A method for heating a steel semi-finished product in a heating furnace, and a related heating furnace

Abstract

The present invention relates in particular to a method for heating a steel semi-finished product (9) in a heating furnace (1), wherein the heating furnace comprises at least two consecutive heating sections (10, 20, 30, 40), and the method comprises supplying two respective fuel gas streams (F1, F2, F3, F4) having different Wobbe indices (Wob1, Wob2, Wob3, Wob4) to the two heating sections (10, 20, 30, 40).

Description

[Technical Field]

[0001] This technical field concerns heating methods and furnaces for heating steel semi-finished products such as slabs, blooms, billets, or ingots. [Background technology]

[0002] In steel production lines, semi-finished steel products such as slabs, blooms, or billets are reheated in a heating furnace before subsequent processing steps such as hot rolling. These heating furnaces are typically walking beam furnaces, in which the semi-finished steel products are placed, heated, and then removed from the furnace.

[0003] To heat the furnace, fuel gas, such as natural gas, is supplied to gas burners positioned along the furnace. The temperature varies along the furnace, and it is usually desirable that the temperature is higher near the furnace's discharge port than near the input port. Therefore, the heat output from the furnace usually varies along the furnace. For this reason, the furnace's gas burners are supplied with various flow rates, which are regulated by individual valves depending on the burner's position along the furnace. Many improvements have been made in recent years to improve combustion conditions, heating efficiency, heating quality (uniformity across each slab), and the impact on yield (oxidation of the slab inside the furnace). [Overview of the project] [Problems that the invention aims to solve]

[0004] Nevertheless, the amount of natural gas, or more generally light alkane gas, that must be supplied to heat such furnaces remains very high, and it is desirable to reduce this amount. [Means for solving the problem]

[0005] In this regard, a method for heating a steel semi-finished product in a heating furnace is provided as described in claim 1. Therefore, instead of using the same gas (or gas mixture) having a high Wobbe index for all heating sections and reducing the gas flow rate for heating sections with low heating demand, the method according to the present invention supplies one or more heating sections with low heating demand with a gas mixture having a lower Wobbe index than the other one or more heating sections. Thus, gas mixtures having different compositions are used depending on the heat required by these heating sections.

[0006] Therefore, this method allows for adjustment of both the flow rate and the composition of the gas mixture, making it possible to further optimize the fuel gas consumption of the heating furnace. In particular, this method allows for the use and supply of large quantities of steelmaking exhaust gas (usually with a considerably lower heat output) to the heating furnace. This is beneficial because steelmaking exhaust gases, such as coke oven gas or blast furnace gas, are internal gases as by-products of the global steelmaking process. Therefore, using these as fuel gases 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 a heating furnace can each be supplied by a fuel gas comprising one or more steelmaking exhaust gases and a supplement gas which is a light alkane gas, dihydrogen, or a mixture thereof, wherein two fuel gas streams having different Wobbe indices contain different proportions of supplement gas to each other.

[0008] The applicant emphasizes that the method according to the present invention, which is based on adjusting the gas mixture composition, differs from supply techniques in which the same gas mixture (for example, having the same proportion of natural gas in this mixture) is supplied to all heating sections, and from supply techniques in which the total flow rate is varied for each heating section to adjust the heat output released at each heating section.

[0009] Furthermore, this demonstrates that when the method according to the present invention is used, the amount of supplemental gas required to supply to the heating furnace is less than when using a supply technique with a constant composition (and varying flow rate).

[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 while its composition remains constant, the amount of steelmaking exhaust gas supplied to the heating section decreases. On the other hand, when the proportion of supplemental gas is reduced, the amount of steelmaking exhaust gas supplied to the heating section remains the same, or approximately the same (or increases). Therefore, in the latter case, the heat output released by the combustion of the steelmaking exhaust gas is higher (than when the composition is not changed). As a result, the heat output that needs to be supplied by the combustion of supplemental gas is less when adjusting the composition of the gas mixture than when adjusting the total flow rate.

[0011] Furthermore, based on calculations that predict the amount of residual NOx generated, no increase in NOx production is expected with the method according to the present invention.

[0012] The methods according to the present invention, when considered individually or in combination, may include one or more further features as defined in claims 2 to 11.

[0013] The present invention also relates to a heating furnace comprising a supply circuit configured to carry out the above method, as defined in claim 12.

[0014] From a structural standpoint, the supply circuit configurations that make it possible to implement this method may be as follows: The supply circuit must have at least: -One or more primary inlets for one or more types of steelmaking exhaust gases, - A secondary inlet for replenishment gas, -A pipe network connecting each of the two heating sections to the primary inlet and the secondary inlet, - At least two adjustable valves, installed in two pipes of the pipe network that are respectively connected to two heating sections of the heating furnace and transport the make-up gas without mixing it with one or more steelmaking exhaust gases.

[0015] The heating furnace can include one or more further features defined in claims 13 to 15. It can also include one or more of the further features defined with respect to the method of claims 2 to 11.

[0016] The present invention also relates to heating equipment comprising a plurality of such heating furnaces, particularly heating equipment as defined by claim 16.

[0017] Here, referring to the accompanying drawings, the present invention will be described in more detail and explained by way of example without introducing limitations.

Brief Description of the Drawings

[0018] [Figure 1] It is a schematic partial view of a heating furnace according to the present invention as seen from the side. [Figure 2] It is a schematic view of the heating furnace of FIG. 1 as seen from above. [Figure 3] It is a schematic view of heating equipment comprising the heating furnace of FIG. 1.

Modes for Carrying Out the Invention

[0019] Some general aspects of the present invention will be presented first. Subsequently, an embodiment of the heating furnace shown in the figures will be presented. Subsequently, the heating method implemented by this heating furnace will be described in more detail.

[0020] As described above, the present invention relates to a method for heating steel semi-finished products and a related heating furnace. The heating furnace includes at least two consecutive heating sections, and the method includes supplying two respective fuel gas flows having different Wobbe indices to the two heating sections.

[0021] These two Wobbe indices can have a relative difference of at least 10%, or even at least 20%. Each of at least two heating sections supplied with different Wobbe indices can be supplied with a fuel gas containing one or more steelmaking exhaust gases and a supplementary gas that is a light alkane gas, dihydrogen, or a mixture thereof. Subsequently, the two fuel gas streams supplied to these two heating sections can contain different proportions of the supplementary gas so as to obtain different Wobbe indices. It should further be noted that different Wobbe indices can also be obtained by adjusting the proportion of such steelmaking exhaust gases (e.g., the COG proportion) without any adjustment of the proportion of the supplementary gas or any use of supplementation.

[0022] The light alkane gas means a gas mainly containing a light alkane or a mixture of light alkanes. For example, the light alkane gas can contain 40% by volume (i.e., volume ratio, for example, exceeding 40% under standard conditions) of a light alkane or a mixture of light alkanes, or 50% by volume or even 70% by volume or 80% by volume of a light alkane or a mixture of light alkanes. The light alkane means an alkane having 1 to 5, or even 1 to 4 carbon atoms, such as methane, ethane, propane or butane. The light alkane gas can be, for example, natural gas NG, liquefied petroleum gas, propane gas, biogas or a mixture thereof.

[0023] Natural gas mainly contains methane, and typically the proportion of methane is higher than 80% by volume, or even higher than 90% by volume.

[0024] Biogas is a renewable energy source that can be obtained by decomposing organic matter in the absence of oxygen (or at least in an oxygen-deficient environment) within a closed system called a bioreactor. Biogas can be produced from raw materials such as agricultural waste, fertilizers, municipal waste, plant materials, sewage, organic waste, food waste, or any biodegradable material. Such biogas may mainly contain biomethane (e.g., 40% to 80% by volume) and carbon dioxide (15% to 50% by volume). Other typical main components of biogas are bioethane, biopropane, or biobutane. When biogas is used as supplemental gas, in this method, the biogas may first be subjected to treatment steps such as desulfurization, water condensate discharge, or carbon dioxide removal before use in the reheating furnace.

[0025] Steelmaking exhaust gases refer to gases generated from any manufacturing process within a steelmaking line's manufacturing unit, and the steelmaking line encompasses the entire process from crude material preparation (conditioning of ore, coal, or scrap) to the final steel product. In other words, steelmaking exhaust gases are internal gases as by-products in the entire steelmaking process. In such an integrated steelmaking process, a coke oven plant, for example, produces coke from coal and emits coke oven gas (COG); a blast furnace produces high-temperature metal or pig iron and emits blast furnace gas (BFG); and a converter, or more generally, a steelmaking furnace, produces steel from molten iron and emits steelmaking gas (BOFG). Steel may also be produced using direct reduction iron and / or steel scrap melting in an electric arc furnace. Therefore, the above-mentioned steelmaking exhaust gases can belong in particular to the following list: coke oven gas, blast furnace gas, converter gas, direct reduction iron gas, and electric arc furnace gas. These gases may be subjected to initial processing steps, such as a cooling step and a dust removal step, before use in the reheating furnace. The coke oven gas is desulfurized, benzene and NH3 are filtered out, and the condensate is discharged.

[0026] Table 1 summarizes the average composition of some of these steelmaking exhaust gases—composition is expressed in volume percent:

[0027] [Table 1]

[0028] The heating sections of a furnace are continuous heating zones arranged sequentially. Each heating section is equipped with one or more gas burners. The heating sections can be physically separated from each other, for example, by constrictions (as shown in Figure 1) or baffles, or without using these (if the internal space of the furnace has certain sections).

[0029] Each heating section is supplied by a dedicated fuel gas flow for that section. These fuel gases refer to the total overall flow rate of steelmaking exhaust gas or light alkane gas supplied to the heating section. These fuel gases may be supplied to the heating section in a pre-mixed state, or they may be piped individually and unmixed. In the latter case, these unmixed fuel gases are piped to different gas burners within that heating section.

[0030] Different types of supplemental gases (e.g., natural gas and propane gas) can be used together and supplied to one or more heating sections. In such cases, the proportion of at least one of these supplemental gases in the fuel gas stream supplied to one of the heating sections is different from the proportion of the supplemental gas in the fuel gas stream supplied to another of the heating sections.

[0031] With regard to the Wobbe index of a fuel gas flow supplied to such a heating section, this is the Wobbe index of the gas mixture supplied to that heating section. In other words, it is the Wobbe index of the gas composition of the overall fuel gas flow supplied to that heating section.

[0032] For reference, a lower Wobbe index of a gas (which may be a mixture of different gases) is equal to the lower calorific value of the gas per unit volume under given reference conditions divided by the square root of the specific gravity of the gas relative to air under the same reference conditions. These reference conditions may, for example, be standard conditions (corresponding to a temperature of 273.15 K and a pressure of 101.315 kPa). Conversely, a higher Wobbe index of a gas is equal to the higher calorific value of the gas per unit volume under given reference conditions divided by the square root of the specific gravity of the gas relative to air under the same reference conditions. In this specification, unless otherwise specified, the Wobbe index is the lower Wobbe index. The Wobbe index of a gas mixture can be measured based on a combustion test, such as a catalytic combustion test. Such measurements can be performed using commercially available Wobbe index meters, such as the RHADOX 7300 model from AMS Analysen-Mess-und Systemtechnik GmbH, or the Hobre WIM Compas Wobbe Index Analyser from HMA Instrumentation. The Wobbe index of the gas mixture can be measured based on the optical spectroscopic characterization of the composition of the gas mixture. Such measurements can be performed using commercially available optical Wobbe index meters, such as the OMA-206P model from Applied Analytics.

[0033] The Wobbe index is an indicator of fuel gas compatibility, used to compare the combustion energy output of fuel gases of different compositions, taking into account both lower or higher calorific value and gas specific gravity. If two fuels have the same Wobbe index, their energy output is the same under the same pressure and valve settings (a variation of + / - 5% is allowed). While calorific value quantifies the heat produced by the fuel, the Wobbe index ensures the compatibility and safe substitutability of different fuel gases, such as different gas mixtures that can be used in the methods according to the present invention.

[0034] Table 2 lists typical lower Wobbe indexes and lower calorific values ​​for several steelmaking exhaust gases and natural gases. The Wobbe index and calorific value are expressed in MJ / Nm 3 This is how it is displayed (under standard conditions, it is displayed in megajoules per cubic meter):

[0035] [Table 2]

[0036] For example, a gas mixture with a Wobbe index of 15 can be obtained by mixing 50 vol% BFG, 40 vol% COG, and 10 vol% natural gas. In addition, a gas mixture with a Wobbe index of 24 can be obtained by mixing 30 vol% BFG, 40 vol% COG, and 30 vol% natural gas. Other compositions can be used to obtain the same Wobbe index with less BFG, more COG, and less natural gas than the above example. The natural gas content can be adjusted in particular depending on the availability of COG.

[0037] Here, the heating furnace 1 shown in Figures 1 and 2 will be described in more detail. The heating furnace 1 is a furnace such as a walking beam furnace for reheating steel semi-finished products 9, such as slabs. The steel semi-finished products may also be billets, blooms, or ingots. They may be long semi-finished products or flat semi-finished products. The heating furnace 1 has an input port 2. It also has an output port 4, which is different from the input port. The heating furnace extends along the longitudinal axis X from the input port 2 to the output port 4. It comprises several consecutive heating sections 10, 20, 30, and 40 arranged consecutively along the heating furnace between the input port 4 and the output port 5. Each heating section 10, 20, 30, and 40 is equipped with a gas burner 6. As shown in the figures, the heating furnace 1 comprises four heating sections 10, 20, 30, and 40. Furthermore, for illustrative purposes only, the heating furnace may comprise a different number of consecutive heating sections, for example, more than five or more than ten different heating sections. Furthermore, the heating furnace may include a transitional input zone without a burner between the input port and the first heating section.

[0038] The heating furnace 1 is connected to a gas burner 6 and includes a supply circuit 7 configured to supply one or more steelmaking exhaust gases and replenishment gases to the gas burner 6. The supply circuit 7 is configured to supply each heating section 10, 20, 30, 40 with corresponding fuel gas flows F1, F2, F3, and F4 dedicated to that heating section, and at least two of these fuel gas flows have different compositions, in particular, different proportions of replenishment gas. The supply circuit 7 is configured so that these two fuel gas flows have different Wobbe indices, for example, one of which is 18 MJ / Nm 3 The other is 16 MJ / Nm 3 They are positioned below [a certain value].

[0039] The supply circuit 7 is - An inlet 102 for refilling gas, -Equipped with one or more inlets 105.1, 105.2 for one or more steelmaking exhaust gases.

[0040] In the embodiments shown in Figures 1 and 2, the supplement gas is light alkane gas, i.e., natural gas NG, and one or more steelmaking exhaust gases are coke oven gas COG, blast furnace gas BFG, and converter gas BOFG. In the embodiments shown in the figures, COG is introduced through a separate inlet 105.1 dedicated to that gas, while BFG and BOFG are already mixed and introduced through another separate inlet 105.2. Furthermore, in other embodiments, the steelmaking exhaust gases can be introduced into the supply circuit through a single common inlet, already mixed together (and possibly mixed with a small amount of light alkane gas).

[0041] The supply circuit 7 comprises different supply sections 71, 72, 73, and 74, each dedicated to a different heating section 10, 20, 30, and 40 (Figure 2). Each supply section comprises a pipe connected to the burner 6 of its dedicated heating section and includes one or more adjustable valves (meaning valves or pressure reducing devices suitable for gradually adjusting the flow, not limited to fully open or closed valves). Each supply section 71, 72, 73, and 74 is configured to supply fuel gas flows F1, F2, F3, and F4, dedicated to the corresponding heating sections 10, 20, 30, and 40.

[0042] The supply circuit 7 connects the supply sections 71, 72, 73, and 74, each equipped with steelmaking exhaust gas inlets 105.1 and 105.2, and includes connecting elements 103 and 106 that connect at least a portion of the supply sections 71, 72, 73, and 74 to the light alkane gas inlet 102.

[0043] More precisely, each supply section 71, 72, 73, and 74 is connected to a common combined gas distribution line 106 and a common light alkane gas distribution line 103.

[0044] The light alkane gas distribution line 103 is connected to the light alkane gas inlet 102 via the depressurization station 104. The combined gas distribution line 106 is connected to the outlet 105.4 of the mixing station 105, whose inlets include steelmaking exhaust gas inlets 105.1 and 105.2, and also includes an additional natural gas inlet 105.3. The mixing station 105 discharges the combined gas CG obtained by mixing steelmaking exhaust gases, which are supplemented with several natural gases.

[0045] The supply circuit may be configured, as in Figure 2, in which the different fuel gases contained in each fuel gas stream F1, F2, F3, and F4 are mixed upstream of the heating sections 10, 20, 30, and 40, and the resulting gas mixture is then piped to the gas burner 6 of the heating section.

[0046] Therefore, each of the supply sections 71, 72, 73, and 74 of the supply circuit 7 is configured to mix light alkane gas and the combined gas CG upstream of the gas burner 6.

[0047] The supply portion 71 is, for example, - The valve 71.1 has an inlet connected to the light alkane gas distribution line 103 and an outlet connected to the mixing element 71.3. - Another valve 71.2, whose inlet is connected to the combined gas distribution line 106 and whose outlet is connected to the mixing element 71.3, -The mixing element 71.3 discharges the fuel gas flow F1 through its outlet 71.4. - It comprises a pipe 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.

[0048] In the example shown in Figure 2, the other supply parts 72, 73, and 74 have the same structure as supply part 71.

[0049] This type of upstream mixing configuration, which has the same gas mixture supplied to different burners 6 in the heating section, is beneficial in that it can be implemented with minimal modification in heating furnaces that were previously operated using a single gas mixture (having the same composition for all burners in the furnace) in a constant composition mode, albeit with adjustable flow rates. In fact, this upstream mixing configuration can be implemented in such furnaces simply by adding a light alkane gas supply line 103, corresponding adjustable valves 71.1-74.1 and mixing elements 71.3-74.3, with the rest of the piping system remaining largely unchanged and the furnace's gas burner configuration remaining largely unchanged.

[0050] In this regard, the present inventors have proposed a system composed of BFG, BOFG, COG, and natural gas, with a 24 MJ / Nm 3 Certain gas burners selected for optimal operation with a fuel gas flow having a Wobbe index are, for example, those with a Wobbe index of 15 or even 10 MJ / Nm 3 It was observed that this is also suitable for combustion of fuel gas streams with low natural gas content. Therefore, surprisingly, these gas burners can actually be supplied with fuel gas streams whose natural gas content is substantially varied, and all gas burners 6 of different heating furnaces can be of the same type (convenient type) having this upstream mixing configuration.

[0051] In the embodiment shown in Figure 2, the heating furnace 1 includes an electronic control unit 8 having at least a processor, memory, an acquisition module, and a communication interface for communicating with valves 71.1 to 74.1 (and 71.2 to 74.2), which are electronically controllable valves (i.e., solenoid valves). When describing a method for heating steel semi-finished products according to the present invention, the electronic control unit 8 is configured and programmed, for example, to control these valves according to the control method presented below.

[0052] In a simplified alternative example of the embodiment in Figure 2, some of the heating sections may be supplied with only the compound gas, rather than only the light alkane gas. Other heating sections may be supplied with both the compound gas and the light alkane gas, while in some cases a certain proportion of the light alkane gas may be supplied to all of these other heating sections (in which case valves 71.1-74.1 may be omitted).

[0053] Not all components of supply circuit 7 are necessarily shown in the diagram. In fact, the supply circuit may include additional components not shown, such as valves, regulators, or other safety or distribution components.

[0054] Furthermore, without departing from the scope of the present invention, detailed configurations of supply circuits different from those shown in Figures 1 and 2 are possible.

[0055] In particular, the pipe and valve configurations of supply sections 71-74 may differ from those presented, but it is still possible to supply different heating sections having different Wobbe indices. For example, different gas burners in the same heating section can be supplied with different gases, instead of supplying them all with the same gas mixture (generated upstream). When such a “separate piping” configuration is used, at least some of the heating sections each have several gas burners, and the supplement gas is then piped to some of the gas burners specifically for the supplement gas, without being mixed with one or more steelmaking exhaust gases, while one or more steelmaking exhaust gases are piped to the other gas burners in the heating section. In such a case, the fuel gas flow supplied to the heating section is a mixture of the supplement gas flow (supplied to specific dedicated gas burners) and the flow of one or more steelmaking exhaust gases supplied to the heating section.

[0056] Figure 3 shows a heating facility 100 comprising several heating furnaces 1, 1', and 1”, including heating furnace 1 and two other heating furnaces 1' and 1'' which are identical to heating furnace 1 in Figures 1 and 2.

[0057] The replenishment gas inlet 102 of the supply circuit 7 for each heating furnace 1, 1', and 1'' is connected to the same global replenishment gas supply line 101.

[0058] Furnaces 1, 1', and 1'' share the same mixing station 105, where the steelmaking exhaust gases are mixed together (and optionally augmented with a small amount of supplemental gas). In other words, the heating equipment 100 has only one such mixing station common to the different furnaces. The same combined gas supply line 106, connected to the mixing station outlet 105.4, supplies the different heating sections of these furnaces 1, 1', and 1''.

[0059] In this example, heating furnaces 1, 1', and 1'' are identical; however, they may be different from one another. For example, the supply circuit of one heating furnace may be simpler than that of the others, and may even be configured to supply the same gas mixture (having the same composition) to all of its heating sections.

[0060] The method for heating a steel semi-finished product in a heating furnace according to the present invention can be carried out, for example, using the heating furnace 1 described above.

[0061] In this method, the steel semi-finished product 9 is fed into the input port 2 of the heating furnace 1, then passes through a series of heating sections 10, 20, 30, and 40, and is finally discharged at the discharge port 4.

[0062] The heat output released from the different heating sections 10, 20, 30, and 40 of the furnace may differ from one another. For example, the heat output released from the last heating section (closer to discharge port 4) may be higher than that of the first heating section (closer to input port 2). More generally, the heat output released from each of the different heating sections is set according to a predetermined, pre-established reheating sequence applied to the steel semi-finished product.

[0063] To obtain these heating powers, the heating sections 10, 20, 30 or 40 are each supplied with a fuel gas flow F1, F2, F3 or F4 containing a proportion of make-up gas that is adjusted to obtain the required heating power. In particular, for each heating section 10, 20, 30, 40, the proportion of make-up gas in the fuel gas flow can be adjusted to obtain a predetermined Wobbe index that is set according to the reheating sequence applied to the semi-finished steel product for that flow.

[0064] For example, - A part of the first heating section (e.g., heating section 10) is supplied by a fuel gas flow (F1) having a Wobbe index (Wob1) that is lower than 16 MJ / Nm, for example equal to 15, or even 12 MJ / Nm 3 (or more generally included between 4 and 16 MJ / Nm 3 ), 3 - On the other hand, the other heating sections (e.g., heating sections 20, 30 and 40) are supplied by fuel gas flows (F2, F3, F4) having a Wobbe index (Wob2, Wob3, Wob4) that is higher than 18 MJ / Nm, for example, equal to 24 MJ / Nm (or more generally included between 22 and 40 MJ / Nm 3 ). 3 (or more generally included between 22 and 40 MJ / Nm 3 ).

[0065] 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 described above. This adjustment can be manual for each valve. It can also be the initial setting at permanent factory shipment (once adjusted, it remains constant thereafter). Furthermore, in the embodiments contemplated herein, the valves 71.1 to 74.1 are electronically controllable and the valve adjustment is carried out by an electronic control device 8.

[0066] For this reason, the electronic control device 8 performs the following steps: - A step of obtaining heating data representing the furnace temperature profile, or the furnace heat profile, or a reheating sequence applied to a steel semi-finished product. - A step of determining, based on the heating data (temperature profile, heat profile, or reheating sequence), the target proportion of supplemental gas or the target Wobbe index for the fuel gas flow supplied to the target heating section for each heating section, -To perform the step of controlling the solenoid valves (here, solenoid valves 71.1 to 74.1) of the supply circuit 7, which adjust the flow of fuel gas supplied to different heating sections based on a predetermined target ratio or target Wobbe index, the system may be configured, for example, to be programmed.

[0067] Furthermore, feedback control may be implemented to adjust the temperature in one or more of the heating sections by adjusting the proportion of supplemental gas supplied to the target heating section. Therefore, the electronic control unit 8 performs the following steps: - A step of measuring the temperature in the heating section. - A step of comparing the measured temperature with the set temperature (for example, specified in the temperature profile data mentioned above), - Depending on the result of the comparison step, the system may be configured (e.g., programmed) to perform a step of controlling a solenoid valve (71.1, 72.1, 73.1 or 74.1) that controls the proportion of supplement gas in the fuel gas flow supplied to the heating section (this control may be achieved, for example, using a PI or PID corrector).

Claims

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

2. The method according to claim 2, - One of the Wobbe indices is 16 MJ / Nm ３ Lower than, - On the other hand, the other side of the Wobbe index is 18 MJ / Nm ３ A higher method.

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

4. A method according to any one of claims 1 to 3, wherein the two heating sections (10, 20, 30, 40) are - One or more types of steelmaking exhaust gases, - Each is supplied by a fuel gas containing light alkane gas (NG), dihydrogen, or a mixture thereof. A method comprising two fuel gas streams (F1, F2, F3, F4) having different Wobbe indices (Wob1, Wob2, Wob3, Wob4), each containing supplement gas (NG) in proportions different from each other.

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

6. The method according to claim 4, wherein the two heating sections each comprise several gas burners, - The supplemental gas is not mixed with one or more types of steelmaking exhaust gases, but is piped to some of the gas burners in the heating section dedicated to the supplemental gas. - On the other hand, one or more types of steelmaking exhaust gases are piped to other gas burners in the heating section. - A method wherein the fuel gas flow supplied to the heating section is a mixed flow of supplemental gas flow and one or more types of steelmaking exhaust gas supplied to the heating section.

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

8. The method according to any one of claims 4 to 7, wherein the supplement gas is light alkane gas (NG), - The proportion of light alkane gas in the first fuel gas flow (F1) of the two fuel gas flows is less than 10 volume percent. - On the other hand, the proportion of light alkane gas in the second fuel gas stream of the two fuel gas streams (F2, F3, F4) is higher than 20% by volume.

9. A method according to any one of claims 4 to 8, wherein the steelmaking exhaust gas, or one of the steelmaking exhaust gases, belongs to the following list: coke oven gas (COG), blast furnace gas (BFG), converter 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: - A step of measuring the measured temperature of one of the heating sections, - A step of comparing the measured temperature with the set temperature. A method comprising the step of controlling solenoid valves (71.1 to 74.1) that adjust the ratio of supplement gas (NG) in the fuel gas stream (F1 to F4) supplied to the heating sections (10 to 40) according to the result of the comparison step.

11. A method according to any one of claims 1 to 10, wherein the steel semi-finished product (9) is a slab, an ingot, a billet, or a bloom.

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

13. A heating furnace (1) according to claims 1 to 12, wherein the supply circuit (7) is - It is equipped with one or more inlets (105.1, 105.2) for one or more types of steelmaking exhaust gases, and an inlet (102) for supplemental gas (NG) which is light alkane gas (NG), dihydrogen, or a mixture thereof, and A heating furnace (1) is configured such that two fuel gas streams (F1, F2, F3, F4) supplied to heating sections (10, 20, 30, 40) each contain supplemental gas (NG) in different proportions.

14. A heating furnace (1) according to claims 1 to 13, wherein the supply circuit (7) is provided for each of two heating sections (10 to 40) in a pipe fluidly connected to the heating section in question, and each includes an adjustable valve (71.1 to 74.1) for transporting replenishment gas (NG) without mixing it with one or more types of steelmaking exhaust gases.

15. A heating furnace (1) according to claim 13 or 14, wherein the supply circuit (7) comprises at least one mixing element (71.3 to 74.3) dedicated to the target heating section for each heating section (10 to 40), is connected to the gas burner (6) of the heating section, and is configured to mix replenishment gas (NG) with one or more types of steelmaking exhaust gas upstream of the gas burner (6) of the heating section.

16. Heating equipment (100), - Each of the following: two or more heating furnaces (1, 1', 1") as described in any of claims 13 to 15, - A joint mixing station (105), configured to mix with steelmaking exhaust gas so as to deliver a combined gas (CG) mixed at the discharge port (105.4) of the joint mixing station, - Heating equipment (100) comprising a combined gas supply line (106) that connects the outlet (105.4) of a joint mixing station (105) to the heating section of heating furnaces (1, 1', 1") of different heating equipment.

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