Heating furnace operation method and heating furnace

Abstract

To provide an operating method for a heating furnace and the heating furnace using ammonia that can suppress discharge of carbon dioxide as combustion fuel of the heating furnace and capable of reducing amounts of nitrogen oxide and unburned ammonia to be discharged to outside of the heating furnace.SOLUTION: This invention relates to an operating method for a heating furnace. The operating method for the heating furnace includes: a first burner heating step of performing burner heating by using first fuel gas containing ammonia and combustion air in which an air ratio to a theoretical air amount of the first fuel gas is 0.9-1.0; a second burner heating step of performing burner heating by using second fuel gas containing ammonia and combustion air in which an air ratio to a theoretical air amount of the second fuel gas is lower than that to the theoretical air amount of the first fuel gas; and an air injection step of injecting air to mixed exhaust gas of exhaust gas through the first burner heating and exhaust gas through the second burner heating.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for operating a heating furnace and to a heating furnace. [Background technology]

[0002] Integrated steelworks have effectively utilized blast furnace gas, which is emitted from the top of a blast furnace that reduces iron ore to produce molten iron, as well as by-product gases generated in converters and coke ovens, as fuel gases. However, in recent years, with the demand for reduced carbon dioxide emissions, combustion technologies have been developed to reduce the amount of by-product gas used. For example, in steel heating furnaces that heat steel, such as those used in hot rolling lines and plate rolling lines in integrated steelworks, there is a demand for reduced by-product gas use and reduced carbon dioxide emissions. In this context, technologies that utilize ammonia as fuel gas for steel heating furnaces have attracted attention. Ammonia, which does not contain carbon, produces mainly water and nitrogen upon combustion, thereby significantly reducing carbon dioxide emissions. Therefore, technological development for its application to steel heating furnaces is desirable.

[0003] However, using ammonia as a fuel for a heating furnace poses a problem in that it generates nitrogen oxides (NOx), which are harmful to the human body and contribute to photochemical smog and acid rain, and are therefore subject to legal emissions restrictions.

[0004] Therefore, in order to solve these problems, heating techniques have been proposed. Patent Document 1 discloses a boiler that includes a combustion device capable of burning ammonia as fuel in a furnace, and a flue that guides combustion gas generated by burning the fuel, and that is installed in at least one of the furnace and the flue at a position downstream of the combustion device in the direction of the combustion gas, and that includes an injection unit that injects ammonia as a reducing agent toward the center of the furnace or the flue in a plan view. This allows ammonia to be supplied to the center of the furnace, and even a small amount of ammonia is said to be able to act as a reducing agent to reduce nitrogen oxides.

[0005] Furthermore, Patent Document 2 discloses a boiler including a burner for burning fossil fuel in a furnace, an additional air supply unit provided downstream of the burner in the flow direction of combustion gas in the furnace, and an ammonia fuel supply unit that supplies ammonia fuel to the furnace upstream of the additional air supply unit in the flow direction of fuel gas. As a result, in a two-stage combustion boiler equipped with an additional air supply unit, if ammonia fuel is fed into a position upstream of the additional air supply unit, the nitrogen content of the ammonia fuel will be reduced to N2 in the reducing atmosphere region inside the furnace, thereby suppressing the generation of nitrogen oxides. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-086191 [Patent Document 2] Japanese Patent Application Publication No. 2018-076985 Summary of the Invention [Problem to be solved by the invention]

[0007] However, when the above-mentioned conventional technology is applied to a heating furnace used for heating steel materials and the like, the following problems arise.

[0008] The technology disclosed in Patent Document 1 targets combustion equipment such as boilers, and reduces nitrogen oxides generated in the combustion equipment by injecting ammonia downstream in the flow direction of combustion gas. In this case, the amount of ammonia injected to reduce nitrogen oxides is extremely small compared to the flow rate of combustion gas generated in the combustion equipment. Therefore, even if ammonia is injected toward the center of the furnace, it may not mix uniformly with the nitrogen oxides contained in the combustion gas. As a result, the nitrogen oxides contained in the combustion gas may not be effectively reduced. This creates a problem in that the ammonia, which serves as a reducing agent, is discharged unburned outside the furnace. Unlike combustion equipment such as boilers, heating furnaces for heating materials such as steel typically have an opening and closing door for loading and unloading the materials. In this case, when the door of the heating furnace is opened, toxic unburned ammonia (also called "unburned ammonia") is discharged outside the heating furnace, causing a problem of deterioration of the environment outside the heating furnace.

[0009] Patent Document 2 also targets combustion equipment such as boilers, and reduces nitrogen oxides with ammonia in a reducing atmosphere region within a furnace. Patent Document 2 discloses that, in order to form a reducing atmosphere region within the furnace, the amount of primary air supplied to the burner is less than the amount of air required to completely combust the fossil fuel. The technology disclosed in Patent Document 2 requires a certain amount of space to be secured within the furnace and a certain reaction time to carry out the reduction reaction of nitrogen oxides. On the other hand, a heating furnace for heating steel or other materials requires not only a combustion device (e.g., a burner) inside the furnace, but also a space for placing and charging the materials.In contrast, a furnace such as a boiler only requires the space necessary to cause a combustion reaction between fuel and combustion air. Therefore, when the technology disclosed in Patent Document 2 is applied to a heating furnace that heats a heated object, the space serving as the reducing atmosphere region expands, resulting in a problem that the reduction reaction of nitrogen oxides does not proceed uniformly within the reducing atmosphere region, and unburned ammonia is discharged outside the heating furnace.

[0010] Furthermore, Patent Document 2 discloses that when the amount of air supplied to combust ammonia is changed between 0.6 and 1.0 relative to the theoretical air amount, the amount of air supplied, the leakage rate of unburned ammonia at the outlet of the furnace, and the conversion rate to NOx have contradictory characteristics. Therefore, in order to reduce both nitrogen oxides (NOx) and unburned ammonia, it becomes necessary to control the primary air ratio within a narrow range, and changes in the operating conditions inside the heating furnace make it easier for nitrogen oxides and unburned ammonia to be emitted to the outside.

[0011] The present invention has been made to solve the above-mentioned problems associated with the conventional technology, and an object of the present invention is to provide a heating furnace operation method and a heating furnace that use ammonia as a combustion fuel for the heating furnace, which can suppress carbon dioxide emissions, and that can reduce the amounts of nitrogen oxides and unburned ammonia emitted outside the heating furnace. [Means for solving the problem]

[0012] The method for operating a heating furnace according to the present invention, which advantageously solves the above problems, is configured as follows.

[0013] [1] A method for operating a heating furnace, comprising: a first burner heating step of burner-heating a first fuel gas containing ammonia with combustion air having an air ratio of 0.9 to 1.0 relative to the theoretical air amount of the first fuel gas; a second burner heating step of burner-heating a second fuel gas containing ammonia with combustion air having an air ratio of the second fuel gas to the theoretical air amount that is lower than the air ratio of the first fuel gas to the theoretical air amount; and an air injection step of injecting air. [2] In the above [1], the air injection step is a method of operating a heating furnace in which air is injected into a mixed exhaust gas obtained by mixing the exhaust gas generated by the first burner heating step and the exhaust gas generated by the second burner heating step. [3] In the above [1] or [2], the second burner heating step is performed in such a manner that the air ratio of the second fuel gas to the theoretical air amount is less than 0.9. [4] In the above [1] or [2], the method for operating a heating furnace is such that burner heating is performed using a mixed gas of ammonia and coal gas as at least one of the first fuel gas and the second fuel gas. [5] The method for operating a heating furnace according to the above item [3], wherein burner heating is performed using a mixed gas of ammonia and coal gas as at least one of the first fuel gas and the second fuel gas.

[0014] The heating furnace according to the present invention, which advantageously solves the above problems, is configured as follows. [6] A heating furnace comprising: two or more burner equipment that performs burner heating using a fuel gas containing ammonia; an air ratio adjustment unit that adjusts the air ratio of the combustion air supplied to the two or more burner equipment relative to the theoretical air amount of the fuel gas; a control unit that controls the air ratio of the combustion air supplied to at least one of the two or more burner equipment to an air ratio different from the air ratio of the combustion air supplied to the other burner equipment; and an air injection unit that injects air into a mixed exhaust gas of exhaust gases discharged from the two or more burner equipment. [7] In the above [6], the burner equipment comprises a first burner equipment that heats a first fuel gas containing ammonia, the air ratio of which has been adjusted by the air ratio adjustment unit, using combustion air having an air ratio of 0.9 to 1.0 relative to the theoretical air amount of the first fuel gas, and a second burner equipment that heats a second fuel gas containing ammonia using combustion air having an air ratio that is lower than the air ratio of the second fuel gas to the theoretical air amount of the first fuel gas, and the first burner equipment, the second burner equipment, and the air injection equipment are arranged in this order from the upstream side of the gas flow inside the heating furnace. [8] In the above [6], the heating furnace has an opening through which the mixed exhaust gas is discharged, and the air injection device is a heating furnace arranged at a position closer to the opening than the first burner equipment and the second burner equipment. [Effects of the Invention]

[0015] According to the present invention, by using ammonia as a combustion fuel in a heating furnace, it is possible to suppress carbon dioxide emissions and reduce emissions of nitrogen oxides and unburned ammonia produced by the combustion of ammonia to the outside of the heating furnace. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 2 is a schematic diagram illustrating a heating furnace. [Figure 2] FIG. 2 is a configuration diagram showing the arrangement of burner equipment in a heating furnace as viewed from the front in the steel material moving direction of FIG. 1. [Figure 3] 1 is a configuration diagram of a heating furnace equipped with a burner device and an air injection device arranged in parallel according to an embodiment of the present invention. [Figure 4] Schematic diagrams to explain chemical reactions inside a heating furnace. A) Nitrogen oxides and unburned ammonia exist in the exhaust gas heated by the first burner. B) Nitrogen oxides and unburned ammonia exist in the exhaust gas heated by the second burner. C) Chemical reaction between nitrogen oxides and unburned ammonia in the mixed exhaust gas. [Figure 5] 1 is a configuration diagram of a heating furnace according to an embodiment of the present invention, which includes a burner device and an air injection device arranged opposite to each other. [Figure 6] 1A and 1B are a configuration diagram and a schematic diagram for explaining the chemical reactions in a heating furnace equipped with a burner and an air injection system according to the present embodiment. A) Nitrogen oxides and unburned ammonia are present in the exhaust gas heated by the first burner. B) Nitrogen oxides and unburned ammonia are present in the exhaust gas heated by the second burner. [Figure 7] 1 is a schematic diagram illustrating a configuration of a heating furnace according to an embodiment of the present invention. [Figure 8]FIG. 10 is a configuration diagram of a heating furnace according to another embodiment of the present invention, which is equipped with an air ratio adjusting unit, a burner unit having a control unit, and an air injection unit. DETAILED DESCRIPTION OF THE INVENTION

[0017] The heating furnace according to this embodiment will be described below. <Heating furnace> A heating furnace according to an embodiment of the present invention is a facility equipped with a burner that burns fuel gas as a heat source, and heats an object to be heated up to a predetermined temperature. The object to be heated is primarily a metal, but may be either an ferrous metal or a non-ferrous metal. The heating temperature of the object to be heated is 700 to 1400°C. 1 and 2 show an example of a heating furnace according to the present embodiment, in which the object to be heated is steel. For example, a heating furnace used in a hot rolling line for steel is used to heat a cast slab to a predetermined heating temperature (approximately 1100 to 1300°C).

[0018] The heating furnace 1 shown in FIG. 1 includes a charging section 30 into which the steel material S (slab) to be heated is charged, and an unloading section 31 into which the heated steel material S is unloaded (extracted). For example, the steel material S produced in a continuous casting line is transported to a yard on the charging side of the heating furnace and is charged into the heating furnace 1 from the charging section 30 according to a production schedule of a hot rolling line or the like. The interior of the heating furnace 1 is divided into multiple zones, and the upstream side often includes a heating zone divided into 2 to 8 zones and 1 to 3 soaking zones. The interior of the heating furnace 1 is generally equipped with a fixed skid 33 on which the steel material S is placed and a movable skid 32 for transporting the steel material S. A heating furnace equipped with a fixed skid 33 and a movable skid 32 is called a walking beam continuous heating furnace.

[0019] During operation of the heating furnace, the atmospheric temperature is controlled to be different for each zone inside the heating furnace, and the average temperature of the steel material S charged into the heating furnace 1 is gradually increased. This controls the steel material S to reach a predetermined target heating temperature (the target temperature of the slab when it is removed from the heating furnace). Once the steel material S has reached the target temperature, it passes through the discharge section 31 and is subjected to hot rolling.

[0020] A plurality of burners are provided inside the heating furnace 1 along the conveying direction of the steel material S. Burner B is arranged to heat the inside of the heating furnace by combustion. When the inside of the heating furnace is heated by the burner, the temperature of the steel material rises due to radiation from the furnace walls. In addition, a flow of atmospheric gas occurs inside the heating furnace, and the temperature of the steel material may rise due to convection. Furthermore, the temperature of the steel material may be raised by the direct contact of the burner flame with the steel material. In either case, the burner burns fuel gas as a heat source to heat the inside of the heating furnace and thereby raise the temperature of the material to be heated inside the heating furnace.

[0021] The interior of the heating furnace 1 is equipped with a space where the flame is emitted from the burner, as well as a space for placing and transporting the material to be heated. Therefore, compared to boilers and other devices whose purpose is to cause a combustion reaction inside, the furnace has a large volume relative to the combustion energy input into the furnace. The furnace volume (m2) per combustion energy in gas turbines, pulverized coal boilers, and gas and oil boilers is 3 / MW) is a typical value for a gas turbine of 2m 3 / MW, pulverized coal boiler 6m 3 / MW, gas and oil boiler 2m 3 / MW. In contrast, the heating furnace is 10 to 16 m 3 For example, the heating furnaces used in hot rolling lines for steel materials have a maximum speed of 11 to 13 m / MW. 3 / MW.

[0022] When the heating furnace 1 is in operation, the doors (opening and closing doors) of the charging section 30 and the unloading section 31 are closed, and a higher pressure is generated inside than in the atmosphere. The doors are temporarily opened when charging and unloading the steel material S. When the doors are open, a pressure difference occurs between the pressure inside the heating furnace and the pressure near the doors, so the combustion gas inside the heating furnace flows from areas of high pressure to areas of low pressure. When the door of the heating furnace 1 is open, the combustion gas often flows in the direction in which it is discharged outside the heating furnace 1 through the opening.

[0023] 2 is a diagram showing a cross section of the heating furnace 1. Inside the heating furnace 1, burners B are often placed on both the upper and lower sides of the steel material S so as to prevent a temperature difference between the upper and lower surfaces of the steel material S. Furthermore, burners B are often placed on both sides in the conveying direction of the steel material S so as to prevent a temperature difference between the leading end S1 and the trailing end S2 of the steel material S.

[0024] The heating furnace 1 of this embodiment is a heating furnace including two or more burner facilities that perform burner heating using a fuel gas containing ammonia, an air ratio adjusting unit that adjusts the air ratio of the combustion air supplied to the two or more burner facilities relative to the theoretical air amount of the fuel gas, a control unit that controls the air ratio of the combustion air supplied to at least one of the two or more burner facilities to an air ratio different from the air ratio of the combustion air supplied to the other burner facilities, and an air injection facility that injects air into a mixed exhaust gas of exhaust gases discharged from the two or more burner facilities. <Burner equipment> It is preferable to have a first burner facility that heats a first fuel gas containing ammonia using combustion air having an air ratio of 0.9 to 1.0 relative to the theoretical air amount of the first fuel gas, and a second burner facility that heats a second fuel gas containing ammonia using combustion air having an air ratio of the second fuel gas to the theoretical air amount that is lower than the air ratio of the first fuel gas to the theoretical air amount.

[0025] In addition, in the heating furnace 1 of this embodiment, at least one of the burners B arranged inside is a first burner equipment that performs burner heating of a first fuel gas containing ammonia with combustion air, and at least one of the other burners B is a second burner equipment that performs burner heating of a second fuel gas containing ammonia with combustion air.

[0026] The first burner equipment and the second burner equipment will be explained using Figure 3. Figure 3 includes a part of the furnace wall 35 on one side of the heating furnace 1 shown in Figure 1, and shows the arrangement of the first burner equipment 2, the second burner equipment 3, and the air injection equipment 4 of the heating furnace 1 as seen from above.

[0027] The first burner equipment 2 performs first burner heating by injecting a flame into the furnace using a first fuel gas 5 containing ammonia gas as the fuel gas and combustion air 12. The first burner equipment 2 includes a first burner nozzle 7 for injecting the flame into the furnace, a first fuel gas supply system 14 for supplying the first fuel gas 5 to the first burner nozzle 7, and a combustion air supply system 18 for supplying the combustion air 12 to the first burner nozzle 7. The first burner nozzle 7 is, for example, a double-pipe nozzle, and the first fuel gas 5 is injected into the furnace from the inside, while the combustion air 12 is supplied to the outside. As a result, the first fuel gas 5 and the combustion air 12 mix to form a combustible mixture, and a flame is injected from the tip of the first burner nozzle 7 toward the inside of the heating furnace 1.

[0028] The second burner equipment 3 may have a configuration similar to that of the first burner equipment 2. The second burner equipment 3 performs second burner heating by injecting a flame into the furnace using a second fuel gas 6 containing ammonia gas as the fuel gas and combustion air 12. The second burner equipment 3 includes a second burner nozzle 8 for injecting the flame into the furnace, a second fuel gas supply system 15 for supplying the second fuel gas 6 to the second burner nozzle 8, and a combustion air supply system 19 for supplying the combustion air 12 to the second burner nozzle 8. The second burner nozzle 8 is also, for example, a double-pipe nozzle, with the second fuel gas 6 being injected into the furnace from the inner pipe and the combustion air 12 being supplied from the outer pipe. As a result, the second fuel gas 6 and the combustion air 12 mix to form a combustible mixture, and a flame is injected from the tip of the second burner nozzle 8 toward the interior of the heating furnace 1.

[0029] In addition, the first burner equipment 2 and the second burner equipment 3 may be a swirl burner that has the function of stirring the fuel gas injected from the burner nozzle, or a tubular flame burner that blows fuel gas and combustion air tangentially into the combustion tube, forming a swirling flow within the combustion tube and causing combustion.

[0030] The first fuel gas 5 and the second fuel gas 6 both use a fuel gas containing ammonia. Ammonia gas may be used alone as the fuel gas, or a mixed gas in which ammonia gas is mixed with other fuels may be used as the fuel gas. The first fuel gas 5 and the second fuel gas 6 may have different or the same ammonia gas mixing ratios. Furthermore, the other fuels constituting the mixed gas may be different or the same for the first fuel gas 5 and the second fuel gas 6. However, since the equipment for supplying fuel gas to the heating furnace 1 may become complicated and the equipment costs may increase, it is economical to use the same fuel gas containing ammonia for the first fuel gas 5 and the second fuel gas 6.

[0031] Ammonia gas is a flame-retardant fuel, which is more difficult to ignite and burns slower than general fuels. To improve combustion stability, a mixed gas containing ammonia gas and other fuels can be used. Coal gas is preferably used as the fuel to be mixed with ammonia gas. Coal gas is a gas derived from coal. Coal gas preferably includes coke oven gas, blast furnace gas, converter gas, or electric furnace gas. These are by-product gases produced in steelworks and have the effect of stabilizing the combustion of ammonia gas. Blast furnace gas is a by-product gas produced when iron ore is reduced in a blast furnace to produce pig iron. Coke oven gas is a by-product gas produced by high-temperature carbonization of coal to produce coke. Converter furnace gas is a by-product gas produced in the steelmaking process in a converter furnace. Electric furnace gas is a gas produced by incomplete combustion of auxiliary fuel (recarburizer) in an electric furnace. The coal gas used in the mixed gas may be a suitable mixture of blast furnace gas, coke oven gas, and converter gas (sometimes referred to as M gas). By mixing coal gases with different calorific values, the amount of heat required to heat the object to be heated can be supplied, ensuring stable operation of the heating furnace.

[0032] In this example, the first fuel gas 5 used in the first burner equipment 2 and the second fuel gas 6 used in the second burner equipment 3 shown in FIG. 3 are both mixed gases of ammonia gas and coal gas. The first fuel gas supply system 14 is connected to an ammonia gas supply system 25 and a coal gas supply system 27, and ammonia gas 10 and coal gas 11 are mixed in a mixing section 16 and supplied to the first burner nozzle 7. It is preferable to provide a flow rate control valve 53 for adjusting the amount of each gas supplied to the mixing section 16 and a flow meter 52 for measuring the supply flow rate in the ammonia gas supply system 25 and the coal gas supply system 27. This makes it possible to adjust the mixing ratio of ammonia gas and coal gas contained in the mixed gas. The second fuel gas supply system 15 is also connected to an ammonia gas supply system 26 and a coal gas supply system 28, and ammonia gas 10 and coal gas 11 are mixed in a mixing section 17 and supplied to the second burner nozzle 8. The second burner equipment 3 may also be provided, midway between the ammonia gas supply system 26 and the coal gas supply system 28, with a flow rate control valve 53 for adjusting the amount of ammonia gas 10 and coal gas 11 supplied to the mixing section 17, and a flow meter 52 for measuring the supply flow rate.

[0033] The mixing sections (16, 17) refer to the portions where the supply pipes of the coal gas supply systems (27, 28) and the supply pipes of the ammonia gas supply systems (25, 26) join together. Ammonia gas 10 and coal gas 11 are supplied from their respective supply pipes and join together, so that mixing is achieved without the need for a special stirring mechanism. The mixing sections (16, 17) may be configured as a fixed space where these supply pipes intersect. However, the mixing sections (16, 17) may also be equipped with static mixing equipment such as a static mixer or a dynamic mixer with a stirring function. This is preferred in that a mixed gas in which coal gas and ammonia gas are more uniformly mixed is produced.

[0034] It is advisable to provide a flow rate adjustment valve 53 for adjusting the flow rate of combustion air 12 supplied to the first burner nozzle 7 and the second burner nozzle 8, and a flow meter 52 for measuring the supply flow rate, in the combustion air supply system 18 of the first burner equipment 2 and the combustion air supply system 19 of the second burner equipment 3. The amount of combustion air for the first burner equipment 2 and the second burner equipment 3 is adjusted, making it easy to adjust the air ratio for each burner heating of the first burner equipment 2 and the second burner equipment 3.

[0035] The combustion air used for the first burner equipment 2 and the second burner equipment 3 may be air collected from the atmosphere and supplied from a combustion air supply system. However, reformed air, such as by removing nitrogen from the air or adding pure oxygen, may be used as the combustion air 12. Increasing the oxygen content of the combustion air promotes the oxidation reaction of the fuel gas and allows the flow rate of the combustion air supplied from the combustion air supply system to be reduced, thereby reducing the power consumption of pumps, etc. Furthermore, reducing the oxygen content of the combustion air makes it possible to create a reducing atmosphere inside the heating furnace, promoting the reduction of nitrogen oxides.

[0036] <Air injection equipment> In addition to the first burner equipment 2 and the second burner equipment 3, the heating furnace 1 of this embodiment is equipped with an air injection equipment 4 that injects air into a mixed exhaust gas 23 which is a mixture of the exhaust gas 21 discharged from the first burner equipment 2 and the exhaust gas 22 discharged from the second burner equipment 3. The air injection equipment 4 is connected to an air supply system 29, and injects air 13 from air injection nozzles 9 toward the inside of the furnace. It is preferable to provide a flow rate adjustment valve 53 for adjusting the flow rate of air 13 supplied to the air injection nozzles 9, and a flow meter 52 for measuring the supply flow rate, along the air supply system 29. This makes it possible to adjust the amount of air injected into the mixed exhaust gas of the exhaust gas from the first burner equipment 2 and the exhaust gas from the second burner equipment 3, and to promote the reduction reaction of nitrogen oxides contained in the mixed exhaust gas.

[0037] The air injected from the air injection equipment 4 may be air collected from the atmosphere. However, air that has been modified by removing nitrogen from the air or adding pure oxygen may be supplied to the air injection nozzle 9 via the air supply system 29. Increasing the oxygen content of the air 13 promotes the reduction reaction of nitrogen oxides contained in the mixed exhaust gas 23.

[0038] <Burner equipment layout for heating furnace> The arrangement of the burner equipment of the heating furnace will be described. In the heating furnace of this embodiment, the following are arranged in order from the upstream side of the gas flow along the gas flow inside the heating furnace: a first burner equipment that performs burner heating with an air ratio to a first fuel gas of 0.9 to 1.0, a second burner equipment that performs burner heating with an air ratio to a second fuel gas that is smaller than the air ratio to the first fuel gas, and an air injection equipment that injects air into a mixed exhaust gas of exhaust gas discharged from the first burner equipment and exhaust gas discharged from the second burner. This is because it is believed that injecting oxygen into a mixed gas of NOx and unburned ammonia promotes the reduction reaction of NOx with ammonia, thereby reducing the amounts of NOx and unburned ammonia emitted from the heating furnace. Furthermore, when the heating furnace is provided with an opening through which combustion gas is discharged, the air injection device is preferably disposed at a position closer to the opening than the first burner equipment and the second burner equipment.

[0039] Fig. 7 shows an example of the configuration of a heating furnace according to this embodiment. The heating furnace shown in Fig. 7 includes a loading section 30 for loading the object to be heated into the heating furnace, a discharge section 31 for unloading the object to be heated, and a flue 34 for discharging exhaust gas (combustion gas) from the inside of the heating furnace 1 to the outside of the heating furnace. The loading section 30 is an opening that is temporarily opened when the object to be heated is loaded into the heating furnace. The discharge section 31 is also an opening that is temporarily opened when the object to be heated is unloaded from the heating furnace. On the other hand, the flue 34 is provided to discharge exhaust gas from inside the heating furnace 1 and to adjust the pressure inside the heating furnace so that it does not become excessive, and is an opening that is always open because it is partially open to the outside of the heating furnace. Therefore, inside the heating furnace 1 shown in Figure 7, a gas flow of combustion gas occurs at least from inside the heating furnace toward the flue 34.

[0040] In this embodiment, a first burner equipment 2, a second burner equipment 3, and an air injection equipment 4 are arranged in this order from the upstream side of the gas flow of combustion gas toward the flue 34. In the example shown in Fig. 7, the first burner equipment 2 is arranged above and below the object to be heated near the center of the heating furnace 1 in the transport direction. Downstream of the combustion gas flow from the first burner equipment 2, one second burner equipment 3 is arranged above the object to be heated and two second burner equipment 3 are arranged below the object to be heated. Then, along the gas flow F of combustion gas, air injection equipment 4 is arranged downstream of the second burner equipment 3.

[0041] In FIG. 7 , the first burner 2 performs burner heating with an air / fuel ratio of 0.9 to 1.0 for the first fuel gas, and the second burner 3 performs burner heating with an air / fuel ratio of the second fuel gas that is lower than the air / fuel ratio for the first fuel gas. As a result, exhaust gas 21, which contains a larger amount of nitrogen oxides, moves through the heating furnace along the combustion gas flow F and mixes with exhaust gas 22, which contains a larger amount of unburned ammonia, to generate mixed exhaust gas 23. The mixed exhaust gas 23 moves through the heating furnace along the combustion gas flow F and further toward the flue 34, which is an opening. Because the air injection device 4 is located downstream of the first heating device 2 and the second heating device 3 in the gas flow, air 13 is injected into the mixed exhaust gas 23 before the mixed exhaust gas 23 is discharged from the opening. This allows the oxygen in the air 13 to promote the reduction of nitrogen oxides by ammonia, thereby reducing the concentrations of nitrogen oxides and ammonia in the exhaust gas discharged to the outside of the heating furnace through the flue 34.

[0042] The heating furnace 1 may have burners other than the first burner equipment 2 and the second burner equipment 3. However, the burner equipment other than the first burner equipment 2 and the second burner equipment 3 (referred to as the third burner equipment) is equipment that performs burner heating using a fuel that does not contain ammonia. The third burner equipment does not emit nitrogen oxides and unburned ammonia, or if it does emit them, the amount of nitrogen oxides and unburned ammonia emitted is low compared to the first burner equipment and the second burner equipment (for example, 1 / 10 or less), so that it does not disturb the reduction reaction of nitrogen oxides in the mixed exhaust gas. The third burner equipment may perform burner heating using, for example, coal gas as fuel gas.

[0043] Fig. 8 shows the configuration of the heating furnace according to this embodiment. The heating furnace shown in Fig. 8 is provided with two burner equipment (44A, 44B) and an air injection equipment 4. The two burner equipment (44A, 44B) may have the same structure, and the same fuel gas 45 may be supplied to the burner equipment 44.

[0044] The burner equipment 44 is provided with an air ratio adjusting unit 40, and the air ratio adjusting units 40 corresponding to the two burner equipment (44A, 44B) are connected to the control unit 42. The air ratio adjusting units 40 have the function of adjusting the air ratio of combustion air to fuel gas 45 for each burner equipment 44. For example, the air ratio adjusting unit 40 measures the flow rate of the fuel gas supplied to the burner nozzle as the fuel gas 45, and calculates the theoretical amount of air required to completely combust the fuel gas 45 from the measured flow rate of the fuel gas 45 and the fuel composition of the fuel gas 45. Then, based on the air ratio set for each burner equipment (44A, 44B), the air ratio for burner heating is set for each burner equipment (44A, 44B) by adjusting the aperture of a flow control valve arranged in a combustion air supply system.

[0045] The control unit 42 provides a set value of the air ratio to the air ratio adjustment unit 40 of each burner equipment (44A, 44B). The control unit 42 provides a set value of the air ratio to the air ratio adjustment unit 40 so that the air ratio of one of the burner equipment 44A is 0.9 to 1.0. The control unit 42 provides a set value of the air ratio to the air ratio adjustment unit 40 so that the other burner equipment 44B performs burner heating at an air ratio smaller than the air ratio of the one burner equipment 44A. In this case, as shown in the positional relationship of each equipment in Figure 8, the control unit 42 sets the air ratio of the burner equipment 44A located far from the air injection equipment 4 to be 0.9 to 1.0, and sets the air ratio of the burner equipment 44B located close to the air injection equipment 4 to be smaller than the air ratio of the burner equipment 44A located far from the air injection equipment 4.

[0046] Burner equipment 44A, which is located far from the air injection equipment 4 and has an air ratio set to 0.9 to 1.0, functions as the first burner equipment 2, while burner equipment 44B, which is located close to the air injection equipment 4, functions as the second burner equipment 3. Therefore, by providing two burner equipment (44A, 44B) equipped with an air ratio adjustment unit 40 and a control unit 42 that sets the air ratio between them, a mixed exhaust gas 23 containing nitrogen oxides and unburned ammonia can be generated, and the reduction reaction of nitrogen oxides by ammonia is promoted by the air injection equipment 4.

[0047] Next, a method for operating the heating furnace according to this embodiment will be described. <Operation method of heating furnace> The present embodiment is a method for operating a heating furnace, including: a first burner heating step of burner-heating a first fuel gas containing ammonia with combustion air having an air ratio of 0.9 to 1.0 relative to the theoretical air amount of the first fuel gas; a second burner heating step of burner-heating a second fuel gas containing ammonia with combustion air having an air ratio of the second fuel gas to the theoretical air amount that is lower than the air ratio of the first fuel gas to the theoretical air amount; and an air injection step of injecting air.

[0048] In a heating furnace, nitrogen oxides are generated by burning ammonia-containing fuel gas, producing a mixed exhaust gas in which nitrogen oxides and ammonia coexist. Air containing oxygen is then injected into the produced mixed exhaust gas. As a result, the reduction reaction of nitrogen oxides by ammonia is promoted. The ammonia is oxidized by the oxygen in the air, and the oxidized ammonia decomposes the nitrogen oxides. As a result, the ammonia is decomposed and rendered harmless along with the nitrogen oxides contained in the mixed exhaust gas. The reason for combining the two burner heating methods, the first burner heating and the second burner heating, is to make the exhaust gas heated by the first burner contain a relatively large amount of nitrogen oxides and the exhaust gas heated by the second burner contain a relatively large amount of unburned ammonia, and by mixing these, a mixed exhaust gas in which nitrogen oxides and ammonia coexist is produced.

[0049] The method of operating the heating furnace will be described using the first burner heater 2, the second burner equipment 3 and the air injection equipment 4 shown in FIG. In this embodiment, first burner heating is performed by using combustion air 12 whose air ratio (sometimes simply referred to as air ratio) to the theoretical air amount of the first fuel gas 5 is 0.9 to 1.0. Here, the theoretical air amount is the amount of air required to completely combust the fuel gas. Furthermore, the air ratio to the theoretical air amount is the ratio of the amount of air supplied to the burner equipment as combustion air to the amount of air required to completely combust the fuel gas.

[0050] The air ratio for first burner heating is set to 0.9 to 1.0 in order to contain nitrogen oxides in exhaust gas 21 heated by the first burner. If the air ratio for first burner heating is less than 0.9, combustion of ammonia gas is suppressed, and the amount of unburned ammonia increases compared to nitrogen oxides in exhaust gas 21 heated by the first burner. On the other hand, if the air ratio for first burner heating exceeds 1.0, combustion of ammonia contained in the first fuel gas is promoted, and the amount of nitrogen oxides in exhaust gas 21 becomes excessive, making it difficult to sufficiently reduce the nitrogen oxides in mixed exhaust gas 23. The concentration of nitrogen oxides contained in exhaust gas 21 generated by setting the air ratio for first burner heating to 0.9 to 1.0 is approximately 400 to 5000 ppm. Exhaust gas 21 heated by the first burner may also contain unburned ammonia, but its concentration is 5 ppm or less when the air ratio is 0.9, and is nearly zero when the air ratio is 0.95 to 1.0. As a result, exhaust gas 21 heated by the first burner contains a relatively large amount of nitrogen oxides.

[0051] On the other hand, in the present embodiment, second burner heating is performed in which the second fuel gas containing ammonia is burner heated using combustion air having an air ratio in which the air ratio of the second fuel gas to the theoretical air amount is lower than the air ratio of the first fuel gas to the theoretical air amount. This is because the exhaust gas 22 heated by the second burner contains a relatively large amount of unburned ammonia. If the air ratio of the second burner heating is equal to or greater than the air ratio of the first burner heating, the effect of the unburned ammonia contained in the exhaust gas 22 in reducing the nitrogen oxides in the exhaust gas 21 decreases.

[0052] For second burner heating, it is preferable that the air ratio of the second fuel gas to the theoretical air amount is less than 0.9. This is because the amount of unburned ammonia contained in the exhaust gas 22 heated by the second burner increases, accelerating the reduction reaction of nitrogen oxides in the mixed exhaust gas 23. The lower limit of the air ratio for second burner heating is 0.7. If the air ratio for second burner heating is less than 0.7, the combustion for second burner heating becomes unstable.

[0053] Although the exhaust gas 22 heated by the second burner may contain both nitrogen oxides and unburned ammonia, by setting the air ratio for the second burner heating lower than that for the first burner heating, the exhaust gas 22 contains more unburned ammonia than the exhaust gas 21. Furthermore, by setting the air ratio for the second burner heating to 0.7 or higher but lower than 0.9, the concentration of unburned ammonia contained in the exhaust gas 22 can be set to 10 to 24,000 ppm. The concentration of unburned ammonia contained in the exhaust gas 22 increases as the air ratio for the second burner heating decreases, reaching approximately 1,200 ppm at an air ratio of 0.85 and approximately 6,400 ppm at an air ratio of 0.8. In this case, although the exhaust gas 22 also contains nitrogen oxides, the concentration is 400 ppm or less and decreases to approximately 15 ppm at an air ratio of 0.85. In other words, a relatively large amount of unburned ammonia can be contained in the exhaust gas 22 heated by the second burner.

[0054] When a flame is injected into the heating furnace by the first burner heating, exhaust gas 21 diffuses within the heating furnace. At this time, as shown in FIG. 3, a gas flow of combustion gas (exhaust gas) is generated within the heating furnace. The exhaust gas 21 moves along the gas flow within the heating furnace toward the second burner equipment 3. Similarly, when a flame is injected into the heating furnace by the second burner heating, exhaust gas 22 generated by the second burner heating also moves along the gas flow within the heating furnace. As a result, exhaust gas 21 containing a relatively large amount of nitrogen oxides and exhaust gas 22 containing a relatively large amount of unburned ammonia are mixed within the heating furnace, generating mixed exhaust gas 23 containing both nitrogen oxides and unburned ammonia. The balance between the amounts of nitrogen oxides and unburned ammonia contained in mixed exhaust gas 23 can be changed by adjusting the air ratio for heating the first burner and the air ratio for heating the second burner. The ratio between the flow rate of first fuel gas 5 used for heating the first burner and the flow rate of second fuel gas 6 used for heating the second burner can also be adjusted by adjusting the settings.

[0055] In this embodiment, air 13 is injected into a mixed exhaust gas 23 containing both nitrogen oxides and unburned ammonia using an air injection system 4. This is based on the finding that the reduction reaction of nitrogen oxides by ammonia is promoted by the presence of a certain amount of oxygen. That is, by injecting air 13 toward mixed exhaust gas 23 containing both nitrogen oxides and ammonia, the oxygen contained in air 13 promotes the reduction reaction of nitrogen oxides by ammonia, thereby reducing the nitrogen oxides and ammonia in mixed exhaust gas 23. The gas injected using air injection equipment 4 may be any gas containing oxygen, and modified air may be injected by removing nitrogen from the air or adding pure oxygen.

[0056] 4 is a schematic diagram illustrating the chemical reactions that occur when air is injected into mixed exhaust gas 23. Exhaust gas 21 heated by the first burner contains more nitrogen oxides, which are produced by the combustion of ammonia, than unburned ammonia. Exhaust gas 22 heated by the second burner contains more ammonia, which is ammonia gas contained in the fuel gas that remains unburned, than nitrogen oxides. Mixed exhaust gas 23 is a mixture of these nitrogen oxides and unburned ammonia, and oxygen is injected into the mixed exhaust gas.

[0057] This promotes the following reaction: Ammonia (NH3) is oxidized by oxygen to generate NH radicals and HO2 radicals. Meanwhile, the nitrogen oxides contained in the mixed exhaust gas 23 are mainly nitric oxide (NO), which is reduced by the NH radicals to generate nitrogen and OH radicals. In this way, the nitrogen oxides in the mixed exhaust gas 23 are reduced. On the other hand, oxygen contained in the air 13 injected from the air injection equipment 4 decomposes the ammonia while the mixed exhaust gas 23 contains unburned ammonia, generating NH radicals. In other words, if there is a sufficient amount of oxygen injected into the mixed exhaust gas 23, the unburned ammonia will be decomposed. Also, if there are a sufficient number of NH radicals generated, it is possible to reduce the nitrogen oxides in the mixed exhaust gas 23. As a result, it is possible to reduce both the nitrogen oxides and ammonia in the mixed exhaust gas 23.

[0058] As described above, in this embodiment, nitrogen oxides and unburned ammonia can be effectively decomposed by injecting air into the mixed exhaust gas of the exhaust gas heated by the first burner and the exhaust gas heated by the second burner. This prevents nitrogen oxides and unburned ammonia from being discharged outside the heating furnace 1. In contrast, the technology disclosed in Patent Document 2 pre-sets the air ratio for burning ammonia, making it difficult to allow nitrogen oxides and ammonia to coexist. Even if nitrogen oxides and ammonia coexist, it is difficult to adjust the balance between them. Therefore, even if an additional air supply unit is provided downstream of the burner in the flow direction of the combustion gas in the furnace to supply oxygen, the reduction reaction of nitrogen oxides by ammonia does not proceed efficiently. Therefore, a certain space called a reducing atmosphere region is required to promote the reduction reaction of nitrogen oxides by ammonia. On the other hand, according to the above embodiment, the burners are heated so that the air ratio of the first burner heating and the air ratio of the second burner heating have a predetermined relationship, so that nitrogen oxides and unburned ammonia can coexist in a balanced manner, and the reduction reaction of nitrogen oxides by ammonia can proceed efficiently. In this case, the gas temperature of the mixed exhaust gas 23 obtained by mixing the exhaust gas 21 heated by the first burner and the exhaust gas 22 heated by the second burner is preferably 700 to 1450°C, because this generates NH radicals and promotes the reduction reaction of nitrogen oxides.

[0059] It is preferable that air 13 be injected into mixed exhaust gas 23, which is obtained by mixing exhaust gas 21 heated by the first burner with exhaust gas 22 heated by the second burner. In other words, it is preferable to generate exhaust gas 21 heated by the first burner first, and then mix exhaust gas 22 heated by the second burner with generated exhaust gas 21. In both of the burner systems shown in Figures 3 and 5, second burner heating system 3 is disposed downstream of first burner system 2 with respect to the gas flow of combustion gas in the heating furnace.

[0060] In contrast, Figure 6 shows an example in which the second burner heating equipment 3 is arranged upstream of the first burner equipment 2. In this case, exhaust gas 22 containing a relatively large amount of unburned ammonia is generated from the second burner equipment 3 upstream of the combustion gas flow. However, as the exhaust gas 22 approaches the position of the first burner equipment 2 along the combustion gas flow, it may approach the area of ​​the flame injected from the first burner equipment 2. In particular, when the combustion gas flow is fast, the exhaust gas 22 from the second burner equipment 3 moves downstream at a position close to the furnace wall. In this case, some of the unburned ammonia contained in the exhaust gas 22 is burned by the flame from the first burner equipment 2, reducing the amount of unburned ammonia contained in the exhaust gas 22 and causing some to become nitrogen oxides. As a result, the amount of unburned ammonia contained in the mixed exhaust gas 23 formed downstream of the first burner equipment 2 decreases, which may inhibit the reduction reaction of nitrogen oxides by ammonia.

[0061] As described above, the exhaust gas 21 heated by the first burner is mixed with the exhaust gas 22 heated by the second burner to form a mixed exhaust gas 23, to which air is injected. Therefore, in the heating furnace 1, first burner heating, second burner heating, and air injection are performed from the upstream side of the gas flow along the gas flow inside the heating furnace. [Example]

[0062] The effects of this embodiment will be specifically described below based on examples, but the present invention is not limited to these examples. As an embodiment of the present invention, an example will be described in which exhaust gas was collected downstream of the gas flow of combustion gas using the burner equipment shown in Figure 3 and the concentrations of nitrogen oxides and unburned ammonia contained in the exhaust gas were measured.

[0063] The burner equipment was arranged with the first burner equipment and the second burner equipment placed from the upstream side of the gas flow F of the combustion gas (flow occurring from left to right in Figure 3). An air injection equipment was installed downstream of the second burner equipment along the gas flow.

[0064] A mixed gas of ammonia and methane (CH4) was used as the fuel gas for the first burner equipment and the second burner equipment. In Figure 3, ammonia was supplied from ammonia gas supply systems 25 and 26 to mixing sections 16 and 17, and methane was sent from coal gas supply systems 27 and 28 to mixing sections 16 and 17 to generate a mixed gas of ammonia and methane, which was supplied to the burner nozzles as first fuel gas 5 and second fuel gas 6. However, flow control valves were provided in the ammonia gas supply systems 25 and 26 and the coal gas supply systems 27 and 28 to adjust the mixing ratio of the mixed gases.Furthermore, flow control valves were also provided in the fuel air supply systems 18 and 19, so that the air ratio of the first fuel gas 5 and the second fuel gas 6 to the theoretical air amount could be adjusted. On the other hand, the air injection equipment 4 is configured to inject air containing oxygen into the mixed exhaust gas of the exhaust gas discharged from the first burner equipment and the exhaust gas discharged from the second burner. Also, the air supply system 29 is provided with a flow rate adjustment valve, so that it is possible to change whether or not air is injected into the mixed exhaust gas (ON / OFF).

[0065] The first and second burner equipment are capable of outputting a rated heat capacity of 800,000 kcal / hr. The first and second burner equipment are located 2 m apart in the direction of the combustion gas flow, with air injection equipment located 2 m further downstream.

[0066] The flow rates of ammonia and methane supplied to the first and second burner equipment are set at 79 Nm3 when the calorific value ratio of ammonia to methane is 40% and 60%, respectively. 3 / hr, methane flow rate 51Nm 3 When methane was used alone without using it as a fuel gas for ammonia, the flow rate of methane was 84 Nm 3 The flow rate of the air injected from the air injection equipment was 0.1 Nm 3 / hr. In this example, combustion experiments were conducted by changing the mixture ratio and air ratio of the mixed gas in the first burner heating equipment and the second burner heating equipment, and exhaust gas was sampled downstream of the air injection equipment 4 along the gas flow F of the combustion gas. The concentrations of nitrogen oxides (NOx), unburned ammonia (NH3), and carbon dioxide (CO2) contained in the exhaust gas were then measured.

[0067] The examples of the invention and comparative examples are summarized in Table 1. The carbon dioxide (CO2) emissions in the exhaust gas are shown in the table as a ratio under each condition, with the conventional example (production No. 3), which does not use ammonia as fuel gas, set as the reference (1.0).

[0068] Since this example is a combustion experiment using a small number of burner equipment, the conditions are such that nitrogen oxides and unburned ammonia are not emitted as much as in a case where a large number of burner equipment is installed, such as in a heating furnace. Therefore, the standard values ​​for nitrogen oxide concentration and unburned ammonia concentration were set stricter than those for a normal heating furnace, with the standard value for nitrogen oxide concentration set at 100 ppm and the standard value for unburned ammonia concentration set at 20 ppm. The test was judged as failing if either the nitrogen oxide concentration or the unburned ammonia concentration exceeded the standard value, and passing if both were below the standard value.

[0069] The conventional example (production No. 3) is an example in which ammonia is not used as fuel gas for heating the first and second burners. In this case, emissions of nitrogen oxides and unburned ammonia are suppressed. However, like conventional burner equipment, there is the problem of high carbon dioxide emissions.

[0070] In the comparative example (production No. 4), a mixed gas of ammonia and methane was used only for heating by the second burner, but air was not injected from the air injection equipment 4. By using ammonia as the fuel gas, the concentration of carbon dioxide was reduced compared to the conventional example, but the amount of nitrogen oxides and unburned ammonia emissions was high. In the comparative example (production No. 5), a mixed gas of ammonia and methane was used only for heating with the first burner, but air injection from the air injection equipment 4 was not performed. In the comparative example (production No. 5), the exhaust gas heated with the second burner did not contain unburned ammonia, so the nitrogen oxides contained in the exhaust gas generated by heating with the first burner were not reduced. Furthermore, although the exhaust gas heated with the first burner may contain a small amount of unburned ammonia, the unburned ammonia was oxidized by heating with the second burner, promoting the generation of nitrogen oxides. Therefore, although unburned ammonia was not detected in the exhaust gas, the concentration of nitrogen oxides increased.

[0071] In the comparative example (production No. 6), a mixed gas of ammonia and methane was burned in both the first burner heating and the second burner heating, but air was not injected from the air injection equipment 4. In this case, oxygen was not supplied to the mixed exhaust gas heated by the first burner and the second burner heating, so the reduction reaction of nitrogen oxides by unburned ammonia was not promoted, resulting in both nitrogen oxides and unburned ammonia exceeding the standard values.

[0072] In the comparative example (production No. 7), a mixed gas of ammonia and methane was burned in both the first burner heating and the second burner heating, and air was injected from the air injection equipment 4. However, because the air ratio in the first burner heating was greater than 1.0, it is believed that a large amount of nitrogen oxides was produced in the exhaust gas heated by the first burner. Therefore, even though unburned ammonia was produced in the exhaust gas heated by the second burner, the concentration of nitrogen oxides in the mixed exhaust gas was high, so it is believed that nitrogen oxides remained in the exhaust gas.

[0073] In contrast, in the invention example (production No. 1), a mixed gas of ammonia and methane is burned in both the first burner heating and the second burner heating, with the air ratio in the first burner heating being in the range of 0.9 to 1.0, and the air ratio in the second burner heating being lower than the air ratio in the first burner heating. Furthermore, air is injected by air injection equipment 4 toward the mixed exhaust gas of the exhaust gas heated by the first burner and the exhaust gas heated by the second burner. This significantly reduces the amount of carbon dioxide contained in the exhaust gas compared to the conventional example, and also reduces the concentrations of nitrogen oxides and unburned ammonia contained in the exhaust gas. Furthermore, in the invention example (production No. 2), by setting the air ratio in the second burner heating to less than 0.9, it was possible to reduce the concentration of nitrogen oxides while maintaining the same concentration of unburned ammonia as in invention example 1.

[0074] [Table 1] [Explanation of symbols]

[0075] 1 Furnace B burner F Combustion gas flow S steel material S1 Steel tip S2 Steel tail end 2. First burner equipment 3. Second burner equipment 4. Air injection equipment 5. First fuel gas 6 Second fuel gas 7. First burner nozzle 8. Second burner nozzle 9 Air injection nozzle 10. Ammonia gas 11 Coal Gas 12 Combustion air 13. Air 14. First fuel gas supply system 15 Second fuel gas supply system 16, 17 Mixing section 18, 19 Combustion air supply system 21, 22 Exhaust gas 23 Mixed exhaust gas 24 Air Injection 25, 26 Ammonia gas supply system 27, 28 Coal gas supply system 29 Air supply system 30 Charging side 31 Unloading section 32 Moving Skid 33 Fixed Skid 34 Flue 35 Furnace wall 36 Inside the furnace 40 Air ratio adjustment unit 41 Air Injection 42 Control Unit 44 Burner equipment 45 Fuel Gas 50 NOx concentration meter 51 Ammonia concentration meter 52 Flow meter 53 Flow control valve 54 First air ratio adjustment section 55 Second air ratio adjustment section 100 Steel material movement direction

Claims

1. a first burner heating step of burner-heating a first fuel gas containing ammonia with combustion air such that an air ratio of the first fuel gas to a theoretical air amount is 0.9 to 1.0; a second burner heating step of burner-heating a second fuel gas containing ammonia with combustion air having an air ratio relative to a theoretical air amount of the second fuel gas that is lower than an air ratio relative to a theoretical air amount of the first fuel gas; an air injection step of injecting air; Including, A method for operating a heating furnace, comprising the steps of: a first burner heating step, a second burner heating step, and an air injection step, in that order from the upstream side along the gas flow of combustion gas.

2. 2. The method for operating a heating furnace according to claim 1, wherein the air injection step injects air into a mixed exhaust gas obtained by mixing the exhaust gas generated in the first burner heating step and the exhaust gas generated in the second burner heating step.

3. 3. The method for operating a heating furnace according to claim 1, wherein in the second burner heating step, an air ratio of the second fuel gas to a theoretical air amount is less than 0.

9.

4. At least one of the first fuel gas and the second fuel gas is a mixed gas of ammonia and coal gas, and burner heating is performed. A method for operating a heating furnace according to claim 1 or 2.

5. At least one of the first fuel gas and the second fuel gas is a mixed gas of ammonia and coal gas, and burner heating is performed.

4. The method for operating a heating furnace according to claim 3.

6. two or more burner facilities that perform burner heating using a fuel gas containing ammonia; an air ratio adjusting unit that adjusts the air ratio of each of the combustion air supplied to the two or more burner devices relative to the theoretical air amount of the fuel gas; a control unit that controls an air ratio of combustion air supplied to at least one of the two or more burner facilities to be different from an air ratio of combustion air supplied to the other burner facilities; an air injection device that injects air into a mixed exhaust gas of exhaust gases discharged from the two or more burner devices; Including, the burner equipment includes a first burner equipment that heats a first fuel gas containing ammonia, the air ratio of which has been adjusted by the air ratio adjusting unit, using combustion air such that the air ratio of the first fuel gas to a theoretical air amount is 0.9 to 1.0; a second burner facility for burner-heating a second fuel gas containing ammonia with combustion air having an air ratio relative to a theoretical air amount of the second fuel gas that is lower than an air ratio relative to a theoretical air amount of the first fuel gas; and the first burner equipment, the second burner equipment, and the air injection equipment are arranged in this order from the upstream side of the gas flow along the gas flow inside the heating furnace; Heating furnace.

7. the heating furnace has an opening through which the mixed exhaust gas is discharged, The air injection equipment is arranged at a position closer to the opening than the first burner equipment and the second burner equipment. The heating furnace according to claim 6.

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