a brief overview
Steam power cycles usually consist of four separate elements
and related hardware:
GENERATION - The production of steam itself within
a boiler (or steam generator).
EXPANSION – Transforming steam pressure into
work by causing the steam to expand, usually in a
reciprocating engine or turbine.
CONDENSATION – Removing the latent heat of
vaporization, transforming expander exhaust back into
water which may be reused (sometimes omitted,
expanders may exhaust to the environment instead of to
* FEED - Forcing water into the boiler with a pump.
Let’s examine the elements in the above drawing as they relate to our four steam cycle stages:
GENERATION – The boiler (or steam generator) is found in the upper left hand corner of the
above illustration. A heat source boils pressurized water, which is converted to steam.
Boiling temperature rises with pressure, boilers are much hotter than a pot on the stove.
EXPANSION - Steam travels through piping into the Prime Mover, a fancy term for a
reciprocating engine or turbine, also sometimes called an expander. The prime mover
expands the steam, causing both the temperature and pressure to fall, and harnesses this
expansion to perform work.
CONDENSATION – The prime mover exhausts low pressure steam to the condenser which
transfers some remaining heat to a coolant like air or water, causing the steam to revert to
water (condensate). Condensing steam cycles are closed, meaning ideally no water or steam
leaves or enters the system while non-condensing systems (think of the emanations of an old-
time steam locomotive) are open.
FEED – In closed systems a Feed Pump removes condensate from the condenser and returns it
to the boiler, usually by way of a Boiler Feed Heater which transfers some heat from the
expander exhaust steam to the boiler feed water; reducing the heat the boiler must add. In
open systems the feed water comes from a storage tank.
This was merely a fast-and-dirty introduction to the basics of steam power;
we have barely scratched the surface.
Click any of the four elements below
for somewhat more in-depth discussion.