STEAM/GAS TURBINE PRESSURE STAGE WITH UNIVERSAL SHROUD

ETAGE DE PRESSION D'UNE TURBINE A VAPEUR/GAZ PRESENTANT UN ANNEAU DE RENFORCEMENT UNIVERSEL

English Abstract

There is provided a steam turbine pressure stage designed with a nozzle
(directional) block with nozzle (directional) blades and shield, a rotor
wheel, consisting of
disc, rotor blades, a shroud and shroud seals, incorporated in the nozzle
block or located on
the shroud of rotor blades.

French Abstract

Selon l'invention, une conception imparfaite d'un anneau de renforcement (8) ou de parties identiques des aubes (7) de turbines à vapeur/gaz, y compris les joints d'étanchéité contigus, sont à l'origine d'une baisse de la fiabilité et de l'efficacité. Ces lacunes sont éliminées grâce à des trous latéraux forés dans l'anneau de renforcement et les aubes (7). Le transfert de vapeur par les trous (12) de l'anneau de renforcement donne lieu à l'allègement du gradient de pression à la surface de l'anneau de renforcement (8) et empêche la formation d'oxyde métallique, de sel et d'autres dépôts sur les surfaces intérieures de l'anneau de renforcement (8). La quantité et le diamètre des trous (12), ainsi que leur dépôt correspondant et les valeurs de jeux radiaux dans les joints d'étanchéité bombés (4, 5) de l'anneau régulent leur efficacité.

Claims

6
What is claimed is:
1. An axial flow fluid machine for use with steam or gas comprising:
a stationary housing;
a rotor member having an inner disc, an outer shroud, and a plurality of
blades
mounted between the disc and the shroud;
shroud seals including two sealing combs located either on an outer surface of
the
outer shroud or on an inner surface of the stationary housing radially facing
the outer
shroud, the two sealing combs providing two radial clearances h1 and h2
between the
rotor member and the housing, the clearance h2 being less than the clearance
h1; and
a plurality of radial discharge openings arranged in the outer shroud, the
openings
being distributed either evenly or staggered such that steam or gas flowing
radially
outwardly through the openings prevents the formation of metal and salt oxides
on the
inner surface of the outer shroud and wherein the diameter d of the openings,
the number
n of the openings, and the surface area Sk of the outer shroud covering the
flow channel
through the rotor satisfies the relationship:
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Description

CA 02562712 2010-02-10
TITLE
[0001] Steam/gas turbine pressure stage with universal shroud
FIELD
[0002] This relates to the manufacture and operation of steam and gas
turbines,
compressed air plants and gas force pumps.
[0003] Imperfect design of belt shrouds or identical parts of the blades of
such machines,
including the adjoining seals, leads to the decrease in reliability and
efficiency.
1. Uneven distribution of radial clearances along the shrouds' circumference
induces the
effect of air-dynamic Thomas forces, decreasing vibration behavior.
2. The inner surface of shrouds is subjected to formation of metal oxide and
salt
deposits.
[0004] These drawbacks are eliminated by way of drilling of radial holes in
the shrouds
of the blades. The transfer of steam through the shroud holes results in the
relief of the
pressures gradient on the surface of the shroud and prevents the formation of
metal oxide, salt
and other deposits on the inner surfaces of the shrouds.
[0005] The quantity and diameter of the holes, as well as their corresponding
disposition
and the values of radial clearances in shroud crowning seals regulate their
efficiency.
BACKGROUND
[0006] Steam or gas turbine stages possess the following significant flaws,
revealed in the
course of turbine operation:
a) Due to the uneven distribution of clearances in shroud seals around the
stage, there
emerge air dynamic shroud and ridge Thomas forces, inducing unstable operation
of
turbine rotor and its supports;
b) Inner surface 8 of rotor blade shroud is subject to the formation of metal
and salt
oxides 10, the presence of which closes a portion of rotor blade open flow
area, which
leads to the decrease of rated efficiency factor with subsequent reduction of
turbine
power.
c) Excessive fuel combustion, owing to p. b) with varying comparative turbine
loads

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leads to the extra consumption of fuel resources.
SUMMARY
[0007] The purpose of the steam/gas turbine pressure stage with universal
shroud is the
improvement of steam and gas turbines operation reliability, the increase of
actual efficiency
factor and power as compared to the existing parameters.
[0008] There is provided a steam turbine pressure stage designed with a nozzle
(directional) block with nozzle (directional) blades and shield, a rotor
wheel, consisting of
disc, rotor blades, a shroud and shroud seals, incorporated in the of the
nozzle block or located
on the shroud of rotor blades.
[0009] Shroud seals of a turbine stage consist as a rule of two ridges, with
the first ridge
following the direction of steam flow located in the seal and the second
ridge, both of which
form a shroud chamber, located over the shroud, comprising radial clearances
hl and h2,
determining the flow rate of steam, coming through seal.
[0010] Clearances hl and h2 are set equal in absolute value for each stage or
stage group,
the value depending on the conditions of thermal expansion of turbine parts,
as well as on the
conditions of turbo-unit threshold power, i.e. power, producing low frequency
vibration.
Rotor blade shroud, are in the form of a strip with openings for rotor blade
pins, which are
unriveted after their mounting on rotor blades, forming a pack of six or more
blades. Parts of
the shroud, covering single flow channel do not have any openings. The ratio
between the
number of openings n and their diameter d is the following:
d-2 0.02-20.50). Sk
nor
where Sk is the surface area of the outer shroud, covering each single inter-
blade channel in
rotor wheel.

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BRIEF DESCRIPTION OF THE DRAWINGS
[0011] These and other features will become more apparent from the following
description in which reference is made to the appended drawings, the drawings
are for the
purpose of illustration only and are not intended to be in any way limiting,
wherein:
FIG. 1 is a longitudinal section of turbine pressure stage with shroud seals
in the
nozzle block shield.
FIG. 2 is a longitudinal section of turbine pressure stage with shroud seals,
located
in rotor blade shrouds
FIG. 3 is a shroud section of FIG. 1.
FIG. 4 is a shroud section of FIG. 2.
FIG. 5 is a detail of FIG. 4 with section along D-D
FIG. 6 is a detail of FIG. 3 with section along C-C
DETAILED DESCRIPTION
[0012] A steam (gas) turbine (compressor) pressure stage FIG. 1 and FIG.2.
comprising a
nozzle (directional) block 1 with nozzle (directional) blades 2 and a shield
3, seal shroud
ridges 4 and 5 or ridges 4 and 5, located on the shroud 8 FIG.2 and rotor
wheel with shroud 8,
located on rotor blades 7 differs in the respect, that with the purpose of
increasing the
efficiency factor and operational reliability of turbine, radial clearance h2
of the second ridge
5 of shroud seal, located along the steam/gas flow is made less than radial
clearance hl of the
ridge 4 of the shroud seal and in parts 13, 14, 15 of the shroud 8, closing
the single inter-blade
channel there is a system of radial discharge openings 12 FIG.3, FIG.4, FIG.5
and FIG.6,
distributed evenly in relation to the surfaces of parts 13, 14, 16 of shroud
8. The radial
discharge openings can also be organized in staggered order 16, as well as
along medium
steam flow line 14 and 18, or in symmetrical position to steam flow line 18
FIG.4 in the inter-
blade channel, for steam (gas) overflow from the enclosure 17 above the shroud
FIG.5 and
chamber 11 above the shroud to the flow channel and the discharge of above
shroud pressure,
the pressure being the source of air dynamic above shroud and ridge "Thomas
forces", which
induce unstable operation of turbine rotor and its supports, whereas steam
(gas), entering
through the discharge openings 12 in shroud 8 to the above shroud enclosure of
the flow
channel prevents the formation of metal and salt oxides 10 on the inner
surface of shroud 8

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with the diameter d of the openings 12 and their number n on each surface Sk
of each flow
channel of shroud parts 13, 14, 16, covering the single inter-blade channel
stand in the
following ratio:
d=2 0.02=0.50 - Sk
n-z
[0013] Improvement of steam and gas turbines operation reliability, the
increase of actual
efficiency factor and power is achieved by way of making of clearances hl and
h2 in the
ridges of shroud seals in such a manner, that the radial seal h2 on the second
ridge 5 is smaller
than the radial clearance hl on the first ridge 4, which permits to regulate
the flow rate of
steam, coming through shroud chamber 11 within specified limits. A system of
discharge
openings 12 is implemented in rotor blade shroud parts 13, covering single
inter-blade
channel, by way of drilling of the shroud FIG. 5 and FIG.6. The openings are
located evenly
along the surface of parts 13 and 14 of the shroud 8, following the direction
of steam flow 18
FIG. 4 in inter-blade channel 14. The openings may be organized in staggered
order 16,
depending on the properties of deposits and their volume, as well as on seals
design.
[0014] Due to openings 12 in the shroud 8 of rotor blades 7 there occurs in
the course of
turbine operation a steam overflow from the chamber 11 located above the
shroud and
enclosure 17, also above the shroud FIG. 5 to the part of flow channel,
located under the
shroud, which leads to the creation of an obstacle effect, preventing the
formation of metal
and salt oxides on the inner surface of the shroud.
[0015] The discharge of pressure from the chamber 11 located over the shroud
and
enclosure 17 over the shrouds is implemented by similar process of steam
overflow, which
process excludes the onset of air dynamic above shroud and ridge Thomas
forces, inducing
unstable operation of turbine rotor and its supports. This, in turn,
facilitates the reduction of
radial clearance h2 on the second ridge 5, controlling the turbo-unit
threshold power, which
results in additional increase of the efficiency factor owing to the reduction
of steam overflow
over the seal.

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[0016] Thus, the steam/gas turbine can be used for the following purposes:
a) as means, preventing the formation of metal and salt oxides on the inner
surfaces of
rotor blade shrouds;
5 b) as means for the enhancement of turbo-unit vibration state
c) with the purpose of prolongation of period between repairs owing to p.p. a)
and b) and
that of turbine service life.
[0017] In this patent document, the word "comprising" is used in its non-
limiting sense to
mean that items following the word are included, but items not specifically
mentioned are not
excluded. A reference to an element by the indefinite article "a" does not
exclude the
possibility that more than one of the element is present, unless the context
clearly requires that
there be one and only one of the elements.
[0018] The following claims are to be understood to include what is
specifically
illustrated and described above, what is conceptually equivalent, and what can
be obviously
substituted. Those skilled in the art will appreciate that various adaptations
and modifications
of the described embodiments can be configured without departing from the
scope of the
claims. The illustrated embodiments have been set forth only as examples and
should not be
taken as limiting the invention. It is to be understood that, within the scope
of the following
claims, the invention may be practiced other than as specifically illustrated
and described.

Representative Drawing