Mid-span gas bearing

1. A centrifugal compressor, comprising:

a rotor assembly including a shaft and a plurality of impellers;

a pair of bearings located at ends of the shaft and configured to support the rotor assembly;

a sealing mechanism disposed between the rotor assembly and the bearings; and

a first gas bearing disposed between the plurality of impellers and configured to support the shaft, the first gas bearing receiving a working gas from an impeller located downstream from a location of the first gas bearing, wherein downstream is relative to a direction of a flow of the working gas.

2. The centrifugal compressor of claim 1 , wherein the first gas bearing is located at a point that is half way between the plurality of impellers in the compressor.

3. The centrifugal compressor of claim 1 , wherein the first gas bearing is located at a point beyond a half way between the plurality of impellers in the centrifugal compressor.

4. The centrifugal compressor of claim 1 , wherein the working gas is one of carbon dioxide, hydrogen sulfide, butane, methane, ethane, propane, liquefied natural gas, or a combination thereof.

5. The centrifugal compressor of claim 1 , wherein the pair of bearings are oil bearings.

6. The centrifugal compressor of claim 5 , wherein an operating surface speed of the first gas bearing is higher than an operating surface speed of the oil bearings.

7. The centrifugal compressor of claim 6 , wherein the operating surface speed of the first gas bearing is at least twice the operating surface speed of the oil bearings.

8. The centrifugal compressor of claim 1 , further comprising:

a filter for purifying the working gas before the working gas is received by the first gas bearing.

9. The centrifugal compressor of claim 1 , further comprising:

a second gas bearing disposed between the plurality of impellers, wherein the second gas bearing is located downstream from the first gas bearing.

10. The centrifugal compressor of claim 1 , wherein the working gas is received by the first gas bearing from an impeller that is one compression stage beyond the first gas bearing.

11. The centrifugal compressor of claim 1 , wherein the working gas is received by the first gas bearing from an impeller that is at least two compression stages beyond the first gas bearing.

12. The centrifugal compressor of claim 1 , wherein the working gas received by the first gas bearing is less than about 0.1% of the working gas flowing through the centrifugal compressor.

13. The centrifugal compressor of claim 1 , wherein the shaft is a single shaft.

14. A method of processing a working gas in a centrifugal compressor, the method comprising:

providing the working gas to an inlet duct of the compressor;

processing the gas through a plurality of compression stages, each stage accelerating the speed of the gas;

bleeding a portion of the accelerated gas after a stage that is downstream from a midway point of the compression stages, wherein downstream is relative to a direction of a flow of the working gas;

providing the bled gas to a gas bearing located between the plurality of compression stages;

reintroducing the gas from the gas bearing to the working gas flowing in the compressor; and

expelling the working gas from an outlet duct of the compressor.

15. The method of claim 14 , further comprising:

filtering the gas that has been bled to remove impurities before providing the gas to the gas bearing.

16. The method of claim 14 , further comprising:

flushing a rotor assembly of the compressor with gas from the gas bearing to remove heat from the rotor assembly.

17. A centrifugal compressor comprising:

a rotor assembly including a shaft and a plurality of impellers;

a pair of bearings located at ends of the shaft and configured to support the rotor assembly;

a sealing mechanism disposed between the rotor assembly and the pair of bearings; and

a plurality of gas bearings disposed between the plurality of impellers and configured to support the shaft,

wherein each of the plurality of gas bearings receives a working gas from a respective impeller located downstream from a location of the gas bearing, and

wherein downstream is relative to a direction of a flow of the working gas.

18. The centrifugal compressor of claim 17 , wherein a number of compression stages between an input of the compressor and a first of the plurality of gas bearings is equal to a number of compression stages between a last of the plurality of gas bearings and an output of the compressor.

19. The centrifugal compressor of claim 18 , wherein a number of compression stages between each of the plurality of gas bearings is equal to the number of compression stages between the input and the first of the plurality of gas bearings.

20. The centrifugal compressor of claim 17 , wherein a first of the plurality of gas bearings receives working gas from an impeller that is downstream of a first of the plurality of gas bearings and upstream of a second of the plurality of gas bearings.