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SOLAR THERMAL POWER PLANTS ENGINEERING
Advanced
courses and specialized training that aims to deepen in the Engineering
of Solar Thermal Power Plants, form Construction to Operation.
We offer the following courses to be conducted individually, of 13 hours each one:
1.1 Central Towers.
1.2 Dish Stirling.
1.3 Fresnel.
1.4 Parabolic trough.
1.1 Central Towers.
The
first commercial power plant of this kind was completed in June 2007 in
Spain, there are some with powers of 11 MW and 20 MW in
construction.
1.2
Dish Stirling.
In
Europe only there are pilot plants of this type, the typical power is
of 10 kW. They consist of dish-shaped mirrors that reflect light
to a central point.
Figure 2. Dish Stirling.
1.3
Fresnel.
In
Europe there is no power plant of this type. The operating principle is
the same as for parabolic trough plants. In this case the pipeline with
heat-carrier fluid passes over a horizontal surface of mirrors that are
orientated along the long day to affect the sun's rays on the pipe as
shown in the following image.
Figure 3. Fresnel field.
1.4 Parabolic trough.
This
technology was started using in the 80s, and nowadays there are plants
in Europe and USA, being the most used by it will go into more
detail, the power between 50 MW and 200 MW. Solar concentrators collect
light energy that reaches us directly from the sun as multitude of
rays, focusing at one point or focus where it is transferred in the
form of thermal energy, the parabolic trough are inside the
concentrators, where the focus is placed on the line. Due to his form
the concentratios as the focus is in the range of 30 to 100 times the
normal intensity, his mode operation consists of being orientated so
that the plane of the opening is perpendicular to the planes in which
solar rays are. For it, follows to the sun with a follower of a single
axis so that to be continually focused transfers the energy to the
fluid that circulates inside the absorber tube.
Figure 4. Field of parabolic trough collectors.
The main parts that make up the installation of a parabolic trough collector are:
1) Foundation.
Supports the collectors and fixes them to the floor so that the
structural assembly can support the loads for which is it designed,
usually of reinforced concrete. Are made according to the dimensions of
the collectors and the characterisitic structures, which are a function
of weight, wind loads and soil type.
2) Structure.
Its function is to stiffen the set of component parts, tipically made
of metal, but now are investigating other materials such as fiberglass,
plastics and even wood. It's important that the stucture is of quality
since any deformation along his life affect the concentration of light
and thus energy production.
Figure 5. Structure.
3) The parabolic trough reflector.
It is the concentrated part of the collector and consists of
reflecting the solar radiation incident on it and projecting it in a
concentrated form on the absorber tube. The reflectors used are mirrors
made of silver or aluminium applied on sheet metal, plastic or glass.
The mirrors ot be outdoors tend to get dirty so they must be cleaned,
which could reduce the yield, the main problem for cleaning the mirrors
are the delicate central tubes.
Figure 6. Reflector.
4) The absorbent tube or receiver tube.
It is the responsible for converting concentrated sunlight into thermal
energy in the heat transfer fluid, mainly consists of two tubes, one
indoors of metal, coated with a special layer of black paint on the
basis of highly absorbent materials over 90% and low emissivity at high
temperatures and a transparent glass tube of high transmittance in the
solar interval. To join the two tubes should be used special seals
capable of withstanding the expansion. Also inside the tubes are
inserted 'Getters', which are responsible of absorbing the molecules of
substances that can penetrate between the metal tube and glass, to
maintain the vacuum.
Figure 7. Absorbent tube or receiver tube.
5) Transmission.
It is the solar tracking mechanism wich is responsible for changing the
position of the collector as the sun is moving, can be electric,
motor-reducer and hydraulic, the most common. Normally to lower cost
one single mechanism is responsible for moving six collectors in
serie.
Figure 8. Electrical transmission to the left and hydraulics to the right.
6)
The sun tracking system or 'suntracking system'.
This system is responsible for adjusting the position of the collector
so that the yield is maximum, for orientation are use photocells
separated by a band of shadow, which in case of blur, produces a
tension that causes the motor turn or the pistons are moved
in desired direction. In addition to allowing the maximum use of
solar, the tracking system serves to get out of focus the mirror when
the captured energy is excessive, another of its functions is to place
mirrors in a position to cleaning or maintenance.
Figure 9. Suntracking system.
7) Connection between the collectors.
The collectors are connected in series in rows and these in turn are
attached parallel. These parts allow the fluid to circulate between the
modules, moving parts and circulation pipelines, fixed parts, etc. May
be of two types or rotary joints or flexible pipelines.
Figure 10. Connecting joints between panels.
8) Heat transfer fluid.
They're in charge of absorbing solar energy in the tubes of the solar
field and transport it to the salt deposits. There are different types
of fluid used for this mission of them can highlight the
following:
- Water-steam.
Its advantages are: cheap, readily available, abundant, excellent heat
transfer medium, high specific heat, well-known properties and
behaviour, is not toxic and not flammable. Its disadvantages are that
it is aggressive, highly oxidizing, corrosion occurs, certain salts
precipitate producing scale, expands as it solidifies and pressure
increases strongly with temperature.
- Mixtures fo inorganic salts.
- Alkyl benzenes.
They are very stable, can withstand temperatures up to 300 ºC, do not
emit toxic gases, or corrosive and have a low freezing point between
-45 to -50 ºC.
- Mercury.
Very rarely used for reasons of toxicity and price, works up to
temperatures of 540 ºC, requires great vigilance to detect leakage of
vapors, as from 360 ºC requires pressure in the installation doing that
the costs are very high.
- Mixtures diphenyl and diphenyl oxide.
They have very high melting points, unpleasant smell phenol at high
temperatures (up to 410 ºC), are very expensive and have a low boiling
point of the installation requires a pressure control.
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