Methods of operating a turbomachine combustor on hydrogen

1. A method of operating a combustor of a turbomachine on a total fuel input that contains a concentration of hydrogen that is greater than about 8000, the method comprising:

injecting, with at least one fuel nozzle, a first mixture of air and a first fuel containing hydrogen into a primary combustion zone of the combustor to generate a first flow of combustion gases having a first temperature;

injecting, with one or more premix injectors disposed downstream of the fuel nozzles, a second mixture of air and a second fuel containing hydrogen into a secondary combustion zone of the combustor as a cross-flow to generate a second flow of combustion gases having a second temperature; and

separately injecting a third fuel as a pure fuel into the secondary combustion zone, the third fuel igniting and mixing with the first flow and the second flow of combustion gases to generate outlet combustion gases having a third temperature.

2. The method as in claim 1 , wherein the third temperature is greater than the first temperature.

3. The method as in claim 1 , wherein the third fuel is injected at an axial location of the one or more premix injectors into the secondary combustion zone.

4. The method as in claim 1 , wherein the third fuel is injected downstream of the one or more premix injectors into the secondary combustion zone.

5. The method as in claim 1 , wherein separating injecting the third fuel as a pure fuel comprises injecting hydrogen gas in a concentration greater than 80% of the third fuel, the balance being natural gas.

6. The method as in claim 5 , wherein the amount of the third fuel injected into the secondary combustion zone comprises up to about 10% of the total fuel input.

7. The method as in claim 1 , further comprising mixing the first flow of combustion gases, the second flow of combustion gases, and the third flow of combustion gases within the secondary combustion zone to generate outlet combustion gases having an outlet temperature.

8. The method as in claim 1 , wherein the combustor comprises an end cover, the at least one fuel nozzle extending from the end cover and at least partially surrounded by a combustion liner, the combustion liner extending from the at least one fuel nozzle toward an aft frame, wherein the combustion liner defines a combustion chamber that includes the primary combustion zone downstream extending from the at least one fuel nozzle to the one or more premix injectors and the secondary combustion zone extending downstream from the one or more premix injectors to the aft frame.

9. The method as in claim 1 , wherein the total fuel input comprises greater than about 80% hydrogen with a remainder of the total fuel input being natural gas.

10. The method as in claim 1 , wherein the first fuel and the second fuel further comprise natural gas.

11. The method as in claim 9 , wherein the outlet temperature is between about 2500° F. and about 3100° F.

12. A method of operating a combustor:

injecting, with at least one fuel nozzle, a first mixture of air and a first fuel into a primary combustion zone of the combustor to generate a first flow of combustion gases having a first temperature;

injecting, with one or more premix injectors disposed downstream of the fuel nozzles, a second mixture of air and a second fuel into a secondary combustion zone of the combustor as a cross-flow to generate a second flow of combustion gases having a second temperature; and

separately injecting a third fuel as a pure fuel into the secondary combustion zone, the third fuel igniting and mixing with the first flow and the second flow of combustion gases to generate outlet combustion gases having a third temperature.

13. The method as in claim 12 , wherein the third temperature is greater than the first temperature.

14. The method as in claim 12 , wherein the third fuel is injected at an axial location of the one or more premix injectors into the secondary combustion zone.

15. The method as in claim 12 , wherein the third fuel is injected downstream of the one or more premix injectors into the secondary combustion zone.

16. The method as in claim 12 , further comprising mixing the first flow of combustion gases, the second flow of combustion gases, and the third flow of combustion gases within the secondary combustion zone to generate the outlet combustion gases having an outlet temperature of between about 2500° F. and about 3100° F.

17. A combustor of a turbomachine configured to operate on a total fuel input that contains at least 80% concentration of hydrogen, the combustor comprising:

at least one fuel nozzle mounted to an end cover and configured to inject a first mixture of air and hydrogen into a primary combustion zone of the combustor;

a combustion liner extending downstream from the at least one fuel nozzle to an aft frame;

one or more premix injectors disposed downstream of the fuel nozzles, the one or more premix injectors coupled to the combustion liner and configured to inject a second mixture of air and hydrogen into a secondary combustion zone of the combustor; and

one or more injectors configured to inject a flow of pure fuel into the secondary combustion zone of the combustor;

wherein the at least one fuel nozzle generates a first flow of combustion gases having a first temperature, the one or more premix injectors generate a second flow of combustion gases having a second temperature greater than the first temperature, and the one or more injectors generate a third flow of combustion gases having a third temperature.

18. The combustor as in claim 17 , wherein the one or more injectors are disposed at an axial location of the one or more premix injectors.

19. The combustor as in claim 17 , wherein the one or more injectors inject pure hydrogen into the secondary combustion zone.