Station design and 4aygut

2.4 Gas turbine stations

Gas turbine stations are a further method of providing generation capacity. Two types of gas turbines are available for this purpose, the acro-engine-derived units employing modified aircraft engines as the gas generators, and a heavy duty or industrial type which is purpose-built for power generation purposes. Both types employ a similar conversion process where high temperature gas at low pressure is expanded in a power turbine which is directly coupled to an electrical generator.

The two types of plant have different performance characteristics. The aero-derived units range in capac­ ity to about 70 MW by utilising up to four separate jet engines to provide the necessary gas flow rates. A par­

of starting. Figure 2.8 shows the CEGB gas turbine station at Cowes, Isle of Wight.

The heavy duty gas turbines have longer starting times, typically about 15 to 20 minutes from cold, but

Chapter 2

have individual capacities ranging up to some 190 MW at the present time. Two such heavy duty units arc installed at the CEGB's Leicester Power Station, see Fig 2.9.

Gas turbine plant utilises a simple generation cycle which, apart from fuel delivery and transmission con­ nections, requires little in the way of site facilities. Such simplicity of cycle leads to the plant being compara­ tively cheap in capital cost terms and fairly cheap to construct.

To achieve peak performance, clean premium fuels strch as natural gas or distillate oil is required, but because of the relatively high cost of these fuels, the overall economics of operation tend to limit their application on the CEGB system to peak lopping or emergency duties. Typical annual load factors of less then 5% are achieved when used in the system support role. Less expensive oil fuels can be used with the heavy duty machines provided pre-treatment is under­ taken to remove some impurities. However, oper­ ational experience tends to be limited and that which is