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- Type of Document: Ph.D. Dissertation
- Language: Farsi
- Document No: 43322 (06)
- University: Sharif University of Technology
- Department: Chemical and Petroleum Engineering
- Advisor(s): Farhadi, Fathollah; Pishvaie, Mahmoud Reza; Bozorgmehri, Ramin
- Abstract:
- The main objective of the present work is to achieve green design of a methanol plant by using life cycle process design (LCPD) and multi-objective optimization. As a starting point, simulation of Lurgi’s combined reforming process as a conventional reference methanol case (RMC) was performed in order to obtain its operational and kinetic parameters as well as its environmental impacts. The environmental concerns were calculated using one of the modern environmental impact assessment methods, i.e. life cycle assessment (LCA). To perform life cycle assessment of RMC, methanol production plant as well as its auxiliary units should be considered. The auxiliary units in the RMC include cryogenic air separation and gas turbine power plants. Preliminary results show that amongst different environmental impacts, global warming which is directly related to CO2 emission is the main impact of the RMC. To account for the green design considerations and making use of the produced CO2 (as a stoichiometric adjusting agent), some modifications were made on the RMC and a green integrated methanol case (GIMC) was proposed. The proposed GIMC was also simulated and a sensitivity analysis of the operational parameters was performed to determine the process variables that affect synthesis gas production and thereby methanol yield. In order to properly compare GIMC and RMC, two types of objective functions were introduced. The first one was defined so that SynGas production, and thereby methanol production, in the GIMC is equal to that of RMC. In this case no environmental concerns have been incorporated and merely the ability of proposed GIMC to produce the same amount of RMC was assessed. In the second type of objective function, it has been tried to not only maximize methanol production (as a conventional objective function) but also to minimize the pollutants emission. Applying Pareto sense and by using eco-efficiency indicator and environmental damage cost, five scenarios were defined. The objective function was optimized fulfilling the given constraints using Genetic Algorithm (GA) as the most appropriate technique in evolutionary computational optimization. In the present work, the optimization procedure was done using coded Genetic Algorithm application linked to the simulator by using Object Linking and Embedding (OLE). Optimization procedure was controlled by means of time limit, rate of convergence, diversity in the generation and social disaster. The results of the first objective function show that CO2 needed in GIMC could be provided by an environmentally friendly process and the GIMC is a cleaner process compared to the RMC. Furthermore, the proposed GIMC would be capable of reducing CO2 emission in the range of 140,000 and 160,000 tone/yr while its mitigation potential depends significantly on the type of solvent employed in the GIMC. Obtained results in the multi-objective optimization show that when eco-efficiency indicator is subject to optimization, GIMC indicator is about 77 kg of CO2 per tonne of methanol production lower than that of RMC. In addition, considering the environmental damage costs and introducing gross benefit as an objective function, gross benefit of the GIMC could be greater than that of RMC in the range of 13% to 41% depending on the case of scenario.
- Keywords:
- Methanol ; Synthesis Gas ; Green Design ; Life Cycle Assessment ; Environmental Damage Costs
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