REVERSE OSMOSIS USING AWE

SUMMARY

Conventional RO compresses water using a high pressure pump and passes the water through a suitable membrane. An alternate method is to use the hydrostatic pressure at depth in the ocean or lake to force the water through a membrane. One method is described in US Patent #5,229,005 where a sphere is submerged, filled with RO water and then lifted out of the ocean. I suggest an alternate method where the RO water is lifted out of a long tube which remains submerged. This lifting of water can be performed by the pulling force of a kite operating in crosswind mode. In this concept no electrical power or high pressure pumping is required which is a major cost of an RO system.

DETAILS

Small diameter tubes are capable of withstanding high hydrostatic pressure without collapsing. If the tube is reinforced by a mesh of tensile wires, then the chance of the tube buckling due to the bending forces will be minimized. The wall thickness of the tube can be progressively increased as the depth increases to withstand the hydrostatic pressure. At the bottom of the tube, we expand the tube to include a larger diameter cylinder with a piston and check valve and attach an RO module which can be a bundle of spaghetti tubes or a spiral wound cartridge. The check valve prevents the RO water from flowing back during each cycle. During the cycle, the piston is lifted by steel wire or high tensile cable and a slug of RO water is discharged at the top. The piston is lowered after each stroke by return spring. The cable in the tube lifts a column of water with each stroke and this lifting force is the only energy required. At the top, the cable passes over a pulley and is connected to the kite tether. (See drawing).

A kite operating in crosswind mode performing figure-of-eights will provide the pulling force. Each loop of the figure-of-eight will provide the lifting force. In this application, we want to increase the difference between maximum and minimum tether tension to provide an oscillating force to drive the piston. The best way to achieve this is to fly the kite to the edge of the wind window. In the case of lazy-eights we will have low tension on both sides, whereas with a narrow figure-of-eight low tension will only occur at the top. This process is not the same as yo-yo operation where tether tension remains high most of the time.


Seawater RO requires a depth of approximately 226 meters. The weight of water in a 25 mm diameter tube this long is 114 Kg and the weight of water in the RO cylinder is 65 Kg. If each cycle lifts the column of water 2 meters and the cylinder diameter is 200 mm then the RO discharge will be 0.063m3 per cycle. If the lift period is 20 sec. and the return stroke is 10 sec. then the production rate is 0.126 m3 /min. For higher wind speeds the cycle can be made shorter.
If too much lifting force is applied to the piston, there is a danger that the filtered water below the piston vaporizes (cavitation). This might adversely affect the filter performance. To prevent this we can control the force of the kite or control the rotation speed of the pulley (governor).
Since lake water, because of its low salinity only requires a depth of about 100 meters for RO, the numbers are much more favorable. We can locate installations closer to the shore for this purpose.
Because the device will be situated on a ship or a barge, we can reorient it to face the wind. Alternately the tube and the pulley support structure can be designed to rotate.
Typical small RO installations produce water for a cost of $1.50/m3 of which approximately $0.50/m3 is energy costs. I estimate that this method will save approximately half the equipment and operational costs and so we can produce RO water at 1/3 the cost of conventional methods. We can scale up the system by using larger kites and larger diameter cylinders , but this would necessitate employing a system like Skysails which would involve automatic launch and retrieval.
I doubt that the upcoming presentation at AWEC 2021 “ Airborne Wind Energy for Sea Water Desalination” will include these concepts.

1 Like

Water-pumping from depth, for whatever reason, has consistently been a main use for wind energy.

Conventional windmill pumping converts rotary motion to a reciprocating rigid rod which activates a piston at the bottom of the well. This proposed system eliminates rotary motion and conversion. We eliminate the weight of a long rod (it would probably buckle) and replace it with a cable and return spring.

Yeah everybody on the internet is an instant genius when it comes to wind energy. Meanwhile, I’ve always wondered, why aren’t kite-reelers pumping water today? As you say, it would use the intermittent pulling motion directly. As far as “eliminating the long rod”, do you think there is a reason they use a rod instead of a cable today, or do you believe nobody thought of it til now?

I can say again what I say every time something like this shows up. Is it not better to generate electricity with the kite, then use the electricity to run the pump/osmosis process?

You are creating a coupling between osmosis and kite which again is heavily wind dependent. That probably means both are not running at optimal conditions. Eg: if the kite is generating too much power, why not feed it to the grid rather than disposing it? What if its blowing but no demand for water at that time? What if the osmosis needs a constant cycle time?

Isn’t the deciding factor the levelised cost of producing potable water? If my predictions are correct there should be no contest. Isn’t it easier to store water than electricity? Why do we need a steady stream of water?

1 Like

That is indeed a good argument. Though I thought Hydrogen was the preferred option. I would say even crypto mining seems
simpler that what you are describing

My take is “hydrogen” is over-hyped as a means of energy storage. I believe the reason is it sounds “scientific”. Similar to global warming: all a person needs to know is a single scientific “fact”. They don’t need to do any math, or understand any pesky details beyond what fits on a bumper-sticker. So if someone remembers third-grade science class, they know that water is H2O, so burning hydrogen produces water as “ash”. And a fuel cell can generate electricity directly, without burning hydrogen in an engine, so it is more efficient. So that’s what fits on a bumper-sticker, which is good enough for many investors and most politicians. Why a company like Toyota is pursuing “hydrogen” is beyond me.

  1. If you burn hydrogen in an internal combustion engine, the power is a fraction of what the same engine will deliver from hydrocarbons, so a car with the same size engine burning hydrogen will be very underpowered. So you’d need a bigger engine = more weight, and just carrying hydrogen as a fuel requires a huge tank or cryogenic cooling etc.
  2. The total cycle of hydrogen is abysmally inefficient.
    a) Producing hydrogen by electrolysis is very inefficient - as bad as 50% - a huge waste of energy.
    b) Storing hydrogen is energy intensive, whether it is compressed or cryogenically cooled, it takes a lot of energy and infrastructure.
    c) For vehicles, perhaps half the the space in the vehicle must be devoted to carrying fuel. Such a tank will cost a lot, weigh a lot, and use up space.

So by the time you are fueled up, you’ve already lost more than half of the energy put in.

  1. Then you have to get the energy back, which introduces MORE inefficiency: The fuel cell is maybe 50% efficient. So you are down to about a quarter of the energy put in.

  2. The motor may lose another 10%. We can’t ignore that. So realistically, you’d be lucky to return 20% of the original energy put in to get the hydrogen.

If you think of the fuel cell as a type of battery, which it is, (cell) you’re looking at ~20% energy return, compared to modern lithium-based batteries which typically return 80-90% of the energy put in depending on conditions such as shelf life and temperature.

So why do people still talk about hydrogen as energy storage? I’m still scratching my head over that question. I know as a young lad I envisioned a future of solar panels producing hydrogen. But by the time I was in my teens or twenties, I was already learning about the real story.

So yeah, hydrogen “sounds scientific” and “fits on a bumper sticker” (slogan-based thinking) but looking at the whole picture, someone would really have to explain to me why anyone would still be pursuing hydrogen as a major energy storage solution.

There is a need for hydrogen in industrial processes apparently, so the market is there. My point being that if hydrogen+awe is farfetched, osmosis+awe is maybe even more. awe+electricity and electricity+osmosis sound better to me…

Well, part of “The Professor Crackpot Syndrome” is the good professor always wants to ruin any possible good invention by including a bad invention, or in some way sabotaging his effort by making things more complicated. Since most windmills in the world are used for pumping water using a reciprocating action, why hasn’t AWE targeted wells and water pumping? My answer would be global warming derangement syndrome, where reason and normal thinking are abandoned in lieu of “saving the planet”. The only science they need to know fits on a bumper sticker. The sad thing is, even if the planet goes back to cooling, these people will never give up on claiming to have all the facts and science behind their proclamations, and the right to tell everyone how to live their lives. They will simply reverse course and pretend it is just a slight adjustment, still lecturing to everyone and telling us all we are “the problem” and that they, as usual, are always right, even if they were temporarily wrong, and that “the beatings will stop when morale improves.”
Meanwhile, why not just pump some water and call it a day? No extra details needed.

Im not sure who of us you are referring to here, but would be nice if you stick to the matter in question

Hello Tallakt:
Well the subject at least included the idea of pumping water with an AWE system.
Not talking specifically about you or anyone on here, so much as sharing an entertaining theme I’ve noted since long before AWE entered its current publicity cycle. You’ve got a generation of people whose entire life experience is based on their little digital devices and all the “information” spoon fed to them through these devices, and meanwhile, very few people experience the physical world even to the point of understanding simple things like most windmills are for pumping water. I’ve wondered for well over a decade when someone from this “new reality” would notice that the intermittent pulling from a kite-reeling setup might be directly applied to pumping water. Pumping water for livestock is simply not on the official agenda of “concerns” to freak out about, so nobody thinks about it. 100 years ago, people were more in touch with their physical world, and maybe then, such a thought might have been the first use seen for a pumping kite. Pumping… hmmm… Gee ya think? Use a pumping action for a pumping purpose? Oh no, that would be too simple. That might stop people from raising endless cash for AWE implying that somehow they just need to get some computer programming right to make it all happen while ignoring the basic aspects of possible configurations, with or without computer guidance.
I developed the “professor crackpot” character long before AWE reared its questionable head, and one influence I remember was a professor at Cal State Long Beach who was promoting a Savonius drag-type turbine he had tested in a wind tunnel (which can force air through an otherwise not-so-great turbine). Of course my opinion was he was a crackpot, and of course his shizzle went nowhere. But really, I told one major figure from the previous AWE forum he represented the epitome of this syndrome, since he made never-ending extreme claims, such as re-powering nuke power plants with kites, while never showing a single significant result. He was not associated with academia per se, and cartainly not a real “professor”. As I’ve explained, the term does not require or even imply any academic involvement.
Meanwhile, when you take a huge step back and look at the whole situation, and take into account the social sciences as a part of the reality, you realize that what is presented to us as “facts” or “science” is a result of people directing the flow of this information we receive, for their own social reasons, such as making a lot of money.
Look at the foundations insisting on limiting drilling, for example. Take the Rockefeller Foundation as an example. Rockefeller bought up a huge percentage of early oil companies in order to intentionally dominate the market. If you watch the financial channel, you know oil prices are balanced on a knife-edge of limiting production to match demand, with a few days worth of storage providing the only buffer between $100 oil versus the actual negative price for oil we saw a little over a year ago. This explains why drilling on public lands and even private lands is prohibited or very limited wherever oil is in high abundance. The Rockefeller Foundation is key in limiting drilling. There is a name for this: “Controlled opposition”. Al Gore - the poster child for global warming hysteria comes from where? Oh yeah, another oil family. What country has the largest known oil reserves in the world? Argentina. So do you think the communist revolution there that has shut down oil production is a coincidence? Well on the financial channel they say that if Venezuela was producing oil, it would lower prices. Do the math. Remember the Iraq war? Remember all the burning oil fields there? How their production was shut down? Do you think it is just a coincidence? Remember, due to limited storage capacity, even a tiny percentage of production exceeding demand would quickly crater oil prices and kill profits for the oil companies. Meanwhile, wind energy is an extension of getting power from natural fluid flows. I was first intrigued during a visit touring the hydroelectric plants at Niagara Falls where I witnessed the GIANT generators in a huge hall, looking like some kind of science-fiction movie, powering the entire Western half of New York State using NO FUEL. I was so “blown away” realizing that the wind could do the same thing. So I started learning all I could about wind energy.
By the time I was ready to build an experimental airborne system, Discovery Channel and Popular Science had started ringing the phone off the hook, and before I knew it I had won the Popular Science Invention of the Year Award with my first Airborne experimental prototype. Between that article and the spectre of Makani starting their effort, AWE suddenly became popular.
Still, by that time, I knew the symptoms of bad or unworkable attempts at wind energy, and tried to convey what I saw to the people hoping to make a difference in AWE, so I openly stated that from what I could see, nobody really knew what they were doing, and most really had no idea how difficult and punishing wind energy could be, and had no idea what they were getting into. I said at the time I felt like a representative of AA trying to warn people about the dangers of alcoholism after midnight at an all-night drinking party - nobody wanted to listen. Still seems to be the case. Oh well. :slight_smile: