METHODS AND SYSTEMS FOR REDUCED NOx COMBUSTION OF COAL WITH INJECTION OF HEATED NITROGEN-CONTAINING GAS
A stream of nitrogen-containing gas is heated and injected into a stream of coal and conveying gas to produce a stream of mixed nitrogen-containing gas, coal, and conveying gas. Oxygen is injected into the stream of mixed nitrogen-containing gas, coal, and conveying gas to produce a stream of mixed nitrogen-containing gas, coal, conveying gas, and oxygen. The mixed nitrogen-containing gas, coal, conveying gas, and oxygen are combusted in a combustion chamber.
This application claims the benefit under 35 U.S.C. § 119(e) to provisional application No. 60/742,119, filed Dec. 2, 2005, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTIONNOx generally refers to nitrogen monoxide NO and nitrogen dioxide NO2. Both are major contributors to acid rain and smog (ground level ozone) issues. The NOx partition in the flue gases of pulverized coal boilers is typically more than 95% NO and the remainder NO2 (Mitchell S. C., NOx in Pulverized Coal Combustion, IEA Clean Coal Center Report CCC/05, 1998). During coal-combustion, the NOx production originates from three different mechanisms:
Fuel-NOx mechanism,
Thermal-NOx mechanism, and
Prompt-NOx mechanism.
In pulverized coal boilers, 70% to 80% of NOx is formed from the fuel-bound nitrogen species (ftiel-N) via the fuel-NOx mechanism, and the remaining NOx is formed from atmospheric nitrogen (N2), via the thermal-NOx mechanism (5-25%) and via the prompt-NOx mechanism (less than 5%) (Wu Z., NOx controlfor pulverized coal-fired power stations, IEA Clean Coal Center Report CCC/69, 2002). Understanding and limiting the NOx formation in pulverized coal combustion is therefore strongly related to the fuel-N conversion mechanism. A complex series of reactions explains the transformation of coal bound fuel-nitrogen into NOx or N2, including more than 50 intermediate species and hundreds of reactions.
The two main parameters affecting the fuel-NOx formation process are the volatile matter content of the fuel and the stoichiometry (air/fuel ratio). Coal nitrogen content (bound nitrogen only), also strongly impacts NOx emission levels. Coal typically contains 0.5% to 3% nitrogen by weight on a dry basis. For comparison, natural gas also contains some nitrogen (0.5 to 20%); however it is molecular nitrogen N2, and thus is not affected by the fuel-NOx mechanism.
1—Devolatilization releasing coal nitrogen compounds (coal-N) in a gaseous phase (Volatile-N), mainly as HCN, some as NHi. The remaining coal-nitrogen compounds stay in the solid phase (char), and are referred to as char-N,
2—HCN evolution to NHi species,
3—NHi oxidation to NO or reduction to N2 depending on local conditions, and
4—Reburning, as some NO is recirculated back to the hot reducing zone of the flame and converted back to N2 while contacting CHi radicals.
Both volatile-N and char-N can be evolved as NO or as N2. Fuel-NOx formation is minimized by implementing specific conditions leading to N2 rather than NO (see Van Der Lans R. P., Glarborg P. and Dam-Johansen K., Influence of process parameters on nitrogen oxide formation in pulverized coal burners, Prog. Energy Combust. Sci. Vol. 23, p. 349-377, 1997; Bowman C. T., Kinetics of Pollutant Formation and Destruction on Combustion, Prog Energy Combust Sci 1 33-45, 1975; and Proceedings of the 6th International Conference on Technologies and Combustion for a Cleaner Environment, Oporto, Portugal, 2001).
For a given coal and particle size, three main conditions will independently or in combination promote fuel-bound nitrogen conversion into molecular nitrogen N2 rather than NO:
Fuel rich (reducing) conditions at the burner level: by arranging fuel-rich “zones” in the furnace during the devolatilization stage, the nitrogen species in gas phase (volatiles) are more likely to be reduced to molecular nitrogen (N2) rather than oxidized to NO.
High temperature in the early stages of combustion increases the volatiles yield. As volatiles burn close to the burner exit, controlling the volatile-N (gas) to N2 conversion is much easier than the char-N (solid) to N2 conversion. High temperature at the burner exit also increases both the reburning rate of recirculated NO and the conversion rate of volatile-N into N2 (see Sarofim A. F., Pohl J. H., Taylor B. R., Strategies for Controlling Nitrogen Oxide Emissions during Combustion of Nitrogen-bearing fuels, 69th Annual Meeting of the AIChe, Chicago, Ill., 1976; and Bose A. C., Dannecker K. M. and Wendt J. O. L., Energ. Fuel, Vol. 2, p. 301, 1988).
Long residence times in the high temperature and reducing zones in the boiler lead to higher fuel-N to N2 and NO to N2 conversion.
Prior research indicates that oxygen was used alone to decrease the NOx formation. Due to safety and other concerns, oxygen was injected at a relatively low temperature and also in the burner just before the combustion.
BRIEF SUMMARY OF THE INVENTIONA method is provided and a system for performing the method. A stream of nitrogen-containing gas is heated and injected into a stream of coal and conveying gas to produce a stream of mixed nitrogen-containing gas, coal, and conveying gas. The mixed nitrogen-containing gas, coal, and conveying gas are combusted with oxygen in a combustion chamber.
BRIEF DESCRIPTION OF THE DRAWINGSFor a further understanding of the nature and objects of the present system and method, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:
Increasing the temperature of the coal to safely release volatiles in an oxygen deficit environment prior to combustion can hinder the NOx formation mechanism. This is achieved in the proposed method and system by injecting high temperature nitrogen-containing gas upstream of the burner and optionally by injecting oxygen-containing gas in the burner or just upstream of the burner. Injection of hot nitrogen-containing gas in an O2-deficit environment causes devolatilization of the coal to release volatiles and can also decompose them to N2. The fuel-bound nitrogen in char can also be decomposed to N2. This process also increases the residence time of the volatiles-N and char-N in the main combustion zone thereby favoring decomposition to N2. Further NOx reductions are obtained by the optional injection of oxygen-containing gas in the burner or just upstream of the burner to compensate the injected nitrogen and to increase the temperature of the flame in fuel rich condition. Both the processes promote formation of N2 instead of NOx.
The system for burning coal with reduced NOx emissions includes the following: a source of a mixture of coal and conveying gas; a source of oxygen-containing gas; a source of nitrogen-containing gas; a heating device adapted and configured to heat nitrogen from the nitrogen source; a combustion chamber; a burner disposed at a wall of the combustion chamber; a burner operatively associated with a combustion chamber; a fuel duct in fluid communication with the source of a mixture of coal and conveying gas, the fuel duct extending towards the burner; and a nitrogen-containing gas injection element in fluid communication with the heating device and the fuel duct, the nitrogen injection element being adapted and configured to inject heated nitrogen-containing gas from the heating device into a stream of a mixture of coal and conveying gas and mix therewith inside the fuel duct.
A method of combusting coal with reduced NOx emissions includes the following steps. A stream of nitrogen-containing gas is heated. The heated stream of nitrogen-containing gas is injected into a stream of coal and conveying gas to produce a stream of mixed nitrogen-containing gas, coal, and conveying gas. The mixed nitrogen-containing gas, coal, and conveying gas are introduced at a burner disposed at a wall of a combustion chamber. The coal is combusted with oxygen in the combustion chamber.
The system or method can include any one or more of the following aspects:
an oxygen-containing gas injection element is in fluid communication with the source of oxygen and the fuel duct, the oxygen-containing gas injection element fluidly communicating with the fuel duct downstream of where the nitrogen-containing gas injection element fluidly communicates with the fuel duct and upstream of or at the burner, the oxygen-containing gas injection element being adapted and configured to inject oxygen-containing gas from the oxygen-containing gas source into the stream of mixed heated nitrogen-containing gas, coal, and conveying gas;
the source of oxygen-containing gas and the source of nitrogen-containing gas comprise an Air Separation Unit (ASU);
the conveying gas comprises flue gas from the combustion chamber mixed with oxygen-containing gas from the oxygen-containing gas source;
the heating device is adapted and configured to directly impart heat to nitrogen from the nitrogen-containing gas source from a flame;
the heating device is a heat exchanger adapted and configured to exchange heat between nitrogen-containing gas from the nitrogen-containing gas source and heat from combustion of the coal and oxygen in the combustion chamber;
the conveying gas is flue gas from the combustion chamber mixed with oxygen;
the heating device is a heat exchanger adapted and configured to exchange heat between nitrogen-containing gas from the nitrogen-containing gas source and heat from combustion of the coal and oxygen in the combustion chamber;
the heating device is a heat exchanger adapted and configured to exchange heat between nitrogen-containing gas from the nitrogen-containing gas source and heat from combustion of the coal and oxygen in the combustion chamber;
the conveying gas is air;
the oxygen-containing gas injection element fluidly communicates with the fuel duct at the burner;
the nitrogen-containing gas injection element fluidly communicates with the fuel duct at a peripheral portion of the fuel duct;
the nitrogen-containing gas injection element fluidly communicates with the fuel duct along a central axis of the fuel duct;
the oxygen-containing gas injection element fluidly communicates with the fuel duct at a peripheral portion of the fuel duct;
the oxygen-containing gas injection element fluidly communicates with the fuel duct along a central axis of the fuel duct;
the nitrogen-containing gas and oxygen are obtained from an ASU;
the step of heating a nitrogen-containing gas stream comprises directly imparting heat from a flame to the nitrogen stream;
the step of heating a nitrogen-,containing gas stream comprises indirectly imparting heat from a flame to the nitrogen stream via a heat exchanger;
the step of heating a nitrogen-containing gas stream comprises indirectly imparting heat from the step of combusting to the nitrogen stream via a heat exchanger;
the stream of nitrogen-containing gas is heated to a temperature such that a desired level of devolatilization occurs;
the stream of nitrogen-containing gas is heated to a temperature in the range of from about 1,000° F. to about 1,800° F.;
injection of the heated stream of nitrogen-containing gas causes devolatilization of most of a volatile species content in the coal;
collecting at least some of any flue gas produced from the step of combusting, injecting oxygen-containing gas into the collected flue gas to mix therewith, and introducing the mixed oxygen and flue gas to the burner;
oxygen-containing gas is injected into the collected flue gas in an amount such that an oxygen concentration in the mixed oxygen-containing gas and flue gas is from about 3% to about 20%.; and
the step of heating a nitrogen-containing gas stream comprises indirectly imparting heat from the step of combusting to the nitrogen stream via a heat exchanger.
The proposed method and system also reduces the fuel-NOx formation in a coal combustion process. As described in the above section, the fuel bound N can be transformed into either molecular N (N2) or NO depending on the local conditions where the devolatilization took place. Injecting hot nitrogen-containing gas into the coal stream releases volatiles and fuel-bound N compounds in a reducing environment. The reducing environment drives the coal derived N compounds to convert to N2.
The temperature and quantity of nitrogen-containing gas to be injected depends on the type of coal and the NOx reduction targets. The temperature of the nitrogen-containing gas is chosen to be above the devolatilization temperature of the volatile species in the coal. The volatilization characteristics of various general types of coals are well known. In the case of a specific type of coal, the volatilization characteristics may be determined experimentally in a known manner. Generally speaking, the temperature should be selected such that a desired degree of devolatilization occurs for the particular type of coal being combusted. A suitable temperature is in the range of from about 1,000° F. to about 1,800° F. The location of nitrogen-containing gas injection should be strategically placed so that just enough residence time is available for the devolatilization and the conversion to nitrogen-containing gas to occur. Injecting hot nitrogen-containing gas more than this distance can pose safety issues as volatiles are very flammable and unfavorable combustion could occur.
The nitrogen-containing gas need not be pure nitrogen. Indeed, gaseous mixtures having a majority of nitrogen with minor amounts of other gases are suitable for use with the process and system. Such minor constituents include O2 and inert gases such as Ar and CO2. A preferred source for both the nitrogen-containing gas to be heated and the O2 is from an air separation unit (ASU). Suitable ASU's include those operated via pressure swing adsorption (PSA), vacuum swing adsorption (VSA), cryogenic distillation, and membrane permeation. Typical N2 and O2 concentrations in nitrogen-enriched and oxygen-enriched streams from these types of ASU's are well known and need not be repeated here. Other sources of the nitrogen can include a gaseous mixture comprising nitrogen and flue gas.
The oxygen-containing gas to be optionally injected into the mixed nitrogen-containing gas, conveying gas, and coal also need not be pure. Suitable gases include those having an oxygen concentration greater than that of air up to 100% pure oxygen.
In the case of N2 from an ASU, the nitrogen-containing gas can be heated in “direct fired mode” or “indirect fired mode”. In a direct fired mode the incoming nitrogen-containing gas is heated by direct contact with a small flame. In indirect fired mode, the nitrogen-containing gas is heated at a heat exchanger taking heat from a small flame or from a combustion process.
In fuel-rich flame conditions, injection of oxygen in the main combustion zone increases the temperature. This higher temperature reducing environment promotes formation of N2 from the remaining volatiles released from the coal. If optional oxygen-containing gas injection is selected, the oxygen-containing gas is injected at a location which achieves both safety goals and good mixing with the stream of coal/conveying gas/nitrogen-containing gas. The location is desirably upstream of the burner throat in order to reduce the risk of incurring partial combustion of coal particles in local pockets that are oxygen-enriched. At the same time, the location is not so close to the burner that little mixing of the oxygen-containing gas and coal/conveying gas/nitrogen-containing gas is achieved.
The conveying gas comprises any gas to convey fuel particles from a particle storage or generation location, e.g., mills, to the burner level and the combustion chamber. For example, this gas can comprise the primary air used to convey pulverized or micronized coal in a coal-fired boiler. Preferred conveying gases are air and mixtures of recirculated flue gas and oxygen. Typically, these mixtures of recirculated flue gas and oxygen include about 60-90% CO2, 5-20% N2, and 3-20% O2. An especially preferred mixture of recirculated flue gas and oxygen contains about 80% CO2 and about 20% O2.
Several different types of injection elements may be employed. It should be noted that each of the nitrogen-containing gas and oxygen-containing gas injection elements may be the same as one another or different. Several examples of injection elements follow.
A system for performing the method is best illustrated in
As best illustrated in
It should be noted that injection elements 3, 5 need not be disposed centrally along an axis of the fuel duct 8. Rather, they may be disposed along a peripheral portion of the fuel duct 8. Some of these various configurations are best illustrated in some of the following injection element designs.
Radially Injecting Injection Elements Designs:
As illustrated in
The length, D1, and width, D2, of these apertures, as well as the circumferential arc distance, D0, between two adjacent apertures may be varied to control the momentum ratio J (ratio of the oxygen-containing gas or nitrogen-containing gas jet momentum to the momentum of the stream of non-gaseous fuel/conveying gas). D1, D2, and D0 also control the penetration of the injection gas into the primary stream or primary stream mixed with nitrogen-containing gas as appropriate. A small D2/D1 ratio (streamlined rectangular apertures) will minimize the perturbation to solid fuel particles, such as coal. A big D2/D1 ratio (bluff-body slots) will have a greater influence on the solid phase and will push solid fuel particles, such as pulverized coal, away from the centerline of the burner primary air duct. Those two different aspect ratios will lead to different distribution of particles and nitrogen or oxygen at the duct outlet.
Those three parameters, S1, D1, and D2, in turn, control the penetration of the injection gas into the primary stream or primary stream mixed with nitrogen-containing gas as appropriate. A small D2/D1 ratio (streamlined slots) will minimize the perturbation to the solid phase. A big D2/D1 ratio (bluff-body slots) will have a greater influence on the solid phase and will push the coal particles away from the centerline of the burner primary air duct. Those two different aspect ratios will lead to different distribution of particles and nitrogen or oxygen at the duct outlet. As shown in
As depicted in
As best illustrated in
As shown in
As depicted in
Similar to the injection element designs 10, 20, 30, 40, the apertures 53 may be staggered and vary in size in the axial and azimuthal directions. The distance between apertures 53, the number of rows of apertures 53, or the surface area of apertures 53 could also be varied.
This injection element 50 has a particularly beneficial application to coal-fired boilers whose burner geometry include coal concentrators or splitters (identified technique in the prior art for reducing NOx emissions from pulverized coal burners). Varying levels of nitrogen-containing gas or oxygen-containing gas injection may be located to achieve higher concentration of N2 or O2 in coal richer zones. As a result, the equivalence ratio between coal and N2 (in the case of nitrogen-containing gas injection) coal and O2 (in the case of oxygen-containing gas injection) can be controlled in the coal richer zone (concentrated zone) as well as in the coal leaner zones.
Aerodynamic Injection Element Designs:
As depicted in
Referring to the injection element 100 of
Referring to the injection element 110 of
As illustrated in
As shown in
Swirl-Type Injection Element Designs:
The designs presented in this section are based upon the patented Oxynator® (U.S. Pat. No. 5,356,213) concept. It is designed to minimize mixing distance and to prevent high nitrogen or oxygen concentrations near the pipe walls.
With respect to the first configuration and as illustrated in
With respect to the second configuration, the conduit 239 may actually be a plurality of conduits surrounding the fuel duct 231, any or all of which feeds injection element 234.
As shown in
As shown in
All of the Oxynator®-based designs of
Bluff Body Injection Element Designs:
Oxygen-containing gas may be injected at several locations at roughly a single axial position by several different injection elements.
As shown by
As illustrated by
As depicted in
The lance 402 portion terminates in an aerodynamic body 405 having an aerodynamic tip 406. Each of the fins 402 is aerodynamically streamlined in shape. The apertures 403 are configured as circular holes, slots, slits, and other shaped openings such as those depicted in
In all the bluff body designs of
Axially Injecting Injection Element Designs:
Another type of injection element is configured to inject nitrogen-containing gas or oxygen-containing gas axially into the flow of coal/conveying gas from a surface that faces downstream. This surface could have any number of apertures of any shape. Some exemplary shapes 701A-F are best shown in FIGS. 24A-F. The number of apertures, size, shape and angle of injection could be adjusted in order to optimize mixing and solid fuel loading.
Baffles arranged near the outlet end can facilitate a uniform mixing of nitrogen-containing gas and/or oxygen-containing gas (the use of baffles is an improvement over prior art designs as it accomplishes more efficient mixing by increasing the turbulence at the outlet end). Various baffles number, shape and size may be utilized. As the velocity control of the jet outgoing from the pipe is a crucial parameter governing burner aerodynamics, the cross-sectional area of those baffles will be chosen carefully.
Similar types of axially injecting injection elements have a modified cross-section. As gravity has an influence on motion of the particles, a vertical elliptical cross-section, for example, will cause fewer disturbances to the particle trajectories and at the same time could provide improved mixing. Modifications of the cross-section of the pipe allow decreasing or increasing the velocity of the axial nitrogen-containing gas or oxygen-containing gas jet. As best illustrated in
As depicted in
Preferred processes and apparatus for practicing the present invention have been described. It will be understood and readily apparent to the skilled artisan that many changes and modifications may be made to the above-described embodiments without departing from the spirit and the scope of the invention. The foregoing is illustrative only and that other embodiments of the method and system may be employed without departing from the true scope of the invention whose aspects are described in the following claims.
Claims
1. A system for burning coal with reduced NOx emissions, comprising:
- a) a source of a mixture of coal and conveying gas;
- b) a source of oxygen-containing gas;
- c) a source of nitrogen-containing gas;
- d) a heating device adapted and configured to heat nitrogen from said nitrogen-containing gas source;
- e) a combustion chamber;
- f) a burner disposed at a wall of said combustion chamber;
- a burner operatively associated with a combustion chamber;
- g) a fuel duct in fluid communication with said source of a mixture of coal and conveying gas, said fuel duct extending towards said burner; and
- h) a nitrogen-containing gas injection element in fluid communication with said heating device and said fuel duct, said first injection element being adapted and configured to inject heated nitrogen-containing gas from said heating device into a stream of a mixture of coal and conveying gas and mix therewith inside said fuel duct.
2. The system of claim 1, further comprising an oxygen-containing gas injection element in fluid communication with said source of oxygen-containing gas and said fuel duct, said oxygen-containing gas injection element fluidly communicating with said fuel duct downstream of where said nitrogen-containing gas injection element fluidly communicates with said fuel duct and upstream of or at said burner, said oxygen-containing gas injection element being adapted and configured to inject oxygen-containing gas from said oxygen-containing gas source into the stream of mixed heated nitrogen-containing gas, coal, and conveying gas.
3. The system of claim 1, wherein said source of oxygen-containing gas and said source of nitrogen comprises an ASU.
4. The system of claim 1, wherein said conveying gas comprises flue gas from said combustion chamber mixed with oxygen-containing gas from said oxygen source.
5. The system of claim 1, wherein said heating device is adapted and configured to directly impart heat to nitrogen-containing gas from said nitrogen-containing gas source from a flame.
6. The system of claim 1, wherein said heating device is a heat exchanger adapted and configured to exchange heat between nitrogen-containing gas from said nitrogen-containing gas source and heat from combustion of said coal and oxygen in said combustion chamber.
7. The system of claim 2, wherein said conveying gas is flue gas from said combustion chamber mixed with oxygen-containing gas.
8. The system of claim 2, wherein said heating device is a heat exchanger adapted and configured to exchange heat between nitrogen-containing gas from said nitrogen-containing gas source and heat from combustion of said coal and oxygen in said combustion chamber.
9. The system of claim 6, wherein said heating device is a heat exchanger adapted and configured to exchange heat between nitrogen-containing gas from said nitrogen-containing gas source and heat from combustion of said coal and oxygen in said combustion chamber.
10. The system of claim 1, wherein said conveying gas is air.
11. The system of claim 2, wherein said oxygen-containing gas injection element fluidly communicates with said fuel duct at said burner.
12. The system of claim 1, wherein said nitrogen-containing gas injection element fluidly communicates with said fuel duct at a peripheral portion of said fuel duct.
13. The system of claim 1, wherein said nitrogen-containing gas injection element fluidly communicates with said fuel duct along a central axis of said fuel duct.
14. The system of claim 1, wherein said oxygen element fluidly communicates with said fuel duct at a peripheral portion of said fuel duct.
15. The system of claim 1, wherein said oxygen element fluidly communicates with said fuel duct along a central axis of said fuel duct.
16. A method of combusting coal with reduced NOx emissions, comprising the steps of:
- heating a stream of nitrogen-containing gas;
- injecting the heated stream of nitrogen-containing gas into a stream of coal and conveying gas to produce a stream of mixed nitrogen-containing gas, coal, and conveying gas; and
- combusting the coal from the stream of mixed nitrogen-containing gas, coal, and conveying gas with oxygen-containing gas at a burner in the combustion chamber.
17. The method of 16, further comprising the step of injecting oxygen-containing gas into the stream of mixed nitrogen-containing gas, coal, and conveying gas upstream or at the burner.
18. The method of claim 16, wherein the nitrogen-containing gas and oxygen are obtained from an ASU.
19. The method of claim 16, wherein said step of heating a nitrogen-containing gas stream comprises directly imparting heat from a flame to the nitrogen stream.
20. The method of claim 16, wherein said step of heating a nitrogen-containing gas stream comprises indirectly imparting heat from a flame to the nitrogen-containing gas stream via a heat exchanger.
21. The method of claim 16, wherein said step of heating a nitrogen-containing gas stream comprises indirectly imparting heat from said step of combusting to the nitrogen-containing gas stream via a heat exchanger.
22. The method of claim 16, wherein the stream of nitrogen-containing gas is heated to a temperature in the range of from about 1,000° F. to about 1,800° F.
23. The method of claim 16, wherein injection of the heated stream of nitrogen-containing gas causes devolatilization of most of a volatile species content in the coal.
24. The method 16, wherein the conveying gas is air.
25. The method of claim 16, further comprising the steps of:
- collecting at least some of any flue gas produced from said step of combusting;
- injection oxygen-containing gas into the collected flue gas to mix therewith; and
- introducing the oxygen-containing gas oxygen and flue gas to the burner.
26. The method of claim 25 wherein oxygen-containing gas is injected into the collected flue gas in an amount such that an oxygen concentration in the mixed oxygen-containing gas and flue gas is from about 3% to about 20%.
27. The method of claim 17, wherein said step of heating a nitrogen-containing gas stream comprises indirectly imparting heat from said step of combusting to the nitrogen-containing gas stream via a heat exchanger.
28. The method of claim 17, wherein the stream of nitrogen-containing gas is heated to a temperature in the range of from about 1,000° F. to about 1,800° F.
29. The method claim 17, wherein the conveying gas is air.
30. The method of claim 17, further comprising the steps of:
- collecting at least some of any flue gas produced from said step of combusting;
- injection oxygen-containing gas into the collected flue gas to mix therewith; and
- introducing the mixed oxygen and flue gas to the burner.
31. The method of claim 27, wherein the stream of nitrogen-containing gas is heated to a temperature in the range of from about 1,000° F. to about 1,800° F.
32. The method of claim 31, further comprising the steps of:
- collecting at least some of any flue gas produced from said step of combusting;
- injection oxygen-containing gas into the collected flue gas to mix therewith; and
- introducing the mixed oxygen-containing gas and flue gas to the burner.
Type: Application
Filed: Nov 27, 2006
Publication Date: Jun 7, 2007
Inventor: Rajani Varagani (Willowbrook, IL)
Application Number: 11/563,374
International Classification: F23D 1/00 (20060101); F23J 15/00 (20060101);