Gas Turbine

It obtains its power by utilizing the energy of burnt gases and air which is at high temp and pressure by expanding through the several ring of fixed and moving blades.

• It is similar to Steam Turbine but it uses Gas instead of Steam.
• Turbine drives the compressor (as they are coupled to each other by a shaft).
• Compressor absorbs power produced by turbine (lowers efficiency).
• Compressor utilizes 40-45% of total power produced by Turbine. 
• A simple gas turbine cycle consists of:
• Compressor 
• Combustion Chamber 
• Turbine

Steps:

Inlet (air comes in)  →  Compressed to a very high pressure (by compressor, Cpair)  →  which goes to combustion chamber where it burns (Cpgas)  →  produce combustion gases  →  hit turbine blades  →  it starts rotating  →  electricity produce  →  flue gases leaves the gas turbine.

Limitations:

• When burning not started, compressor is run by an external source.

Applications: 

• To power all aircrafts.
• Mechanical equipment (pumps, compressors, generators). 

Advantages:

• Small size, mass and initial cost per unit output.
• Quick starting (as low as 10 Seconds) or Remote Control.
• It uses variety of liquids/gases fuels including gasified coal, synthesis fuels.

Disadvantages:

• Large compressor work input.

Brayton Cycle

It is the Ideal cycle for Gas Turbine Engines.

Notes:

1. Common design, pressure ratio of gas turbines (rp) ranges from 11 to 16.
2. In gas turbine powerplants, "Ratio of Compressor Work to Turbine Work is called Back Work Ratio" is very high.

Mostly,    

                          Compressor Work Output  =  0.5 x Turbine Work Output

Types of Gas Turbines

1. Open Cycle Gas Turbine  →  No Condenser (Cooler/Heat Exchanger), less efficient, greater emissions.
2. Closed Cycle Gas Turbine  →  Have Condenser.

Combined Cycle Power Plant

It couples two power cycles such that the energy discharged by heat transfer from one cycle is used partly as the input for the other cycle.

• Temperature in a dry bottom cycle does not exceed 600℃ (Exit Boiler Temp).
• High thermal irreversibility and a decrease in availability because of heat transfer from combustion gases to steam through such a large temp difference.

Types of Combined Cycle Power Plant

1. Gas Turbine-Steam Turbine Power Plant (GT-ST Power Plant)
2. Gas Turbine-Stirling Engine Power Plant
3. Diesel-Steam Turbine Power Plant (mostly in Textile Industry)

GT-ST Combined Cycle Power Plant With Supplementary Fuel Combustion

Major components used in GT-ST Power Plant:

• Gas Turbine 
• Heat Recovery Steam Generator (HRSG)
• Steam Turbine 
• Brayton Cycle is at the Top (High temp gas turbine power plant) while Rankine Cycle is at the bottom (Lower temp steam turbine power plant).
• Steam Turbine utilizes the energy from the gas turbine exhaust as its input.
• If temperature of the exhaust gas from GT is not up to mark (for desired power output), we use combustion chamber called Supplementary Combustion of Fuel.

Note:

• Gas Turbine Components
• Roll Royce Turbojet Engines
• Jet Engine Thrust Test
• Gas Turbine Different Tests

References:

• Material from Class Lectures + Book named Power plant Engineering by P.K Nag (4th Edition) + My knowledge. 
• Photoshoped pics are developed. 
• Some pics and GIF from Google.  
• Videos from YouTube (Engineering Sights).