Annual Report 2006 - Plataforma Solar de Almería

ENVIRONMENTAL APPLICATIONS OF SOLAR ENERGY
Duration: March 2002 – February 2006
Motivation: Seawater desalination is one of the possible solutions to the
severe water shortage problem that our planet is going to undergo during the
first half of this century, a problem which is not exclusively in developing
countries, as the appearance of persistent seasonal droughts are more and
more frequent in some regions of developed countries.
In spite of all of the advances of the last few decades, seawater desalination
technologies continue being intensive fossil-fuel consumers. In the present
world framework, with growing instability of oil market prices and environmental
demands derived fro compliance with the Kyoto Protocol, sustainable
desalination must unavoidably be arrived at through improved efficiency
of the technologies involved as well as the use of renewable energy resources.
The AQUASOL project faces both options by using solar thermal energy as the
renewable energy resource and contributes to increasing the thermal efficiency
of the multi-effect distillation process. The environmental impact of the
desalination process has also been reduced by recovering the salt contained in
the brine.
Purposes: The main goal of the AQUASOL project is the development of a hybrid
solar/gas seawater desalination technology based on multi-effect distillation
(MED) which also meets the principles of energy efficiency, low cost and
zero discharge.
Objectives met in 2006: The implementation of the different subsystems was
completed during this period and their testing under real weather conditions
was begun at the PSA facilities (MED Plant, heat pump and solar field) and the
Greek saltern Hellenic Saltworks on the Island of Lesbos (Solar Dryer).
The AQUASOL system has three different operating modes depending on
the origin of the thermal energy:
• Solar-only mode: the thermal energy supply to the first effect of the
distillation plant comes exclusively from the solar collector field.
• Fossil-only mode: the double-effect heat pump supplies all of the energy
required by the distillation plant
• Hybrid mode: the energy supply comes from both the heat pump and
the solar field. Two different operating philosophies are considered: in
the first the heat pump works continuously 24 hours a day supplying
the minimum 30%, while in the second it starts up and stops, depending
on the solar resource availability.
The operating and maintenance experience with the AQUASOL system has
been shown to be highly reliable, with no important problems being recorded
during testing. The solar collector field has demonstrated an average daily
efficiency (ratio between the thermal power delivered to the storage tanks
and the global solar radiation incident on the tilted surface of the collectors)
of 48%. The plant performance factor (kg distillate produced per 2316 kJ
thermal energy supplied to the system) in solar-only mode is over 10.
As a result of evaluation of the new absorption heat puma after the first
tests, it was decided to change the initial configuration of parallel flow to series
flow, to improve the controllability of the equipment, especially during
transients. After this modification, the unit showed excellent behavior, increasing
the plant performance factor from 10 to over 20, which is a 100%
increase in thermal process efficiency. In hybrid mode, it should be mentioned
that the absorption pump showed strong thermal inertia, mainly due to the
fact that the maximum power delivered by the steam boiler is much more
than required by the pump under stationary conditions. The best results were
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