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Simulation and Estimation of Power Generation in Natural Gas Network by Micro Turboexpanders

Hejazi, Bijan | 2011

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 41874 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Farhadi, Fatolah
  7. Abstract:
  8. This thesis studies the economic feasibility of replacing a throttling valve with an expansion turbine in a city gate station for the purpose of distributed electricity generation through exergy recovery from pressurized natural gas. Conventionally, high pressure natural gas stream enters a pressure reduction station with its physical exergy completely destroyed in an irreversible Joule-Thompson effect of a throttling valve. To avoid hydrate formation at the outlet of the turboexpander, the inlet stream should be preheated. Although pressure reduction stations are inherently subject to seasonal fluctuations of inlet natural gas pressure and flow rate, the preheating temperature should be adjusted accordingly and the outlet pressure should be kept at a constant level.
    Hence, the proposed models in this study are designed not only based on fixed yearly operating conditions, but also on variable monthly design specifications. Performing exergy and energy analyses for a selected model, thermodynamic indicators of the system are introduced. Economic evaluations of various design models show that the most attractive design is related to an expansion turbine in parallel with a throttling valve where total preheating requirement is provided by the combustion of a small fraction of the outlet stream. Calculations based on a case study (Tehran No.2 City Gate Station) demonstrate an exergy loss of 40 million kilowatt-hours per year for the present throttling valves. The preheating requirements of the pre-heaters would be half of the current amount if the preheating temperature were adjusted according to the seasonal operating conditions. For the selected model if design parameters are chosen appropriately, work-to-fuel ratio of higher than unity, exergy recovery of higher than 60 percent and payback period of around 3 years are possible. Sensitivity analysis over costs to generate power involving natural gas price shows the economical limit and the optimum preheating temperature of the proposed model
  9. Keywords:
  10. Expansion Turbine ; Hysis Software ; Natural Gas Pressure Reduction Station ; Exergy Recovery ; Operating Conditions Fluctuations

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