Heating furnace operation method and heating furnace

Abstract

Provided are a heating furnace operation method and a heating furnace, whereby it becomes possible to highly efficiently produce, as a fuel gas for the heating furnace, an ammonia with which the emission of carbon dioxide can be suppressed.　The heating furnace operation method is a method in which, by using a thermal-storage-type combustion device equipped with a pair of combustion units facing each other and each having a heat storage unit, the temperature of the interior of the heating furnace is controlled by alternately performing a combustion operation and a suction operation in the pair of combustion units facing each other. In the suction operation, sensible heat of a suction gas that has been sucked from the interior of the heating furnace is recovered in the heat storage unit. In the combustion operation, the temperature of combustion air is raised by allowing the combustion air to pass through the heat storage unit and then the combustion air is ejected toward the interior of the heating furnace, and liquid ammonia is sprayed from a fuel feeding nozzle toward an ejection flow path for the combustion air that has passed through the heat storage unit.

Description

Heating furnace operation method and heating furnace

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

[0002] In integrated steelworks, blast furnace gas discharged from the top of a blast furnace, which reduces iron ore to produce molten iron, as well as by-product gases generated in converters and coke ovens, are effectively utilized (recycled) as fuel gas. However, in response to recent demands for reduced carbon dioxide emissions, combustion technologies are needed to reduce the consumption of these by-product gases. For example, in heating furnaces that heat steel materials in hot rolling lines and plate rolling lines of integrated steelworks, it is necessary to reduce the consumption of by-product gases and carbon dioxide emissions. In this case, technology using ammonia as fuel gas for heating furnaces has attracted attention. Ammonia, which does not contain carbon, produces mainly water and nitrogen upon combustion, which is effective in reducing carbon dioxide emissions. Therefore, technological development for using ammonia as fuel gas for heating furnaces is desired.

[0003] Ammonia used as a fuel for combustion is transported and stored in a liquid state. When ammonia in a liquid state (liquid ammonia) is directly burned, the ammonia does not evaporate sufficiently during combustion due to the high latent heat of vaporization of ammonia, resulting in a problem of reduced efficiency in conversion to thermal energy. Therefore, in order to obtain a predetermined combustion energy, it is necessary to supply an excess amount of liquid ammonia as fuel, which increases the amount of ammonia consumed. On the other hand, when liquid ammonia is vaporized in advance before being burned, it is necessary to heat the ammonia in advance to vaporize it, which requires additional energy.

[0004] In this regard, Patent Document 1 discloses a combustion device such as a gas turbine that uses an ammonia vaporizer that vaporizes liquid ammonia using the heat of combustion exhaust gas. Since the combustion exhaust gas from the combustor maintains a temperature of, for example, about 800°C, it is said that liquid ammonia can be easily vaporized by heat exchange with gas passing through the exhaust system of the combustor.

[0005] Furthermore, Patent Document 2 discloses a combustion device such as a gas turbine, which generates steam using exhaust gas from the gas turbine and generates ammonia vapor by spraying liquid ammonia into a flow path of the generated steam. In this case, it is said that the liquid ammonia can be vaporized by heat exchange between the high-temperature steam and the liquid ammonia.

[0006] JP 2015-190466 A JP 2020-165603 A

[0007] "Effect of Ambient Velocity on the Evaporation Rate Constant of a Free Droplet," Journal of the Japan Institute of Energy, Vol. 74, 1995, pp. 39-45

[0008] However, when the above-mentioned conventional technology is applied to heating equipment such as a heating furnace, the following problems arise.

[0009] The technology described in Patent Document 1 can be applied to cases where a large amount of gas is discharged as exhaust gas, such as a gas turbine, and the exhaust gas has a large amount of sensible heat. However, in heating equipment such as industrial heating furnaces, the sensible heat of the exhaust gas is used to preheat the combustion air, so it does not have enough heat to vaporize liquid ammonia. Furthermore, when applied to an existing heating furnace, it is necessary to add a new heat exchanger to exchange heat between the exhaust gas and liquid ammonia, which increases the equipment cost.

[0010] In the technology described in Patent Document 2, when steam is generated using exhaust gas discharged from a heating furnace, the exhaust gas does not have enough heat to vaporize the amount of ammonia gas required for combustion in the heating furnace. Furthermore, since steam is supplied to the inside of the heating furnace, oxidation of the material to be heated (target material) such as steel is promoted, resulting in a problem of reduced product yield of the material to be heated.

[0011] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a heating furnace and an operating method thereof that can efficiently generate ammonia gas, which can suppress carbon dioxide emissions as fuel gas for the heating furnace, by using sensible heat recovered in a heat storage section.

[0012] [1] A method for operating a heating furnace, in which a regenerative combustion device is provided with opposing combustion sections each having a heat storage section, and the pair of opposing combustion sections alternately performs a combustion operation and a suction operation to control the temperature inside the heating furnace, wherein in the suction operation, the heat storage section recovers sensible heat contained in suction gas suctioned from the inside of the heating furnace, and in the combustion operation, the combustion air is heated by passing through the heat storage section and discharged into the heating furnace, and liquid ammonia is sprayed from a fuel supply nozzle toward the discharge flow path of the combustion air that has passed through the heat storage section. [2] The method for operating a heating furnace described in [1], in which the sprayed liquid ammonia is in the form of droplets having a Sauter mean diameter of 5 to 3000 μm. [3] The sprayed liquid ammonia has a Sauter mean diameter d ０ (mm) is the distance L (mm) from the discharge port of the discharge flow path to the connection position where the fuel supply nozzle is connected, and V is the average velocity of the velocity of the combustion air that has passed through the heat storage unit and the velocity of the component of the velocity of the sprayed liquid ammonia in the direction of the discharge flow path. Ｍ The method for operating a heating furnace according to [1] or [2], wherein the following formula (1) is satisfied as the speed (mm / s): where K is the evaporation rate constant of liquid ammonia (mm ２ / s). [4] A method for operating a heating furnace according to any one of [1] to [3], wherein the liquid ammonia is sprayed toward the discharge flow path of the combustion air that has passed through the heat storage unit, and at least one gaseous fuel selected from coal gas and hydrocarbon gas is supplied. [5] A heating furnace comprising a regenerative combustion device having combustion units disposed opposite each other, and controlling the temperature inside the furnace by alternately performing a combustion operation and a suction operation in the pair of opposing combustion units, the heating furnace having an alternating combustion control unit that controls the pair of combustion units to alternately perform the combustion operation and the suction operation, the combustion units having a heat storage unit that recovers sensible heat of suction gas sucked from the interior of the heating furnace in the suction operation, a discharge flow path that heats the combustion air by passing it through the heat storage unit in the combustion operation and discharges the heated combustion air toward the interior of the heating furnace, and a fuel supply nozzle that sprays liquid ammonia toward the discharge flow path in the combustion operation.

[0013] According to the present invention, it is possible to efficiently generate ammonia gas, which can suppress carbon dioxide emissions, as a fuel gas for a heating furnace by using sensible heat recovered in a heat storage section.

[0014] FIG. 1 is a schematic side view showing an example of a heating furnace. FIG. 2 is a schematic cross-sectional view showing an example of a heating furnace. FIG. 3 is a diagram showing the configuration of flow paths related to the supply and suction of combustion air, suction gas, and liquid ammonia in a regenerative combustion device. FIG. 4 is a diagram showing the configuration related to the supply of combustion air and fuel to a first combustion nozzle. FIG. 5 is a diagram showing a schematic positional relationship of a first fuel supply nozzle with respect to a first combustion nozzle. FIG. 6 is a diagram showing a schematic configuration of a first combustion section of a second embodiment. FIG. 7 is a diagram showing a schematic configuration of a first combustion section of a third embodiment. FIG. 8 is a diagram showing a schematic configuration of a first combustion section of a fourth embodiment.

[0015] First Embodiment A first embodiment of the present invention will now be described in detail. FIGS. 1 and 2 show the configuration of a heating furnace 10 according to this embodiment. FIG. 1 shows a schematic side view of an example of the heating furnace 10. FIG. 2 shows a schematic cross-sectional view of an example of the heating furnace 10. The heating furnace 10 includes a charging section 11, a combustion device 12, a conveying device 15, an extraction section 16, and a flue section 17. The heating furnace 10 heats a target material S, which is a heated object, to a temperature of 500 to 1400°C. Furthermore, when applied to a hot rolling line, for example, the heating furnace 10 is used to heat a target material S, such as a cast slab, to a predetermined temperature (approximately 1100 to 1300°C). While the target material S is primarily a metal, it may also be an ferrous metal or a non-ferrous metal.

[0016] The charging section 11 charges (carries in) the target material S into the heating furnace 10. The extraction section 16 extracts (carries out) the heated target material S to the outside of the heating furnace 10. For example, steel (target material S), such as a slab produced on a continuous casting line, is transported to a yard on the charging side of the heating furnace 10 and charged into the heating furnace 10 from the charging section 11 according to a production schedule of a hot rolling line or the like. The interior of the heating furnace 10 is divided into multiple zones, with a heating zone divided into 2 to 8 zones provided on the upstream side and 1 to 3 soaking zones provided on the downstream side.

[0017] During operation of the heating furnace 10, the atmospheric temperature is controlled to be different for each zone within the furnace, and the average temperature of the target material S charged into the heating furnace 10 is gradually increased and controlled to reach a predetermined target heating temperature (the target temperature of the target material S when extracted from the heating furnace 10). The target material S heated to the target heating temperature passes through the extraction section 16 and is subjected to hot rolling.

[0018] The heating furnace 10 is equipped inside with a fixed transport section 15a such as a fixed skid on which the target material S is placed, and a mobile transport section 15b such as a moving skid that transports the target material S. The heating furnace 10 equipped with the fixed transport section 15a and the mobile transport section 15b is called a walking beam continuous heating furnace.

[0019] The heating furnace 10 has a plurality of combustion devices 12, such as burners, arranged inside the furnace along the transport direction D of the target material S. The combustion devices 12 raise the temperature inside the furnace by combustion. When the temperature inside the furnace is raised by combustion in the combustion devices 12, the temperature of the target material S rises due to radiation from the wall 19 of the heating furnace 10. In addition, a flow of atmospheric gas occurs inside the furnace, and the target material S is raised by convection of the atmospheric gas. Furthermore, the target material S may be raised in temperature by contacting the combustion flame F of the combustion devices 12 with the target material S. That is, the combustion devices 12 burn fuel gas as a heat source for heating, thereby raising the temperature inside the heating furnace 10 and raising the temperature of the target material S placed in the furnace.

[0020] In this embodiment, a regenerative combustion device 13 having opposing combustion sections with heat storage units is used as at least a part of the combustion device 12 of the heating furnace 10. The regenerative combustion device 13 alternates between combustion and suction operations in the pair of opposing combustion sections to control the temperature inside the heating furnace 10. The regenerative combustion device 13 is also called a regenerative burner and is widely used in industrial heating furnaces.

[0021] As shown in FIG. 1 , the combustion devices 12 are disposed on the upper and lower sides of the target material S within the heating furnace 10 to minimize temperature differences between the upper and lower surfaces. The regenerative combustion device 13 has a configuration in which a pair of first and second combustion sections 13a and 13n are disposed facing each other within the furnace. The opposed pair of first and second combustion sections 13a and 13n are controllably connected to an alternating combustion control unit 14d to perform alternating combustion, which alternately switches between combustion and suction operations. Multiple regenerative combustion devices 13 may be disposed within the heating furnace 10. In this case, multiple opposed pairs of first and second combustion sections 13a and 13n may be disposed within the heating furnace 10, and the alternating combustion control unit 14d may be connected to control the alternating combustion of the multiple pairs of first and second combustion sections 13a and 13n.

[0022] Next, the configuration related to the supply of combustion air, the suction of suction gas, and the supply of liquid ammonia in the regenerative combustion device 13 will be described with reference to Fig. 3. Fig. 3 is a diagram showing the configuration of flow paths related to the supply and suction of combustion air, suction gas, and liquid ammonia. Fig. 3(a) is a diagram showing a state in which the combustion operation is performed in the first combustion section 13a and the suction operation is performed in the second combustion section 13n. Fig. 3(b) is a diagram showing a state in which the combustion operation is performed in the second combustion section 13n and the suction operation is performed in the first combustion section 13a.

[0023] The regenerative combustion device 13 has a first combustion section 13a, a second combustion section 13n, an air supply blower 14a, a suction pump 14b, a four-way valve 14c, and an alternating combustion control section 14d. That is, the regenerative combustion device 13 has a pair of combustion sections (the first combustion section 13a and the second combustion section 13n).

[0024] The first combustion section 13a includes a first combustion nozzle 13b, a first heat storage section 13c, a first gas flow path 13d, a first gas discharge path 13g, a first gas discharge port 13h, a first fuel supply nozzle 13i, a first fuel spray section 13j, and a first fuel flow path 13k. The first gas flow path 13d includes a first gas flow meter 13e and a first gas flow control valve 13f. The first fuel flow path 13k includes a first fuel flow meter 13l and a first fuel flow control valve 13m.

[0025] The second combustion section 13n has the same configuration as the first combustion section 13a. That is, the second combustion section 13n has a second combustion nozzle 13o, a second heat storage section 13p, a second gas flow path 13q, a second gas discharge path 13t, a second gas discharge port 13u, a second fuel supply nozzle 13v, a second fuel spray section 13w, and a second fuel flow path 13x. The second gas flow path 13q has a second gas flow meter 13r and a second gas flow control valve 13s. The second fuel flow path 13x has a second fuel flow meter 13y and a second fuel flow control valve 13z.

[0026] Here, a state in which the combustion operation is performed in the first combustion section 13a and the suction operation is performed in the second combustion section 13n will be described with reference to FIG. 3(a). The intake air blower 14a supplies combustion air O to the first combustion nozzle 13b via the first gas flow path 13d. The first gas flow control valve 13f adjusts the flow rate of the combustion air O in the first gas flow path 13d. The combustion air O passes through the first heat storage section 13c, where it is heated by the sensible heat of the first heat storage section 13c and supplied to the first combustion nozzle 13b. That is, the heated combustion air O is supplied to the first combustion nozzle 13b, and a combustion flame F is generated in the first combustion nozzle 13b, thereby improving the thermal efficiency of the first combustion section 13a. The velocity of the combustion air O supplied to the first combustion nozzle 13b is preferably 1 to 10 m / s.

[0027] The combustion air O is not limited to air collected from the atmosphere, but may be a gas with an increased oxygen content compared to the atmosphere, for example, by removing nitrogen from the air or adding pure oxygen. This not only efficiently promotes the oxidation reaction of the fuel, but also enables a reduction in the flow rate of the supplied combustion air O. This also enables a reduction in the power consumption of the intake air blower 14a, etc. On the other hand, the amount of oxygen contained in the combustion air O may be reduced by mixing exhaust gas (suction gas Q) from the heating furnace 10 with the combustion air O. This makes it easier to create a reducing atmosphere inside the heating furnace 10, thereby enabling a reduction in nitrogen oxides generated during combustion operation.

[0028] The first combustion nozzle 13b is connected to a first fuel flow path 13k that supplies fuel. Therefore, the fuel supplied from the first fuel flow path 13k is supplied to the first combustion nozzle 13b and mixed with the combustion air O to become a flammable gas, and a combustion flame F is sprayed toward the interior of the heating furnace 10.

[0029] The suction pump 14b sucks gas inside the furnace (hereinafter referred to as "in-furnace combustion gas") from the second combustion nozzle 13o, which is in a non-combustion state, through the second gas flow path 13q as suction gas Q. The suction pump 14b exhausts the suctioned and recovered suction gas Q to the outside of the heating furnace 10 as exhaust gas. Because the in-furnace combustion gas is in a high-temperature state when the heating furnace 10 is in operation, the suction gas Q sucked from the second combustion nozzle 13o is also at a high temperature. Therefore, when the suction gas Q is sucked into the second gas flow path 13q by the suction pump 14b, heat accumulates in the second heat storage unit 13p as it passes through the second heat storage unit 13p.

[0030] The second heat storage unit 13p may be made of a material known for use as a heat storage unit for the regenerative combustion device 13, such as silicon carbide ceramics, alumina ceramics, cordierite ceramics, or mullite ceramics. The second heat storage unit 13p may be constructed with a structure filled with a large number of ceramic balls, or may have a honeycomb structure. The speed of the suction gas Q passing through the second heat storage unit 13p is preferably 1 to 10 m / s. The same configurations as those in the second heat storage unit 13p are also applicable to the first heat storage unit 13c.

[0031] In the first combustion section 13a and the second combustion section 13n, the alternating switching between the combustion operation and the suction operation is performed by reversing the flow of the combustion air O and the suction gas Q shown in Fig. 3(a). Specifically, a four-way valve 14c for switching the first gas flow path 13d and the second gas flow path 13q connected to the air supply blower 14a and the suction pump 14b is installed. By switching between the first gas flow path 13d and the second gas flow path 13q using the four-way valve 14c, the flow direction of the gas flowing through the first gas flow path 13d and the second gas flow path 13q can be reversed.

[0032] As a result, the first gas flow passage 13d functions to supply combustion air O during the combustion operation (during combustion) in the first combustion section 13a, and functions to draw in the suction gas Q during the suction operation (during non-combustion) in the first combustion section 13a. Similarly, the second gas flow passage 13q functions to draw in the suction gas Q during the suction operation (during non-combustion) in the second combustion section 13n, and functions to supply combustion air O during the combustion operation (during combustion) in the second combustion section 13n.

[0033] 3(b), when combustion operation is performed in the second combustion section 13n, combustion air O is supplied from the air supply blower 14a via the second gas passage 13q toward the second combustion nozzle 13o. In the second combustion section 13n, the combustion air O supplied from the second gas passage 13q is heated by passing through the second heat storage section 13p and mixed with the fuel supplied from the second fuel passage 13x to generate combustible gas, and a combustion flame F is sprayed toward the furnace. At this time, in the first combustion section 13a where a suction operation is performed, the suction pump 14b suctions in-furnace combustion gas as suction gas Q via the first gas passage 13d.

[0034] The fuel supplied to the first combustion nozzle 13b and the second combustion nozzle 13o may be supplied by opening and closing the openings of the first fuel flow control valve 13m and the second fuel flow control valve 13z installed in the first fuel flow path 13k and the second fuel flow path 13x in accordance with the timing of the combustion operation or the suction operation.

[0035] The alternating combustion control unit 14d controls switching between the combustion operation and the suction operation in the first combustion unit 13a and the second combustion unit 13n. The alternating combustion control unit 14d controls the first combustion unit 13a and the second combustion unit 13n to perform either the combustion operation or the suction operation. The alternating combustion control unit 14d controls the first combustion unit 13a and the second combustion unit 13n to perform the suction operation while one of the combustion units 13a and 13n is performing the combustion operation. The alternating combustion control unit 14d may control switching between the combustion operation and the suction operation at predetermined intervals. The switching cycle between the combustion operation and the suction operation in the first combustion unit 13a and the second combustion unit 13n is preferably 20 to 120 seconds. If the switching cycle between the combustion operation and the suction operation is less than 20 seconds, the frequency of switching between the first gas flow path 13d and the second gas flow path 13q increases, which may lead to early deterioration of equipment such as the four-way valve 14c. Furthermore, if the switching period between the combustion operation and the suction operation exceeds 120 seconds, the amount of heat stored in the first heat storage section 13c and the second heat storage section 13p will increase, which will require the first heat storage section 13c and the second heat storage section 13p to be made larger, resulting in problems such as high equipment costs.

[0036] As described above, in the regenerative combustion device 13, the pair of combustion sections (the first combustion section 13a and the second combustion section 13n) alternately switch between the combustion operation and the suction operation, thereby alternately supplying the combustion air O and suctioning the suction gas Q. This produces the effect of storing the sensible heat of the suction gas Q in the heat storage sections (the first heat storage section 13c and the second heat storage section 13p) during the suction operation, and raising the temperature of the combustion air O in the heat storage sections (the first heat storage section 13c and the second heat storage section 13p) during the combustion operation, thereby making effective use of the heat of the suction gas Q.

[0037] Next, the configuration related to the supply of combustion air O and fuel to the first combustion nozzle 13b during the combustion operation in the first combustion section 13a will be described using Fig. 4. Fig. 4 is a diagram showing the configuration related to the supply of combustion air O and fuel to the first combustion nozzle 13b. In the following description of the embodiment, the configuration related to the supply of combustion air O and fuel will be described using the first combustion section 13a as an example, but since the supply of combustion air O and fuel in the second combustion section 13n is similar, a description of the second combustion section 13n will be omitted.

[0038] As shown in Fig. 4, first combustion nozzle 13b has first heat storage unit 13c therein. First gas discharge flow path 13g is a flow path through which combustion air O, which has been heated in first heat storage unit 13c and passed through first heat storage unit 13c in first combustion nozzle 13b, moves to first gas discharge port 13h, which is the boundary with the furnace interior. First fuel supply nozzle 13i has first fuel spray unit 13j therein. First fuel supply nozzle 13i is connected to first fuel flow path 13k.

[0039] During combustion operation, liquid ammonia Al is supplied as fuel to the first combustion nozzle 13b via the first fuel flow path 13k. The liquid ammonia Al is sprayed by the first fuel spray unit 13j and passed through the first fuel supply nozzle 13i before being supplied to the first combustion nozzle 13b. Also, during combustion operation, combustion air O is supplied to the first combustion nozzle 13b via the first gas flow path 13d. The combustion air O undergoes heat exchange as it passes through the first thermal storage unit 13c, and is heated. The combustion air O that has passed through the first thermal storage unit 13c is heated to a temperature of, for example, 500 to 1400°C. The liquid ammonia Al supplied from the first fuel supply nozzle 13i to the first combustion nozzle 13b undergoes heat exchange with the combustion air O and is vaporized. Therefore, the liquid ammonia Al mixes with the combustion air O as ammonia gas Ag to form a combustible gas, and a combustion flame F is ejected from the first gas discharge port 13h toward the furnace interior.

[0040] Liquid ammonia Al used as fuel is supplied from a liquid ammonia reservoir 50. The liquid ammonia reservoir 50 is a container such as a tank that stores a predetermined amount of liquid ammonia Al. Ammonia can be liquefied at about 8 atmospheres at room temperature, so it can be easily stored in a liquid state. If ammonia is in a liquefied state, the volume of the container that stores the fuel can be reduced, improving transportability and storability.

[0041] The liquid ammonia Al stored in the liquid ammonia storage unit 50 is supplied to the first fuel flow path 13k using a supply pump (not shown). A first fuel flow meter 13l and a first fuel flow rate adjustment valve 13m may be arranged in the first fuel flow path 13k between the supply pump and the first fuel sprayer 13j. The first fuel flow meter 13l measures the flow rate of the liquid ammonia Al supplied to the first fuel sprayer 13j. The first fuel flow rate adjustment valve 13m adjusts the flow rate of the liquid ammonia Al supplied to the first fuel sprayer 13j. In this case, the first fuel flow rate adjustment valve 13m may be configured as an electromagnetic valve to control the flow rate of the liquid ammonia Al supplied to the first fuel sprayer 13j.

[0042] The first fuel spraying unit 13j sprays liquid ammonia Al toward the first gas discharge passage 13g of the combustion air O that has passed through the first heat storage unit 13c. "Spraying" means spraying the liquid in the form of a mist. The first fuel spraying unit 13j may use a known nozzle used for spraying a liquid in the form of a mist.

[0043] The liquid ammonia Al sprayed from the first fuel spray section 13j passes through the first fuel supply nozzle 13i and merges with the flow of combustion air O in the first combustion nozzle 13b. As a result, the liquid ammonia Al sprayed from the first fuel spray section 13j and passing through the first fuel supply nozzle 13i mixes with the combustion air O flowing through the first combustion nozzle 13b, and at the same time, heat exchange occurs between the liquid ammonia Al and the combustion air O.

[0044] The first fuel supply nozzle 13i applied to the first fuel spraying unit 13j may be a one-fluid nozzle that sprays only liquid ammonia Al, or a two-fluid nozzle that sprays liquid ammonia Al using compressed air. A one-fluid nozzle has a simple structure and is less subject to installation space constraints. A two-fluid nozzle can reduce the droplet size of the spray, and the droplet size of the spray can be controlled by adjusting the pressure and flow rate of the compressed air. In this case, a pump, blower, compressor, etc. may be used to pressurize the air. Furthermore, when a two-fluid nozzle is used, the liquid ammonia Al may be pressurized. The droplet size of the spray can be reduced by pressurizing the liquid ammonia Al, and the droplet size of the liquid ammonia Al can be adjusted by the applied pressure.

[0045] Here, from the viewpoint of uniform mixing with the combustion air O, the liquid ammonia Al sprayed by the first fuel spraying section 13j preferably has a Sauter mean diameter of 5 to 3000 μm, more preferably 10 to 800 μm, and even more preferably 50 to 300 μm. The Sauter mean diameter (D32), also known as the area mean diameter, is used as a representative diameter of droplets in heat or mass transport processes. The Sauter mean diameter is an average diameter obtained by weighting the droplet diameter d of each droplet by the ratio of the surface area of ​​droplets with diameter d to the sum of the surface areas of all droplets. Specifically, for a droplet group containing nd droplets with a droplet diameter d, the Sauter mean diameter is calculated using the following equation (2):

[0046]

[0047] If the Sauter mean diameter of the liquid ammonia Al is less than 5 μm, the momentum of the combustion air O discharged into the first combustion nozzle 13b during combustion operation becomes excessively large compared to the momentum of the liquid ammonia Al, resulting in insufficient mixing of the combustion air O and the liquid ammonia Al. This results in an uneven temperature distribution of the combustion flame F generated from the first gas outlet 13h at the tip of the first combustion nozzle 13b, which undesirably results in excessive generation of nitrogen oxides. On the other hand, if the Sauter mean diameter of the liquid ammonia Al exceeds 3000 μm, it takes time to vaporize the liquid ammonia Al. Therefore, when the liquid ammonia Al mixes with the combustion air O and is injected into the combustion flame F from the first gas outlet 13h at the tip of the first combustion nozzle 13b, the ammonia concentration distribution becomes uneven, which results in unburned ammonia remaining, which is undesirable.

[0048] The first fuel supply nozzle 13i is provided with a first fuel spray section 13j at one end, which forms a flow path for liquid ammonia Al sprayed from the first fuel spray section 13j. The other end of the first fuel supply nozzle 13i is connected to the first combustion nozzle 13b, and is configured so that the liquid ammonia Al passing through the first fuel supply nozzle 13i is mixed with the combustion air O flowing through the first gas discharge flow path 13g. The first fuel supply nozzle 13i may be disposed so as to be inclined with respect to the first gas discharge flow path 13g, which extends in the flow direction of the combustion air O of the first combustion nozzle 13b. Furthermore, the velocity of the liquid ammonia Al passing through the first fuel supply nozzle 13i in the spray direction has the same velocity component as the flow direction of the combustion air O, which makes it easier for the liquid ammonia Al to be mixed with the combustion air O.

[0049] Here, the positional relationship of the first fuel supply nozzle 13i with respect to the first combustion nozzle 13b will be described with reference to Fig. 5. Fig. 5 is a diagram schematically showing the positional relationship of the first fuel supply nozzle 13i with respect to the first combustion nozzle 13b.

[0050] 5, first fuel supply nozzle 13i is disposed so as to be inclined at angle θ with respect to first gas discharge flow path 13g, which extends in the flow direction of combustion air O flowing through first combustion nozzle 13b. Connection position M of first fuel supply nozzle 13i with first combustion nozzle 13b is a position spaced a distance L (mm) from first gas discharge port 13h.

[0051] Here, the velocity of the combustion air O passing through the first heat storage section 13c is V ０ (mm / s), and the velocity of the liquid ammonia Al sprayed from the first fuel supply nozzle 13i toward the first gas discharge passage 13g is V １ In this case, the first fuel supply nozzle 13i is inclined at an angle θ with respect to the first gas discharge passage 13g extending in the flow direction of the combustion air O. Therefore, the velocity V of the component of the velocity of the sprayed liquid ammonia Al in the direction of the first gas discharge passage 13g (the flow direction of the combustion air O) is Ｆ (mm / s) is V １ In this case, the velocity of the combustion air O passing through the first heat storage section 13c may have a velocity distribution in the cross section of the first gas discharge passage 13g, but the velocity V ０ means the average velocity within the cross section of the first gas discharge passage 13g. In addition, since the size of the droplets of liquid ammonia Al sprayed from the first fuel supply nozzle 13i toward the first gas discharge passage 13g is various, there is a velocity distribution within the first fuel supply nozzle 13i depending on the droplet diameter. Therefore, the velocity V １ denotes the average velocity of the liquid ammonia Al droplet.

[0052] The liquid ammonia Al that has passed through the first fuel supply nozzle 13i reaches the first gas discharge port 13h while exchanging momentum with the combustion air O. Therefore, the liquid ammonia Al sprayed into the first combustion nozzle 13b moves at a velocity V ０ and velocity V Ｆ and the average speed V Ｍ It can be considered that the liquid ammonia Al passes through the first gas discharge passage 13g at a speed of 1 / 2 mm / s. Therefore, the time tT (s) required for the liquid ammonia Al sprayed into the first combustion nozzle 13b to reach the first gas discharge port 13h is expressed by the following equation (3):

[0053]

[0054] The droplet diameter of the liquid ammonia Al sprayed from the first fuel supply nozzle 13i to the first combustion nozzle 13b is d ０ (mm), the droplet diameter d (mm) at time tT is the evaporation rate constant Ke (mm ２ / s), it is expressed by the following equation (4).

[0055]

[0056] Here, the evaporation rate constant Ke refers to the rate at which the square of the droplet diameter decreases over time during the steady-state evaporation period that occurs when fuel droplets are introduced into a high-temperature atmosphere. That is, in the early stages after the droplets are introduced into the high-temperature atmosphere, most of the heat flowing into the droplets is consumed in heating the droplets themselves, so the droplets do not evaporate much and the amount of decrease in droplet diameter is small. However, once the droplet temperature reaches the wet-bulb temperature (the temperature at which all of the heat flowing into the droplets is used to evaporate the droplets) (steady-state evaporation period), the square of the droplet diameter decreases linearly with time, and this rate of decrease is called the evaporation constant.

[0057] The evaporation rate constant Ke may be determined by an experiment using droplets of liquid ammonia. However, it may also be determined by using the following formula (5) described in Non-Patent Document 1, for example. ０ is V in the above ０ and V Ｆ and Re are the evaporation rate constants when the temperature is equal to the evaporation rate.

[0058]

[0059] In this case, the following equation (6) can be derived from equation (4) based on the condition that the droplets of liquid ammonia Al evaporate at time tT (d=0).

[0060]

[0061] Based on the above formulas (3) and (6), the condition for the droplets of liquid ammonia Al that have passed through the first fuel supply nozzle 13i to vaporize before reaching the first gas discharge port 13h, which is the tip of the first combustion nozzle 13b, is expressed as the following formula (1): That is, if the droplet diameter of the liquid ammonia Al that has passed through the first fuel supply nozzle 13i is smaller than the droplet diameter calculated by formula (6), the liquid ammonia Al can be vaporized before reaching the first gas discharge port 13h.

[0062]

[0063] The liquid ammonia Al droplet d ０ can be expressed using the Sauter mean diameter of liquid ammonia Al as a representative value. Therefore, the Sauter mean diameter d ０ satisfies formula (1), it is considered that the liquid ammonia Al sprayed from the first fuel supply nozzle 13i becomes vaporized ammonia gas when the combustion flame F is injected from the first gas discharge port 13h. Furthermore, the Sauter mean diameter of the liquid ammonia Al sprayed from the first fuel spray section 13j is the same as the Sauter mean diameter of the liquid ammonia Al supplied from the first fuel supply nozzle 13i to the first combustion nozzle 13b, or the droplet diameter of the liquid ammonia Al sprayed from the first fuel spray section 13j is slightly larger. Therefore, if the Sauter mean diameter of the liquid ammonia Al sprayed from the first fuel spray section 13j satisfies formula (1), the liquid ammonia Al becomes ammonia gas Ag when the combustion flame F is injected from the first gas discharge port 13h, which is the tip of the first combustion nozzle 13b.

[0064] Specifically, the distance L between the connection position M of the first fuel supply nozzle 13i and the first gas discharge port 13h is 100 mm, and the evaporation rate constant Ke is 0.1 mm. ２ / s, average speed V Ｍ When the flow rate is 5000 mm / s, the Reynolds number Re is approximately 16000. In this case, the Sauter mean diameter d ０By making the gap between the first gas discharge ports 13h and the liquid ammonia Al smaller than 0.84 mm, when the combustion flame F is generated at the first gas discharge ports 13h, the liquid ammonia Al becomes ammonia gas Ag.

[0065] As described above, this embodiment is a method for operating a heating furnace 10 using a regenerative combustion device 13. During combustion, combustion air O supplied to the first combustion nozzle 13b is heated by passing it through the first thermal storage unit 13c, and liquid ammonia Al is sprayed from the first fuel spray unit 13j as combustion fuel toward the first gas discharge flow path 13g of the combustion air O passing through the first thermal storage unit 13c and the first combustion nozzle 13b. Heat exchange occurs while the liquid ammonia Al is mixed with the heated combustion air O, and the liquid ammonia Al is vaporized in the first combustion nozzle 13b to generate ammonia gas Ag. The generated ammonia gas Ag is mixed with the combustion air O as a combustible gas, and a combustion flame F is sprayed toward the interior of the heating furnace 10. That is, by performing combustion operation in the combustion device 12 using liquid ammonia Al as fuel, it is possible to reduce carbon dioxide emissions from the heating furnace 10 and omit the supply of external energy required for vaporizing the liquid ammonia Al. Furthermore, in the first combustion nozzle 13b, heat exchange also takes place between the ammonia gas Al and the combustion air O, so the temperature of the ammonia gas Ag rises. In other words, it becomes possible to efficiently generate ammonia gas as fuel gas for the heating furnace 10 using the sensible heat recovered in the heat storage unit. Furthermore, since the ammonia gas Ag has the property of thermally decomposing into nitrogen and hydrogen at high temperatures, the combustion rate of ammonia, which is a flame-retardant fuel, increases, and the stability of burner combustion improves.

[0066] Here, the "heat storage section" according to the present invention corresponds to the first heat storage section 13c and the second heat storage section 13p. The "combustion section" according to the present invention corresponds to the first combustion section 13a and the second combustion section 13n. The "discharge flow path" according to the present invention corresponds to the first gas discharge flow path 13g and the second gas discharge flow path 13t. The "fuel supply nozzle" according to the present invention corresponds to the first fuel supply nozzle 13i and the second fuel supply nozzle 13v. The "discharge port" according to the present invention corresponds to the first gas discharge port 13h and the second gas discharge port 13u.

[0067] Second Embodiment Next, a second embodiment of the present invention will be described in detail. Fig. 6 schematically shows the configuration of the first combustion section 23a of the second embodiment. Fig. 6 shows a first example of a fuel supply system when another gaseous fuel R is used as fuel. The configuration shown in Fig. 6 is a configuration including a plurality of supply nozzles for supplying fuel to the first combustion nozzle 23b, and is an example of an individual fuel injection system in which different types of fuel are supplied individually.

[0068] In the second embodiment, in addition to the first fuel supply nozzle 23i that supplies liquid ammonia Al to the first combustion nozzle 23b, the gaseous fuel supply nozzle 20 that supplies gaseous fuel R is provided. When a plurality of supply nozzles that supply fuel to the first combustion nozzle 23b are provided, one of them may be the first fuel supply nozzle 23i that supplies liquid ammonia Al. In this case, the combustion air O that has been heated by passing through the first heat storage unit 23c, the liquid ammonia Al that has been turned into droplets by the first fuel spray unit 23j, and the gaseous fuel R supplied from the gaseous fuel supply nozzle 20 are mixed and heat exchanged in the first combustion nozzle 23b. Ammonia gas Ag is generated from the liquid ammonia Al supplied to the first combustion nozzle 23b, and the mixed fuel of the ammonia gas Ag and the gaseous fuel R is combusted, generating a combustion flame F from the first gas discharge port 23h. The temperature of the gaseous fuel R supplied from the gaseous fuel supply nozzle 20 is also increased by the combustion air O, which improves the combustibility of the gaseous fuel R and achieves further energy savings.

[0069] In this embodiment (second embodiment), liquid ammonia Al is sprayed as a fuel for combustion toward the first gas discharge flow path 23g into which the combustion air O that has passed through the first heat storage unit 23c is discharged, and other gaseous fuel R can be used as the fuel for combustion. Since ammonia gas Ag is a flame-retardant fuel, using ammonia gas Ag in combination with other gaseous fuel R can promote the combustion of the ammonia gas Ag and increase the stability of the combustion flame F generated in the first combustion nozzle 23b.

[0070] Coal gas Cg may be used as another gaseous fuel R that promotes the combustion of ammonia gas Ag. Here, coal gas Cg refers to a gas obtained from coal. The coal gas Cg preferably includes any one of coke oven gas, blast furnace gas, converter gas, and electric furnace gas. These gases are by-product gases generated in steelworks and have the effect of stabilizing the combustion of ammonia gas Ag. Blast furnace gas is a by-product gas generated when iron ore is reduced in a blast furnace to produce pig iron. Coke oven gas is a by-product gas generated by high-temperature carbonization of coal to produce coke. Converter gas is a by-product gas generated in the steelmaking process in a converter. Electric furnace gas is a gas generated by incomplete combustion of auxiliary fuel (recarburizer) in an electric furnace. The coal gas Cg may be a mixed gas containing these by-product gases. The coal gas constituting the mixed gas may be a gas obtained by appropriately mixing blast furnace gas, coke oven gas, and converter gas (hereinafter also referred to as "M gas"). By mixing coal gas Cg, which has a different calorific value compared to ammonia gas Ag, the amount of heat required to heat the target material S in the heating furnace 10 can be supplied, enabling stable operation of the heating furnace 10.

[0071] Hydrocarbon gas Hg may be used as another gaseous fuel R that promotes the combustion of ammonia gas Ag. Here, the hydrocarbon gas Hg refers to a fuel gas in which hydrocarbons are vaporized. The hydrocarbon gas Hg includes methane (CH ), which is a paraffinic hydrocarbon. ４ ), ethane (C ２ H ６ ), propane (C ３ H ８ ), butane (C ４ H １０ ), and olefinic hydrocarbon ethylene (C ２ H ４ ), propylene (C ３ H ６ ), butylene (C ４ H ８) can be used. These gases have the effect of stabilizing the combustion of ammonia gas Ag. Furthermore, compared to coal gas, emissions of nitrogen oxides and sulfur oxides can be suppressed. By mixing hydrocarbon gas Hg, which has a different calorific value compared to ammonia gas Ag, the amount of heat required to heat the target material S in the heating furnace 10 can be supplied, enabling stable operation of the heating furnace 10. In this embodiment, at least one gaseous fuel selected from coal gas Cg and hydrocarbon gas Hg is preferably used as the other gaseous fuel R that promotes the combustion of ammonia gas Ag.

[0072] Third Embodiment Next, a third embodiment of the present invention will be described in detail. FIG. 7 schematically illustrates the configuration of a first combustion unit 33a according to the third embodiment. FIG. 7 illustrates a second example of a fuel supply system when another gaseous fuel R is used as fuel. The configuration illustrated in FIG. 7 is configured such that liquid ammonia Al is supplied from a first fuel flow path 33k, droplets of the liquid ammonia Al are generated by a first fuel spray unit 33j, and then a mixed fuel with the gaseous fuel R is generated, and the mixed fuel is supplied from a first fuel supply nozzle 33i to a first combustion nozzle 33b. The configuration illustrated in FIG. 7 is an example of a post-spray mixed fuel generation system. In this embodiment, as in the second embodiment, coal gas Cg may be used as the other gaseous fuel R that promotes the combustion of ammonia gas Ag.

[0073] In the third embodiment, liquid ammonia Al is sprayed by the first fuel spray unit 33j, and gaseous fuel R is supplied from the gaseous fuel supply nozzle 30 to a flow of liquid ammonia Al droplets moving inside the first fuel supply nozzle 33i toward the first combustion nozzle 33b. As a result, a mixed fuel of liquid ammonia Al and gaseous fuel R is supplied from the first fuel supply nozzle 33i to the first combustion nozzle 33b. A two-fluid nozzle using compressed air may be applied to the first fuel spray unit 33j. The injection of compressed air increases the flow velocity of the liquid ammonia Al droplets inside the first fuel supply nozzle 33i, thereby promoting mixing of the liquid ammonia Al and the gaseous fuel R. In this case, heat exchange occurs between the combustion air O heated by passing through the first heat storage unit 33c and the liquid ammonia Al in the mixed fuel supplied from the first fuel supply nozzle 33i, generating ammonia gas Ag. The mixed gas of ammonia gas Ag and gaseous fuel R becomes fuel gas, and a combustion flame F is ejected from the first gas discharge port 33h. In this case, too, the gaseous fuel R supplied from the first fuel supply nozzle 33i is heated by the combustion air O, thereby improving the combustibility of the gaseous fuel R.

[0074] <Fourth Embodiment> Next, a fourth embodiment of the present invention will be described in detail. FIG. 8 schematically shows the configuration of a first combustion unit 43a of the fourth embodiment. FIG. 8 shows a third example of a fuel supply system when another gaseous fuel R is used as fuel. The configuration shown in FIG. 8 is a system in which liquid ammonia Al is supplied from a first fuel flow path 43k, and before droplets of the liquid ammonia Al are generated by the fluid spray unit 42, a mixed fuel with the gaseous fuel R is generated, and the mixed fuel is supplied from the gaseous fuel supply nozzle 40 to the first combustion nozzle 43b. The configuration shown in FIG. 8 is an example of a pre-spray mixed fuel generation system. In this embodiment, as in the second and third embodiments, coal gas Cg may be used as the other gaseous fuel R that promotes combustion of ammonia gas Ag.

[0075] In the fourth embodiment, liquid ammonia Al supplied from the first fuel flow path 43k is mixed with gaseous fuel R supplied from the gaseous fuel flow path 41, and then the liquid ammonia Al is sprayed by the fluid spraying unit 42. The gaseous fuel R supplied from the gaseous fuel flow path 41 may be supplied as a compressed gas compressed by a pump, compressor, or the like and mixed with the liquid ammonia Al. Pressure generated within the supply pipe reduces the Sauter mean diameter of the liquid ammonia Al sprayed from the fluid spraying unit 42, facilitating vaporization of the liquid ammonia Al. Even in this case, heat exchange occurs between the combustion air O heated by passing through the first heat storage unit 43c and the liquid ammonia Al in the mixed fuel supplied from the gaseous fuel supply nozzle 40, generating ammonia gas Ag. The mixed gas of ammonia gas Ag and gaseous fuel R then becomes fuel gas, and a combustion flame F is ejected from the first gas outlet 43h.

[0076] Next, the results of a combustion experiment conducted on a heating furnace operating method according to the present invention will be described. The combustion experiment was conducted using a first combustion section 23a (second embodiment) shown in Fig. 6. The first combustion section 23a shown in Fig. 6 is an example of an individual fuel injection system, and includes a first gas flow path 23d, a first heat storage section 23c, a gaseous fuel supply nozzle 20, a first fuel supply nozzle 23i, a first fuel spray section 23j, and a first combustion nozzle 23b.

[0077] In this embodiment, a combustible gas selected from methane, which is a hydrocarbon gas Hg, and coke oven gas, which is a coal gas Cg, was used as the gaseous fuel R. The gaseous fuel R selected from methane and coke oven gas was supplied to the gaseous fuel supply nozzle 20 via a gaseous fuel flow path (not shown). Liquid ammonia Al was supplied from the first fuel flow path 23k to the first fuel spray unit 23j, and the liquid ammonia Al sprayed by the first fuel spray unit 23j was supplied to the first fuel supply nozzle 23i. In addition, flow control valves were provided in the gaseous fuel flow path and the first fuel flow path 23k to adjust the mixture ratio of the liquid ammonia Al and the gaseous fuel R supplied to the first combustion nozzle 23b. In addition, a flow control valve was also provided in the first gas flow path 23d to adjust the air ratio of the fuel gas (liquid ammonia Al and gaseous fuel R) relative to the theoretical air ratio to be 0.9.

[0078] The first combustion section 23a had a rated capacity of 800,000 kcal / hr. The distance L between the connection position M of the first fuel supply nozzle 23i and the first gas discharge port 23h, which is the tip of the first combustion nozzle 23b, was 100 mm. The flow rate of the fuel gas supplied in the combustion operation was set to 79 Nm3 when a mixed fuel containing ammonia at 40% calorific value and methane at 60% calorific value was used. ３ The flow rate of liquid ammonia Al was set to 51 Nm / hr. ３ When coke oven gas was used as the gaseous fuel R, the flow rate of the coke oven gas was set so that the calorific value was approximately the same as that of a mixed fuel containing ammonia at 40% of its calorific value and methane at 60% of its calorific value.

[0079] On the other hand, as a conventional example, in the first combustion section 23a shown in FIG. 6, liquid ammonia Al was not supplied from the first fuel flow path 23k, and methane was supplied as the gaseous fuel R to the gaseous fuel supply nozzle 20. In this case, the flow rate of methane when used as fuel gas was 84 Nm ３ / hr.

[0080] In this example, a combustion experiment was conducted by changing the mixture ratio of the combustion gas in the combustion operation of the first combustion unit 23 a and the spray diameter of the liquid ammonia Al sprayed by the first fuel spray unit 23 j. In this case, the Sauter mean diameter was used as the spray diameter of the liquid ammonia Al.

[0081] In the comparative example, the first combustion section 23a shown in FIG. 6 was configured so that a mixed gas of methane and ammonia gas Ag was supplied as gaseous fuel from the gaseous fuel supply nozzle 20 without supplying liquid ammonia Al from the first fuel flow path 23k. In this case, ammonia gas Ag was supplied by first vaporizing liquid ammonia Al using an electric heater-type evaporator and then mixing it with methane in a mixer. The amount of energy (vaporization energy) required to vaporize liquid ammonia Al using the evaporator was 1942 kJ per kg of liquid ammonia Al. Since the theoretical latent heat of vaporization of ammonia (0°C, 1 atm) is 1262 kJ / kg, the efficiency of the evaporator used was 65%. Since the higher heating value of ammonia gas Ag is 22.5 MJ / kg, the ratio of the energy required to vaporize liquid ammonia Al to the higher heating value of ammonia gas Ag was 8.63%.

[0082] Furthermore, the combustion gas inside the heating furnace 10 was sampled at a position downstream of the first combustion nozzle 23b. Then, the carbon dioxide (CO ２ The concentrations of carbon dioxide (CO ) and nitrogen oxides (NOx) were measured. In addition, the state of the combustion flame F injected from the first combustion nozzle 23b was photographed with a video camera, and the stability of the flame was evaluated visually. That is, the evaluation was performed by marking "◎" when the combustion flame F was stably formed, "◯" when the combustion flame F fluctuated but continued to burn without misfire, and "×" when the combustion flame F disappeared due to misfire. The evaluation results for the examples are shown in Table 1. The carbon dioxide (CO ) contained in the combustion gas inside the furnace was evaluated by marking "◎" when the combustion flame F was stably formed, "◯" when the combustion flame F fluctuated but continued to burn without misfire, and "×" when the combustion flame F disappeared due to misfire. ２ The amount of carbon dioxide (CO ２ The ratio under each condition is shown with the amount of ) as the standard (1.0).

[0083]

[0084] The conventional example used only methane, which is a gaseous fuel, as the fuel for the combustion operation in the first combustion section 23a, and the amount of carbon dioxide generated by combustion was the largest compared to the other examples.

[0085] In Comparative Examples 1 to 3, a mixed gas produced by mixing methane with ammonia gas Ag, which was previously vaporized from liquid ammonia Al, was burned as fuel for the combustion operation in the first combustion section 23a. Since vaporization energy was required to vaporize the liquid ammonia Al in advance, the larger the mixture ratio of ammonia gas Ag in the gaseous fuel, the more additional energy was required.

[0086] In Examples 1 to 3, the Sauter mean diameter of the liquid ammonia Al sprayed by the first fuel spray unit 23j was set to 200 μm. The amount of carbon dioxide contained in the in-furnace combustion gas was reduced compared to the conventional example. Furthermore, in Examples 1 to 3, no additional vaporization energy was required, as shown in the results of Comparative Examples 1 to 3, and therefore ammonia gas could be efficiently produced using the sensible heat recovered in the first heat storage unit 23c.

[0087] In Examples 4 to 6, a mixed fuel containing ammonia at 35% of its calorific value and methane at 65% of its calorific value was used. Furthermore, the Sauter mean diameter of the liquid ammonia Al sprayed by the first fuel spray unit 23j was changed compared to Examples 1 to 3. In Examples 4 to 6, the amount of carbon dioxide contained in the in-furnace combustion gas was reduced compared to the conventional example. Furthermore, because additional vaporization energy was not required, as shown in the results of Comparative Examples 1 to 3, ammonia gas could be efficiently generated using the sensible heat recovered in the first heat storage unit 23c.

[0088] The reason why the concentration of nitrogen oxides (NOx) in Examples 4 to 6 was lower than that in Comparative Example 3 is thought to be because a portion of the liquid ammonia Al remained as unburned ammonia in the in-furnace combustion gas, reducing the nitrogen oxides produced by the combustion of ammonia and reducing the nitrogen oxide concentration in the in-furnace combustion gas. On the other hand, Examples 5 and 6 did not satisfy the condition of formula (1), which means that a portion of the liquid ammonia Al was not vaporized between the connection position M of the first fuel supply nozzle 23i and the first gas discharge port 23h, which is the tip of the first combustion nozzle 23b, causing fluctuations in the combustion flame F.

[0089] In Example 7, a mixed fuel containing ammonia at 35% of its calorific value and coke oven gas at 65% of its calorific value was used. Furthermore, the Sauter mean diameter of the liquid ammonia Al sprayed by the first fuel spray unit 23j was set to 200 μm. The amount of carbon dioxide contained in the in-furnace combustion gas was reduced compared to the conventional example. Furthermore, in Example 7, no additional vaporization energy was required, as shown in the results of Comparative Examples 1 to 3. Therefore, ammonia gas could be efficiently generated using the sensible heat recovered in the first heat storage unit 23c.

[0090] 10 Heating furnace 11 Charging section 12 Combustion device 13 Regenerative combustion device 13a First combustion section 13n Second combustion section 14a Air supply blower 14b Suction pump 14c Four-way valve 14d Alternating combustion control unit 15 Conveying device 16 Extraction section 17 Flue section L Distance D Conveying direction S Target material F Combustion flame O Combustion air Q Suction gas M Connection position Al Liquid ammonia Ag Ammonia gas Cg Coal gas Hg Hydrocarbon gas

Claims

1. A method for operating a heating furnace, comprising: a regenerative combustion apparatus having a pair of combustion sections each having a heat storage section, the method comprising alternately performing a combustion operation and a suction operation in the pair of combustion sections, the pair being opposed to each other, to control a temperature inside the heating furnace, the method comprising: In the suction operation, sensible heat of the suction gas suctioned from the inside of the heating furnace is recovered by the heat storage unit; In the combustion operation, the combustion air is heated by passing through the heat storage section and discharged into the heating furnace, and liquid ammonia is sprayed from a fuel supply nozzle toward a discharge flow path of the combustion air that has passed through the heat storage section.

2. 2. The method for operating a heating furnace according to claim 1, wherein the sprayed liquid ammonia is in the form of droplets having a Sauter mean diameter of 5 to 3000 μm.

3. The Sauter mean diameter d of the sprayed liquid ammonia ０ where L (mm) is the distance from the discharge port of the discharge flow path to the connection position where the fuel supply nozzle is connected, and V is the average velocity of the velocity of the combustion air passing through the heat storage unit and the velocity of the component of the velocity of the sprayed liquid ammonia in the direction of the discharge flow path. Ｍ 2. The method for operating a heating furnace according to claim 1 , wherein the speed (mm / s) satisfies the following formula (1): [0010] Here, Ke is the evaporation rate constant of liquid ammonia (mm ２ / s).

4. The Sauter mean diameter d of the sprayed liquid ammonia ０ where L (mm) is the distance from the discharge port of the discharge flow path to the connection position where the fuel supply nozzle is connected, and V is the average velocity of the velocity of the combustion air passing through the heat storage unit and the velocity of the component of the velocity of the sprayed liquid ammonia in the direction of the discharge flow path. Ｍ 3. The method for operating a heating furnace according to claim 2, wherein the speed (mm / s) satisfies the following formula (1): [0010] Here, Ke is the evaporation rate constant of liquid ammonia (mm ２ / s).

5. The method for operating a heating furnace according to any one of claims 1 to 4, wherein the liquid ammonia is sprayed toward the discharge flow path of the combustion air that has passed through the heat storage unit, and at least one gaseous fuel selected from coal gas and a hydrocarbon gas is supplied.

6. A heating furnace including a regenerative combustion device having combustion sections disposed opposite each other, and a combustion operation and a suction operation are alternately performed in the pair of opposed combustion sections to control the temperature inside the furnace, an alternating combustion control unit that controls the pair of combustion units to alternately switch between the combustion operation and the suction operation; The combustion section has a heat storage section that recovers sensible heat of the suction gas sucked from inside the heating furnace during the suction operation, a discharge flow path that heats combustion air by passing it through the heat storage section during the combustion operation and discharges it toward the inside of the heating furnace, and a fuel supply nozzle that sprays liquid ammonia toward the discharge flow path during the combustion operation.

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