Environmental Engineering Reference
In-Depth Information
to nuclear units near the North Sea and to furnish inexpensive peak power.
[Note: Black start is the ability of a plant to start up during a complete grid
outage.] Because nuclear power stations require some power to resume oper-
ation, the Huntorf plant was built in part to provide black-start power. It has
operated successfully for over three decades, primarily as a peak shaving
unit and to supplement other (hydroelectric) storage facilities on the system
to fill the generation gap left by slow-responding medium-load coal plants.
Availability and starting reliability for this unit are reported as 90 and 99%,
respectively.
Because Huntorf was designed for peaking and black-start applications, it
was initially designed with a storage volume capable of 2 hours of rated out-
put. The plant has since been modified to provide up to 3 hours of storage
and has been used increasingly to help balance the rapidly growing wind
output from North Germany [36,54]. The underground portion of the plant
consists of two salt caverns (310,000 m
3
total) designed to operate between
48 and 66 bar. The air from the salt caverns was found to cause oxidation
upstream of the gas turbine during the first year of operation, leading to the
installation of fiberglass reinforced plastic (FRP) tubing. Because the tur-
bine expanders are sensitive to salt in the combustion air, special measures
were taken to ensure acceptable conditions were met at the turbine inlet as
well [36].
The compression and expansion sections draw 108 and 417 kg/s of air,
respectively, and each is comprised of two stages. The first turbine stage
expands air from 46 bar to 11 bar. Because gas turbine technology was not
compatible with this pressure range, steam turbine technology was chosen
for the high-pressure (hp) expansion stage. Due to the increase in heat trans-
fer coefficient at elevated pressure and temperature and to ensure proper
cooling and control NO
x
emissions, the hp turbine inlet temperature was
held to only 550°C compared to 825°C for the low pressure (lp) turbine (typi-
cal for a gas turbine without blade cooling). Moderate combustion inlet tem-
peratures also facilitate the daily turbine starts needed for CAES operation
[55]. Although the plant could operate at a lower heat rate if equipped with
heat recuperators (to recover exhaust heat from the lp turbine for preheating
the gas entering the hp turbine), this addition was omitted to minimize sys-
tem start-up time [56,57].
McIntosh
Although high oil and gas prices through the early 1980s continued to
draw the attention of utilities to CAES as a source for inexpensive peak
power [48], not until a decade later did a CAES facility began operating
in the United States. The 110 MW plant was built by the Alabama Electric
Cooperative on the McIntosh salt dome in southwestern Alabama and has
