Energy & Fuels, Vol.27, No.8, 4859-4868, 2013
Pyrolytic Gasification of Post-consumer Polyolefins To Allow for "Clean" Premixed Combustion
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 degrees C in N-2- or CO2-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/CO2 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.