Patent Application
20100192817
The present invention relates to a burner for pulverized coal and more particularly to a stationary coal nozzle for a burner on a pulverized coal fired furnace.
A wide variety of burner designs have been developed over the years for burners used in furnaces, boilers and the like for burning pulverized coal. Problems incurred in burning pulverized coal often can be associated with coal roping in the fuel delivery system. Fuel roping is believed to be caused by centrifugal flow patterns established by elbows and pipe bends.
Pulverized coal fired boilers have coal pipe networks which transport the coal from the pulverizers to the individual burners using air as the conveying medium. For the specific case of a wall fired boiler, the last turn in the coal/air mixture makes is a hard 90° turn in the burner. Coal roping is caused primarily by surface tension and pressure differentials within the coal pipes. The dense areas of coal flow or coal ropes lead to poor flow distribution exiting the coal pipe and nozzle, which in turn has a negative effect on combustion.
Coal roping causes poor fuel distribution exiting the nozzle tip or outlet which results in flame variations. These flame variations range from substoichiometric fuel rich zones, where the reducing atmosphere contributes to slagging and water wall erosion, to high oxygen zones, which potentially create high thermal generation oxides of nitrogen. With these wide variations at each burner of a multiple burner unit, unit control is difficult. Accordingly, if the coal rope can be effectively broken up, flow distribution at the exit of the coal pipes is greatly improved.
In an attempt to reduce nitrogen oxide levels and to reduce fuel roping, many stationary coal nozzles and nozzle tips have been developed over the years. Many of them incorporate convergers and/or divergers. For example, see U.S. Pat. Nos. 4,348,170; 4,380,202; 4,479,442 and 4,634,054. Others incorporate rib segments or dispersing devices within the coal nozzle which extend or protrude from the inside wall of the nozzle for distributing and diffusing a flowing stream of pulverized coal. For example, see U.S. Pat. No. 6,367,394 and U.S. Pat. No. 6,105,516. All of these references have attempted to disrupt the coal roping flow into and out of the stationary coal nozzles with limited success.
It is accordingly a major object of the present invention to provide a coal nozzle design which provides effective breakup of coal ropes.
The coal nozzle of the present invention includes an elongated tubular nozzle having an inlet for receiving a flowing of coal/air mixture and an outlet for discharging the flowing stream into a combustion zone of a furnace for combustion. An inlet elbow is connected to the inlet of the tubular nozzle.
In accordance with the teachings of the present invention, to effectively eliminate coal roping, interior outer surfaces of the elbow include a sawtooth or staircase surface configuration for engaging the incoming flowing stream of coal/air whereby coal ropes in the stream are broken up for thereby improving flow distribution of the stream.
Additional improvement in flow distribution is provided by including a plurality of annularly arranged and axially aligned fins in the tubular nozzle downstream of the elbow.
Conventional elbows used in coal nozzle burner configurations are either flatback elbows or lobsterback elbows. The flatback elbows have a removable flatback cover plate with a flat interior surface and the conventional lobsterback elbows have a removable back cover plate with a segmented flat surface interior. With the flatback elbow, the staircase surface configuration of the present invention is applied to the interior surface of this removable cover plate. With the lobsterback elbow, the staircase surface configuration is applied in staircase segments to the respective interior flat segments of the removable back. The staircase surface configuration generally has spaces thereof which are set at even intervals.
The staircase surface configuration is constructed of any suitable wear resistant durable material, such as steel or a ceramic, such as silicone carbide.
Other objects and advantages appear hereinafter in the following description and claims. The accompanying drawings show, for the purpose of illustration, without limiting the invention or the appended claims, certain practical embodiments of the present invention wherein:
Referring to
Also included is an inlet elbow 14 connected to the inlet 12 of tubular nozzle 11. The flowing stream of coal/air mixture is provided from an upright supply pipe 15 from a conventional source (not shown).
The elbow 14 illustrated here is a conventional flatback elbow with a removable flatback cover plate 16, which may be removed for wear replacement and clean out. The tubular nozzle 11 is generally lined with ceramic and may also include many types of deflectors or diffusers as previously described in the background. The elbow 14 and the cover plate 16 are generally constructed of cast and machined carbon steel.
As previously discussed, elbow 14 induces the creation of coal ropes, which, as previously explained, are undesirable and need to be eliminated.
The elimination of coal ropes is accomplished by the embodiment of the present invention as illustrated in
In the embodiment of the present invention, interior outer surfaces 17 of elbow 14, which in this instance is also the inside surface of flatback cover 16, are provided with a sawtooth or staircase surface configuration 18 for engaging the incoming flowing stream of the coal/air mixture whereby coal ropes in the stream are broken up for thereby improving flow distribution of the stream.
This staircase surface configuration is attached or secured to the interior outer surfaces 17 of elbow 14 by any conventional means, such as machine screws 20. The staircase surface configuration 18 is constructed of any suitable wear resistant material, such as steel or ceramic, including silicone carbide.
The set of faces of alternating angles of the staircase configuration 18 are more or less perpendicular and parallel to the incoming flow whereby the faces which are somewhat perpendicular to the flow break up the dense coal rope. These faces are generally, but not necessarily, set at even intervals and not in the same plane whereby they destroy the rope and distribute it evenly throughout the tubular nozzle 11.
To supplement distribution enhancement, a set of fins 21 are set at even circumferential intervals in the inlet 12 of tubular nozzle 11. The longitudinal edge of the fins 21 are parallel to the tubular nozzle axis, and stand off of the inside diameter of the tubular nozzle 11 by approximately 2 inches.
The entire inside of the tubular nozzle 11 is lined with ceramic blocks 22 and fins 21 are also constructed of a wear resistant material, such as steel or a ceramic, such as silicone carbide and the fins 1 are secured to inside walls of tubular nozzle 11 by means of machine screws inserted through passages 23, as best seen in
The element 24 on the flatback cover plate 16 provides a conventional clean out access and eye 25 provides a means for lifting the cover plate 16 when it is removed from elbow 14.
The embodiment illustrated in
Instead of the conventional flatback elbow as shown at 14 in
These flat surface segments 28 are positioned at the interior outer surfaces 17 of the elbow 14. For the purposes of breaking up coal ropes in accordance with the teachings of the present invention the lobsterback elbow 14 is adapted in accordance with the teachings of the present invention as shown in
