Fuel delivery system with purge gas step and fuel gas flushing step and method thereof

1. A fuel delivery system for a gas turbine engine, the fuel delivery system comprising:

a first fuel line for connection to a cryogenic fuel tank;

a fuel pump connected to receive fuel via the first fuel line;

a plurality of fuel lines connecting the fuel pump to a combustor of the gas turbine engine;

a controller configured to operate the fuel delivery system;

a purge gas tank connected to the first fuel line and configured to store a purge gas for purging the plurality of fuel lines; and

a fuel gas tank connected to the first fuel line and configured to store a fuel gas for flushing purge gas from the plurality of fuel lines;

a purge gas valve between the purge gas tank and the first fuel line; and

a fuel gas valve between the fuel gas tank and the first fuel line;

an oxygen sensor at an end of the plurality of fuel lines proximate the combustor;

wherein the controller is configured to open the purge gas valve to purge gas from the plurality of fuel lines in a first gas purging procedure, and following the first purging procedure, open the fuel gas valve to flush purge gas from the plurality of fuel lines with fuel gas in a second gas purging procedure;

wherein the controller is configured to operate the fuel delivery system to perform the first gas purging procedure by:

opening valves in the plurality of fuel lines;

opening a vent valve at the end of the plurality of fuel lines;

opening the purge gas valve connecting the purge gas tank to the first fuel line to allow purge gas from the purge gas tank to enter the first fuel line;

determining a level of oxygen at the end of the plurality of fuel lines from the oxygen sensor; and

once the level of oxygen falls below a predetermined level, closing the vent valve and the valve connecting the purge gas tank to the first fuel line.

2. The fuel delivery system of claim 1 , in which the fuel gas is hydrogen and the purge gas is an inert gas.

3. The fuel delivery system of claim 1 , wherein the controller is further configured to open and then close a plurality of vent valves connected along the plurality of fuel lines after closing the first purge gas tank valve.

4. The fuel delivery system of claim 1 , further comprising:

a fuel gas sensor at the end of the plurality of fuel lines proximate the combustor, wherein the controller is configured to operate the fuel delivery system to perform the second gas purging procedure by:

opening valves in the plurality of fuel lines;

opening a vent valve at an end of the plurality of fuel lines proximate the combustor;

opening the fuel gas valve connecting the fuel gas tank to the first fuel line to allow fuel gas from the fuel gas tank to enter the first fuel line;

determining a level of fuel gas at the end of the plurality of fuel lines from the fuel gas sensor; and

once the level of fuel gas rises above a predetermined level, closing the vent valve and the valve connecting the fuel gas tank to the first fuel line.

5. The fuel delivery system of claim 4 , wherein the controller is further configured to open and then close a plurality of vent valves connected to the plurality of fuel lines after closing the valve connecting the fuel gas tank to the first fuel line.

6. The fuel delivery system of claim 1 , wherein the plurality of fuel lines comprises second, third, fourth, fifth and sixth fuel lines, the system comprising:

a recuperator connected to a turbine of the gas turbine engine and connected to receive fuel from the fuel pump via series connected second and third fuel lines;

a vaporiser connected to receive fuel from the liquid fuel pump via series connected second and fourth fuel lines;

a buffer tank having an inlet connected to receive fuel from the recuperator and vaporiser via the fifth fuel line; and

the sixth fuel line connecting an outlet of the buffer tank to the combustor of the gas turbine engine.

7. The fuel delivery system of claim 6 , further comprising a pressure sensor configured to measure a pressure in the buffer tank, wherein the controller is further configured to operate the fuel delivery system to perform an engine start-up procedure by:

cranking the engine;

closing a valve in the third fuel line leading to the recuperator;

opening a valve in the fourth fuel line leading to the vaporiser;

opening valves in the first, fifth and sixth fuel lines;

opening a valve in the first fuel line to allow liquid fuel from the cryogenic fuel tank to flow through the first fuel line to the liquid fuel pump;

operating the liquid fuel pump;

monitoring a pressure in the buffer tank sensed by the pressure sensor;

once the pressure in the buffer tank reaches a threshold value, opening a control valve connecting the sixth fuel line to provide fuel to the combustor; and

igniting the fuel in the combustor.

8. The fuel delivery system of claim 7 , wherein the controller is further configured to operate the fuel delivery system by:

ceasing cranking of the engine;

monitoring a temperature of the recuperator; and

opening the valve in the third fuel line leading to the recuperator once the monitored temperature reaches a threshold value.

9. The fuel delivery system of claim 6 , further comprising:

a first pressure sensor configured to measure a pressure in the buffer tank; and

a second pressure sensor configured to measure a pressure in the first fuel line, wherein the controller is further configured to operate the fuel delivery system to perform an engine shutdown procedure by:

closing a liquid fuel valve between the cryogenic fuel tank and the liquid fuel pump;

closing a control valve between the sixth fuel line and the combustor;

shutting down the liquid fuel pump;

modulating a vent valve connected to the buffer tank to maintain a pressure in the buffer tank; and

when a pressure in the first fuel line measured by the second pressure sensor reaches a pressure in the buffer tank measured by the first pressure sensor, turning off the vaporiser.

10. The fuel delivery system of claim 9 , wherein the controller is further configured to close a valve in the fifth fuel line and open vent valves in third and fourth fuel lines.

11. The fuel delivery system of claim 9 , wherein the controller is further configured to open the pressure relief valve connected to the buffer tank until a pressure measured in the buffer tank reaches a threshold.

12. A method of operating a gas turbine engine fuel delivery system, comprising:

purging gas from a plurality of fuel lines connecting a fuel pump to a combustor of the gas turbine engine with a purge gas in a first gas purging procedure, wherein the first gas purging procedure comprises

opening valves in the plurality of fuel lines;

opening a vent valve at the end of the plurality of fuel lines;

opening a valve connecting the purge gas tank to the first fuel line to allow purge gas from the purge gas tank to enter the first fuel line;

determining a level of oxygen at the end of the plurality of fuel lines; and

once the level of oxygen falls below a predetermined level, closing the vent valve and the valve connecting the purge gas tank to the first fuel line; and

following the first gas purging procedure, flushing purge gas from the plurality of fuel lines with a fuel gas in a second gas purging procedure.

13. The method of claim 12 , in which the fuel gas is hydrogen and the purge gas is an inert gas.

14. The method of claim 12 , wherein the second gas purging procedure comprises:

opening valves in the plurality of fuel lines;

opening a vent valve at an end of the plurality of fuel lines proximate the combustor;

opening a valve connecting the fuel gas tank to the first fuel line to allow fuel gas from the fuel gas tank to enter the first fuel line;

determining a level of fuel gas at the end of the plurality of fuel lines from the fuel gas sensor; and

once the level of fuel gas rises above a predetermined level, closing the vent valve and the valve connecting the fuel gas tank to the first fuel line.

15. A fuel delivery system for a gas turbine engine, the fuel delivery system comprising:

a first fuel line for connection to a cryogenic fuel tank;

a fuel pump connected to receive fuel via the first fuel line;

a plurality of fuel lines connecting the fuel pump to a combustor of the gas turbine engine;

a controller configured to operate the fuel delivery system;

a purge gas tank connected to the first fuel line and configured to store a purge gas for purging the plurality of fuel lines; and

a fuel gas tank connected to the first fuel line and configured to store a fuel gas for flushing purge gas from the plurality of fuel lines;

a purge gas valve between the purge gas tank and the first fuel line; and

a fuel gas valve between the fuel gas tank and the first fuel line;

a fuel gas sensor at the end of the plurality of fuel lines proximate the combustor;

wherein the controller is configured to open the purge gas valve to purge gas from the plurality of fuel lines in a first gas purging procedure, and following the first purging procedure, open the fuel gas valve to flush purge gas from the plurality of fuel lines with fuel gas in a second gas purging procedure;

wherein the controller is configured to operate the fuel delivery system to perform the second gas purging procedure by:

opening valves in the plurality of fuel lines;

opening a vent valve at an end of the plurality of fuel lines proximate the combustor;

opening the fuel gas valve connecting the fuel gas tank to the first fuel line to allow fuel gas from the fuel gas tank to enter the first fuel line;

determining a level of fuel gas at the end of the plurality of fuel lines from the fuel gas sensor; and

once the level of fuel gas rises above a predetermined level, closing the vent valve and the valve connecting the fuel gas tank to the first fuel line.

16. The fuel delivery system of claim 15 , wherein the plurality of fuel lines comprises second, third, fourth, fifth and sixth fuel lines, the system comprising:

a recuperator connected to a turbine of the gas turbine engine and connected to receive fuel from the fuel pump via series connected second and third fuel lines;

a vaporiser connected to receive fuel from the liquid fuel pump via series connected second and fourth fuel lines;

a buffer tank having an inlet connected to receive fuel from the recuperator and vaporiser via the fifth fuel line; and

the sixth fuel line connecting an outlet of the buffer tank to the combustor of the gas turbine engine.

17. The fuel delivery system of claim 16 , further comprising a pressure sensor configured to measure a pressure in the buffer tank, wherein the controller is further configured to operate the fuel delivery system to perform an engine start-up procedure by:

cranking the engine;

closing a valve in the third fuel line leading to the recuperator;

opening a valve in the fourth fuel line leading to the vaporiser;

opening valves in the first, fifth and sixth fuel lines;

opening a valve in the first fuel line to allow liquid fuel from the cryogenic fuel tank to flow through the first fuel line to the liquid fuel pump;

operating the liquid fuel pump;

monitoring a pressure in the buffer tank sensed by the pressure sensor;

once the pressure in the buffer tank reaches a threshold value, opening a control valve connecting the sixth fuel line to provide fuel to the combustor; and

igniting the fuel in the combustor.

18. The fuel delivery system of claim 17 , wherein the controller is further configured to operate the fuel delivery system by:

ceasing cranking of the engine;

monitoring a temperature of the recuperator; and

opening the valve in the third fuel line leading to the recuperator once the monitored temperature reaches a threshold value.

19. The fuel delivery system of claim 16 , further comprising:

a first pressure sensor configured to measure a pressure in the buffer tank; and

a second pressure sensor configured to measure a pressure in the first fuel line, wherein the controller is further configured to operate the fuel delivery system to perform an engine shutdown procedure by:

closing a liquid fuel valve between the cryogenic fuel tank and the liquid fuel pump;

closing a control valve between the sixth fuel line and the combustor;

shutting down the liquid fuel pump;

modulating a vent valve connected to the buffer tank to maintain a pressure in the buffer tank; and

when a pressure in the first fuel line measured by the second pressure sensor reaches a pressure in the buffer tank measured by the first pressure sensor, turning off the vaporiser.

20. The fuel delivery system of claim 19 , wherein the controller is further configured to open the pressure relief valve connected to the buffer tank until a pressure measured in the buffer tank reaches a threshold.