Environmental Engineering Reference
In-Depth Information
However, it may be advantageous to allow the inlet pressure to vary,
depending on the geologic characteristics of a system. For aquifer systems,
for example, due to the large amount of cushion gas needed, the storage
pressure ratio p
s2
/p
s1
is relatively small (<1.5), such that the hp turbine can
operate over the full storage reservoir pressure range with relatively small
penalties relative to design point performance (see Figure 5.13) [52,55].
Although a variable pressure reservoir CAES system requires a larger
storage volume than a compensated reservoir, volume requirements may be
reduced substantially by appropriate design of the storage volume pressure
range to an extent consistent with the pressure limits of the reservoir and
the turbo machinery. The ratio of the energy storage density for hydraulic
compensated storage to constant volume storage with inlet throttling (see
Appendix) is given by
1
−
p
p
k
S
S
S
1
1
(5.1)
2
1
1
0.9
0.9
Alstom (2004):
ps2/ps1 = 2.0
0.8
0.8
0.7
0.7
0.6
0.6
Huntorf:
ps2/ps1 = 1.38
0.5
0.5
0.4
0.4
1
k
S
p
S1
p
S2
0.3
0.3
1-
0.2
0.2
0.1
0.1
0
0
0
0.5
1
1.5 2 2.5
Pressure Ratio (ps2/ps1)
3
3.5
4
4.5
FIGURE 5.13
Ratio of storage energy density between constant volume CAES with constant turbine inlet
pressure (case 3) and pressure compensated CAES reservoir (case 1) as a function of ratio of
operating pressures of case 3 system (ps
2
/ps
1
). We assume ks = 1.4 and (ps
2
/Ts
2
)/(ps
1
/Ts
1
) = 1.
