|
Many cogeneration systems, particularly at old college
campuses and large hospitals, use steam turbines to drive electric
generators and chillers. The systems are relatively simple and easy to
maintain (typically less than $0.004 per kWh of power generated per hour).
Steam at high pressure is "let down" through the turbine with the lower
pressure steam used in process, space, domestic water heating, and similar
uses. The intrinsic energy efficiency of the design means the boiler only
produces slightly more steam than would be required if power generation were
not co-produced. This also makes the design a relatively low emitter of NOx
and CO2. These steam turbines are also often relatively inexpensive power
generators.
In some special situations where electrical demand charges or ratchets
warrant, condensing steam turbine designs may be specified. Here, steam
leaving the steam turbine goes straight to a steam condenser. This is a
relatively expensive design, and one that requires significant cooling
water. Also, steam turbines are typically not a good fit in applications
calling for intermittent power generation.
|
