Mansouri, Seyed Soheil2; Ismail, Muhammad I.4; Babi, Deenesh Kavi3; Huusom, Jakob Kjøbsted2; Gani, Rafiqul2
1 Department of Energy Conversion and Storage, Technical University of Denmark2 Department of Chemical and Biochemical Engineering, Technical University of Denmark3 Computer Aided Process Engineering Center, Department of Chemical and Biochemical Engineering, Technical University of Denmark4 Technical University of Denmark
The growing concerns about the global warming and greenhouse gas emissions (GHG) have led to an increase in the interest to produce fuel from biomass and from the fact that such fuels can relieve the reliance on imported oil and price. To this end, numerous production facilities are being set up, at different scales and using different methods of manufacture based on different raw materials and component properties . It is therefore timely to study the sustainability and feasibility of these various manufacturing routes. Therefore, finding the best alternative and design with minimum environmental impact and maximum profitability is needed. In this work a computer-aided framework for process synthesis and process intensification is applied for sustainable production of biodiesel from pure/waste palm oil as the feedstock. This approach examines several biodiesel processing routes that were collected through available data and current technologies reported in the literature. Using this information, a generic superstructure of processing routes was created that described a network of configurations representing multiple designs for the production of biodiesel. Therefore, based on the currently known technologies, this superstructure includes all possible alternatives. The next step was to analyze the superstructure in terms of economic and sustainability metrics. This was done by first performing simulation to obtain the steady state mass and energy balance data for the entire superstructure. These data were then used for a sustainability analysis  where a set of calculated closed- and open-path indicators were employed to identify the structural bottlenecks within the superstructure. Based on this analysis the number of process alternatives within the superstructure was reduced and a set of feasible flowsheet alternatives were identified. These were further reduced through economic and lifecycle assessment analysis (LCA) to determine the alternative that best matched a specified set of performance criteria (or design targets). A rigorous simulation was performed on this flowsheet, which at this stage was considered as the base case design for the next step of the framework. To further improve the base case design, process intensification was considered  with the targets set by LCA, economic and sustainability analyses in the previous step. Out of the three available levels for achieving PI, the phenomena-level, which is the lowest level of aggregation, was considered so that potentially new and improved alternatives to the base case design could be obtained. The objective (or target) for the intensified process design was to overcome the bottlenecks of the base case design. The optimization problem was further refined in terms of logical, operational, structural constraints, using a PI knowledge base tool. The next step was to identify the phenomena representing the tasks performed within the base case design and the operating window of each phenomenon, by applying thermodynamic insights  and the PI knowledge base. Next, the phenomena needed to overcome all identified process bottlenecks were identified, sorted in terms of operation (task) types and the phenomena present in them, and, screened using structural, operational and thermodynamic information. Note that different combinations of phenomena can perform the same specified task. The phenomena were then combined according to a set of rules to form unit operations, which in turn were combined to form new and innovative process alternatives. Finally, from the remaining set of feasible intensified process alternatives, the best in terms of economic and environmental sustainability was identified. For the case of biodiesel production, the intensified process alternative turned out to be the most economical and more sustainable than other alternatives. The computer-aided methods and tools used in this work are: SustainPro (method and tool for process sustainability analysis), ECON (method and tool for process economic analysis), LCSoft (method and tool for process lifecycle assessment analysis) and process simulation software (e.g. PRO/II, ASPEN Plus, ICAS). They are all used in an integrated framework for process synthesis.