Combined cycle power plant

Multiple stage turbine or steam cycles can also be used, but CCGT plants have advantages for both electricity generation and marine power.

[2] In addition the capital costs of combined cycle power is relatively low, at around $1000/kW, making it one of the cheapest types of generation to install.

This has been used since the mid 1970s and allows recovery of waste heat with less total complexity, but at the loss of the additional power and redundancy of a true combined cycle system.

For gas turbines the amount of metal that must withstand the high temperatures and pressures is small, and lower quantities of expensive materials can be used.

The larger plant sizes benefit from economies of scale (lower initial cost per kilowatt) and improved efficiency.

Gas turbines for large-scale power generation are manufactured by at least four separate groups – General Electric, Siemens, Mitsubishi-Hitachi, and Ansaldo Energia.

Hot gas turbine exhaust enters the super heater, then passes through the evaporator and finally through the economiser section as it flows out from the boiler.

[5] In order to remove the maximum amount of heat from the gasses exiting the high temperature cycle, a dual pressure boiler is often employed.

The turbine exhaust is already hot, so a regenerative air preheater is not required as in a conventional steam plant.

However, a fresh air fan blowing directly into the duct permits a duct-burning steam plant to operate even when the gas turbine cannot.

Where the extension of a gas pipeline is impractical or cannot be economically justified, electricity needs in remote areas can be met with small-scale combined cycle plants using renewable fuels.

Instead of natural gas, these gasify and burn agricultural and forestry waste, which is often readily available in rural areas.

These unfired steam cycles are also the lowest in initial cost, and they are often part of a single shaft system that is installed as a unit.

Multishaft systems with supplementary firing can provide a wider range of temperatures or heat to electric power.

Having only one large steam turbine and heat sink has economies of scale and can have lower cost operations and maintenance.

A collection of single shaft combined cycle power plants can be more costly to operate and maintain, because there are more pieces of equipment.

In general, combined cycle efficiencies in service are over 50% on a lower heating value and Gross Output basis.

Some vendors might now utilize single-crystal turbine blades in the hot section, a technique already common in military aircraft engines.

This is achieved by evaporative cooling of water using a moist matrix placed in the turbine's inlet, or by using Ice storage air conditioning.

A typical focus is to combine aerodynamic and chemical computer simulations to find combustor designs that assure complete fuel burn up, yet minimize both pollution and dilution of the hot exhaust gases.

[16] Modern CCGT plants also need software that is precisely tuned to every choice of fuel, equipment, temperature, humidity and pressure.

[citation needed] Nearly 60% LHV efficiency (54% HHV efficiency) was reached in the Baglan Bay power station, using a GE H-technology gas turbine with a NEM 3 pressure reheat boiler, using steam from the heat recovery steam generator (HRSG) to cool the turbine blades.

[citation needed] In May 2011 Siemens AG announced they had achieved a 60.75% efficiency with a 578 megawatt SGT5-8000H gas turbine at the Irsching Power Station.

[17] The Chubu Electric’s Nishi-ku, Nagoya power plant 405 MW 7HA is expected to have 62% gross combined cycle efficiency.

[1] An integrated gasification combined cycle, or IGCC, is a power plant using synthesis gas (syngas).

In ISCC plants, solar energy is used as an auxiliary heat supply, supporting the steam cycle, which results in increased generation capacity or a reduction of fossil fuel use.

The solar component, if the plant is started after sunshine, or before, if there is heat storage, allows the preheat of the steam to the required conditions.

Bottoming cycles producing electricity from the steam condenser's heat exhaust are theoretically possible, but conventional turbines are uneconomically large.

The small temperature differences between condensing steam and outside air or water require very large movements of mass to drive the turbines.

Corrosion of the turbine from the water vapor from the hydrogen flame could reduce plant life or parts may need to be replaced more often.