NAMS 2002 Workshop - ICOM 2008

Desalination II – 1 – Keynote
Thursday July 17, 2:15 PM-3:00 PM, Honolulu/Kahuku
Memstill: A Near-Future Technology for Sea Water Desalination
C. Dotremont (Speaker), Keppel Environmental Technology Centre, Singapore -
chris_dotremont@keppelseghers.com
B. Kregersman, Keppel Seghers Belgium NV, Williebroek, Belgium
S. Puttemans, Keppel Seghers Belgium NV, Williebroek, Belgium
P. Ho, Keppel Environmental Technology Centre, Singapore
J. Hanemaaijer, TNO Science and Industry, The Netherlands
The Memstill development history started some 10 years ago at TNO Science
and Industry - the Netherlands. In 2002, Keppel Seghers joined the R&D
consortium. Ten years of development work resulted in a box module concept
which is leakage-free, resistant to hot sea water and has a salt reduction factor >
10.000 in scaled-up modules of 300 m 2 membrane area.
Memstill is a membrane-based distillation technique which makes use of
hydrophobic membranes to separate sea water from pure distillate. In a
countercurrent flow process, the cold sea water enters the module and takes up
heat in the condenser channel through condensation of water vapour, after which
a small amount of (waste) heat is added, and flows counter currently back via the
membrane channel. Driven by the small added heat, water evaporates through
the membrane, and is discharged as cold condensate. The brine is disposed, or
further concentrated in a next module. A heat exchanger between the condenser
and membrane envelop supplies the necessary heat to the module. Because a
Memstill module houses a continuum of evaporation stages in an almost ideal
countercurrent flow process, a very high recovery of evaporation heat is possible:
Gained Output Ratios (GOR) of 15-30 are achievable.
This technology is especially attractive in case low grade waste steam or solar
heat is available, i.e. top temperatures between 60 and 90 degrees Celsius and a
temperature difference over the membrane/condenser of 5 to 10 degrees Celsius
are already sufficient to drive the process. In other words, memstill is energy/CO2
- neutral and is driven by relatively small quantities (100 - 200 MJ/m 3 ) of heat. If
operated in a once pass through system, memstill operates at recoveries of 5-
10%, without any additives like acids and anti-scalants, producing high quality
fresh water and a brine which is only 10% concentrated and with only 2 to 5
degrees Celsius increase in temperature, thus without any proven environmental
damage.
A first pilot plant - equipped with the first generation of modules - was operated
for 14 months in Singapore (March 2006 - June 2007). And although the intake of
sea water at the Strait of Johor was of low quality, the pilot showed good