23-11-2012, 01:35 PM
TECHNICAL SEMINAR ON GAS TURBINES
TECHNICAL SEMINAR.pptx (Size: 1.09 MB / Downloads: 71)
Gas Turbines – Introduction
It’s a type of IC Engine
It has an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in-between.
Energy can be extracted in the form of shaft power, compressed air or thrust or any combination of these
Principle
Energy added to Gas stream in Combustor, Where Fuel Mixes with air and Ignited
In the high pressure environment of the combustor, combustion of the fuel increases the temperature.
The products of the combustion are forced into the turbine section.
There, the high velocity and volume of the gas flow is directed through a nozzle over the turbine's blades, spinning the turbine which powers the compressor and, for some turbines, drives their mechanical output.
Three thermodynamic processes. These are isentropic compression, isobaric combustion and isentropic expansion. Together these make up the Brayton cycle.
Types of Gas Turbines
Jet engines
Turboprop engines
Industrial gas turbines for power generation
Compressed air energy storage
Turboshaft engines etc.,
Parts of Gas Turbine
Compressor - Compresses the incoming air to high pressure
Combustion area - Burns the fuel and produces high-pressure, high-velocity gas
Diffuser
Turbine - Extracts the energy from the high-pressure, high-velocity gas flowing from the combustion chamber
Combustion Area
This high-pressure air then enters the combustion area, where a ring of fuel injectors injects a steady stream of fuel. The fuel is generally kerosene, jet fuel, propane or natural gas.
The Turbine
There are 2 sets of Turbines, High Pressure Turbines and Low pressure Turbines.
HP turbine and HP compressor together form
High spool.
The LP Turbine, LP compressor and Turbo fan together form the Low spool.
Advances in Gas Turbines
Development is active in producing both smaller gas turbines and more powerful and efficient engines.
Base materials with superior high temperature strength or thermal barrier coatings that protect the structural material underneath from ever higher temperatures.
On the emissions side, the challenge in technology is increasing turbine inlet temperature while reducing peak flame temperature to achieve lower NOx emissions
Advantages and Disadvantagesof Gas Turbines
Advantages :
Very high power-to-weight ratio, compared to reciprocating engines;
Smaller than most reciprocating engines of the same power rating.
Moves in one direction only, with far less vibration than a reciprocating engine.
Fewer moving parts than reciprocating engines.
Greater reliability, particularly in applications where sustained high power output is required
Waste heat is dissipated almost entirely in the exhaust. This results in a high temperature exhaust stream that is very usable for boiling water in a combined cycle, or for cogeneration.
Low operating pressures.
High operation speeds.
Low lubricating oil cost and consumption.
Can run on a wide variety of fuels.
Very low toxic emissions of CO and HC due to excess air, complete combustion
Disadvantages :
Cost is very high
Less efficient than reciprocating engines at idle speed
Longer startup than reciprocating engines
Less responsive to changes in power demand compared with reciprocating engines