Mining Hydrothermal Vents For Renewable Electricity, Drinking Water + Valuable Minerals

Only after I snoozed my way through high school science class did science become more compelling than science fiction.

Back then, there was just no compelling reason to pay attention. Just a browzy fly buzzing in a smelly boring lab full of long agreed-upon dull principles that were really neither here nor there. In those days there were no colliding continents or hydrothermal vents or extremophile lifeforms. We looked to sci-fi for that.

Who knew that our planet would soon be busting at the seams with 7 billion of us. That our fossil fuel use would threaten our survival with climate changes — on a level unseen on the planet since Cyanobacteria made it safe it for oxygen-breathers 4 billion years ago.

Or that we would not only discover vast strange heat sources under the ocean but that we’d actually consider mining these hydrothermal vents for renewable energy: That was the sort of story you’d only find in science fiction back then.

But yet, here we are. This is not science fiction:

» See also: Chilled Water Cools MIT Physics Department
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The energy potential is staggering. In the Gigawatt range per vent.

The Marshall Hydrothermal Recovery System would use the heat from hydrothermal vents 7,000 feet under the sea to make electricity. Its temperature is incredibly high, 750 degrees Fahrenheit; hot enough to melt lead, but it does not boil because of the intense pressures at the depths where the vents are located.

Superheated fluid would be propelled up through a through a (well insulated!) pipe to an oil platform located on the surface above the vent. The superheated fluid is carried by means of flow velocity, convection, conduction, and flash steam pressure as it rises and the ambient pressure is decreased.

Once delivered to the platform, the heat energy contained in the fluid can be extracted to generate electricity. Since the amount of energy available from any thermal system is dependent on the difference in temperature between two points, the system also includes a Thermal Enhancement Pipe.

This is simply an open pipe, like a large drinking straw, which extends down below the layer of relatively warm water on the surface to the permanently frigid waters below. By withdrawing water from that pipe and using it as the cold side of any heat reaction, much more energy can be extracted from the process than could be delivered without it.

But what about those extremophile lifeforms down there at the vent? This has got to be ecologically disruptive!

Marshall Hydrothermal is pretty frank about the horrible ecological consequences: The company says that there is no way to sugar-coat the fact that these organisms will die so that we humans can live our much more exciting lives though electricity.

The company “plans” to relocate the local flora and fauna to another vent nearby. But can people work 7,000 feet down to carefully pull these limpet-like creatures off the sides of volcanic vents? I’m not quite sure how that would happen.

Or, perhaps a closed loop system would be safer? Marshall offers this alternative method:

Rather than bringing up the hydrothermal fluid itself with bits and pieces of sea creatures as well, a simple heat exchange is effected within a closed loop: all the fluid is contained in the pipe and heated at the vent and circulated up for use to drive the turbines on the surface.

The cooled fluid is then sent back to be reheated by the vent again and again, but the hydrothermal fluid itself is never actually brought to the surface. More than just a huge renewable energy supply is at stake here.

20 million gallons of hot fluid would flash to steam at the surface and that could be distilled back into fresh water. Further purification would be needed, but the natural heat from the process itself provides the most important part of the energy needed for the process. Fresh water is the new oil.

If even only 50% of the total volume could be recovered, that would still provide about 264 million gallons of fresh water daily.

Unfortunately, desalination apparently requires the (more ecologically disruptive) open loop system, to work. (See first diagram) But, if that could be solved, there is another argument for mining the actual fluid (open loop); not just the heat (closed loop) system.

The materials in these geologically ancient vent fluids include iron, gold, silver, copper, zinc, cadmium, manganese, and sulfur. Halides, sulphates, chromates, molybdates and tungstates are also abundant.

When the fluid is trapped, the slurry left over after the heat is extracted can be loaded aboard ships for processing elsewhere, or processed on-site.

Cap and Trade would also help fund this completely new form of renewable energy extraction. Who better to carry it out than the oil industry. They already have the expertize with ocean drilling extraction.

Turns out there is also significant amounts of methane gas mixed into the fluid. Maybe there is a way to cap that for remediation-cum-fossil energy at the same time, as well as selling the renewable electricity, fresh water and minerals produced by the vents.

For the oil industry, with all these inducements, surely switching to mining renewable energy would be more cost effective than having to keep on paying media outlets and school districts and think-tanksfull of talking heads to keep enough people ignorant enough about climate change to slow the legislation needed to stop it; decade after decade.