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Steam Turbine

Steam Turbine

A steam turbine is a device that is used to convert the high pressure of the steam into the rotation of an axis that provides power output (shaft). This type of turbine is mainly used in power plants (for example, in high temperature solar thermal power plants), but also in other applications where large capacities are required, such as offshore vessels.

With a modern steam turbine, the steam is guided against a row of rotor blades, which changes the steam direction as much as possible. Then, the steam passes through a row of stator blades, where it again rotates from the direction to the next row of rotor blades. This process continues until the steam has expanded to the maximum. When the steam energy is depleted to such an extent that water droplets begin to form, it is expelled from the turbine because water droplets moving at a supersonic velocity in the turbine blades cause erosion. This happens when approximately 20% of water molecules condense.

History of the steam turbine

The steam turbine was invented around 1883 by the Swedish engineer Gustav de Laval in its simplest form, the lava turbine. This turbine consisted of a large number of cube-shaped vanes that collected the steam and turned it into a circular motion. He used this turbine to drive a milk centrifuge.

In 1884, the British engineer Charles Algernon Parsons designed the reaction turbine. This turbine allows the steam to flow in the longitudinal direction of the shaft and gradually reduces the pressure, distributed over several blade wheels.

Together with Parsons, Auguste Rateau designed a turbine where the pressure is reduced only in the stator blades. This difference leads to a significant increase in yields. Nowadays this is called Zoellyturbines and they are actually lava turbines connected in series. Due to the presence of several successive pressure and velocity stages, the peripheral speed "U" decreases. The reason for this is that the peripheral speed and the heat drop in the pressure stage are proportional. The heat trap per pressure stage will be smaller and, therefore, the peripheral speed will also decrease. However, the heat trap of each pressure stage (taking into account the turbines connected to each other) must remain the same, otherwise, different peripheral speeds would be obtained in a main axis.

Classification of the steam turbine

Power source

The steam used in steam turbines can be heated by burning oil or gas, by nuclear energy, by solar energy or by geothermal energy.

Basic

Steam turbines are classified into several bases: Axial / radial, direct pressure (impulse) / overpressure (reaction), compound type and condensation / drainage.

The basic distinction is made in the expansion properties. For example, the main classification is generally based on the question of whether the pressure and overpressure turbines are. This expansion can be carried out in two different ways:

DC Turbines

Equal pressure turbines are so named because the inlet pressure in the blade wheel equals the outlet pressure after the blade. The complete vapor expansion takes place in the nozzles / nozzles. These are classified under impulse turbines. For example, laval, curtis and rat turbines can be found under this form of expansion, each of course with its specific field of application, which in turn can be classified according to various criteria, for example, efficiency, optimal speed ratio , blade speed, blade angle, cost, maintenance and power consumption / delivery.

  • Lava turbine Invented by engineer Gustav de Laval. This turbine consists of a wheel with a large number of bucket-shaped vanes that collect the steam and turn it into a circular movement. This type of turbine is not very efficient, since it worked too fast between 20,000 and 25,000 rpm.
  • Curtist turbine. This turbine consists of two rotating wheels with a large number of cube-shaped blades that collect the steam and turn it into a circular movement. Between these two wheels there is a set of reaction blades that stop. This type of turbine is not as efficient, but the speed (rpm) is lower. This turbine can consist of two stages or a single stage. The turbine is used as ballast, it is often used in power plants of the high pressure turbine to lower the temperature and pressure of the steam.
  • Rateauturbine or Zoellyturbine. Auguste Rateau designed a turbine that reduces the vapor pressure in steps. This leads to an increase in efficiency. They are called Zoelly turbines and are basically lava turbines connected in series, each at a lower pressure. Because it has several stages of pressure and speed that occur, the speed is reduced.

Pressure turbine

This is a turbine where the outlet pressure is lower than the entrance. The expansion occurs partly in the guide vanes and partly in the guide vanes. These are called impulse / reaction turbines or simply reaction turbines. The parson turbine is housed here. The guide and the moving pallets are made relatively uniformly and because with this turbine the difference of enthalpy per stage (lei + loop) is the same, the power obtained or obtainable can be calculated from the number of stages. However, with this type of turbines, there is an axial load of the shaft due to the pressure drop per stage.

Parson turbine. In 1884, the British engineer Charles Algernon Parsons designed the reaction turbine, this turbine allows the steam to flow in the longitudinal direction of the shaft and gradually reduces the pressure, distributed over several blade wheels. The speed is now 1500 or 3000 rpm. All contemporary turbines are parson turbines.

Ljungström turbine, a turbine with two opposite rotating axes. The guide vanes also rotate, but in the opposite direction.

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Last review: April 26, 2019

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