heating furnace

Abstract

To provide a heating furnace that uses ammonia as a fuel gas and can ensure good heating and flame stability. [Solution] A heating furnace having a burner that heats an object to be heated by burning a fuel gas with an oxidizing gas, wherein the fuel gas contains ammonia and the oxidizing gas has an oxygen concentration of 90% or more.

Description

[Technical Field]

[0001] This invention relates to a heating furnace. [Background technology]

[0002] A burner is known that heats an object to be heated by burning a fuel gas with an oxidizing gas (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 4261753 [Overview of the project] [Problems that the invention aims to solve]

[0004] In heating furnaces that heat objects using burners as described above, fossil fuels are generally used as fuel gas. However, since this results in a large amount of CO2 as a greenhouse gas in the exhaust gas, the use of ammonia has been proposed in recent years.

[0005] Ammonia has the advantage of not producing CO2 when burned, but on the other hand, because it does not contain carbon, the radiation intensity of the flame is low, and the flame is unstable due to the slow combustion rate.

[0006] Therefore, the object of the present invention is to provide a heating furnace that uses ammonia as a fuel gas and can ensure good heating and flame stability. [Means for solving the problem]

[0007] One embodiment of the present invention is as follows:

[0008] [1] It has a burner that heats an object to be heated by burning a fuel gas with an oxidizing gas, The aforementioned fuel gas contains ammonia. The oxidizing gas is a heating furnace with an oxygen concentration of 90% or higher.

[0009] [2] The furnace side wall has a burner on which the burner is installed, The heating furnace according to [1], wherein the burner has a fuel injection port, a first oxidizer injection port surrounding the fuel injection port, and a second oxidizer injection port located radially outward of the first oxidizer injection port without surrounding the first oxidizer injection port.

[0010] [3] The heating furnace according to [2], wherein the ejection direction of the second oxidizing agent ejection hole is inclined radially outward from the first oxidizing agent ejection hole toward the ejection direction of the first oxidizing agent ejection hole.

[0011] [4] The ejection direction of the second oxidizing agent ejection hole is inclined radially outward from the first oxidizing agent ejection hole toward the ejection direction of the first oxidizing agent ejection hole by an inclination angle θ. α [°] is 0≦θ α A heating furnace as described in [3], wherein the number of heating elements is ≤ 15.

[0012] [5] When the surface of the object to be heated that is melted by the burner is referred to as the upper surface, the heating furnace according to any one of items [2] to [5], wherein the second oxidizing agent ejection hole is located below the first oxidizing agent ejection hole.

[0013] [6] The furnace side wall has a burner on which the burner is installed, When the surface of the object to be heated that is melted by the burner is referred to as the top surface, the height H [m] from the top surface of the object to be heated to the center of the fuel injection hole, the distance L [m] between the furnace side wall and the opposite furnace side wall facing the furnace side wall in the left-right direction when viewed in the front-rear direction perpendicular to the plane containing the injection axis of the fuel injection hole along the vertical direction, and the inclination angle θ when viewed in the front-rear direction such that the injection axis of the fuel injection hole is tilted downward in the injection direction relative to the top surface of the object to be heated. β [°] means that 0.1 ≤ H ≤ 2 and H / L ≤ tanθβ The heating furnace according to any one of [2] to [5], which satisfies ≦ 2H / L.

[0014] [7] The heating furnace according to any one of [1] to [6], wherein the burner is embedded in the furnace side wall.

Advantages of the Invention

[0015] According to the present invention, it is possible to provide a heating furnace that uses ammonia in fuel gas and can ensure good heating and flame stability.

Brief Description of the Drawings

[0016] [Figure 1] It is a cross-sectional view showing a heating furnace according to an embodiment of the present invention. [Figure 2] It is a cross-sectional view of the burner shown in FIG. 1. [Figure 3] It is an external view when viewed in the direction of arrow A in FIG. 2. [Figure 4] It is an external view showing a modified example of the burner shown in FIG. 3. [Figure 5] It is a graph showing the relationship between the oxygen concentration of the oxidant gas and the adiabatic theoretical flame temperature. [Figure 6] It is a graph showing the relationship between the oxygen concentration of the oxidant gas and the combustion rate. [Figure 7] It is a graph showing the relationship between the oxygen concentration of the oxidant gas and the heat transfer coefficient ratio.

Modes for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention will be exemplarily described with reference to the drawings.

[0018] [[ID=5l]] As shown in FIG. 1, in one embodiment of the present invention, a heating furnace 1 has a burner 3 that heats a workpiece 2 by burning fuel gas with an oxidant gas. The fuel gas contains ammonia, and the oxidant gas has an oxygen concentration of 90% or more.

[0019] The fuel gas is not particularly limited as long as it contains ammonia, but it is preferable that it contains ammonia as its main component (i.e., the ammonia component is greater than 50% but less than or equal to 100%). The oxidizer gas is not particularly limited as long as it has an oxygen concentration of 90% or more, but it is preferable to use oxygen-enriched air and configure the oxidizer gas so that the oxygen concentration in the oxidizer gas is 90% or more.

[0020] The heating furnace 1 heats the object to be heated 2 by radiant heat transfer from the flame produced by burning fuel gas in the burner 3, and by convective heat transfer from the flow of combustion gases generated by the combustion, and melts it as needed. The object to be heated 2 is not particularly limited and may be, for example, a metal such as aluminum or glass.

[0021] The radiant intensity and flame stability of burner 3 are related to the flame temperature and combustion rate, which in turn are related to the oxygen concentration of the oxidizer gas. Figure 5 shows the relationship between the oxygen concentration of the oxidizer gas and the adiabatic theoretical flame temperature of ammonia, and Figure 6 shows the relationship between the oxygen concentration of the oxidizer gas and the combustion rate of ammonia. As can be seen from Figures 5 and 6, increasing the oxygen concentration to over 90% can nearly maximize the flame temperature (radiant intensity) and combustion rate (flame stability). Increasing the oxygen concentration of the oxidizer gas also leads to a higher combustion gas temperature, which is advantageous for convective heat transfer.

[0022] Figures 5 and 6 show a comparison of the relationship not only with ammonia but also with methane (CH4), a representative fossil fuel. It can be seen that ammonia has a lower flame temperature and combustion rate compared to fossil fuels (CH4), which puts it at a disadvantage.

[0023] The chemical formulas for the combustion of CH4 (methane) and NH3 (ammonia) are as follows: CH4+ 2O2+8N2→CO2+ 2H2O+ 8N2...Formula (1) CH4+ 2O2 →CO2+ 2H2O ...Equation (2) NH3 + 0.75O2 + 3N2 → 1.5H2O+3.5N2...Equation (3) NH3 + 0.75O2 → 1.5H2O + 0.5N2 ··· Equation (4) Equation (1) is the case when CH4 is burned in air. Equation (2) is the case when CH4 is burned in oxygen. Equation (3) is the case when NH3 is burned in air. Equation (4) is the case when NH3 is burned in oxygen.

[0024] The CO2 and H2O contained in the right side of each equation are known as radiative gases, and these gases contribute to the radiative performance of the flame. Comparing each equation, the concentration of each radiative gas is as shown in the following table, and it can be seen that changing the oxidizer from air to oxygen improves the radiative performance of the flame. However, in Equation (2), the CO2 concentration in the exhaust gas increases. Also, in Equation (3), the CO2 concentration is zero, and the concentration of radiative gases is higher than that in Equation (1). In Equation (4) where the oxidizer is changed from air to oxygen, the concentration of radiative gases is further improved.

Table 1

[0025] Figure 7 shows the relationship between the overall heat transfer coefficient (heat transfer coefficient) due to the flame and combustion gas and the oxygen concentration of the oxidizer gas (considering convective and radiant heat transfer). Figure 7 compares the case where CH4 is used as the fuel gas and the case where ammonia is used. In Figure 7, the heat transfer coefficient is shown as an indexed heat transfer coefficient ratio, such that the value when CH4 is used as the fuel gas and air is used as the oxidizer gas (i.e., the oxygen concentration is approximately 20%) is the baseline value of 1. Since the flow rate of the fuel gas is kept constant, as the oxygen concentration increases, the flow rate of the combustion gas decreases, the average flow velocity of the combustion gas passing through the furnace decreases, and the convective heat transfer coefficient also decreases. Therefore, although the heat transfer coefficient decreases due to the decrease in the convective heat transfer coefficient, the radiant heat transfer coefficient (gas emissivity) increases as the water vapor concentration in the combustion gas increases, so the overall heat transfer coefficient remains almost constant even if the oxygen concentration increases. Therefore, even if the oxygen concentration of the oxidizer gas is 90% or higher, it has almost no effect on the overall heat transfer coefficient. Furthermore, compared to CH4, ammonia has a higher heat transfer coefficient because the water vapor concentration in the combustion gas is higher for ammonia.

[0026] For the reasons stated above, according to this embodiment, by having an oxygen concentration of 90% or more in the oxidizing gas, it is possible to realize a heating furnace 1 that uses ammonia as the fuel gas and can ensure good heating and flame stability.

[0027] As shown in Figures 1-3, the heating furnace 1 of this embodiment has a furnace side wall 4 on which a burner 3 is placed. The burner 3 has a fuel injection hole 3a1 centered on a first central axis O, a first oxidizer injection hole 3b1 surrounding the fuel injection hole 3a1 and coaxial with the fuel injection hole 3a1, and a second oxidizer injection hole 3c1 located radially outside the first oxidizer injection hole 3b1 without surrounding it. It is preferable that the burner 3 is embedded in the furnace side wall 4, as in this embodiment. The burner 3 heats the object to be heated 2 by burning the fuel gas injected from the fuel injection hole 3a1 with the oxidizer gas injected from the first oxidizer injection hole 3b1 and the second oxidizer injection hole 3c1. Furthermore, it is preferable that the oxidizing gas ejected from both the first oxidizing gas nozzle 3b1 and the second oxidizing gas nozzle 3c1 have an oxygen concentration of 90% or higher. The flow rate ratio of the oxygen ejected from the first oxidizing gas nozzle 3b1 to the oxygen ejected from the second oxidizing gas nozzle 3c1 can be appropriately set according to the required flame formation conditions, etc.

[0028] In this embodiment, it is preferable that the burner 3 includes a fuel supply pipe 3a having a fuel injection hole 3a1 at its downstream end and forming a fuel supply passage 3d radially inward for supplying fuel gas, a first oxidizer supply pipe 3b having a first oxidizer injection hole 3b1 at its downstream end and forming a first oxidizer supply passage 3e radially inward for supplying oxidizer gas, a second oxidizer supply pipe 3c having a second oxidizer injection hole 3c1 at its downstream end and forming a second oxidizer supply passage 3f radially inward for supplying oxidizer gas, and a burner block 3g that holds the fuel supply pipe 3a, the first oxidizer supply pipe 3b, and the second oxidizer supply pipe 3c. The first oxidizer supply passage 3e is formed by being separated by the outer circumferential surface of the fuel supply pipe 3a and the inner circumferential surface of the first oxidizer supply pipe 3b. The burner block 3g contacts and holds the outer circumferential surface of the first oxidizer supply pipe 3b and the outer circumferential surface of the second oxidizer supply pipe 3c. The fuel supply pipe 3a and the first oxidizer supply pipe 3b share a common first central axis O and extend along the first central axis O, respectively. The second oxidizer supply pipe 3c has a second central axis P and extends along the second central axis P.

[0029] The ejection direction of the second oxidizer ejection port 3c1 (i.e., the direction toward the downstream side from the second oxidizer ejection port 3c1 along the second central axis P) is inclined radially outward from the first oxidizer ejection port 3b1 toward the ejection direction of the first oxidizer ejection port 3b1 (i.e., the direction toward the downstream side from the first oxidizer ejection port 3b1 along the first central axis O). With the above configuration, the mixed flow of fuel gas ejected from the fuel ejection port 3a1 and oxidizer gas ejected from the first oxidizer ejection port 3b1 is disturbed by the flow of oxidizer gas ejected from the second oxidizer ejection port 3c1, thereby suppressing combustion conditions that were not intended by the designer.

[0030] The ejection direction of the second oxidant ejection port 3c1 is tilted radially outward from the first oxidant ejection port 3b1 towards the ejection direction of the first oxidant ejection port 3b1 at an inclination angle θ. α [°] is 0≦θ α It is preferable that the value is ≤15. With the above configuration, the oxidizer gas ejected from the second oxidizer injection port 3c1 can be effectively merged with the mixed flow of fuel gas ejected from the fuel injection port 3a1 and oxidizer gas ejected from the first oxidizer injection port 3b1, thereby enabling good combustion.

[0031] In this embodiment, the surface of the object to be heated 2 that is melted by the burner 3 is referred to as the top surface, and the second oxidant ejection hole 3c1 is located below the first oxidant ejection hole 3b1. The top surface is preferably the top surface in the vertical direction.

[0032] The burner 3 is not limited to having one second oxidant ejection hole 3c1 as in this embodiment, but may also have two second oxidant ejection holes 3c1 as shown in the modified example in Figure 4, or it may have three or more second oxidant ejection holes 3c1.

[0033] The flow rates of the oxidizer gas injected from the first oxidizer injection port 3b1 and the second oxidizer injection port 3c1 can be determined arbitrarily, but it is undesirable if the sum of these rates is either too low or too high compared to the stoichiometrically required flow rate for complete combustion of the fuel gas injected from the fuel injection port 3a1. If the rate is too low, ammonia will be generated as unburned fuel in the heating furnace 1, raising concerns about adverse effects on the heating furnace 1 and the object being heated 2. Furthermore, since it is released outside the furnace without being converted into heat, it is undesirable from the perspective of the energy efficiency of the heating furnace 1. Similarly, if the rate is too high, there are concerns that the oxidizer, which does not contribute to combustion, will be heated to a high temperature, affecting the refractory materials and the object being heated 2 inside the furnace. Moreover, since it is released outside the furnace while retaining high-temperature energy, the energy efficiency will be poor. Therefore, it is preferable to set the total flow rate of the oxidizer gas to 0.8 to 1.2 in stoichiometric ratios, where the theoretical amount for complete combustion is 1.0.

[0034] The fuel supply pipe 3a, the first oxidizer supply pipe 3b, and the second oxidizer supply pipe 3c are preferably made of metal for ease of manufacture. If they are made of metal, it is preferable to implement protective measures against high-temperature oxidation, as the furnace temperature is 1000°C or higher. For this reason, the burner block 3g is preferably made of refractory material. The burner block 3g may also be configured to have a protective structure such as a water-cooling jacket.

[0035] The height H [m] from the top surface of the object to be heated 2 to the center of the fuel injection hole 3a1, the distance L [m] between the furnace side wall 4 and the opposite furnace side wall 4 facing left and right of the furnace side wall 4 when viewed in the front-to-back direction perpendicular to the plane containing the ejection axis of the fuel injection hole 3a1 (i.e., the first central axis O extended from the fuel injection hole 3a1 in the ejection direction) along the vertical direction, and the inclination angle θ when viewed in the front-to-back direction such that the ejection axis of the fuel injection hole 3a1 is tilted downward in the ejection direction relative to the top surface of the object to be heated 2. β [°] means that 0.1 ≤ H ≤ 2 and H / L ≤ tanθ β It is preferable that the concentration is ≤2H / L.

[0036] When a burner 3 is installed on the side wall 4 of a furnace and a workpiece 2 to be heated is placed at the bottom of the heating furnace 1, the workpiece 2 may be heated by directly impacting it with a flame. However, if a flame that has not yet completed combustion is used, unburned fuel and oxygen may impact the workpiece 2, potentially affecting its quality, which is undesirable. For this reason, it is preferable to maintain a certain distance between the burner 3 and the workpiece 2, and specifically, as described above, it is preferable to set the distance to 0.1 ≤ H ≤ 2.

[0037] Furthermore, when the burner 3 is installed on the furnace side wall 4, the angle between the top surface of the object to be heated 2 and the flame axis of the burner 3 (which coincides with the ejection axis of the fuel ejection hole 3a1) is important. In particular, in this embodiment, using ammonia as the fuel gas improves convective heat transfer compared to fossil fuels such as natural gas. To enhance this effect, it is desirable to angle the flame axis of the burner 3 slightly downward relative to the object to be heated 2. The reason for angling it downward is to enhance the effect of convective heat transfer by the completely combusted combustion gas in addition to radiant heat transfer from the flame. Also, in order to allow the combustion gas to reach the top surface of the object to be heated 2 while the flame is completely combusted, the inclination angle θ β As mentioned above, H / L ≤ tanθ β It is preferable that the concentration is ≤2H / L.

[0038] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and the embodiments described above can be modified in various ways without departing from the spirit of the present invention. [Explanation of Symbols]

[0039] 1 Furnace 2 Object to be heated 3 burners 3a Fuel supply pipe 3a1 Fuel injection hole 3b First oxidizer supply pipe 3b1 First oxidizing agent ejection port 3c Second oxidizing agent supply pipe 3c1 Second oxidizing agent nozzle 3d fuel supply path 3e First oxidizer supply channel 3f Second oxidizer supply channel 3g バーナブロック 4. Furnace sidewalls O First central axis (ejection axis) P Second Central Axis θ α tilt angle θ β tilt angle H high L distance

Claims

1. It has a burner that heats an object to be heated by burning a fuel gas with an oxidizing gas, The aforementioned fuel gas contains ammonia. The oxidizing gas is a heating furnace with an oxygen concentration of 90% or more.

2. The furnace side wall has a burner on which the burner is installed, The heating furnace according to claim 1, wherein the burner has a fuel injection port, a first oxidizer injection port surrounding the fuel injection port, and a second oxidizer injection port located radially outward of the first oxidizer injection port without surrounding it.

3. The heating furnace according to claim 2, wherein the ejection direction of the second oxidizing agent ejection hole is inclined radially outward from the first oxidizing agent ejection hole toward the ejection direction of the first oxidizing agent ejection hole.

4. The ejection direction of the second oxidizing agent ejection hole is inclined radially outward from the first oxidizing agent ejection hole toward the ejection direction of the first oxidizing agent ejection hole by an inclination angle θ. α [°] is 0 ≤ θ α The heating furnace according to claim 3, wherein ≤ 15.

5. The heating furnace according to claim 2, wherein, when the surface of the object to be heated that is melted by the burner is referred to as the upper surface, the second oxidizing agent ejection hole is located below the first oxidizing agent ejection hole.

6. The furnace side wall has a burner on which the burner is installed, When the surface of the object to be heated that is melted by the burner is referred to as the top surface, the height H [m] from the top surface of the object to be heated to the center of the fuel injection hole, the distance L [m] between the furnace side wall and the opposite furnace side wall facing the furnace side wall in the left-right direction when viewed in the front-rear direction perpendicular to the plane containing the injection axis of the fuel injection hole along the vertical direction, and the inclination angle θ when viewed in the front-rear direction such that the injection axis of the fuel injection hole is tilted downward in the injection direction relative to the top surface of the object to be heated. β [°] is defined as 0.1 ≤ H ≤ 2 and H / L ≤ tanθ β The heating furnace according to claim 2, wherein the density is ≤ 2H / L.

7. The heating furnace according to claim 1, wherein the burner is embedded in the side wall of the furnace.

Images