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Assessment and Application of Solid Oxide fuel Cell-Gas Turbine Hybrid System to Improve the Performance of Wastewater Treatment Plant

Aliee, Mohammad Hossein | 2016

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 48954 (46)
  4. University: Sharif University of Technology
  5. Department: Energy Engineering
  6. Advisor(s): Roshandel, Ramin; Avami, Akram
  7. Abstract:
  8. Wastewater treatment plants play an important role within the urban water cycle in protecting receiving waters from untreated discharges. In the developed and developing countries, Energy consumption of these units are 3 and 5 % of the electrical energy demand, respectively. As far as sustainable development is concerned, not only the reduction of WWTP’s energy consumption is mandatory, but also these units should produce energy. To this end, several techniques are available namely: energy audits, replacement of equipment and improvement of process efficiency. Moreover, Energy can be generated by converting biogas -from anaerobic digesters- to heat and power. Todays, Biogas is well-known as an alternative and renewable fuel that can mitigate greenhouse gas emissions. Heat and electricity, generated form Biogas of digesters, could be harvested to meet the energy demand of WWT unites and facilitate their energy independency. Solid oxide fuel cells are one of the leading energy conversion systems in order to work with biogas.In this project, a dynamic model of mass and energy for wastewater treatment plants has been developed. This model can determine energy consumption, biogas production and the effluent quality by given load and fixed concentration. Then a solid oxide fuel cell-gas turbine hybrid system with maximum efficiency and minimum total investment cost is used to generate power from biogas. To this end, a multi-objective optimization with aim of genetic algorithm is employed to seek the optimal design variables of the system. The objective functions are electrical energy efficiency to be maximized and total investment cost to be minimized. Design variables are steam to methane ratio, utilization factor, gas turbine isentropic efficiency, fuel cell current, compressor isentropic efficiency and compressor pressure ratio. Optimal values of design variables has been determined in single-objective and multi-objective optimization. Then applying Sobol’s sensitivity analysis method, effect of each design variable on the electrical energy efficiency and the total investment cost has been determined. Results show that compressor pressure ratio has the paramount influence on the electrical energy efficiency of the hybrid system. Also, isentropic efficiency of the gas turbine and fuel cell current has the maximum influence on the total investment cost of the hybrid system. After determining the optimal values of the design variables, economic analysis has been done. The results show that for a certain feed in a BSM2 model, hybrid energy conversion system could provide the total energy required in the aeration unit. In addition, this conversion system could partially meet the energy demand of pump and sludge processing units. Levelized cost of electricity (LOCE) in this hybrid energy system is 6.3 cent/kWh. Finally, sensitivity analysis on some variables such as standard aeration efficiency in the aeration unit and concentration of input feed components is implemented in order to observe the effect of these variables on the Energy self-sufficiency of the WWTP. In conclusion, standard aeration efficiency has a major effects on the net electrical energy generation. The more increase in Standard aeration efficiency, the more increase in net electrical energy generation. Besides, investigating effects of concentration of input feed components this conclusion could be drawn that effective components contain organic materials and heterotrophic microorganisms and they can affect biogas production and Levelized unit cost of electricity
  9. Keywords:
  10. Wastewater Treatment Plant ; Biogas ; Energy Consumption ; Performance Improvement ; Solid Oxide Full Cell - Gas Turbine System

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