U.S. patent application number 11/077062 was filed with the patent office on 2006-09-14 for cyclone furnace for oxygen fired boilers with flue gas recirculation.
Invention is credited to Douglas J. Devault, Dennis K. McDonald.
Application Number | 20060201405 11/077062 |
Document ID | / |
Family ID | 36969466 |
Filed Date | 2006-09-14 |
United States Patent
Application |
20060201405 |
Kind Code |
A1 |
Devault; Douglas J. ; et
al. |
September 14, 2006 |
Cyclone furnace for oxygen fired boilers with flue gas
recirculation
Abstract
A cyclone furnace and method uses a cyclone burner having a
cyclone barrel with a re-entrant throat connected to a main furnace
for passing combustion products including flue gas that is rich in
carbon dioxide. Crushed coal and oxygen are supplied the cyclone
burner and at least some of the flue gas from the main furnace is
recirculated to the cyclone barrel.
Inventors: |
Devault; Douglas J.;
(Rootstown, OH) ; McDonald; Dennis K.; (Massillon,
OH) |
Correspondence
Address: |
THE BABCOCK & WILCOX COMPANY
PATENT DEPARTMENT
20 SOUTH VAN BUREN AVENUE
BARBERTON
OH
44203
US
|
Family ID: |
36969466 |
Appl. No.: |
11/077062 |
Filed: |
March 10, 2005 |
Current U.S.
Class: |
110/266 ;
110/347 |
Current CPC
Class: |
F23C 5/12 20130101; F23C
9/003 20130101; F23C 6/04 20130101 |
Class at
Publication: |
110/266 ;
110/347 |
International
Class: |
F23D 1/00 20060101
F23D001/00 |
Claims
1. A cyclone furnace comprising: a cyclone burner having a cyclone
barrel with a re-entrant throat; a main furnace connected to the
re-entrant throat for passing combustion products from the
re-entrant throat to and along the main furnace, the combustion
products including flue gas that is rich in carbon dioxide; crushed
solid fuel supply means connected to the cyclone barrel for
supplying fuel to the cyclone burner; oxygen supply means connected
to the cyclone barrel for supplying oxygen that is substantially
free of nitrogen to the cyclone burner; and means for recirculating
at least some of the flue gas from the main furnace to the cyclone
barrel.
2. A cyclone furnace according to claim 1, including means for
supplying primary, secondary and tertiary flue gas to the cyclone
furnace, at least one of the primary, secondary and tertiary flue
gas supply means forming the oxygen supply means.
3. A cyclone furnace according to claim 1, wherein the crushed
solid fuel supply means comprise means for supplying crushed coal
to the cyclone furnace.
4. A method of operating a cyclone furnace having a cyclone burner
with a cyclone barrel and a re-entrant throat, and a main furnace
connected to the re-entrant throat, the method comprising:
supplying crushed solid fuel to the cyclone barrel; supplying
oxygen that is substantially free of nitrogen to the cyclone
barrel; igniting the oxygen and crushed fuel in the cyclone burner
for creating combustion products that are passed to and along the
main furnace, the combustion products including flue gas that is
rich in carbon dioxide; and recirculating at least some of the flue
gas from the main furnace to the cyclone barrel.
5. A method according to claim 4, including supplying primary,
secondary and tertiary flue gas to the cyclone furnace, wherein at
least one of the primary, secondary and tertiary flue gas is
enriched with oxygen.
6. A method according to claim 4, including supplying crushed coal
as the crushed solid fuel.
Description
FIELD AND BACKGROUND OF INVENTION
[0001] The present invention relates generally to the field of
furnaces, and in particular to a new and useful cyclone furnace
which produces reduced emissions of NOx.
[0002] Cyclone furnaces have been in use since the early 1950's as
an efficient method for combusting coal. They also allow for a
smaller boiler because up to 90% of the ash is tapped out of the
furnace bottom permitting a smaller convection pass without
slagging on the heat transfer surface. However, with the more
stringent NOx emissions in today's environment, cyclone furnaces
are no longer a desirable method of coal combustion because of
their heavy NOx production.
[0003] More information about the construction and operation of
cyclone furnaces can be found in the publication STEAM--ITS
GENERATION AND USE, 40.sup.TH EDITION, published by Babock &
Wilcox, a McDermott Company, at Chapter 14.
SUMMARY OF INVENTION
[0004] It is an object of the present invention to provide a
cyclone furnace method and apparatus which reduces NOx emissions
while retaining many of the advantages of cyclone furnaces.
[0005] One new technology being studied to facilitate carbon
sequestration by concentrating carbon dioxide is firing a boiler
with oxygen injected into recirculated flue gas instead of air. A
concentrated CO.sub.2 stream is of interest because it can be more
easily sequestered. An additional benefit of oxygen firing a boiler
is that it also results in very low NOx emissions because the
nitrogen normally introduced with air firing is no longer present
in the recirculated flue gas. However, along with the high
concentration of carbon dioxide in the recirculated flue gas is
also a high concentration of moisture. Because of these two
concentrations, complete combustion of the coal becomes problematic
with pulverized coal firing methods.
[0006] The present invention uses cyclone burners in a new boiler
utilizing oxygen combustion with recirculated flue gas for the
purpose of concentrating carbon dioxide. This combination takes
advantage of the combustion efficiency of cyclone furnaces to
overcome the problems of high moisture inherent in recirculated
flue gas and eliminates the high NOx levels produced by air-fired
cyclones. Additional benefits are: 1) the lower fly-ash produced
allows high convection pass velocities resulting in a closer spaced
convection pass design and a smaller boiler and 2) the elimination
of pulverizers, since only crushed coal is needed, reduces
auxiliary power helping to compensate for the power consumption
needed to produce oxygen.
[0007] Accordingly, an object of the present invention is to
provide a cyclone furnace comprising: a cyclone burner having a
cyclone barrel with a re-entrant throat; a main furnace connected
to the re-entrant throat for passing combustion products from the
re-entrant throat to and along the main furnace, the combustion
products including flue gas that is rich in carbon dioxide; crushed
solid fuel supply means connected to the cyclone barrel for
supplying fuel to the cyclone burner; oxygen supply means connected
to the cyclone barrel for supplying oxygen that is substantially
free of nitrogen to the cyclone burner; and means for recirculating
at least some of the flue gas from the main furnace to the cyclone
barrel.
[0008] Another object of the present invention is to provide a
method of operating a cyclone furnace having a cyclone burner with
a cyclone barrel and a re-entrant throat, and a main furnace
connected to the re-entrant throat, the method comprising:
supplying crushed solid fuel to the cyclone barrel; supplying
oxygen that is substantially free of nitrogen to the cyclone
barrel; igniting the oxygen and crushed fuel in the cyclone burner
for creating combustion products that are passed to and along the
main furnace, the combustion products including flue gas that is
rich in carbon dioxide; and recirculating at least some of the flue
gas from the main furnace to the cyclone barrel.
[0009] The various features of novelty which characterize the
invention are pointed out with particularity in the claims annexed
to and forming a part of this disclosure. For a better
understanding of the invention, its operating advantages and
specific objects attained by its uses, reference is made to the
accompanying drawings and descriptive matter in which a preferred
embodiment of the invention is illustrated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] In the drawings:
[0011] FIG. 1 is the only figure in the drawings and is a schematic
side elevation view of a cyclone furnace according to the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0012] Referring now to the drawing, FIG. 1 shows a cyclone furnace
generally designated 10 having a cyclone burner generally
designated 12 with a generally cylindrical cyclone barrel 14 having
an outlet or re-entrant throat 16 for discharging combustion
products that have been produced in the cyclone furnace as will be
explained later in this disclosure. The throat 16 is connected to
the lower end of a main furnace 18 with the upwardly directed
arrows identify the combustion products which include flue gases
that are rich in carbon dioxide.
[0013] Heat from these hot combustion products are taken away
preferably by tubes containing water and/or steam in the
environment of a boiler where the heat is used for other
purposes.
[0014] Crushed rather than pulverized coal is stored in a coal
bunker 20 and, using known equipment, is supplied along a fuel
supply line 22 to a crushed coal inlet at the top of a radial
burner 24. Primary and tertiary flue gas are supplied to burner 24
by supply means 26 while primary flue gas is supplied in a
tangential direction to the cyclone barrel 14 by primary flue gas
supply means 28.
[0015] According to the present invention, one or more of the
primary, secondary and tertiary flue gas supplies, rather than
supplying air to the cyclone furnace, supply oxygen which is
substantially free of nitrogen although pure oxygen is not
necessary.
[0016] The oxygen enriched flue gas is then mixed with the crushed
coal and ignited by a main oil or gas burner in a known manner to
produce a swirling mass of combustion products symbolized by the
swirl lines within barrel 14.
[0017] According to a significant feature of the present invention,
at least some of the carbon dioxide rich flue gases are recycled or
recircluated along a recirculation line 30 back to the cyclone
furnace. The recirculated flue gas is supplied separately or as
part of any one of the primary, secondary or tertiary flue gas
streams or oxygen mixed in the streams.
[0018] It has been found that by reducing or eliminating the
presence of nitrogen by using oxygen enriched flue gas instead of
air and by recirculating the carbon dioxide rich flue gas that the
efficiency of the cyclone furnace is maintained while the NOx
emissions are significantly reduced.
[0019] Various gas purifying mechanisms symbolized by box 32 can be
provided before the flue gas is returned to the cyclone furnace
which may be nothing more than filtering out of larger particles or
may be a more elaborate scrubbing and filtration process.
[0020] Although crush coal is the preferred fuel for the present
invention, other crushed solid fuel may be utilized.
[0021] Advantages of the invention over conventional pulverized
coal firing include: [0022] 1. High combustion efficiency of the
coal even with high concentrations of carbon dioxide and moisture
in the recycled flue gas. [0023] 2. Low fly-ash discharge in the
flue gas allows for smaller particulate removal equipment. [0024]
3. Low fly-ash discharge in the flue gas allows for higher
convection pass velocities and thus a smaller boiler. [0025] 4.
Because the cyclone furnaces use crushed coal, no expensive
pulverizers are required saving capital cost and eliminating
significant auxiliary power
[0026] 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 may be embodied otherwise without departing from such
principles.
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