Controller, for use in a power plant having a liquid cooling system and an air cooling system

1. A controller, for use in a power plant having a liquid cooling system and an air cooling system, comprising:

one or more inputs, configured to receive a signal from at least one deposit sensor, wherein the signal from the deposit sensor is indicative of deposits in the liquid cooling system; and

one or more processors, configured to process the signal received from the deposit sensor to control the air cooling system.

2. A controller as claimed in claim 1 , wherein the signal from the at least one deposit sensor varies with an amount of deposits in the liquid cooling system.

3. A controller as claimed in claim 1 , wherein the signal from the at least one deposit sensor varies with a rate of deposition of deposits in the liquid cooling system.

4. A controller as claimed in claim 1 , wherein the one or more processors are further configured to process the signal received from the one or more deposit sensors to set a control temperature of the liquid cooling system.

5. A controller as claimed in claim 4 , further comprising one or more inputs configured to receive a signal, from a temperature sensor, that is indicative of a temperature of the liquid cooling system, wherein the one or more processors are configured to process the signal received from the temperature sensor to control the air cooling system in dependence upon a difference between the temperature of the liquid cooling system and the control temperature.

6. A controller as claimed in claim 1 , wherein the one or more processors are configured to transmit a signal to operate a valve to control the air cooling system.

7. A power plant comprising:

a liquid cooling system;

an air cooling system;

at least one deposit sensor configured to transmit a signal that is indicative of deposits in the liquid cooling system; and

control circuitry configured to process a signal received from the deposit sensor to control the air cooling system.

8. A power plant as claimed in claim 7 , wherein the liquid in the liquid cooling system is comprised substantially of fuel for the power plant.

9. A power plant as claimed in claim 7 , wherein the power plant further comprises a further liquid cooling system and wherein the liquid cooling system and the further liquid cooling system are configured such that there is heat exchange between them.

10. A power plant as claimed in claim 9 , wherein the liquid in the liquid cooling system is substantially comprised of fuel for the power plant and the liquid in the further liquid cooling system is substantially comprised of oil and wherein the liquid cooling system and the further liquid cooling system are configured such that heat is exchanged from the oil liquid cooling system to the fuel liquid cooling system.

11. A power plant as claimed in claim 9 , wherein the air cooling system is configured to cool the liquid in the further liquid cooling system and wherein the control circuitry is configured to control the amount of cooling of the further liquid cooling system provided by the air cooling system in dependence upon the signal received from the deposit sensor.

12. A power plant as claimed in claim 7 , wherein the deposit sensor comprises a light source and a photocell, wherein the photocell is configured to change its electrical resistance in dependence upon the amount of light received at the photocell.

13. A power plant as claimed in claim 7 , wherein the deposit sensor comprises a light source and a photovoltaic device, wherein the photovoltaic device is configured to produce a voltage dependent upon the amount or type of light received at the photovoltaic device.

14. A power plant as claimed in claim 9 , wherein the control circuitry is configured to process a further signal received from at least one further deposit sensor to control the air cooling system.

15. A power plant as claimed in claim 14 , wherein the further signal varies with an amount of deposits in the further liquid cooling system.

16. A method of cooling a power plant comprising:

receiving a signal indicative of deposits in a liquid cooling system of the power plant; and

controlling an air cooling system of the power plant in dependence upon the received signal.

17. A method as claimed in claim 16 , wherein controlling the air cooling system comprises setting a control temperature for the liquid cooling system.

18. A method as claimed in claim 17 , further comprising:

receiving a signal indicative of the temperature of the liquid cooling system; and

controlling the air cooling system in dependence upon a difference between the temperature of the liquid cooling system and the control temperature.

19. A method as claimed in claim 16 , wherein controlling the air cooling system comprises controlling the amount of air cooling of a further liquid cooling system provided by the air cooling system.

20. A computer program, that when executed by a processor performs the method of claim 16 .

21. A power plant as claimed in claim 7 , wherein the power plant is a gas turbine engine.