Utilization of post-consumer waste plastics as fuels is of technological interest because their energy contents (heating values) are comparable to those of premium fuels. Pyrolytic gasification of these solid polymers yields a mixture of predominately gaseous hydrocarbons and hydrogen. This gaseous fuel mixture can then be suitably blended with air and burned in well-controlled premixed flames. Such flames are much less polluting than diffusion flames, which would have been generated had the polymers been burned in their solid state. In this work, an apparatus was designed and built to continuously process polymers, in pelletized form, and to pyrolytically gasify them at temperatures in the range of 800−900°C in N 2 -or CO 2 -containing environments. Subsequently, the gaseous pyrolyzates were mixed with air, ignited, and burned in a Bunsen-type burner in a manner similar to natural gas. Polyethylene and polypropylene pyrolyzates burned with blue-tint flames akin to those of natural gas. The flames were fairly steady and nearly stoichiometric, generating effluents with low CO/CO 2 ratios. The combustion reactions released heat in a small water boiler coupled to a miniature steam engine, which produced electricity, illustrating the feasibility of "clean" power generation from waste plastics. Because pyrolysis of polyolefins requires a nominal heat input that amounts to only a minuscule fraction of the heat released during their combustion, large-scale implementation of this technique is deemed to be technologically viable and economically favorable.
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.
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