Extracting dry gas from a wet-gas compressor

1. A wet-gas centrifugal compressor, the centrifugal compressor comprising:

a compressor casing;

at least one impeller arranged in the compressor casing for rotation around a rotation axis;

a stationary diffuser arranged in the compressor casing and developing around the impeller, the diffuser having a curved end portion with a radially inner curved wall and a radially outer curved wall; longitudinally, the inner curved wall having a smaller radius of curvature than the outer curved wall; and

a plurality of dry-gas extraction holes, each provided with a respective inlet port, the inlet ports being arranged circumferentially on the inner curved wall of the curved end portion of the diffuser;

wherein each dry-gas extraction hole extends from the respective inlet port towards the rotation axis and is inclined over a radial direction, such that at least at the respective inlet port each dry-gas extraction hole is oriented in a counter-flow direction with respect to a direction of the gas flow in the curved end portion of the diffuser.

2. A wet-gas centrifugal compressor, the centrifugal compressor comprising:

a compressor casing;

a plurality of sequentially arranged impellers, arranged in the compressor casing for rotation around a rotation axis;

a respective stationary diffuser arranged in the compressor casing and developing around each impeller, each diffuser having a curved end portion with a radially inner curved wall and a radially outer curved wall; longitudinally, the inner curved wall having a smaller radius of curvature than the outer curved wall; and

a plurality of dry-gas extraction hole provided with respective inlet ports, the inlet ports being arranged circumferentially on the inner curved wall of the curved end portion of the diffuser of the most downstream impeller;

wherein each dry-gas extraction hole extends from the respective inlet port towards the rotation axis and is inclined over a radial direction, such that at least at the respective inlet port each dry-gas extraction hole is oriented in a counter-flow direction with respect to a direction of the gas flow in the curved end portion of the diffuser.

3. The centrifugal compressor of claim 1 , wherein the curved end portion of the diffuser, where the dry-gas extraction holes are arranged, is in direct fluid communication with a volute arranged and configured for collecting gas from the diffuser and conveying compressed gas towards a delivery duct of the centrifugal compressor.

4. The centrifugal compressor of claim 1 , wherein the dry-gas extraction holes are formed in at least one removable component, mounted on a stationary diaphragm arranged in the compressor casing.

5. The centrifugal compressor of claim 1 , wherein at least some of the dry-gas extraction holes are in fluid communication with a machine component requiring a dry-gas flow.

6. The centrifugal compressor of claim 1 , wherein at least some of the dry-gas extraction holes are in fluid communication with a dry-gas seal skid.

7. The centrifugal compressor of claim 1 , wherein at least some of the dry-gas extraction holes are in fluid communication with at least one dry-gas seal of the centrifugal compressor.

8. The centrifugal compressor of claim 1 , wherein at least some of the dry-gas extraction holes are in fluid communication with at least one active magnetic bearing of the centrifugal compressor and providing a cooling flow to the active magnetic bearing.

9. The centrifugal compressor of claim 1 , further comprising a balancing drum, which is provided with a seal arrangement with at least one shunt hole, wherein at least some of the dry-gas extraction holes are in fluid communication with the at least one shunt hole.

10. The centrifugal compressor of claim 1 , wherein the compressor casing is divided into a first compartment, which houses the impeller(s) of the centrifugal compressor, and a second compartment, which houses an electric motor drivingly connected to the impeller(s) of the centrifugal compressor, the first and second compartments being separated by a separation arrangement; and wherein at least some of the dry-gas extraction holes are in fluid communication with the separation arrangement providing a buffering gas thereto.

11. The centrifugal compressor of claim 10 , wherein the separation arrangement comprises at least one seal and wherein the buffering gas is delivered in or at the seal.

12. The centrifugal compressor of claim 10 , wherein at least some of the dry-gas extraction holes are in fluid communication with the second compartment, for providing cooling dry gas for cooling the electric motor.

13. A method for providing a dry-gas flow to a component in a wet-gas centrifugal compressor comprised of: a compressor casing; at least one impeller arranged in the compressor casing for rotation around a rotation axis; a stationary diffuser arranged in the compressor casing and developing around the impeller, the diffuser having a curved end portion with a radially inner curved wall and a radially outer curved wall; longitudinally, the inner curved wall having a smaller radius of curvature than the outer curved wall; the method comprising the following:

providing a plurality of dry-gas extraction holes, each provided with a respective inlet port, the inlet ports being arranged circumferentially on the inner curved wall of the curved end portion of the diffuser; each dry-gas extraction hole extending from the respective inlet port towards the rotation axis and being inclined over a radial direction, such that at least at the respective inlet port each dry-gas extraction hole is oriented in a counter-flow direction with respect to a direction of the gas flow in the curved end portion of the diffuser;

extracting a dry-gas flow through the dry-gas extraction holes; and

delivering the dry-gas to a component of the centrifugal compressor.

14. A method for providing a dry-gas flow to a component in a wet-gas centrifugal compressor comprised of: a compressor casing; a plurality of impellers arranged in the compressor casing for rotation around a rotation axis; for each impeller, a stationary diffuser arranged in the compressor casing and developing around the respective impeller, each diffuser having a curved end portion with a radially inner curved wall and a radially outer curved wall, in a sectional plane containing the rotation axis the inner curved wall having a smaller radius of curvature than the outer curved wall; the method comprising the following:

providing a plurality of dry-gas extraction holes, each provided with a respective inlet port, the inlet ports being arranged around the rotation axis and on the inner curved wall of the curved end portion of the most downstream one of the diffuser; each dry-gas extraction hole extending from the respective inlet port towards the rotation axis and being inclined over a radial direction, such that at least at the respective inlet port each dry-gas extraction hole is oriented in a counter-flow direction with respect to a direction of the gas flow in the curved end portion of the diffuser;

extracting a dry-gas flow through the dry-gas extraction holes; and

delivering the dry-gas to a component of the centrifugal compressor.

15. The method of claim 13 , wherein the component is selected from the group consisting of: a dry-gas seal; an active magnetic bearing; a balancing drum; a seal; and a compartment containing a motor drivingly connected to the impeller(s) of the centrifugal compressor.

16. The centrifugal compressor of claim 2 , wherein the curved end portion of the diffuser, where the dry-gas extraction holes are arranged, is in direct fluid communication with a volute arranged and configured for collecting gas from the diffuser and conveying compressed gas towards a delivery duct of the centrifugal compressor.

17. The method of claim 14 , wherein the component is selected from the group consisting of: a dry-gas seal; an active magnetic bearing; a balancing drum; a seal; and a compartment containing a motor drivingly connected to the impeller(s) of the centrifugal compressor.

18. The centrifugal compressor of claim 2 , wherein the dry-gas extraction holes are formed in at least one removable component, mounted on a stationary diaphragm arranged in the compressor casing.

19. The centrifugal compressor of claim 2 , wherein at least some of the dry-gas extraction holes are in fluid communication with at least one of: a machine component requiring a dry-gas flow, a dry-gas seal skid, at least one dry-gas seal of the centrifugal compressor, and at least one active magnetic bearing of the centrifugal compressor and providing a cooling flow to the active magnetic bearing.

20. The centrifugal compressor of claim 2 , further comprising a balancing drum, which is provided with a seal arrangement with at least one shunt hole, wherein at least some of the dry-gas extraction holes are in fluid communication with the at least one shunt hole.

21. The centrifugal compressor of claim 2 , wherein the compressor casing is divided into a first compartment, which houses the impeller(s) of the centrifugal compressor, and a second compartment, which houses an electric motor drivingly connected to the impeller(s) of the centrifugal compressor, the first and second compartments being separated by a separation arrangement; and wherein at least some of the dry-gas extraction holes are in fluid communication with the separation arrangement providing a buffering gas thereto.