desalination
Kim Cheetham
Pat recently asked about desalination and energy costs. I reproduce a paragraph from David MacKay’s book.
I think that this book is entirely reliable, and a very good source of information. You can buy it, or download it free.
Kim
At the moment the UK doesn’t spend
energy on water desalination. But
there’s talk of creating desalination
plants in London. What’s the energy
cost of turning salt water into drinking
water? The least energy-intensive
method is reverse osmosis. Take a membrane
that lets through only water,
put salt water on one side of it, and
pressurize the salt water. Water
reluctantly oozes through the membrane,
producing purer water – reluc-
tantly, because pure water separated from salt
has low entropy, and nature
prefers high entropy states where everything is
mixed up. We must pay
high-grade energy to achieve unmixing.
The Island of Jersey has a desalination plant
that can produce 6000 m3
of pure water per day (figure 15.10).
Including the pumps for bringing
the water up from the sea and through a
series of filters, the whole plant
uses a power of 2 MW. That’s an energy
cost of 8 kWh per m3 of water
produced. At a cost of 8 kWh per
m3, a daily water consumption of 160
litres would require 1.3 kWh per day.
Mark Brown
If you want a good over-view as to how desalination will be used in the middle-east then have a browse through Jeff Rubin’s “Why your world is about to get a whole lot smaller”. His analysis suggest that convention desalination will end up consuming all the spare oil and gas production from that area. They have a rapidly growing population needing water.
David MacKay is the man behind the DECC models that you can visit online and play with certain sliders to plan a low-carbon future. Although a good source of raw data and analysis it is a but mechanistic and selectively excludes an array of externalities. It should not be the only thing you read….
Many thanks,
Mark Brown | Energy Group Coordinator
Transition Town High Wycombe | mark-...@transition-wycombe.org.uk | 01494 858390 | Skype: krofire
www.transition-wycombe.org.uk | www.twitter.com/TTWycombe | www.facebook.com/TTWycombe
Superhome 59 | Krofire House | 5 Richard Gardens | High Wycombe | Buckinghamshire | HP13 7LT | www.superhome59.info to book a visit.
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