This work addresses the development of a decision-making framework for optimal process integration with enhanced sustainability. Decision-Making is a fundamental activity of management, business, research, and all kinds of human behaviors. The decision-making framework has been analyzed and developed in order to make a better decision and to solve a problem effectively. The trend of decision-making in process systems engineering has evolved toward sustainable development, or simply sustainability. In the 21st century, economy, energy, and environment are the three main issues in the world in terms of sustainability. With globally growing concerns on climate change and these issues, governments and companies are making more efforts to reduce carbon emission and to upgrade energy efficiency and other factors of sustainability. The industry has faced with challenges, i.e. maximizing profit under economic problems, environmental regulations, and social problems. The demand for sustainable design is getting higher since the 1990s. A great deal of work has been performed to obtain a better solution to increase process efficiency with rational investment. Process integration is a methodology to increase the efficiency and to manipulate the system for a desired target in process systems engineering as well as industry. However, a decision-making framework for optimal process integration with enhanced sustainability has not been yet developed in a systematic approach. The life cycle assessment methodology has been utilized as a tool for evaluating sustainability of project. However there is a limitation to evaluate various aspects including environmental impact. In order to obtain a more efficient and practical sustainable solution, the environmental aspect should be integrated with the economic aspect in the deci-sion-making framework.
In this study, the concept of eco-cost is introduced as the sustainability cost in order to solve the problem toward a sustainable design. The sustainability cost assessment framework is applied to the overall decision-making framework. The process model integrating molten carbonate fuel cell and coal-based synthetic natural gas production (SNG-MCFC) is newly developed for applying and evaluating this methodology. The coal-to-electricity superstructure has been developed to obtain the optimal solution. In the superstructure, pulverized coal-fired power plant (PC), and integrated gasification combined cycle (IGCC) are compared with the proposed model. The objective is to maximize the total profit considering process efficiency, environmental policy and sustainability. The operating principle of MCFC, that carbon dioxide is transferred from cathode side to anode side as carbonate ion, facilitates the carbon sequestration. In this regard, the process integration of MCFC with coal-based synthetic natural gas (SNG) production process has been developed. To evaluate the overall efficiency of the integrated system, the simulation has been performed by AspenPlus V.7.3. This strategic process integration enables the use of coal as a raw material for cleaner power generation in a MCFC while increasing the efficiency of the overall process by means of stream and heat integration. The simulation results show that the proposed process is more efficient than other progressive coal-based power generation processes. The reduction of the capital costs was confirmed in both the SNG and the MCFC processes by the integration. Moreover, the emissions of $SO_x$, $NO_x$, and $CO_2$ are successfully restrained. The result also shows the mutual benefit, that the integrated system represents high efficiency of $CO_2$ sequestration and clean power generation and has the potential of the most profitable process with increasing renewable energy policy credit, i.e. REC price under the Korean renewable regulatory policy. The proposed process model will significantly contribute to developing a high efficient $CO_2$ sequestration process as well as more profitable process in terms of sustainability. This decision-making framework of process integration is applicable to other processes for enhancing sustainability. The sustainability-enhanced process design is a challenge of the era. The goal of the development of a sustainable decision-making framework is to support decision makers and policy makers. Conclusively, this proposed framework and methodology will contribute to develop decisions for process integration with enhanced sustainability.