Patent Grant
8147121
Exemplary embodiments of the invention pertain to the art of turbomachine combustion systems and, more particularly, to a pre-mixing apparatus for a turbomachine combustor.
In general, gas turbine engines combust a fuel/air mixture which releases heat energy to form a high temperature gas stream. The high temperature gas stream is channeled to a turbine via a hot gas path. The turbine converts thermal energy from the high temperature gas stream to mechanical energy that rotates a turbine shaft. The shaft may be used in a variety of applications, such as for providing power to a pump or an electrical generator.
In a gas turbine, engine efficiency increases as combustion gas stream temperatures increase. Unfortunately, higher gas stream temperatures produce higher levels of nitrogen oxide (NOx), an emission that is subject to both federal and state regulation. Therefore, there exists a careful balancing act between operating gas turbines in an efficient range, while also ensuring that the output of NOx remains below mandated levels.
Low NOx levels can be achieved by ensuring very good mixing of the fuel and air. Various techniques, such as Dry-low NOx (DLN) combustors including lean premixed combustors and lean direct injection combustors, are utilized to ensure proper mixing. In turbines that employ lean pre-mixed combustors, fuel is pre-mixed with air in a pre-mixing apparatus prior to being admitted to a reaction or combustion zone. Pre-mixing reduces combustion temperatures and, as a consequence, also reduces NOx output. However, depending on the particular fuel employed, pre-mixing may cause auto-ignition, flashback and/or flame holding within the pre-mixing apparatus.
In turbines that employ lean direct injection (LDI) concepts, fuel and air are introduced directly and separately into a combustion liner arranged at an upstream end of a combustor prior to mixing. However, some systems that employ LDI concepts experience difficulties in rapid and uniform mixing of lean-fuel and rich-air within the combustion liner. Local flame temperatures in such zones may exceed minimum NOx formation threshold temperatures and elevate the production of NOx to unacceptable levels. In certain cases, diluents are added to reduce NOx levels. However, inert diluents are not always readily available, may adversely affect engine heat rate, and may increase capital and operating costs.
Other systems may employ a combustor having a dilution zone situated downstream of the reaction zone. In this case, inert diluents are introduced directly into the dilution zone and mix with the fuel/air mixture to achieve a pre-determined mixture and/or temperature of the gas stream entering the turbine section. However, as discussed above, inert diluents are not always available, may adversely affect engine heat rate and may increase capital and operating costs. Moreover, adding diluents downstream of the reaction zone does not provide any significant improvement in NOx levels.
In accordance with one exemplary embodiment of the invention, a pre-mixing apparatus for a turbine engine includes a main body having an inlet portion, an outlet portion and an exterior wall that collectively establish at least one fluid delivery plenum, and a plurality of fluid delivery tubes extending through at least a portion of the at least one fluid delivery plenum. Each of the plurality of fluid delivery tubes includes at least one fluid delivery opening fluidly connected to the at least one fluid delivery plenum. With this arrangement, a first fluid is selectively delivered to the at least one fluid delivery plenum, passed through the at least one fluid delivery opening and mixed with a second fluid flowing through the plurality of fluid delivery tubes prior to being combusted in a combustion chamber of a turbine engine.
In accordance with another exemplary embodiment of the invention, a method of forming a combustible mixture in a mixing apparatus having a main body including an inlet portion, an outlet portion and an exterior wall that collectively establish at least one fluid delivery plenum is provided. The method includes guiding a first fluid into the at least one fluid delivery plenum, and delivering a second fluid though a plurality of fluid delivery tubes that extend through the at least one fluid delivery plenum. Each of the plurality of fluid delivery tubes includes an inlet end section, an outlet end section and an intermediate section. The method further includes passing the first fluid through a fluid delivery opening formed in each of the plurality of fluid delivery tubes, mixing the first and second fluids in the plurality of fluid delivery tubes, and delivering the first and second fluids from the outlet end section of each of the plurality of fluid delivery tubes into a combustion chamber.
In accordance with still another exemplary embodiment of the invention, a turbine engine includes at least one first fluid source containing a first fluid, at least one second fluid source containing a second fluid, and an apparatus for mixing the at least one first fluid and the at least one second fluid. The apparatus includes a main body having an inlet portion, an outlet portion and an exterior wall that collectively establish at least one fluid delivery plenum, and a plurality of fluid delivery tubes that extend through the at least one fluid delivery plenum. Each of the plurality of fluid delivery tubes includes a first end section exposed at the inlet portion of the main body, a second end section exposed at the outlet portion of the main body and an intermediate section, and at least one fluid delivery opening fluidly connected to the at least one fluid delivery plenum. With this arrangement, the first fluid is selectively delivered to the at least one fluid delivery plenum, passed through the at least one fluid delivery opening and mixed with the second fluid flowing through at least a portion of the plurality of fluid delivery tubes prior to being combusted in a combustion chamber of the turbine engine.
In operation, air flows into compressor 4 and is compressed into a high pressure gas. The high pressure gas is supplied to combustor assembly 8 and mixed with fuel, for example process gas and/or synthetic gas (syngas), in nozzle 14. The fuel/air or combustible mixture is passed into combustion chamber 12 and ignited to form a high pressure, high temperature combustion gas stream. Alternatively, combustor assembly 8 can combust fuels that include, but are not limited to natural gas and/or fuel oil. In any event, combustor assembly 8 channels the combustion gas stream to turbine 30 which coverts thermal energy to mechanical, rotational energy.
Reference will now be made to
Tube 60 provides a passage for delivering the second fluid and the combustible mixture into combustion chamber 12. It should be understood that more than one passage per tube could be provided, with each tube 60 being formed at a variety of angles depending upon operating requirements for engine 2 (
In accordance with the exemplary embodiment shown, tube 60 includes a generally circular cross-section having a diameter that is sized based on enhancing performance and manufacturability. As will be discussed more fully below, the diameter of tube 60 could vary along a length of tube 60. In accordance with one example, tube 60 is formed having a diameter of approximately 2.54 mm-22.23 mm or larger. Tube 60 also includes a length that is approximately ten (10) times the diameter. Of course, the particular diameter and length relationship can vary depending on the particular application chosen for engine 2. In further accordance with the embodiment shown, intermediate section 90, shown in
In accordance with the exemplary embodiment illustrated in
More specifically, first fluid delivering opening 103 enables the introduction of the first fluid or fuel into tube 60 which already contains a stream of second fluid or air. The particular location of first fluid delivery opening 103 ensures that the first fluid mixes with the second fluid just prior to entering combustion chamber 12. In this manner, fuel and air remain substantially unmixed until entering combustion chamber 12. Second fluid delivery opening 104 enables the introduction of the first fluid into the second fluid at a point spaced from outlet end section 89. By spacing second first fluid delivery opening 104 from outlet end section 89, fuel and air are allowed to partially mix prior to being introduced into combustion chamber 12. Finally, third fluid delivery opening 105 is substantially spaced from outlet end section 89 and preferably up-stream from angled portion 93, so that the first fluid and second fluid are substantially completely pre-mixed prior to being introduced into combustion chamber 12. As the fuel and air travel along tube 60, angled portion 93 creates a swirling action that contributes to mixing. In addition to forming fluid delivery openings 103-105 at a variety of angles, protrusions could be added to each tube 60 that direct the fluid off of tube walls (not separately labeled). The protrusions can be formed at the same angle as the corresponding fluid delivery opening 103-105 or at a different angle in order to adjust an injection angle of incoming fluid.
With this overall arrangement, fuel is selectively delivered through first fluid inlet 48 and into one or more of plenums 74, 76 and 78 to mix with air at different points along tube 60 in order to adjust the fuel/air mixture and accommodate differences in ambient or operating conditions. That is, fully mixed fuel/air tends to produce lower NOx levels than partially or un-mixed fuel/air. However, under cold start and/or turn down conditions, richer mixtures are preferable. Thus, exemplary embodiments of the invention advantageously provide for greater control over combustion byproducts by selectively controlling the fuel/air mixture in order to accommodate various operating or ambient conditions of engine 2.
In addition to selectively introducing fuel, other substances or diluents can be introduced into the fuel/air mixture to adjust combustion characteristics. That is, while fuel is typically introduced into third plenum 78, diluents can be introduced into, for example, second plenum 76 and mixed with the fuel and air prior to being introduced into combustion chamber 12. Another benefit of the above-arrangement is that fuel or other substances in plenums 74, 76 and 78 will cool the fuel/air mixture passing through tube 60 quenching the flame and thus provide better flame holding capabilities. In any event, while there are obvious benefits to multiple plenums and delivery openings, it should be understood that nozzle 14 could be formed with a single fuel delivery opening fluidly connected to a single fuel plenum that is strategically positioned to facilitate efficient combustion in order to accommodate various applications for engine 2. Moreover, nozzle 14 could be provided with any other number of openings/plenums depending on various operating parameters, ambient conditions and combustion goals of engine 2.
Reference will now be made to
At this point it should be appreciated that the various exemplary embodiments of the present invention selectively enable various stages of mixing of the first and second fluids, e.g., fuel and air, to ensure that NOx levels remain within government mandated limits while simultaneously avoiding many of the drawbacks associated with other mixing devices such as auto-ignition, flashback and/or flame holding and high local flame temperatures.
In general, this written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of exemplary embodiments of the present invention if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
This invention was made with Government support under Contract No. DE-FC26-05NT4263, awarded by the US Department of Energy (DOE). The Government has certain rights in this invention.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4100733 | Striebel et al. | Jul 1978 | A |
| 4429527 | Teets | Feb 1984 | A |
| 4845952 | Beebe | Jul 1989 | A |
| 5263325 | McVey et al. | Nov 1993 | A |
| 5339635 | Iwai et al. | Aug 1994 | A |
| 5680766 | Joshi et al. | Oct 1997 | A |
| 5746048 | Shah | May 1998 | A |
| 5865030 | Matsuhama | Feb 1999 | A |
| 5930999 | Howell et al. | Aug 1999 | A |
| 6019596 | Knopfel et al. | Feb 2000 | A |
| 6438961 | Tuthill et al. | Aug 2002 | B2 |
| 6442939 | Stuttaford et al. | Sep 2002 | B1 |
| 6453673 | Bechtel et al. | Sep 2002 | B1 |
| 6672073 | Wiebe | Jan 2004 | B2 |
| 6993916 | Johnson et al. | Feb 2006 | B2 |
| 7107772 | Chen et al. | Sep 2006 | B2 |
| 7412833 | Widener | Aug 2008 | B2 |
| 7556031 | Russell | Jul 2009 | B2 |
| 7886991 | Zuo et al. | Feb 2011 | B2 |
| 20070062197 | Hannum et al. | Mar 2007 | A1 |
| 20080078160 | Kraemer et al. | Apr 2008 | A1 |
| 20090229269 | Lacy et al. | Sep 2009 | A1 |
| 20100008179 | Lacy et al. | Jan 2010 | A1 |
| 20100031662 | Zuo | Feb 2010 | A1 |
| 20100101229 | York et al. | Apr 2010 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20100008179 A1 | Jan 2010 | US |
