FR3148789A1 - Floating desalination and pollution control modules powered by solar heat - Google Patents

Abstract

The invention relates to a modular and floating water distillation system, very low energy consumption and "low tech", using solar energy to heat the air and cause the evaporation of the water to be distilled. The modules can be individual or connected to cover a larger surface area. The air flow is controlled to optimize the efficiency. The condensation of the distilled water is achieved by cooling, either passively using the temperature of the surrounding water or air, or actively with a dedicated cooling system. The modules are manufactured with accessible materials and can be improved to maximize solar absorption, thermal insulation and the heated water/air interface. The system floats on insulating materials and is designed to maximize the internal temperature of the module, allowing an optimal evaporation rate.

Description

Floating desalination and pollution control modules powered by solar heat

The invention presented concerns the field of desalination and decontamination with very low energy consumption and is called "low tech", applicable on a small scale and on an industrial scale.

The invention more specifically concerns floating modules capturing solar heat in order to saturate the air with humidity. The water contained in the air is then recovered by condensation.

Prior art

Different technologies currently exist around water desalination:

Multi-stage distillation (MSF): Multi-stage distillation is a thermal desalination process that uses heat to evaporate salt water and then condense fresh water. Salt water is heated and passed through multiple stages with decreasing temperatures and pressures, resulting in fresh water being condensed. This method is energy intensive, but has a long history of use in drinking and industrial water production. (EP2039407)

Multiple Effect Distillation (MED): Multiple effect distillation is another method of thermal desalination. It works by using the water vapor produced in one effect (an evaporation chamber) to heat salt water in the next effect, thereby saving energy. The water vapor is then condensed to recover fresh water. (EP2862842)

Reverse Osmosis (RO): Reverse osmosis is a desalination process based on membrane filtration. Salt water is pressurized and pushed through a semi-permeable membrane that retains dissolved salts and allows fresh water to pass through. Reverse osmosis is currently the most widespread and energy-efficient desalination technology, especially for small and medium-sized installations. (EP2377817)

Nanofiltration (NF): Nanofiltration is another membrane filtration technology that works on similar principles to reverse osmosis, but with slightly larger membrane pores. It is typically used for specific applications, such as reducing water hardness or removing organic contaminants.

Solar desalination: This method uses solar energy to heat salt water and cause it to evaporate. The water vapor is then condensed to recover fresh water. Although this method is less efficient than other desalination technologies, it has the advantage of using a renewable energy source and is particularly suitable for small, decentralized installations. (WO2022006681, WO2006021139, WO2006077593, WO2008006253, EP0345236, WO2007054143)

The invention presented is part of this last category. Its particularity is its deployment in aquatic surfaces, in particular maritime, salt marshes, brine or polluted water, and its modularity. It operates either by modules of the order of a square meter, or on a surface of several tens of square meters, according to the needs and the stability of the surface exploited (sea or artificial basins for example).

General description of the invention

The basic principle of the invention presented is based on the variation of the absolute humidity in water of the air as a function of the temperature.

In fact, this rate is close to 10 to 20 g/m3 for an ambient temperature between 20 and 30° and increases exponentially to reach values of 150 to 300 g/m3 for temperatures between 60 and 80°.

Thus, cooling a volume of one cubic meter of air at 80° saturated with water to 20° produces the condensation of approximately 1/4l of distilled water.

The aim of the invention is to propose a system that is easy to build and deploy using simple technologies and accessible materials.

Knowing this, the invention described is based on the manufacture of floating modules on the sea or on any flat surface of water requiring distillation (1.7) (desalination, depollution, purification) exposed to the sun.

These modules can be individual or connected successively by the same air flow (2.1) in order to increase the covered surface.

An air flow optimized for profitability is imposed in the inlet (1.1) and outlet (1.5) modules, either mechanically (motor, pump) or by wind capture and regulation.

The heat absorbed by the surface of the modules (1.4) increases the temperature of the volume of air contained in the module, causing the evaporation of the water to be distilled contained in the module, causing the humidity to tend towards saturation at the temperature reached, and this depending on the air renewal rate in the modules.

For condensation , the air is pumped (3.1), therefore renewed in the module, and cooled after the outlet (3.2), ideally using the temperature of the surrounding water, which can be improved with the help of diffusers (type of radiators) of temperature in contact with the water (3.4). An equivalent system above the surface of the sea can also be realized in order to have air cooling to avoid heating the surrounding water (for ecological reasons). In both cases, it is the passive condensation variant of the invention.

A variant uses a heat exchanger cooling system (4.2). This cooling causes the condensation of water contained in the air, thus producing distilled water. The heat produced by the system is recovered and reinjected into the module by an air flow entering at (4.3) and injected into the module at (4.1).

The injected air then passes through the module and is discharged in (4.4) after condensation in the cooling system taking advantage of the cold emission from the heat exchanger. This is the active condensation variant of the invention.

In all cases the distilled water is collected in a tank (3.5, 4.5).

The module containing the air volume can be built in any materials (wood, metal, etc.), but typically in plastic (EHD, PE, polyethylene, polypropylene, PVC depending on their resistance), preferably black to absorb maximum solar radiation. These materials must be resistant to seawater and the damage it can cause, such as corrosion or the accumulation of marine organisms.

A heat diffusion radiator (1.2) optimizes the heating of the air in the module, and can be made of a metal surface, a very good conductor of heat.

These radiators can reach the water and can be covered with a material with high capillarity power in order to maximize the heated water/air interface in order to maximize the evaporation speed. (such as terry cloth fabrics, made from cotton, viscose, polyester or polyamide fibres) (5.1).

A simple system of projection and vaporization of water from the module into the volume of the module can also be added to actively increase the air/water interface.

The part exposed to the sun (1.4) can be covered with a black paint with high absorbency, for example black silicone or epoxy paint which can exceed 95% absorbency.

Finally, the exterior part can be covered with a glass or plastic canopy system (1.3) in order to benefit from a "greenhouse effect" by leaving an air gap between the canopy and the module, called an insulation space.

It should be noted that the performance of this insulation space can be improved by being placed under vacuum.

This module is placed on a permeable float system (1.6). The hydrostatic balance will allow to have a sufficient level of water to be distilled in order to allow saturation. The float also allows to thermally isolate the water contained in the module from the outside water by being composed of neoprene, aerogel, polystyrene, or even wood. In short, any material allowing good thermal insulation while providing flotation. To achieve hydrostatic balance, the floats can cover all or part of the outside part of said module, beyond the waterline if necessary.

The objective is to increase and maintain the temperature of the volume of air contained in the volume as much as possible.

The prototypes have demonstrated that at maximum exposures the temperature can easily exceed 60°. It has been estimated that, in an optimal construction, the temperature of the air volume can exceed 100°, the boiling temperature at sea level, but the important thing remains the optimization between temperature, air circulation and water evaporation time.

An electronic system for measuring the quantity of distilled water per hour and regulating the air flow to optimize said air flow according to the quantity of water produced, in order to obtain the maximum quantity, may be added.

Physical considerations and profitability expectations:

In this description, the present patent takes each element considered in the numerical simulation which made it possible to arrive at the final forecast result.

Absorption of heat by solar radiation

Low cost materials that can absorb a very high rate of solar energy, from 0.9 to 0.95 absorption. These paints are the

Matte or Satin Black Acrylic Paint: Acrylic paints are generally less expensive than epoxy paints and are available in a variety of finishes. They are easy to apply and dry quickly. However, they may be less durable than epoxy paints, especially when exposed to extreme marine conditions.

Matte or Satin Black Epoxy Paint: Epoxy paints offer excellent resistance to seawater, corrosion and harsh conditions. Although they are generally more expensive than acrylic paints, they are more durable and offer better long-term protection.

Matte or Satin Black Silicone Paint: Silicone paints offer excellent resistance to marine conditions, moisture and corrosion. They are hydrophobic, making them ideal for marine applications. Silicone paints are also flexible, UV resistant and can be formulated with biocides to prevent algae and mould growth. However, they can be more expensive than acrylic and epoxy paints, and their application may require a little more skill to ensure even coverage and optimum adhesion.

Thus, Mediterranean areas at the equator receive 800 to 1000W of solar energy at the zenith. This allows us to estimate the total quantity per sunny day to be of the order of 5 kW.

It should be noted, in comparison with profitability, that photovoltaic energy is profitable at around 20%, which puts into perspective the direct use of total solar energy in a desalination framework.

Water evaporation rate

Since the present invention is based on the evaporation of water within a continuous air flow, the speed of this flow is to be considered in the efficiency of the invention. It is important to note that the thermal energy carried away by the air leaving the invention is lost energy, this flow will therefore have to optimize the evaporation profitability and the energy loss described later.

The evaporation rate follows a classical exponential charge law defined by

Or :

is the charge of the capacitor at time ,

is the maximum humidity (100% in terms of relative humidity),

is the time elapsed since the start of evaporation,

is the vaporization time constant, which determines the rate of increase in relative humidity of the air in the invention.
The important thing in optimizing the invention is the reduction of this parameter by increasing the air/water interface in particular (by increasing the surface area, or even by vaporization).

Diffusion loss

• sa surface extérieure exposée à l'air,
• sa surface extérieure exposée à l'eau,
• sa qualité d'isolation sur ces deux interfaces.

The loss of invention is directly proportional to:

• its outer surface exposed to the air,
• its outer surface exposed to water,
• its insulation quality on these two interfaces.

This loss can be defined by

Or is the amount of heat transferred (in watts), is the total surface area to be insulated (in m²), is the temperature difference between the two sides of the insulation (in Kelvin) and is the thermal resistance (in m².K/W).

This loss can be managed thanks to the different materials and floats as well as their thickness used in the invention.

Loss by extraction

A very significant part of the energy lost is due to the energy stored by the fluids leaving the module, i.e. hot air and water vapor.

This flow can be easily calculated by the difference in total incoming enthalpy (for example, water-saturated air at 20° and the enthalpy of liquid water), and outgoing (for example, air loaded with humidity at 60°). The outgoing enthalpy depends on the air flow, the humidity rate, the outgoing temperature, etc. and can be simulated. This value is dominated by the enthalpy of water vapor (2600 kJ/kg), and allows us to calculate that the maximum theoretical flow of distilled water produced is approximately 2 l/h/² of surface exposed to a solar exposure of 1kW.

Simulation and experimental results

Based on the considerations described above, the simulation of an ideal but realistic installation is approximately 1 to 1.5 l/h/m² in a sunny Mediterranean area between 12 p.m. and 2 p.m. (Marseille).

The experience enabled by a prototype gives us the same order of magnitude, validating the calculations.

Additional descriptions of the figures

• La est une schématisation du module de l'invention. Le module contient l'entrée d'air (1.1), le radiateur propageant la chaleur de l'extérieur à l'intérieur du module (1.2), la serre améliorant l'accumulation de chaleur (1.3), le corps du module contenant l'air chaud provocant l'évaporation (1.4), l'évacuation d'air saturé d'eau (1.5) et le système de flotteur couvrant toute la partie inférieure (1.6).
• La est une schématisation de la mise en série de deux modules (plus de modules pouvant être mis en série) reliés l'un à l'autre pour le flux d'air (2.1).

• La est une schématisation du module et du système passif de condensation utilisant la température de l'eau. L'air entrant en (3.1) dans le module se sature, est évacué par (3.2), est refroidi par des radiateurs passifs (3.4) par la température environnante de l'eau, l'eau est recueillie en (3.5), et l'air asséché est évacué en (3.3).
• La est une schématisation du module et du système actif de condensation utilisant typiquement un échangeur thermique. L'air entre en (4.3), est réchauffé par l'échangeur thermique en (4.2), puis injecté dans le module en (4.1). Après saturation l'air arrive en (4.5) et est refroidi par l'échangeur thermique (4.2). L'air asséché est enfin évacué en (4.4).
• La donne le détail du radiateur (1.2) équipé d'une surface absorbant et répartissant l'eau à distiller le long du radiateur (5.1) afin d'augmenter l'interface eau/air, et donc d'optimiser l'évaporation de l'eau.

The figures illustrate the various aspects and examples of the invention presented, as well as certain elements of its structure, its components and similar materials. They are indexed using different numbers, which may be repeated for the same elements, and different for different elements. This indexing indicates the number of the figure as well as the number of the element, separated by a point. (1.2) indicates element 2 of the , (3.6) element 6 of the . In the text, the indexing may include several values separated by a comma, indicating several elements at once, such as (1.1, 1.2) refers to elements (1.1) and (1.2). The same indexing is used in the figure and in the text. Where necessary for the clarity of the figures, a thin black line links the elements and their reference in the figures.

• There is a schematic representation of the module of the invention. The module contains the air inlet (1.1), the radiator propagating heat from the outside to the inside of the module (1.2), the greenhouse improving heat accumulation (1.3), the body of the module containing the hot air causing evaporation (1.4), the evacuation of water-saturated air (1.5) and the float system covering the entire lower part (1.6).
• There is a schematic of the series connection of two modules (more modules can be connected in series) connected to each other for the air flow (2.1).

• There is a schematic of the module and the passive condensation system using the water temperature. The air entering the module at (3.1) becomes saturated, is evacuated by (3.2), is cooled by passive radiators (3.4) by the surrounding water temperature, the water is collected at (3.5), and the dried air is evacuated at (3.3).
• There is a schematic of the module and the active condensation system typically using a heat exchanger. The air enters at (4.3), is heated by the heat exchanger at (4.2), then injected into the module at (4.1). After saturation the air arrives at (4.5) and is cooled by the heat exchanger (4.2). The dried air is finally evacuated at (4.4).
• There gives the details of the radiator (1.2) equipped with a surface absorbing and distributing the water to be distilled along the radiator (5.1) in order to increase the water/air interface, and therefore to optimize the evaporation of the water.

Claims (10)

A water distillation module characterized in that it is floating and in that it comprises: a) a module body (1.4, 1.6) adapted to float on a water surface (1.7); b) a direct solar heating system (1.2, 1.4) for increasing the temperature of the air and water inside the module; c) an incoming air flow (1.1), absorbing the evaporating water to be distilled, and exiting (1.5) outside the module; d) a passive (3.4) or active (4.2) cooling system for cooling the water-saturated air leaving the module; e) means for recovering water from the cooled air. The floating water distillation module according to claim 1, characterized in that the body of the module is made from a seawater-resistant material, such as plastic, wood or metal (1.4). The floating water distillation module according to claim 1 or 2 characterized in that the surface of the module must have a high absorbency, by its nature or the application of a black silicone or epoxy paint. The floating water distillation module according to one or more of the preceding claims, further characterized by the provision of a radiator (1.2), typically metallic, for conducting heat inside the module by a thermal conduction system. The floating water distillation module according to one or more of the preceding claims, characterized by radiators covered with a material with high capillarity power to increase the heated water/air interface and maximize the evaporation rate, such as, for example, a terry cloth (5.1). The floating water distillation module according to one or more of the preceding claims, further characterized by a glass or plastic canopy system (1.3) for creating a greenhouse effect and thermal insulation. The floating water distillation module according to one or more of the preceding claims, characterized by permeable floats allowing the continuous entry of sea water as well as thermal insulation between the water contained in the module and the external water by covering all or part of the lower external part of said module (1.6). A water distillation system characterized by the plurality of floating water distillation modules according to one or more of the preceding claims, connected together to increase the total covered surface area. The water distillation system according to claim 8, characterized in that the modules are successively connected to the same air flow (2.1). A method of distilling water using the floating water distillation module according to one or more of claims 1 to 7 or the water distillation system according to claims 8 or 9, characterized by the steps of: a) heating the air inside the module to increase the temperature and cause evaporation of the water to be distilled; b) cooling the water-saturated air inside the module; c) condensing the water from an active or passive cooling system; d) collecting the water.