WITH RE-BURNING

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 _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. Patent 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, N0 ₂ , NO _x ) and sulfur oxides (e.g. S0 ₂ , S0 ₃ , SO _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 rebumer 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 _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 _x emitted as a ratio in which a pound of NO _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 _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 stoichiometrics 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 rebumer 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 _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 Figure 7 identifies the percentage of the NO _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 rebumer 30 as compared to the total amount of fuel fed into the combustion apparatus for combustion. Line 74 of the graph of Figure 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 Figure 7 illustrates the calculated results from a conventional combustion apparatus utilizing a conventional rebumer system. [0014] Fig. 8 is a graph illustrating an extent of the rebum of NO _x reduction efficiency provided by an embodiment of the combustion apparatus as compared to an amount of NO _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 Figure 8 illustrates that the NO _x reduction efficiency is independent of the inlet NO _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 Figure 8 is the amount of the NO _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 _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 Figure 9. The fuel ratio is a measure of the reactivity of a fuel. The vertical axis of the graph of Figure 9 illustrates calculated levels of NO _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 Figures 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, 5 c can include a first combustion zone (or main burner zone) 5 a, 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 5 a. 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 Figure 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 5 a. 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 5 a. The fourth, eighth, twelfth, and sixteenth compartments 2d, 2h, 21, 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 3 a as indicated by broken line in Figure 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. 10027] 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 Figure 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 3 a 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 3 a 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 Figure 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 3 a 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 _x , sulfur oxides (e.g. S0 ₂ , S0 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 _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 _x ) or elements that contribute to the formation of NO _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 rebumer or fuel nozzle 30. An example of a reburner 30 is shown in Figure 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 rebumer 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 3 a 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 earner 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 tltrough 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 earner 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.

100351 While the reagent is shown to be provided to the second combustion zone 5b through the rebu ner 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 _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 _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 _x to form elemental nitrogen, water vapor, carbon monoxide, carbon dioxide, and other reduced species and compounds. One of the primary chemical NO _x destruction mechanisms of the reburn process via the fuel fed to the second combustion zone 5b is set forth below:

[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 _x based on producing amine radicals. The chemical NO _x destruction mechanism of the high temperature reagent injection process can be illustrated by the formula: NO + NH ₂ → N ₂ + H ₂ 0.

[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 _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 5 c 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 5 c 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 _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 earner 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 earner 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 _x formation can be changed within each of the combustion zones 5a, 5b, 5c of the combustion apparatus 5 to provide low NO _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 5 a 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 5 c) 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 US Patent 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 comers 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 5 b and 5 c 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 _x formation. The reduction in NO _x 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 Figures 5-9, it has been determined that a reduction of between 65-70% in the formation of NO _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 _x emissions can be reduced to below 0.10 pound/10 ⁶ BTU (e.g.

between 0.03 to 0.10 pound/10 ⁶ BTU). Such low NO _x emissions can be achieved while maintaining acceptable levels of unburned carbon, carbon monoxide emissions, and unreacted ammonia. Further, the reduction in NO _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 Figure 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 _x emissions. Moreover, as can be appreciated from Figure 9, the reduction in NO _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.