Operation method of heating furnace for steel materials and heating furnace for steel materials

Abstract

To provide a steel material heating furnace operation method and a steel material heating furnace which use ammonia as a fuel gas, so as to suppress emission of carbon dioxide, as well as, to suppress emission of nitrogen oxides and unburnt ammonia outward from a furnace.SOLUTION: Provided is a steel material heating furnace which comprises: a first burner facility having a coal gas feed part for feeding a coal gas as a fuel gas; a second burner facility having a mixed gas feed part for feeding a mixed gas obtained by mixing the coal gas and ammonia as the fuel gas; and optionally a hydrogen gas feed part for mixing a hydrogen gas into the fuel gas or replacing the fuel gas with the hydrogen gas. Also provided is a steel material heating furnace operation method of executing burner heating using the coal gas as the fuel gas and burner-heating, using the mixed gas of the coal gas and the ammonia gas as the fuel gas and optionally executing mixing of the hydrogen gas into the fuel gas or replacing the hydrogen gas with burner-heating.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an operation method of a reheating furnace for steel materials and a reheating furnace for steel materials.

Background Art

[0002] In an integrated steelworks, by-products such as blast furnace gas discharged from the top of a blast furnace that reduces iron ore to produce hot metal, as well as by-product gases generated in converters and coke ovens, have been effectively utilized as fuel gases. However, in recent years, with the demand for reducing carbon dioxide emissions, combustion technologies for reducing the usage of these by-product gases have been required. For example, in a reheating furnace for steel materials that heats steel materials in a hot rolling line or a heavy plate rolling line of an integrated steelworks, it has become necessary to reduce the usage of by-product gases and reduce carbon dioxide emissions. In this case, a technology using ammonia as the fuel gas for the reheating furnace for steel materials has attracted attention. That is, ammonia that does not contain carbon elements mainly generates only water and nitrogen even when burned, so it has a great effect on reducing carbon dioxide emissions, and technological development for applying it to a reheating furnace for steel materials is desired.

[0003] On the other hand, ammonia is a difficult-to-burn fuel and has the characteristics of being more difficult to ignite and having a slower combustion rate than general fuels. For example, ammonia has a combustion rate of about one-seventh compared to widely used hydrocarbon fuels such as methane and propane.

[0004] Therefore, heating technologies have been proposed to solve these problems. Patent Document 1 discloses a technology in which ammonia is mixed with an oxidizing agent, and when the mixed gas is supplied into a combustion chamber, a swirler for swirling the mixed gas in the combustion chamber is provided to promote the combustion of ammonia and realize stable combustion.

[0005] Further, Patent Document 2 discloses a technique in which hydrogen gas is separated and generated from ammonia gas, the separated and generated hydrogen gas is supplied into a combustion chamber, and the hydrogen gas supplied into the combustion chamber is ignited and discharged to burn the hydrogen gas, thereby igniting the ammonia gas in the combustion chamber from the burned hydrogen gas.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, when applying the above prior art to a heating furnace for steel materials, the following problems occur.

[0008] The technique described in Patent Document 1 requires the newly manufacturing of burners used for heating steel materials, and it is necessary to replace a large number (for example, about 60 to 100) of burners arranged in the heating furnace for steel materials. Therefore, when applying it to an existing heating furnace for steel materials, the equipment modification cost becomes high, and it is necessary to stop the operation of the heating furnace for steel materials during the equipment modification, so there is a problem that the opportunity loss is large and it is not economical.

[0009] The same applies to the technique described in Patent Document 2. It is necessary to newly install burner equipment including a reformer for separating and generating hydrogen gas from ammonia gas, and it is not practical in terms of equipment modification cost and equipment downtime when applying it to an existing heating furnace for steel materials. Furthermore, the heating furnace for steel materials has a charging section for charging steel plates into the heating furnace and a discharging section for discharging the heated steel materials. At least when charging and discharging the steel materials, a part of the heating furnace is in a state of being open to the atmosphere (open state). Therefore, there is a problem that nitrogen oxides (NOx) generated by the combustion of ammonia and unburned ammonia (unburned NH₃) are likely to be released into the atmosphere. Nitrogen oxides are a type of greenhouse gas, and there are legal regulations on their emission amounts, so it is required to suppress the emission of nitrogen oxides. In addition, since ammonia is toxic, high-concentration ammonia gas is harmful to the human body, and when unburned ammonia leaks out, it causes a bad smell in the workplace and harms the working environment. Therefore, it is necessary to prevent unburned ammonia from flowing out into the workplace.

[0010] The present invention has been developed in view of the above problems of the prior art, and its object is to be applicable to an existing heating furnace for steel materials without significant equipment modification, and by using ammonia as a fuel gas, to suppress the emission of carbon dioxide, and to provide an operation method for a heating furnace for steel materials and a heating furnace for steel materials that suppress the emission of nitrogen oxides and unburned ammonia outside the furnace.

Means for Solving the Problems

[0011] The operation method of the heating furnace for steel materials according to the present invention that advantageously solves the above problems is configured as follows.

[0012] [1] An operation method of a heating furnace for steel materials for heating while conveying the steel materials from the charging section to the discharging section, 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 a fuel gas, and optionally mixes hydrogen gas with the fuel gas or replaces it with burner heating using hydrogen gas as a fuel gas. [2] In the above [1], at a position close to the charging section in the heating furnace for steel materials, burner heating is performed using the coal gas, and at a position close to the discharging section in the heating furnace for steel materials, it is an operating method of a heating furnace for steel materials that performs burner heating using the coal gas. [3] In the above [2], the burner heating using the coal gas is an operating method of a heating furnace for steel materials that is performed when the charging section or the discharging section is open. [4] In any one of the above [1] to [3], it is an operating method of a heating furnace for steel materials that sets the mixing ratio of ammonia contained in the mixed gas based on the measured value of the pressure inside the heating furnace along the conveying direction of the steel materials.

[0013] The heating furnace for steel materials according to the present invention that advantageously solves the above problems is configured as follows. [5] A heating furnace for steel materials having burner equipment, wherein the burner equipment includes a first burner equipment having a coal gas supply section that supplies coal gas as a fuel gas and is arranged in a plurality along the conveying direction of the steel materials for heating while conveying the steel materials from the charging section to the discharging section of the heating furnace, and a second burner equipment having a mixed gas supply section that supplies a mixed gas obtained by mixing coal gas and ammonia as a fuel gas, and optionally, it is a heating furnace for steel materials having a hydrogen gas supply section capable of mixing and supplying hydrogen gas to the fuel gas or replacing the fuel gas with hydrogen gas. [6] In the above [5], the first burner equipment is arranged at positions close to the charging section and the discharging section of the heating furnace for steel materials, and the other burner equipment is the second burner equipment, which is a heating furnace for steel materials. [7] In the above [5] or [6], the heating furnace for steel materials further includes a control section that controls the mixing ratio of ammonia contained in the mixed gas supplied from the mixed gas supply section, which is a heating furnace for steel materials. [8]A heating furnace for steel materials having burner equipment, wherein the burner equipment is arranged in a plurality along the conveying direction of the steel materials for heating while conveying the steel materials from the charging section to the discharging section of the heating furnace, and includes a mixed gas supply section for supplying a mixed gas obtained by mixing coal gas and ammonia as fuel gas, and a control section for controlling the mixing ratio of ammonia contained in the mixed gas supplied from the mixed gas supply section. A heating furnace for steel materials including burner equipment. [9]In the above [8], the heating furnace for steel materials further includes a plurality of in-furnace pressure gauges for measuring the pressure inside the heating furnace along the conveying direction of the steel materials, and a setting section for setting the mixing ratio of ammonia contained in the mixed gas controlled by the control section based on the measured values of the plurality of in-furnace pressure gauges. A heating furnace for steel materials.

Advantages of the Invention

[0014] According to the present invention, it can be applied to an existing heating furnace for steel materials without significant equipment modification. By using ammonia as fuel gas, it can suppress carbon dioxide emissions and also suppress the discharge of nitrogen oxides and unburned ammonia outside the furnace.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0016] Hereinafter, the reheating furnace for steel materials according to this embodiment will be described. <Reheating Furnace for Steel Materials> FIG. 1 schematically shows a cross-sectional view of a reheating furnace for steel materials according to an embodiment of the present invention. The reheating furnace for steel materials is installed, for example, in a hot rolling line for manufacturing steel plates, and is used to heat a cast slab to a predetermined heating temperature (about 1100 to 1300°C). However, the reheating furnace for steel materials is not limited to the purpose of heating slabs, and may be installed to heat steel pieces such as billets, blooms and other shaped steels, bars, wires, steel pipes, etc. which are raw materials. The reheating furnace for steel materials according to the present invention (hereinafter also referred to as "reheating furnace") includes a charging section for charging the steel materials to be heated and a discharging section for discharging (extracting) the heated steel materials. For example, slabs manufactured in a continuous casting line are transported to the yard on the charging side of the reheating furnace and charged into the reheating furnace from the charging section according to the production schedule of a hot rolling line or the like. The inside of the reheating furnace for steel materials is divided into a plurality of zones, and generally, on the upstream side, it is composed of a heating zone divided into 2 to 8 zones and a soaking zone of 1 to 3 zones.

[0017] In the operation of the reheating furnace, it is controlled to have different ambient temperatures for each zone inside the reheating furnace, and the average temperature of the slabs charged into the reheating furnace is gradually increased and controlled to reach a predetermined target heating temperature (the target temperature of the slabs when extracted from the reheating furnace). The slabs charged into the reheating furnace pass through the inside of the reheating furnace from the charging section toward the discharging section by a conveying facility (not shown) called a walking beam inside the reheating furnace. Also, a plurality of slabs are simultaneously charged into the reheating furnace, and they are discharged to the extraction side of the reheating furnace in the order in which they are charged into the reheating furnace, and hot rolling is sequentially performed.

[0018] The charging section of the reheating furnace for steel materials is provided with an opening for charging the slab into the furnace and an opening / closing charging door that covers the opening. When the slab of the reheating furnace for steel materials is charged, the charging door is opened and the opening is in an open state, and the slab is charged. On the other hand, in a state other than when charging the slab, the opening of the charging door is in a closed state. This is to prevent heat energy from leaking to the outside when it is not necessary because the inside of the heating furnace is maintained at a high temperature. Similarly, the discharging section of the reheating furnace for steel materials is also provided with an opening for discharging the slab out of the furnace and an opening / closing discharging door that covers the opening. When the slab of the reheating furnace for steel materials is discharged to the hot rolling line, the discharging door is opened and the opening is in an open state, and the slab is discharged. On the other hand, in a state other than when discharging the slab, the opening of the discharging door is in a closed state. In the embodiment of the present invention, the state in which the charging door of the charging section is open is referred to as the state in which the charging section is open, and the state in which the discharging door of the discharging section is open is referred to as the state in which the discharging section is open.

[0019] Inside the heating furnace, a plurality of burner facilities are provided along the conveying direction of the steel material. The burner facilities are arranged to raise the temperature inside the heating furnace by combustion. When the temperature inside the heating furnace is raised by the burner facilities, the temperature of the steel material rises due to radiation from the furnace wall of the heating furnace. Also, in the heating furnace, a flow of the ambient gas may occur, and the temperature of the steel material may be raised by convection. Furthermore, the steel material may be heated by the flame of the burner facilities directly contacting the steel material. In any case, the burner facilities raise the temperature of the steel material conveyed inside the heating furnace by raising the temperature inside the heating furnace.

[0020] The burner facilities are arranged for each of a plurality of zones inside the heating furnace. However, the number of zones and the number of burner facilities do not necessarily have to match. In the heating furnace shown in FIG. 1, five burner facilities U1 to U5 are arranged on the upper surface side of the steel material from the charging section toward the discharging section. Also, five burner facilities L1 to L5 are arranged on the lower surface side of the steel material, and a total of ten burner facilities are arranged. However, the burner facilities may be arranged from the side surface of the heating furnace toward the inside of the heating furnace.

[0021] Each burner facility is supplied with fuel gas and combustion air (air). The fuel gas diffuses in the air and burns, and the flame is blown into the interior of the heating furnace. As the combustion air, air is usually used, but oxygen-containing gases containing oxygen, such as oxygen, oxygen-enriched air, and a mixed gas of oxygen and exhaust gas, may also be used.

[0022] The combustion air is sent to the burner facility using a blower (not shown). At this time, the combustion air is adjusted by a combustion air flow valve and measured by a combustion air flow meter. However, the combustion air flow valve and the combustion air flow meter do not necessarily need to be provided for each individual burner facility. For example, it is sufficient to adjust the flow rate of the combustion air supplied to the entire burner facilities U1 to U5 arranged on the upper surface side of the heating furnace. The flow rate of the combustion air may be adjusted in units of groups, with a plurality of burner facilities grouped together.

[0023] The supply amount of the fuel gas to the burner facility is adjusted by a fuel gas flow control valve installed for each burner facility, 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 raise the temperature of the steel material to a predetermined temperature in the heating furnace. Also, the flow rate of the fuel gas may be adjusted so as to achieve the target temperature for each zone, where different target values of the ambient temperature are set for each zone inside the heating furnace.

[0024] A heating furnace for steel materials may be provided with a flue for discharging exhaust gas generated inside 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 gas is not discharged into the atmosphere outside the heating furnace through the flue. Therefore, even if nitrogen oxides and unburned ammonia are generated inside the heating furnace for steel materials by burning ammonia, for example, they will not be discharged outside the heating furnace for steel materials through the flue. However, as described above, the heating furnace for steel materials includes a charging section and a discharging section, and at least when loading and unloading steel materials, it will be in an open state. Therefore, it is difficult to install an exhaust gas treatment device at the opening, and there is a problem that nitrogen oxides and unburned ammonia may be discharged to the outside through these openings.

[0025] Next, the first form of the heating furnace for steel materials and its operation method according to the present embodiment will be described. <Burner equipment of the first form> The heating furnace for steel materials according to the first form includes a first burner equipment having a coal gas supply section for supplying coal gas as fuel gas, and a second burner equipment having a mixed gas supply section for supplying a mixed gas of coal gas and ammonia as fuel gas. The heating furnace H for steel materials of the first form is shown in FIG. 1. In the embodiment shown in FIG. 1, the burner equipment U1, U5, L1, L5 to which ammonia 3 is not supplied as fuel gas are the first burner equipment. Also, the burner equipment U2 to U4, L2 to L4 to which ammonia 3 is supplied as fuel gas are the second burner equipment. The coal gas supply section of the first burner equipment and the mixed gas supply section of the second burner equipment will be described later.

[0026] The coal gas, which is the fuel gas used in the burner equipment of the present embodiment, means gas obtained from coal. In particular, it is preferable to use by-product gas generated in blast furnaces, coke ovens, converters, etc. in steelworks. Blast furnace gas is by-product gas generated when reducing iron ore in a blast furnace to produce pig iron. Coke oven gas is by-product gas generated by high-temperature carbonization of coal to produce coke. Converter gas is by-product gas generated in the steelmaking process in a converter.

[0027] The by-product gas has various component compositions depending on the production process. For example, blast furnace gas typically has a composition of 21 - 30 vol% of combustible carbon monoxide, 50 - 60 vol% of non-combustible 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 calorific value of blast furnace gas is 3.45 MJ / Nm 3 is a typical example. Coke oven gas typically has a composition of 46 - 60 vol% hydrogen, 20 - 35 vol% methane, 5 - 10 vol% carbon monoxide, and 2 - 4 vol% hydrocarbons such as ethylene. The lower calorific value of coke oven gas is 18.0 MJ / Nm 3 is a typical example. Converter gas contains approximately 75 vol% carbon monoxide and approximately 13 vol% carbon dioxide, along with trace amounts of oxygen, nitrogen, and hydrogen. The lower calorific value of converter gas is 8.2 MJ / Nm 3 is a typical example.

[0028] Coal gas may use a gas (sometimes called M gas) obtained by appropriately mixing blast furnace gas, coke oven gas, and converter gas. By mixing coal gases with different calorific values, the amount of heat required for heating steel materials is supplied to perform stable operation of the heating furnace for steel materials. In addition, the fuel gas used in the burner equipment of this embodiment may have gaseous fuels such as petroleum gas and trace amounts of solid fuels added to these coal gases. This is because if the content of coal gas is 50 vol% or more, the main heat source for heating steel materials can be regarded as coal gas.

[0029] The ammonia used in the second burner equipment refers to a colorless gas at normal temperature represented by the chemical formula NH3. The ignition point of ammonia is 651°C, and the combustion range is 15.5 - 27 vol% when mixed with air. The lower calorific value of ammonia is 14.1 MJ / Nm 3However, for the ammonia used in the second burner facility, a gas in which hydrogen is optionally mixed may be used. This is because hydrogen, like ammonia, does not emit carbon dioxide by combustion. Also, when ammonia is burned, hydrogen is generated at a high temperature, so it may exhibit combustion characteristics similar to those of a gas in which ammonia and hydrogen are pre-mixed. In this case, the maximum volume percentage of hydrogen gas added to ammonia is allowed to be 50%. That is, the ammonia used in the second burner facility of the present embodiment may contain up to 50% by volume of hydrogen.

[0030] First burner facility A configuration example of the first burner facility is shown in FIG. 2. The first burner facility includes a burner 1 that mixes coal gas 10, which is a fuel gas, and combustion air 11 and emits a flame from the tip, a coal gas flow rate adjustment 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 section in the present embodiment refers to the coal gas flow rate adjustment valve 101 and the coal gas flow meter 102 for supplying coal gas to the burner.

[0031] For the first burner facility, as shown in Fig. 2, a nozzle mix type burner that mixes coal gas 10 and combustion air 11 inside the burner may be used. In this case, by preheating the combustion air with exhaust gas or the like before mixing it with the fuel gas, energy savings can be achieved. Also, for the first burner facility, a regenerative burner that alternately burns a pair of two burners integrated with a heat storage body at intervals of several tens of seconds may be used. In this case, when one burner is burning, its exhaust is passed through the heat storage body of the other burner to heat the other heat storage body, thereby recovering the thermal energy of the exhaust from one burner. Then, when the other burner burns next, the combustion air is preheated by passing it through the other heat storage body. Thereby, combustion with better energy efficiency can be realized. However, the first burner facility is not limited to the nozzle mix type burner shown in Fig. 2, and a premix type burner may be used. The premix type burner is a burner facility in which a mixer for mixing coal gas 10 and combustion air 11 is provided on the downstream side of the coal gas flow meter 102 in the flow direction of the coal gas, and the gas in which the coal gas 10 and the combustion air 11 are mixed is ejected from the tip of the burner 1.

[0032] In the first burner facility, as an example, the combustion air is 625 Nm 3 / hr, and the combustion is carried out under operating conditions where the coal gas is 185 Nm 3 / hr. However, the supply amount of the coal gas, which is the fuel gas, may be adjusted by setting the opening degree of the coal gas flow control valve 101 so as to control the inside of the heating furnace to a predetermined temperature.

[0033] Second burner facility On the other hand, a configuration example of the second burner facility applied to this embodiment is shown in Fig. 3. The burner used in the second burner facility can be of the same type as the first burner facility. The second burner facility includes a coal gas flow control valve 101 for adjusting the flow rate of the coal gas, a coal gas flow meter 102 for measuring the flow rate of the coal gas, an ammonia flow control valve 31 for adjusting the flow rate of ammonia, and an ammonia flow meter 32 for measuring the flow rate of ammonia.

[0034] Further, the second burner facility includes a mixing section 15 that mixes coal gas and ammonia in a pipe. The mixed gas supply section in the present embodiment refers to a coal gas flow rate adjustment valve 101, a coal gas flow meter 102, an ammonia flow rate adjustment valve 31, an ammonia flow meter 32, and the mixing section 15 for supplying the mixed gas to the burner.

[0035] The second burner facility shown in FIG. 3 mixes the gas flowing inside by the confluence of the coal gas and ammonia pipes. In this case, the mixing section refers to the portion where the supply pipe of the coal gas and the supply pipe of the ammonia converge. However, since the coal gas and ammonia are supplied from their respective supply pipes and mixing is performed without providing a special stirring mechanism, the mixing section 15 may be configured as a certain space upstream of the supply pipe of the combustion air 11. The second burner facility 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 is provided on the downstream side of the mixing section 15 in the flow direction of the fuel gas, and a burner facility in which the gas obtained by mixing the fuel gas and the combustion air 11 is ejected from the tip of the burner can be used.

[0036] Preferably, in addition to the mixed gas supply section, the second burner facility includes a control section 14 that controls the mixing ratio of the ammonia 3 contained in the mixed gas 16 supplied by the mixed gas supply section. The control section 14 sets the ratio of the opening degree of the coal gas flow rate adjustment valve 101 and the opening degree of the ammonia flow rate adjustment valve 32 to control the mixing ratio of the ammonia contained in the mixed gas. In this case, it is preferably configured using solenoid valves for the coal gas flow rate adjustment valve 101 and the ammonia flow rate adjustment valve 32, and the control section controls the opening degree of the solenoid valves so that the flow rates of the coal gas and ammonia become a predetermined mixing ratio. In the control unit 14, increasing the ratio of ammonia to coal gas can reduce the amount of carbon dioxide generated in the heating furnace for steel materials. However, since the combustion rate of ammonia is slow, the flame stability decreases. On the other hand, decreasing the ratio of ammonia to coal gas improves the flame stability, but the effect of reducing the amount of carbon dioxide generated in the heating furnace for steel materials becomes insufficient. Therefore, in the second burner facility of the present embodiment, the ratio of ammonia in the mixed gas is preferably 2 to 60% by volume.

[0037] In the second burner facility, as an example, for 625 Nm 3 / hr of combustion air, about 150 Nm 3 / hr of coal gas and 30 Nm 3 / hr of ammonia can be used as the mixed gas. Thereby, the same amount of heat as in the example of the first burner facility described above can be obtained.

[0038] As described above, the first burner facility and the second burner facility differ in the configuration of the supply equipment for the fuel gas supplied to the burner. However, since the burner and the supply equipment for the combustion air can use common equipment, a part of the first burner facility applied to the heating furnace for steel materials can be updated to the second burner facility without major equipment updates.

[0039] The mixing ratio of ammonia contained in the mixed gas used in the second burner facility can be set based on the Wobbe index of the coal gas. The Wobbe index is an index representing the interchangeability of fuel gases and is used to specify the relative ability of fuel gases to generate thermal energy. The Wobbe index WI is obtained by the following formula (1) using the gross 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)

[0040] When changing the fuel gas without changing the combustion equipment, the Wobbe index needs to be kept within a predetermined range together with the combustion rate. Therefore, the mixing ratio controlled by the control unit is preferably set based on the Wobbe indices of coal gas and ammonia.

[0041] Table 1 shows representative examples of the Wobbe indices and maximum combustion rates of ammonia and coal gas. The M gas described in Table 1 refers to coal gas obtained by mixing blast furnace gas, coke oven gas, and converter gas. Note that since coal gas varies greatly depending on the origin of the coal used as a by-product gas raw material and the operating conditions of the coal gas production source, the numerical values shown in Table 1 are merely examples. From Table 1, it can be seen that the combustion rate of ammonia is very slow and, due to its low Wobbe index, the thermal energy generated by combustion is lower compared to others. Therefore, in a burner facility using coke oven gas as coal gas, when ammonia is mixed with coke oven gas, the combustibility (maximum combustion rate and Wobbe index) is likely to decrease, so the mixing ratio of ammonia is set so as not to become excessive. On the other hand, in a burner facility using M gas as coal gas, since the Wobbe index of M gas is lower than that of ammonia, increasing the mixing ratio of ammonia may result in an excessive heat load. In this case, the Wobbe index of the mixed gas can be adjusted by adding nitrogen, an incombustible gas, to the mixed gas of M gas and ammonia. Also, since blast furnace gas, which constitutes M gas, contains a relatively large amount of nitrogen, it is advisable to increase the ratio of blast furnace gas contained in M gas to produce the mixed gas.

[0042]

Table 1

[0043] Optionally, it is possible to have a hydrogen gas supply unit that mixes hydrogen gas into the fuel gas of the first burner facility or the second burner facility for supply, or replaces the fuel gas with hydrogen gas.

[0044] <Operating method of the first form> A method for operating a reheating furnace for steel materials, which comprises performing burner heating using coal gas as a fuel gas and burner heating using a mixed gas of coal gas and ammonia gas as a fuel gas, and optionally mixing hydrogen gas with the fuel gas or replacing the burner heating with hydrogen gas as the fuel gas.

[0045] Burner arrangement in the reheating furnace The reheating furnace for steel materials in the first embodiment has a plurality of burner facilities along the conveying direction of the steel materials. At least one of the plurality of burner facilities is the first burner facility, and at least one of the other burner facilities uses the second burner facility. In this case, burner facilities other than the first burner facility and the second burner facility may be used in the reheating furnace for steel materials. For example, those using a fuel gas mainly composed of petroleum gas, those using hydrogen as the fuel gas, and those generating combustion mainly using solid fuel may include burner facilities different from the first burner facility and the second burner facility in part.

[0046] In the heating furnace H for steel materials shown in FIG. 1, first burner facilities U1, U5, L1, and L5 are arranged, and second burner facilities U2 to U4 and L2 to L4 are arranged. The first burner facilities use coal gas, so although they are excellent in combustion stability, the carbon dioxide emission amount is the same as that of conventional heating furnaces. On the other hand, since the second burner facilities use a mixed gas of coal gas and ammonia, the carbon dioxide emission amount can be reduced as the mixing ratio of ammonia increases. On the other hand, when ammonia is burned in the second burner facilities, nitrogen oxides (NOx) may be generated. When nitrogen oxides are released into the atmosphere from the charging section and discharging section of the heating furnace for steel materials, they act as greenhouse gases, so it is necessary to suppress their emission amount. In this case, in the second burner facilities, by increasing the mixing ratio of ammonia, a denitrification reaction of ammonia occurs, and thereby nitrogen oxides (NOx) are decomposed into nitrogen and water and detoxified. Also, in this case, although it is necessary to burn with the ammonia equivalent ratio on the rich side (ammonia excess side), unburned ammonia is likely to be generated, and the risk of leakage of unburned ammonia to the outside of the heating furnace for steel materials increases. That is, in the second burner facilities, when ammonia is used as the fuel gas, either nitrogen oxides or unburned ammonia is generated, and the problem is that the environmental risk due to these increases.

[0047] In contrast, in the present embodiment, since burner heating is performed with the first burner facilities and the second burner facilities, nitrogen oxides and unburned ammonia that may be generated in the second burner facilities are decomposed by the first burner facilities that do not contain ammonia as the fuel gas and changed into nitrogen and water. Thereby, even if the heating furnace for steel materials has a charging section and a discharging section for steel materials and a state in which it opens to the outside occurs during charging and discharging of the steel materials, it is possible to prevent nitrogen oxides and unburned ammonia from flowing out of the heating furnace for steel materials.

[0048] In the first burner facility that uses coal gas as the fuel gas, nitrogen oxides are decomposed because hydrogen cyanide (HCN) and the like are generated as reducing substances in the flame generated by the first burner facility. As a result, the nitrogen oxides generated in the second burner facility are decomposed into nitrogen. Also, the unburned ammonia is decomposed by the first burner facility because the unburned ammonia burns in the flame emitted from the burner of the first burner facility and is decomposed into nitrogen and water. Usually, the first burner facility burns with rich combustion air (under the condition that the equivalence ratio of coal gas to combustion air is less than 1), so the unburned ammonia is decomposed by the surplus oxygen generated in the first burner facility.

[0049] In the second burner facility, by burning with the ammonia equivalence ratio on the rich side (excess side), a denitration reaction of ammonia occurs, and nitrogen oxides are more easily decomposed into nitrogen and water. However, by setting the ammonia equivalence ratio on the rich side, unburned ammonia is more likely to be generated. On the other hand, by burning the unburned ammonia generated in the second burner facility with the first burner facility, the generation of nitrogen oxides in the second burner facility can be suppressed, and by burning the unburned ammonia in the first burner facility, both nitrogen oxides and unburned ammonia can be reduced. In particular, in the first burner facility, it is preferable to burn with a lean fuel side where the equivalence ratio of coal gas to combustion air is less than 1 because it becomes easier to burn the unburned ammonia in the first burner facility.

[0050] Furthermore, in the above first embodiment, it is preferable that the first burner facility is arranged at a position close to the charging section 51 and the discharging section 61 of the heating furnace for steel materials, and other burner facilities are the second burner facility. Here, the position close to the charging section 51 of the heating furnace for steel materials refers to the position closest to the charging section among a plurality of burner facilities installed along the conveying direction of the steel material S. Also, the position close to the discharging section 61 of the heating furnace for steel materials refers to the position closest to the discharging section among a plurality of burner facilities installed along the conveying direction of the steel material S. That is, it means that no burner facilities other than the first burner facility are arranged at the positions closest to the charging section 51 and the discharging section 61 of the heating furnace for steel materials.

[0051] The reason for arranging the first burner facility at a position close to the charging section 51 of the heating furnace for steel materials is that even if nitrogen oxides and unburned ammonia are generated by the second burner facility, they will be decomposed by the first burner facility arranged at a position close to the charging section. Thereby, it is possible to prevent nitrogen oxides and unburned ammonia from flowing out from the heating furnace for steel materials to the outside from the charging section 51 which is in an open state when charging the slab into the heating furnace for steel materials. Similarly, the reason for arranging the first burner facility at a position close to the discharging section 61 of the heating furnace for steel materials is that even if nitrogen oxides and unburned ammonia are generated by the second burner facility, they will be decomposed by the first burner facility arranged at a position close to the discharging section 61. Thereby, it is possible to prevent nitrogen oxides and unburned ammonia from flowing out from the heating furnace for steel materials to the outside from the discharging section which is in an open state when discharging the slab from the heating furnace for steel materials.

[0052] Note that the heating furnace H for steel materials shown in FIG. 1 is provided with a flue 9 for discharging the exhaust gas generated inside the furnace to the outside. The flue partitions the gas flow path for discharging the gas inside the heating furnace to the outside. In this case, an exhaust gas treatment device (not shown) is arranged in the flue 9, and it is configured such that harmful gases containing nitrogen oxides and unburned ammonia are not discharged into the atmosphere from the heating furnace through the flue. However, in the charging section 51 and the discharging section 61 of the heating furnace for steel materials, since the gas flow path in the heating furnace cannot be limited, it is difficult to install an exhaust gas treatment device. On the other hand, by using the heating furnace for steel materials of the present embodiment, it is possible to prevent nitrogen oxides and unburned ammonia from flowing out to the outside through the opening even when the charging section 51 and the discharging section 61 are open. As a result, it is possible to prevent nitrogen oxides and unburned ammonia from being discharged to the outside of the heating furnace for steel materials together with the exhaust gas treatment device arranged in the flue.

[0053] Optionally, it is possible to mix hydrogen gas with the above fuel gas or replace the burner heating using hydrogen gas as the fuel gas to carry out the operation of heating the steel material.

[0054] Next, a second form of the heating furnace for steel materials and its operation method according to the present embodiment will be described. <Burner equipment of the second form> The burner equipment of the second form of the present invention has, as in the first form, a plurality of burner equipment for raising the temperature inside the heating furnace for steel materials along the conveying direction of the steel materials. At least one of the plurality of burner equipment includes a mixed gas supply section that supplies a mixed gas in which coal gas and ammonia are mixed as the fuel gas, and a control section 1 that controls the mixing ratio of ammonia contained in the mixed gas supplied from the mixed gas supply section.

[0055] The furnace body structure of the heating furnace in the second form, the conveying device for steel materials, etc. are the same as those in the first form. The second form has at least one of the second burner equipment in the first form in the heating furnace, and the mixed gas supply section of the second burner equipment has a control section 14 that controls the mixing ratio of ammonia contained in the mixed gas 16 respectively. In this case, the control section 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 section 14, the function of the first burner equipment that supplies coal gas in the first form can be exhibited.

[0056] When a first burner facility using coal gas as a fuel gas is provided inside a heating furnace for steel materials, the burner facility having the mixed gas supply unit and the control unit of the second embodiment may perform combustion using a mixed gas of coal gas and ammonia as the fuel gas. Thereby, while reducing the amount of carbon dioxide emissions, nitrogen oxides and unburned ammonia can be burned and decomposed by the first burner facility. On the other hand, when a second burner facility using a mixed gas of coal gas and ammonia as a fuel gas is provided inside the heating furnace for steel materials, the burner facility having the mixed gas supply unit and the control unit of the present embodiment may set the ammonia mixing ratio of the mixed gas to zero. Even in such a mode, the same effect can be obtained.

[0057] On the other hand, it is preferable to use a burner facility including a mixed gas supply unit that supplies a mixed gas in which coal gas and ammonia are mixed as a fuel gas, and a control unit that controls the mixing ratio of the mixed gas supplied from the mixed gas supply unit for at least two or more of the plurality of burner facilities. This is because the same effect can be obtained by causing at least one of the burner facilities having the mixed gas supply unit and the control unit to perform combustion using a mixed gas of coal gas and ammonia as a fuel gas, and causing the others to perform combustion with the ammonia mixing ratio of the mixed gas set to zero by the control unit.

[0058] <Operating Method of the Second Embodiment> The heating furnace H for steel materials of the second embodiment will be described with reference to FIG. 4. The burner facilities U1 to U5 and L1 to L5 shown in FIG. 4 each have a control unit 14, and the control unit 14 is configured to be able to control the mixing ratio of coal gas and ammonia. Thereby, a part of the burner facilities U1 to U5 and L1 to L5 can raise the temperature inside the heating furnace using coal gas 2 as a fuel gas by the control unit 14, and the other burner facilities can raise the temperature inside the heating furnace using a mixed gas of coal gas 2 and ammonia 3 as a fuel gas. Therefore, nitrogen oxides and unburned ammonia that can be generated by combustion using the mixed gas 16 of coal gas and ammonia can be decomposed by combustion using coal gas as a fuel gas, and the outflow of nitrogen oxides and unburned ammonia to the outside of the heating furnace can be prevented.

[0059] For example, as an operation using the heating furnace H for steel materials shown in FIG. 4, for at least one of the burner facilities U1 or L1 disposed at a position close to the charging section 51 of the heating furnace for steel materials, the control unit 14 controls the ammonia mixing ratio of the mixed gas to zero. Also, for at least one of the burner facilities U5 or L5 disposed at a position close to the discharging section 61 of the heating furnace for steel materials, the control unit 14 controls the ammonia mixing ratio of the fuel gas to zero. And for at least one of the burner facilities U2 to U4, L2 to L4 disposed at positions other than the positions close to the charging section and the discharging section of the heating furnace for steel materials, the control unit 14 controls to use a mixed gas containing ammonia. Thereby, the amount of carbon dioxide discharged from the heating furnace for steel materials by combustion using a mixed gas containing ammonia can be reduced, and the outflow of nitrogen oxides and unburned ammonia to the outside of the heating furnace can be prevented.

[0060] Furthermore, the mixing ratio of ammonia contained in the mixed gas 16 may be set for each burner facility. For example, with respect to the conveyance direction of the steel materials inside the heating furnace, a mixed gas 16 of coal gas 10 and ammonia 3 may be used as the fuel gas for one of the adjacent burner facilities, and coal gas without mixing ammonia may be used for the other. Thereby, nitrogen oxides and unburned ammonia generated in one of the adjacent burner facilities can be decomposed by the other burner facility.

[0061] Next, a third aspect of the heating furnace for steel materials and its operation method according to the present embodiment will be described. <Burner Facility of the Third Aspect> The third aspect of the present invention is a heating furnace including a plurality of in-furnace pressure gauges that measure the pressure inside the heating furnace along the conveyance direction of the steel materials in the heating furnace for steel materials of the second aspect, and has a setting unit that sets the mixing ratio of the mixed gas controlled by the control unit based on the measured values of the plurality of in-furnace pressure gauges.

[0062] The in-furnace pressure gauges in this embodiment are arranged in a plurality in the direction in which the steel material is conveyed inside the heating furnace. In the example of FIG. 5, the in-furnace pressure gauges are arranged near the positions where the respective burner facilities are arranged. In this embodiment, it has a setting unit that sets the mixing ratio of the mixed gas controlled by the control unit. FIG. 6 shows a configuration example of the setting unit. The setting unit acquires the measured values of the pressure inside the furnace measured by a plurality of in-furnace pressure gauges. The setting unit specifies the flow direction of the atmospheric gas based on the relative magnitude relationship of the measured values by the plurality of in-furnace pressure gauges in correspondence with the fact that the atmospheric gas inside the heating furnace flows from a position with a high in-furnace pressure to a position with a low in-furnace pressure. Then, in the burner facility arranged on the downstream side of the flow direction of the atmospheric gas, the setting unit reduces the mixing ratio of ammonia with respect to the fuel gas. Furthermore, the setting unit sets the mixing ratio of the mixed gas so that the mixing ratio of ammonia with respect to the fuel gas is increased in the burner facility arranged on the upstream side of the flow direction of the atmospheric gas. Thereby, the burner facility located on the upstream side of the flow direction of the atmospheric gas can reduce the carbon dioxide emission amount of the heating furnace by burning with ammonia-rich. Also, in the burner facility located on the downstream side of the flow direction of the atmospheric gas, nitrogen oxides and unburned ammonia generated on the upstream side can be decomposed.

[0063] <Operating method of the third embodiment> For example, in FIG. 5, when the in-furnace pressure is high at the charging side 5 and low at the discharging side 6, it is presumed that the flow direction of the atmospheric gas is from the charging side 5 to the discharging side 6. In this case, the setting unit sets so that the mixing ratio of ammonia in at least one of the burner facilities U5 or L5 on the downstream side of the flow direction of the atmospheric gas is lower than that of the burner facilities located on the upstream side of the flow direction of the atmospheric gas. Also, not only the burner facilities U5 and L5 on the downstream side of the flow direction of the atmospheric gas, but also the mixing ratio of ammonia in the burner facilities U4 and L4 may be set to be lower than that of the burner facilities U1 to U3 and L1 to L3. Thereby, it is possible to prevent nitrogen oxides and unburned ammonia from flowing out from the discharge port 61.

[0064] On the one hand, when the furnace pressure is low on the charging side 5 and high on the discharging side 6, it is presumed that the flow direction of the atmosphere gas is from the discharging side 6 to the charging side 5. In this case, the setting unit sets at least one of the burner facilities U1 or L1 on the upstream side of the flow direction of the atmosphere gas to have a lower ammonia mixing ratio than the burner facilities located on the upstream side of the flow direction of the atmosphere gas. Thereby, it is possible to prevent unburned ammonia from flowing out through the charging port 51.

[0065] Incidentally, the flow direction of the atmosphere gas inside the heating furnace may change according to the opening and closing of the charging door of the charging section 51 and the opening and closing of the discharging door of the discharging section 61. The inside of the heating furnace is often in a state of higher pressure than the outside. When the charging section is open, the atmosphere gas inside the heating furnace flows in the direction of the opening of the charging section and is likely to flow out from the charging section to the outside. The same applies when the discharging section is open. In that case, the atmosphere gas inside the heating furnace flows in the direction of the opening of the discharging section and is likely to flow out from the discharging section to the outside.

[0066] Therefore, it is preferable that the burner facility arranged at a position close to the charging section of the heating furnace performs combustion using coal gas as the fuel gas when the charging section 51 is open. Also, it is preferable that the burner facility arranged at a position close to the discharging section of the heating furnace performs combustion using coal gas as the fuel gas when the discharging section 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 on the downstream side of the position close to the charging section. Even in such a case, as described above, by the setting unit specifying the flow direction of the atmosphere gas based on the relative magnitude relationship of the measured values by a plurality of furnace pressure gauges, and reducing the mixing ratio of ammonia to the fuel gas of the burner facility arranged on the downstream side of the flow direction of the atmosphere gas, the same effect can be obtained.

[0067] Similarly, in the state where the carry-out section 61 is open, the measurement by the in-furnace pressure gauge installed at a position close to the carry-out section is smaller than the measurement by the in-furnace pressure gauge installed on the upstream side of the position close to the carry-out section. Therefore, the setting unit may specify the flow direction of the atmosphere gas based on the relative magnitude relationship of the measured values by the plurality of in-furnace pressure gauges, and reduce the mixing ratio of ammonia to the fuel gas of the burner equipment arranged on the downstream side of the flow direction of the atmosphere gas.

[0068] A gas detector may be further arranged in the heating furnace for steel materials of the present embodiment to detect nitrogen oxides or unburned ammonia. In the example of FIG. 5, gas detectors 17 are arranged outside the charging side, outside the carry-out side, and in the flue of the heating furnace. The gas detector uses one that can detect nitrogen oxides (NOx) or unburned ammonia (NH3). Preferably, a gas detector capable of detecting nitrogen oxides and unburned ammonia is used.

[0069] The measured value of the gas concentration by the gas detector 17 is sent to, for example, the setting unit. Thereby, when the gas concentration (nitrogen oxide concentration, unburned ammonia concentration) detected by the gas detector exceeds a preset value, the setting unit re-sets to lower the ammonia mixing ratio of the mixed gas used in the burner equipment U1 to U5, L1 to L5. This is because discharging 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. Note that the nitrogen oxide concentration set in advance may be set to about 5 ppm, for example, when the gas detector is installed outside the heating furnace. On the other hand, the unburned ammonia concentration set in advance may be set to about 5 ppm, for example, when the gas detector is installed outside the heating furnace.

[0070] Further, when it is determined that the concentration of nitrogen oxides or unburned ammonia exceeds a preset value by the gas detector, the setting unit may set to lower the ammonia mixing ratio of the burner equipment arranged at the position closest to the gas detector thus detected. This promotes the decomposition of nitrogen oxides and unburned ammonia inside the heating furnace, and can prevent the outflow of nitrogen oxides and unburned ammonia to the outside of the heating furnace. In particular, even when the operating conditions of the heating furnace for steel materials change over time, and as a result, the flow state of the atmospheric gas inside the heating furnace changes, the setting unit can surely prevent the outflow of nitrogen oxides and unburned ammonia to the outside of the furnace by resetting the ammonia mixing ratio of the burner equipment.

[0071] By the way, in the above embodiment, as shown in FIG. 5, when the flue 9, which is a gas flow path for discharging the gas inside the furnace, is arranged, the furnace internal pressure gauge 18 may also be arranged in the flue 9. Further, a gas detector 17 for detecting nitrogen oxides or unburned ammonia may be provided in the flue 9. By detecting the flow direction of the atmospheric gas inside the heating furnace including the measured value of the furnace internal pressure gauge arranged in the flue, not only the horizontal gas flow from the charging section to the discharging section of the heating furnace but also the vertical gas flow can be detected. This can adjust the ammonia mixing ratio of the mixed gas of the burner equipment arranged on the upper and lower surfaces of the steel material, such as the burner equipment U1 and L1, and more effectively promote the combustion and decomposition of nitrogen oxides and unburned ammonia.

[0072] Furthermore, when the measured value of the furnace internal pressure gauge arranged in the flue is lower than others, it is preferable to set the ammonia mixing ratio of the burner equipment (for example, the burner equipment U1 in the heating furnace shown in FIG. 5) arranged at a position close to the flue to be lowered. This is because the treatment load of the exhaust gas treatment device can be reduced by reducing the concentration of nitrogen oxides and unburned ammonia discharged from the flue. Also, when it is determined that the concentration of nitrogen oxides or unburned ammonia exceeds a preset value by the gas detector installed in the flue, it is preferable for the setting unit to set the ammonia mixing ratio of the burner equipment arranged at a position close to the flue to be lowered. This is because the treatment load of the exhaust gas treatment device can be reduced. Incidentally, the concentration of nitrogen oxides preset in the gas detector disposed in the flue may be set to about 100 ppm. Also, the concentration of unburned ammonia preset in the gas detector disposed in the flue may be set to about 25 ppm. This is because the concentration of nitrogen oxides and unburned ammonia is sufficiently suppressed outside the furnace of the heating furnace by the exhaust gas treatment device disposed in the flue.

[0073] By the way, regarding the measured value of the pressure measured by the in-furnace pressure gauge, it is advisable to perform correction according to the height at which the in-furnace pressure gauge is disposed. Usually, the atmospheric gas inside the heating furnace is at a high temperature and has a lower density than the outside air. Therefore, the higher the height at which the in-furnace pressure gauge is disposed, the higher the measured value of the pressure. In this case, if the installation heights of a plurality of in-furnace pressure gauges are different, the difference in their measured values may include the influence of the height at which the in-furnace pressure gauge is disposed. However, since the pressure difference due to the influence of the height at which the in-furnace pressure gauge is disposed does not affect the lateral flow of the atmospheric gas inside the heating furnace, in order to specify the flow direction of the atmospheric gas inside the heating furnace, it is necessary to exclude the influence of the height at which the in-furnace pressure gauge is disposed. Specifically, a reference height for pressure measurement is set, and using the difference ΔH from the height at which each in-furnace pressure gauge is installed, the pressure correction amount ΔP by the in-furnace pressure gauge is expressed by the following formula (2). 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 acceleration due to gravity. In this way, even when the heights at which the in-furnace pressure gauges are disposed are different, the flow direction of the atmospheric gas inside the furnace can be specified by performing the above correction.

Example

[0074] Hereinafter, the effects of the present embodiment will be specifically described based on examples, but the present invention is not limited to these examples. As an example of the present invention, an example applied to a reheating furnace in a hot rolling line for manufacturing hot-rolled steel sheets will be described. The reheating furnace for steel materials used in this example has the configuration shown in FIG. 5. Slabs (steel materials) manufactured on a continuous casting line are transported to the yard on the charging side of the reheating furnace and are sequentially charged into the interior of the reheating furnace from the charging section of the reheating furnace. Then, the slabs heated to a predetermined extraction temperature are discharged from the discharging section, and steel sheets are manufactured on a hot rolling line arranged on the extraction side.

[0075] The burner facilities U1 to U5 and L1 to L5 arranged in the reheating furnace have a mixed gas supply section that supplies a mixed gas obtained by mixing coal gas and ammonia as fuel gas, and are provided with a control section that controls the mixing ratio of ammonia contained in the mixed gas. As shown in FIG. 3, the burner facilities U1 to U5 and L1 to L5 have a structure in which combustion air and a mixed gas of coal gas and ammonia are supplied to the burners. Further, the control section can control the ammonia mixing ratio of the mixed gas by controlling the opening degrees of the coal gas flow rate adjustment valve and the ammonia flow rate adjustment valve. In this case, the control section can set the ammonia mixing ratio to zero, and in this case, only coal gas can be supplied to the burners as fuel gas, and a condition of not supplying ammonia can be realized.

[0076] Furthermore, in this example, a pressure gauge for measuring pressure in the direction along the transport direction of the steel material in the reheating furnace was arranged. Also, gas detectors for measuring the concentrations of nitrogen oxides NOx and unburned ammonia NH3 were arranged outside the charging side and the extraction side of the reheating furnace.

[0077] In this example, an operation of heating slabs for hot rolling was performed using such a reheating furnace for steel materials. As the operating conditions of the reheating furnace, with a slab thickness of 235 mm, width of 1500 mm, and length of 7200 mm as the average size, slabs with an average weight of 20 tons were heated at a reheating furnace capacity of 160 tons / hr. Note that the reheating furnace capacity in this case corresponds to a condition of heating approximately eight slabs in one hour. The average heating temperature of the slabs was 1200°C, and the average heating time was 60 minutes.

[0078] The reference conditions for combustion using coal gas with a zero mixing ratio of ammonia as the fuel gas for the burner equipment in this embodiment are as follows. That is, the conventional operating conditions in the above heating furnace for steel materials use the M gas shown in Table 2 as the fuel gas, and the flow rate of the fuel gas is 188 Nm 3 / hr per burner equipment, and the flow rate of combustion air is 625 Nm 3 / hr. In this case, from the composition of the M gas shown in Table 2, the theoretical air volume (the amount of air required to completely burn the fuel gas) is 2.47, and since the equivalence ratio (the reciprocal of the air ratio) is 0.74, it is in the condition of lean combustion (excess air).

[0079] On the other hand, the operating conditions when using a mixed gas of coal gas and ammonia as the fuel gas for the burner equipment in this embodiment were set as follows. Let the flow rate of coal gas be Vc and the flow rate of ammonia be Va, and their lower calorific values be Hc and Ha respectively. Then, the lower calorific value due to the combustion of coal gas is Vc×Hc, and the lower calorific value due to the combustion of ammonia is Va×Ha. In this case, since the lower calorific value of the mixed gas is the sum of Vc×Hc and Va×Ha, the flow rate and mixing ratio of the mixed gas were set so that this value would be equal to the lower calorific value using the above coal gas.

[0080] For example, when the flow rate of M gas is 150.5 Nm 3 / hr and the flow rate of ammonia is 28.5 Nm 3 / hr, the mixing ratio of ammonia contained in the mixed gas is 15.9%, and the lower calorific value of the mixed gas is 2012 KJ / hr. This lower calorific value is equal to the lower calorific value when burning coal gas with a flow rate of 188 Nm 3 / hr using only M gas. In this way, the mixing ratio of ammonia contained in the mixed gas was set, and the operation was carried out by setting the flow rates of coal gas and ammonia so that the lower calorific value by the mixed gas would be the same as the lower calorific value when burning only the above coal gas.

[0081] Here, the ratio of the lower calorific value by the combustion of ammonia to the lower calorific value by the combustion of the mixed gas is called the "fuel ratio" or "ammonia fuel ratio". That is, the fuel ratio is represented by Va×Ha / (Va×Ha+Vc×Hc). And the control unit calculates the flow rate Vc of the coal gas and the flow rate Va of the ammonia so that the lower calorific value (Va×Ha+Vc×Hc) of the mixed gas becomes a constant value. Furthermore, the control unit determines the mixing ratio Va / (Va+Vc) from the calculated flow rate Vc of the coal gas and the flow rate Va of the ammonia, and sets the coal gas flow rate adjustment valve and the ammonia flow rate adjustment valve of the burner equipment based on these values.

[0082] Table 3-3 shows the operation results including the maximum value of the nitrogen oxide concentration (maximum NOx outside the furnace) and the maximum value of the unburned ammonia concentration (maximum NH3 outside the furnace) detected by the gas detector during the operation of the heating furnace. However, since the charging section and the discharging section are temporarily opened during the operation of the heating furnace, Tables 3-1 and 3-2 show the maximum values of the nitrogen oxide and unburned ammonia concentrations measured when the charging section and the discharging section are both closed (conditions 1A to 4A) and when only the discharging section is opened (conditions 1B to 4B), respectively.

[0083] Also, the "pressure" in Tables 3-1 and 3-2 indicates the value obtained by correcting the measured value of the pressure measured by using the in-furnace pressure gauge near each burner equipment according to the above formula (2). The fuel ratio of each burner equipment is as described above, and the "average fuel ratio" in Table 3-3 represents the ratio of the total lower calorific value of ammonia to the total lower calorific value of the fuel gas input to the heating furnace used in this embodiment. That is, the larger the average fuel ratio, the larger the contribution rate of ammonia to the combustion energy of the heating furnace, which becomes an index representing the reduction effect of the carbon dioxide emission amount of the heating furnace.

[0084] Condition 1 (A, B) shows the operation results under the reference conditions without using ammonia. Under the reference conditions, since the mixed combustion of ammonia is not carried out, the fuel ratio of all burner facilities is zero, the maximum NOx outside the furnace satisfies the regulatory standard of 5 ppm, and the operation is carried out under the condition that the maximum NH3 outside the furnace also satisfies the regulatory standard of 5 ppm. However, since ammonia is not used, the carbon dioxide emissions are the same as before.

[0085] For Condition 2 (A, B), the ammonia fuel ratios of burner facilities U1 - U5, L1 - L5 were set to 15%. As a result, the average fuel ratio also became 15%. On the other hand, the maximum NOx outside the furnace increased compared to Condition 1 and showed a concentration exceeding the regulatory standard of 5 ppm. Also, the maximum NH3 outside the furnace showed a concentration exceeding the regulatory standard of 5 ppm. That is, by performing ammonia mixed combustion in all the burner facilities in the heating furnace, the nitrogen oxides and unburned ammonia discharged outside the heating furnace increased significantly compared to Condition 1 using only coal gas.

[0086] In contrast, for Condition 3 (A, B), the ammonia fuel ratios of burner facility U1 arranged at a position close to the charging section of the heating furnace, and burner facilities U5 and L5 arranged at positions close to the discharging section were set to zero. For the other burner facilities U2 - U4, L1 - L4, the ammonia fuel ratios were set to 20% or 30%. In this case, since the pressure measured by the in - furnace pressure gauge arranged near burner facility L3 was higher than others, it was determined that the position of burner facility L3 was upstream of the gas flow in the heating furnace, and the fuel ratio of burner facility L3 was made larger than others. Regarding burner facility L1 arranged at the lower part of the heating furnace at a position close to the charging section of the heating furnace, since the measured pressure in its vicinity was higher than the measured pressure in the vicinity of burner facility U1 arranged at the upper part, it was determined that in the vicinity of the charging section of the heating furnace, the ambient gas in the heating furnace flowed from the lower part to the upper part of the furnace. The fuel ratio of burner facility U1 was set to zero, and the fuel ratio of burner facility L1 was set to 20%.

[0087] As a result, under Conditions 3 (A, B), while maintaining the average fuel ratio of the heating furnace at 15%, the maximum NOx outside the furnace and the maximum NH3 outside the furnace could be suppressed to almost the same level as in Condition 1 using coal gas as fuel. In this case, for the maximum NOx outside the furnace, the concentration is 0.1 ppm when the unloading section is open. Although it has increased compared to Condition 1 (A, B), it is significantly lower than that in Condition 2 (A, B) and fully meets the regulatory standard of 5 ppm.

[0088] Furthermore, in this embodiment, as Condition 4 (A, B), an example is shown where the setting unit sets the mixed gas ratio of the burner equipment based on the change in the furnace internal pressure caused by the opening and closing of the door of the unloading section of the heating furnace for steel materials. Condition 4 is an example where the average fuel ratio of the heating furnace is set high when the door of the unloading section is closed (Condition 4A), and the average fuel ratios of the burner equipment U5 and L5 arranged near the unloading section are reduced when the door of the unloading section is open (Condition 4B). In this case, the furnace internal pressure assumed near the burner equipment U5 decreased from 11.6 Pa to 7.8 Pa as the door of the unloading section changed from closed to open, and the furnace internal pressure assumed near the burner equipment L5 also decreased from 12.7 Pa to 2.1 Pa. Therefore, when the unloading section is open (Condition 4B), a gas flow from the furnace interior towards the unloading section is formed near the burner equipment U5 and L5. Thus, the setting unit reduced the ammonia fuel ratios of the burner equipment U5 and L5 when the unloading section was open. As a result, it was possible to maintain the average fuel ratio of the heating furnace as high as 34% when the unloading section of the heating furnace was not open (Condition 4A), and also as high as 26% when the unloading section of the heating furnace was open (Condition 4B). Thereby, Condition 4 (A, B) was able to make the maximum NOx outside the furnace and the maximum NH3 outside the furnace equivalent to those in Condition 3 (A, B) while reducing the carbon dioxide emissions more than in Condition 3 (A, B).

[0089] From the above, it was found that according to this embodiment, it is possible to operate a heating furnace that reduces carbon dioxide emissions and suppresses the emissions of nitrogen oxides and unburned ammonia compared to a conventional heating furnace using coal gas as fuel gas.

[0090]

Table 2

[0091]

Table 3-1

[0092]

Table 3-2

[0093]

Table 3-3

Explanation of Symbols

[0094] H Heating furnace S Steel material 1 Burner 2 By-product gas 3 Ammonia gas 31 Ammonia flow control valve 32 Ammonia flow meter 4 Air 5 Loading side 51 Insertion part 6 Unloading side 61 Unloading part 7 Flow control valve 8 Flow meter 9 Flue 10 Coal gas 101 Coal gas flow control valve 102 Coal gas flow meter 11 Combustion air 12 Inside the furnace 13 Furnace wall 14 Control unit 15 Mixing part 16 Mixed gas 17 Gas detector 18 Furnace pressure gauge

Claims

1. An operating method for a heating furnace for steel materials, which heats the steel materials while conveying them from a charging section to a discharging section, performing burner heating using coal gas as a fuel gas and burner heating using a mixed gas of coal gas and ammonia gas as a fuel gas, at a position close to the charging section in the heating furnace for steel materials, burner heating is performed using the coal gas, and at a position close to the discharging section in the heating furnace for steel materials, burner heating is performed using the coal gas, optionally, hydrogen gas is mixed into the fuel gas, An operating method for a heating furnace for steel materials.

2. The burner heating using the coal gas is performed when the charging section or the discharging section is open. The operating method for a heating furnace for steel materials according to Claim 1.

3. The mixing ratio of ammonia contained in the mixed gas is set based on the measured value of the pressure inside the heating furnace along the conveying direction of the steel materials. The operating method for a heating furnace for steel materials according to Claim 1 or 2.

4. A heating furnace for steel materials having burner equipment, wherein the burner equipment includes a first burner equipment having a coal gas supply section that supplies coal gas as a fuel gas and is arranged in a plurality along the conveying direction of the steel materials to heat the steel materials while conveying them from the charging section to the discharging section of the heating furnace, and a second burner equipment having a mixed gas supply section that supplies a mixed gas of coal gas and ammonia as a fuel gas, and is provided with the first burner equipment is arranged at positions close to the charging section and the discharging section of the heating furnace for steel materials, and the other burner equipment is the second burner equipment, optionally, a heating furnace for steel materials having a hydrogen gas supply section capable of mixing and supplying hydrogen gas to the fuel gas.

5. The heating furnace for steel materials further includes a control section for controlling the mixing ratio of ammonia contained in the mixed gas supplied from the mixed gas supply section. The heating furnace for steel materials according to Claim 4.

6. A heating furnace for steel materials having burner equipment, wherein the burner equipment is arranged in a plurality along the conveying direction of the steel materials to heat the steel materials while conveying them from the charging section to the discharging section of the heating furnace, and includes a burner equipment having a mixed gas supply section that supplies a mixed gas of coal gas and ammonia as a fuel gas and a control section for controlling the mixing ratio of ammonia contained in the mixed gas supplied from the mixed gas supply section.

7. The heating furnace for steel materials further includes a plurality of in-furnace pressure gauges that measure the pressure inside the heating furnace along the conveying direction of the steel materials, and a setting unit that sets the mixing ratio of ammonia contained in the mixed gas controlled by the control unit based on the measured values of the plurality of in-furnace pressure gauges. The heating furnace for steel materials according to claim 6.

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