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MPhil in Engineering for Sustainable Development

global challenges, engineering solutions

Studying at Cambridge

Pasita Leesakul

The Viability of Turning Waste Plastic Bags into Diesel in Bangkok

 

There is currently a big focus on the idea of ’waste-to-energy’ in Thailand specifically in Bangkok due to the ever-increasing demand for petroleum along sides the fast decreasing amount of available petroleum oil and limited available space for landfill sites. Currently, almost all the municipal waste in Bangkok goes straight to landfill. People are increasingly perceiving this as an opportunity to make money out of waste; leading to an emergence of numerous projects. This dissertation will focus on ‘waste plastic bags to diesel’ technology.
Plastics are very popular with both retailers and consumers because they are cheap, strong, lightweight, and functional. However, they pose a huge problem when it comes to disposal. Like litters, they lead to the death of a significant number of animals, results in localised flooding and visual pollution; and pose a huge health hazard to the society. Most plastic bags are made from polyethylene which is derived from petroleum; hence they have the potential to revert back to their original form which are petroleum substances like diesel. This occurs through a process called ‘pyrolysis’. This process presents an opportunity to solve the disposal problems mentioned above by closing the loop of the plastic bags cycle, and recapturing at least some of the energy inside them.

Pyrolysis is a fairly new technology and this dissertation investigates its practicality and suitability for use in Bangkok. Pyrolysis pilot plant in Bangkok was visited and experiments were conducted to determine the true feasibility and sustainability of this process. To ascertain the most suitable technology for disposal of plastic bags in Bangkok, the pyrolysis process as well as other alternative disposal technologies were investigated. Analytical Hierarchy Process was used as a tool to evaluate each of the technologies and their social, technological, economic, and environmental aspects.

From the experiments conducted, it was discovered that plastic diesel from the pyrolysis process is compatible with commercial diesel and can be used to drive a real engine. The process does not release a significant amount of CO2 and is partially self-sustained.  The APH result suggests that pyrolysis is the best-fit solution for plastic bags and other plastic waste disposal in Bangkok from both public and government’s perceptions.