Steam Turbine Industry Analysis: Types & Applications

A steam turbine is a device that extracts thermal energy from pressurized steam and utilizes it to do mechanical work on a rotating shaft. Over the years, the model of a steam turbine has modified a lot to meet the ever changing demands from industries. A steam turbine is powered by the hot and gaseous steam and works like a cross between a wind turbine and a water turbine. Similar to a wind turbine, it has revolving blades that move when steam blows past them and like a water turbine, the blades fit securely inside a closed outer container so the steam is controlled and forced past through them at a high speed. Steam turbines use pressurized steam to turn electricity generators at a very high speed, so they rotate much faster than either wind or water turbines.

Types of Steam Turbines:

Modern steam turbines are broadly classified into:

•Impulse Turbines

In this type of turbine, the heated steam is projected at a very high velocity from fixed nozzles in the casing. When the steam hits the blades or sometimes buckets, it causes the turbine shaft to rotate. Thus, in this type of steam turbine, the rotor spins due to the force, or the direct push of steam on the blades. The high pressure and intermediary pressure stages of a steam turbine are usually of this type.

•Reaction turbines

In this type of steam turbine, the steam passes through the fixed blades via the rotor blades nozzles causing a reaction and rotating the turbine shaft. This type of steam turbine works on the principle that the rotor rotates from a reaction force rather than an impulse force. The low-pressure stage of a steam turbine is typical of this type. The steam having already expanded through the previous stages of the turbine is now of low pressure and temperature, ideally suited for a reaction turbine.

Although steam turbines are primarily of two types, steam turbine industry analysis highlights that there are numerous other mechanical arrangements, which include reheat steam turbines, single casing turbines, tandem steam turbines, condensing & exhaust steam turbines, cross compound steam turbines and axial & radial flow steam turbines.

Impulse versus Reaction:

An impulse turbine utilizes, the force of steam and to a lesser extent, a reactive force when the curved blades cause the steam to change its direction and pressure. While in a reaction turbine, a rotor is moved by a reactive force and again to a lesser extent, some of the rotation is caused by the impulse force of the steam hitting the blades.

The principle of working and construction:

An ideal steam turbine is regarded as an isentropic process, in which the entropy of the steam entering inside the turbine is equal to the entropy of the steam exiting the turbine. However, as per the steam turbine market trends, no steam turbine is truly isentropic and typical isentropic efficiencies of the turbines are ranging from 20% to 90%, based on the application. A steam turbine is essentially an engine, where the energy of working fluid or gas is directly used to rotate the turbine blades. In the turbine, the working fluid undergoing a process of expansion, pressure drop and moves continuously. Steam turbine classification is done on the basis of steam flow direction, steam pressure, working principle and exit steam.

In terms of construction, the steam turbine system consists of various components including compressors, boilers, condenser, combustion chamber, pumps, and turbine. Steam turbines are used in several industries including power generation, aircraft, telecommunications and others.

Advantages of the steam engine:

•Very high power to mass ratio when compared with other reciprocating engines.
•Smaller in size than most of the reciprocating engines of the same power rating.
•Moves in one direction only, with far less vibration than other turbines.
•Fewer moving parts thus requires less maintenance.
•Greater reliability, especially in applications where persistent high power output is required
•Waste heat is dissipated almost entirely from the exhaust and this high-temperature exhaust can be utilized for boiling water in a combined cycle, or for cogeneration.
•Low operating pressures and temperature.
•High operating speeds
•Can work on a wide range of fuels.
•Low toxic emissions of hydrocarbon and carbon monoxide, because of excess air, complete combustion and no quenching on cold surfaces.

Disadvantages of the steam engine:

•Less efficient than other reciprocating engines at idle speeds.
•Longer starting process than the reciprocating engines.
•Lesser responsiveness to changes in power demand, when compared with other engines.
•Characteristic noise can be hard to remove.

Future Prospect of the steam engine:

The future of steam turbine technology lies in its ability to increase the capacity and efficiency. Nuclear fission will continue to compete with conventional fuel combustion for the production of steam for the turbine. But the most vital part is the technological change that is to be done in order to make it more environmentally friendly and to meet the ever-changing demands of various industries.