Furnaces – Process – Treating fuel constituent or combustion product
Reexamination Certificate
2000-03-01
2001-10-09
Bennett, Henry (Department: 3749)
Furnaces
Process
Treating fuel constituent or combustion product
C110S342000, C110S261000, C110S265000
Reexamination Certificate
active
06298796
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a combustion burner of fine coal powder, wherein the fine coal powder is transported by an air flow, and a combustion apparatus of fine coal powder using same. Particularly, the present invention relates to a combustion burner for burning fine coal powder and a combustion apparatus of fine coal powder, both of which are preferable for decreasing concentration of nitrogen oxide (hereinafter, called as NOx) and unburned component in ashes.
Generally, suppression of NOx, which is generated in combustion, becomes a problem for combustion burners. Particularly, coal has a larger nitrogen content in comparison with gaseous fuels and liquid fuels.
Therefore, decreasing the amount of NOx generated in operation of the fine coal powder combustion burner is more important than the cases of the gaseous fuels and liquid fuels. Most of the NOx generated in burning coal (fine coal powder) is NOx (fuel NOx), which is generated by oxidizing nitrogen components contained in the coal.
Hitherto, various burner structures and combustion methods have been studied for decreasing the NOx. One of the effective combustion methods is a method (two stage combustion method) for burning the coal completely by supplying a deficient amount of air for complete combustion of the fine coal powder from the fine coal powder burner, and then, supplying additional air to make the amount of air sufficient for complete combustion in the downstream of the fine coal powder burner.
One other method is a method utilizing a reducing reaction of NOx, which is activated when oxygen concentration is low, by forming a region having a low oxygen concentration in flame. For instance, JP-A-1-305206 (1989), JP-A-3-211304 (1991), JP-A-3-110308 (1991), and others disclosed a method for burning coal completely by forming flame (reducing flame) having a low oxygen concentration atmosphere, and a structure, wherein a fine coal powder nozzle for transporting fine coal powder by an air flow is set at a center, and air nozzles for injecting air are arranged outside around the fine coal powder nozzle.
In accordance with these low NOx burners, a region having a low oxygen concentration is formed in flame, and NOx is reduced to harmless nitrogen molecules by generating NOx reducing materials such as ammonia and hydrogen cyanide from the nitrogen components contained in the fine coal powder in the reducing flame region. That is, the amount of NOx generated in the flame is decreased, because the NOx is reduced to nitrogen molecules.
In the case of using the two stage combustion method, the amount of air supplied to the fine coal powder burner is smaller than the amount of air necessary for complete combustion of the fine coal powder. Accordingly, air (air for second stage combustion) is further supplied in the downstream of the fine coal powder burner for complete combustion. Therefore, the combustion apparatus for the two stage combustion method must be provided with a space for mixing the air for second stage combustion with the fine coal powder.
For instance, a boiler furnace (combustion apparatus) for 1000 MW power generation requires to ensure approximately five meters in height as a mixing space for second stage combustion air per sixty meters in height of the furnace. In accordance with a single stage combustion method, wherein all the air for combustion is supplied by the fine coal powder burner, the mixing space can be omitted, and the height of the furnace can be decreased. However, in the case of the single stage combustion method, the air for combustion is readily mixed with the fine coal powder flow, and, even if the low NOx burner is used, the releasing amount of NOx tends to increase significantly in comparison with the case of the two stage combustion method. If a strong swirl is given to the combustion air in order to suppress mixing the fine coal powder with the combustion air supplied from the air nozzle, the fine coal powder is not mixed completely with the combustion air even in the downstream region of the burner, and the amount of unburned component in the ashes is increased.
SUMMARY OF THE INVENTION
The present invention is achieved in consideration of the above problems.
One of the objects of the present invention is to provide a combustion apparatus of fine coal powder, and a combustion burner of fine coal powder, whereby the generating amount of NOx and the unburned component in the ashes are decreased without increasing the height of the furnace.
In accordance with the present invention, a fine coal powder combustion burner is provided, which comprises: fine coal powder nozzles, which inject a mixture of air and the fine coal powder; and air nozzles, which inject air: wherein the sufficient amount of air for burning the fine coal powder completely is supplied from the air nozzles; a flame at a high temperature is formed by igniting the fine coal powder rapidly in the vicinity of the outlet of the burner in order to form a reducing flame at a high temperature (flame, wherein a ratio of actual amount of air to a necessary amount of air for burning completely the components released from the fine coal powder as gases is smaller than 1) by consuming oxygen rapidly; and an oxidizing flame (flame, wherein a ratio of actual amount of air to a necessary amount of air for burning completely the components released from the fine coal powder as gases is larger than 1) having an uniform distribution of gas composition in radial direction from the central axis of the burner is formed by mixing the air injected from the air nozzle in the downstream of the reducing flame at the high temperature, in order to achieve the object of the present invention.
Furthermore, in accordance with the present invention, a fine coal powder combustion burner is provided, which comprises: fine coal powder nozzles, which inject a mixture of air and the fine coal powder, and air nozzles, which inject air: wherein the sufficient amount of air for burning the fine coal powder completely is supplied from the air nozzles; flame at a high temperature higher than 1200° C. is formed by igniting the fine coal powder rapidly in the vicinity of the outlet of the burner (within three times of the burner throat diameter from the fine coal powder nozzle outlet in the fine coal powder injecting direction); a reducing flame (flame, wherein a ratio of actual amount of air to a necessary amount of air for burning completely the components released from the fine coal powder as gases is smaller than 1) is formed in the vicinity of the burner; and an oxidizing flame (flame, wherein a ratio of actual amount of air to a necessary amount of air for burning completely the components released from the fine coal powder as gases is larger than 1) having an uniform distribution of gas composition in radial direction from the central axis of the burner is formed by mixing the air injected from the air nozzle in the downstream of the reducing flame at the high temperature, in order to burn the fine coal powder.
In this case, a flame having a length of 1 to 1.5 times of the burner throat diameter is formed in a perpendicular direction (radial direction) to the injecting direction of the fine coal powder in the vicinity of the burner (a position at two times of the burner throat diameter from the tip of the fine coal powder burner in the injecting direction of the fine coal powder), and a flame having a length of at least two times of the burner throat diameter is formed in the radial direction in the downstream of the vicinity of the burner.
A ratio of momentum of fine coal powder flow at the outlet of the fine coal powder nozzle in the injecting direction (axial direction) to momentum of the air flow at the outlet of the air nozzle is set as 1:5-7 by supplying sufficient amount of air for perfect combustion of the fine coal powder from the burner and making the injecting velocity of the fine coal powder flow injected from the fine coal powder nozzle at least 20 m/s.
Furthermore, the tip of the air nozzle is formed in
Jinbo Tadashi
Kiyama Kenji
Kobayashi Hironobu
Kuramashi Koji
Morita Shigeki
Bennett Henry
Hitachi , Ltd.
Mattingly, Stanger & Malur
Rinehart Kenneth B
LandOfFree
Fine coal powder combustion method for a fine coal powder... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fine coal powder combustion method for a fine coal powder..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fine coal powder combustion method for a fine coal powder... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2596997