Transforming waste plastic into an alternative fuel was the task set to Northeastern University researchers by Engineering Professor Yiannis Levendis. The capstone of that nine-month project is what the team calls a waste combustor—a device that breaks down non-biodegradable plastics into a gaseous fuel that can be burned to generate steam that drives an electricity generator.
U.S. Department of Energy (DoE) design for a combustor that converts gaseous fuel into heat that boils water to drive an electricity turbine with steam.
"We envision our prototype being used at recycling centers which separate out the non-biodegradable plastics and burn them to generate electrical power," says Levendis.
For over two decades, Levendis has been researching various methods of using combustion to rid landfills of post-consumer wastes. Of late, he has been concentrating on vaporizing the worst offenders—non-biodegradable plastics—but it took many years to perfect a process that did not create toxic emissions. Because of the large number of U.S. landfills surrounding every metropolitan area, the researchers believe that making waste combustors a standard part of recycling centers nationwide could save billions of dollars a year. In particular, the researchers estimate that the waste combustor has the potential to eliminate the need for up to 462 million gallons of gasoline per year.
"It will also help get rid of unsightly, non-biodegradable plastic waste that cannot be recycled," says Levendis.
Levendis' team members included Brendan Hall and Chuanwei Zhuo, both engineering doctoral candidates; and Jeff Young, Shane McElroy, Jason Lee, David Laskowski, David Garufi and Paul Conroy, all senior undergraduate students. Their prototype waste combustor was demonstrated breaking down non-biodegradable plastics to create an alternative source of fuel at the fifth annual MIT Energy Conference this spring.
Professor Levendis and David Laskowski working on the waste combustor apparatus (source: Mary Knox Merrill).
The waste combustor houses two subsystems that divide and conquer the task of disposing non-biodegradable waste while simultaneously generating electricity for power. The top section of the waste combustor houses the chamber that breaks down the nonbiodegradable plastic and converts it into fuel. Then, in a second lower chamber, the resulting fuel is burned to generate steam, which can be used to drive an electric turbine that generates electricity.
In the double-tank combustor design, the plastic is subjected to the process of pyrolysis in the upper tank—a high-temperature procedure that converts the solid waste into a combustible gas. The gas then flows into the bottom tank, where it is combined with oxygen and burned to generate heat for an external boiler that produces steam. The steam can then be routed to a turbine that produces the actual electricity.