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CONVERTING WASTE PLASTICS INTO ARESOURCE
Plastics Waste Disposal through Pyrolysis Technology (PT)
Pyrolysis Technology (PT) - An Introduction
Pyrolysis is a state of the art technology, which integrates the
thermo-chemical properties of plasma with the pyrolysis process. The
intense and versatile heat generation capabilities of Pyrolysis
technology enable it to dispose of all types of plastic waste including
polymeric, biomedical and hazardous waste in a safe and reliable
manner. Pyrolysis is the thermal disintegration of carbonaceous
material in oxygen-starved atmosphere. When optimized, the most
likely compounds formed are methane, carbon monoxide, hydrogen
carbon dioxide and water molecules.
All plastics are polymers mostly containing carbon and hydrogen and few other elements like chlorine, nitrogen etc. polymers are made up of small molecules called as monomers which combine and form single large molecule called polymer. When this long chain of monomers breaks at certain points or when lower molecular weight fractions are formed this is termed as degradation of polymer. This is reverse of polymerization. If such scission of bonds occurs randomly it is called as ‘Random De-Polymerization’.
In the process of conversion of waste plastic into fuels random De-Polymerization is carried out in a specially designed Reactor in absence of oxygen & in the presence of coal and certain catalytic additive. The maximum reaction temperature is 550°C. There is Total conversion of waste plastic into value added fuel products.
Environment Related Observations
�� There are no liquid industrial effluents and no floor washing as waste
material is not washed.
�� There is no organized stack and process emissions are let out.
�� Odour of volatile organics has been experienced in the processing area
due to some leakages or lack of proper sealing
�� Since, absolute conversion of liquid-vapor was possible into liquid,
some portion of gas (about 20%) is connected to the generator.
However, the process will be improved in full scale plant.
�� PVC plastics waste is not used and if used, it was less than 1%. In
case PVC is used, the chlorine can be converted into hydrochloric
acid as a by-product.
�� The charcoal (Charcoal is formed due to tapping of tarry waste)
generated during the process has been analysed and contain heavy
metals, poly aromatic hydrocarbon (PAH) which appears to be
hazardous in nature. The source of metals in charcoal could be due to
presence of additives in plastics and multilayer & laminated
�� Monitoring of process fugitive emissions in the work area as well as
emissions from the engines/diesel generator sets, where this liquid fuel
is used, for various parameters such as CO, HCl, Styrene, Benzene,
VOCs is necessarily required.
Liquid Fuel Production
Scope of liquid fuel in this compendium
Liquid fuel within this compendium is defined as plastic-derived liquid hydrocarbons at a
normal temperature and pressure. Only several types of thermoplastics undergo thermal
decomposition to yield liquid hydrocarbons used as liquid fuel. PE, PP, and PS, are preferred for the
feedstock of the production of liquid hydrocarbons. The addition of thermosetting plastics, wood,
and paper to feedstock leads to the formation of carbonous substance. It lowers the rate and yields
of liquid products.
Depending on the components of the waste plastic being used as feedstock for fuel production,
the resulting liquid fuel may contain other contaminants such as amines, waxy
hydrocarbons and some inorganic substances. Contamination of nitrogen, sulfur and halogens gives
flu gas pollution. Unexpected contamination and high water contents may lower the product yields
and shorten the lifetime of a reactor for pyrolysis
Liquid fuel users require petroleum substitutes such as gasoline, diesel fuel and heavy oil. In
these fuels, various additives are often mixed with the liquid hydrocarbons to improve the burner or
the engine performance. The fuel properties such as viscosity and ash content should conform to the
specifications of the fuel user’s burners or engines. No additives would be needed for fuel used in a
boiler. A JIS technical specification was proposed for pyrolytic oil generated from waste plastic for
use as boiler and diesel generator fuel (TS Z 0025:2004).
Skillful operators and a well-equipped facility are required due to the formation of highly
flammable liquids and gases.
The production method for the conversion of plastics to liquid fuel is based on the pyrolysis of
the plastics and the condensation of the resulting hydrocarbons. Pyrolysis refers to the thermal
decomposition of the matter under an inert gas like nitrogen.
For the production process of liquid fuel, the plastics that are suitable for the conversion are
introduced into a reactor where they will decompose at 450 to 550 C. Depending on the pyrolysis
conditions and the type of plastic used, carbonous matter gradually develops as a deposit on the
inner surface of the reactor. After pyrolysis, this deposit should be removed from the reactor in
order to maintain the heat conduction efficiency of the reactor.
The resulting oil (mixture of liquid hydrocarbons) is continuously distilled once the waste plastics inside the reactor are decomposed enough to evaporate upon reaching the reaction
temperature. The evaporated oil is further cracked with a catalyst. The boiling point of the produced
oil is controlled by the operation conditions of the reactor, the cracker and the condenser. In some
cases, distillation equipment is installed to perform fractional distillation to meet the user’s
After the resulting hydrocarbons are distilled from the reactor, some hydrocarbons with high
boiling points such as diesel, kerosene and gasoline are condensed in a water-cooled condenser. The
liquid hydrocarbons are then collected in a storage tank through a receiver tank. Gaseous
hydrocarbons such as methane, ethane, propylene and butanes cannot be condensed and are
therefore incinerated in a flare stack. This flare stack is required when the volume of the exhaust
gas emitted from the reactor is expected to be large.
There may be variations in the feeding methods used depending on the characteristics of the
waste plastic. The easiest way is to simply introduce the waste plastics into the reactor without any
pretreatment. Soft plastics such as films and bags are often treated with a shredder and a melter (hot
melt extruder) in order to feed them into the reactor because otherwise they would occupy a large
volume of the reactor.
There are also different types of reactors and heating equipment. Both kiln-type and
screw-type reactors have been proposed, while induction heating by electric power has been
developed as an alternative to using a burner.
Due to the formation of carbonous matter in the reactor, which acts as a heat insulator, in
some tank reactors the stirrer is used to remove the carbonous matter rather than for stirring. After
the liquid product of the pyrolysis is distilled, the carbonous matter is taken out either with a
vacuum cleaner or in some cases reactors are equipped with a screw conveyor at the bottom of the
tank reactor to remove the carbonous matter.
Operators should understand the relationship between the amount and composition of the
waste plastics as well as the operating conditions. Energy consumption and plant costs relative to
the plastic treatment capacity are the typical criteria for evaluating the plant performance. Operating
skill and safety considerations are important in this type of chemical conversion due to the highly
flammable liquid fuels which are formed.
Schematic diagram of fuel oil production system
Fuel / Energy Shortage
On the other hand, our country faces the critical problem of fuel and energy deficiency. The fast depletion of petroleum reserves in the world and frequent rise in prices of crude oil affect our economy adversely. India is not self sufficient in case of petroleum and crude oil. The national production capacity is capable of fulfilling not even 20% of the total fuel demand. The remaining whooping 80% is fulfilled by importing crude. Most of our precious foreign exchange is spent on importing crude.
Calculation of oil consumption
Crude Oil Consumption in India
Waste plastic generated in India
(excluding almost equal amount of
Imported waste dumped in India
Liquid Hydrocarbons obtained in the invented process
saving indian rupees