Note: Descriptions are shown in the official language in which they were submitted.
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Description
Turbine having compact inflow housing thanks to internal
control valves
The present invention relates to a turbine with an inflow
housing which comprises an inlet for an inflowing working
fluid, wherein the inlet can be closed by a quick closing
valve, a plurality of control valves and at least two nozzle
groups, the flow of the working fluid being controllable from
the inlet into the nozzle groups via the control valves.
This type of turbine is known from the publication DE 1 915
267 Al of the same applicant. The inflow housing is the part
of the turbine housing into which the working fluid flows into
the turbine and in which the working fluid is directed onto
the rotor. For applying the fluid to the rotor the inflow
housing has a number of nozzle groups which extend in the
shape of a ring sector at a common diameter around the rotor.
Each nozzle group combines a number of nozzles which are
directed onto the rotor. The inflowing working fluid flowing
in through the inlet is directed into the nozzle groups, exits
from the nozzles and flows through the rotor blading. The
division of the nozzles into nozzle groups is used for power
regulation. Since the mass throughput is restricted by the
nozzle cross section, the overall mass throughput and thereby
the power of the turbine can be controlled by variation of the
nozzle groups to which the working fluid is applied. The
distribution of the working fluid to the individual nozzle
groups and the individual mass throughput per nozzle group is
controlled by the control valves. A quick closing valve is
provided for an emergency shutdown which closes off the inlet
and can therefore suppress the overall flow through the
turbine.
The inflow housing of a known steam turbine is shown in Figure
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2a of DE 1 915 267 Al. With the housing design basically still
manufactured today the control valves are located in what is
referred to as a valve housing or valve compartment above the
actual turbine housing. The working fluid flows in laterally
through arl inlet, passes through a quick closing valve and
reaches the valve compartment from which five parallel-
switched supply 1_ines above a control valve in each case
branch off to nozzle groups. Each valve group thus has its own
supply line available to it and a separate control valve. The
respective feed lines and valves are connected in parallel.
The enclosed Figure 1 shows a circuit diagram of this
arrangement. With current designs of such a valve arrangement
the linearly-guided valve spindles of the control valves are
each driven with an individual motor and not, as shown in this
publication, via a control bar.
In another known design of steam turbines the control valves
are arranged outside the turbine housing and linked via
welded-on pipes or pipe bends to the nozzle housing. The fresh
steam flow divided up remotely from the inflow housing is
thereby guided through the comparatively long pipes to the
nozzle groups.
However both designs have the disadvantage that the inflow
housing with the external valve compartments or the pipes
occupy a great deal of space. In addition these constructions
are very costly, since very high-quality materials must be
used for the cast housings of the valves, pipes and flanges.
The many diversions of the flow in the pipes or in the supply
pipes to the nozzle groups inevitably lead to significant
energy losses. In addition the control valves described in DE
1 915 267, through which the flow is axial, also demand high
setting forces.
In respect of this prior art the present invention is based on
the object of developing a turbine of the type described at
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the outset so that its inflow housirig is as compact a design
as possible, and that the flow losses caused by long lines are
reduced. This object is achieved first of all by the control
valves being functionally divided into a primary control valve
and at least one secondary control valve. Furthermore the
inlet is to be connected to the first nozzle group via the
inlet line, whereby the inlet line is to be guided through the
primary control valve such that the flow of the working fluid
along the inlet line is able to be controlled by means of the
secondary control valve. In accordance with the invention the
secondary control valve connects the first nozzle group to the
second nozzle group such that the flow of the working fluid
from the first nozzle group and the second nozzle group is
able to be controlled by means of the secondary control valve.
The present invention is based on the underlying idea of no
longer controlling individual nozzle groups with control
valves connected in parallel, but of connecting the nozzle
groups in series via the secondary control valves. This
measure basically allows savings to be made in pipe runs in
the inflow housing and thus to achieve a more compact
construction. The flow losses are also reduced by the savings
in pipes. The valve control of a primary control valve is
decisive in the control of turbine since this can control the
entire flow of the working fluid through the turbine. Since
the first nozzle group is connected directly to the inlet via
the primary control valve and the quick closing valve working
fluid is always applied to the first nozzle group when the
primary control valve and the quick closing valve are open. To
increase the power, the subordinate rlozzle groups are
successively switched in by the secondary control valves.
A preferred development of the invention makes provision for
at least three nozzle groups connected in series to be
Qrovided in the inflow housing, so that at least two secondary
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control valves are necessary that connect the first nozzle
group to the second or the second nozzle group to the third.
To enable the power to be controlled in even smaller steps, it
is also recommended that an additional fourth or fifth nozzle
group be provided; the number of secondary control valves
necessary would consequently increase to three or four.
As already mentioned the entire flow of the working fluid
flows to the primary control valve. To keep the actuation
forces low and to allow a soft start-up of the turbine, it is
recommended that this valve being equipped with a pilot valve.
The starting up of such a turbine is preferably undertaken by
the following steps: With the turbine at rest the quick
closing valve is initially opened which causes the pressure of
the working fluid to build up as far as the valve seat of the
primary control valve. The first nozzle group is activated
directly by the primary control valve. With the aid of a small
pilot valve on the primary control valve the turbine is
initiated and brought up to its operating speed. After the
machine has accepted a load and the first nozzle group has
been fully activated, the main control valve is started and
thus releases the entire cross-section for the overall mass
flow of the working fluid. Since the mass throughput is capped
by the valve cross sections of the first group, the power of
the turbine remains constant on reaching the maximum mass
throughput. If the power of the turbine is to be increased
further, the first secondary control valve is opened so that
the flow now also reaches the second nozzle group. This
increases the mass throughput. Provided the turbine has
available to it further downstream nozzle groups, these will
be switched-in later by opening the respective secondary
control valves.
The inventive circuit of the individual nozzle groups allows
the shut-off facilities of the secondary control valves to be
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arranged directly between the nozzle groups extending in the
shape of a ring sector around the rotor, i.e. at the same
radius as the nozzle groups. The flow paths in the inflow
housing are further shortened in this way.
The space occupied by the irlflow housing can be significantly
reduced in this design by the axes of actuation of the
secondary control valves being arranged radially to the axis
of rotation of the rotor. The actuation path of the shut-off
facilities is then not actually located tangentially to the
diameter of the nozzle groups, but radially. The necessary
external diameter of the inflow housing is reduced in this
way.
Preferably in this embodiment the shut-off facilities of the
secondary control valves are designed as rotationally-
switchable control flaps so that the actuation axis involved
is an axis of rotation. The rotationally-switched shut-off
facilities occupy less space than the linearly-switched shut-
off facilities, require lower actuation forces and do not have
to be completely sealed. The use of rotationally-switched, not
completely sealed shut-off facilities is also possible since
no quick closing function is required for the secondary
control valves. This quick closing function is performed by
the quick closing valve and the downstream primary control
valve. Preferably the inflow housing of the inventive turbine
is an essentially annular design and is subdivided into at
least two housing halves, with the inlet line being an
integral component of a housing half. The advantage of this
embodiment is that the line of the working fluid can be welded
on without a flange connection, that only one entry into the
turbine housing must be sealed off with the piston ring and
that all components warm up well during the start of phase.
With a large volume of steam the two housing halves can each
be provided with an integrated inlet in order to double the
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normal width of the inlet steam connection overall.
'I'he present invention is preferably employed in the area of
axial designs of steam turbine.
The present invention will now be explained in greater detail
with reference to an exemplary embodiment. The figures show:
Fig. 1: a conventi_onal valve circuit (prior art);
Fig. 2: an inventive valve circuit;
Fig. 3: an inflow housing in a part-exploded perspective
view;
Fig. 4: an inflow of housirlg in a part-exploded rearview;
Fig. 5: a section through the inflow housing;
Fig. 6: an inflow housing with two inlets.
Figure 1 shows a schematic diagram of the last circuit of a
conventional steam turbine, as is known from the publication
mentioned at the start. The housing of the turbine comprises
an inflow housing 1 in which the rotor not shown in the
diagram is supported to allow rotation. The rotor has working
fluid applied to it via four nozzle groups 21, 22, 23, 24
which extend in the shape of an annular sector on a common
diameter D around the rotor.
'I'he working medium - steam in the case of a steam turbine -
flows through an inlet 3 into the inflow housing 1. Directly
behind the inlet 3 is arranged a quick closirlg valve 4 through
which the inlet 3 can be rapidly closed in an emergency.
Behind the quick closing valve 4, the flow fans out in four
supply lines 51, 52, 53, 54 which connect the inlet 3 with the
nozzle groups 21, 22, 23, 24 in each case. The flow of the
working fluid through the supply lines 51, 52, 53, 54 is
controlled by respective control valves 61, 62, 63, 64. The
nozzle groups 21 through 24 are consequently connected in
parallel via their respective supply lines 51 through 54 and
the associated control valves 61 through 64.
The inventive circuit is shown in figure 2. Here the inlet 3
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(fresh steam connection) able to be closed off via the quick
closing valve 4 is connected via an inlet line 7 directly and
exclusively to the first nozzle group 21. The inlet line 7 is
routed through the primary control valve 8 which controls the
overall flow through the turbine. The primary control valve 8
i.s advantageously equipped with a pilot valve which can be
realized for example by a pilot valve connected in parallel
(not shown in the diagram). Quick closing valve 4, primary
control valve 8 and first nozzle group 21 are thus connected
in series via the inlet line 7. The series circuit continues
into the second to 22, third 23 and fourth nozzle group 24.
The second nozzle group 22 is connected to the first nozzle
group 21 exclusively via a first secondary control valve 91.
The connection of the second nozzle group 22 to the third
nozzle group 23 is made in the same way via a second secondary
control valve 92, the connection into the fourth nozzle group
24 is made accordingly via a third secondary control valve 93.
The shut-off facilities 10 of the secondary control valves 91,
92, 93 are located on the same diameter D as the nozzle groups
21, 22, 23, 24. In this way an especially compact design of
the inflow housing 1 is achieved. The axes of actuation 11 of
the secondary control valves extend radialiy to the axis of
rotation of the rotor, i.e. the center of the housing. Through
these measures the setting motors 12 of the actuation
facilities can be arranged outside the inflow housing 1.
Concrete proposed layouts of this design can be seen in
Figures 3 through 5. The secondary control valves 91, 92, 93
are to be activated rotationally here so that the shut-off
facilities 10 are rotary flaps. The setting motors 12 are
placed on the inflow housing 1, i.e. in the pressure-free
area. Only the axis of actuation left in the housing 11 must
be sealed, which is easy to do with axes of rotation.
The inflow housing 1 itself is therefore essentially annular
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and far more compact than in the prior art since it merely
accommodates the nozzle groups 21, 22, 23 and the shut-off
facilities 10.
The inflow housing 1 is cast and divi_ded up into and upper
housing half la and a lower housing half lb, with the inlet
line 7 being an integral component of the lower housing half
lb. Prirnary control valve 8 and quick closing valve 4 are
arranged outside the housing 1. Thus only one steam feed into
the turbine housing is to be sealed with piston rings. The
steam line can thus be welded on without a flange connection.
With a very large volume of steam it is likewise possible to
provide the inflow housing with two inlet lines, in order to
double the nominal width of the inflowing steam connection in
this way. Two primary control valves and two quick closing
valves are then accordingly also required, one for each inlet.
Figure 6 shows and inflow housing with two integrated inlet
lines 7.
As well as the compact dimensions and the lower flow losses, a
particular advantage of the construction shown lies in the
lower setting forces of the valves. Thus especially the inner
control flaps only need small setting forces and especially no
quick closing facility since they are connected in series with
the primary control valve 8 and the quick closing valve 4. In
addition the inner control flaps can be removed and replaced
without opening the turbine housing.
