Hydrothermal Energy System

Dry Steam Hydrothermal Energy

Hydrothermal vent is a fissure in a planet's surface from which geothermally heated water issues. Hydrothermal vents are commonly found near volcanically active places, areas where tectonic plates are moving apart, ocean basins, and hotspots. Hydrothermal vents exist because the earth is both geologically active and has large amounts of water on its surface and within its crust. Common land types include hot springs, fumaroles and geysers.

The most famous hydrothermal vent system on land is probably within Yellowstone National Park in the United States. Under the sea, hydrothermal vents may form features called black smokers. Relative to the majority of the deep sea, the areas around submarine hydrothermal vents are biologically more productive, often hosting complex communities fueled by the chemicals dissolved in the vent fluids. Chemosynthetic archaea form the base of the food chain, supporting diverse organisms, including giant tube worms, clams, limpets and shrimp. Active hydrothermal vents are believed to exist on Jupiter's moon Europa, and ancient hydrothermal vents have been speculated to exist on Mars.

Hydrothermal Vents

Günter Wächtershäuser proposed the Iron-sulfur world theory and suggested that life might have originated at hydrothermal vents. Wächtershäuser proposed that an early form of metabolism predated genetics. By metabolism he meant a cycle of chemical reactions that produce energy in a form that can be harnessed by other processes.

It has been proposed that amino-acid synthesis could have occurred deep in the Earth's crust and that these amino-acids were subsequently shot up along with hydrothermal fluids into cooler waters, where lower temperatures and the presence of clay minerals would have fostered the formation of peptides and protocells. This is an attractive hypothesis because of the abundance of CH4 and NH3 present in hydrothermal vent regions, a condition that was not provided by the Earth's primitive atmosphere. A major limitation to this hypothesis is the lack of stability of organic molecules at high temperatures, but some have suggested that life would have originated outside of the zones of highest temperature. There are numerous species of extremophiles and other organisms currently living immediately around deep-sea vents, suggesting that this is indeed a possible scenario.

The water that issues from seafloor hydrothermal vents consists mostly of sea water drawn into the hydrothermal system close to the volcanic edifice through faults and porous sediments or volcanic strata, plus some magmatic water released by the upwelling magma. In terrestrial hydrothermal systems the majority of water circulated within the fumarole and geyser systems is meteoric water plus ground water that has percolated down into the thermal system from the surface, but it also commonly contains some portion of metamorphic water, magmatic water, and sedimentary formational brine that is released by the magma. The proportion of each varies from location to location.

In contrast to the approximately 2°C ambient water temperature at these depths, water emerges from these vents at temperatures ranging from 60°C up to as high as 464°C. Due to the high barometric pressure at these depths, water may exist in either its liquid form or as a supercritical fluid at such temperatures. At a barometric pressure of 218 atmospheres, the critical point of water is 375°C. At a depth of 3,000 meters, the barometric pressure of sea water is more than 300 atmospheres (as salt water is denser than fresh water). At this depth and pressure, seawater becomes supercritical at a temperature of 407°C. However the increase in salinity at this depth pushes the water closer to its critical point. Thus, water emerging from the hottest parts of some hydrothermal vents can be a supercritical fluid, possessing physical properties between those of a gas and those of a liquid Besides being superheated, the water is also extremely acidic, often having a pH value as low as 2.8 approximately that of vinegar.

Sister Peak (Comfortless Cove Hydrothermal Field, 4°48′S 12°22′W, elevation -2996 m), Shrimp Farm and Mephisto (Red Lion Hydrothermal Field, 4°48′S 12°23′W, elevation -3047 m), are three hydrothermal vents of the black smoker category, located on the Mid-Atlantic Ridge near Ascension Island. They are presumed to have been active since an earthquake shook the region in 2002. These vents have been observed to vent phase-separated, vapor-type fluids. In 2008, sustained exit temperatures of up to 407°C were recorded at one of these vents, with a peak recorded temperature of up to 464°C. These thermodynamic conditions exceed the critical point of seawater, and are the highest temperatures recorded to date from the seafloor. This is the first reported evidence for direct magmatic-hydrothermal interaction on a slow-spreading mid-ocean ridge