U.S. patent application number 13/147601 was filed with the patent office on 2011-11-24 for turbomachine having a compensating piston.
Invention is credited to Patrick Van Der Span.
Application Number | 20110286835 13/147601 |
Document ID | / |
Family ID | 42542444 |
Filed Date | 2011-11-24 |
United States Patent
Application |
20110286835 |
Kind Code |
A1 |
Van Der Span; Patrick |
November 24, 2011 |
TURBOMACHINE HAVING A COMPENSATING PISTON
Abstract
A turbomachine including a compensating piston that is sealed by
means of a seal with respect to a stator is provided. Conventional
compensating pistons consume significant amounts of process fluid,
which can cause a considerable loss of efficiency. The turbomachine
provides the solution in that the stator partially carrying the
seal is designed to be axially moveable in the housing such that
the permeability of the seal can be changed in this way.
Inventors: |
Van Der Span; Patrick;
(Hengelo, NL) |
Family ID: |
42542444 |
Appl. No.: |
13/147601 |
Filed: |
January 20, 2010 |
PCT Filed: |
January 20, 2010 |
PCT NO: |
PCT/EP10/50643 |
371 Date: |
August 3, 2011 |
Current U.S.
Class: |
415/133 |
Current CPC
Class: |
F04D 29/0516 20130101;
F01D 3/04 20130101; F04D 29/0416 20130101 |
Class at
Publication: |
415/133 |
International
Class: |
F01D 11/20 20060101
F01D011/20 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 5, 2009 |
DE |
10 2009 007 713.8 |
Claims
1.-6. (canceled)
7. A turbomachine, comprising: a balance piston, wherein the
balance piston includes a shaft step on a rotor, which extends
along a machine axis, and a seal seals a gap between the rotor and
a stator so that a cavity, which is adjacent to a first side of the
seal and is filled with process fluid during operation may have a
pressure which by a differential pressure across the seal, differs
from that on the other side of the seal, wherein the shaft step is
adjacent to the cavity, wherein the stator is designed with guided
movement capability in such a way that the gap may be increased and
decreased, and wherein a balance line opens into the cavity, by
means of which process fluid may be fed to the cavity or may be
drained from the cavity.
8. The turbomachine as claimed in claim 7, wherein a surface of the
stator is adjacent to the cavity and is designed in such a way
that, depending upon the pressure in the cavity, it is displaced in
such a way that the gap increases or decreases.
9. The turbomachine as claimed in claims 7, wherein the stator
comprises an elastic element which, depending upon a position of
the stator, creates a restoring force.
10. The turbomachine as claimed in claim 7, wherein the gap does
not extend parallel to the machine axis.
11. The turbomachine as claimed in claim 9, wherein a control valve
is in the balance line, by means of which feeding the process fluid
or draining of process fluid may be adjusted.
12. The turbomachine as claimed in claim 11, wherein the position
of the stator may be adjusted in axial movability by means of the
control valve during operation.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the US National Stage of International
Application No. PCT/EP2010/050643, filed Jan. 20, 2010 and claims
the benefit thereof. The International Application claims the
benefits of German application No. 10 2009 007 713.8 DE filed Feb.
5, 2009. All of the applications are incorporated by reference
herein in their entirety.
FIELD OF INVENTION
[0002] The invention refers to a turbomachine with a balance
piston, which balance piston has at least one shaft step on a rotor
which extends along a machine axis, and a seal, which seal seals a
gap between the rotor and a stator so that during operation a
cavity which is adjacent to a first side of the seal can have a
pressure which, by a pressure differential across the seal, differs
from that on the other side of the seal, wherein the shaft step is
adjacent to the cavity.
BACKGROUND OF INVENTION
[0003] In turbomachines, for example steam turbines, gas turbines
or compressors, especially axial and radial compressors, a pressure
difference across the impeller is created as a result of the
expansion or compression of the process fluid, which pressure
difference, acting on the adjacent surfaces of the rotor, brings
about an axial thrust of said rotor. This axial thrust is dependent
upon the operating conditions of the turbomachine and can also act
in different directions depending upon the operating conditions.
Depending upon the differential pressure and the surface conditions
of the rotor, the axial thrust is a substantial force which, with
an exclusive counter force by means of a thrust bearing, gives rise
to a considerable overall size of said thrust bearing. Therefore,
turbomachines regularly have a so-called balance piston which
serves for thrust compensation. This is regularly designed in such
a way that a lower thrust remains in a specified direction under
all operating conditions, so that no load change reactions take
place and the rotor is not moved back and forth within a possible
axial clearance.
[0004] Balance pistons regularly have at least one shaft step,
wherein they are frequently designed as a radially extending disk
on the rotor and a shaft seal which is adjacent to the at least one
shaft step seals the rotor to a stator. The most frequent type of
construction is the mentioned disk type, so that on the two flanks
or shaft steps, which are defined by the disk, different pressures
create the necessary axial thrust for compensation. Formed adjacent
to the shaft step or the shaft seal and the stator is a cavity in
which prevails a first pressure of a process fluid, which differs
from a second pressure on the other side of the cavity by a
differential pressure across the shaft seal. Acting upon the shaft
step, the first pressure, with the surface of the shaft step,
results in a force which, correspondingly dimensioned, at least
partially compensates the axial thrust and consequently facilitates
the task of the thrust bearing of the shaft by the amount of the
compensating force.
[0005] In order to permanently maintain a pressure difference
across the shaft seal of the balance piston, it is necessary to
feed process fluid through a balance line to the cavity or to
extract process fluid from this, since conventional shaft seals
always have a significant leakage. The quantity of process fluid
which flows through the balance line can have a significant value
and can considerably lower the efficiency. This effect becomes
worse if the shaft seal on the balance piston is worn as a result
of erosion or rubbing on the stator, and consequently slackness
increases.
[0006] A system for balancing axial thrust, with a balance piston
which is acted upon by a pressure for thrust compensation only in
case of requirement, is already known from European patent EP 1 418
341 B1, wherein during normal operation the thrust compensation is
carried out by means of the applicable shaft seals at the
penetrations through the casing, so that during normal operation
supplying the balance piston with process fluid is not
required.
SUMMARY OF INVENTION
[0007] Starting from the aforesaid problems, the invention has been
based upon the object of reducing the loss of process fluid which
arises on the balance piston and thus improving the efficiency of
the machine.
[0008] For achieving the object, it is proposed according to the
invention that the stator is designed with guided movement
capability in such a way that the gap can be increased and
decreased. On account of the design of the stator with guided
movement capability, a gap width which is adapted to the current
operating conditions of the turbomachine can be established, the
gap width being smaller than that which is required under other
operating conditions, so that the differential amount of the
quantity of process fluid which flows through the balance piston is
saved for the benefit of efficiency improvement.
[0009] An advantageous development of the invention provides that
the stator by one surface is adjacent to the cavity and is designed
in such a way that, depending upon the pressure in the cavity, it
is displaced in such a way that the gap increases or decreases.
This type of design opens up the possibility of realizing a gap
width of the seal on the balance piston which is automatically
adapted to the pressure in the cavity without additional actuators,
which move the stator, or without a complicated control system.
[0010] The stator can advantageously have an elastic element which,
depending upon the position within the limits of the guided,
preferably axial movability, creates a restoring force which
counteracts the pressure in the cavity. Depending upon the pressure
conditions in the cavity and on the opposite side of the balance
piston, the force from the elastic element acts upon the stator in
the same or opposite direction of the force from the pressure in
the cavity upon the stator.
[0011] This elastic element can be expediently designed in such a
way that, for each pressure in the cavity, a gap which matches the
operating state associated with this pressure is established. The
widening or decreasing of the gap can be produced in a particularly
simple manner by the annulus of the gap which extends
circumferentially around the machine axis not extending parallel to
the machine axis in the axial direction, but extending obliquely to
it, and by the movability of the stator being guided in the axial
direction. This design has the advantage that the gap can be varied
without a variation of the involved components with regard to their
circumferential dimensions. In this case, the surfaces of the rotor
and of the stator which delimit the gap are designed as a cone in
each case. The cone of the rotor and of the stator can have
different cone angles to each other, which, in specific operating
ranges, can have positive effects upon rotor stability.
[0012] A balance line to the cavity for feeding or draining process
fluid in order to establish a pressure in the cavity, which is
advantageous for the operating state, proves to be particularly
expedient. On the other side of the cavity, this balance line opens
into a pressure reservoir of the process fluid or into a pressure
sink or suction line, and provision is particularly advantageously
made in the balance line for a control valve by means of which a
defined pressure difference across the control valve can be
applied. The control valve enables the controlling of the pressure
in the cavity by means of controlling the inflowing or outflowing
quantity of process fluid.
[0013] With the device according to the invention, the efficiency
of the turbomachine, especially of a compressor, can be
particularly advantageously increased, after a starting process of
the turbomachine, by the quantity of process fluid which flows
through the balance line being reduced by means of the control
valve--during steady state operation--to the extent that it allows
the remaining clearance of the seal on the balance piston. The
elastic element, the stator and the inclined position of the seal
are expediently matched to one another in such a way that a
reduction of the quantity of process fluid which flows through the
balance line and the seal by means of the control valve results in
a decrease of the gap width of the seal. Vice versa, it makes sense
if, with an increase of the quantity of process fluid which flows
through the balance line, the gap width in the seal on the balance
piston also increases.
[0014] In the following text, the invention is explained based on a
special exemplary embodiment with reference to a drawing. The
exemplary embodiment serves simply for the better understanding of
the invention, wherein further embodiment possibilities of the
invention are opened up to the person skilled in the art from the
present description and especially from any combination of the
features which are mentioned in the patent claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] In the drawing:
[0016] FIG. 1 shows a schematic view of the turbomachine according
to the invention with balance piston, in a longitudinal
section.
DETAILED DESCRIPTION OF INVENTION
[0017] FIG. 1 shows a compressor or a turbomachine T with a casing
CAS and a rotor R which extends along a machine axis X. The rotor R
has an impeller IMP--being the rotor wheel of a centrifugal
compressor in this case--by means of which a process fluid PF, by a
rotation at the speed n of the rotor R, is compressed from a first
pressure pl to a higher second pressure p2. For this purpose, the
process fluid PF enters the casing CAS through an inflow IN and
leaves the casing through an outflow EX. Before the process fluid
PF leaves the casing CAS through the outflow EX, it accumulates
partially in a pressure chamber PCH. Adjacent to the pressure
chamber, the rotor R is provided with a balance piston BP. The
balance piston BP basically has a disk shape which, with the
two-dimensional extent, extends perpendicularly to the machine axis
X, that is to say correspondingly has a first shaft step RS1, which
in this case is adjacent to the pressure chamber PCH, and a second
shaft step RS2, which is adjacent to a cavity CH.
[0018] A gap between the balance piston BP and a stator ST, which
is capable of guided axial movement in the casing CAS, is sealed by
means of a seal SS which is designed as a shaft seal--in this case
as a labyrinth seal--so that a pressure difference ensues between
the pressure p2 in the pressure chamber PCH and the pressure p3 in
the cavity CH, the pressure chamber and cavity being sealed in
relation to each other. So that this pressure difference .DELTA.PBD
is maintained, despite the slackness of the seal SS, provision is
made for a balance line BPL. For draining overflowing process fluid
PF which flows from the pressure chamber PCH to the cavity CH via
the seal SS, the balance line BPL is connected to a pressure sink
which in this case is the inlet IN into the casing CAS.
[0019] Provision can also be made for the case in which the balance
line is connected to a pressure reservoir if the pressure
difference .DELTA.PBD across the balance piston BP is oriented in
reverse (in the case of a different orientation of the impeller,
for example).
[0020] The balance line BPL is provided with a control valve CF via
which a pressure difference .DELTA.PCV is created depending on the
position of the control valve CF.
[0021] A part of the seal SS is attached to the stator ST which is
designed with guided axial movement capability, wherein the gap GP
to be sealed extends obliquely to the machine axis X. In this way,
the spatial geometry which is defined by the gap GP forms a cone
which extends concentrically around the machine axis X in the
circumferential direction. Since the turbomachine T of this
exemplary embodiment is a centrifugal compressor or compressor, and
the balance piston BP is located on the side of the higher pressure
of the impeller IMP so that the pressure chamber PCH has a higher
pressure in comparison to the cavity CH, it is expedient if a
displacement of the stator ST in the direction of the chamber with
the lower pressure (in this case the cavity CH or p3) brings about
an increase of the gap GP or of the gap width H, and as a result
therefore creates greater slackness of the seal SS. The stator ST
is pretensioned by means of an elastic element EE in such a way
that the restoring force of the elastic element EE acts in the
direction of a decreasing of the gap width H. If during steady
state operation, with initially constant gap width H, the control
valve CV is throttled, the pressure p3 is increased and a new
equilibrium state of the arrangement is established in such a way
that the gap width H decreases as a result of the greater thrust
upon the stator ST in the direction of the pressure chamber PCH.
According to the invention, by means of the control valve position
CV, the axial thrust from the balance piston BP can be adjusted and
the consumption of process fluid PF through the balance line can be
reduced.
* * * * *