What is Steam Turbine?

 

What is Steam Turbine?

What is Steam Turbine – Description and Characteristics

In general, a steam turbine is a rotary heat engine that converts thermal energy contained in the steam to mechanical energy or electrical energy. 

A steam turbine consists of a boiler (steam generator), turbine, condenser, feed pump, and various auxiliary devices in its simplest form. 

Unlike reciprocating engines, for instance, compression, heating, and expansion are continuous and occur simultaneously. The basic operation of the steam turbine is similar to the gas turbine, except that the working fluid is water and steam instead of air or gas.

Steam Turbine

Since the steam turbine is a rotary heat engine, it is particularly suited to drive an electrical generator. Note that about 90% of all electricity generation in the world is by use of steam turbines. Steam turbine was invented in 1884 by Sir Charles Parsons, whose first model was connected to a dynamo that generated 7.5 kW (10 hp) of electricity. 

The steam turbine is a common feature of all modern and also future thermal power plants. Also, the power production of fusion power plants is based on the use of conventional steam turbines.

Properties of Steam – 

What is steam

Steam is an invisible gas consisting of vaporized water, which is formed when water boils. When steam is visible, it contains the visible mist of water droplets. 

Such steam is referred to as “wet steam”, but “dry steam” is always invisible. At lower pressures, such as in the upper atmosphere or the condenser of thermal power plants, steam can exist at a lower temperature than the nominal 100 °C at standard temperature and pressure.

Since water and steam are common media used for heat exchange and energy conversion, steam is generated largely by energy systems, such as in thermal power plants.  As is typical in all conventional thermal power plants, the heat is used to generate steam which drives a steam turbine connected to a generator that produces electricity. 

Note that modern steam turbines are used to generate more than 80% of the world’s electricity.

Steam is generally categorized according to the vapor/(liquid + vapor) fraction. 

This fraction is a very important parameter of steam, and it is known as vapor quality

There are several types of steam turbines, categorized based on how they expand steam and how they handle pressure and flow. Here's a breakdown of the main types:

🔹 1. Impulse Turbine

How it works: Steam hits the blades at high velocity and impulses the rotor to turn.

Key feature: 

Pressure drops in nozzles only.

Example: 

De Laval turbine, Curtis turbine.

Use: 

Often in small-scale or high-speed applications.

🔹 2. Reaction Turbine

How it works: 

Steam expands gradually as it flows over both fixed and moving blades.

Key feature: 

Pressure drops in both fixed and moving blades.

Example: 

Parsons turbine.

Use: 

Used in most modern power stations.

🔹 3. Condensing Turbine

Exhaust steam is released into a condenser, which maintains low pressure to improve efficiency.

Use: 

In electric power plants to maximize output.

🔹 4. Back-Pressure Turbine

Exhaust steam is used for heating or other processes.

Use: In industrial plants with combined heat and power (CHP).

🔹 5. Reheat Turbine

Steam is expanded in stages and reheated between stages.

Use:

 In high-efficiency power plants to avoid excessive moisture in later stages.

🔹 6. Extraction Turbine

Allows steam to be extracted at intermediate pressures for process use.

Use: 

In industrial processes needing steam at different pressure levels.