U.S. patent application number 13/811943 was filed with the patent office on 2013-05-16 for exhaust diffuser for a gas turbine, and method thereof.
The applicant listed for this patent is Alexander R. Beeck, Bonnie D. Marini. Invention is credited to Alexander R. Beeck, Bonnie D. Marini.
Application Number | 20130121806 13/811943 |
Document ID | / |
Family ID | 43242599 |
Filed Date | 2013-05-16 |
United States Patent
Application |
20130121806 |
Kind Code |
A1 |
Beeck; Alexander R. ; et
al. |
May 16, 2013 |
EXHAUST DIFFUSER FOR A GAS TURBINE, AND METHOD THEREOF
Abstract
An exhaust diffuser assembly is provided, particularly for a
stationary gas turbine. The exhaust diffuser assembly includes a
longitudinal axis, a diffuser inlet for receiving a turbine
mainflow gas, a diffuser outlet, and a diverging diffuser wall
having an adjustable geometry and forming a conduit for flow of the
gas therethrough from the diffuser inlet to the diffuser outlet.
The diffuser wall has a divergence angle `.alpha.` with respect to
the longitudinal axis. The diffuser assembly also has a diffuser
geometry control device for controlling a recovery of pressure from
the gas between the diffuser inlet and the diffuser outlet by
adjusting the divergence angle `.alpha.` of the diffuser wall to
cause a resultant flow field of the gas that is attached to the
diffuser wall.
Inventors: |
Beeck; Alexander R.;
(Orlando, FL) ; Marini; Bonnie D.; (Oviedo,
FL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Beeck; Alexander R.
Marini; Bonnie D. |
Orlando
Oviedo |
FL
FL |
US
US |
|
|
Family ID: |
43242599 |
Appl. No.: |
13/811943 |
Filed: |
July 18, 2011 |
PCT Filed: |
July 18, 2011 |
PCT NO: |
PCT/EP2011/062246 |
371 Date: |
January 24, 2013 |
Current U.S.
Class: |
415/1 ;
415/207 |
Current CPC
Class: |
F01D 25/30 20130101;
F05D 2270/301 20130101; F05D 2270/17 20130101; F05D 2220/32
20130101; F05D 2250/232 20130101 |
Class at
Publication: |
415/1 ;
415/207 |
International
Class: |
F01D 25/30 20060101
F01D025/30 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 26, 2010 |
EP |
10007757.7 |
Claims
1-15. (canceled)
16. An exhaust diffuser assembly for a stationary gas turbine,
comprising: a longitudinal axis, a diffuser inlet for receiving a
turbine mainflow gas, a diffuser outlet, a diverging diffuser wall
having an adjustable geometry and forming a conduit for flow of the
gas therethrough from the diffuser inlet to the diffuser outlet,
the diffuser wall having a divergence angle `.alpha.` with respect
to the longitudinal axis, and a diffuser geometry control device
for controlling a recovery of pressure from the gas between the
diffuser inlet and the diffuser outlet by adjusting the divergence
angle `.alpha.` of the diffuser wall to cause a resultant flow
field of the gas that is attached to the diffuser wall.
17. The diffuser assembly according to claim 16, wherein the
diffuser geometry control device comprises one or more actuators
disposed on a surface the diffuser wall, the one or more actuators
being adapted to exert an adjustable pressure the diffuser wall to
resultantly adjust the divergence angle `.alpha.` of the diffuser
wall.
18. The diffuser assembly according to claim 17, wherein the one or
more actuators adapted for increasing the divergence angle
`.alpha.` to cause a resultant flow field beyond a point of flow
separation of the gas from the diffuser wall and subsequently
reducing the divergence angle `.alpha.` to re-attach the flow of
the gas to the diffuser wall, so as to cause a resultant flow of
the gas through the diffuser wall that is substantially proximate
and prior to the point of flow separation.
19. The diffuser assembly according to claim 18, further comprising
a pressure probe disposed in a flow path of the gas inside the
diffuser wall, wherein the point of flow separation is detected
based on a decrease in sensed pressure between two progressively
increasing settings of the divergence angle `.alpha.`.
20. The diffuser assembly according to claim 18, further comprising
a sonic probe disposed in a flow path of the gas inside the
diffuser wall to detect the point of flow separation.
21. The diffuser assembly according to claim 18, wherein the point
of flow separation is determined by a flow visualization device
adapted for detecting local direction of flow.
22. The diffuser assembly according to claim 16, wherein the
diffuser wall is made of a piece of sheet metal wound to spiral
form.
23. The diffuser assembly according to claim 16, wherein the
diffuser wall is made from a piece of sheet metal wound into a
conical shape, wherein the edges of the piece of sheet metal are
slidable against each other.
24. The diffuser assembly according to claim 16, wherein the
diffuser wall comprises an adjustable portion having a rectangular
cross-section, wherein the diffuser wall at the adjustable portion
is flexibly attached to a fixed portion by a hinge.
25. The diffuser assembly according to claim 16, wherein the
diffuser wall has a rectangular cross-sectional geometry formed by
angular plates forming corners of the rectangle, the angular plates
being interspaced by and flat plates over which the angular plates
are slidable such that the rectangular cross-sectional shape is
adjustable along diagonal directions.
26. A method for operating an exhaust diffuser for a stationary gas
turbine, comprising: receiving a turbine mainflow gas at a diffuser
inlet, passing the gas through a diverging diffuser wall having an
adjustable geometry defining a conduit for flow the gas between the
diffuser inlet and a diffuser outlet, the diffuser wall having a
divergence angle `.alpha.` with respect to a diffuser longitudinal
axis, and controlling a recovery of pressure from the gas between
the diffuser inlet and the diffuser outlet by controlling a
geometry of the diffuser wall, the controlling of the geometry
comprising adjusting the divergence angle `.alpha.` of the diffuser
wall to cause a resultant flow field of the gas that is attached to
the diffuser wall.
27. The method according to claim 26, wherein controlling the
geometry of the diffuser wall comprises disposing one or more
actuators on a surface of the diffuser wall and controlling the one
or more actuators to exert an adjustable pressure on the diffuser
wall to resultantly adjust the divergence angle `.alpha.` of the
diffuser wall.
28. The method according to claim 27, comprising controlling the
one or more actuators to increase the divergence angle `.alpha.` to
cause a resultant flow field beyond a point of flow separation of
the gas from the diffuser wall and subsequently reducing the
divergence angle `.alpha.` to re-attach the flow of the gas to the
diffuser wall, so as to cause a resultant flow of the gas through
the diffuser wall that is substantially proximate and prior to the
point of flow separation.
29. The method according to claim 28, further comprising disposing
a pressure probe in a flow path of the gas inside the diffuser
wall, and detecting the point of flow separation based on a
decrease in sensed pressure between two progressively increasing
settings of the divergence angle `.alpha.`.
30. The method according to claim 28, further comprising detecting
the point of flow separation by a sonic probe disposed in a flow
path of the gas inside the diffuser wall.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the US National Stage of International
Application No. PCT/EP2011/062246, filed Jul. 18, 2011 and claims
the benefit thereof. The International Application claims the
benefits of European application No. 10007757.7 EP filed Jul. 26,
2010. All of the applications are incorporated by reference herein
in their entirety.
FIELD OF INVENTION
[0002] The present invention relates to exhaust diffusers for gas
turbines, particularly for gas turbines in stationary or land based
applications.
BACKGROUND OF INVENTION
[0003] In gas turbines, for example those used in power generation,
exhaust diffusers serve to reduce the speed of the exhaust flow in
a gas turbine and to thus recover pressure from the exhaust gas
coming from the last stage of the turbine. The reduction in gas
speed reduces the stress associated with the fluid flow on the
exhaust equipment and enhances the performance levels of the
turbine by recovering pressure from the exhaust gas, thus limiting
head loss of the flow.
[0004] In an exhaust diffuser, the pressure recovery from the
exhaust gas is directly proportional to the outlet to inlet area
ratio of the diffuser, which controls amount of effective flow
diffusion following the last turbine stage. However, a high outlet
to inlet area ratio for a given axial length of the diffuser (i.e.,
large diffuser angle) causes rapid expansion of the gas leading to
a separation of flow of the gas from the diffuser wall, which, in
turn, causes a reduction in the pressure recovery by the diffuser.
Past attempts to solve the issue of flow separation from the
diffuser wall involve the use of boundary layer control, for
example, by suction or blowing, turbulators, among others.
[0005] In practice, exhaust diffusers are designed to have area
ratios that provide a maximum pressure recovery at full load,
taking into account the flow separation at full load. In such a
case, the pressure recovery, and hence the work extracted by the
turbine, is substantially reduced when the gas turbine operates at
part-load.
SUMMARY OF INVENTION
[0006] The object of the present invention is to provide an exhaust
diffuser assembly for a stationary gas turbine, and a method
thereof, for achieving higher pressure recovery at different
operating loads by reducing or eliminating excessive flow
separation.
[0007] The above object is achieved by the features of the
independent claim(s).
[0008] The underlying idea of the present invention is to provide a
mechanism of controlling pressure recovery in an exhaust diffuser
by controlling the geometry of the diffuser. To that end, the
proposed exhaust diffuser assembly has a variable geometry diffuser
wall, which allows the divergence angle of the diffuser wall with
respect to the longitudinal diffuser axis to be adjusted, so as to
cause a resultant flow field of the gas that is attached to the
diffuser wall. The variability of diffuser wall geometry allows
adaptability of the proposed diffuser assembly for adjustments in
mass flows, i.e., operating loads.
[0009] In one embodiment, said diffuser geometry control means
comprises one or more actuators disposed on a surface said diffuser
wall, said one or more actuators being adapted to exert an
adjustable pressure said diffuser wall to resultantly adjust said
divergence angle `.alpha.` of said diffuser wall.
[0010] In a preferred embodiment, wherein said one or more
actuators are controllable for increasing said divergence angle
`.alpha.` to cause a resultant flow field beyond a point of flow
separation of said gas from said diffuser wall and subsequently
reducing said divergence angle `.alpha.` to re-attach the flow of
said gas to said diffuser wall, so as to cause a resultant flow of
said gas through said diffuser wall that is substantially proximate
and prior to said point of flow separation. Since pressure recovery
increases with increase in the rate of expansion (i.e., divergence
angle) for attached flow, maintaining the flow field just before
separation point for any given mass-flow rate would maximize the
pressure recovery at that mass-flow rate
[0011] In one embodiment, the proposed diffuser assembly further
comprises a pressure probe disposed in a flow path of said gas
through flowing said diffuser wall, wherein said point of flow
separation is detected based on a decrease in sensed pressure
between two progressively increasing settings of the divergence
angle `.alpha.`. The above embodiment provides a simple means to
detect flow separation, since pressure in the gas flow path
decreases sharply after flow separation occurs
[0012] In an alternate embodiment, the proposed diffuser assembly
further comprises a sonic probe disposed in a flow path of said gas
inside said diffuser wall to detect said point of flow
separation.
[0013] In a still further embodiment, said point of flow separation
is determined by flow visualization means adapted for detecting
local direction of flow.
[0014] In an exemplary embodiment, said diffuser wall is made of a
piece of sheet metal wound to spiral form. Such a diffuser wall
provides increased elasticity for adjustment of divergence
angle.
[0015] In another exemplary embodiment, said diffuser wall is made
from a piece of sheet metal wound into a conical shape, wherein the
edges of said piece of sheet metal are slidable against each other.
The above embodiment provides manufacturing simplicity.
[0016] In yet another exemplary embodiment, said diffuser wall
comprises an adjustable portion having a rectangular cross-section,
wherein the diffuser wall at said adjustable portion is flexible
attached to a fixed portion by a hinge. The above embodiment
provides higher accuracy and increased geometric control.
[0017] In still another embodiment, said diffuser wall has a
rectangular cross-sectional geometry formed by angular plates
forming corners of the rectangle, said angular plates being
interspaced by and flat plates over which said angular plates are
slidable such that said rectangular cross-sectional shape is
adjustable along diagonal directions. This allows the rectangular
geometry of the diffuser wall to be uniformly varied (maintaining
the same aspect ratio) along the direction of the diagonals of the
rectangle by placing actuators at the corner of the rectangle.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The present invention is further described hereinafter with
reference to illustrated embodiments shown in the accompanying
drawings, in which:
[0019] FIG. 1 a schematic illustration of an exhaust diffuser
assembly for a gas turbine,
[0020] FIG. 2 is an exemplary graphical representation showing
variation of pressure of the gas with diffuser geometry, also
indicating the point of flow separation,
[0021] FIG. 3 is a schematic illustration of a first embodiment of
an adjustable geometry diffuser wall,
[0022] FIG. 4 is a schematic illustration of a second embodiment of
an adjustable geometry diffuser wall,
[0023] FIG. 5 is a schematic illustration of a third embodiment of
an adjustable geometry diffuser wall,
[0024] FIG. 6 is a schematic illustration of a fourth embodiment of
an adjustable geometry diffuser wall, and
[0025] FIG. 7 is a schematic illustration of a fifth embodiment of
an adjustable geometry diffuser wall.
DETAILED DESCRIPTION OF INVENTION
[0026] Referring now to FIG. 1 is illustrated an exhaust diffuser
assembly 1 (also referred to as "diffuser 1") for a stationary gas
turbine, for example, used in power generation and mechanical
drives in land based applications. The diffuser 1 has an inlet 3
having a first cross-sectional area A.sub.1 for receiving a
mainflow gas from a last stage of a turbine section 60. The gas 5
flows along a longitudinal axis 2 through a conduit defined by a
diverging diffuser wall 7 extending from the diffuser inlet 3 to a
diffuser outlet 4 having a second cross-sectional area A.sub.2. The
diffuser outlet 4 directs the gas 5 to an exhaust duct 80.
[0027] The diffuser wall 7 serves to recover pressure from the gas
by expanding the gas between the inlet 3 and the outlet 4. This
reduces the total head loss of the gas, thereby increasing the work
extracted from the gas 5. The diffuser wall 7 makes an angle of
divergence `.alpha.` with respect to the longitudinal axis 2. In
conventional diffusers, the divergence angle is normally fixed at
about 5-6.degree. . In accordance with the proposed technique, the
pressure recovery from the gas 5 is controlled by controlling the
geometry of the diffuser wall 7, i.e., by adjusting the divergence
angle `.alpha.`, and resultantly, the ratio `R` of the outlet area
A.sub.2 to the inlet area A.sub.1 (where R=A.sub.2/A.sub.1). It is
to be understood that for fixed length diffusers, the area ratio
`R` increases with increase in divergence angle `.alpha.`. In
general, the pressure recovery increases with increase in
divergence angle `.alpha.` or area ratio R, till the flow of the
gas 5 is separated from the diffuser wall 7. Separation of flow
reduces the pressure recovery from the gas 5. To achieve higher
pressure recovery, the divergence angle `.alpha.` is adjusted to
cause a resultant flow of the gas 5 that is attached to the
diffuser wall 7. To that end, the diffuser wall 7 has an adjustable
geometry wherein the angle `.alpha.` may be varied. Exemplary
embodiments of an adjustable geometry diffuser wall are discussed
below referring to FIGS. 3-7. Referring back to FIG. 1, to
accommodate the resulting variation of cross-sectional area A.sub.2
of the outlet 5, variable seals 12 are provided at the connection
of the diffuser wall 7 to the exhaust duct 80. In the illustrated
embodiment, one or more actuators 9 are disposed on a surface
(inner or outer) of the diffuser wall 7. In the illustrated
embodiment, the actuators 9 are disposed on the outer surface of
the diffuser wall 7. The actuators 9 may comprise, for example,
hydraulically or pneumatically operated actuators that are
controlled by a controller 10 to exert an adjustable pressure on
the diffuser wall 7 to resultantly adjust the divergence angle
`.alpha.` of the diffuser wall 7.
[0028] As mentioned above, for attached flow, the pressure recovery
increases with increase in divergence angle `.alpha.` or area ratio
`R` In a preferred embodiment, the pressure recovery is maximized
by maintaining a flow field of the gas 5 within the diffuser wall 7
that is just before the point of flow separation. For this, the
actuators 9 are controlled to first increase the divergence angle
`.alpha.` or area ratio `R` to cause a resultant flow field beyond
a point of flow separation. Subsequently, the actuators 9 are
controlled to reduce the divergence angle `.alpha.` or area ratio
`R` to re-attach the flow to the diffuser wall 7 and to cause a
resultant flow field that is prior to and proximate to the point of
flow separation.
[0029] The point of flow separation is detected by a flow sensor 11
disposed in the flow path of the gas 5 inside the diffuser wall 7.
The flow sensor 7 may include, for example, a pressure probe. For
attached flow, with increase in the divergence angle `.alpha.`, the
sensed pressure values by the pressure probe 11 increases. This is
illustrated by a curve 13 in FIG. 2, wherein the axis 14 represents
angle of divergence `.alpha.` and the axis 15 represents the
corresponding sensed pressure `P` by the pressure probe 11 disposed
in the flow path of the gas 5. As can be seen, with increase in
`.alpha.`, the sensed pressure increases till a point 16 is reached
where the sensed pressure attains a maximum value, for
.alpha.=.alpha..sub.S. When `.alpha.` is increased beyond this
threshold angle .alpha..sub.S, the flow begins to separate from the
diffuser wall, as a result of which, the sensed pressure decreases,
which is detected by a change in slope of the curve 13 from
positive negative. The point 16 of flow separation is thus detected
based on a decrease in sensed pressure `P` between two
progressively increasing settings of the divergence angle
`.alpha.`. The proposed technique in this embodiment involves
increasing `.alpha.` to cause a flow field beyond the point 16 of
flow separation, to identify the threshold angle .alpha..sub.S, and
to then reduce `.alpha.` to a value .alpha..sub.D less than
.alpha..sub.S so as to re-attach the flow to the diffuser wall and
to cause the resultant flow field to reach a point 17 that is just
before the point 16 of flow separation. Typically, a portion of the
curve 13 in the region of the separation point 16 is flat having a
slope equal or nearly equal to zero. The flow field corresponding
to this portion is preferably avoided as this indicates is an
unstable flow field where separated and attached flow alternate.
The desired point 17 that is "substantially proximate and prior to"
the point 16 of flow separation is determined, in this case, as the
closest point to the point 16 on the curve 13 that has a positive
slope.
[0030] Referring back to FIG. 1, in an alternate embodiment, the
flow sensor 11 to detect the point of flow separation may comprise
a sonic probe. Still alternately, the point of flow separation may
be detected using flow visualization or imaging techniques which
detect the local direction of flow. In all cases, the adjustable
geometry which enables the forcing of the flow beyond the point of
flow separation point allows the identification of the point of
flow separation. Once the point of flow separation is identified,
the geometry of the diffuser may be adjusted to re-attach the flow
to the diffuser wall. The adjustable geometry proposed herein
allows for adaptability of the technique discussed above to changes
in mass-flow, such that the pressure recovery may be maximized even
when the gas turbine is operating at part load.
[0031] Referring to FIG. 3 is illustrated a first embodiment of an
adjustable geometry diffuser wall 7. Herein, the diffuser wall 7 is
made of a sheet 18 of metal wound in several turns in a spiral form
to form conical shape. The spiral form provides the required
elasticity for geometric adjustments. Actuators 9 may be disposed
on the outer surface of one or more of these turns to, which, when
actuated, apply the required pressure to increase or decrease the
divergence angle of the diffuser wall 7. In a second embodiment
illustrated in FIG. 4, the diffuser wall 7 may be made from a sheet
20 of metal wound in a conical shape, such that the ends 21 and 22
are not welded to each other, but slide against each other on the
application of pressure by one or more actuators 9 disposed on the
outer surface of the diffuser wall 7, such that divergence angle or
area ratio may be varied.
[0032] In a third embodiment illustrated in FIG. 5, the diffuser
wall 7 is made of sheet metal and includes an adjustable portion 23
having a rectangular cross-section and a fixed portion 24, which
may have a circular cross-section at the inlet 3. The rectangular
portion 23 is made of flat plates 25, 26, 27, 28, one or more of
which are flexibly connected to the fixed portion 24 by means of
hinges 29, that allow the respective side 25, 26, 27, 28 to swivel
with respect to the fixed portion 24 on application of pressure
from the actuator 9 disposed thereon, to thus adjust the divergence
angle/area ratio. In the shown example, the plates 25 and 27 are
hinged such that the direction of angular movement is as
illustrated by the arrows 30. Although the sides 26 and 28 are
subject to bending during movement of the sides 25 and 27, this
embodiment provides greater accuracy and control of angular
movements. In a similar embodiment depicted in FIG. 6, the diffuser
wall 7 has a rectangular cross-section formed by flat plates 31,
32, 33, 34 that are directly connected to a circular turbine
manifold 35 by flexible joints 36 so as to allow angular movements
of opposite plates 31 and 33 as depicted by the arrow 37. In yet
another embodiment of a rectangular diffuser wall illustrated in
FIG. 7, the diffuser wall 7 is made of angular plates 38, 39, 40,
41 that define the corners of a rectangle (herein, square). The
angular plates 38, 39, 40, 41 are interspaced by flat plates 42,
43, 44, 45, which, together with the angular plates 38, 39, 40, 41
form the sides of the rectangular diffuser wall 7. As illustrated,
the angular plates are slidable against the flat plates 42, 43, 44,
45 such that the rectangular cross-sectional geometry of the
diffuser wall 7 may be adjusted along diagonal directions 46 and 47
by actuators (not shown) disposed on the corners 48, 49, 50, 51 of
the rectangular diffuser wall 7.
[0033] While this invention has been described in detail with
reference to certain preferred embodiments, it should be
appreciated that the present invention is not limited to those
precise embodiments. Rather, in view of the present disclosure
which describes the current best mode for practicing the invention,
many modifications and variations would present themselves, to
those of skill in the art without departing from the scope and
spirit of this invention. The scope of the invention is, therefore,
indicated by the following claims rather than by the foregoing
description. All changes, modifications, and variations coming
within the meaning and range of equivalency of the claims are to be
considered within their scope.
* * * * *