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Numerical Simulation to Improve the Performance of Air-cooled Steam Condenser Ejector and Steam Turbine Operation in a Rankine Cycle

Sabzpoushan, Ali | 2018

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50675 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Darbandi, Masoud
  7. Abstract:
  8. Nowadays, widespread needs for creating low pressure ambient in various industries make vacuum systems have different research and industrial applications. One of these applications is in cooling system of Rankine power cycle. In this case, the performance of the vacuum system has a direct and significant effect on the cooling performance of the condenser and consequently, power production of the steam turbine. Also, a considerable part of deration in thermal power plants industry is due to the thermal deration of the cooling systems. This is mostly because of malfunction of the condenser due to ambient temperature rise. Therefore, by providing suitable solutions to improve the efficiency and reliability of the vacuum system, it is possible to increase the power production in hot weather conditions and save valuable natural resources. The aim of the present study which is applied to the industry is to introduce an improved geometry and a set of operating conditions for an ejector-type vacuum system, which supports the air-cooled condenser in a Rankine power cycle. For this purpose, the computational fluid dynamics tool has been implemented considering complexities such as water phase change along the ejector. The significance of this research comes to matter particularly when we show that no serious effort has been made previously in the literature on the ejectors utilized in large-scale thermal power cycles. This is while the outcomes of this work will be very applicable from economic perspective and for saving valuable natural resources like water and fossil fuels. This is owing to the large dimensions of such ejectors and their ultra-high working pressure ratios and their considerable effects on the performance and efficiency of megawatt power cycles. In the process of fulfilling this research, by considering the desired vacuum level at the system design point and using some existing geometries, the ejector performance is studied under the variation of its main geometrical parameters. Next, we define a new operating point for the ejector by changing the operating conditions of the geometrically-optimized configuration in addition to studying its off-design performance. These could be achieved by targeting at criteria like higher entrainment ratio, lower thermal dissipation, etc. It should be mentioned that prior to performing numerical simulations, primary modeling of the ejector is to be performed using analytical and empirical relations. By doing so, we aim to better understand the flow physics of the ejector and evaluate its behavior under different operating conditions. Finally, in order to investigate the effect of the ejector improvements on the performance of the air-cooled condenser and power production of the steam turbine in hot weather conditions, we perform the thermodynamic modeling of the target power cycle. The results show that after geometrical modifications and altering the operating conditions, ejector entrainment ratio is increased from 16 percent to more than 51 percent. In addition to saving of about 3000 m3 water per year, this can also lead to prevent the annual energy of about 10 GWh to be derated for one unit of the target combined power cycle
  9. Keywords:
  10. Ejector ; Shock Wave ; Air Cooled Condenser ; Vacuum ; Steam Turbines ; Secondary Flow ; Rankin Cycle ; Entrainment Rate

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