Modular design of turboexpander components

1. An apparatus comprising:

an electric generator comprising:

a rotor shaft comprising a node position, the node position defining a position of a node of a first bending mode of the rotor shaft;

a turbine wheel coupled to the rotor shaft at the node position that corresponds to the first bending mode of the rotor shaft, the turbine wheel configured to receive process gas and rotate in response to expansion of the process gas flowing into an inlet of the turbine wheel and out of the outlet of the turbine wheel, the rotor shaft configured to rotate with the turbine wheel; and

a stationary stator, the electric generator to generate an alternating current upon rotation of the rotor shaft within the stationary stator.

2. The apparatus of claim 1 , wherein the electric generator comprises a first magnetic bearing at a first position and a second magnetic bearing at a second position, the turbine wheel coupled to the rotor shaft between the first magnetic bearing and the second bearing.

3. The apparatus of claim 2 , wherein the node of the first bending mode of the rotor shaft is proximate to the first position.

4. The apparatus of claim 1 , wherein the rotor shaft comprises a turbine wheel attachment interface compatible with a first turbine wheel comprising a first gas inlet size and a second turbine wheel comprising a second gas inlet size, the first gas inlet size different from the second gas inlet size.

5. The apparatus of claim 1 , the electric generator further comprising a housing assembly comprising:

a main housing supporting the stator;

an inlet funnel removably affixed to a first flange of the main housing; and

an inlet cone disposed within the inlet funnel and removably affixed to the main housing.

6. The apparatus of claim 5 , further comprising:

an outlet funnel removably affixed to a second flange of the main housing; and

an outlet cone disposed within the outlet funnel and removably affixed to the main housing.

7. The apparatus of claim 1 , wherein the turbine wheel is a first turbine wheel, the node of the first bending mode is a first node at a first node position, and wherein:

the rotor shaft comprises a second node of the first bending mode at a second node position on the rotor shaft; and

the electric generator comprises a second turbine wheel coupled to the rotor shaft at the second node position.

8. The apparatus of claim 1 , wherein the turbine wheel comprises a shroud.

9. The apparatus of claim 1 , the electric generator comprising a plurality of electrical outlets, each of the plurality of electrical outlets configured to receive a blanking plate.

10. The apparatus of claim 1 , the rotor shaft comprising a plurality of permanent magnets.

11. A method comprising:

identifying a first bending mode of the rotor shaft;

identifying a node position of the first bending mode on the rotor shaft;

identifying an operational condition for an electric generator;

selecting a turbine wheel, from a plurality of different turbine wheels, based on the operational condition;

coupling the selected turbine wheel to the node position of the rotor shaft of the electric generator; and

providing the electric generator;

wherein coupling the selected turbine wheel to the rotor shaft of the electric generator comprises coupling the selected turbine wheel to the rotor shaft at a location collocated with the node of the first bending mode.

12. The method of claim 11 , wherein the operational condition comprises one or both of a process gas flow rate or a power output rating for the electric generator.

13. The method of claim 11 , further comprising:

selecting an inlet cone and an inlet funnel based on the operational condition;

coupling the selected inlet cone and inlet funnel to a main housing of the electric generator.

14. The method of claim 11 , further comprising:

selecting an outlet cone and an outlet funnel based on the operational condition;

coupling the selected outlet cone and outlet funnel to a main housing of the electric generator.

15. A system comprising:

a flow control valve to control a flow of a process gas; and

an electric generator comprising:

a process gas inlet on a downstream side of the flow control valve to receive process gas into the electric generator,

a rotor shaft comprising a node position, the node position defining a position of a node of a first bending mode of the rotor shaft,

a turbine wheel coupled to the rotor shaft at the node position that corresponds to the first bending mode of the rotor shaft, the turbine wheel configured to receive process gas and rotate in response to expansion of the process gas flowing into an inlet of the turbine wheel and out of an outlet of the turbine wheel, the rotor shaft configured to rotate with the turbine wheel, and

a stationary stator, the electric generator to generate an alternating current upon rotation of the rotor shaft within the stator.

16. The system of claim 15 , wherein the electric generator comprises a first magnetic bearing at a first position and a second magnetic bearing at a second position, the turbine wheel coupled to the rotor shaft between the first magnetic bearing and the second bearing.

17. The system of claim 16 , wherein the node of the first bending mode of the rotor shaft is proximate to the first position.

18. The system of claim 15 , wherein the rotor shaft comprises a turbine wheel attachment interface compatible with a first turbine wheel comprising a first gas inlet size and a second turbine wheel comprising a second gas inlet size, the first gas inlet size different from the second gas inlet size.

19. The system of claim 15 , the electric generator further comprising a housing assembly comprising:

a main housing supporting the stator; and

an inlet funnel removably affixed to a first flange of the main housing.