How to reverse global warming - IRRIGATE deserts

[Airbrush]

A way to reverse global warming by reducing CO2 in the atmosphere is to irrigate the deserts. I don't know how to do this, but it will take a huge magnitude of fresh water and maybe that can be made in many desalination plants all over the world. Then you need a lot of explosives to dig out huge irrigation ditches extending into all the great deserts of the world. Then plant LOTS of trees.

Edited July 25, 2013 by Airbrush

[EdEarl]

Do you know how much energy is needed to desalinate a kg of water, and the cost of that energy?

[Airbrush]

Do you know how much energy is needed to desalinate a kg of water, and the cost of that energy?

 

No how much? Maybe a cheaper method can be found?

[iNow]

No how much?

 

I cannot recall if the measurement is in metric or imperial units, but the official number is a shit ton... also known as a metric assload.

[EdEarl]

No how much? Maybe a cheaper method can be found?

Your idea, it's your responsibility to calculate. I agree with iNow. It's easy, heat of vaporization of water is 2260 kJ/kg.

Edited July 25, 2013 by EdEarl

[Airbrush]

What's the basic desalination method? Dig a pit and fill it with salt water and cover it with clear plastic with a weight at the center for the distilate to drip into the coffee can at the center.

 

Just do something like that only on large scale, but everywhere near the ocean, even floating on the ocean.

[EdEarl]

The ocean already evaporates water, so you would have to build evaporation pools on land. A sq m gets about .75 kJ each second at noon. How much area in evaporation pools do you need to irrigate a sq km of trees.

[John Cuthber]

Your idea, it's your responsibility to calculate. I agree with iNow. It's easy, heat of vaporization of water is 2260 kJ/kg.

Unfortunately, it's easy to get the wrong answer.

http://en.wikipedia.org/wiki/Multiple-effect_evaporator

[EdEarl]

John, increasing efficiency does not change physics. The heat of vaporization remains unchanged.

 

A multiple-effect evaporator, as defined in chemical engineering, is an apparatus for efficiently using the heat from steam to evaporate water.

From: http://en.wikipedia.org/wiki/Multiple-effect_evaporator Edited July 27, 2013 by EdEarl

[John Cuthber]

John, increasing efficiency does not change physics. The heat of vaporization remains unchanged.

 

From: http://en.wikipedia.org/wiki/Multiple-effect_evaporator

Nobody said it did.

However, you are overlooking the conservation of energy.

The energy which is used to make steam can be captured when that steam is condensed back to water.

So you can use the same energy to evaporate several sets of water.

Did you actually read the article?

[EdEarl]

Yes, I read it. The op suggested a simple glazed evaporator; whether it produces steam at high enough temperature for a multiple effect evaporator or not, idk. The limiting factors are solar heat per sq m and heat of evaporation. Assuming 100% efficiency the area for the solar collector is very large to produce enough water to grow a sq km forest.

[Airbrush]

There can be coastal floating barges one square mile that take on enough seawater to maintain a water depth of over a foot. The bottom can be lined with solar cells if you need more energy. But mostly the sunshine passes thru a clear plastic roof and creates a greenhouse effect heating the water to high temperatures naturally. The distilled water is transported by pipeline onshore. The water then is efficiently channeled by hose to each tree so no water is wasted.

[EdEarl]

Using heat of vaporization and km/sq m, how much water can you get per sq km or sq mi if you want to convert? BTW a diciduous forest needs about 1 m rainfall per year.

 

I calculated about 300 gal/s from 1 sq km, which is just enough for 1 sq km forest, assuming 100% efficiency. Realistically, it is impossible to get 100% efficiency, 33-50% is more realistic. PV are usually less efficient.

 

IMO making salt marsh would be more economical, but salt marsh is being made into beaches for recreation and housing.

Edited July 28, 2013 by EdEarl

[John Cuthber]

On any meaningful scale the maintenance costs are probably the killer so the salt-marsh probably wins.

However, if you are going tu use desalination then a single effect solar still is about the least efficient solution (though it has the advantages of being cheap and simple).

There isn't the information to hand to calculate the benefits of using multiple effect evaporators.

I don't have figures for the difference in heat of evaporation of water from salt and fresh water at different temperatures and pressures, not have I the data on the typical gas concentrations in sea water.

However, real chemical engineers who build sea water distillation plants (and who do have the data) use multiple effect evaporators.

http://en.wikipedia.org/wiki/Multiple-effect_distillation

And there's nothing to stop those being powered by concentrated solar power.

 

Of course, unless the desert happens to be below sea level, the other big energy cost is pumping the water uphill to the place where you want it.

[EdEarl]

Perhaps Airbrush had a premonition.

 

Trees Mitigate Climate

 

I still think recovering salt marsh would be better, but perhaps it is not economically viable.

Edited July 31, 2013 by EdEarl

[Airbrush]

Thanks for posting that EdEarl. That is new to me. I suppose by terriforming our own planet, by making deserts productive, would also increase the food and water supply and allow for larger populations. Also, who knows what other benefits and hazards there are to productive deserts. The climate could change radically.

 

Could you please explain how recovering salt marshes works?

 

Is there a way to get ocean plants to help remove CO2 from the atmosphere?

Edited August 1, 2013 by Airbrush

[EdEarl]

Convince people who like to live where salt marsh was in the past to move elsewhere, remove artifact from human habitation, and let nature reclaim the coast.

[FX]

Greenhouses, using salt water and using solar pumps to move the water, the sun to evaporate it, work quite well in deserts, and a large project is underway. They found the leakage from inside the greenhouse to the desert outside actually allowed plants to simply grow around the greenhouses, which already produce food.

 

Solar power, quite available in deserts, can pump water, desalinate it, grow food, and green the surrounding desert, all with less cost that building one nuclear power pant. Or fighting a war.

[EdEarl]

FX,

And, the salt water ponds are great for growing algae, which can be used in many ways, including pellets for pellet stoves, separating algae oil to make biodiesel, separating protein to make animal or human food, separating biochemicals for industrial use, spreading it directly as fertilizer, etc.

[swansont]

Greenhouses, using salt water and using solar pumps to move the water, the sun to evaporate it, work quite well in deserts, and a large project is underway. They found the leakage from inside the greenhouse to the desert outside actually allowed plants to simply grow around the greenhouses, which already produce food.

 

Solar power, quite available in deserts, can pump water, desalinate it, grow food, and green the surrounding desert, all with less cost that building one nuclear power pant. Or fighting a war.

 

Links to give more detail and back up these points would be great.

[FX]

http://news.sciencemag.org/asiapacific/2013/11/desert-farming-experiment-yields-first-results

 

http://www.smartplanet.com/blog/bulletin/saltwater-cooled-greenhouse-grows-crops-in-the-sahara/

Edited February 22, 2014 by FX

[Enthalpy]

Desalination is rarely done by evaporation, because this takes much energy, even if heat is reused 10 times.

The present-day process is reverse osmosis, which uses a membrane permeable to water only, and just a pump to compensate the osmotic pressure and the losses.

http://en.wikipedia.org/wiki/Reverse_osmosis

"40–82 bar for seawater" which is still expensive.

 

When engineering at the planet scale, it's good to evaluate the costs and other limiting factors. Transporting water horizontally is much easier than desalinating the big scale, and though that's the best humans achieve.

 

Rather than irrigating the deserts, I'd find easier to cut swathes of the rainforest and bury the wood in a way that keeps the carbon in the soil and releases no methane. Then the forest growing back would absorb dioxide, as opposed to a constant-size forest.

[PaulS]

I believe I solved this one. Please visit www.currentelectric.org for the full explanation regarding the perfection of Submarine Hydrodynamic Electrical Generation. I have been requesting anyone with any knowledge in this area of engineering, metallurgy or physics to please review and respond. I would greatly appreciate any feedback. Thank you

[EdEarl]

The site you referenced seems to be a partial business plan, without any technical information. Thus, it is not possible to assess viability of the incomplete business plan.

[FX]

The other way to simply remove an unwanted carbon from the atmosphere is to fertilize the oceans with minerals. Powdered rust for example allows algae to grow in an otherwise sterile regions of the oceans. But rock dust or even desert sand works as well.

 

If it was actually about removing CO2, this would simply be done and problem over.