U.S. patent application number 15/341649 was filed with the patent office on 2017-02-16 for apparatus and method of controlling the thermal performance of an oxygen-fired boiler.
This patent application is currently assigned to General Electric Technology GmbH. The applicant listed for this patent is General Electric Technology GmbH. Invention is credited to Carl Edberg, Armand Levasseur, Wei Zhang.
Application Number | 20170045219 15/341649 |
Document ID | / |
Family ID | 57995513 |
Filed Date | 2017-02-16 |
United States Patent
Application |
20170045219 |
Kind Code |
A1 |
Levasseur; Armand ; et
al. |
February 16, 2017 |
APPARATUS AND METHOD OF CONTROLLING THE THERMAL PERFORMANCE OF AN
OXYGEN-FIRED BOILER
Abstract
A method of controlling the operation of an oxy-fired boiler
includes combusting a fuel that comprises oil heavy residues in a
boiler, the oil heavy residues including hydrocarbon molecules
having a number average molecular weight from approximately 200 to
approximately 3000 grams per mole, discharging flue gas from the
boiler, recycling a portion of the flue gas to the boiler,
combining a first oxidant stream with the recycled flue gas to form
a combined stream, splitting the combined stream into a plurality
of independent split streams, introducing each independent split
stream at a different elevation of the boiler, and controlling
independently a parameter of each of the independent split streams
to adjust the heat release at each respective elevation of the
boiler to vary the heat release profile of the boiler by adding a
second oxidant stream to each respective independent split stream
to form respective independent oxygen enriched split streams.
Inventors: |
Levasseur; Armand; (Windsor
Locks, CT) ; Zhang; Wei; (South Windsor, CT) ;
Edberg; Carl; (Stafford Springs, CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
General Electric Technology GmbH |
Baden |
|
CH |
|
|
Assignee: |
General Electric Technology
GmbH
Baden
CH
|
Family ID: |
57995513 |
Appl. No.: |
15/341649 |
Filed: |
November 2, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13298147 |
Nov 16, 2011 |
|
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15341649 |
|
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|
61414175 |
Nov 16, 2010 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y02E 20/32 20130101;
F23C 9/00 20130101; F23L 2900/07001 20130101; F23C 2202/30
20130101; F23L 7/007 20130101; F23N 1/022 20130101; Y02E 20/322
20130101; F23C 9/006 20130101; Y02E 20/344 20130101; F23C 5/12
20130101; F23C 2201/101 20130101; F23L 9/04 20130101; Y02E 20/34
20130101; F23C 2202/20 20130101; F23C 5/32 20130101; F23C 2200/00
20130101 |
International
Class: |
F23C 5/32 20060101
F23C005/32; F23L 7/00 20060101 F23L007/00; F23C 9/00 20060101
F23C009/00 |
Claims
1. A method of controlling the operation of an oxy-fired boiler,
the method comprising: combusting a fuel that comprises oil heavy
residues in a boiler, the oil heavy residues including hydrocarbon
molecules having a number average molecular weight from
approximately 200 to approximately 3000 grams per mole; discharging
flue gas from the boiler; recycling a portion of the flue gas to
the boiler; combining a first oxidant stream with the recycled flue
gas to form a combined stream; splitting the combined stream into a
plurality of independent split streams; introducing each
independent split stream at a different elevation of the boiler;
and controlling independently a parameter of each of the
independent split streams to adjust the heat release at each
respective elevation of the boiler to vary the heat release profile
of the boiler by adding a second oxidant stream to each respective
independent split stream to form respective independent oxygen
enriched split streams.
2. The method according to claim 1, wherein: the oil heavy residues
comprise asphaltene.
3. The method according to claim 1, wherein: the boiler is a
tangentially fired boiler.
4. The method according to claim 1, wherein: controlling
independently the parameter of each independent split stream
further includes changing a heat absorption in the boiler to a
desired heat absorption pattern.
5. The method according to claim 1, wherein: at least one of the
split streams is introduced into the boiler at a hopper zone
located below a windbox, at the windbox and/or in an overfire
compartment located above the windbox.
6. The method according to claim 1, wherein: at least a portion of
the combined stream is introduced into the boiler in a lower
portion of the windbox.
7. The method according to claim 6, wherein: the at least one split
stream that is introduced into the boiler at the windbox is about
50 to about 100 weight percent of the combined stream.
8. The method according to claim 1, wherein: the at least one split
stream is introduced into the boiler in a lower portion of an
overfire compartment.
9. The method according to claim 1, wherein: the at least one split
stream is introduced into the boiler in an upper portion of an
overfire compartment.
10. A method comprising: combusting a fuel that comprises oil heavy
residues in a boiler, where the oil heavy residues that comprise
hydrocarbon molecules having a number average molecular weight from
200 to 3000 grams per mole; discharging flue gas from the boiler;
recycling a portion of the flue gas to the boiler; combining a
first oxidant stream with the recycled flue gases to form a first
combined stream; splitting the first combined stream into a
plurality of independent split streams; combining a second oxidant
stream to each respective independent split stream provided to the
boiler to form respective independent oxygen enriched split
streams; introducing each independent oxygen enriched split stream
to a different elevation of the boiler; and controlling
independently the amount of the second oxidant stream added to each
respective independent split stream to adjust the heat release at
each respective elevation of the boiler to vary the heat release
profile of the boiler; wherein the first combined stream, the
independent split streams, and the independent oxygen enriched
split streams do not carry the fuel for the boiler.
11. The method according to claim 10, wherein: the boiler is a
tangentially fired boiler.
12. The method according to claim 10, wherein: adding the second
oxidant stream to form the respective oxygen enriched split streams
is conducted at a position proximate to a point of entry into the
boiler.
13. The method according to claim 10, wherein: the respective split
streams are sequentially introduced into the boiler.
14. The method according to claim 10, wherein: at least one
respective oxygen enriched split stream is introduced into the
boiler at a hopper zone located below a windbox.
15. The method according to claim 14, wherein: the oxygen enriched
split stream introduced into the boiler at the windbox comprises
about 50 to about 100 wt % oxygen, based on the total weight of the
stream.
16. The method according to claim 14, wherein: each oxygen enriched
split stream is introduced into the boiler via an annular space
disposed around an inner port, where the inner port introduces the
fuel and transport air into the boiler.
17. The method according to claim 10, wherein: the boiler is a wall
fired boiler.
18. The method according to claim 10, wherein: controlling
independently the parameter of each respective oxygen enriched
split stream introduced to the boiler changes the heat pattern of
the boiler.
19. The method according to claim 14, wherein: at least one
respective oxygen enriched split stream is introduced into the
boiler at an overfire compartment at the hopper zone; and wherein
the oxygen enriched split stream introduced into the overfire
compartment at the hopper zone comprises up to 50 wt % oxygen based
on the total weight of the oxygen enriched split stream.
20. A system comprising: an air separation unit; a boiler
configured to combust oil heavy residues, the oil heavy residues
comprising hydrocarbon molecules having a number average molecular
weight from 200 to 3000 grams per mole; a pollution control system;
a gas processing unit, wherein the air separation unit is upstream
of the boiler, the pollution control system and the gas processing
unit, wherein the boiler is upstream of the pollution control
system and the gas processing unit, and wherein flue gas is
recycled from the gas processing unit to the boiler via the air
separation unit; and a control system configured to control the
addition of a first oxidant stream to the recycled flue gas to form
a combined stream and to control the addition of a second oxidant
stream to a plurality of independent split streams formed from the
combined stream to vary the heat release profile of the boiler;
wherein each of the independent split streams to which the second
oxidant stream is added is introduced to a different elevation of
the boiler.
Description
CROSS-REFERENCE
[0001] This Application is a Continuation-in-Part of U.S. patent
application Ser. No. 13/298,147, filed on Nov. 16, 2011, which
claims the benefit of U.S. Provisional Application Ser. No.
61/414,175, filed on Nov. 16, 2010, both of which are hereby
incorporated by reference herein in their entireties.
BACKGROUND
[0002] Technical Field
[0003] This disclosure relates generally to oxy-fired boilers, and
more specifically to an oxy-fired boiler that burns heavy oil
residues as fuel.
[0004] Discussion of Art
[0005] Oxy-combustion has been developed for carbon dioxide capture
and sequestration in fossil fuel fired power plants. The concept of
oxy-combustion (also sometimes referred to as `oxyfuel` and
`oxy-firing`) is to replace combustion air with a mixture of oxygen
and recycled flue gas, thereby creating a high carbon dioxide
content flue gas stream that can be more simply processed for
sequestration. A simplified exemplary schematic of the
oxy-combustion process for pulverized coal (pc) power plants is
shown in prior art depicted in FIG. 1.
[0006] FIG. 1 depicts an oxy-combustion system 100, comprising an
air separation unit 102, a boiler 104, a pollution control system
106 and a gas processing unit 108. The air separation unit 102 is
located upstream of the boiler 104, which is located upstream of
the pollution control system 106 and the gas processing unit 108.
The pollution control system 106 is located upstream of the gas
processing unit 108. Gas recycle is shown taken after the pollution
control system, but could be taken from any location between the
boiler and the gas processing unit.
[0007] The boiler 104 may be a tangentially fired boiler (also
known as a T-fired) or a wall fired boiler. T-firing is different
from wall firing in that it utilizes burner assemblies with fuel
admission compartments located at the corners of the boiler
furnace, which generate a rotating fireball that fills most of the
furnace cross section. Wall firing (not shown), on the other hand,
utilizes burner assemblies that are perpendicular to a side (of the
shell) of the boiler.
[0008] FIG. 2 depicts a tangentially fired boiler 104. Tangentially
fired boilers have a rectangular cross-section and have burner
assemblies 105 positioned at the corners. Fuel and transport air
are introduced into the boiler 104 via the burner assemblies 105
and are directed tangentially to an imaginary circle located at the
center of the furnace and with a diameter greater than zero. This
generates a rotating fireball that fills most of the furnace cross
section. The fuel and air mixing is limited until the streams join
together in the furnace volume and generate a rotation. This has
often been described, as "the entire boiler is the burner." Global
boiler aerodynamics and mixing is much more important to the
combustion process and the resulting boiler performance during
T-firing as compared with wall-firing. During wall-firing, fuel and
air/oxygen mixing occurs in or near the burners and less mixing
occurs in the boiler.
[0009] With reference now once again to FIG. 1, in one method of
operating the oxy-combustion system 100, oxygen is first separated
from nitrogen in the air separation unit 102. The nitrogen is
discharged separately from the air separation unit. The air
separation unit 102 extracts oxygen from the atmosphere.
[0010] The oxygen is then discharged from the air separation unit
102 to combine with recycled flue gas, the combination of which is
fed to the boiler 104. The boiler 104 uses the oxygen present in
the flue gas stream to combust a fuel (e.g., coal, oil, or the
like) to generate heat and flue gases. As a result of combusting
the fuel with oxygen instead of with air, the flue gas produced has
a high carbon dioxide content. The other constituents of the flue
gas are water vapor and small amounts of oxygen, nitrogen, and
pollutants such as sulfur oxides, nitrogen oxides, and carbon
monoxide. Removing the water and other components produces a very
pure carbon dioxide stream suitable for sequestration or other
use.
[0011] The heat is used to generate steam, which may be used to
drive a generator (not shown) to produce electricity, while the
flue gases are discharged to the pollution control system 106 where
particulate matter and other pollutants (e.g., NOx, SOx, and the
like) are removed. A portion of the purified flue gases is recycled
to the boiler 104 as shown in FIG. 1. The remaining flue gases
(that substantially comprise carbon dioxide) are discharged to the
gas processing unit 108 from where it is sequestered.
[0012] As will be readily appreciated, recycling large amounts of
flue gases to the boiler 104 require large. On the other hand,
burning the fuel with pure oxygen generally produces flame
temperatures much too high for practical boiler materials, so a
portion of the high-carbon dioxide flue gas is used to dilute the
oxygen and moderate the boiler temperature. The amount of oxygen
added to the recycled flue gas is based on the amount of fuel
combusted in the boiler. The fuel uses a certain amount of oxygen
in addition to some amount of excess oxygen to ensure complete
combustion.
[0013] While most of the aforementioned discussion has been
directed to the oxy-fired boilers that use coal for combustion, it
is desirable to use other fuels, such as, for example, liquid fuels
in oxy-fired boilers.
[0014] One such liquid fuel is oil heavy residue. Oil heavy
residues comprise primarily high molecular weight hydrocarbon
products of crude oil that may be unsuitable for use in other
applications or that cannot easily be converted into lower
molecular weight products that can be used in other applications.
Oil refineries convert crude oil into a range of useable products
(e.g., gasoline, diesel and fuel oil components) that are used
commercially. The first step in the manufacture of petroleum
products is the separation of crude oil into the main fractions by
atmospheric distillation. When crude oil is heated, the lightest
and most volatile hydrocarbons boil off as vapors first and the
heaviest (i.e., those having higher molecular weights) and least
volatile last. The vapors are then cooled and condensed back into
liquids, which are then supplied for commercial use.
[0015] The residue from atmospheric distillation is sometimes
referred to as long residue and to recover more distillate product,
further distillation is carried out at a reduced pressure and high
temperature. Vacuum distillation is one such process and is used to
further recover useful products from the long residue. The
percentage of residue varies depending on the composition of crude
processed. For a typical "light" North African crude the residue is
28%, whilst for a "heavy" Venezuelan crude it is as high as 85%.
The proportion of products produced does not always match the
product demand and is primarily determined by the particular
composition of crude oil.
[0016] Further refining such as thermal cracking at temperatures of
450 to 750.degree. C. and pressures from atmospheric to 70 bar are
used to convert the long residue into useful commercial product.
The temperature and pressure depends on the type of feedstock and
the product requirement. At these elevated temperatures, the large
hydrocarbon molecules become unstable and spontaneously break into
smaller molecules. Several different thermal cracking processes may
be performed on the residues to convert them to useful commercial
products. However, not all of the high molecular weight hydrocarbon
molecules can be converted to lower weight molecules that can be
marketed commercially. The high molecular weight hydrocarbon
molecules that are finally left behind after all of the useful
product is extracted for commercial use is called oil heavy
residue. It is desirable to find uses for the oil heavy residue
that cannot be used for conventional commercial products such as
gasoline and fuel oil.
[0017] It is therefore desirable to use the oil heavy residue in
oxy-fired boilers to reduce waste and to reduce the environmental
impact by employing these liquids in and efficient combustion
processes that has a very low environmental signature as compared
with other comparative combustion processes.
BRIEF DESCRIPTION
[0018] In an embodiment, a method of controlling the operation of
an oxy-fired boiler is provided. The method includes combusting a
fuel that comprises oil heavy residues in a boiler, the oil heavy
residues including hydrocarbon molecules having a number average
molecular weight from approximately 200 to approximately 3000 grams
per mole, discharging flue gas from the boiler, recycling a portion
of the flue gas to the boiler, combining a first oxidant stream
with the recycled flue gas to form a combined stream, splitting the
combined stream into a plurality of independent split streams,
introducing each independent split stream at a different elevation
of the boiler, and controlling independently a parameter of each of
the independent split streams to adjust the heat release at each
respective elevation of the boiler to vary the heat release profile
of the boiler by adding a second oxidant stream to each respective
independent split stream to form respective independent oxygen
enriched split streams.
[0019] In another embodiment, a method is provided. The method
includes the steps of combusting a fuel that comprises oil heavy
residues in a boiler, where the oil heavy residues that comprise
hydrocarbon molecules having a number average molecular weight from
200 to 3000 grams per mole, discharging flue gas from the boiler,
recycling a portion of the flue gas to the boiler, combining a
first oxidant stream with the recycled flue gases to form a first
combined stream, splitting the first combined stream into a
plurality of independent split streams, combining a second oxidant
stream to each respective independent split stream provided to the
boiler to form respective independent oxygen enriched split
streams, introducing each independent oxygen enriched split stream
to a different elevation of the boiler, and controlling
independently the amount of the second oxidant stream added to each
respective independent split stream to adjust the heat release at
each respective elevation of the boiler to vary the heat release
profile of the boiler. The first combined stream, the independent
split streams, and the independent oxygen enriched split streams do
not carry the fuel for the boiler.
[0020] In yet another embodiment, a system is provided. The system
includes an air separation unit, a boiler configured to combust oil
heavy residues, the oil heavy residues comprising hydrocarbon
molecules having a number average molecular weight from 200 to 3000
grams per mole, a pollution control system, a gas processing unit
and a control system. The air separation unit is upstream of the
boiler, the pollution control system and the gas processing unit.
The boiler is upstream of the pollution control system and the gas
processing unit. The control system is configured to control the
addition of a first oxidant stream to the recycled flue gas to form
a combined stream and to control the addition of a second oxidant
stream to a plurality of independent split streams formed from the
combined stream to vary the heat release profile of the boiler.
Each of the independent split streams to which the second oxidant
stream is added is introduced to a different elevation of the
boiler.
DRAWINGS
[0021] The present invention will be better understood from reading
the following description of non-limiting embodiments, with
reference to the attached drawings, wherein below:
[0022] FIG. 1 represents the prior art and depicts a combustion
system where flue gases are recycled to the boiler;
[0023] FIG. 2 depicts a prior art tangentially fired boiler;
[0024] FIG. 3 is a depiction of the various points at which a
combined stream that comprises a first oxidant stream (that
comprises substantially oxygen) and a second stream (that comprises
substantially recycled flue gases) can be introduced into the
boiler;
[0025] FIG. 4 is another depiction of an exemplary embodiment of
introducing oxygen into the flue gas stream into the boiler;
[0026] FIG. 5 represents a depiction of one embodiment of the
introduction of the combined stream into a tangentially fired
boiler;
[0027] FIG. 6 depicts one embodiment of nozzle orientation that is
used for the combustion of oil heavy residues in concentric firing
boilers;
[0028] FIG. 7 depicts a nozzle for injecting highly concentrated
oxygen streams in a concentric firing system;
[0029] FIG. 8 is a graph that shows improved carbon burnout/carbon
heat loss with oxygen enrichment in the fuel compartment during 15
MW testing; and
[0030] FIG. 9 is a graph that illustrations the impact of oxygen
enrichment on heat flux to the furnace wall near the burner/windbox
during 15 MW testing.
DETAILED DESCRIPTION
[0031] Reference will be made below in detail to exemplary
embodiments of the invention, examples of which are illustrated in
the accompanying drawings. Wherever possible, the same reference
characters used throughout the drawings refer to the same or like
parts. While embodiments of the invention are suitable for use with
a tangentially fired boiler, embodiments of the invention may also
be utilized in connection with any oxygen fired boiler, including
an oxygen wall fired boiler.
[0032] Embodiments of the invention relate to an oxyfuel combustion
system that uses oil heavy residue (OHR) such as vacuum bottoms
from petroleum refineries or high asphaltene materials, for boiler
applications to enhance thermal performance and reduce emissions.
The method disclosed herein includes applying selective oxygen
injection into oxidant streams, into the furnace windbox and into
over fire air (OFA) nozzles to control combustion rate and furnace
heat flux distribution. Features include local oxygen enrichment to
promote combustion and to improve the gaseous environment near the
waterwall tubes to reduce corrosion. Features also include options
for injection through special oxygen sub-compartments through the
burner/windbox into the furnace allowing more of the windbox and
associated equipment to be fabricated from lower cost material such
as carbon steel.
[0033] As used herein, "oil heavy residue" refers to primarily high
molecular weight hydrocarbon products of crude oil that may be
unsuitable for use in other applications or that cannot easily be
converted into lower molecular weight products that can be used in
other applications. The oil heavy residues have number average
molecular weights of 200 to 3,000 grams per mole and comprise
primarily hydrocarbon molecules. Substituted and unsubstituted
hydrocarbon molecules may be used. In an embodiment, the oil heavy
residues comprise heavy oils, oil sands, bitumen, biodegraded oils,
and the like, some of which may contain asphaltene. Asphaltenes are
molecular substances that are found in crude oil, along with
resins, aromatic hydrocarbons, and saturates (i.e., saturated
hydrocarbons such as alkanes). Asphaltenes consist primarily of
carbon, hydrogen, nitrogen, oxygen, and sulfur, as well as trace
amounts of vanadium and nickel. The carbon to hydrogen (C:H) ratio
is approximately 1:1.2, depending on the asphaltene source.
Asphaltenes are defined operationally as the n-heptane
(C.sub.7H.sub.16)-insoluble, toluene
(C.sub.6H.sub.5CH.sub.3)-soluble component of a carbonaceous
material such as crude oil, bitumen, or coal. Asphaltenes generally
have a distribution of molecular weight in the range of 400 to 1500
grams per mole.
[0034] In an embodiment, the method includes varying the amount,
proportion and/or distribution of oxygen, the amount, proportion
and/or distribution of recycled flue gases, or both the amount,
proportion and/or distribution of both oxygen and recycled flue
gases in a combined stream that is fed to various inputs to the
boiler, an input stream provided to the boiler and/or various zones
of the boiler. For example, the volume of oxygen sufficient for the
desired amount of combustion of the fuel provided to the boiler in
accordance with desired stoichiometric parameters may be portioned
or distributed to different zones or locations of the boiler to
provide a desired heat release profile in the boiler. Further, the
recycled flue gas and/or volume of oxygen may be proportioned
and/or distributed to different areas within a zone of the boiler
to provide a desired heat release profile in that zone.
Furthermore, the proportion and/or distribution of addition of a
volume or proportion of oxygen and/or recycled flue gas to an input
stream to the boiler may be controlled to provide a desired heat
release profile.
[0035] In one embodiment similar to that shown in FIG. 3, a system
and method includes supplying a first combined stream of recycled
flue gas and a first oxidant stream to different sections or zones
of the boiler. The first combined stream may be supplied to a
hopper zone, the windbox zone and/or one or more overfired oxidant
compartments at different volumes, which are each controlled by a
respective fluid flow control device. In this embodiment, the ratio
of oxygen to the recycled flue gas is constant in any of the zones
of the boiler to which it is introduced, however, the distribution
of the first combined stream is controlled by providing varying
portions of the first combined stream to different zones of the
boiler and/or different locations within a particular zone to
provide a desired heat release profile.
[0036] In another embodiment similar to that shown in FIG. 4, a
system and method comprises combining the first combined stream
with a second oxidant stream to form a second combined stream that
may be supplied to the boiler at the hopper zone, the windbox zone
and/or one or more overfired oxidant compartments at different
volumes amounts, wherein the volumetric flow of the second oxidant
is controlled by a fluid flow control device. This method of
enriching the first combined stream is conducted just prior to the
introduction of the second combined stream into the boiler. In this
system and method, the amount of oxygen to the hopper zone, the
windbox zone, the hopper zone and/or the overfired oxidant
compartments is varied relative to the amount of the recycled flue
gas. This system and method can be advantageously used to vary the
heat release pattern in the boiler.
[0037] This system and method of controlling the distribution of
oxygen and/or recycled flue gas to the boiler is advantageous in
that it permits localized oxygen enrichment of the atmosphere in
the boiler and hence increasing the localized heat release and
modifying the temperature profiles in desired areas of the
boiler.
[0038] In yet another embodiment similar to that in FIGS. 3 and 4,
the amount of flue gas in the combined stream may be varied instead
of or in addition to varying the amount of the oxygen. In yet
another embodiment, the invention details modulating or changing
the proportion or distribution of the recycled flue gas admitted to
the boiler at varying elevations relative to the furnace outlet
plane. This method of controlling the flow rates of flue gases is
advantageous in that it allows for maintaining a constant steam
temperature control as fuel properties or furnace conditions vary.
This provides a means of steam temperature control as loads vary.
Another method of steam temperature control can be achieved by
modulating the amount of oxygen to the varying elevations.
[0039] An advantage of the present invention the amount of oxygen
and flue gas provided to a fluid stream in an oxygen fired boiler
may be independently controlled to provide great flexibility to
optimize the operation of the boiler and provide or modify the heat
release profile of the boiler. One skilled in the art will
appreciate that an increase of oxygen with an input fluid stream to
the boiler will result in an increase heat flux at the location of
the input fluid stream.
[0040] FIG. 3 is a depiction of a boiler 200, such as a T-fired
boiler, having a control system 290 that controls the proportion or
distribution of a combined stream 320 to various locations or zones
of the boiler. The combined stream 320 comprises a first oxidant
stream 310 (that comprises 0-100 weight % of oxygen, wherein in one
embodiment stream 310 is substantially oxygen) and a second stream
350 (that comprises substantially recycled flue gases). The
volumetric flow of the first oxidant stream 310 and second stream
350 are controlled by respective fluid flow control devices 311,
such as baffles, fans, dampers, valves, and eductors. These flow
control devices may be controlled in an open loop or closed loop
control system, which will be described in greater detail
hereinafter.
[0041] The oxidant is injected into three main zones (all of which
are detailed below): 1) a windbox/main burner zone, where it is
injected at the lowest stoichiometric ratio of flue gas to oxygen,
(2) a furnace located above the windbox (also termed an over-fire
zone), where the stoichiometric ratio of flue gas to oxygen is more
than 1; and 3) a furnace hopper located below the windbox.
[0042] The bulk of the oxygen for combustion is injected and mixed
into the main gas recirculation flow taken from after a pollution
control system (not shown) to form a premix oxidant 320 which is
heated in a regenerative gas-gas heater 390 and sent to the windbox
and over fire air system. The total quantity of flue gas
recirculation is established based on the size and heat transfer
surfacing of the boiler.
[0043] With reference again to the FIG. 3, the boiler 200 includes
a hopper zone 210 located below the main burner zone 208 from which
ash can be removed, a main burner zone 208 (hereinafter windbox
208) where an oxidant and an oxidant-fuel mixture (or alternatively
a gas-fuel mixture) is introduced into the boiler 200, a burnout
zone 216 where any oxygen or fuel that is not combusted in the main
burner zone gets combusted, a superheater zone 212 where steam can
be superheated, and an economizer zone 214 where water can be
preheated prior to entering the superheater zone 212. The burnout
zone 216 can utilize a lower overfired oxidant compartment 206 and
an upper overfired oxidant compartment 204. The boiler 200 also
includes a horizontal boiler outlet plane 304 and a vertical boiler
outlet plane 302. The boiler 200 also includes waterwalls 202 in
which the water is transformed to steam.
[0044] As noted above, a first oxidant stream 310 and a second
stream 350 are combined to form the combined stream 320 that is
then fed to the boiler. The combined stream 320 can comprise about
15 to about 40 volume percent oxygen, with the remainder being
recycled flue gases. As can be seen in FIG. 3, the combined stream
320 can be fed to the boiler 200 into the hopper zone 210, into the
windbox 208, into the lower overfired oxidant compartment 206
and/or into an upper overfired oxidant compartment 204. In other
words, the combined stream 320 can be split up and distributed into
several split streams (320A, 320B, 320C and/or 320D) and fed into
different parts of the boiler to vary the heat release profile in
the boiler and to improve its thermal performance, whereby the
volumetric flow rate of one or more of the split streams 320A,
320B, 320C, 320D is controlled by a respective fluid flow control
device 312. For example a higher percentage of the combined stream
320 may be provided to the windbox 208 to increase the heat release
profile in this zone, or vice versa. This method of enriching the
second stream 350 with oxygen and splitting the combined stream 320
into different streams 320A, 320B, 320C, 320D permits varying the
amount of flue gas and oxygen into different parts of the boiler to
improve its thermal performance or provide a desired heat release
profile.
[0045] For purposes of identification, the combined stream 320 that
is fed into the boiler 200 at the hopper zone 210 is identified as
320A and can comprise up to about 25 weight percent of the total
weight of the combined stream 320. In one embodiment, the combined
stream 320A stream can comprise about 0 to about 10 weight percent
of the total weight of the combined stream 320. In another
embodiment, the combined stream 320 that is fed into the boiler 200
at the windbox zone 208 is identified as 320B and can comprise
about 50 weight percent to about 100 weight percent of the total
weight of the combined stream 320. In one embodiment, the combined
stream 320B stream can comprise about 50 to about 80 weight percent
of the total weight of the combined stream 320. In yet another
embodiment, the combined stream 320 that is fed into the boiler 200
at the lower overfired oxidant compartment 206 is identified as
320C and can comprise up to about 50 weight percent of the total
weight of the combined stream 320. In one embodiment, the combined
stream 320C stream can comprise about 10 to about 30 weight percent
of the total weight of the combined stream 320.
[0046] In yet another embodiment, the combined stream 320 that is
fed into the boiler 200 at the upper overfired oxidant compartment
204 is identified as 320D and can comprise up to about 50 weight
percent of the total weight of the combined stream 320. In one
embodiment, the combined stream 320D stream can comprise about 10
to about 30 weight percent of the total weight of the combined
stream 320.
[0047] FIG. 4 depicts another embodiment of a boiler 200, such as a
T-fired boiler, having a control system 291 that controls the
proportion or distribution of a combined stream 360 and the oxygen
ratio of each split stream 360A, 360B, 360C, 360D to various
locations or zones of the boiler, using a combined stream 360 and a
second oxidant stream 370 to enrich or deplete the flue gas of
oxygen of each respective input stream supplied to the boiler 200
to define or vary the heat release profile in the boiler and to
improve its thermal performance or provide a desired heat release
profile.
[0048] The control logic for a boiler that burns oil heavy residues
requires controlling the specific oxygen concentrations to
predetermined values for each of the three main furnace zones--the
oxidant compartments 204 and 206, the windbox zone 208 and the
hopper zone 210. This includes controlling oxygen flow rates and
oxygen concentrations in each split stream 360A, 360B, 360C, and
360D as well any further subdivisions of these streams (not shown
here). The flow rate and oxygen concentration of each of the
streams is adjusted to provide a final value based on the oxygen
concentration in the flue gas leaving the boiler in order to
maintain the optimize amount of oxygen efficient combustion.
[0049] The distribution of this oxygen into the furnace is
specifically optimized in dependence upon the specific composition
and properties of the oil heavy residue fuel and the design of the
boiler. Control of the oxygen added to specific oxidant or flue gas
recirculation streams provides a means to control combustion rate
and heat release allowing control of furnace heat flux profiles and
steam temperature control. Moreover, it provides a means to
optimize and improve combustion performance including flame
stability/turndown and carbon burnout. It also provides a means to
improve combustion performance allowing more aggressive staging for
NOx control and lower NOx emissions.
[0050] In an embodiment, streams having different oxygen
concentrations are fed to the hopper zone 210, the windbox zone
208, the upper overfired oxidant zone 204 and the lower overfired
oxidant zone 206. One skilled in the art will appreciate that the
control oxygen concentration or ratio of each zone may be
controlled in any configuration or combination of locations or
zones of the boiler. The recycled flue gases 350 may be first
pre-mixed with an oxidant stream 310 to form a first combined
stream 360. The first combined stream 360 is then discharged
towards different locations or zones of the boiler in different
amounts or volumes. However, each combined stream 360 is enriched
with oxygen from a respective second oxidant stream 370 to provide
each respective input (split) stream 360A, 360B, 360C, 360D with
the desired concentration of oxygen as well as the desired overall
volumetric flow for each input stream. The ratio of oxygen in the
different split streams can therefore be the same or different from
one another.
[0051] As shown in FIG. 4, the control system 291 controls the
concentration of oxygen and volumetric flow of the combined stream
360 by controlling the fluid flow of stream 350 and oxidant stream
310 using the respective fluid flow control devices 311. The
control system 291 further controls the concentration of oxygen and
volumetric flow rate for each respective input stream 360A, 360B,
360C, 360D by controlling the respective fluid flow control devices
312 to control the flow of the combined stream 360 and controlling
respective fluid flow control devices 313 to control the flow of
respective fluid flow control devices 313. The fluid flow control
device 312 may be disposed upstream or downstream of the point that
the second oxidant stream 370 is added. However, when the fluid
flow control device 312 is disposed upstream of the point that the
second oxidant stream 370 is added, the control system 291 provides
greater flexibility and concentration range to locally control both
the concentration of oxygen and the overall volume of input stream
360A, 360B, 360C, 360D to the boiler. In summary as shown in FIG.
4, the fluid flow control devices 311, 312, 313 of the control
system 291 can control the oxygen concentration of each input
stream 360A, 360B, 360C, 360D the distribution of oxygen to each
input stream and thus zone of the boiler, and the desired
volumetric gas flow of each input stream.
[0052] With reference once again to FIG. 4, a first oxidant stream
310 of the total added oxygen is mixed with a second stream 350
that comprises recycled flue gases to form a first combined stream
360. In an exemplary embodiment, the first oxidant stream 310
comprises about 50 to about 95 percent of the total added oxygen,
specifically about 80 to about 90 percent. The remaining percentage
of oxygen necessary for the desired amount of combustion in the
boiler 200 is provided in the second oxidant stream 370. Note that
the recycled flue gas and the transport gas may include a small
percentage of oxygen that may need to be considered in the control
of the input streams 360A, 360B, 360C, 360D.
[0053] As can be seen in FIG. 4, the second combined stream 360A
which comprises the first combined stream 360 and the second
oxidant stream 370 comprising up to 20% of the total added is fed
to the hopper zone 210. In an exemplary embodiment, the second
combined stream 360A can comprise about 0 to about 18%, and more
specifically about 2 to about 15% of the total added oxygen.
[0054] In another embodiment, a second oxidant stream 370 that
comprises oxygen in an amount of up to 100% of the total added
oxygen is combined with the first combined stream 360 and fed to
the windbox 208. In an exemplary embodiment, the second oxidant
stream comprises oxygen in an amount of about 50 to about 80% of
the total added oxygen is combined with the first combined stream
360 and fed to the windbox 208.
[0055] In yet another embodiment, a second oxidant stream 370 that
comprises oxygen in an amount of up to 50 wt % is combined with the
first combined stream 360 and fed to the lower overfired oxidant
compartment 206. In an exemplary embodiment, the second oxidant
stream comprises oxygen in an amount of about 10 to about 30% of
the total added oxygen is combined with the first combined stream
360 and fed to the lower overfired oxidant compartment 206 and/or
to the upper overfired oxidant compartment 204.
[0056] The second oxidant stream 370 is generally mixed with the
first combined stream 360 to form the combined stream 360A, 360B,
360C or 360D as close as possible to the boiler 200. A finer level
of control over oxygen distributions can be achieved by mixing in
oxygen closer to the boiler, for example adding additional oxygen
at the positions depicted in FIG. 4 to locally enrich the oxygen
content in one area of the windbox 208. This mode of enrichment of
the first combined stream 360 can be used in the tangentially fired
boilers as well as in wall fired boilers.
[0057] While the control systems 290, 291 of FIGS. 3 and 4 control
the distribution and concentration of oxygen to particular zones of
the boiler 200, the present invention contemplates that each zone
having a plurality of separate input streams may also be controlled
by the control systems. FIG. 5 depicts one exemplary apparatus and
method of introducing the combined stream 320B (from FIG. 3) or
360B (from FIG. 4) into the windbox 208 of the boiler 200. FIG. 5
illustrates the details of the input compartments or input streams
of a windbox 208 of a tangentially fired boiler, and the apparatus
and method of controlling the oxygen concentration and volumetric
flow of respective input streams provided by the windbox 208.
Varying oxygen concentrations are introduced in different
compartments of the windbox 208.
[0058] FIG. 5 depicts a plurality of assemblies, e.g. primary
nozzles 402, 404, 406, in the windbox 208 of a tangentially fired
boiler 200. FIG. 5 contains an expanded view of the windbox 208 of
the boiler 200 to illustrate a configuration of the nozzles 2a
through 2k of nozzle assemblies 402, 404, 406. In one embodiment,
the windbox 208 can comprise about 2 to about 10 such assemblies of
nozzles. It is to be appreciated that a number of different
configurations between the nozzles that introduce the combined
stream 360B, and those that deliver heavy oil residues to the
windbox and those that deliver auxiliary air to the windbox may be
used.
[0059] Oil heavy residue and transport gas, along with a mixture of
recycled flue gas and oxygen (e.g., the combined stream 360B or
320B) can be introduced into the respective nozzles. As can be seen
in the FIG. 5, nozzles that supply the fuel to the windbox 208 may
be alternated with nozzles that supply a mixture of recycled flue
gas and oxygen to the windbox. Further nozzles that supply
auxiliary air may also be alternated with nozzles that supply
recycled flue gas and oxygen to the windbox.
[0060] The nozzles can be arranged into assemblies. For example, a
first nozzle assembly 402 can contain a first nozzle that introduce
the combined stream 360B, a second nozzle that introduces the oil
heavy residue and a third optional nozzle that introduces auxiliary
air. A second nozzle assembly 404, a third nozzle assembly 406, and
so on may be arranged in a similar fashion to the first nozzle
assembly 402 in order to introduce the combined stream 360B, the
oil heavy residue and the auxiliary air into the windbox 208. It is
to be noted that the second and third nozzle assemblies may
alternatively have different configurations from the first nozzle
assembly 402, if desired.
[0061] In an embodiment, it is desirable to introduce the combined
stream 360B (with localized oxygen enrichment) into the nozzles 2a,
2c, 2e, 2g, 2i and 2k respectively, while nozzles 2b, 2f, and 2j
deliver oil heavy residues to the windbox 208. In an embodiment,
auxiliary air is supplied to the windbox 208 via nozzles 2d and 2h.
From FIG. 5 it may therefore be seen that the first nozzle assembly
402 contains the nozzles 2a, 2b, 2c and 2d, while the second nozzle
assembly 404 contains nozzles 2e, 2f, 2g and 2h, and third nozzle
assembly 406 contains nozzles 2i, 2j, 2k, and so on.
[0062] The ratio of oxygen to the recycled flue gas in the combined
stream 360B that is fed to the respective assemblies 402, 404, and
so on can be varied similar to the configuration shown and
described in FIGS. 3 and 4. Specifically, control systems 290, 291
of FIGS. 3 and 4 may have the same configuration of fluid flow
control devices to control the concentration, proportion and/or
distribution of each respective split input stream that feeds into
each nozzle 2a, 2c, 2e, 2g, 2i and 2k. In other words, the
locations of nozzles (i.e., windbox zones) of the windbox 208 may
be controlled in the same or similar manner as each zone of the
boiler 200, whereby the input stream 360B would be functionally the
same as the combined stream 360 in FIGS. 3 and 4. While this
functionality has been shown for the windbox 208, one will
appreciate that this level of control is contemplated by the
invention for other zones of the boiler 200.
[0063] For example, the first nozzle 2a can receive a first ratio
of oxygen to recycled flue gases, while the second nozzle 2c can
receive a second ratio of oxygen to the recycled flue gases, and so
on. In one embodiment, the first ratio can be the same as the
second ratio. In another embodiment, the mass ratio of the combined
stream 360B to the oil heavy residue fed to the first assembly 402
can be the same or different from the mass ratio fed to the second
assembly 404. By changing the ratio of oxygen to the recycled flue
gas, the heat release profile at different portions of the windbox
208 can be varied.
[0064] In an embodiment, the system used for the combustion of oil
heavy residues may use concentric firing system (CFS) compartments
which increase the oxidizing environment at the waterwall, thereby
reducing corrosion potential. FIG. 6 depicts one such embodiment.
In this embodiment, the combined stream 360B of the FIG. 4 (or 320B
in the FIG. 3) is directed through a concentric firing nozzle
system that is angled towards the walls (i.e., the waterwalls) of
the furnace rather than towards the center of the furnace. The
effect of this angular adjustment of the nozzles is enhanced by
supplying enriched oxygen concentrations as part of the stream 360B
through the nozzles. The enriched oxygen concentrations in the
streams through the concentric firing system (CFS) compartments
increase the oxidizing environment at the waterwall thereby
reducing corrosion potential.
[0065] FIG. 6 illustrates CFS nozzles 506 that are adjusted to
direct the stream 360B away from the center fireball circle 504
more toward the waterwalls 508 of the boiler 502. Enriching the
oxygen in this concentric firing system flow increases the oxygen
concentration near the waterwalls 508. This is particularly
valuable for high sulfur, high nitrogen content oil heavy residues,
where the nozzle angles could be staged more aggressively for NOx
control while controlling corrosive behavior as well.
[0066] Enrichment of oxygen concentrations in the stream 360B
requires the selection of a appropriate materials for use in nozzle
components that contact the stream 360B (see FIG. 4). Appropriate
materials such as stainless steel (SS 304, SS 316, and the like)
are desirable for use in the windbox compartments, and other
components exposed to heated (>300.degree. F.) oxygen streams
that have oxygen concentrations of greater than 23.5 wt %, based on
the total weight of the stream. In certain embodiments, material
savings can be achieved by restricting the oxygen flow in a
separate conduit through the windbox compartment to the existing
nozzles into the furnace.
[0067] FIG. 7 depicts a nozzle 600 for transporting highly
concentrated oxygen streams through the concentric firing system of
FIG. 6. As shown therein, the nozzle 600 includes an outer wall 602
that houses a conduit 604 for transporting the stream 360B that may
contain amounts of oxygen in amounts of greater than 23 wt % (based
on the total weight of the stream 360B) into the windbox 208 (see
FIGS. 3 and 4) of the boiler. In an embodiment, only the conduit
604 that is exposed to nearly pure oxygen would need to be of
higher grade, oxygen compatible material, and the other windbox
compartments could remain constructed using conventional air-fired
design and materials. In an embodiment, a concentric conduit 606
may be used for transporting the oil heavy residues.
[0068] Referring once again to FIG. 4, in one embodiment, the
combined stream 360 and the second oxidant stream 370 may be
introduced into the boiler 200 at the upper overfired oxidant
compartment 204 or at the lower overfired oxidant compartment 206.
The enrichment with oxygen can thus take place in the upper
overfired oxidant compartment 204 relative to the lower overfired
oxidant compartment 206, the windbox 208 and/or the hopper zone
210. In another embodiment, the enrichment with oxygen can take
place in the lower overfired oxidant compartment 206 relative to
the upper overfired oxidant compartment 204, the windbox 208 and/or
the hopper zone 210. Referring to FIG. 4, one embodiment where the
combined stream 360 and the secondary oxidant stream 370 is
introduced into the upper or lower overfired oxidant compartment
204 or 206 respectively. The upper overfired oxidant compartment
204 is closest to the horizontal boiler outlet plane 304, while the
lower overfired compartment 206 is the compartment farthest from
the horizontal boiler outlet plane 304.
[0069] When the combined stream 360 is introduced into the lower
overfired oxidant compartment 206, the second oxidant stream 370 is
introduced into the upper overfired oxidant compartment 204 and
vice versa. By introducing the combined stream 360 into the lower
overfired oxidant compartment 206, the oxidant stream in the lower
overfired oxidant compartment 206 is enriched in oxygen relative to
the upper overfired oxidant compartment 204, the windbox 208 and
the inlet header zone 210.
[0070] Sufficient oxygen is used in the overfired oxidant
compartments so that the combustion process may continue from the
lower boiler while allowing for the lower boiler to operate at a
ratio of oxygen to fuel lower than the stoichiometric ratio than
the combustion process requires. The purpose of enriching the flue
gas stream to the overfired oxidant compartments is to control the
amount of nitrogen oxides (NOx) formed as well as to control the
temperatures in the lower furnace.
[0071] Referring to FIG. 4, another embodiment related to varying
oxygen concentrations in the upper and lower overfire oxidant
compartments 204 and 206 is illustrated. The oxygen concentration
of the upper overfired oxidant compartment 204 can be depleted
relative to the bulk of the second oxidant stream 370 by the
introduction of a supplemental flue gas recirculation stream 380 to
the upper overfired oxidant compartment 204. Furthermore, depletion
of the upper overfired oxidant compartment 204 relative to the bulk
of the secondary oxidant stream 370 may be accomplished by
introducing the combined stream 360 into the lower overfired
oxidant compartment 206 and/or the windbox 208. In one embodiment,
the second oxidant stream 370 can be introduced into the windbox
208, while the supplemental flue gas recirculation stream 380 is
fed to the upper overfired oxidant compartment 204.
[0072] Upper overfire oxidant compartments depleted in oxygen
relative to the global oxygen concentration (i.e., 15 to 40 wt %)
will allow for higher combustion temperatures and result in higher
heat transfer rates in the lower portions of the boiler where there
is a lower working fluid temperature, while decreasing the
combustion temperature and resultant heat transfer rates higher in
the boiler.
[0073] Due to the energy required to increase the temperature of
the upper overfire oxidant, the temperature of the combustion gases
will decrease (most of the combustion will have been completed). At
a decreased temperature of the combustion gases, the resultant flux
to the boiler walls in the portion of the boiler closest to the
outlet plane will decrease. The resulting alteration in the heat
transfer profile will be beneficial for waterwall materials, in
particular for supercritical steam generators. The primary benefit
is to reduce the heat transfer in the boiler close to the boiler
outlet plane where the working fluid temperatures are highest.
[0074] The use of the additional oxygen in the combustion of oil
heavy residues has a number of advantages. Adding oxygen to the
oxidant stream located below the lowest burner assembly alters the
heat absorption profile in the boiler. The ability to alter and
control the heat absorption profile can increase utilization of
heat transfer surfaces located in the lower boiler. This allows for
more total heat absorption in the radiant section of the boiler.
This could also reduce peak temperatures and heat transfer rates
which generally occur above the windbox, and thereby reduce
material requirements and the potential for ash slagging
problems.
[0075] Altering the heat release profile in the boiler can decrease
peak boiler material temperatures at a constant thermal heat input
and the flue gas recirculation rate. The advantage is that flue gas
recirculation rates can be lowered without peak heat fluxes that
causes slagging problems and/or waterwall tube overheating. Another
beneficial result of altering of the heat release profile in the
boiler is to allow for a more efficient utilization of the heat
transfer surface. The benefits for a retrofit boiler is an increase
in thermal heat input and thus working fluid power, while for a new
boiler it results in a decrease in boiler size.
[0076] A further beneficial result is an improvement in emission
characteristics, including carbon monoxide emissions, excess oxygen
required, unburned carbon, and mineral matter properties. Another
result is a beneficial impact on ash fouling properties in the
convective section of the boiler, by controlling the boiler outlet
temperature. Yet another advantageous result is a beneficial impact
on ash slagging properties in the lower section of the boiler.
Another benefit is that ductwork used in the first combined streams
360 to the boiler do not need to tolerate increased oxygen
concentrations. The benefit being that ductwork can be constructed
from a wider variety of materials thereby decreasing cost. Only the
shorter ductwork containing the second combined streams 360A, and
the like, need tolerate higher oxygen concentrations after mixing
with the second oxidant stream 370. Another benefit for retrofit
applications is utilizing existing plant ductwork.
[0077] The control systems 290, 291 of the present invention may be
an open loop system, whereby fluid flow control devices are
adjusted or set at predetermined settings or set by an operator, or
may be a closed loop system. As a closed loop system, the fluid
flow control devices may be adjusted or set in response to an
operation and/or conditional parameter of the boiler and/or boiler
island. For example, the fluid flow control devices may control the
fluid flow in response to thermal parameters of the boiler or
boiler island such as steam temperature, boiler temperature, or
other thermal zones of the boiler or boiler island. Similarly the
fluid flow control devices may control fluid flow in response
operational parameters such as system load or changes to the load
of the boiler or boiler island. The present invention contemplates
that a processor or DCS may provide a respective control signal to
a respective fluid flow control device in response to a sensed
input signal, such as an operational or system condition
parameter.
[0078] FIG. 8 illustrates an example of the carbon heat loss that
can be achieved by varying the oxygen content in the stream 360B.
The tests were conducted in a 15 MW pilot plant. The tests were
conducted using an oxygen stoichiometry of 1 and 0.85 respectively
in the fuel compartment (the windbox 208--see FIG. 4). A test was
also conducted using air-fired asphalt (the oil heavy residue). As
shown therein, improved carbon burnout/carbon heat loss with oxygen
enrichment in the fuel compartment during 15 MW testing was
achieved. Significant improvement in carbon heat loss is achieved
by increasing the concentration of oxygen in the oxidant flow
through the fuel compartment from 25% to 30%. Control of the oxygen
concentration and total flow of oxygen into the fuel compartment is
a therefore a useful aspect in optimizing thermal performance when
oil heavy residues are used as fuels.
[0079] The enrichment of oxygen in the oxidant to the fuel
compartment also impacts heat release and heat absorption in the
furnace waterwalls. FIG. 9 is a graph that illustrates the impact
of oxygen enrichment on heat flux to the furnace wall near the
burner/windbox during 15 MW testing. The system controls the oxygen
concentrations and distribution of oxidant along the height of the
windbox allowing for adjustment of the heat flux profile in the
furnace walls. This is done in concert with the oxygen
concentration and oxygen flows to the OFA locations to optimize
overall furnace waterwall heat flux while maintaining desired
combustion efficiency and emission levels. Further adjustment of
this oxygen distribution can provide an active control of superheat
reheat steam temperature by shifting furnace waterwall heat
absorption and convective section absorption.
[0080] In an embodiment, a method of controlling the operation of
an oxy-fired boiler is provided. The method includes combusting a
fuel that comprises oil heavy residues in a boiler, the oil heavy
residues including hydrocarbon molecules having a number average
molecular weight from approximately 200 to approximately 3000 grams
per mole, discharging flue gas from the boiler, recycling a portion
of the flue gas to the boiler, combining a first oxidant stream
with the recycled flue gas to form a combined stream, splitting the
combined stream into a plurality of independent split streams,
introducing each independent split stream at a different elevation
of the boiler, and controlling independently a parameter of each of
the independent split streams to adjust the heat release at each
respective elevation of the boiler to vary the heat release profile
of the boiler by adding a second oxidant stream to each respective
independent split stream to form respective independent oxygen
enriched split streams. In an embodiment, the oil heavy residues
comprise asphaltene. In an embodiment, the boiler is a tangentially
fired boiler. In an embodiment, the step of controlling
independently the parameter of each independent split stream
further includes changing a heat absorption in the boiler to a
desired heat absorption pattern. In an embodiment, at least one of
the split streams is introduced into the boiler at a hopper zone
located below a windbox, at the windbox and/or in an overfire
compartment located above the windbox. In an embodiment, at least a
portion of the combined stream is introduced into the boiler in a
lower portion of the windbox. In an embodiment, the at least one
split stream that is introduced into the boiler at the windbox is
about 50 to about 100 weight percent of the combined stream. In an
embodiment, the at least one split stream is introduced into the
boiler in a lower portion of an overfire compartment. In an
embodiment, the at least one split stream is introduced into the
boiler in an upper portion of an overfire compartment.
[0081] In another embodiment, a method is provided. The method
includes the steps of combusting a fuel that comprises oil heavy
residues in a boiler, where the oil heavy residues that comprise
hydrocarbon molecules having a number average molecular weight from
200 to 3000 grams per mole, discharging flue gas from the boiler,
recycling a portion of the flue gas to the boiler, combining a
first oxidant stream with the recycled flue gases to form a first
combined stream, splitting the first combined stream into a
plurality of independent split streams, combining a second oxidant
stream to each respective independent split stream provided to the
boiler to form respective independent oxygen enriched split
streams, introducing each independent oxygen enriched split stream
to a different elevation of the boiler, and controlling
independently the amount of the second oxidant stream added to each
respective independent split stream to adjust the heat release at
each respective elevation of the boiler to vary the heat release
profile of the boiler. The first combined stream, the independent
split streams, and the independent oxygen enriched split streams do
not carry the fuel for the boiler. In an embodiment, the boiler is
a tangentially fired boiler. In an embodiment, adding the second
oxidant stream to form the respective oxygen enriched split streams
is conducted at a position proximate to a point of entry into the
boiler. In an embodiment, the respective split streams are
sequentially introduced into the boiler. In an embodiment, at least
one respective oxygen enriched split stream is introduced into the
boiler at a hopper zone located below a windbox. In an embodiment,
the oxygen enriched split stream introduced into the boiler at the
windbox comprises about 50 to about 100 wt % oxygen, based on the
total weight of the stream. In an embodiment, each oxygen enriched
split stream is introduced into the boiler via an annular space
disposed around an inner port, where the inner port introduces the
fuel and transport air into the boiler. In an embodiment, the
boiler is a wall fired boiler. In an embodiment, the step of
controlling independently the parameter of each respective oxygen
enriched split stream introduced to the boiler changes the heat
pattern of the boiler. In an embodiment, at least one respective
oxygen enriched split stream is introduced into the boiler at an
overfire compartment at the hopper zone, wherein the oxygen
enriched split stream introduced into the overfire compartment at
the hopper zone comprises up to 50 wt % oxygen based on the total
weight of the oxygen enriched split stream.
[0082] In yet another embodiment, a system is provided. The system
includes an air separation unit, a boiler configured to combust oil
heavy residues, the oil heavy residues comprising hydrocarbon
molecules having a number average molecular weight from 200 to 3000
grams per mole, a pollution control system, a gas processing unit
and a control system. The air separation unit is upstream of the
boiler, the pollution control system and the gas processing unit.
The boiler is upstream of the pollution control system and the gas
processing unit. Flue gas is recycled from the gas processing unit
to the boiler via the air separation unit. The control system is
configured to control the addition of a first oxidant stream to the
recycled flue gas to form a combined stream and to control the
addition of a second oxidant stream to a plurality of independent
split streams formed from the combined stream to vary the heat
release profile of the boiler. Each of the independent split
streams to which the second oxidant stream is added is introduced
to a different elevation of the boiler.
[0083] As used herein, an element or step recited in the singular
and proceeded with the word "a" or "an" should be understood as not
excluding plural of said elements or steps, unless such exclusion
is explicitly stated. Furthermore, references to "one embodiment"
of the present invention are not intended to be interpreted as
excluding the existence of additional embodiments that also
incorporate the recited features. Moreover, unless explicitly
stated to the contrary, embodiments "comprising," "including," or
"having" an element or a plurality of elements having a particular
property may include additional such elements not having that
property
[0084] This written description uses examples to disclose several
embodiments of the invention, including the best mode, and also to
enable one of ordinary skill in the art to practice the embodiments
of invention, including making and using any devices or systems and
performing any incorporated methods. The patentable scope of the
invention is defined by the claims, and may include other examples
that occur to one of ordinary skill in the art. Such other examples
are intended to be within the scope of the claims if they have
structural elements that do not differ from the literal language of
the claims, or if they include equivalent structural elements with
insubstantial differences from the literal languages of the
claims.
* * * * *