As soon as the existence of the first
hydrothermal vent was confirmed in 1977, every observer understood
the enormous energy potential they contained, but utilizing it seemed
an impossible task. Located at average depths of 2,300 m or about
7,500 ft, no one had the slightest idea of what kind of system could
be placed at the bottom of the ocean to generate electricity. Although
the promise was there, the reality has remained unattainable in
the 30 years since their presence became known.
The Marshall Hydrothermal Recovery
System is a deceptively simple leap of logic. Instead of trying
to work with the vents at the bottom of the ocean, the vents are
capped, and their flow is fed into a continuous, highly insulated
pipe, which leads 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 teperature
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.
Another embodiment of the system
uses a closed loop. Rather than bringing the hydrothermal fluid
from the depths to the surface, clean working fluid recirculated
within a closed loop is heated by the vent through a heat exchanger.
The vent's heat is transferred to the fluid, which is then utilized
directly to drive 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.