How to operate a heating furnace

Abstract

The present invention provides a method for operating a heating furnace and a heating furnace that use ammonia as a combustion fuel for the heating furnace, which can suppress the emission of carbon dioxide, and that can reduce the amounts of nitrogen oxides and unburned ammonia discharged outside the heating furnace. [Solution] This is a method of operating a heating furnace, in which 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, and in the charging area, the central area and the unloading area, heating is performed with burners that burn 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, and in the central area, the burner heating is performed such that the average air ratio to the theoretical air volume of the fuel gas is greater than 1.0 and is not greater than 1.2, and in the unloading area, the average air ratio to the theoretical air volume of the fuel gas is greater than 1.0 and is smaller than the average air ratio to the theoretical air volume of the fuel gas in the central area.

Description

[Technical field]

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

[0002] In integrated steelworks, blast furnace gas discharged 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, have been effectively used as fuel gas. However, in recent years, with the demand for reducing carbon dioxide emissions, combustion technologies have been required to reduce the amount of by-product gas used. For example, in steel heating furnaces that heat steel in hot rolling lines and plate rolling lines in integrated steelworks, it has been required to reduce the amount of by-product gas used and the amount of carbon dioxide emissions. In this case, a technology that uses ammonia as fuel gas for steel heating furnaces has attracted attention. That is, ammonia does not contain carbon elements, and when burned, it mainly produces water and nitrogen, so it has a large effect of reducing carbon dioxide emissions, and technological development for applying it to steel heating furnaces is desired.

[0003] On the other hand, using ammonia as fuel for a heating furnace is problematic 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] 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 for guiding 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 is also equipped with 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 upstream of the additional air supply unit in the flow direction of fuel gas, which supplies ammonia fuel to the furnace. 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, nitrogen oxides generated by the combustion of ammonia fuel in the reducing atmosphere region inside the furnace will be reduced to N2, thereby suppressing the generation of nitrogen oxides. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2019-086191 A [Patent Document 2] JP 2018-076985 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, when attempting to apply the above-mentioned conventional technology 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 a combustion device such as a boiler, and reduces nitrogen oxides generated in the combustion device by injecting ammonia downstream in the flow direction of the combustion gas. In this case, the amount of ammonia injected to reduce the nitrogen oxides is extremely small compared to the flow rate of the combustion gas generated in the combustion device, so even if ammonia is injected toward the center of the furnace, it may not be mixed 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 causes a problem in that ammonia, which is a reducing agent, is discharged outside the furnace without being burned. Unlike combustion devices such as boilers, heating furnaces for heating objects to be heated such as steel materials generally have an opening and closing door for loading and extracting the objects to be heated into the heating furnace. In that case, when the furnace door is opened, toxic unburned ammonia ("unburned ammonia") is released. The problem is that the exhaust gas, ammonia, is discharged outside the heating furnace, causing the environment outside the furnace to deteriorate. A problem arises.

[0009] Patent Document 2 also targets combustion equipment such as boilers, and reduces nitrogen oxides with ammonia in a reducing atmosphere region in a furnace. Patent Document 2 discloses that in order to form a reducing atmosphere region in the furnace, the amount of primary air supplied to the burner is less than the amount of air required to completely combust fossil fuels. The technology disclosed in Patent Document 2 requires a certain amount of space to be secured in the furnace and a certain amount of reaction time to carry out the reduction reaction of nitrogen oxides. On the other hand, a heating furnace for heating objects such as steel requires not only a combustion device (e.g., a burner) inside the heating furnace, but also a space for placing and charging the objects. In contrast, a furnace such as a boiler differs in that it only needs to have 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 inside 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 burn ammonia is changed between 0.6 and 1.0 with respect to the theoretical air amount, the amount of air supplied, the leak 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 (air ratio of about 0.8), and changes in the operating conditions in the heating furnace make it easier for nitrogen oxides and unburned ammonia to be discharged to the outside.

[0011] The present invention has been made to solve the above-mentioned problems associated with the conventional techniques, and has an object to provide a method for operating a heating furnace that uses ammonia, which can suppress the emission of carbon dioxide, as a combustion fuel for the heating furnace, and that can reduce the amounts of nitrogen oxides and unburned ammonia discharged 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 in which a 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, the charging area, the central area, and the unloading area are heated by burners that burn a fuel gas containing ammonia, and exhaust gas is discharged from a flue installed in a position near the charging section inside the heating furnace, the burner heating in the central area is performed such that the average air ratio to the theoretical air volume of the fuel gas is greater than 1.0 and is not greater than 1.2, and the burner heating in the unloading area is performed such that the average air ratio to the theoretical air volume of the fuel gas is 1.0 or more and is smaller than the average air ratio to the theoretical air volume of the fuel gas in the central area. [2] In the above [1], the burner heating in the discharge area is performed in such a manner that the average air ratio of the fuel gas to the theoretical air amount is less than 1.1. [3] In the above [1] or [2], the burner heating in the discharge area is a method for operating a heating furnace, wherein an average air ratio of the fuel gas to the theoretical air volume is set according to the opening operation of the opening / closing door of the discharge section. [4] In the above [1] or [2], the burner heating in the charging region is performed so that the average air ratio of the fuel gas to the theoretical air volume is 1.0 or more, and is smaller than the average air ratio of the fuel gas to the theoretical air volume in the central region. [5] In the above [4], the burner heating in the charging area is performed in such a manner that the average air ratio of the fuel gas to the theoretical air amount is less than 1.1. [6] In the above [4], the burner heating in the loading area is a method for operating a heating furnace, in which the average air ratio of the fuel gas to the theoretical air volume is set according to the opening operation of the opening / closing door of the loading section. [7] In the above [5], the burner heating in the loading area is a method of operating a heating furnace, in which the average air ratio of the fuel gas to the theoretical air volume is set according to the opening operation of the opening / closing door of the loading section. Effect of the Invention

[0014] According to the present invention, by using ammonia as the combustion fuel in the heating furnace, it is possible to suppress the emission of carbon dioxide and reduce the emission of nitrogen oxides and unburned ammonia produced by the combustion of ammonia to the outside of the heating furnace. [Brief description of the drawings]

[0015] [Figure 1] FIG. 2 is a schematic diagram showing a configuration of a heating furnace. [Diagram 2] FIG. 2 is a configuration diagram showing an example of the arrangement of burner equipment in a heating furnace (on both sides in the conveying direction). [Diagram 3] FIG. 2 is a configuration diagram showing an example of the arrangement of burner equipment in a heating furnace according to the present embodiment. [Figure 4] 1 is a configuration diagram of an example of a burner facility that supplies a mixed gas of coal gas and ammonia gas as a fuel gas, and a burner nozzle 17 is a cross-sectional view of the wall surface of a furnace wall 3. [Diagram 5] FIG. 2 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. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The heating furnace according to this embodiment will be described below. The heating furnace according to this embodiment is a heating furnace that heats the material to be heated while transporting it from a loading section to an unloading section, and divides the interior of the heating furnace into a loading area on the loading section side, an unloading area on the unloading section side, and a central area sandwiched between the loading area and the unloading area. A flue for discharging exhaust gas is provided at a position close to the loading section inside the heating furnace. A first burner section is disposed in the loading area in the transport direction of the material to be heated, a second burner section is disposed in the central area, and a third burner section is disposed in the unloading area. The heating furnace is equipped with a fuel gas supply section that 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 that 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. <Heating furnace> The heating furnace according to the embodiment of the present invention is a facility equipped with a burner that burns fuel gas as a heat source for heating, and in which an object to be heated is placed inside and heated to a predetermined temperature. The object to be heated is mainly metal, but may be either ferrous metal or non-ferrous metal. The heating temperature of the object to be heated is 700 to 1400°C. 1 to 3 show an example of a heating furnace according to the present 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 products heats a cast slab to a specified temperature. It is used to heat the material to temperatures between 1100 and 1300°C.

[0017] The heating furnace 1 shown in FIG. 1 includes a charging section 30 for charging the steel material S (slab) to be heated, and an unloading section 31 for unloading (extracting) the heated steel material S. 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 inside of the heating furnace 1 is divided into a plurality of zones, and the upstream side is often composed of a heating zone divided into 2 to 8 zones and 1 to 3 soaking zones. The inside of the heating furnace 1 is generally equipped with a fixed skid 33 on which the steel material S is placed, and a moving skid 32 for transporting the steel material S. A heating furnace equipped with a fixed skid 33 and a moving skid 32 is called a walking beam type continuous heating furnace.

[0018] In the 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). The steel material S that has reached the target heating temperature passes through the discharge section 31 and is subjected to hot rolling.

[0019] Inside the heating furnace 1, multiple burners are provided along the transport direction TD of the steel material S. Burners B are arranged to heat the inside of the heating furnace by combustion. When the inside of the heating furnace is heated by the burners, 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 flame of the burner directly contacting the steel material. In any case, the burners burn fuel gas as a heat source for heating, thereby raising the temperature inside the heating furnace and raising the temperature of the material to be heated inside the heating furnace.

[0020] The inside 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 for 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.

[0021] 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 the atmosphere. The doors are temporarily opened when the steel material S is charged and unloaded. When the doors are open, a pressure difference occurs between the pressure inside the heating furnace and the vicinity of 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 the combustion gas is discharged outside the heating furnace 1 through the opening.

[0022] The heating furnace 1 is provided 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 in the exhaust gas. The exhaust gas treatment device 35 performs treatment so that the concentrations of nitrogen oxides and unburned ammonia in the exhaust gas satisfy a predetermined emission standard. As a result, even if nitrogen oxides or unburned ammonia are contained in the exhaust gas, the concentrations of nitrogen oxides and unburned ammonia are reduced by the exhaust gas treatment device 35 connected to the flue 34, so that the emission of nitrogen oxides and unburned ammonia to the outside of the heating furnace 1 is suppressed. In the following, "suppressed" means that the concentrations of nitrogen oxides and unburned ammonia are reduced to or below the upper limit values ​​of the concentrations that are preset so as not to exceed the upper limit values ​​of legal regulations.

[0023] The flue 34 may be equipped with a heat recovery device (not shown) for recovering sensible heat of the exhaust gas. As shown in Fig. 1, the flue 34 is disposed in a position relatively close to the charging section 30 of the heating furnace 1, which is advantageous in terms of thermal efficiency when preheating slabs to be transported to the yard on the charging side of the heating furnace 1.

[0024] 2 is a diagram showing a cross section 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, they are often arranged on both sides of the conveying direction TD 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.

[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 section 11 arranged in a charging area US in the conveying direction TD of the steel material S, a third burner section 13 arranged in a discharge area DS in the conveying direction TD of the steel material S, and a second burner section 12 arranged in a central area CS between the charging area US and the discharge area DS. In this manner, the first burner section 11, the second burner section 12, and the third burner section 13 are arranged from the upstream side in the transport direction TD of the material to be heated.

[0026] The charging area US of the heating furnace 1 refers to a section including the burner B arranged at the position closest to the charging section 30 in the conveying direction TD. When the burners B are arranged at the upper and lower parts of the heating furnace 1 as shown in FIG. 1 and FIG. 2, the burner B arranged at the position closest to the charging section 30 includes both the burner B arranged at the upper part that is closest to the charging section 30 and the burner B arranged at the lower part that is closest to the charging section 30. In other words, the section including both the burner B arranged at the upper part that is closest to the charging section 30 and the burner B arranged at the lower part that is closest to the charging section 30 is called the charging area US. However, the charging area US may include not only the burner B arranged at the lower part that is closest to the charging section 30, but also one or more burners B arranged continuously downstream in the conveying direction TD. The burner B arranged in the charging area US divided in this way is called the first burner section.

[0027] The discharge area DS of the heating furnace 1 refers to a section including the burner B arranged at the position closest to the discharge section 31 in the conveying direction TD. When the burners B are arranged at the upper and lower parts of the heating furnace 1, the burner B arranged at the position closest to the discharge section 31 includes both the burner B arranged at the upper part that is closest to the discharge section 31 and the burner B arranged at the lower part that is closest to the discharge section 31. In other words, the section including both the burner B arranged at the upper part that is closest to the discharge section 31 and the burner B arranged at the lower part that is closest to the discharge section 31 is called the discharge area DS. However, the discharge area DS may include not only the burner B arranged at the lower part that is closest to the discharge section 31, but also one or more burners B arranged continuously on the upstream side of the conveying direction TD. The burner B arranged in the discharge area DS divided in this way is called the third burner section.

[0028] The section between the charging area US and the unloading area DS is called the central area CS, and the The burner B is referred to as a second burner section 12.

[0029] The heating furnace 1 of this embodiment is a heating furnace including 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, respectively. 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 burners arranged in the heating furnace in order 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, the second burner section, and the third burner section 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 ammonia-containing fuel gas 5 as the fuel gas and combustion air 8. The burner equipment 2 is equipped with a burner nozzle 17 for injecting a 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 is equipped with an air ratio control unit 40 that controls the air ratio of the fuel gas 5 supplied to the burner nozzle 17 to the theoretical air amount (sometimes simply referred to as the air ratio).

[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-tube nozzle, and the fuel gas 5 is injected from the inside toward the furnace interior, while the combustion air 8 is supplied to the outside. As a result, the fuel gas 5 and the combustion air 8 are mixed 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 portion and the combustion air 8 discharge portion are different, as shown in Fig. 4, 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 means ammonia gas in a gaseous state at room temperature. The fuel gas 5 may use ammonia gas as a single fuel gas, or a mixed gas in which ammonia gas is mixed 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 in 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 another fuel, or it may be the weight ratio or the calorific value ratio. The mixing ratio shall be defined by any one of them.

[0036] Ammonia gas is a flame-retardant fuel, and is more difficult to ignite than general fuels and has a slower burning speed. In order to improve the stability of combustion, 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 gas obtained from coal. Coal gas includes coke oven gas, blast furnace gas, etc. It is preferable that the gas mixture contains any one of 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 produced when reducing iron ore 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 gas is a by-product gas produced in the steelmaking process in a converter. Electric furnace gas is a gas produced by incomplete combustion of auxiliary fuel (recarburizer) in an electric furnace. As the coal gas constituting the mixed gas, a gas in which blast furnace gas, coke oven gas, and converter gas are appropriately mixed (sometimes called M gas) may be used. This is because by mixing coal gases with different heating values, the amount of heat required to heat the heated object is supplied and stable operation of the heating furnace is performed.

[0038] Hydrocarbon gas is a fuel made by gasifying hydrocarbons. Examples of hydrocarbons that can be used include methane, ethane, ethylene, acetylene, and propane.

[0039] FIG. 4 shows an example in which a mixed gas of ammonia gas and coal gas 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 ammonia gas 6 and 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. A flow rate control valve 20 for adjusting the amount of each gas supplied to the mixing section 16 and a flow meter 21 for measuring the supply flow rate may be provided midway between the ammonia gas supply system 18 and the coal gas supply system 19. This allows the mixing ratio of ammonia gas and coal gas contained in the mixed gas to be adjusted. The flow meter 21 may estimate the flow rate of the ammonia gas 6 or the coal gas 7 by measuring the pressure of the gas transported by the ammonia gas supply system 18 or the coal gas supply system 19. This is because the gas flow rate can be easily estimated by using a pressure gauge.

[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, so that mixing can be performed without providing a special stirring mechanism. The mixing section 16 may be configured as a certain space at the portion where these supply pipes intersect. 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 the coal gas and ammonia gas are mixed more uniformly is generated.

[0041] It is preferable to provide 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 in the middle of 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 the 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 transported combustion air.

[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 relative 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 the flowmeter 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. Then, the air ratio control unit 40 adjusts the opening degree 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 by the control computer 45, thereby controlling the air ratio of the burner heating in the burner equipment 2.

[0043] <Burner equipment layout for heating furnace> The arrangement of the burner equipment of the heating furnace will be described with reference to FIG. A first burner section, a second burner section, and a third burner section are arranged from upstream in the transport direction of the heated material, and the system is equipped with a fuel gas supply section that 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 that 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. That is, the furnace includes a first burner section 11 arranged in a charging area US in the conveying direction TD of the steel material S, a second burner section 12 arranged in a central area CS between the charging area US and the unloading area DS, and a third burner section 13 arranged in the unloading area DS in the conveying direction TD of the steel material S. The heating furnace of this embodiment further includes a fuel gas supply section that supplies ammonia-containing fuel gas 5 to the first burner section 11, the second burner section 12, and the third burner section 13, and an air ratio control section that controls the air ratio of the fuel gas 5 supplied to the first burner section 11, the second burner section 12, and the third burner section 13 to a theoretical air amount.

[0044] In the example shown in FIG. 5, the conveyor 10 is disposed at a position closest to the loading section 30 in the conveying direction TD. A section including the burner equipment is set as a charging area US, and the burner equipment 11U and 11L arranged in the charging area US constitute the first burner section. In addition, a section including the burner equipment arranged at the position closest to the unloading section 31 in the conveying direction TD and the burner equipment arranged continuously on the upstream side of the conveying direction TD is set as an unloading area DS. As a result, the burner equipment 13U1, 13U2, 13L1, and 13L2 arranged in the unloading area DS constitute the third burner section. Then, a central area CS is set as a section between the charging area US and the unloading area DS, and the burner equipment 12U1, 12U2, 12L1, and 12L2 arranged in the central area CS constitute the second burner section.

[0045] Each of the burner equipment of the first burner section (11U, 11L), the second burner section (12U1, 12U2, 12L1, 12L2) and the third burner section (13U1, 13U2, 13L1, 13L2) is provided with a fuel gas supply section that supplies ammonia-containing fuel gas 5, and an air ratio control section that controls the air ratio. An air ratio control section may be provided for each of the burner equipment constituting the first burner section, the second burner section and the third burner section. However, as shown in FIG. 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 of the above, the heating furnace 1 can set the air ratio of the fuel gas to the theoretical air volume for burner heating in 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 the amount of air supplied to the burner nozzle relative to the theoretical amount of air required for complete combustion of the fuel gas. It is defined by the ratio of the amount of combustion air. In other words, when the air ratio is 1.0, the fuel gas 5 theoretically consumes all the oxygen contained in the combustion air 8, achieving complete combustion. This state is called the "complete combustion state." When the air ratio is less than 1.0, the oxygen contained in the combustion air 8 alone is theoretically not enough to burn all of the components that make up the fuel gas 5, leaving some unburned fuel gas. This state is called the "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, achieving complete combustion, but some of the oxygen contained in the combustion air 8 remains. This state is called the "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, respectively, so that the combustion state of the fuel gas can be changed in the charging zone US, the central zone CS, and the discharge zone DS of the heating furnace 1. As a result, even if an air shortage state occurs in any 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, and unburned ammonia remaining unburned in the fuel gas 5 is generated in the first section, if an air excess state is realized in the other section, the unburned ammonia generated in the first section is burned in the other section, thereby reducing the discharge of unburned ammonia from the heating furnace 1 to the outside of the furnace. In addition, if an air excess state occurs in any 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 are 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 section due to the combustion of ammonia contained in the fuel gas 5, if an air shortage state is realized in another section, unburned ammonia will be generated due to the air shortage state, which has the effect of reducing the nitrogen oxides generated in the one section. As a result, the nitrogen oxides are reduced in the other section, and it is possible to reduce the amount of nitrogen oxides discharged outside the heating furnace 1.

[0049] In the heating furnace according to the present 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, so that unburned ammonia and nitrogen oxides generated in some zones can be rendered harmless in other zones. In other words, in burner heating in which multiple burner equipment is burned under a single combustion condition, it was 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 the present embodiment can realize different combustion conditions in multiple compartments. Therefore, nitrogen oxides and unburned ammonia generated in some sections are 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 even if there are fluctuations in the operating conditions, such as changes in the heating temperature of the steel material S, the emissions of nitrogen oxides and unburned ammonia from the heating furnace 1 can be effectively reduced.

[0050] <Operation method of heating furnace> Next, a method for operating the heating furnace according to this embodiment will be described. This embodiment is a method for operating a heating furnace in which the material to be heated is heated while being transported from a charging section to an unloading section, and the inside 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, and in the charging region, the material is heated by a burner that burns a fuel gas containing ammonia in the charging region, the central region, and the unloading region, and exhaust gas is discharged from a flue installed in a position close to the charging section in the heating furnace, and the burner heating in the central region is set so that the average air ratio to the theoretical air volume of the fuel gas is greater than 1.0 and is not greater than 1.2, and the burner heating in the unloading region is set so that the average air ratio to the theoretical air volume of the fuel gas is 1.0 or more and is smaller than the average air ratio to the theoretical air volume of the fuel gas in the central region.

[0051] Furthermore, the burner heating in the discharge area may have an average air ratio of fuel gas to theoretical air amount of less than 1.1. In addition, it is preferable that the average air ratio of the fuel gas to the theoretical air amount in the charging region is 1.0 or more and is smaller than the average air ratio of the fuel gas to the theoretical air amount in the central region. 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 region, i.e., the average air ratio refers to the ratio of the total amount of combustion air supplied in each region to the total amount of theoretical air volume relative to the total amount of fuel gas supplied in that region.

[0052] A method of operating the heating furnace will be described with reference to the heating furnace 1 shown in Fig. 5. The division of the heating furnace 1 into the charging zone US, the central zone CS, and the unloading zone DS is as described above. This embodiment includes a process of heating the steel material S in the charging zone US using the first burner section 11, a process of heating the steel material S in the central zone CS using the second burner section 12, and a process of heating the steel material S in the unloading zone DS using the third burner section 13. The average air ratio in the central region is set to be greater than 1.0 and equal to or less than 1.2, while the average air ratio in the discharge region is set to be greater than 1.0 and smaller than the average air ratio for the theoretical air amount of fuel gas in the central region. The air ratio in each region is controlled for each section by air ratio control units 41, 42, and 43.

[0053] Since the average air ratio in the central region is greater than 1.0, an excess air state is formed. Then, in the central region CS, nitrogen oxides are easily generated by the combustion of ammonia contained in the fuel gas 5. On the other hand, since the average air ratio in the discharge region is smaller than the average air ratio to the theoretical air amount of the fuel gas in the central region, a small amount of unburned ammonia is easily generated in the exhaust gas in the discharge region DS compared to the central region CS. Here, when the average air ratio in the discharge region is 1.0 or more, a complete combustion state or an excess air state is theoretically formed. However, in reality, it is often difficult for the fuel gas 5 injected from the burner nozzle 17 of the burner equipment 2 to form a combustible mixture completely mixed with the combustion air 8. Therefore, even if the average air ratio in the discharge region is 1.0 or more, a certain amount of unburned ammonia is generated. As a result, the exhaust gas generated in the discharge region DS contains a relatively large amount of unburned ammonia compared to the exhaust gas generated in the central region CS.

[0054] In this embodiment, even if nitrogen oxides are generated in the central region CS, they pass through the discharge region DS on the way from the discharge part 31 to the outside of the heating furnace 1, and therefore the nitrogen oxides are reduced by the unburned ammonia generated in the discharge region DS. In other words, even if nitrogen oxides are generated in the central region CS, the generated nitrogen oxides can be prevented from passing through the discharge part 31 and being discharged to the outside of the furnace. However, if the average air ratio in the central region exceeds 1.2, the amount of nitrogen oxides generated in the central region CS increases significantly, and the reduction action of the unburned ammonia generated in the discharge region becomes insufficient. Therefore, the average air ratio in the central region is set to 1.2 or less.

[0055] Furthermore, when the average air ratio in the discharge zone is increased, the amount of unburned ammonia generated in the discharge zone decreases, and the effect of reducing nitrogen oxides becomes insufficient. Also, when the average air ratio in the discharge zone is increased, the amount of nitrogen oxides generated in the discharge zone increases. In order to avoid an increase in the amount of nitrogen oxides discharged outside the furnace due to these factors, the average air ratio in the discharge zone is preferably less than 1.1, and the upper limit value of the average air ratio in the discharge zone is more preferably 1.07.

[0056] In the heating furnace 1 shown in FIG. 5, the flue 34 is disposed in a position close to the charging section 30, so that on the upstream side of the heating furnace 1, exhaust gas is discharged from the charging section 30 and the flue 34. On the other hand, on the downstream side of the heating furnace 1, exhaust gas is discharged only from the discharge section 31. Carrying out 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 to the outside of the furnace. The flue 34 is connected to an exhaust gas treatment device (not shown), so that the discharge of unburned ammonia and nitrogen oxides from the flue 34 to the outside of the furnace is suppressed. However, the charging section 30 and the discharge section 31 have doors temporarily opened to the atmosphere to allow the steel material S to pass through, so there is a risk that unburned ammonia and nitrogen oxides will be discharged outside 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, which discharges a large amount of exhaust gas.

[0057] As an example, the second burner section 12 in the central region has a flow rate of 943 Nm 3 / hr, Fuel gas 5 flow rate 349Nm 3 / hr (coal gas 200Nm 3 / hr, ammonia 149Nm 3 The flow rate of the fuel gas 5 is appropriately adjusted according to the target temperature value inside the heating furnace 1. The third burner section 13 in the discharge area has a flow rate of 934 Nm3 of the combustion air 8. 3 / hr, Fuel gas 5 flow rate 349Nm 3 / hr (coal gas 200Nm 3 / hr, ammonia 149Nm 3 The flow rate of the fuel gas 5 is appropriately adjusted according to the target temperature value inside the heating furnace 1.

[0058] In addition, it is preferable that the ratio V2 / V3 of the total flow rate V3 of the fuel gas used in 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 in all the burner equipment constituting the second burner section 12 is 1 to 20. If the ratio V2 / V3 is smaller than 1, the amount of unburned ammonia generated by the third burner section will be greater than the amount of nitrogen oxides generated by the second burner section, making it easier for unburned ammonia to be discharged outside the furnace. On the other hand, if the ratio V2 / V3 exceeds 20, the amount of nitrogen oxides generated by the second burner section will be greater than the amount of unburned ammonia generated by the third burner section, and there is a risk that the effect of reducing nitrogen oxides will decrease. Furthermore, the burner heating in the charging region may be set so that the average air ratio to the theoretical air amount of the fuel gas is 1.0 or more and is smaller than the average air ratio to the theoretical air amount of the fuel gas in the central region.

[0059] From a similar viewpoint, it is preferable that the burner heating in the charging region has an average air ratio of 1.0 or more and less than 1.1, and the average air ratio in the central region is greater than the average air ratio in the charging region.

[0060] By making the average air ratio in the central zone larger than that in the charging zone, the burner heating in the central zone CS is in a state of relatively excess oxygen compared to the charging zone US. As a result, nitrogen oxides are more likely to be generated in the central zone CS than in the charging zone US. Conversely, unburned ammonia is more likely to be generated in the charging zone US than in the central zone CS. Therefore, even if nitrogen oxides are generated in the central region CS, they pass through the charging region US on the way from the charging section 30 to being discharged outside the heating furnace 1, and the nitrogen oxides generated in the central region CS are reduced by unburned ammonia. As a result, even if nitrogen oxides are generated in the central region CS, the generated nitrogen oxides 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 is less than 1.0, the amount of unburned ammonia generated in the charging region US increases, and there is a risk that the amount of unburned ammonia discharged to the outside of the furnace via the charging section 30 increases. For this reason, the burner heating in the charging region is set to an average air ratio of 1.0 or more.

[0061] 5, the flue 34 is disposed 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, since some of the exhaust gas may pass through the charging section 30 and be discharged to the outside of the furnace, the above embodiment can suppress the discharge of unburned ammonia and nitrogen oxides from the charging section 30.

[0062] In this embodiment, the charging zone US is preferably set as a section including the exhaust port of the flue 34. Since the flue 34 is connected to an exhaust gas treatment device, even if unburned ammonia and nitrogen oxides are exhausted from the flue 34, the discharge 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 exhaust port 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 of exhaust gas treatment by the exhaust gas treatment device.

[0063] As an example, the first burner section 11 in the charging area has a flow rate of 1083 Nm3 of combustion air 8. 3 / hr, Fuel gas 5 flow rate 349Nm 3 / hr (coal gas 200Nm 3 / hr, ammonia 149Nm 3 The flow rate of the fuel gas 5 is appropriately adjusted according to the target temperature value inside the heating furnace 1.

[0064] The ratio V2 / V1 between the total flow rate V1 of the fuel gas used in 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 in all the burner equipment constituting the second burner section 12 is preferably 1 to 20. If the ratio V2 / V1 is smaller than 1, the amount of unburned ammonia generated by the first burner section is greater than the amount of nitrogen oxides generated by the second burner section, and the unburned ammonia is more likely to be discharged outside the furnace. On the other hand, if the ratio V2 / V1 exceeds 20, the amount of nitrogen oxides generated by the second burner section is greater than the amount of unburned ammonia generated by the first burner section, and the effect of reducing nitrogen oxides may decrease.

[0065] Furthermore, when the average air ratio in the charging zone is increased, the amount of unburned ammonia produced in the charging zone decreases, and the effect of reducing nitrogen oxides becomes insufficient. In addition, when the average air ratio in the charging zone is increased, the amount of nitrogen oxides generated in the charging zone increases. In order to avoid an increase in the amount of nitrogen oxides discharged outside the furnace, the average air ratio in the charging zone is preferably less than 1.1, and the upper limit of the average air ratio in the charging zone is more preferably 1.07.

[0066] In the above embodiment, it is preferable that the average air ratio of the burner heating in the loading area is set according to the opening operation of the door of the loading section, and the average air ratio of the burner heating in the unloading area is set according to the opening operation of the door of the unloading section.

[0067] 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, whereas in any other state than when the steel material S is being charged, the door of the charging section is kept closed. This is to prevent thermal energy from leaking to the outside unless necessary, since the inside 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 to the outside of the furnace, and an openable / closable door that covers the opening. When the steel material S is discharged from the heating furnace 1, the door of the discharge section is opened and the steel material S is discharged, whereas in any other state than when the steel material S is being discharged, the door of the discharge section is closed. In this embodiment, the state in which the door of the loading section 30 is open is referred to as the loading section being open, and the state in which the door of the unloading section 31 is open is referred to as the unloading section being open. In addition, the operation of opening the door of the loading section 30 and the operation of opening the unloading door of the unloading section 31 are referred to as opening operations.

[0068] 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 and the door of the unloading section 31. The inside of the heating furnace 1 is often in a state of higher pressure than the outside, and when the loading section 30 is open, the exhaust gas generated inside the heating furnace flows in the direction of the opening of the loading section 30 and is likely to flow out from the loading section 30 to the outside. The same is true when the unloading section 31 is open, in which case the exhaust gas generated inside the heating furnace flows in the direction of the opening of the unloading section 31 and is likely to flow out from the unloading section 31 to the outside.

[0069] Therefore, it is preferable to control the average air ratio in the central region to be greater than 1.0 and equal to or less than 1.2 in response to the opening operation of the door of the unloading section 31, and to control the average air ratio in the discharge region to be equal to or greater than 1.0 and smaller than the average air ratio in the central region. Furthermore, it is preferable to perform the above control in response to the opening operation of the door of the unloading section 31, with the average air ratio in the discharge region being less than 1.1.

[0070] In addition, it is preferable to control the average air ratio in the charging area to be 1.0 or more and smaller than the average air ratio in the central area according to the opening operation of the door of the charging section 30. Furthermore, the above control is preferably performed according to the opening operation of the door of the charging section 30, with the air ratio in the charging area being less than 1.1.

[0071] The opening operation of the door of the charging section 30 and the opening operation of the door of the unloading 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 the 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 opening operation of the door of the unloading section 31. Note that the control command for the air ratio in each burner unit to the air ratio control units (41, 42, 43) may be issued by the control computer 45. This prevents the discharge of unburned ammonia and nitrogen oxides from the heating furnace 1 even when the doors of the charging section 30 and the discharge section 31 are open.

[0072] <Variations> The heating furnace 1 of the above embodiment includes a first burner section 11 arranged in the charging area US, a second burner section 12 arranged in the central area CS, and a third burner section 13 arranged in the discharge area DS. However, the heating furnace 1 may include a burner that burns a fuel gas that does not contain ammonia as another burner section. The fuel gas used in the other burner section may be, for example, coal gas to which ammonia is not 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 amount for the total amount of fuel gas containing ammonia supplied in each region and the total flow rate of fuel gas supplied to other burners arranged in each region, and determining the ratio of the total amount of combustion air supplied in that region to the calculated theoretical air amount.

[0073] 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 control valve and flow meter arranged in the coal gas supply system. Also, it is not necessary to include the mixer 16.

[0074] 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 droplets of the liquid fuel finely divided into 1 mm or less at the tip of the burner nozzle 17. Combustion is promoted by forming the liquid fuel into fine droplets. Also, a mixture of gaseous fuel and liquid fuel may be used as the fuel gas 5.

[0075] The burner equipment 2 applied in the above embodiment is not limited to a diffusion combustion type burner that mixes the fuel gas 5 and the combustion air 8 at the tip of the burner nozzle 17. A premix type 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 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 the combustion air in a tangential direction into the combustion tube and forms a swirling flow in the combustion tube to burn the fuel gas and the combustion air. In addition, a regenerative burner that alternately burns a pair of burners integrated with a heat storage body at intervals of several tens of seconds may be applied as the burner equipment 2.

[0076] When a double-tube type 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 tube and the combustion air 8 is supplied from the outer tube. A mixed gas of the fuel gas 5 and the combustion air 8 may be supplied to either or both of the inner and outer tubes of the double-tube type nozzle. Note that the fuel gas 5 and the combustion air 8 may be preheated as necessary.

[0077] The burner equipment 2 shown in Fig. 4 includes an ammonia gas supply system 18 and a coal gas supply system 19 that are paired with one burner nozzle 17. A flow 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, 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 may be mixed in advance, and the fuel gas 5 may be supplied from one fuel gas supply system 14 to two or more burner nozzles 17. In this case, by installing the flow rate adjustment valve 20 and the flow rate meter 21 in the fuel gas supply system 14, the fuel gas 5 supplied to each burner nozzle can be measured and controlled.

[0078] A gas composition analyzer that performs a component analysis of the gas being transported may be disposed 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 the component analysis may be performed offline using equipment such as a gas chromatograph.

[0079] 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 may be applied to the combustion air 8 by removing nitrogen from the air or adding pure oxygen. 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 the like. In addition, decreasing the oxygen content of the combustion air makes it possible to make the atmosphere inside the heating furnace a reducing atmosphere, and promotes the reduction of nitrogen oxides. In this case, when the oxygen concentration in the combustion air 8 is different from the oxygen concentration 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. That is, the average air ratio can be defined 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, and the operating method of the heating furnace according to this embodiment can be applied.

[0080] In the flue 34 of the heating furnace 1 of the above embodiment, a NOx concentration meter, an ammonia concentration meter, a CO concentration meter, or the like may be disposed as an analyzer for the exhaust gas discharged from the heating furnace 1. It is possible to manage whether nitrogen oxides, unburned ammonia, and carbon monoxide are sufficiently suppressed. EXAMPLES

[0081] 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, a test operation of a heating furnace shown in FIG. 5 will be described.

[0082] As shown in FIG. 5, the heating furnace used in this embodiment is arranged with a first burner section (11U, 11L) in the loading area US, a second burner section (12U1, 12U2, 12L1, 12L2) in the central area CS, and a third burner section (13U1, 13U2, 13L1, 13L2) in the unloading area DS. The heating furnace also includes 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). The burners used in the heating furnaces were all diffusion combustion type burners as shown in Figure 4, with a rated capacity of 800,000 kcal / hr.

[0083] A mixed gas of ammonia and methane (CH4) was used as the fuel gas supplied to the first burner section, the second burner section, and the third burner section. 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 the embodiment, the mixture ratio of ammonia gas and methane contained in the fuel gas 5 was adjusted by the flow rate control valve 20 provided in the ammonia gas supply system 18 and the coal gas supply system 19. In this embodiment, the mixture ratio is used to mean the calorific value ratio of ammonia and methane. In addition, the air ratio of the fuel gas 5 to the theoretical air amount was adjusted by adjusting the supply amount of the combustion air 8 by the flow rate control valve 20 provided in the combustion air supply system 15.

[0084] 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 embodiment, the mixture ratio of ammonia and 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 of 46.7Nm 3 A mixed gas was generated at a flow rate of 93.5 Nm3 / 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. 3 / hr.

[0085] The following describes the results of test operations in which 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.

[0086] Samples of exhaust gas were taken 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 concentrations of nitrogen oxides (NOx), unburned ammonia (NH3), and carbon dioxide (CO2) contained in the exhaust gas were measured. In addition, at the positions of the loading section 30 and the discharge section 31, exhaust gas samples were taken with the doors of the loading section 30 and the discharge section 31 open, and the nitrogen oxide (NOx) concentration and unburned ammonia (NH3) concentration contained in the exhaust gas were measured.

[0087] Table 1 shows the results of NOx concentration, NH3 concentration, and CO2 concentration of exhaust gas corresponding to the operating conditions of the heating furnace. Note that the evaluation of the CO2 concentration is based on the CO2 concentration emitted when only methane containing no ammonia gas is used as fuel gas as a conventional example, and the values ​​of the invention example and comparative example are expressed as relative values ​​to the CO2 concentration of the conventional example. The air ratio in Table 1 is the ratio 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 is expressed as an average air ratio.

[0088] At this time, the upper limit of the NOx concentration of the exhaust gas discharged from the heating furnace was set to 150 ppm. Also, the upper limit of the NH3 concentration of the exhaust gas discharged from the heating furnace was set to 25 ppm. And, when either the NOx concentration or the NH3 concentration of the sampled exhaust gas was equal to or higher than the upper limit at any of the positions of the charging section 30, the discharge section 31, and the flue 34, it was indicated as failing (×), and when the NOx concentration and the NH3 concentration of the exhaust gas were less than the upper limit at any of the positions, it was indicated as passing (◯).

[0089] In the conventional example, ammonia is not used 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, the invention example and the comparative example are both under conditions in which the amount of carbon dioxide emissions is reduced by half compared to the conventional example.

[0090] Comparative Examples 1 to 3 are examples in which the air ratio in the third burner section is less than 1.0. Unburned ammonia is generated by burner heating in the third burner section, and this increases the unburned ammonia concentration in the exhaust gas collected at the discharge section. In particular, when the air ratio in the second burner section is low, the unburned ammonia concentration in the exhaust gas increases.

[0091] In Comparative Examples 4 and 5, the air ratio in the third burner section was set to 1.1 or more. The amount of nitrogen oxides produced increased due to burner heating in the third burner section, and this increased the nitrogen oxide concentration in the exhaust gas sampled at the discharge section.

[0092] In Comparative Example 6, the air ratio in the first burner section and the third burner section was 1.0 or more and less than 1.1, but the air ratio in the second burner section was more than 1.2. Therefore, 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, and the NOx concentration in the exhaust gas was particularly high at the charging section and the flue.

[0093] In Examples 1 to 5, the air ratio in the second burner section is greater than 1.0 and equal to or less than 1.2, and the air ratio in the third burner section is equal to or greater than 1.0 and smaller than the air ratio in the second burner section. However, the air ratio in the first burner section is less than 1.0. In this case, the unburned ammonia concentration in the exhaust gas at the position of the charging section 30 tends to be slightly high, but the nitrogen oxide concentration and unburned ammonia concentration in the exhaust gas at the position of the charging section 30, the position of the discharge section 31, and the position of the flue 34 were sufficiently suppressed.

[0094] On the other hand, in Examples 6 to 10, the air ratio in the second burner section was greater than 1.0 and equal to or less than 1.2, and the air ratio in the third burner section was greater than 1.0 and smaller than the air ratio in the second burner section. Furthermore, the air ratio in the first burner section was greater than 1.0 and smaller than the air ratio in the second burner section. In this case, the nitrogen oxide concentration and unburned ammonia concentration of the exhaust gas at the position of the charging section 30, the position of the discharge section 31, and the position of the flue 34 were sufficiently suppressed.

[0095] [Table 1] [Explanation of symbols]

[0096] B Burner TD Transport direction S steel material S1 Steel tip S2 Steel tail end US charging area CS central area DS unloading area 1 Furnace 2 Burner equipment 3 Furnace wall 4 Inside the furnace 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 3rd burner section 14 Fuel gas supply system 15 Combustion air supply system 16 Mixing section 17 Burner nozzle 18 Ammonia gas supply system 19 Oil and Gas Supply System 20 Flow Control Valve 21 Flow meter 30 Charging side 31 Unloading section 32 Moving Skid 33 Fixed Skid 34 Flue 35 Exhaust gas treatment equipment 36 NOx concentration meter 37 Ammonia concentration meter 40 Air ratio control unit 41 Air ratio control section (charging area) 42 Air ratio control section (central area) 43 Air ratio control section (discharge area) 45 Control computer

Claims

1. A method for operating a heating furnace in which a material to be heated is heated while being transported from a charging section to a discharge section, comprising the steps of: The inside of the heating furnace is divided into a charging region on the charging section side, a discharge region on the discharge section side, and a central region sandwiched between the charging region and the discharge region, In the charging region, the central region, and the discharge region, burner heating is performed by burning a fuel gas containing ammonia, Exhaust gas is discharged from a flue installed near the charging section of the heating furnace. The burner heating in the central region is performed by setting an average air ratio of the fuel gas to a theoretical air amount of more than 1.00 and not more than 1.2, The burner heating in the discharge region is set to an average air ratio of the fuel gas to the theoretical air amount of 1.00 or more and is set to be smaller than the average air ratio of the fuel gas to the theoretical air amount of the central region. How to operate a heating furnace.

2. The burner heating in the discharge area is performed to set the average air ratio of the fuel gas to the theoretical air amount to less than 1.

10. A method for operating a heating furnace according to claim 1.

3. The burner heating in the discharge area is set by setting an average air ratio of the fuel gas to a theoretical air amount in accordance with an opening operation of an opening / closing door of the discharge section. A method for operating a heating furnace according to claim 1 or 2.

4. The burner heating in the charging region is set to an average air ratio of the fuel gas to the theoretical air amount of 1.00 or more and is set to be smaller than the average air ratio of the fuel gas to the theoretical air amount of the central region. A method for operating a heating furnace according to claim 1 or 2.

5. The burner heating in the charging area is set to an average air ratio of fuel gas to theoretical air of less than 1.

10. A method for operating a heating furnace according to claim 4.

6. The burner heating in the charging area is set by setting the average air ratio of the fuel gas to the theoretical air amount according to the opening operation of the opening and closing door of the charging section. A method for operating a heating furnace according to claim 4.

7. The burner heating in the charging area is set by setting the average air ratio of the fuel gas to the theoretical air amount according to the opening operation of the opening and closing door of the charging section. A method for operating a heating furnace according to claim 5.

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