Plastics are almost all derived from oil wastes which are of a high calorific value. Energy recovered from plastic waste can make a major contribution to energy production. Plastics can be co-incinerated with other wastes or used as alternative fuel (e.g., coal) in several industry processes (cement kilns). The energy content of plastic waste can be recovered in other thermal and chemical processes such as pyrolysis. As plastic waste is continuously being recycled, the plastics lose their physical and chemical properties at their end-of-life cycle. Continuous recycling could lead to substandard and low-quality products. Hence, it would no longer be economically profitable to recycle any longer . Incineration with energy recovery would be the economically preferred option at this stage.
Conversion of Plastics Waste into Liquid Fuel
A research-cum-demonstration plant was set up at Nagpur, Maharashtra, for conversion of waste plastics into liquid fuel. The process adopted is based on random depolymerization of waste plastics into liquid fuel in the presence of a catalyst. The entire process is undertaken in a closed reactor vessel followed by condensation, if required. Waste plastics while heating up to 2700°C to 3000°C convert into the liquid-vapor state, which is collected in a condensation chamber in the form of liquid fuel, while the tarry liquid waste is topped- down from the heating reactor vessel. The organic gas is generated which is vented owing to lack of storage facility. However, the gas can be used in a dual fuel diesel-generator set for generation of electricity .
Plasma Pyrolysis Technology
In plasma pyrolysis, firstly, the plastics waste is fed into the primary chamber at 8500°C through a feeder. The waste material dissociates into carbon monoxide, hydrogen, methane, higher hydrocarbons, etc. Induced draft fan drains the pyrolysis gases as well as plastics waste into the secondary chamber, where these gases are combusted in the presence of excess air . The inflammable gases are ignited with a high-voltage spark. The secondary chamber temperature is maintained at around 10,500°C. The hydrocarbon, carbon monoxide and hydrogen are combusted into safe carbon dioxide and water. The process conditions are maintained so that it eliminates the possibility of formation of toxic dioxins and furans molecules (in case of chlorinated waste) . The conversion of organic waste into nontoxic gases (CO,, H,0) is more than 99%. The extreme conditions of plasma kill stable bacteria such as Bacillus stereothermopbilus and Bacillus subtilis
immediately. Segregation of the waste is not necessary, as very high temperatures ensure treatment of all types of waste without discrimination .
Creation of more legislative bodies such as which the United Nations Agency and the International Maritime Organization (IMO) introduced the marine pollution (MARPOL) convention in 1983, an international protocol to prevent and reduce pollution from ships. The protocol is referred to as MARPOL 73/78, from the fact that the convention was signed in 1973 and the protocol was added in 1978. The protocol has been approved by 169 countries, which together are responsible for 98% of the world’s total shipping pollution, and prevents ships from releasing garbage and totally prohibits the disposal of plastics anywhere into the sea. Further, it obligates governments to keep terminal facilities and harbors clean of garbage . According to the terms of this agreement, every ship having a certain weight and able to carry more than 14 persons is obligated to maintain a garbage record book, in which records of all disposal operations will be kept. Information required includes date, time, position of the ship and description and estimated amount of garbage that is incinerated or discharged. In addition to maintaining a garbage record book, marines are asked to prepare a garbage management plan that gives procedures for collecting, storing and processing on-board waste .