Combined cycle Adv. & Disadv.

Main features

- Combined cycle power generation combines 2 cycles for operation, namely the gas

turbine cycle and the vapour power (or steam turbine) cycle.

- In a gas turbine power plant, natural gas and compressed air undergo combustion.

The resultant high pressure gas drives the gas turbine which in turn produces

electricity. Although it is clean and fast in starting up, the gas turbine power plant

suffers from low thermo efficiency of about 25 to 30% (4). Much of the energy is

wasted in the form of gas turbine exhaust.

- The combined cycle power generation makes use of the merits of the high
temperature (1100 to 1650°C) gas turbine cycle and the lower temperature (540 to
650°C) steam turbine cycle (5). The hot exhaust gas from the gas turbine, instead of
being released as waste, is captured and channelled to the steam turbine where

steam is heated by the exhaust to drive the turbine

There are various types of combined cycle power generation : 

- combined cycle with supplementary firing,
- combined cycle with regeneration,
- combined cycle with feedwater heating,
- combined cycle with multipressure steam cycle
- combined cycle for nuclear power plants



Advantages : 

- As most combined cycle generation systems use natural gas as the fuel, the
environmental emissions are low.Transportation of fuel via pipelines is also easier than that of coal and oil.

- It is also cheaper to build a combined cycle power plant than coal, nuclear or renewable energy power plant .

- The combined cycle power generation system also offers quick part-load starting.

- Fast Ramp Rates :  51 MW per minute ramping capability and improved load adjustment capability ..  !!

- To reduce CO2 emissions : above 50 %

Disadvantages : 

- A colorless and an odorless substance, detection of gas leaks can be difficult...

- As natural gas is the fuel used, its higher cost compared to coal and oil will result in higher operating cost ..

- Also, the combined cycle power generation system is a combination of two
technologies, the complexity will result in higher maintenance cost ..and also it will require highly skilled and better trained operating staffs

- The capital cost of a combined cycle power generation plant is higher than that of gas turbine plant

Ref. : http://www.slideshare.net/chillycraps/combined-cycle?from_search=5

Combined Cycle components : 

http://solarcombinedcycle.blogspot.com/2013/10/my-first-search-project-general-notes.html

note : 
http://www.scribd.com/doc/53730177/Combined-Cycle-Gas-Turbine