طراحی فرآیند سبز، انرژی سبز، و پایداری: چشم انداز تجزیه و تحلیل سیستم

This paper presents a systems analysis perspective that extends the traditional process design framework to green process design, green energy and industrial ecology leading to sustainability. For green process design this involves starting the design decisions as early as chemical and material selection stages on one end, and managing and planning decisions at the other end. However, uncertainties and multiple and conflicting objectives are inherent in such a design process. Uncertainties increase further in industrial ecology. The concept of overall sustainability goes beyond industrial ecology and brings in time dependent nature of the ecosystem and multi-disciplinary decision making. Optimal control methods and theories from financial literature can be useful in handling the time dependent uncertainties in this problem. Decision making at various stages starting from green process design, green energy, to industrial ecology, and sustainability is illustrated for the mercury cycling. Power plant sector is a major source of mercury pollution. In order to circumvent the persistent, bioaccumulative effect of mercury, one has to take decisions at various levels of the cycle starting with greener power systems, industrial symbiosis through trading, and controlling the toxic methyl mercury formation in water bodies and accumulation in aquatic biota.

Chemical process simulation tools and models allow engineers to design, simulate and optimize a process. Steady state simulators like PRO-II and ASPEN Plus are well known in this area and are extensively used for the simulation of continuous processes. In recent years, chemical process industries have become aware of the importance of waste reduction, and environmental consciousness demands an effort extending far beyond the capability of existing process simulation to model processes with environmental control options. For tracking trace components non-equilibrium-based models are implemented. Packages like Waste Reduction Algorithm (WAR) (EPA, 2002) provide data related to various environmental impacts like toxicity and exposure data. Designing green processes with “process integration” which takes into consideration the entire process is now possible with the new tools. However, there is still a long way to attain the goal of sustainability. Unlike traditional design where engineers are looking for low cost options, environmental considerations include objectives like the long-term and short-term environmental impacts. Green process design and green energy involve not only extending the design framework to include process integration, environmental control technologies, starting as early as the material selection stage, and going beyond just green energy, green processing, and green management, but also to look at industrial sector level management through industrial ecology as shown in Fig. 1. In industrial ecology, this decision making changes from the small scale of a single unit operation or industrial production plant to the larger scales of integrated industrial park, community, firm or sector. Uncertainties increase as one goes from traditional process design to green design and to industrial ecology. The concept of overall sustainability goes beyond industrial ecology and brings in time dependent nature of ecosystem. Decisions regarding regulations, human interactions with ecosystem come in picture. It involves dealing with various time scales and time dependent uncertainties. This work presents a systems analysis approach to various steps involved from green process design to sustainability.Mercury has been recognized as a global threat to our ecosystem, and is fast becoming a major concern to the environmentalist and policy makers. Mercury is a major pollutant from power plants. The task of mercury pollution management is arduous due to the complex environmental cycling of mercury compounds. Successful handling of the issues calls for a sustainability-based approach. This work presents the systems analysis approach to sustainability with the case study of mercury. The next section briefly describes the mercury cycle that highlights its complex nature. This discussion is necessary to justify the proposed integrated algorithmic framework that is subsequently described in the article.

The primary objective of this work is to emphasize the role of an integrated systems theory-based approach to address issues in green process design, green energy leading towards overall sustainability. This includes not only the traditional process engineering related issues such as process and product design, but also the associated ecological and social aspects. This requires integration and application of various systems theory-based approaches, and some of the important ones are presented in this paper. It is mentioned that the role of uncertainty is important is this analysis to ensure robust results. The paper then analyzes the case of mercury pollution management and illustrates how these concepts can be applied to a real and existing problem. The role of pollutant trading at the industrial sector level is discussed to achieve compliance at reduced financial and social costs. Moreover, the role of liming and systematic manipulation of aquatic population at the ecosystem level is analyzed to further mitigate the harmful impacts of mercury pollution. It is proposed that both of these approached should be synergistically explored for the mercury pollution management problem. Thus, application of liming for a watershed will have an impact on the final regulation such as TMDL, which in turn will affect the trading decisions. Ultimately, a multi-objective optimization problem as considered in level 5 of the proposed approach, will be formulated that will juxtapose the economic objectives with social and environmental performance indicators. Only an integrated analysis, such as the one proposed here, will be able to look at these inter-dependencies and hence determine the globally optimal solution. Although the specific management options discussed here pertain to mercury pollution, it is proposed that similar approaches should be explored for other issues in the field of sustainability. That is where the role of systems theory and analysis as a tool becomes very valuable.