A Feasibility Study - Aaltodoc - Aalto-yliopisto

flow rates. However they generally have high capital costs. The situation is more or less
reversed with centrifugal devices.
Based on Table 5 alone, the choice of an appropriate ERD for AaltoRO would be very
difficult, since weighing the advantages and disadvantages of positive displacement
devices and centrifugal devices is hard. Therefore, the selection process is simplified by
excluding those ERDs that are designed for electricity production, since it is not a target
in AaltoRO. To clarify the differences between the two ERD types, one example of each
is chosen: the hydraulic turbocharger for centrifugal devices and the Clark pump for
positive displacement devices.
The basic configuration of the Clark pump is that it pressurizes a portion of the feed
water while the high-pressure pump pressurizes the remaining part of the feed water.
Figure 32 presents the basic configuration of the Clark pump. Basically this means that
the high-pressure pump can be of smaller size but that it has to be able to pressurize up
to the desired pressure level. On the other hand, the hydraulic turbocharger operates by
increasing the pressure of the entire volume flow rate of the feed water. Thus, the highpressure
pump needs to be able to handle the entire volume flow rate but it does not
need to be able to pressurize to the desired pressure level (Jatzlau 2011).
Figure 32. Basic configuration of a Clark pump. Adapted from (Jatzlau 2011).
The operating principle of AaltoRO agrees well with the hydraulic turbocharger, but not
with the Clark pump. This is mainly due to the fact that the “high-pressure pump” of
AaltoRO is the WEC at the bottom of the sea, while the ERD will be situated onshore.
If the Clark pump would be chosen, it would require another standard high-pressure
pump for the entire system to operate. This would increase the capital costs and also
complicate the system without sufficient increases in production.
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