A Detailed Thermodynamic Accounting of a Route to Obtaining World Motor Fuels from Solar and Wind.

[NNadir]

8. I go around and around on desalination. A talk I attended recently gave me a new perspective.

The talk is on line. It can be accessed here: Science on Saturday: Managing Coastal Risk in an Age of Sea-level Rise. Scroll down for the lecture video.

One of the things Bob Kopp covered in the lecture is something I've been wondering about for some time, which is to what extent does the mining of fossil water, as in the Ogallala Aquifer, on which a significant portion of US grain production depends effect sea levels.

According to him - and he's a fascinating thinker - about 10% of the currently observed rise in sea levels is attributed to the mining of fossil water and it's release into the hydrosphere.

One one hand, I'm concerned about the effects of saline gradients on ecosystems, on the other hand, the seas are being diluted by climate change, the change of saline gradients is out of control with or without desalination.

Some compromises are going to need to be made.

There are good reasons why I think that supercritical water desalination in the Gulf of Mexico, for one place, is a very good idea, for the reasons I gave in the OP. The water there is in trouble and it the quality of the water can be greatly improved by supercritical water oxidation. Of course, they don't necessarily need water in Louisiana, at least most of the time, and as we know, they often have way too much of it. On the other hand it might be pumped or sucked to places where it is needed.

I personally think that process intensification, as is possible with supercritical water desalination, can produce very high efficiency energy use which can, among other things, drive pumps on what was once considered waste energy.

However, from where I stand, the only possible approach to cleaning the air of the dangerous fossil fuel waste carbon dioxide must go through extraction and concentration in seawater.

It is also an approach to making uranium supplies essentially infinite, and in a moral world, each generation would extract exactly what it uses. However uranium requirements to power the whole world are rather small. Suppose we decided to raise world energy consumption to 1000 exajoules a year in an effort to clean up the mess of carbon dioxide waste in our atmosphere, eliminate human poverty and do a host of other useful and good things. It can be shown that this would require the fission of 395 grams of plutonium each second, or about 12,500 tons per year, which is less than the amount of unused uranium already in US used fabricated nuclear fuel.

At the accepted concentration of uranium in seawater, this would involve processing 3 trillion cubic meters, slightly less than the volume of Lake Michigan, but the main things to be recovered would be water and carbon.

This sounds like a lot of water, until one realizes that the State of Kansas, for example irrigates with about 4 billion cubic meters every year, much of it coming from the increasingly depleted Ogallala. With this in mind, it's very clear that world fresh water demand is easily on a trillion cubic meter per year scale.

There are many places all over the world where water supplies are severely threatened, particularly, over the long term the vastly populated portions of Asia that have depended on Himalayan glaciers, glaciers that are threatened. Of course, it may be absurd to discuss this today with much of Nebraska recovering from massive flooding, but to the extent we have a mechanism for moving vast sums of water, we might manage our survival better.

To the extent that depleted fossil water reserves are replenished, like, but certainly not limited to the Ogallala, this will serve to slow sea level rise, apparently, if Dr. Kopp is to believed, by an appreciable, if minor, amount. However coupled with the removal of carbon dioxide from the air, it might do something. The big things though, are glaciers and ice caps.

Right now, except for the cheer leading for solar and wind and hyping electric cars, nothing useful is happening.

The key to recovering from the energy waste situation is, in fact, energy, but energy with a low pollution profile, the only one to have worked, to be scalable, and to be sustainable, being nuclear energy.

This is all a little dreamy, I know, but it's the most practically approachable thing that seems even remotely feasible. It's a very challenging task, and no, getting one's underwear in a wedgie thinking about Elon Musk and wind turbines is not going to cut it. I have no illusions that these things will be done, but I believe that they are possible. I am reluctant to use the word "could" as is often used here with the word "study" to claim for example, "Greenpeace study shows that the world could be powered 100% renewable energy [insert year du jour here." Still, while the possible is often improbable, everything that is was once improbable.

The issue is scale. I don't think we have any idea of the scale of the disaster we are leaving for all future generations.

We will not be forgiven, nor should we be.