Environmental Engineering Reference
In-Depth Information
15.5
Pressure swing adsorption plant (copyright: Fraunhofer IWES).
part of the in the first column co-adsorbed CH
4
passes the molecular sieve in
this second column without adsorption and is therefore available in the
product gas flow. After balancing the pressure between these two columns,
the pipe between them is closed. The first column is then discharged
completely by pressure release down to ambient pressure and is finally
evacuated [7, 11]. According to a manufacturer [10] as well as information
from a plant operator [30] controllability in the range 40-100% (compared
to nominal load) is possible. Figure 15.4 illustrates the PSA process of a
four-bed system, but five-bed and six-bed systems are also available; another
manufacturer offers rotating valve systems using nine-bed systems. A PSA
plant is shown in Fig. 15.5.
The electricity demand varies from 0.16 to 0.35 kWh
el
/m
n
3
raw gas. One
technology provider reports specific electricity demands of 0.35 kWh
el
/m
n
3
for their first plants in the mid-1980s but the current (2012) plant generation
should be able to reach specific demands of 0.16-0.18 kWh
el
/m
n
3
depending
on the methane concentration in the raw biogas [10]. Warranty values from
the same technology provider are 0.17 kWh
el
/m
n
3
(methane concentration in
biogas of 65%) and 0.18 kWh
el
/m
n
3
(methane concentration in biogas of
55%) referring to operation pressures of 3 bar (absolute pressure) [16].
Another plant provider reported specific demands of 0.19-0.23 kWh
el
/m
n
3
[31]. One plant operator reported an average specific electricity demand of
0.23 kWh
el
/m
n
3
for an operation pressure of 5.4 bar, methane concentrations
in the product gas of 96-97%, energy crops as biogas feedstock and a raw
gas capacity of 1000 m
n
3
/h (start of operation in 2008) [30].
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