WO2005121030A1

WO2005121030A1 - Integrated device for the decontamination of water and production of electrical power

Info

Publication number: WO2005121030A1
Application number: PCT/ES2005/000318
Authority: WO
Inventors: Julian Blanco Galvez; Rodriguez Sixto Malato; Cesar Octavio Pulgarin; Victor Manuel Sarria; Simeon Kenfack
Original assignee: Centro De Investigaciones Energeticas Medioambientales Y Tecnologicas (C.I.E.M.A.T.)
Priority date: 2004-06-07
Filing date: 2005-06-03
Publication date: 2005-12-22
Also published as: MA28654B1; MXPA06014285A; EG24192A; ES2245243B1; ES2245243A1

Abstract

The invention relates to an integrated device for the decontamination of water and the production of electrical power. The inventive device consists of a photocatalytic/photovoltaic hybrid system comprising a photocatalytic reactor (2) which is made from a material that is transparent at least to visible radiation from the sun, which contains a photocatalyst of titanium dioxide, iron (II) or iron (III) and which is stacked on a photovoltaic panel (3), both the photocatalytic reactor and the photovoltaic panel being disposed on the same support (4) which can be inclined at a suitable angle (10) such as to make optical use of the incident radiation. The photocatalytic reactor (2) protects the photovoltaic panel (3) from solar infrared and ultraviolet radiation which are absorbed by the photocatalyst and the water respectively. Moreover, a recirculation pump (5), which is powered by the photovoltaic panel (3), ensures the flow of water through the photocatalytic reactor (2), which also cools the photovoltaic panel (3). The invention is particularly suitable for the treatment of water in remote locations.

Description

INTEGRATED DEVICE FOR WATER DECONTAMINATION AND ELECTRICAL ENERGY PRODUCTION

Object and field of application The present invention relates to the realization of a new device that combines the decontamination and disinfection of water by photocatalysis, together with the capture of solar radiation for conversion into electricity by means of a photovoltaic panel. The objective is to increase the useful life of the system of conversion of solar energy into electricity, reduce the space needed by both systems and achieve the energy autonomy of the photocatalytic system. For this, a change in the design of both the photocatalytic and photovoltaic systems is proposed. This change fundamentally affects the superimposed installation of both systems. The field of application of the invention would be water treatment plants by solar photocatalysis that are located in places where there is no easy access to conventional electricity. This is common in developing countries and, in general, anywhere isolated and away from a power line. Since water consumption in perfect sanitary conditions is increasingly a priority, these systems can avoid problems related to the lack of electricity needed to achieve it, in addition to significantly increasing the life of the photovoltaic panels responsible for generating it. Throughout the document the following terms will be used, with the meaning described: - titanium dioxide photocatalyst. Titanium dioxide is a solid and water insoluble substance that is characterized by having semiconductor characteristics. When illuminated by radiation photons of suitable wavelength (less than 400 nm), a change in its surface structure occurs. Each photon generates an electron / hole pair on the surface of the oxide, so that the electron (of negative charge) migrates from the valence band of the oxide to the conduction band, leaving a positive charge gap on the surface. Under these conditions, if the illuminated titanium dioxide is in contact with water, hydroxyl radicals are generated from the interaction between it and the gaps. -photo iron catalyst (II). Iron (II) dissolved in water at pH = 3 and in contact with hydrogen peroxide (hydrogen peroxide) generates iron (III) and hydroxyl radicals. If this system is illuminated by radiation photons of adequate wavelength (less than 550 nm), iron (lll) regenerates iron (II) and more hydroxyl radicals. From so that the system is catalytic (there is no iron consumption) with the only need to add hydrogen peroxide. -photo iron catalyst (III). If the iron (III) dissolved in water at pH = 3 is illuminated by radiation photons of suitable wavelength (less than 550 nm), the iron (lll) generates iron (II) and hydroxyl radicals. Iron (ll) can regenerate iron (lll) by the effect of radiation, although the generation of iron (lll) is much slower than if this is done by the addition of hydrogen peroxide. This process is completely catalytic, although the amount of hydroxyl radicals generated is smaller. -radical hydroxyl. Hydroxyl radicals are chemical species that can be generated from water in many different ways, but whose main characteristic is their high oxidizing power. This oxidizing power allows decomposing (up to carbon dioxide and inorganic salts) polluting organic molecules that are present in the water. This oxidizing power also allows to inhibit bacterial growth in that water and even destroy those microorganisms. Background of the invention In recent years, the use of photocatalytic systems based on the use of titanium dioxide or iron (II) or iron (III) that use solar radiation for the degradation of non-biodegradable compounds in water has been increasing and It is presented as a very promising technology. In addition, the same technology has also been used for water disinfection, as an alternative to ozone or chlorine. These systems use solar radiation (in particular ultraviolet radiation) to cause, in the presence of a catalyst, the breakdown of organic molecules such as pesticides, dyes, solvents and other pollutants of a very different nature. In the same way, the chemical reaction caused is capable of inhibiting bacterial (or other microorganisms) growth and even causing its destruction. Solar photocatalytic technology can be defined as one that efficiently captures solar photons and introduces them into a suitable reactor to promote specific photocatalytic reactions. The equipment that performs this function is called the solar collector. Traditionally, solar collector systems have been classified into three large groups depending on the level of concentration that can be achieved. The concentration factor (FC) of a solar collector is defined as the ratio between the opening area of the collector and the area of the absorber. The opening area is the area that intercepts the radiation, and the area of the absorber, the area of the component that receives the solar radiation. These three groups are as follows: • Non-concentrating systems, which are static and have no solar tracking. They are generally flat-shaped plates oriented towards the equator with a specific inclination, depending on the geographical situation, to maximize solar collection. Its main advantage is its simplicity and low cost. An example is the traditional domestic water heater.

• Medium concentration systems, which concentrate sunlight between 5 and 50 times, so they require a solar tracking system. They have a reflective surface that concentrates the radiation in a tubular receptor located in the focus of the parabola.

• High concentration systems, which have a focal point instead of a linear focus and are based on a paraboloid with solar tracking. Typical concentration values are in the range of 100 to 1000 and high precision optical elements are needed. This group includes parabolic discs, central tower systems and solar furnaces, which are used primarily for the production of energy from concentrated solar radiation. Photocatalytic processes use the UV ultraviolet spectrum (300 to 400 nm) of sunlight. The technology necessary to carry out applications of solar photochemistry, in liquid phase, has much in common with the technology used in thermal applications.

This is the reason why the design of photochemical systems and reactors, in its initial phase, was based on conventional designs of solar thermal collectors, as is the case of parabolic trough collectors. However, there are also important differences between thermal and photochemical processes, the main ones being the following:

• The fluid must be directly exposed to solar radiation and, therefore, the reactor must be transparent to photons, mainly from the UV range. • The fluid must capture the maximum possible photons useful for the photocatalytic process, avoiding that none of them pass through it without being absorbed.

• Reflective elements and / or concentrators must be optimized to reflect the appropriate wavelength radiation for the process.

• Thermal insulation is not required since temperature does not play a significant role in photocatalytic processes. Due precisely to this last point, the associated technology has been based on solar devices of medium, low or no solar concentration from the outset. Static collectors without solar concentration are, in principle, the most economical since they have no moving parts or tracking mechanisms. However, they are less efficient devices when it comes to capturing sunlight, although their performance is not reduced by factors associated with concentration and solar tracking. They have developed and tested a large number of non-concentrating solar reactors for photocatalytic applications: reactors based on an inclined plate on which the process water slowly falls; others consisting of two plates between which the flow circulates using a separation wall; tubular, consisting of a series of variable sized tubes connected in parallel to circulate the flow faster than on a flat surface; systems consisting of a kind of shallow pool where the water to be treated is exposed to solar radiation, which may have some type of agitation or not. In the case of static collectors without monitoring, the annual solar energy collection is maximized when the angle of inclination with respect to the ground coincides with the latitude of the place. This analysis automatically leads us to consider the possible convenience of static systems for the implementation of photocatalytic processes since the apparent small performance disadvantage seems to be easily offset by the much lower cost of static systems. However, there is also another relevant factor in favor of static systems, such as the fact that they can take advantage of diffuse solar radiation, which is not feasible with tracked concentration collectors. Since diffuse radiation (that which, after interacting with the particles of the atmosphere, reaches the surface of the earth in a random direction) can be an important percentage of the total UV radiation useful for the process, its possible use is something that should be to take into account The photovoltaic (PV) process converts solar radiation into electricity. The basic component of a photovoltaic panel is the photovoltaic cell, which when illuminated with solar radiation (fundamentally visible, 400-800 nm) produces electricity.

However, other components of the photovoltaic panel (joints, protective materials, etc.) absorb radiation of other wavelengths and cause the panel temperature to reach 80 ° C, which adversely affects its performance and deteriorates it . Normally, the efficiency drops by 30% when the temperature rises from 20 to 60 ° C. The use of photocatalysis in water purification is described in various documents, for example EP 634 363. Document US 6,204,545 describes a device for the joint use of photocatalysis and photovoltaic energy to produce a combined photoelectric effect. Document DE 196 07 862 describes a photocatalytic semiconductor that uses an ultraviolet (UV) light source to purify gaseous streams, especially the exhaust gases of internal combustion engines. For its part, document DE 28 47 433 describes a device for heating water that additionally uses the photoelectric effect. In summary, some known applications that combine both techniques are focused on taking advantage of the joint effect, but in no case do they refer to the use presented here. Document JP11009965-A describes the arrangement of a photocatalyst on the outer surface of a hollow plastic sphere, forming a transparent photocatalytic layer. In turn, the photocatalytic layer is superimposed on a photoelectric layer that can act as a photovoltaic cell. These spheres (other geometries and different shapes are also described in the document) can be suspended in water or air to achieve two simultaneous effects: fluid purification (water or air) and electricity production. The fundamental differences with the use presented here are several: a) The protection of the photovoltaic device with the photocatalytic device is not intended at any time. Neither by filtering ultraviolet radiation, nor by a cooling effect. b) The photocatalytic-photovoltaic element is suspended in the fluid to be purified, without it being confined to any photoreactor. It is water or air from the environment where the "spheres" mentioned above are suspended. c) There is no mention at any time available to you as part of a solar photoreactor, nor to use the electricity produced to move a pump. In conclusion, none of the known photocatalytic devices has a photovoltaic system coupled to it so that it protects it from the harmful effects caused by photons of certain wavelengths and temperature increases. In addition, in the device of the invention the coupling of both systems allows the use of photocatalytic reactors in isolated locations. Consequently, since a PV panel mainly converts visible solar light into electricity, that a PV panel is damaged by the high temperature reached on its surface and by the UV radiation that reaches it, than the water contained in a reactor Photocatalytic is transparent to visible radiation and that photocatalytic degradation makes use mainly of UV radiation (and therefore absorbs it), it is an objective of the present invention to have a photocatalytic-photovoltaic hybrid device so constructed and operated that the photocatalytic component is capable of filtering the UV radiation that damages the PV panel, that the photocatalytic component is capable of cooling the PV panel by means of the water contained therein and of decontaminating or disinfecting water by means of a photocatalytic process. It is another objective of the present invention to have an integrated photocatalytic-photovoltaic device so constructed and operated that it produces electricity sufficient by means of the photovoltaic component that allows water to be recirculated by the photocatalytic component, for its treatment. Description of the invention To achieve the proposed objective the photocatalytic reactor must be superimposed on the photovoltaic panel, both on the same support. This can be achieved by combining the following elements:

1. A photocatalytic reactor through which water can circulate, based on the superposition of two transparent panels, closed so that water circulates between them. In order to achieve sufficient turbulence, the space contained between the two panels will be divided into sections by means of open partitions at one end and arranged so that the water zigzags in its path.

2. The material from which the photocatalytic reactor panels must be made must be transparent to ultraviolet and visible solar radiation (300-800 nm). This can be achieved by borosilicate glass of low iron content or by a plastic material of similar characteristics Plexiglas type.

3. The arrangement of the photocatalytic reactor must be superimposed and in solidarity with the photovoltaic panel in order to cool the surface of the latter by means of the water flowing through it.

4. All of the above must be arranged on a support that is tilted the same degrees as the latitude of the site in order to maximize the annual efficiency of solar radiation collection by means of a flat collector. A device like the one described, due to the compactness of its design and its reduced maintenance, has great advantages in its use in remote places or developing countries, where it can ensure the supply of water and electricity in places far from conventional networks of distribution. BRIEF DESCRIPTION OF THE DRAWINGS To complete the foregoing description and in order to help a better understanding of the features of the invention, a detailed description of a preferred embodiment will be made based on a set of drawings that are attached hereto. descriptive and where the following has been represented: Figure 1 shows a schematic elevation of the integrated device object of the invention. Figure 2 shows, schematically, the behavior of the 3 components of solar radiation when affecting the integrated device. Figure 3 shows, schematically, a plan view and the water path within the photocatalytic reactor. Figure 4 shows a side view of the hybrid system object of the invention. In these figures the numerical references correspond to the following parts and elements I. Solar radiation incident. 2. Photocatalytic reactor. 3. Photovoltaic panel. 4. Support structure. 5. Recirculation pump. 6. Water output from photocatalytic reactor. 7. Open partitions for water circulation in photocatalytic reactor. 8. Photocatalytic reactor water inlet. 9. Power supply to the pump from the photovoltaic panel. 10. Tilt angle of the entire system. II. Ultraviolet solar radiation 12. Visible solar radiation 13. Infrared solar radiation Detailed description of a preferred embodiment As can be seen in Figure 1, in general, the integrated device object of the invention comprises a photocatalytic reactor (2), which has a flat shape and which is arranged on top of a photovoltaic panel (3), all placed on a support structure (4). In this way, solar radiation (1) illuminates the photocatalytic reactor (2) and after passing through it, it affects the photovoltaic panel (3). The solar radiation that reaches this photovoltaic panel is able to make it generate enough electricity to move a pump (5) that drives the water that passes through the photocatalytic reactor (2). This pump is placed under the entire system to take advantage of the shadow it generates and increase its durability. In figure 2 one of the main advantages related to this invention is schematically represented. In this figure 2 it can be seen that on the photocatalytic reactor (2) the solar radiation has three components, based on its wavelength, such as the ultraviolet component (11), the visible component (12) and the infrared component (13). The superimposed arrangement ensures that only the visible component (12) falls on the photovoltaic panel (2), since the ultraviolet component (11) is absorbed by the catalyst disposed inside the photocatalytic reactor (2) and is responsible of water decontamination. The infrared component (13) is absorbed by the water itself. The titanium dioxide catalyst is suspended in the water before recirculating it in the photocatalytic reactor. Once the treatment, removed by sedimentation. If instead iron (II) or iron (III) is used, these would dissolve in the water after fixing a pH of 3 by adding acid. In this case, it would then be removed by increasing the pH until neutralization (pH = 7), which would cause the precipitation of iron with iron hydroxide, a solid that can also be removed by sedimentation. In a preferred embodiment, which we will call an inclined arrangement, the photocatalytic reactor (2) is superimposed on the photovoltaic panel (3), but all placed on a support structure (4) that allows the entire device to have an inclination angle ( 10) equal to the latitude of the place, so that the maximum annual average efficiency is achieved (if that inclination does not change) or the maximum efficiency at each moment (if that inclination is varied depending on the solar height). Referring now to Figure 3, we can see that the photocatalytic reactor (2) has partitions (7) made of the same transparent material as the upper and lower panels thereof. These partitions have the objective that the water that enters the photocatalytic reactor (2) through the water inlet (8) and out through the water outlet (6), circulates through it following a zigzagent path that allows greater turbulence, which improves the yield of the photocatalytic reaction. In addition, in this way the circulation of water is more homogeneous and the non-accumulation of it in dead areas is guaranteed (mainly the corners). In the same way, a better heat transfer is also guaranteed with the photovoltaic panel (3) placed underneath and, therefore, a better cooling of the latter. A series of alternative embodiments that allow adapting the design to the specific technical and economic conditions of a specific embodiment will be evident to a person skilled in the art. Thus, for example, in the construction of the lower panel of the photocatalytic reactor (2) that is superimposed and integral with the photovoltaic panel (3), conventional glass can be used since only visible radiation must pass through it. But this will always depend on the ease of composing the photocatalytic reactor (2) by combining different materials. Also with respect to the photocatalytic reactor (2), this can be formed by a series of tubes (constructed with a material similar to those mentioned above) and placed on top of the photovoltaic panel (3) in parallel and covering it completely. Water would circulate through them in a manner similar to that shown in Figure 3. Another example could be related to the location of the recirculation pump (5), which should not necessarily be below if it correctly supports the weather. The catalyst could also be handled differently. Titanium dioxide or iron hydroxide could be removed by filtration. This would involve the installation of an additional pump, which also It could be powered by electricity generated in the photovoltaic panel, in order to drive the water to the pressure necessary to pass through the filter necessary for filtration. In addition, another possibility would be to arrange the catalyst (be it titanium dioxide or iron) in an inert support such that it is not necessary to remove it from the water. This is a solution that could be made only if that support were transparent to visible radiation, so that the lighting of the photovoltaic panel was not prevented. This type of support has not been developed so far. Likewise, and for reasons of clarity, different elements that are necessary for the correct operation of the device of the invention have been described conventionally and well known. Thus, it will be necessary to provide the water circuit with a water outlet to be purified and an outlet of purified water to a storage container. For this reason it will be necessary to provide the device with electrical storage means (for example batteries) if it is desired to have electricity at night.

Claims

1. Integrated device for water decontamination and electric power production comprising; a photocatalytic reactor (2) and a photovoltaic panel (3), superimposed the first over the second so that the photocatalytic reactor protects the photovoltaic panel and both solidaries of a structure (4) capable of being able to tilt with the angle (10) suitable for take advantage of the incident radiation, a recirculation pump (5) whose power is provided by the photovoltaic panel (3), and characterized by being manufactured the photocatalytic reactor (2) with a material transparent at least to the visible radiation from the sun , and incorporate partitions (7), open at one end, arranged so that the water zigzags in its path.

2. Integrated device for water decontamination and electric energy production according to claim 1, characterized by using titanium dioxide or iron (III) as photocatalysts in the photocatalytic reactor (2).