WO2008142459A2

WO2008142459A2 - Composite solar tower chimney

Info

Publication number: WO2008142459A2
Application number: PCT/GR2008/000039
Authority: WO
Inventors: Emmanuil Dermitzakis; Aristeidis Dermitzakis
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-05-17
Filing date: 2008-05-16
Publication date: 2008-11-27
Anticipated expiration: 2009-11-17
Also published as: GR1005806B; WO2008142459A3

Abstract

The invention relates to a composite solar tower- chimney composed of the cylinder (1) positioned at the centre of a covered greenhouse (8). A central solar boiler (2) -which is sufficiently elevated from the ground and set outside, on the periphery of the cylinder- gathers the radiation of a great number of two-axis heliostats (7) and produces steam capable of setting into motion the power-generating steam turbine; the rejected steam is utilised for the operation of a conventional ground distillation plant. Additional power i generated by the water turbine (32) actuated by the additional desalinated water or by liquid solutions flowing back by gravity to the base structure of the solar tower-chimney.

Description

COMPOSITE SOLAR TOWER CHIMNEY

The invention refers to a composite solar tower chimney which serves as both a solar chimney as well as a solar tower steam boiler for the generation of electrical energy, desalinated water and probably industrial cooling.

STATE OF THE ART

The conventional, known solar tower cooperates with two axis heliostats, which reflect and focus the solar radiation upon a solar steam boiler which is found at the peak of a tower at a height of 150-250 meters. The solar steam boiler, with its solar collectors, heats water for the generation of steam and electrical energy with steam turbines .

The common solar chimney correspondingly uses the solar energy for the heating of air in a greenhouse which is found around its base. The air is directed into a chimney of a great height of 600-1000 meters. The difference of the specific weights of the air inside and outside the greenhouse, combined with the height of the chimney itself, creates a great static pressures' difference which is converted into mechanical energy and, by means of a system of wind turbines, into electrical energy. Characteristic to both of the aforementioned systems and the more important cost factor is the high tower which supports the central solar steam boiler of the first system and the high solar chimney of the second. Particularly in the case of the solar chimney, the initial investment of the tower and the greenhouse is cost prohibitive.

Because the peak of energy production does not always coincide with that of consumption, the renewable forms of energy production engage passive systems for the storing of thermal energy.

In the case of the solar chimney, a great number of sealed transparent plastic bags of water are placed on the ground beneath the surface of the greenhouse, which simply store the thermal energy during the day and release it in an uncontrolled manner during the night. This particular expensive and uncontrolled exchange proves to be of but small benefit. The solar chimney cannot be combined as is with the simultaneous production of an additional different form of energy or the desalination of water. The investment for the greenhouse to solely heat the air is entirely financially disadvantageous . For every energy plant or installation there is a size below which it ceases to be competitive in market terms . The key element for the subsequent gain in additional efficiency is the large-scale size of the project-plant and the combination of collective actions, plants and installations. Because the cost of each produced kWh of every renewable energy system is being compared to the cost of one which is produced by conventional fossil fuels, none of the aforementioned solar systems can be by themselves, as it is today, competitive in market terms. Not even the distillation with the use of rejected low pressure steam of the solar tower -solar steam turbine system can be competitive.

Moreover, the production of electrical energy from the solar chimney or the solar tower requires an additional effective installation for the storing of thermal energy, i.e. a solar gradient pond, as to insure uninterrupted, continuous operation. However, a solar gradient pond solely for the service of the solar chimney is not only cost inefficient but also practically impossible to achieve. With respect to its operation, it requires enormous volumes of both clean water and brine for the maintenance of the salt gradient, which cannot be found, let alone provided in the installation of the solar chimney. This results in the applied systems of thermal storage for the technologies referenced above not being effective.

There are patents like DE 3401833 Al and ES 20007433 which describe desalination with direct application of solar energy for the evaporation of water covered with transparent material. The second of these is not energy producing but, on the contrary, uses electrical power for the operation of a fan which directs air down again so as to dehumidify it. The first one produces mechanical energy, although not with a normal wind turbine, but rather with a simple rotor which is connected mechanically by a propeller found inside the sea water in order to agitate it and thereby achieve a more intense evaporation. A characteristic disadvantage of the rotor is that first its movement originates not directly from the warm, humid air ascending inside the tower, but rather indirectly from the dry, external ambient air, which is used for cooling the system and which has anyway a lower temperature and energy in comparison to the air inside the tower. A second disadvantage is that the inner cycle of air which undergoes successive humidifications and dehumidifications is of closed type. The closed cycle is known to be disadvantageous in comparison to the open cycle in that the difference of specific weights between the ascending and descending air currents is dramatically low, and consequently that of the static pressures developed at the base which are responsible for the ascension and acceleration of the air flow. Thirdly, the mounting of the rotor at such a great height on the top of the tower creates vibrations that compromise the stability of the tower itself. BRIEF DESCRIPTION OF THE INVENTION

The invention described herein aims to reduce the cost and to increase the rate of efficiency by the combination and synergy of both innovative and known systems as well as the common use of their components or of the complete integration of these systems.

The composite solar tower-chimney consists of a cylindrical column of considerable height positioned on a base of a greater diameter raised above the ground and open at its circumference. Around this base are found a great number of solar sun-tracing heliostats, reflecting the solar radiation and directing it to a number of solar steam boilers, which are set at different heights outside and around the chimney tower. The solar steam boiler heats up either water for the immediate production of steam or salt solution for the indirect and post dated production of steam and the consequent production of electrical energy by means of a system of steam turbine-generators. The rejected low pressure steam is directed to a conventional ground distillation plant to which it contributes the needed amount of heat and then returns to its closed cycle. Adjacent to and all around the area of the solar tower is constructed a greenhouse of considerable dimension with peripheral openings for the entering of ambient air and is completely covered by a transparent cover. The air is heated in the greenhouse by solar radiation and is directed to the tower chimney, where its thermal energy is converted by means of wind turbines to mechanical energy and finally to electrical energy. The majority of the ground area covered by the greenhouse, is covered by both shallow ponds of sea water and special shallow ponds characterized by an increasing salinity with depth, called solar lakes or solar gradient ponds. Both of them capture and save solar thermal energy during the day and release it in a controlled manner during the evening hours or even during the day to supply the system of the thermal power engines, the conventional ground distillation plant of the solar tower, as well as the heating of the air that goes through the solar tower-chimney. Large volumes of water, both clean water and brine, needed for the maintenance of the gradient of salinity, are provided by the conventional ground distillation plant. This also resolves a significant economic and environmental issue regarding the salt waste, in that the brine is used for the creation and maintenance of the solar ponds. The accelerated passing of air over the surface of the sea water evaporates sea water and the hot humid air is now directed to the solar chimney, moving the wind turbines at its base, rising to and exiting from the peak. In the solar chimney, at a certain height, through several methods e.g. successive cooling and reheating, the humidity that the air received along the way is concentrated in the form of clean desalinated water or is absorbed by some means which contributes to a parallel production of industrial cooling energy. The flow of the water or that of the solution back to the base of the tower moves a water turbine for the generation of significant, additional electrical energy. The system can function as a whole fully and completely, since the waste of one part is a vital element for the other.

DESCRIPTION OF FIGURES

Figure 1: Section AA of the solar tower-chimney.

Figure 2: Ground plan of the solar tower-chimney.

Figure 3: Section BB of the solar tower-chimney.

Figure 4: Detail A of the shallow solar gradient pond. Figure 5: Section of the shallow solar gradient pond. Figure 6: Detail B of the solar tower-chimney. Figure 7: Detail of the solar tower-chimney.

DETAILED DESCRIPTION OF THE INVENTION

Figures 1,2,3 and 6 depict the ground plan and the sections of the composite solar tower-chimney consisting of a cylindrical column 1 of considerable height H, which is positioned on a base 3 raised above the ground level and bearing a greater diameter than the column, open at its circumference. Adjacent to and around the base 3 lies a second area 6 defined by a circle of an even greater diameter, on which there are a great number of solar sun tracing heliostats 7. The solar sun tracing heliostats 7 are two-axis mirrors which reflect and direct solar radiation to a solar steam boiler collector 2, which is set outside and around the composite solar tower-chimney 1, at a height Hl from the ground level. The solar steam boiler 2 heats water for the immediate production of steam or salt solution for the indirect and post dated production of steam and the consequent production of electrical energy by means of a system of steam turbine-generators. The rejected low pressure steam is, following the steam turbine, directed to a conventional desalination plant as for example that of distillation, where it provides the needed amount of heat, is thereby condensated and then returns to the closed system of solar steam boiler 2. (This has not been designed). Adjacent to and around the area of the solar sun tracing heliostats 7, within circle 6, is constructed a greenhouse 8 of expansive dimensions bearing peripheral openings 19 for the intake of air from the environment, and is entirely covered by transparent covering 9 The majority of the area 8 beneath the greenhouse is taken up by a shallow pond of sea water, while a lesser part of the area also takes up special shallow ponds 10 characterized by an increasing salinity with depth. These are, in other words, the solar ponds or solar gradient ponds as depicted « in figures 4 and 5.

The greenhouse can possibly even be built upon the sea, where the majority of which would be a floating construction. The air of the greenhouse is heated by solar energy, passes at an accelerating rate over the sea water, and is conducted by means of radialized covered passages 15 to the solar tower-chimney 1. There, due to the difference of the specific weights of the air inside and outside the greenhouse 8, combined with the height of the chimney 1 itself, a great difference in static pressures at the base of chimney 1 is created, which by means of a system of wind turbines 4 is in turn converted into mechanical energy and finally into electrical energy. The hot and dry air, through its passage over the sea water at a great speed, evaporates and carries along vapors which, by reason of its small specific weight, ascends together with the hot air to the solar tower-chimney. There, at a great height, they are condensated by different methods for the production of desalinated water. The evaporation can be accelerated by agitating the surface of the water or by creating an artificial rain comprised of sea water. The conventional ground distillation plant of the solar towers uses the very same pond for its supplying with sea water. The solar gradient ponds 10 are covered by a transparent plastic sheet 11 which floats on the water and consists of three zones, a, b and c. Both the solar gradient ponds 10 and the ponds of sea water capture and store the solar heat during periods of sunshine and release it in the evening hours: a) To the conventional ground distillation and to the system of solar towers-solar steam boilers-steam turbine thermal power plants, for example, that of the Rankine cycle:

- Directly, with the circulation of part of the thermal zone c of the pond into heat exchangers and thermal power plants of the system through the intakes and outtakes 12 and 13.

- Indirectly, through heat exchangers 16, submerged in the bottom of thermal zone c. b) To the composite solar tower-chimney 1:

Heating the air 5 through its passage over the transparent plastic sheet 11 of the upper zone a. -Through the submerged heat exchangers, e.g. a network of air ducts 14, figures 4 and 5. Preparative to the accommodation of the natural circulation of air, the air ducts in the shape of upsilon 14 are isolated along the entire height of the vertical part of intake 14a, and along the height of the non-submerged vertical part of outtake 14b. The air ducts remain closed during the day and open at night .

The upper and cooler zone a can function as a cool means of condensation of steam of the thermal generators and of other co-generative complexes. Water of the upper zone a is conducted directly through passages 17 to condensers and returns through passages 18, hotter, to the same zone of the solar pond. The same function can be executed indirectly by means of submerged heat exchangers. The zone a can also receive thermal loads from the wasted brine of the conventional ground distillation plant. The large quantities of water required for the function of this solar pond, both of clean water which evaporates as well as brackish brine for the maintenance of the salt gradient, are provided by the conventional ground distillation plant. Here the extraction and supply of brine to the particular solar pond is the ideal solution, as the disposal ^■ of the wasted brine is a significant economical and environmental issue. Reciprocal filling and synergy: The wastes of one, a vital part for the other. The proposed system can also work well with a different conventional desalination system, i.e. that of reverse osmosis. The fact that the solar gradient ponds 10 are placed within the greenhouse 8, in a sheltered and warm environment, results in a significant advantage which reduces the thermal losses of the pond, increases the temperature of energy storage in zone c, increases the capacity and the time of the stored energy and generally makes the whole system more competitive. Another significant advantage which the covered space affords the solar gradient ponds is that dust or foreign bodies carried by the wind reduce the transparency of the water and cause a reduction of absorption of solar radiation, a fact which, in the case of an open solar pond, must be dealt with the raising of a peripheral curtain wall with a height corresponding to the area of the pond. This great additional expense, which doesn't even bring sure results, can now be avoided thanks to the sheltering. Likewise, the periodic cleaning of the varying concentrations of the solutions of the solar gradient ponds, apart from the high cost, disturbs the salt gradient and by extent the normal function of the pond.

In Figure 6 there is depicted a process of vapour condensation by method of multiple successive coolings and reheatings of humid air between two somewhat stable temperatures The solar tower-chimney and by extent the air passing through it is divided for this purpose into segments and independent currents. For example, with the inner cylinder 23, the passing air is divided into part or current 24 and into part or current 25. The successive coolings are combined with traditional condensation, which delivers the desalinated water, while with the respective reheatings, only heat is added to the system. For the reheatings, the heat exchangers 27 are used in combination with the heat exchangers 21, which indirectly convey the heat from the solar ponds or the thermal wastes, or low pressure steam, of the other systems. For the successive coolings and humidifications, the heat exchangers 22 are found half on a segment inside tower 1, and half on the respective exterior cooling upstreams. These currents are created between tower 1 and its shell Ia or between shells Ia and Ib, respectively, which surround the tower at this height.

These secondary chimneys can also not be coaxial but independent and can engage secondary wind turbines 4a as well. The drop collectors 26 and 36 function to collect desalinated water which, with water turbine 32, contribute to the generation of additional electrical energy.

The condensation of water vapours from the hot air can also occur indirectly by mean of the conventional method of absorption by hygroscopic solid materials, like silica gel, or hygroscopic fluids, as for example a water-based solution of lithium bromide.

These solutions, or absorbers, are used in the cooling systems working by absorption. In the case of the solid absorbers," variations of a conventional dehumidifier rotor with its distinguishing functions, that of the absorption of humidity and that of its rejection, or regeneration, are used The phase of regeneration requires heat and is combined with condensation and the final reception of the vapours in the form of desalinated water. This has not been designed.

In Figure 7 is depicted a variation with fluid absorbers. The solar tower-chimney 1 bulges at the height which has been chosen for the absorption of warm air vapours and creates chamber 28. The ascending air is deflected 90 degrees from its path to area 28, guided by the vanes 33 in order to return again to the vertical after having passed the bulge. At the top of chamber 28, the solution of the absorber, rich but poor in water, is distributed in the form of microscopic droplets by an array of nozzles 30, in order to achieve the maximum possible surface contact. In this phase there occurs a release of heat both to the passing air as well as to the absorber. The humidity gives back the heat which it had received in the phase of evaporation.

The droplets which escape are captured by the drop collectors 26 and 36. The result, the rich in water, but diluted mixture of the absorber, is collected in vessel 29, going through the pipe 31 down to the base and setting into operation water turbine 32 for the generation of additional electrical energy.

The rich in water mixture of the absorber is directed after water turbine 32 to the system of regeneration and the final reception of desalinated water, while the dense and regenerated solution of the absorber that is created is directed by means of pump 35 and pipe 34 to the nozzles 30 and, consequently, completing the cycle. The process of reception of the desalinated water, or regeneration, is connected by the heat of the absorber from other energy sources, both renewable and nonrenewable, and which already exist in other parts of the same plant, in order to produce steam.

This phase of regeneration of the absorber will be a part of another general system, or cycle, or part of a cycle producing cooling by absorption, where water is both the cooling medium and also the medium of creation of electrical energy. The system in which the above will ultimately be imbedded will depend upon the needs and priorities of the region of the plant for cooling or electrical energy. Should, for example, one be interested in the production of cooling by absorption, the phase of regeneration of the absorber will be the corresponding "regeneration" of the cooling cycle, while the phase of vapour absorption will be the corresponding "absorption" of the same cycle. Should, likewise, one be interested in the production of electrical energy, the produced steam will expand in a steam turbine. The price of energy in the respective country of the plant will be a deciding factor in determining which to use. The suggested systems function in an extremely complementary manner, perfectly, controlled and flexible. Nothing remains unexploited. If the enriched-regeneration of the absorber and the reception of desalinated water occur at the level of absorption, namely, in chamber 28, then water turbine 32 is moved by the desalinated water which, in a pure state, descends to the base of tower 1.

Claims

1. Composite solar tower-chimney (1), consisting of a vertical cylinder which is positioned on an elevated base of a greater diameter (3) open at the periphery, where adjacent to and around the base (3) is found a second, bigger area, inside which is constructed a greenhouse (8) , which is "covered by a transparent covering (9) with peripheral openings (19) for the intake of ambient air (5), where the greatest part of the covered area of the greenhouse (8) contains shallow sea water ponds, where the air (5) is heated by solar radiation, passes over the surface of sea water at a continuously increasing rate of speed, evaporates sea or brackish water and with a very high percentage of humidity is directed to the solar tower-chimney (1) , where at a different height the humidity which was taken during its passage is condensated into desalinated water, with the characteristic that the ascending hot air of a high humidity (5) is of an open cycle, directed by a constant ascent to the top and to the outtake of the chimney, moves the wind turbines (4) which are found inside the tower, while simultaneously the fluid which has been collected at different heights flows by gravity back to the ground and base of the tower, where it moves water turbine (32) for the generation of additional electrical energy.

2. Composite solar tower-chimney (1), according to claim 1, with the characteristic that the fluid which has been collected at different heights, is desalinated water

3. Composite solar tower-chimney (1), according to claims 1, 2 with the characteristic that the greenhouse, or a great part of it, is a floating construction or a construction on the sea.

4. Composite solar tower-chimney (1), according to claims 1, 2, 3 with the characteristic that inside the second area which is enclosed by a circle of greater diameter

(6), exists a great number of heliostats (7) which consist of two-axis mirrors which reflect the solar radiation and direct it to a solar steam boiler (2) set outside and around the tower at height Hl from the surface, and subsequently create electrical energy by means of steam generators.

5. Composite solar tower-chimney (1), according to claims 1, 2, 3, 4 with the characteristic that inside the second area which is surrounded by a circle of greater diameter (6), are situated solar gradient ponds (10) which capture and store solar heat during the period of sunshine and give it back by means of heat exchangers into the system of steam turbines - thermal power plants as well as into the solar tower-chimney (1) , heating directly and indirectly the air (5) .

6. Composite solar tower-chimney (1), according to claim 5, with the characteristic that the solar gradient ponds

(10) are covered by the greenhouse (8) itself.

7. Composite solar tower-chimney (1), according to claims 1, 2, 3, 4, 5, 6 with the characteristic that the rate of evaporation is increased by an artificial rain of sea water.

8. Composite solar tower-chimney (1), according to claims 1, 2, 3, 4, 5, 6, 7 with the characteristic that the wind turbines (4) are found at the base of tower (1) .

9. Composite solar tower-chimney (1), according to claims 1, 2, 3, 4, 5, 6, 7,8 with the characteristic that there exists a conventional ground distillation plant that uses the rejected low pressure steam of the thermal or co-generation power plants of the system.

10. Composite solar tower-chimney (1), according to claims 1, 2, 3, 4, 5, 6, 7, 8, 9 with the characteristic that the humidity of the ascending air is concentrated at different heights and phases.

11. Composite solar tower-chimney (1), according to claims 1, 2, 3, 4, 5, 6, 7, 8, 9,10 with the characteristic that the humidity of the ascending air is absorbed by absorbers of solid materials.

12. Composite solar tower-chimney (1), according to claims 1, 2, 3, 4, 5, 6, 7, 8, 9,10 with the characteristic that the humidity of the ascending air is absorbed by absorbers of liquid solutions.

13. Composite solar tower-chimney (1), according to claim 12 with the characteristic that the absorption of humidity is achieved by the distribution of the solution of the absorber into the area of the bulge (28) of the solar tower-chimney (1) .

14. Composite solar tower-chimney (1), according to claims 11, 12, 13, with the characteristic that the enrichment-regeneration of the absorber and the removal of the desalinated water occur at the height of the absorption of the humidity from the absorber.

15. Composite solar tower-chimney (1), according to claims 12, 13, 14, with the characteristic that the process of the regeneration of the absorber occurs by using heat and is connected with the production of steam.

16. Composite solar tower-chimney (1), according to claim 15 with the characteristic that the created steam will expand in the steam turbine.

17. Composite solar tower-chimney [I), according to claim 16, with the characteristic that the creation of steam from the absorber is the "regenerator" of the cycle of the cooling production by absorption, where water is the cooling medium.

18. Composite solar tower-chimney (1), according to claim 16 with the characteristic that the absorption of humidity from the passing air is the "evaporator" of a cycle of production of cooling by absorption where the water is the cooling medium.

19. Composite solar tower-chimney (1), according to claims 1, 2, 3, 4, 5, 6, 7,8 with the characteristic that the condensation of the humidity of the ascending air occurs by method of successive coolings and reheatings of hot humid air.

20. Composite solar tower-chimney (I)_/ according to claim 19 with the characteristic that the tower chimney and the passing air are divided into segments of independent currents (24 and 25) .

21. Composite solar tower-chimney (1), according to claims 9, 14, 15, 16, 17, 18, 19,20 with the characteristic that the heat exchangers take their heat from the solar ponds or the rejected heat from the other power plants of the system.

22. Composite solar tower-chimney (1), according to claims 19, 20, 21 with the characteristic that in between the tower (1) and shell (1 a) as well as in between shell (1 a) and shell (1 b) are developed secondary external coaxial chimneys .

23. Composite solar tower-chimney (1), according to claims 19, 20 with the characteristic that the secondary external chimneys are not coaxial.

24. Composite solar tower-chimney (1), according to claims 19, 20,21,22,23 with the characteristic that for the successive process of coolings-dehumidifications, the heat exchangers (22) are found half inside the tower (1) , the other half in the corresponding external independent ascending current of cooling or secondary chimney.

25. Composite solar tower-chimney (1), according to claims 22, 23, 24 with the characteristic that the ascending air in the secondary chimneys move the secondary wind turbines (4 a) .

26. Composite solar tower-chimney (1) , according to claims 5, 6, with the characteristic that the air ducts of solar gradient pond (10) are insulated along the entire vertical height of intake (14 a) , and are insulated only along the non-submerged vertical portion of the outtake.