How a Gas Turbine Generates Electricity  

Materials for Gas Turbines

Recent Developments in Materials for Gas Turbines

Possible Future Developments

How a Gas Turbine Generates Electricity  

How a Gas Turbine Generates Electricity  
(PHOTO)A gas turbine consists of three main segments – (i) compressor (ii) combustor and (iii) turbine. Ambient air is compressed to 11-30 bar pressure and as a consequence its temperature rises. Most of this warm air is used in the combustor to burn the fuel (natural gas or a liquid e.g. oil etc.). The resulting hot gas expands through the turbine, doing work, and exits at nearly atmospheric pressure but a temperature of up to 500-640 °C. Work extracted during the expansion is used to turn the turbine which drives the generator that produces electricity.

The hot exit gas from the turbine still has significant amounts of energy which is used to raise steam to drive a steam-turbine and another generator. This combination of gas and steam cycle gives rise to the term ‘combined cycle gas turbine’ (CCGT) plant.

Materials for Gas Turbines  

Materials for Gas Turbines 

(PHOTO)The gas temperature in the turbine combustor is around 1450-1500 °C, which is close to, if not above, the melting point of commercially viable metals. Therefore, the following measures are taken to ensure turbine components are safe to use throughout their working life. The hot gas is diluted with the compressed air until its temperature drops to an allowable value, which is determined by the strength of the available materials

Components (e.g. turbine blades and vanes) have to be cooled effectively to ensure their safe operation.

Even so, the components like blades and vanes must operate for commercially meaningful lives (typically 5 years or more), at around 80% of the melting point temperature and very high stresses. This demanding duty takes the materials to their limit.

Recent Developments in Materials for Gas Turbines
A reduction in the gas temperature is undesirable because of its adverse effect on the efficiency. However, it is necessary because of the limitations of available materials. Over the last five years there have been a some materials-related innovations which have increased efficiency to up to 60%.

	It has become commercially possible to grow the entire blade, weighing around 15 kg, as a single crystal from the molten metal. The chemistry of these alloys is highly optimised and very closely controlled to ensure optimum performance.
	Reliable coating systems to protect against oxidation and corrosion as well as thermal insulation of blades with a thin ceramic layers.

	High strength engineering ceramics or composites
	Design rules for such materials
	Use of intermetallics

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