Gas Turbine_ Combustion Chamber. Mayk

Dr. Eng. Walid Abdelghaffar

Dr. Walid AbdelghaffarGas Turbine: Combustion Chamber

The air leaves the compressor outlet at a velocity of The air leaves the compressor outlet at a velocity of 100 meter per second100 meter per second, but , but the speed of burning fuel at normal mixture ratios is only the speed of burning fuel at normal mixture ratios is only a few meter per a few meter per second.second.Thus, not to blow out the flame, the airflow must be deceleratedThus, not to blow out the flame, the airflow must be decelerated. A region of . A region of low axial velocity and relow axial velocity and re--circulating flow has to be created inside the circulating flow has to be created inside the combustion chamber allowing the flame to remain burning throughocombustion chamber allowing the flame to remain burning throughout the ut the normal engine operating range.normal engine operating range.

Double cone burner

Function PrincipleFunction Principle

Diffuser & Combustion

•14 liners which fuel is added and burned with a portion of the compressed air.

•Connected to turbine by transition pieces.

•Fuel added by fuel nozzles.•Fuel ignited by electric igniters. •Once the fire is started, the combustion process is self–sustaining as long as fuel and air are available.

Combustion

Fuel is continuously injected in to the combustion chamber throuFuel is continuously injected in to the combustion chamber through the burners andgh the burners andcombustion takes place using oxygen in the air supplied by the ccombustion takes place using oxygen in the air supplied by the compressor. Heat isompressor. Heat isreleased and the gas is expanded and accelerated to deliver a smreleased and the gas is expanded and accelerated to deliver a smooth stream ofooth stream ofuniformly heated gas to the turbine for all operating conditionsuniformly heated gas to the turbine for all operating conditions. .

The Combustion ChamberThe Combustion Chamber

The diffuser is located between the compressor section and the main components of the combustion section.

The purpose of the diffuser is to prepare the air for entry into the combustion section.

The front end of the diffuser is bolted to the compressor case

The back end is attached to the combustion section.

Diffuser: Purpose

The diffuser has an expanding internal diameter that looks like an upside down funnel.

This provides additional space, like the air plenum, for the compressed air to expand.

In an operating gas turbine, the point of highest pressure is in the diffuser exit.

Diffuser

Bleed air ports are usually built into the diffuser case.

Some ports are opened and closed automatically to aid in start-up and shutdown.

The primary purpose of the ports is to provide bleed air for:

· cooling internal engine parts· operating engine sensors and controls· preventing compressor surge

Diffuser Bleed Air Ports

The diffuser straightens the flow of air into the combustion section and provides equal distribution to each chamber.

When the air leaves the diffuser, it enters the next main section of the gas turbine, the combustion section.

Diffuser: Airflow

The combustion section is located between the compressor and turbine sections.

The purpose of the combustion section is to add heat energy to the flowing gases.

This addition of heat causes the gases to expand and accelerate into the turbine section.

The hot gases that are generated by burning fuel in the combustion chambers are used to power the turbine and the load.

Combustion Chamber

The main component of the combustion section is the combustion chamber (burner).

A basic combustion chamber consists of the following:

· outer case· perforated inner liner· fuel injectors· source of ignition

Combustion Chamber: Components

Combustion Chamber ( Combustor ) Most of the commonly used combustors or combustion chambers are designed with several main parts and areas so that combustion is continuous and complete

The Parts of the Combustor are- The Combustion Chamber

housing ( Combustor ) is the outside housing

-The Combustion Chamber Liner ( Flame Tubes ) is the inside of the housing

- The Fuel Nozzle ( Fuel Injector, Atomizer, or Vaporizer ) Injects the fuel

- The Igniter Ignites the Fuel/Air Mixture

The outer case forms the shell or chamber in which the combustion process takes place.

The perforated inner liner, also called a combustion liner, is designed to provide paths for compressed air and gases to flow through the chamber for efficient combustion and expansion.

The fuel injectors are located at the inlet of the combustion chamber.

The fuel system supplies clean, pressure-regulated fuel to the combustion chamber where it is mixed with the incoming compressed air from the diffuser.

During start-up, the fuel and air mixture is ignited by a spark plug (source of ignition).

After combustion occurs, the spark plug stops firing.

The burning gases supply the heat energy required to operate the turbine and load.

Coaxial ArrangementCombustion chambers are arranged coaxially (common axis) with the compressor and turbine to allow efficient flow-through operation.

The figure shows a typical combustion chamber arrangement.

Note the location of the spark plugs. Not all combustion chambers have spark plugs. Some are equipped with only crossfire tubes.

To supply the needed source of ignition, the flame from the combustion chamber is carried through a crossfire tube to the next chamber.

It is then used as the source of ignition for the next chamber.

This process continues until all chambers are ignited.

Compressed air enters the combustion chamber, fuel is injected, and the fuel/air mixture is ignited and burned.

The burning or combustion gases expand and travel toward a point of lower pressure at the rear of the chambers. Because high pressure compressed air surrounds the burner on all sides except the rear, the hot, expanding gases are directed toward the turbine section.

Combustion Chamber: Operation

Airflow

To operate efficiently, a combustion chamber must provide:

· means for proper mixing of air and fuel· a way to cool the hot combustion products to a temperature the turbine section components can tolerate.

AirflowTo accomplish these actions, airflow through the combustor is divided into two air paths:

· primary

· secondary

The primary air is approximately 25% of the total air that enters the chamber. Primary air is sent to the fuel nozzle area for combustion.

About half of the primary air flows axially through the front of the combustion liner in the area of the fuel nozzles.

The rest of the primary air enters radially through small holes in the front third of the combustion liner.

All primary airflow supports combustion.

The remaining air that enters the chamber, approximately 75%, is secondary air.

Half of this air provides a cooling air blanket over the inside and the outside surfaces of the combustion liner.

Some of this airflow also centers the flame and keeps it from contacting the combustion liner.

The other half of the secondary air enters the combustion liner toward the rear.

This part of the airflow dilutes the combustion gases to an acceptable temperature to improve the turbine components service life.

The combustion process is accomplished in the first third of the combustion liner.

In the remaining two thirds of the combustion liner, combusted gas and air mix to provide even heat distribution to the turbine nozzle.

Combustion Chambers ( Combustors ) Types

Can Type

Annular Type

Can-Annular Type

H-25 Gas Turbine with DLNC

Dr. Eng. Walid AbdelghaffarTel: (+2) 0104667022

(+203) 5501188Fax: (+203) 5501188

wabdelghaffar@hotmail.comwww.mechaworks.net

Gas Turbine_ Combustion Chamber. Mayk

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turbine section

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combustion

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combustion

spark plugs

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