Patent Application
20130081731
This application claims priority to Polish Application No. P.396520 filed on Oct. 3, 2011, the entire contents of which are incorporated herein by reference.
The subject matter disclosed herein relates to turbines and, in particular, to diffusers for use with gas turbines and steam turbines.
Gas turbines may include a diffuser cone, or diffuser, coupled to the last stage bucket of the rotor. It is desirable for the diffuser to increase static pressure of the exhaust gas by decreasing the kinetic energy of the exhaust gas by reducing the exhaust gas velocity. In some cases, this may be achieved by increasing a cross-sectional area of the flow path in the diffuser in the direction of exhaust gas flow. The boundaries of the flow path may be affected by the geometry of the diffuser. In embodiments, the diffuser geometry may form disruptive flow, such as disruptive vortices, that may adversely affect the flow path, thus reducing the cross-sectional area of the flow path. For example, a hub or center portion of the diffuser forms an inner wall or boundary of the exhaust gas flow path, wherein an end portion of the hub leads to formation of a wake or disruptive vortex in the fluid flow. The wake may interfere with flow downstream of the inner wall and decrease the cross-sectional area of the flow path, thereby reduces kinetic energy conversion to static pressure rise and causes flow with high kinetic energy to downstream components.
According to one aspect of the invention, an exhaust gas diffuser includes an outer casing disposed about a center line of the exhaust gas diffuser, a hub disposed about the center line, and an end portion of the hub comprises a recess configured to cause a flow of exhaust gas toward the center line as the exhaust gas flows in a downstream direction.
According to another aspect of the invention, an exhaust gas diffuser includes a casing, a hub disposed inside the casing, wherein an exhaust gas flow is received via an inlet formed between the casing and hub, and an end portion of the hub including a recess configured to cause formation of a vortex elongated about a center line of the exhaust gas diffuser downstream of the end portion
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.
In an aspect, the combustor 104 uses liquid and/or gas fuel, such as natural gas or a hydrogen rich synthetic gas, to run the turbine engine. For example, fuel nozzles 110 are in fluid communication with a fuel supply 112 and pressurized air from the compressor 102. The fuel nozzles 110 create an air-fuel mix, and discharge the air-fuel mix into the combustor 104, thereby causing a combustion that creates a hot pressurized exhaust gas. The combustor 104 directs the hot pressurized exhaust gas through a transition piece into a turbine nozzle (or “stage one nozzle”), causing turbine 106 rotation as the gas exits the nozzle or vane and gets directed to the turbine bucket or blade. After the gas flow from the last stage of the turbine 106, exhaust gas flow is received by a diffuser (not shown) configured to increase static pressure of the flow across the diffuser.
In an embodiment, the exhaust gas flows into the diffuser, wherein a cross-sectional area of the exhaust gas flow substantially increases as the gas flows in a downstream direction. Accordingly, a velocity of the gas flow is reduced due to the increasing volume of the flow area, while a static pressure of the gas flow is increased. As discussed in detail below, a hub portion of the diffuser includes a recess configured to cause entrainment or drawing in of the exhaust gas flow path towards a center line of the diffuser to improve distribution of the exhaust gas flow proximate the diffuser outlet. Improved distribution of the exhaust gas flow proximate the diffuser outlet causes substantially uniform velocity and pressure profiles proximate the outlet, thereby improving diffuser performance and robustness.
As used herein, “downstream” and “upstream” are terms that indicate a direction relative to the flow of working fluid through the gas turbine system 100. As such, the term “downstream” refers to a direction that generally corresponds to the direction of the flow of working fluid, and the term “upstream” generally refers to the direction that is opposite of the direction of flow of working fluid. The term “radial” refers to movement or position perpendicular to an axis or center line (205,
Referring now to
As depicted, a reduced velocity and reduced static pressure loss may be accomplished by the substantially flared (radially outward) or angled casing 202 (also referred to as an outer wall) and angled hub 204 (also referred to as an inner wall), which creates an expanding flow area or flow path in the downstream direction. The angled casing 202 has a reduced radius as it extends in a downstream direction. An effective flow path, as discussed herein, is the exhaust gas flow path along the cavity within the diffuser 200 wherein the flow is substantially uniform in velocity and pressure across a cross-section of the path. For example, an effective flow path may be bounded by walls defining the cavity, wherein the flow path includes a laminar flow that occurs proximate the walls. The cross sectional area of the effective flow path may be reduced in portions of the cavity where disruptive flow, such as disruptive vortices, are formed. The exemplary effective flow path shown is defined or bounded by an inner flow 230 along hub 204 and outer flow 232 along casing 202, wherein a distance 234 defines the radial distance of the effective flow path.
As shown, a cross-sectional area of effective flow path increases in a downstream direction, wherein the radial distance 234 increases to radial distance 240 proximate the outlet 208. In an aspect, an end portion 214 of the hub 204 is configured to cause a flow of exhaust gas toward the center line 205, thereby reducing the formation and/or size of vortex 226 which reduces the effective flow path or area available for flow diffusion as the exhaust gas flows in a downstream direction 207. In the downstream portion of diffuser, the effective flow path for the exhaust gas is defined by an inner flow 236 and outer flow 232. In an embodiment, the inner flow 236 is defined by and flows along an outer portion of the vortex 226 while the outer flow 232 is defined by and flows along the casing 202. In an embodiment, a recess 216 in the end portion 214 of the hub 204 causes the inner flow 236 of the exhaust gas to flow towards the center line 205. The recess 216 causes formation of a vortex 226 of substantially swirling or circular flow, which may be described as elongated along the center line 205. The recess 216 reduces formation of a wake near the diffuser dump region 210 to reduce flow disruption. In other embodiments that have a flat surface instead of the recess 216 formed in the hub 204, a wake is formed proximate the dump region, which disrupts inner flow 236 and reduces effective flow area for the gas. The resulting reduced effective flow area causes increased fluid flow velocity, which is not desirable for operation of the heat recovery steam generator. In an embodiment, the vortex 226 is elongated, thus having an axial dimension greater than a radial dimension. The exemplary vortex 226 reduces wake or disruptive vortex formation and interference with the exhaust gas effective flow path to improve diffuser 200 performance by providing a substantially uniform fluid flow proximate the outlet.
In embodiments, the diffuser dump region 210 has increasing volume downstream of the hub 204. The diffuser dump region 210 may have a substantially high diffusion gradient, which, in operation, leads to the formation of a disruptive vortex or vortices (not shown) that interfere with and reduce an effective flow path for the exhaust gas. The resulting reduced effective flow path reduces the efficiency of the diffuser 200. As depicted, an end portion 214 of the hub 204 and recess 216 are configured to form the vortex 226 to reduce formation of disruptive vortices, thereby increasing a cross-sectional area of the effective flow path proximate the diffuser dump 210 region. It should be understood that development of disruptive vortices may interfere with the substantially uniform flow of exhaust gas and thereby will reduce the size of the effective flow path. The exemplary recess 216 includes a wall or surface 218 that is substantially perpendicular to the center line 205 and a wall or surface 220 that is angled with respect to the surface 218. In an aspect, the surface 218 may be substantially parallel to the centerline 205. In embodiments, the recess 216 may be any suitable cavity formed in the end portion 214 to cause formation of a vortex to reduce interference with the effective flow path of the exhaust gas. Exemplary recesses may include curved and/or angled surfaces forming a cavity in the upstream direction within the end portion 214.
In an aspect, the vortex 307 may be described as substantially elongated along the center line 308 and creating a tortuous path for a radial flow component of the vortex 307 into the effective flow path, thus enabling an increased cross-sectional area of the effective flow path in a downstream direction. In an aspect, the vortex 307 may further be described as a “vortex trap” encouraging substantially axial (along center line 308) flow and discouraging radial flow of the exhaust gas. Accordingly, the arrangement for the diffuser 300 and the recess 304 in the end portion 306 improves diffuser performance by reducing flow velocity and increasing static pressure across the effective flow path as the exhaust gas flows through the outlet 320. In an aspect, due to the formation of the vortex 307, the flow velocity and pressure are substantially uniform across the cross-section of the effective flow path proximate the outlet 320. Improved distribution of the exhaust gas flow proximate the diffuser outlet causes substantially uniform velocity and pressure profiles proximate the outlet, thereby improving diffuser performance and robustness.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| P.396520 | Oct 2011 | PL | national |
