Gas turbine cool-down phase operation methods for controlling turbine clearance by adjusting air flow rate

1. A method of operating a gas turbine during a cool-down phase, the gas turbine providing a compressor, a combustor downstream of the compressor, and a turbine downstream of the combustor, the turbine providing a turbine vane carrier, the method comprising:

feeding a flow of cooling air from the compressor to the turbine vane carrier;

measuring a temperature of the flow of cooling air; and

measuring a temperature of the turbine vane carrier;

wherein the flow of cooling air is fed at a first flow rate when the temperature of the turbine vane carrier is lower than the temperature of the cooling air; and

wherein the flow of cooling air is fed at a second flow rate when the temperature of the turbine vane carrier is higher than the temperature of the cooling air,

wherein the first flow rate is higher than the second flow rate.

2. The method of claim 1 , wherein the flow of cooling air is fed from the compressor to the turbine vane carrier through a cooling unit.

3. The method of claim 2 , wherein the flow of cooling air is fed from the compressor to the turbine vane carrier through a once-through cooler.

4. The method of claim 2 , wherein a fan is used to direct the flow of cooling air through the cooling unit.

5. The method of claim 1 , wherein the flow of cooling air is a first flow of cooling air and a second flow of cooling air is also fed from the compressor to the turbine vane carrier; and

wherein the first flow of cooling air is fed from a first point in the compressor and the second flow of cooling air is fed from a second point in the compressor, the first point being downstream from the second point in a fluid flow direction.

6. The method of claim 5 , wherein measuring includes measuring the temperature of the second flow of cooling air; and

the second flow of cooling air is fed at a third flow rate when the temperature of the turbine vane carrier is lower than the temperature of the second flow of cooling air;

wherein the second flow is fed at a fourth flow rate when the temperature of the turbine vane carrier is higher than the temperature of the second flow of cooling air; and

wherein the third flow rate is higher than the fourth flow rate.

7. The method of claim 1 , wherein a clearance within the turbine is monitored, and wherein the flow rate of the flow of cooling air is only altered from the first rate to the second rate when the clearance is below a set minimum clearance.

8. The method of claim 1 , wherein the temperature of the flow of cooling air is measured by directly measuring the temperature of the flow of cooling air, or is measured indirectly by measuring a gas turbine parameter and estimating the temperature of the flow of cooling air.

9. The method of claim 8 , wherein the gas turbine parameter is a temperature of a different gas turbine component or a time since a start of a cool-down phase of the gas turbine.

10. A gas turbine comprising a compressor, a combustor downstream of the compressor, a turbine downstream of the combustor, the turbine providing a turbine vane carrier, and a controller configured and arranged for feeding a flow of cooling air from the compressor to the turbine vane carrier;

measuring a temperature of the flow of cooling air; and

measuring a temperature of the turbine vane carrier;

wherein the flow of cooling air is to be fed at a first flow rate when the temperature of the turbine vane carrier is lower than the temperature of the cooling air; and

wherein the flow of cooling air is to be fed at a second flow rate when the temperature of the turbine vane carrier is higher than the temperature of the cooling air,

wherein the first flow rate is higher than the second flow rate.