Seawater desalination

[mistermack]

Fresh water is losing the battle. Around much of the globe.

Too many people want too much of it. And people don't want to live in the cold wet places that have loads to spare.
As the price goes up, desalination gets more and more attractive.
I thought I'd start a thread about it, for people to post links on.

As a background starter, reverse osmosis is the current WORKING best technology. (although there are claimed to be more efficient systems under development).

It's more expensive than surface water, or underground aquifer extraction, but these are being done to the limit in many hot dry places. So the alternative is desalination, and RO is king for now.
Here's a new one being built in Oz, one of the biggest in the world :
https://www.youtube.com/watch?v=nJKWqdQtPqo&t=1737s

This is a different system under development, but it has the potential to force down the costs lower than pumping water from wetter places to where it's wanted :
https://www.youtube.com/watch?v=XuGwfZGWACE

[Rum]

Those effing Pakis - steeling all our water!

[Strontium Dog]

I am a fan of desalination. They always talk about it being expensive, energy-wise, but neglect the fact that most regions in need of fresh water are absolutely overwhelmed with solar energy. Someone will join the dots, eventually.

[mistermack]

I am a fan of desalination. They always talk about it being expensive, energy-wise, but neglect the fact that most regions in need of fresh water are absolutely overwhelmed with solar energy. Someone will join the dots, eventually.

Yeh, if you could combine wind power and solar in the desalination process, you could be making the best of all of it.
After all, water lasts ages. It doesn't matter if you make it on a windy night, or a sunny day, or if you don't make any for a couple of days when neither are producing.
Use windmills to pump it around, and solar to desalinate it. Or a combination of all that.
No need for fossil fuel in a lot of places.

[Jason]

So solar energy they could be selling to the grid at market prices is expected to be made available free of charge to these desalinization plants? I don't think that's very likely.

[mistermack]

So solar energy they could be selling to the grid at market prices is expected to be made available free of charge to these desalinization plants? I don't think that's very likely.

It doesn't work like that at the industrial level.
They will buy solar energy from home producers at uneconomic prices as an incentive. But at the level of mass-production, the price would drop when the sun shines, and rise when it goes away if there was a lot of solar generation.
Making fresh water would be a way to use the energy and store the product, at times when there is a glut of solar. You could choose to sell the power to the grid when the price rises above a certain level.

[JimC]

I am a fan of desalination. They always talk about it being expensive, energy-wise, but neglect the fact that most regions in need of fresh water are absolutely overwhelmed with solar energy. Someone will join the dots, eventually.

Yeh, if you could combine wind power and solar in the desalination process, you could be making the best of all of it.
After all, water lasts ages. It doesn't matter if you make it on a windy night, or a sunny day, or if you don't make any for a couple of days when neither are producing.
Use windmills to pump it around, and solar to desalinate it. Or a combination of all that.
No need for fossil fuel in a lot of places.

Quite true, this...

[rainbow]

So solar energy they could be selling to the grid at market prices is expected to be made available free of charge to these desalinization plants? I don't think that's very likely.

It doesn't work like that at the industrial level.
They will buy solar energy from home producers at uneconomic prices as an incentive. But at the level of mass-production, the price would drop when the sun shines, and rise when it goes away if there was a lot of solar generation.
Making fresh water would be a way to use the energy and store the product, at times when there is a glut of solar. You could choose to sell the power to the grid when the price rises above a certain level.

Nice in theory, but it won't work.

The RO membranes are very tough in one direction but weak in the opposite. That means that they should be operated under constant forward flow, or they will delaminate.

Better would be Capacitive Deionisation (CDI)
https://en.wikipedia.org/wiki/Capacitive_deionization

Could even be operated in reverse to generate power in off-peak periods.

[mistermack]

Nice in theory, but it won't work.

The RO membranes are very tough in one direction but weak in the opposite. That means that they should be operated under constant forward flow, or they will delaminate.

Better would be Capacitive Deionisation (CDI)
https://en.wikipedia.org/wiki/Capacitive_deionization

Could even be operated in reverse to generate power in off-peak periods.

Consumes too much electricity per cubic metre.
Very good for smaller volumes, as it doesn't require too much hardware expenditure, but not competitive in the seawater desalination field. (as yet)
It can compete for slightly salty water, as reverse osmosis requires ALL of the water to pass through the membrane, which is wasteful when the water is not very salty in the first place.

[laklak]

I want a reverse osmosis water maker for the boat, but they're pretty expensive. Around $4,000 for a 20 gph setup. The best ones drive the pump directly from the diesel engine rather than using an electric pump, you need pressures in the range of 800 psi for ocean water.

[mistermack]

I want a reverse osmosis water maker for the boat, but they're pretty expensive. Around $4,000 for a 20 gph setup. The best ones drive the pump directly from the diesel engine rather than using an electric pump, you need pressures in the range of 800 psi for ocean water.

How the hell do you use 20 gallons per hour on a boat?

[JimC]

I want a reverse osmosis water maker for the boat, but they're pretty expensive. Around $4,000 for a 20 gph setup. The best ones drive the pump directly from the diesel engine rather than using an electric pump, you need pressures in the range of 800 psi for ocean water.

How the hell do you use 20 gallons per hour on a boat?

You might only have it on for 2 hours, and use it to replenish your freshwater tank.

[mistermack]

I want a reverse osmosis water maker for the boat, but they're pretty expensive. Around $4,000 for a 20 gph setup. The best ones drive the pump directly from the diesel engine rather than using an electric pump, you need pressures in the range of 800 psi for ocean water.

How the hell do you use 20 gallons per hour on a boat?

You might only have it on for 2 hours, and use it to replenish your freshwater tank.

Yeh, I thought that afterwards. Still seems like overkill though, I couldn't think what you could need all that fresh water for.

[JimC]

I want a reverse osmosis water maker for the boat, but they're pretty expensive. Around $4,000 for a 20 gph setup. The best ones drive the pump directly from the diesel engine rather than using an electric pump, you need pressures in the range of 800 psi for ocean water.

How the hell do you use 20 gallons per hour on a boat?

You might only have it on for 2 hours, and use it to replenish your freshwater tank.

Yeh, I thought that afterwards. Still seems like overkill though, I couldn't think what you could need all that fresh water for.

Being British, you probably don't understand the concept of showering...

[laklak]

Flushing toilets, showers, fresh water for flushing the dinghy outboard, cooking, washing clothes (soon, I'm putting in a combo washer/dryer next summer) - same stuff you use water for on land. The water tank is 140 gallons, we can get a week out of that when not at a dock if we're careful and ration it. 20 gph is about the smallest water maker produced, there are smaller "survival" units for life rafts but they're manually operated and aren't designed for long term use. A couple of hours a day and we'd have all the water we need and wouldn't have to come back into port for weeks on end. Well, as long as we pump the shit overboard, and you're supposed to be 9 miles out to do that. Never mind one manatee shits more in an afternoon than I do in a week.