The Complete Guide to Steam Turbine

What is a Steam Turbine?

Steam turbines are one of the first and most accomplished prime mover technologies persisting in general applications. They drive countless machines and generate power in numerous plants worldwide. Steam turbines have been in employment for more than 120 years when they replaced reciprocating steam engines because of their greater efficiencies and economic costs. The capacity of a steam turbine can vary from 20 kilowatts to several hundred megawatts (MW) for huge drivers.

A steam turbine is a sort of heat engine that receives much of its increase in thermodynamic efficiency from multiple stages in expanding the steam, which ends in a closer approach to the ideal reversible expansion process. Because the turbine produces rotary motion, it is expressly befitted to be employed to drive an electrical generator. In this regard, roughly 85% of all electricity production in the United States in 2014 was by use of modern steam turbines. A steam turbine joined to an electric generator is called a turbo generator.

A steam turbine is utilized to provide the maximum amount of mechanical power, applying the minimum amount of steam in a compact driver configuration, regularly in a direct-drive arrangement. Speed variation or speed adjustment abilities are also crucial for steam turbines. Currently, steam turbines are extensively used in diverse driver applications for power generation units and mechanical drives and generate nearly 1 million (MW) of capacity worldwide.

What is Steam Turbine Types?

The two main types of steam turbines most extensively employed are the backpressure and the extraction-condensing types. The decision between the selection of backpressure turbine and extraction-condensing turbine depends principally on the economic factors, quantities of power and heat, and quality of heat. The steam extraction points from the turbine could be more than one, mostly depending on the temperature levels of heat needed by the processes.

Backpressure turbine: The backpressure turbine is utilized for providing process steam to the facilities in private-use power generators. This type of steam turbine fulfills not only electricity but also steam to several process requirements.

Extraction-condensing turbine: Extraction-condensing turbines are used when steady power generation and steam extraction at a solid pressure are required. Based on the plant requirements of the client, more than one type of extraction can be received from the steam turbine for processes in the plant. Extraction pressure is regulated internally in the turbine, providing a wide range of extraction flow rates. Extraction can also be performed within a wide range of operating load points.

What is Steam Turbine Working Principles?

In plain terms, a steam turbine operates by employing a heat source (e.g., coal, gas, oil, nuclear, solar) to heat water to remarkably high temperatures until it is transformed into steam. As that steam flows past the spinning blades of a turbine (which is called a rotor), the steam expands and, as a result of losing energy, cools. The potential energy of the steam is therefore transformed into kinetic energy in the rotor. Because steam turbines produce rotary motion, they are expressly suited for inducing electrical generators for electrical power generation. The turbines are joined to a generator with an axle, which in turn creates energy via a magnetic field that generates an electric current.

The blades of a steam turbine are intended to control the velocity, direction, and pressure of the steam as it crosses through the turbine. For modern massive turbines, there are tens of blades connected to the rotor, typically in various sets. Each set of blades helps obtain energy from the steam while also preserving the pressure at optimal levels.

This multi-stage approach indicates that the turbine blades diminish the steam pressure by very tiny increments during each stage. This, instead, reduces the forces on them and considerably increases the overall output of the turbine.

What is Steam Turbine Advantages and Disadvantages?

Advantages

Steam turbines have numerous advantages, such as:

• Since the steam turbine is a rotary heat engine, it is especially suited to drive an electrical generator.
• The very high power-to-weight ratio, in comparison with reciprocating engines.
• The thermal efficiency of a steam turbine is normally higher than that of a reciprocating engine.
• Steam turbines have fewer moving parts than reciprocating engines.
• Generally, steam contains a high amount of enthalpy (especially in the form of heat of vaporization). This means lower mass flow rates compared to gas turbines.
• Steam turbines are proper for large thermal power plants. They are made in various sizes up to 1.5 GW (2,000,000 hp).
• Steam turbines have more superior reliability, individually in applications where sustained high power output is needed.
• In general, a turbine runs in one direction only, with far more limited vibration than a reciprocating engine.

Disadvantages

Although roughly 90% of all electricity generation in the world is using steam turbines, they also have some disadvantages:

• They are relatively high overnight costs.
• They have longer startups than gas turbines and certainly reciprocating engines.
• Steam turbines are less efficient than reciprocating engines at part load operation.
• Less responsive to fluctuations in power demand compared with reciprocating engines and with gas turbines.

What is Steam Turbine Applications?

Steam turbines are a member of various industries, from small to large scale, and include numerous institutional applications.

• Chemical Industry: In this application, they typically provide electricity and heat to drive various processes in the chemical and pharmaceutical applications; steam turbines are integrated into the process of generating power.
• Waste Plants: Steam turbines help create the power required to harness energy from wastes.
• Oil & Gas: They are used as a compressor or a pump drive; steam turbines support tens of operations in the oil and gas industry.
• Sugar Mills: They offer high levels of efficiency and sustainable operations; steam turbines are utilized to generate green carbon dioxide energy from bagasse.

Some of the most widespread applications of a steam turbine in various industries include combined heat and power (CHP) systems, driving mechanical equipment, combined cycle power plants, and direct heating and cooling systems.