THERMALLY-INSULATED TUBULAR-TOWER SOLAR RECEIVER COMPRISING A SYSTEM FOR REDUCE ENERGY LOSSES
The invention relates to different elements for increasing the yield of tubular-tower solar receivers, reducing losses through radiation. The term tubular receiver is used to mean receivers that use a heat-transfer fluid of the liquid or liquid/vapour mix type, which flows through generally circular ducts or tubes acting as an absorber, in which the heat-transfer fluid can be any fluid having physical properties suitable for the working conditions of the receiver (water, oils, molten salts and others).
This invention relates to different designs for increasing the yield of tubular-tower solar receivers, reducing losses through radiation. The term tubular receiver is used to mean receivers that use a heat-transfer fluid of the liquid or liquid/vapour mix type, which flows through generally circular ducts or tubes acting as an absorber, in which the heat-transfer fluid can be any fluid having physical properties suitable for the working conditions of the receiver (water, oils, molten salts and others).
STATE OF THE ARTCurrent solar tower power plants, which can be considered as state of the art are planus that generate electrical energy from solar radiation. They are basically composed of a receiver (which can be inside a cavity or totally exposed to the outside) located at the top of a tower that is surrounded, total or partially, by a field of heliostats.
There is a receiver at the top of the tower, which may be circular, and in this case it is surrounded by heliostats on all sides or non-circular, and in this case it is surrounded by heliostats preferably on one side.
Heliostats are mirrors that reflect solar radiation, concentrating it on the receiver. A heat-transfer fluid circulates inside the receiver, this fluid could be air, in the case of the volumetric receivers, or a liquid and/or a liquid-steam mixture in the case of tubular receivers, which are heated by solar rays and the thermal energy thus obtained is used to generate electrical energy.
Patent U.S. Pat. No. 3,924,604 contains one of the first descriptions of a solar tower power plant. Solar tower power plant with different and very diverse designs have been built up to now (with an exterior receiver or located inside a cavity. All of which have a tower in the centre of the heliostat field or to one side, using different heat-transfer fluid, etc.), but they all share the same basic characteristics, (field of heliostats and receiver located in a tower) mentioned in this patent.
In order to achieve the maximum performance in a conventional solar tower power plant, it is necessary to maximise each of its elements. This invention intends to increase the efficiency of tubular receivers using liquid and/or liquid/steam mixtures as a heat-transfer fluid. The most significant heat losses that affect the receiver are losses by convection, caused by the contact of the receiver with the outside air, by radiation, caused by the temperature differences between the receiver and the surfaces that are in its field of view (walls of the receiver cavity, sky, etc.) and reflected heat, due to the fact that not all the solar radiation falling on the receiver is absorbed.
Scope of the InventionThis invention aims to increase the performance of solar tower receivers with tubular receivers that absorb the solar energy concentrated from a field of heliostats and convert it into high temperature thermal energy, reducing losses by radiation.
Different elements are proposed for this purpose: a visor at the top of the receiver; a strategic placement of the receiver tubes, with or without selective surfaces in different areas, making the best use of solar and thermal radiation and minimizing losses; fins connecting the tubes with the aim of homogenising the behaviour of the assembly and minimising losses by radiation.
DESCRIPTION OF THE INVENTIONThis invention consists of different elements that aim to increase the efficiency of the tubular solar tower receivers. For this purpose, different strategies are applied to reduce energy losses in the form of heat by radiation.
Strategies to reduce radiation losses are the following:
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- A visor, will reduce the exposure of the panels of the receiver to the sky, also reducing thermal radiation losses.
- Placing the tubes of the solar receiver in different rows with regard to the outside, it could be achieved that solar radiation reflected by the tubes of the inner rows would mostly end up at the rear of the tubes they had opposite, thus reducing losses by reflection of solar radiation. A large proportion of the thermal radiation emitted by the inner tubes would also, in the same manner, end up in the rear of the tubes located opposite, thus reducing losses due to thermal radiation. There is the possibility of using appropriate selective surfaces to strengthen this effect, according to the predominant type of incident radiation (solar or thermal), in each tube area.
- With regard to the aforementioned fins connecting the tubes, it would be necessary to pay special attention to the selective behaviour of the fins for their efficiency with regard to radiation and to how they are attached to the tubes, so that good contact is compatible with expansion and thermal gradients between different areas of the receiver.
Other details and features will be detailed in the description given below, which illustrate several examples of the invention shown for illustrative but not limiting purposes, with the help of the corresponding drawings.
Below is a list of the different parts of the invention, which are indicated in the following drawings with their respective numbers: (1) receiver cavity, (2) tubular tubes or conduits through which the heat-transfer fluid circulates and which, also act as an absorbent surface, (3) absorber, (4) visor, (7) central area of the receiver, (8) fins, (9) receiver, (10) heliostats, (11) tower in which the receiver is placed, (12) front selective surface, (13) rear selective surface, (17) bundle of tubes.
In
One of the preferred embodiments of this invention for solar tower power plants has non-circular type receivers, as can be seen in
Another preferred embodiment shown in
Another preferred embodiment, as can be seen in
Another preferred embodiment (see
Although in all preferred embodiments the receiver is in vertical position, the inclination thereof can be any from vertical until completely horizontal.
Claims
1-14. (canceled)
15. A thermally-insulated tubular-tower solar receiver comprising a system for reduce energy losses, used in solar tower power plants which are devised to concentrate solar energy onto a receiver by means of the strategic placement of heliostats, and transform it into high temperature thermal energy contained in tubes and/or conduits through which a heat-transfer fluid circulates, being heated by the solar radiation concentrated by the aforementioned heliostats, wherein the receiver has a least one of the following elements
- a visor,
- a bundle of tubes, wherein the tubes are placed horizontally or vertically in said bundle aligned in two or more rows or columns.
16. The thermally-insulated tubular-tower solar receiver comprising a system for reduce energy losses, according to claim 15 wherein these elements are applied to a receiver of a circular type solar tower power plant.
17. The thermally-insulated tubular-tower solar receiver comprising a system for reduce energy losses, according to claim 15 wherein these elements are applied to a receiver of a non-circular type solar tower power plant.
18. The thermally-insulated tubular-tower solar receiver comprising a system for reduce energy losses, according to claim 15, wherein a visor is added on the upper part of the receiver.
19. The thermally-insulated tubular-tower solar receiver comprising a system for reduce energy losses, according to claim 15 wherein the tubes of the bundle meet with at least one of the following specifications.
- 1. The tubes are composed of different selective materials at the from and rear with regard to the incidence of the solar radiation.
- 2. The tubes are joined together with fins.
Type: Application
Filed: Apr 23, 2014
Publication Date: Mar 17, 2016
Inventors: Oriol LEHMKUHL BARBA (Sabadell (Barcelona)), Guillem COLOMER REY (Sabadell (Barcelona)), Ricard BORRELL POL (Sabadell (Barcelona))
Application Number: 14/787,881