The Basics of Steam Turbine Engines

Steam turbines extract thermal energy from pressurized steam and use it to do mechanical work on a rotating output shaft. Because it generates rotary motion, it’s widely used in power generation, refineries, and petrochemical industries.

Turbine casings are what go around the blades and working fluid. Because turbines work with steam at different temperatures and pressure levels, they have different shapes, constructions, and materials. For example, low-pressure and low-temperature up to 230? steam needs single shell casings made of cast iron; intermediate-pressure and medium-temperature up to 425? need carbon steel, and high-pressure and high-temperature steam exceeding 550? needs alloy steel such as 3Cr1Mo.

Turbine rotors blades are the most stressed component in the turbine and are designed based on their operating principles, impulse or reaction. Impulse turbines have a pressure drop across the stationary blades and have steam leakage between the stationary blades and rotor, so they use disc rotors. Reaction turbines have a pressure drop across the moving and stationary blades and cannot deal with added axial thrust, so they use drum rotors to eliminate the axial thrust caused by discs.

Turbine blades determine the efficiency of the turbine. Impulse blades have to be designed to convert the steam’s kinetic energy into mechanical energy while the reaction blades have to do that and convert pressure energy into kinetic energy. They have to be strong enough to deal with high temperatures, stresses, and damage. As a result, a shroud is often used to reinforce the free ends of the blade and reduce vibration and leakage.

Barring devices, bearings, couplings, seals, governors, and an oil flood lubrication system are all other crucial parts of a steam turbine. Barring devices are used to help the rotor when it is too hot, too cold, or has been shut off for too long. Bearings rotary and couplings help bear the loads, reduce friction, and keep everything in place. Seals reduce the leakage of steam between the rotary and stationary parts. Governors control the steam turbine’s operations. And the lubrication steam keeps the turbine running smoothly by reducing friction.  


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