Fuel blowing-in method

Abstract

To provide a fuel blowing-in method which enables using a combustible gas as a fuel for clinker burning, while suppressing increase of a generation volume of NOx.SOLUTION: This method is a fuel blowing-in method which blows a fuel in a rotary kiln for cement burning through a burner. The burner includes a flow channel. The method has a process (a) for blowing-in of a gas mixture of a combustible gas and primary air through the flow channel. The process (a) is executed in a condition in which a relative ratio of the volume of the primary air contained in the gas mixture to a theoretical air volume of the combustible gas is within a range of 0.15 to 0.80.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a method for injecting a fuel-laden air stream into the interior of a rotary kiln for burning cement. [Background technology]

[0002] The production of cement requires firing at temperatures exceeding 1,400°C. A chemical reaction during this firing process causes limestone, the main raw material, to decarbonate (CaCO3 → CaO + CO2). For these reasons, it is known that a large amount of CO2 is generated during the cement production process.

[0003] Approximately 40% of the CO2 generated in the cement manufacturing process is derived from energy sources such as fossil fuel and electricity consumption. For this reason, in consideration of the impact on global warming, consideration is being given to using combustible gases such as natural gas, which has a lower CO2 emission intensity than coal, the main fuel used until now, and synthetic methane (e-methane) made from CO2, as a substitute for the main fuel or as a supplementary fuel to the main fuel.

[0004] The following Patent Document 1 discloses a technology in which a burner that injects a main fuel such as coal is provided with a dedicated port separate from the port through which the main fuel is fed, and ammonia gas, a type of combustible gas, is injected into a rotary kiln for burning cement from this dedicated port. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-185122 Summary of the Invention [Problem to be solved by the invention]

[0006] Because combustible gas is a gas, it tends to burn faster than coal, which is a solid. Therefore, when combustible gas is used as a fuel for cement burning by injecting it from a burner, the combustion reaction of combustible gas proceeds more rapidly than that of coal, making it more likely to form localized high-temperature areas inside the rotary kiln.

[0007] More specifically, coal combustion involves the combustion of volatile matter released into the gas phase by pyrolysis (volatile matter combustion) and the combustion of solid matter known as fixed carbon (char combustion). While volatile matter combustion ends quickly, char combustion takes time and is the rate-limiting step for the overall combustion reaction. Natural gas combustion, on the other hand, is a gas-phase combustion only, so combustion is completed earlier than coal. Therefore, replacing coal with combustible gas as fuel can result in localized high-temperature areas (a tendency toward shorter flames) within the rotary kiln, potentially increasing thermal NOx emissions.

[0008] Because NOx is one of the sources of air pollution, the cement industry is also being asked to reduce the amount of NOx contained in exhaust gases. If the amount of NOx generated increases, it becomes necessary to increase the amount of denitrification agents used to reduce the amount of NOx contained in exhaust gases, which leads to an increase in cement production costs.

[0009] In view of the above problems, the present invention aims to provide a fuel injection method that makes it possible to use combustible gas as fuel for clinker burning while suppressing an increase in the amount of NOx generated. [Means for solving the problem]

[0010] A fuel injection method for injecting a fuel-containing airflow into a rotary kiln for cement burning through a burner, comprising: the burner comprises a flow path; a step (a) of blowing a mixed gas of a flammable gas and primary air through the flow path; The step (a) is characterized in that it is carried out under conditions such that the relative ratio γ of the amount of primary air contained in the mixed gas to the theoretical air amount of the combustible gas is within the range of 0.15 to 0.80.

[0011] The theoretical air amount of a combustible gas is a value calculated from the ratio of components contained in the combustible gas and the flow rate. In other words, once the type of combustible gas to be used is determined, the relative ratio γ is a value determined by the flow rate of the combustible gas contained in the mixed gas and the flow rate of primary air.

[0012] By injecting the mixed gas into the rotary kiln under conditions such that the value of the relative ratio γ is within the range of 0.15 to 0.80, it becomes possible to inject a combustible gas as fuel into the rotary kiln while suppressing the amount of NOx generated, as will be described in detail later.

[0013] The step (a) may be carried out under conditions such that the flow velocity of the mixed gas at the tip of the burner is within a range of 50 m / s to 525 m / s.

[0014] By injecting the mixed gas within the above flow rate range, it is possible to inject a combustible gas as fuel into the rotary kiln while suppressing the amount of NOx generated and excessive combustion. [Effects of the Invention]

[0015] According to the present invention, it is possible to suppress an increase in the amount of NOx generated while using combustible gas as fuel for burning clinker. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a cross-sectional view showing a part of a cement manufacturing facility in which a fuel injection device is attached to a rotary kiln for cement burning. [Figure 2] FIG. 2 is an example of a plan view schematically illustrating a tip portion of a burner on the rotary kiln side. [Figure 3]FIG. 10 is another example of a plan view schematically showing the tip portion of the burner on the rotary kiln side. [Figure 4] FIG. 10 is another example of a plan view schematically showing the tip portion of the burner on the rotary kiln side. [Figure 5] 1 is a schematic diagram of a test facility used in verifying the examples. [Figure 6] 1 is a graph showing the temperature distribution in a kiln. [Figure 7] 7 is a graph comparing peak temperatures in the kiln at different levels based on the results of FIG. 6. [Figure 8] 10 is a graph showing the relationship between the relative ratio γ for each level and the rate of increase in the NOx concentration in exhaust gas. DETAILED DESCRIPTION OF THE INVENTION

[0017] An embodiment of a fuel injection method according to the present invention will be described with reference to the accompanying drawings. The drawings are schematic illustrations, and the dimensional ratios in the drawings do not necessarily correspond to the actual dimensional ratios. Furthermore, the dimensional ratios between the drawings do not necessarily correspond to each other.

[0018] 1 is a cross-sectional view showing a part of a cement production facility 1 in which a fuel injection device is attached to a rotary kiln for cement burning, as an example suitable for carrying out the fuel injection method of this embodiment. The cement production facility 1 includes a rotary kiln 2 and a kiln hood 4 connected to the rotary kiln 2.

[0019] The rotary kiln 2 is a device that produces cement clinker (hereinafter referred to as "clinker 5") by burning clinker raw materials. Typically, the clinker raw materials are calcined via a preheater (not shown) installed upstream and flow into the kiln's base. The rotary kiln 2 has a horizontal cylindrical shape that is slightly inclined downward toward the downstream side (toward the kiln hood 4), and burns the clinker raw materials (or partially burned clinker) while rotating.

[0020] The upstream side of the kiln hood 4 is connected to the downstream end of the rotary kiln 2 and surrounds the downstream end of the rotary kiln 2. The lower side of the kiln hood 4 is connected to the clinker cooler 3. A burner 10 is fixed to the downstream wall surface 4a of the kiln hood 4. A portion of the downstream wall surface 4a of the kiln hood 4 is typically in the form of an openable door, which is opened when repairing the rotary kiln 2 or installing or replacing the burner 10.

[0021] Burners 10 attached to the kiln hood 4 burn the clinker raw material descending inside the rotary kiln 2. After burning, the clinker 5 falls toward the clinker cooler 3 disposed below the kiln hood 4 and is cooled in the clinker cooler 3.

[0022] The temperature of the burned clinker 5 is 1000°C or higher, typically about 1200°C to 1500°C. This clinker 5 is cooled by the ambient air AA1 at room temperature (about 20°C to 30°C) sent in from a cooling fan (not shown) connected to the clinker cooler 3. The cooled clinker 5 is discharged from the outlet end of the clinker cooler 3 and stored in a clinker silo (not shown).

[0023] The air AA1 that flows into the clinker cooler 3 is heat exchanged with the high-temperature clinker 5 and then supplied as secondary air AA2 into the rotary kiln 2. This secondary air AA2 is used as combustion air in the burner 10.

[0024] 1 also shows an XYZ coordinate system in which the vertical direction is the Z direction, the axial direction of the rotary kiln 2 on the kiln hood 4 side is the X direction, and the direction perpendicular to the X and Z directions is the Y direction. The same applies to FIGS. 2 to 4.

[0025] 2 is an example of a plan view schematically showing the tip portion of the burner 10 on the rotary kiln 2 side. The burner 10 shown in FIG. 2 includes a plurality of concentrically arranged flow paths (11, 12). In this embodiment, a mixed gas G0 obtained by mixing a combustible gas G1 and combustion air G2 is blown through the flow paths 11 and 12.

[0026] As shown in Fig. 3, the burner 10 may additionally include flow paths (13, 14). As shown in Fig. 4, the burner 10 may include a single tubular flow path 15. The mixed gas G0 may be blown into the rotary kiln 2 through multiple flow paths, or may be blown into the rotary kiln 2 through a single flow path. In the latter case, air may be blown into the rotary kiln 2 through another flow path.

[0027] Furthermore, when the burner 10 is provided with a plurality of flow paths, some of the flow paths may not allow gas to flow through them. For example, as shown in Fig. 4, when the burner 10 is provided with flow paths (11, 12, 15), the mixed gas G0 may be blown only through flow path 15.

[0028] In this embodiment, the ratio between the supply flow rate from a supply source of flammable gas G1 (not shown) and the supply flow rate from a supply source of air G2 (not shown) is controllable via an adjustment valve or the like.

[0029] In the fuel injection method of this embodiment, the flow rates of the combustible gas G1 and air G2 constituting the mixed gas G0 injected from the burner 10 are adjusted so that the relative ratio γ of the amount of air G2 contained in the mixed gas G0 to the theoretical air amount of the combustible gas G1 contained in the mixed gas G0 is within the range of 0.15 to 0.80.

[0030] The theoretical air volume A0 of flammable gas G1 can be calculated using the following method.

[0031] For example, if the combustible gas G1 contains methane, ethane, propane, butane, ammonia, and hydrogen, it can be assumed that each substance undergoes complete combustion with oxygen according to the following equation (1).

[0032] [ka]

[0033] The amount of oxygen required for complete combustion of combustible gas G1 (theoretical amount of oxygen O o ) is calculated by the following formula (2) based on the above formula (1). Note that CH4 in the following formula (2) represents the volume ratio of CH4 contained in the combustible gas G1. The same applies to C2H4, C3H8, etc.

[0034]

number

[0035] Therefore, the amount of air required to completely combust the combustible gas G1 (theoretical air amount A0) is calculated by the theoretical oxygen amount O calculated by equation (2). o Based on this, it can be calculated according to the following equation (3).

[0036]

number

[0037] In other words, the relative ratio γ of the amount of air G2 contained in the mixed gas G0 to the theoretical air amount of the combustible gas G1 contained in the mixed gas G0 corresponds to the ratio of the amount of air G2 actually contained in the mixed gas to the theoretical air amount A0 calculated by the above formula (3). In other words, when the relative ratio γ is greater than 1, it means that the amount of air G2 mixed with the combustible gas G1 is equal to or greater than the amount necessary to completely combust the combustible gas G1. Conversely, when the relative ratio γ is less than 1, it means that the amount of air G2 mixed with the combustible gas G1 is insufficient to completely combust the combustible gas G1, resulting in a combustion environment in which the combustible gas G1 is in an incomplete combustion state.

[0038] As described above, the value of the relative ratio γ of the mixed gas G0 can be calculated based on the theoretical air volume A0 of the combustible gas G1, which is determined from the component ratio and flow rate of the combustible gas G1, and the amount of air G2 mixed with the combustible gas G1. Here, since the component ratio of the combustible gas G1 used as fuel is usually specified, the value of the relative ratio γ is determined by the flow rates of the combustible gas G1 and air G2 contained in the mixed gas G0. In other words, in the fuel injection method of this embodiment, the mixed gas G0 is injected from the burner 10 into the rotary kiln 2, with the flow rates of the combustible gas G1 and air G2 adjusted so that the relative ratio γ is within a range of 0.15 to 0.80.

[0039] The fact that an increase in the amount of NOx produced can be suppressed by blowing in the mixed gas G0 under conditions in which the mixing conditions of the combustible gas G1 and the combustion air G2 are adjusted so that the relative ratio γ is within the range of 0.15 to 0.80 will be explained with reference to examples. [Example]

[0040] FIG. 5 is a schematic diagram of the test equipment used in the verification of the examples. The test equipment 20 includes a kiln front 22, a kiln 23, and a kiln end 24. A mixed gas G0 of combustible gas G1 and combustion air G2 can be injected into the kiln 23 from the kiln front 22 side through a burner 21. The kiln 23 is a cylindrical member having a diameter of 450 mm and a length of 8,340 mm. The test equipment 20 is equipped with multiple thermometers 25 for measuring the temperature at each axial position within the kiln 23. Air G3 is blown into the kiln 23 from the bottom side of the kiln front 22. This air G3 simulates secondary air introduced into the kiln from the clinker cooler.

[0041] Table 1 shows the composition of the combustible gas G1 used in the verification.

[0042] [Table 1]

[0043] (Evaluation of mixed gas injection) The combustion environment inside the kiln 23 was compared when a mixed gas G0 made by mixing combustible gas G1 and air G2 was injected, and when combustible gas G1 was injected independently from a different flow path than air G2.

[0044] Specifically, the burner 21 used had connected flow paths 11 to 14 as shown in Figure 3. Air was passed through the flow path 12 located in the outermost shell and the flow path 14 located in the innermost shell under the same conditions. In the level without premixing (hereinafter referred to as "Level #A" for convenience), a combustible gas G1 was injected through the flow path 11, and air G2 was injected through the flow path 12. In the level with premixing (hereinafter referred to as "Level #B" for convenience), a mixed gas G0 of combustible gas G1 and air G2 was injected through the flow path 11, and no gas was injected through the flow path 13.

[0045] The flow rate of the flammable gas G1 flowing through the flow path 11 in level #A and the flow rate of the flammable gas G1 contained in the mixed gas G0 injected through the flow path 11 in level #B were set to be the same. The flow rate of the air G2 flowing through the flow path 13 in level #A and the flow rate of the air G2 contained in the mixed gas G0 injected through the flow path 11 in level #B were set to be the same.

[0046] Furthermore, the flow velocity at the tip of the burner 21 of the combustible gas G1 blown through the flow path 11 at level #A, and the flow velocity at the tip of the burner 21 of the air G2 blown through the flow path 12 at level #B were made the same.

[0047] The verification results are shown in Figures 6 and 7. Figure 6 is a graph showing the temperature distribution inside the kiln 23, and shows the relationship between the axial distance from the tip of the burner 21 and the measured temperature for each level. Figure 7 is a graph comparing the peak temperatures inside the kiln 23 for each level based on the results of Figure 6.

[0048] 6 and 7, in level #B where mixed gas G0 was injected, a higher temperature was observed near the tip of burner 21 compared to level #A where combustible gas G1 was injected without mixing air G2. The reason for this is thought to be that in level #B, air G2 was present around combustible gas G1 immediately after it was injected into burner 21, causing a rapid combustion reaction near the tip of burner 21.

[0049] 6 and 7 suggest that when mixed gas G0 obtained by mixing combustible gas G1 with air G2 in advance is injected from burner 21, the peak temperature inside kiln 23 rises, the amount of NO generated by the Zeldovich mechanism (Zeldovich NO) increases, and the NOx concentration in the exhaust gas may increase. In other words, when mixed gas G0 obtained by mixing combustible gas G1 with air G2 is injected from burner 21, it is suggested that the NOx concentration in the exhaust gas may be more likely to increase than before.

[0050] (Adjustment of relative ratio γ) Next, when a mixed gas G0, which is a mixture of combustible gas G1 and air G2, is blown from the burner 21, the flow rates of the combustible gas G1 and the air G2 are adjusted to change the relative ratio γ of the amount of air G2 contained in the mixed gas G0 to the theoretical air amount of combustible gas G1 contained in the mixed gas G0, and the effect on the NOx concentration in the exhaust gas is evaluated. The relative ratio γ was determined by calculating the ratio of the flow rate of air G2 to the theoretical air amount A0 of combustible gas G1 calculated based on the above-mentioned formulas (1) to (3).

[0051] In this verification, in order to simplify the verification conditions, a test facility 20 equipped with a burner 21 having a configuration similar to that of the burner 10 shown in Figure 4 was used, and a combustion environment was created within the kiln 23 by injecting mixed gas G0 only through the flow path 15.

[0052] The test levels are shown in Table 2. The evaluation results are shown in Table 2 and Figure 8.

[0053] [Table 2]

[0054] The results were evaluated based on a comparison of the NOx concentration in the exhaust gas when the fuel flow and air flow were introduced into the kiln 23 under conventional conditions, using pulverized coal as the main fuel. Specifically, a case in which the NOx concentration in the exhaust gas was lower than before was evaluated as "Evaluation A," and a case in which the NOx concentration in the exhaust gas was higher than before was evaluated as "Evaluation C." Figure 8 plots the results for each level on a graph, with the horizontal axis representing the relative ratio γ and the vertical axis representing the relative ratio (rate of increase) of the NOx concentration in the exhaust gas compared to combustion under conventional conditions.

[0055] 8, it was confirmed that, for a mixed gas G0 of combustible gas G1 and air G2 injected from the burner 21, the NOx concentration in the exhaust gas could be reduced compared to the conventional method by adjusting the relative ratio γ of the amount of air G2 contained in the mixed gas G0 to the theoretical air amount of combustible gas G1 contained in the mixed gas G0 to within the range of 0.15 to 0.80. As described above, in view of the results of FIGS. 6 and 7, it was confirmed that the NOx concentration in the exhaust gas is likely to increase when the mixed gas G0 of combustible gas G1 and air G2 is injected from the burner 21. However, by setting the relative ratio γ within the range of 0.15 to 0.80, a remarkable result was obtained that the NOx concentration in the exhaust gas could be reduced compared to the conventional method, even when the mixed gas G0 of combustible gas G1 and air G2 is injected from the burner 21.

[0056] When the relative ratio γ is too low, it means that the amount of air G2 contained in the mixed gas G0 is too small, creating an environment in which the combustible gas G1 is incompletely combusted near the tip of the burner 10 and inside the kiln 23. In this case, the inside of the kiln 23 becomes a fuel-rich combustion environment, which is thought to increase prompt NO and increase the NOx concentration in the exhaust gas.

[0057] Conversely, when the relative ratio γ is too high, the amount of air G2 (more specifically, the amount of oxygen) as a combustion-supporting gas is excessive compared to the combustible gas G1, creating an environment in which the combustible gas G1 is likely to combust violently near the tip of the burner 10 and within the kiln 23. In this case, the flame accompanying the combustion of the combustible gas G1 may backflow, potentially causing a fire or explosion. Furthermore, at level #6, where the relative ratio γ is set to 1.00, the NOx concentration in the exhaust gas increases. This is presumably because, as described above with reference to the results of Figures 6 and 7, oxygen (air G2) as a combustion-supporting gas is already present around the mixed gas G0. The high ratio of the combustion-supporting gas in the mixed gas G0 promotes the combustion reaction, raising the peak temperature in the kiln 23 and increasing the Zeldovich NOx generated by the Zeldovich mechanism.

[0058] In contrast, according to the results of FIG. 8, by blowing the mixed gas G0 into the kiln 23 while adjusting the flow rates of the combustible gas G1 and air G2 that form the mixed gas G0 so that the relative ratio γ is within the range of 0.15 to 0.80, it is possible to burn the cement raw materials while suppressing the production amounts of both Zeldovich NO and Prompt NO.

[0059] In each of the levels #1 to #6 in Table 2, the flow velocity of the mixed gas G0 at the tip of the burner 21 was set within a range of 50 m / s to 525 m / s. The flow velocity of the mixed gas G0 varied for each level, depending on the flow rates of the combustible gas G1 and air G2 contained in the mixed gas G0, in order to adjust the relative ratio γ, as in each of the levels #1 to #6. However, the results in Table 2 and Figure 8 suggest that even if the flow velocity fluctuates within a range of 50 m / s to 525 m / s, the NOx concentration in the exhaust gas can be reduced more than conventionally if the flow rates of the combustible gas G1 and air G2 forming the mixed gas G0 are adjusted so that the relative ratio γ is within a range of 0.15 to 0.80. [Explanation of symbols]

[0060] 1: Cement manufacturing facility 2: Rotary kiln 3: Clinker cooler 4: Kilnhood 4a: Downstream wall 5: Clinker 10: Burner 11, 12, 13, 14, 15: Flow path 20: Testing facilities 21: Burner 22: Front of the kiln 23: Kiln 24: Bottom of the kiln 25:Thermometer AA1: Atmosphere AA2: Secondary air G0: Mixed gas G3: Air

Claims

1. A fuel injection method for injecting a fuel-containing airflow into a rotary kiln for cement burning through a burner, comprising: the burner comprises a flow path; a step (a) of blowing a mixed gas of a flammable gas and primary air through the flow path; a fuel injection method characterized in that the step (a) is carried out under conditions such that a relative ratio of an amount of primary air contained in the mixed gas to a theoretical air amount of the combustible gas is within a range of 0.15 to 0.

80.

2. 2. The fuel injection method according to claim 1, wherein the step (a) is carried out under conditions such that the flow velocity of the mixed gas at the tip of the burner is within a range of 50 m / s to 525 m / s.

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