Gas Turbines

In a gas turbine, a mixture of air and fuel is heated – through the combustion of the fuel; be it natural gas or renewable gases such as biogas or hydrogen –, reaching very high temperatures, causing the turbine blades to spin. The energy is then converted into electricity through a generator.

The main components of a gas turbine are:

  • Compressor, where the incoming air is compressed and pressurised and fed into the combustion chamber
  • Combustion chamber, where the fuel is injected and ignited, generating a high temperature-pressure gas stream that expands
  • Turbine blades, where the expanding gas is converted into mechanical energy, making them spin and drive a generator to produce electrical energy

Gas turbines can operate with a wide variety of gases and gas qualities. In connection with the progressive replacement of natural gas by low-carbon and renewable gases in the gas pipeline, the gas turbine technology needs to adapt to the use of potentially more challenging gases, such as hydrogen. Hydrogen leads to higher reactivity, which results in increased flame speed, higher autoignition risk due to lower ignition delay time and higher flame temperatures. These aspects primarily affect the combustion performance of the gas turbine – where combustion systems and fuel flexibility need to be analysed and adequately modified as needed. Other areas influenced by these differences in behaviour include materials and lifetime of components as well as health and safety.

There are several different types of gas turbines:

  • Heavy duty gas turbines – with a robust, heavier, and larger frame –, able to operate at highest firing temperatures and have a more defined operating range
  • Aeroderivative gas turbines – based on aircraft engines –, capable of handling load changes with relative ease, including shutting down
  • Industrial gas turbines – with a heavier construction than aeroderivative gas turbines in terms of frame, bearings, and blading –, can provide reliable and efficient electrical or mechanical power
  • Micro-turbines – a simple form of gas turbines, approximately the size of a refrigerator –, can provide power in buildings, such as offices, hotels, hospitals or schools.

Gas power plants may be also called OCGTs or CCGTs, depending on their configuration:

  • Open Cycle Gas Turbines (OCGTs), able to fulfil the highest flexibility requirements with an efficiency up to above 40%. In OCGTs, a stand-alone gas turbine is the central component of the power plant.
  • Combined Cycle Gas Turbines (CCGTs), designed for maximum efficiency and able to reach efficiency levels above 60%. The waste heat from the gas turbine is recovered for producing steam, which then drives an additional steam turbine, generating additional electricity.

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