(245b) Second Law of Thermodynamics and the Notion of Externalities of Macro-Economics: Two Pillars of Assessing the Sustainability of a Manufacturing System

Sustainability engineering, an emerging discipline of engineering, can be regarded as an engineering discipline to craft frameworks, or establish paradigms, for attaining sustainability in any social or human endeavor including sustainable manufacturing.  No discipline or branch of engineering can be enduring without theoretical principles underlying it or without a firm theoretical foundation. In this regard, two cornerstones of sustainability assessment of any system or process should be the second law of thermodynamics and the notion of externalities of macro-economics.

The inevitable entropy increase attributable to a process of concern manifests itself in exergy dissipation by the process, which can be evaluated by resorting to the available energy balance; this balance results from integrating the first and second laws of thermodynamics. In reality, however, the available energy balance also implicitly embodies the mass conservation law: It entails the detailed accounting of every material species involved in the process in light of the species’ matter-energy.

Economic externalities attributable to a system or process of concern manifest themselves in the process’ external costs. These external costs inherent to the system can be evaluated through cost accounting or estimation in conjunction with the process’ internal costs, such as the labor and equipment costs.           

Various methodologies are available for assessing the sustainability of manufacturing or process systems, which take into account exergy dissipation as well as cost, or can possibly take both into account. One of such methodologies is sustainability potential; this hierarchical approach is proposed to estimate the sustainability-potential of a system based on any of the alternative manufacturing or synthetic routes. This novel notion of sustainability-potential is a generalization of the notion of profit-potential, the estimation of which renders it possible to screen out unsustainable processes derived from the alternative synthetic routes at the earliest stage. The efficacy of sustainability potential is illustrated with the manufacture of vinyl chloride.