Desalination and the Global Water crisis

[The Cat]

Being a student of urban development and having grown up in the Southwest, water conservation has always been a concern. I don't think the Rio Grande has seen water in quite some time and the reservoir levels are dropping at an alarming rate. This is to say nothing about the water quality. Currently, desalination efforts fall short mainly due to the high energy cost. However, with breakthroughs in membrane technology and the development of " The Long Beach Method", scientists and engineers are coming closer and closer to making large scale desalination a reality.

So, my question is, would it be possible to bring water in from the ocean using gravity or a gravity siphon and capitalize on the hydroelectric energy it would produce? Could this combined with the "Long Beach Method" make desalination affordable?

I understand that digging below the water table would be a monumental if not impossible undertaking. Obviously Geologist and the construction crew from Sea World would need to get into it, but is it possible? If affordable and done on the state level, California (The greatest state in the country) could sell bonds to raise the money, and sell its water rights at a premium to Nevada and Arizona. I think the water rights alone would be a great liquid asset. Excuse the pun. Remember the shit that Enron Pulled? Quien es su papa Arizona! Feel the Love!

If done on the Federal Level, I imagine it would be much like the Hoover dam project. I believe this project to be a necessity if this region is to be a going concern. I can't think of a better time to do it. Salton Sea could be a good research area. It has salt water and many areas below sea level...

To the Scientists:

How much energy would be required to run a full scale desalination plant?

How many pounds of pressure would be required to generate that energy?

How deep would they need to dig in order to obtain that pressure?

Thoughts on Gravity.

[Azrael]

I'm not sure what you're envisioning for the seawater inlet, but regardless of how deep (and/or how far inland) you dig, the water in the outflow pipe will only ever reach sea level. You'd have to put the generation turbines significantly below ground to develop any pressure drop across them.

Even the best & largest desalination plants do not have even close to 100% yield (I've found GE literature on smaller units claiming 35%), so you'd have to worry about returning the excess salt water as well. Pumping that back could quite easily destroy any energy gains you've made.

For what it's worth, I think you'd be better off killing two birds with the same stone -- using the cooling water from nuclear reactors to power flash distillers. Since you're combining the processes, overall efficiency is increased by using that excess heat for a meaningful purpose. Plus, more base load generation. The Japanese have been doing it for years, so it's a proven technology that can be optimized and commoditized as time and technology allow.

[The Cat]

significantly below ground to develop any pressure drop across them.

I was thinking it would be significantly below ground and the energy created would be used to operate the plant. The math either works or it doesn't. Turbines within the pressurized system. There could be any number of hurdles with regard to pressure, flow.... The problem is energy cost. Cost per meter of potable water. Create a little energy, lower the cost.

I love the idea of using the nuclear plant. San Onofre Nuclear Generating Station. You never need more than a spring suit! I'm just picturing the Springfield two headed fish signs marching out front. Your not gonna give my kids nuke water! The sad part is, in reality, the nuke water would be better than what their currently drinking. Oh wait, the protesters don't drink city water, never mind. Hell, they're having environmental problems with the water inlet pipes.

[Ivora]

Concerning the water crisis, Canada has a alarming amount of fresh water in its northern frozen glaciers. Only a matter of time til debate breaks out.

Trouble is abrewing.

[The Cat]

Fire up the stove! we're getting thirsty down here!

[stevey_frac]

significantly below ground to develop any pressure drop across them.

I was thinking it would be significantly below ground and the energy created would be used to operate the plant. The math either works or it doesn't. Turbines within the pressurized system. There could be any number of hurdles with regard to pressure, flow.... The problem is energy cost. Cost per meter of potable water. Create a little energy, lower the cost.

Unless your city is below sea level, and it's waste processing is lower then that, you would lose energy pumping the water back up to the city, and pumping the brine back to the sea. It's a law of thermodynamics violation. No free lunch kinda thing.

Using the nuclear plants for flash distillation is a good idea. Especially since most of the cost of a nuclear plant is the cost of the plant anyways, and fuel is relatively cheap.

There is also a bit of interest in using future fusion plants for flash distillation. Fusion is inherently safe, and therefore hopefully one day will be cheaper then fission plants.

The main cost of fission plants is making them safe. Candu reactors have three methods of achieving complete rapid shutdown. If any one is triggered, they all trigger. And then there is the whole containment building, and the witches hat. That's all very expensive. Since fusion is inherently safe, none of that will be necessary (well, the containment building still is but... ) it should one day be cheaper. It should be able to make significant contributions towards cheap desalination plants, and make a dent in the global water crisis. In theory.

[Minerva]

As has been pointed out by other posters above... desalination is great, it's hugely important. Sure, you need energy to drive desalination... but that brings us back to the entirely different issue of how we can get plenty of energy in an environmentally sustainable way.

There's a kind of conventional wisdom assumption that reverse osmosis is the most efficient kind of desalination... but then you need to take heat from burning coal or nuclear fission, convert it to electricity inefficiently in the plant's heat engine, transmit that electricity over a distance with associated losses, and then use that electricity to drive the pumps in the RO plant.

If you combined the nuclear reactor with on-site flash distillation (look at the BN-350 fast reactor for a great example) it's far more efficient, because you don't have the significant unavoidable inefficiency of the heat engine, and you don't have transmission losses - so it would probably give RO a run for its money for the overall efficiency - amount of water produced for a given amount of thermal energy output from the reactor.

And then you can use a "cogeneration" type arrangement as mentioned above, where you're using the waste heat from the electricity-generating engine, and get even better efficiency.

[The Cat]

It's a law of thermodynamics violation

Thank you!

How close are they to making it cost effective?

Solar-nanobiology
Wind- Santa Cruz/Catalina Channel
Hydro- Ocean currents/rivers?

Could the sale of water rights subsidize production cost?

Could they sell the nuclear option? They could use the revenue from water rights.

[Azrael]

Could the sale of water rights subsidize production cost?

The (non-capitalized) price of 'traditional' desalination currently relies on the costs of transporting the water and buying the power consumed during the process. So, from a very basic standpoint, it would not be able to subsidize any sort of more expensive-than-normal power generation -- it would always be more cost effective to buy from the traditional grid.

In particularly water strapped areas, you probably *could* charge a premium for the water, allowing a company to make an acceptable profit using more expensive generation -- but that's not a very ethical choice.

A non-profit model could absorb the increased cost of generation by eliminating the need for profit, or government grants could reduce the capitalization costs. But for the majority of scenarios it's simply not going to be cost competitive. In the long run, alternate sources of energy for desalination will not be cost effective until [the price of wholesale energy has risen / the price of alternate generation has decreased] to the point where the alternate energies are cost effective themselves.

[The Cat]

Very informative, thanks Azrael.

In particularly water strapped areas, you probably *could* charge a premium for the water, allowing a company to make an acceptable profit using more expensive generation -- but that's not a very ethical choice.

I'm sorry Mr/Mrs. Azrael. I have a tendency to bypass the filtration process and pump raw sewage into the water supply. You were kind enough to respond to something that is of interest to me. You certainly didn't have to take time out of your day to educate me on the hurdles associated with desalination. My response was rude and sarcastic. As usual, I thought only about the humor, not knowing the audience or background. I hope you can forgive me.

Sincerely, C

[black_hat_guy]

In particularly water strapped areas, you probably *could* charge a premium for the water, allowing a company to make an acceptable profit using more expensive generation -- but that's not a very ethical choice.

Sure it is. They need water and you're giving it to them. Unless you're a government or a very rich person, you have to make at least as much money as it cost just to be able to do it. The people working on it need to feed their families and you need to make a profit because you're spending your time on making water and can't work. Furthermore, what good does being allowed to use rainwater do thirsty people? You can't drink rainwater, but without your generation and owning the water rights, people will try.

[EdgarJPublius]

It's not really an economics question, or even one of technical feasibility.

A well designed nuclear infrastructure easily makes economic sense in and of itself. Building nuclear plants is relatively low risk from a purely technical/economic standpoint and inexpensive compared to the profit potential.
You could say basically the same thing for large scale desalination in some areas, in both cases the oft-quoted 'high costs' are red herrings, distracting from the massive utility and profit potential of such projects.

Putting large scale desalination together with nuclear power, from an economic perspective is a no-brainer.

What I've been leaving out of course is the politics. Energy politics in general, and specifically nuclear politics is practically impenetrable. What should be a relatively simple, low risk investment in a nuclear power plant is humongous complicated by a brobdingnagian morass of protesters and permit requirements that have led to most nuclear power projects defaulting before the ground is even broken.

And adding desalination to the mix is just adding insult to injury, because water politicking is probably the only game more impenetrable than energy politics, though for different reasons. It's practically impossible to actually profit off of water in any water-starved area. Int he U.S. there are various state and local agencies that oversee the distribution and pricing of all freshwater, often with over-lapping jurisdictions and mandates all fighting over every drop that goes in or comes out of their pool.
Which is admittedly better than the old system, or the system that still exists in some parts of the world, which is literal water barons. At least the state and local agencies make sure everyone gets some water if any is available.

[Azrael]

Unless you're a government or a very rich person, you have to make at least as much money as it cost just to be able to do it.

You miss my point (from a year and a half ago) entirely. I'm not saying you shouldn't cover costs, or even turn a profit. I'm saying it's unethical to price gouge just because a market in a particular area might support it out of dire necessity so that you can subsidize higher-cost alternate energy schemes just because those would be nifty.

[Abgrund]

BTW, I calculated that a conventional nuclear plant driving reverse osmosis desalination via electric pumps would need 3% of the freshwater output for its own cooling. Just in case you were wondering.

[Zamfir]

BTW, I calculated that a conventional nuclear plant driving reverse osmosis desalination via electric pumps would need 3% of the freshwater output for its own cooling. Just in case you were wondering.

Why would you need fresh water for that? Nuclear plants have special water inside running in a loop, and that water gets cooled by heat exchange with water from outside. That outside water its often sea water, there is no need to desalinate that.

[SummerGlauFan]

BTW, I calculated that a conventional nuclear plant driving reverse osmosis desalination via electric pumps would need 3% of the freshwater output for its own cooling. Just in case you were wondering.

Why would you need fresh water for that? Nuclear plants have special water inside running in a loop, and that water gets cooled by heat exchange with water from outside. That outside water its often sea water, there is no need to desalinate that.

Plus you could use the waste water as another means of driving desalination. Win?

[EdgarJPublius]

BTW, I calculated that a conventional nuclear plant driving reverse osmosis desalination via electric pumps would need 3% of the freshwater output for its own cooling. Just in case you were wondering.

Why would you need fresh water for that? Nuclear plants have special water inside running in a loop, and that water gets cooled by heat exchange with water from outside. That outside water its often sea water, there is no need to desalinate that.

The primary coolant doesn't even need to be water, it could be liquid metal like sodium or sodium-potassium alloy. Then the reactor doesn't even need to be pressurized, leading to improved safety (though admittedly sodium tends to be a bit um... reactive, which creates a different set of risks)

[Zamfir]

I doubt that liquid metal core cooling requires less water than using water. After all, metal production and purification tends to use enormous amounts of water, so a kg of liquid metal presumably took much more water than a kg to produce. But in all cases, the stuff in the closed loop(s) is a negligible amount compared to the volumes needed for cooling to the environment. And for desalization plants, a lack of sea water will hardly be an issue

[bigglesworth]

Hmmm, while we're in a thread that began with an out-of-the-box idea, how local is rain? I'm thinking this because presumably it'd be possible to pump seawater inland, create a salty lake, then let it evaporate in the sun. The water would fall as rain, but locally enough to be worthwhile?

[EdgarJPublius]

I doubt that liquid metal core cooling requires less water than using water. After all, metal production and purification tends to use enormous amounts of water, so a kg of liquid metal presumably took much more water than a kg to produce. But in all cases, the stuff in the closed loop(s) is a negligible amount compared to the volumes needed for cooling to the environment. And for desalization plants, a lack of sea water will hardly be an issue

You'd also have to account for liquid metal being a more efficient coolant than water, so it would require less liquid metal to maintain the same output.

[pinochet]

Hmmm, while we're in a thread that began with an out-of-the-box idea, how local is rain? I'm thinking this because presumably it'd be possible to pump seawater inland, create a salty lake, then let it evaporate in the sun. The water would fall as rain, but locally enough to be worthwhile?

I doubt it. Without even attempting napkin map, I see some pretty big obstacles.
(disclaimer: The following assumes a US focus, since this is all I am familiar with)

Consider:

• If wikipedia is to be trusted, only 10% of Salt Lake City's precip is caused by the lake effect, and the great salt lake is pretty much a direct natural analogue of what you're considering. http://en.wikipedia.org/wiki/Salt_lake_city#Climate
• If you just eyeball a mean annual precip map, the great lakes create visible lake-effect precipitation but the great salt lake doesn't. This suggests that, at least in areas arid enough to need artificial rainfall, more than 4400km^2 of salt water surface area is necessary to have a strong impact. (presumably due to how far humidity carries in dry air, as speculated by biggles)
• The lake would need to be located in a huge area that is largely uninhabited by humans and doesn't include protected wilderness and endangered species habitat, but is upwind of a watershed to dump rain into. Considering that you're limited to flooding areas that don't naturally drain into an existing watershed (or won't after constructing dams), I'd be surprised if you could find more than a handful of feasible locations in the States. Considering the distribution of protected lands in the States, the locations that meet the population/watershed criteria tend to fail the protected area criterion, and vice versa. If you mean to try this in another country, this may be less of an issue. (Congress loves protecting semi-worthless desert)
• The areas that would need artificial rainfall the most in the States are mostly 500+ meters in elevation and a good 400+ km away from an ocean. This is an awful lot of work--in the physics sense of the term--just to replace however much water your lake is losing to evaporation.
• You'd probably have to construct a pipeline the whole way to cut down on open channel evaporation loss and to cross existing rivers. Admittedly, this is probably trivial in comparison to the other costs.

Water shortages in the west are somewhat artificial, having developed form long-term market distortions:

• The "use it or lose it" nature of prior appropriation water law which discourages conservation by agriculture and industry.
• A two-tiered water market where agricultural/industrial water is largely removed from the municipal water market, causing over-use of artificially cheap water by ag and industry.
• The unsustainable agricultural development of lands with negative net economic productivity after subsidies. This development has taken place in response to irrigation infrastructure (dams) built with a negative return on investment by public works agencies (USACE, BLM, BuRec, the TVA in the south).

I'm actually not much of a free marketer when it comes to resource management (uncorrected externalities being such a huge deal in NR economics), but in this case a carefully deregulated market and some water rights reform might solve water problems very effectively. Provided we don't consider an economically painful shift from agriculture to grazing a "policy failure". Not the sort of thing a state would ever vote for, of course.

Anyway I'm getting off topic. Artificial lakes, like cloud seeding aren't economically viable because the rainfall benefits are too random and diffuse, and the cost is too high. All in all, it is hard to beat conventional irrigation systems in terms of getting water where it needs to go.

(yay first p0st!!oneone)

[Abgrund]

Using the output fresh water for cooling has advantages over using seawater. You don't have to worry (nearly as much) about corrosion or deposits, and any organic material has already been filtered out.

Perhaps I should have specified "end cooling". Hopefully the reactor core coolant is not the final heat sink!

[Zamfir]

Using the output fresh water for cooling has advantages over using seawater. You don't have to worry (nearly as much) about corrosion or deposits, and any organic material has already been filtered out.

Yes, those are serious challenges for all power plants, even plants using fresh water. Cooling inlets grow full with shellfish and algae, concrete rots, steel corrodes. So there are filters for sand and organisms in place, and poisons are sent though the pipes once in a while to kill off the organisms that grew out of spores. But not too much poison of course, since it ends up in the water outside. All out that costs money, but cleaning and desalinization would be even more expensive overkill.