FUELS FROM PLASTIC WASTES
1. INTRODUCTION Plastics are polymeric materials, a material built up from long repeating chains of molecules. Polymers such as rubber occur naturally, but it wasn't until the development of synthetic polymers around 1910 that the polymers tailored to the needs of the engineer first started to appear. One of the first commercial plastics developed was Bakelite and was used for the casing of early radios. radios. Because the early plastics were not completely chemically stable, they gained a reputation for being cheap and unreliable. However, advances in plastic technology since then, mean that plastics are a very important and reliable class of materials for product design. Plastic is a marvel of polymer chemistry, plastics have become an indispensable part of our daily life. But repeated reprocessing of plastic waste, and its disposal cause environmental problems, pose health hazards, in addition to being a public nuisance. The biggest current threat to the conventional plastics industry is likely to be environmental concerns, including the release of toxic pollutants, greenh greenhous ousee gas and non-biodegrable landfill impact as a result of the production and disposal of petroleum and petroleum based plastics. Various methodologies have been tried and tested to process waste plastics for many years, with recycling becoming the most common method reflecting today’s environmental requirements. Liquefaction of plastic is a superior method of reusing this resource. The distillate product is an excellent fuel and makes ThermoFuel one of the best, economically feasible and environmentally sensitive recycling systems in the world today. ThermoFuel diesels can be used in any standard diesel engine, trucks, buses, trains, boats, heavy equipment and generators.
2. WHAT ARE PLASTICS? The term "plastic" covers a wide range of synthetic polymer materials. What they have in common is that they are all made by joining together or "polymerizing" a
bunch of molecules (monomers). There are two main families of plastics, thermosetting and thermoplastics. thermoplastics.
3. CONVERTING WASTE PLASTIC INTO LIQUID FUEL Many may not realize throwing away plastic is throwing away a ready fuel source. Plastic is primarily petroleum and burns with high efficiency. Plastics are commonly made from fossil fuels which is usually an irreversible process, process have been developed which recycles plastic waste back into oil.
ThermoFuel ThermoFuel technology technology is used to convert convert Waste Plastic into Liquid Liquid Fuel. ThermoFuel is a ten year old commercially proven proven technology with nine operational plants in Japan. Thermofuel is a process where scrap and waste plastics are converted into synthetic fuel. The system uses liquefaction, pyrolysis and the catalytic breakdown of plastics. The system can handle almost all the plastic that is currently being sent to landfills. A major advantage of the process is its ability to handle unsorted, unwashed plastic and its extremely high efficiency. A ThermoFuel plant can produce up to 9,500 liter of high-grade synthetic fuel from 10 tonnes of waste plastics, with systems ranging from 10 to 20 tonnes per day. This means that heavily contaminated plastics can be processed without difficulty. 4. STRUCTURE OF THE SYSTEM
The system consists of stock in feed system, pyrolysis gasification chamber, catalytic converter, condensers, centrifuge, oil recovery line, off-gas cleaning, and adulterant removal. Waste plastics are loaded via a hot-melt in feed system directly into main pyrolysi pyrolysiss chamber. When the chamber chamber temperature temperature is raised, agitation agitation commences to even the temperature and homogenize the feed stocks. Pyrolysis then commences to the point of product gasification. Non-plastic materials fall to the bottom of the chamber. The gas goes through the (patented) catalytic converter and is converted into the distillate fractions by the catalytic cracking process. The distillate then passes into the recovery tank after cooling in the condensers. From the recovery tank, the product is sent to a centrifuge to remove contaminants such as water or
carbon. The cleaned distillate is then pumped to the reserve tank, then to the storage tanks.
Figure-3 Figure-3 Structure Structure of the System System
5. OPERATIONS 5.1 PRE-TREATMENT
Pre-treatment, depending on the form of delivery of plastics to the plant, may include shredding and granulating. The system accepts granulated to a flake size of 2.5 cm or less in order for it to be conveyed and metered uniformly via a melt infeed system into the chamber. However, Thermofuel can process most sizes and types of plastics with suitable pre-treatment equipment. 5.2 PYROLYSIS
The heart of the pyrolysis system is the prime chamber, which performs the essential functions of homogenization, controlled decomposition and out gassing in a single process. The process requires minimal maintenance apart from carbon residue removal, and produces consistent quality distillate from mixed and low-grade plastic waste. The key to an efficient pyrolysis process is to ensure the plastic is heated uniformly and rapidly. If temperature gradients develop in the molten plastic mass
then different degrees of cracking will occur and products with a wide distribution of chain lengths will be formed.
Pyrolysis is a process of thermal degradation in the absence of oxygen. Plastic waste is continuously treated in a cylindrical chamber and the pyrolytic gases condensed in a specially-designed condenser system to yield a hydrocarbon distillate comprising straight and branched chain aliphatics, cyclic aliphatics and aromatic hydrocarbons. The resulting mixture is essentially equivalent to petroleum distillate. The plastic is pyrolised at 370ºC-420ºC and the pyrolysis gases are condensed in a 2stage condenser to give a low sulphur content distillate.
The essential steps in the pyrolysis of plastics involve :
Evenly heating the plastic to a narrow temperature range without excessive temperature variations.
Purging oxygen from pyrolysis chamber. chamber.
Managing Managing the carbonaceo carbonaceous us char by-produ by-product ct before it acts acts as a thermal insulator and lowers the heat transfer to the plastic .
Careful condensation and fractionation of the pyrolysis vapours to produce distillate of good quality and consistency. Pyrolysis is used as a form of the of therma rmall treatm treatment ent to reduce waste volumes and
produce liquid or gaseous fuels as a byproduct. There is also the possibility of using pyrolysis systems integrated with other processes such as mechan mechanica icall biolog biologica icall treatment and anaerobic anaerobic digestion digestion.. The agricultural waste is pyrolised at a temperature of 450 to 550 ºC. There are 3 pyrolysis products: 1. A combustibl combustiblee gas that that is burned burned to generate generate the heat heat required required for the endothermic pyrolysis reaction. No extra heat or fuel source is required. 2. A liquid bio-oil bio-oil that that can be used as as a fuel. The bio-oi bio-oill cannot be used used directly directly in car engines. It is converted to a syngas from which clean fuels and petrochemicals can be synthesized, using well-established technologies. 3. A solid char char that can can either either be burned burned for for energy energy or recycled recycled as as a fertilizer .
5.3 THE CATALYTIC BREAKDOWN
The core technology technology of the Thermofuel Thermofuel process is the catalytic reaction tower (or catalytic converter) on the exit side of the main pyrolysis chamber. The catalyst is important because it lowers the amount of energy that is required to break down the structure of the waste plastics. As well as promoting the initial cracking of the polymers, the catalysts are used to promote the production of a heavier fuel suitable for the manufacture of diesel and gasoline. Only a small amount of catalyst material is lost during the conversion process. The catalytic reaction tower contains a system of plates made from a special catalytic catalytic metal alloy. Thermofue Thermofuell requires requires no additives additives or consumable consumable catalytic consumables. The metal plates do get fouled with a tar-like residue and terephthalic acid and therefore the reaction tower needs to be stripped down periodically and the plates polished, generally every 6 months to once a year. The maintenance service can be quickly performed (approx. 1 hour) with minimal plant down time, using spare catalytic plates. The catalyst chamber is heated using the exhaust gases from the furnace of the pyrolysis chamber. The gas from the pyrolysis chamber is feed to the catalytic converter and is converted into the distillate fractions fractions by the catalytic cracking process. The metal catalyst ’cracks’ parafinic chains longer than C25 and ’reforms’ chains shorter than C6. The catalyst ensures that the final fuel has a carbon chain distribution in the range C8-C25 and peaking at C16 (cetane), which is very similar to standard fuels. The liquid liquid distillate distillate then passes passes into the the operating operating tank after after cooling cooling in the condensers. From the operating tank, the product is sent to a centrifuge to remove contaminants such as water or carbon.
5.4 COLLECTION OF LIQUID FUEL
As the plastics are reduced, the gases are collected and cooled, yielding liquid fuel. This liquid fuel or crude oil is a complex mixture that has to be separated in a fraction chamber to form gasoline and diesel. The remaining incondensable gases pass
through the top of the fraction chamber and are either burnt off in a flare stack or fed back to the initial stage of the process where they are used as an additional fuel to heat the incoming plastic materials.
6. OPERATING FEATURES OF THERMOFUEL 6.1 PLASTICS SUITABLE SUITABLE FOR TREATMENT
ThermoFuel process can be done on waste plastics such as: 1. Plastic packagi packaging ng scrap scrap from materia materiall recovery/so recovery/sorting rting faciliti facilities es 2. Oil Oil and and dete deterg rgen entt bott bottles les 3. Mixed Mixed pos post-c t-cons onsume umerr plas plastics tics,, 4. Caps/Labels/R Caps/Labels/Rejected ejected bottles bottles from bottle bottle recyclin recycling g operations, operations, 5. Commer Commercia ciall stretch stretch and and shrin shrink k wrap. wrap. THERMOFUEL SYSTEM
RESIN
SUTABILITY
Polyethylene (PE)
Very good.
Polypropylene (PP)
Very good.
Polystyrene (PS)
Very good.
ABS resin (ABS)
Good.
Fiber Reinforced Plastics ((F FRP)
Fair.
PET
Not suitable.
Polyvinylchloride (PVC)
Not suitable.
Table-1 Suitability of plastic
6.2 PRE-TREATMENT
Input feedstock plastics do not require washing or sorting. The plastics can be shredded or granulated prior to being fed through a melt-infeed system into the chamber so almost any shape or size of waste plastics can be handled. The system is
designed to cope with these foreign materials up to approximately 10% by weight or volume. So no pre-treatment is needed. 6.3 MAINTENANCE
Coking occurs in the chamber when the pyrolysis of the waste plastics is almost complete. However, ThermoFuel is designed to minimize coking coking by stabilizing heat conductivit conductivity y within within the the pyrolys pyrolysis is chamber. chamber. The pyrolysis pyrolysis chamber chamber require requiress cleaning cleaning every second second process, process, and and takes just 30 minutes. minutes. The catalytic catalytic reaction reaction tower needs to be stripped down periodically and the plates polished, generally every 6 months to once a year. The maintenance service can be quickly performed (approx. 1 hour) with minimal plant down time.
6.4 POLLUTION POLLUTION
ThermoFuel produces extremely low level of emissions, due due to the capture of almost all of the output, both liquids and gases, inside the system. Pyrolysis of plastics tends to occur on irregular basis, hence the carbon chain lengths of the pyrolytic gases vary between 1-25. Most of the gas is liquefied in the condensers but some remains as gas. This high calorific gas contains methane, ethane, propane, propane, butane, etc. This gas is reused to heat the Pyrolysis chamber.
7. OUTPUTS
7.1 THE CHAR STREAM
A carb carbon onac aceo eous us cha charr is form formed ed in the the cha chamb mber er dur durin ing g pyr pyrol olys ysis. is. The The char char residue produced produced is generally generally proportional to the level of contaminants which are adhering to the feedstocks. Since the char passes acid leaching tests it can simply be land filled. filled. Inorganic Inorganic additives additives such such as cadmium cadmium pigments pigments from from the plastics plastics end up in the char stream.
7.2 OFF GAS
Pyrolysis of plastics tends to occur on an irregular basis. Hence, the carbon chain lengths of the pyrolytic gases vary from 1 to 25. Most of the gas is liquefied in
the condensers but some gas remains uncondensed. Hydrocarbons with carbon count of 4 and lower remain as a gas under room temperature. This off-gas contains methane, ethane, propane, butane, etc. Although volume of the gas differentiates, depending upon the types of the plastics, it is generally no more than 2 to 5%.The incondensable gases pass through the top of the fraction chamber and are either burnt off in a flare stack or fed fe d back to the initial stage of the process where they are used as an additional fuel to heat the incoming plastic materials. 7.3 OUTPUT OUTPUT FUEL FUEL
The typical mass balance for one tonne of mixed polyolefin plastic entering the process is approximately 90% hydrocarbon distillate, 5% char, as well as 5% gaseous material known as non-condensable gases. The non-condensable gas from the ThermoFuel plant is passed through a water scrubber and then fed into the natural gas flow for the burner, which heats the unit so there are no net hydrocarbon emissions. The hydrocarbon fraction in turn comprises approximately 75% distillate cut and 25% paraffin material. The paraffin fraction is continuously cracked after the first condenser until it reaches the desired chain-length range and then added to the primary fuel stream.
7.3.1 COMPARISON
A comparison of the distillate produced from a commingled plastic mix compared with regular synthetic fuel has been conducted by gas chromatography, and shows good similarity between fuels. A key indicator of diesel is the Cetane Number which is analogous to the octane rating for petrol. Cetane is a measure of the ignition delay, that is, the time between injection into the cylinder and the moment of autoignition. This is most significant in relation to low-temperature start ability, warm-up, and smooth, balanced combustion.
Distillates Distillates with a higher cetane cetane rating show show increased increased power and and superior superior performan performance ce characteristics characteristics.. Ideal diesel diesel will have a high proportion proportion of hydrocarbo hydrocarbon n chains that are 16 carbon carbon atoms. Thermo Fuel-produced Fuel-produced diesel has a cetane number in
the range of 57, similar similar to or higher convention conventional al diesel, which which averages averages 51-54. Most Most engine engine manufacturer manufacturerss recommend recommend diesel diesel fuels with a cetane number of at least 50.
7.3.2APPLICATIONS:
The distillate is designed to operate in a diesel engine where it is injected into the compresse compressed, d, high-temper high-temperature ature air in the combustio combustion n chamber chamber and ignites ignites spontaneously. Thermo Fuel is perfectly suited to any standard application.
7.3.3 7.3.3 LUBRICITY LUBRICITY::
Thermo Fuel is extremely high in lubricity. In diesel engines some components like fuel pumps and injectors are lubricated by the fuel, so good lubricity is a key element in reducing wear on these parts. 7.3.4 7.3.4 COST COST
The cost of producing one tonne of liquid fuel is around US$200, with the largest single cost being the purchase price of the waste plastic from the recycling companies which is between US$70 and US$85, depending on the quality of the plastic. Thermofuel derived diesel fuel generally costs less than 35 cents per litre depending on feedstock type, labour and certain costs cost s particular to your operations.
8. CONVER CONVERTING TING WASTE WASTE PLASTIC PLASTIC INTO FUEL FUEL IN INDIA
A plant, Unique Unique Plastic Waste Manageme Management nt & Research Co Pvt Ltd, was set up at the industrial estate in Nagpur in 2004.Industrial units in the area are running their captive power plants on this fuel and are happy with its pricing and performance. The fuel is priced at Rs30 per litre. The fuel scores over petrol/diesel because it ignites faster. Besides, several test reports by government and non-government institutions say it has smaller sulphur content and low reaction temperature. Above all, the Maharashtra Pollution Control Board has found that the conversion of plastic waste into fuel is non-polluting.
Engine output is nearly as much as produced by other fuels. A test drive on a Kinetic Honda gave a mileage of 44 km/l iter on plastic fuel as compared to 44.4km/ltr on petrol. It accelerated from 0 to 60 km in 18 seconds against 22.5 seconds seconds on petrol. Today a 25 MT plant supplies supplies fuel to neighboring neighboring industrial industrial units. units. There ultimate ultimate aim is to take take the capacity capacity up to 450 450 MT. Most Most of their their raw material material comes comes from the plastic waste dumped in their premises by the factories in the area.
9. CONCLUSION
ThermoFuel is a truly sustainable waste solution, diverting plastic waste from landfills, utilizing the embodied energy content of plastics and producing a highly usable commodity that is more environmentally friendly than any conventional distillate. distillate. The Thermofuel Thermofuel system convert convertss these waste plastics into high-grad high-gradee "green" distillate fuel. The result of this process is claimed to be a virtually non polluting, (100%) synthetic fuel that does not require engine modification for maximum efficiency. Post consumer, post-industrial unwashed and unsorted waste plastics plastics are the feedstoc feedstock k for the Thermof Thermofuel uel process, process, and with an expected expected production efficiency of over 93%, the resultant diesel output would almost equal the waste material input.
10. REFFERENCE 1. http://www.b http://www.biofue iofuelsforu lsforum.com m.com/gener /general_bio al_biodiesel diesel_discu _discussion/6 ssion/65858 plastic_diesel.html 2. www.biofuel.com 3. www.thermofuel.com 4. www.envofuel.com 5. www. www.Cy Cyna narp rplc lc.c .com om 6. http://www.ftns.wau.nl/agridata/apme/plastics.htm 7. http://www.packagingtoday.com/introplasticexplosion.htm
