CHENNAI: Is necessity the mother of invention? Well, not always. Determined to find a cheap and sustainable fuel, engineer Chitra Thiyagarajan developed a unit that converts plastic waste into a fuel similar to diesel. After a series of tests in a sustained three-year effort, Thiyagarajan finally perfected the device and applied for a patent.

C S M Sundaram, Thiyagarajan's guide, said the device was the result of backbreaking work, persistence and dogged tenacity. “It involved research, fieldwork and frequent upgrading of design,” he said. “I may have helped her occasionally but the credit is all hers,” said Sundaram, 80, a retired professor of St Xavier's College, Mumbai.

She applied for a patent for the device in June 2013. “The patent authorities checked the machine for two months and verified that it could be patented. They accepted my application in August,” Thiyagarajan said.

Explaining how her ‘pyro-plant' functions, she said, all plastics except PET bottles are put in a chamber and heated in the absence of oxygen over chromium micro band heaters (similar to those used in water immersion rods) to temperatures of between 350ºC and 375ºC. The gas generated passes into another chamber with a water coolants coils on two sides. It is then pumped into another compartment half-filled with water. The fuel floats on the surface. Non-soluble gas that passes into a condenser can be used as an LPG alternative.

The device is not expensive and requires just three hours to generate fuel. A 5kg unit costs around Rs 75,000 and a 25kg variant, Rs3 lakh. Each kg of plastic produces 800ml of diesel. While the diesel can be stored, the LPG generated has to be used directly and cannot be compressed, Thiyagarajan said.

“A similar process is used to generate fuel in China but the production costs are high and it is a time-consuming process,” Thiyagarajan said.

Indian Institute of Technology-Madras chemical engineering professor S Pushpavanam said the invention is feasible and could be used to produce fuel.

Thiyagarajan's other inventions include a night vision camera and an electromagnetic belt for physiotherapy.