JPH0222289B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the combustion method of solid pulverized fuel such as pulverized coal and coke powder, and an apparatus therefor. As shown in Fig. 1, a conventional solid pulverized fuel burner burns a mixture 1 of solid pulverized fuel and primary air for transporting the solid pulverized fuel.
A solid pulverized fuel burner with a circular or square cross section 2
from the jet nozzle 3 to create a jet 4 of solid pulverized fuel in the shape of a cone or pyramid in the combustion chamber.Secondary air 5 is supplied from the outside of this jet 4, and the A common method is to diffuse air 5 and burn solid pulverized fuel. That is, a mixture 1 of solid pulverized fuel and primary air is injected into the furnace at high speed to form a blowing jet 4 of the mixture, and secondary air 5 is further diffused into this jet 4 to form solid pulverized fuel. The basic combustion method is to burn it. As a modification, as shown in Fig. 2, the burner 2
An air jet port 6 for spouting high-pressure primary air is provided in the center of the air jet 4, and a jet 4 having a central part as shown in the figure is formed in the mixture 1 of solid pulverized fuel and air. A combustion method using a solid pulverized fuel burner is also known, in which a solid pulverized fuel burner is provided with a jet nozzle 7 and a solid pulverized fuel burner is provided. A combustion method is also known in which swirling vanes are attached to each of the fuels to give a swirling flow to the fuel, thereby increasing contact and mixing between the solid pulverized fuel and the air. Hereinafter, a method for burning solid pulverized fuel in a rotary kiln for firing cement and an apparatus thereof will be described in detail by way of example. When burning solid pulverized fuel in a rotary kiln for cement firing, the solid pulverized fuel injected into the kiln must be completely combusted without leaving any unburned matter before it passes through the firing zone.
In a long kiln, the burner flame must be kept to a certain length or less to form a so-called firing zone to complete the final stage of the clinker production reaction. When feedstock with high decarboxylation, for example close to 100%, is fed to the kiln, it is required to burn it with a shorter flame than when the feedstock entering the kiln does not have a high degree of calcination. Furthermore, it is also necessary to adjust the length of the burner flame in order to move the position of the firing zone back and forth somewhat within the kiln, that is, to move the position of the so-called burning point back and forth within the kiln. As described above, in a rotary kiln for firing cement, it is required to complete the combustion of solid pulverized fuel at a high speed to form and maintain a stable combustion state in order to generate clinker minerals. In the first place, the above request is met by turning solid pulverized fuel into pulverized fuel and injecting it into the burner.The mixture of solid pulverized fuel and primary air is blown into the furnace at high speed from the solid pulverized fuel jet. Methods and means such as giving a swirling flow to the clinker cooler and supplying it with high-temperature air from a clinker cooler are based on this requirement. However, conventional combustion methods for solid pulverized fuel are still far from being sufficient to meet the above requirements, and the present inventors have focused on this point and have completed the present invention as a result of various studies. The purpose of the present invention is to further accelerate the combustion speed of solid pulverized fuel and shorten the burner flame, while reducing the primary air (cold air) and replacing it with secondary air at a high temperature of 800 to 900°C. The present invention provides a combustion method with improved combustion efficiency and thermal efficiency. In the present invention, the air used for conveying the solid pulverized fuel and which passes through the burner is referred to as primary air, and the combustion air that does not pass through the burner is referred to as secondary air. The combustion method of the present invention can be applied not only to coal but also to the combustion of solid pulverized fuels such as coke powder, and has a remarkable effect. Furthermore, this technical idea can also be applied to gas fuels and liquid fuels and exhibits its effects. It is. The gist of the method of the present invention is that a mixture of solid pulverized fuel and primary air is blown into a combustion chamber, and the mixture and high-temperature secondary air are mutually diffused and mixed to burn the solid pulverized fuel. By creating a difference in flow resistance at the blowing end face of the burner and making the density distribution of the solid pulverized fuel uneven, the fuel density distribution in the cross section of the injection jet of the solid pulverized fuel is made uneven and the combustion rate is increased. A method of burning a solid pulverized fuel is characterized by forming a short flame. The method of the present invention basically involves blowing a mixture of solid pulverized fuel and primary air into a combustion chamber at high speed to form a cone-shaped jet, and then diffusing and mixing high-temperature secondary air into this jet to fuel the solid pulverized fuel. It burns. In the method of the present invention, if we focus on a part of the blown jet formed by the mixture, the ratio of solid pulverized fuel to combustion air (total of primary and secondary air), that is, the solid-air ratio, is low, and the blown jet Looking at other parts of the tank, it is a method of injecting solid pulverized fuel to increase the solid-air ratio here, and if you do this,
The fact that the combustion of the entire solid pulverized fuel is completed quickly compared to the conventional combustion method in which the distribution of the solid pulverized fuel injected from the blowing end face of the burner with a uniform density distribution is uniform in the cross section of the injection jet. This is based on the findings of the present inventors. In a portion of the jet formed by the mixture of solid pulverized fuel and secondary air, the portion with a low solid-air ratio burns quickly after ignition. This part with a low solid-air ratio takes in high-temperature secondary air supplied from the surroundings of the jet and forms part of the flame, but turbulence is generated during combustion, which causes other parts of the jet, i.e. To advance the timing of intake of secondary air to a portion with a high air ratio and to increase the intake speed. Therefore, the overall combustion rate of the all-solid pulverized fuel is faster than with previous methods. Combustion occurs quickly in a part of the jet formed by the mixture of solid pulverized fuel and primary air in the combustion chamber, and as a result, high-temperature secondary air from around the jet starts to diffuse into the jet at an early stage, and In the combustion method of the present invention in which the diffusion rate is high, the overall combustion is completed quickly as described above, but the amount of air that forms the mixture, in other words, the amount of other primary air for conveying the solid pulverized fuel, is can be reduced compared to conventional methods. If the method of the present invention is carried out with the same amount of primary air as before, the length of the flame will be shorter than before, and even if the primary air is reduced, it is still possible to form a flame of the same length as before. can. As described above, according to the method of the present invention, solid pulverized fuel can be burned efficiently and quickly, and combustion efficiency and thermal efficiency can be improved. Next, a combustion apparatus that can easily implement the method of the present invention will be described with reference to the drawings. 3 and 4 show an embodiment of a solid pulverized fuel burner 10 suitable for carrying out the method of the present invention, FIG. 3 is a longitudinal cross-sectional view, and FIG. 4 is an A-A in FIG.
It is an arrow view. The burner 10 of the embodiment includes a heavy oil burner insertion passage 11 for igniting solid pulverized fuel in the center, a primary air passage 12 located outside of the insertion passage 11 through which only air passes, and a primary air passage 12 provided outside of the insertion passage 11 for igniting solid pulverized fuel and conveying the solid pulverized fuel. It consists of a passage 13 through which a mixture with air passes, and a primary air passage 14 surrounding the outside and through which only air passes. The insertion path 11 and the passages 12, 13, 14 have fuel and air supply ports 11a, 12a, 13a, respectively.
14a are provided in communication with each other. The heavy oil burner gun insertion passage 11 in the center of the burner is used to insert the heavy oil burner gun only when igniting the solid powder fuel, and after ignition, the gun should be pulled out and closed, or the supply port 11a
It can also be used as a passage for sending primary air from. There is a primary air passage 12 outside the heavy oil burner gun insertion passage 11, and a taper 12c is provided at the tip of the primary air passage 12 to narrow the passage.
b is installed. From the passage 12, primary air is given a swirling motion and blown into the combustion chamber. A passage for a mixture of solid pulverized fuel and conveying air, that is, a fuel wheel feed passage 13 is located outside the primary air passage 12.
The outside of the fuel wheel feed path 13 is surrounded by a straight air path 14. The fuel wheel feed path 13 has a taper 13c in the passage near the tip. Furthermore, a diffusion blade 13b is provided at a portion near the tip of the fuel wheel feed path 13. The diffusion blade 13b functions to diffuse and mix the mixture of solid pulverized fuel and primary air with secondary air. The diffusion blade 13b has a spiral shape, and the pitch of the spiral is not the same in the upper half and the lower half in FIG. is small, and the fuel wheel feed passage 13 has a wide opening area in the upper half portion and a narrow opening area in the lower half portion at the tip of the burner. That is, the device of the present invention is a burner injected with solid pulverized fuel, which is characterized in that jet ports are disposed at the tips of the fuel wheel passages and are divided into two and have different opening areas. Fuel wheel feed path 13 divided by diffusion blades 13b
At the tip of the burner, each dividing path has an opening area that is large in the upper half of FIG.
The upper and lower halves of the burner have different resistances to the flow of the mixture because their pitches are non-identical. Note that even if the pitch is the same, substantially the same effect can be obtained by changing the opening area in the cross section. When a mixture of solid pulverized fuel and conveying air is supplied to the burner 10, as mentioned above, since there is a difference in flow resistance in the fuel wheel passage, a large amount of the mixture, and thus A large amount of solid pulverized fuel is blown into the combustion chamber, and a relatively small amount of solid pulverized fuel is blown from the lower half. The distribution of solid pulverized fuel in the cross section of the jet blown into the combustion chamber is non-uniform; in the lower half of the jet, the ratio between the amount of solid pulverized fuel and the amount of combustion air, that is, the solid-air ratio, is low, and the jet The solid-air ratio is high in the upper half. In the lower half of the injection jet, firstly, the solid-air ratio is low, so the solid pulverized fuel ignites quickly, and secondly, as combustion begins, turbulence is generated, so high-temperature secondary air is taken in, that is, the secondary The air is diffused and mixed with the solid pulverized fuel quickly, and thirdly, the swirling flow given to the mixture by the diffusion vanes 13b is also stronger than that in the upper half, resulting in early ignition of the solid pulverized fuel. This increases the combustion speed and shortens the combustion completion time. The above-mentioned turbulence in the lower half of the blowing jet also affects the upper half of the jet, and the intake of secondary air is accelerated in the upper half as well, and combustion is completed early here as well. Compared to the burner, the burner of the present invention burns the all-solid pulverized fuel faster.
As a result, a short flame is obtained in the burner of the invention. In the above explanation, the burner is expressed as an upper half and a lower half in the posture shown in Fig. 4, but it is not necessary to use the burner with the top and bottom in the same position as in Fig. 4, and Fig. 4 is optional. The effect is the same even when the angle is rotated. Figure 4 shows the arrangement of solid pulverized fuel jet ports arranged within a range of 180° at the central angle θ, but the arrangement of the jet ports is arranged within a range of 160° to 200° at the central angle. The same effect can be obtained even if it is placed in Alternatively, the arrangement of the jet ports may be divided into many parts in the circumferential direction. Although the above-mentioned embodiment is a burner in which the method of the present invention can be carried out most suitably and easily, it goes without saying that the method of the present invention can also be realized with a different combustion apparatus. For example, the mixture passage 13 is partitioned into a plurality of partitions, and different amounts of solid pulverized fuel are supplied to the mixture passage 13 to create a difference in the solid-air ratio within the cone of the blown jet. The pitch of the diffusion vanes may be varied as described above, or the diffusion vanes may have the same pitch. Further, the amount of conveyed air in each of the divided passages 13 may be the same or may be slightly different. In addition, before feeding into the burner, a mixture of solid pulverized fuel with different concentrations is made and supplied to each divided passage of the passage 13 or to a different type of burner or a separate burner. It would also be possible to carry out the method according to the invention with a device that supplies differentially. The method of the present invention differentiates the fuel density distribution in the cross section of the injection jet of solid pulverized fuel to locally increase the combustion rate, thereby increasing the combustion rate of the entire jet and significantly reducing the primary air. Even when burning coal or coke fine powder with extremely low volatile content, it is possible to easily achieve complete combustion quickly and obtain a short flame, and it is possible to achieve complete combustion using inexpensive fuel, which has great economic effects. In addition, by adjusting the amount of primary air, the length of the flame can be adjusted over a wider range than before, and the amount of primary air (cold air) can be significantly reduced, replacing the decreased amount of cold air with high-temperature secondary air. By doing so, thermal efficiency can be increased. Furthermore, in conventional combustion methods, it is necessary to pulverize the solid fuel in order to obtain a short flame. For example, in the case of coal combustion, the solid fuel is pulverized until the residue on the 88 μm sieve screen is about 10 to 20%. With the method of the present invention, it has become possible to increase the residue on the 88 μm sieve to 30 to 40% with the same type of coal. Therefore, there is a significant effect in terms of reducing the crushing power. Furthermore, the combustion device of the present invention can easily implement the above method by making slight changes to the burner, and has excellent effects such as improved combustion efficiency, reduced fuel cost, improved thermal efficiency, and reduced fuel crushing power. Its industrial value is particularly great. When the burner of the present invention is used for cement firing, a short flame can be obtained, so if the cement raw material is calcined (decarboxylated) to almost 100% in a preheater and then supplied to the rotary kiln, as is the case recently, the rotary kiln The length can be about 20% shorter than before. Example The burner shown in Fig. 3 and Fig. 4 is used in a rotary kiln for firing cement, and the non-uniformity of the pulverized coal in the jet stream is determined by setting the ratio of the amount of pulverized coal in the upper half of the burner to the lower half of the burner to be 2:1. Solid pulverized fuel was burned according to the method of the present invention. The results are shown in Table 1 when compared with firing using a conventional burner (comparative example). Namely: (1) The amount of solid pulverized fuel used per unit of cement clinker production, that is, the fuel consumption rate has decreased by approximately 4% compared to the conventional method. (2) The combustion effect of pulverized coal has improved and there is no unburned coal. 1000 at the bottom of the kiln using conventional combustion methods.
~2000 ppm of CO was detected, but the method of the invention does not detect any CO. (3) The primary air for transporting solid pulverized fuel can be as small as 3 to 4% of the total air amount relative to the theoretical air amount;
The total amount of primary air passing through the passages 12, 13, and 14 was previously 12-15%, but has been reduced to 8-11%. The reduced cold air is replaced by high temperature (800-900°C) secondary air from the clinker cooler, which is thermally advantageous for the entire kiln system. (4) Even though the amount of primary air was smaller than that of conventional burners, a short flame was ultimately obtained because the high-temperature secondary air diffused quickly into the jet of combustion inside the combustion chamber. 【table】

[Brief explanation of drawings]

Figure 1 Figure 2 is a longitudinal sectional view of a conventional burner, Figure 3
The figure is a longitudinal sectional view of a burner according to an embodiment of the present invention, and FIG. 4 is a view taken along the line A--A in FIG. 3. 1...Mixture of solid pulverized fuel and air, 2...
Burner, 3... Jet nozzle, 4... Jet stream, 5... Secondary air, 6, 7... Primary air outlet, 10... Burner, 11... Insertion path, 12, 14... Primary air passage, 13...Mixture passage, 11a, 12a, 13
a, 14a...supply port, 12b...swivel blade, 13
b...Diffusion wing.

Claims (1)

[Claims] 1. A method for combusting solid pulverized fuel by blowing a mixture of solid pulverized fuel and primary air into a combustion chamber from a burner, and making the mixture and high-temperature secondary air diffuse and mix with each other. By creating a difference in flow resistance at the blowing end face of the burner and making the density distribution of the solid pulverized fuel non-uniform, the fuel density distribution in the cross section of the injection jet of the solid pulverized fuel is made non-uniform, and the combustion rate is increased. A method of combustion of solid pulverized fuel, characterized by forming a short flame. 2. A burner injected with solid pulverized fuel, characterized in that jet ports are disposed at the tip of a fuel transport path and are mutually divided and have different opening areas.