The news source for Ocean Thermal Energy Conversion (OTEC)

 

  by L. A. Vega, Ph.D., Hawaii, USA.

Previous: Open Cycle OTEC

The 210 kW OC-OTEC Experimental Apparatus

As stated above, a 210 kW OC-OTEC Experimental Apparatus was conceived as the next step towards answering questions related to operation of OTEC plants.  The apparatus was operated for six years (1993-1998) providing valuable data and pointing the way for future modifications and improvements in the OC-OTEC process.  The turbine-generator was designed for an output is 210 kW for 26 °C warm surface water and a deep water temperature 6 °C.  A small fraction (10 percent) of the steam produced was diverted to a surface condenser for the production of desalinated water. The highest production rates achieved were 255 kW (gross) with a corresponding net power of 10 ³ kW and 0.4 l s^-1 of desalinated water. These are world records for OTEC.  It must be noted that the net power was not optimized because pumping losses were relatively high due to the use of a seawater system that was already available.  It is expected that for a commercial size plant the ratio of net to gross power will be approximately 0.7.
 
The data and experience obtained demonstrated that the OC-OTEC process is technically feasible for the production of base load electricity and desalinated water.  It was also demonstrated that frequency control in the island mode is achieved with either a load-diversion-governor (LDG) or with the vacuum compression system.  The most significant and exciting lessons learned were those that were fundamental new insights into the OC-OTEC process.  The two main discoveries were the unstable synchronous generator output, and the violent outgassing of seawater in the heat exchangers.  The most annoying problem was the frequent failures of the grease lubricated bearings of the centrifugal pumps used for the vacuum and exhaust system.  In retrospect, this was due to a major design oversight.  Equipment operating at speeds higher than approximately 27,000 revolutions-per-minute should, in general, not use grease lubricated bearings. It was concluded that high speed centrifugal pumps with, for example, magnetic bearings can be used in future OC-OTEC systems to achieve extended life cycles, relatively low power consumption and, therefore, optimum net power.

Next: Design of a Small Land-Based OC-OTEC Plant

© 1999. L. A. Vega. All rights reserved.
Published here with the kind permission of the author.