Furnaces – Process – Burning pulverized fuel
Reexamination Certificate
1999-01-28
2001-02-20
Lazarus, Ira S. (Department: 3743)
Furnaces
Process
Burning pulverized fuel
C110S263000, C110S265000
Reexamination Certificate
active
06189464
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a pulverized coal combustion burner and a combustion method utilizing such a burner and, more particularly, to a combustion method using a pulverized coal combustion burner which pneumatically transfers and burns pulverized coal.
Hitherto, in this kind of pulverized coal combustion burners, occurrence of NOx during combustion is a large problem. Particularly, coal has a larger content of nitrogen, compared with gaseous fuel and liquid fuel. Therefore, it is more difficult to decrease NOx produced by combustion of pulverized coals than in the case of combustion of gaseous fuel or liquid fuel.
NOx produced by combustion of pulverized coal is almost all NOx that is produced by oxidizing nitrogen contained in coal, that is, so-called fuel NOx. In order to decrease the fuel NOx, various burner structures and combustion methods have been studied.
As one of the burning methods, there is a method of forming a low oxygen concentration zone within a flame and utilizing reducing reaction of NOx which becomes active when the oxygen concentration is low. For example, JP A 1-305206, JP A 3-211304, JP A 9-170714, JP A 3-110308, disclose methods of producing flame (reducing flame) of low oxygen concentration atmosphere and completely burning coal, and a structure having a fuel nozzle for pneumatically transferring coal at the center thereof and an air injecting nozzle arranged outside the fuel nozzle. In these methods, a low oxygen concentration zone is formed inside the flame, reducing reactions of NOx are progressed in the reducing flame zone, and an amount of NOx occurred within flame is suppressed.
Further, JP A 3-211304, JP A 9-170714 and JP A 3-110308 disclose formation of recirculating flows at a downstream side of the tip of a pulverized coal nozzle by providing a flame stabilizing ring or obstacle at the tip of the pulverized coal nozzle. That is, since a high temperature gas stays inside the recirculating flows, ignition of pulverized coals progresses and the stability of flame can be raised.
In general, since the ignitability of coal is not better than other fuel, it is difficult to raise the ignitability of the coal even if the above-mentioned various methods are adopted. Therefore, in combustion of coal, consumption of oxygen does not progress and a reducing zone is hard to be formed. In order to form a reducing zone, it is necessary to suppress mixing of fuel and air jetted from an air nozzle in the vicinity of the pulverized coal nozzle. The the mixing with fuel is suppressed by supplying the air to be supplied from the air nozzle in a swirling flow. However, when strong swirling is imparted to air, mixing of the air and fuel does not progress even at a downstream portion (more than three times as large as the diameter of a burner throat) separated from the burner due to centrifugal force, and it is hard to effect complete combustion. Therefore, in this kind of pulverized coal combustion, there is the problem that NOx occurs and unburned carbons are left in combustion ashes of pulverized coal.
SUMMARY OF THE INVENTION
The present invention is directed to solving the above-mentioned matters, and an object of the present invention is to provide a pulverized coal combustion burner by which an amount of occurrence of NOx is small and unburnt carbons left in combustion ashes of pulverized coal is small, and to provided a combustion method utilizing the pulverized coal combustion burner.
The present invention attains the above object by a combustion method utilizing a pulverized coal combustion burner comprising a pulverized coal nozzle for injecting a mixture of pulverized coal and air and an air nozzle, provided at an outer peripheral portion of the pulverized coal nozzle so as to surround the pulverized coal nozzle, for injecting air, wherein combustion flame formed by the pulverized coal burner has a zone of a gas phase air ratio of 1 or less formed at a radially central portion of the flame and a zone of a gas phase a air ratio of larger than 1 formed outside the zone in the vicinity of an injection port of the pulverized coal combustion burner, and a zone of a gas phase air ratio of 1 or less formed inside the flame at a downstream side.
Further, in a combustion method utilizing a pulverized coal combustion burner provided with a pulverized coal nozzle for injecting a mixture of pulverized coal and air and an air nozzle, arranged at an outer peripheral side of the pulverized coal nozzle so as to surround the pulverized coal nozzle, for injecting air, the present invention is so made that a pulverized coal mixture fluid is jetted in a straight stream from the pulverized coal nozzle, an air is jetted from the air nozzle in a straight stream without being swirled or in a weak swirling stream of a swirl number of 0.8 or less in a direction separating from the pulverized coal nozzle at an angle of at least 30° but no more than 50° to the central axis of the pulverized coal nozzle, and a jetting speed of the air supplied from the air nozzle is larger than a jetting speed of the pulverized coal mixture fluid supplied from the pulverized coal nozzle.
Further, in this case, a ratio of a jetting speed of air jetted from the air nozzle to a jetting speed of the mixture fluid is in a range between 2:1 and 3:1.
Further, in a combustion method utilizing a pulverized coal combustion burner having a pulverized coal nozzle for injecting a mixture of pulverized coal and air and an air nozzle, provided at an outer peripheral portion of the pulverized coal nozzle so as to surround the pulverized coal nozzle, for injecting air, and an air supply means, arranged at a downstream side of the pulverized coal nozzle, for supplying second combustion air, and which is formed so as to effect two stage combustion, the method includes supplying a substoichiometric quantity of air, i.e., an amount less than that necessary for complete combustion of the fuel supplied from the pulverized coal nozzle and an air quantity in short supply thereby is supplied from the air supply means and combustion flame formed by the pulverized coal combustion burner before mixing with the second combustion air has a zone of a gas phase air ratio of 1 or less formed at a radially central portion and a zone of a gas phase air ratio of 1 or larger formed outside the zone in the vicinity of an injection port of the pulverized coal combustion burner, and a zone of a gas phase air ratio of 1 or less formed inside the flame at a downstream side.
Further, in a combustion method utilizing a pulverized coal combustion burner having a pulverized coal nozzle for injecting a mixture of pulverized coal and air and an air nozzle, provided at an outer peripheral portion of the pulverized coal nozzle so as to surround the pulverized coal nozzle, for injecting air, and an air supply means, arranged at a downstream side of the pulverized coal nozzle, for supplying second combustion air, and which is formed so as to effect two stage combustion, the method includes supplying a substoichiometric quantity of air, i.e., an amount less than that necessary for complete combustion of the fuel supplied from the pulverized coal nozzle, a pulverized coal mixture fluid is in a straight stream from the pulverized coal nozzle, a substoichiometric quantity of air from the air nozzle is supplied from the air supply means and an air is jetted from the air nozzle in a straight stream without being swirled or in a weak swirling stream of a swirl number of 0.8 or less in a direction separating from the pulverized coal nozzle at an angle of at least 30°
0
but no more than 50° to the central axis of the pulverized coal nozzle, and a jetting speed of the air supplied from the air nozzle is larger than a jetting speed of the pulverized coal mixture fluid supplied from the pulverized coal nozzle.
Further, the present invention, in a pulverized coal combustion burner provided with a pulverized coal nozzle for injecting a mixture of pulverized coal and air and an air nozzle, arranged at an outer periphery of the
Jimbo Tadashi
Kiyama Kenji
Kobayashi Hironobu
Kuramashi Kouji
Morita Shigeki
Ciric Ljiljana V.
Hitachi , Ltd.
Lazarus Ira S.
Mattingly, Stanger & Malur
LandOfFree
Pulverized coal combustion burner and combustion method thereby does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pulverized coal combustion burner and combustion method thereby, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pulverized coal combustion burner and combustion method thereby will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2577066