STEAM TURBINE VARIABLE CLEARANCE PACKING
BACKGROUND OF THE INVENTION
Formatted: Bullets and Numbering This application relates generally to steam turbines, and more specifically, to seals
between rotating and stationary components of a steam turbine.
In rotary machines such as turbines, seals are provided between rotating and
stationary components. For example, in steam turbines it is customary to provide a
plurality of arcuate packing ring segments (sometimes referred to as seal ring
segments) to form a labyrinth seal between the stationary and rotating components.
Generally, the arcuate packing ring segments are disposed in an annular groove in the
stationary component concentric to the axis of rotation of the machine and hence
concentric to the sealing surface of the rotating component. Each arcuate seal
segment carries an arcuate seal face in opposition to the sealing surface of the rotating
component. In labyrinth type seals, the seal faces carry a radially directed array of
axially spaced teeth, and which teeth are radially spaced from an array of axially
spaced annular teeth forming the sealing surface of the rotating component. The
sealing function is achieved by creating turbulent flow of a working media, for
example, steam, as it passes through the relatively tight clearances within the
labyrinth defined by the seal face teeth and the opposing surface of the rotating
component.
The ability to maintain proper clearances without physical contact between the
rotating equipment and stationary components allows for the formation of an effective
seal. If this radial clearance between the seal faces of the segments and the opposing
seal surfaces of the rotating component becomes too large, the flow area increases,
less turbulence is produced and the sealing action is compromised. Conversely, if the
clearance is too tight, the sealing teeth may contact the rotating element, with the
result that the teeth lose their sharp profile and tight clearance and thereafter create
less turbulence, and possesses an increased flow area, likewise compromising the
sealing action.
In order to avoid damage to the rotor and packing ring segment during transient
conditions such as startup and shutdown, positive pressure, variable clearance packing
rings are sometimes used. In positive pressure, variable clearance packing rings, the
packing ring segments are commonly spring biased into outer or large clearance
positions causing the seal faces carried by the packing ring to be spaced substantially
outwardly of the rotary component. After start-up, the working fluid medium, e.g.,
steam, enters the grooves of the stationary component, urging the segments to move
inwardly against the bias of the springs, toward the inner or small clearance positions.
These springs are located within the annular groove defined by the stationary
component, and are sized relative to the annular grooves in which they reside. In
large turbine units, the annular groove is typically large enough to accommodate large
springs having an elasticity capable of tolerating the pressure-force resulting from
inlet of the fluid medium. In addition, the packing ring is typically large enough to
allow springs to be affixed to the portion of the packing ring residing in the annular
groove.
However, when working with smaller turbine units used in applications such as boiler
feed pumps, reactor feed pumps, mechanical drives for compressors and pumps, and
some generator drive units, it can become difficult and impractical to install capable
springs within the narrow width/diameter annular grooves present in the smaller
turbine unit. Thus, in these instances, there is a need for a variable clearance packing
ring assembly that can be used in conjunction with annular grooves having too small a
width and diameter to accommodate conventional springs.
BRIEF SUMMARY OF THE INVENTION
Disclosed herein is a packing ring assembly including a packing ring segment, a bar, a
cover plate, and a spring. The packing ring segment has an axial slot. The bar is
disposed within the slot. The cover plate is disposed along an outer periphery of the
packing ring segment And, the spring is compressed between the bar and the cover
plate.
Further disclosed herein is a packing ring assembly having a first packing ring
segment, a second packing ring segment, and one or more seal keys. The first
packing ring segment has a spring loaded bar disposed within a first half of a
stationary component. The second packing ring segment has a spring loaded bar
disposed within the first half of the stationary component adjacent to the first packing
ring segment. And, the one or more seal keys are disposed at a midline between the
first half and the second half of the stationary component wherein each of the seal
keys supports the first or second packing ring segment.
Yet further disclosed herein is a steam turbine having a shaft, a stationary component,
and a packing ring assembly. The components are arranged such that the packing ring
assembly extends around the shaft having a spring loaded bar in contact with the
stationary component.
BRIEF DESCRIPTION OF THE DRAWINGS
Formatted: Bullets and Numbering Referring to the drawings wherein like elements are numbered alike in the several
Figures:
FIGURE 1 is a section view of a portion of a steam turbine for use in accordance with
an embodiment of the invention;
FIGURE 2 is an enlarged view of the exemplary steam turbine of Figure 1 for use in
accordance with an embodiment of the invention;
FIGURE 3 is a cross-section view of the exemplary steam turbine of Figure 2 for use
in accordance with an embodiment of the invention;
FIGURE 4 is a cross-section view of the exemplary steam turbine of Figure 2 for use
in accordance with an embodiment of the invention;
FIGURE 5 is a section view of a portion of a steam turbine for use in accordance with
an embodiment of the invention;
FIGURE 6 is an enlarged view of the exemplary steam turbine of Figure 5 for use in
accordance with an embodiment of the invention; and
FIGURE 7 is a cross-section view of the exemplary steam turbine of Figure 6 for use
in accordance with an embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Formatted: Bullets and Numbering Rererrmg to figure 1, a portion or a steam turbine 10 is illustrated having a turbine k
shaft 12 disposed in a stationary component, for example a turbine diaphragm 14
comprising first and second diaphragm halves 16 and 18, respectively. A labyrinth
seal is provided at the turbine shaft-to-diaphragm interface to prevent leakage. The
labyrinth seal includes a variable clearance packing ring assembly 20a, sometimes
referred to as a seal ring assembly, as shown in Figure 1 having four arcuate packing
ring segments, 22a, 24a, 26a, and 28a, extending around the turbine shaft 12. The
packing ring segments are movable between an outermost large clearance position
and an innermost small clearance position about the turbine shaft 12 at startup and at
speed operations, respectively.
Each of the packing ring segments includes two spring loaded bars 30 (better
illustrated in Figure 2, which is rotated from its position in Figure 1 for clarity) which
allow the packing ring segments to move in a radial direction between a large
clearance position and a small clearance position. The spring loaded bar 30 is
disposed within an axial slot 32 located along an outer perimeter of the packing ring
segment. Further disposed within the axial slot 32 is a spring 34 which contacts the
bar 30 on one end and contacts a cover plate 36 on another end. The cover plate 36,
which contains the bar 30 and spring 34 within the slot, is secured to the outer
periphery of the packing ring segments by fasteners 38.
As further illustrated in Figures 3 and 4, each packing ring segment has a sealing face
40 and radially projecting teeth 42, each sealing face 40 is formed by a pair of
segment sealing flanges 44 extending axially away from one another. The radial outer
portions of the packing ring segments include segment locating flanges 46 that
similarly extend from the packing ring segment in axially opposite directions away
from one another. An axially reduced neck 48 extends between the segment sealing
flanges 44 and the segment locating flanges 46. The packing ring segments are
disposed in a generally dovetail-shaped annular groove 50 within the diaphragm 14.
The annular groove 50 is defined along the radially innermost portions of the
diaphragm 14 by a pair of diaphragm locating flanges 52 which extend axially toward
one another defining a slot 54 therebetween. The packing ring segments are
positioned such that the axially reduced neck 48 of the packing ring segments is fitted
within the diaphragm slot 54.
The spring loaded bar 30 (illustrated by hidden/dashed lines in Figures 3 and 4)
extends radially inwardly beyond the segment locating flanges under a spring force
from the spring 34. The bar has a pair of axially extending bar locating flanges 56
which extend from the bar in axially opposite directions away from one another. The
bar 30 further includes a recessed portion 58 which provides a mating surface for one
end of the spring 34. The cover plate 36 provides a mating surface for the other end
of the spring 34. The spring 30 is a compression spring, which applies a resistive
force as it is compressed. Therefore, when the spring 34 is installed between the bar
30 and the cover plate 34, the spring 34 urges the bar 30 to translate into its innermost
radial position. When the packing ring is installed into the diaphragm, the bar
locating flanges 56 contact the diaphragm locating flanges 52 and therefore the
pressure from the spring is applied on to the cover plate 36 (which is fastened to the
packing ring segment), thus resulting in a radial outward movement of the packing
ring segment which places the packing ring segment in the outermost large clearance
position (as shown in Figure 3). When the packing ring segment is in the outermost
large clearance position, a gap 60 is present between the segment locating flanges 46
and the diaphragm locating flanges 52.
To displace the packing ring segments into their closed smaller diameter position, a
plurality of passages (not shown) are provided in the diaphragm or the packing ring
segment to introduce a flowing medium, for example, steam, along the outer diameter
62 of the packing ring segments. The flowing medium exerts a radially inward
pressure force along the outer diameter of the packing ring segment whereby the
packing ring segment may be displaced inwardly toward the turbine shaft 12 against
the bias of the springs 34 (as shown in Figure 4). When the packing ring segment is
in the innermost small clearance position, there in no gap present between the
segment locating flanges 46 and the diaphragm locating flanges 52 as they are in
direct contact with each other.
The springs 34 operate in a manner such that they have sufficient spring resistive
force to maintain the large clearance position but are compressible within a desired
range to allow the fluid pressure to overcome the spring pressure to maintain the small
clearance position.
In an alternative embodiment, the packing ring assembly may be arranged as
illustrated in Figure 5 wherein a packing ring assembly 20b, includes packing ring
segments arranged such that a first packing ring segment 22b and a second packing
ring segment 24b are disposed on a first side of a midline between the first diaphragm
half 16 and the second diaphragm half 18, while a third packing ring segment 26b and
a fourth packing ring segment 28b are disposed on a second side of the midline
between the first diaphragm half 16 and the second diaphragm half 18. Additionally, a
pair of seal keys 64 may be installed at the outermost radial positions of the packing
ring segments at the midline between the first diaphragm half 16 and the second
diaphragm half 18, as illustrated in Figures 5-7. The seal keys 64 are secured, for
example, by bolts 66, to the first diaphragm half 16 in diaphragm slot 68 and projects
radially inwardly to extend into packing ring segment slot 70 formed along an end,
adjacent to the midline between the first diaphragm half 16 and the second diaphragm
half 18, of each of the packing ring segments. In other words, each of the packing
ring segments define one half of the packing ring segment slot 70, more specifically,
the first 22b and fourth 28b packing ring segments define one segment slot 70 and the
second 24b and third 26b packing ring segments define the other diametrically
opposed segment slot 70.
The seal keys 64 support the first 22b and second 24b packing ring segments against
circumferential displacement under gravity forces. The seal keys 64 further prevent
the first 22b and second 24b packing ring segments from applying forces, resulting
from circumferential displacement, on the third 26b and fourth 28b packing ring
segments. The seal keys 64 contain the first 22b and second 24b packing ring
segments within the first diaphragm half 16 and therefore the seal keys 64 also
minimize the gap between the first 22b and second 24b packing ring segments.
Additionally the seal keys 64 allow for horizontal displacement (the horizontal
direction is defined as the horizontal plane of Figures 5 and 6 formed by the midline
between the first and second diaphragm halves and the central axis of the turbine shaft
12) of the first 22b and second 24b segments while allowing radial displacement for
the third 26b and fourth 28b segments. Radial displacement in the third 26b and
fourth 28b packing ring segments allows for greater radial clearance at the lower half
vertical centerline of the turbine shaft 12, where turbine shaft 12 bowing is the
greatest.
The seal keys 64 further comprise a threaded hole 72 for engagement of a setscrew 74
(best illustrated in Figures 6 and 7). The threaded hole 72 is oriented such that
adjustment of the setscrew 74 results in displacement of the first 22b or second 24b
packing ring segment. As the setscrew 74 is adjusted to extend beyond the seal key
64, the exposed setscrew 74 end comes into contact with the packing ring segment
and drives the packing ring segment circumferentially away from the seal key 64.
Adjustment of the first 22b and/or second 24b packing ring segment allows for proper
alignment of all packing ring segments into true center positions.
The above mentioned characteristics allow for the packing ring assemblies 20a (best
illustrated in Figure 1) and 20b (best illustrated in Figure 5) to be entirely enclosed in
their respective diaphragm halves thus preventing assembly problems. Additionally,
the spring loaded bar and its associated mating components are self contained within
the packing ring assemblies 20a and 20b. Further, the packing ring assemblies 20a
and 20b may be installed and utilized with any existing dovetail size and any existing
diaphragm assembly. Therefore, the packing ring assemblies 20a and 20b may be
installed in existing industrial steam turbines with little or no modification to
diaphragm components. Additionally, the packing ring assemblies 20a and 20b may
be retrofitted into existing steam turbines. The packing ring assemblies 20a and 20b
may be provided as a kit having the desired parts and hardware to easily remove the
existing packing ring assembly from the diaphragm and replace it with the packing
ring assembly 20a or 20b, with little or no modifications to the diaphragm, at a
maintenance interval or overhaul of the steam turbine.
While the invention has been described with reference to a preferred embodiment or
embodiments, it will be understood by those skilled in the art that various changes
may be made and equivalents may be substituted for elements thereof without
departing from the scope of the invention. In addition, many modifications may be
made to adapt a particular situation or material to the teachings of the invention
without departing from the essential scope thereof. Therefore, it is intended that the
invention not be limited to the particular embodiment disclosed as the best mode
contemplated for carrying out this invention, but that the invention will include all
embodiments falling within the scope of the claims.

CLAIMS
What is claimed is:
1. A packing ring assembly (20a or 20b) comprising:
a packing ring segment (22 through 28 a and b) having an axial slot (32);
a bar (30) disposed within the slot; (32)
a cover plate (36) disposed along an outer periphery of the packing ring segment (22
through 28 a and b); and
a spring (34) compressed between the bar (30) and the cover plate.(36)
2. The packing ring assembly (20 a or b) of claim 1 wherein the packing ring
segment (22 through 28 a and b) moves between an innermost small clearance
position and an outermost large clearance position in relation to a rotary component.
3. The packing ring assembly (22 through 28 a and b) of claim 2 wherein the
spring (34) applies a resistive force between the bar (30) and the cover plate (36)
while the packing ring segment (22 through 28 a and b) is in the outermost large
clearance position.
4. The packing ring assembly (20 a or b) of claim 3 wherein a flowing medium
exerts a force on the packing ring segment, (22 through 28 a and b) which overcomes
the spring (34) resistive force, and moves the packing ring segment (22 through 28 a
and b) to the innermost small clearance position.
5. A packing ring assembly (20 b) comprising:
a first packing ring segment (22 b) having a spring loaded bar (30) disposed within a
first half of a stationary component; (16)
a second packing ring (24 b) segment having a spring loaded bar (30) disposed within
the first half of the stationary component (16) adjacent to the first packing ring
segment; (22 b) and,
one or more seal keys (64) disposed at a midline between the first half (16) and the
second half (18) of the stationary component wherein each of the seal keys (64)
supports the first (22 b) or second (24 b)packing ring segment.
6. The packing ring assembly (20 b) of claim 5 wherein the spring loaded bar
(30) applies a force on to the stationary component resulting in movement of the
packing ring segment (22 b or 24 b) between an innermost small clearance position
and an outermost large clearance position in relation to a rotary component.
7. The packing ring assembly (20 b) of claim 6 further comprising a cover plate
(36) securing the spring loaded bar (30) within the packing ring assembly. (20 b)
8. A steam turbine (10) comprising:
a shaft; (12)
a stationary component; (14) and
a packing ring assembly (20 a or 20 b) extending around the shaft (12) having a spring
loaded bar (30) in contact with the stationary component. (14)
9. The steam turbine (10) of claim 8 wherein the packing ring assembly (20 a or
b) further comprises a plurality of packing ring segments (22 through 28 a and b) each
having one or more spring loaded bars (30).
10. The steam turbine (10) of claim 9 wherein the spring loaded bar (30) applies a
force on to die stationary component (14) resulting in movement of the packing ring
segment (22 through 28 a and b) between an innermost small clearance position and
an outermost large clearance position in relation to a rotary component (12).