Patent Application
20110289933
The invention relates to a dual-fuel nozzle in a gas turbine combustor and, more particularly, to a hybrid prefilming airblast, prevaporizing, lean-premixing dual-fuel nozzle for a gas turbine combustor that allows liquid fuels to be injected from a removable breech-loaded centerbody stick and then atomized, dispersed, and vaporized.
When fuel is injected in air for combustion in a combustion chamber of the gas turbine, high temperature regions are formed locally in the combustion gas, which increase NOx emissions. Previous designs have used multi-point atomizer injection inside the premixer, but these designs have suffered from high emissions due to maldistribution of the fuel and from poor reliability due to internal (in the fuel passages) and external (on the premixer walls) fuel coking.
In an exemplary embodiment, a dual fuel nozzle for a gas turbine combustor includes an annular air passage and a swirler disposed in the annular air passage. The swirler imparts swirl to air flowing in the annular air passage. A splitter ring is disposed in the annular air passage. A hub defines a liquid fuel inlet. A plurality of liquid fuel jets surround a downstream end of the hub and are in fluid communication with the liquid fuel inlet. Each of the plurality of liquid fuel jets is positioned to radially eject liquid fuel into the annular air passage into contact with the splitter ring.
In another exemplary embodiment, a dual fuel nozzle for a gas turbine combustor includes a hub defining a fuel inlet, a plurality of liquid fuel jets disposed at a downstream end of the hub and oriented to eject liquid fuel radially outward from the hub, an annular air passage including a swirler that imparts swirl to air flowing in the annular air passage, and a splitter ring disposed in the annular air passage and surrounding the plurality of liquid fuel jets.
In yet another exemplary embodiment, a method of mixing liquid fuel and air in a dual fuel nozzle for a gas turbine combustor includes the steps of flowing air through the annular air passage and imparting swirl to the flowing air by the swirler; inputting liquid fuel through the fuel inlet; and ejecting liquid fuel radially from the liquid fuel jets into contact with the splitter ring, wherein liquid fuel impinging on the splitter ring forms a fuel film on the splitter ring that mixes with the swirling air flowing in the annular air passage.
These and other aspects and advantages will be described in detail with reference to the accompanying drawings, in which:
Air enters the burner from a high pressure plenum 6, which surrounds the entire assembly except the discharge end, which enters the combustor reaction zone 5. Most of the air for combustion enters the premixer via the inlet flow conditioner (IFC) 1. The IFC includes an annular flow passage 15 that is bounded by a solid cylindrical inner wall 13 at the inside diameter, a perforated cylindrical outer wall 12 at the outside diameter, and a perforated end cap 11 at the upstream end. In the center of the flow passage 15 is one or more annular turning vanes 14. Premixer air enters the IFC 1 via the perforations in the end cap and cylindrical outer wall.
The function of the IFC 1 is to prepare the air flow velocity distribution for entry into the premixer. The principle of the IFC 1 is based on the concept of backpressuring the premix air before it enters the premixer. This allows for better angular distribution of premix air flow. The perforated walls 11, 12 perform the function of backpressuring the system and evenly distributing the flow circumferentially around the IFC annulus 15, whereas the turning vane(s) 14 work in conjunction with the perforated walls to produce proper radial distribution of incoming air in the IFC annulus 15. Depending on the desired flow distribution within the premixer as well as flow splits among individual premixers for a multiple burner combustor, appropriate hole patterns for the perforated walls are selected in conjunction with axial position of the turning vane(s) 14. A computer fluid dynamic code is used to calculate flow distribution to determine an appropriate hole pattern for the perforated walls.
To eliminate low velocity regions near the shroud wall at the inlet to the swozzle 2, a bell-mouth shaped transition 26 may be used between the IFC and the swozzle.
After combustion air exits the IFC 1, it enters the swozzle assembly 2. The swozzle assembly includes a hub and a shroud connected by a series of air foil shaped turning vanes, which impart swirl to the combustion air passing through the premixer. Each turning vane contains a primary natural gas fuel supply passage and a secondary natural gas fuel supply passage through the core of the air foil. These fuel passages distribute natural gas fuel to primary gas fuel injection holes and secondary gas fuel injection holes, which penetrate the wall of the air foil. The fuel injection holes may be located on the pressure side, the suction side, or both sides of the turning vanes. Natural gas fuel enters the swozzle assembly 2 through inlet ports 29 and annular passages 27, 28, which feed the primary and secondary turning vane passages, respectively. The natural gas fuel begins mixing with combustion air in the swozzle assembly, and fuel/air mixing is completed in the annular passage 3, which is formed by a swozzle hub extension 31 and a swozzle shroud extension 32. After exiting the annular passage 3, the fuel/air mixture enters the combustor reaction zone 5 where combustion takes place.
An atomizer 45 is preferably associated with each of the plurality of liquid fuel jets 44. The atomizer 45 mixes air with the liquid fuel injected from the fuel jets 44. The atomizer defines a cooled atomizing assist air passage that encapsulates and insulates the liquid fuel passages, keeping the fuel-oil wetted wall temperature below the coking temperature (approximately 290° F.). The atomizer 45 includes an airblast slot 46 disposed in alignment with each of the plurality of fuel jets 44. The airblast slots 46 define insulators for the liquid fuel.
It is preferable that the liquid fuel injection parts including the hub 42 are breech-loaded through the combustor end cover, so they can be removed/replaced without disassembling the combustor.
In use, the airblasted liquid fuel jets are injected radially outward from the liquid fuel jets 44 into the axi-symmetric, annular swirling cross flow in the annular air passage 3. The liquid fuel impinges on the splitter ring 40 where it films and is prefilm airblasted off of the splitter ring 40 trailing edge 41, which is preferably tapered as shown. The splitter ring 40 creates a shear layer between two concentric annular streams of swirling air flow. The splitter ring 40 in fact enhances shear, and therefore mixing, by allowing two air streams with different swirl angles to rejoin at the trailing edge of the splitter 40, therefore enhancing shear in the flow to promote mixing. The airblasted film is more evenly azimuthally distributed and has finer droplets than the starting finite number of radial two-phase jets.
Using the prefilming splitter ring 40 prevents overpenetration and fuel impingement on the outer burner tube, allowing the well distributed droplets to rapidly vaporize and premix with the air prior to combustion. The design reduces overall fuel spray drop diameter by re-atomizing larger droplets and improves circumferential (azimuthal) distribution by filming the finite number of impinging jets prior to the prefilm airblasting. The design insulates the liquid fuel passages with sub-300° F. atomizing assist air, thereby preventing internal coking.
With the dual fuel capacity design, the structure allows the nozzle to run on either gas or liquid fuels, both in a lean premixed manner, using the same combustor.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
