TWI903358B - Operating methods and heating furnace - Google Patents

Abstract

This invention provides an operating method for a heating furnace and a heating furnace that can use ammonia, which can suppress the emission of carbon dioxide, as the combustion fuel for the heating furnace, and can reduce the amount of nitrogen oxides and unburned ammonia emitted from the heating furnace. The operation method of the furnace of the present invention includes: a first burner heating step, wherein a first fuel gas containing ammonia is heated by combustion air with an air ratio of the first fuel gas to the theoretical air volume of 0.9 to 1.0; a second burner heating step, wherein a second fuel gas containing ammonia is heated by combustion air with an air ratio of the second fuel gas to the theoretical air volume that is lower than that of the first fuel gas to the theoretical air volume; and an air injection step, wherein air is injected into the mixture of exhaust gas generated by heating the first burner and exhaust gas generated by heating the second burner.

Description

Operating methods and heating furnace

This invention relates to a method of operating a heating furnace and the heating furnace itself.

In integrated steel plants, blast furnace gases, particularly those emitted from the top of the blast furnace used to produce molten iron from iron ore, are a prime example of the effective utilization of byproduct gases generated in converters or coking furnaces as fuel gases. However, in recent years, with increasing demands for reducing carbon dioxide emissions, there is a growing need for combustion technologies to minimize the use of these byproduct gases. For instance, even in steel heating furnaces used to heat steel in hot rolling mills or plate rolling mills in integrated steel plants, there is a requirement to reduce the use of byproduct gases to decrease carbon dioxide emissions. At this time, the use of ammonia as fuel gas in steel heating furnaces is attracting considerable attention. That is, ammonia, which does not contain carbon, mainly produces water and nitrogen when burned, thus greatly reducing carbon dioxide emissions. It is expected to be used in the development of technology suitable for steel heating furnaces.

On the other hand, if ammonia is used as fuel for the heating furnace, the generation of nitrogen oxides (NOx) becomes a problem. Nitrogen oxides are harmful to human health and are a cause of photochemical fumes or acid rain, thus becoming a legally restricted emission target.

Therefore, to solve these problems, a heating technology has been proposed. Patent 1 discloses a boiler comprising: a combustion device for burning ammonia as fuel in the boiler; and a flue for guiding the combustion gases produced by the combustion of fuel. The boiler includes an injection unit disposed downstream of the combustion device from at least one of the boiler and the flue, and injects ammonia as a reducing agent toward the central portion of the boiler or the flue in a top view. This allows ammonia to be supplied to the central portion of the boiler, and even a small amount of ammonia can act as a reducing agent to reduce nitrogen oxides.

Furthermore, Patent Document 2 discloses a boiler comprising: a burner for burning fossil fuels within the boiler; an additional air supply unit disposed downstream of the burner in the direction of combustion gas flow within the boiler; and an ammonia fuel supply unit that supplies ammonia fuel to the boiler upstream of the additional air supply unit in the direction of fuel gas flow. Thus, in a two-stage combustion boiler including the additional air supply unit, by introducing ammonia fuel upstream of the additional air supply unit, the nitrogen component of the ammonia fuel will be reduced to _N₂ in the reducing environment region within the boiler, thereby suppressing the formation of nitrogen oxides. [Prior Art Documents] [Patent Documents]

Patent Document 1: Japanese Patent Application Publication No. 2019-086191 Patent Document 2: Japanese Patent Application Publication No. 2018-076985

[Problem to be Solved by the Invention] However, if the aforementioned prior art is applied to heating furnaces used for heating steel and the like, the following problems arise.

The technology disclosed in Patent Document 1 targets a combustion device such as a boiler, injecting ammonia downstream of the flow direction of the combustion gas to reduce nitrogen oxides generated in the combustion device. However, compared to the flow rate of the combustion gas generated in the combustion device, the amount of ammonia injected for reducing nitrogen oxides is extremely small. Therefore, even when ammonia is injected towards the center of the furnace, it sometimes does not mix uniformly with the nitrogen oxides contained in the combustion gas. As a result, the nitrogen oxides contained in the combustion gas are sometimes not effectively reduced. Therefore, the following problem arises: the ammonia, as a reducing agent, is not burned and is directly discharged to the outside of the furnace. In heating furnaces used to heat materials such as steel, unlike combustion devices like boilers, they typically include a door for loading and unloading the heated material. This can cause a problem: when the furnace door is open, toxic unburned ammonia (also known as "unburned ammonia") is released outside the furnace, leading to environmental degradation.

Patent document 2 also targets combustion devices such as boilers, using ammonia to reduce nitrogen oxides in a reducing environment zone within the boiler. Patent document 2 discloses that, in order to create a reducing environment zone within the boiler, the primary air supplied to the burner is set to be less than the amount of air required for complete combustion of fossil fuels. In the technology disclosed in patent document 2, a certain space and a certain reaction time are required within the boiler for the reduction reaction of nitrogen oxides. On the other hand, in heating furnaces used to heat materials such as steel, not only a combustion device (e.g., a burner) is needed inside the furnace, but also space is required to accommodate the heated material. In contrast, in furnaces such as boilers, the following difference exists: only the space required for the combustion reaction between fuel and combustion air is needed. Therefore, if the technology disclosed in Patent 2 is applied to a heating furnace for heating a heated body, and the space of the reduction environment zone is enlarged, the following problem arises: within the reduction environment zone, the reduction reaction of nitrogen oxides cannot proceed uniformly, resulting in unburned ammonia being discharged to the outside of the heating furnace.

Furthermore, Patent Document 2 reveals that when the air supply for ammonia combustion varies between 0.6 and 1.0 relative to the theoretical air supply, the following characteristic is observed: the leakage rate of unburned ammonia from the furnace outlet is inversely proportional to the air supply and the conversion rate to NOx. Therefore, to reduce both nitrogen oxides (NOx) and unburned ammonia, the primary air ratio must be controlled within a narrow range, which can easily lead to the discharge of nitrogen oxides or unburned ammonia to the outside due to changes in the operating conditions within the furnace.

This invention was made to solve the problems existing in the prior art. Its purpose is to provide an operating method for a heating furnace and a heating furnace that can use ammonia, which suppresses carbon dioxide emissions, as the combustion fuel for the heating furnace, and can reduce the amount of nitrogen oxides and unburned ammonia emitted from the heating furnace. [Means of Solving the Problem]

The operating method of the heating furnace of the present invention, which advantageously solves the aforementioned problem, is configured as follows.

[1] A method of operating a heating furnace includes: a first burner heating step, wherein burner heating is performed by means of a first fuel gas containing ammonia and combustion air having an air-to-fuel ratio of 0.9 to 1.0 relative to the theoretical air volume of the first fuel gas; a second burner heating step, wherein burner heating is performed by means of a second fuel gas containing ammonia and combustion air having an air-to-fuel ratio having a lower air-to-fuel ratio relative to the theoretical air volume of the second fuel gas than that relative to the theoretical air volume of the first fuel gas; and an air injection step, wherein air is injected. [2] The method of operating the furnace as described in [1], wherein the air injection step involves injecting air into a mixed waste gas formed by mixing the waste gas generated by the first burner heating step and the waste gas generated by the second burner heating step. [3] The method of operating the furnace as described in [1] or [2], wherein in the second burner heating step, the air ratio relative to the theoretical air volume of the second fuel gas is less than 0.9. [4] The method of operating the furnace as described in [1] or [2], wherein at least one of the first fuel gas and the second fuel gas is heated by a mixture of ammonia and coal gas. [5] The method of operating the furnace as described in [3], wherein at least one of the first fuel gas and the second fuel gas is heated by a mixture of ammonia and coal gas.

The present invention, which advantageously solves the aforementioned problem, is configured as follows: [6] A heating furnace includes: two or more burner devices that perform burner heating using a fuel gas containing ammonia; an air ratio adjusting unit that adjusts the air ratios of the combustion air supplied to the two or more burner devices relative to the theoretical air volume of the fuel gas; a control unit that controls the air ratio of the combustion air supplied to at least one of the two or more burner devices to be different from the air ratio of the combustion air supplied to the other burner devices; and an air injection device that injects air into a mixture of exhaust gases discharged from the two or more burner devices. [7] The heating furnace as described in [6], wherein the burner equipment comprises: a first burner equipment, wherein burner heating is performed by a first fuel gas containing ammonia, the air ratio of which has been adjusted by the air ratio adjustment unit, and combustion air having an air ratio of 0.9 to 1.0 relative to the theoretical air volume of the first fuel gas; and a second burner equipment, wherein burner heating is performed by a second fuel gas containing ammonia, and combustion air having an air ratio of a lower air ratio relative to the theoretical air volume of the second fuel gas than that relative to the theoretical air volume of the first fuel gas, wherein the first burner equipment, the second burner equipment, and the air injection equipment are sequentially arranged along the airflow inside the heating furnace, starting from the upstream side of the airflow. [8] The heating furnace as described in [6], wherein the heating furnace includes an opening for discharging the mixed exhaust gas, and the air injection device is positioned closer to the opening than the first burner device and the second burner device. [Effects of the Invention]

According to the present invention, by using ammonia as the combustion fuel for a heating furnace, the emission of carbon dioxide can be suppressed, and the emission of nitrogen oxides and unburned ammonia generated by the combustion of ammonia towards the outside of the heating furnace can be reduced.

The heating furnace of this embodiment will now be described. <Heating Furnace> The heating furnace of this embodiment includes a burner that burns fuel gas, which serves as a heat source, and houses a heated object to raise its temperature to a predetermined temperature. The heated object is primarily a metal, but can be either a ferrous or non-ferrous metal. The heating temperature of the heated object is 700°C to 1400°C. Figures 1 and 2 show an example of the heating furnace of this embodiment where the heated object is made of steel. For example, the heating furnace used in hot rolling mills for steel is used to heat the cast slabs to a specified heating temperature (approximately 1100℃ to 1300℃).

The heating furnace 1 shown in Figure 1 includes: a loading section 30 for loading steel S (slabs) as the heated material; and a unloading section 31 for unloading (extracting) the heated steel S. For example, steel S manufactured using a continuous casting line is transported to the loading side yard of the heating furnace and loaded into the heating furnace 1 from the loading section 30 according to the production schedule of the hot rolling line, etc. The interior of the heating furnace 1 is divided into multiple zones, and the upstream side typically includes a heating zone divided into two to eight zones and one to three soaking zones. Inside the heating furnace 1, there are generally fixed skids 33 for holding the steel S and moving skids 32 for transporting the steel S. The heating furnace, which includes a fixed slide 33 and a movable slide 32, is called a walking beam continuous heating furnace.

During the operation of the heating furnace, each zone inside the furnace is controlled to a different ambient temperature, and the average temperature of the steel S loaded into the heating furnace 1 gradually increases. In this way, the steel S is controlled to a predetermined target heating temperature (the target temperature of the slab when it is extracted from the heating furnace). The steel S, having reached the target temperature, is then supplied for hot rolling via the discharge section 31.

Inside the heating furnace 1, multiple burners are arranged along the conveying direction of the steel S (steel movement direction 100). Burners B are configured to heat the interior of the heating furnace through combustion. When the interior of the heating furnace is heated by the burners, the temperature of the steel rises due to radiation from the furnace walls. Furthermore, sometimes the flow of ambient gas inside the heating furnace causes the steel to heat up through convection. Alternatively, the steel can be heated by direct contact between the burner flame and the steel. In summary, a burner heats the interior of a furnace by burning fuel gas, which serves as a heat source, thereby raising the temperature of the material being heated inside the furnace.

The interior of the heating furnace 1 includes, in addition to the space for the flame emitted by the self-igniting burner, a space for placing and transporting the heated material. Therefore, it is characterized by a larger internal volume relative to the combustion energy input into the furnace compared to boilers or similar vessels designed to generate an internal combustion reaction. Representative values for the furnace internal volume per unit combustion energy ( ^m³ /MW) in gas turbines, pulverized coal boilers, and oil/gas boilers are, for example: 2 ^m³ /MW for gas turbines, 6 ^m³ /MW for pulverized coal boilers, and 2 ^m³ /MW for oil/gas boilers. In contrast, heating furnaces are as large as 10 ^m³ /MW to 16 ^m³ /MW, for example, the heating furnace used in hot rolling mills for steel is about 11 ^m³ /MW to 13 ^m³ /MW.

During the operation of the heating furnace 1, the doors (opening and closing doors) of the loading section 30 and the unloading section 31 are closed, generating a relatively high atmospheric pressure inside. The doors are temporarily opened when steel S is loaded and unloaded. When the doors are open, a pressure difference is created between the pressure inside the heating furnace and the area near the doors, causing the combustion gas inside the heating furnace to flow from the area of higher pressure to the area of lower pressure. When the doors of the heating furnace 1 are fully open, the combustion gas flows primarily in the direction of being discharged from the furnace through the opening to the outside of the heating furnace 1.

Figure 2 is a cross-sectional view of the heating furnace 1. The burners B are mostly arranged inside the heating furnace 1 on the upper and lower surfaces of the steel S to avoid a temperature difference between the upper and lower surfaces of the steel S. Moreover, they are mostly arranged on both sides of the conveying direction of the steel S to avoid a temperature difference between the front end S1 and the rear end S2 of the steel S.

The heating furnace 1 of this embodiment is a heating furnace as described below, comprising: two or more combustion devices that use fuel gas containing ammonia for combustion heating; an air ratio adjustment unit that adjusts the air ratios of the combustion air supplied to the two or more combustion devices relative to the theoretical air volume of the fuel gas; a control unit that controls the air ratio of the combustion air supplied to at least one of the two or more combustion devices to be different from the air ratio of the combustion air supplied to the other combustion devices; and an air injection device that injects air into the mixed waste gas discharged from the two or more combustion devices. <Combustion Equipment> Preferredly, the device comprises: a first combustion equipment, wherein combustion heating is performed using a first fuel gas containing ammonia and combustion air with an air-to-fuel ratio of 0.9 to 1.0 relative to the theoretical air volume of the first fuel gas; and a second combustion equipment, wherein combustion heating is performed using a second fuel gas containing ammonia and combustion air with an air-to-fuel ratio having a lower air-to-fuel ratio relative to the theoretical air volume of the second fuel gas than that relative to the theoretical air volume of the first fuel gas.

Furthermore, in the heating furnace 1 of this embodiment, at least one of the burners B disposed inside is a first burner device that heats a first fuel gas containing ammonia by means of combustion air, and at least one of the other burners B is a second burner device that heats a second fuel gas containing ammonia by means of combustion air.

Figure 3 is used to illustrate the first burner device and the second burner device. Figure 3 is a diagram showing the configuration of the first burner device 2, the second burner device 3, and the air injection device 4 of the heating furnace 1, viewed from the top surface, including a portion of the furnace wall 35 located on one side of the heating furnace 1 shown in Figure 1.

The first burner apparatus 2 uses a first fuel gas 5 containing ammonia as fuel gas and combustion air 12 to heat the first burner by injecting a flame into the furnace. The first burner apparatus 2 includes: a first burner nozzle 7 for injecting a flame into the furnace; a first fuel gas supply system 14 for supplying the first fuel gas 5 to the first burner nozzle 7; and a combustion air supply system 18 for supplying combustion air 12 to the first burner nozzle 7. The first burner nozzle 7 is, for example, a double-tube nozzle, injecting the first fuel gas 5 into the furnace from the inside, while the outside is supplied with combustion air 12. In this way, a combustible mixture of the first fuel gas 5 and the combustion air 12 is formed, and a flame is ejected from the front end of the first burner nozzle 7 toward the interior of the heating furnace 1.

The second burner device 3 may be configured with the same structure as the first burner device 2. The second burner device 3 uses a second fuel gas 6 containing ammonia as fuel gas and combustion air 12 to heat the second burner by injecting flames into the furnace. The second burner device 3 includes: a second burner nozzle 8 for injecting flames into the furnace; a second fuel gas supply system 15 for supplying the second fuel gas 6 to the second burner nozzle 8; and a combustion air supply system 19 for supplying combustion air 12 to the second burner nozzle 8. The second burner nozzle 8 also uses a double-tube nozzle, for example, to inject the second fuel gas 6 into the furnace from the inner tube and to supply combustion air 12 from the outer tube. In this way, a combustible mixture of the second fuel gas 6 and the combustion air 12 is formed, and a flame is injected from the front end of the second burner nozzle 8 into the interior of the heating furnace 1.

Furthermore, for the first burner device 2 and the second burner device 3, a vortex burner that can agitate the fuel gas ejected by the self-igniting burner nozzle or a tubular flame burner that blows fuel gas and combustion air into the combustion chamber tangentially to form a circulating flow inside the combustion chamber for combustion can also be used.

Both the first fuel gas 5 and the second fuel gas 6 use fuel gas containing ammonia. Ammonia can be used as a single fuel gas, or a mixture of ammonia and other fuels can be used. The mixing ratio of ammonia in the first fuel gas 5 and the second fuel gas 6 can be different or the same. Furthermore, the other fuels constituting the mixture can be different or the same in the first fuel gas 5 and the second fuel gas 6. However, since there is a possibility that the supply equipment for supplying fuel gas to the heating furnace 1 becomes more complex and equipment costs increase, it is economical to use the same fuel gas containing ammonia for both the first fuel gas 5 and the second fuel gas 6.

Ammonia is a difficult-to-ignite fuel, harder to ignite and burns more slowly than other fuels. To improve combustion stability, a mixture of ammonia and other fuels can be used. The preferred fuel to mix with ammonia is coal gas. Coal gas refers to any gas obtained from coal. Preferably, the coal gas includes any of the following: coke oven gas, blast furnace gas, converter gas, or electric furnace gas. These are byproduct gases generated in steel mills and have a stabilizing effect on ammonia combustion. Blast furnace gas is a byproduct gas generated during the reduction of iron ore in a blast furnace to produce molten iron. Coke oven gas is a byproduct gas generated during the high-temperature dry distillation of coal to produce coke. Converter gas is a byproduct gas produced during the steelmaking process in a converter. Electric furnace gas refers to the gas generated by the incomplete combustion of auxiliary fuel (carburizer) in the electric furnace. As a component of the mixed gas, a gas appropriately mixed with blast furnace gas, coke oven gas, and converter gas (sometimes called M gas) can be used. This is because by mixing gases with different calorific values, the heat required for heating the heated object can be supplied, thus ensuring stable furnace operation.

This embodiment is an example in which the first fuel gas 5 used in the first burner device 2 shown in FIG. 3 and the second fuel gas 6 used in the second burner device 3 are both mixtures of ammonia and coal gas. The first fuel gas supply system 14 is connected to the ammonia supply system 25 and the coal gas supply system 27. Ammonia 10 and coal gas 11 are mixed in the mixing section 16 and supplied to the first burner nozzle 7. A flow regulating valve 53 for adjusting the supply amount of each gas to the mixing section 16 and a flow meter 52 for measuring the supply flow rate can be included midway between the ammonia supply system 25 and the coal gas supply system 27. This allows adjustment of the mixing ratio of ammonia and coal gas in the mixed gas. The second fuel gas supply system 15 is also connected to the ammonia supply system 26 and the coal gas supply system 28. Ammonia 10 and coal gas 11 are mixed in the mixing section 17 and then supplied to the second burner nozzle 8. The second burner device 3 may also include, midway between the ammonia supply system 26 and the coal gas supply system 28, a flow regulating valve 53 for adjusting the supply amount of ammonia 10 and coal gas 11 to the mixing section 17, and a flow meter 52 for measuring the supply flow rate.

The mixing section (16, 17) refers to the section where the supply pipes of the coal gas supply system (27, 28) and the supply pipes of the ammonia supply system (25, 26) converge. Ammonia 10 and coal gas 11 are supplied from their respective supply pipes and converge, thereby allowing mixing even without a special stirring mechanism. The mixing section (16, 17) simply needs to form a defined space at the convergence of these supply pipes. However, the mixing section (16, 17) may include a static mixer or a dynamic mixer with stirring capabilities. This is preferable in generating a more uniform mixture of coal gas and ammonia.

The combustion air supply system 18 of the first burner device 2 and the combustion air supply system 19 of the second burner device 3 may also include a flow regulating valve 53 for adjusting the flow rate of combustion air 12 supplied to the first burner nozzle 7 and the second burner nozzle 8, and a flow meter 52 for measuring the supply flow rate. The amount of combustion air in the first burner device 2 and the second burner device 3 is adjusted, thereby making it easier to adjust the air ratio during the heating of each burner in the first burner device 2 and the second burner device 3.

The combustion air used in the first burner unit 2 and the combustion air used in the second burner unit 3 can be supplied by an auto-combustion air supply system from air collected from the atmosphere. However, air modified by removing nitrogen or adding pure oxygen can be used for the combustion air 12. By increasing the oxygen content of the combustion air, the oxidation reaction of the fuel gas can be promoted, and the flow rate of the combustion air supplied by the auto-combustion air supply system can be reduced, thus reducing the power consumption of pumps, etc. Moreover, by reducing the oxygen content of the combustion air, the furnace environment of the heater can be set as a reducing environment, promoting the reduction of nitrogen oxides.

<Air Jet Equipment> In addition to the first burner 2 and the second burner 3, the heating furnace 1 of this embodiment also includes an air jetting device 4, which jets air into a mixture of exhaust gas 23, consisting of exhaust gas 21 discharged from the first burner 2 and exhaust gas 22 discharged from the second burner 3. The air jetting device 4 is connected to an air supply system 29 and jets air 13 into the furnace from air jet nozzles 9. The air supply system 29 may include a flow regulating valve 53 for adjusting the flow rate of the air 13 supplied to the air jet nozzles 9, and a flow meter 52 for measuring the supply flow rate. This allows for adjustment of the air injection rate when injecting the mixed exhaust gas from the first burner 2 and the second burner 3, thereby promoting the reduction reaction of nitrogen oxides contained in the mixed exhaust gas.

The air ejected by the air jet device 4 can be air collected from the atmosphere. However, air that has been modified by removing nitrogen or adding pure oxygen can also be supplied to the air jet nozzle 9 via the air supply system 29. By increasing the oxygen content of the air 13, the reduction reaction of nitrogen oxides contained in the mixed exhaust gas 23 is promoted.

<Configuration of the Combustion Equipment in the Heating Furnace> The configuration of the combustion equipment in the heating furnace will be explained. In the heating furnace of this embodiment, along the airflow inside the heating furnace, starting from the upstream side of the airflow, there is a first combustion equipment that heats the fuel gas with an air-to-fuel ratio of 0.9 to 1.0; a second combustion equipment that heats the fuel gas with an air-to-fuel ratio that is smaller than that of the first fuel gas; and an air jetting device that injects air into the mixture of exhaust gas discharged from the first combustion equipment and exhaust gas discharged from the second combustion equipment. The reason for this is that by injecting oxygen into the mixture of NOx and unburned ammonia, the reduction reaction of NOx by ammonia is promoted, thereby reducing the NOx and unburned ammonia emitted from the heating furnace. Furthermore, in the case where the heating furnace includes an opening for emitting combustion gases, it is preferable that the air injection device be positioned closer to the opening than the first and second burners.

Figure 7 illustrates an example of the structure of the heating furnace according to this embodiment. The heating furnace shown in Figure 7 includes: a loading section 30 for loading the object to be heated into the heating furnace; a removal section 31 for removing the object to be heated; and a flue 34 for discharging exhaust gas (combustion gas) from inside the heating furnace 1 to the outside of the heating furnace. The loading section 30 is a temporarily open opening when the object to be heated is loaded into the heating furnace. The removal section 31 is also a temporarily open opening when the object to be heated is removed from the heating furnace. On the other hand, flue 34 is designed to regulate the pressure inside the heating furnace 1 to prevent it from becoming excessive, thus discharging exhaust gas from within the furnace. It is a partially open opening towards the outside of the heating furnace, and therefore remains open at all times. Therefore, inside the heating furnace 1 shown in Figure 7, at least a flow of combustion gas is generated from inside the heating furnace towards flue 34.

In this embodiment, starting from the upstream side of the combustion gas flow towards the flue 34, the first burner device 2, the second burner device 3, and the air injection device 4 are arranged in sequence. In the example shown in Figure 7, the first burner device 2 is arranged near the center of the heating furnace 1 in the conveying direction, both above and below the heated body. Downstream of the combustion gas flow of the first burner device 2, one second burner device 3 is arranged above the heated body, and two second burner devices 3 are arranged below it. Furthermore, along the combustion gas flow F, the air injection device 4 is arranged downstream of the second burner device 3.

In Figure 7, the first burner device 2 heats the burner with an air-to-fuel gas ratio of 0.9 to 1.0, while the second burner device 3 heats the burner with an air-to-fuel gas ratio that is smaller than the air-to-fuel gas ratio of the first fuel gas. As a result, exhaust gas 21, which contains more nitrogen oxides, moves along the combustion gas flow F within the heating furnace and mixes with exhaust gas 22, which contains more unburned ammonia, to generate mixed exhaust gas 23. Mixed exhaust gas 23 moves along the combustion gas flow F within the heating furnace and further moves toward the flue 34, which serves as an opening. The air jetting device 4 is positioned further downstream in the airflow than the first heating device 2 and the second heating device 3, thus injecting air 13 into the mixed waste gas 23 before it is discharged from the opening. In this way, the oxygen in the air 13 promotes the reduction of nitrogen oxides by ammonia, thereby reducing the concentration of nitrogen oxides and ammonia in the waste gas discharged to the outside of the heating furnace through the flue 34.

Furthermore, the burner within the heating furnace 1 may also include a burner other than the first burner device 2 and the second burner device 3. However, the burner other than the first burner device 2 and the second burner device 3 (referred to as the third burner device) is a device that uses ammonia-free fuel for burner heating. The third burner device does not emit nitrogen oxides and unburned ammonia, or even if it does, as long as the emission amounts of nitrogen oxides and unburned ammonia are lower than those of the first burner device or the second burner device (e.g., less than 1/10), it will not cause external interference to the reduction reaction of nitrogen oxides in the mixed exhaust gas. The third burner device may, for example, perform burner heating using coal gas as fuel gas.

Figure 8 shows the structure of the heating furnace of this embodiment. The heating furnace shown in Figure 8 is equipped with two burner devices (44A, 44B) and an air injection device 4. The two burner devices (44A, 44B) can be burner devices with the same structure, and the fuel gas 45 supplied to the burner devices 44 can also be the same.

An air-to-fuel ratio adjustment unit 40 is provided in each burner unit 44, and the air-to-fuel ratio adjustment units 40 corresponding to the two burner units (44A, 44B) are connected to the control unit 42. The air-to-fuel ratio adjustment unit 40 has the function of adjusting the air-to-fuel ratio of combustion air to fuel gas 45 for each burner unit 44. For example, the air-to-fuel ratio adjustment unit 40 measures the flow rate of the fuel gas 45 supplied to the burner nozzle, and calculates the theoretical air volume required for complete combustion of the fuel gas 45 based on the measured flow rate and fuel composition of the fuel gas 45. Furthermore, based on the air ratio set for each burner unit (44A, 44B), the opening degree of the flow regulating valves configured in the combustion air supply system is adjusted, thereby setting the air ratio for burner heating for each burner unit (44A, 44B).

The control unit 42 sets the air ratio in the air ratio adjustment unit 40 for each burner device (44A, 44B). The control unit 42 sets the air ratio in the air ratio adjustment unit 40 such that the air ratio of one of the burner devices 44A is between 0.9 and 1.0. The control unit 42 sets the air ratio in the air ratio adjustment unit 40 such that the other burner device 44B heats the burner with an air ratio lower than that of one of the burner devices 44A. At this time, as shown in the configuration of the devices in Figure 8, the control unit 42 can set the air ratio of the burner device 44A, which is located far from the air injection device 4, to 0.9 to 1.0, and set the air ratio of the burner device 44B, which is located close to the air injection device 4, to be smaller than the air ratio of the burner device 44A, which is located far from the air injection device 4.

A burner device 44A, positioned far from the air injection device 4 and with an air ratio set to 0.9 to 1.0, functions as the first burner device 2. A burner device 44B, positioned close to the air injection device 4, functions as the second burner device 3. Therefore, by using two burner devices (44A, 44B) including an air ratio adjustment unit 40 and a control unit 42 that sets their air ratio, a mixed exhaust gas 23 containing nitrogen oxides and unburned ammonia can be generated. The air injection device 4 then promotes the reduction reaction of nitrogen oxides with the aid of ammonia.

Next, the operation method of the heating furnace according to this embodiment will be described. <Operation Method of Heating Furnace> This embodiment is an operation method of a heating furnace, including: a first burner heating step, wherein the burner is heated by a first fuel gas containing ammonia and combustion air with an air-to-fuel ratio of 0.9 to 1.0 relative to the theoretical air volume of the first fuel gas; a second burner heating step, wherein the burner is heated by a second fuel gas containing ammonia and combustion air with an air-to-fuel ratio that is lower than the air-to-fuel ratio of the theoretical air volume of the first fuel gas; and an air injection step, wherein air is injected.

In the heating furnace, nitrogen oxides are produced by burning ammonia-containing fuel gas, generating a mixed exhaust gas containing both nitrogen oxides and ammonia. Oxygen-containing air is then injected into this mixed exhaust gas. This process promotes the reduction reaction of nitrogen oxides by ammonia. The ammonia is oxidized by the oxygen in the air, and the oxidized ammonia decomposes the nitrogen oxides. Thus, ammonia, along with the nitrogen oxides in the mixed exhaust gas, is decomposed and rendered harmless. The reason for combining the first and second burner heating processes is that the exhaust gas from the first burner contains a relatively higher amount of nitrogen oxides, while the exhaust gas from the second burner contains a relatively higher amount of unburned ammonia. Mixing them creates the mixed exhaust gas containing both nitrogen oxides and ammonia.

The operation of the heating furnace will be explained using the first burner heating 2, the second burner apparatus 3, and the air injection apparatus 4 shown in Figure 3. In this embodiment, the first burner heating is performed as described below: the burner is heated by a first fuel gas 5 containing ammonia and combustion air 12 with an air-to-fuel ratio (sometimes simply referred to as air-to-fuel ratio) of 0.9 to 1.0 relative to the theoretical air volume of the first fuel gas 5. Here, the theoretical air volume refers to the amount of air required for complete combustion of the fuel gas. Furthermore, the air-to-fuel ratio relative to the theoretical air volume refers to the ratio of the amount of air supplied to the burner apparatus as combustion air to the amount of air required for complete combustion of the fuel gas.

The air-to-fuel ratio for heating the first burner is set to 0.9–1.0 to ensure that the exhaust gas 21 from the first burner contains nitrogen oxides. If the air-to-fuel ratio is less than 0.9, ammonia combustion is suppressed, and the amount of unburned ammonia in the exhaust gas 21 increases compared to nitrogen oxides. Conversely, if the air-to-fuel ratio exceeds 1.0, ammonia combustion in the first fuel gas is promoted, resulting in excessive nitrogen oxides in the exhaust gas 21, making it difficult to fully reduce the nitrogen oxides in the mixed exhaust gas 23. Furthermore, the nitrogen oxide concentration in the exhaust gas 21 generated by setting the air-to-fuel ratio of the first burner to 0.9–1.0 is approximately 400 ppm to 5000 ppm. The exhaust gas 21 from the first burner sometimes also contains unburned ammonia, but its concentration is below 5 ppm at an air-to-fuel ratio of 0.9, and approximately zero at an air-to-fuel ratio of 0.95–1.0. Therefore, the exhaust gas 21 generated from the first burner contains a relatively high amount of nitrogen oxides.

On the other hand, in this embodiment, the second burner heating is performed as described below: the burner is heated by a second fuel gas containing ammonia and combustion air with an air ratio that is lower than the theoretical air ratio of the second fuel gas relative to its volume. This is to ensure that the exhaust gas 22 heated by the second burner contains a relatively large amount of unburned ammonia. If the air ratio for the second burner heating is higher than that for the first burner heating, the effectiveness of using the unburned ammonia contained in the exhaust gas 22 to reduce nitrogen oxides in the exhaust gas 21 will decrease.

Preferably, the air-to-air ratio of the second burner heating gas to the theoretical air volume of the second fuel gas is less than 0.9. This is because the increased amount of unburned ammonia in the exhaust gas 22 heated by the second burner promotes the reduction reaction of nitrogen oxides in the mixed exhaust gas 23. The lower limit of the air-to-air ratio for the second burner heating gas is set at 0.7. If the air-to-air ratio for the second burner heating gas is less than 0.7, the combustion in the second burner heating gas will become unstable.

Furthermore, the exhaust gas 22 heated by the second burner sometimes contains both nitrogen oxides and unburned ammonia. However, by making the air-to-air ratio for heating the second burner smaller than that for heating the first burner, the exhaust gas 22 contains more unburned ammonia than the exhaust gas 21. Moreover, by setting the air-to-air ratio for heating the second burner to 0.7 or higher and less than 0.9, the concentration of unburned ammonia in the exhaust gas 22 can be set to 10 ppm to 24000 ppm. The smaller the air-to-air ratio for heating the second burner, the higher the concentration of unburned ammonia in the exhaust gas 22. When the air-to-air ratio is 0.85, the concentration of unburned ammonia is approximately 1200 ppm; when the air-to-air ratio is 0.8, the concentration of unburned ammonia is approximately 6400 ppm. At this point, although the exhaust gas 22 also contains nitrogen oxides, its concentration is below 400 ppm, decreasing to about 15 ppm when the air-to-air ratio is 0.85. That is, the exhaust gas 22 produced by heating the second burner contains a relatively large amount of unburned ammonia.

When a flame is injected into the heating furnace by heating with the first burner, the exhaust gas 21 diffuses within the heating furnace. At this time, as shown in Figure 3, when a flow of combustion gas (exhaust gas) is generated within the heating furnace, the exhaust gas 21 moves along the flow of gas within the heating furnace towards the second burner device 3. Similarly, when a flame is injected into the heating furnace by heating with the second burner, the exhaust gas 22 generated by the heating with the second burner also moves along the flow of gas within the heating furnace. As a result, exhaust gas 21, which contains a relatively higher amount of nitrogen oxides, and exhaust gas 22, which contains a relatively higher amount of unburned ammonia, mix in the heating furnace to generate mixed exhaust gas 23 containing both nitrogen oxides and unburned ammonia. The balance of the amounts of nitrogen oxides and unburned ammonia contained in the mixed exhaust gas 23 can be changed by setting the air ratio for heating in the first burner and the air ratio for heating in the second burner. Furthermore, the ratio of the flow rate of the first fuel gas 5 heated in the first burner to the flow rate of the second fuel gas 6 heated in the second burner can be changed by setting.

In this embodiment, an air jetting device 4 is used to jet air 13 onto a mixed waste gas 23 containing nitrogen oxides and unburned ammonia. This is based on the understanding that the reduction reaction of nitrogen oxides with ammonia is promoted by the presence of a certain amount of oxygen. That is, by jetting air 13 onto the mixed waste gas 23 containing nitrogen oxides and ammonia, the oxygen contained in the air 13 promotes the reduction reaction of nitrogen oxides with ammonia. This reduces the nitrogen oxides and ammonia content in the mixed waste gas 23. The gas jetted using the air jetting device 4 can be any oxygen-containing gas; air that has been modified by removing nitrogen or adding pure oxygen can also be jetted.

Figure 4 is a schematic diagram illustrating the chemical reaction when air is injected into the mixed exhaust gas 23. The exhaust gas 21 heated by the first burner contains more nitrogen oxides generated by the combustion of ammonia than unburned ammonia. The exhaust gas 22 heated by the second burner contains more ammonia residue from the fuel gas as it remains in an unburned state than nitrogen oxides. Furthermore, the mixed exhaust gas 23 is in a state where these nitrogen oxides and unburned ammonia are mixed, and oxygen is injected into the mixed exhaust gas.

This facilitates the following reactions: Ammonia ( _NH₃ ) is oxidized by oxygen to generate NH₃ radicals and _HO₂ radicals. Meanwhile, nitric oxide (NO) is the main component of the nitrogen oxides contained in the mixed waste gas 23. NH₃ is reduced by NH₃ radicals to generate nitrogen and OH radicals. Thus, the nitrogen oxides in the mixed waste gas 23 are reduced. Furthermore, oxygen contained in the air 13 ejected from the air ejector device 4 decomposes ammonia in the mixed waste gas 23 while unburned ammonia is present, generating NH₃ radicals. In other words, if sufficient oxygen is ejected into the mixed waste gas 23, unburned ammonia will be decomposed. Moreover, sufficient generation of NH₃ radicals reduces the nitrogen oxides in the mixed waste gas 23. Therefore, both nitrogen oxides and ammonia in the mixed waste gas 23 can be reduced.

As described above, in this embodiment, by injecting air into a mixture of exhaust gas generated from heating the first burner and exhaust gas generated from heating the second burner, nitrogen oxides and unburned ammonia can be effectively decomposed. This prevents nitrogen oxides or unburned ammonia from being discharged outside the heating furnace 1. In contrast, in the technology disclosed in Patent 2, because the air-to-air ratio for ammonia combustion is pre-set, it is difficult to make nitrogen oxides and ammonia coexist. Moreover, even if nitrogen oxides and ammonia coexist, it is difficult to adjust their balance. Therefore, there is a problem that even if an additional air supply unit is provided downstream of the burner in the direction of combustion gas flow within the furnace to supply oxygen, the reduction reaction of nitrogen oxides with the aid of ammonia cannot be efficiently promoted. Therefore, a fixed space, the reduction environment zone, must be provided to advance the reduction reaction of nitrogen oxides using ammonia. On the other hand, according to the embodiment described above, the burners are heated in a predetermined manner with a fixed air-to-fuel ratio between the first and second burners. This allows nitrogen oxides and unburned ammonia to coexist optimally in equilibrium, thereby efficiently advancing the reduction reaction of nitrogen oxides using ammonia. At this time, the gas temperature of the mixed exhaust gas 23, formed by the mixture of exhaust gas 21 from the first burner and exhaust gas 22 from the second burner, is preferably set to 700°C to 1450°C. This is because the reduction reaction of nitrogen oxides is promoted by the generation of NH radicals.

Regarding the injection of air 13 toward the mixed exhaust gas 23, it is preferable to mix the exhaust gas 22 generated by heating the second burner with the exhaust gas 21 generated by heating the first burner in the mixed exhaust gas 23. That is, the exhaust gas 21 generated by heating the first burner can be generated first, and the exhaust gas 22 generated by heating the second burner can be mixed into the generated exhaust gas 21. The burner devices shown in Figures 3 and 5 are all arranged downstream of the first burner device 2 relative to the gas flow of the combustion gas in the heating furnace, with the second burner device 3 disposed downstream of the first burner device 2.

In contrast, Figure 6 shows an example where the second burner device 3 is positioned upstream of the first burner device 2. In this case, a relatively large amount of waste gas 22 containing unburned ammonia is generated from the second burner device 3 upstream of the combustion gas flow. However, if the waste gas 22 moves along the combustion gas flow towards the first burner device 2, it may sometimes approach the area of the flame ejected from the first burner device 2. Especially when the combustion gas flow is fast, the waste gas 22 from the second burner device 3 may move downstream near the furnace wall. At this time, some of the unburned ammonia contained in exhaust gas 22 may be combusted by the flame from the first burner device 2, resulting in a reduction in the amount of unburned ammonia in exhaust gas 22, and some of it becoming nitrogen oxides. As a result, the amount of unburned ammonia contained in the mixed exhaust gas 23 formed downstream of the first burner device 2 decreases, and the reduction reaction of nitrogen oxides by ammonia may sometimes be hindered.

Through the above, the exhaust gas 22 generated by heating the second burner is mixed with the exhaust gas 21 generated by heating the first burner to form a mixed exhaust gas 23, which is then injected with air. Therefore, within the heating furnace 1, heating of the first burner, heating of the second burner, and air injection occur from the upstream side of the airflow along the internal airflow of the heating furnace. [Example]

The effects of this embodiment will be specifically explained below based on examples, but the invention is not limited to these examples. As an embodiment of the invention, the following example illustrates how, using the burner device shown in Figure 3, waste gas is collected downstream of the combustion gas flow, and the concentrations of nitrogen oxides and unburned ammonia contained in the waste gas are measured.

The combustion apparatus has a first combustion device and a second combustion device arranged inside along the gas flow F (flow generated from left to right in Figure 3) starting from the upstream side of the gas flow. Furthermore, an air injection device is included on the downstream side of the gas flow along the second combustion device.

For the fuel gas in the first and second burners, a mixture of ammonia and methane ( _CH4 ) is used. In Figure 3, ammonia is supplied from ammonia supply systems 25 and 26 to mixing sections 16 and 17, respectively, while methane is supplied from coal gas supply systems 27 and 28 to mixing sections 16 and 17, generating a mixture of ammonia and methane, which is then supplied to the burner nozzles as the first fuel gas 5 and the second fuel gas 6. However, flow regulating valves are installed in ammonia supply systems 25 and 26, and coal gas supply systems 27 and 28, to adjust the mixing ratio of the mixture. Furthermore, the combustion air supply system 18 and combustion air supply system 19 are also equipped with flow regulating valves, thereby allowing adjustment of the air ratio relative to the theoretical air volume of the first fuel gas 5 and the second fuel gas 6. On the other hand, oxygen-containing air is injected from the air injection device 4 into the mixed exhaust gas from the first burner and the second burner. Moreover, the air supply system 29 is equipped with a flow regulating valve, thereby allowing the presence or absence (on/off) of the injected air mixed with the exhaust gas to be changed.

The first and second burners are devices capable of outputting a rated heat capacity of 800,000 kcal/hr. The first and second burners are positioned 2 m apart in the direction of combustion gas flow, and an air jet device is provided 2 m downstream of them.

Regarding the flow rates of ammonia and methane supplied to the first and second burners, when the calorific value ratio of ammonia to methane is 40% and 60%, respectively, the ammonia flow rate is set to 79 ^Nm³ /hr and the methane flow rate is set to 51 ^Nm³ /hr for combustion. Furthermore, when only methane is used in the fuel gas without ammonia, the methane flow rate is 84 ^Nm³ /hr. The flow rate of the air injected from the air injection device is set to 0.1 ^Nm³ /hr. In this embodiment, combustion experiments are conducted by varying the mixing ratio and air ratio of the mixed gas in the first and second burners, and exhaust gas is collected downstream of the combustion gas flow F via the air injection device 4. Furthermore, the concentrations of nitrogen oxides (NOx), unburned ammonia ( _NH3 ), and carbon dioxide ( _CO2 ) contained in the exhaust gas were measured.

Table 1 summarizes the invention examples and comparative examples. Furthermore, for the amount of carbon dioxide ( _CO2 ) emitted in the exhaust gas, the previous example (Manufacture No. 3) that did not use ammonia as fuel gas was set as the standard (1.0), and the ratio under each condition is shown in the table.

This embodiment is a combustion experiment using a small number of burners. Therefore, the more numerous the burners, such as in a heating furnace, the more likely it is to prevent the emission of nitrogen oxides or unburned ammonia. Consequently, the baseline values for nitrogen oxide and unburned ammonia concentrations are set more stringent than those for a typical heating furnace, with a baseline value of 100 ppm for nitrogen oxides and 20 ppm for unburned ammonia. Any nitrogen oxide or unburned ammonia concentration exceeding the baseline value is considered unacceptable, while concentrations below the baseline value are considered acceptable.

The previous example (Manufacturing No. 3) was an example in which ammonia was not used as fuel gas in the heating of the first and second burners. In this case, the emission of nitrogen oxides and unburned ammonia was suppressed. However, the problem of high carbon dioxide emission still existed, just like with conventional combustion equipment.

Comparative Example (Manufacturing No. 4) is an example in which a mixture of ammonia and methane is used only in the heating of the second burner, but air injection from air injection device 4 is not performed. By using ammonia in the fuel gas, the concentration of carbon dioxide is reduced compared to the previous example, but the emissions of nitrogen oxides and unburned ammonia are higher. Comparative Example (Manufacturing No. 5) is an example in which a mixture of ammonia and methane is used only in the heating of the first burner, but air injection from air injection device 4 is not performed. In Comparative Example (Manufacturing No. 5), since the exhaust gas from the heating of the second burner does not contain unburned ammonia, the nitrogen oxides contained in the exhaust gas generated during the heating of the first burner are not reduced. Furthermore, although the exhaust gas heated by the first burner sometimes contains small amounts of unburned ammonia, this unburned ammonia is oxidized by the heating in the second burner, thereby promoting the formation of nitrogen oxides. Therefore, unburned ammonia may not be detected in the exhaust gas, but the concentration of nitrogen oxides increases.

Comparative example (Manufacturing No. 6) is an example in which a mixture of ammonia and methane is combusted together with heating of the first and second burners, but without air injection from air injection device 4. In this case, since oxygen is not supplied to the mixed exhaust gas produced by heating of the first and second burners, the reduction reaction of nitrogen oxides by unburned ammonia is not promoted, resulting in both nitrogen oxides and unburned ammonia exceeding the reference value.

The comparative example (Manufacturing No. 7) involved burning a mixture of ammonia and methane in conjunction with heating in both the first and second burners, and included air injection from the air injection device 4. However, because the air-to-air ratio exceeded 1.0 during the heating in the first burner, it was assumed that a large amount of nitrogen oxides would be generated in the exhaust gas from the first burner heating. Therefore, even though unburned ammonia was generated in the exhaust gas from the second burner heating, the high concentration of nitrogen oxides in the mixed exhaust gas meant that nitrogen oxides would still remain in the exhaust gas.

In contrast, the invention (Manufacture No. 1) involves burning a mixture of ammonia and methane in conjunction with heating in both a first and second burner. The air-to-air ratio in the first burner heating is in the range of 0.9 to 1.0, while the air-to-air ratio in the second burner heating is lower than that in the first burner heating. Furthermore, air is injected into the mixture of the exhaust gas heated in the first and second burners using an air injection device 4. This significantly reduces the amount of carbon dioxide in the exhaust gas compared to conventional methods, and also reduces the concentrations of nitrogen oxides and unburned ammonia in the exhaust gas. Furthermore, in Invention Example (Manufacturing No. 2), by setting the air-to-air ratio in the second burner heating process to less than 0.9, the concentration of unburned ammonia, the same as in Invention Example 1, can be maintained while reducing the concentration of nitrogen oxides.

[Table 1] Manufacturing No. First burner heating Second burner heating Air jet exhaust gas Remarks Caloric ratio of _NH3 (%) The caloric ratio of _CH4 (%) air ratio Caloric ratio of _NH3 (%) The caloric ratio of _CH4 (%) air ratio The presence or absence of air spray Nitrogen oxides (ppm) Unburned ammonia (ppm) carbon dioxide emission ratio 1 40 60 0.95 40 60 0.92 have 65 13 0.6 Invention Example 2 40 60 0.95 40 60 0.88 have 55 15 0.6 Invention Example 3 0 100 1.10 0 100 1.10 without 40 0 1.0 Previous examples 4 0 100 1.10 40 60 0.95 without 500 40 0.8 Comparative example 5 40 60 0.95 0 100 1.10 without 600 0 0.8 Comparative example 6 40 60 0.95 40 60 0.88 without 200 42 0.6 Comparative example 7 40 60 1.10 40 60 0.88 have 300 12 0.6 Comparative example

1: Heating Furnace 2: First Combustion Unit 3: Second Combustion Unit 4: Air Injection System 5: First Fuel Gas 6: Second Fuel Gas 7: First Combustion Nozzle 8: Second Combustion Nozzle 9: Air Injection Nozzle 10: Ammonia 11: Coal Gas 12: Combustion Air 13: Air 14: First Fuel Gas Supply System 15: Second Fuel Gas Supply System 16, 17: Mixing Section 18, 19: Combustion Air Supply System 21, 22: Exhaust Gas 23: Mixed Exhaust Gas 24, 41: Air Injection 25, 26: Ammonia Supply System 27, 28: Gas supply system 29: Air supply system 30: Loading section 31: Unloading section 32: Moving slide 33: Fixed slide 34: Flue 35: Furnace wall 36: Furnace interior 40: Air ratio adjustment section 42: Control section 44, 44A, 44B: Burner equipment 45: Fuel gas 50: NOx concentration meter 51: Ammonia concentration meter 52: Flow meter 53: Flow regulating valve 54: First air ratio adjustment section 55: Second air ratio adjustment section 100: Steel movement direction B: Burner F: Combustion gas flow S: Steel S1: Steel front end S2: Steel tail end

Figure 1 is a schematic structural diagram of the heating furnace. Figure 2 is a structural diagram showing the arrangement of the burner equipment in the heating furnace, viewed from the front direction of the steel movement in Figure 1. Figure 3 is a structural diagram of the heating furnace of this embodiment, including the burner equipment and air injection equipment arranged in parallel. Figure 4 is a schematic diagram illustrating the chemical reactions within the heating furnace. A) Nitrogen oxides and unburned ammonia are present in the exhaust gas produced by heating from the first burner. B) Nitrogen oxides and unburned ammonia are present in the exhaust gas produced by heating from the second burner. C) The chemical reaction between nitrogen oxides and unburned ammonia in the mixed exhaust gas is shown. Figure 5 is a structural diagram of a heating furnace according to this embodiment, including burners and air injection devices arranged in opposite directions. Figure 6 is a structural diagram of a heating furnace according to this embodiment, including burners and air injection devices, and a schematic diagram of the chemical reactions within the heating furnace. A) Nitrogen oxides and unburned ammonia are present in the exhaust gas generated from heating by the first burner. B) Nitrogen oxides and unburned ammonia are present in the exhaust gas generated from heating by the second burner. Figure 7 is a schematic structural diagram of a heating furnace according to this embodiment. Figure 8 is a structural diagram of a heating furnace according to another embodiment, including burners and air injection devices with an air ratio adjustment unit and a control unit.

2: First burner equipment

3: Second burner equipment

4: Air jet equipment

5: First fuel gas

6: Second fuel gas

7: First burner nozzle

8: Second burner nozzle

9: Air jet nozzle

10: Ammonia

11: Gas

12: Combustion of air

13: Air

14: First fuel gas supply system

15: Second fuel gas supply system

16, 17: Mixing Section

18, 19: Combustion air supply system

21, 22: Exhaust gas

23: Mixed exhaust gas

24: Air Jet

25, 26: Ammonia Supply System

27, 28: Gas Supply System

29: Air Supply System

35: Furnace Wall

36: Inside the furnace

52: Flow meter

53: Flow regulating valve

F: The flow of combustion gas

Claims (8)

An operating method for a heating furnace includes: a first burner heating step, wherein burner heating is performed using a first fuel gas containing ammonia and combustion air with an air-to-fuel ratio of 0.9 to 1.0 relative to the theoretical air volume of the first fuel gas; a second burner heating step, wherein burner heating is performed using a second fuel gas containing ammonia and combustion air with an air-to-fuel ratio having a lower air-to-fuel ratio relative to the theoretical air volume of the second fuel gas than that relative to the theoretical air volume of the first fuel gas; and an air injection step, wherein air is injected. The method of operating the furnace as described in claim 1, wherein the air injection step involves injecting air into a mixture of waste gas generated by the first burner heating step and waste gas generated by the second burner heating step. The method of operating the furnace as described in claim 1 or claim 2, wherein in the second burner heating step, the air-to-air ratio relative to the theoretical air volume of the second fuel gas is less than 0.9. The method of operating the heating furnace as described in claim 1 or claim 2, wherein at least one of the first fuel gas and the second fuel gas is heated by a mixture of ammonia and coal gas. The method of operating the furnace as described in claim 3, wherein at least one of the first fuel gas and the second fuel gas is used as a mixture of ammonia and coal gas for burner heating. A heating furnace includes: two or more combustion devices for combustion heating using a fuel gas containing ammonia; an air ratio adjustment unit for adjusting the air ratios of the combustion air supplied to the two or more combustion devices relative to the theoretical air volume of the fuel gas; a control unit for controlling the air ratio of the combustion air supplied to at least one of the two or more combustion devices to be different from the air ratio of the combustion air supplied to the other combustion devices; and an air injection device for injecting air into a mixture of exhaust gases discharged from the two or more combustion devices. The heating furnace as described in claim 6, wherein the burner apparatus comprises: a first burner apparatus, which performs burner heating using a first fuel gas containing ammonia, the air ratio of which has been adjusted by the air ratio adjustment unit, and combustion air having an air ratio of 0.9 to 1.0 relative to the theoretical air volume of the first fuel gas; and a second burner apparatus, which performs burner heating using a second fuel gas containing ammonia, and combustion air having an air ratio lower than the theoretical air volume of the first fuel gas; the first burner apparatus, the second burner apparatus, and the air injection apparatus are sequentially arranged along the airflow inside the heating furnace, starting from the upstream side of the airflow. The heating furnace as described in claim 7, wherein the heating furnace includes an opening for discharging the mixed exhaust gas, the air injection device is positioned closer to the opening than the first burner device and the second burner device.