Compressor unit with pressure compensator

1. A compressor unit for compressing a process fluid, comprising:

a compressor with an inlet, a compressing stage, and an outlet;

a motor with a stator and a rotor;

a cooling system with a cooling fluid for cooling the motor; and

a pressure compensator,

wherein the cooling system is connected to a first terminal of the pressure compensator in a pressure transmitting way,

wherein a second terminal of the pressure compensator is connected to a point in a flow path of the process fluid flowing from the inlet through the compression stage and through the outlet, and

wherein the pressure compensator establishes a relation between a fluid pressure of the cooling fluid in the cooling system and a process fluid pressure of the process fluid in the flow path of the compressor,

wherein the compressor comprises two compression stages connected in series via a crossover connection, and wherein the second terminal of the pressure compensator is connected to the crossover connection between a first stage and a second stage of the compressor.

2. The compressor unit according to claim 1 ,

wherein the pressure compensator comprises a cell which is partly filled with the process fluid and partly filled with the cooling fluid.

3. The compressor unit according to claim 2 ,

wherein a moveable separation element, which is provided between the cooling fluid and the process fluid, allows establishment of an mechanical equilibrium state between the pressures of the fluids and prevents mixing the fluids.

4. The compressor unit according to claim 3 , wherein the separation element is a piston.

5. The compressor unit according to claim 3 , wherein the separation element is a membrane.

6. The compressor unit according to claim 1 , wherein the motor and the compressor are mutually enclosed by a gas tight casing.

7. The compressor unit according to claim 1 , wherein the compressor and the rotor of the motor are supported by a common shaft, the common shaft being supported by magnetic bearings.

8. The compressor unit according to claim 7 , wherein the magnetic bearings are cooled by the process fluid.

9. The compressor unit according to claim 1 , wherein a gap between the stator and the rotor of the motor is filled with the process fluid and a partition separates the process fluid from the cooling fluid of the cooling system.

10. The compressor unit according to claim 9 , wherein the second terminal of the compensator is connected to the flow path such that the cooling fluid has a higher pressure than the process fluid in the area of the partition.

11. The compressor unit according to claim 9 , wherein the cooling system includes a pump increasing the pressure of the cooling fluid in the stator in order to maintain a higher pressure of the cooling fluid in relation to the process fluid in the area of the partition.

12. The compressor unit according to claim 11 , wherein the cooling system comprises a heat exchanger for cooling the cooling fluid.

13. The compressor unit according to claim 1 , wherein a circulation of the cooling fluid is impelled by natural convection.

14. The compressor unit according to claim 13 , wherein the cooling fluid circulates by principal of a thermal siphon.

15. The compressor unit according to claim 12 , wherein the heat exchanger is located downstream of the pump.

16. The compressor unit according to claim 11 , wherein the pump is located downstream of the connection to the first terminal.