[0001] The method and system relates to reducing start-up time of a steam turbine, by enabling
faster heating of the turbine rotor during start-up.
[0002] The rotor of the steam turbine is subjected to high temperature during operation.
However, during start-up the rotor of the steam turbine will be at a much lower temperature
than that of the steam. However, if such high temperature steam is introduced during
the start-up of steam turbine, the rotor may experience a thermal shock, due to the
temperature gradient existing between the outer surface (hot) and the inner core (cold)
of rotor. Generally, the components such as rotor of the steam turbine are pre-heated
to certain temperature before starting the normal operation of the turbine. The turbine
is started up according to predefined start-up curves where the components such as
rotors and valves are gradually preheated. Preheating of the rotor reduces the thermal
stress experienced and increases the life of the rotor. But the pre-heating cycles
are generally time consuming and non-productive.
[0003] Currently, various methods are used to preheat the rotor of the turbine during startup.
For example, structural modifications are used to prevent the rotor from experiencing
thermal shock. The rotor is designed to having a smaller cross section. In some cases,
the rotor is rotated at a pre-defined low speed to uniformly pre-heat the rotor. In
some instances, the rotor is kept warm during standstill by using heating means, which
is very costly.
[0004] Further, the existing methods for preheating the rotor are either time consuming
or economically unviable. The start-up time for a turbine is crucial for a customer
as it is non-productive. The start-up time is critical for small turbines used in
industrial or solar applications where daily start-up and shutdown is a norm. Therefore,
the start-up time must be reduced for increasing the productivity of the turbine and
decreasing the idle time.
[0005] Therefore, it is an object of the invention to reduce the start-up time for a turbine.
It is also the object of the invention to provide a cost effective solution for minimizing
the start-up time by expediting the heating of the rotor assembly.
[0006] The invention solves the object by providing a steam turbine comprising a rotor assembly
having a rotor core extending in a longitudinal direction and one or more extended
portions coupled to the rotor core and extending the rotor core in a radial direction.
The steam turbine includes at least one thermal exchange channel located on the one
or more extended portions, wherein the thermal exchange channel is capable of having
thermal communication between the rotor core and a steam surrounding the rotor core.
The rotor core is a solid metal part which extends longitudinally and has blades attached
to it. The rotor core has protrusions or extensions at many places for structural
reasons. The portions of the rotor core with protrusions require a relatively large
amount of time to get heated during start-up cycle. The thermal exchange channels
provide additional surface area for thermal exchange between the steam and the rotor
core. During the preheating cycle, the thermal exchange channels exposes additional
area to the surrounding steam for better heat exchange. Further, the preheating cycle
or start-up cycle time is reduced by the aforementioned enhancement.
[0007] According to an embodiment of the invention, the rotor core has a first diameter
and the one or more extended portions have a second diameter. The rotor core is cylindrical
in shape and extends longitudinally. The rotor core has a first diameter along the
longitudinal axis. The one or more extended portions along the longitudinal axis have
a second diameter.
[0008] According to another embodiment of the invention, the second diameter (of the extended
portions) is greater than the first diameter (of the rotor core). The extended portions
at certain locations on the rotor core extend the rotor core in the radial direction.
Therefore, the extended portions have a cross sectional diameter greater than that
of the t rotor core.
[0009] According to yet another embodiment of the invention, the at least one thermal exchange
channel is a tubular bore. The thermal exchange channel can be for example, straight
or contoured. In some cases, the thermal exchange channel may be fabricated to have
an 'L' shape or a 'U' shape, in the extended portions of the rotor core. Further,
the thermal exchange channel may have any orientation and cross section in order to
increase the thermal exchange.
[0010] In an embodiment of the invention, a plurality thermal exchange channel is interconnected.
The thermal exchange channels are interconnected to form a network. For example, the
thermal exchange channels can be fabricated to be connected to each other in the extended
portion and not extending to the first diameter of the rotor core. The interconnection
of thermal exchange channels enables efficient thermal communication between the surround
steam and the rotor core.
[0011] In another embodiment, the interconnection of the plurality of thermal exchange channel
provides a draining mechanism to drain condensed steam. The interconnection of the
plurality of thermal exchange channel prevents the accumulation of water in the thermal
exchange channel, thus preventing formation of rust.
[0012] In yet another embodiment, the draining mechanism includes at least one of a slanted
thermal exchange channel. In this case, the thermal exchange channel is slanted to
enable the accumulated water to drain from the rotor core.
[0013] In a further embodiment of the invention, the rotor core is enclosed by an outer
casing. The steam may be released within the outer casing during start-up cycle. The
steam released during the start-up cycle is at a relatively lower temperature than
the steam used during normal operation of the turbine. The steam released during the
start-up cycle is at a higher temperature than the rotor core thereby creating a thermal
gradient.
[0014] The figures illustrate in a schematic manner further examples of the embodiments
of the invention, in which:
- FIG 1
- illustrates an exemplary rotor core assembly of a turbine, according to a state of
the art;
- FIG 2A
- illustrates a perspective view of the rotor core assembly with thermal exchange channels,
in accordance with the invention;
- FIG 2B
- illustrates a cross sectional view of the rotor core assembly with thermal exchange
channels, in accordance with the invention;
- FIG 3A
- illustrates a perspective view of the rotor core assembly with 'L' shaped thermal
exchange channels, in accordance with the invention;
- FIG 3B
- illustrates a cross sectional view of the rotor core with 'L' shaped thermal exchange
channels, in accordance with the invention;
- FIG 4A
- illustrates a perspective view of the rotor core assembly with 'U' shaped thermal
exchange channels, in accordance with the invention;
- FIG 4B
- illustrates a cross sectional view of the rotor core with 'U' shaped thermal exchange
channels 4, in accordance with the invention;
- FIG 5A
- illustrates a perspective view of the rotor core assembly with slanted thermal exchange
channels, in accordance with an embodiment of the invention;
- FIG 5B
- illustrates a cross sectional view of the rotor core assembly with slanted thermal
exchange channels 4, in accordance with an embodiment of the invention;
- FIG 6A
- illustrates a perspective sectional view of the rotor core assembly with interconnected
thermal exchange channels, in accordance with the invention; and
- FIG 6B
- illustrates a cross sectional view of the rotor core with interconnected thermal exchange
channels, in accordance with the invention.
[0015] Turbines are used in the industry mainly to generate power. The turbines may include,
for example, a steam turbine and a steam turbine. The turbines normally include a
rotor core to which blades are attached. During operation the rotor core rotates due
to the impingement of pressurized fluids, thereby generating energy. FIG 1 illustrates
an exemplary rotor core assembly 1 according to a state of the art. As shown in FIG
1, the rotor core 2 is cylindrical and extends longitudinally within an outer casing
of the turbine (not shown in Figures). There rotor core may have a diameter d1. Along
the rotor core 2, there may be one or more extended portions, such as extended portions
3, which radially extend the rotor core 2. The diameter at the extended portions 3
may be d2, where d2 is greater than the diameter d1 of the rotor core 2. The thickness
of the metal increases at the regions on the rotor core where one or more extended
portions, such as extended portions 3, are located. For example, regions such as balance
pistons located on the rotor core. The rotor core 2 is generally made up of high strength
alloys or super alloys such as nickel and ferrous based alloys. Before the turbine
is operated at normal levels, the rotor assembly needs to be pre-heated to avoid thermal
shock. When the turbine is to be operated, a start-up cycle is initiated wherein the
rotor is rotated at a low speed and steam at a relatively lower temperature is introduced
into the outer casing. The start-up cycle is performed to prevent the components of
the turbine from experiencing thermal shock in case a high temperature steam is suddenly
introduced into the casing. During start-up cycle, thermal exchange takes place between
the rotor core and the steam. The rotor core which is at a lower temperature than
the steam slowly begins to heat up. The time taken for the rotor core and the associated
components to heat depends upon the capacity of the turbine. The time taken for the
completion of the start-up cycle may range between 2-3 hours in some cases. The start-up
cycle is unproductive and affects the customers who need to run the start-up cycle
on a daily basis.
[0016] FIG 2A illustrates a perspective view of the rotor core assembly with thermal exchange
channels, in accordance with the invention. The extended portions 3 of the rotor core
assembly 1 are provided with one or more thermal exchange channels 4 for expediting
the heating of the rotor core. The thermal exchange channels 4 exposes additional
area for the steam for efficient thermal communication. The steam which is at a higher
temperature than the rotor core interacts with the surface of the thermal exchange
channels 4 and heats the rotor core. Therefore, the heating of the rotor core takes
lesser time to heat up as compared with the heating time of the rotor core assembly
1 without the thermal exchange channels 4. The thermal exchange channels 4 can have
varying depth and diameter based on the location on the rotor core. For example, the
depth and diameter of the thermal exchange channels 4 are based on a location such
as, axial sections, exhaust and balance piston. In general, bigger thermal exchange
channels 4 are preferred for better thermal interaction, provided the sizes of the
thermal exchange channels 4 meet other requirements such as, strength and rotor dynamics,
which varies according to the design. FIG 2A illustrates the thermal exchange channels
4 which are generated by boring the extended portions 3 of the rotor core assembly
1. The thermal exchange channels 4 in FIG 2A are horizontal in orientation and a spaced
apart on the periphery of the extended portion 2. FIG 2B illustrates a cross sectional
view of the rotor core assembly with the thermal exchange channels, in accordance
with the invention. In fig 2B, we can see that the thermal exchange channels 4 extend
into the extended portion 3 of the rotor core assembly but do not penetrate completely.
The thermal exchange channels 4 allow the steam, released during the start-up cycle
to interact with the rotor core and expedite the heating up of the rotor core assembly
1.
[0017] FIG 3A illustrates a perspective view of the rotor core assembly with 'L' shaped
thermal exchange channels, in accordance with the invention. In this embodiment, the
thermal exchange channels are longer and extend deeper into the rotor core. In this
case, the steam enters into the thermal exchange channels 4 and heats the rotor core.
FIG 3B illustrates a cross sectional view of the rotor core with 'L' shaped thermal
exchange channels, in accordance with the invention. In FIG 2B, it can be seen that
the thermal exchange channels 4 extend deep into the extended portion of the rotor
core 2 and expedite the heating of the rotor core.
[0018] FIG 4A illustrates a perspective view of the rotor core assembly with 'U' shaped
thermal exchange channels, in accordance with the invention. In this embodiment, the
thermal exchange channels 4 are longer than the 'L' shaped thermal exchange channels,
thereby exposing more area for thermal exchange. Thus, there is faster heat transfer
between the surrounding steam and the rotor core 2, resulting in reduced start-up
time. FIG 4B illustrates a cross sectional view of the rotor core with 'U' shaped
thermal exchange channels 4, in accordance with the invention.
[0019] FIG 5A illustrates a perspective view of the rotor core assembly with slanted thermal
exchange channels 4, in accordance with an embodiment of the invention. The slanted
thermal exchange channels 4 facilitate in draining condensed steam which might get
accumulated in the thermal exchange channels 4. FIG 5B illustrates a cross sectional
view of the rotor core assembly with the slanted thermal exchange channels 4, in accordance
with the invention. In FIG 5B, it can be observed that due to the slanted thermal
exchange channels 4 any condensed steam accumulated in the thermal exchange channels
4 are drained.
[0020] FIG 6A illustrates a perspective view of the rotor core assembly with interconnected
thermal exchange channels, in accordance with the invention. The thermal exchange
channels 6 are parallel to the plane of the extended portion of the rotor core. FIG
6B illustrates a cross sectional view of the rotor core with interconnected thermal
exchange channels, in accordance with the invention. The interconnection channel 6
connecting the thermal exchange channels 4 forms a draining mechanism to drain condensed
steam. Further, the inner end of the thermal exchange channels 4 are connected to
each other by an interconnection channel 6, as shown in FIG 6B. Such an arrangement
facilitates in draining any condensed steam within the thermal exchange channels 4.
The steam accumulated in the thermal exchange channels 4 may condense when the rotor
core is decelerating. The steam condensed in the thermal exchange channels 4 at the
upper half of the rotor core is drained through one of the thermal exchange channels
4 in the lower half of the rotor core 2. The thermal exchange channels 4 with interconnection
thus prevent rusting of the metal in the rotor core assembly due to accumulation of
moisture.
[0021] According to the foregoing embodiments, the thermal exchange channels reduce the
start-up time of a turbine by expediting the pre-heating process. The thermal exchange
channels expose additional surface of the rotor core to the surrounding steam in order
to heat up the rotor core faster. The thermal exchange channels result in lesser downtime
for the customers. Further, the thermal exchange channels can be used for rotor balancing.
Balancing mass can be coupled to the thermal exchange channels to balance the rotor
core assembly 1.
[0022] Though the invention has been described herein with reference to specific embodiments,
this description is not meant to be construed in a limiting sense. Various examples
of the disclosed embodiments, as well as alternate embodiments of the invention, will
become apparent to persons skilled in the art upon reference to the description of
the invention. It is therefore contemplated that such modifications can be made without
departing from the embodiments of the invention as defined.
1. A steam turbine comprising a rotor core assembly (1), wherein the rotor core assembly
(1) comprises:
a rotor core (2) extending in a longitudinal direction and one or more extended portions
(3) coupled to the rotor core (2) and extending the rotor core in a radial direction,
characterized in that,
at least one thermal exchange channel (4) located on the one or more extended portions
(3), wherein the at least one thermal exchange channel (4) is capable of having thermal
communication between the rotor core and a steam surrounding the rotor core.
2. The steam turbine according to claim 1, wherein the rotor core has a first diameter
(d1) and the one or more extended portions have a second diameter (d2).
3. The steam turbine according to claim 2, wherein the second diameter (d2) is greater
than the first diameter (d1).
4. The steam turbine according to claim 1, wherein the at least one thermal exchange
channel (4) is a tubular bore.
5. The steam turbine according to claim 1, wherein a plurality of thermal exchange channels
(4) is interconnected.
6. The steam turbine according to claim 5, wherein the interconnection (6) of the plurality
of thermal exchange channels (4) provides a draining mechanism to drain condensed
steam.
7. The steam turbine according to claim 6, wherein the draining mechanism includes at
least one of a slanted thermal exchange channel (4).
8. The steam turbine according any of the preceding claims, wherein the rotor core (2)
is enclosed by an outer casing.