How does a Steam Turbine Work?

A steam turbine is a device that converts the thermal energy of steam pressure into mechanical energy, where the steam is expanded in stages in the turbine to do the required work. Steam turbine engines are used worldwide to generate countless electric motors (such as the master switch for pumps, compressors, and other equipment used on the shaft). The capacity of a steam turbine can range from a few kilowatts to several hundred megawatts. Sir Charles Parsons built the first modern steam turbine in 1884.

The energy in a steam turbine is generated by changing the speed of a high-speed jet of steam hitting free-spinning curved blades.

How does a steam turbine work?

In other words, the principle of a steam turbine is to use a heat source (gas, coal, nuclear energy, solar energy) to heat the water to a very high temperature until it turns it into steam. As the steam passes through the turbine blades, the steam expands and cools. Thus, the potential energy of the steam is converted into the driving force in the rotating blades of the turbine. Since steam turbines generate circular motion, they are particularly suitable for generators in motion to generate electricity. The turbine links with the generator through a shaft, and the generator generates energy through a magnetic field that produces electricity.

Types of Steam Turbines

1) Impulse Turbine

Stationary nozzles drive the jet of steam in the impulse turbine in the form of cube turbine rubble, where the force applied by the jet rotor rotates while the steam speed on the blade is reduced due to the kinetics of the force. The blades, in turn, change the direction of the steam flow, and this change of movement corresponds to an increase in the movement of the rotor. (Descartes – Maintain acceleration). There is no pressure drop as steam passes through the rotor blades because the cross-sectional area of ​​the chamber between the blades is fixed. Therefore, impulse turbines are also called constant pressure turbines.

Impulse steam valves generally operate at very high speeds of 30,000 rpm. Or more, thus exposed to a great centrifugal force. For most practical applications, the speed must be reduced. Furthermore, the design is relatively simple, and the turbine chamber does not necessarily withstand pressure.

In a compound turbine, the next row reverses the fixed blades in the direction of the steam before the steam passes through the second row of rotor blades. 

2) Reaction Turbines

The stationary blades and rotor blades of the jet turbine are similar to the aerodynamic blades. They are arranged such that the cross-sectional area of ​​the blades decreases from the opening edge of the blade to the edge. This means that the cross-sectional area of ​​the steam passing between the two sets of stationary blades and the rotor blades increases with the turbine stage. In this way, two sets of blades usually form a nozzle, so as steam passes through the stator and rotor, its pressure decreases, and its speed increases. The rotor usually turns into a series of rotating nozzles.

When steam escapes from any set of rotor blades, it creates a reaction force on the blades, which in turn generates torque to the turbine rotor, like the Hero steam engine. 

Turbine reactions are generally better than pulse turbines and run at lower speeds, which means they don’t necessarily need gears. However, they are more complex, and the high vapor pressure allows them to be easily filtered between phases. 

3) Compound Steam turbine

Combined steam turbines use a series of steam turbine stages, where the outgoing steam is fed from one stage to the other. By properly modeling the rotor and stator blades to produce the nozzle, the pressure or velocity of the steam can be slowly reduced in several steps instead of one. The possibility of using steam pressures and speeds is very high, resulting in a very high turbine yield. 

4) Pressure compounding

The pressure combination uses a series of turbine reaction steps to solve the problem of very high blade speeds in single-pulse turbine stages. The vapor pressure decreases with each stage as the pressure decreases, while the vapor velocity remains relatively constant and changes direction as it passes through each stage. As the vapor pressure decreases at each stage of the turbine and the volume of steam increases at each stage, in high-capacity turbines, the turbine blades and chamber must be successively larger to accommodate each subsequent stage. As the vapor pressure decreases at each stage of the turbine, the volume of the steam also increases at each stage, so in a high-capacity turbine, the blades and the turbine chamber must subsequently be larger.

Advantages and disadvantages of steam turbines

Advantages of Steam turbines

  • Since the steam turbine is a rotating heat engine, it is particularly suitable for generating motion.
  • The thermal efficiency of steam turbines is generally higher than that of equivalent engines.
  • Compared to reciprocating engines, it has a very high power/weight ratio.
  • There are fewer moving parts than equivalent motors.
  • Steam turbines are best for large thermal power plants. They consist of turbines of various sizes up to 1.5 gigawatts (200,000 horsepower) which are used to generate electricity.
  • In general, vapor contains a large amount of enthalpy (mainly in the form of heat of vaporization). This means that the mass flow is lower than with gas turbines.
  • In general, the turbine only moves in one direction, and the vibration is less than that of the gearbox motor.
  • Steam turbines are more reliable, especially in applications that require continuous high-power output.

Disadvantages of steam turbines

  1. Although nearly 90% of the world’s electricity is generated through the use of steam turbines, it also has drawbacks.
  2. The cost of an overnight stay is very high.
  3. When operating under load, the efficiency of steam turbines is lower than equivalent engines.
  4. They run longer than gas turbines and certainly longer than similar engines.
  5. Compared to gas turbines and reciprocating engines, the response to changes in energy demand is less.

These turbines have higher efficiency than wind turbines.

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