Operation method for heating furnace and heating furnace

Abstract

Provided are an operation method for a heating furnace and a heating furnace capable of using ammonia as fuel for combustion and reducing a discharge amount of nitrogen oxides and unburned ammonia. In the operation method for a heating furnace in which a material to be heated is heated while being conveyed from a charging unit to a carry-out unit, the inside of the heating furnace is divided into a charging region on the charging unit side, a carry-out region on the carry-out unit side, and a central region between the charging region and the carry-out region. In the charging region, the central region, and the carry-out region, burner heating for burning ammonia-containing fuel gas is performed, and exhaust gas is discharged from a flue installed at a position close to the charging unit in the heating furnace. In the burner heating in the carry-out region, the average air ratio with respect to the theoretical air amount for the fuel gas is set to be larger than 1.0 and not more than 1.1, and in the burner heating in the central region, the average air ratio with respect to the theoretical air amount for the fuel gas is made smaller than the average air ratio with respect to the theoretical air amount for the fuel gas in the carry-out region.

Description

Heating furnace operation method and heating furnace

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

[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 humans and contribute to photochemical smog and acid rain, and are therefore subject to legal emissions restrictions.

[0004] Therefore, various heating technologies have been proposed to solve these problems. For example, Patent Document 1 discloses a boiler that includes a combustion device capable of burning ammonia as fuel in a furnace, a flue for guiding combustion gas generated by combustion of the fuel, and an injection unit 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 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 can be used as a reducing agent to reduce nitrogen oxides.

[0005] Furthermore, Patent Document 2 discloses a boiler that includes 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 introduced at a position upstream of the additional air supply unit, nitrogen oxides generated by combustion of ammonia fuel in a reducing atmosphere region in the furnace can be reduced to N ２ This is said to be able to suppress the production of nitrogen oxides.

[0006] JP 2019-086191 A JP 2018-076985 A

[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 a door for loading and unloading the materials. In this case, opening the door of the heating furnace releases toxic unburned ammonia (also known as "unburned ammonia") outside the furnace, potentially deteriorating the environment outside the furnace.

[0009] Patent Document 2 also targets combustion equipment such as boilers, and reduces nitrogen oxides with ammonia in a reducing atmosphere region within the furnace. Patent Document 2 discloses that, 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 for complete combustion of fossil fuel. The technology disclosed in Patent Document 2 requires a certain amount of space within the furnace and a certain reaction time to carry out the reduction reaction of nitrogen oxides. On the other hand, heating furnaces for heating objects such as steel require not only a combustion device (e.g., a burner) but also a space for placing and charging the objects. In contrast, furnaces such as boilers require only the space required for the combustion reaction between fuel and combustion air. Therefore, when the technology disclosed in Patent Document 2 is applied to a heating furnace for heating objects, the space designated as the reducing atmosphere region is enlarged, resulting in an uneven progress of the reduction reaction of nitrogen oxides 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 (around 0.8 as an air ratio). Changes in the operating conditions in the heating furnace also fluctuate the air ratio, making 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 of the prior art, and an object of the present invention is to provide a method for operating a heating furnace that uses ammonia as a combustion fuel and is capable of reducing emissions of nitrogen oxides and unburned ammonia. Another object of the present invention is to provide a heating furnace that uses ammonia as a combustion fuel and is capable of reducing emissions of nitrogen oxides and unburned ammonia.

[0012] The method of operating a heating furnace according to the present invention, which advantageously solves the above problems, is configured as follows: [1] A method of operating a heating furnace in which material to be heated is heated while being transported from a charging section to an unloading section, the method comprising: dividing the interior of the heating furnace into a charging region on the charging section side, an unloading region on the unloading section side, and a central region sandwiched between the charging region and the unloading region; in the charging region, the central region, and the unloading region, burner heating is performed by burning a fuel gas containing ammonia, and exhaust gas is discharged from a flue installed near the charging section inside the heating furnace; in the burner heating in the unloading region, the average air ratio of the fuel gas to the theoretical air volume is set to be greater than 1.0 and not greater than 1.1; and in the burner heating in the central region, the average air ratio of the fuel gas to the theoretical air volume is set to be smaller than the average air ratio of the fuel gas to the theoretical air volume in the unloading region. [2] A method for operating a heating furnace according to the above [1], wherein the burner heating in the central region sets the average air ratio of the fuel gas to the theoretical air volume to 1.0 or less. [3] A method for operating a heating furnace according to the above [1] or [2], wherein the burner heating in the discharge region sets the average air ratio of the fuel gas to the theoretical air volume in accordance with the opening operation of the door of the discharge section. [4] A method for operating a heating furnace according to any one of the above [1] to [3], wherein the burner heating in the charging region sets the average air ratio of the fuel gas to the theoretical air volume to be greater than 1.0 and less than or equal to 1.1, and wherein the burner heating in the central region sets the average air ratio of the fuel gas to the theoretical air volume to be smaller than the average air ratio of the fuel gas to the theoretical air volume in the charging region. [5] A method for operating a heating furnace according to the above [4], wherein the burner heating in the charging region sets the average air ratio of the fuel gas to the theoretical air volume in accordance with the opening operation of the door of the charging section.

[0013] A heating furnace according to the present invention that advantageously solves the above problems is configured as follows: [6] A heating furnace that heats material to be heated while transporting it from a charging section to an unloading section, the interior of the heating furnace being divided into a charging area on the charging section side, an unloading area on the unloading section side, and a central area sandwiched between the charging area and the unloading area, a flue for discharging exhaust gas is provided at a position within the heating furnace close to the charging section, a first burner unit is arranged in the charging area, a second burner unit in the central area, and a third burner unit in the unloading area, and the heating furnace is equipped with a fuel gas supply unit that supplies fuel gas containing ammonia to the first burner unit, the second burner unit, and the third burner unit, and an air ratio control unit that controls the air ratio of the fuel gas supplied to the first burner unit, the second burner unit, and the third burner unit relative to a theoretical air amount.

[0014] 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.

[0015] FIG. 1 is a configuration diagram showing an outline of a heating furnace. FIG. 2 is a schematic cross-sectional view perpendicular to the conveying direction showing an example of the arrangement of burner equipment in a heating furnace. FIG. 3 is a configuration diagram showing an example of the arrangement of burner equipment in a heating furnace according to the present embodiment. (a) is a configuration diagram of an example of burner equipment that supplies a mixed gas of coal gas and ammonia gas as fuel gas, and (b) is a cross-sectional view along a wall surface showing the tip of a burner nozzle. FIG. 4 is a configuration diagram showing an example of the arrangement of an air ratio control unit in a heating furnace according to the present embodiment.

[0016] <Heating Furnace> The heating furnace according to this embodiment will be described below. The heating furnace according to this embodiment heats materials while transporting them from a charging section to an unloading section. The interior of the heating furnace is divided into a charging area on the charging section side, an unloading area on the unloading section side, and a central area sandwiched between the charging and unloading areas. A flue for discharging exhaust gas is provided near the charging section within the heating furnace. A first burner unit is disposed in the charging area, a second burner unit in the central area, and a third burner unit in the unloading area. The heating furnace includes a fuel gas supply unit that supplies ammonia-containing fuel gas to the first, second, and third burner units, and an air ratio control unit that controls the air ratio of the fuel gas supplied to the first, second, and third burner units relative to the theoretical air amount. The heating furnace according to this embodiment includes a burner that burns fuel gas as a heat source for heating, and is a facility in which materials to be heated are charged and heated to a predetermined temperature. The object to be heated is primarily a metal. It 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. Figures 1 to 3 show an example of a heating furnace according to this embodiment, in which the object to be heated is a steel material. For example, a heating furnace used in a hot rolling line for steel material is used to heat a cast slab to a predetermined heating temperature (approximately 1100 to 1300°C).

[0017] The heating furnace 1 shown in FIG. 1 includes a charging section 30 for charging a steel material S, such as a steel slab, which is the object to be heated, and an unloading section 31 for unloading (extracting) the heated steel material S. For example, the steel material S produced on 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 two to eight zones and one to three soaking zones. The interior of the heating furnace 1 generally includes 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.

[0018] In 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, for example, the target temperature of a steel slab when it is extracted from the heating furnace. The steel material S that has reached the target heating temperature passes through the discharge section 31 and is discharged, and then is subjected to hot rolling.

[0019] A plurality of burners B are provided inside the heating furnace 1 along the transport direction TD of the steel material S. The burners B are arranged to heat the inside of the heating furnace 1 by combustion. When the inside of the heating furnace 1 is heated by the burners B, the temperature of the steel material S rises due to radiation from the furnace wall of the heating furnace 1. In addition, a flow of atmospheric gas occurs inside the heating furnace 1, and the steel material S may be heated by convection. Furthermore, the steel material S may be heated by the flame of the burners B coming into direct contact with the steel material S. In any case, the burners B burn fuel gas as a heat source for heating, thereby heating the inside of the heating furnace 1 and raising the temperature of the material to be heated inside the heating furnace 1.

[0020] The interior of the heating furnace 1 is provided with a space for placing and transporting materials to be heated, in addition to the space where the flame is emitted from the burner B. Therefore, compared to boilers and the like which are intended 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, for example, a typical value for a gas turbine of 2 m ３ / MW, pulverized coal boiler 6m ３ / MW, gas and oil boiler 2m ３ In contrast, the heating furnace is 10 to 16 m ３ For example, in a heating furnace used in a hot rolling line for steel, the ３ / MW.

[0021] During operation of the heating furnace 1, the doors of the loading section 30 and the unloading section 31, i.e., the open / close doors, are closed. Therefore, a pressure higher than the atmospheric pressure is generated inside the heating furnace 1. When the steel material S is loaded or unloaded, the corresponding door is temporarily opened. When the door is open, a pressure difference occurs between the pressure inside the heating furnace and the vicinity of the door, so that the combustion gas inside the heating furnace 1 flows from an area of ​​high pressure to an area of ​​low pressure. When the door of the heating furnace 1 is open, the combustion gas often flows in the direction in which the combustion gas is discharged outside the heating furnace 1 through the opening.

[0022] The heating furnace 1 is equipped with a flue 34 for exhausting gas (hereinafter referred to as exhaust gas) generated in the furnace by burner heating. The flue 34 is connected to an exhaust gas treatment device 35 for removing nitrogen oxides and unburned ammonia from the exhaust gas. The exhaust gas treatment device 35 treats the exhaust gas so that the concentrations of nitrogen oxides and unburned ammonia satisfy predetermined emission standards. As a result, even if nitrogen oxides or unburned ammonia are contained in the exhaust gas, the emission of nitrogen oxides and unburned ammonia to the outside of the heating furnace 1 through the flue 34 is suppressed. Note that hereinafter, "the emission of nitrogen oxides and unburned ammonia is suppressed" means that the concentrations of nitrogen oxides and unburned ammonia are reduced to or below upper limits that are preset so as not to exceed the upper limits of legal regulations.

[0023] The flue 34 may be equipped with a heat recovery device (not shown) that recovers sensible heat from the exhaust gas. As shown in Figure 1, the flue 34 is located relatively close to the charging section 30 of the heating furnace 1, which is advantageous in terms of thermal efficiency when using the heat recovered by the heat recovery device to preheat slabs transported to the yard on the charging side of the heating furnace 1.

[0024] 2 is a diagram showing a cross section perpendicular to the conveying direction TD of the heating furnace 1. Inside the heating furnace 1, the burners B are often arranged 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. Also, in order to prevent a temperature difference between the leading end S1 and the trailing end S2 of the steel material S, the burners are often arranged on both sides of the conveying direction TD of the steel material S (the direction into the paper in FIG. 2).

[0025] 3 is a diagram showing the burner arrangement inside the heating furnace 1 of this embodiment. The heating furnace 1 includes a first burner unit 11 arranged in a charging area US in the conveying direction TD of the steel material S, a third burner unit 13 arranged in a discharge area DS in the conveying direction TD of the steel material S, and a second burner unit 12 arranged in a central area CS between the charging area US and the discharge area DS. In this way, the first burner unit 11, the second burner unit 12, and the third burner unit 13 are arranged in this order from upstream in the conveying direction TD of the material to be heated.

[0026] The charging zone US of the heating furnace 1 refers to a section including the burner B located closest to the charging section 30 in the conveying direction TD. When burners B are located at the top and bottom of the heating furnace 1 as shown in FIGS. 1 and 2 , the burner B located closest to the charging section 30 includes both the burner B located at the top closest to the charging section 30 and the burner B located at the bottom closest to the charging section 30. In other words, the charging zone US refers to a section including both the burner B located at the top closest to the charging section 30 and the burner B located at the bottom closest to the charging section 30. However, the charging zone US may include not only the burner B located at the top or bottom closest to the charging section 30, but also one or more burners B located downstream in the conveying direction TD. The burners B located in the charging zone US thus defined are referred to as the first burner section 11.

[0027] The discharge area DS of the heating furnace 1 refers to a section including the burner B located closest to the discharge section 31 in the transport direction TD. When burners B are located in the upper and lower parts of the heating furnace 1, the burner B located closest to the discharge section 31 includes both the burner B located in the upper part that is closest to the discharge section 31 and the burner B located in the lower part that is closest to the discharge section 31. In other words, the discharge area DS refers to a section including both the burner B located in the upper part that is closest to the discharge section 31 and the burner B located in the lower part that is closest to the discharge section 31. However, the discharge area DS may include not only the burner B located in the upper or lower part that is closest to the discharge section 31, but also one or more burners B located consecutively upstream in the transport direction TD. The burners B located in the discharge area DS thus defined are referred to as the third burner section 13.

[0028] The section between the loading area US and the unloading area DS is called a central area CS, and the burner B arranged in the central area CS is called a second burner section 12.

[0029] The heating furnace 1 of this embodiment includes a fuel gas supply unit that supplies fuel gas containing ammonia to the first burner unit 11, the second burner unit 12, and the third burner unit 13, and an air ratio control unit that controls the air ratio of the fuel gas supplied to the first burner unit 11, the second burner unit 12, and the third burner unit 13 relative to the theoretical air amount. The heating furnace 1 is equipped with a control computer 45 for controlling the operating state of the heating furnace. The control computer 45 sets the operating conditions of the burner B arranged in the heating furnace 1 so as to heat the steel material S to a predetermined target heating temperature. The control computer 45 controls the operations of charging the steel material S into the heating furnace 1, transporting it within the heating furnace 1, and unloading it from the heating furnace 1.

[0030] <Burner Equipment> The burner equipment applied to the first burner section 11, the second burner section 12, and the third burner section 13 will be described with reference to Fig. 4. The burner equipment 2 shown in Fig. 4 can be applied to any of the first burner section 11, the second burner section 12, and the third burner section 13.

[0031] The burner equipment 2 performs burner heating by injecting a flame into the furnace using a fuel gas 5 containing ammonia as the fuel gas and combustion air 8. The burner equipment 2 includes a burner nozzle 17 for injecting the flame into the furnace, a fuel gas supply system 14 that supplies the fuel gas 5 to the burner nozzle 17, and a combustion air supply system 15 that supplies the combustion air 8 to the burner nozzle 17. The burner equipment 2 includes an air ratio control unit 40 that controls the air ratio (sometimes simply referred to as the air ratio) of the fuel gas 5 supplied to the burner nozzle 17 relative to the theoretical air amount.

[0032] The fuel gas supply system 14 is a pipe that supplies a fuel gas containing ammonia to the burner nozzle 17. In this embodiment, the fuel gas supply system 14 functions as a fuel gas supply unit that supplies a fuel gas containing ammonia. The combustion air supply system 15 is a pipe that supplies combustion air 8 to the burner nozzle 17.

[0033] The burner nozzle 17 is, for example, a double-pipe nozzle, and fuel gas 5 is injected from the inside toward the furnace interior, while combustion air 8 is supplied from the outside. As a result, the fuel gas 5 and the combustion air 8 mix to form a combustible mixture, and a flame is injected from the tip of the burner nozzle 17 toward the inside of the heating furnace 1. Note that a burner of the type in which the fuel gas 5 discharge port and the combustion air 8 discharge port are different, as shown in the front view of Figure 4(b), is called a diffusion combustion type burner.

[0034] The fuel gas 5 uses a fuel gas containing ammonia. Hereinafter, the ammonia used in the fuel gas 5 refers to ammonia gas in a gaseous state at room temperature. The fuel gas 5 may be ammonia gas alone, or a mixed gas obtained by mixing ammonia gas with other fuels. The fuel gas 5 supplied to the first burner section 11, the second burner section 12, and the third burner section 13 may have different or the same ammonia gas mixture ratios. Furthermore, the other fuels constituting the mixed gas may be different or the same for the first burner section 11, the second burner section 12, and the third burner section 13.

[0035] 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 as the fuel gas 5 supplied to the first burner section 11, the second burner section 12, and the third burner section 13. The mixing ratio in the mixed gas may be the volume ratio of ammonia gas to other fuel, or may be the mass ratio or calorific value ratio. The mixing ratio shall be defined by any of these.

[0036] Ammonia gas is a flame-retardant fuel, and is more difficult to ignite and burns slower than general fuels. To improve combustion stability, it is recommended to use a mixed gas in which ammonia gas is mixed with other fuels. The fuel to be mixed with ammonia gas is preferably one or more gases selected from coal gas and hydrocarbon gases.

[0037] Coal gas is a gas obtained from coal. Coal gas preferably includes any of coke oven gas, blast furnace gas, converter gas, and electric furnace gas. These are by-product gases generated in steelworks and have the effect of stabilizing the combustion of ammonia gas. Blast furnace gas is a by-product gas generated when iron ore is reduced in a blast furnace to produce pig iron. Coke oven gas is a by-product gas generated by high-temperature carbonization of coal to produce coke. Converter gas is a by-product gas generated in the steelmaking process using a converter. Electric furnace gas is a gas generated by the incomplete combustion of auxiliary fuel (recarburizer) in an electric furnace. The coal gas constituting the mixed gas may be a gas obtained by appropriately mixing blast furnace gas, coke oven gas, and converter gas, known as M gas. By mixing coal gases with different calorific values, the amount of heat required to heat the heated object can be adjusted, enabling stable operation of the heating furnace.

[0038] Hydrocarbon gas is a fuel made by gasifying hydrocarbons, such as methane, ethane, ethylene, acetylene, and propane.

[0039] 4 shows an example in which a mixed gas of ammonia gas 6 and coal gas 7 is used as the fuel gas 5 of the burner equipment 2. The fuel gas supply system 14 is connected to an ammonia gas supply system 18 and a coal gas supply system 19, and the ammonia gas 6 and the coal gas 7 are mixed in a mixing section 16 and supplied to a burner nozzle 17. The ammonia gas supply system 18 is supplied with ammonia gas 6 from, for example, a tank that stores ammonia, and sends the ammonia gas 6 to the burner nozzle 17. The coal gas supply system 19 is supplied with coal gas 7 from, for example, a tank that stores coal gas, and sends the coal gas 7 to the burner nozzle 17. It is preferable that the ammonia gas supply system 18 and the coal gas supply system 19 are provided with flow rate adjustment valves 20 that adjust the amounts of the respective gases supplied to the mixing section 16, and a flow meter 21 that measures the supply flow rates. This makes it possible to adjust the mixing ratio of the ammonia gas 6 and the coal gas 7 contained in the mixed gas. The flow meter 21 may estimate the flow rates of the ammonia gas 6 and the coal gas 7 by measuring the pressure of the gas transported by the ammonia gas supply system 18 and the coal gas supply system 19. This is because the gas flow rates can be easily estimated by using a pressure meter.

[0040] The mixing section 16 refers to a portion where the supply pipe of the coal gas supply system 19 and the supply pipe of the ammonia gas supply system 18 join together. Ammonia gas 6 and coal gas 7 are supplied from their respective supply pipes and joined together, thereby allowing mixing to be performed without providing a special stirring mechanism. The mixing section 16 may be configured as a fixed space at the portion where these supply pipes join together. However, the mixing section 16 may be equipped with a static mixing device such as a static mixer, or a dynamic mixer with a stirring function. This is preferable in that a mixed gas in which coal gas and ammonia gas are mixed more uniformly is generated.

[0041] A flow rate control valve 20 for adjusting the flow rate of the combustion air 8 supplied to the burner nozzle 17 and a flow meter 21 for measuring the supply flow rate may be provided midway in the combustion air supply system 15 of the burner equipment 2. This adjusts the amount of combustion air in the burner equipment 2, making it possible to adjust the air ratio in burner heating of the burner equipment 2. The flow rate of the flow meter 21 of the combustion air supply system 15 may also be estimated by measuring the pressure of the combustion air being transported.

[0042] The air ratio control unit 40 controls the air ratio of the fuel gas 5 in the burner equipment 2 relative to the theoretical air amount. The air ratio control unit 40 has a function of adjusting the air ratio of the combustion air 8 to the fuel gas 5 for each burner equipment 2. The air ratio control unit 40 measures the flow rate of the fuel gas 5 supplied to the burner nozzle 17 using flow meters 21 provided in the ammonia gas supply system 18 and the coal gas supply system 19, and calculates the theoretical air amount for completely combusting the fuel gas 5 from the measured flow rate of the fuel gas 5 and the fuel composition of the fuel gas 5. The air ratio control unit 40 then adjusts the aperture of the flow rate adjustment valve 20 arranged in the combustion air supply system 15 so that the air ratio becomes the air ratio set in the control computer 45, thereby controlling the air ratio for burner heating in the burner equipment 2.

[0043] <Arrangement of Burner Equipment in a Heating Furnace> The arrangement of the burner equipment in a heating furnace will be described using Figure 5. The heating furnace of this embodiment is arranged, from upstream to downstream, in the conveying direction TD of the material to be heated. The heating furnace includes a fuel gas supply unit that supplies ammonia-containing fuel gas to the first burner unit, the second burner unit, and the third burner unit, and an air ratio control unit that controls the air ratio of the fuel gas supplied to the first burner unit, the second burner unit, and the third burner unit relative to the theoretical air amount. That is, the heating furnace includes a first burner unit 11 arranged in a charging region US in the conveying direction TD of the steel material S, a second burner unit 12 arranged in a central region CS between the charging region US and the unloading region DS, and a third burner unit 13 arranged in the unloading region DS in the conveying direction TD of the steel material S. The heating furnace 1 of this embodiment further includes a fuel gas supply unit that supplies fuel gas 5 containing ammonia to the first burner unit 11, the second burner unit 12, and the third burner unit 13, and an air ratio control unit that controls the air ratio of the fuel gas 5 supplied to the first burner unit 11, the second burner unit 12, and the third burner unit 13 relative to the theoretical air amount.

[0044] In the example shown in FIG. 5 , a section including the burner equipment located closest to the charging section 30 in the conveying direction TD is defined as the charging zone US, and the burner equipment 11U and 11L located in the charging zone US constitute the first burner section. Furthermore, a section including the burner equipment located closest to the unloading section 31 in the conveying direction TD and adjacent to the burner equipment located upstream in the conveying direction TD is defined as the unloading zone DS. Thus, the burner equipment 13U1, 13U2, 13L1, and 13L2 located in the unloading zone DS constitute the third burner section. A central zone CS is defined as a section between the charging zone US and the unloading zone DS, and the burner equipment 12U1, 12U2, 12L1, and 12L2 located in the central zone CS constitute the second burner section. The symbol U attached to the reference numerals of each burner section indicates the upper side, and the symbol L indicates the lower side.

[0045] Each of the burner equipment of the first burner unit (11U, 11L), second burner unit (12U1, 12U2, 12L1, 12L2) and third burner unit (13U1, 13U2, 13L1, 13L2) is provided with a fuel gas supply unit that supplies fuel gas 5 containing ammonia, and an air ratio control unit that controls the air ratio. An air ratio control unit may be provided for each of the burner equipment constituting the first burner unit, second burner unit and third burner unit. However, as shown in Figure 5, an air ratio control unit may be provided for each of the first burner unit, the second burner unit, and the third burner unit, such as an air ratio control unit 41 that controls the air ratio of the first burner unit (11U, 11L), an air ratio control unit 42 that controls the air ratio of the second burner unit (12U1, 12U2, 12L1, 12L2), and an air ratio control unit 43 that controls the air ratio of the third burner unit (13U1, 13U2, 13L1, 13L2).

[0046] As a result, the heating furnace 1 can set the air ratio of the fuel gas to the theoretical air volume during burner heating at each of the first burner section 11 located in the loading area US, the second burner section 12 located in the central area CS, and the third burner section 13 located in the unloading area DS.

[0047] The air ratio is defined as the ratio of the amount of combustion air supplied to the burner nozzle to the theoretical amount of air required for complete combustion of the fuel gas. That is, when the air ratio is 1.0, the fuel gas 5 theoretically consumes all of the oxygen contained in the combustion air 8, thereby achieving complete combustion. This state is called a "complete combustion state." When the air ratio is less than 1.0, the oxygen contained in the combustion air 8 alone is theoretically insufficient to burn all of the components that make up the fuel gas 5, leaving some unburned fuel gas. This state is called an "air shortage state." When the air ratio is greater than 1.0, the fuel gas 5 theoretically consumes some of the oxygen contained in the combustion air 8 to achieve complete combustion, but some of the oxygen contained in the combustion air 8 remains. This state is called an "excess air state."

[0048] In the heating furnace 1, the air ratios in the first burner section 11 and the third burner section 13 can be set independently, allowing the combustion state of the fuel gas to be changed in the charging zone US, the central zone CS, and the discharge zone DS of the heating furnace 1. For example, if an air shortage occurs in one of the sections (first section) of the charging zone US, the central zone CS, and the discharge zone DS in the heating furnace 1, unburned ammonia will be generated in that section. However, if an air excess state is achieved in the other sections, the unburned ammonia generated in the first section will be burned in the other section, thereby reducing the amount of unburned ammonia discharged from the heating furnace 1 to the outside. Furthermore, if an air excess state occurs in one of the sections (first section) of the charging zone US, the central zone CS, and the discharge zone DS in the heating furnace 1, nitrogen oxides will be more likely to be generated in the first section due to the combustion of ammonia contained in the fuel gas 5. However, even if nitrogen oxides are generated in one compartment due to the combustion of ammonia contained in the fuel gas 5, if an air shortage state is realized in another compartment, unburned ammonia will be generated due to the air shortage state, which has the effect of reducing the nitrogen oxides generated in the one compartment. As a result, the nitrogen oxides are reduced in the other compartment, and it is possible to reduce the nitrogen oxides emitted outside the heating furnace 1.

[0049] In the heating furnace according to this embodiment, the combustion state of the fuel gas can be changed between the charging zone US, the central zone CS, and the discharge zone DS. Therefore, unburned ammonia and nitrogen oxides generated in some sections can be rendered harmless in other sections. In other words, in burner heating, in which multiple burner equipment is burned under a single combustion condition, it is necessary to control the air ratio within a narrow range, making it difficult to reduce both nitrogen oxides and unburned ammonia. In contrast, the heating furnace according to this embodiment can achieve different combustion states in multiple sections. Therefore, nitrogen oxides and unburned ammonia generated in some sections can be reduced or combusted in other sections, thereby reducing the emissions of nitrogen oxides and unburned ammonia from the heating furnace 1. This eliminates the need to control the operating conditions of the heating furnace 1 within a narrow range, and effectively reduces the emissions of nitrogen oxides and unburned ammonia from the heating furnace 1 even when operating conditions, such as changes in the heating temperature of the steel material S, change.

[0050] <Method of Operating a Heating Furnace> Next, a method of operating a heating furnace according to this embodiment will be described. This embodiment is a method of operating a heating furnace in which material to be heated is heated while being transported from a charging section to an unloading section. In this embodiment, the interior of the heating furnace is divided into a charging region on the charging section side, an unloading region on the unloading section side, and a central region sandwiched between the charging region and the unloading region. In the charging region, the central region, and the unloading region, a burner is used to heat the material by burning ammonia-containing fuel gas, and exhaust gas is discharged from a flue installed near the charging section inside the heating furnace. The burner heating in the unloading region is performed such that the average air ratio of the fuel gas to the theoretical air volume is greater than 1.0 and equal to or less than 1.1. The burner heating in the central region is performed such that the average air ratio of the fuel gas to the theoretical air volume is smaller than the average air ratio of the fuel gas to the theoretical air volume in the unloading region.

[0051] In addition, the average air ratio of the fuel gas to the theoretical air volume in the charging zone may be set to greater than 1.0 and equal to or less than 1.1, and the average air ratio of the fuel gas to the theoretical air volume in the central zone may be set to be smaller than the air ratio of the fuel gas to the theoretical air volume in the charging zone. Furthermore, the average air ratio of the fuel gas to the theoretical air volume in the central zone may be set to be equal to or less than 1.0. Here, the average air ratio refers to the ratio of the actual air volume to the theoretical air volume of the fuel gas in each zone. In other words, the average air ratio refers to the ratio of the total amount of combustion air supplied in each zone to the total amount of theoretical air volume relative to the total amount of fuel gas supplied in that zone.

[0052] A method of operating the heating furnace will be described with reference to the heating furnace 1 shown in Figure 5. The divisions of the heating furnace 1 into the charging zone US, the central zone CS, and the unloading zone DS are as described above. This embodiment includes a process of heating the steel material S using the first burner unit 11 in the charging zone US, a process of heating the steel material S using the second burner unit 12 in the central zone CS, and a process of heating the steel material S using the third burner unit 13 in the unloading zone DS. The average air ratio in the unloading zone is set to be greater than 1.0 and equal to or less than 1.1, and the average air ratio in the central zone is set to be smaller than the average air ratio in the unloading zone. The average air ratio in each zone is controlled for each zone by air ratio control units 41, 42, and 43.

[0053] Because the average air ratio in the central region CS is smaller than the average air ratio in the discharge region DS, burner heating in the central region CS is in a state of oxygen deficiency compared to the discharge region DS. As a result, unburned ammonia, which is ammonia contained in the fuel gas 5 remaining unburned, is more likely to be generated in the central region CS than in the discharge region DS. In contrast, by making the average air ratio in the discharge region greater than 1.0, an excess air state can be achieved in the discharge region DS. Therefore, even if unburned ammonia is generated in the central region CS, the unburned ammonia passes through the discharge region DS before being discharged from the discharge section 31 to the outside of the heating furnace 1. The unburned ammonia then burns in the discharge region DS, which is in an excess air state. As a result, even if unburned ammonia is generated in the central region CS, it is possible to prevent the generated unburned ammonia from passing through the discharge section 31 and being discharged to the outside of the furnace. However, if the average air ratio in the discharge zone DS exceeds 1.1, the amount of nitrogen oxides produced in the discharge zone DS increases, which may result in an increase in the amount of nitrogen oxides discharged to the outside of the furnace via the discharge section 31. Therefore, the average air ratio in the discharge zone is set to 1.1 or less. From this perspective, it is preferable that the average air ratio in the discharge zone be greater than 1.0 and less than or equal to 1.07.

[0054] If the average air ratio in the discharge area is set to be greater than 1.0, conditions will be created that make it easier for nitrogen oxides to be generated in the discharge area DS. However, when unburned ammonia generated in the central area CS passes through the discharge area DS, the unburned ammonia acts to reduce nitrogen oxides under conditions where excess oxygen is present. Therefore, in the discharge area DS, unburned ammonia is burned and the effect of reducing nitrogen oxides can be expected, thereby further suppressing the emission of nitrogen oxides from the discharge section 31.

[0055] In the heating furnace 1 shown in FIG. 5 , the flue 34 is located near the charging section 30, so that exhaust gas is discharged from the charging section 30 and the flue 34 on the upstream side of the heating furnace 1. On the other hand, exhaust gas is discharged only from the discharge section 31 on the downstream side of the heating furnace 1. Therefore, when comparing the charging section 30 and the discharge section 31, the amount of exhaust gas discharged from the discharge section 31 is greater than the amount of exhaust gas discharged from the charging section 30. The flue 34 is connected to an exhaust gas treatment device (not shown), so the discharge of unburned ammonia and nitrogen oxides from the flue 34 to the outside of the furnace is suppressed. However, the doors of the charging section 30 and the discharge section 31 are temporarily opened to the atmosphere to allow the steel material S to pass through. Therefore, there is a risk that unburned ammonia and nitrogen oxides may be discharged to the outside of the furnace from the charging section 30 or the discharge section 31. The above embodiment can suppress the discharge of unburned ammonia and nitrogen oxides from the discharge section 31, where a large amount of exhaust gas is discharged.

[0056] As an example, the third burner unit 13 in the discharge area has a flow rate of 1083 Nm ３ / hr, flow rate of fuel gas 5 349 Nm ３ / hr (coal gas 200 Nm ３ / hr, ammonia 149 Nm ３ The flow rate of the fuel gas 5 is adjusted appropriately according to the target temperature value inside the heating furnace 1.

[0057] The ratio V2 / V3 of the total flow rate V3 of the fuel gas used by all the burner equipment constituting the third burner section 13 of the heating furnace 1 to the total flow rate V2 of the fuel gas used by all the burner equipment constituting the second burner section 12 is preferably 0.1 to 30.0. If the ratio V2 / V3 is less than 0.1, the amount of oxygen supplied from the third burner section becomes greater than the amount of unburned ammonia produced by the second burner section 12, and nitrogen oxides are more likely to be produced by combustion in the third burner section 13, making it easier for nitrogen oxides to be discharged outside the furnace. On the other hand, if the ratio V2 / V3 exceeds 30.0, the amount of unburned ammonia produced by the second burner section becomes greater than the amount of oxygen supplied from the third burner section, which may reduce the effectiveness of burning the unburned ammonia.

[0058] From the same viewpoint, it is preferable that the average air ratio in the charging zone US is greater than 1.0 and not greater than 1.1, and that the average air ratio in the central zone CS is smaller than the average air ratio in the charging zone US.

[0059] If the average air ratio in the central region is smaller than the average air ratio in the charging region, the burner heating in the central region CS will be in an oxygen-deficient state compared to the charging region US. As a result, unburned ammonia is more likely to be generated in the central region CS than in the charging region US. On the other hand, by increasing the average air ratio in the charging region to greater than 1.0, an excess air state can be achieved in the charging region US. Therefore, even if unburned ammonia is generated in the central region CS, it passes through the charging region US before being discharged from the charging section 30 to the outside of the heating furnace 1. Therefore, the unburned ammonia will be burned in the charging region US, which is in an excess air state. As a result, even if unburned ammonia is generated in the central region CS, it can be prevented from passing through the charging section 30 and being discharged to the outside of the furnace. However, if the average air ratio in the charging region exceeds 1.1, the amount of nitrogen oxides generated in the charging region US will increase, which may increase the amount of nitrogen oxides discharged to the outside of the furnace via the charging section 30. Therefore, it is preferable that the average air ratio in the charging region is 1.1 or less.

[0060] 5, the flue 34 is located close to the charging section 30, so most of the exhaust gas flowing from the central region CS toward the charging region US is discharged to the outside of the furnace through the flue 34. However, some of the exhaust gas may pass through the charging section 30 and be discharged to the outside of the furnace. Therefore, the above embodiment can suppress the discharge of unburned ammonia and nitrogen oxides from the charging section 30.

[0061] In this embodiment, the charging zone US is preferably set as a section including the outlet of the flue 34. Since the flue 34 is connected to the exhaust gas treatment device 35, even if unburned ammonia and nitrogen oxides are exhausted from the flue 34, the emission of unburned ammonia and nitrogen oxides to the outside of the furnace is suppressed. However, by setting the charging zone US as a section including the outlet of the flue 34, the amount of unburned ammonia and nitrogen oxides exhausted from the charging zone US toward the flue 34 is reduced. This reduces the load on the exhaust gas treatment by the exhaust gas treatment device 35.

[0062] As an example, the first burner section 11 in the charging area has a flow rate of 1083 Nm3 for combustion air 8. ３ / hr, flow rate of fuel gas 5 349 Nm ３ / hr (coal gas 200 Nm ３ / hr, ammonia 149 Nm ３ The flow rate of the fuel gas 5 is adjusted appropriately according to the target temperature value inside the heating furnace 1.

[0063] The ratio V2 / V1 between the total flow rate V1 of the fuel gas used by all the burner equipment constituting the first burner section 11 of the heating furnace 1 and the total flow rate V2 of the fuel gas used by all the burner equipment constituting the second burner section 12 is preferably 0.1 to 30.0. If the ratio V2 / V1 is less than 0.1, the amount of oxygen supplied from the first burner section will be greater than the amount of unburned ammonia generated by the second burner section, and nitrogen oxides will be more likely to be generated by combustion in the first burner section, making it easier for nitrogen oxides to be discharged outside the furnace. On the other hand, if the ratio V2 / V1 exceeds 30.0, the amount of unburned ammonia generated by the second burner section will be greater than the amount of oxygen supplied from the first burner section, which may reduce the effectiveness of burning the unburned ammonia.

[0064] In the above embodiment, the average air ratio in the central region is preferably 1.0 or less. By setting the average air ratio in the central region to 1.0 or less, the central region CS is in an "air shortage state" or "complete combustion state." This reduces the generation of nitrogen oxides and generates unburned ammonia in the central region CS. Although a theoretically "complete combustion state" is achieved when the average air ratio in the central region is 1.0, it is often difficult in practice for the fuel gas 5 injected from the burner nozzle 17 of the second burner section 12 to completely mix with the combustion air 8 to form a combustible mixture. Therefore, even when the average air ratio in the central region is 1.0, a certain amount of unburned ammonia is generated. Furthermore, because the generation of nitrogen oxides is reduced in the central region CS, the concentration of nitrogen oxides is suppressed when the exhaust gas generated in the central region CS is discharged to the outside of the furnace through the charging section 30 or the discharge section 31. Meanwhile, the unburned ammonia generated in the central region CS is burned by the oxygen present in the charging region US or the discharge region DS. Furthermore, the unburned ammonia generated in the central zone CS reduces nitrogen oxides present in the charging zone US or the discharge zone DS, thereby suppressing the amount of unburned ammonia and nitrogen oxides discharged from the heating furnace 1 via the charging section 30 and the discharge section 31.

[0065] From the above viewpoints, it is more preferable that the average air ratio in the central region is less than 1.0. Furthermore, from the viewpoint of stabilizing combustion in the second burner section, it is preferable that the average air ratio in the central region is 0.8 or more.

[0066] As an example, the second burner section 12 in the central region has a flow rate of 1011 Nm ３ / hr, flow rate of fuel gas 5 349 Nm ３ / hr (coal gas 200 Nm ３ / hr, ammonia 149 Nm ３ The flow rate of the fuel gas 5 is adjusted appropriately according to the target temperature value inside the heating furnace 1.

[0067] In the above embodiment, it is preferable that the average air ratio in the loading area is set according to the opening operation of the opening / closing door of the loading section, and the average air ratio in the unloading area is set according to the opening operation of the opening / closing door of the unloading section.

[0068] The charging section 30 of the heating furnace 1 has an opening for charging the steel material S into the furnace and an openable door that covers the opening. When the steel material S is charged into the heating furnace 1, the door of the charging section is opened and the steel material S is charged. On the other hand, the door of the charging section is closed when the steel material S is not being charged. This is to prevent thermal energy from leaking to the outside unless necessary, because the interior of the heating furnace is maintained at a high temperature. Similarly, the discharge section 31 of the heating furnace 1 also has an opening for discharging the steel material S out of the furnace and an openable door that covers the opening. When the steel material S is being discharged from the heating furnace 1, the door of the discharge section is opened and the steel material S is discharged. On the other hand, the door of the discharge section is closed when the steel material S is not being discharged. In this embodiment, the state in which the door of the charging section 30 is open is referred to as the charging section being open, and the state in which the door of the discharge section 31 is open is referred to as the discharge section being open. In addition, the operation of opening the door of the loading section 30 and the operation of opening the discharge door of the discharge section 31 are called opening operations.

[0069] The flow direction of the exhaust gas generated inside the heating furnace 1 may change depending on the opening operation of the door of the loading section 30 or the door of the unloading section 31. The pressure inside the heating furnace 1 is often higher than the outside, and when the loading section 30 is open, the exhaust gas generated inside the heating furnace flows toward the opening of the loading section 30, making it easier for the exhaust gas to flow out of the loading section 30. The same is true when the unloading section 31 is open, in which case the exhaust gas generated inside the heating furnace flows toward the opening of the unloading section 31, making it easier for the exhaust gas to flow out of the unloading section 31.

[0070] Therefore, it is preferable to control the average air ratio in the unloading region to be greater than 1.0 and less than 1.1, and to control the average air ratio in the central region to be smaller than the average air ratio in the unloading region, in response to the opening operation of the door of the unloading section 31. It is also preferable to control the average air ratio in the loading region and the unloading region to be greater than 1.0 and less than 1.1, and to control the average air ratio in the central region to be smaller than the average air ratio in the loading region and the average air ratio in the unloading region, in response to the opening operation of the door of the unloading section 31. It is even more preferable to control the average air ratio in the central region to be 1.0 or less, in response to the opening operation of the door of the unloading section 31.

[0071] Furthermore, it is preferable to control the average air ratio in the charging region to be greater than 1.0 and less than 1.1 in accordance with the opening operation of the door of the charging section 30, and to control the average air ratio in the central region to be smaller than the average air ratio in the charging region. It is also preferable to control the average air ratio in the charging region and the average air ratio in the unloading region to be greater than 1.0 and less than 1.1 in accordance with the opening operation of the door of the charging section 30, and to control the average air ratio in the central region to be smaller than the average air ratio in the charging region and the average air ratio in the unloading region. It is even more preferable to control the average air ratio in the central region to be 1.0 or less in accordance with the opening operation of the door of the charging section 30.

[0072] The opening operation of the door of the charging section 30 and the opening operation of the door of the discharge section 31 in the heating furnace 1 are performed by a control computer 45 that controls the charging of the steel material S into the heating furnace 1 and the unloading of the steel material S from the heating furnace 1. Therefore, the above control may be performed by an air ratio control unit (41, 42, 43) controlling the air ratio in burner heating of the first burner unit 11, the second burner unit 12, and the third burner unit 13 in response to a control command from the control computer 45 of the heating furnace 1 for the opening operation of the door of the charging section 30 and the unloading section 31. Note that the control command for the air ratio in each burner unit to the air ratio control unit (41, 42, 43) may be issued by the control computer 45. This suppresses the emission of unburned ammonia and nitrogen oxides from the heating furnace 1 even when the doors of the charging section 30 and the unloading section 31 are open.

[0073] <Modification> The heating furnace 1 of the above embodiment includes a first burner unit 11 arranged in the charging zone US, a second burner unit 12 arranged in the central zone CS, and a third burner unit 13 arranged in the discharge zone DS. However, the heating furnace 1 may include other burner units that burn ammonia-free fuel gas. The fuel gas used in the other burner units may be, for example, coal gas to which ammonia has not been intentionally added. The coal gas may include any of coke oven gas, blast furnace gas, converter gas, and electric furnace gas. In this case, the average air ratio in the above embodiment can be determined by calculating a theoretical air volume for the total flow rate of the ammonia-containing fuel gas supplied to each zone and the fuel gas supplied to the other burners arranged in that zone, and then determining the ratio of the calculated theoretical air volume to the total amount of combustion air supplied to that zone.

[0074] On the other hand, the heating furnace 1 of the above embodiment may perform burner heating using only ammonia gas as the fuel gas 5 supplied to the burner equipment 2. In this case, the burner equipment 2 shown in Fig. 4 can be implemented by a burner equipment that does not include the coal gas supply system 19 and the flow rate control valve and flow meter that are arranged in the coal gas supply system. Also, there is no need to include the mixer 16.

[0075] Furthermore, instead of gaseous fuel, liquid fuel may be used as the fuel gas 5 of the burner equipment 2. For example, liquid ammonia may be used instead of the ammonia gas 6. When liquid fuel is used, it is preferable to inject the liquid fuel as fine droplets of 1 mm or less from the tip of the burner nozzle 17. By converting the liquid fuel into fine droplets, combustion is promoted. Furthermore, a mixture of gaseous fuel and liquid fuel may be used as the fuel gas 5.

[0076] The burner equipment 2 applied in the above embodiment is not limited to a diffusion combustion burner that mixes the fuel gas 5 and the combustion air 8 at the tip of the burner nozzle 17. A premix burner that mixes the fuel gas 5 and the combustion air 8 upstream of the tip of the burner nozzle 17 may be used as the burner equipment 2. In addition to a double-tube burner nozzle, the burner equipment 2 may also be a swirl burner that has a function of stirring the fuel gas injected from the burner nozzle, or a tubular flame burner that blows the fuel gas and combustion air tangentially into the combustion chamber, forming a swirling flow within the combustion chamber, and burning the fuel gas and combustion air. Furthermore, a regenerative burner that alternately burns a pair of burners integrated with a heat storage body at intervals of several tens of seconds may also be used as the burner equipment 2.

[0077] When a double-pipe burner nozzle is used as the burner nozzle 17, it is not limited to the configuration in which the fuel gas 5 is injected from the inner pipe and the combustion air 8 is supplied from the outer pipe. A mixed gas of the fuel gas 5 and the combustion air 8 may be supplied to either or both of the inner pipe and the outer pipe of the double-pipe nozzle. Note that the fuel gas 5 and the combustion air 8 may be preheated as necessary.

[0078] The burner equipment 2 shown in Fig. 4 is provided with an ammonia gas supply system 18 and a coal gas supply system 19 that are paired with one burner nozzle 17. Furthermore, a flow rate control valve 20 and a flow meter 21 are provided in each of the ammonia gas supply system 18 and the coal gas supply system 19. However, it may also be configured such that the ammonia gas 6 supplied by the ammonia gas supply system 18 and the coal gas 7 supplied by the coal gas supply system 19 are mixed in advance, and the fuel gas 5 is supplied from one fuel gas supply system 14 to two or more burner nozzles 17. In this case, by installing the flow rate control valve 20 and the flow meter 21 in the fuel gas supply system 14, it is possible to measure and control the fuel gas 5 supplied to each individual burner nozzle.

[0079] A gas composition analyzer that analyzes the components of the gas being transported may be installed in the fuel gas supply system 14 or the coal gas supply system 19. The theoretical amount of air required for complete combustion of the fuel gas 5 varies depending on the composition of the gas components contained in the fuel gas 5. Therefore, by identifying the composition of the gas components contained in the fuel gas 5 online, the air ratios in the first burner section 11, the second burner section 12, and the third burner section 13 can be appropriately controlled. Note that instead of online component analysis, the fuel gas 5 may be sampled and then analyzed offline using equipment such as a gas chromatograph.

[0080] In the above embodiment, the combustion air may be air collected from the atmosphere and supplied from the combustion air supply unit. However, reformed air, such as by removing nitrogen from the air or adding pure oxygen, may be used as the combustion air 8. Increasing the oxygen content of the combustion air promotes the oxidation reaction of the fuel gas and reduces the flow rate of the combustion air supplied from the combustion air supply system, thereby reducing the power consumption of pumps and other devices. Furthermore, decreasing the oxygen content of the combustion air can create a reducing atmosphere inside the heating furnace, promoting the reduction of nitrogen oxides. In this case, if the oxygen concentration in the combustion air 8 is different from that in the atmosphere, the air ratio may be defined as the ratio of the amount of oxygen contained in the combustion air 8 to the theoretical amount of oxygen required for complete combustion of the fuel gas. In other words, the method for operating a heating furnace according to the present invention can be applied by defining the average air ratio as the ratio of the actual amount of oxygen to the theoretical amount of oxygen required for complete combustion of the fuel gas in each region.

[0081] In the flue 34 of the heating furnace 1 of the above embodiment, a NOx concentration meter 36, an ammonia concentration meter 37, a CO concentration meter, etc. may be arranged as analyzers for the exhaust gas discharged from the heating furnace 1. This makes it possible to manage whether nitrogen oxides, unburned ammonia, and carbon monoxide are sufficiently suppressed.

[0082] The effects of this embodiment will be specifically described below based on examples, but the present invention is not limited to these examples. As examples of the present invention, an example of test operation of a heating furnace using the heating furnace shown in Figure 5 will be described.

[0083] As shown in Figure 5, the heating furnace used in this example has a first burner section (11U, 11L) in the charging zone US, a second burner section (12U1, 12U2, 12L1, 12L2) in the central zone CS, and a third burner section (13U1, 13U2, 13L1, 13L2) in the discharge zone DS. The heating furnace also includes an air ratio control unit 41 for controlling the air ratio of the first burner section (11U, 11L), an air ratio control unit 42 for controlling the air ratio of the second burner section (12U1, 12U2, 12L1, 12L2), and an air ratio control unit 43 for controlling the air ratio of the third burner section (13U1, 13U2, 13L1, 13L2). The burners used in the heating furnace were all diffusion combustion burners shown in Figure 4, with a rated capacity of 800,000 kcal / hr.

[0084] The fuel gas supplied to the first burner section, the second burner section, and the third burner section contains ammonia and methane (CH ４ ) was used. That is, in the burner equipment 2 of FIG. 4 , ammonia gas was supplied from the ammonia gas supply system 18, and methane was supplied from the coal gas supply system 19. In this example, the mixture ratio of ammonia gas and methane contained in the fuel gas 5 was adjusted by the flow rate control valves 20 provided in the ammonia gas supply system 18 and the coal gas supply system 19. Note that in this example, the term "mixture ratio" is used to mean the calorific value ratio of ammonia and methane. Also, the air ratio of the fuel gas 5 to the theoretical air amount was adjusted by adjusting the supply amount of combustion air 8 using the flow rate control valve 20 provided in the combustion air supply system 15.

[0085] In this way, the first burner section, the second burner section, and the third burner section were all adjusted to have the same mixture ratio and to output the same amount of heat. In the example, the mixture ratio of ammonia to methane was set to 50%:50% in the first burner section, the second burner section, and the third burner section. Specifically, the flow rate of ammonia was set to 119 Nm ３ / hr, methane flow rate 46.7 Nm ３ A mixed gas was generated at a rate of 93.5 Nm / hr and burned. As a conventional example, only methane containing no ammonia gas was used as the fuel gas. In this case, the flow rate of methane was 93.5 Nm３ / hr.

[0086] The following describes the results of test operations in which the air ratio control units 41, 42, and 43 were individually adjusted to change the air ratios in the first burner section, the second burner section, and the third burner section.

[0087] A sample of the exhaust gas was collected from the upstream side of the exhaust gas treatment device 35 in the flue 34 of the heating furnace, i.e., before treatment by the exhaust gas treatment device 35, and the concentration of nitrogen oxides (NOx) and unburned ammonia (NH ３ ) concentration, and carbon dioxide (CO ２ In addition, at the positions of the charging section 30 and the discharge section 31, samples of the exhaust gas were collected with the doors of the charging section 30 and the discharge section 31 open, and the concentrations of nitrogen oxides (NOx) and unburned ammonia (NH ３ ) concentration was measured.

[0088] Table 1 shows the NOx concentration and NH concentration of the exhaust gas corresponding to the operating conditions of the heating furnace. ３ Concentration, CO ２ The results of CO concentration are shown below. ２ The concentration was evaluated based on the CO2 emitted when methane containing no ammonia gas was used as the fuel gas in the conventional example shown in No. 1. ２ The CO concentration of the invention example and the comparative example is the conventional example. ２ The air ratios in Table 1 are the ratios of the actual air amount to the theoretical air amount of the fuel gas in each of the charging zone, the central zone, and the discharge zone, and are expressed as average air ratios.

[0089] At this time, the upper limit of the NOx concentration in the exhaust gas discharged from the heating furnace was set to 150 ppm. ３ The upper limit of the concentration was set to 25 ppm. The NOx concentration and NH ３ If any of the concentrations was equal to or greater than the upper limit, it was marked as "fail" (x) in the evaluation column. ３When the concentration was less than the upper limit, it was marked as pass (◯) in the evaluation column.

[0090] The conventional example No. 1 does not use ammonia as fuel gas, so nitrogen oxides and unburned ammonia in the exhaust gas are suppressed. However, the amount of carbon dioxide emitted from the heating furnace is large. In this respect, both the invention example and the comparative example meet the conditions for reducing the amount of carbon dioxide emitted by half compared to the conventional example.

[0091] Nos. 2 to 4 are examples in which the air ratio in the third burner section was set to 1.0 or less. Unburned ammonia was generated by burner heating in the third burner section, which increased the unburned ammonia concentration in the exhaust gas sampled at the discharge section. In particular, when the air ratio in the second burner section was low, the unburned ammonia concentration in the exhaust gas increased.

[0092] Nos. 5 to 7 are examples in which the air ratio in the third burner section was set to a value exceeding 1.1. Burner heating in the third burner section increased the amount of nitrogen oxides produced, which in turn increased the nitrogen oxide concentration in the exhaust gas sampled at the discharge section. In particular, when the air ratio in the second burner section was high, the nitrogen oxide concentration in the exhaust gas increased.

[0093] In Nos. 8 and 9, the air ratio in the third burner section was greater than 1.0 but less than 1.1, but the air ratio in the second burner section was a large value exceeding 1.2. In these cases, high concentrations of nitrogen oxides were generated in the central region CS, and were difficult to reduce in the charging region US and the discharge region DS, resulting in high NOx concentrations in the exhaust gas, particularly at the charging region and the flue.

[0094] On the other hand, Nos. 10, 11, 19 to 21, 24, and 25 are examples in which the air ratio in the first burner section was greater than 1.0 and equal to or less than 1.1, the air ratio in the third burner section was greater than 1.0 and equal to or less than 1.1, and the air ratio in the second burner section was smaller than the air ratios in the first and third burner sections. In these cases, the concentrations of nitrogen oxides and unburned ammonia in the exhaust gas at the positions of the charging section 30, the discharge section 31, and the flue 34 were sufficiently suppressed.

[0095] Nos. 12 to 18, 22, and 23 are examples in which the air ratio in the third burner section was greater than 1.0 and less than or equal to 1.1, and the air ratio in the second burner section was smaller than the air ratio in the third burner section. However, Nos. 12, 13, and 16 to 18 were examples in which the air ratio in the first burner section was less than 1.0. Nos. 14 and 15 were examples in which the air ratio in the first burner section exceeded 1.1. In these cases, the conditions in Nos. 12 and 13 favored the generation of unburned ammonia in the first burner section. As a result, the unburned ammonia concentration in the exhaust gas at the charging section was higher than in Nos. 10 and 11. However, the values ​​were below the upper limit at all positions. On the other hand, the conditions in Nos. 14 and 15 favored the generation of nitrogen oxides in the first burner section. As a result, the nitrogen oxide concentration in the exhaust gas at the charging section was higher than in Nos. 10 and 11. However, the values ​​were below the upper limit at all positions.

[0096]

[0097] B Burner TD Conveying direction (of steel material) S Steel material S1 Leading edge of steel material S2 Tail end of steel material US Charging area CS Central area DS Unloading area 1 Heating furnace 2 Burner equipment 3 Furnace wall 4 Furnace interior 5 Fuel gas 6 Ammonia gas 7 Coal gas 8 Combustion air 11, 11U, 11L First burner section 12, 12U1, 12U2, 12L1, 12L2 Second burner section 13, 13U1, 13U2, 13L1, 13L2 Third burner section 14 Fuel gas supply system 15 Combustion air supply system 16 Mixing section 17 Burner nozzle 18 Ammonia gas supply system 19 Petroleum gas supply system 20 Flow rate adjustment valve 21 Flow meter 30 Charging side 31 Unloading section 32 Moving skid 33 Fixed skid 34 Flue 35 Exhaust gas treatment device 36 NOx concentration meter 37 Ammonia concentration meter 40 Air ratio control unit 41 Air ratio control unit (charging area) 42 Air ratio control unit (central area) 43 Air ratio control unit (unloading area) 45 Control computer

Claims

1. A method of operating a heating furnace in which material to be heated is heated while being transported from a charging section to an unloading section, the inside of the heating furnace is divided into a charging area on the charging section side, an unloading area on the unloading section side, and a central area sandwiched between the charging area and the unloading area, burner heating is performed in the charging area, the central area, and the unloading area by burning a fuel gas containing ammonia, and exhaust gas is discharged from a flue installed in a position close to the charging section inside the heating furnace, the burner heating in the unloading area sets the average air ratio of the fuel gas to the theoretical air volume to be greater than 1.0 and not greater than 1.1, and the burner heating in the central area sets the average air ratio of the fuel gas to the theoretical air volume to be smaller than the average air ratio of the fuel gas to the theoretical air volume in the unloading area.

2. The method of operating a heating furnace according to claim 1, wherein the burner heating in the central region is performed so that the average air ratio of the fuel gas to the theoretical air amount is 1.0 or less.

3. A method for operating a heating furnace as claimed in claim 1 or 2, wherein the burner heating in the discharge area is performed by setting the average air ratio of the fuel gas to the theoretical air amount in accordance with the opening operation of the opening and closing door of the discharge section.

4. A method for operating a heating furnace as claimed in any one of claims 1 to 3, wherein the burner heating in the charging area is performed so that the average air ratio to the theoretical air volume of the fuel gas is greater than 1.0 and not greater than 1.1, and the burner heating in the central area is performed so that the average air ratio to the theoretical air volume of the fuel gas is smaller than the average air ratio to the theoretical air volume of the fuel gas in the charging area.

5. A method for operating a heating furnace as described in claim 4, wherein burner heating in the charging area is performed by setting an average air ratio of the fuel gas to the theoretical air amount in accordance with the opening operation of an opening / closing door of the charging section.

6. A heating furnace which heats the material to be heated while transporting it from a charging section to an unloading section, the interior of the heating furnace being divided into a charging area on the charging section side, an unloading area on the unloading section side, and a central area sandwiched between the charging area and the unloading area, a flue for discharging exhaust gas is provided at a position within the heating furnace close to the charging section, a first burner section being disposed in the charging area, a second burner section being disposed in the central area, and a third burner section being disposed in the unloading area, and the heating furnace comprising: a fuel gas supply section which supplies fuel gas containing ammonia to the first burner section, the second burner section, and the third burner section, and an air ratio control section which controls the air ratio of the fuel gas supplied to the first burner section, the second burner section, and the third burner section relative to the theoretical air amount.

Images