U.S. patent application number 09/864645 was filed with the patent office on 2002-11-28 for nozzle assembly for a pulverized coal burner.
Invention is credited to Courtemanche, Bonnie, Dube, Richard J., Penterson, Craig A..
Application Number | 20020174810 09/864645 |
Document ID | / |
Family ID | 25343743 |
Filed Date | 2002-11-28 |
United States Patent
Application |
20020174810 |
Kind Code |
A1 |
Penterson, Craig A. ; et
al. |
November 28, 2002 |
NOZZLE ASSEMBLY FOR A PULVERIZED COAL BURNER
Abstract
A mixture of pulverized coal and primary air travels axially
through a tubular nozzle body having an outlet end in and
surrounded by axially flowing concentric streams of secondary and
often tertiary air. In the nozzle body, the coal/air mixture flows
through a venturi that concentrates the coal in a fuel rich central
zone. The coal/air mixture then flows through a spreader that
imparts a swirling motion to the mixture and divides the mixture
into multiple discrete lobes or streams. At the outlet end of the
nozzle body, a flame stabilizer ring produces a separation zone
between the coal/air mixture exiting the nozzle body and the
surrounding flow of secondary air. The flame stabilizer ring
includes an outwardly flared skirt section that spreads the
secondary air flow and inwardly directed teeth that extend into the
streams of coal/air mixture flowing from the nozzle body
outlet.
Inventors: |
Penterson, Craig A.;
(Sutton, MA) ; Dube, Richard J.; (Billerica,
MA) ; Courtemanche, Bonnie; (Holden, MA) |
Correspondence
Address: |
PHILIP M. KOLEHMAINEN
GREER, BURNS & CRAIN, LTD.
SUITE 2500, 300 SOUTH WACKER DRIVE
CHICAGO
IL
60606
US
|
Family ID: |
25343743 |
Appl. No.: |
09/864645 |
Filed: |
May 24, 2001 |
Current U.S.
Class: |
110/261 ;
431/186 |
Current CPC
Class: |
F23D 2201/10 20130101;
F23D 2201/20 20130101; F23D 2209/20 20130101; F23D 1/02
20130101 |
Class at
Publication: |
110/261 ;
431/186 |
International
Class: |
F23C 001/10 |
Claims
What is claimed is:
1. A nozzle assembly for use in a pulverized coal burner of the
type wherein the nozzle assembly discharges into a surrounding
stream of axially flowing air, the nozzle assembly comprising: an
elongated tubular nozzle body having a central longitudinal axis
and axially spaced inlet and outlet ends; a coal/air supply
introducing a flowing mass of pulverized coal and primary air into
said inlet end of said nozzle body for axial flow through said
nozzle body to said outlet end; a venturi in said nozzle body
between said inlet and outlet ends for concentrating the flow of
pulverized coal and primary air at the center of said nozzle tube
and creating a fuel rich central region, said venturi including an
upstream converging wall section and a restricted venturi throat; a
spreader in said nozzle body between said venturi throat and said
outlet end, said spreader including a plurality of swirl vanes
inclined relative to said axis for imparting a swirling motion to
the flow of pulverized coal and primary air; and a flow stabilizer
mounted at said outlet end of said nozzle body; said stabilizer
including a first portion extending radially outward from said
nozzle body into the surrounding air stream for deflecting the air
stream away from said axis; and said stabilizer including a second
portion extending radially inward from the nozzle body into the
swirling flow of pulverized coal and primary air.
2. A nozzle assembly as claimed in claim 1, said outlet end of said
nozzle body comprising a circular edge, and said stabilizer
comprising a ring mounted at said circular edge.
3. A nozzle assembly as claimed in claim 2, said first portion of
said stabilizer comprising a flared skirt portion extending
radially outwardly at an inclined angle from said circular
edge.
4. A nozzle assembly as claimed in claim 2, said second portion of
said stabilizer comprising an annular wall lying in a plane
perpendicular to said axis.
5. A nozzle assembly as claimed in claim 3, said second portion of
said stabilizer comprising an annular wall lying in a plane
perpendicular to said axis.
6. A nozzle assembly as claimed in claim 4, said wall having
circumferentially spaced teeth extending radially inwardly from
said circular edge toward said axis.
7. A nozzle assembly as claimed in claim 2, said ring comprising a
plurality of discrete ring segments connected to said nozzle
body.
8. A nozzle assembly as claimed in claim 7, further comprising a
plurality of lugs attached to the inner surface of said nozzle body
adjacent said circular edge, said ring segments being fastened to
said lugs.
9 A nozzle assembly as claimed in claim 1, said venturi including a
diverging wall portion extending from said venturi throat to said
outlet end, said spreader being located within said diverging wall
portion.
10. A nozzle assembly as claimed in claim 9, said spreader
including a central hub located at said axis, said swirl vanes
extending from said central hub toward said diverging wall portion
for dividing the flow of pulverized coal and primary air into a
plurality of helically flowing stream segments.
11. A nozzle assembly as claimed in claim 1, said coal/air supply
including a coal head having an entry leg extending at an angle
relative to said axis and communicating with said nozzle body
adjacent said inlet end, and a ceramic liner disposed at the
intersection of said coal head and said nozzle body.
12. A pulverized coal burner assembly for introducing a combustible
fuel-air mixture through the wall of a furnace, said burner
assembly comprising: an axially extending tubular secondary air
duct having a secondary air outlet adjacent the furnace wall; a
nozzle assembly located axially in said secondary air duct; said
nozzle assembly including an elongated tubular nozzle body having a
central longitudinal axis and axially spaced inlet and outlet ends,
said outlet end of said nozzle body being located adjacent said
secondary air outlet; a coal head adjacent said inlet end of said
nozzle body introducing a flowing mass of pulverized coal and
primary air into said inlet end of said nozzle body for axial flow
through said nozzle body to said outlet end; a venturi in said
nozzle body between said inlet and outlet ends for concentrating
the flow of pulverized coal and primary air at the center of said
nozzle tube and creating a fuel rich central region, said venturi
including an upstream converging wall section and a restricted
venturi throat; a spreader in said nozzle body between said venturi
throat and said outlet end, said spreader including a plurality of
swirl vanes inclined relative to said axis for imparting a swirling
motion to the flow of pulverized coal and primary air; and a flow
stabilizer mounted at said outlet end of said nozzle body; said
stabilizer including a first portion extending radially outward
from said nozzle body into the secondary air outlet for deflecting
the secondary air away from said axis; and said stabilizer
including a second portion extending radially inward from the
nozzle body into the swirling flow of pulverized coal and primary
air.
13. A pulverized coal burner assembly as claimed in claim 12
further comprising an annular tertiary air duct surrounding said
secondary air duct.
14. A pulverized coal burner assembly as claimed in claim 12, said
outlet end of said nozzle body comprising a circular edge, and said
stabilizer comprising a ring mounted at said circular edge.
15. A pulverized coal burner assembly as claimed in claim 14, said
first portion of said stabilizer comprising a flared skirt portion
extending radially outwardly at an inclined angle from said
circular edge.
16. A pulverized coal burner assembly as claimed in claim 15, said
second portion of said stabilizer comprising an annular wall lying
in a plane perpendicular to said axis.
17. A pulverized coal burner assembly as claimed in claim 16, said
wall having circumferentially spaced teeth extending radially
inwardly from said circular edge toward said axis.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an improved burner nozzle
assembly for a pulverized coal burner, and more particularly to a
nozzle assembly that promotes fuel rich combustion and reduces the
formation of nitrogen oxide emissions.
DESCRIPTION OF THE PRIOR ART
[0002] Many burner configurations have been designed for burning
pulverized coal. A problem confronted by such designs is to reduce
the production of oxides of nitrogen (NOx) in the combustion
process.
[0003] U.S. Pat. Nos. 4,479,442 and 4,457,241 disclose a dual air
zone, controlled combustion venturi, pulverized coal burner
assembly used with front or opposed fired utility boilers to
provide low NOx combustion. US. Pat. No. 4,517,904 discloses a
tertiary staged venturi burner system for reducing NOx emissions
from turbo furnace type steam generators. Although the burner
assemblies disclosed in these patents have achieved success in
providing pulverized coal combustion with low levels of NOx, it
would be desirable to provide an improved nozzle assembly for use
in these and other burner systems that provides even greater NOx
reduction.
SUMMARY OF THE INVENTION
[0004] A principal object of the present invention is to provide an
improved pulverized coal burner nozzle assembly. Other objects are
to provide a pulverized coal burner nozzle assembly that promotes
fuel rich combustion and reduces the formation of nitrogen oxides;
and to provide a pulverized coal burner nozzle assembly that
provides an improvement over known burner assemblies.
[0005] In brief, in accordance with the invention there is provided
a nozzle assembly for use in a pulverized coal burner of the type
wherein the nozzle assembly discharges into a surrounding stream of
axially flowing air. The nozzle assembly includes an elongated
tubular nozzle body having a central longitudinal axis and axially
spaced inlet and outlet ends. A coal/air supply introduces a
flowing mass of pulverized coal and primary air into the inlet end
of the nozzle body for axial flow through the nozzle body to the
outlet end. A venturi in the nozzle body between the inlet and
outlet ends concentrates the flow of pulverized coal and primary
air at the center of the nozzle tube and creates a fuel rich
central region,. The venturi includes an upstream converging wall
section and a restricted venturi throat. A spreader in the nozzle
body between the venturi throat and the outlet end includes a
plurality of swirl vanes inclined relative to the axis for
imparting a swirling motion to the flow of pulverized coal and
primary air. A flow stabilizer mounted at the outlet end of the
nozzle body includes a first portion extending radially outward
from the nozzle body into the surrounding air stream for deflecting
the air stream away from the axis. The stabilizer includes a second
portion extending radially inward from the nozzle body into the
swirling flow of pulverized coal and primary air.
BRIEF DESCRIPTION OF THE DRAWING
[0006] The present invention together with the above and other
objects and advantages may best be understood from the following
detailed description of the preferred embodiment of the invention
illustrated in the drawings, wherein:
[0007] FIG. 1 is an isometric view, partly broken away, of a burner
nozzle assembly for pulverized coal in accordance with the present
invention;
[0008] FIG. 2 is an axial sectional view of a burner assembly
including the burner nozzle assembly of claim 1, together with flow
arrows showing the flow pattern produced in a furnace combustion
region by the burner assembly and burner nozzle assembly;
[0009] FIG. 3 is an enlarged isometric view showing the outlet end
of the nozzle body and the flame stabilizer of the burner nozzle
assembly; and
[0010] FIG. 4 is an enlarged cross sectional view taken along the
line 4-4 of FIG. 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0011] Having reference now to the drawings, FIG. 1 illustrates a
burner nozzle assembly generally designated as 10 and constructed
in accordance with the principles of the present invention. The
nozzle assembly 10 is used in burner assemblies of the type wherein
the outlet of the nozzle assembly is in a stream of air such as
secondary air or secondary and tertiary air. The nozzle assembly 10
is seen in FIG. 2 with a controlled combustion venturi burner
assembly generally designated as 12. The nozzle assembly 10 can
also be used with other types of burner assemblies.
[0012] The burner assembly 12 of FIG. 2 supplies a combustible
fuel-air mixture into a combustion area 14 defined within a burner
wall 16 through a frusto-conical burner throat 18. The burner
assembly 12 has a air ducting system 20 including generally
tubular, telescoped secondary and tertiary air ducts 22 and 24. The
secondary air duct 22 has a flared outlet 26 located within the
burner throat 18. The tertiary air duct 24 surrounds the secondary
air duct 22 and has an outlet 28 coinciding with the burner throat
18. The flared secondary air outlet 26 is located within the
tertiary air duct outlet 28 and diverts the tertiary air flow in an
inclined, radially outward direction as it enters the combustion
area 14.
[0013] Swirling motion is imparted to secondary air flowing through
the secondary air duct 22 by fixed swirl vanes 30 located in the
secondary air flow path. Similarly, swirling motion is imparted to
tertiary air flowing through the tertiary air duct 24 by adjustable
swirl vanes 32 located in the tertiary air flow path. A tertiary
air swirl adjustment mechanism 34 is operated by a tertiary air
actuator 36 to tailor the tertiary air swirling motion to the
requirements of a specific furnace application. If desired, the
swirl vanes 30 for the secondary air flow could also be adjustable
in a similar manner.
[0014] The volume of secondary air flowing through the secondary
air duct 22 is determined by the position of a secondary air
control damper 38. The volume of tertiary air flowing through the
tertiary air duct 24 is adjustable by operating a tertiary air
shroud actuator 40 in order to move a tertiary air flow control
shroud 42. The tertiary air actuator 36 and the tertiary air shroud
actuator 40 are located in an accessible position outside of a
burner front wall 43. A further description of the controlled
combustion venturi burner assembly 12 beyond that needed for a
complete understanding of the present invention can be found in
U.S. Pat. No. 4,479,442, incorporated herein by reference. The
burner nozzle assembly 10 can also be used with the tertiary staged
venturi burner system disclosed in US. Pat. No. 4,517,904,
incorporated herein by reference.
[0015] The burner nozzle assembly 10 is illustrated in FIG. 1.
Nozzle assembly 10 includes an elongated tubular nozzle body 44
extending in an axial direction from an inlet end 46 to an outlet
end 48. A coal/air supply port 50 introduces pulverized coal and
primary air into the nozzle body adjacent the inlet end 46, and the
coal/air mixture flows axially from the inlet end 46 to the outlet
end 48. As it moves along this flow path, in accordance with the
present invention, the coal/air mixture flows through a venturi 52,
through a spreader 54 and through a flame stabilizer 56 as
described in more detail below.
[0016] The burner assembly 12 is used in a furnace system including
coal pulverizers that deliver a slurry or mixture of coal and
primary air to the supply port 50. The supply port 50 is part of a
coal head 58 having an entry leg 60 generally perpendicular to the
axis of the nozzle body 44 and an axial portion 62 aligned with and
attached to the inlet end of the nozzle body 44. The upstream end
of the axial portion 62 is closed by an end wall 64 seen in FIG. 2.
Resistance to abrasion by pulverized coal is provided by a ceramic
tile lining 66 in the axial portion 62. Vanes 68 (FIG. 2) may be
used to guide the entering coal/air stream into the burner nozzle
body 44 and produce a uniform, homogeneous mixture of primary air
and coal.
[0017] The nozzle body 44 is preferably a right circular
cylindrical tube with a main section 70 having a flange 72 bolted
to the axial coal head portion 62 and a nozzle tip portion 74
attached to the forward end of the main section 70. The outlet end
48 of the nozzle body 44 is a circular edge 76 (FIG. 4) and is
located within the flared outlet 26 of the secondary air duct 22
(FIG. 2). Abrasion resistance can be provided by a lining 77 of
ceramic tiles in the main section 70.
[0018] As the coal/air mixture moves axially through the nozzle
assembly 12 toward the outlet end 48, the mixture travels through
the venturi 52. The venturi 52 includes a frustoconical, converging
entry wall section 78 leading to a restricted venturi throat 80
having a diameter smaller than the diameter of the remainder of the
nozzle body 44. A diverging exit wall section 82 extends from the
throat 80 to the nozzle body outlet end 48. The venturi 52
concentrates the coal in the traveling coal/air mixture toward the
center of the coal nozzle, creating a fuel-rich center core.
[0019] After it leaves the venturi throat 80, the coal/air mixture
with the fuel-rich center core passes through the spreader 54. The
spreader 54 includes a central hub 84 carried by a spreader support
tube 86 extending axially to the rear of the of the burner nozzle
assembly. As seen in FIG. 2, the support tube 86 extends rearward
through the end wall 64 of the coal head, and can be manipulated to
adjust the position of the spreader 54 for optimum performance. A
sleeve 88 protects the tube 86 from abrasion.
[0020] Inclined swirl vanes 90 extend outward from the hub 84 and
produce a moderate swirling motion of the coal/air mixture. The
vanes 90 are located within the diverging wall section 82 and
extend to or near the surface of the wall section 82 in order to
divide the single entering coal/air stream into multiple, distinct
swirling concentrated lobes or coal streams exiting the nozzle body
44. The multiple coal streams leaving the spreader 54 enter the
furnace combustion area 14 in a gradual helical pattern, assisting
control of the location and size of the primary ignition zone,
flame length, and combustion characteristics of the burner assembly
10.
[0021] To ensure that primary ignition and pyrolysis of the
multiple coal streams occur in a localized reducing environment,
the flame stabilizer 56 is mounted at the coal nozzle outlet end
48. The outlet end 48 is located in and surrounded by the axially
flowing secondary air and tertiary air streams entering the
combustion area 14 from the flared secondary air outlet 26 and from
the burner throat 18. The flame stabilizer 56 includes a first
portion 92 that extends radially outward from the nozzle body 44
into the surrounding stream of air. The flame stabilizer 56 also
includes a second portion 94 that extends radially inward into the
path of the multiple coal/air streams exiting the spreader 54.
[0022] More specifically, in the preferred arrangement, the flame
stabilizer 56 is preferably a ring attached to the outlet end 48 of
the nozzle body tip portion 74. To simplify fabrication, the ring
is segmented, with four quadrant sections 96 seen in FIG. 3. Each
section is fastened by bolts 98 to lugs 100 welded to the interior
of the nozzle body tip portion 74 at the circular edge 76. The
flame stabilizer ring 56 includes a circular base ring section 102.
The first portion 92 extending into the surrounding air stream is a
flared skirt section 104 that extends outward beyond the periphery
of the coal nozzle body 44 into the secondary air flow path. The
second flame stabilization portion 94 takes the form of multiple
teeth 106 protruding radially inwardly into the outlet of the
burner nozzle body 44.
[0023] The flame stabilizer ring 56 produces a distinct separation
zone 107 between the primary air/coal mixture and the flow of
secondary air. The separation effect is illustrated by flow arrows
seen in FIG. 2. The effect is symmetrical about the central axis of
the nozzle assembly 12, and arrows are shown in only one half of
the ignition zone in the furnace combustion area 14. The pattern in
the other half is similar. Arrows 108 illustrate the smooth, flared
boundary region provided by tertiary air flow. Arrows 110
illustrate the secondary air flow within the tertiary air flow, and
show the radially outward spreading effect that is imparted to the
secondary air flow by the skirt section 102 of the flame stabilizer
56.
[0024] The improved pulverized coal combustion characteristics
achieved with the burner nozzle assembly 12 of the present
invention reduce undesirable NOx emissions released to the
surrounding environment from utility boilers and furnaces. The
separation zone 107 created by the flame stabilizer 56 is within
the flared secondary air flow path shown by arrows 110. Within this
separation zone 107 created by the flame stabilizer 56, as shown in
FIG. 2, hot combustion products recirculate back to the nozzle tip
in a primary internal recirculation zone near the coal nozzle. This
recirculation is indicated by arrows 112. The flow patterns then
reverse flow direction back downstream and mix with secondary air
in a secondary recirculation zone adjacent to the secondary air
stream from the burner. The mixing reverse flow is indicated by
arrows 114.
[0025] The primary internal recirculation zone creates a secondary
ignition zone along the primary air/coal stream leaving the coal
nozzle. This ensures that hot combustion products from the primary
ignition zone are brought back to the burner discharge around the
periphery of the nozzle outlet end 48 to create flame attachment
and separation of the primary air/coal from the secondary air. The
combustion and hot combustion products in the primary internal
recirculation zone adjacent to the nozzle tip heat the incoming
coal and primary air streams and create conditions for proper
ignition, pyrolysis, and stability of the low NOx coal flame.
Because the venturi 52 in the nozzle body 44 concentrates the
larger-sized coal particles toward the center of the coal/air
stream, only the finer, smaller coal particles flow over the flame
stabilizing ring 56. This envelope of smaller coal particles
enhances ignition and pyrolysis of the pulverized coal stream.
[0026] While the present invention has been described with
reference to the details of the embodiment of the invention shown
in the drawing, these details are not intended to limit the scope
of the invention as claimed in the appended claims.
* * * * *