In the last century, the economic growth has been accompanied by a worldwide diffusion of polymers for multiple applications. However, there is a growing attention to the environmental pollution and energy consumption linked to the unconditional use of plastic. In the present work, exergy is used as a measure of the resource consumption during the life cycle of polymers. Nine commercially diffused polymers are chosen, and their production chains are identified according to the “grave to cradle” approach. The global Embodied Exergy (EE) is calculated as the sum of the contribution of each step of the chain, including the production process and the Exergy Replacement Cost (ERC) of the fossil fuel. Then, recycling routes and the associated exergy consumption are analysed. Thermodynamic recycling indexes are developed depending on the final product, namely the crude polymeric material and the oil derivatives or structural molecules. The main results show that some commonly used polymers have a considerable impact in terms of EE (e.g., PET). Recycling indexes encourage the recycling processes, which are always energetically convenient (from 10% to 60% of exergy savings) compared with the production from virgin raw material. Results from EE calculation are used for the thermodynamic assessment of the plastic content of vehicle components, to obtain useful information for recycling practices development.
Implementing a recycling route for vehicle plastics surely represents a challenging mission for a company. In general, the recyclability of automotive plastic is influenced by the nature of the polymer (i.e. the material cannot be recycled or recycling would cause deterioration of its properties) or by the lack of an industrial recycling system. In general, there are several technological and economic barriers that must be overcome through design innovation and logistical measures. Based on these factors, an arbitrary scale has been first developed to translate the qualitative indicators into a numerical score that can be useful for comparing different plastic components in a vehicle. Then, the various indicators have been translated in exergy terms, for giving an idea of the order of magnitude of the resources invested in developing the recycling process. Therefore, a new methodology for including critical recycling factors in the total exergy recycling cost is here presented.
Development of an Integrated Solid Waste Management (ISWM) system is a continuous challenge for local communities. These systems should be properly designed, paying particular attention to the optimal connection of their subsystems. Among them, the Solid Waste (SW) collection system has a primary influence. The design variables (e.g. unit collection basin and weekly removal) can be optimized according to the variation of external parameters (e.g. penetration of selective collection, population density). The objective is the minimization of specific collection cost, maintaining the maximum collection efficiency. Once the collection system is optimized, its influence on the entire SW treatment chain is evaluated. To this end, a multi-objective optimization is implemented taking into account the global cost and exergy efficiency of waste treatment. The analysed system is composed by a paper recycling plant for cardboard production and a Mechanical Biological Treatment plant for the Residual Unsorted Waste treatment, with production of Refused Derived Fuel.
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