A Feasibility Study - Aaltodoc - Aalto-yliopisto

Other factors also favor the choice of the hydraulic turbocharger as the ERD for
AaltoRO. It has small capital costs and it is also not so susceptible to low quality feed
waters as is the Clark pump (Meyer-Steele, Beamguard 2008). The latter is a crucial
factor since unlike in a standard RO system, the feed water will be of inferior quality
and therefore also the ERD must be able to reliably operate in these conditions.
However, the hydraulic turbocharger also has some drawbacks, mainly relating to its
efficiency. The low efficiency of less than 75 % is an inconvenience, but the major
disadvantage is its inability to maintain efficiency with variable flow rates (Meyer-
Steele, Beamguard 2008). Still, the RO membranes themselves can operate only with
certain flow rates and it is estimated that the efficiency of the hydraulic turbocharger
will not diminish too much during this range.
The hydraulic turbocharger operates by transferring the pressure energy of the brine to
the feed water. This is accomplished with an energy recovery turbine, which receives
the energy from the brine, and a centrifugal pump, which increases the pressure of the
feed. These two are connected with a shaft and thus the brine gives a pressure boost to
the entire volume flow rate of the feed, enabling lower initial pressures from the WEC.
Figure 33 has a picture of a hydraulic turbocharger.
Figure 33. Hydraulic turbocharger (FEDCO 2012).
To sum up, the hydraulic turbocharger will be the ERD for AaltoRO. It can operate with
low quality feed waters and has moderate capital costs. It has a lower efficiency than the
Clark pump, but it has been estimated the loss in power will not be too high. Most of all,
the hydraulic turbocharger goes well with the overall operating principle of AaltoRO.
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