Energy conservation and renewable energy are not new topics, although the public focus on them cycles periodically. Steam is one source of energy that is versatile and good for the environment although how it is produced can vary greatly. Reciprocating steam engines, used since the late 19th century, powered everything from farm equipment to automobiles, although they are seldom seen today.
Steam turbines are made up of rows of blades, like an ordinary house fan, which are attached to a central shaft or rotor. Unlike the fan which uses electricity to move the rotor and thus the blades, steam flowing across the turbine blades causes a difference in pressure on the two sides of the blade. This means that there is more pressure on one side of the blade than the other. This will cause the blade to move in the direction of the lower pressure. Steam turbines are classified according to their construction and the steam flow through them.
One of the simplest types of turbines is the impulse turbine. This turbine gets its name from the high-velocity steam that forces the rotor to turn by impinging on the rotor blades (or buckets).
As steam leaves the nozzle, its pressure and temperature decrease; however, its velocity increases. Steam pressure and temperature are lower at the rotor than in the boiler. After steam strikes the buckets, its velocity decreases. In the interim, steam striking the bucket produces mechanical work. To produce more work, it is not a matter of adding more pressure and temperature, but rather adding more steam. Adding more blades will improve the efficiency of the stage.
There are many types of steam turbines. Their uses and construction vary, but the outcome is the same. Next time we’ll look at a reaction turbine.
