Turbine including seal air valve system

1. A turbine, comprising:

a rotor;

a stator portion;

a fluid bearing for rotatably supporting the rotor;

at least one labyrinth seal configured to seal an annular gap between the rotor and the stator portion;

an air supply conduit system for supplying a stream of air through the annular gap towards the fluid bearing from conduits that feed into the annular gap at first and second positions on opposed sides of the at least one labyrinth seal;

a discharge conduit system for discharging a portion of air supplied by the air supply conduit system from the annular gap between the first and second positions and from the annular gap downstream of both the first and second positions and upstream of the fluid bearing; and

a control system arranged to change an amount of air discharging through the discharge conduit system based on a running condition of the turbine.

2. The turbine according to claim 1 , wherein the control system is adapted to reduce the amount of air discharging through the discharge conduit system when a rotational speed of the rotor is less than an predetermined value.

3. The turbine according to claim 1 , further comprising:

an external compressor for supplying air to the air supply conduit system.

4. The turbine according to claim 3 , wherein the control system is further adapted to change an amount of air supplied by the external compressor to the air supply conduit system.

5. The turbine according to claim 1 , wherein the fluid bearing comprises

a fluid bearing chamber, and

a bearing fluid supply pipe for supplying bearing fluid to the fluid bearing chamber.

6. The turbine according to claim 1 , further comprising:

a turbine compressor comprising plural rotor blades fixed at the rotor at different axial positions, wherein the control system is adapted to supply air taken from an intermediate axial position of the turbine compressor to the air supply conduit system.

7. The turbine according to claim 6 ,

wherein the stator portion encases the fluid bearing chamber wherein the annular gap is in communication with an exit of the turbine compressor as well as with the fluid bearing chamber, the exit of the turbine compressor being arranged downstream of the intermediate axial position.

8. The turbine according to claim 7 , wherein the annular gap is sealed via plural labyrinth seals.

9. The turbine according to claim 7 , wherein the control system is further configured to adjust

an amount of air supplied through the air supply conduit system towards the fluid bearing and

an amount of the air discharged through the discharge conduit system

such that the bearing fluid is prevented from passing through the gap to the turbine compressor exit.

10. The turbine according to claim 1 , wherein the discharge conduit system comprises a first set, a second set, a third set and a fourth set of discharge conduits, the first set and second set being spaced at different axial positions with respect to the fluid bearing in a first axial direction running along a rotation axis of the rotor and the third set and fourth set being spaced at different axial positions with respect to the fluid bearing in a second axial direction opposite to the first axial direction.

11. The turbine according to claim 10 , wherein the first set and the second set of discharge conduits lead to a common discharge conduit and the third set and the fourth set of discharge conduits lead to a further common discharge conduit.

12. The turbine according to claim 3 , wherein the control system comprises a valve arranged in the discharge conduit system.

13. The turbine according to claim 12 , wherein the valve is pneumatically controlled by air supplied by the external compressor.

14. The turbine according to claim 1 , wherein the fluid bearing comprises a fluid bearing chamber such that a thin layer of fluid fills a clearance between a bearing face of the rotor and a bearing face of a stator part of the turbine to support the rotor.