Inner casing cooling passage for double flow turbine

1. A turbomachine structure, comprising:

a first inner casing including an inlet for a working fluid, a first flowpath segment, a second flowpath segment, a first axial end, and a second axial end, wherein the first flowpath segment and the second flowpath segment are oriented in opposing axial directions to one another, wherein the inlet is fluidly connected to both the first flowpath segment and the second flowpath segment, wherein the first flowpath segment exits through the first axial end, and wherein the second flowpath segment exits through the second axial end;

a second inner casing surrounding the first inner casing, the second inner casing including a third flowpath segment and a fourth flowpath segment, wherein the third flowpath segment is fluidly connected to the first flowpath segment and the fourth flowpath segment is fluidly connected to the second flowpath segment;

an extraction chamber defined between the first inner casing and the second inner casing adjacent the second axial end;

a cooling passage defined between the first inner casing and the second inner casing and extending from the first axial end to the extraction chamber;

a first extraction port positioned proximate to the first axial end and fluidly connected to the cooling passage and to the first flowpath segment at a location in the first flowpath segment having a first pressure; and

a second extraction port positioned proximate to the second axial end and fluidly connected to the extraction chamber and to the second flowpath segment at a location in the second flowpath segment having a second pressure, wherein the second pressure is less than the first pressure.

2. The turbomachine structure of claim 1 , wherein the working fluid is steam.

3. The turbomachine structure of claim 1 , wherein the first extraction port is defined between the first inner casing and the second inner casing.

4. The turbomachine structure of claim 1 , wherein the first extraction port is positioned within the first inner casing.

5. The turbomachine structure of claim 1 , wherein the second extraction port is defined between the first inner casing and the second inner casing.

6. The turbomachine structure of claim 1 , wherein the second extraction port is positioned within the first inner casing.

7. The turbomachine structure of claim 1 , wherein the first inner casing includes a first upper portion and a first lower portion coupled together, and wherein the second inner casing includes a second upper portion and a second lower portion coupled together.

8. The turbomachine structure of claim 1 , wherein the first inner casing includes at least 50% nickel and the second inner casing includes less than 50% nickel.

9. The turbomachine structure of claim 1 , wherein the first inner casing includes a material resistant to temperatures above 630° C.

10. A turbomachine, comprising:

a rotor configured to rotate around a rotation axis;

a plurality of blades connected to the rotor;

an inner casing enclosing the rotor, the inner casing including:

a first inner casing including an inlet for a working fluid, a first flowpath segment, a second flowpath segment, a first axial end, and a second axial end, wherein the first flowpath segment and the second flowpath segment are oriented in opposing axial directions to one another, wherein the inlet is fluidly connected to both the first flowpath segment and the second flowpath segment, wherein the first flowpath segment exits through the first axial end, and wherein the second flowpath segment exits through the second axial end;

a second inner casing surrounding the first inner casing, the second inner casing including a third flowpath segment and a fourth flowpath segment, wherein the third flowpath segment is fluidly connected to the first flowpath segment and the fourth flowpath segment is fluidly connected to the second flowpath segment;

an extraction chamber defined between the first inner casing and the second inner casing adjacent the second axial end;

a cooling passage defined between the first inner casing and the second inner casing and extending from the first axial end to the extraction chamber;

a first extraction port positioned proximate to the first axial end and fluidly connected to the cooling passage and to the first flowpath segment at a location in the first flowpath segment having a first pressure; and

a second extraction port positioned proximate to the second axial end and fluidly connected to the extraction chamber and to the second flowpath segment at a location in the second flowpath segment having a second pressure, wherein the second pressure is less than the first pressure; and

an outer casing enclosing the inner casing.

11. The turbomachine of claim 10 , wherein the working fluid is steam.

12. The turbomachine of claim 10 , wherein the first extraction port is defined between the first inner casing and the second inner casing.

13. The turbomachine of claim 10 , wherein the first extraction port is positioned within the first inner casing.

14. The turbomachine of claim 10 , wherein the second extraction port is defined between the first inner casing and the second inner casing.

15. The turbomachine of claim 10 , wherein the second extraction port is positioned within the first inner casing.

16. A turbomachine, comprising:

a rotor configured to rotate around a rotation axis;

a plurality of blades connected to the rotor;

an inner casing enclosing the rotor, the inner casing including:

a first inner casing including an inlet for a working fluid, a first flowpath segment, a second flowpath segment, a first axial end, and a second axial end, wherein the first flowpath segment and the second flowpath segment are oriented in opposing axial directions to one another, wherein the inlet is fluidly connected to both the first flowpath segment and the second flowpath segment, wherein the first flowpath segment exits through the first axial end, and wherein the second flowpath segment exits through the second axial end;

a second inner casing surrounding the first inner casing, the second inner casing including a third flowpath segment and a fourth flowpath segment, wherein the third flowpath segment is fluidly connected to the first flowpath segment and the fourth flowpath segment is fluidly connected to the second flowpath segment;

a cooling passage defined between the first inner casing and the second inner casing and extending from the first axial end towards the second axial end;

a first extraction port positioned proximate to the first axial end and fluidly connected to the cooling passage and to the first flowpath segment at a location in the first flowpath segment having a first pressure; and

an injection port positioned proximate to the second axial end and fluidly connected to the cooling passage and to the second flowpath segment at a location in the second flowpath segment having a second pressure, wherein the second pressure is less than the first pressure; and

an outer casing enclosing the inner casing.

17. The turbomachine of claim 16 , wherein the working fluid is steam.

18. The turbomachine of claim 16 , wherein the first extraction port is defined between the first inner casing and the second inner casing.

19. The turbomachine of claim 16 , wherein the first extraction port is positioned within the first inner casing.

20. The turbomachine of claim 16 , wherein the first inner casing includes at least 50% nickel and the second inner casing includes less than 50% nickel.