Method for cooling down a steam turbine
A steam-turbine unit has a steam turbine and an option for cooling the steam turbine by forced cooling, wherein cooling air is drawn through the steam turbine via a suction device and a drainage line of the live-steam valve is used as the access option.
1. A steam turbine unit comprising:
a steam turbine which comprises a steam inlet region, an exhaust steam region and a blading region which is surrounded by a turbine housing and is arranged axially in between,
a cooling fluid inlet which is closeable and openable by a closure member, and which is arranged upstream of the exhaust steam region with respect to a flow direction of steam,
a valve comprising a steam inlet and a steam outlet, and
a drainage device comprising: a junction that is disposed downstream of the steam inlet and upstream of the steam turbine; and a drainage device line that connects the junction to the cooling fluid inlet and to a drain,
wherein during normal power operation the steam flows through the valve, through the junction, and into the steam turbine, and the drainage device line leads drainage from the junction toward the drain in a drainage direction, and
wherein during a cooling operation cooling fluid flows from the cooling fluid inlet, through the drainage device line in a direction opposite the drainage direction, to the junction, and then to the steam turbine.
2. The steam turbine unit as claimed in claim 1 ,
further comprising a cooling fluid line from the cooling fluid inlet to the drainage device line through which the cooling fluid flows.
3. The steam turbine unit as claimed in claim 2 ,
wherein the closure member is arranged in the cooling fluid line.
4. The steam turbine unit as claimed in claim 2 ,
wherein a second closure member is arranged in the cooling fluid line.
5. The steam turbine unit as claimed in claim 4 ,
wherein, between the closure member and the second closure member, the cooling fluid line comprises a second junction.
6. The steam turbine unit as claimed in claim 5 ,
wherein the second junction is connected in terms of flow to a second drainage line, and a second drainage device or a steam trap for draining the cooling fluid line is arranged in said second drainage line.
7. The steam turbine unit as claimed in claim 6 ,
wherein the second drainage line is connected in terms of flow to a condenser.
8. A method for cooling the steam turbine unit of claim 1 , the method comprising:
after a power cut-off, performing a cooling operation by conducting the cooling fluid flowing through the cooling fluid inlet, through the drainage device line in the direction opposite the drainage direction, through the junction, and then through the steam turbine while at the same time absorbing heat, through the turbine housing.
9. The method as claimed in claim 8 , wherein the cooling fluid flows via a closure member in a cooling fluid line that connects the cooling fluid inlet to the drainage device line.
10. The method as claimed in claim 9 , further comprising:
arranging a second closure member in the cooling fluid line, and wherein the cooling fluid line between the closure member and the second closure member comprises a second junction,
arranging a second drainage device or steam trap in a second drainage line which is connected in terms of flow to the second junction.
11. The method as claimed in claim 10 ,
wherein the closure member and the second closure member comprise limit switches, and starting of the steam turbine is possible only with closure member closed and second closure member closed.
12. The method as claimed in claim 8 , wherein the cooling fluid comprises air.