U.S. patent application number 14/550101 was filed with the patent office on 2016-05-26 for plant, combustion apparatus, and method for reduction of nox emissions.
The applicant listed for this patent is ALSTOM Technology Ltd. Invention is credited to Mitchell B. COHEN, Todd D. Hellewell.
Application Number | 20160146462 14/550101 |
Document ID | / |
Family ID | 54608974 |
Filed Date | 2016-05-26 |
United States Patent
Application |
20160146462 |
Kind Code |
A1 |
COHEN; Mitchell B. ; et
al. |
May 26, 2016 |
PLANT, COMBUSTION APPARATUS, AND METHOD FOR REDUCTION OF NOx
EMISSIONS
Abstract
A combustion apparatus includes a combustion chamber having
multiple combustion zones. A first wind box is in communication
with the first combustion zone to feed the fuel to be fed into the
combustion chamber for initial combustion of the fuel within the
first combustion zone. A second wind box has a reburner in
communication with the second combustion zone. The reburner is
configured to feed fuel, a reagent and a first portion of the flue
gas to be recycled to the second combustion zone into the second
combustion zone to reduce nitrogen oxide emissions of the
apparatus. A third wind box is in communication with the third
combustion zone to feed air to the third combustion zone to
complete the combustion process.
Inventors: |
COHEN; Mitchell B.; (West
Hartford, CT) ; Hellewell; Todd D.; (Windsor,
CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ALSTOM Technology Ltd |
Baden |
|
CH |
|
|
Family ID: |
54608974 |
Appl. No.: |
14/550101 |
Filed: |
November 21, 2014 |
Current U.S.
Class: |
110/342 ;
110/205; 110/208; 110/212; 110/214; 431/9 |
Current CPC
Class: |
F23C 6/047 20130101;
F23C 2201/101 20130101; F23C 9/00 20130101; F23D 1/00 20130101;
F23D 14/20 20130101; F23C 2900/06041 20130101; F23C 5/32 20130101;
F23C 2201/301 20130101; F23C 6/045 20130101; F23J 7/00 20130101;
Y02E 20/34 20130101; F23L 9/04 20130101; F23C 5/12 20130101; F23C
2201/20 20130101; Y02E 20/344 20130101; F23L 7/007 20130101; F23C
2900/99004 20130101; F23C 9/06 20130101 |
International
Class: |
F23J 7/00 20060101
F23J007/00; F23C 9/00 20060101 F23C009/00; F23C 6/04 20060101
F23C006/04; F23D 14/20 20060101 F23D014/20; F23C 9/06 20060101
F23C009/06 |
Claims
1. A combustion apparatus, comprising: a combustion chamber having
multiple combustion zones for combustion of fuel, the combustion
zones including a first combustion zone, a second combustion zone,
and a third combustion zone wherein the second combustion zone is
located between the first and third combustion zones, the
combustion chamber having at least one outlet configured to emit
flue gas formed from combustion of the fuel in the combustion
chamber; a first wind box in communication with the first
combustion zone for feeding of fuel into the combustion chamber for
initial combustion within the first combustion zone; a second wind
box in communication with second combustion zone to feed a first
gas having oxygen into the second combustion zone; a third wind box
in communication with the third combustion zone to feed a second
gas having oxygen into the third combustion zone; and a conduit in
communication with the second combustion zone to feed a reagent
into the second combustion zone.
2. The combustion apparatus of claim 1, wherein the second wind box
has a reburner in communication with the second combustion zone,
the reburner configured to feed fuel into the second combustion
zone and also feed the reagent into the second combustion zone.
3. The combustion apparatus of claim 2, wherein the reburner
comprises a nozzle that is configured to spray the reagent into the
second combustion zone with the fuel fed to the second combustion
zone via the second feed conduit.
4. The combustion apparatus of claim 1, wherein the first and
second gases are air.
5. The combustion apparatus of claim 2, wherein each of the first,
second and third feed conduits comprise at least one wind box.
6. The combustion apparatus of claim 5, wherein the reburner is
positioned at an upper compartment of the second wind box or is
positioned above the second wind box between the second wind box
and the third wind box.
7. The combustion apparatus of claim 1, wherein at least one of the
first, second, and third wind boxes are configured to facilitate
tangential firing of fuel.
8. The combustion apparatus of claim 2, wherein the reburner is
also configured to feed a first portion of the flue gas to be
recycled into the second combustion zone.
9. The combustion apparatus of claim 1, wherein the reagent is
provided to the second combustion zone at an upper compartment of
the second wind box or is positioned above the second wind box
between the second wind box and the third wind box.
10. The combustion apparatus of claim 1, wherein the second wind
box is configured to feed a first portion of the flue gas to be
recycled into the second combustion zone with the reagent to
facilitate mixing of the reagent within the second combustion
zone.
11. A method of operating a combustion apparatus having a
combustion chamber including a first combustion zone, a second
combustion zone, and a third combustion zone wherein the second
combustion zone is located between the first and third combustion
zones; the method comprising: providing a first fuel into the first
combustion zone of the combustion chamber; providing a reagent and
a first gas having oxygen to the second combustion zone of the
combustion chamber; and providing a second gas having oxygen to the
third combustion zone of the combustion chamber.
12. The method of claim 11 further comprising: feeding a second
fuel to the second combustion zone, wherein the reagent and the
second fuel are simultaneously fed to the second combustion
zone.
13. The method of claim 12 further comprising: recycling a first
portion of flue gas exiting the combustion chamber to the second
combustion zone such that the reagent, the second fuel and the
first portion of the flue gas are simultaneously fed to the second
combustion zone.
14. The method of claim 13 wherein the first and second gases are
air.
15. The method of claim 12, wherein: the first fuel is coal and the
first fuel is fed into the first combustion zone; the second fuel
is natural gas or oil; and the reagent is one of aqueous ammonia,
aqueous urea, and anhydrous ammonia.
16. The method of claim 12, wherein: the first, second, and third
combustion zones are each positioned adjacent to a respective wind
box; and the second fuel being fed into the second combustion zone
via a sole reburner of the wind box of the second combustion zone,
the reburner being positioned at one of: an upper compartment of
the wind box of the second combustion zone, and above the wind box
of the second combustion zone between the wind box of the second
combustion zone and the wind box of the third combustion zone.
17. The method of claim 11, wherein the feeding of the first fuel
into the combustion chamber comprises feeding the first fuel into
the first combustion zone, the method also comprising: feeding a
second fuel to the second combustion zone, the second fuel
differing from the first fuel such that the reagent and the second
fuel are simultaneously fed to the second combustion zone; and
combusting the first fuel in the combustion chamber via a
tangential firing system.
18. The method of claim 11, wherein the reagent is a liquid and is
sprayed into the second combustion zone.
19. The method of claim 18, wherein the reagent is fed into the
second combustion zone while no fuel is fed into the second
combustion zone via a reburner.
20. The method of claim 12, wherein the reagent is provided to the
second combustion zone above the location where the gas having
oxygen is provided to the second combustion zone.
Description
FIELD
[0001] The present innovation is related to apparatuses configured
to combust a fuel and methods of making and using the same, and
more specifically a combustion apparatus for burning a fuel with
reduced NO.sub.x emissions.
BACKGROUND
[0002] Combustion systems can include combustors such as a boiler,
an incinerator system, or a furnace. Examples of combustion systems
are disclosed in U.S. Pat. Nos. 4,719,587, 5,315,939, 5,443,805,
5,626,085, 6,258,336, 6,598,399, 8,375,723, and 8,434,311 and
European Patent No. 1 530 994. Pollutants such as nitrogen oxides
(e.g. NO, NO.sub.2, NO.sub.x) and sulfur oxides (e.g. SO.sub.2,
SO.sub.3, SO.sub.x) can be emitted from operation of combustion
systems. Operators of combustion systems may utilize pollution
control equipment (e.g. desulfurization units, scrubbers, etc.) to
help ensure clean and environmentally sound operation of the
combustion systems.
SUMMARY
[0003] According to aspects illustrated herein, a combustion
apparatus includes a combustion chamber having multiple combustion
zones for combustion of fuel. The combustion zones can include a
first combustion zone, a second combustion zone, and a third
combustion zone. The second combustion zone can be located between
the first and third combustion zones. The combustion chamber can
have at least one outlet configured to emit flue gas formed from
combustion of the fuel in the combustion chamber. A first wind box
can be in communication with the first combustion zone for feeding
of fuel into the combustion chamber for initial combustion within
the first combustion zone. A second wind box can be configured to
feed a gas having oxygen into the second combustion zone. A third
wind box can be in communication with the third combustion zone to
feed a gas having oxygen into the third combustion zone. A conduit
provides a reagent to the second combustion zone.
[0004] According to other aspects illustrated herein, a method of
operating a combustion apparatus can include the step of feeding a
first fuel into a combustion chamber having multiple combustion
zones for combustion of the first fuel. The combustion zones can
include a first combustion zone, a second combustion zone, and a
third combustion zone. The second combustion zone can be located
between the first and third combustion zones. The vessel can have
at least one outlet configured to emit flue gas from the combustion
chamber after the flue gas is formed from combustion of the first
fuel. The method can also include the step of feeding a gas having
oxygen and a reagent to the second combustion zone. Further, the
method includes feeding a gas having oxygen to the second
combustion zone.
[0005] The above described and other features are exemplified by
the following figures and Detailed Description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] Exemplary embodiments of an apparatus, a plant, and
associated exemplary methods are shown in the accompanying
drawings. It should be understood that like reference numbers used
in the drawings may identify like components, wherein:
[0007] FIG. 1 is a schematic diagram of an exemplary embodiment of
a plant in accordance with the present invention.
[0008] FIG. 2 is a cross-sectional view of an embodiment of a
reburner disposed in an upper compartment of a second wind box of a
combustion apparatus in accordance with the present invention.
[0009] FIG. 3 is a block diagram illustrating a plurality of
stacked compartments of respective vertically-aligned first, second
and third wind boxes to provide material to a combustion apparatus
of a plant in accordance with the present invention.
[0010] FIG. 4 is a fragmentary side view of an exemplary air nozzle
disposed within a compartment of a third wind box to provide air to
a third combustion zone of a combustion chamber of a plant in
accordance with the present invention.
[0011] FIG. 5 is a bar graph illustrating an amount of nitrogen
oxides (NO.sub.x) that may be emitted from a combustion apparatus 5
using different types of fuel, types A, B, C, D, and E for 3
different configurations of combustion apparatus. Type A is a low
volatile bituminous coal, type B is a medium volatile bituminous
coal, type C is a high volatile bituminous coal, type D is a
subbituminous coal, and type E is lignite. The vertical axis of the
chart identifies the amount of NO.sub.x emitted as a ratio in which
a pound of NO.sub.x is emitted per every million British Thermal
Unit (BTU) of heat fired from the combustion of the fuel fed into
the combustion apparatus 5. The horizontal axis of the chart
identifies the type of fuels being compared. A conventional
combustion apparatus is identified as bars 61 in the chart, an
embodiment of the combustion apparatus disclosed herein that only
utilizes a reburner without the feeding of a reagent is identified
as bars 62 in the chart and an embodiment of the combustion
apparatus that utilizes a reburner and the feeding of a reagent
into the second combustion zone, which is identified as bars 63 in
the chart.
[0012] FIG. 6 is a graph illustrating a percentage reduction of
NO.sub.x versus the stoichiometry within the second combustion zone
of a combustion apparatus in accordance with the present invention.
As shown in the vertical axis of the graph, that was calculated for
given stoichiometries within the second combustion zone 5b for
embodiments of the plant and combustion apparatus 5. The
stoichiometry ratio within the second combustion zone 5b for the
combustion apparatus is identified in the horizontal axis of the
graph. The stoichiometry ratio expresses a ratio for an amount of
the oxygen needed to fully combust the fuel within the second
combustion zone 5b as compared to the amount of fuel within the
second combustion zone 5b. A number over 1.0 indicates that that
there is an excess of oxygen needed to fully combust the fuel and a
number below 1.0 indicates that there is not enough oxygen to
completely combust the fuel within the second combustion zone. The
Line 71 of the graph refers to an embodiment of the combustion
apparatus in which only a reburner 30 of the second wind box 4 is
utilized. Line 72 of the graph identifies an embodiment of the
combustion apparatus in which only the feeding of a reagent via the
second wind box 4 of the combustion apparatus is utilized. Line 73
of the graph identifies an embodiment of the combustion apparatus
that utilizes both the reburner 30 and the feeding of the reagent
via the second wind box 4.
[0013] FIG. 7 is a graph illustrating a percentage of the reburn
NO.sub.x reduction efficiency as compared to a percentage of heat
input provided by the reburner fuel fed into the second combustion
zone as compared to the entire amount of fuel fed into the
combustion apparatus for embodiments of the combustion apparatus in
accordance with the present invention. The vertical axis of the
graph of FIG. 7 identifies the percentage of the NO.sub.x reduction
efficiency and the horizontal axis of the graph identifies the
percentage of heat input provided by the fuel fed into the second
combustion zone 5b via the reburner 30 as compared to the total
amount of fuel fed into the combustion apparatus for combustion.
Line 74 of the graph of FIG. 7 illustrates the calculated results
for an embodiment of the combustion apparatus utilizing the
reburner 30 of the second wind box 4 as well as the feeding of a
reagent into the second combustion zone 5b. Line 75 of the graph of
FIG. 7 illustrates the calculated results from a conventional
combustion apparatus utilizing a conventional reburner system.
[0014] FIG. 8 is a graph illustrating an extent of the reburn of
NO.sub.x reduction efficiency provided by an embodiment of the
combustion apparatus as compared to an amount of NO.sub.x fed from
the first combustion zone into the second combustion zone 5b in
parts per million volumetric dry (ppmvd) concentration based on a
reference percentage oxygen. The vertical axis of the graph of FIG.
8 illustrates that the NO.sub.x reduction efficiency is independent
of the inlet NO.sub.x concentration entering the second combustion
zone 5b. A calculated maximum efficiency level (MAX) is identified
on the vertical axis. The horizontal axis of the graph of FIG. 8 is
the amount of the NO.sub.x initially fed into the second combustion
zone 5b in ppmvd concentration referenced to percentage oxygen.
[0015] FIG. 9 is a graph illustrating an extent of the reburn of
NO.sub.x reduction efficiency provided by an embodiment of the
combustion apparatus as compared to a fuel ratio of the fuel being
fed into the combustion apparatus for combustion in accordance with
the present invention. The fuel ratio defined as the fixed carbon
to volatile ratio from a fuel's proximate analysis is identified in
the horizontal axis of the graph of FIG. 9. The fuel ratio is a
measure of the reactivity of a fuel. The vertical axis of the graph
of FIG. 9 illustrates calculated levels of NO.sub.x reduction
efficiency and identifies a calculated maximum efficiency level
(MAX).
[0016] FIG. 10 is a plan view of a combustion chamber of a
tangentially-fired system in accordance with the present
invention.
[0017] Other details, objects, and advantages of embodiments of the
innovations disclosed herein will become apparent from the
following description of exemplary embodiments and associated
exemplary methods.
DETAILED DESCRIPTION
[0018] Referring to FIGS. 1-4, a plant 1 is shown that is
configured to generate electricity. In some embodiments, the plant
can be an industrial plant, a power plant, or an electricity
generation plant. The plant 1 includes a combustion apparatus 5,
such as, for example, a boiler or a furnace. The combustion
apparatus 5 can include a vessel defining a combustion chamber 10.
Fuel is provided to and combusted in the combustion chamber 10
which generates a flue gas having steam and other combustion
products (e.g. carbon dioxide, nitrogen, oxygen, water vapor,
etc.). The combustion process can be utilized to heat water and
steam which can be used to generate electricity and/or other
desirable process elements that can be used downstream of the
combustion apparatus 5. The flue gas formed in the combustion
chamber 10 of the combustion apparatus 5 may be provided to at
least one outlet 7.
[0019] Heat from the flue gas can be transferred to water, steam
and/or other fluids passing through water wall tubes (not shown) or
other heat exchangers to generate heated gas or fluid for use by a
generator unit 19 of the plant 1. For instance, flue gas passing
through the outlet 7 may pass through one or more heat exchangers
(i.e., superheaters and economizers) for heating water and/or steam
to be fed to a turbine of the generator unit 19 to generate
electricity.
[0020] The fuel can be a fossil fuel such as coal, oil, or natural
gas or any another type of carbonaceous fuel. The fuel can be fed
from a first fuel source 3. The first fuel source 3 may include,
for example, a coal mill that is configured to comminute coal and
mix the comminuted coal with air for feeding the fuel to the
combustion apparatus 5. In other embodiments, the source of fuel
for the first fuel source 3 may be a vessel or other storage device
that retain the fuel, such as pulverized coal, natural gas or oil
for feeding to the combustion apparatus 5.
[0021] As best shown in FIG. 1, the combustion chamber 10 of the
combustion apparatus 5 can include multiple combustion zones 5a,
5b, 5c. For example, the combustion zones 5a, 5b, 5c can include a
first combustion zone (or main burner zone) 5a, a second combustion
zone (or lower separated over fired air (SOFA) zone) 5b, and a
third combustion zone (or upper separated over fired air (SOFA)
zone) 5c. The second combustion zone 5b is located between the
first and third combustion zones 5a, 5c. In some embodiments in
which flue gas flows vertically upward through the combustion
chamber 10 along its longitudinal axis, the second combustion zone
5b is an intermediate combustion zone within the combustion chamber
10 that is vertically higher than and downstream of the first
combustion zone 5a and vertically lower than and upstream of the
third combustion zone 5c. Similarly for embodiments in which the
longitudinal axis of the combustion chamber 10 is horizontal, the
second combustion zone 5b may be disposed intermediate to the first
combustion zone 5a and the third combustion zone 5c, both of which
are disposed at opposing ends of the combustion chamber 10. Each
combustion zone 5a, 5b, 5c includes a burnout zone disposed in the
upper portion or downstream portion of each respective combustion
zone which will be described in greater detail hereinafter.
[0022] As best shown in FIGS. 1 and 3, a plurality of wind boxes 2,
4, 6 are in fluid communication with respective combustion zones
5a, 5b, 5c of the combustion chamber 10 to provide the material
needed for combustion. Each wind box 2, 4, 6 includes a plurality
of longitudinally stacked compartments, which will be described in
greater detail hereinafter, wherein each compartment includes an
associated nozzle, burner, ejector, conduit, duct or other
apparatus disposed therein for providing material into the
combustion chamber 10 of the combustion apparatus 5. For instance,
a first wind box 2 provides material to the first combustion zone
5a. A second wind box 4 provides material to the second combustion
zone 5b. A third wind box 6 provides material to the third
combustion zone 5c. Fuel from the first fuel source 3 can be fed to
the first wind box 2 via a fuel feed conduit connected between the
first fuel source 3 and the first wind box 2 to provide the fuel to
the first combustion zone 5a. Air from a source of air 17 is also
provided to the first wind box 2 via an air feed conduit connected
between the source of air 17 and the first wind box 2. At least one
fan or other type of air flow driving mechanism (not shown) can be
included in the source of air 17 or may be in communication with
the source of air to drive the flow of air from the source of air
17 into the first combustion zone 5a via the first wind box 2. The
air may be mixed with the fuel prior to the fuel and the air being
provided into the first wind box 2 or into the first combustion
zone 5a. The fuel and air provided into the first combustion zone
5a via the first wind box 2 may be fed to the first combustion zone
for initial combustion of the fuel in the first combustion zone 5a.
While the air source 17 provides air, the present invention
contemplates the air source 17 may provide any gas having oxygen,
including a pure oxygen stream.
[0023] An exemplary structure of the first, second, and third wind
boxes 2, 4, and 6 can be appreciated from FIG. 3. The first wind
box 2 can be configured as a main wind box and the second and third
wind boxes 4 and 6 can be configured as multi-level separated over
fire air (SOFA) wind boxes. In some embodiments, the second wind
box 4 can be configured as a lower separated over fire air wind box
and the third wind box 6 can be configured as an upper separated
over fire air wind box.
[0024] The first wind box 2 can be configured to include multiple
compartments 2a-2q that are positioned in longitudinal or vertical
alignment for the feeding of fuel and other material into the first
combustion zone 5a. For example, the first wind box 2 may include
first and second compartments 2a and 2b that are configured to
provide close couple over fire air (CCOFA) to the first combustion
zone 5a. The third compartment 2c, sixth compartment 2f, tenth
compartment 2j, and seventeenth compartment 2q can be configured to
feed air or oxygen to the first combustion zone 5a. The fourth,
eighth, twelfth, and sixteenth compartments 2d, 2h, 2l, and 2p can
be configured to feed fuel from the first fuel source 3 to the
first combustion zone 5a. The fifth compartment 2e, seventh
compartment 2g, ninth compartment 2i, eleventh compartment 2k,
thirteenth compartment 2m, and fifteenth compartment 2o can be
configured to provide additional offset air to the first combustion
zone 5a. The fourteenth compartment 2n can be configured to feed
fuel from the second fuel source 3a as indicated by broken line in
FIG. 1 for startup and shut-down operations of the combustion
apparatus 5 when the second fuel source is natural gas or oil. In
some embodiments, the fourteenth compartment 2n can be configured
to feed oil, natural gas, or other fuel source from a third fuel
source (not shown). The combustion region above the close coupled
over fire air (CCOFA) compartments 2a, 2b of the first wind box 2
and below the second wind box 4 is the burnout region of the first
combustion zone 5a where combustion continues above or downstream
of the first wind box.
[0025] The second wind box 4 and third wind box 6 can each be
configured to have fewer compartments than the first wind box 2.
For instance, the second wind box 4 can be configured to include an
upper compartment 4a, a lower compartment 4c, and an intermediate
compartment 4b that is between the upper and lower compartments 4a,
4c. In one embodiment, the upper or topmost compartment 4a can
include a reburner 30 in some embodiments. The reburner 30 can be
the sole reburner for feeding fuel into the second combustion zone
5b in some embodiments. In addition, a reagent can also be fed into
the second combustion zone via the upper compartment 4a in addition
to the use of the sole reburner 30 or as an alternative to the
reburner 30. The intermediate and lower compartments 4b and 4c can
be configured to feed air into the second combustion zone 5b. The
combustion region above the second wind box 4 and below the third
wind box 6 is the burnout region of the second combustion zone 5a
where combustion and reaction of the reagent continues above or
downstream of the second wind box.
[0026] The third wind box 6 can also have upper, intermediate and
lower compartments 6a, 6b, and 6c. Each of these compartments of
the third wind box 6 can be configured to feed air into the third
combustion zone 5c. The combustion region above the upper separated
over fire air (SOFA) compartments 6a, 6b, 6c of the third wind box
6 is the burnout region of the third combustion zone 5a where
combustion continues above or downstream of the third wind box.
[0027] The first, second and third wind boxes 2, 4, and 6 can each
be configured to emit a flow of fluid into the combustion chamber
of the combustion apparatus 5 so that the pitch and yaw of the flow
of fluid is adjustable. For instance, as may be appreciated from
FIG. 4, the third wind box 4 can be configured to include an air
nozzle assembly 43 having a tilting mechanism 45 that can be
actuated to vertically tilt the nozzles 44 through which material,
for example air, is output from the compartments 6a, 6b, 6c of the
third wind box 6 to adjust the pitch (i.e., vertical tilt) at which
the material is fed into the third combustion zone 5c and to
actuate horizontal adjustment via a horizontal adjustment mechanism
46 to adjust the yaw (i.e., horizontal angle) at which the material
is fed into the third combustion zone 5c. The tilting mechanism 45
may include at least one actuator (e.g. a pneumatic or electric
cylinder) that is connected to the tilting mechanism 45 for
actuating vertical adjustments (pitch) of the nozzles 44. The
second wind box 4 can also include a tilting mechanism 45 for
adjusting the pitch and yaw of the nozzles 44 providing material
(for example air) from the top, intermediate and bottom
compartments 4a, 4b, 4c of the second wind box 4 into the second
combustion zone 5b of the combustion apparatus 5 in one embodiment.
Alternatively, the nozzle assembly 43 may include a tilt mechanism
45 for a pair of nozzles 44 that provide air to the intermediate
and lower compartments 4b, 4c, wherein the upper compartment 4a
provides the reburner 30 and/or reagent.
[0028] Fuel can also be fed to a fuel nozzle 30 (see FIG. 2) of the
reburner 30 which provides fuel to the second combustion zone 5b of
the combustion chamber 10 for combustion therein. The fuel fed to
the second combustion zone 5b can be fuel from the first and/or
second fuel source 3, 3a. A fuel feed conduit provides the second
fuel source 3a to the second wind box 4 for feeding the fuel to the
second combustion zone 5b via the second wind box 4. The fuel of
the second fuel source 3a can be different than the fuel from the
first fuel source 3. For example, the fuel of the first fuel source
3 can be coal and the fuel of the second fuel source 3a can be
natural gas or oil. As another example, the fuel of the first fuel
source 3 may be a first type of coal and the fuel of the second
fuel source 3a may be another type of coal (e.g. micronized coal).
In other embodiments, the fuel fed into the second combustion zone
5b can be from the first fuel source 3 as indicated by broken line
in FIG. 1 so that the same type of fuel is fed to the first and
second combustion zones 5a, 5b.
[0029] In some embodiments, the amount of fuel fed from the second
fuel source 3a to the reburner 30 of the second wind box 6 may be
between 10-15% of the total amount of heat fired from the fuel fed
to the combustion apparatus 5 for combusting therein. It has been
determined that use of a second type of fuel at the second
combustion zone 5b can provide a reduced amount of NO.sub.x, sulfur
oxides (e.g. SO.sub.2, SO.sub.3, etc.), carbon dioxide, and other
pollutants (e.g. particulates such as fly ash) being formed in the
flue gas formed from combustion of fuel in the combustion chamber
of the combustion apparatus 5. For example, use of natural gas as
the fuel of the second fuel source 3a when coal is used as the fuel
of the first fuel source 3 can help reduce the amount of NO.sub.x,
sulfur oxides, particulates, and carbon dioxide formed from further
combustion of the second fuel added at the second combustion zone
5b as compared to the use of the same coal as fed to the first
combustion zone 5a.
[0030] The second wind box 4 can also be configured to receive flue
gas and a reagent for feeding into the second combustion zone 5b.
The reagent can be received from a source of the reagent 15, which
may be a vessel, tank or other storage device that retains the
reagent. The reagent may be stored therein. The reagent may be
urea, ammonia, an amine based chemical compound (e.g. methylamine,
a primary amine, a secondary amine, a tertiary amine, or a cyclic
amine, etc.) or another type of reagent that can be fed into the
combustion chamber to remove nitrogen oxides (NO.sub.x) or elements
that contribute to the formation of NO.sub.x from the flue gas
formed when the fuel is combusted. The reagent may be in a liquid
state or a gaseous state. For example, in some embodiments the urea
may be an aqueous urea mixture (e.g. urea mixed with water), the
ammonia may be an aqueous ammonia (e.g. ammonia mixed with water),
or the reagent may be another type of aqueous state reagent that is
suitable for being sprayed into the second combustion zone via a
mechanical spray mechanism or an atomizer mechanism. As another
example, the reagent may be in a gaseous state such as anhydrous
ammonia, an anhydrous urea or other type of anhydrous reagent. In
some embodiments, a portion of the reagent material may be from
other process elements of the plant that emit the reagent and send
that reagent to the source of the reagent 15 for temporary storage
until it is fed to the second combustion zone 5b. The source of the
reagent 15 can be connected to the second wind box 4 via a reagent
feed conduit.
[0031] A portion of flue gas emitted from an outlet 7 of the
combustion apparatus 5 can be recycled to the nozzle or reburner 10
disposed in the second wind box 4 for feeding the flue gas, reagent
and fuel into the second combustion zone 5b. The recycled flue gas
to be recycled to the second wind box 4 may first pass through an
economizer 9 positioned in the outlet 7. The economizer 9 can be
configured to transfer heat from the flue gas passing therethrough
to another fluid (e.g. water) that passes through the economizer 9
to heat that fluid to a pre-selected temperature for use in another
process element of the plant 1, and thereby cool the flue gas prior
to being recycled. A flow control mechanism 11, such as a fan or
other type of gas flow driving mechanism, may be used to drive the
flue gas to be recycled back to the combustion apparatus 5 from the
economizer 9 to the second wind box 6. Another portion of the flue
gas may be provided to a gas processing unit 13 via a gas
processing unit feed conduit.
[0032] The gas processing unit 13 can be configured to remove fly
ash, sulfur oxides, and other elements from the flue gas prior to
that flue gas being emitted from the plant 1 or used in another
plant process. For instance, the gas processing unit 13 may include
a precipitator, a bag house, a desulfurization unit, and other gas
processing elements that are configured to remove elements from the
flue gas prior to the flue gas being emitted from the plant 1
and/or utilized in another plant process.
[0033] In one embodiment as describe hereinbefore, the second wind
box 4 can also include a reburner or fuel nozzle 30. An example of
a reburner 30 is shown in FIG. 2. The reburner 30 can be positioned
in an upper compartment 4a of the second wind box 4. For instance,
in some embodiments a sole reburner 30 may be the only reburner of
the second wind box 4 and may be located at the top compartment 4a
of the second wind box 4 or may be located in the compartment 4a of
the second wind box that is closest to the third combustion zone
5c. The reburner 30 may be disposed in the second wind box 4 so
that the second combustion zone 5b receives a flow of flue gas 21
from the recycle conduit after that flue gas has passed through the
economizer 9, a flow of reagent 23 from the source of the reagent
15, and a flow of fuel 25 from the first fuel source 3 or the
second fuel source 3a so that the reagent, flue gas, and fuel can
be simultaneously fed to the second combustion zone 5b. In some
embodiments, the reagent, fuel and flue gas can be fed in the
second combustion zone 5b via a concentric ring nozzle 39. One will
appreciate that the flue gas functions as a carrier gas to improve
penetration and distribution of the gaseous reagent into the second
combustion zone 5b to enable more efficient reaction between the
reagent and the flue gas flowing through the combustion chamber 10.
The recycled flue gas further increases the mass and volume of the
flue gas and reagent mixture to increase the penetration and
distribution of the gaseous reagent into the second combustion zone
5b.
[0034] While recycled flue gas is provided to the reburner 30 to
function as a carrier gas to optimize penetration of the reagent
into the second combustion zone 5b, one will appreciate that the
carrier gas may be any oxygen-deficient carrier gas, for example
steam, to provide the optimum stoichiometric condition within the
second combustion zone 5b. Depending upon the amount of reagent
being provided to the combustion chamber 10 and the condition
within the combustion chamber, the carrier gas (e.g., flue gas and
steam) may not be needed. In another embodiment, the reagent may be
injected as a liquid wherein a carrier gas may not be needed. For
example, a pump or other type of liquid reagent flow control device
(not shown) can be in communication with a liquid reagent storage
vessel 15 and be configured to drive the flow of the liquid reagent
into the second combustion zone 5b. In this embodiment, the liquid
reagent can be fed via an atomizer that is configured to inject the
reagent as an atomized liquid spray to inject the liquid reagent
into the second combustion zone 5b to help facilitate optimum
penetration and mixing of the liquid reagent with the flue gas
flowing through the combustion chamber 10. Embodiments that utilize
a liquid reagent for injection into the second combustion chamber
5b can allow for the removal of a carrier gas (e.g. flue gas or
steam) and may allow for the elimination of costly equipment, such
as gas recirculation fans, ductwork, and controls for such
elements.
[0035] While the reagent is shown to be provided to the second
combustion zone 5b through the reburner 30 or second wind box 4,
one will appreciate that the reagent can be injected at a location
above the second wind box 4. For instance, the reagent may be
injected at a location above the reburner 30 and/or the second wind
box 4, but below the third wind box 6. Reagent injection can also
be provided at this location, provided the injection location is
disposed at a sufficient distance from the third wind box 6 to
provide sufficient resident time for the reagent to react with the
flue gas.
[0036] The invention further contemplates that the feeding of the
fuel and/or reagent to the second combustion zone 5b may be
selectively stopped by a control valve in response to the
stoichiometric conditions within the combustion chamber 10, such
that fuel or reagent is provided to the second combustion zone of
the combustion chamber via the upper portion of the second wind box
4.
[0037] The use of the reburner 30 can help provide a reduction of
NO.sub.x emissions based upon the injection of the fuel into the
second combustion zone so that an oxygen deficient volume within
the second combustion zone exists so that the reburn fuel can help
break down the formation of nitrogen containing hydrocarbon
radicals that can contribute to formation of NO.sub.x when reacting
with the products of the combustion of the fuel fed into the first
combustion zone 5a. Hydrocarbon radicals from the fuel fed into the
second combustion zone 5b can function to strip the oxygen from the
NO.sub.x to form elemental nitrogen, water vapor, carbon monoxide,
carbon dioxide, and other reduced species and compounds. One of the
primary chemical NO.sub.x destruction mechanisms of the reburn
process via the fuel fed to the second combustion zone 5b is set
forth below:
##STR00001##
[0038] High temperature reagent injection utilizing the reagent
from the upper compartment of the second wind box 4 can provide a
further mechanism for reducing NO.sub.x based on producing amine
radicals. The chemical NO.sub.x destruction mechanism of the high
temperature reagent injection process can be illustrated by the
formula: NO+NH.sub.2.fwdarw.N.sub.2+H.sub.2O.
[0039] The amount of fuel and/or reagent injected into the second
combustion zone 5b can be a relatively small amount as compared to
the volume of flue gases generated from combustion of the fuel in
the first combustion zone 5a that subsequently passes into the
second combustion zone 5b. A higher reburn fuel feed velocity
and/or reagent feed velocity can help provide effective penetration
and rapid mixing of the reagent and fuel. Fuel and/or reagent feed
line pressures can be set to help ensure that the fuel and/or
reagent is fed into the second combustion zone 5b at a pre-selected
velocity to facilitate effective penetration and mixing. The mixing
of the reagent can also be facilitated by use of an atomized liquid
spray mechanism. The flue gas fed to the second wind box 4 can also
help facilitate the higher velocities of the reagent and/or fuel
fed to the second combustion zone 5b. The recycled flue gas can be
considered a carrier gas that is output with the fuel and/or
reagent to provide an output of the fuel and/or reagent at a
pre-selected velocity.
[0040] Referring to FIG. 2, the reburner 30 can include a body 33,
which can be configured as a lance, an injector, an eductor, a
swirl body, or other type of body. The body 33 can include an inlet
end 33a and an outlet end 33b. The fuel 25 may be received in the
inlet end 33a and subsequently pass out of the outlet end 33b of
the body 33 toward the second combustion zone 5b. The body 33 can
receive the flow of fuel 25 and be positioned within a portion of
an upper compartment of the second wind box 4 so that it is
structured to facilitate mixing of the flow of fuel with a flow of
the reagent 23 that may pass along the body 33. The body 33 can
have holes along a periphery of the body so that the fuel can pass
out of these holes and into a passageway 35 defined between the
exterior of the body 33 and the wall of an inner conduit defining
an inner passageway 35 through which the reagent and fuel can pass
through toward the second combustion zone 5b via the second wind
box 4.
[0041] A nozzle tip 39 can be pivotally connected to the inner
conduit defining the inner passageway 35 in which the body 33 is
positioned by a tilting connection 31. The tilting connection 31
allows the nozzle tip 39 to be tilted vertically about an axis,
which can also adjust the flow direction of the flow of flue gas 21
passing through the outer passageway 37. For instance, the tilting
connection 31 of the nozzle tip 39 can permit the pitch angles of
the flow of the flue gas, reagent, and fuel being fed into the
second combustion zone 5b via the reburner 30 to be adjusted at the
same time via tilting of the nozzle tip 39.
[0042] The flow of the recycled flue gas 21 or other oxygen
deficient carrier gas can pass through an outer passageway 37 that
surrounds the inner passageway 35 and fuel passageway defined by
the body 33 that is within the inner passageway 35. The flow of the
flue gas 21 can be a first portion of the flue gas that is recycled
from the outlet 7 and economizer 9 back to the second combustion
zone 5b of the combustion apparatus 5.
[0043] The flow of the flue gas 21 can pass through the second feed
conduit and wind box 4 and out of a concentric nozzle tip 39. The
direction of the flow of the flue gas passing through the outer
passageway 37 to the second combustion zone 5b can be adjusted by
tilting of the nozzle tip 39 at which the flue gas passes into the
second combustion zone 5b. Tilting of the nozzle tip 39 changes the
size and shape of the opening of the outer passageway 37 to adjust
the flow velocity profile of the flue gas passing through the outer
passageway 37 to the second combustion zone 5b.
[0044] The second and third wind boxes 4, 6 can receive a flow of
air from the source of air 17 for feeding into the second and third
combustion zones 5b, 5c of the combustion chamber 10. In other
embodiments, the second and third wind boxes 4, 6 can receive a
flow of other gas containing oxygen from another oxidant source
(e.g. an air separation unit). The gas that can be fed into the
second and third combustion zones 5b, 5c via the respective second
and third wind boxes 4, 6 via air nozzles or other nozzles that are
configured to be tillable about at least two axes so that the pitch
and yaw of the nozzles can be adjusted.
[0045] The flow rate of oxygen containing gas fed into the first,
second and third combustion zones 5a-5c via the first, second and
third wind boxes 2, 4, and 6 can be controlled to help facilitate a
low creation of NO.sub.x within the flue gas. For instance for a
combustion apparatus 5 having fuel (via a reburner 30) and a
reagent being provided into the second combustion zone 5b of the
combustion chamber of the present invention, the stoichiometry or
the amount of oxygen within the gas fed to the first combustion
zone via the first wind box 2 can be between 50-70% of the oxygen
needed to fully combust the fuel. The first wind box 2 can also
include close-coupled over fired air (CCOFA) compartments for
feeding an oxygen containing gas (e.g. air or other type of oxidant
flow) into the first combustion zone to increase stoichiometry or
the amount of oxygen within the upper portion (a reburn zone) of
the first zone to be between 70-96% of the oxygen needed to fully
combust the fuel. The amount of oxygen within the gas fed to the
second combustion zone 5b via the second wind box 4 can be
configured to increase stoichiometry or the amount of oxygen within
the second combustion zone 5b of the combustion chamber to be
between 96-105% of the oxygen needed to fully combust the fuel, so
that at least 96% of the fuel in the second combustion zone 5b
would be combusted therein, and at most 105% of the fuel within the
second combustion zone 5b would be combusted therein (e.g. there is
a 5% excess of oxygen needed to fully combust the fuel passing
through the second combustion zone 5b) via the oxygen within the
gas fed into the second combustion zone 5b via the second wind box
4. The amount of oxygen fed into the third combustion zone 5c via
the third wind box 6 can be configured to increase the
stoichiometry or the amount of oxygen needed to fully combust the
fuel passing through the third combustion zone 5c so that more than
105% of the fuel within the third combustion zone would be
combustible in the third combustion zone (e.g. there is an excess
of oxygen so that there is between 15%-25% more oxygen than
theoretically needed to fully combust the fuel within the third
combustion zone 5c).
[0046] In another embodiment of the present invention, the
combustion apparatus 5 is similar to the combustion apparatus
described herein having a reburner 30 however, this embodiment does
not include the reburner 30 for providing fuel to the second
combustion zone 5b. In this other embodiment, the reagent is
provided to the second combustion zone as described hereinbefore.
For example, only the reagent may be fed into the second combustion
zone 5b at such a location above the second wind box 4 and below
the third wind box 6 without the use of any reburner or the feeding
of reburn fuel into the second combustion zone 5b For such
embodiments, the reagent injection system can be positioned for
injection of the reagent so that there is a sufficient residence
time within the combustion chamber prior to the flow of fluid
entering the third combustion zone 5c to allow for the reagent to
react with elements of the fluid passing through the combustion
chamber to facilitate removal of elements that can contribute to
formation of NO.sub.x. Alternatively, the reagent may be injected
or provided to the upper chamber 4a of the second wind box 4 as a
liquid or gas, which may be mixed with over fire air and/or an
oxygen deficient carrier gas, such as recycled flue gas, steam or
other oxygen-deficient gas. Alternatively, the reagent and flue gas
can be fed separately, but at the same time, into the second
combustion zone 5b via the second wind box 4 such that the flue gas
acts as a carrier gas to help penetrate and disperse the reagent
into the second combustion zone 5b. In yet other embodiments, the
reagent may be injected into the second combustion zone 5b as a
liquid such that no carrier gas is utilized to facilitate injection
of the reagent into the second combustion zone 5b.
[0047] For embodiments which do not include a reburner 30 and where
fuel is not fed into the combustion chamber 10 at the second
combustion zone 5b, the stoichiometry for low NO.sub.x formation
can be changed within each of the combustion zones 5a, 5b, 5c of
the combustion apparatus 5 to provide low NO.sub.x formation within
the flue gas formed via combustion of the fuel. The stoichiometry
within each of the combustion zones of the combustion apparatus can
be configured for such embodiments having no reburner 30 or fuel
provided to the second combustion zone 5b, wherein the first
combustion zone 5a has a stoichiometry between 50% and 70% of the
oxygen needed to fully combust the fuel within the first combustion
zone 5a and 70-85% of the oxygen needed to fully combust the fuel
within the upper portion (the reburn zone) of the first combustion
zone 5a. The stoichiometry or the amount of oxygen within the
second combustion zone 5b can be between 85-95% of the oxygen
needed for full combustion of the fuel within the second combustion
zone 5b. The third wind box 6 can be configured to provide oxygen
within the gas fed into the third combustion zone 5c so that the
stoichiometry or the amount of oxygen therein is more than 95% of
the oxygen (e.g. 95% to more than 105% of the oxygen needed to
fully combust the fuel within the third combustion zone 5c) is
present in the third combustion zone.
[0048] The present invention further contemplates that the
combustion apparatus 5 can be configured for tangential firing and
includes a tangential firing system, similar to that described in
U.S. Pat. No. 5,315,939, which is incorporated herein by reference.
As shown in FIG. 10, the wind boxes 2, 4, 6 of FIGS. 1 and 2 may be
located at the four corners of the combustion chamber 10. FIG. 1
schematically shows the complementary wind boxes 2, 4, 6 (shown in
dotted line) disposed at or near the other corners of the
combustion chamber 10. As shown in FIG. 10, the air and fuel
nozzles disposed in the compartments of the wind boxes 2, 4, 6 are
angled to create a fireball 80 flowing in a circular pattern. In
the tangentially fired system of FIG. 10, the fuel via a reburner
30 and/or the reagent may be provided by or above the second wind
boxes 2, 4, 6 at one, two, three or four of the corners of the
combustion chamber 10 in any combination of locations or corners.
Alternatively, the one or more stacked wind boxes 2, 4, 6 may be
disposed in one or more walls defining the combustion chamber 10 to
provide a wall firing combustion system or apparatus.
[0049] Embodiments of the combustion apparatus 5 and plant 1 can be
configured so that a furnace or combustion chamber 10 having a
shorter height or length as compared to conventional furnaces may
be utilized, which can reduce the costs associated with material,
fabrication, maintenance and operation of embodiments of the plant
or embodiments of the combustion apparatus. For instance, it has
been determined that the incorporation of a reburner 30 and/or the
feeding of a reagent into the top compartment of the second wind
box 4 can permit adequate residence time within the second and
third combustion zones 5b and 5c to complete combustion of the fuel
passing therethrough and can eliminate a need for additional
furnace height that may be required in a conventional furnace that
utilizes a reburner on top of an unstaged combustion system or
after a final over fire air wind box. Additionally, it has been
determined that embodiments of the combustion apparatus and plant
that utilize the feeding of a reagent in the second combustion zone
5b can help facilitate a reduction in NO.sub.x formation. The
reduction in NO formation can be further improved by integration of
the feeding of the reagent into the second combustion zone 5b with
the feeding of fuel into the second combustion zone 5b via the
reburner 30. For example, as can be appreciated from FIGS. 5-9, it
has been determined that a reduction of between 65-70% in the
formation of NO.sub.x from the combustion of coal fed to the first
combustion zone 5a of a combustion apparatus 5 can be facilitated
by utilization of the reburner 30 in combination with reagent
injection via the second wind box 4 for embodiments of the plant 1
and combustion apparatus 5 disclosed herein. For some embodiments,
NO.sub.x emissions can be reduced to below 0.10 pound/10.sup.6 BTU
(e.g. between 0.03 to 0.10 pound/10.sup.6 BTU). Such low NO.sub.x
emissions can be achieved while maintaining acceptable levels of
unburned carbon, carbon monoxide emissions, and unreacted ammonia.
Further, the reduction in NO.sub.x emissions can be obtained more
efficiently with less heat input provided by the reburner as
compared to conventional systems as can be seen from FIG. 7. This
can allow for embodiments to be configured so that the quantity of
reburn fuel used is lower as compared to conventional designs while
also providing for a substantial reduction in NO.sub.x emissions.
Moreover, as can be appreciated from FIG. 9, the reduction in
NO.sub.x formation that can be facilitated by embodiments, can
allow coal to be used as a fuel that has a fuel ratio under 3.0, so
that a larger array of fuel options can be utilized in the
combustion apparatus 5 while still complying with emission
requirements, which can allow embodiments of the plant to be
utilized that operate at a lower fuel operating cost.
[0050] It should be appreciated the different modifications can be
made to embodiments of the plant, combustion apparatus, and method
of utilizing the same to meet different sets of design criteria.
For instance, embodiments of the plant and combustion apparatus may
utilize a control system to control operation of the combustion
apparatus and plant. The control system can include hardware such
as a processor, memory, and a transceiver and be configured to
communication with sensors and valves and other plant elements to
monitor operation of the plant 1 and combustion apparatus 5 and
communicate with those plant elements to adjust operational
parameters of the plant 1 and combustion apparatus 5. As another
example, the source of air 17 may provide a flow of oxygen
containing gas via an air separation unit for some embodiments of
the plant and combustion apparatus. As yet another example, the
temperature and pressures at which the combustion apparatus is to
operate may vary to accommodate different design objectives or
performance objectives. As yet another example, the type of reagent
and/or type of fuel fed into the second combustion zone 5b may be
any type of suitable reagent and/or fuel that accommodates a
particular set of design criteria. As yet another example, the
number of fans or pumps and positioning of such fans or pumps
utilized to control flow rates of fluid or fuel to the combustion
apparatus can be any configuration that is able to meet a
particular set of design criteria. As yet another example, the
reburner 30 can be configured to inject fuel, the reagent and/or
flue gas into the second combustion zone 5b via only one outlet or
in multiple feed outlets positioned in the second combustion zone
5b (e.g. at outlets that are each located in a respective corner of
the combustion chamber in the second combustion zone 5b). As yet
another example, some embodiments of the plant can include a gas
processing unit 13 that has one or more elements to facilitate
carbon capture from the flue gas.
[0051] While the invention has been described with reference to
various exemplary embodiments, it will be understood by those
skilled in the art that various changes can be made and equivalents
can be substituted for elements thereof without departing from the
scope of the invention. In addition, many modifications can be made
to adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended
claims.
* * * * *