Thermodynamic Criteria for Sustainability Analysis

Sustainability is a critical issue and the word is often bandied about. However, how can we measure whether a process is genuinely sustainable This section relates to the evolution of a model that can be used to help decide on the sustainability of a given practice and is based on two of our earlier papers [16,36]. Key advances include the quantification of renewability beyond a renewable/not renewable basis. 

Industry is under increasing pressure from governments and environmental groups to improve the sustainability of its processes. However, how this higher level of sustainability should be achieved is not really clear, and even the definition of sustainability is often only qualitative, as we have seen earlier. There is a need for a tangible quantitative description that allows the sustainability of technological processes to be systematically evaluated, compared, and improved as Lems [16] argued. 

In an earlier work by De Wulf et al. [36], we showed that different aspects of process sustainability can be quantified by using thermodynamic principles. Indeed, the thermodynamic concept of exergy is used as the basis for the construction of sustainability parameters, which conveniently express particular aspects of process sustainability on a scale of zero to one. Elements of this work were used to analyze the sustainability of several industrial processes, and new insights have led to some meaningful improvements. 

It is clear that ultimately our only limitation to sustainable production is obtaining the exergy to run the production processes and to drive closed material cycles. In view of this, exergy can be considered the ultimate scarce resource in our technological processes, and exergy flows to or from these 

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