AU3138101A - Air distribution devices for low-nox pulverized fuel burners - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): MCDERMOTT TECHNOLOGY, INC THE BABCOCK WILCOX COMPANY Invention Title: AIR DISTRIBUTION DEVICES FOR LOW-NOX PULVERIZED FUEL

BURNERS

The following statement is a full description of this invention, including the best method of performing it known to me/us: la AIR DISTRIBUTION DEVICES FOR LOW-NO, PULVERIZED FUEL BURNERS FIELD AND BACKGROUND OF THE INVENTION The present invention relates generally to the field of industrial power plants and in particular to a new and useful air distribution baffle configuration for a low-NOx burner.

A type of low-NOx pulverized fuel burner for a furnace is taught by U.S. Patent 5,829,369, the entire specification of which is hereby incorporated by reference. The burner has a main cylindrical coal nozzle surrounded by several concentric cylindrical tubes. The tube immediately surrounding the coal nozzle creates a primary-secondary air transition zone. The tube extends along the furnace end of the coal nozzle and forms an annulus that is the transition zone. A transition zone air flow control sleeve is positioned on the tube upstream of the burner furnace opening for controlling air flow through the annulus.

The air flow in the annulus is parallel to the primary air and coal mixture being injected into the combustion chamber. When the transition zone air leaves the burner at the end adjacent the combustion zone, it is still travelling substantially parallel to the primary air and coal as it is injected into the combustion zone.

2 One or more secondary air zones are created around the combustion chamber end of the burner by concentric shells surrounding the coal nozzle. Air flow swirl vanes are provided within the secondary air zones and may be adjustable or fixed. An air distribution cone oriented outwardly from an intermediate shell is provided at the edge adjacent the combustion chamber.

The cone deflects some secondary air outwardly.

U.S. Patent 5,680,823, also incorporated by reference herein, illustrates different cone shapes and orientations that can be used with a low-NO, burner. The conical device is used to outwardly divert and swirl pulverized coal at the exit of the coal nozzle to reduce NO, formation and unburned fuel losses.

SUMMARY OF THE INVENTION According to the present invention there is provided an air deflection device for a low- NO. burner having an annular primary/secondary air transition zone with an inner wall formed by a coal nozzle and an outer wall formed by a tube concentric with the coal nozzle, the annular zone having an open end adjacent a combustion chamber end of the low-NO, burner, the air deflection device comprising: ooeee an inner ramped portion formed on the inner wall adjacent the combustion chamber end of the burner; an outer ramped portion formed on the outer wall adjacent the combustion chamber end of the burner, the outer ramped portion having at least one face in spaced opposed relation to the inner ramped portion and having a complimentary shape to the inner ramped portion.

Preferably, the invention provides a device for directing a portion of the combustion air flow radially outward from the burner centerline.

Preferably, the invention provides an apparatus for deflecting at least a portion of the transition zone air outwardly.

Preferably, the invention further reduces NO, formation and emissions from fossil-fuel burners, particularly pulverized coal burners.

Preferably, a deflection device for a low-NO. pulverized coal burner is positioned at the combustion chamber end of the transition zone annulus of the burner and has an inner ramp mounted on a coal nozzle forming the inner wall of the annulus and an outer ramp mounted on the outer wall of the annulus. Preferably, the ramps have complimentary opposed surfaces forming a reduced cross-section path for the transition air with the path opening adjacent the coal nozzle and the path outlet adjacent the outer wall of the transition zone annulus. Preferably, the ramps are 3oriented so that the reduced cross-section path is angled radially outwardly from the burner mouth into the combustion chamber. Preferably, the outer ramp has a section inside the annulus for gradually reducing the cross-sectional area to the path between the ramps.

In an alternative embodiment, the coal nozzle may be flared at the end in place of the inner ramp. Further, a swirler could be present inside the coal nozzle.

BRIEF DESCRIPTION OF THE DRA WINGS A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a sectional side elevational view of a burner having the air deflection device of S-the invention; Fig. 2 is a perspective view of the burner end of a coal nozzle having the device shown "i in Fig. 1; and Fig. 3 is a sectional side elevational view of a burner using another embodiment of the air deflection device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, in which like reference numerals are used to refer to the 2.(l2 same or similar elements, Fig. 1 shows a low-NOx pulverized coal burner 10 for a furnace or boiler S having a coal nozzle 20 with a fuel outlet 25 at one end adjacent a combustion chamber (not S shown). The coal nozzle 20 has a centerline, or longitudinal axis 15 directed along the path of coal and primary air through coal nozzle Primary air and coal supply 80 enters burner 10 at one end. Deflector 52 and conical diffuser 54 are also located at one end of burner 10. Secondary air 56 is provided as shown in both Figs. 1 and 3, along with transition zone air flow control sleeve 58, sliding disk 60, fixed vanes 62, adjustable vanes 64, burner quarl 66, and air distribution cone 68. The shape of burner 10 also defines secondary air zones 70, also depicted in both Figs. 1 and 3.

A cylindrical wall 40 is concentric with and surrounds the coal nozzle 20 forming an annular space that is transition air zone 30. Coal nozzle 20 forms the inner wall of transition air zone 30, while cylindrical wall 40 forms the outer wall of the transition air zone 30. The ends of the cylindrical wall 40 and coal nozzle 20 are substantially co-planar adjacent the combustion chamber, so that the transition air zone 30 ends at the same point as coal nozzle CASE- 6035 -4 A pair of ramps 100, 200 forming an air deflection device are positioned just inside the combustion chamber end of the transition air zone 30. Both ramps 100, 200 are rings within the transition air zone 30 annulus. Inner ramp 200 is formed on the coal nozzle 20. Outer ramp 100 is formed on cylindrical wall 40. Outer ramp 100 has two exposed faces as seen in Fig. 2. Inner face 110 and outer face 120 are sloped in opposite directions and meet at a point in the middle of outer ramp 100. Inner face 110 slopes inwardly from cylindrical wall 40 toward the coal nozzle 20, while outer face 120 slopes back toward the cylindrical wall Inner ramp 200 has a single inner ramp face 220 that slopes outwardly from coal nozzle toward cylindrical wall 40 and is complimentary and opposed to the outer face 120 of outer ramp 100. The inner ramp face 220 and outer face 120 form a deflection jet path 300 between which redirects air flowing through the transition air zone 30 radially outward from the longitudinal axis 15 of the burner S. In an alternative embodiment shown in Fig. 3, inner ramp 200 is formed by a flared end 205 of coal nozzle 20. Further, burner 10 may include a swirler 50, control rod 72, and distribution cone 74.

S The air deflection device formed by ramps 100, 200 redirects about 10% of the total combustion air into a radially diverging jet resembling a hollow cone. The air deflection device oo formed by the ramps 100, 200 can be oriented to a specific angle, depending on burner use conditions. The amount of transition air present in the transition zone can be controlled to control the velocity of the redirected air as well.

The redirected air jet interacts with the primary and secondary combustion air flows to create flow characteristics and entrainment effects in the combustion chamber that are conducive S to increased flame stability, higher combustion efficiency and lower NOx emissions than burners lacking the air deflection device. Radial deflection of the air jet outwardly from the coal nozzle increases the near-burner flow recirculation and expands the volume of the oxygen-deficient primary combustion zone. These conditions minimize NOx formation, and therefore, pollutant emissions, by producing nitrogen-bearing species such as HCN, CN, N, NH and NH 2 which react with NOx to convert the NOx to N 2 (elemental nitrogen). Further, flame ignition and stability increase combustion efficiency and fuel burnout, which reduces the emissions of CO and unburned combustibles from the furnace.

5 Testing of a pulverized coal burner as shown in Fig. 1 at 100 million Btu/hour heat input with a high volatile pulverized eastern bituminous coal revealed 10-20% lower NOx emissions, lower CO emissions and up to 35% lower loss on ignition relative to Babcock Wilcox's standard DRB-4Z (a trademark of Babcock Wilcox) burner. Loss on ignition refers to a measure of combustion inefficiency.

The testing used a ramp path angle of 250 with respect to the longitudinal axis 15 of the burner 10. Thus, the total angle of the cone-shaped jet was 500. The velocity of the secondary air was nominally 5,500 feet per minute (fpm) during the testing.

The reduced NOx emissions and other benefits of the invention can be obtained with other angles and velocities. Preferred angles of deflection for the air deflection path created by the ramps 100, 200 are between 100 to 400 or 200 to 800 total divergence angle from the longitudinal axis 15. Nominal secondary air velocities can range from about 4,500 fpm to 7,500 fpm.

While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention :o may be embodied otherwise without departing from'such principles.

It is to be understood that, if any reference to prior art is made herein, such reference does not constitute an admission that the prior art forms a part of the common general knowledge in the art, in Australia or any other country.

00In the claims which follow and in the preceding summary of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprising" is used in the sense of "including", that is the features specified may be associated S with further features in various embodiments of the invention.

Claims (10)

1. An air deflection device for a low-NO x burner having an annular primary/secondary air transition zone with an inner wall formed by a coal nozzle and an outer wall formed by a tube concentric with the coal nozzle, the annular zone having an open end adjacent a combustion chamber end of the low-NOx burner, the air deflection device comprising: an inner ramped portion formed on the inner wall adjacent the combustion chamber end of the burner; an outer ramped portion formed on the outer wall adjacent the combustion chamber end of the burner, the outer ramped portion having at least one face in spaced opposed relation to the inner ramped portion and having a complimentary shape to the inner ramped portion. .O

2. An air deflection device according to claim 1, wherein the at least one face of the .e .outer ramped portion and the inner ramped portion form an air deflection path oriented radially outward from a longitudinal axis of the burner. eeeei

3. An air deflection device according to claim 2, wherein the path is oriented between 10 and 40 degrees outward from the longitudinal axis.

4. An air deflection device according to claim 3, wherein the path is oriented degrees outward.

5. An air deflection device according to claim 2, wherein the outer ramped portion further comprises two faces, the first face being in spaced opposed relation to the inner ramped portion, the second face extending from the outer wall toward the coal nozzle inside the annular zone, the first and second faces having a common edge.

6. An air deflection device according to claim 1, wherein the inner ramped portion is formed by an outwardly flared end of the coal nozzle.

7- 7. An air deflection device according to claim 6, wherein the at least one face of the outer ramped portion and the inner ramped portion form an air deflection path orientated radially outward from a longitudinal axis of the burner.

8. An air deflection device according to claim 7, wherein the path is orientated between 10 and 40 degrees outward from the longitudinal axis.

9. An air deflection device according to claim 8, wherein the path is orientated between 10 and 40 degrees outward from the longitudinal axis. *0

10. An air deflection device for a low-NOx burner substantially as herein described with reference to the accompanying drawings. Dated this 7th day of March 2001 5: McDermott Technology, Inc. and The Babcock Wilcox Company By their Patent Attorneys GRIFFITH HACK 0