Technological advancement of U-TEC power generation owes very much to the enduring research and development works by Saga University, Japan, who have succeeded, after more than a quarter century of enduring years, to invent an unprecedented high efficient system, which made the hitherto academic studies practical for commercial implementation of the knowledge. This invention is widely known as Uehara Cycle named after the inventor Prof. Dr. Haruo UEHARA, Saga University. We have been collaborating with Saga University on many fronts. Our System Engineering Department Manager Dr. S. Jitsuhara had spent 10 years at the University to study the optimization of OTEC system and got his doctorate for engineering there. Our expertise on heat exchanger, which is one of the vital components in the system, is what Saga University regards very highly. We are pleased to announce hereby that we are the titleholders of exclusive right for use of all of the patents registered by OTEC research team of Saga University at home and abroad.

Name

Uehara Cycle (New cycle)

Rankine Cycle (Conventional cycle)

History

1994

In 1850s

Inventor

Prof.H. Uehara, Saga University, Japan

Rankine(UK)

Theory

Working fluid

Mixture of ammonia and water

Pure ammonia substance

Energy diagram

Features

1. Temperature of this working fluid changes during boiling and condensing processes.
2. Vapor pressure can be manipulated to stay low by varying ratio between ammonia and water.

1. 1.Temperature of working fluid remains same as certain level during boiling and condensing processes.
2. 2.Available vapor pressure is dependant on temperature.

Heat Efficiency

5-6%
(1.5-2 times of Rankine Cycle)

Approx. 3%

Factors for
efficiency
improvement

1. Energy to be obtained from differential temperatures can be increased owing to the varying temperatures during boiling and condensing processes.
2. Turbine outlet temperature can be controlled to stay lower than turbine inlet temperature by use of an Absorber , which will absorbs mixed vapor of ammonia and water, which comes out of turbine, by saturated liquid of ammonia and water. Thus, we can obtain enlarged energy from differential temperatures for greater turbine performance.
3. Load of condenser will be lessened by heating up the working fluid coming from Turbine with vapor partly taken out of Turbine.

Thus、
�@Size of condenser can be squeezed.
�ALess seawater volume will allow to deploy smaller diameter in-take pipe.

―

Net output

80-85 %

Approx. 55 %

SW volume

Approx. 50 % of Rankine cycle

-

Plant cost

Approx. 60-70 % of Rankine cycle

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1. Pump #2 will feed the mixture of ammonia and water into Regenerator and to Evaporator to be warmed up by the warm surface seawater taken in from warm seawater pump.
2. As the working fluid evaporates, it will become a saturated vapor that will have to be separated in Separator into ammonia-water liquid and ammonia-water vapor.
3. The mixed ammonia-water vapor will drive Turbine#1 and trigger Generator #1 to produce electricity. 1-5% of the mixed vapor in Turbine#1 will be diverted into Heater, while the rest will generate Turbine#2.
4. Heater will warm up the ammonia-water liquid arriving from Tank#1. The warmed up working fluid will make its way to Tank#2 in which it will be mixed with the 1-5% vapor mentioned above.
5. The separated ammonia-water liquid will pass through Regenerator via Diffuser into Absorber that will have collected the mixed vapor of Turbine#2. All mixed vapor outside Absorber will be routed to Condenser to be cooler off the condensed by deep cold seawater.
6. At this stage, OTEC cycle will be repeated as from the beginning.