Fuel from Waste Plastics

Dr.S.S.VermaDepartment of Physics, S.L.I.E.T. (Deemed to be University), Longowal

Distt.-Sangrur (Punjab)-148 106; E-mail: ssverma@fastmail.fm

Plastic Waste in different forms is a present day common sight and a growing environmental problem as an outcome of present “plastic dependent” civilization. Plastic dependent lifestyle of present civilization is currently disposing large volumes of plastic every where. Waste plastics are either burnt in a non-environmental manner or left to choke the drainage systems or consumed by stray animals or turning into heaps/landfills of waste all around. For those who try to help the environment, one of the last ideas that come to mind is burning things in the open. Every body wants the magic wand to convert the world's most daunting environmental problem of plastic waste Plastic wastesinto its most precious commodity, fossil fuels including diesel and petrol.

There is a great need to find out ways to recycle and reuse the waste plastics besides, technologies actively seeking waste plastics feedstock for turning them into useful end products in an environment friendly manner should also make an integral part of our society. Given the limits of plastic recycling (output degrades after each cycle) coupled with the fact that incineration is highly expensive and can be hazardous, emitting toxic gases if not done properly, biodegradable plastics still far away and in view of the future energy crunch it will be beneficial to think about the conversion of waste plastics to hydrocarbon fuels. A zero-pollution industrial process to convert non-biodegradable - and mostly non-recyclable - plastic waste into liquid hydrocarbons is highly desired. Various methodologies based on pyrolysis (e.g., gasification, liquefaction) with/without catalytic conversion and briquette of plastics have been tried and tested to process waste plastics for many years. Plastic, a product of petroleum, gives a fuel better than petrol and diesel as the impurities are less when compared to the crude oil. The new technology can convert the waste plastic into oil (70%), gas (20%) and coke (10%).

Plastofuel (Briquetting):The mission is to burn plastic fuel at a high temperature and gets a high-quality burn with minimum toxic emissions. Plastofuel -- charcoal briquette-sized nuggets made of various waste plastics which burns plastic pellets, produces a lot of heat which could also be used to generate electricity. Plastofuel process uses less energy than the traditional pellet-production process does. The drawback with these pellets is that mulch film must be cleaned before the sheets are melted down.

Pyrolysis:Pyrolysis is a process of thermal degradation in the absence of oxygen. Plastic waste is continuously treated in a 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 two-stage condenser to give a low sulphur content distillate. The essential steps in the pyrolysis of plastics involves:

i) Evenly heating the plastic to a narrow temperature range without excessive temperature variations

ii) Purging oxygen from pyrolysis chamber, iii) Managing the carbonaceous char by-product before it acts as a thermal insulator

and lowers the heat transfer to the plastic iv) Careful condensation and fractionation of the pyrolysis vapours to produce

distillate of good quality and consistency

Structure of the System:The system consists of stock infeed 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 infeed system directly into main pyrolysis chamber. The chamber can generally be filled within 30min.When the chamber temperature is raised, agitation commences to even the temperature and homogenise the feedstocks. Pyrolysis then commences to the point of product gasification. Non-plastic materials fall to the bottom of the chamber. The gas goes through the 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.

The heart of the pyrolysis system is the prime chamber, which performs the essential functions of homogenization, controlled decomposition and outgassing 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.

Another important aspect of pyrolysis is to use a negative pressure (or a partial vacuum) environment. This ensures that oxidation reactions are minimized and that gaseous pyrolysis vapours are quickly removed from the process chamber thereby reducing the incidence of secondary reactions and the formation of undesirable by-products. The polymer is gently 'cracked' at relatively low temperatures to give predominantly straight chain aliphatic hydrocarbons with little formation of by-products. These hydrocarbons are then selectively condensed and cleaved further catalytically to produce the average carbon chain length required for distillate fuel. The system used for pyrolysis of waste plastics have following advantages:

It operates under normal pressure and is safe, efficient, easy to operate and highly economical.

Designed to minimize coking by stabilizing heat conductivity within the pyrolysis chamber.

System produces extremely low level of emissions, due to the capture of almost all of the output, both liquids and gases, inside the system.

The system has very few moving parts, and accordingly there is no excessivenoise or vibration.

Foreign matters such as soil, sand or papers are often attached to waste plastics are also taken care off in the system

Liquefaction:In recent years, the building or expanding of gasifiers has become difficult due to opposition from governments and community groups with environmental concerns, most notably the levels of emissions. Therefore, liquefaction of plastic is a superior method of reusing waste plastics resource. Recently a process called ThermoFuel is developed in which scrap and waste plastics are converted into synthetic fuel. This technology recovers synthetic fuel from a variety of used plastic sources. A major advantage of the process is its ability to handle unsorted, unwashed plastic and its extremely high efficiency. It is a truly sustainable waste solution utilizing the embodied energy content of plastics and producing a highly usable commodity that, due to its cleaner burning characteristics, is in itself more environmentally friendly than conventional distillate.

A ThermoFuel plant can produce up to 9,500 litres 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 also be processed without difficulty. The same applies to silage wrap, trickle tape and other agricultural plastics. Other normally hard to recycle plastics such as laminates of incompatible polymers, multilayer films or polymer mixtures can also be processed with ease unlike in conventional plastic recycling techniques. In fact, most plastics can be processed directly even if contaminated with dirt, aluminium laminates, printing inks, oil residues, etc. tempor porttitor pede. 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

synthetic fuels can be used in any standard synthetic engine, trucks, buses, trains, boats, heavy equipment and generators.

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