A nature-inspired photothermal mechanism for reducing energy and equipment desalination costs

Abstract

A seawater desalination plant for reducing desalination costs comprises an evaporation tank 10 with a glazed opening, seawater spray nozzles which spray seawater in the evaporation tank, and an infrar

Description

.. Desalination plants are a useful method of converting seawater to potable water In countries with arid and seml-arld climates. The said plants consist of seawater Intake structures, Intake pipes, pump stations, feeder pipes,de-aeratersbrlne heaters,boilers, evaporator units and discharge channels. Various machinery and equipment are required for the said conversion and are connected through pipes of different sizes and types to meet the temperature and pressure variations. Seawater is first taken into the system via the intake structure and heated in the boilers using crude oil. Steam generation requires more energy input due to the high latent heat requirement of seawater. Atmospheric pressure in the evaporator is then reduced to bring down the boiling point of the seawater for energy saving. Seawater at low temperature is circulated in the cooling tubes. The steam is condensed on the cooling tubes for distillate production for potable water production. Multi-stage flash evaporation or MSF desalination plants are at present the most commonly used methods for converting seawater to potable water. Seawater Reverse osmosis (SWRO) removes the salt content In the seawater by using membranes and pumps which pressurize the seawater. The process is more direct and simplified than the above thermal method. The problem is that it cannot convert high salinity seawater to potable water. This is because the membranes are prone to fouling or collection of salt particle which make seawater filtration more difficult However, existing desalination systems have a number of disadvantages affecting their product development. A typical MSF desalination plant consists of 16-30 stages to increase production of potable water. However, the desalination process is energy intensive and requires high equipment investment which increases costs for middle and low income countries causing water scarcity around the world. Seawater reverse osmosis( SWRO) plants consume 3.5 to 5.5 kWh per meter cube of electricity while MSF plants require 190 -390 kJ / m3 to operate. They do not require thermal input but require 5-9 kW / m3 of electricity. The average cost of drinkable water from large desalination plant costs is between $0.5 / m3 to $1,5m3 which is too high for limited income countries facing water scarcity. MSF desalination plants also cover large land areas increasing costs further.. One of the reasons for the high cost is that existing desalination plants utilize crude oil for seawater heating and evaporation for steam generation. Fossil fuels have their origins in plant material and the combustion process is hence very similar to burning wood. Thermal heating of fossil fuels is a highly scattered heating method. The main purpose of desalination is to evaporate seawater which removes the dissolved salts. This is hampering product development. The scattered nature of fossil fuel heating cannot achieve this instantly. As a result only about 10% of the incoming seawater is converted to potable water and the remaining 90% mostly rejected as brine and returned to sea often at high temperatures at a considerable energy loss in the system. Large amounts of seawater are therefore unnecessarily handled and this increases the amount of equipment required which increases costs for low income countries thus perpetuating the water scarcity in these regions.. The regions facing water scarcity are in tropical regions which receive 2000 watts / m2 of solar radiation for most of the year. However, existing desalination plants are not adapted to make use of this vast energy source in these regions thus perpetuating the water scarcity. Solar energy is also too scattered to bring about the levels of evaporation required for desalination purposes. The other problem is that salts are deposited on the internal surfaces of components such as evaporators, condensing tubes and brine recirculation tubes. These salts form a scale of nonconducting material which interferes with the heat exchange performance of these components. Scaling and fouling are therefore a major problem in the operation and maintenance of the said plants. The scaling problem increases with temperature. However, high energy is required for increasing evaporation rate and meeting the increasing demand for potable water. CSP can provide the high energy input to result in high temperatures of 200 Deg. C. But existing desalination is intentionally operated at 80 De. C to avoid evaporator scaling and extend equipment life cycle. This is a major limiting factor which hampers more advanced desalination product development. A nonthermal desalination redesign therefore offers solutions. Seawater contains dissolved gasses such as oxygen and carbon dioxide which are liberated at higher temperatures in the desalination process. Conventional desalination plants handle large amounts of seawater at uniformly high temperatures. This increases the amount of gasses and de-aerators have to be used to remove these gasses prior to brine heating. Dissolved gasses are a major problem in conventional plants because of the large volume they occupy. Moreover, conventional desalination plants depend on a vacuum system which decreases the pressure in the evaporation vessel to cause the water to flash below its normal boiling point of 212 E This is achieved by reducing the pressure on the water surface below the atmospheric value of 14.7 psi in a number of gradual stages. Air ejectors are used for this purpose. Lower seawater temperatures require higher pressure reductions for continuous evaporation and desalinated water production. Air ejectors are volumetric devices and the amount of vacuum generated depends on their internal dimensions.which cannot be increased optimally to increase the production of desalinated water. Air ejectors can reduce the said pressures down to 1 psi. Further pressure reduction would impose external atmospheric pressure stresses on the evaporators and other components and therefore cannot be used for Increasing production. This limits the utility of the vacuum system and the development of the said plants. Seawater has high and low absorption regions in the electromagnetic spectrum. The low absorption area is in the visible range at 400-700 nm. The high absorption range in the near infrared (NIR) and far Infrared (FIR) regions. Existing solar desalination methods utilize energy absorbers which convert the NIR and FIR Infrared energy to thermal energy and utilize the heat for seawater evaporation. We believe this is a wrong approach for seawater desalination because high water absorption wavelength infrared is converted to low water absorption wavelength infrared thus affecting the utility of the desalination process.. The above challenges in existing desalination plants makes them highly complex industrial units which require constant maintenance and highly skilled labour to operate them around the clock which most low income countries do have thus perpetuating the water scarcity in these regions. Furthermore, rain is a form of desalinated water through the natural water cycle. The problem is that rainfall is not well distributed thus causing floods in some regions and water scarcity in others. We do not have a method of controlling this and it is therefore important to work on new designs which work with natural systems and do not introduce harmful chemicals into the environment. They require huge investment in air planes and chemicals. The airplanes used in cloud seeding increase equipment and fuel costs which are in short supply...They are only effective where clouds are available. The clouds also must contain moisture or rain drops in the first place. Cloudless skies are common in many tropical regions. Existing cloud seeding methods are ineffective in these areas and conditions. The area of cloud seeding is along the flight path of the airplanes. The method is not scalable thus increasing the number of flights and the amount of chemical required for cloud seeding thus inereasmg costs further. The effect of the chemicals cannot be controlled once they are in the atmosphere. They can cause negative effects like flooding and cause unwanted damages due to increased rainfail. We believe a nature-inspired method offer solutions Existing desalination methods therefore fall short of overcoming the water scarcity affecting different regions of the world. OBJECT OF THE INVENTION 1) Lasers and optics have played a major role in product development in transportation,telecommunication, medicine, information technology etc. These are economically vital fields and lasers have been a major enabling factor for advanced product development. Desalination must therefore follow the steps of these industries. The major object of the invention is to utilize infrared optics for advanced product development in solar energy to reduce equipment costs for more affordable desalination. 2) Another object of the invention is to provide a photothermal desalination method which reduces the amount of scaling in existing desalination plants so that energy input can be increased without increase of temperature to prevent scaling and fouling. 3) Another objective of the invention is to provide a mechanism which increases the operational energy density for optimal seawater evaporation by utilizing the correct high water absorption region of the electromagnetic spectrum for seawater evaporation. 4) Another object of the invention is to provide a renewable clean energy method for converting seawater to potable water to reduce emissions in existing desalination plants which bum fossil fuels 5) Another object of the invention is to provide an optical method of seawater desalination which utilizes the safe and environmentally friendly atmospheric components and its electromagnetic spectrum for advanced product development. 6) Another object of the invention is to provide a new product with a lower profile to reduce the Irg footprint of existing desalination plants. 7) Another object of the invention is to provide an alternative to the high manufacturing, transport, installation and maintenance costs of existing solar desalination equipment to impact water scarcity. According to the attached drawing the phototherma^ mechanism for reducing energy and equipment desalination costs comprises solar panels, batteries,an infrared lamps, seawater spray nozzles, an intake pipe, intake pump, evaporation tank, steam funnels, cooling tubes, distillate tank, an external intake tank, discharge pipe and distillate pump, product water pipeline and product water tank in the solar panels convert solar radiation to electricity power to energize the the infrared lamp and generate infrared beams of a suitable wavelength to interact, vibrate and beak the hydrogen bonds in the seawater and resulting into a photothermal evaporation without using conventional heating methods and simultaneously leaving behind the salt resulting from the said evaporation in the water layers below and in which the steam funnels collect the steam resulting from the said evaporation and delivering the steam to the cooling tubes to condense the steam and the distillate is stored in the condensation tank and further pumped onshore as potable water to the consumers. At lower energy and equipment costs. Nature-inspired designs have the potential to reduce energy and consumption as well as the number of moving parts and have the potential to provide more sustainable seawater desalination methods. It is estimated the cost of parabolic mirrors is responsible for 50 % of the overall cost of the desalination process. Parabolic mirrors are made of steel and other solid materials which require manufacturing , transportation, installations. The present invention includes an infrared lamp which is non-solid and hence more easily scalable than solid based parabolic mirrors . We have a separate patent for this invention but we are including it for desalination purposes. . We believe this will reduce the cost of desalination. The present invention is also inspired by the water cycle which simplifies the process of converting seawater to drinkable water with advantages in energy and equipment savings. The water cycle utilizes infrared radiation from the sun for seawater evaporation. This is because water molecules respond to specific wavelengths of the solar spectrum at quantum level. It is also a clean energy source without emissions. Only the top layer of the sea is heated and evaporated. This is because the infrared radiation from the sun is coherent and only heats the uppermost layer of the sea. Fortunately, there is no need to heat all the seawater. Othersie all life in the sea will perish. The process is therefore selective which saves in energy generation and overall energy consumption. The water cycle also does not require any chemical additives or pretreatment. It does not require intake structures or heavy machinery for handling or pumping the seawater. This has the potential to reduce equipment costs. Together these innovations have the potential to reduce the costs of desalination and help overcome water scarcity. In the present invention the seawater level is initially the same inside and outside the evaporation tank. But the level inside the evaporation tanks becomes lower when the laser beam causes the seawater to evaporate. The bottom of the evaporation is provided with an inlet which acts as an intake for the seawater. . Fresh seawater then replaces the evaporated seawater so the original level is continuously regained. Similarly, the brine discharges outside the evaporation via the brine outlet which acts as discharge channel. Together the inlet and outlets eliminate the need for inlet structure , seawater pumping as well as the need for a discharge channel thus resulting in the cost saving in existing desalination plants. Seawater also has peak Infrared laser beams absorption at 1500 nm . The absorption process is direct and does not require any intermediate absorber as commonly believed by many people. This reduces salt deposit scaling and fouling common in existing desalination methods thus greatly improving the efficiency of the desalination in the present invention. The present invention also directly utilizes infrared radiation which contains 50% high water absorption for optimal heating and evaporation of the seawater to provide a more affordable and sustainable alternative to burning fossil fuels common in existing desalination plants.save on energy costs. In this invention we utilize infrared radiation which contains infrared at wavelengths of 1550 nm or 2000 nm for direct water molecular absorption. This prevents salt accumulation and foaling in the system for the more advanced product development. The present invention therefore has the potential to help overcome the above mentioned challenges facing the desalination industry for more affordable clean water access. A specific embodiment of the invention wiII now be described by way of example with reference to the attached drawings in which: Fig. 1 shows a section through proposed desalination mechanism and the infrared lamp connected to the batteries and the seawater intake pipe connected to the external tank and further to evaporation tank and the cooling tubes installed around the distillate tank., Fig. 2 shows a plan view of the proposed desalination mechanics showing steel waveguides deliver infrared radiation and the seawater intake pipe and nozzles similarly deliver seawater sprays inside the evaporation so that the infrared radiation directly interacts with the seawater spray bubble. Fig. 3 shows the water electromagnetic radiation absorption spectrum and the low absorption in the visible spectrum where most fossil fuels emit(hence visible to the naked eye and the high absorption in the NIR which is invisible to the human eye. Fig. 4 showing the water heating curve showing the temperature and energy input requirement of the desalination system.on tank. Fig. 5 Shows different infrared electromagnetic waves penetration and their visibility at various depths into the seawater as a measure of the seawater as a measure of their absorption herein. Fig. 6 shows the temperature variation with the sub mm depth within the “ocean skin” layer. Referring to the drawings, the phototherma? mechanism for reducing energy and equipment desalination costs, comprises solar panels 1, batterries 2, infrared lamps 3, Glazed opening 4, Seawater spray nozzles 4 , an intake pipe 8, intake pump 9, evaporation tank 10, steam funnels 6, cooling tubes 12, distillate tank 14, an external intake tank 15, discharge pipe 16 and distillate pump 18 and product water pipeline 20 and product water tank 21. Seawater contains dissolved ions of sodium chloride, calcium carbonate, calcium sulphate, magnesium sulphate and calcium bicarbonate in various proportions. These salts make seawater unsuitable for human consumption and prolonged plant life and desalination is the most economical way of removing them to help overcome the water scarcity affecting many regions of the world. The desalination process consists of different methods of removing these salts so that the processed water can be used for human consumption after further suitable treatment. Evaporation of the seawater is the common method utilized for this purpose. The method of evaporation employed depends greatly on the portion of the heating curve of water used which then governs the type of equipment utilized. The MSF desalination plants utilize a combination of heat and pressure reduction to cause the seawater to evaporate or flash for distillate production, seawater is first heated from 90 Deg F to 220 Deg. F in a brine heater increasing its pressure to about 17.2 psi. Then it is fed into the evaporator where the pressure on the surface of the water is reduced using a vacuum system so that the water flashes at lower temperatures instead of its normal boiling point of 212 F. The evaporated water is cooled when the resulting steam comes in contact with the outside. The surface of tubes carrying seawater circulated in the system at around 90 F. The resulting condensate is collected in trays for further treatment. The unevaporated brine is recirculated, for further heat exchange with the incoming seawater. Conventional thermal heating is highly energy intensive. Evaporation is achieved by increasing the thermal heat content which breaks the hydrogen bonds in the water molecules. Fig 4 represents the water heating curve with the heat content of water (Q) plotted against its temperature (T). A given mass of water at W has a heat content of 28.0 Btu / lb at 60 F. If the heat content is increased to 180 Btu / lb then the water temperature rises to 212 F which is the boiling point of water at atmospheric pressure of 14.7 psi. The heat content must be increased to Y before any evaporation can take place. This requires an additional energy of 970 Btu / lb. This is known as the latent of water needed to overcome the molecular bonds holding the water structure together. We can see from this that much more energy is required to evaporate a given mass of water than to heat it to its boiling point. The steam absorbs more energy if its heat content is increased and the heating curve shifts towards Z at increasing temperature and pressure as superheated steam. Conventional desalination plants such those using the MSF systems utilize the lower end of the said curve as shown in Fig 4. In existing desalination MSF plants large amounts of water are first heated from 90 F to 212 F along the line WX. The pressure on the surface of the water is then reduced in a number of descending stages using a vacuum system, so that evaporation can take place at temperatures lower than the normal boiling point of water at 212 F. Air ejectors are utilized for generating the required vacuum which depends on the amount of air they cain remove.and hence on their internal volume. Each air ejector therefore has a certain capacity which cannot be adjusted to increase the amount of vacuum for higher production. The alternative in the said plants is to increase the number of pressure reduction stages which increases their size and the equipment used for the desalination process. The increased size also extends the distance separating the heat rejection and the heat recovery sections in the said plants which further contributes to their complexity. Large amounts of seawater are heated in the said plants and brought to their boiling point using vacuum systems before evaporation can take place. Furthermore, the electromagnetic spectrum of the flame ranges from 400 nm to 800 nm. This is within the visible spectrum and hence visible to the human eye as shown in Fig. 3 . The problem is that water has a very low absorption capacity in this range of the visible spectrum. Evaporation in existing desalination plants must therefore shift to higher absorption regions of the electromagnetic spectrum to increase energy use efficiency and for more affordable and accessible drinking water. . It is therefore important to reduce the above high energy consumption and energy waste methods in the desalination process to reduce costs. From the above description we can see that the desalination process is highly complex, requires a large energy input and requires heavy and costly equipment. On the other hand , the rain or water cycle is a much more simplified method of converting seawater to potable water. It is important to reduce desalinations to impact water scarcity. The main hurdles facing the desalination system is high energy consumption in MEF and membrane fouling in SWRO. We believe the water cycle provides a simplified method of converting seawater to potable water and has the potential to offer a desalination systems redesign. The rain cycle consists of seawater evaporation, in situ salt removal, steam generation, condensation , cloud formation and eventual rainfall. The simplification process has the following advantages 1. It does not heat seawater to high temperatures to avoid harming the fish, coral and other living organisms. 2. It doesn’t utilize intermediate costly nano material metals to absorb and convert the solar radiation to thermal energy. 3. The seawater has high absorption for infrared radiation of wavelengths above 600 nm and has lower absorption for the wavelengths below this value in the visible spectrum. 4. It doesn’t require membranes which are often prone to fouling. 5. It doesn’t also require solid electrodes and to attract the salt ions which collect on their surface which only have a limited capacity for storing salt ions and hence affecting the salt removal efficiency. Oceans utilize a photothermal heating which takes place at the “ocean skin “ layer which ocean-air interface.The ocean temperature. Fig. 6 shows the ocean temperature T variation varies with depth during the daytime and nighttime hours. The temperature variation starts at the ocean-air interface where most of the energy absorption takes place. The ocean top layer is known ocean skin. This is divided into thermal, electromagnetic and viscous layers as shown in Fig. 6. The oceans are mostly cooler than the air. The thermal layer absorbs the thermal or visible spectrum at 400 -700 nm wavelength. Some evaporation takes place at the ocean surface but this requires the absorption of energy which cools the thermal layer. Infrared radiation penetrates the ocean surface to a depth beyond the thermal layer. But the latent heat effect hampers evaporation. Infrared radiation from the sun is also scattered and cannot be used for practical desalination purposes. More infrared radiation absorption is required at 1550 nm where the water has a higher absorption. In the rain cycle the equatorial regions often have more rainfall because of the higher solar intensities which deliver more infrared radiation at higher water absorptions. It is therefore important to design a method of increasing infrared intensity desalination systems redesign. However, the water cycle is a very large system which cannot be simulated for reducing desalination costs as it stands. It also utilizes natural solar intensities in which both the thermal energy and infrared radiation are too scattered for practical application. The main question is how does continuous evaporation take place without heating the seawater to high temperatures. This is because the rain cycle relies on infrared heating which is different from thermal heating. In infrared heating the . We take a cue from the above characteristics of the water cycle for the desalination systems redesign in our invention. Fig. 1 represents a section through the arrangement of the solar panels connected to the batteries and further to the infrared lamps and seawater, intake pump, batteries, and the infrared lamp installed externally outside the evaporation, ct and focus the incoming solar radiation.. Fig. 2 represents a section through the photothermal mechanism for reducing energy and equipment desalination costs showing the delivery of the infrared radiation through the glazed inlet and the seawater spray bubbles via the intake pipe line to the inside of the evaporation tank. The infrared radiation therefore comes in direct contact with the seawater spray bubbles. In the water cycle the waves in oceans are in constant turbulent motion which creates seawater sprays to encounter the incoming infrared radiation from the sun. for seawater evaporation. However, the solar radiation from the sun is somewhat scattered and evaporation is slow. In the present the infrared lamp has the potential to concentrate solar radiation to high intensities reaching many suns to enhance evaporation and potable water production and hence has the potential to impact the water scarcity affecting many regions. Table 1 shows the different types of infrared lamps , the wavelength of the emitted radiation, frequency, photon energy and operating temperatures. Region Abbrevatio n Wavelength(p m) Frequency(TH z) Photo Energy(meV) Temperature ange(°F) Near-Infrared Lamps NIR 0.75-1.4 214-400 886-1653 6495.8 to 3266.6 (3591-1797°C) Short Wavelength Infrared lamp SWIR 1.4-3 100-214 413-886 3266.6 to 1279.4 (1797-693°C) Mid-Wavelength Infrared lamps MWIR 3-8 37-100 155-413 1279.4 to 192.2 (693-89°C) Long-Wavelength Infrared lamp LWIR 8-15 20-37 83-115 192.2 to-112 (89 - -80°C) Far Infrared FIR 15-1000 0.3-20 1.2-83 -112.27 to -454.27 (-80.15 -270.15°C) There are different types of infrared lamps to meet customer needs. The type depends on the wavelength of radiation which the infrared lamp generates. Therefore they are divided into short wavelength, medium wavelength and long wavelength types. Short wavelength lamps have more radiant energy than medium and long wavelength types. From Table 1 we can see that the FIR region has an operating temperature between 80.15- 270.15 Deg. C and hence suitable for optimal water evaporation and desalination.This region also has the lowest power input requirements and can be operated from a small number of solar panels and battery electric storage for 24 / 7 desalination operations. The above version of the Invention is useful for small and medium size desalination purposes. Larger projects require mors solar energy input. We plan to utilize an optical and hence non-soHd and airborne solar radiation concentrator for which we have been recently granted a ( UK patent GB2S97236). Our optical approach utilizes the natural concept of mirages which already operates in the atmosphere. The infrared laser beams used for heating air layers are also present in the natural atmosphere. The invention therefore does not introduce foreign components into the atmosphere. The total internal reflection can reach an efficiency of 100 % reflectivity for optimal solar radiation management. The direction and size of the conical laser beams are both controllable. This Invention offers major advantages for reducing desalination costs further to Impact water scarcity and for waste water recycling affecting many Industries. The advantages are as follows.. The optical solar radiation concentrator provides the following advantages .. 1) An inventive method of optical, photothermal and solar energy generation which reflects, refracts and focuses solar radiation for clean energy generation to replace existing solids-based parabolic mirrors to reduce equipment costs for desalination and clean energy generation in other industries.. 2) An inventive method of solar radiation focusing in which the interface results from heating air layers in the atmosphere. 3) An inventive method of solar energy generation in which the generate beams of suitable wavelength for absorption by atmospheric water vapor for heating the air layers to different temperatures resulting in a temperature gradient herein. 4) An inventive method of solar radiation focusing in which the temperature gradient results in a refractive index gradient for total internal reflection. 5) An inventive method of solar radiation focusing in which the Axicon can be machined to accommodate the amplitude of microwave beams. 6) An inventive method of solar radiation focusing which the Axicon generates concentric rings which enlarge during their propagation through the atmosphere and hence result in hollow and concentric cones. 7) An inventive method of solar radiation focusing in which the refractive index gradient operates in the space separating the conical walls can be adjusted to suit the amplitude of the solar radiation to receive the incoming solar radiation thus acting as waveguides for the solar radiation. 8) An inventive method of solar radiation focusing in which the environmentally friendly H2O molecules in the atmosphere absorb the microwave to result in a molecular vibration which is then transferred to the ambient air to heat the air layers to result in an optical and hence non-solid waveguide herein. 9) An inventive method of solar radiation focusing in which the cones can be scaled up to harvest the infrared radiation which the earth emits at night to reduce the need for battery energy storage and insure 24 / 7 clean energy access. 10) An inventive method of solar radiation focusing which the total internal reflection operates at 100% reflectivity to increase solar energy conversion Efficiency. 11) An inventive method of solar radiation focusing which is mounted onto a solar tracking mechanism so that the non-solid microwave cones reduce the total weight of existing parabolic mirrors to enable the manufacture of low profile solar equipment suitable for high-rise, offices, factories and domestic buildings in Urban areas. 12) An inventive method of solar radiation focusing with the potential to reduce the cost of solar thermal below that of photovoltaics to provide a more scale -able method of reducing desalination costs and also impact carbon emissions. 13) The sun is never over-head in the countries in the northern hemisphere. This is affecting their clean energy access from the sun and efforts to reduce carbon emissions. But microwaves can travel thousands of kilometers in space. The photothermal method in these inventions can be launched over a long distance, Therefore it offers an inventive way to help overcome this problem. The present invention therefore has the capacity for reducing the amount of equipment, energy consumption and energy costs in f desalination plants to help impact water scarcity.

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