GAS TURBINE

Gas Turbine is a internal combustion engine that extract energy (chemical energy) stored in combustion fuel which is mixed with compressed air to drive a turbine which in turn produces work.

INTRODUCTION

Compressor

compacts and pressurizes the outside air molecules through a series of rotating and stationary compressor blades.

Combustor

In the combustor, fuel is added to the pressurized air molecules and ignited. The heated molecules expand and move at high velocity into the turbine section.

Turbine

The turbine converts the energy from the high velocity gas into useful rotational power though expansion of the heated compressed gas over a series of turbine rotor blades.

Output Shaft & Gearbox

Rotational power from the turbine section is delivered to driven equipment through the output shaft via a speed reduction gearbox.

Exhaust

The engine’s exhaust section directs the spent gas out of the turbine section and into the atmosphere.

4. Gas Turbine – Basic Components

3

- Compressor supply the air needed by turbine. At the same time, turbine supply the power to drive compressor.- Combustor supply the energy for accommodate the losses ( mechanical inefficiencies/ friction/ heat ) to allow a perpetual process to operate

4. Gas Turbine – Perpetual Motion Machine

4

Major application

Gas turbine engine

Aircraft propulsion

Electric power generation

aircraft propulsion

The gas turbine produces just enough power to drive the compressor and a small generator to power the auxiliary equipment. The high-velocity exhaust gases are responsible for producing the necessary thrust to propel the aircraft.

Modern jet engine used to power Boeing 777 aircraft.

Schematic for an aircraft jet engine

Electric power generation ( land base unit)

2 type land-based gas turbine• Aeroderivative gas turbine - a lighter weight unit derived from an aircraft jet engine - most frequently used to drive compressors for natural gas pipelines, power ships and provide peaking and intermittent power for electric utility applications• Industrial @ frame machine - Heavier weight units designed specifically for land uses.

An aeroderivative gas turbineA land-based gas turbine.

Simple-cycle gas turbine1-2 Isentropic compression (in a compressor)2-3 Constant-pressure heat addition3-4 Isentropic expansion (in a turbine)4-1 Constant-pressure heat rejection

1-2 Isentropic compression (in a compressor)2-3 Constant-pressure heat addition3-4 Isentropic expansion (in a turbine)4 Constant-pressure exhaust gases

IDEAL BRAYTON CYCLEHighest temperature

Isentropic compression• Gases are accelerated in centrifugal/ axial compressor.• Air leave the compressor and flow through the diffuser. The divergence duct shape (diffuser)

convert air’s velocity into pressure. • The temperature and pressure increase in compressor & diffuser.

Isobaric combustion• Increase temperature, pressure constant• Air go through the combustion process, and the remaining flow at the side of chamber use for

cooling.

Isentropic expansion• The hot gas expanded and accelerated by nozzle guided vanes before energy is extracted by the

turbine

Isobaric exhaust heat• Energy given up to turbine from the reduction of temperature.• Shaft power output

BRAYTON CYCLE

11

Finished http://www.kengen.co.ke/index.php?page=aboutus&subpage=thermal

• Compressor consists of stages of rotating row of blades that adds velocity energy to the air, followed by a stationery row of blades that converts the velocity energy to a pressure increase.

• the combustion system is designed to provide mixture, burning, dilution and cooling. Thus by the time the combustion mixture leaves the combustion system and enters the turbine at point 3, it is at a mixed average temperature.

• The stationery nozzles of the Turbine have a high-pressure drop across them that convert the high-pressure gases from the combustion system into high velocity jets that impinge against the turbine blades (buckets) that are attached to the turbine rotor. The kinetic energy of the hot gases is converted into useful rotational, mechanical energy by the turbine buckets. This produces the power necessary to meet the load requirements and to drive the axial-flow compressor.

Reduce energy used by air compressor

GAS TURBINE EFFICIENCY

High temperature- Outlet combustors- Inlet turbine

Low temperature for exhaust gas from turbine.

Less pressure drop across - inlet air filters - exhaust gas silencers - ducts - stack

http://www.cospp.com/articles/2005/09/gas-turbine-efficiency.htmlsource13

OPERATION

• Although simple cycle is less efficient than combined cycle, the plant is quicker and cheaper to build and has certain operational advantages. One key advantage of the gas-fired simple cycle plant is its operational flexibility. It can be started up quickly, bringing electricity on-line whenever it is needed. That’s why simple cycle power plants are often used to provide peak load or standby service.

• Function of axial flow compressor :• furnish a large volume of high-pressure air to

the combustion chambers for the production of the hot gases necessary to operate the turbine.

• Only a portion of this air is used for combustion, the remainder is used as dilution air to lower the temperature of the products of combustion and also serves as a source of cooling air for the turbine nozzles, turbine wheels and other portions of the hot gas path

The gas turbine driven by GT generator in order to turn a shaft which powers the compressor

Air is compressed to higher pressure and temperature in the gas compressor

The hot compressed air is expanded through a gas turbine, which drives back the compressor and uses.

Energy is added to the compressed air by gaseous fuel in the combustor.

GAS TURBINE_ OPERATION

The General Electric T700 Gas Turbine Engine

• A gas-turbine with a regenerator (heat exchanger) recaptures some of the energy in the exhaust gas, pre-heating the air entering the combustor. This cycle is typically used on low pressure ratio turbines.

• Gas-turbines with high pressure ratios can use an intercooler to cool the air between stages of compression, allowing you to burn more fuel and generate more power. Remember, the limiting factor on fuel input is the temperature of the hot gas created, because of the metallurgy of the first stage nozzle and turbine blades. With the advances in materials technology this physical limit is always climbing

• Gas generator turbine • - connected directed to compressor• - sole purpse is to drive the compressor

•