Method for heating semi-finished steel product in heating furnace and associated heating furnace

Abstract

The invention relates in particular to a method for heating a semi-finished steel product (9) in a heating furnace (1) comprising at least two consecutive heating sections (10, 20, 30, 40), comprising feeding two respective fuel gas streams (F1, F2, F3, F4) having respective Wobbe indexes (Wob1, Wob2, Wob3, Wob4) to said two heating sections (10, 20, 30, 40), said Wobbe indexes (Wob1, Wob2, Wob3, Wob4) being different from each other.

Description

Technical Field

[0001] The technical field is a heating method and a heating furnace for heating semi-finished steel products such as slabs, briquettes, billets or ingots. Background Art

[0002] In steel production lines, semi-finished steel products such as slabs, billets or ingots are reheated in a heating furnace before subsequent processing steps, such as hot rolling. Such a furnace is usually a walking beam furnace, into which the semi-finished steel products are fed, heated and then discharged.

[0003] To heat the furnace, fuel gas, such as natural gas, is supplied to gas burners distributed along the furnace. It is generally desirable for the temperature to vary along the furnace, for example, with the temperature near the furnace's output port being higher than near its input port. Therefore, the heating power delivered by the furnace typically varies along the furnace. To this end, the furnace's gas burners are supplied with different flow rates, which are regulated by individual valves depending on the burner's position along the furnace. In recent years, numerous improvements have been made to improve combustion conditions, heating efficiency, heating quality (uniformity of each slab), and yield (oxidation of the slabs within the furnace).

[0004] Despite this, the amount of natural gas, or more generally light alkane gas, that must be supplied for heating such furnaces remains very high, and it would be desirable to reduce this amount. Summary of the Invention

[0005] In this context, a method for heating semi-finished steel products in a heating furnace according to claim 1 is provided. Thus, instead of using the same gas (or gas mixture) with a high Wobbe index for all heating sections and reducing the gas flow for heating sections with a lower heating demand, in the method according to the invention, the heating sections with a lower heating demand are supplied with a gas mixture having a lower Wobbe index than the Wobbe index for the other heating sections. Thus, depending on the required heating power of the heating section or sections, gas mixtures with different compositions are used.

[0006] In this method, both the flow rate and composition of the gas mixture can be adjusted, which allows for better optimization of the furnace's fuel gas consumption. In particular, this method allows large quantities of steelmaking waste gases (which typically have a relatively low heating power) to be used to supply the furnace. This is beneficial because steelmaking waste gases, such as coke oven gas or blast furnace gas, are internal gases produced as byproducts of the overall steelmaking process. Therefore, using steelmaking waste gases as fuel gas on-site instead of using externally supplied fuel gases (such as natural gas) reduces the carbon footprint and environmental impact of the heating operation and, more generally, the steelmaking process.

[0007] In the method according to the present invention, at least two heating sections of the heating furnace can each be supplied with fuel gas, wherein the fuel gas includes: one or more steelmaking waste gases and a supplementary gas, which is a light alkane gas, dihydrogen or a mixture of light alkane gas and dihydrogen, and wherein two fuel gas flows with different Wobbe indices include corresponding proportions of supplementary gas, and the proportions of the supplementary gas are different from each other.

[0008] The applicant emphasizes that the method based on gas mixture composition regulation according to the present invention is different from the following supply technology, in which all heating sections are supplied with the same gas mixture (for example, with the same proportion of natural gas in this mixture) and are supplied with a total flow rate that varies from one heating section to another in order to regulate the heating power released in each heating section.

[0009] And the results show that the amount of make-up gas required to feed the furnace is smaller when using the method according to the invention rather than using a constant composition (and variable flow) feeding technique.

[0010] This reduction in consumption can be explained as follows. When the total amount of the gas mixture supplied to a given heating section is reduced, but the composition of the gas mixture is kept constant, the amount of steelmaking waste gas supplied to the heating section is reduced. However, when the proportion of make-up gas is reduced, the amount of steelmaking waste gas supplied to the heating section remains the same, or approximately the same (or even increases). Consequently, the heating power released by burning the steelmaking waste gas is higher when the proportion of make-up gas is reduced (compared to when the composition is kept constant), and consequently, the heating power still supplied by burning the make-up gas is lower when the composition of the gas mixture is adjusted rather than the total flow rate of the gas mixture.

[0011] Furthermore, based on the calculation of the amount of residual NOx predicted to be produced, no increase in NOx production is expected using the method according to the present invention.

[0012] The method according to the invention may comprise one or several of the additional features defined in claims 2 to 11 considered alone or in combination.

[0013] The invention also relates to a heating furnace comprising a feed circuit as defined in claim 12 arranged to implement the method proposed above.

[0014] From a structural point of view, the supply circuit arrangement that can implement this method can be as follows: the supply circuit includes at least:

[0015] - one or more main inlets for one or more steelmaking waste gases,

[0016] - an auxiliary inlet for replenishing gas,

[0017] - a pipe network connecting each of said two heating sections to said primary inlet and said secondary inlet,

[0018] at least two adjustable valves, mounted on two pipes of the pipe network, the two pipes of the pipe network being connected to two heating sections of the heating furnace, respectively, and conveying unmixed make-up gas to one or more steelmaking waste gases.

[0019] The heating furnace presented above may comprise one or several of the additional features defined in claims 13 to 15. The heating furnace may also comprise one or several of the additional features defined in accordance with the method in claims 2 to 11.

[0020] The invention also relates to a heating installation comprising several such heating furnaces, in particular a heating installation as defined in claim 16 . BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The invention will now be described and illustrated in more detail by way of example without introducing limitations, with reference to the accompanying drawings.

[0022] - Figure 1 is a schematic partial view of a heating furnace according to the present invention, viewed from the side.

[0023] - Figure 2 It is observed from above Figure 1 Schematic diagram of the heating furnace.

[0024] - Figure 3 is included Figure 1 Schematic diagram of the heating facilities of the heating furnace. DETAILED DESCRIPTION

[0025] First, some general aspects of the invention will be presented. Then, an embodiment of a heating furnace illustrated in the accompanying drawings will be presented. And then, the heating method implemented by this heating furnace will be described in more detail.

[0026] As mentioned above, the present invention relates to a method for heating a semi-finished steel product and an associated heating furnace, the heating furnace comprising at least two consecutive heating sections, the method comprising supplying two respective fuel gas flows having respective Wobbe indices, which are different from each other, to the two heating sections.

[0027] The two Wobbe indices may have a relative difference of at least 10%, or even at least 20%. At least two heating sections supplied with different Wobbe indices may each be supplied with a fuel gas comprising: one or more steelmaking waste gases, and a make-up gas which is a light alkane gas, dihydrogen or a mixture of a light alkane gas and dihydrogen. The two fuel gas streams supplied to the two heating sections, respectively, may then comprise different proportions of make-up gas to obtain different Wobbe indices. Nevertheless, it may be noted that different Wobbe indices may also be obtained by adjusting this or such steelmaking waste gas (e.g. the COG proportion) without adjusting the proportion of make-up gas or even without using make-up gas at all.

[0028] Light alkane gas refers to the gas comprising a mixture of light alkanes or light alkanes of considerable proportion. For example, light alkane gas can comprise a mixture of light alkanes or light alkanes higher than 40 volume % (that is, for example, a volume ratio higher than 40% under normal conditions), or comprises a mixture of light alkanes or light alkanes higher than 50 volume % or even 70 volume % or 80 volume %. Light alkane refers to an alkane with one to five or even one to four carbon atoms, such as methane, ethane, propane or butane. For example, light alkane gas can be natural gas NG, liquefied petroleum gas, propane gas, biogas or its mixture.

[0029] Natural gas mainly comprises methane, wherein the proportion of methane is usually higher than 80% by volume, or even higher than 90% by volume.

[0030] Biogas is a renewable energy source that can be obtained by decomposing organic matter in a closed system called a bioreactor in the absence of oxygen (or at least in an anoxic environment). Biogas can be produced by raw materials such as agricultural waste, fertilizer, municipal waste, plant material, sewage, green waste, food waste or any biodegradable material. This biogas can mainly include biomethane (for example, with a ratio of 40 volume % to 80 volume %) and carbon dioxide (15 volume % to 50 volume %). The main components of other typical biogases are bioethane, biopropane or biobutane. When biogas is applied as supplementary gas in this method, biogas can first be subjected to a treatment step such as desulfurization, discharge water condensate or remove carbon dioxide before it is used in a reheating furnace.

[0031] Steelmaking offgas refers to gases generated by any production process within a steelmaking line, from raw material processing (ore, coal, or scrap) to finished steel production. In other words, steelmaking offgas is the internal gas produced as a byproduct of the overall steelmaking process. For example, within this integrated steelmaking process, coke oven facilities produce coke from coal and emit coke oven gas (COG); blast furnaces produce hot metal or pig iron and emit blast furnace gas (BFG); and basic oxygen furnaces, or more generally steelmaking furnaces, produce steel from hot metal and emit steelmaking gas (BOFG). Steel can also be produced using direct reduced iron (DRI) and / or steel scrap melted in electric arc furnaces. Thus, the steelmaking offgases mentioned above can specifically fall into the following categories: coke oven gas, blast furnace gas, basic oxygen furnace gas, direct reduced iron gas, and electric arc furnace gas. These gases may have undergone treatment steps, such as cooling and dust removal, before being used in the reheating furnace. Coke oven gas is also desulfurized, filtered to remove benzene and NH3, and the condensate is discharged.

[0032] The average compositions of some of these steelmaking waste gases are summarized in Table 1 - the compositions are expressed in volume %:

[0033] CO CO2 H2 H20 CH4 N2 BFG 19-27 15-25 1-8 - - 45-60 BOFG 55-65 14-16 3-5 - 0-1 14-16 COG 3-6 1-5 36-65 - 16-27 1-7

[0034] Table 1

[0035] The heating sections of the heating furnace are successive heating zones of the heating furnace positioned one after another. Each heating section comprises one or more gas burners. The heating sections can be formed, for example, by means of a constriction (e.g. Figure 1 The heating sections may be physically separated from each other by the baffles (in the case of a furnace having a constant cross-section), or the heating sections may not be physically separated from each other.

[0036] Each heating section is supplied with a fuel gas stream dedicated to the heating section in question. The fuel gas stream is the total flux of one or more steelmaking waste gases and light alkane gases supplied to the heating section in question, these fuel gases supplied to the heating section should be mixed together, or they should be piped to the heating section separately and unmixed (these unmixed fuel gases are then piped to different gas burners in the heating section).

[0037] Different types of supplementary gases (e.g., natural gas and propane gas) may be used together to supply one or more of the heating sections. In this case, the proportion of at least one of these supplementary gases in the fuel gas flow supplied to one of the heating sections is different from the proportion of the supplementary gas in the fuel gas flow supplied to another of the heating sections.

[0038] Regarding the Wobbe index of the fuel gas flow supplied to this or such heating section, the Wobbe index is the Wobbe index of the mixture of gases supplied to the heating section. In other words, the Wobbe index is the Wobbe index of the gas composition of the entire fuel gas flow supplied to the heating section.

[0039] It should be noted that the lower Wobbe index of a gas (which may be a mixture of different gases) is equal to the lower heating value per unit volume of the gas under given reference conditions divided by the square root of the density of the gas relative to air under the same reference conditions. For example, the reference conditions in question may be normal conditions (which correspond to a temperature of 273.15 K and a pressure of 101.315 kPa). The upper Wobbe index of a gas is equal to the higher heating value per unit volume of the gas under given reference conditions divided by the square root of the density of the gas relative to air under the same reference conditions. In this document, when not specified, the Wobbe index is the lower Wobbe index. The Wobbe index of the gas mixture in question can be measured based on a combustion test, such as a catalytic combustion test. Such measurements can be performed using a commercially available Wobbe index meter, such as the RHADOX 7300 model from AMS Analysen-, Mess- und Systemtechnik GmbH or the Hobré WIM Compas Wobbe Index Analyzer model from HMA Instrumentation. The Wobbe index of the gas mixture in question can also be measured based on optical spectroscopic characterization of the gas mixture components. Such measurements can be performed using a commercially available optical Wobbe index meter, such as the OMA-206P model from Applied Analytics.

[0040] The Wobbe Index is an indicator of the interchangeability of fuel gases. It takes into account both the lower or higher calorific value and specific gravity of the gas and is used to compare the combustion energy output of fuel gases of different compositions. If two fuels have the same Wobbe Index, their energy output will be the same (allowing for + / - 5% variation) at the same pressure and valve settings. While calorific value quantifies the heat generated by a fuel, the Wobbe Index ensures the compatibility and safe interchangeability of different fuel gases, such as the different gas mixtures that can be used in the methods according to the present invention.

[0041] Typical lower Wobbe indices and lower calorific values ​​for some steelmaking off-gases and natural gases are listed in Table 2. Wobbe indices and calorific values ​​are given in MJ / Nm². 3 (i.e., expressed in megajoules per cubic meter under normal conditions):

[0042]

[0043] Table 2

[0044] For example, a gas mixture with a Wobbe index of 15 can be obtained by mixing 50% by volume of BFG, 40% by volume of COG, and 10% by volume of natural gas. Furthermore, a gas mixture with a Wobbe index of 24 can be obtained by mixing 30% by volume of BFG, 40% by volume of COG, and 30% by volume of natural gas. Other compositions can be used, such as with less BFG, more COG, and less natural gas than in the above example, to achieve the same Wobbe index. The natural gas content can be adjusted, in particular, depending on the availability of COG.

[0045] Now describe in more detail Figure 1 and Figure 2 The heating furnace 1 illustrated in FIG. The heating furnace 1 is a furnace, such as a walking beam furnace, for reheating a semi-finished steel product 9, such as a slab. The semi-finished steel product may also be a billet, briquette, or ingot. The semi-finished steel product may be a long semi-finished product or a flat semi-finished product. The heating furnace 1 has an input port 2. The heating furnace 1 also has an output port 4, which is distinct from the input port. The heating furnace extends from the input port 2 along a longitudinal axis X to the output port 4. The heating furnace includes several continuous heating sections 10, 20, 30, and 40, located one after another along the furnace between the input port 4 and the output port 5. Each heating section 10, 20, 30, and 40 includes a gas burner 6. As illustrated in the figures, the heating furnace 1 includes four heating sections 10, 20, 30, and 40. However, this is for illustrative purposes, and the heating furnace may include a different number of continuous heating sections, for example, more than five or even more than ten different heating sections. Furthermore, the heating furnace may include a transitional input zone, located between the input port and the first heating section, that is devoid of burners.

[0046] The heating furnace 1 comprises a supply circuit 7 connected to the gas burner 6 and arranged to supply one or more steelmaking waste gases and a make-up gas to the gas burner 6. The supply circuit 7 is arranged so that each heating section 10, 20, 30, 40 is supplied with a corresponding fuel gas flow F1, F2, F3, F4 dedicated to the heating section, and so that at least two of these fuel gas flows have different compositions, in particular different proportions of make-up gas. The supply circuit 7 is arranged so that the two fuel gas flows have different Wobbe indices, for example one Wobbe index higher than 18 MJ / Nm 3 , and another Wobbe index is less than 16MJ / Nm 3 .

[0047] The supply circuit 7 comprises:

[0048] - an inlet 102 for replenishing gas; and

[0049] - One or more inlets 105.1, 105.2 for one or more steelmaking waste gases.

[0050] exist Figure 1 and Figure 2 In the embodiment illustrated in the accompanying drawings, the supplemental gas is a light alkane gas, i.e., natural gas (NG), and the one or more steelmaking waste gases are coke oven gas (COG), blast furnace gas (BFG), and basic oxygen furnace gas (BOFG). In the embodiment illustrated in the accompanying drawings, COG is introduced through a separate inlet 105.1 dedicated to that gas, while the already mixed BFG and BOFG are introduced through another separate inlet 105.2. However, in other embodiments, the steelmaking waste gases may be introduced into the supply circuit through a single, common inlet, all already mixed together (and possibly with a small amount of light alkane gas).

[0051] The supply circuit 7 comprises different supply portions 71, 72, 73, 74 ( Figure 2 ). Each supply section comprises a conduit connected to the burner 6 of the heating section dedicated to it and comprises one or several adjustable valves (an adjustable valve is a valve or pressure reducer suitable for regulating the flow gradually, not just in a full-on-full-off manner). Each supply section 71, 72, 73, 74 is arranged to supply the corresponding heating section 10, 20, 30, 40 with a fuel gas flow F1, F2, F3, F4 dedicated to that heating section.

[0052] The supply circuit 7 further comprises connecting elements 103 , 106 which connect each supply portion 71 , 72 , 73 , 74 with a steelmaking waste gas inlet 105 . 1 , 105 . 2 and which connect at least some of the supply portions 71 , 72 , 73 , 74 with a light alkane gas inlet 102 .

[0053] More specifically, each supply portion 71 , 72 , 73 , 74 is connected to the common composite gas distribution line 106 and the common light alkane gas distribution line 103 .

[0054] Light alkane gas distribution line 103 is connected to light alkane gas inlet 102 via pressure reducing station 104. Composite gas distribution line 106 is connected to outlet 105.4 of mixing station 105, which includes steelmaking waste gas inlets 105.1 and 105.2, and also includes an additional natural gas inlet 105.3. Mixing station 105 outputs composite gas CG, which is obtained by mixing steelmaking waste gas and supplemented with some natural gas.

[0055] As in Figure 2 In this case, the supply circuit can be arranged so that the different fuel gases comprised in each fuel gas flow F1, F2, F3, F4 are mixed upstream of the heating section 10, 20, 30, 40, and the resulting gas mixture is then piped to the gas burner 6 of the heating section.

[0056] For this purpose, each supply portion 71 , 72 , 73 , 74 of the feed circuit 7 is here arranged to mix the light alkane gas with the compounding gas CG upstream of the gas burner 6 .

[0057] The supply section 71 includes, for example:

[0058] a valve 71 . 1 , the inlet of which is connected to the light alkane gas distribution line 103 and the outlet of which is connected to the mixing element 71 . 3 ,

[0059] a further valve 71 . 2 , the inlet of which is connected to the composite gas distribution line 106 and the outlet of which is connected to the mixing element 71 . 3 ,

[0060] the mixing element 71.3 in question, which outputs the fuel gas flow F1 via an outlet 71.4 of the mixing element 71.3,

[0061] A conduit connecting the outlet 71 . 4 of the mixing element 71 . 3 and the gas burner 6 for distributing the fuel gas flow F1 to the burner.

[0062] exist Figure 2 In the example shown in FIG, the other supply parts 72 , 73 , and 74 have the same structure as the supply part 71 .

[0063] This upstream mixing arrangement, in which the same gas mixture is supplied to the different burners 6 of the heating section, is beneficial because it can be implemented with minimal changes to a furnace that was previously operating with a single gas mixture (having the same composition for all burners of the furnace) in an adjustable flow but constant composition mode. In fact, this upstream mixing arrangement can be implemented in such a furnace with almost no modifications to the rest of the piping system and without substantially modifying the gas burner arrangement in the furnace, by simply adding a light alkane gas supply line 103, corresponding adjustable valves 71.1 to 74.1, and mixing elements 71.3 to 74.3.

[0064] In this regard, the inventors have observed that for a fuel cell comprising BFG, BOFG, COG and natural gas and having a mass fraction of, for example, 24 MJ / Nm 3 The Wobbe index of the fuel gas flow is used for optimal operation and the type of gas burner selected is also suitable for burning less natural gas with a gas flow rate as low as 15MJ / Nm 3 Or even 10MJ / Nm 3 Thus, surprisingly, such a gas burner can indeed be supplied with a fuel gas stream having a significantly varying natural gas content and, in the case of this upstream mixing arrangement, the different gas burners 6 of the furnace can all be of the same type (which is convenient).

[0065] exist Figure 2 In the embodiment of the present invention, the heating furnace 1 is equipped with an electronic control device 8, which includes at least a processor, a memory, a data acquisition module, and a communication interface for communicating with valves 71.1 to 74.1 (and 71.2 to 74.2), which are electrically controllable valves (i.e., electrovalves) in this embodiment. When describing the method for heating the semi-finished steel product according to the present invention, the electronic control device 8 is configured, for example, programmed, to control the valves according to the control method presented below.

[0066] exist Figure 2 In a simplified alternative embodiment of the present invention, some of the heating sections may be supplied with only the composite gas and no light alkane gas. Other heating sections may be supplied with both the composite gas and the light alkane gas, with all of these heating sections having a constant proportion of light alkane gas (in this case, valves 71.1 to 74.1 may be omitted).

[0067] Not all components of the supply circuit 7 have necessarily been illustrated in the figures. In practice, the supply circuit may comprise additional, not illustrated components such as valves, regulators or other safety or distribution components.

[0068] In addition, without departing from the scope of the present invention, Figures 1 to 2 Detailed arrangements of the feed circuits are possible, such as the one illustrated in FIG.

[0069] In particular, the piping and valve arrangements of the supply sections 71 to 74 can be different from the piping and valve arrangements of the supply sections 71 to 74 shown, while still enabling the supply of different heating sections with different Wobbe indices. For example, different gases can be supplied to different gas burners in the same heating section, rather than supplying the same gas mixture (generated upstream) to all burners in the burner system. When such a "separate piping" arrangement is employed, at least some of the heating sections in the heating section each include several gas burners, and then, the make-up gas is piped to some of the gas burners dedicated to the make-up gas without being mixed with one or more steelmaking waste gases, while the one or more steelmaking waste gases are piped to other gas burners in the heating section. In this case, the fuel gas flow supplied to the heating section is the sum of the make-up gas flux (supplied to the specific, dedicated gas burners) and the one or more steelmaking waste gas fluxes supplied to the heating section.

[0070] Figure 3 The figure shows a heating facility 100 comprising several heating furnaces 1, 1', 1", including Figures 1 to 2 heating furnace 1 and two other heating furnaces 1' and 1" that are identical to heating furnace 1.

[0071] The make-up gas inlet 102 of the feed circuit 7 of each furnace 1 , 1 ′, 1 ″ is connected to the same overall make-up gas supply line 101 .

[0072] The heating furnaces 1, 1', 1" share the same mixing station 105, in which the steelmaking waste gases are mixed together (and optionally enriched with small amounts of make-up gas). In other words, the heating facility 100 comprises only one such mixing station, which is shared with the different heating furnaces. The same composite gas supply line 106, connected to the outlet 105.4 of the mixing station, supplies the different heating sections of these heating furnaces 1, 1', 1".

[0073] In this example, the furnaces 1 , 1 ′ and 1 ″ are identical. Nevertheless, the furnaces 1 , 1 ′ and 1 ″ may differ from one another. For example, the feed circuit of one of the furnaces may be simpler than the feed circuits for the other furnaces and may even be arranged to feed the same gas mixture (with the same composition) to all heating sections of the furnaces.

[0074] The method according to the invention for heating a semi-finished steel product in a heating furnace can be performed using, for example, the heating furnace 1 presented above.

[0075] In the method, a semi-finished steel product 9 is input at an input port 2 of a heating furnace 1 , then passes through successive heating sections 10 , 20 , 30 , 40 , and finally output at an output port 4 .

[0076] The heating powers delivered in the different heating sections 10, 20, 30, 40 of the heating furnace can be different from one another. For example, the heating power delivered in the last heating section (near the output port 4) can be higher than in the first heating section (near the input port 2). More generally, the heating powers delivered in the different heating sections are set according to a given, pre-established reheating sequence to be applied to the semi-finished steel product.

[0077] In order to achieve these heating powers, each heating section 10, 20, 30 or 40 is supplied with a fuel gas flow F1, F2, F3 or F4 comprising a proportion of supplementary gas, which is adjusted to achieve the desired heating power. In particular, for each heating section 10, 20, 30, 40, the proportion of supplementary gas in the fuel gas flow can be adjusted to achieve a given Wobbe index for that flow, which is set according to the reheating sequence to be applied to the semi-finished steel product.

[0078] For example:

[0079] - Some of the first heating sections (e.g. heating section 10) may each be composed of a heating element having a heat release rate of less than 16 MJ / Nm 3 , for example, equal to 15MJ / Nm 3 Or even 12MJ / Nm 3 (or more generally included in 4MJ / Nm 3 and 16MJ / Nm 3 The fuel gas flow (F1) is supplied with a Wobbe index (Wob1) between

[0080] - while the other heating sections (e.g. heating sections 20, 30 and 40) are made of heating elements with a temperature higher than 18 MJ / Nm 3 , for example, equal to 24MJ / Nm 3 (or more generally included in 22MJ / Nm 3 and 40MJ / Nm 3 Fuel gas flows (F2, F3, F4) with Wobbe indices (Wob2, Wob3, Wob4) between and are supplied.

[0081] In practice, the proportion of make-up gas in the different fuel gas flows can be adjusted by controlling the valves 71.1 to 74.1 mentioned above. This adjustment can be manual for each valve. This adjustment can even be a permanent, initial, factory setting (adjusted once and then kept constant). Nevertheless, in the embodiment considered here, the valves 71.1 to 74.1 are electrically controllable, and the valve adjustment is performed by the electronic control unit 8.

[0082] To this end, the electronic control unit 8 may be configured, for example programmed, to perform the following steps:

[0083] - acquiring heating data representative of a furnace temperature profile or a furnace heating power profile, or a reheating sequence to be applied to the semi-finished steel product,

[0084] - determining, for each heating section, a target proportion of make-up gas or a target Wobbe index for the fuel gas flow supplying the heating section under consideration based on said heating data (in order to obtain the temperature profile, heating power profile or reheating sequence in question),

[0085] Based on the previously determined target ratio or target Wobbe index, the electric valves of the supply circuit 7 (here the electric valves 71 . 1 to 74 . 1 ) are controlled, which regulate the flow of fuel gas supplied to the different heating sections.

[0086] Furthermore, feedback control may be implemented to regulate the temperature in one or more of the heating sections by adjusting the proportion of make-up gas supplied to the heating section in question. To this end, the electronic control unit 8 may be configured (e.g., programmed) to perform the following steps:

[0087] - measuring the measured temperature in the heating section,

[0088] - comparing the measured temperature with a set temperature (e.g., the temperature specified in the temperature distribution data mentioned above), and

[0089] - depending on the result of the comparison step, controlling an electrovalve (71.1, 72.1, 73.1 or 74.1) which controls the proportion of make-up gas in the fuel gas flow supplied to the heating section (for example, this control can be implemented using a PI or PID corrector).

Claims

1. A method for heating a semi-finished steel product (9) in a heating furnace (1), the heating furnace comprising at least two consecutive heating sections (10, 20, 30, 40), the method comprising supplying two respective fuel gas flows (F1, F2, F3, F4) having respective Wobbe indices (Wob1, Wob2, Wob3, Wob4) to the two heating sections (10, 20, 30, 40), the Wobbe indices (Wob1, Wob2, Wob3, Wob4) being different from one another.

2. The method according to claim 2, wherein: - one of the Wobbe indices is less than 16 MJ / Nm 3 , - another of the Wobbe indices is higher than 18 MJ / Nm 3 .

3. The method according to claim 1 or 2, wherein: The heating furnace (1) comprises: an input port (2) for inputting the semi-finished steel product (9) to be heated; and an output port (4) for outputting the semi-finished steel product, and wherein, of the two heating sections (10, 20), the heating section (20) closer to the output port (4) is supplied with the fuel gas flow (F2) having the highest Wobbe index (Wob2).

4. The method according to any one of the preceding claims, wherein The two heating sections (10, 20, 30, 40) are each supplied with a fuel gas comprising: - one or more steelmaking waste gases, and - a supplementary gas, wherein the supplementary gas is a light alkane gas (NG), dihydrogen or a mixture thereof, And wherein two fuel gas flows (F1, F2, F3, F4) having different Wobbe indices (Wob1, Wob2, Wob3, Wob4) include corresponding proportions of said supplementary gas (NG), and the proportions of said supplementary gas (NG) are different from each other.

5. The method according to claim 4, wherein The two fuel gas flows (F1, F2, F3, F4) having different Wobbe indices (Wob1, Wob2, Wob3, Wob4) are each produced by mixing the supplementary gas (NG) with the one or more steelmaking waste gases upstream of the heating section (10, 20, 30, 40) supplied by the fuel gas flows.

6. The method according to claim 4, wherein: The two heating sections each comprise several gas burners, and wherein, - the supplementary gas is piped to some of the gas burners of the heating section dedicated to the supplementary gas without mixing with the one or more steelmaking waste gases, - and the one or more steelmaking waste gases are piped to other gas burners in the heating section, - the fuel gas flow supplied to the heating section is the sum of the flux of the supplementary gas and the flux of the one or more steelmaking waste gases supplied to the heating section.

7. The method according to any one of claims 4 to 6, wherein: The supplementary gas is natural gas (NG), biogas or a mixture thereof.

8. The method according to any one of claims 4 to 7, wherein: The supplemental gas is light alkane gas (NG), and wherein: - in the first fuel gas stream (F1) of the two fuel gas streams, the proportion of light alkane gas is less than 10% by volume, - In the second fuel gas stream (F2, F3, F4) of the two fuel gas streams, the proportion of the light alkane gas is higher than 20% by volume.

9. The method according to any one of claims 4 to 8, wherein: The steelmaking waste gas or one of the steelmaking waste gases belongs to the following list: coke oven gas (COG), blast furnace gas (BFG), basic oxygen furnace gas (BOFG), electric arc furnace gas, direct reduced iron gas or a mixture thereof.

10. The method according to any one of claims 4 to 9, wherein The electronic control unit (8) performs the following steps: - measuring a measurement temperature in one of said heating sections, - comparing said measured temperature with a set temperature, - depending on the result of the comparison step, controlling electric valves (71.1 to 74.1) which regulate the proportion of the make-up gas (NG) in the fuel gas flow (F1 to F4) supplied to the heating section (10 to 40).

11. The method according to any one of the preceding claims, wherein The semi-finished steel product (9) is a slab, an ingot, a billet or a briquette.

12. A heating furnace (1) for heating semi-finished steel products (9), the heating furnace comprising at least two consecutive heating sections (10, 20, 30, 40) and comprising a supply circuit (7), the supply circuit (7) being arranged to supply two respective fuel gas flows (F1, F2, F3, F4) having respective Wobbe indices (Wob1, Wob2, Wob3, Wob4) to the two heating sections (10, 20, 30, 40), the Wobbe indices (Wob1, Wob2, Wob3, Wob4) being different from each other.

13. Heating furnace (1) according to the preceding claim, wherein The supply circuit (7): - comprises one or more inlets (105.1, 105.2) for one or more steelmaking waste gases and an inlet (102) for make-up gas (NG), the make-up gas (NG) being light alkane gas (NG), dihydrogen or a mixture thereof, and - arranged so that the two fuel gas flows (F1, F2, F3, F4) respectively supplied to the two heating sections (10, 20, 30, 40) comprise respective proportions of the supplementary gas (NG), the proportions of the supplementary gas (NG) being different from each other.

14. Heating furnace (1) according to the preceding claim, wherein For each of the two heating sections (10 to 40), the supply circuit (7) comprises a respective adjustable valve (71.1 to 74.1) arranged on a pipe which is in fluid connection with the heating section in question and which conveys the unmixed make-up gas (NG) to the one or more steelmaking waste gases.

15. The heating furnace (1) according to claim 13 or 14, wherein: For each heating section (10 to 40), the supply circuit (7) comprises at least one mixing element (71.3 to 74.3) dedicated to the heating section in question, the at least one mixing element (71.3 to 74.3) being connected to the gas burner (6) of the heating section and being arranged to mix the supplementary gas (NG) with the one or more steelmaking waste gases upstream of the gas burner (6) of the heating section.

16. A heating facility (100), comprising: - two or more heating furnaces (1, 1', 1"), each of the two or more heating furnaces (1, 1', 1") being a heating furnace according to any one of claims 13 to 15, - a common mixing station (105) arranged to mix the steelmaking waste gases together to deliver a mixed composite gas (CG) at an outlet (105.4) of the common mixing station, and A composite gas supply line (106) connecting the outlet (105.4) of the common mixing station (105) to the heating sections of the different furnaces (1, 1', 1") of the heating facility.

Images