Eureka GDV direct steam generation
Info available at Abengoa's website:
Existing commercial parabolic trough power plants transform direct solar radiation into thermal energy, heating a working fluid to temperatures in the region of 400 ºC using thermal oil as heat transfer fluid.
In order to achieve more efficient generating systems, development of a second generation of parabolic troughs that operate at a higher temperature than indicated has been undertaken. The practical limitations of this development are imposed mainly by the working fluid, usually thermal oil, whose working temperature range can not exceed 400 ºC.
To this end, Abengoa is assessing, along with other fluids, the use of direct steam generation (DSG) inside parabolic troughs, to achieve a higher operating temperature of around 550 ºC. With DSG technology, the use of an intermediate fluid and of the exchanger adapted to this fluid, responsible for generating the steam, is eliminated. The direct consequences of this development are cost reductions and improved overall efficiency of the installation.
With DSG technology in parabolic trough power plants, water enters the interior of the receiver tubes and absorbs the energy reflected by the collectors, changing from liquid state into saturated steam and subsequently to superheated steam.
In comparison with existing commercial plants that use thermal oil as heat transfer fluid, the advantages of DSG are:
- The use of thermal oil is replaced by water, thus eliminating the risk of fire and of contaminating leaks.
- The oil/water heat exchanger is eliminated and water/steam separators are incorporated.
- The maximum temperature limitations of the solar field imposed by degradation of the heat transfer oil (400 ºC) disappear and, therefore, more efficient power cycles can be accessed.
- Solar field performance improves due to the average operating temperature of the collectors being slightly lower than that of systems that operate with oil, and, moreover, the necessary temperature jump in the oil/water exchanger is suppressed.
- Investment costs, associated mainly with elimination of the exchanger train, expansion tank, the thermal oil itself and other systems related with the use of this oil, are reduced.
- Operation and maintenance costs are reduced.
In order to validate direct steam generation in parabolic trough technology, Abengoa has built an 8 MW pilot plant (Eureka GDV) at the Solucar Platform, Sanlucar la Mayor, Seville, Spain.
The following are being validated in this plant:
- The control system, mainly in transitory periods of radiation.
- The interconnections between collectors and the absorber tubes themselves, which are especially critical due to coexistence in the solar field of a two-phase fluid at high pressure and temperature.
- Stability of the annular fluid inside the tubes, ensuring internal cooling of the wall, thereby preventing the occurrence of hot spots.
The Eureka GDV plant came into operation with its new configuration in September 2011 following the tests conducted with an earlier configuration in 2009.
This plant has been operating for more than 500 hours, the first 200 of which were with the field operating in saturation mode to enable tuning of controllers. Operation with the superheated field began in February this year (2012)
The high stability of the facility and the production models being validated allow optimism regarding commercial implementation of this technology.