Creating oil products that can be reused to make more plastic is the simplest, most 'closed-loop' solution for converting mixed waste packaging plastic into fuels when using plastics not suitable for recycling, says senior engineer of consulting firm
March 14, 2014
Innovative options for converting mixed waste packaging plastic into fuels and the costs associated with new technological capabilities will be explored by Axion Consulting at Sustainability Live on April 3rd.
In his presentation entitled ‘Fuels from Plastics: An independent review and economic assessment of current technologies’, Senior Engineer Sam Haig will report on the current state of development of processes and solutions for using plastics not suitable for recycling, which would otherwise be landfilled.
Recovering post-consumer flexible plastic films for direct reuse can be problematic because of the wide range of different plastic types, applications and formats. This can result in a mixed, contaminated fraction that is unsuitable for existing mechanical recycling methods, which rely on a relatively uncontaminated feed.
The current disposal routes for this unrecoverable material are incineration or landfill. The latter is widely considered to be an unacceptable option; however, incineration of plastics also has several issues, not least the release of ‘long-life’ fossil carbon into the atmosphere, while recovering only a fraction of the potential energy.
An alternative method is to change the plastic mixture into a reusable product via a chemical process. As most plastic is originally created from crude oil, the simplest and most ‘closed-loop’ solution is to create oil products that can be reused to make more plastic, as a fuel (which can be burned more efficiently than the original mixture), or in another application.
Processes identified by our research as having the most technical and commercial potential fall into three categories:
fast gas phase pyrolysis to make synthetic crude oil mixtures;
liquid-phase catalytic depolymerisation to make mixed distillates, and
gasification, followed by chemical or biological synthesis, to make high-quality fuels.
While pyrolysis and catalytic depolymerisation processes have a relatively low capital cost and a relatively high yield (60–70% of the feedstock is converted to a liquid), the low quality of these oil products means that significant further processing is required to achieve stringent liquid fuel standards.
Despite this, the high yield improves the environmental and economic viability of these processes. They are also economical at smaller sizes, making them ideal for operators with low tonnages of waste.
In comparison, gasification processes with downstream synthesis of high-quality fuels are much more capital intensive, requiring larger economies of scale.
These processes have lower product yields (30–60% of the feedstock is recovered as a liquid fuel) but recover energy as electricity from the high-pressure, high-temperature processes. In contrast to the previous two processes, gasification benefits from economies of scale and is therefore more suitable for larger waste volumes.
Sam explains: “If recycling is not possible, then extracting value from lower-grade plastics as fuel products, such as ethanol or methanol that can be blended or used in other applications is preferable to incineration or landfilling, neither considered to be the best routes.
“If plastics sent for incineration with energy recovery generate too much heat as a result of their high calorific values, then some EfW plants have to be slowed down to run at a reduced tonnage throughput, reducing their rate of ‘gate fee earning’ and making this infeed a less desirable raw material. Plastic in municipal waste is a significant source of fossil CO2 from incineration (80-90%).”
He adds: “Only with high energy recoveries from waste incineration, such as in combined heat and power plants (CHP), and when the recovered energy substitutes for that produced from coal or gas, can the energy recovered compensate for the CO2 emissions caused by plastics.”