NEED FOR RECYCLING
 The problem of processing scrap is a major
concern with the ever increasing production
and population.
 Automobile industry is a major contributor of
scrap, especially scrap steel and rubber (tires).
 Rubber (tires) recycling not only has economic
value, but also helps reduce the disposal
problem of a worldwide production of more
than 300 million tires per year, leading to land
filling.
 From coast-to-coast and also in the heartland,
landfill costs and tipping fees have risen
dramatically in the last few years and are
expected to continue to rise.
NEED FOR RECYCLING (contd…)
 A number of landfills have closed their doors to
tires and scrap steel, already making re-utilization
of scrap by manufacturers a viable economic
alternative.
 Concern over nitrosoamines, heavy metal
contamination, and concern about effects on the
water table of deteriorating rubber products
further drives the incentive toward recycling of
these materials.
 From an environmental standpoint, cryogenic
recycling makes solid economic sense and is in the
best interest of both manufacturer and consumer.
WASTE TO A USEFUL RAW MATERIAL
 In rubber processing there will always
be some scrap, which needs to be
minimized, otherwise it will lead to
land filling.
 The cryogenic recycling system can
economically turn the scrap into a
raw material again - even if we
produce as little rubber scrap as 200
kg per day.
 It is widely believed that the finer the
rubber powder reintroduced into
compound, the less visible the defects
and change of properties.
WASTE TO A USEFUL RAW MATERIAL
(contd…)
 Cryogenic treatment processes can reduce rubber
scrap to less than 100 micron powder.
 The rubber granules are put through a highly
efficient cooling conveyor, sized for particular
purpose.
 The liquid nitrogen embrittles the rubber crushing
it, before it is fed into the mill for grinding.
 Steel scraps in auto-industries can also be treated
by cooling it to cryogenic temperatures where
impact resistance offered is minimal and the
scraps can easily be shredded.
TEMPERATURE EFFECT ON FAILURE RATE
 Straining rate is the rate
of change of shape of the
object without it
breaking.
 It can be observed from
the graph that the strain
rate decreases with
decrease in temperature.
 The advantage of this fact
could be utilised in the
cryogenic recycling
process
SCRAP SEPARATION PRINCIPLE
 Many scrap materials are mixtures of materials having
vastly different ductility at common low temperatures
which permit separation.
 At 210K, rubber is very brittle & steel is not as brittle.
 Thus, an automobile tire can be cryogenically crushed
to give rubber powder and separated steel.
 Copper, aluminium and stainless steel retain their
ductility at 145K, but steel does not.
 Thus articles in a cryogenic crusher would provide
steel particles and copper uncrushed which can be
separated by various screening and magnetic
processes.
SCRAP RECYCLING PROCESS
RECYCLING PROCESS
 The cryogen, liquid nitrogen at 77K is in the cryo tank
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and is thermally insulated.
A conveyor is used to charge the scrap into the tank
through a tunnel.
It is charged to the cryogen bath and cooled to 145K.
Cooling of the scrap simultaneously leads to
vaporisation of liquid nitrogen.
Then,the scrap is removed from the bath and is broken
by a breaker.
A curtain is used to seal the cryogen on the withdrawal
of scrap steel from the tank.
RECYCLING PROCESS (contd…)
 The scrap is cooled counter currently with the
vaporised effluent nitrogen which rises from the
cryo tank and is exhausted through the tunnel.
 Additional liquid nitrogen may be introduced to
make up for the losses in the system.
 A gas recycle duct is employed with a blower to
recycle refrigerant gas from the tunnel back to the
refrigeration recovery tunnel.
 If, we consider steel for instance, the required
refrigeration is approximately1gm of liquid
nitrogen for 45.5gm of steel.
UTILITIES OF RECYCLING
 The recycled scrap can be used as a raw material in
various applications.
 About 12 million scrap tires a year are made into
rubberised asphalt which is used to resurface federal
interstates and highways in many states in the USA.
 In northern Virginia, road builders have combined
shredded tire rubber with cement to form ‘whisper
walls’ that reflect sound waves from traffic and reduces
noise level, sparing local residents’ ears.
 They are also used for tracks, RR crossings and tennis
courts. Also, some are burned in coal fires for power
and cement plants reduces mercury pollution.
FUTURE SCOPE
 As opportunities for disposal of scrap materials
diminish, similar opportunities arise by necessity
for alternative uses of recycled rubber materials.
 Advances in state-of-the-art partitioning and
separation technology will allow particle size
reduction costs.
 Printed circuit boards (PCBs) in tvs, computers, &
other electronic items produce lot of scrap. The
rich content of precious metals like gold, silver,
palladium in PCB scraps provides a strong
economic justification for their recycling.
FUTURE SCOPE (contd…)
 The liquefied gas industry is less susceptible to price
increases associated with petroleum dependent
materials and technologies.
 Thus increases in processing costs in the cryogenic
recycling industry are forecast to increase at a rate
lower than the general increase in the majority of
petroleum-derived materials used in rubber.
 This encourages utilization of the technology for
continued cost reduction and performance
improvement.
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