SERRANO, Enrique (Avda. Gregorio Peces Barba 1, Leganés Madrid, E-28918, ES)
WIESENBERG, Ralf (Avda. Gregorio Peces Barba 1, Leganés Madrid, E-28918, ES)
SERRANO, Enrique (Avda. Gregorio Peces Barba 1, Leganés Madrid, E-28918, ES)
1- A Solar receiver characterized because it comprises a supporting mean (2) of a plurality of solar receiving modules, each solar receiving modules comprising:
- a graphite block (1 ) with at least one graphite open horizontal channel (4) situated in the outer side of the graphite module (1 ),
- at least one vertical conduct (3) in the inner part of the graphite block (1 ) for the heat transfer fluid,
so that the outer side of the graphite modules (1 ) transfer high solar energy to the heat transfer fluid situated inside the vertical conducts (3).
2. - The solar receiver according to claim 1 wherein each graphite module (1 ) comprises a plurality of isolated mounting legs (7) and
3. - The solar receiver according to claims 1-2 wherein each graphite module (1 ) comprises at least one isolated fixing part (8) to the supporting mean, situated in the inner side of the graphite module (1 ).
The present invention relates to solar power tower generation systems. In particular, the invention relates to a receiver and heat exchanger of a solar power tower generation system with high operating temperatures of up to 650 °C using molten salts or other heat transfer fluids
There is a continuing demand for clean renewable energy sources like solar energy to generate electricity. The central receiver concept for solar energy concentration and collection is based on a field of individually sun-tracking mirrors, called heliostats that reflect the incident solar radiation to a receiver at the top of a centrally located tower.
The solar receiver is typically positioned at the upper end of a tower and is heated by the heliostats. The heliostats redirect and concentrate direct solar radiation from the sun onto the solar receiver, which converts the redirected sunlight to thermal energy. Typically 80 to 95 percent of the reflected energy is absorbed and transferred to the working fluid which is pumped up the tower and into the receiver. Solar power tower systems typically include a "cold" storage tank, a solar receiver, heliostats, a "hot" storage tank, and an energy conversion system, such as a steam generator or turbine/generator set.
In operation, a heat transfer fluid is pumped from the cold storage tank to the solar receiver. The heat transfer fluid can be any medium that has the capability to transfer heat and thermally maintain the heat in the medium, such molten salts or high temperature synthetic thermal oils.
The heat transfer fluid flows through solar receiver where it is heated by the concentrated solar energy. Generally, in order to achieve high efficiency of operation, a solar receiver which operates at high temperatures requires high energy flux
These indirect-absorption type solar receivers, also known as non-volumetric solar receivers, comprise a front side facing the incident solar radiation and an inner layer contacting the working fluid. The absorbed incident solar radiation is converted in the receiver into thermal energy and stored and conducted to the interior and transferred to the working fluid. In this kind of receiver the receiver itself works like a heat exchanger by transferring the energy to the molten salt or other high temperature heat transfer fluid. One shortcoming in the commercial use of such tower systems is the high material costs associated therewith. One relevant cost of the systems is the receiver and heat exchanger. Nowadays, the receivers are made of special steels which are relatively expensive and increase the cost of the system.
A primary limitation on current receiver design is the heat flux that can be absorbed through the receiver surface and into the heat transfer fluid, without overheating the receiver walls or the heat transfer fluid within them.
Another disadvantage of current solar power receivers is the disability of store sufficient thermal energy by itself in order to overcome the abrupt lack of solar radiation provoked by small clouds. This disability can provoke receiver fatigue by repeated unnecessary stress in materials used for the receiver and heat exchanger.
It is therefore be desirable to decrease the cost and increase the technical life, the reliability and operability of a solar tower system by using better suited material for the solar receiver and heat exchanger.
The present invention provides an improved external solar receiver design that reduces the cost and improves the efficiency, the reliability and dispatchability of such devices.
The invention relates to a solar receiver made of a plurality (preferably from four to sixteen) identical receiver modules made of high temperature resistant graphite blocks which work as receiver, short term storage and heat exchanger at the same time. It is a high temperature solar power tower external receiver system which uses high temperature resistant graphite as main receiver material which can be heated to a temperature of up to 650°C facilitating higher steam cycle temperatures and therefore higher efficiencies. The specific material characteristics of graphite are used in the present invention in order to overcome these limitations avoiding receiver fatigue. As a result of the invention, technical life of the receiver can be increased and the operability of the whole system can be improved.
Graphite has at the same time, a very good ability to store and to conduct thermal energy, so that the body of the block is used as a short-term storage device.
Another advantage is that graphite is a relatively low-cost high-temperature resistant material that is chemically compatible with molten salts or most of the thermal oils. Therefore no extra piping is required inside the graphite receiver blocks. The high temperature heat transfer fluid is directly pumped through several conduits at the back side of the graphite block. The solar receiver of the invention comprises an inner wall, or supporting mean, in which is mounted a plurality of solar receiving modules, each solar receiving module comprising:
- A graphite block with at least one open horizontal channels situated in the outer side of the graphite block, simulating in part a cavity (inner) receiver reducing the reflection of solar irradiance,
- at least one vertical conduct in the inner part of the graphite block for the heat transfer fluid, which avoids the direct use of piping in the receiver and facilitate the fast and easy change of receiver modules in case incidences or for maintenance purposes.
a plurality of isolated mounting legs and
at least one isolated fixing parts to the inner receiver wall or any other construction.
so that the outer side of the graphite modules serves as a solar radiance receiver, increasing the absorption of solar energy and its efficiency, transferring more solar energy to the heat transfer fluid situated inside the vertical conducts.
These aspects of the presented invention improves therefore the efficiency of the external receiver and overcome short term transient weather situation minimizing material stress and fatigue of the solar receiver system.
BRIEF DESCRIPTION OF THE DRAWINGS
The description of the different components of the system provided above is complemented with a series of drawings aimed at facilitating understanding of its structure and operation.
Figure 1 is a simplified view of a solar receiver system according to the present invention
Figure 2 is a perspective of a solar receiver.
Figure 3 is a perspective of one solar receiver module.
Figure 4 is longitudinal cutaway side view of the receiver module of figure 3
Figure 5 is a detailed view of the receiver module of figure 4.
In said figures the following references are indicated:
1. - Graphite block
2. - Inner Wall
3. - Conduct
4. - Horizontal Channel
5. - Round receiver platform
6. - Solar Tower 7. - Legs
8. - Isolated mounting parts
9 - Heliostat DETAILED DESCRIPTION OF THE INVENTION
As shown in figure 1 , the solar receiver is typically positioned at the upper end of a tower (6) and is heated by the heliostats (9).
The solar receiver of the invention, shown in Figure 2, comprises a plurality of receiving modules, which are mounted on a round receiver platform (5) and supported to an inner wall (2).
Each of the receiving modules comprises, as shown in figures 3 and 4, a graphite block (1 ) and a plurality of conducts (3) for the heat transfer fluid on the inner side of the graphite block (1 ) and a plurality of open horizontal channels (4).
Additionally, each receiving module comprises isolated mounting legs (7) and isolated mounting parts (8) which can be fixed to the inner receiver wall (2) or any other construction.
Figure 5 shows that the solar irradiance is partly absorbed and partly reflected from the outer receiver surface. Because of the open horizontal channels the reflection will be reduced and more thermal energy will be absorbed.
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