Integrated cooling air boost compressor and fuel pump

1. A gas turbine engine comprising:

a main compressor section, a combustor, and a main turbine section;

a fuel pump for delivering fuel to said combustor;

a tap for tapping air compressed by said main compressor section, and connected for delivering the tapped air through a first heat exchanger and to a boost compressor, air downstream of the boost compressor being connected to cool at least one rotatable component in said main compressor section or said main turbine section;

air being connected to be delivered to a power turbine, said power turbine being connected to drive both said boost compressor and said fuel pump;

wherein a control is programmed to control at least one valve to vary the amount of air delivered across said power turbine; and

wherein said control provides a greater amount of air to said power turbine at higher power operation of the engine, and reduces the amount of air provided to said power turbine from said greater amount of air at lower power operation, said higher power operation at least includes take-off of an associated aircraft and said lower power operation at least includes cruise of the associated aircraft.

2. The gas turbine engine as set forth in claim 1 , wherein a junction downstream of said first heat exchanger splits the tapped air into a first flow connected to said boost compressor and into a second flow connected to said power turbine.

3. The gas turbine engine as set forth in claim 2 , wherein the at least one valve includes a first valve is located at said junction and is operable to vary the amount of air delivered to said power turbine.

4. The gas turbine engine as set forth in claim 3 , wherein the at least one valve also includes a second valve is positioned downstream of said power turbine and is operable to control the amount of air delivered across said power turbine.

5. The gas turbine engine as set forth in claim 4 , the second valve is selectively moved to increase resistance to air flow and, thus, limit the air flow across the power turbine.

6. The gas turbine engine as set forth in claim 5 , wherein a shaft is connected between said boost compressor and said fuel pump.

7. The gas turbine section as set forth in claim 6 , wherein the control is programmed to control the first and second valves to vary the amount of air delivered across said power turbine.

8. The gas turbine engine as set forth in claim 1 , wherein the at least one valve includes a first valve is located at said junction and is operable to vary the amount of air delivered to said power turbine.

9. The gas turbine engine as set forth in claim 8 , wherein the at least one valve also includes a second valve is positioned downstream of said power turbine and is operable to control the amount of air delivered across said power turbine.

10. The gas turbine engine as set forth in claim 9 , the second valve is selectively moved to increase resistance to air flow and, thus, limit the air flow across the power turbine.

11. The gas turbine engine as set forth in claim 10 , wherein a shaft is connected between said boost compressor and said fuel pump.

12. The gas turbine engine as set forth in claim 11 , the second valve is selectively moved to increase resistance to air flow and, thus, limit the air flow across the power turbine.

13. The gas turbine engine as set forth in claim 12 , wherein a shaft is connected between said boost compressor and said fuel pump.

14. The gas turbine engine as set forth in claim 1 , wherein a second heat exchanger is positioned downstream of said boost compressor, and the air downstream of said second heat exchanger is split between a first flow being connected to cool said at least one rotatable component in at least one of said main compressor section and said main turbine section, and a second flow connected to flow across said power turbine.

15. A gas turbine engine comprising:

a main compressor section, a combustor, and a main turbine section;

a fuel pump for delivering fuel to said combustor;

a tap for tapping air compressed by said main compressor section, and connected for delivering the tapped air through a first heat exchanger and to a boost compressor, air downstream of the boost compressor being connected to cool at least one rotatable component in said main compressor section or said main turbine section;

air being connected to be delivered to a power turbine, said power turbine being connected to drive both said boost compressor and said fuel pump; and

wherein a junction downstream of said first heat exchanger splits the tapped air into a first flow connected to said boost compressor and into a second flow connected to said power turbine.

16. The gas turbine engine as set forth in claim 15 , wherein a first valve is located at said junction and is operable to vary the amount of air delivered to said power turbine, wherein a second valve is positioned downstream of said power turbine and is operable to control the amount of air delivered across said power turbine.