TW202436795A - Operating method of heating furnace and heating furnace - Google Patents

Abstract

Provided are an operation method for a heating furnace and a heating furnace that use, as a combustion fuel of the heating furnace, ammonia with which the emission of carbon dioxide can be suppressed, and that are capable of reducing the amount of nitrogen oxide and uncombusted ammonia exhausted out of the heating furnace. This operation method for a heating furnace includes: a first burner heating step for performing burner heating, of a first fuel gas containing ammonia, by using combustion air for which an air ratio of the first fuel gas to a theoretical amount of air is from 0.9 to 1.0; a second burner heating step for performing burner heating, of a second fuel gas containing ammonia, by using combustion air for which an air ratio of the second fuel gas to the theoretical amount of air is less than the air ratio of the first fuel gas to the theoretical amount of air; and an air spraying step for spraying air at a mixed exhaust gas including exhaust gas from the first burner heating and exhaust gas from the second burner heating.

Description

Operating method of heating furnace and heating furnace

The present invention relates to an operating method of a heating furnace and the heating furnace.

In integrated steelmaking plants, by-product gases produced in converters or coke furnaces are effectively utilized as fuel gases, represented by blast furnace gas discharged from the top of a blast furnace that reduces iron ore to produce molten iron. However, in recent years, along with the demand for reducing carbon dioxide emissions, there is a demand for combustion technologies that reduce the use of these by-product gases. For example, even in steel heating furnaces that heat steel in hot rolling mills or thick plate rolling mills, there is a demand to reduce the use of by-product gases in order to reduce carbon dioxide emissions. At this time, the technology of utilizing ammonia as a fuel gas for steel heating furnaces has attracted much attention. That is, ammonia, which does not contain carbon, mainly produces only water and nitrogen even when burned, so it has a significant effect on reducing carbon dioxide emissions and is expected to be used in the development of technology applicable to steel heating furnaces.

On the other hand, if ammonia is used as a heating furnace fuel, the generation of nitrogen oxides (NOx) becomes a problem. Nitrogen oxides are harmful to the human body and cause photochemical smog and acid rain, so they are subject to legal emission restrictions.

Therefore, in order to solve these problems, a heating technology has been proposed. Patent document 1 discloses a boiler, which includes: a combustion device that can burn ammonia as fuel in a furnace; and a flue that guides the combustion gas generated by the combustion of the fuel, and the boiler includes a spray portion, which is arranged in at least one of the furnace and the flue at a position downstream of the combustion gas relative to the combustion device, and sprays ammonia as a reducing agent toward the center of the furnace or the flue in a top view. In this way, ammonia can be supplied to the center of the furnace, and even a small amount of ammonia can be used as a reducing agent to reduce nitrogen oxides.

Furthermore, Patent Document 2 discloses a boiler comprising: a burner for burning fossil fuel in the furnace; an additional air supply unit disposed on the downstream side of the burner in the flow direction of the combustion gas in the furnace; and an ammonia fuel supply unit for supplying ammonia fuel to the furnace on the upstream side of the additional air supply unit in the flow direction of the fuel gas. Thus, in a two-stage combustion boiler including an additional air supply unit, as long as ammonia fuel is added at a position further upstream than the additional air supply unit, the nitrogen component of the ammonia fuel will be reduced to _N2 in the reducing environment region in the furnace, thereby suppressing the generation of nitrogen oxides. [Prior Art Document] [Patent Document]

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

[Problems to be solved by the invention] However, if the above-mentioned conventional technology is applied to a heating furnace for heating steel materials, etc., the following problems will arise.

The technology disclosed in Patent Document 1 is to reduce nitrogen oxides generated in a combustion device such as a boiler by injecting ammonia on the downstream side in the flow direction of the combustion gas. At this time, the amount of ammonia injected to reduce nitrogen oxides is extremely small compared to the flow rate of the combustion gas generated in the combustion device. Therefore, even if ammonia is injected toward the center of the furnace, it may not be evenly mixed 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. Therefore, the following problem arises: ammonia as a reducing agent is not burned and is directly discharged to the outside of the furnace. In a heating furnace used to heat a heated object such as steel, unlike a combustion device such as a boiler, a door is generally provided for loading/extracting the heated object into/from the heating furnace. At this time, the following problem occurs: when the door of the heating furnace is opened, toxic unburned ammonia (also called "unburned ammonia") is discharged to the outside of the heating furnace, causing the environment outside the heating furnace to deteriorate.

Patent document 2 also targets combustion devices such as boilers, and uses ammonia to reduce nitrogen oxides in the reducing environment area in the furnace. Patent document 2 discloses that in order to form a reducing environment area in the furnace, the primary air supplied to the burner is set to be less than the amount of air required to completely burn the fossil fuel. In the technology disclosed in patent document 2, in order to carry out the reduction reaction of nitrogen oxides, a certain space must be ensured in the furnace and a certain reaction time is required. On the other hand, in a heating furnace used to heat a heated object such as steel, not only a combustion device (such as a burner) is required inside the heating furnace, but also a space for placing and loading the heated object. In contrast, furnaces such as boilers have the following difference, that is, they only need to include the space required for the combustion reaction between the fuel and the combustion air. Therefore, if the technology disclosed in Patent Document 2 is applied to a heating furnace for heating a heated object, the space of the reduction environment area is expanded, resulting in the following problem: the reduction reaction of nitrogen oxides cannot be carried out uniformly inside the reduction environment area, resulting in unburned ammonia being discharged to the outside of the heating furnace.

Furthermore, Patent Document 2 discloses that when the amount of air supplied for burning ammonia is changed between 0.6 and 1.0 relative to the theoretical air amount, the amount of air supplied and the leakage rate of unburned ammonia at the furnace outlet are opposite to the conversion rate to NOx. Therefore, in order to reduce both nitrogen oxides (NOx) and unburned ammonia, the primary air ratio must be controlled within a narrow range, and nitrogen oxides or unburned ammonia are easily discharged to the outside due to changes in the operating conditions in the heating furnace.

The present invention is completed to solve the above-mentioned problems existing in the prior art, and its purpose is to provide a method for operating a heating furnace and a heating furnace, which can use ammonia that can suppress the emission of carbon dioxide as the combustion fuel of the heating furnace, and can reduce the amount of nitrogen oxides and unburned ammonia emitted to the outside of the heating furnace. [Means for solving the problem]

The operating method of the heating furnace of the present invention that advantageously solves the above-mentioned problems is constructed as follows.

[1] A method for operating a heating furnace, comprising: a first burner heating step, performing burner heating using a first fuel gas containing ammonia and combustion air having an air ratio of 0.9 to 1.0 relative to the theoretical air volume of the first fuel gas; a second burner heating step, performing burner heating using a second fuel gas containing ammonia and combustion air having an air ratio relative to the theoretical air volume of the second fuel gas that is lower than the air ratio relative to the theoretical air volume of the first fuel gas; and an air injection step, injecting air. [2] The method for operating a heating furnace as described in [1], wherein the air injection step is to inject air into a mixed exhaust gas formed by mixing the exhaust gas generated by the first burner heating step and the exhaust gas generated by the second burner heating step. [3] The method for operating a heating furnace as described in [1] or [2], wherein in the second burner heating step, the air ratio relative to the theoretical air amount of the second fuel gas is less than 0.9. [4] The method for operating a heating furnace as described in [1] or [2], wherein at least one of the first fuel gas and the second fuel gas is burner heated using a mixed gas of ammonia and coal gas. [5] The method for operating a heating furnace as described in [3], wherein at least one of the first fuel gas and the second fuel gas uses a mixed gas of ammonia and coal gas to heat the burner.

The heating furnace of the present invention that advantageously solves the above-mentioned problem is configured as follows. [6] A heating furnace comprising: two or more burner devices that perform burner heating using a fuel gas containing ammonia; an air ratio adjustment 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 the mixed exhaust gas discharged from the two or more burner devices. [7] The heating furnace as described in [6], wherein the burner device comprises: a first burner device for performing burner heating by using a first fuel gas containing ammonia whose air ratio is adjusted by the air ratio adjusting unit and combustion air whose air ratio relative to the theoretical air amount of the first fuel gas is 0.9 to 1.0; and a second burner device for performing burner heating by using a second fuel gas containing ammonia and combustion air whose air ratio relative to the theoretical air amount of the second fuel gas is lower than the air ratio relative to the theoretical air amount of the first fuel gas, and the first burner device, the second burner device, and the air injection device are arranged in order from the upstream side of the airflow along the airflow inside the heating furnace. [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 arranged at a position closer to the opening than the first burner device and the second burner device. [Effect of the invention]

According to the present invention, by using ammonia as a 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 to the outside of the heating furnace can be reduced.

The following is a description of the heating furnace of the present embodiment. <Heating furnace> The heating furnace of the present embodiment is a device including a burner that burns a fuel gas as a heat source for heating, and a heated object is placed inside and heated to a predetermined temperature. The heated object is mainly metal, but can be either ferrous metal 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 the present embodiment in which the heated object is a steel material. For example, a heating furnace used in a hot rolling mill for steel is used to heat the cast slab to a specified heating temperature (about 1100℃ to 1300℃).

The heating furnace 1 shown in FIG1 includes: a loading section 30 for loading steel material S (slab) as a heated body; and a carrying-out section 31 for carrying out (extracting) the heated steel material S. For example, the steel material S manufactured by a continuous casting line is transported to a yard on the loading side of the heating furnace, and is loaded into the heating furnace 1 from the loading section 30 according to the production schedule of a hot rolling line, etc. The interior of the heating furnace 1 is divided into a plurality of belt areas, and the upstream side generally includes a heating belt divided into two to eight belt areas and one to three soaking belts. The interior of the heating furnace 1 generally includes a fixed skid 33 for placing the steel material S and a movable skid 32 for carrying the steel material S. The heating furnace including the fixed slide 33 and the movable slide 32 is called a walking beam type continuous heating furnace.

During the operation of the heating furnace, each zone in the heating furnace is controlled to a different ambient temperature, and the average temperature of the steel material S loaded into the heating furnace 1 gradually increases. Thereby, the steel material S is controlled to a predetermined target heating temperature (target temperature of the slab when it is withdrawn from the heating furnace). The steel material S reaching the target temperature passes through the unloading section 31 and is supplied to hot rolling.

Inside the heating furnace 1, a plurality of burners are arranged along the conveying direction of the steel material S (steel material moving direction 100). The burner B is arranged to increase the temperature inside the heating furnace by combustion. When the temperature inside the heating furnace is increased by the burner, the temperature of the steel material increases by radiation from the furnace wall of the heating furnace. In addition, sometimes the flow of the ambient gas is generated inside the heating furnace, and the temperature of the steel material increases by convection. Furthermore, the temperature of the steel material can also be increased by directly contacting the steel material with the flame of the burner. In short, the burner burns the fuel gas as a heating source to increase the temperature of the interior of the heating furnace, thereby increasing the temperature of the heated material inside the heating furnace.

The heating furnace 1 includes a space for placing and transporting the heated material in addition to the space for emitting flames from the combustion burner. Therefore, the furnace has a characteristic that the volume inside the furnace is large relative to the combustion energy input into the furnace, compared with a boiler or the like whose purpose is to generate a combustion reaction inside. Representative values of the furnace volume per unit combustion energy (m ³ / MW) in a gas turbine, a pulverized coal boiler, and an oil-gas boiler are, for example, 2 m ³ / MW for a gas turbine, 6 m ³ / MW for a pulverized coal boiler, and 2 m ³ / MW for an oil-gas boiler. On the other hand, the heating furnace has a large capacity of about 10 m ³ /MW to 16 m ³ /MW. For example, the heating furnace used for hot rolling of steel materials has a capacity of about 11 m ³ /MW to 13 m ³ /MW.

During the operation of the heating furnace 1, the doors (opening and closing doors) of the loading part 30 and the unloading part 31 are closed, and a higher pressure than the atmosphere is generated inside. When the steel material S is loaded and unloaded, the door is temporarily opened. When the door is opened, a pressure difference is generated between the pressure inside the heating furnace and the pressure near the door, so the combustion gas inside the heating furnace flows from the high pressure area to the low pressure area. When the door of the heating furnace 1 is open, the flow of the combustion gas is mostly generated in the direction in which the combustion gas passes through the opening and is discharged to the outside of the heating furnace 1.

Fig. 2 is a diagram showing a cross section of the heating furnace 1. The burners B are often arranged inside the heating furnace 1 on the upper surface side and the lower surface side of the steel material S, respectively, to avoid a temperature difference between the upper surface and the lower surface of the steel material S. Furthermore, they are often arranged on both sides of the conveying direction of the steel material S, to avoid a temperature difference between the front end S1 and the rear end S2 of the steel material S.

The heating furnace 1 of the present embodiment is a heating furnace as described below, which includes: two or more burner devices that perform burner heating using a fuel gas containing ammonia; an air ratio adjustment 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 the mixed exhaust gas discharged from the two or more burner devices. <Burner equipment> Preferably, it has: a first burner equipment that performs burner heating by using a first fuel gas containing ammonia 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 that performs burner heating by using a second fuel gas containing ammonia and combustion air having an air ratio lower than the air ratio relative to the theoretical air volume of the second fuel gas than the air ratio relative to the theoretical air volume of the first fuel gas.

Moreover, in the heating furnace 1 of the present embodiment, at least one of the burners B arranged inside is a first burner device for performing burner heating on a first fuel gas containing ammonia by using combustion air, and at least one of the other burners B is a second burner device for performing burner heating on a second fuel gas containing ammonia by using combustion air.

The first burner device and the second burner device are described using Fig. 3. Fig. 3 is a diagram showing the arrangement of the first burner device 2, the second burner device 3, and the air injection device 4 of the heating furnace 1 as viewed from the top surface, including a portion of the furnace wall 35 located on one side of the heating furnace 1 shown in Fig. 1.

The first burner device 2 uses the first fuel gas 5 containing ammonia as the fuel gas and the combustion air 12 to perform the first burner heating for spraying the flame into the furnace. The first burner device 2 includes: a first burner nozzle 7 for spraying the flame into the furnace; a first fuel gas supply system 14 for supplying the first fuel gas 5 to the first burner nozzle 7; and a combustion air supply system 18 for supplying the combustion air 12 to the first burner nozzle 7. The first burner nozzle 7 is, for example, a double-tube nozzle, which sprays the first fuel gas 5 into the furnace from the inside, and the combustion air 12 is supplied to the outside. Thereby, 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 portion of the first burner nozzle 7 toward the inside of the heating furnace 1.

The second burner device 3 can be configured to have the same structure as the first burner device 2. The second burner device 3 uses a second fuel gas 6 containing ammonia as a fuel gas and combustion air 12 to perform second burner heating for spraying flames into the furnace. The second burner device 3 includes: a second burner nozzle 8 for spraying 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 the combustion air 12 to the second burner nozzle 8. The second burner nozzle 8 also uses a double-tube nozzle, for example, and injects the second fuel gas 6 from the inner tube into the furnace, and supplies the combustion air 12 from the outer tube. Thereby, 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 toward the inside of the heating furnace 1.

Moreover, for the first burner device 2 and the second burner device 3, a vortex burner having the function of stirring the fuel gas ejected from the burner nozzle, or a tubular flame burner that blows fuel gas and combustion air into the burner in a tangential direction to form a surrounding flow in the burner for combustion can also be used.

Both the first fuel gas 5 and the second fuel gas 6 use a fuel gas containing ammonia. Ammonia may be used as a fuel gas alone, or a mixed gas obtained by mixing ammonia with other fuels may be used as a fuel gas. The mixing ratio of ammonia in the first fuel gas 5 and the second fuel gas 6 may be different or the same. Furthermore, other fuels constituting the mixed gas may 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 complicated and the equipment cost increases, it is economical to use the same fuel gas containing ammonia for the first fuel gas 5 and the second fuel gas 6.

Ammonia is a flame-retardant fuel that is more difficult to ignite than general fuels and also burns more slowly. In order to improve the stability of combustion, a mixed gas mixed with other fuels can be used. The fuel mixed into the ammonia is preferably coal gas. The so-called coal gas refers to a gas that can be obtained from coal. The coal gas is preferably any one of coke furnace gas, blast furnace gas, converter gas, and electric furnace gas. These are by-product gases generated in steel mills and have the effect of stabilizing the combustion of ammonia. Blast furnace gas is a by-product gas produced when iron ore is reduced in a blast furnace to produce molten iron. Coke furnace gas is a by-product gas produced by high-temperature dry distillation of coal in order to produce coke. Converter gas is a byproduct gas generated in the steelmaking step in the converter. Electric furnace gas refers to the gas generated by the incomplete combustion of auxiliary fuel (carburizer) in the electric furnace. As the coal gas constituting the mixed gas, a gas (sometimes referred to as M gas) appropriately mixed with blast furnace gas, coke furnace gas, and converter gas can be used. The reason is that by mixing coal gases with different calorific values, the heat required for heating the heated object can be supplied and the heating furnace can be operated stably.

This embodiment is an example in which the first fuel gas 5 used in the first burner device 2 and the second fuel gas 6 used in the second burner device 3 shown in FIG. 3 are both set as a mixed gas 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, and the ammonia 10 and the coal gas 11 are mixed in the mixing section 16 and supplied to the first burner nozzle 7. In the middle of the ammonia supply system 25 and the coal gas supply system 27, 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 may be included. In this way, the mixing ratio of ammonia and coal gas contained in the mixed gas can be adjusted. The second fuel gas supply system 15 is also connected to the ammonia supply system 26 and the coal gas supply system 28. The ammonia 10 and the coal gas 11 are mixed in the mixing section 17 and supplied to the second burner nozzle 8. The second burner device 3 may also include 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 in the middle of the ammonia supply system 26 and the coal gas supply system 28.

The mixing section (16, 17) refers to the portion 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) only needs to constitute a certain space in the portion where these supply pipes converge. However, the mixing section (16, 17) may include a static mixing machine such as a static mixer or a dynamic mixer with a stirring function. This is better in generating a mixed gas in which the coal gas and ammonia are more evenly mixed.

A flow regulating valve 53 for adjusting the flow rate of the 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 may also be included in 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. The amount of the combustion air of the first burner device 2 and the second burner device 3 is adjusted, so that the adjustment of the air ratio in the heating of the respective burners of the first burner device 2 and the second burner device 3 becomes easy.

The combustion air used in the first burner device 2 and the combustion air used in the second burner device 3 can be supplied from the combustion air supply system by air collected from the atmosphere. However, air modified by removing nitrogen from the air or adding pure oxygen, etc., can be applied to 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 from the combustion air supply system can be reduced, thereby reducing the power consumption of the pump, etc. In addition, by reducing the oxygen content of the combustion air, the furnace environment of the heating furnace can be set to a reducing environment, promoting the reduction of nitrogen oxides.

<Air injection device> The heating furnace 1 of this embodiment includes, in addition to the first burner device 2 and the second burner device 3, an air injection device 4 that injects air into a mixed exhaust gas 23 in which the exhaust gas 21 discharged from the first burner device 2 and the exhaust gas 22 discharged from the second burner device 3 are mixed. The air injection device 4 is connected to the air supply system 29, and injects air 13 from the air injection nozzle 9 toward the furnace. In the middle of the air supply system 29, a flow regulating valve 53 for adjusting the flow rate of the air 13 supplied to the air injection nozzle 9 and a flow meter 52 for measuring the supply flow rate may be included. In this way, the amount of air injected into the mixed exhaust gas of the exhaust gas from the first burner device 2 and the exhaust gas from the second burner device 3 can be adjusted to promote the reduction reaction of nitrogen oxides contained in the mixed exhaust gas.

The air injected from the air injection device 4 may be air collected from the atmosphere. However, air modified by removing nitrogen from the air or adding pure oxygen may be supplied to the air injection nozzle 9 via the air supply system 29. 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 burner equipment of heating furnace> The configuration of the burner equipment of the heating furnace is explained. In the heating furnace of the present embodiment, a first burner equipment for performing burner heating by setting the air ratio relative to the first fuel gas to 0.9 to 1.0, a second burner equipment for performing burner heating by setting the air ratio relative to the second fuel gas to be smaller than the air ratio relative to the first fuel gas, and an air injection equipment for injecting air into the mixed exhaust gas of the exhaust gas discharged from the first burner equipment and the exhaust gas discharged from the second burner are sequentially arranged from the upstream side of the air flow along the air flow inside the heating furnace. The reason for this is that it is believed that by injecting oxygen into the mixed gas of NOx and unburned ammonia, the reduction reaction of NOx by ammonia is promoted, thereby reducing the NOx and unburned ammonia discharged from the heating furnace. In addition, in the case of a heating furnace including an opening for discharging combustion gas, it is preferable that the air injection device is arranged at a position closer to the opening than the first burner device and the second burner device.

FIG7 shows an example of the structure of the heating furnace of the present embodiment. The heating furnace shown in FIG7 includes: a loading part 30 for loading the heated object into the heating furnace; a carrying-out part 31 for carrying out the heated object; and a flue 34 for discharging the exhaust gas (combustion gas) from the inside of the heating furnace 1 to the outside of the heating furnace. The loading part 30 becomes an opening part that is temporarily opened when the heated object is loaded into the heating furnace. The carrying-out part 31 also becomes an opening part that is temporarily opened when the heated object is carried out from the heating furnace. On the other hand, the flue 34 is provided to discharge the exhaust gas from the inside of the heating furnace 1 and adjust the pressure inside the heating furnace to prevent it from becoming too large. It is partially open to the outside of the heating furnace, so it is always open. Therefore, inside the heating furnace 1 shown in Figure 7, at least a flow of combustion gas from the inside of the heating furnace toward the flue 34 is generated.

In this embodiment, the first burner device 2, the second burner device 3, and the air injection device 4 are arranged in this order from the upstream side of the flow of the combustion gas toward the flue 34. In the example shown in FIG7, the first burner device 2 is arranged on the upper and lower sides of the heated object near the center of the conveying direction of the heating furnace 1. On the downstream side of the combustion gas flow of the first burner device 2, one second burner device 3 is arranged on the upper side of the heated object, and two second burner devices 3 are arranged on the lower side. In addition, the air injection device 4 is arranged on the downstream side of the second burner device 3 along the flow F of the combustion gas.

In FIG. 7 , the first burner device 2 performs burner heating by setting the air ratio relative to the first fuel gas to 0.9 to 1.0, and the second burner device 3 performs burner heating by setting the air ratio relative to the second fuel gas to be smaller than the air ratio relative to the first fuel gas. As a result, the exhaust gas 21 containing more nitrogen oxides moves along the gas flow F of the combustion gas in the heating furnace, and is mixed with the exhaust gas 22 containing more unburned ammonia to generate a mixed exhaust gas 23. The mixed exhaust gas 23 moves along the gas flow F of the combustion gas in the heating furnace, and further moves toward the flue 34 which is an opening. The air injection device 4 is arranged at the downstream side of the air flow relative to the first heating device 2 and the second heating device 3, so the air 13 is injected into the mixed exhaust gas 23 before the mixed exhaust gas 23 is discharged from the opening. Thus, the oxygen in the air 13 promotes the reduction of nitrogen oxides by ammonia, and the concentration of nitrogen oxides and ammonia in the exhaust gas discharged to the outside of the heating furnace through the flue 34 can be reduced.

Furthermore, as a burner in the heating furnace 1, there may be a burner device other than the first burner device 2 and the second burner device 3. However, the burner device 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 a fuel that does not contain ammonia 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 of nitrogen oxides and unburned ammonia is lower than that of the first burner device or the second burner device (for example, 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 can, for example, perform burner heating using coal gas as a fuel gas.

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

The burner device 44 is provided with an air ratio adjusting unit 40, and the air ratio adjusting units 40 corresponding to the two burner devices (44A, 44B) are connected to the control unit 42. The air ratio adjusting unit 40 has a function of adjusting the air ratio of the combustion air relative to the fuel gas 45 for each burner device 44. For example, the air ratio adjusting unit 40 measures the flow rate of the fuel gas supplied to the burner nozzle as the fuel gas 45, and calculates the theoretical air volume for complete combustion of the fuel gas 45 based on the measured flow rate of the fuel gas 45 and the fuel composition of the fuel gas 45. Furthermore, based on the air ratio set for each burner device (44A, 44B), the opening of the flow regulating valve disposed in the combustion air supply system is adjusted, thereby setting the air ratio for burner heating for each burner device (44A, 44B).

The control unit 42 gives the set value of the air ratio in the air ratio adjustment unit 40 of each burner device (44A, 44B). The control unit 42 gives the set value of the air ratio to the air ratio adjustment unit 40 in such a way that the air ratio of one of the burner devices 44A becomes 0.9 to 1.0. The control unit 42 gives the set value of the air ratio to the air ratio adjustment unit 40 in such a way that the other burner device 44B performs burner heating at an air ratio smaller than the air ratio of the one of the burner devices 44A. At this time, as shown in the arrangement relationship of each device in FIG8 , the control unit 42 can set the air ratio of the burner device 44A arranged at a position far from the air injection device 4 to 0.9-1.0, and set the air ratio of the burner device 44B arranged at a position close to the air injection device 4 to be smaller than the air ratio of the burner device 44A arranged at a position far from the air injection device 4.

The burner device 44A disposed at a position far from the air injection device 4 and having an air ratio set to 0.9 to 1.0 functions as the first burner device 2, and the burner device 44B disposed at a position close to the air injection device 4 functions as the second burner device 3. Therefore, by including two burner devices (44A, 44B) including an air ratio adjustment unit 40 and a control unit 42 for setting their air ratios, a mixed exhaust gas 23 containing nitrogen oxides and unburned ammonia can be generated, and the reduction reaction of nitrogen oxides by ammonia can be promoted by the air injection device 4.

Next, the operation method of the heating furnace of the present embodiment is described. <Operation method of heating furnace> The present embodiment is an operation method of a heating furnace, comprising: a first burner heating step, performing burner heating by using a first fuel gas containing ammonia and combustion air having an air ratio of 0.9 to 1.0 relative to the theoretical air amount of the first fuel gas; a second burner heating step, performing burner heating by using a second fuel gas containing ammonia and combustion air having an air ratio relative to the theoretical air amount of the second fuel gas that is lower than the air ratio relative to the theoretical air amount of the first fuel gas; and an air injection step, injecting air.

In the heating furnace, nitrogen oxides are generated by burning fuel gas containing ammonia, and a mixed exhaust gas in which nitrogen oxides and ammonia coexist is generated. Then, air containing oxygen is injected into the generated mixed exhaust gas. As a result, the reduction reaction of nitrogen oxides by ammonia is promoted. Ammonia is oxidized by oxygen in the air, and the oxidized ammonia decomposes nitrogen oxides. In this way, ammonia is also decomposed and rendered harmless together with nitrogen oxides contained in the mixed exhaust gas. The reason why the first burner heating and the second burner heating are combined is that the exhaust gas heated by the first burner contains relatively more nitrogen oxides, and the exhaust gas heated by the second burner contains relatively more unburned ammonia. By mixing them, a mixed exhaust gas in which nitrogen oxides and ammonia coexist is generated.

The operation method of the heating furnace is described using the first burner heating 2, the second burner equipment 3 and the air injection equipment 4 shown in FIG3. In this embodiment, the first burner heating is performed as follows, that is, the burner heating is performed by the first fuel gas 5 containing ammonia and the combustion air 12 with an air ratio (sometimes referred to as the air ratio) of 0.9 to 1.0 relative to the theoretical air amount of the first fuel gas 5. Here, the so-called theoretical air amount refers to the amount of air required for complete combustion of the fuel gas. Moreover, the so-called air ratio relative to the theoretical air amount refers to the ratio of the amount of air supplied to the burner equipment as combustion air to the amount of air required for complete combustion of the fuel gas.

The air ratio of the first burner heating is set to 0.9-1.0 in order to make the exhaust gas 21 heated by the first burner contain nitrogen oxides. If the air ratio of the first burner heating is less than 0.9, the combustion of ammonia is suppressed, and the amount of unburned ammonia in the exhaust gas 21 generated by the first burner heating will increase compared with nitrogen oxides. On the other hand, if the air ratio of the first burner heating exceeds 1.0, the combustion of ammonia contained in the first fuel gas is promoted, and the amount of nitrogen oxides in the exhaust gas 21 will become too much, making it difficult to fully reduce the nitrogen oxides in the mixed exhaust gas 23. Furthermore, the concentration of nitrogen oxides contained in the exhaust gas 21 generated by setting the air ratio of the first burner heating to 0.9 to 1.0 is about 400 ppm to 5000 ppm. The exhaust gas 21 heated by the first burner sometimes also contains unburned ammonia, but its concentration is less than 5 ppm when the air ratio is 0.9, and is approximately zero when the air ratio is 0.95 to 1.0. As a result, the exhaust gas 21 generated by the first burner heating contains relatively more nitrogen oxides.

On the other hand, in the present embodiment, the second burner heating is performed as follows, that is, the burner heating is performed by the second fuel gas containing ammonia and the air for combustion having an air ratio lower than the air ratio relative to the theoretical air amount of the second fuel gas than the air ratio relative to the theoretical air amount of the first fuel gas. This is to make the exhaust gas 22 heated by the second burner contain relatively more unburned ammonia. If the air ratio of the second burner heating is higher than the air ratio of the first burner heating, the effect of reducing nitrogen oxides in the exhaust gas 21 by the unburned ammonia contained in the exhaust gas 22 will decrease.

The second burner heating is preferably performed at an air ratio of less than 0.9 relative to the theoretical air amount of the second fuel gas. The reason for this is that the amount of unburned ammonia contained in the exhaust gas 22 heated by the second burner increases, thereby promoting the reduction reaction of nitrogen oxides in the mixed exhaust gas 23. The lower limit of the air ratio for the second burner heating is set to 0.7. If the air ratio for the second burner heating is less than 0.7, the combustion of the second burner heating becomes unstable.

Furthermore, the exhaust gas 22 heated by the second burner may contain both nitrogen oxides and unburned ammonia, but by making the air ratio of the second burner heating smaller than the air ratio of the first burner heating, the exhaust gas 22 contains more unburned ammonia than the exhaust gas 21. Furthermore, by setting the air ratio of the second burner heating to 0.7 or more and less than 0.9, the concentration of unburned ammonia contained in the exhaust gas 22 can be set to 10 ppm to 24000 ppm. The smaller the air ratio of the second burner heating, the greater the concentration of unburned ammonia contained in the exhaust gas 22. When the air ratio is 0.85, the concentration of unburned ammonia is about 1200 ppm, and when the air ratio is 0.8, the concentration of unburned ammonia is about 6400 ppm. At this time, although nitrogen oxides are also contained in the exhaust gas 22, the concentration thereof is below 400 ppm, and drops to about 15 ppm when the air ratio is 0.85. That is, the exhaust gas 22 generated by heating the second burner can contain relatively more unburned ammonia.

When the first burner is heated and the flame is sprayed into the heating furnace, the exhaust gas 21 diffuses in the heating furnace. At this time, as shown in FIG3, when the airflow of the combustion gas (exhaust gas) in the heating furnace is generated, the exhaust gas 21 moves along the airflow in the heating furnace toward the second burner device 3. Similarly, when the second burner is heated and the flame is sprayed into the heating furnace, the exhaust gas 22 generated by the heating of the second burner also moves along the airflow in the heating furnace. As a result, the exhaust gas 21 containing relatively more nitrogen oxides and the exhaust gas 22 containing relatively more unburned ammonia are mixed in the heating furnace to generate a mixed exhaust gas 23 containing both nitrogen oxides and unburned ammonia. The balance of the amount of nitrogen oxides and unburned ammonia contained in the mixed exhaust gas 23 can be changed by setting the air ratio for heating by the first burner and the air ratio for heating by the second burner. In addition, the ratio of the flow rate of the first fuel gas 5 for heating by the first burner and the flow rate of the second fuel gas 6 for heating by the second burner can be changed by setting.

In this embodiment, air 13 is sprayed toward the mixed exhaust gas 23 containing both nitrogen oxides and unburned ammonia using air spray equipment 4. This is based on the following view: the reduction reaction of nitrogen oxides by ammonia is promoted by the presence of a certain amount of oxygen. That is, by spraying air 13 toward the mixed exhaust gas 23 containing both nitrogen oxides and ammonia, the oxygen contained in the air 13 promotes the reduction reaction of nitrogen oxides by ammonia. Thereby, nitrogen oxides and ammonia in the mixed exhaust gas 23 can be reduced. For the gas sprayed using the air spray equipment 4, as long as it is a gas containing oxygen, it is also possible to spray air that has been modified by removing nitrogen from the air or adding pure oxygen, etc.

FIG4 is a schematic diagram for explaining 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 remaining in the fuel gas as 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.

Thereby, the following reaction is promoted. That is, ammonia (NH ₃ ) is oxidized by oxygen to generate NH radicals and HO ₂ radicals. On the other hand, among the nitrogen oxides contained in the mixed exhaust gas 23, nitrogen monoxide NO is mainly present, and nitrogen monoxide NO is reduced by NH radicals to generate nitrogen and OH radicals. In this way, the nitrogen oxides in the mixed exhaust gas 23 are reduced. On the other hand, the oxygen contained in the air 13 injected from the air injection device 4 decomposes ammonia to generate NH radicals during the period when the mixed exhaust gas 23 contains unburned ammonia. That is, if the oxygen injected into the mixed exhaust gas 23 is sufficient, the unburned ammonia will be decomposed. Moreover, as long as the NH radicals are sufficiently generated, the nitrogen oxides in the mixed exhaust gas 23 can be reduced. Thereby, both nitrogen oxides and ammonia in the mixed exhaust gas 23 can be reduced.

As described above, in the present embodiment, nitrogen oxides and unburned ammonia can be effectively decomposed by injecting air as a mixed exhaust gas of the exhaust gas generated by heating the first burner and the exhaust gas heated by the second burner. In this way, it is possible to suppress the nitrogen oxides or unburned ammonia from being discharged to the outside of the heating furnace 1. In contrast, in the technology disclosed in Patent Document 2, since the air ratio for burning ammonia 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 the following problem: even if an additional air supply unit is provided on the downstream side of the burner in the flow direction of the combustion gas in the furnace to supply oxygen, the reduction reaction of nitrogen oxides with the aid of ammonia cannot be efficiently promoted. Therefore, in order to promote the reduction reaction of nitrogen oxides with the aid of ammonia, a fixed space called a reduction environment area must be set. On the other hand, according to the embodiment, the burner heating is performed in a manner in which the air ratio of the first burner heating and the air ratio of the second burner heating become a prescribed relationship, so that nitrogen oxides and unburned ammonia can coexist in a good balance, thereby efficiently promoting the reduction reaction of nitrogen oxides with the aid of ammonia. At this time, the gas temperature of the mixed exhaust gas 23 in which the exhaust gas 21 generated by the first burner heating and the exhaust gas 22 generated by the second burner heating are mixed is preferably set to 700°C to 1450°C. The reason is that NH free radicals are generated and the reduction reaction of nitrogen oxides is promoted.

The injection of the air 13 toward the mixed exhaust gas 23 is preferably performed by mixing the exhaust gas 22 generated by the second burner heating with the mixed exhaust gas 23 in the exhaust gas 21 generated by the first burner heating. That is, the exhaust gas 21 generated by the first burner heating can be generated first, and the exhaust gas 22 generated by the second burner heating can be mixed with the generated exhaust gas 21. The burner devices shown in Figures 3 and 5 are both configured with the second burner device 3 on the downstream side of the first burner device 2 relative to the gas flow of the combustion gas in the heating furnace.

In contrast, FIG6 shows an example in which the second burner device 3 is arranged on the upstream side of the first burner device 2. At this time, the exhaust gas 22 containing relatively more unburned ammonia is generated from the second burner device 3 on the upstream side of the gas flow of the combustion gas. However, if the exhaust gas 22 approaches the position of the first burner device 2 along the gas flow of the combustion gas, it may approach the area of the flame ejected from the first burner device 2. In particular, when the gas flow of the combustion gas is fast, the exhaust gas 22 from the second burner device 3 moves toward the downstream direction at a position close to the furnace wall. At this time, a part of the unburned ammonia contained in the exhaust gas 22 may be burned by the flame from the first burner device 2, resulting in a decrease in the unburned ammonia contained in the exhaust gas 22, and a part of it becomes nitrogen oxides. As a result, the amount of unburned ammonia contained in the mixed exhaust gas 23 formed on the downstream side of the first burner device 2 is reduced, and the reduction reaction of nitrogen oxides by ammonia may be hindered.

By the above, the exhaust gas 22 generated by the second burner heating is mixed with the exhaust gas 21 generated by the first burner heating to form a mixed exhaust gas 23, and air is injected into it. Therefore, in the heating furnace 1, along the airflow inside the heating furnace, the first burner heating, the second burner heating and the air injection are performed from the upstream side of the airflow. [Example]

The effects of the present embodiment are described in detail below based on the embodiments, but the present invention is not limited to these embodiments. As an embodiment of the present invention, the following example is described, that is, using the burner equipment shown in FIG. 3, exhaust gas is collected on the downstream side of the gas flow of the combustion gas, and the concentration of nitrogen oxides and unburned ammonia contained in the exhaust gas is measured.

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

A mixed gas of ammonia and methane (CH ₄ ) is used as the fuel gas of the first burner device and the second burner device. In FIG3 , ammonia is supplied to the mixing section 16 and the mixing section 17 from the ammonia supply system 25 and the ammonia supply system 26, and methane is sent to the mixing section 16 and the mixing section 17 from the coal gas supply system 27 and the coal gas supply system 28 to generate a mixed gas of ammonia and methane, and is supplied to the burner nozzle as the first fuel gas 5 and the second fuel gas 6. However, flow regulating valves are provided in the ammonia supply system 25 and the ammonia supply system 26 and the coal gas supply system 27 and the coal gas supply system 28 to adjust the mixing ratio of the mixed gas. Furthermore, the combustion air supply system 18 and the combustion air supply system 19 are also configured to be equipped with flow regulating valves, so that the air ratio relative to the theoretical air amount of the first fuel gas 5 and the second fuel gas 6 can be adjusted. On the other hand, the air containing oxygen is injected from the air injection device 4 to the mixed exhaust gas of the exhaust gas discharged from the first burner device and the exhaust gas discharged from the second burner. Furthermore, the air supply system 29 is equipped with a flow regulating valve, so that the presence or absence of air injected into the mixed exhaust gas can be changed (open/close).

The first burner device and the second burner device are devices that can output a heat amount of 800,000 kcal/hr at a rated capacity. The first burner device and the second burner device are arranged at positions 2 m apart in the flow direction of the combustion gas, and an air injection device is further provided at a position 2 m apart on the downstream side thereof.

Regarding the flow rates of ammonia and methane supplied to the first burner device and the second burner device, when the heat ratio of ammonia to methane is 40% and 60%, the flow rate of ammonia is set to 79 Nm ³ /hr and the flow rate of methane is set to 51 Nm ³ /hr for combustion. Moreover, when only methane is used in the fuel gas without using ammonia, the flow rate of methane is 84 Nm ³ /hr. The flow rate of air injected from the air injection device is set to 0.1 Nm ³ /hr. In this embodiment, the mixing ratio and air ratio of the mixed gas in the first burner device and the second burner device are changed to perform a combustion experiment, and the exhaust gas is collected on the downstream side of the air injection device 4 along the airflow F of the combustion gas. In addition, the concentrations of nitrogen oxides (NOx), unburned ammonia (NH ₃ ) and carbon dioxide (CO ₂ ) contained in the exhaust gas are measured.

The inventive examples and comparative examples are summarized in Table 1. In addition, regarding the carbon dioxide (CO ₂ ) emission in the exhaust gas, the conventional example (Manufacture No. 3) which does not use ammonia as the fuel gas is set as a standard (1.0), and the ratio under each condition is shown in the table.

This embodiment is a combustion experiment using a small amount of burner equipment. Therefore, the more a large amount of burner equipment is arranged like a heating furnace, the more it becomes a condition that no nitrogen oxides or unburned ammonia are discharged. Therefore, the reference values of nitrogen oxide concentration and unburned ammonia concentration are set more strictly than those of a normal heating furnace, and the reference value of nitrogen oxide concentration is set to 100 ppm, and the reference value of unburned ammonia concentration is set to 20 ppm. If either the nitrogen oxide concentration or the unburned ammonia concentration exceeds the reference value, it is considered unqualified, and if both are below the reference value, it is judged as qualified.

The conventional example (Manufacture No. 3) is an example in which ammonia is not used as the fuel gas in the first burner heating and the second burner heating. In this case, the emission of nitrogen oxides and unburned ammonia is suppressed. However, there is the problem of high emission of carbon dioxide, as in the conventional burner equipment.

Comparative Example (Manufacture No. 4) is an example in which a mixed gas of ammonia and methane is used only in the second burner heating, but air injection from the air injection device 4 is not performed. By using ammonia in the fuel gas, the concentration of carbon dioxide is lower than that of the conventional example, but the emission of nitrogen oxides and unburned ammonia is large. Comparative Example (Manufacture No. 5) is an example in which a mixed gas of ammonia and methane is used only in the first burner heating, but air injection from the air injection device 4 is not performed. In Comparative Example (Manufacture No. 5), since the exhaust gas heated by the second burner does not contain unburned ammonia, the nitrogen oxides contained in the exhaust gas generated by the first burner heating are not reduced. Furthermore, although the exhaust gas heated by the first burner sometimes contains a small amount of unburned ammonia, the unburned ammonia is oxidized by the heating of the second burner, thereby promoting the generation of nitrogen oxides. Therefore, unburned ammonia is not detected in the exhaust gas, but the concentration of nitrogen oxides increases.

The comparative example (Manufacture No. 6) is an example in which a mixed gas of ammonia and methane is burned together with the first burner heating and the second burner heating, but air injection is not performed from the air injection device 4. At this time, since oxygen is not supplied to the mixed exhaust gas generated by the first burner heating and the second burner heating, 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 (Manufacture No. 7) is an example in which a mixed gas of ammonia and methane is burned together with the first burner heating and the second burner heating, and air injection is performed from the air injection device 4. However, since the air ratio in the first burner heating is more than 1.0, it is considered that a large amount of nitrogen oxides are generated in the exhaust gas heated by the first burner. Therefore, even if unburned ammonia is generated in the exhaust gas heated by the second burner, since the concentration of nitrogen oxides in the mixed exhaust gas is high, it is considered that nitrogen oxides remain in the exhaust gas.

In contrast, the invention example (manufacture No. 1) burns a mixed gas of ammonia and methane together with the first burner heating and the second burner heating, and the air ratio in the first burner heating is in the range of 0.9 to 1.0, and the air ratio in the second burner heating is lower than the air ratio in the first burner heating. Furthermore, the air is injected toward the mixed exhaust gas of the exhaust gas heated by the first burner and the exhaust gas heated by the second burner by the air injection device 4. In this way, the amount of carbon dioxide contained in the exhaust gas can be greatly reduced compared with the previous example, and the concentration of nitrogen oxides and unburned ammonia contained in the exhaust gas can be reduced. Furthermore, in the invention example (production No. 2), by setting the air ratio during heating of the second burner to less than 0.9, the concentration of unburned ammonia can be maintained at the same level as that of the invention example 1, while the concentration of nitrogen oxides can be reduced.

[Table 1] Manufacturing No. First burner heating Second burner heating Air jet Exhaust gas Remarks Heat ratio of NH ₃ (%) Heat ratio of CH ₄ (%) Air ratio Heat ratio of NH ₃ (%) Heat ratio of CH ₄ (%) Air ratio Presence of air jets 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 Comparison Example 5 40 60 0.95 0 100 1.10 without 600 0 0.8 Comparison Example 6 40 60 0.95 40 60 0.88 without 200 42 0.6 Comparison Example 7 40 60 1.10 40 60 0.88 have 300 12 0.6 Comparison Example

1: Heating furnace 2: First burner equipment 3: Second burner equipment 4: Air injection equipment 5: First fuel gas 6: Second fuel gas 7: First burner nozzle 8: Second burner nozzle 9: Air injection nozzle 10: Ammonia 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 side 31: Unloading section 32: Moving slideway 33: Fixed slideway 34: Flue gas 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 adjustment valve 54: First air ratio adjustment section 55: Second air ratio adjustment section 100: Steel moving direction B: Burner F: Combustion gas flow S: Steel S1: front end of steel S2: rear end of steel

FIG. 1 is a schematic structural diagram of a heating furnace. FIG. 2 is a structural diagram showing the arrangement of the burner equipment in the heating furnace as viewed from the front in the direction of movement of the steel material in FIG. 1. FIG. 3 is a structural diagram of a heating furnace including burner equipment and air injection equipment arranged in parallel according to the present embodiment. FIG. 4 is a schematic diagram for explaining the chemical reaction in the heating furnace. A) Nitrogen oxides and unburned ammonia exist in the exhaust gas generated by heating with the first burner. B) Nitrogen oxides and unburned ammonia exist in the exhaust gas generated by heating with the second burner. C) Represents the chemical reaction of nitrogen oxides and unburned ammonia in the mixed exhaust gas. FIG. 5 is a structural diagram of a heating furnace including burner equipment and air injection equipment arranged opposite to each other according to the present embodiment. FIG6 is a structural diagram of a heating furnace including a burner device and an air injection device and a schematic diagram of chemical reactions in the heating furnace for explaining the present embodiment. A) Nitrogen oxides and unburned ammonia exist in the exhaust gas generated by heating with the first burner. B) Nitrogen oxides and unburned ammonia exist in the exhaust gas generated by heating with the second burner. FIG7 is a schematic structural diagram of a heating furnace of the present embodiment. FIG8 is a structural diagram of another heating furnace including a burner device having an air ratio adjustment unit and a control unit and an air injection device of the present embodiment.

2: First burner equipment

3: Second burner equipment

4: Air jet equipment

5: First fuel gas

6: Second fuel gas

7: Nozzle of the first burner

8: Second burner nozzle

9: Air jet nozzle

10: Ammonia

11: 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: Waste gas

23: Mixed exhaust gas

24: Air jets

25, 26: Ammonia supply system

27, 28: Gas supply system

29: Air supply system

35: Fireplace wall

36:Inside the furnace

52: Flow meter

53: Flow regulating valve

F: Combustion gas flow

Claims (8)

A method for operating a heating furnace comprises: a first burner heating step, heating the burner by using a first fuel gas containing ammonia and combustion air having an air ratio of 0.9 to 1.0 relative to the theoretical air volume of the first fuel gas; a second burner heating step, heating the burner by using a second fuel gas containing ammonia and combustion air having an air ratio relative to the theoretical air volume of the second fuel gas that is lower than the air ratio relative to the theoretical air volume of the first fuel gas; and an air injection step, injecting air. The method for operating a heating furnace as described in claim 1, wherein the air injection step is to inject air into a mixed exhaust gas formed by mixing the exhaust gas generated by the first burner heating step and the exhaust gas generated by the second burner heating step. The method for operating a heating furnace as described in claim 1 or claim 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. The method for operating a heating furnace as described in claim 1 or claim 2, wherein at least one of the first fuel gas and the second fuel gas uses a mixed gas of ammonia and coal gas for burner heating. The method for operating a heating furnace as described in claim 3, wherein at least one of the first fuel gas and the second fuel gas uses a mixed gas of ammonia and coal gas for burner heating. A heating furnace comprises: Two or more burner devices, which use a fuel gas containing ammonia to perform burner heating; An air ratio adjustment unit, which 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, which 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, which injects air into the mixed exhaust gas of the exhaust gas discharged from the two or more burner devices. A heating furnace as described in claim 6, wherein the burner device comprises: a first burner device for performing burner heating by using a first fuel gas containing ammonia whose air ratio is adjusted by the air ratio adjusting unit and combustion air whose air ratio relative to the theoretical air amount of the first fuel gas is 0.9 to 1.0; and a second burner device for performing burner heating by using a second fuel gas containing ammonia and combustion air whose air ratio relative to the theoretical air amount of the second fuel gas is lower than the air ratio relative to the theoretical air amount of the first fuel gas, and the first burner device, the second burner device, and the air injection device are arranged in sequence from the upstream side of the airflow along the airflow inside the heating furnace. The heating furnace as described in claim 6, wherein the heating furnace includes an opening for discharging the mixed exhaust gas, the air injection device is arranged at a position closer to the opening than the first burner device and the second burner device.