Desalination breakthrough...

Discussion in 'Off-Topic' started by cmartinez, Jun 7, 2016.

  1. cmartinez

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  2. #12

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    This sounds like a smart move caused by actual thinking.
     
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  3. killivolt

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    I wonder if "California" could adopt this and save water supply from the Colorado River which would help us in Utah, since we do live in a desert:(

    kv
     
  4. cmartinez

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    I have no doubt that they could, but in the end it all boils down to economics.
     
  5. killivolt

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    I must say though, you come up with the most interesting things. Your keen on finding things that interest me.


    kv
     
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  6. wayneh

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    I'm skeptical. I'm all in favor of running it down to find out what the limits are, but I bet dollars to donuts that there ARE limits that prevent this from being practical unless/until things get far worse. These limits may be well known by people already in the field. It's not like any new technology has been unearthed. Trying to revive old technology for new applications is a noble effort, but success is rare.

    Researchers are often, understandably, way off base about the economics of things, in this case the various bulk chemicals; calcium oxide, calcium chloride, ammonia, sodium bicarbonate. So many times I've seen pie-in-the-sky blurbs like this but when you really look into it, the cost assumptions value the inputs at bulk wholesale and value the outputs at small-scale retail. It doesn't work like that! And they rarely adjust for the impact of their project on the market prices. That can be OK if the project is small compared to the market. But in this case, what happens to the price of sodium bicarbonate if the supply suddenly doubles? These issues may or may not have any impact on this project but to me it seems silly to talk about the project without acknowledging them. It's like talking about a fusion energy project without noting how far away from breakeven it is.

    I'm not completely negative on this. It makes sense to look for a way to use the concentrated brine besides just throwing it back into the same water you're trying to purify. Concentration represents reduced entropy, and it's silly to waste that.
     
  7. joeyd999

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    Jun 6, 2011
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    I am curious: why does the brine from desalinization increase salinity in the Gulf, but evaporation (of pure H2o!) does not?

    I don't have any data to back this up, but common sense tells me that natural evaporation removes many times more H20 from the Gulf on a given day than desalinization.

    Anyone want to work the numbers?
     
  8. killivolt

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    Correct me if I'm wrong. But, I think it's the dumping of the left over brine back into the gulf that is increasing the salinity of the Gulf.

    You have an interesting point though, what would the amount be of normal vaporization of H2O minus rainfall within a year amount to?

    kv
     
  9. wayneh

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    From this summary,

    "Out of approximately 17,346 contracted and online desalination plants across the globe, the GCC countries hold 7,499 which is 43% of the share. In-terms of capacity, the total global contracted and online capacity as of 2013 is approximately 94,500,000 m3/d, from which 62,340,000 m3/d comes from the GCC countries with a share of almost 70%(Table 1)."​

    The capacity is growing and the report is a couple years old, so let's say the Gulf desalination capacity removes 65 million cubic meters of fresh water per day. Many reports talk about the brine problem, but the brine starts in and returns to the Gulf, so it's not really a bulk problem. It seems to be a localized problem, where the brine is dumped and doesn't get sufficiently diluted.

    The Gulf has a surface area of 251,000 km^2. So water removal for desalination is 65 x 10^6 m^3 per day, or 259m^3 per km^2 per day. That works out to 259x10^-3 meters per day, or 259mm or 25.9cm (about 1") of depth per day.

    My first reaction is that this is a lot!

    There are many estimates of evaporation from the gulf. Here's one. It looks like 2 meters per year. That's just 0.55cm/day.

    Unless I've slipped a decimal here or there, it looks like desalination is removing ~47X more fresh water than natural evaporation does. Sounds unsustainable to me.

    Other references that may be relevant
    http://onlinelibrary.wiley.com/stor...wy&s=ad046c3ad83478fe859972188a36346f6e2e2c2a

    http://www.rmrco.com/docs/pub93_PersianGulf_MarPolBul.pdf

    http://www.ocean-sci.net/2/27/2006/os-2-27-2006.pdf

    http://www.sciencedirect.com/science/article/pii/S0307904X06002241
     
    Last edited: Jun 20, 2016
  10. joeyd999

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    Yes, your numbers look surprising.

    An inch per day, over the area of the Gulf, seems like a heck of a lot of water -- enough to pin the needle on the wrong side of my "plausible" meter.

    If I have some time, I'll check your math.
     
  11. wayneh

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    I threw in some other references above. Also, note that the desalination capacity is not all online at the moment. The growth rate in capacity is high and there are many contracted projects underway but not online yet. It's a moving target.

    Bottom line: I'm glad to live within an hour's drive of the world's largest fresh water supply.
     
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