Page 391 - Advanced thermodynamics for engineers

CHAPTER
17
GAS TURBINES

Gas turbines have a number of distinct characteristics which make them attractive for certain
applications:
• low weight;
• low basic volume;
• low vibration level;
• low noise output;
• good multi-fuel capability;
• rapid start-up and load changes.
However, at present they have a major drawback to general use which is poor fuel consumption
(relative to the diesel engine), particularly at part-load conditions.
This has resulted in gas turbines finding application in certain well-defined areas, viz.:
• aircraft;
• high-performance ships;
• off-peak power generation – although hardly used;
• oil rigs.
All these applications have a common factor of high power/weight (power density) or power/bulk
ratio. Another application is the combined cycle gas turbine (CCGT) for power generation. In this
cycle a gas turbine is used as the first stage of a two stage power generator, with a steam turbine being
used as the next – bottoming – stage. This type of plant has a number of advantages over the more
traditional steam turbine, and these include the following:
• lower first cost;
• faster construction time;
• less SO x production because of natural gas fuel;
• faster warm-up time when coming on load;
• higher thermal efficiency;
• better part-load efficiency.
It is also presaged that the next generation of intercooled regenerated (ICR) gas turbines will
compete in terms of fuel consumption with low-speed diesel engines in marine propulsion. The current
minimum size of this plant does not bring them into the diesel engine power envelope at present.

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