Below 1000 kW a diesel engine is normally preferred usually because it is an emergency generator running on diesel oil fuel.
There are different types of gas turbine-driven generators. Gas turbines can be classified in several ways, common forms are:-
- Aero-derivative gas turbines.
- Light industrial gas turbines.
- Heavy industrial gas turbines.
Aero-derivative Gas Turbines
Aircraft engines are used as ‘gas generators’, i.e. as a source of hot, high-velocity gas. This gas is then directed into a power turbine, which is placed close up to the exhaust of the gas generator. The power turbine drives the generator.
- Easy maintenance since the gas generator can be removed as a single, simple module. This can be achieved very quickly when compared with other systems.
- High power-to-weight ratio, which is very beneficial in an offshore situation.
- Can be easily designed for single lift modular installations.
- Easy to operate.
- They use the minimum floor area.
Disadvantages of Aero-derivative Gas Turbines
- Relatively high costs of maintenance due to short running times between overhauls.
- Fuel economy is usually lower than other types of gas turbines.
- The gas generators are expensive to replace.
Light Industrial Gas Turbines
Heavy Industrial Gas Turbines
|Heavy Industrial Gas Turbines|
Heavy industrial machines are unsuitable for offshore applications because:-
- Their poor power-to-weight ratio means that the structures supporting them would need to be much larger and stronger.
- Maintenance shutdown time is usually much longer and is inconvenient because the machine must be disassembled into many separate components. A modular concept is not possible in the design of these heavy industrial machines.
- The thermodynamic performance is usually poorer than that of the light and medium machines. This is partly due to the need for low compression ratios in the compressor.