PostHeaderIcon Desalination Oil Rig In The Gulf of Mexico

Recently,¬†¬† a Minnesota company announced plans to use a oil derrick off the Texas coast to site¬† wave power energy production devices to power a desalination plant. It would serve as demonstration pilot. Desalination has never been done quite this way before. They started work in August. They’re interested in producing bottled water from shallower depths than the water harvested off the Big Island in Hawaii–where water is first pumped ashore –before its desalinated.

I think something like  an oil derrick platform would be the model that DVX Technologies should use whenever they go out to sea. The platform would house the maintenance crewРwhile the desalination work was done 850-900 feet below.

I have written a number of blogs about DVX Technologies in the last year or so on the idea of¬† using ocean pressures to desalinate water. On several occasions I have mentioned that one way to bring water ashore would be to drill a slant well from onshore (or offshore–whichever is cheaper) so that the water runs down hill toward shore. On shore, then, the fresh water could be pumped up as from a well. What’s the cost/benefit of this procedure amortized over, say, 30 years? Beats me. A good water–or more likely an oil — consultant would have the tools to figure¬† out the capital energy and maintenance costs.

How do you evaluate the costs?¬† You’d do that by comparing the costs of comparable procedures for getting water ashore.

As far as I can see, the other procedures involve various technologies for pumping water in pipes along the ocean bottom up hill to shore.

So this time I’ll discuss various power sources to pump fresh water ashore uphill along the ocean bottom from the underwater desalination plant . I’ll make the assumption that the oil companies will already have optimized the best way to lay and maintain pipe. Further, I’ll assume that the oil companies will already have optimized the best practices for installing & maintaining an offshore platform–and that their crews would be best suited for installing and maintaining a water platform. Finally I’ll assume that the rough cost of oil or gas generators to pump water ahsore is already known; that this can also be used as a baseline against which to evaluate¬† other¬† ways to power the pumps.

Oil rigs have desalinized ocean water for years– but they have done so for their own use. They don’t produce fresh water on a commercial scale. (However, except for the membrane plants themselves, the oil companies have all the skills/tools necessary to do offshore commercial grade desalination.)

Most off shore drilling rigs have diesel or  gas powered generators.

If a desal plant on the ocean floor was sited over a natural gas deposit below the ocean floor being drilled by¬† an oil rig…then the natural gas could be used to power the pumps that pumped fresh water ashore from the underwater desalination plant. Did you get that? This won’t happen very often–especially not in the waters off southern california where more coastal drilling is frowned on.

So how else could you power big offshore pumps onsite?  That is, without importing power to the platform by means of oil or gas.

Another way to power pumps — to send desalinized water ashore–would be with wind generators on rigs. Something like this is currently in planning in the north sea. If you read the article you’ll notice that they have all the attendant construction and installation issues resolved. However, the waters off southern California are not as world famous for wind as is the north sea.

I should also mention that it would be easy to drop a portable nuclear reactor onshore opposite the oil rig desalination plant–and run a power cable out to sea. Here’s another company. At present¬† its unlikely¬† that any kind of nuclear plant would be built in Southern California. But that could change.

So what other sources of power might be used to drive a pump?

Four properties of salt water can be exploited for energy to power pumps.

1.)The most esoteric/furthest from commercialization/expensive is R&D by which the navy is looking for  ways to turn salt water into diesal and jet fuel.

2.)Another exploitable power source is thermal conversion power plants. These are  big on shore because of new technologies especially in Utah. However, offshore the temperature differences are narrower and the opportunities fewer. But they exist. In 2008 Hawaii entered into an agreement to develop thermal conversion power plant off the Big Island.

November 20, 2008 (ENS) – Hawaii Governor Linda Lingle Tuesday announced a new energy partnership to develop a 10 megawatt ocean thermal energy conversion pilot plant in Hawaii. Electricity will be generated from the difference in temperature between the ocean’s warm surface and its colder depths.
During the Governor’s official state visit to Taiwan, she came to an agreement with the Taiwan Industrial Technology Research Institute and the Lockheed Martin Corporation to build the initial pilot plant in Hawaii.

The energy produced is used to desalinize bottled water for export to Japan. The water depths they are talking about +-2000 feet. It would take more research to know whether the same technology could be used for 850-900 feet ie shallower depths and lower temperature differences. For now, I don’t think the temperature differences are great enough for commercial grade energy production. But I could be wrong about that because Oasys they can exploit only 20 degree differences to produce power. The jury is still out on this.

3. Osmotic power plant might be developed to take advantage of the¬† salinity differences between the desalinized water and seawater to produce energy to pump¬† water ashore. The Norwegians are currently trying to develop this technology. Its a pilot. IBM is looking into it as well.¬† The technology isn’t anywhere near mature. Moreover the volumes of water needed to make energy are too large. However, this technology can be reversed. As I first mentioned in this piece from 2007 on Forward Osmosis and again this year, Oasys promises to desalinate water for US$ 0.37-0.44/m¬? once fully scaled up. (That was in the Spring of 2009. By the Fall, Oasys was promising much cheaper costs.) Oasys promises to use the use the same process as the Norwegians to produce electricity only much more efficiently. Their procedures for producing desalinated water looks more mature than their electrical generation idea.

4.  Ocean pressures at 900 feet should convert  to electrical power. Trouble is I have not seen any examples of companies actually doing this.

This technology developed by Energy Recovery Inc. might  be adapted to convert the waste stream from a deep water desalination plantРinto energy to drive a pump. According to this Forbes Magazine article

Competing pressure exchangers work by capturing energy in the exit water via a turbine (analogous to a waterwheel), then transferring that shaft power to a pump (waterwheel in reverse) for the entering seawater.

It shouldn’t be too tough to create an exit stream. (Think WWII sea war movie. The submarine has just been hit by a depth charge. Water hisses into the hold through the cracked hull.) You convert that water to shaft power to power a pump — to pump water ashore.

5. As used on the Texas oil derrick, wave power could be harnessed to pump water ashore. This article about wave power generation in San Francisco lists the companies under consideration.¬† All are in various stages of prototype. They could be used to either generate electricity to run the pumps that pump the water ashore… or pump the water ashore directly. Here is another article about wave power being used to generate power for the¬† small scale desalination plant for bottled water on a platform in the gulf of Mexico

Of the choices mentioned above, I think the best ie cheapest– would be¬† 4.)Energy Recovery’s tool. It could be adapted to convert 850 ft depth ocean pressures into electricity to drive a pump to push water onshore. imho it would cost +-400k to make the adaption.

DVX¬† about whom I’ve done several blogs on deep water desalination currently has a ” small installation of the technology in the San Joaquin Reservoir near Newport Beach.”¬† (Here’s a diagram.)They’re looking to set up another test site in the near future.¬† They experienced biofouling problems at the first site. Now they are looking into pretreatement technologies. Here is one. They expect to license out their technology in 2010.

Finally, I should mention again that NanoH2O has a much more efficient membrane coming out in the next couple months. However, its not likely that they’ll have the membrane configured to the specs for DVX Technologies. It would be helpful if someone could find the ways/means to get some prototype NanoH2O membranes for the DVX Technologies work.

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