OXY/FUEL COMBUSTION SYSTEM WITH LITTLE OR NO EXCESS OXYGEN
The disclosure includes a combustion system including a primary reactor arranged and disposed to receive a solid fuel and a first oxygen stream and deliver a first substantially gaseous product and a substantially solid or molten product, a secondary reactor in fluid communication with the primary reactor, and a furnace in fluid communication with the secondary reactor.
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This Application is related to Application No. ______, entitled “COMBUSTION SYSTEM WITH STEAM OR WATER INJECTION”, Attorney Docket No. 07238 USA, filed contemporaneously with this Application on Sep. 26, 2008, assigned to the assignee of the present disclosure and which is herein incorporated by reference in its entirety, Application No. ______, entitled “COMBUSTION SYSTEM WITH PRECOMBUSTOR”, Attorney Docket No. 07255 USA, filed contemporaneously with this Application on Sep. 26, 2008, assigned to the assignee of the present disclosure and which is herein incorporated by reference in its entirety, Application No. ______, entitled “OXY/FUEL COMBUSTION SYSTEM WITH MINIMIZED FLUE GAS RECIRCULATION”, Attorney Docket No. 07257 USA, filed contemporaneously with this Application on Sep. 26, 2008, assigned to the assignee of the present disclosure and which is herein incorporated by reference in its entirety, Application No. ______, entitled “CONVECTIVE SECTION COMBUSTION”, Attorney Docket No. 07254 USA, filed contemporaneously with this Application on Sep. 26, 2008, assigned to the assignee of the present disclosure and which is herein incorporated by reference in its entirety, Application No. ______, entitled “OXY/FUEL COMBUSTION SYSTEM HAVING COMBINED CONVECTIVE SECTION AND RADIANT SECTION”, Attorney Docket No. 07247 USA, filed contemporaneously with this Application on Sep. 26, 2008, assigned to the assignee of the present disclosure and which is herein incorporated by reference in its entirety, Application No. ______, entitled “PROCESS TEMPERATURE CONTROL IN OXY/FUEL COMBUSTION SYSTEM”, Attorney Docket No. 07239 USA, filed contemporaneously with this Application on Sep. 26, 2008, assigned to the assignee of the present disclosure and which is herein incorporated by reference in its entirety, Application No. ______, entitled “COMBUSTION SYSTEM WITH PRECOMBUSTOR”, Attorney Docket No. 07262Z USA, filed contemporaneously with this Application on Sep. 26, 2008, assigned to the assignee of the present disclosure and which is herein incorporated by reference in its entirety, and application Ser. No. 12/138,755, entitled “OXYGEN CONTROL SYSTEM FOR OXYGEN ENHANCED COMBUSTION OF SOLID FUELS”, Attorney Docket No. 07162 USA, filed Jun. 13, 2008, assigned to the assignee of the present disclosure and which is incorporated herein by reference in its entirety.
FIELD OF THE DISCLOSUREThe present disclosure is directed to an oxy/fuel combustion system and method. In particular, the present disclosure is directed to an oxygen-enriched solid fuel combustion system and method.
BACKGROUND OF THE DISCLOSUREAs the world-wide demand for electric power continues to grow, so does the urgency for developing sustainable and environmentally responsible methods for power generation. Considering the abundance of global coal reserves, the recent emergence of oxygen fired coal technology, which is ideally suited for CO2 capture, will be called upon to play a leading role. There is consequently a need to develop refinements to the technology which will improve its energy efficiency and reduce its cost of implementation. The disclosure disclosed herein is directed toward the accomplishment of this objective.
Due to slower overall combustion kinetics, excess oxygen requirements for coal combustion are generally much higher than for gaseous and liquid fuels. For example, whereas the stoichiometric ratio (i.e. ratio of actual to theoretical minimum O2 required) for gaseous phase combustion (e.g. natural gas) is often 1.05 (5% excess) or less, the stoichiometric ratio for coal combustion is more typically in the vicinity of 1.2 (20% excess).
Therefore, there is an unmet need to provide efficient methods and systems for generating energy by solid fuel combustion in oxygen-based systems.
SUMMARY OF THE DISCLOSUREThis disclosure provides a device and method for burning solid fuel, such as coal, with oxygen and recycled flue gas in a multi-stage combustion process.
According to an embodiment, a combustion system includes a primary reactor arranged and disposed to receive a solid fuel and a first oxygen stream and deliver a first substantially gaseous product and a substantially solid or molten product, a secondary reactor in fluid communication with the primary reactor, and a furnace in fluid communication with the secondary reactor. In the embodiment, the secondary reactor is disposed to receive a second oxygen stream thereby converting the first substantially gaseous product from being oxygen deficient upon entering the secondary reactor to oxygen rich upon exiting the secondary reactor.
According to another embodiment, a method of operating a combustion system includes providing a primary reactor arranged and disposed to receive a solid fuel and a first oxygen stream and deliver a first substantially gaseous product and a substantially solid or molten product, providing a secondary reactor in fluid communication with the primary reactor, providing a furnace in fluid communication with the secondary reactor, and determining a stoichiometric ratio selected from the group consisting of the stoichiometric ratio of the primary reactor, the stoichiometric ratio of the secondary reactor, the stoichiometric ratio of the furnace, and combinations thereof. In the embodiment, the secondary reactor is disposed to receive a second oxygen stream converting the first substantially gaseous product from being oxygen deficient upon entering the secondary reactor to oxygen rich upon exiting the secondary reactor.
An advantage of the present disclosure is the ability to achieve substantially complete combustion of coal with a reduced amount of O2.
Another advantage of the present disclosure is the ability to produce a product gas with high CO2 purity.
Yet another advantage of the present disclosure is the ability to remove fly ash and other contaminants resulting in reduced fouling.
Further aspects of the method and system are disclosed herein. The features as discussed above, as well as other features and advantages of the present disclosure will be appreciated and understood by those skilled in the art from the following detailed description and drawings.
Wherever possible, the same reference numbers will be used throughout the drawings to represent the same parts.
DETAILED DESCRIPTION OF THE DISCLOSUREThe present disclosure now will be described more fully hereinafter with reference to the accompanying drawings, in which a preferred embodiment of the disclosure is shown. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the disclosure to those skilled in the art.
Certain embodiments of the present disclosure include systems and methods for combusting solid fuel. As used herein, the term “solid fuel” and grammatical variations thereof refers to any solid fuel suitable for combustion purposes. For example, the disclosure may be used with many types of carbon-containing solid fuels, including but not limited to: anthracite, bituminous, sub-bituminous, and lignite coals; tar; bitumen; petroleum coke; paper mill sludge solids and sewage sludge solids; wood; peat; grass; and combinations and mixtures of all of those fuels. As used herein, the term “oxygen” and grammatical variations thereof refers to an oxidizer having an O2 concentration greater than that of atmospheric or ambient conditions. As used herein, the term “oxy/coal combustion” and grammatical variations thereof refers to coal combustion in oxygen, the term “air/coal combustion” and grammatical variations thereof refers to coal combustion in air, the term “oxy/fuel combustion” and grammatical variations thereof refers to fuel combustion in oxygen, and the term “air/fuel combustion” and grammatical variations thereof refers to fuel combustion in air. As used herein, the term “combustion fluid” and grammatical variations thereof refers to a fluid formed from and/or mixed with the products of combustion, which may be utilized for convective heat transfer. The term is not limited to the products of combustion and may include fluids mixed with or otherwise traveling through at least a portion of combustion system. Although not so limited, one such example is flue gas. As used herein, the term “recycled flue gas” and grammatical variations thereof refers to combustion fluid exiting the system that is recirculated to any portion of the system. As used herein, the term “flue gas recycle” and grammatical variations thereof refers to a configuration permitting the combustion fluid to be recirculated.
Another reason for the greater need for reducing the stoichiometric ratio during oxygen fired coal boiler operation is that the products of oxygen fired coal combustion comprise principally CO2, H2O, and several inert species; the most abundant among them being O2. Hence, as the stoichiometric ratio is reduced, the CO2 concentration of the product gas stream increases, reducing the burden of downstream equipment required for CO2 purification. Moreover, the total volume of gases processed in the CO2 purification is lowered, leading to lower capital and operating costs. It should be noted that CO2 compression power requirements may be of the same order of magnitude as for compression within the ASU.
The challenge in low stoichiometric ratio operation during coal combustion is in attaining high combustion efficiency. Emissions of CO and unburned carbon are known to increase substantially as the stoichiometric ratio is lowered beneath about 1.2, leading to poor thermal efficiency, a higher propensity for fouling, potentially hazardous conditions within the plant and a higher collection burden on downstream particulate control equipment. Known systems do not provide means for generating electric power in oxygen fired coal boilers with simultaneously low stoichiometric ratio and high thermal efficiency.
Specifically,
The combustion system according to certain embodiments operates at stoichiometric ratios of about 1.05 or less. Known coal combustion systems typically operate at a stoichiometric ratio of about 1.2 or greater. Operation of a solid fuel combustion system of a stoichiometric ratio of less than about 1.05 results in additional features being desired for efficient combustion system operation. For example, it is desirable to provide additional residence time between the solid fuel and oxidizer to facilitate complete evolution of fuel carbon into a gaseous phase. It is also desirable to provide oxygen instead of air as an oxidizer in order to attain sufficiently high temperature within the primary reactor to melt ash constituent of the solid fuel, and to increase the combustion reaction rates throughout the system. It is further desirable to provide a controlled environment for mixing of oxygen and fuel evolved from the solid to the gaseous phase in order to minimize the required residence time for complete burnout and avoid high temperature damage that could otherwise result during oxygen fired fuel combustion. It is also desirable to provide close-coupled combustion instrumentation to provide feedback with which to control the combustion process.
In one embodiment, primary reactor 204 may be a slagging combustor/gasifier such as, for example, a slagging cyclone. The type of reactor is selected to provide the ability to achieve relatively long solid particle residence times and withstand high gas temperatures, thus promoting efficient gasification and/or combustion of the feed coal with little or no carbon residue. Residual solid material 212, which includes ash, may be removed as a viscous slag and delivered into the boiler where it is captured in the bottom of furnace 208, thus minimizing the concentration of particulate in flue gas. Residual solid material 203 may be integral, as illustrated in the embodiment of
Referring to
In another embodiment, oxygen fired coal combustion system 202 includes a recirculator 218 arranged and disposed to permit a recycled flue gas 214 to be transported from a recirculator 218 to primary reactor 204. In the embodiment, recycled flue gas 214 is injected into primary reactor 204 with a stream of primary oxygen 207 and crushed or pulverized fuel in a proportion dictated by the preference to maintain a predetermined temperature in primary reactor 204 in excess of residential solid material 212 temperature and convert essentially all of the solid carbon into a gaseous phase. Other process constraints such as moderation of boiler radiant heat flux and final steam temperatures may also contribute to the selection of primary reactor 204 operating conditions. As discussed below, embodiments of the present disclosure also include streams of tertiary oxygen 225 and quaternary oxygen 227. In addition, embodiments include additional streams of recycled flue gas 215, 219.
In one embodiment, secondary reactor 206 may be arranged and disposed to receive recycled flue gas 214 from recirculator 218 thereby adding it to partially combusted gaseous product 216.
The placement of the streams of the oxygen illustrated in
For example, as the amount of oxygen in secondary oxygen 224 is increased relative to fuel 210, equilibrium favors an increase in the extent of fuel oxidation. The increase in fuel oxidation should lead to greater energy release prior to the gases discharging into furnace 208 where the gases are diluted with furnace 208 gases. This in turn translates to higher mixture temperature and faster chemical kinetics within secondary reactor 206. The faster reaction speeds will further increase the extent of reaction (i.e. shortening the approach to equilibrium). Moreover, the higher temperature gas will possess a lower density and, hence, a higher velocity. Therefore it will also possess greater momentum as it enters furnace 208.
As another illustration, if the length of secondary reactor 206 is increased, the time available for reaction also increases. Consequently, the energy release, mixture temperature, velocity and momentum should again increase.
As a further example, the manner of mixing illustrated in
Referring to
As illustrated in
Referring to
Two additional embodiments which incorporate the use of tertiary oxygen 225 are provided in
Systems employing this disclosure operate in a dynamic or changing mode. Moreover, a plurality of reactors (204 and/or 206) may operate in parallel. In such cases, maintaining optimal operation with low excess oxygen requires combustion instruments to measure properties associated with secondary reactor 206 in the system (i.e. local properties). Referring to
In systems operating with a plurality of secondary reactors 206 operating in parallel, an additional “global” combustion instrument 902 is included to sample the mixed products of combustion, in particular the concentrations of excess oxygen and carbon monoxide (CO), from all of secondary reactors 206. Such an embodiment is illustrated in
Another mode of operation of the embodiment illustrated in
Another embodiment of the disclosure is illustrated in
While the disclosure has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.
Claims
1. A combustion system comprising:
- a primary reactor arranged and disposed to receive a solid fuel and a first oxygen stream and deliver a first substantially gaseous product and a substantially solid or molten product;
- a secondary reactor in fluid communication with the primary reactor; disposed to receive a second oxygen stream thereby converting the first substantially gaseous product from being oxygen deficient upon entering the secondary reactor to oxygen rich upon exiting the secondary reactor; and
- a furnace in fluid communication with the secondary reactor.
2. The system of claim 1, wherein at least one of the oxygen streams is substantially devoid of fluids selected from the group consisting of air, nitrogen, and combinations thereof.
3. The system of claim 1, wherein at least one of the oxygen streams comprises at least about 30% by weight O2.
4. The system of claim 1, wherein the primary reactor is configured to operate with a stoichiometric ratio of less than 1.0.
5. The system of claim 1, wherein the secondary reactor is configured to operate with a stoichiometric ratio of greater than 1.0.
6. The system of claim 1, wherein the combustion system is configured to measure one or more properties of the combustion gases that can be correlated with the overall stoichiometric ratio of the system.
7. The system of claim 1, wherein the primary reactor is configured to operate with a stoichiometric ratio of less than 0.95.
8. The system of claim 1, wherein the secondary reactor is configured to operate with a stoichiometric ratio of between 1.0 and 1.10.
9. The system of claim 1, wherein the secondary reactor is configured to operate with a stoichiometric ratio of between 1.0 and 1.05.
10. The system of claim 1, wherein the partially combusted gaseous product is substantially surrounded by an oxidizing gas within at least a portion of the secondary reactor.
11. The system of claim 10, wherein the oxidizing gas includes oxygen.
12. The system of claim 10, wherein the oxidizing gas includes recycled flue gas.
13. The system of claim 10, wherein the oxidizing gas comprises both oxygen and recycled flue gas.
14. The system of claim 1, wherein the second oxygen stream is mixed with the partially combusted gaseous product as it exits the secondary reactor.
15. The system of claim 1, wherein the primary reactor is configured to permit a residual solid material in a molten state and substantially free of residual carbon to be removed from it.
16. The system of claim 1, further comprising a recirculator arranged and disposed to permit a flue gas to be transported from a flue to the primary reactor.
17. The system of claim 1, wherein a local combustion instrument is arranged and disposed to provide information on conditions within the secondary reactor and/or of an expellant fluid from the secondary reactor.
18. The system of claim 1, further comprising at least one additional secondary reactor in fluid communication with the primary reactor; wherein the additional secondary reactor and the first secondary reactor are arranged and disposed to communicate at least one stream of an oxidizing gas to the first substantially gaseous product, wherein the additional secondary reactor and the first secondary reactor are in fluid communication with the furnace, wherein the primary reactor is configured to operate with a stoichiometric ratio of less than 1.0, wherein the secondary reactor is configured to operate with a stoichiometric ratio of greater than 1.0, and wherein the combustion system is configured to measure at least a property of the combustion gases that can be correlated with the overall stoichiometric ratio of the system.
19. The system of claim 1, wherein the furnace is arranged and disposed to receive a fluid selected from the group of fluids consisting of oxygen, recycled flue gas, and combinations thereof, wherein the furnace is arranged and disposed to receive the fluid in a portion of the furnace substantially removed from the secondary reactors thereby permitting an overall stoichiometric ratio of the system greater than 1.0.
20. A combustion system as in claim 1, further comprising:
- a local combustion instrument arranged and disposed to provide information selected from the group consisting of conditions within the secondary reactor, conditions of an expellant fluid from the secondary reactor, and combinations thereof;
- a global combustion instrument arranged and disposed to provide information on conditions within the flue gas at a point downstream from the furnace; and
- a controller arranged and disposed to controllably provide oxygen streams in response to the information.
21. A method of operating a combustion system comprising:
- providing a primary reactor arranged and disposed to receive a solid fuel and a first oxygen stream and deliver a first substantially gaseous product and a substantially solid or molten product;
- providing a secondary reactor in fluid communication with the primary reactor; disposed to receive a second oxygen stream converting the first substantially gaseous product from being oxygen deficient upon entering the secondary reactor to oxygen rich upon exiting the secondary reactor;
- providing a furnace in fluid communication with the secondary reactor; and
- determining a stoichiometric ratio selected from the group consisting of the stoichiometric ratio of the primary reactor, the stoichiometric ratio of the secondary reactor, the stoichiometric ratio of the furnace, and combinations thereof.
22. The method of claim 21, further comprising:
- providing a controlled amount of oxygen to the primary reactor to maintain a stoichiometric ratio of less than about 1.0; and
- providing a controlled amount of oxygen to the secondary reactor to maintain a stoichiometric ratio of greater than about 1.0.
23. The method of claim 22, further comprising operating with the stoichiometric ratio of the primary reactor below 0.95.
24. The method of claim 22, further comprising operating with the stoichiometric ratio of the secondary reactor between 1.0 and 1.10.
25. The method of claim 22, further comprising operating with the stoichiometric ratio of the secondary reactor between 1.0 and 1.05.
Type: Application
Filed: Sep 26, 2008
Publication Date: Apr 1, 2010
Applicant: AIR PRODUCTS AND CHEMICALS, INC. (Allentown, PA)
Inventors: Mark Daniel D'Agostini (Ebensburg, PA), Jeffrey William Kloosterman (Allentown, PA)
Application Number: 12/238,612
International Classification: F23B 80/02 (20060101);