This invention relates generally to rotary machines and more particularly, to methods and apparatus for operating gas turbine engines.
At least some known gas turbine engines combust a fuel and air mixture to release heat energy from the mixture to form a high temperature combustion gas stream that is channeled to a turbine via a hot gas path. The turbine converts thermal energy from the combustion gas stream to mechanical energy that rotates a turbine shaft. The output of the turbine may be used to power a machine, for example, an electric generator or a pump.
At least one by-product of the combustion reaction may be subject to regulatory limitations. For example, within thermally-driven reactions, nitrogen oxide (NOx) may be formed by a reaction between nitrogen and oxygen in the air initiated by the high temperatures within the gas turbine engine. Generally, engine efficiency increases as the combustion gas stream temperature entering a turbine section of the engine increases. However, increasing the combustion gas temperature may facilitate an increased formation of NOx.
Combustion normally occurs at or near an upstream region of a combustor that is normally referred to as the reaction zone or the primary zone. Mixing and combusting of fuel and air may also occur downstream of the reaction zone in a region often referred to as a dilution zone. Inert diluents may be introduced directly into the dilution zone to dilute the fuel and air mixture to facilitate achieving a predetermined mixture and/or temperature of the gas stream entering the turbine section. However, inert diluents are not always available, may adversely affect an engine heat rate, and may increase capital and operating costs. Steam may be introduced as a diluent, however, steam may shorten a life expectancy of the hot gas path components.
To facilitate controlling NOx emissions during turbine engine operation, at least some known gas turbine engines use combustors that operate with a lean fuel/air ratio and/or wherein the combustors are operated such that fuel is premixed with air prior to being admitted into the combustor's reaction zone. Premixing may facilitate reducing combustion temperatures and subsequently reduce NOx formation without requiring diluent addition. However, if the fuel used is a process gas or a synthetic gas, or syngas, the process gas and/or syngas selected may include sufficient hydrogen such that an associated high flame speed may facilitate autoignition, flashback, and/or flame holding within a mixing apparatus. Moreover, such high flame speed may not facilitate uniform fuel and air mixing prior to combustion.
In one aspect, a method of operating a turbine engine is provided. The method includes providing at least one combustor assembly having a combustion chamber defined therein, wherein the combustion chamber has a centerline extending therethrough. The method also includes injecting at least one first fluid stream into the combustion chamber. The method further includes injecting at least one second fluid stream into the combustion chamber at an oblique angle with respect to the at least one first fluid stream, thereby intersecting and mixing the at least one second fluid stream with the at least one first fluid stream.
In another aspect, a combustor assembly is provided. The assembly includes at least one combustor wall defining a combustion chamber. The assembly also includes at least one first fluid passage defining at least one first fluid inlet within the at least one combustor wall. The at least one first fluid passage is coupled in flow communication with the combustion chamber. The at least one first fluid inlet is configured to inject a first fluid stream into the combustion chamber. The assembly further includes at least one second fluid passage defining at least one second fluid inlet within the at least one combustor wall. The at least one second fluid inlet is adjacent to the at least one first fluid inlet and is coupled in flow communication with the combustion chamber. The second fluid inlet is configured to inject a second fluid stream into the combustion chamber at an oblique angle with respect to the first fluid stream such that the second and first fluid streams intersect at a predetermined angle of incidence.
In a further aspect, a turbine engine is provided. The engine includes at least one first fluid source, at least one second fluid source, and a combustor assembly coupled in flow communication with the at least one first fluid source and the at least one second fluid source. The combustor assembly includes at least one combustor wall, at least one first fluid passage, and at least one second fluid passage. The at least one combustor wall defines a combustion chamber The at least one first fluid passage defines at least one first fluid inlet within the at least one combustor wall and the at least one first fluid passage is coupled in flow communication with the combustion chamber. The at least one first fluid inlet is configured to inject a first fluid stream into the combustion chamber. The at least one second fluid passage defines at least one second fluid inlet within the at least one combustor wall. The at least one second fluid inlet is positioned adjacent to the at least one first fluid inlet. The at least one second fluid inlet is coupled in flow communication with the combustion chamber and is configured to inject a second fluid stream into the combustion chamber at an oblique angle with respect to the first fluid stream such that the second fluid and first fluid streams intersect at a predetermined angle of incidence.
In operation, air flows through compressor 102 and a substantial amount of compressed air is supplied to combustor assembly 104. Assembly 104 is also in flow communication with a fuel source (not shown in
Air passage 122 is coupled in flow communication with at least one first fluid source that, in the exemplary embodiment, is compressor 102 (shown in
In the exemplary embodiment, air passage 122 defines an air inlet 124 within a portion of combustor wall 105 that facilitates channeling an air stream 132 (illustrated with the associated arrow). Similarly, in the exemplary embodiment, fuel passages 120 define a plurality of fuel inlets 126 within a portion of a combustor wall 105. Fuel passages 120 facilitate channeling a plurality of fuel streams 130 (illustrated with a plurality of associated arrows). Alternatively, first fluid passages (or, air passage 122) and/or second fluid passages (or, fuel passages 120) may be configured to channel other fluids that include, but are not limited to, premixed fuel and air, inert diluents and exhaust gases.
When assembled, fuel inlets 126, air inlet 124 and combustor wall 105 define a fuel-air array 128. In the exemplary embodiment, array 128 provides a lean direct injection (LDI) method of combustion within combustor assembly 104 as described further below.
A method of operating turbine engine 100 includes providing at least one combustor assembly 104 having combustion chamber 106 defined therein, wherein combustion chamber 106 has centerline 107 extending therethrough. The method also includes injecting at least one first fluid stream into combustion chamber 106, wherein, in the exemplary embodiment, the method includes injecting air stream 132 into combustion chamber 106. The method further includes injecting at least one second fluid stream into the combustion chamber, wherein, in the exemplary embodiment, the method includes injecting fuel stream 130 into combustion chamber 106 at oblique angle 134 with respect to air stream 132, thereby intersecting and mixing fuel stream 130 with air stream 132. Alternatively, first fluid passages (or, air passage 122) and/or second fluid passages (or, fuel passages 120) channel other fluid streams (not shown) that include, but are not limited to, premixed fuel and air, inert diluents and exhaust gases.
In operation, fuel passages 120 channel plurality of fuel streams 130 and air passage 122 channels air stream 132 through fuel-air array 128 into combustion chamber 106. Air stream 132 may flow substantially uniformly or may flow non-uniformly, for example, stream 132 may be swirled prior to entry into fuel-air array 128. In the illustrated embodiment, air stream 132 is injected into combustion chamber 106 substantially parallel to combustion chamber centerline 107 and substantially perpendicular to wall 105. To enhance mixing, fuel streams 130 are each injected into combustion chamber 106 at predetermined oblique radial angles of incidence 134 with respect to air stream 132 and at predetermined oblique circumferential angles of incidence 136 with respect to air stream 132. More specifically, in the exemplary embodiment, fuel streams 130 are each injected at a radial angle of incidence 134 between 0° and 90°, and at a circumferential angle of incidence 136 between 0° to 360°. The number of fuel inlets 126, the values of radial angles 134 and the values of circumferential angles 136 are variably selected based on a variety of operating parameters that facilitate rapid and thorough mixing of the fuel and air subsequent to fuel streams 130 and air stream 132 impingement.
In the exemplary embodiment, fuel streams 130 include process gas and/or syngas as the primary fuels. Alternatively, any fuel that facilitates operation of combustor assembly 104 as described herein may be used. Syngas is synthesized using methods known in the art and typically has a varying chemical composition that at least partially depends upon the method of synthesis. Process gas is typically a byproduct of chemical processes that include, but are not limited to, petroleum refining. Syngas and process gas typically include vaporized hydrocarbons that may include, but are not limited to, liquid fuels, or distillates. Syngas and process gas may also include less reactive combustible constituents, inerts and impurities as compared to the associated primary combustible constituents known in the art.
In the exemplary embodiment, array 128 provides a lean direct injection (LDI) method of combustion within combustor assembly 104. An LDI method of combustion is typically defined as an injection scheme that injects fuel and air into a combustion chamber of a combustor with no premixing of the air and fuel prior to injection. This method is in contrast to a lean premixed injection method of combustion that is typically defined by premixing at least a portion of each of fuel and air within a premixer portion of a combustor, thereby forming a fuel-air mixture that is subsequently injected into a combustion chamber. The lean premixed combustion method of combustion is typically characterized by lower flame temperatures than that typically characterized by traditional non-premixed, or diffusion, methods of combustion. The lower combustion temperatures associated with the lean premixed combustion method facilitates a reduction in the rate and magnitude of formation of NOx, however, the fuel-air mixture is generally flammable, and a potential for undesirable flashback of ignition and combustion into the premixer section of the combustor is facilitated.
Some fuel and air mixtures generally facilitate rapid reaction rates and subsequently facilitate a relatively high flame speed as compared to other fuels. Flame speed may be defined as a rate of ignition, spread and propagation of combustion within a fuel-air mixture. A flame speed that is substantially equal to a fuel flow speed facilitates a substantially stable and stationary flame. Higher flame speeds may facilitate autoignition, flashback, and/or flame holding within areas of a combustor not designed to accomodate an associated nearby heat release. Flame holding is facilitated when a residence time of a mixture of fuel and air in a pre-defined volume is greater than the fuel and air mixture's reaction time within the same volume, and a resultant flame as a result of combustion of fuel and air is realized. Specifically, when a flame speed is substantially similar to a fuel-air mixture flow speed, a resultant flame may be characterized as stable.
Thermal NOx is typically defined as NOx formed during combustion of fuel and air through high temperature oxidation of nitrogen found in air. The formation rate is primarly a function of a temperature associated with the local combustion of fuel and air within a pre-defined region and the residence time of nitrogen at that temperature, wherein the residence time is substantially similar to the fuel and air residence time as described above. Therefore, at least two factors that affect NOx production are combustion temperatures and the residence time of nitrogen at those temperatures. Residence time is further defined as the time period wherein a portion of fuel and a portion of air are mixed together to complete ignition and combustion such that only post-combustion products remain including, but not limited to, heat, water, nitrogen, and carbon dioxide. In general, as the temperature of combustion and/or the residence time increase, a rate of NOx generation increases as well. Optimizing residence times and temperatures facilitates complete combustion and also facilitates the mitigation of NOx generation. The high reaction rate of certain fuels and air as described above facilitates mitigating fuel and air mixing, thereby facilitating NOx production. This is due to the increased localized temperatures associated with the rapid ignition of the fuel as well as the increased residence time needed to combine the fuel and air to facilitate substantially complete combustion. In general, levelizing a pre-determined reaction rate of fuel and air molecules in a pre-determined volume through aggressive fuel and air mixing facilitates levelizing localized exothermic energy release and, therefore, localized temperatures within the volume.
When conditions are such that a fuel-air mixture may ignite, complete ignition that generates a flame does not occur immediately, but rather ignition occurs with a delay, typically referred to as an ignition delay, or an induction period, that depends on factors that include, but are not limited to, the particular type of fuel being ignited, a fuel-air mixture temperature, and the relative concentrations of fuel molecules and air molecules. As the induction period increases, the time available for air and fuel mixing increases. Some fuels typically have a relatively short induction period. In contrast to residence time, a shortened induction period facilitates combustion on a microscopic scale while facilitating a need for a longer residence time to facilitate thorough fuel and air mixing and substantially complete combustion on a macroscopic scale.
Flame stability, completeness of combustion, and NOx production may also be affected by turbulence and/or swirling of fuel and air prior to combustion. A relative magnitude of swirling is often represented with a swirl number. A swirl number is typically defined as a ratio of a tangential momentum of fuel and air molecules as compared to, or divided by, an axial momentum of the same fuel and air molecules. Swirling and turbulence are contrasted in that a swirl number is a characteristic reflecting the magnitude of turbulence. The magnitude of turbulence may also be reflected by characteristics that include, but are not limited to, irregular (or random) flows and diffusive flows. Increasing the turbulence and/or swirl may facilitate decreasing the residence time and the peak and local temperatures of combustion of fuel and air, thereby facilitating a decrease in NOx production.
In some embodiments, fluids that include, but are not limited to, premixed fuel and air, inert diluents and exhaust gases, may also be injected to facilitate methods of establishing flame stability, completeness of combustion, and a decrease in NOx production as described herein. Hereon, wherein only fuel and air are discussed, and unless otherwise noted, the discussion should be assumed to include such fluids for injection into combustion chamber 106 in conjunction with fuel and air.
Impinging multiple stream flows onto each other, for example, fuel and air streams 130 and 132, respectively, as well as inert diluents and/or at least partially premixed fuel and air (neither shown) within fuel-air array 128, with pre-determined angles of incidence, flow velocities, and mass flow rates, forms a predetermined vortex (not shown) that includes at least one localized flow field (not shown) that is defined within a pre-determined volume and with a pre-determined set of characteristics that includes, but is not limited to, a pre-determined turbulence, residence time and temperature. A combustor assembly, for example, assembly 104, with multiple fuel-air arrays 128 will facilitate forming the vortex that includes multiple localized flow fields (not shown). Such multiple localized flow fields may interact with each other to form the vortex (not shown) that includes a bulk flow field (not shown) as discussed further below.
Fuel-air array 128 facilitates rapid mixing of fuel and air within a pre-determined localized flow field (not shown) subsequent to admission into combustion chamber 106. Within array 128, the number of fuel inlets 126, the values of the injection angles of air stream 132 with respect to centerline 107, the values of radial angles 134 and the values of circumferential angles 136, and the size and scale of inlets 124 and 126 are variably selected to form a pre-determined flow field that facilitates rapid and thorough mixing of fuel and air. Specifically, fuel is injected into combustion chamber 106 via inlets 126 with a predetermined velocity that is typically faster than the injection velocity of air injected into chamber 106 via inlet 124, throughout at least a portion of engine 100 (shown in
LDI methods of combustion as facilitated by fuel-air array 128 also facilitate reducing potentials for autoignition, flashback, and flame holding (in other than pre-determined regions of combustion chamber 104) with respect to lean premixed combustion methods. For example, lack of premixing fuel and air upstream of inlets 124 and 126 reduces a potential for autoignition and flashback within array 128 to substantially zero. Therefore, LDI combustion methods provide some of the benefits of diffusion and lean premixed combustion methods without some of the drawbacks.
One embodiment of alternative fuel-air array 150 includes configuring rings 151, 153 and 155 to form substantially concentric, counter-rotating, or counter-swirling, fuel-air mixing/combustion flow fields (not shown) that subsequently form a predetermined bulk flow field (not shown). For example, rings 151 and 155 may be configured to form clockwise rotating flow fields while ring 153 is configured to form a counter-clockwise flow field. Each of the plurality of radially adjacent concentric rings of swirling mixtures that defines the associated flow fields may have associated fluid currents that flow in substantially opposite circumferential directions. The points of intersection of the opposing fluid currents are typically characterized by swirls flowing in the same direction within localized flow fields. The resultant bulk flow field includes interactions of adjacent counter-swirling flow fields that facilitate forming a pre-determined swirl number and turbulence within the bulk flow field, thereby facilitating formation of a substantially swirl-less bulk flow field with good flame holding characteristics.
Moreover, the regions of the bulk flow field wherein the fuel and air streams (not shown in
Another embodiment of alternative fuel-air array 150 includes configuring rings 151, 153 and 155 to form a vortex that includes substantially annular, co-rotating fuel-air mixing/combustion flow fields (not shown) that subsequently form a pre-determined bulk flow field (not shown). For example, rings 151, 153 and 155 may be configured to form clockwise co-rotating, or co-swirling, flow fields. Each of the plurality of radially adjacent concentric rings of swirling mixtures that defines the associated flow fields may have associated fluid currents that flow in substantially similar circumferential directions. The resultant bulk flow field includes interactions of adjacent co-swirling flow fields that oppose each other such that they facilitate swirl and turbulence within the bulk flow field that further facilitates formation of the predetermined vortex with mixing fuel and air characteristics typically superior to those of counter-swirling embodiments as described above.
Another embodiment of alternative fuel-air array 150 includes configuring each of fuel inlets 152 and air inlets 154 such that any combination of inlets 152 and 154 in any of rings 151, 153 and 155 may be in service throughout a range of operation of engine 100 (shown in
Any of arrays 128 (shown in
Typically, combustion of certain fuels within dry low NOx, typically referred to as DLN, gas turbine engines may be difficult because of the properties associated with the combustible constituents, for example, hydrogen, within the fuels, Any of arrays 128, 140, 145, 150, 170, and 180 may be inserted into substantially any gas turbine engine to facilitate combustion and reducing NOx through direct injection of fuel, air and/or diluent streams to supplement injection of premixed fuel, air and/or diluents.
Moreover, arrays 128, 140, 145, 150, 170, and 180 facilitate flexible positioning and orienting such arrays 128, 140, 145, 150, 170, and 180 in a wide variety of geometries that facilitate operation of engine 100 over a wide variety of operational power generation ranges using a wide variety of filets and diluents as is discussed further below. Furthermore, increasing a density of fuel-air arrays 128, 140, 145, 150, 170, and 180 within engine 100 facilitates increasing a heat release rate per unit volume of engine 100, thereby facilitating a reduction in the size and cost of engine 100 for a pre-determined operational power generation range.
Each of air chambers 614 is configured to receive an air stream 616. Each of openings 607 and 608 are configured to receive at least a portion of fuel stream 613. Each of arrays 611 is configured to channel at least a portion of air stream 616 and fuel stream 613 into a combustion chamber 615. Array 611 channels an air stream 618 into combustion chamber 615 and channels at least one fuel stream 620 into combustion chamber 615. Fuel streams 620 are injected into combustion chamber 615 at an oblique angle with respect to air stream 618, thereby intersecting and mixing fuel stream 620 with air stream 618. Stream 618 and 620 may also include any pre-determined mixture of fuel, air, combustion gases and/or inert diluents that facilitate operation of engine 100 as described herein. Moreover, each of arrays 611 is configured to channel a pre-determined mixture as described above that differs from other arrays 611 such that pre-determined localized and bulk flow fields (neither shown) are formed within combustion chamber 615.
In operation, air stream 616 is channeled into swirler vane 612, specifically, air chambers 614. Fuel stream 613 is channeled into chamber 606 and subsequently into openings 607 formed within swirler vane 612. The fuel is channeled from openings 607 to openings 608 via associated passages. Each of arrays 611 facilitates channeling air streams 618 from chambers 614 via openings 617 into combustion chamber 615. Each of arrays 611 also facilitate channeling fuel streams 620 into combustion chamber 615 wherein each of air stream 618 and fuel stream 620 are impinged on each other to mix thoroughly within chamber 615. An air mass flow rate associated with air stream 616 and a fuel/air/diluent mass flow rate associated with stream 613 are controlled such that each chamber 615 receives a predetermined ratio of fuel, air and diluents. Pre-determined angles of impingement (not shown) between streams 618 and 620 facilitate premixing within chamber 615 such that operation of engine 100 as described herein is facilitated. Additional fuel, air and/or diluent passages may be included within swirl vane 612 to facilitate operation of engine 100 as described herein.
The gas turbine engine and combustor assembly described herein facilitates mitigating combustion product emissions while facilitating a pre-determined heat release rate per unit volume. More specifically, the engine includes a lean direct injection combustor assembly that facilitates thorough and rapid fuel and air mixing as a result of fuel and air stream impingement. Such impingement facilitates a reduction in NOx, broader turn-down margins, flame stability, decreasing the size of the combustor assembly necessary to attain a particular rate of heat release, and mitigation of undesirable combustion dynamics while combusting fuels that include process gas and syngas. Subsequently, an associated air pressure drop within the cooling passages defined within a smaller combustion assembly facilitates a more efficient air injection method. As a result, the operating efficiency of such engines may be increased and the engine's capital and operational costs may be reduced.
The methods and apparatus for combusting syngas and process gas as described herein facilitates operation of a gas turbine engine. More specifically, the engine as described above facilitates a more robust combustor assembly configuration. Such combustor assembly configuration also facilitates efficiency, reliability, and reduced maintenance costs and gas turbine engine outages.
Exemplary embodiments of combustor assemblies as associated with gas turbine engines are described above in detail. The methods, apparatus and systems are not limited to the specific embodiments described herein nor to the specific illustrated gas turbine engines and combustor assemblies.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
Number | Name | Date | Kind |
---|---|---|---|
4618323 | Mansour | Oct 1986 | A |
5437158 | Fric | Aug 1995 | A |
5479781 | Fric et al. | Jan 1996 | A |
5494437 | Kubota et al. | Feb 1996 | A |
5680766 | Joshi et al. | Oct 1997 | A |
5746048 | Shah | May 1998 | A |
6067790 | Choi et al. | May 2000 | A |
6192688 | Beebe | Feb 2001 | B1 |
6360525 | Senior et al. | Mar 2002 | B1 |
6474071 | Durbin et al. | Nov 2002 | B1 |
6550696 | Mansour et al. | Apr 2003 | B2 |
6568190 | Tiemann | May 2003 | B1 |
6705855 | Nagayama et al. | Mar 2004 | B2 |
6908298 | Dykema | Jun 2005 | B1 |
20040035114 | Hayashi et al. | Feb 2004 | A1 |
Number | Date | Country | |
---|---|---|---|
20080078160 A1 | Apr 2008 | US |