Solar adsorption cooling

1. SOLAR ADSORPTION COOLING
GRADUATION PROJECT TEAM
DR : AHMED MOSTAFA

2. A:OVERVIEW
Adsorption chillers use solid sorption materials instead of liquid
solutions. Market available systems use water as refrigerant
and silica gel as sorbent; but recently, an alternative to silicagel
is zeolith for some manufacturers. So the two technologies now
available are: Silicagel/H2O and Zeolith/H2O .The machines
consist of two sorbent compartments (see figure1) – one
evaporator and one condenser. While the sorbent in the first
compartment is regenerated using hot water from the external
heat source, e.g. the solar collector (The adsorbent (silica gel) is
dried out by applying heat. Vapor is generated, flows into the
condenser, and is liquefied, while heat is being rejected. When
the material is sufficiently dried out, the heat input into the
adsorber stops). The sorbent in the second compartment
adsorbs the water vapor entering from the evaporator.
Compartment 2 has to be cooled in order to enable a
continuous adsorption (During the adsorption process heat is
being produced, which has to be removed by a cooling tower.).

3. Due to the low pressure conditions in the evaporator(as we need to lower the boiling point of water
refrigerant), the refrigerant in the evaporator is transferred into the gas phase by taking up the
evaporation heat from the chilled water loop and thereby producing the useful "cold". If the
sorption material in the adsorption compartment is saturated with water vapor to a certain degree,
the chambers are switched over in their function. ( they work alternatively one is adsorbing and one
is desorbing)
To date, only a few Asian and European manufacturers produce adsorption chillers. The two
historical actors are Japanese, but now a German manufacturer has entered the market .Under
typical operation conditions with a driving temperature of 80 °C, the systems achieve a coefficient
of performance (COP) of about 0.6, but operation is possible even with temperatures of approx. 60
°C. The capacity of the chillers ranges from 5.5 kW to 500 kW chilling power.

4. The simple mechanical construction of adsorption chillers and their expected robustness is an
advantage. There is no danger of crystallization and thus no limitation in temperatures. There is
no internal solution pump and electricity consumption is reduced to a minimum. A disadvantage
is the comparatively large volume and weight. Furthermore, due to the small number of produced
items, the price of adsorption chillers is currently still high. A large potential for improvements is
expected in the construction of the heat exchangers in the adsorber compartments, which would
reduce volume and weight considerably in future generations of adsorption chillers.
B: Why adsorption cooling?
1. It doesn’t use toxic or ozone harming fereons (as in
absorption) it uses water as a refrigerant (Green
refrigerant) and silica gel as adsorbent. So no hazardous
leaks, corrosion, chemical testing and no replacement (silica
gel can last 30 years.
2. No compressor used.
3. Very low operational costs, Electrical load is too low used
for controls and pumps.
4. It utilizes waste heat in cooling (Regeneration).

5. ADSORPTION / ACTIVE CARBON
Activated carbon adsorption
Adsorption is a process where a solid is used for removing a soluble substance from the
water. In this process active carbon is the solid. Activated carbon is produced specifically
so as to achieve a very big internal surface (between 500 - 1500 m2/g). This big internal
surface makes active carbon ideal for adsorption. Active carbon comes in two variations:
Powder Activated Carbon (PAC) and Granular Activated Carbon (GAC). The GAC version
is mostly used in water treatment, it can adsorb the following soluble substances:
•Adsorption of organic, non-polar substances such as:
•Mineral oil
•BTEX
•Poly aromatic hydrocarbons (PACs)
•(Chloride) phenol
•Adsorption of halogenated substance: I, Br, Cl, H en F
•Odor
•Taste
•Yeasts
•Various fermentation products
•Non-polar substances (Substances which are non soluble in water)

7. Examples from active carbon in different processes:
•Ground water purification
•The de-chlorination of process water
•Water purification for swimming pools
•The polishing of treated effluent
Process description:
Water is pumped in a column which contains active carbon, this water leaves the column
through a draining system. The activity of an active carbon column depends on the
temperature and the nature of the substances. Water goes through the column constantly,
which gives an accumulation of substances in the filter. For that reason the filter needs to
be replace periodically. A used filter can be regenerated in different ways, granular carbon
can be regenerated easily by oxidizing the organic matter. The efficiency of the active
carbon decreases by 5 - 10% 1). A small part of the active carbon is destroyed during the
regeneration process and must be replaced. If you work with different columns in series,
you can assure that you will not have a total exhaustion of your purification system.

8. Factors that influence the performance of active carbon in water:
•The concentration of the compound to be removed. The higher the concentration,
the higher the carbon consumption.
•Presence of other organic compounds which will compete for the available
adsorption sites.
•The pH of the waste stream. For example, acidic compounds are better removed
at lower pH.
The type of compound to be removed. Compounds with high molecular weight
and low solubility are better absorbed.

9. 2,4-D Deisopropyltatrazine Linuron
Alachlor Desethylatrazine Malathion
Aldrin Demeton-O MCPA
Anthracene Di-n-butylphthalate Mecoprop
Atrazine 1,2-Dichlorobenzene Metazachlor
Azinphos-ethyl 1,3-Dichlorobenzene 2-Methyl benzenamine
Bentazone 1,4-Dichlorobenzene Methyl naphthalene
Biphenil 2,4-Dichlorocresol 2-Methylbutane
2,2-Bipyridine 2,5-Dichlorophenol Monuron
Bis(2-Ethylhexyl)Phthalate 3,6-Dichlorophenol Napthalene
Bromacil 2,4-Dichlorophenoxy Nitrobenzene
Bromodichloromethane Dieldrin m-Nitrophenol
p-Bromophenol Diethylphthalate o-Nitrophenol
Butylbenzene 2,4-Dinitrocresol p-Nitrophenol
Calcium Hypochloryte 2,4-Dinitrotoluene Ozone
Carbofuran 2,6-Dinitrotoluene Parathion
Chlorine Diuron Pentachlorophenol
Chlorine dioxide Endosulfan Propazine
Chlorobenzene Endrin Simazine
4-Chloro-2-nitrotoluene Ethylbenzene Terbutryn
2-Chlorophenol Hezachlorobenzene Tetrachloroethylene
Chlorotoluene Hezachlorobutadiene Triclopyr
Chrysene Hexane 1,3,5-Trimethylbenzene
m-Cresol Isodrin m-Xylene
Cyanazine Isooctane o-Xylene
Cyclohexane Isoproturon p-Xylene
DDT Lindane 2,4-Xylenol
According to this we can classify some chemicals by their probability of being efficiently adsorbed
by active carbon in water:
1.- Chemicals with very high probability of being adsorbed by active carbon:

10. Aniline Dibromo-3-chloropropane 1-Pentanol
Benzene Dibromochloromethane Phenol
Benzyl alcohol 1,1-Dichloroethylene Phenylalanine
Benzoic acid cis-1,2- Dichloroethylene o-Phthalic acid
Bis(2-chloroethyl) ether trans-1,2- Dichloroethylene Styrene
Bromodichloromethane 1,2-Dichloropropane 1,1,2,2-Tetrachloroethane
Bromoform Ethylene Toluene
Carbon tetrachloride Hydroquinone 1,1,1-Trichloroethane
1-Chloropropane Methyl Isobutyl Ketone Trichloroethylene
Chlorotoluron 4-Methylbenzenamine Vinyl acetate
2.- Chemicals with high probability of being adsorbed by active carbon:

11. Acetic acid Dimethoate Methionine
Acrylamide Ethyl acetate Methyl-tert-butyl ether
Chloroethane Ethyl ether Methyl ethyl ketone
Chloroform Freon 11 Pyridine
1,1-Dichloroethane Freon 113 1,1,2-Trichloroethane
1,2-Dichloroethane Freon 12 Vinyl chloride
1,3-Dichloropropene Glyphosate
Dikegulac Imazypur
3.- Chemicals with moderate probability of being adsorbed by active carbon*:
*(For this chemicals active carbon is only effective in certain cases).

12. Acetone Methylene chloride
Acetonitrile 1-Propanol
Acrylonitrile Propionitrile
Dimethylformaldehyde Propylene
1,4-Dioxane Tetrahydrofuran
Isopropyl alcohol Urea
Methyl chloride
4.- Chemicals for which adsorption with active carbon is unlikely to be effective.
However it may be viable in certain cases such as for low flow or concentrations:

13. Factors that influence the performance of active carbon in air:
•Type of compound to be removed: In general compounds with a high molecular
weight, lower vapor pressure/higher boiling point and high refractive index are
better adsorbed.
•Concentration: The higher the concentration, the higher the carbon consumption.
•Temperature: The lower the temperature, the better the adsorption capacity.
•Pressure: The higher the pressure, the better the adsorption capacity.
•Humidity: The lower the humidity, the better the adsorption capacity.