Study & Development of machine to generate water out of atmospheric air with the help of Solar Panel
Water scarcity is one of the burning issues of today’s world. Though water covers more than two third (about 70%) of the Earth’s surface but still fresh water which can be used for drinking and carrying out everyday chores remains scarce (only about 2.5%). The acute problem of water shortage is mainly faced by the countries with long coastlines and the island nations, which do not have adequate fresh water sources like rivers and ponds. As a result most of these countries meet their water demands by desalination of sea water which is a very costly affair. Also it may so happen that these desalination plants may fail which will cause acute water shortage. This is what just recently happened in Mumbai. So there is an urgent need for countries like India, Maldives and others, who depend solely on such costly plants to meet their water requirements, to find alternative methods to generate water in order to meet their water requirement needs.
Thus drinking water can be obtained from the atmosphere by adsorbing moisture from humid air through a desiccant like silica gel. This process is known as adsorption where water molecules gets deposited on silica gel and by further heating it to remove the moisture from it to get converted into drinking water. Such a device is called Atmospheric Water Generator.
The aim of the project is to create a portable device that can be used to meet the water requirements of a regular household. The device will first condense water present in the atmosphere and then purify it so that it can be used for drinking.
In desiccant de-humidification and cooling system, moist air stream is allowed to flow through desiccant material and then dry air comes out of the desiccant material. If the adsorption process is continued, ability to adsorb moisture of desiccant material decreases. Therefore, to keep system working constantly, the water vapor adsorbed must be removed. This is done by heating the desiccant material to its temperature of regeneration depending on the type of desiccant material used. Desiccant material can be generated by low grade heat source like solar energy, waste heat, natural gas etc.
When solid desiccant (silica gel) is employed, the desiccant de-humidification system consists of slowly rotating desiccant wheel of adsorbent bed.
What is silica gel?
Silica gel is a granular, vitreous, porous form of silicon dioxide (SiO2) made synthetically from sodium silicate. It is a naturally occurring mineral that is purified and processed into either granular or beaded form. As desiccant, it has an average pore size of 2.4 nanometres and has a strong affinity for water molecules.
Advantages of silica gel in a water adsorption system
Silica gel/water adsorption cycle can be powered using low grade heat sources (55-100 C).
Silica gel/water pair has relatively high equilibrium Adsorption / Desorption rate.
Silica gel exhibits an excellent capacity for adsorption of water up to 35-40% of its dry mass.
It has regeneration capability at low heat source temperature 50-100 C.
It is non-toxic, non-flammable, and non-reactive & stable with ordinary usage.
Silica gel’s high surface area (800m2/g) allows it to adsorb water readily, making it useful as a desiccant (drying agent). Silica gel is an incompletely dehydrated polymeric structure of colloidal silicic acid with the formula SiO2 .nH2O. This amorphous material consists of spherical particles 2-20 nm in size, sticking together to form the adsorbent silica gel. The bulk density of silica gel is 480 - 720 kg/m3. The specific heat is 1.13kJ/kgK
Once saturated with water, the gel can be regenerated by heating it to 120 C (250F) for 1-2 hours. Some types of silica gel will pop when exposed to enough water. This is caused by breakage of the silica spheres when contacting the water.
The moisture of silica gel can be removed by putting the silica gel in hot air oven at 80-100 C for 1 hr. But silica gel degrades after a very few cycles if heated to 110 C and above, so for maximum longevity we shall heat it around 80o C and its regeneration will not get affected.
Once when the moisture is adsorbed by the silica gel, we need to get that water removed from its surface which is deposited in a form of film. By heating it up to a temperature between 50-100 C, its water can get separated and further this water can be filtered to get pure drinking water. It was experimentally observed that silica gel if heated to an average temperature of 80C it will remain long and work well as a desiccant. Also, its regeneration property will not be affected.Most efficient method of removing moisture is with heat. Although silica gel has very high melting temperature (1600 C), it will lose its chemically bound water & hygroscopic properties if heated above 300C. Hence it is recommended not to heat silica gel above 120C. The simplest way of conditioning silica gel is to place it in a room or environmental chamber set to the desired RH level. This can be done by measuring a large amount of silica gel relative to the surrounding air using hygrometer and placing it all in a sealed container or bag so that RH value can be stabilized with the gel mixture for a day long experiment.This method is effective if silica gel is spread into a thin layer or has a fast response time. Increasing or decreasing the surface area can control the rate of water evaporation. It is important to limit the surface area of dry gel to prevent the RH from dropping too quickly. This is because the speed at which dry gel adsorbs moisture is faster than the rate at which it desorbs the moisture. Hence it must be carefully monitored in a closed condition.
How Does it work ?
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Atmospheric air is to be induced into the adsorption unit by the DC exhaust fans over the desiccant wheel.
2. The silica gel present in the desiccant wheel would adsorb moisture content in the atmospheric air while rotated by a DC motor.
3. This silica gel while rotating goes through a desorption unit, when high temperature air (100-120oC) from heater is forced on to these silica gel, thereby regenerating it i.e water molecules are released from silica gel.To power the heater solar panels are used which will generate electricity.
4. This regenerated silica gel goes again into the adsorption unit thus the cycle is repeated.
5.The air containing water molecules passes through the condenser which contains helical copper coil this condenser is buried in the ground where temperature is less enough for the condensation of steam
6.In this way, water is generated using silica gel as a desiccant from atmospheric air.
From all above discussion, it is proved that the moisture in the air can be condensed successfully using above designed setup. This system is perfect for rural areas and can help eliminate some problems while not created as much of a recurring cost for the user. The system can be self-installed and can easily be repaired while on the ground. This seems like it would make it simpler for the user to operate and take care of the maintenance. Altogether This system would help to generate water where there is scarcity of water and This project helps in accounting for the future cleaner and greener environment