JP2024070491A - Method of operating a steel heating furnace and steel heating furnace - Google Patents

Abstract

The present invention provides a method for operating a steel heating furnace that uses ammonia as a fuel gas to suppress carbon dioxide emissions and suppresses the emission of nitrogen oxides and unburned ammonia to the outside of the furnace, and a steel heating furnace.
[Solution] A steel heating furnace including a first burner facility having a coal gas supply unit that supplies coal gas as a fuel gas, and a second burner facility having a mixed gas supply unit that supplies a mixed gas of coal gas and ammonia as a fuel gas, and optionally having a hydrogen gas supply unit that mixes hydrogen gas with the fuel gas or replaces the fuel gas with hydrogen gas. A method of operating a steel heating furnace, which performs burner heating using coal gas as the fuel gas and burner heating using a mixed gas of coal gas and ammonia gas as the fuel gas, and optionally mixes hydrogen gas with the fuel gas or replaces hydrogen gas with burner heating.
[Selected Figure] Figure 1

Description

The present invention relates to a method for operating a steel heating furnace and a steel heating furnace.

In integrated steelworks, blast furnace gas discharged from the top of the blast furnace, which reduces iron ore to produce molten iron, and by-product gases generated in converters and coke ovens have been effectively used as fuel gas. However, in recent years, with the demand for reducing carbon dioxide emissions, combustion technology has been required to reduce the amount of by-product gas used. For example, in steel heating furnaces that heat steel in hot rolling lines and plate rolling lines in integrated steelworks, it is now required to reduce the amount of by-product gas used and the amount of carbon dioxide emissions. In this case, technology that uses ammonia as fuel gas for steel heating furnaces is attracting attention. In other words, ammonia, which does not contain carbon elements, mainly produces water and nitrogen when burned, so it is effective in reducing carbon dioxide emissions, and technological development is desired for application to steel heating furnaces.

On the other hand, ammonia is a flame-retardant fuel, and is characterized by being more difficult to ignite and having a slower burning speed than general fuels. For example, the burning speed of ammonia is about one-seventh that of commonly used hydrocarbon fuels such as methane and propane.

In order to solve these problems, heating techniques have been proposed.
Patent Document 1 discloses a technology in which ammonia is mixed with an oxidizer, and when the mixed gas is supplied to a combustion chamber, a swirler is provided to swirl the mixed gas in the combustion chamber, thereby promoting the combustion of ammonia and realizing stable combustion.

Patent Document 2 also discloses a technology in which hydrogen gas is separated and generated from ammonia gas, the separated and generated hydrogen gas is supplied to a combustion chamber, and the hydrogen gas supplied to the combustion chamber is ignited by discharge to burn the hydrogen gas, thereby igniting the ammonia gas in the combustion chamber from the burned hydrogen gas.

JP 2016-130619 A JP 2021-25715 A

However, when attempting to apply the above conventional technology to a steel heating furnace, the following problems arise:

The technology described in Patent Document 1 requires the manufacture of new burners to be used for heating the steel material, and requires the replacement of many burners (for example, about 60 to 100 burners) installed in the steel heating furnace. Therefore, when applied to an existing steel heating furnace, the equipment modification costs are high, and the steel heating furnace needs to be shut down while the equipment is modified, resulting in a large opportunity loss and being uneconomical.

The technology described in Patent Document 2 is similar, and requires the installation of new burner equipment including a reformer for separating and generating hydrogen gas from ammonia gas. When applied to existing steel heating furnaces, this is not realistic in terms of the equipment modification costs and downtime.
Furthermore, the steel heating furnace has a charging section for charging steel sheets into the heating furnace and a discharge section for discharging the heated steel, and at least when the steel is charged and discharged, a part of the heating furnace is open to the atmosphere (open state). This causes a problem that nitrogen oxides (NOx) and unburned ammonia (unburned ammonia) generated by the combustion of ammonia are easily released into the atmosphere. Nitrogen oxides are a type of greenhouse gas, and their emissions are subject to legal regulations, so it is necessary to suppress the emission of nitrogen oxides. In addition, ammonia is toxic, so high concentrations of ammonia gas are harmful to the human body, and if unburned ammonia leaks out, it will cause a foul odor in the workplace, harming the working environment, so it is necessary to prevent unburned ammonia from leaking out into the workplace.

The present invention was developed in consideration of the above problems with the conventional technology, and its purpose is to provide a method of operating a steel heating furnace and a steel heating furnace that can be applied to existing steel heating furnaces without major equipment modifications, and that uses ammonia as a fuel gas to suppress carbon dioxide emissions and suppresses the emission of nitrogen oxides and unburned ammonia to the outside of the furnace.

The method of operating a steel heating furnace according to the present invention, which advantageously solves the above problems, is configured as follows.

[1] A method for operating a steel heating furnace in which steel materials are heated while being transported from a loading section to an unloading section, the method comprising the steps of: burner heating using coal gas as the fuel gas; and burner heating using a mixed gas of coal gas and ammonia gas as the fuel gas; and optionally mixing hydrogen gas with the fuel gas, or replacing the fuel gas with burner heating using hydrogen gas as the fuel gas.
[2] In the above [1], a method for operating a steel material heating furnace comprises performing burner heating with the coal gas at a position adjacent to the loading section of the steel material heating furnace, and performing burner heating with the coal gas at a position adjacent to the discharge section of the steel material heating furnace.
[3] In the above [2], the burner heating with the coal gas is performed when the charging section or the discharge section is open.
[4] In any one of the above [1] to [3], a mixing ratio of ammonia contained in the mixed gas is set based on a measured value of a pressure inside the heating furnace along a transport direction of the steel material.

The steel heating furnace according to the present invention, which advantageously solves the above problems, is configured as follows.
[5] A steel heating furnace having burner equipment, the burner equipment being arranged in a plurality of units along a transport direction of steel material as it is heated while being transported from an inlet section to an outlet section of the heating furnace, the burner equipment comprising: a first burner equipment having a coal gas supply unit which supplies coal gas as a fuel gas; and a second burner equipment having a mixed gas supply unit which supplies a mixed gas of coal gas and ammonia as the fuel gas, and optionally having a hydrogen gas supply unit which is capable of mixing and supplying hydrogen gas to the fuel gas or which replaces the fuel gas with hydrogen gas.
[6] In the above [5], the first burner equipment is arranged in a position close to the loading section and the unloading section of the steel material heating furnace, and the other burner equipment is the second burner equipment, which is a steel material heating furnace.
[7] In the above [5] or [6], the steel heating furnace is a steel heating furnace further comprising a control unit that controls a mixing ratio of ammonia contained in the mixed gas supplied from the mixed gas supply unit.
[8] A steel heating furnace having burner equipment, the burner equipment being arranged in a plurality of burner equipment along a transport direction of steel material as it is heated while being transported from an inlet section to an outlet section of the heating furnace, the burner equipment having a mixed gas supply unit that supplies a mixed gas of coal gas and ammonia as a fuel gas, and a control unit that controls the mixing ratio of ammonia contained in the mixed gas supplied from the mixed gas supply unit.
[9] In the above [8], the steel heating furnace further includes a plurality of furnace pressure gauges that measure the pressure inside the heating furnace along the transport direction of the steel, and a setting unit that sets the mixing ratio of ammonia contained in the mixed gas controlled by the control unit based on the measurement values of the plurality of furnace pressure gauges.

The present invention can be applied to existing steel heating furnaces without making major equipment modifications, and by using ammonia as fuel gas, it is possible to suppress carbon dioxide emissions and also suppress the emission of nitrogen oxides and unburned ammonia outside the furnace.

1 is a block diagram showing a schematic configuration of a burner facility for a heating furnace according to one embodiment; FIG. 2 is a configuration diagram of an example of a burner facility for supplying coal gas. FIG. 1 is a configuration diagram of an example of a burner facility that supplies a mixed gas of coal gas and ammonia. FIG. 2 is a block diagram showing a schematic configuration of a burner facility for a heating furnace equipped with a control unit for a mixed gas ratio according to one embodiment. 1 is a block diagram showing a schematic configuration of a burner facility for a heating furnace equipped with a furnace pressure gauge and a control unit according to one embodiment; FIG. 1 is a flow diagram of a mixed gas ratio supply based on the pressure inside the furnace.

Hereinafter, the steel heating furnace according to this embodiment will be described.
<Steel heating furnace>
Fig. 1 is a schematic cross-sectional view of a steel heating furnace according to an embodiment of the present invention. The steel heating furnace is installed in, for example, a hot rolling line for producing steel plates, and is used to heat cast slabs to a predetermined heating temperature (approximately 1100 to 1300°C). However, the steel heating furnace is not limited to the purpose of heating slabs, and may be installed to heat billets, blooms, and other steel pieces that become raw materials for shaped steel, wire rods, steel pipes, and the like.
The steel heating furnace according to the present invention (hereinafter also referred to as "heating furnace") comprises a charging section for charging the steel material to be heated, and a discharge section for unloading (extracting) the heated steel material. For example, slabs produced in a continuous casting line are transported to a yard on the charging side of the heating furnace, and are charged into the heating furnace from the charging section according to a production schedule of a hot rolling line or the like. The interior of the steel heating furnace is divided into a number of zones, and generally consists of a heating zone divided into 2 to 8 zones on the upstream side, and 1 to 3 soaking zones.

When a heating furnace is in operation, the atmospheric temperature is controlled to be different for each zone inside the heating furnace, and the average temperature of the slabs loaded into the heating furnace is gradually increased to a predetermined target heating temperature (the target temperature of the slabs when they are removed from the heating furnace). The slabs loaded into the heating furnace pass through the inside of the heating furnace from the loading section to the unloading section by a transport facility called a walking beam (not shown). In addition, multiple slabs are loaded into the heating furnace at the same time, and are unloaded to the unloading side of the heating furnace in the order in which they were loaded into the heating furnace, and are hot rolled sequentially.

The loading section of the steel heating furnace has an opening for loading slabs into the furnace and an opening/closing loading door that covers the opening. When the slab is loaded into the steel heating furnace, the loading door is opened and the opening is open, and the slab is loaded. On the other hand, the opening of the loading door is closed in all other states. This is to prevent thermal energy from leaking out unless necessary, since the inside of the heating furnace is maintained at a high temperature. Similarly, the unloading section of the steel heating furnace also has an opening for unloading the slab out of the furnace and an opening/closing unloading door that covers the opening. When the slab in the steel heating furnace is unloaded to the hot rolling line, the unloading door is opened and the opening is open, and the slab is unloaded. On the other hand, the opening of the unloading door is closed in all other states. In this embodiment of the invention, the state in which the loading door of the loading section is open is referred to as the loading section being open, and the state in which the discharge door of the discharge section is open is referred to as the discharge section being open.

Inside the heating furnace, multiple burner equipment are provided along the transport direction of the steel material. The burner equipment is arranged to heat the inside of the heating furnace by combustion. When the inside of the heating furnace is heated by the burner equipment, the temperature of the steel material increases due to radiation from the furnace wall. In addition, a flow of atmospheric gas occurs inside the heating furnace, and the temperature of the steel material may increase due to convection. Furthermore, the steel material may be heated by the flame of the burner equipment directly contacting the steel material. In any case, the burner equipment heats the inside of the heating furnace, thereby raising the temperature of the steel material being transported inside the heating furnace.

Burner equipment is arranged in each of several zones inside the heating furnace. However, the number of zones does not necessarily have to match the number of burner equipment. In the heating furnace shown in Figure 1, five burner equipment U1 to U5 are arranged on the upper surface side of the steel material from the loading section toward the unloading section. In addition, five burner equipment L1 to L5 are arranged on the lower surface side of the steel material, for a total of 10 burner equipment. However, the burner equipment may be arranged from the side of the heating furnace toward the inside of the heating furnace.

Fuel gas and fuel air are supplied to each burner equipment, and the fuel gas is burned by diffusing in the air, and the flame is blown into the inside of the heating furnace. Air is usually used as the fuel air, but oxygen-containing gases that contain oxygen, such as oxygen-enriched air and a mixture of oxygen and exhaust gas, may also be used.

The fuel air is sent to the burner equipment using a blower (not shown). At that time, the combustion air is adjusted by a combustion air flow valve and measured by a combustion air flow meter. However, it is not necessary to provide a combustion air flow valve or combustion air flow meter for each burner equipment. For example, it is sufficient to adjust the flow rate of the combustion air supplied to all of the burner equipment U1 to U5 located on the upper side of the heating furnace, and multiple burner equipment may be treated as one group, and the flow rate of the combustion air may be adjusted on a group basis.

The amount of fuel gas supplied to the burner equipment is adjusted by a fuel gas flow control valve installed for each burner equipment, and the flow rate is measured by a fuel gas flow meter. The flow rate of the fuel gas is adjusted so as to ensure the thermal energy required to heat the steel material to a specified temperature in the heating furnace. In addition, different target values for the atmospheric temperature are set for each zone inside the heating furnace, and the flow rate of the fuel gas may be adjusted to achieve the target temperature for each zone.

A steel heating furnace may be provided with a flue for discharging exhaust gas generated in the furnace to the outside. Since gas inside the heating furnace may be discharged from the flue, the flue is connected to an exhaust gas treatment device (not shown) and is usually configured so that harmful gases are not discharged into the atmosphere outside the heating furnace through the flue. Therefore, even if nitrogen oxides or unburned ammonia are generated inside the steel heating furnace, for example, by burning ammonia, they will not be discharged to the outside of the steel heating furnace through the flue. However, as described above, a steel heating furnace has a loading section and an unloading section, and is open at least when steel is loaded and unloaded, so it is difficult to install an exhaust gas treatment device at the opening, and there is a problem in that nitrogen oxides and unburned ammonia may be discharged to the outside through these openings.

Next, a first embodiment of the steel heating furnace and its operating method according to the present embodiment will be described.
<First type of burner equipment>
The steel heating furnace according to the first embodiment includes a first burner equipment having a coal gas supply unit that supplies coal gas as a fuel gas, and a second burner equipment having a mixed gas supply unit that supplies a mixed gas of coal gas and ammonia as a fuel gas. FIG. 1 shows a steel heating furnace H according to the first embodiment. In the embodiment shown in FIG. 1, burner equipment U1, U5, L1, and L5 to which ammonia 3 is not supplied as a fuel gas are the first burner equipment. Also, burner equipment U2 to U4 and L2 to L4 to which ammonia 3 is supplied as a fuel gas are the second burner equipment. The coal gas supply unit of the first burner equipment and the mixed gas supply unit of the second burner equipment will be described later.

The coal gas, which is the fuel gas used in the burner equipment of this embodiment, means gas obtained from coal. In particular, it is preferable to use by-product gases generated in blast furnaces, coke ovens, converters, and the like in steelworks. 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.

By-product gases have various component compositions depending on the process of generation. For example, blast furnace gas has a typical composition of 21-30 vol% of combustible carbon monoxide, 50-60 vol% of incombustible nitrogen, and 10-22 vol% of carbon dioxide. The ignition point of blast furnace gas is 630-650°C, and the combustion range is 27-75 vol% when mixed with air. The lower heating value of blast furnace gas is typically about 3.45 MJ/ ^Nm3 . The typical composition of coke oven gas is 46-60 vol% hydrogen, 20-35 vol% methane, 5-10 vol% carbon monoxide, and 2-4 vol% hydrocarbons such as ethylene. The typical lower heating value of coke oven gas is about 18.0 MJ/ ^Nm3 . Converter gas has about 75 vol% carbon monoxide, about 13 vol% carbon dioxide, and also contains small amounts of oxygen, nitrogen, and hydrogen. A typical example of the lower heating value of converter gas is about 8.2 MJ/ ^Nm3 .

The coal gas used may be a suitable mixture of blast furnace gas, coke oven gas, and converter gas (sometimes called M gas). By mixing coal gases with different heating values, the amount of heat required to heat steel can be supplied, ensuring stable operation of the steel heating furnace. In addition to these coal gases, the fuel gas used in the burner equipment of this embodiment may also contain gaseous fuels such as petroleum gas or small amounts of solid fuel. This is because if the coal gas content is 50 volume % or more, the main heat source for heating steel can be considered to be coal gas.

The ammonia used in the second burner equipment is a colorless gas at room temperature represented by the chemical formula NH _3. The ignition point of ammonia is 651°C, and the combustion range is 15.5 to 27% by volume when mixed with air. The lower heating value of ammonia is 14.1 MJ/Nm ^3. However, the ammonia used in the second burner equipment may be a gas mixed with hydrogen as desired. This is because hydrogen, like ammonia, does not emit carbon dioxide when burned. In addition, when ammonia is burned, hydrogen is generated in a high temperature state, and therefore it may exhibit combustion characteristics similar to those of a gas in which ammonia and hydrogen are mixed in advance. In this case, the amount of hydrogen gas added to the ammonia is allowed to be up to 50% by volume. In other words, the ammonia used in the second burner equipment of this embodiment may contain up to 50% by volume of hydrogen.

First burner equipment A configuration example of the first burner equipment is shown in Fig. 2. The first burner equipment is composed of a burner 1 that mixes coal gas 10, which is a fuel gas, with combustion air 11 and emits a flame from the tip, a coal gas flow rate control valve 101 that adjusts the flow rate of the coal gas, and a coal gas flow meter 102 that measures the flow rate of the coal gas. The coal gas supply unit in this embodiment refers to the coal gas flow rate control valve 101 and the coal gas flow meter 102 for supplying coal gas to the burner.

As shown in FIG. 2, the first burner equipment may be a nozzle mix type burner that mixes coal gas 10 and combustion air 11 inside the burner. In this case, energy saving can be achieved by preheating the fuel air using exhaust gas or the like before mixing it with the fuel gas. In addition, the first burner equipment may be a regenerative burner that alternately burns a pair of burners integrated with a heat storage body at intervals of several tens of seconds. In this case, when one burner is burning, the exhaust gas is passed through the heat storage body of the other burner, and the other heat storage body is heated to recover the thermal energy of the exhaust gas from the one burner. Then, when the other burner next burns, the combustion air is preheated by passing it through the other heat storage body. This allows for more energy-efficient combustion. However, the first burner equipment is not limited to the nozzle mix type burner shown in FIG. 2, and a premix type burner may be used. A premix burner is a burner system in which a mixer that mixes coal gas 10 and combustion air 11 is provided downstream of the coal gas flow meter 102 in the direction of coal gas flow, and the mixed gas of coal gas 10 and combustion air 11 is ejected from the tip of the burner 1.

In the first burner equipment, combustion is performed under operating conditions of, for example, fuel air of 625 ^Nm3 /hr and coal gas of 185 ^Nm3 /hr. However, the supply amount of coal gas as fuel gas may be adjusted by setting the opening of the coal gas flow rate control valve 101 so as to control the inside of the heating furnace to a predetermined temperature.

Second burner equipment An example of the configuration of the second burner equipment applied to this embodiment is shown in Fig. 3. The burner used in the second burner equipment can be of the same type as that of the first burner equipment. The second burner equipment includes a coal gas flow rate control valve 101 that adjusts the flow rate of the coal gas, a coal gas flow meter 102 that measures the flow rate of the coal gas, an ammonia flow rate control valve 31 that adjusts the flow rate of ammonia, and an ammonia flow meter 32 that measures the flow rate of ammonia.

The second burner equipment also includes a mixing section 15 that mixes coal gas and ammonia in the piping. The mixed gas supply section in this embodiment refers to the coal gas flow rate control valve 101, the coal gas flow meter 102, the ammonia flow rate control valve 31, the ammonia flow meter 32, and the mixing section 15 for supplying the mixed gas to the burner.

3 is a burner in which the coal gas and ammonia pipes join together to mix the gases flowing inside, and the mixing section in this case refers to the part where the coal gas supply pipe and the ammonia supply pipe join together. However, since the coal gas and ammonia are supplied from their respective supply pipes, mixing can be performed without providing a special stirring mechanism, and therefore the mixing section 15 may be configured as a certain space upstream of the combustion air 11 supply pipe.
The second burner equipment is not limited to the nozzle mix type burner shown in Fig. 3, and a premix type burner may be used. In this case, a mixer for mixing the fuel gas and the combustion air 11 may be provided downstream of the mixing section 15 in the flow direction of the fuel gas, and the mixed gas of the fuel gas and the combustion air 11 may be ejected from the tip of the burner.

The second burner equipment preferably includes, in addition to the mixed gas supply unit, a control unit 14 that controls the mixing ratio of ammonia 3 contained in the mixed gas 16 supplied by the mixed gas supply unit. The control unit 14 sets the ratio between the aperture of the coal gas flow rate control valve 101 and the aperture of the ammonia flow rate control valve 32, and controls the mixing ratio of ammonia contained in the mixed gas. In this case, it is preferable that the coal gas flow rate control valve 101 and the ammonia flow rate control valve 32 are configured using solenoid valves, and the control unit controls the aperture of the solenoid valves so that the flow rates of the coal gas and ammonia are a predetermined mixing ratio.
In the control unit 14, when the ratio of ammonia to coal gas is increased, the amount of carbon dioxide generated in the steel heating furnace can be reduced, but the flame stability decreases due to the slow combustion speed of ammonia. On the other hand, when the ratio of ammonia to coal gas is decreased, the flame stability improves, but the effect of reducing the amount of carbon dioxide generated in the steel heating furnace becomes insufficient. Therefore, in the second burner equipment of this embodiment, the ratio of ammonia in the mixed gas is preferably 2 to 60 volume %.

In the second burner equipment, for example, a mixture of fuel gas of about ¹⁵⁰ Nm3/hr of coal gas and about 30 ^Nm3 /hr of ammonia may be used with 625 ^Nm3 /hr of fuel air, thereby obtaining the same amount of heat as the above-mentioned example of the first burner equipment.

As described above, the first burner equipment and the second burner equipment have different configurations for the fuel gas supply equipment that supplies the burners. However, common equipment can be used for the burners and the fuel air supply equipment, so part of the first burner equipment applied to a steel heating furnace can be updated to the second burner equipment without major equipment updates.

The mixing ratio of ammonia contained in the mixed gas used in the second burner equipment can be set based on the Wobbe index of the coal gas. The Wobbe index is an index representing the compatibility of fuel gas and is used to identify the relative ability of the fuel gas to generate thermal energy. The Wobbe index WI is calculated by the following formula (1) using the total calorific value H (MJ/Nm ³ ) of the fuel gas and the specific gravity S of the fuel gas (S=1 for air).
WI=H/√S (1)

When changing the fuel gas without changing the combustion equipment, the Wobbe index, together with the combustion speed, must be kept within a specified range. Therefore, it is preferable to set the mixture ratio controlled by the control unit based on the Wobbe index of coal gas and ammonia.

Table 1 shows typical examples of the Wobbe index and maximum combustion speed of ammonia and coal gas. M gas in Table 1 refers to coal gas mixed with blast furnace gas, coke oven gas, and converter gas. Note that coal gas varies greatly depending on the production area of the coal that is the raw material for the by-product gas and the operating conditions of the coal gas generation source, so the values shown in Table 1 are merely examples.
From Table 1, it can be seen that the combustion speed of ammonia is very slow and the Wobbe index is low, so that the thermal energy generated by combustion is lower than other substances. Therefore, in a burner facility using coke oven gas as coal gas, the combustibility (maximum combustion speed and Wobbe index) is likely to decrease when ammonia is mixed with coke oven gas, so the mixing ratio of ammonia is set so as not to be excessive. On the other hand, in a burner facility using M gas as coal gas, the Wobbe index of M gas is lower than that of ammonia, so that increasing the mixing ratio of ammonia may cause excessive heat load. In this case, the Wobbe index of the mixed gas can be adjusted by adding nitrogen, which is a non-combustible gas, to the mixed gas of M gas and ammonia. In addition, since the blast furnace gas constituting M gas contains a relatively large amount of nitrogen, it is preferable to increase the ratio of blast furnace gas contained in M gas to generate the mixed gas.

Optionally, it is possible to have a hydrogen gas supply unit that mixes hydrogen gas with the fuel gas of the first burner equipment or the second burner equipment and supplies it, or replaces the fuel gas with hydrogen gas.

<First type of operation method>
This is a method for operating a steel heating furnace, which performs burner heating using coal gas as a fuel gas and burner heating using a mixed gas of coal gas and ammonia gas as the fuel gas, and optionally mixes hydrogen gas with the fuel gas or replaces the burner heating with hydrogen gas as the fuel gas.

Burner arrangement in the heating furnace The first type of steel heating furnace has a plurality of burner equipment along the steel conveying direction, at least one of the plurality of burner equipment is the first burner equipment, and at least one of the other burner equipment is the second burner equipment. In this case, the steel heating furnace may use burner equipment other than the first burner equipment and the second burner equipment. For example, the steel heating furnace may include burner equipment other than the first burner equipment and the second burner equipment, such as one that uses a fuel gas mainly made of petroleum gas, one that uses hydrogen as a fuel gas, or one that mainly uses solid fuel for combustion.

In the steel heating furnace H shown in FIG. 1, first burner equipment U1, U5, L1, and L5 are arranged, and second burner equipment U2 to U4, L2 to L4 are arranged. The first burner equipment uses coal gas, which has excellent combustion stability, but the amount of carbon dioxide emissions is the same as that of conventional heating furnaces. On the other hand, the second burner equipment uses a mixture of coal gas and ammonia, so the amount of carbon dioxide emissions can be reduced as the mixture ratio of ammonia increases. On the other hand, when ammonia is burned in the second burner equipment, nitrogen oxides (NOx) may be generated. If nitrogen oxides are released into the atmosphere from the charging section or the discharge section of the steel heating furnace, they act as greenhouse gases, so it is necessary to suppress their emissions. In this case, by increasing the mixture ratio of ammonia in the second burner equipment, a denitrification reaction of ammonia occurs, and as a result, nitrogen oxides (NOx) are decomposed into nitrogen and water and rendered harmless. In this case, although it is necessary to burn the ammonia at a rich ammonia equivalence ratio (ammonia excess), unburned ammonia is likely to be generated, increasing the risk of unburned ammonia leaking outside the steel heating furnace. In other words, the second burner equipment uses ammonia as fuel gas, which generates either nitrogen oxides or unburned ammonia, increasing the environmental risk.

In contrast, in this embodiment, the first burner equipment and the second burner equipment are provided for burner heating, so that nitrogen oxides and unburned ammonia that may be generated by the second burner equipment are decomposed by the first burner equipment, which does not contain ammonia as fuel gas, and converted into nitrogen and water. This makes it possible to prevent nitrogen oxides and unburned ammonia from leaking out of the steel material heating furnace, even if the steel material heating furnace has a steel material loading section and a steel material unloading section and is open to the outside when the steel material is loaded or unloaded.

The first burner equipment, which uses coal gas as fuel gas, decomposes nitrogen oxides because the flame generated by the first burner equipment produces hydrogen cyanide (HCN) and other reducing substances, which decompose the nitrogen oxides produced by the second burner equipment into nitrogen. The first burner equipment decomposes unburned ammonia because the flame generated by the burner of the first burner equipment burns unburned ammonia and decomposes it into nitrogen and water. Normally, the first burner equipment burns with rich combustion air (the equivalence ratio of coal gas to fuel air is less than 1), so the excess oxygen produced by the first burner equipment decomposes the unburned ammonia.

In the second burner equipment, by burning the ammonia at a rich (excessive) ammonia equivalence ratio, a denitration reaction of ammonia occurs, which makes it easier for nitrogen oxides to be decomposed into nitrogen and water, but by setting the ammonia equivalence ratio to the rich side, unburned ammonia is more likely to be generated. In contrast, by burning the unburned ammonia generated in the second burner equipment by the first burner equipment, it is possible to suppress the generation of nitrogen oxides in the second burner equipment, and by burning the unburned ammonia in the first burner equipment, it is possible to reduce both nitrogen oxides and unburned ammonia. In particular, it is preferable to burn the unburned ammonia in the first burner equipment on the lean fuel side, where the equivalence ratio of coal gas to fuel air is less than 1, because this makes it easier to burn the unburned ammonia in the first burner equipment.

Furthermore, in the first embodiment, it is preferable that the first burner equipment is disposed in a position close to the loading section 51 and discharge section 61 of the steel material heating furnace, and the other burner equipment is disposed as the second burner equipment. Here, the position close to the loading section 51 of the steel material heating furnace refers to the position closest to the loading section among the multiple burner equipment installed along the conveying direction of the steel material S. Also, the position close to the discharge section 61 of the steel material heating furnace refers to the position closest to the discharge section among the multiple burner equipment installed along the conveying direction of the steel material S. In other words, it means that no burner equipment other than the first burner equipment is disposed in the position closest to the loading section 51 and discharge section 61 of the steel material heating furnace.

The first burner equipment is located in close proximity to the loading section 51 of the steel heating furnace because even if nitrogen oxides or unburned ammonia are generated by the second burner equipment, the nitrogen oxides and unburned ammonia are decomposed by the first burner equipment located in close proximity to the loading section.
This makes it possible to prevent nitrogen oxides and unburned ammonia from leaking out of the steel heating furnace to the outside through the charging section 51 which is open when the slabs are charged into the steel heating furnace.
Similarly, the first burner equipment is located in close proximity to the discharge section 61 of the steel heating furnace because even if nitrogen oxides or unburned ammonia are generated by the second burner equipment, the nitrogen oxides and unburned ammonia are decomposed by the first burner equipment located in close proximity to the discharge section 61.
This makes it possible to prevent nitrogen oxides and unburned ammonia from leaking out of the steel heating furnace through the discharge section that is opened when the slab is discharged from the steel heating furnace.

The steel heating furnace H shown in Fig. 1 is provided with a flue 9 for discharging exhaust gas generated in the furnace to the outside. The flue defines a gas flow path for discharging gas in the heating furnace to the outside. In this case, an exhaust gas treatment device (not shown) is arranged in the flue 9, and is configured to prevent harmful gases including nitrogen oxides and unburned ammonia from being discharged into the atmosphere outside the heating furnace through the flue.
However, since the gas flow path in the steel material heating furnace cannot be limited in the charging section 51 and the discharge section 61, it is difficult to install an exhaust gas treatment device. In contrast, by using the steel material heating furnace of this embodiment, it is possible to prevent nitrogen oxides and unburned ammonia from flowing out through the openings even when the charging section 51 and the discharge section 61 are open. As a result, together with the exhaust gas treatment device arranged in the flue, it is possible to prevent nitrogen oxides and unburned ammonia from being discharged outside the steel material heating furnace.

Optionally, it is possible to mix hydrogen gas with the above fuel gas, or to replace it with burner heating using hydrogen gas as the fuel gas for steel heating operations.

Next, a second embodiment of the steel heating furnace and its operating method according to the present embodiment will be described.
<Burner equipment of the second type>
The burner equipment of the second embodiment of the present invention has a plurality of burner equipments for heating the inside of the steel material heating furnace along the steel material transport direction, similarly to the first embodiment. At least one of the plurality of burner equipments has a mixed gas supply unit for supplying a mixed gas of coal gas and ammonia as a fuel gas, and a control unit 1 for controlling the ammonia mixing ratio contained in the mixed gas supplied from the mixed gas supply unit.

The furnace body structure and steel material transport device of the second embodiment are the same as those of the first embodiment. In the second embodiment, the heating furnace has at least one second burner equipment of the first embodiment, and the mixed gas supply unit of the second burner equipment has a control unit 14 that controls the mixing ratio of ammonia contained in the mixed gas 16. In this case, the control unit 14 of the second burner equipment can not only mix coal gas and ammonia at a predetermined ratio, but also control the mixing ratio of ammonia contained in the mixed gas 16 to zero. By controlling the ammonia mixing ratio of the mixed gas 16 to zero in the control unit 14, the function of the first burner equipment that supplies coal gas in the first embodiment can be exerted.

In the case where a first burner equipment using coal gas as fuel gas is provided inside a steel heating furnace, the burner equipment having a mixed gas supply unit and a control unit of the second embodiment may perform combustion using a mixed gas of coal gas and ammonia as fuel gas.
This allows the first burner equipment to burn and decompose nitrogen oxides and unburned ammonia while reducing carbon dioxide emissions. On the other hand, when a second burner equipment using a mixed gas of coal gas and ammonia as fuel gas is provided inside the steel heating furnace, the burner equipment having the mixed gas supply unit and control unit of this embodiment may set the ammonia mixing ratio of the mixed gas to zero. Even in this embodiment, the same effect can be obtained.

On the other hand, it is preferable that at least two of the multiple burner equipment include a mixed gas supply unit that supplies a mixed gas of coal gas and ammonia as fuel gas, and a control unit that controls the mixture ratio of the mixed gas supplied from the mixed gas supply unit. This is because the same effect can be obtained by burning the mixed gas of coal gas and ammonia as fuel gas in at least one of the burner equipment having a mixed gas supply unit and a control unit, and burning the mixed gas of coal gas and ammonia as fuel gas in the other by setting the ammonia mixture ratio of the mixed gas to zero by the control unit.

<Second type of operation method>
The second embodiment of the steel heating furnace H will be described with reference to Fig. 4. Each of the burner equipment U1 to U5 and L1 to L5 shown in Fig. 4 has a control unit 14, and the control unit 14 is configured to be able to control the mixing ratio of the coal gas and the ammonia.
As a result, some of the burner equipment U1 to U5 and L1 to L5 can heat the inside of the heating furnace using coal gas 2 as fuel gas by the control unit 14, and the other burner equipment can heat the inside of the heating furnace using a mixed gas of coal gas 2 and ammonia 3 as fuel gas. Therefore, nitrogen oxides and unburned ammonia that may be generated by combustion using mixed gas 16 of coal gas and ammonia can be decomposed by combustion using coal gas as fuel gas, and it is possible to prevent the nitrogen oxides and unburned ammonia from leaking out of the heating furnace.

For example, in an operation using the steel heating furnace H shown in Fig. 4, for at least one of the burner equipment U1 or L1 arranged in a position adjacent to the charging section 51 of the steel heating furnace, the control unit 14 controls the ammonia mixing ratio of the mixed gas to zero. Also, for at least one of the burner equipment U5 or L5 arranged in a position adjacent to the discharge section 61 of the steel heating furnace, the control unit 14 controls the ammonia mixing ratio of the fuel gas to zero. Then, for at least one of the burner equipment U2 to U4 and L2 to L4 arranged in a position other than the positions adjacent to the charging section and the discharge section of the steel heating furnace, the control unit 14 controls to use a mixed gas containing ammonia.
This makes it possible to reduce the amount of carbon dioxide emitted from a steel heating furnace due to combustion using a mixed gas containing ammonia, and to prevent nitrogen oxides and unburned ammonia from leaking out of the heating furnace.

Furthermore, the mixing ratio of ammonia contained in the mixed gas 16 may be set for each burner equipment. For example, one of adjacent burner equipment with respect to the conveying direction of the steel material inside the heating furnace may use mixed gas 16 of coal gas 10 and ammonia 3 as a fuel gas, and the other may use coal gas not mixed with ammonia.
This allows nitrogen oxides and unburned ammonia generated in one of the adjacent burner equipment to be decomposed by the other burner equipment.

Next, a third embodiment of the steel heating furnace and its operating method according to the present embodiment will be described.
<Third type burner equipment>
A third embodiment of the present invention is a steel heating furnace according to the second embodiment, which is provided with a plurality of furnace pressure gauges for measuring the pressure inside the heating furnace along the steel transport direction, and has a setting unit for setting the mixing ratio of the mixed gas controlled by the control unit based on the measurement values of the plurality of furnace pressure gauges.

In the present embodiment, a plurality of furnace pressure gauges are arranged in the direction in which the steel material is transported inside the heating furnace. In the example of Fig. 5, the furnace pressure gauges are arranged near the positions where the respective burner equipments are arranged.
In this embodiment, the controller has a setting unit that sets the mixing ratio of the mixed gas controlled by the controller.
An example of the configuration of the setting unit is shown in Fig. 6. The setting unit acquires measurements of pressure inside the furnace measured by a plurality of furnace pressure gauges. In response to the flow of the atmospheric gas inside the heating furnace from a position of high furnace pressure to a position of low furnace pressure, the setting unit specifies the flow direction of the atmospheric gas based on the relative magnitude relationship of the measurements by the plurality of furnace pressure gauges. Then, the setting unit reduces the mixing ratio of ammonia to fuel gas in the burner equipment arranged downstream of the flow direction of the atmospheric gas.
Furthermore, the setting unit sets the mixture ratio of the mixed gas so that the mixture ratio of ammonia to the fuel gas is increased in the burner equipment located upstream in the flow direction of the atmospheric gas. This allows the burner equipment located upstream in the flow direction of the atmospheric gas to burn with ammonia-rich, thereby reducing carbon dioxide emissions from the heating furnace. Also, the burner equipment located downstream in the flow direction of the atmospheric gas can decompose nitrogen oxides and unburned ammonia generated upstream.

<Third type of operation method>
For example, in FIG. 5, when the pressure inside the furnace is high on the charging side 5 and low on the discharge side 6, it is estimated that the flow direction of the atmospheric gas is from the charging side 5 to the discharge side 6. In this case, the setting unit sets at least one of the burner equipment U5 and L5 located downstream in the flow direction of the atmospheric gas to have a lower ammonia mixing ratio than the burner equipment located upstream in the flow direction of the atmospheric gas. In addition, the ammonia mixing ratio of not only the burner equipment U5 and L5 located downstream in the flow direction of the atmospheric gas, but also the burner equipment U4 and L4 may be set to be lower than the burner equipment U1 to U3 and L1 to L3. This makes it possible to prevent nitrogen oxides and unburned ammonia from flowing out from the discharge port 61.

On the other hand, when the pressure inside the furnace is low on the charging side 5 and high on the discharge side 6, it is estimated that the flow direction of the atmospheric gas is from the discharge side 6 to the charging side 5. In this case, the setting unit sets at least one of the burner equipment U1 or L1 located upstream in the flow direction of the atmospheric gas so that the ammonia mixing ratio is lower than that of the burner equipment located upstream in the flow direction of the atmospheric gas. This makes it possible to prevent unburned ammonia from leaking out through the charging port 51.

The flow direction of the atmospheric gas inside the heating furnace may change depending on whether the loading door of the loading section 51 is opened or closed, or whether the unloading door of the unloading section 61 is opened or closed. The inside of the heating furnace is often under higher pressure than the outside, and when the loading section is open, the atmospheric gas inside the heating furnace flows in the direction of the opening of the loading section, making it easier for it to flow out from the loading section to the outside. The same is true when the unloading section is open, in which case the atmospheric gas inside the heating furnace flows in the direction of the opening of the unloading section, making it easier for it to flow out from the unloading section to the outside.

Therefore, the burner equipment arranged in the vicinity of the charging part of the heating furnace preferably performs combustion using coal gas as the fuel gas when the charging part 51 is open. Also, the burner equipment arranged in the vicinity of the discharge part of the heating furnace preferably performs combustion using coal gas as the fuel gas when the discharge part 61 is open.
However, when the charging section 51 is open, the measurement of the furnace pressure gauge installed at a position close to the charging section is smaller than the measurement of the furnace pressure gauge installed downstream of the position close to the charging section. Even in such a case, as described above, the setting section specifies the flow direction of the atmospheric gas based on the relative magnitude relationship of the measurements by the multiple furnace pressure gauges, and the same effect can be obtained by reducing the mixture ratio of ammonia to the fuel gas of the burner equipment installed downstream of the flow direction of the atmospheric gas.

Similarly, when the discharge section 61 is open, the measurement of the furnace pressure gauge installed in a position close to the discharge section will be smaller than the measurement of the furnace pressure gauge installed upstream of the position close to the discharge section. Therefore, the setting section can determine the flow direction of the atmospheric gas based on the relative magnitude relationship of the measurements from the multiple furnace pressure gauges, and reduce the mixture ratio of ammonia to the fuel gas of the burner equipment located downstream of the flow direction of the atmospheric gas.

The steel heating furnace of this embodiment may further include a gas detector to detect nitrogen oxides or unburned ammonia. In the example of Fig. 5, gas detectors 17 are disposed outside the charging side, outside the discharge side, and in the flue of the heating furnace. The gas detector used is capable of detecting nitrogen oxides (NOx) or unburned ammonia ( _NH3 ). Preferably, a gas detector capable of detecting nitrogen oxides and unburned ammonia is used.

The gas concentration measured by the gas detector 17 is sent to, for example, a setting unit. When the gas concentration (nitrogen oxide concentration, unburned ammonia concentration) detected by the gas detector exceeds a preset value, the setting unit resets the ammonia mixing ratio of the mixed gas used in the burner equipment U1 to U5 and L1 to L5 to be lowered. This is because the emission of nitrogen oxides and unburned ammonia to the outside of the heating furnace can be suppressed by lowering the ammonia mixing ratio of the mixed gas used in the burner equipment.
The preset nitrogen oxide concentration may be set to, for example, about 5 ppm when the gas detector is installed outside the heating furnace, whereas the preset unburned ammonia concentration may be set to, for example, about 5 ppm when the gas detector is installed outside the heating furnace.

In addition, when a gas detector determines that the concentration of nitrogen oxides or unburned ammonia has exceeded a preset value, the setting unit may be set to lower the ammonia mixing ratio of the burner equipment located closest to the gas detector that detected the nitrogen oxides or unburned ammonia.
This promotes the decomposition of nitrogen oxides and unburned ammonia inside the heating furnace, and makes it possible to prevent the nitrogen oxides and unburned ammonia from leaking out of the heating furnace.
In particular, even if the operating conditions of the steel heating furnace change over time, causing the flow state of the atmospheric gas inside the heating furnace to change, the setting unit can reliably prevent nitrogen oxides and unburned ammonia from leaking out of the furnace by resetting the ammonia mixing ratio of the burner equipment.

In the above embodiment, when a flue 9, which is a gas flow path for discharging furnace gas, is provided as shown in Fig. 5, a furnace pressure gauge 18 may also be provided in the flue 9. A gas detector 17 for detecting nitrogen oxides or unburned ammonia may also be provided in the flue 9. This is because, by detecting the flow direction of the atmospheric gas inside the heating furnace, including the measurement value of the furnace pressure gauge provided in the flue, not only the horizontal gas flow from the charging part to the discharge part of the heating furnace but also the vertical gas flow can be detected.
This makes it possible to adjust the ammonia mixing ratio of the mixed gas in the burner equipment, such as burner equipment U1 and L1, that are placed on the upper and lower surfaces of the steel material, and more effectively promote the combustion and decomposition of nitrogen oxides and unburned ammonia.

Furthermore, when the measured value of the furnace pressure gauge placed in the flue is lower than the others, it is preferable to set the ammonia mixing ratio of the burner equipment placed in the vicinity of the flue (for example, the burner equipment U1 in the heating furnace shown in FIG. 5) to be lowered. This is because the treatment load of the exhaust gas treatment device can be reduced by lowering the concentration of nitrogen oxides and unburned ammonia discharged from the flue.
Furthermore, when a gas detector installed in the flue determines that the concentration of nitrogen oxides or unburned ammonia exceeds a preset value, the setting unit preferably sets the ammonia mixing ratio of the burner equipment located in the vicinity of the flue to be lowered, because this can reduce the processing load of the exhaust gas treatment device.
The nitrogen oxide concentration preset in the gas detector disposed in the flue may be set to about 100 ppm. The unburned ammonia concentration preset in the gas detector disposed in the flue may be set to about 25 ppm. This is because the concentrations of nitrogen oxides and unburned ammonia outside the heating furnace are sufficiently suppressed by the exhaust gas treatment device disposed in the flue.

Incidentally, it is advisable to correct the pressure measurement value measured by the furnace pressure gauge according to the height at which the furnace pressure gauge is placed. Usually, the atmospheric gas inside a heating furnace is at a high temperature and has a lower density than the outside air. Therefore, the higher the height at which the furnace pressure gauge is placed, the higher the measured pressure value. In this case, if the installation heights of multiple furnace pressure gauges are different, the difference between the measured values may include the influence of the height at which the furnace pressure gauge is placed.
However, since the pressure difference due to the influence of the height at which the in-furnace pressure gauge is placed does not affect the lateral flow of the atmospheric gas in the heating furnace, it is necessary to exclude the influence of the height at which the in-furnace pressure gauge is placed in order to specify the flow direction of the atmospheric gas in the heating furnace. Specifically, a reference height for pressure measurement is set, and the correction amount ΔP of the pressure by the in-furnace pressure gauge is expressed by the following formula (2) using the difference ΔH between the reference height for pressure measurement and the height at which each in-furnace pressure gauge is placed.
ΔP=Δρ×g×ΔH (2)
Here, Δρ is the difference between the density of the outside air and the density of the gas inside the furnace, and g represents the gravitational acceleration.
In this manner, even if the height at which the furnace pressure gauge is disposed varies, the flow direction of the atmospheric gas in the furnace can be identified by carrying out the above-mentioned correction.

The effects of this embodiment will be specifically described below based on examples, but the present invention is not limited to these examples.
As an embodiment of the present invention, an example in which the present invention is applied to a heating furnace of a hot rolling line for manufacturing hot-rolled steel sheets will be described. The steel heating furnace used in this embodiment has a configuration shown in Fig. 5, and slabs (steel materials) manufactured in a continuous casting line are transported to a yard on the charging side of the heating furnace, and are sequentially charged into the heating furnace from the charging section of the heating furnace. The slabs heated to a predetermined extraction temperature are then discharged from the discharge section, and steel sheets are manufactured in the hot rolling line arranged on the discharge side.

Burner equipment U1 to U5, L1 to L5 arranged in the heating furnace has a mixed gas supply unit that supplies a mixed gas of coal gas and ammonia as a fuel gas, and is equipped with a control unit that controls the mixing ratio of ammonia contained in the mixed gas. As shown in Figure 3, burner equipment U1 to U5, L1 to L5 is structured so that combustion air and a mixed gas of coal gas and ammonia are supplied to the burners.
Furthermore, the control unit can control the ammonia mixing ratio of the mixed gas by controlling the openings of the coal gas flow rate control valve and the ammonia flow rate control valve. In this case, the control unit can set the ammonia mixing ratio to zero, and in this case, a condition can be realized in which only coal gas is supplied to the burner as the fuel gas and no ammonia is supplied.

In this embodiment, a pressure gauge was arranged to measure the pressure in the direction along the steel material conveying direction in the heating furnace. Gas detectors for measuring the concentrations of nitrogen oxides NOx and unburned ammonia _NH3 were also arranged on the outside of the charging side and the outside of the extraction side of the heating furnace.

In this example, an operation was carried out to heat slabs for hot rolling using this type of steel heating furnace. The operating conditions of the heating furnace were an average size of slab thickness of 235 mm, width of 1500 mm, and length of 7200 mm, and slabs with an average weight of 20 tons were heated at a heating furnace efficiency of 160 tons/hr. Note that the heating furnace efficiency in this case is equivalent to heating approximately eight slabs per hour. The slab heating temperature was an average of 1200°C, and the heating time was an average of 60 minutes.

The standard conditions for combustion using coal gas with a mixture ratio of ammonia set to zero as the fuel gas for the burner equipment in this embodiment are as follows: That is, the conventional operating conditions for the above-mentioned steel heating furnace are to use M gas shown in Table 2 as the fuel gas, the flow rate of the fuel gas is 188 ^Nm3 /hr per burner equipment, and the flow rate of the combustion air is 625 ^Nm3 /hr. In this case, from the composition of M gas shown in Table 2, the theoretical air amount (amount of air required to completely combust the fuel gas) is 2.47, and the equivalence ratio (the reciprocal of the air ratio) is 0.74, which results in lean combustion conditions (excess air).

On the other hand, in this embodiment, the operating conditions for using a mixed gas of coal gas and ammonia as the fuel gas for the burner equipment were set as follows. If the flow rate of coal gas is Vc, the flow rate of ammonia is Va, and the respective lower heating values are Hc and Ha, the lower heating value due to the combustion of coal gas is Vc x Hc, and the lower heating value due to the combustion of ammonia is Va x Ha. In this case, since the lower heating value of the mixed gas is the sum of Vc x Hc and Va x Ha, the flow rate and mixing ratio of the mixed gas were set so that this value was equivalent to the lower heating value using the above coal gas.

For example, when the flow rate of M gas is 150.5 ^Nm3 /hr and the flow rate of ammonia is 28.5 ^Nm3 /hr, the mixing ratio of ammonia contained in the mixed gas is 15.9%, and the lower heating value of the mixed gas is 2012 KJ/hr. This lower heating value is equal to the lower heating value when coal gas with a flow rate of 188 ^Nm3 /hr is burned using only M gas. In this way, the mixing ratio of ammonia contained in the mixed gas was set, and the flow rates of coal gas and ammonia were set so that the lower heating value of the mixed gas was the same as the lower heating value when only the above-mentioned coal gas was burned, and operation was performed.

Here, the ratio of the lower heating value due to the combustion of ammonia to the lower heating value due to the combustion of the mixed gas is called the "fuel ratio" or the "ammonia fuel ratio". That is, the fuel ratio is expressed by Va×Ha/(Va×Ha+Vc×Hc). Then, the control unit calculates the flow rate Vc of the coal gas and the flow rate Va of the ammonia so that the lower heating value (Va×Ha+Vc×Hc) of the mixed gas becomes a constant value.
Furthermore, the control unit determined the mixing ratio Va/(Va+Vc) from the calculated coal gas flow rate Vc and ammonia flow rate Va, and set the coal gas flow rate control valve and the ammonia flow rate control valve of the burner equipment based on these values.

Table 3-3 shows the operating results, including the maximum nitrogen oxide concentration (maximum NOx outside the furnace) and the maximum unburned ammonia concentration (maximum _NH3 outside the furnace) detected by the gas detector during heating furnace operation. However, since the charging section and discharge section of the heating furnace are temporarily opened during operation, Tables 3-1 and 3-2 show the maximum nitrogen oxide and unburned ammonia concentrations measured when neither the charging section nor the discharge section are open (conditions 1A to 4A) and when only the discharge section is open (conditions 1B to 4B), respectively.

In addition, the "pressure" in Tables 3-1 and 3-2 indicates the value obtained by correcting the pressure measured using an in-furnace pressure gauge near each burner equipment using the above formula (2). The fuel ratio for each burner equipment is as described above, and the "average fuel ratio" in Table 3-3 indicates the ratio of the total amount of lower heating value of ammonia to the total amount of lower heating value of the fuel gas fed into the heating furnace used in this example. In other words, the higher the average fuel ratio, the greater the contribution rate of ammonia to the combustion energy of the heating furnace, and this is an index that represents the effect of reducing carbon dioxide emissions from the heating furnace.

Condition 1 (A, B) shows the results of operation under standard conditions without using ammonia. Under the standard conditions, ammonia is not mixed and burned, so the fuel ratio of all burner equipment is zero, the maximum NOx outside the furnace satisfies the control standard of 5 ppm, and the maximum _NH3 outside the furnace also satisfies the control standard of 5 ppm. However, since ammonia is not used, the carbon dioxide emissions are the same as before.

In condition 2 (A, B), the ammonia fuel ratio of burner equipment U1-U5 and L1-L5 was set to 15%. This resulted in the average fuel ratio being 15%. On the other hand, the maximum NOx outside the furnace increased from condition 1, and showed a concentration exceeding the control standard of 5 ppm. The maximum _NH3 outside the furnace also showed a concentration exceeding the control standard of 5 ppm. In other words, by performing ammonia mixed combustion in all of the burner equipment in the heating furnace, the amount of nitrogen oxides and unburned ammonia discharged outside the heating furnace increased significantly compared to condition 1, in which only coal gas was used.

In contrast, in condition 3 (A, B), the ammonia fuel ratios of burner equipment U1 located near the charging section of the heating furnace and burner equipment U5, L5 located near the discharge section were set to zero. The ammonia fuel ratios of the other burner equipment U2 to U4, L1 to L4 were set to 20% or 30%. In this case, since the pressure measured by the furnace pressure gauge located near burner equipment L3 was higher than the others, it was determined that the position of burner equipment L3 was upstream of the gas flow in the heating furnace, and the fuel ratio of burner equipment L3 was set to be higher than the others.
In addition, with regard to burner equipment L1, which is located at the bottom of the heating furnace in the vicinity of the charging section of the heating furnace, the measured pressure in its vicinity is higher than the measured pressure in the vicinity of burner equipment U1, which is located at the top. Therefore, it was determined that the atmospheric gas inside the heating furnace was flowing from the bottom to the top in the vicinity of the charging section of the heating furnace, and the fuel ratio of burner equipment U1 was set to zero and the fuel ratio of burner equipment L1 was set to 20%.

As a result, under condition 3 (A, B), the average fuel ratio of the heating furnace was kept at 15%, while the maximum NOx outside the furnace and the maximum _NH3 outside the furnace were suppressed to levels almost equivalent to those under condition 1, in which coal gas was used as fuel. In this case, the maximum NOx outside the furnace was at a concentration of 0.1 ppm when the discharge port was open, which was an increase compared to condition 1 (A, B), but was significantly lower than condition 2 (A, B), and was at a level that fully satisfied the management standard of 5 ppm.

Furthermore, in this embodiment, as condition 4 (A, B), an example is shown in which the setting unit sets the mixed gas ratio of the burner equipment based on the change in furnace pressure caused by opening and closing the door of the discharge part of the steel heating furnace. Condition 4 is an example in which the average fuel ratio of the heating furnace is set high when the door of the discharge part is closed (condition 4A), and the average fuel ratio of the burner equipment U5, L5 located near the discharge part is lowered when the door of the discharge part is open (condition 4B).
In this case, the furnace pressure assumed near the burner equipment U5 dropped from 11.6 Pa to 7.8 Pa as the door of the discharge part changed from closed to open, and the furnace pressure assumed near the burner equipment L5 also dropped from 12.7 Pa to 2.1 Pa. Therefore, in the state where the discharge part was open (condition 4B), a gas flow from inside the furnace toward the discharge part was formed in the vicinity of the burner equipment U5 and L5, so the setting part lowered the ammonia fuel ratio of the burner equipment U5 and L5 with the discharge part open.
As a result, when the discharge part of the heating furnace was not open (condition 4A), the average fuel ratio of the heating furnace was kept high at 34%, while when the discharge part of the heating furnace was open (condition 4B), the average fuel ratio could be increased to 26%. As a result, under condition 4 (A, B), the maximum NOx and maximum _NH3 outside the furnace were equivalent to those under condition 3 (A, B) while reducing the amount of carbon dioxide emissions more than under condition 3 (A, B).

From the above, it was found that this embodiment makes it possible to operate a heating furnace that reduces carbon dioxide emissions while suppressing emissions of nitrogen oxides and unburned ammonia compared to conventional heating furnaces that use coal gas as fuel gas.

H: heating furnace S: steel material 1: burner 2: by-product gas 3: ammonia gas 31: ammonia flow rate control valve 32: ammonia flow rate meter 4: air 5: charging side 51: insertion section 6: discharge side 61: discharge section 7: flow rate control valve 8: flow rate meter 9: flue 10: coal gas 101: coal gas flow rate control valve 102: coal gas flow rate meter 11: combustion air 12: furnace interior 13: furnace wall 14: control section 15: mixing section 16: mixed gas 17: gas detector 18: furnace pressure gauge

Claims (9)

A method for operating a steel heating furnace in which steel materials are heated while being transported from a charging section to a discharge section, comprising the steps of:
Burner heating is performed using coal gas as fuel gas and a mixture of coal gas and ammonia gas as fuel gas.
Optionally, hydrogen gas is mixed with the fuel gas or hydrogen gas is used as fuel gas to replace the burner heating.
How to operate a steel heating furnace. At a position adjacent to the charging section in the steel material heating furnace, burner heating with the coal gas is performed, and at a position adjacent to the discharge section in the steel material heating furnace, burner heating with the coal gas is performed.
A method for operating a steel heating furnace according to claim 1. The burner heating with the coal gas is performed when the charging section or the discharge section is open.
A method for operating a steel heating furnace according to claim 2. A method for operating a steel heating furnace according to any one of claims 1 to 3, in which the mixing ratio of ammonia contained in the mixed gas is set based on a measured value of the pressure inside the heating furnace along the transport direction of the steel material. A steel heating furnace having a burner equipment,
The burner equipment includes:
A plurality of such heaters are arranged along the conveying direction of the steel material, which is heated while being conveyed from the charging section to the discharge section of the heating furnace,
a first burner facility having a coal gas supply unit that supplies coal gas as a fuel gas;
a second burner facility having a mixed gas supply unit that supplies a mixed gas of coal gas and ammonia as a fuel gas,
Optionally, the steel heating furnace has a hydrogen gas supplying section capable of mixing and supplying hydrogen gas to the fuel gas or replacing the fuel gas with hydrogen gas. The first burner equipment is disposed at a position adjacent to a charging section and a discharging section of the steel material heating furnace,
The other burner installation is the second burner installation.
The steel heating furnace according to claim 5. The steel heating furnace further comprises:
7. The steel heating furnace according to claim 5, further comprising a control unit for controlling a mixing ratio of ammonia contained in the mixed gas supplied from the mixed gas supply unit. A steel heating furnace having a burner equipment,
The burner equipment includes:
A plurality of such heaters are arranged along the conveying direction of the steel material, which is heated while being conveyed from the charging section to the discharge section of the heating furnace,
A steel heating furnace including a burner facility having a mixed gas supply unit that supplies a mixed gas of coal gas and ammonia as a fuel gas, and a control unit that controls the mixing ratio of ammonia contained in the mixed gas supplied from the mixed gas supply unit. 9. The steel heating furnace according to claim 8, further comprising: a plurality of furnace pressure gauges for measuring a pressure inside the heating furnace along a conveying direction of the steel; and a setting unit for setting a mixing ratio of ammonia contained in the mixed gas controlled by the control unit based on the measured values of the plurality of furnace pressure gauges.

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