A Feasibility Study - Aaltodoc - Aalto-yliopisto

Lastly, an economical evaluation is performed taking into account the capital and
operational costs of the current AaltoRO configuration as well as the use of a suitable
Energy Recovery Device (ERD). Using the annuity method with an operating lifetime
of 25 years and an interest rate of 8 %, the actual cost of desalinated water in €/m³ is
calculated. Then the process is repeated to a suitable amount of design points in order to
reach the most economical point of operation.
The actual calculations will be performed with the spreadsheet program Microsoft Excel
and the reverse osmosis design program ROSA. Detailed information from Excel and
ROSA will be given about the optimum operating point as well as a summary why this
point was chosen.
9.2 Design parameters
Performing calculations to a certain degree of accuracy can be challenging. This thesis
will have the following simplifications relating to the calculations performed in each
site:
Standard seawater, as defined by the Dow Chemical Company (DOW 2009),
will be used as the feed water in all calculations. The TDS of standard seawater
is 35 000 mg/l, and the exact composition is given in the Figure 35 and in the
Appendix A.
o It is assumed that the seawater will have same composition throughout
the year and the possible influence of e.g. algae blooms is disregarded.
The temperature of the seawater will be taken as an annual average:
o Site 1: 21 ºC; Site 2: 20,5 ºC; Site 3: 17,3 ºC and Site 4: 10,4 ºC
Only the direct pressurization of seawater will be examined, not electricity
production.
The feed water will be pressurized to 45 bar. The reason is explained in detail in
Chapter 9.3.
o The WEC will pressurize the water initially to 25 bar pressure and the
ERD will increase the pressure to 45 bar.
The Adaptive Pressure Generator (APG) is assumed to work ideally without any
losses.
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