1. Gas Turbine Power Plant

2. Advantages
It is simple in design as compared to steam power station since no boilers and their auxiliaries are required.
It is much smaller in size as compared to steam power station of the same capacity. This is expected since gas turbine power plant does not require boiler, feed water arrangement etc.

3. The initial and operating costs are much lower than that of equivalent steam power station.
It requires comparatively less water as no condenser is used.
The maintenance charges are quite small.
Gas turbines are much simpler in construction and operation than steam turbines.
It can be started quickly form cold conditions.
There are no standby losses. However, in a steam power station, these losses occur because boiler is kept in operation even when the steam turbine is supplying no load.

4. Disadvantages
There is a problem for starting the unit. It is because before starting the turbine, the compressor has to be operated for which power is required from some external source. However, once the unit starts, the external power is not needed as the turbine itself supplies the necessary power to the compressor.
Since a greater part of power developed by the turbine is used in driving the compressor, the net output is low.
The overall efficiency of such plants is low (about 20%) because the exhaust gases from the turbine contain sufficient heat.
The temperature of combustion chamber is quite high (3000oF) so that its life is comparatively reduced.

6. Working principle :
Air is compressed(squeezed) to high pressure by a compressor.
Then fuel and compressed air are mixed in a combustion chamber and ignited.
Hot gases are given off, which spin the turbine wheels.

7. Description:
Gas turbines burn fuels such as oil, natural gas and pulverized (powdered) coal.
Gas turbines have three main parts:
i) Air compressor
ii) Combustion chamber
iii) Turbine

9. Air compressor:
The air compressor and turbine are mounted at either end on a common shaft, with the combustion chamber between them.
Gas turbines are not self starting. A starting motor is used.
The air compressor sucks in air and compresses it, thereby increasing its pressure.

10. Combustion chamber:
In the combustion chamber, the compressed air combines with fuel and the resulting mixture is burnt.
The greater the pressure of air, the better the fuel air mixture burns.
Modern gas turbines usually use liquid fuel, but they may also use gaseous fuel, natural gas or gas produced artificially by gasification of a solid fuel.

11. guide the moving gases to the rotor blades adjust its velocity.
Turbine:
Hot gases move through a multistage gas turbine.
Like in steam turbine, the gas turbine also has stationary and moving blades.
The stationary blades
guide the moving gases to the rotor blades
adjust its velocity.
The shaft of the turbine is coupled to a generator.

12. Applications of gas turbine:
drive pumps, compressors and high speed cars.
aircraft and ships.
Power generation (used for peak load and as stand-by unit).

13. Open cycle gas turbine power plant

14. Advantages of gas turbine power plant
Storage of fuel requires less area and handling is easy.
The cost of maintenance is less.
It is simple in construction. There is no need for boiler, condenser and other accessories as in the case of steam power plants.
Cheaper fuel such as kerosene , paraffin, benzene and powdered coal can be used which are cheaper than petrol and diesel.
Gas turbine plants can be used in water scarcity areas.
Less pollution and less water is required.

15. Disadvantages Gas Turbine Power Plant
66% of the power developed is used to drive the compressor. Therefore the gas turbine unit has a low thermal efficiency.
The running speed of gas turbine is in the range of (40,000 to 100,000 rpm) and the operating temperature is as high as 1100 – 12600C. For this reason special metals and alloys have to be used for the various parts of the turbine.
High frequency noise from the compressor is objectionable.

16. Combined Cycle Power Plant

17. Combined Cycle Power Plants
Normally combination of gas turbine and comparatively a smaller capacity steam turbine.
Hot exhaust gases are used to produce steam for running the steam turbine.
Steam generator named as heat recovery steam generator (HRSG) and the plant is named combined cycle Gas turbine power plant (CCGT).
Cogeneration plants are similar but use the recovered steam directly for process needs.
Aimed at increasing efficiency.

18. Principle of operation
Plant turbines works on the principle of a Combined Cycle.
Integrates two power conversion cycles – Brayton cycle (Gas turbines) – Rankine cycle (Conventional Steam power plant).
The Principle – Exhaust of one heat engine (Gas turbine) is used as the heat source for another (Steam turbine) – extracting more useful energy from the heat, increasing the system’s overall efficiency.
The combined cycle gas turbine (CCGT) plant can achieve a thermal efficiency of around 60%, in contracts to a single cycle steam power which is limited to efficiencies of around 35 – 42 %.

19. Block Diagram

20. Heat Recovery Steam Generator
A heat recovery steam generator or HRSG is an energy recovery heat exchanger that recovers heat from a hot gas stream. It produces steam that can be used in a process (cogeneration) or used to drive a steam turbine (combined cycle).
HRSGs consist of four major components: the economizer, evaporator, superheater and water preheater. 

21. Operational Flexibilities

22. Advantages Efficiency is Higher
Capital Cost and operational Cost is Low
Rapid Starting and Stopping – accept load variation quickly – helps in maintaining Stability
Cooling water requirement is much Lower
Self-sustained – no startup Power supply required
Less CO2 emissions.

23. Comparison of the Various Plant

24. Cont…