.

[0109] In the following two different variants of the method for operating a blast furnace and the blast furnace installation of the disclosure using either dry reforming or ATR as a secondary reformer with corresponding auxiliary technologies are shown in relation with the annexed drawings.

[0110] FIG. 1 illustrates an embodiment of a first variant of the present method for operating a blast furnace comprising the shaft injection of a stream of syngas at temperatures of 900 to 1100 C., e.g. about 1000 C. and at a pressure of 1 to 6 barg.

[0111] This stream of syngas has been produced starting with natural gas (NG) optionally cleaned from impurities, e.g. about 100 Nm.sup.3/h, and steam, e.g. about 50 Nm.sup.3/h, which are heated in a first heater before or after being mixed together, preferably in a first heat exchanger at temperatures from about 400 C. to 550 C. before being partially reformed in a pre-reformer, preferably a heat exchanger type steam pre-reformer, where 2 to 18% of the methane contained in the natural gas is converted to CO and H.sub.2, thereby forming a stream of partially reformed syngas.

[0112] This stream of partially reformed syngas is then mixed with a first stream of blast furnace gas, e.g. about 300 to 400 Nm.sup.3/h at a pressure of about 1.5 to 6.5 barg, either before or after their heating in a second heater, preferably at temperatures from about 500 to 800 C., more preferably from about 600 C. to 700 C., to form a heated carbon feed stream. The blast furnace gas is generally first cooled to reduce its vapor content, cleaned, in particular by removing dust and/or HCl and/or metal compounds and/or sulfurous components. In preferred embodiments, this first stream of blast furnace gas can first be preheated, such as in any one or more of locations A, B, C or D.

[0113] Additionally, a third stream of blast furnace gas can be advantageously fed to the pre-reformer in step (b), preferably after said third stream of blast furnace gas has been heated in the first heater and/or subjected to a gas cooling and/or cleaning step, preferably a vapor removal step, a dust removal step, metals removal step, HCl removal step and/or sulfurous component removal step. Again, in preferred embodiments, this third stream of blast furnace gas can first be preheated, such as in any one or more of locations A, B, C or D.

[0114] The main reforming is done in the secondary reformer which in this case is a so-called dry reformer. The heat required for the dry reforming reaction is provided by a burner operated with a second stream of blast furnace gas, which is depending on the preheating temperature and the gas streams composition e.g. about 350 to 600 Nm.sup.3/h, such as about 510 Nm.sup.3/h, from the top of the blast furnace. This burner can be fed by air, oxygen-enriched air or even oxygen, in particular if the exhaust gas from the burner is reintroduced into the dry reformer as a CO.sub.2 source.

[0115] The stream of syngas leaving the secondary dry reformer, e.g. about 550 to 700 Nm.sup.3/h, such as about 640 Nm.sup.3/h, has temperatures about 1000 C. and a pressure of about 1 to 6 barg and is thereafter directly injected into the shaft of the shaft furnace.

[0116] Advantageously, the residual heat from the secondary reformer resulting as hot exhaust gas, such as (part of) the exhaust gas from its burner, and can be used to heat the second heat exchanger, the remaining heat is then in turn used to heat the pre-reformer and still further the first heat exchanger, thereby forming an energy efficient counter current flow heat integration concept. When leaving the first heat exchanger, the gas can be released through the stack or further be treated, e.g. such as for making it suitable for carbon capture and storage or carbon capture and utilization, etc. In preferred embodiments, the exhaust gas leaving the first heater can be passed through a further heat exchanger, e.g. for preheating the second stream of blast furnace gas and/or the air, oxygen-enriched air or oxygen used in the burner of the secondary reformer.

[0117] FIG. 2 illustrates an embodiment of a second variant of the present method for operating a blast furnace comprising the shaft injection of a stream of syngas at temperatures of about 900 to 1100 C., e.g. about 1000 C. and at a pressure of about 1 to 6 barg.

[0118] This stream of syngas has been produced starting with natural gas (NG) optionally cleaned from impurities, e.g. about 100 Nm.sup.3/h, and steam, e.g. about 50 Nm.sup.3/h, which are heated in a first heater before or after being mixed together, preferably a first heat exchanger at temperatures from about 400 C. to 550 C. before being partially reformed in a pre-reformer, preferably a heat exchanger type steam pre-reformer, where 2 to 25% of the methane contained in the natural gas is converted CO and H.sub.2, thereby forming a stream of partially reformed syngas.

[0119] This stream of partially reformed syngas is then mixed with a first stream of blast furnace gas, e.g. about 60 Nm.sup.3/h at a pressure of about 1.5 to 6.5 barg, either before or after their heating in a second heater, preferably at temperatures from about 750 to 950 C., preferably about 800 C. to 900 C., to form a heated carbon feed stream. In preferred embodiments, this first stream of blast furnace gas can first be preheated, such as in any one or more of locations B, C or D. As above, the blast furnace gas is generally first cooled and/or cleaned, in particular by vapor, dust, metals, sulfurous components and/or HCl removal.

[0120] The main reforming is done in the secondary reformer which in this case is an autothermal reformer. The heat required for the second heater can be provided by a burner attached to it and operated with a second stream of blast furnace gas, e.g. about 230 Nm.sup.3/h, from the top of the blast furnace. This burner can be fed by air, oxygen-enriched air or even oxygen, in particular if the exhaust gas from the burner is reintroduced into the autothermal reformer. In the autothermal reformer oxygen is needed for the exothermic oxidation reaction. Hence, oxygen, e.g. about 40 Nm.sup.3/h is injected in the autothermal reformer, optionally preheated, such as in any one or more of locations B, C or D.

[0121] The stream of syngas leaving the secondary autothermal reformer, e.g. about 340 Nm.sup.3/h has temperatures about 1000 C. and a pressure of about 1 to 6 barg and is thereafter directly injected into the shaft of the shaft furnace.

[0122] Advantageously, the residual heat from the second heat exchanger resulting as hot gas, such as exhaust gas from its burner, can be used to heat the pre-reformer, the remaining heat is then in turn used to heat the first heat exchanger, thereby forming an energy efficient counter current flow heat integration concept. When leaving the first heat exchanger, the gas can be released through the stack or further be treated, e.g. such as for making it suitable for carbon capture and storage or carbon capture and utilization, etc. In preferred embodiments, the exhaust gas leaving the first heater can be passed through a further heat exchanger, e.g. for preheating the second stream of blast furnace gas and/or the air, oxygen-enriched air or oxygen used in the burner of the second heater.