Energy consumption modelling - ADU-RES

Minimum Energy (kWh/m 3 )
3.5
3
2.5
2
1.5
1
0.5
0
0 10 20 30 40 50 60 70 80 90 100
Water Recovery Ratio (%)
Figure 1 – Theoretical minimum energy required to desalinate
seawater at 25 ºC 1
The above discussion, including Figure 1, refers to the complete removal of
salt, which is not generally necessary in the production of drinking water.
Product concentrations of up to 600 mg/L can be acceptable and this slightly
reduces the energy required. The reduction is usually insignificant in seawater
systems but is worth noting in the case of brackish water.
The temperature of the water also has a slight affect: osmotic pressure is
roughly proportional to absolute temperature in Kelvin. This factor is generally
insignificant in RO systems and should not be confused with the temperature
dependence of RO membranes.
2.4 Pre-treatment losses
Almost all practical RO systems include some form of pre-treatment. Usually,
this includes filtration, and requires energy to overcome the associated
pressure drops. Provided that filters are appropriately sized and properly
maintained, the energy required is generally small compared to that for the
actual desalination and is not included in the modelling presented here.
1 Johnson, James S., Lawrence Dresner and Kurt A. Kraus (1966). Hyperfiltration (Reverse
Osmosis). Principles of Desalination. K. S. Spiegler. New York, Academic Press, page 357.
ADU–RES WP6 Deliverable 6.1 Page 6 of 69