Waste-to-Energy Conversion by Stepwise Liquefaction, Pyrolysis and “Clean Combustion” of Waste Plastics

As petroleum resources are finite, it is imperative to use them wisely in energy conversion applications. Plastics, a petroleum-based product, are widely used in manufacturing disposable products and have created a solid waste issue. Due to their abundant supply, and given their high energy content, their use for power generation is of technological interest. However, whereas waste plastics have found limited use in incineration, such a conventional direct combustion technique is ill-controlled and produces considerable amounts of health-hazardous airborne compounds. Thus, an alternative technology is proposed herein to further address our increasing energy needs and, at the same time, utilize our waste plastics streams in an environmentally-benign manner. More specifically, a multi-step process/device is proposed to accept post-consumer plastics, of various types and shapes, and generate an easily-identifiable form of energy as a final product. To achieve low emissions of products of incomplete combustion, the plastics are liquefied, pyrolyzed, mixed with air, ignited and, finally, burned forming pre-mixed low-emission flames. Combustion is thus indirect, since the solid polymer is not directly burned, instead its gaseous pyrolyzates are burned upon mixing with air. Thereby, combustion is well-controlled and can be complete. A demonstration device has been constructed to convert the internal energy of plastics into clean thermal energy and, eventually to electricity.