10-04-2017, 09:17 PM
PRESENTED BY
T.ANBHUSELIAN
A.KARTHIKEYASRIDHARAN
G.KARTHI
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INTRODUCTION
Chlorofluorocarbons (CFCs) are man-made chemicals used in the refrigeration and air conditioning industry as a Halogenated refrigerant.
One single liberated chlorine atom may destroy up to100,000 ozone molecules, thus depleting the ozone layer.
Damage caused by ozone depletion decreases the filtering process allowing more ultraviolet (UV) radiation to pass through to the Earth's surface.
Bromine atoms used in halons cause the same type of damage as chlorine.
OZONE
The ozone layer is a layer in Earth's atmosphere which contains relatively high concentrations of ozone (O3). This layer absorbs 97 99% of the Sun's high frequency ultraviolet light, which is damaging to life on Earth. It is mainly located in the lower portion of the stratosphere from approximately 13 to 40 kilometers (8.1 to 25 mi) above Earth, though the thickness varies seasonally and geographically
OZONE
Ozone is formed in the stratosphere when oxygen molecules photo dissociate after absorbing an ultraviolet photon whose wavelength is shorter than 240 nm. This produces two oxygen atoms. The atomic oxygen then combines with O2 to create O3.
O + O3 2 O2
OZONE DEPLETION
Ozone layer prevents most harmful UV RAYS of wavelengths (280 315 nm) of ultraviolet light (UV light) from passing through the Earth's atmosphere
Ozone can be destroyed by a number of free radical catalysts, the most important of which are the hydroxyl radical (OH.), the nitric oxide radical (NO.), atomic chlorine (Cl.) and bromine (Br.).
OZONE DEPLETION
OZONE DEPLETION
CHLORINE and BROMINE are found in certain stable organic organic compoundsespecially chlorofluorocarbons (CFCs), which may find their way to the stratosphere without being destroyed in the troposphere due to their low reactivity. Once in the stratosphere, the Cl and Br atoms are liberated from the parent compounds by the action of ultraviolet light, e.g. ('h' is Planck's constant, ' ' is frequency of electromagnetic radiation)
CFCl3 + h CFCl2 + Cl
CAUSES
In 1985, Antarctica was found to have a massive "hole" in the ozone layer. This allows more UV light (radiation) to strike the surface of the Earth. Stratospheric ozone filters much of the UV radiation emitted by the Sun from hitting the Earth. With diminished UV filtering, there is a corresponding increase of skin cancer. There is also evidence that plant growth and crop yields will be inhibited due to the increase of UV radiation.
Another damaging effect of ozone depletion is erosion of photoplankton, the very foundation of our food chain. According to scientists, photoplankton are responsible for about 80 percent of carbon dioxide absorption and about 60 percent of oxygen production in the world.
CAUSES BY UV light
Because of holes in ozone layer, following are the causes of UV RAYS:
Sunburn
Clouding of the cornea and formation of cataract
Skin cancer
Reduced rates of photosynthesis
CAUSES
CAUSES OF CFC
CFC breakdown under the effect of UV light to release chlorine radicals (Cl), Especially under cold conditions.
The chlorine radicals react with O3 converting it to O2 and more radicals ClO
Ozone pollution in the troposphere
BIGGEST HOLE IN ANTARTICA
URGENCY OF ACTION
Ozone losses have occurred over populated regions of the northern and southern hemispheres. Indications are that ozone layer depletion is occurring in the middle and high latitudes of both hemispheres in spring summer and winter. Data from this report and the existing pool of knowledge about man-made chlorine and bromine compounds combine to reaffirm that these compounds are the main cause of ozone depletion.
There are continuing indicators that the depletion rate of stratospheric ozone is increasing which underscores the urgency for even more rapid action.
TYPES OF CFC S USED IN REFRIGERANTS
CFC-11 R-11: Refrigerant in large centrifugal chillers providing air conditioning; blowing agent in rigid insulation.
CFC-12 R-12: Refrigerant in residential and small commercial refrigeration, water coolers, walk-in freezers and mobile refrigeration.
CFC-113 R113: Refrigerant in large centrifugal chillers when less capacity is needed; cleaning agent in dry cleaning.
CFC-114 R114: Refrigerant in small rotary compressors for refrigeration systems and large centrifugal compressors and air conditioning systems.
CFC-12 HFC-152a R-500: Refrigerant in small reciprocating a compressors and large hermetic centrifugal R-500 compressors, residential and commercial air conditioning, refrigeration, and water coolers.
CONCLUSION
There is a problem with the use of CFCs and HCFCs in our electric chillers. The compounds contribute to ozone depletion and global warming. Present legislation requires total phase-out of these refrigerants.
Coping without CFCs requires rethinking in the design and specification of chiller equipment and systems for new facilities and major remodel projects. The appropriate action is to change all equipment specifications away from CFCs and HCFCs. Immediate action is necessary in some cases to insure we do not order outdated equipment designed to use CFCs or HCFCs. Equipment should be capable of using either HFC-134a or lithium bromide, for electric or gas chilling equipment respectively.
For equipment using CFCs and HCFCs we must inspect and certify systems for leaks annually, keep required records of maintenance and employ strategies to recover, reclaim and recycle refrigerants. This may make it possible to continue operation of present equipment until a viable alternative refrigerant is developed at a cost effective price to replace CFC-11, CFC-22 and HCFC-123.