NYT article on ocean thermal water & electric generator



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Japanese Technology May Help Islands Reap Pacific's Waters By AGENCE FRANCE-PRESSE A number of Pacific island nations may use new Japanese technology that can both desalinate seawater for drinking and produce electricity.

http://www.nytimes.com/2003/03/23/international/asia/23WATE.html?th

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This article from March 23 2003 New York Times describes a planned project for Palau that will exploit the temperature difference between deep ocean water and surface water to produce electricity and drinking water for about $1/ 250 gallons. Maybe somebody can explain the technical details better because I'm guessing. It uses ammonia, but it is not the ammonia absorption cycle I'm familiar with. My bet is they inject liquid ammonia into the cold water at the bottom of the intake, where the heat of absorption is easily carried away. Then the "strong" solution of seawater and NH3 is pumped to the surface. The NH3 boils off at the top and blows a turbine, generating electricity. It would take considerable energy to collect the NH3 gas and push it back down to the bottom, but the cooling and condensing would happen when it got to the cold bottom. The "weak" solution of water at the top after the NH3 boils off is the source of the clean water, but this is mysterious to me. As with NH3 absorption cooling, the weak solution is put into a lower pressure container after much of the NH3 boils off; but in this scheme the pressure is low enough that the H2O boils. Surely more NH3 would boil off too, but somehow they separate it, because the boiling low pressure H20 is condensed without any NH3 and the H20 is pumped ashore for drinking.

Here's the text:
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Japanese Technology May Help Islands Reap Pacific's Waters

*By AGENCE FRANCE-PRESSE*

KYOTO, Japan, March 22 ? A number of Pacific island nations are
discussing using new Japanese technology that can both desalinate
seawater for drinking and produce electricity by exploiting the
difference in temperatures between the surface of the sea and the depths
of the ocean.

The Republic of Palau in the western Pacific is working with Saga
University in southern Japan to build a system that can produce enough
drinking water to meet the needs of its 20,000 residents, while
producing electricity, said the country's president, Tommy Remengesau Jr.

The concept was highlighted this week at one of the 350 sessions at the
Third World Water Forum, which is under way here. It has attracted
10,000 participants from around the world, along with ministers and some
heads of state from more than 150 countries.

The university is preparing to build an experimental power plant off the
coast of Palau that brings up cold seawater from the depths of the sea
to an evaporator chamber near the ocean surface.

As the water is heated by the surrounding warm surface water, it
releases ammonia gas, which then drives the system's power generator,
said Yasuyuki Ikegami, deputy director of the Institute of Ocean Energy
at Saga University.

Meanwhile, the heated water would be transferred to a separate
low-pressure chamber where it boils at a lower temperature, producing
steam, which would be condensed and collected as fresh water for human
consumption, leaving salt crystals behind.

One experimental system, which produces power but no usable water, is
scheduled to be put into use off the coast of India this month, Mr.
Ikegami added.

"It works well especially in the western Pacific, where the temperature
difference between the ocean's surface and deep seawater is" as much as
43 degrees Fahrenheit, he said. "It is environmentally sound."

With some financial assistance from the Japanese government, the
university was hoping to build the experimental plant in Palau for $7.5
million, said Haruo Uehara, president of Saga University, although he
declined to disclose details of the financing because it was still being
negotiated.

Palau was hoping the plant could be built next year, Mr. Remengesau said.

"It is a big help for us," he said. "When there is rain, we have no
problem. But we are hit by the drying effects of El NiÒo. When there is
no rain, where can we get drinking water?"

The fresh water produced by the system will cost less than $1 for more
than 250 gallons, Mr. Uehara said. "It is no more costly than regular
tap water in other countries, including Japan," he said.

The system, while more expensive than ordinary generators, has raised
hopes among leaders of other Pacific islands, which are too small to
build many dams to catch water and are trying to cut back on their
consumption of oil to run power generators.

Allan Marat, deputy prime minister of Papua New Guinea, said Pacific
island nations had fallen victim to global warming, adding that he too
was interested in the university's system.

"We are in the middle of the largest body of water" on earth, said
Robert Woonton, prime minister of the Cook Islands. "Yet, we are faced
with lack of safe potable water." He said he wanted to consider setting
up Saga University's system in his country.

Other countries in arid zones have also shown interest, including Saudi
Arabia, which was sending a delegation to the university, Mr. Uehara said.


Copyright 2003 The New York Times Company







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