Operation method of heating furnace and heating furnace

Abstract

The invention provides a method for operating a heating furnace and a heating furnace, which uses ammonia capable of suppressing emission of carbon dioxide as a fuel for combustion of the heating furnace and can reduce emission of nitrogen oxides to the outside of the heating furnace. A method for operating a heating furnace, the method comprising: a mixed gas generation step for mixing ammonia gas and a coal gas containing a carbon monoxide gas; and a burner heating step for burning the obtained mixed gas as a fuel gas. In the burner heating step, the mixed gas is discharged to a flame region to suppress the generation of nitrogen oxides. In the mixed gas generation step, the volume ratio of the ammonia gas to the carbon monoxide gas contained in the mixed gas is preferably 0.1-4.35. Furthermore, in the burner heating step, the burner heating is preferably performed by supplying combustion air having an air ratio of 0.80-1.20 with respect to the theoretical air amount of the fuel gas.

Description

Technical Field

[0001] The invention relates to an operating method of a heating furnace and the heating furnace. Background Art

[0002] In integrated steel mills, by-product gases produced in converters and coke ovens, represented by blast furnace gas discharged from the top of a blast furnace that reduces iron ore to produce molten iron, are being effectively utilized as fuel gas. However, in recent years, with the demand for reducing carbon dioxide emissions, there is a demand for combustion technology that reduces the amount of these by-product gases used. For example, in steel heating furnaces that heat steel in hot rolling lines, thick plate rolling lines, etc. in integrated steel mills, there is also a demand to reduce the amount of by-product gases used and reduce carbon dioxide emissions. In this case, as a fuel gas for steel heating furnaces, attention is being paid to technologies that utilize ammonia. That is, even if ammonia, which does not contain carbon elements, is burned, it mainly produces only water and nitrogen, so the effect of reducing carbon dioxide emissions is significant, and it is expected that it will be applied to the development of technologies for steel heating furnaces.

[0003] On the other hand, using ammonia as a furnace fuel creates a problem with the generation of nitrogen oxides (NOx). Nitrogen oxides are harmful to the human body and contribute to photochemical smog and acid rain, and are therefore subject to legal emission controls.

[0004] Therefore, in order to solve these problems, heating technology has been proposed.

[0005] Patent Document 1 discloses a boiler comprising a combustion device that burns ammonia as fuel in a furnace, a flue that guides the combustion gases generated by the fuel combustion, and an injection unit disposed downstream of the combustion device on at least one of the furnace and the flue. The injection unit injects ammonia as a reducing agent toward the center of the furnace or flue when viewed from above. This allows ammonia to be supplied to the center of the furnace, enabling even small amounts of ammonia to act as a reducing agent and reduce nitrogen oxides.

[0006] Patent Document 2 discloses a boiler comprising: a burner for burning fossil fuel within a furnace; an additional air supply unit located downstream of the burner in the direction of combustion gas flow within the furnace; and an ammonia fuel supply unit for supplying ammonia fuel to the furnace upstream of the additional air supply unit in the direction of fuel gas flow. Thus, in a two-stage combustion boiler equipped with the additional air supply unit, if the ammonia fuel is introduced upstream of the additional air supply unit, the nitrogen content of the ammonia fuel is reduced to N₂ in the reducing atmosphere within the furnace, thereby suppressing the formation of nitrogen oxides.

[0007] Patent Document 2 discloses connecting a second fuel supply line for mixing ammonia fuel to a first fuel supply line for supplying fossil fuel to a burner. In this case, the fossil fuel used as fuel may be pulverized coal, heavy oil, light oil, liquefied natural gas (LNG), or the like.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 2019-086191

[0011] Patent Document 2: Japanese Patent Application Laid-Open No. 2018-076985 Summary of the Invention

[0012] However, if the above-mentioned conventional technology is applied to a heating furnace used for heating steel materials, etc., the following problems arise.

[0013] The technology disclosed in Patent Document 1 targets combustion equipment such as boilers and reduces nitrogen oxides produced in the combustion equipment by injecting ammonia downstream of the combustion gas flow direction. Therefore, it targets combustion equipment where the combustion gas flow direction is fixed.

[0014] However, heating furnaces used to heat objects such as steel generally feature an opening and closing door for loading and unloading the objects. In this case, the pressure distribution within the furnace changes when the door is closed and open, and this change in pressure distribution alters the flow direction of the combustion gas within the furnace. Consequently, applying the technology disclosed in Patent Document 1 presents a problem in that the effect of reducing nitrogen oxides with ammonia cannot be fully achieved due to this change in the flow direction of the combustion gas.

[0015] Furthermore, the amount of ammonia injected downstream of the combustion gas flow is only small enough to reduce the nitrogen oxides generated in the combustion device, making it difficult to evenly mix the combustion gas and ammonia. Consequently, the nitrogen oxides generated in the combustion device may not be effectively reduced.

[0016] Patent Document 2 presupposes a two-stage combustion system comprising a burner that burns fossil fuel and ammonia as fuel, and an additional air supply unit located downstream of the burner in the direction of combustion gas flow. In this case, the system also targets combustion systems with a fixed combustion gas flow direction.

[0017] However, if the technology disclosed in Patent Document 2 is applied to a heating furnace, the position of the reducing atmosphere zone changes due to a change in the flow direction of the combustion gas. Therefore, there is a problem that the residence time of the ammonia fuel in the reducing atmosphere zone cannot be sufficiently ensured, making it difficult to reduce nitrogen oxides.

[0018] The present invention has been made to solve the above-mentioned problems, and its object is to provide a method for operating a heating furnace and a heating furnace that can reduce nitrogen oxide emissions outside the heating furnace while using ammonia, which can suppress carbon dioxide emissions, as a combustion fuel for the heating furnace.

[0019] The operating method of the heating furnace of the present invention that effectively solves the above-mentioned problems is configured as follows.

[0020] [1] A method for operating a heating furnace, comprising: a mixed gas generation step of mixing coal gas containing carbon monoxide gas and ammonia gas, and a burner heating step of burning the obtained mixed gas as fuel gas; wherein the burner heating step releases the mixed gas in a flame region to suppress the generation of nitrogen oxides.

[0021] [2] The method for operating a heating furnace according to [1] above, wherein, in the mixed gas generating step, the volume ratio of ammonia gas to carbon monoxide gas contained in the mixed gas is 0.1 to 4.35.

[0022] [3] The method for operating a heating furnace according to [1] or [2] above, wherein, in the mixed gas generation step, the coal gas includes any one of coke oven gas, blast furnace gas, converter gas, and electric furnace gas.

[0023] [4] The method for operating a heating furnace according to [1] or [2] above, wherein, in the burner heating step, the burner heating is performed by supplying combustion air in a manner such that the air ratio relative to the theoretical air amount of the fuel gas is 0.80 to 1.20.

[0024] [5] The method for operating a heating furnace according to [3] above, wherein, in the burner heating step, the burner heating is performed by supplying combustion air in a manner such that the air ratio relative to the theoretical air amount of the fuel gas is 0.80 to 1.20.

[0025] The heating furnace of the present invention that effectively solves the above-mentioned problems is configured as follows.

[0026] [6] A heating furnace includes a burner device, wherein the burner device has: a mixing section for mixing coal gas containing carbon monoxide and ammonia to generate a mixed gas; and a burner for simultaneously releasing ammonia and carbon monoxide into a flame region using the mixed gas as fuel gas.

[0027] [7] The heating furnace according to [6] above, wherein the burner device includes a mixing ratio control unit that controls the mixing ratio of coal gas containing carbon monoxide gas and ammonia gas as fuel gas.

[0028] According to the present invention, by using a fuel gas containing ammonia, it is possible to suppress the emission of carbon dioxide and the emission of nitrogen oxides outside the furnace. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a diagram schematically showing the structure of a heating furnace.

[0030] Figure 2 It means from Figure 1 A structural diagram of the configuration of the burner equipment in the heating furnace, viewed from the front in the direction of steel movement.

[0031] Figure 3 This is a structural diagram of an example of burner equipment that supplies a mixed gas of coal gas and ammonia as fuel gas.

[0032] Figure 4 This is a structural diagram of an example of a two-stage air combustion burner type burner equipment that supplies a mixed gas of coal gas and ammonia as fuel gas.

[0033] Figure 5 This is a structural diagram of an example of a two-stage fuel combustion burner type burner equipment that supplies a mixed gas of coal gas and ammonia as fuel gas. DETAILED DESCRIPTION

[0034] Hereinafter, the heating furnace of this embodiment will be described.

[0035] <Heating furnace>

[0036] The heating furnace according to an embodiment of the present invention is equipped with a burner that burns fuel gas as a heat source. The heated object is placed inside and heated to a predetermined temperature. The heated object is primarily metal, and can be either ferrous or non-ferrous. The heating temperature of the heated object is 500-1400°C.

[0037] Figure 1 、 2 This shows an example of a heating furnace for steel. For example, a heating furnace used in a hot rolling line for steel is used to heat a cast slab to a predetermined temperature (approximately 1100 to 1300°C).

[0038] Figure 1The heating furnace 1 shown is provided with a loading section 25 for loading (carrying in) the steel material S (slab) to be heated, and a carrying-out section 26 for carrying out (taking out) the heated steel material S. For example, the steel material S manufactured in the continuous casting line is transported to the stockyard on the loading side of the heating furnace, and is loaded into the heating furnace 1 from the loading section 25 according to the production schedule of the hot rolling line, etc. The interior of the heating furnace 1 is divided into a plurality of belt areas, and most of the time it is composed of a heating belt on the upstream side divided into 2 to 8 belt areas and 1 to 3 soaking belts. The interior of the heating furnace 1 is generally provided with a fixed slide rail 28 for loading the steel material S and a movable slide rail 27 for conveying the steel material S. A heating furnace provided with a fixed slide rail 28 and a movable slide rail 27 is called a walking beam type continuous heating furnace.

[0039] During operation of the heating furnace, each zone within the heating furnace is controlled to a different atmospheric temperature, and the average temperature of the steel material S loaded into the heating furnace 1 gradually rises. As a result, the steel material S is controlled to a predetermined target heating temperature (the target temperature of the slab when it is removed from the heating furnace).

[0040] Then, the steel material S reaching the predetermined target temperature passes through the unloading section 26 and is supplied to hot rolling.

[0041] Inside the heating furnace 1, a plurality of burners are provided along the conveying direction of the steel S (steel moving direction 100). The burners are arranged to heat up the interior of the heating furnace by combustion. If the burners are used to heat up the interior of the heating furnace, the temperature of the steel rises due to radiation from the furnace wall of the heating furnace. In addition, sometimes a flow of atmospheric gas is generated inside the heating furnace, and the temperature of the steel rises by convection. In addition, the temperature of the steel can also be raised by the flame of the burner directly contacting the steel. In short, the burner heats up the interior of the heating furnace by burning the fuel gas serving as a heat source for heating, thereby raising the temperature of the heated material inside the heating furnace.

[0042] During operation of the heating furnace 1, the retractable doors (doors) of the loading section 25 and unloading section 26 are closed, generating a pressure higher than atmospheric pressure inside the furnace. However, during loading and unloading of steel materials S, the doors are temporarily opened. When the doors are open, a pressure difference occurs between the pressure inside the furnace and the area near the doors, causing the combustion gases inside the furnace to flow from higher pressure areas to lower pressure areas. Since steel materials S are constantly being loaded and unloaded, the flow direction of the combustion gases inside the furnace also changes depending on the movement of the doors.

[0043] On the other hand, in combustion devices such as boilers that do not require the heated object to be loaded and unloaded, the flow direction of the combustion gas is fixed, so it is believed that the methods described in Patent Documents 1 and 2 can be applied. However, in the case of heating furnaces that heat the heated object by loading it inside, the application of such conventional techniques is difficult because doors are opened and closed for loading and unloading the heated object.

[0044] Figure 2 This figure shows a cross-section of the heating furnace 1. Typically, burners B are located within the heating furnace 1, one on the upper surface side and one on the lower surface side of the steel material S, to minimize temperature differences between the upper and lower surfaces of the steel material S. Furthermore, burners are often located on both sides of the steel material S in the conveying direction to minimize temperature differences between the leading end S1 and the trailing end S2 of the steel material S.

[0045] Burner equipment

[0046] The heating furnace of this embodiment includes a burner system comprising a mixing unit that mixes coal gas containing carbon monoxide with ammonia to produce a mixed gas, and a burner that generates a flame using the mixed gas as fuel and air as an oxidant. At least one of the burners disposed in the heating furnace 1 is the burner system described below.

[0047] Figure 3 This is a schematic diagram illustrating the configuration of the burner equipment used in this embodiment. The burner equipment 2 includes a burner nozzle 3 that emits flames within a heating furnace, a fuel gas supply system 8 that supplies fuel gas to the burner nozzle 3, and a combustion air supply system 9 that supplies combustion air to the burner nozzle 3.

[0048] The fuel gas supply system 8 supplies a mixed gas 7, which is obtained by mixing coal gas 4 supplied from a coal gas supply unit 10 and ammonia gas 5 supplied from an ammonia gas supply unit 11 in a mixing unit 6. The mixed gas 7 is used as fuel gas in the burner device 2. The combustion air supply system 9 is connected to the combustion air supply unit and supplies combustion air 12. A combustible mixture of fuel gas and combustion air is formed inside the burner nozzle 3, and a flame is emitted from the tip of the burner nozzle 3 into the heating furnace.

[0049] The mixing section 6 is where the coal gas 4 supply pipe and the ammonia 5 supply pipe merge. The coal gas 4 and ammonia 5 are supplied from their respective supply pipes and merge, allowing them to mix without a special stirring mechanism. Therefore, the mixing section 6 only needs to be a fixed space where these supply pipes intersect.

[0050] However, the mixing unit 6 may include a static mixer such as a static mixer or a dynamic mixer having a stirring function. This is preferable in that a mixed gas in which the coal gas and the ammonia gas are more uniformly mixed is obtained.

[0051] The burner device 2 may include a gas flow rate regulating valve 20 for regulating the flow rate of the gas 4 supplied from the gas supply unit 10 to the mixing unit 6 , and a gas flow meter 22 for measuring the flow rate of the gas 4 .

[0052] The burner device 2 may also include an ammonia flow rate regulating valve 21 for regulating the flow rate of the ammonia gas 5 supplied from the ammonia supply unit 11 to the mixing unit 6 , and an ammonia flow meter 23 for measuring the flow rate of the ammonia gas 5 .

[0053] By doing so, the mixing ratio of ammonia gas 5 to coal gas 4 in the mixed gas 7 serving as the fuel gas can be adjusted. If the mixing ratio of ammonia gas 5 contained in the mixed gas 7 is increased, the effect of reducing carbon dioxide emissions emitted from the heating furnace 1 is greater than when only coal gas 4 is used as the fuel gas.

[0054] On the other hand, ammonia is a flame-retardant fuel that is more difficult to ignite and burns more slowly than typical fuel gases. Therefore, if the ammonia ratio in the mixed gas increases, combustion in the burner may become unstable. By adjusting the ratio of ammonia 5 to coal gas 4 in the mixed gas 7, carbon dioxide emissions can be reduced and burner heating stability can be ensured.

[0055] The burner preferably includes a mixing ratio control unit that controls the mixing ratio of ammonia gas to coal gas in the mixed gas. The mixing ratio control unit 13 controls the mixing ratio of ammonia gas 5 to coal gas 4 in the mixed gas 7 by varying the openings of the coal gas flow control valve 20 and the ammonia flow control valve 21.

[0056] Thereby, it is possible to simultaneously achieve reduction in carbon dioxide emissions from the heating furnace and stability in burner heating.

[0057] The combustion air 12 supplied to the burner device 2 through the combustion air supply system 9 may use air collected from the atmosphere.

[0058] However, air modified by removing nitrogen from the air or adding pure oxygen can be used as the combustion air 12. By increasing the oxygen content of the combustion air, the oxidation reaction of the fuel gas can be promoted, and the flow rate of the combustion air supplied from the combustion air supply system 9 can be reduced, thereby reducing the power consumption of the pump and the like.

[0059] Furthermore, by reducing the oxygen content of the combustion air, the atmosphere inside the heating furnace can be made a reducing atmosphere, thereby promoting the reduction of nitrogen oxides.

[0060] The burner used in the burner device 2 can be of any type, as long as it uses a mixture of coal gas containing carbon monoxide and ammonia as fuel gas, forming a combustible mixture of the fuel gas and combustion air to emit a flame. This is because as long as the coal gas and ammonia are injected simultaneously into approximately the same area, the carbon monoxide can be used to reduce the nitrogen oxides generated by the combustion of the ammonia.

[0061] Other burner equipment

[0062] Figure 4 and Figure 5 are examples of other burner structures.

[0063] Figure 4 The burner device 2 shown is called a two-stage air combustion burner, and is composed of a main nozzle and a sub-nozzle. The above-mentioned main nozzle uses combustion air 12 supplied from the combustion air supply system 9 to generate flames, and the above-mentioned sub-nozzle is arranged around the main nozzle and uses secondary air 92 supplied from the secondary air supply system 91 to assist the combustion of the flame ejected from the main nozzle.

[0064] By injecting air (secondary air 92) into the furnace from the secondary nozzles, the temperature distribution of the flame injected from the main nozzles can be made uniform. If the flame injected from the main nozzles experiences a localized temperature rise, the formation of nitrogen oxides will be promoted in the high-temperature area. Therefore, the use of secondary nozzles can suppress the formation of nitrogen oxides. When using a two-stage air combustion burner, the coal gas and ammonia injected from the main nozzles are injected simultaneously into approximately the same range. Therefore, the nitrogen oxides generated by the combustion of the ammonia are reduced by carbon monoxide.

[0065] In addition, the secondary air injected from the sub-nozzle can be used to promote the reduction reaction of nitrogen oxides.

[0066] It should be explained that Figure 4 The tip of the main nozzle of the two-stage air combustion burner shown is positioned further back than the furnace wall. This ensures that the flame emitted from the main nozzle maintains the combustion time of the primary air supplied from the combustion air supply system 9 and promotes the reduction reaction of nitrogen oxides using carbon monoxide. Furthermore, the secondary air injected from the sub-nozzle promotes a uniform reduction reaction.

[0067] Figure 5The burner device 2 shown is called a two-stage fuel combustion burner. It is an example of a configuration in which combustion air 12 is injected from the center of a main nozzle, and a mixed gas of coal gas 4 containing carbon monoxide and ammonia 5 is injected from its outer periphery as fuel gas. A two-stage fuel combustion burner can also be configured so that auxiliary fuel 82 is supplied separately from the mixed gas 7 supplied from a fuel gas supply system 8, from an auxiliary fuel supply system 81 located in auxiliary nozzles surrounding the main nozzle. Ammonia can sometimes have low combustion stability, and this can assist the combustion of the fuel gas injected from the main nozzle and improve combustion stability. The auxiliary fuel used in this case can be hydrogen, methane, natural gas, biogas, propane, or the like.

[0068] Ammonia

[0069] Ammonia is a colorless gas represented by the chemical formula NH 3 at room temperature. Ammonia 5 , which is a fuel gas used for burner heating, is supplied to the mixing unit 6 through an ammonia supply unit 11 .

[0070] The ammonia gas supply unit 11 is connected to an ammonia tank that temporarily stores ammonia, and supplies the ammonia gas 5 to the burner equipment 2 by a pressure-increasing means such as a pump connected to the ammonia tank.

[0071] The ammonia tank preferably stores liquid ammonia in a liquefied state. Ammonia can be liquefied even at room temperature by applying a pressure of approximately 8 atmospheres. Liquid ammonia is easily transported and stored. When storing liquid ammonia in the ammonia tank, it is forcibly vaporized by heat exchange with externally supplied heat and then delivered to the ammonia gas supply unit 11.

[0072] gas

[0073] The coal gas used in the embodiments of the present invention contains carbon monoxide gas. Coal gas refers to gas obtained from coal. Gas obtained from coal often contains carbon monoxide gas generated by incomplete combustion of coal.

[0074] Carbon monoxide acts as a gas that reduces nitrogen oxides (reducing gas), and thus can reduce nitrogen oxides generated by the combustion of a mixed gas containing ammonia. That is, since ammonia contains nitrogen, it easily generates fuel NOx, which is nitrogen oxide, during combustion.

[0075] However, by mixing carbon monoxide gas with the fuel gas, nitrogen oxides contained in the exhaust gas after combustion are reduced to nitrogen by the carbon monoxide, thereby reducing the amount of nitrogen oxides emitted from the heating furnace.

[0076] The methods described in Patent Documents 1 and 2 use ammonia as a reducing agent for reducing nitrogen oxides. The method aims to reduce nitrogen oxide emissions by self-reduction, in which nitrogen oxides generated by combustion of ammonia are reduced by ammonia.

[0077] That is, it goes through two basic processes: a step of burning ammonia as fuel to generate nitrogen oxides and a step of reducing the generated nitrogen oxides with ammonia.

[0078] In this case, if unburned ammonia does not remain in the combustion gas after the ammonia is burned, the reduction reaction will not proceed. Therefore, the technology of Patent Document 1 supplies ammonia at a location separate from the combustion device. On the other hand, the technology of Patent Document 2 reduces nitrogen oxides by ensuring a fixed space called a reducing atmosphere zone within the furnace after nitrogen oxides are generated by heating with a burner.

[0079] Thus, the methods described in Patent Documents 1 and 2 require two basic steps to reduce nitrogen oxides. Consequently, they require the installation of an ammonia supply mechanism and a reducing atmosphere zone at locations separate from the burner heating. Consequently, effective nitrogen oxide reduction cannot be achieved unless the flow direction of the combustion gas within the furnace is constant.

[0080] In the present embodiment, carbon monoxide gas is used as the reducing gas for reducing nitrogen oxides, and a fuel gas in which ammonia gas and carbon monoxide are mixed in advance is injected from a burner and combusted.

[0081] Specifically, ammonia and carbon monoxide injected from the burner are injected simultaneously into approximately the same area within the heating furnace, thereby suppressing the generation of nitrogen oxides. This is believed to be because nitrogen oxides generated by the combustion of ammonia are reduced by carbon monoxide almost simultaneously with their generation. Consequently, even if the flow direction of the combustion gas within the heating furnace fluctuates, nitrogen oxides generated by the combustion of ammonia are reliably reduced, reducing nitrogen oxide emissions from the heating furnace.

[0082] In this case, the atmospheric temperature in the range where the ammonia gas and carbon monoxide are injected from the burner is preferably 500 to 1450° C. This is because the reduction reaction of nitrogen oxides by carbon monoxide can be promoted, and the generation of nitrogen oxides can be suppressed.

[0083] The volume ratio of ammonia gas to carbon monoxide gas in the mixed gas is preferably 0.1 to 4.35, more preferably 0.50 to 3.00. This is because if the volume ratio of ammonia gas to carbon monoxide gas exceeds 4.35, the effect of reducing nitrogen oxides generated by the combustion of ammonia gas by carbon monoxide decreases.

[0084] On the other hand, if the volume ratio of ammonia gas to carbon monoxide gas is low, nitrogen oxide reduction cannot be fully achieved, and the effect of using ammonia to suppress carbon dioxide emissions from the heating furnace becomes insufficient. Therefore, the volume ratio of ammonia gas to carbon monoxide gas is set to 0.1 or more.

[0085] It should be noted that the reduction of nitrogen oxides by carbon monoxide oxidizes carbon monoxide into carbon dioxide, but the concentration of the generated carbon dioxide is approximately 20 to 5000 ppm. Therefore, compared with the effect of using ammonia as fuel gas to suppress carbon dioxide emissions from the heating furnace, the amount of carbon dioxide generated is negligible.

[0086] The coal gas 4 preferably contains any of coke oven gas, blast furnace gas, converter gas, and electric furnace gas. These are by-product gases generated in upstream processes of steel mills. As coal gas containing carbon monoxide, it has the function of reducing nitrogen oxides and the effect of stabilizing the combustion of ammonia.

[0087] Blast furnace gas is a byproduct gas produced when iron ore is reduced in a blast furnace to produce pig iron. Coke oven gas is a byproduct gas generated by the high-temperature dry distillation of coal to produce coke. Converter gas is a byproduct gas produced during the steelmaking process in a converter. Electric furnace gas is a byproduct gas generated by the incomplete combustion of auxiliary fuel (carburizing material) used in electric furnaces.

[0088] The by-product gas has various component compositions depending on the process in which it is generated.

[0089] For example, a typical composition of blast furnace gas is 21-30% by volume of carbon monoxide (combustible component), 50-60% by volume of nitrogen (non-combustible component), and 10-22% by volume of carbon dioxide. The ignition point of blast furnace gas is 630-650°C, and when mixed with air, the combustion range is 27-75% by volume. A typical example of the low calorific value of blast furnace gas is 3.45 MJ / Nm 3 about.

[0090] The typical composition of coke oven gas is 46-60% by volume of hydrogen, 20-35% by volume of methane, 5-10% by volume of carbon monoxide, and 2-4% by volume of hydrocarbons such as ethylene. The typical low calorific value of coke oven gas is 18.0 MJ / Nm 3 about.

[0091] The converter gas contains about 75% carbon monoxide by volume, about 13% carbon dioxide by volume, and trace amounts of oxygen, nitrogen, and hydrogen. A typical example of the low calorific value of converter gas is 8.2 MJ / Nm 3 about.

[0092] The typical composition of electric furnace gas is about 10% by volume of carbon monoxide, about 22% by volume of carbon dioxide, about 5% by volume of oxygen, and about 56% by volume of nitrogen. The low calorific value of electric furnace gas is 2.8MJ / Nm 3 about.

[0093] The coal gas 4 may be a mixture of blast furnace gas, coke oven gas, and converter gas (sometimes referred to as M gas). This is because mixing coal gases with different calorific values ​​can supply the heat required to heat the object to be heated, allowing for stable operation of the heating furnace.

[0094] Furthermore, by removing nitrogen and carbon dioxide from the by-product gas in advance, the total amount of fuel gas can be reduced, improving energy conversion efficiency. This reduces the power required by the gas supply unit 10 and contributes to energy conservation.

[0095] Furthermore, by removing carbon dioxide contained in the by-product gas in advance, the amount of carbon dioxide emitted from the heating furnace can be further reduced.

[0096] In addition to the mixed gas 7 of the coal gas 4 containing carbon monoxide gas and the ammonia gas 5, other gaseous fuels may be added to the fuel gas.

[0097] Examples of other gaseous fuels include hydrogen, methane gas, natural gas, biogas, and propane gas. This allows the low calorific value of the fuel gas to be adjusted, further reducing the amount of carbon dioxide emitted from the heating furnace.

[0098] When hydrogen is used as another gaseous fuel, the volume ratio of hydrogen contained in the fuel gas to the ammonia gas 5 is preferably less than 1.78, and more preferably less than 0.81.

[0099] When methane gas is used as another gaseous fuel, the volume ratio of methane gas to ammonia gas 5 in the fuel gas is preferably less than 0.87, and more preferably less than 0.35. This is because hydrogen and methane gases have a higher combustion rate than ammonia, so the combustion (oxidation) reaction of carbon monoxide contained in the mixed gas proceeds first, and sometimes there is no carbon monoxide remaining to reduce the nitrogen oxides generated by the combustion of ammonia.

[0100] <How to operate a heating furnace>

[0101] Next, a method for operating the heating furnace of this embodiment will be described.

[0102] Specifically, the invention relates to a method for operating a heating furnace having a mixed gas generating step of mixing coal gas containing carbon monoxide gas with ammonia gas and a burner heating step of burning the obtained mixed gas as fuel gas, and wherein the mixed gas is released into the flame area during the burner heating step to suppress the generation of nitrogen oxides.

[0103] The heating furnace is operated by using a mixed gas of coal gas containing carbon monoxide and ammonia as the fuel gas, as described above, for burner heating. In this case, burner heating is preferably performed such that the volume ratio of ammonia to carbon monoxide in the mixed gas is 0.1 to 4.35. The coal gas containing carbon monoxide can be any of coke oven gas, blast furnace gas, converter gas, and electric furnace gas.

[0104] Specifically, if Figure 1 As shown, when a heating furnace is equipped with multiple burners, it is not necessary to use all burners for heating using a mixture of coal gas containing carbon monoxide and ammonia as the fuel gas. At least one burner can be used for heating using a mixture of coal gas containing carbon monoxide and ammonia as the fuel gas. This is because the amount of carbon dioxide emitted from the heating furnace is reduced compared to conventional heating furnaces in which all burners use coal gas as the fuel gas.

[0105] Burner heating is preferably performed by supplying combustion air at an air ratio of 0.80 to 1.20 relative to the theoretical air volume of the fuel gas. An air ratio less than 0.80 results in incomplete combustion of ammonia, leaving unburned ammonia in the exhaust gas heated by the burner. This can lead to excessive ammonia concentrations in the exhaust gas. An air ratio exceeding 1.20 promotes the oxidation of ammonia, raising the flame temperature and significantly increasing the production of nitrogen oxides. Consequently, there can be a shortage of carbon monoxide, which is used as a reducing agent.

[0106] The air ratio relative to the theoretical air volume of the fuel gas can be adjusted by adjusting the openings of the gas flow control valve 20 and the ammonia flow control valve 21 of the burner device 2, thereby adjusting the flow rate ratio of the combustion air supplied from the combustion air supply system 9. Alternatively, the air ratio can be adjusted by providing a combustion air flow control valve in the combustion air supply system 9 to adjust the flow rate of the combustion air.

[0107] In addition to the burners described above, the present invention may also employ vortex burners that agitate the fuel gas injected from the burner tip, or tubular flame burners that inject fuel gas and combustion air tangentially into the combustion chamber, creating a swirling flow within the combustion chamber for combustion. By injecting coal gas and ammonia simultaneously into approximately the same area, nitrogen oxides generated by the combustion of ammonia can be reduced by carbon monoxide.

[0108] Example

[0109] Hereinafter, the effects of the present embodiment will be described in detail based on examples, but the present invention is not limited to these examples.

[0110] As an embodiment of the present invention, the following describes an example of a heating furnace in a hot rolling line for steel. Figure 1 The walking beam continuous heating furnace shown here is designed for heating steel materials, which are loaded into the furnace from a loading station, heated to a target temperature of 1200°C, and then unloaded from a discharge station to a hot rolling line. The average dimensions of the steel materials heated in the furnace are 220 mm thick, 1800 mm wide, and 8 m long, with an average weight of 24 tons.

[0111] The coal gas used in this example is M gas (mixed gas) obtained by mixing coke oven gas, blast furnace gas, and converter gas, which are by-product gases produced in steel mills. Table 1 shows the composition of the M gas used in this example. As can be seen from Table 1, the M gas used in this example contains 23.9% by volume of carbon monoxide.

[0112] In this embodiment, the Figure 3 The burner device shown. For the mixing section, M gas is supplied from the gas supply section, and ammonia gas obtained by vaporizing liquid ammonia is supplied from the ammonia supply section. The volume ratio of ammonia gas contained in the mixed gas to carbon monoxide gas is changed by adjusting the opening of the gas flow regulating valve and the ammonia flow regulating valve. In addition, with respect to the flow rate of the mixed gas, the flow rate of the mixed gas supplied to the fuel gas supply system is adjusted while maintaining the opening ratio of the gas flow regulating valve and the ammonia flow regulating valve, so that the efficiency of the heating furnace meets the above-mentioned operating conditions. On the other hand, the air ratio relative to the theoretical air amount of the fuel gas is adjusted in the range of 0.75 to 1.25 by changing the combustion air flow regulating valve provided in the combustion air supply system.

[0113] Furthermore, in this embodiment, pressure gauges for measuring pressure are placed along the direction of conveyance of the steel within the heating furnace. Furthermore, gas detectors for measuring the concentrations of nitrogen oxides (NOx) and unburned ammonia (NH3) are placed outside the loading and unloading sides of the heating furnace.

[0114] In contrast, as a comparative example of the present invention, the fuel gas was made to contain no ammonia and only M gas was used as the fuel gas, and the heating furnace was operated so as to achieve the same degree of heating furnace efficiency as described above.

[0115] In the examples and comparative examples, during the operation of the heating furnace, the concentration of nitrogen oxides discharged to the outside of the heating furnace was measured using a NOx concentration meter installed in the flue of the heating furnace. It should be noted that the reference value (reference concentration) of the nitrogen oxide concentration measured by the NOx concentration meter installed in the flue is based on 320 ppm. If the discharge concentration does not exceed this value, it is qualified. It should be noted that the heating furnace used in the embodiment is equipped with a denitrification device for exhaust gas on the downstream side of the flue. If the nitrogen oxide concentration of the exhaust gas passing through the flue is 350 ppm or less, the nitrogen oxides in the exhaust gas discharged from the heating furnace can be sufficiently reduced. However, from the perspective of reducing the treatment of the denitrification equipment, it is preferred to set the reference value of the nitrogen oxide concentration of the exhaust gas in the flue to 160 ppm, which is a stricter reference.

[0116] Meanwhile, during operation of the heating furnace, exhaust gas discharged from the heating furnace was sampled and the carbon dioxide concentration contained in the exhaust gas was measured. The carbon dioxide concentration ratio (CO2 emission ratio) in the example was calculated using the comparative example (a fuel gas without ammonia) as the reference (1.0).

[0117] Table 2 shows the results of the inventive examples and comparative examples. The "heat ratio" in the table indicates the ratio of the heat content, calculated by multiplying the flow rate of the M gas or ammonia gas supplied as the fuel gas by its lower heating value, to the total heat content of the fuel gas. In other words, it indicates the contribution of the M gas or ammonia gas to the heat generated by burner combustion.

[0118] In the inventive example (Manufacture No. 2), the calorific value ratio of ammonia to fuel gas was set at 4.3%. Due to the lower calorific value of ammonia, the effect on reducing carbon dioxide emissions was smaller than in the comparative example (Manufacture No. 1). However, compared to the comparative example (Manufacture No. 1), which operated the heating furnace using only M gas as fuel gas, the concentration of nitrogen oxide emissions was reduced. This is believed to be due to the reduction of nitrogen oxides in the combustion gas through the combustion of M gas containing carbon monoxide and ammonia.

[0119] Inventive Examples (Production Nos. 2-8) set the air ratio relative to the theoretical air volume of the fuel gas at 0.95, while increasing the ammonia mixing ratio. While increasing the ammonia mixing ratio in the mixed gas reduces carbon dioxide emissions from the heating furnace, the nitrogen oxide concentration also increases. While Inventive Example (Production No. 7) achieved the stricter flue gas threshold of 160 ppm or less, when the ammonia calorific value reaches 68%, as in Inventive Example (Production No. 8), the nitrogen oxide concentration exceeds the stricter threshold.

[0120] However, even under the conditions of the invention example (Manufacture No. 8), the nitrogen oxide concentration was suppressed to a reference value of 320 ppm or less during normal operation.

[0121] The inventive examples (Production Nos. 9-11) show the results obtained by maintaining the heat ratio of ammonia at a fixed value while varying the air ratio of the fuel gas. When the heat ratio of ammonia is 35%, reducing the air ratio to 0.8 not only reduces nitrogen oxides due to carbon monoxide but also suppresses the formation of nitrogen oxides. This significantly reduces carbon dioxide emissions and suppresses nitrogen oxide emissions compared to the comparative example (Production No. 1).

[0122] However, when the air ratio is reduced to a value lower than 0.8, unburned ammonia remains in the exhaust gas. Therefore, the nitrogen oxide concentration cannot be measured under the condition that the air ratio is lower than 0.8.

[0123] On the other hand, as in the inventive examples (Manufacture Nos. 10 and 11), when the air ratio to the fuel gas is increased, if the air ratio exceeds 1.0, the exhaust concentration of nitrogen oxides increases. In the inventive example (Manufacture No. 10), which set the air ratio to 1.2, the more stringent reference value of 160 ppm in the flue is met. In the inventive example (Manufacture No. 11), which increased the air ratio to 1.25, the nitrogen oxide concentration remained below the reference value of 320 ppm during normal operation, but did not meet the more stringent reference value.

[0124] As can be seen from the above, according to this embodiment, by using coal gas containing carbon monoxide and ammonia gas as fuel gases for burner heating at the same time, it is possible to reduce carbon dioxide emissions and suppress nitrogen oxide emissions outside the furnace.

[0125] [Table 1]

[0126]

[0127] [Table 2]

[0128]

[0129] Explanation of symbols

[0130] S steel

[0131] S1 Steel Front

[0132] S2 Steel end

[0133] B Burner

[0134] 1 Heating furnace

[0135] 2 Burner equipment

[0136] 20 Gas flow regulating valve

[0137] 21 Ammonia flow control valve

[0138] 22 Gas flow meter

[0139] 23 Ammonia flow meter

[0140] 3 Burner nozzles

[0141] 31 Furnace Wall

[0142] 32 Furnace

[0143] 33 Cross-sectional shape of burner nozzle

[0144] 4 Gas

[0145] 5 Ammonia

[0146] 6 Mixing section

[0147] 7 Mixed gases

[0148] 8 Fuel gas supply system

[0149] 81 Auxiliary fuel supply system

[0150] 82 Auxiliary fuel, secondary fuel

[0151] 9 Combustion air supply system

[0152] 91 Secondary air supply system

[0153] 92 Secondary Air

[0154] 10 Gas Supply Department

[0155] 11 Ammonia supply unit

[0156] 12 Combustion air

[0157] 13 Mixing ratio control unit

[0158] 24 NOx concentration meter

[0159] 25 Loading Department

[0160] 26 Moving out department

[0161] 27 Mobile rails

[0162] 28 fixed rails

[0163] 29 Flue

[0164] 100 Steel moving direction

Claims

1. A method for operating a heating furnace, comprising: The mixed gas generation process is to mix the coal gas containing carbon monoxide gas with ammonia gas, and The burner heating process burns the obtained mixed gas as fuel gas; The burner heating step releases the mixed gas into the flame region to suppress the generation of nitrogen oxides.

2. The method for operating a heating furnace according to claim 1, wherein: In the mixed gas generating step, a volume ratio of ammonia gas to carbon monoxide gas contained in the mixed gas is 0.1 to 4.

35.

3. The method for operating a heating furnace according to claim 1 or 2, wherein: In the mixed gas generating step, the coal gas includes any one of coke oven gas, blast furnace gas, converter gas, and electric furnace gas.

4. The method for operating a heating furnace according to claim 1 or 2, wherein: In the burner heating step, the burner heating is performed by supplying combustion air so that the air ratio relative to the theoretical air amount of the fuel gas becomes 0.80 to 1.

20.

5. The method for operating a heating furnace according to claim 3, wherein: In the burner heating step, the burner heating is performed by supplying combustion air so that the air ratio relative to the theoretical air amount of the fuel gas becomes 0.80 to 1.

20.

6. A heating furnace comprising a burner device, The burner device has: A mixing section that mixes the coal gas containing carbon monoxide with ammonia to generate a mixed gas, and The burner uses the mixed gas as fuel gas and releases ammonia and carbon monoxide into the flame area at the same time.

7. The heating furnace according to claim 6, wherein: The burner device includes a mixing ratio control unit that controls a mixing ratio of coal gas containing carbon monoxide gas and ammonia gas as fuel gas.

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