GAS TURBINE BASED POWER PLANTS (Open Cycle & Combined Cycle)
Refer to text books for addl. points / ideas
For internal circulation only
TURBINES: Machines to extract fluid power from flowing fluids
Steam Turbine Water Turbines Gas Turbines Wind Turbines
Aircraft Engines Power Generation
High Pressure, High Temperature gas Generated inside the engine Expands through a specially designed TURBINE
GAS TURBINE BASED POWER PLANTS
Gas Turbines Invented in 1930 by Frank Whittle
Patented in 1934
First used for aircraft propulsion in 1942 on Me262 by Germans during second world war
Currently most of the aircrafts and ships use GT for propulsion.
Used for power generation
Manufacturers: General Electric, Pratt &Whitney, Rolls Royce, Honeywell, Siemens Westinghouse, Alstom, BHEL.
GAS TURBINE BASED POWER PLANTS
Gas 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.
GAS TURBINE BASED POWER PLANTS
Types of Gas Turbine Power Plants
The gas turbine power plants can be classified mainly into two categories. These are : i). Simple or open cycle gas turbine power plant and ii). Closed cycle gas turbine power plant.
Open Cycle (simple cycle) Gas Turbine Power Plant: In this
type of plant, the atmospheric air is charged into the combustor through a compressor and the exhaust of the turbine is also discharged to the atmosphere.
Combined Cycle Gas Turbine Power Plant: The combined cycle aims at utilizing the heat of exhaust gases from the gas turbine thus, improve the overall plant efficiency. The popular designs are:
1. Heating feed water with exhaust gases. 2. Employing the gasses as combustion air in the steam boiler.
GAS TURBINE BASED POWER PLANTS
Simple Cycle
Operate When Demand is High Peak Demand
Operate for Short / Variable Times
Designed for Quick Start-Up
Not designed to be Efficient but Reliable.
Not Cost Effective
Combined Cycle
Operate for Peak and Economic Dispatch
Designed for Quick Start-Up
Designed to Efficient, Cost-Effective Operation
Types of Gas Turbine Plants
GAS TURBINE BASED POWER PLANTS
Main Components of GT based Plant (Open Cycle)
Inlet system Air Compressor Regenerator Combustion Chamber Gas Turbine Alternator Starting Motor
GAS TURBINE BASED POWER PLANTS
Comp- ressor
air
Combustion Chamber
fuel
Gas Turbine
gases to the stack
Gen
compressed air
hot gases
Gas Turbine Based Power Plant s (Open cycle)
2-2-16
Gas turbine based power plants
Air compressor:
Sucks in air and compresses it, thereby increasing its pressure.
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.
Inlet system: Collects and directs air into the gas
turbine. Often, an air cleaner and silencer are part of the
inlet system. It is designated for a min. pressure drop
while maximizing clean airflow into the gas turbine.
Combustion chamber:
In the combustion chamber, the compressed air combines with fuel and the resulting mixture is burnt. The output power of the gas turbine is directly proportional to the
combustor firing temperature.
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.
Gas turbine based power plants
Gas turbine based power plants
Gas 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.
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.
Gas Turbine Based Power Plants
R. Shanthini 15
Aug 2010
Gas Turbine driving a Jet Engine
Brayton Cycle Gas Turbine Cycle (open cycle) GAS TURBINE BASED POWER PLANTS
Efficiency is 20 to 30% whereas that of steam power
plant is 38 To 40%
Advantages 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 & other accessories as in the case of steam power plants. Gas turbine plants can be used in water scarcity areas. Less pollution and less water is required.
GAS TURBINE BASED POWER PLANTS
Disadvantages 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 (10,000 to 30,000 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.
GAS TURBINE BASED POWER PLANTS
What is a Combined Cycle Power Plant?
A combined cycle system uses the same heat energy
to generate power by using two different
thermodynamic cycles.
The advantage : high overall efficiency of the plant electrical energy out compared with heat energy in is greatly improved over either the simple gas turbine
cycle or simple steam turbine cycle.
This plant uses two distinctly different thermodynamic
cycles to perform useful work (generate electricity).
The Brayton (Gas Turbine) Cycle The Rankine (Steam Plant) Cycle.
GAS TURBINE BASED POWER PLANTS
Combined Cycle: The plant contains a gas and a steam turbine. The hot exhaust gases of the gas turbine
feed a steam generator which supplies a steam turbine. The gas turbine is similar to a large aircraft engine.
Both turbines drive a generator and produce electrical power.
The plant efficiency is high.
CompressorCombustion
Turbine
Cooling Tower
CondenserFeedwater Pump
Hot
Exhaust
Gases
Warm
Exhaust
Gases
Air
Gas/Oil Fuel
Steam
TurbineHeat Recovery
Steam Generator
Steam Line Generator
Gas Turbine (Brayton) Cycle
Steam (Rankine) Cycle
Generator
GAS TURBINE BASED POWER PLANTS
Heat recovery steam generator
Steam turbine plant
Exhaust gas
Life steam
Condensate
Electrical energy
4
9 8
10
Cooling tower
Cooling air
Electrical energy
6 5 1 2 3
Air Fuel
Gas turbine plant
Gas turbine plant:
11
12
7
9
Fresh water
1 Air intake
2 Compressor
3 Gas turbine
4 Heat recovery steam generator
5 Generator
6 Transformer
Steam turbine plant:
7 Steam turbine
8 Condenser
9 Feeding pump
10 Generator
11 Transformer
12 Circulating pump
Schematic of a Combined Cycle Power Plant
GAS TURBINE BASED POWER PLANTS
GAS TURBINE BASED POWER PLANTS
Adv. & Dis-adv. (combined cycle)
Advantages
High efficiency
Less cost per unit (KW) ?
Disadvantages
Complexity
Fuel requirement
GAS TURBINE BASED POWER PLANTS
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).
GAS TURBINE BASED POWER PLANTS
End of Unit 2, Part 2
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