0 20 40 60 80 100 120 140 160 180 200 220 240 GAS TURBINE-FRAME TYPE-RATED POWER (MW)
Type of Fuel Expected Actual Maintenance .ost Relative Maintenance .ost Factor
Natural gas No. 2 Distillate Oil 0.35 0.49 1.0 1.4
Typical crude Oil No. 6 Residual Oil 0.77 1.23 2.2 3.5
Aero-derivative gas turbines cannot operate on heavy fuels， thus if heavyfuels was a criteria then the frame type turbines would have to be used.认ithheavy fuels， the power delivered would be reduced after about a weeks of operation by about 10%. On-line turbine wash is recommended for turbines with highvanadium content in theirfuel， since to counteract vanadium magnesium salts have to be added. These salts cause the vanadium when combusted in the turbine to be turned to ashes. This ash settles on theturbine blades and reduces the cross sectionalarea， thus reducing the turbine power.
Enclosures
Gas turbines usually come packaged in their own enclosures. These enclos-ures are designed so that they limit the noise to 70dB at a 100ft (30 meters) from the gas turbine. In the case of a combined cycle power plant consistingof the gas turbine， HRSG， and the steam turbine can be either inside oroutside.认hile open plants are less expensive than enclosed plants， some owners prefer to enclose their steam turbines in a building and use perman-ent cranes for maintenance. Thus leaving the gas turbine and the HRSG inthe open environment. In severe climateareas， the entire plant is enclosed in a building. Single-shaft combined cycle power plant with the generator in the middle require a wider building to allow the generator to be moved to facilitate rotor removal and inspection. Plant arrangements that do not use axial or side exhaust steam turbines result in a taller building and higher building costs.
Plant Operation Mode: Base or Peaking
Gas turbines in the petrochemical industries are usually used under baseload conditions powering compressors or pumps. In the power industry， thegas turbine has traditionally been used in peaking service， especially in the
U.S. and Europe. In the developing world， the gas turbine has been used asa base loaded plant since the 1960s. Since the1990s， the gas turbine， beingthe prime mover in combined cycle power plants， has been developed tooperate at high pressures and temperatures， consequently high efficiencies have been achieved. combined cycle power plants are not as were originally planned base loaded plants. It is not uncommon for the plant to be cycledfrom 40-100% load in a singleday， every day of the year. This type of cycling effects the life of many of the hot section components in the gas turbine.
Start-up Techniques
The start-up of a gas turbine is done by the use of electricalmotors， dieselmotors， and in plants where there is an independent source of steam by a steam turbine. New turbines use the generator as a motor for start-up. After combustion occurs and the turbine reaches a certainspeed， the motor declutches and becomes a generator. Use of a synchronous clutch between two rotating pieces of equipment is not new. It is very common in use withstart-up equipment. In the case of single-shaft combined cycle powerplants， a synchronous clutch can be used to connect the steam turbine to the gasturbine. However， use of a clutch in transmitting over 100 M认 of power is new and has not found unequivocal customer acceptance.认hile use ofa synchronous clutch leads to additional space requirements， additional cap-ital and O&M costs， and potentially reduced availability， it does offer the tangible benefit of easy and fast plant startup. A major drawback of a single-shaft combined cycle power plant with a clutch is that the generator installa-tion and maintenance and power evacuation are more complex and costly because the generator is located in the middle.
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