Waterise - Low energy water reverse osmosis at 400m depths - Page 1
Forum section: electronics / general

author: DavidAlfa
author_rank: Super Contributor
timestamp: October 31, 2023, 10:17:32 am
content: To me this is BS, laughting at science.The gravity won't actually save any energy, as you must later pump the water those 400m up, so it's the same thing!Am I wrong?https://www.aquatechtrade.com/news/desalination/waterise-novel-underwater-desalination

author: Marco
author_rank: Super Contributor
timestamp: October 31, 2023, 11:02:56 am
content: The article just does a really poor job of explaining why it saves energy.The point is that you need to only suck vacuum the fresh water instead of pressurize the salt water. The salt water side needs much more flow than the fresh water side. Less to pump means less energy, also the pump doesn't have to deal with salt water.PS. I had the same reaction.

author: DavidAlfa
author_rank: Super Contributor
timestamp: October 31, 2023, 11:06:37 am
content: Normally you would push the water against the filter, then no resistance.Now you get "free" pumping, but later you need to pump it 400m up, which is the same work you got for free in first place.So there's no difference.This is basically the same thing I said earlier.

author: wraper
author_rank: Unknown
timestamp: October 31, 2023, 11:15:51 am
content: Quote from: DavidAlfa on October 31, 2023, 11:06:37 amIt's not really that you need to pump 400mup. You need to create only a small pressure difference for water to go up as sea water in the deep is already under high pressure that will push water from the back.

author: wraper
author_rank: Unknown
timestamp: October 31, 2023, 11:24:21 am
content: Think about it like this. You put 400m long vertical pipe into the sea with top slightly above the water. It obviously will get filled with water from the bottom to the same level as water level outside the pipe. What will happen if you pump out 1 meter of water from the pipe? It will just get refilled from the bottom by itself. So you don't need to push water to 400 meter height.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 31, 2023, 12:30:18 pm
content: The osmosis creates a pressure different between the fresh and salt water side.So one would really have to pump the fresh water up, as most of the static pressure is lost.The article is not that bad written. The main point is getting relatively pure salt water at depth and this way less need to filter the water. This way the water can discharges at a lower concentration and thus less pressure needed. At depth it may be easier to pass more salt water through.On land one needs to pump more salt water than freshwater, but one can get much of the extra energy back, when the extra salty water goes from high to low pressure.The extra effort with this water is more for filtering, as the membranes need to be kept clean. So the incomming water needs good filtering.A small (maybe some 3%) extra saving could be from cooler water in the deep sea, as the osmotic pressure is proportional to the absolute temperature.

author: Marco
author_rank: Super Contributor
timestamp: October 31, 2023, 12:40:23 pm
content: Quote from: DavidAlfa on October 31, 2023, 11:06:37 amOnly a fraction of the salt from the salt water side is removed, you pump more salt water across the pressure difference in an ordinary setup than fresh water in a deep sea setup. You have to still pump across roughly the same pressure difference, but you pump less.

author: DavidAlfa
author_rank: Super Contributor
timestamp: October 31, 2023, 01:22:50 pm
content: Aha, I got it now.It would help bit as the water wants to rise again.