Seeking Potable Water from the Sea

water

By Harry Valentine 2017-03-04 17:42:51

There is much research underway internationally that seeks to reduce the cost of seawater desalination. One interesting alternative is to allow for the development of a micro-climate that could provide some rain in critical mountain watershed areas.

Solar Cycles

The cycle of solar-driven natural desalinization of seawater provides the world’s supply of potable water. Over a period of centuries, human survival has depended on the natural world providing a steady supply of potable.

The advent of steam power first alerted mankind to the possibility of using heat to produce potable water from seawater. Ready and easy access to cheap fuel in oil producing, Middle Eastern desert locations prompted development of large scale thermal desalinization plants in the Middle East. However, such technology significantly raised the price of desalinated potable water.

Drought and Weather

Changes in weather patterns such as El Nino and La Nina have periodically reduced seasonal rainfall in various locations and produced seasonal drought. During a period when populations were smaller and mobile, people could move to another location where sufficient potable water was available to sustain human populations.

When local populations grow over extended periods, movement of populations becomes less practical. Seeking alternative means by which to deliver potable water to established populations located in large cities becomes more practical, as is evident by the still functioning aqueducts built by the Roman Empire.

Internationally and over a period of millennia, towns and cities developed and grew along large rivers that not only provided potable water but also provided transportation access to other towns and villages. The combination of easy and reliable access to potable water as well as maritime transportation also led to the development of the early coastal towns and cities.

During times of drought, modern oceanic coastal cities have explored a variety of options, including using large tanker ships to carry potable water from nearby regions.

New Technologies

The development of new technologies such as microporous membrane technology and ultrahigh-intensity ultraviolet (UV) lighting technology has led to these technologies finding application in the potable water industry. Microporous membrane technology forms the basis of reverse-osmosis (R-O) water purification, including a high-pressure variant that can desalinate seawater. The UV light destroys bacteria including fecal bacteria that can sometimes contaminate potable water supplies.

As growing populations progressively demand more potable water, coastal cities are introducing and increasing their recycling of waste water using the combination of R-O and UV water purification technology.

The combination of recurrent droughts and growing populations is prompting several coastal cities to consider increased usage of seawater for applications that once used potable water. Some areas of Hong Kong and a populated island off the coast of California use a mixture of seawater and recycled water to flush the toilets.

Several coastal cities are examining advances and alternatives in lowering the cost of seawater desalinization. One option is to apply low-cost, overnight off-peak electric power (11:00 PM to 5:00 AM) to operate high-pressure reverse-osmosis desalinization technology along with high-intensity UV-light technology to purify the water.

Salt Ponds

Salt ponds (saline ponds, brine ponds) are effective collectors of solar thermal energy. As water salinity increases, reflection of solar infrared to the sky decreases to the point of 100 percent infrared capture. Extreme high salinity occurs at bottom levels of these ponds where temperatures can rise to 60 degrees C to over 90 degrees C and sufficient to sustain the operation of thermal desalinization. Excavating unproductive coastal land installing heat collector pipes on the floor can form the basis of a salt pond. The combination of ocean wave energy and ram pumps can transfer seawater into the excavated area.

Natural evaporation could increase salinity of the pond with an ongoing exchange of a small amount of seawater maintaining a layer of reduced salinity near the pond surface. Coastal salt ponds located near a cold ocean current could also sustain the operation of Organic Rankin Cycle (ORC) engines that could generate electric power.

Optimally designed salt ponds in warm climates could produce temperatures of 90 degrees C while making productive use of desalination brine in terms of local power generation and seawater desalination. Salt ponds also involve lower capital cost and lower long-term maintenance cost that solar collection technologies.

Off-Peak Power Desalinization

Several power technologies can generate electric power during periods of minimal market demand. The list includes wind power, ocean turbines, ocean wave energy conversion and even large-scale coastal steam power stations that operate most reliably when maintained at steady output and steady temperature.

One ocean wave conversion technology from Australia drives a water pump to supply high-pressure water via a pipe to a beach mounted turbine, provide seawater under high pressure to reverse-osmosis (R-O) desalination membrane technology. Some ocean turbines and vertical-axis offshore wind turbines can be modified to drive high-pressure water pump technology to supply R-O technology.

Off-peak high-temperature steam can maintain turbines and steam pipe distribution systems at steady temperature while also sustaining thermal desalinization of seawater. Long-proven steam jet technology can maintain vacuum pressure inside large tanks of seawater, removing moisture (potable water) while cooling the seawater to near freezing point.

In humid climates, cold water piped through radiators can assist in condensing potable water from humid air. During daytime operation, the temperature of turbine exhaust steam from a coastal steam-based power station is sufficiently high to sustain operation of a seawater thermal desalinization installation.

Ocean Water Spouts

The oceanic water spout is driven by weather and occurs naturally in many parts of the world. It is cyclone the picks up droplets of water that evaporate as the water spout swirls skyward, dropping sea salt back to the ocean as a cloud drifts from the top of the water spout. A warm spot occurs on warm surface ocean water that is at 26 degrees C and caused a funnel of air to rise skyward. Advances in modern technology and a combining of technologies offer the promise of artificially producing oceanic water spouts at select offshore locations.

Such locations would need to be upwind of coastal mountains, with prevailing winds pushing the cloud generated by the water spouts toward watershed areas in the mountains. Fine mesh fog fences are able to harvest potable water from humid air and installation of such fences in the mountains and downwind of the waterspouts would provide an additional source of humidity.

Multiple sources such as thermal power station exhaust heat and low-grade geothermal energy can provide the thermal energy needed to initiate and sustain the water spouts. Many other technologies could also sustain water spout operation.

Water Spout Technologies

Offshore vertical-axis wind turbines and a new Australian ocean wave conversion technology can both drive submerged water pumps and push water under pressure through pipes and drive a submerged heat pump. It would source heat from warm seawater at a distant location and releases the cooled seawater to greater depth also at a distant location. Every unit of pump energy input to the heat pump would transfer four to six units of heat from distant seawater to heating coils under the offshore water spout that could be initiated with much hotter water piped through insulated piping from shore.

Pontoons could carry chimney technology built with angled air inlets to swirl an incoming airstream that would be heated by surrounding warm seawater and heated further by much warmer seawater inside the chimney.

Such technology would borrow from solar thermal chimney technology that is being tested and developed for future power generation, with one version being dubbed Vortex Engine. Heat pump driven vortex engine water spout technology would be placed offshore in regions with warm surface seawater and that are prone to summer time cyclonic activity, where winds would blow the water spout cloud toward coastal mountains.

Conclusions

Steam-based thermal power stations located next to the ocean coast have ready access to nearby seawater to cool the exhaust-steam condensers as well as to sustain the operation of thermal seawater desalination.

Further development of the Australian ocean wave powered pump technology promises to sustain reverse-osmosis desalination as well as sustain the operation of a submerged heat pump intended to sustain the operation of an offshore water spout. Further research is required in the area of water spout development and operation.

Coastal cities that experience water shortages and are located near coastal mountains may need to consider multiple desalination technologies, including creating oceanic waterspouts that could produce cloud that winds could push toward watershed areas of mountain dams. Residents of such cities have the choice to endure minimum potable water conditions for many years into the future.

One alternative is to allow for the development of a micro-climate that could provide some rain in critical mountain watershed areas. Changing weather patterns are affecting many regions in many countries and the additional of microclimates may actually benefit some regions.

The opinions expressed herein are the author's and not necessarily those of The Maritime Executive.

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