STEAM AND GAS TURBINES….!

ANKIT GUPTA,4JC13ME007ROLL NO: 07

Turbines• A turbine is a rotary engine that exerts

energy from a fluid flow and converts it into useful work.

There are two basic types of turbines according to the mode of steam.

1. Impulse turbine2. Reaction turbine

Impulse turbineWorking principleIt runs by impulse of steam.Nozzle directs the steam on the curved

blades, which causes them to rotate.The blades are in the shape of buckets.

The energy to rotate an impulse turbine is derived from the kinetic energy of the steam flowing through the nozzle.

The potential energy is converted into kinetic energy when it passes through the nozzle.

The velocity of steam is reduced when it passes over the blades.

In an Impulse turbine, the whole of the available energy of the fluid is converted to Kinetic Energy before the water acts on the moving parts of the turbine.

Pelton Wheel is an example of Impulse turbine.

Pelton Wheel (Impulse Turbine)

Pelton Wheels in a hydroplant

Components in a Pelton Wheel

Water is blasted at these cups by one or more jets mounted in the surrounding casing. Momentum is transferred from water to cups, and a torque is created, causing the wheel to rotate.

This type of turbine is highly efficient.

Reaction turbineWorking principle It has no nozzle.Two rows of moveable blades are separated by one row of

fixed blades.Fixed blades are attached to the casing & act as nozzles.Blades are like the wings of a plane.

Velocity of steam is increased when it passes through the fixed blades.

The enthalpy drop in moving blades is called degree of reaction.

A common arrangement can have 50% of enthalpy drop in moving blades, it is said to have 50% reaction.

If all enthalpy drops in moving blades then it is said to be 100% reaction.

There are two main types of Reaction Turbine – Francis and Kaplan Turbines.

Sectional and Top View of a Francis Reaction Turbine

Francis Turbine

A Francis turbine runner, rated at nearly one million hp (750 MW), being installed at the Grand

Coulee Dam, United States.

Sectional View of a Kaplan Reaction Turbine

Various types of water turbine runners. From left to right: Pelton Wheel, two types of Francis Turbine and Kaplan Turbine

Pressure velocity graph of impulse and reaction turbines.

Difference between impulse and reaction turbine S.NO Impulse turbine Reaction turbine 1.

The steam flows through the nozzle and impinges on the moving blades.

The steam first flows through the guide mechanism and then through the moving blades.

2.

The steam impinges on the buckets with kinetic energy.

The steam glides over the moving vanes with pressure and kinetic energy.

3.The steam may or may not be admitted over the whole circumference.

The steam pressure is reduced during its flow through the moving blades.

4. The blades are symmetrical The blades are not

symmetrical

Euler Head and Efficiencies of Hydraulic Turbines

Efficiency of turbines is a function of the available head.Euler's Head: It is defined as energy transfer per unit

weight.

Hydraulic Efficiency - It is the ratio of power developed by the runner to the head of water (or energy) actually supplied to the turbine i.e.

Mechanical Efficiency - It is the ratio of actual work available at the turbine shaft to energy imparted to the wheel.

Overall Efficiency – The overall efficiency is based on the useful work output divided by the water power input.

EfficiencyTo maximize the efficiency of steam turbine

the steam is expanded, generating work in a number of stages.

Multiple stages turbines are highly efficient.Most steam turbines use a mixture of both

impulse and reaction design.Higher pressure sections are impulse type

and lower pressure sections are reaction type.

Advantages of steam turbineIt can develop higher speeds.The steam consumption is less.All the parts are enclosed in a casing so it is

safe.It requires less space and lighter foundations.There is very less friction in the turbine due

to few sliding parts.

UsesTurbines are used in force draft blowers,

pumps and main propulsion turbines.Used in the jet engines and air crafts.They are also used in power plants , ships

and submarines.

The working principle of a gas turbine also known as ‘ Internal Combustion Turbine ’ is similar to a steam turbine, but its working fluid is the products of combustion of fuel with air instead of steam.

A simple gas turbine consists of an air compressor combustion chamber and a turbine. The function of the air compressor is to compress the air required for combustion.

The fuel is burnt in the combustion chamber and the combustion products flow through the turbine. The function of the turbine is to convert the heat energy into mechanical work.

GAS TURBINES AND ITS TYPES:

In this type of turbine, the compressed air from an air compressor C admitted into the combustion chamber A through the valve U.

When the valve U is closed, the fuel admitted into the chamber is ignited by means of a spark plugs.

The combustion takes place at CONSTANT VOLUME with increase of pressure.

The valve V opens and the hot burning gases flow to the turbine T and finally they are discharged into the atmosphere.

The energy of hot gases is thereby converted into mechanical work. These operations are repeated for running the Turbine.

CONSTANT VOLUME GAS TURBINE :

The compressor C is coupled with a turbine shaft and it is driven by the turbine T. Air taken from the atmosphere is compressed by the compressor to a high pressure.

The compressed air then flows into the combustion chamber M where the fuel is injected y means of a pump P..

The fuel burns at CONSTANT PRESSURE and the hot gases flow through the turbine and finally discharged into the atmosphere.

CONSTANT PRESSURE GAS TURBINE:

CONSTANT PRESSURE GAS TURBINE :

It is suitable where the supply of water is a difficult problem.

Water required for a steam turbine imposes a serious problems,when it is used as a portable engine.Even in ships, when it is floating over a vast amount of water it produces much difficulty as sea water is not suitable for the engine.

A steam turbine requires a boiler for supply of steam and it therefore requires additional space than what is required by a gas turbine.

THE ADVANTAGES OF GAS TURBINES OVER STEAM TURBINES:

THANK YOU…..!