STEAM TURBINE AND APPLICATION

A  device that extracts thermal energy from pressurized stem and

uses it to do mechanical work on rotating output shaft.

Turbine generates rotary motion which is particularly suited

to drive an electrical generator.

The modern manifestation was invented by sir Charles parsons.

About 90% of all electricity generation in US(1996)is by steam turbine.

Some installations use geo-thermal steam or use concentrated solar power to create the steam.

An ideal steam turbine is considered to be an isentropic process

i.e. entropy of the steam entering the turbine is equal to the

entropy of the steam leaving the turbine. Generally, efficiency

ranges from 20% to 90%.

The interior of a turbine comprises several sets of blades. One set

of stationary blades is connected to the casing and one set of

rotating blades is connected to shaft.

TYPES OF STEAM TURBINE

Impulse turbine

A turbine composed of blades alternating with fixed nozzles is

called an impulse turbine.

Blades move entirely due to the impact of steam on them and their

profiles do not coverage this result drop  in steam velocity but no

pressure drops

Reaction turbines or parson’s turbine

A turbine composed of moving nozzles altering with fixed nozzles

is called a reaction turbine.

Nozzles appear similar to blades but their profiles coverage near

the exit. This results in steam pressure drop and velocity increase

as steam moves through the nozzles. Nozzles move due to both the

impact of steam on them and the reaction due to the high

velocitysteam at the exit.

Efficiency

To maximize turbine efficiency the steam is expanded, doing

work, in a number of stages.

Blade efficiency=work done on blade/K. E supplied  to fluid

Turbine blades are arranged in multiple stages in series called

compounding, which greatly improves efficiency at low speeds.

Applications

In 1905 steam turbines were coming into use on a fast moving

ships 

Steam turbine can be used directly to drive large centrifugal

pumps such as feed water pumps at thermal power plants.

They are used in electrical power station.

They are also used in a land-based power application.