https://orcid.org/0000-0001-9510-8599
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ABSTRACT
Repowering of old steam power plants is a viable solution to increase power and improve efficiency. This study investigates the feasibility of feed water heating repowering for the Neka steam power plant by considering the influences of steam mass flow rate on the condenser performance and the heat rate of the new cycle. Energy and exergy analyses were conducted using the first and second laws of thermodynamics and heat transfer relations in each scheme. The effect of increasing the steam mass flow rate on the performance of the condenser and the cycle was also investigated. The repowered cycle was simulated using Thermoflow software, and the results were validated with small errors. The results showed that replacing low and high-pressure heaters with new heat exchangers increased the power of the steam unit and the repowered cycle, energy, and exergy efficiencies by 15.7%, 49.3%, 5.93%, and 2.17%, respectively. Although the condenser pressure increased by 19 millibars, leading to a 0.63% increase in the heat rate, the total heat rate of the repowered cycle improved by 4.62%. Overall, the findings demonstrate that feed water heating repowering can be an effective strategy to increase the efficiency and power of conventional steam power plants.
Nomenclature
| Symbols | = | Definitions |
| AC | = | Air Compressor |
| aux.cond | = | Auxiliary Condenser |
| BFPT | = | Boiler Feed Pump Turbine |
| c | = | Specific Heat |
| CCh | = | Combustion Chamber |
| cond | = | Condenser |
| CP | = | Condensate Pump |
| dea | = | Deaerator |
| E | = | Energy |
| Eff | = | Efficiency |
| Ėx | = | Exergy Flow Rate |
| ex | = | Specific Exergy |
| ēx | = | Molar Specific Exergy |
| FR | = | Full Repowering |
| FWH | = | Feed Water Heater |
| FWHR | = | Feed Water Heating Repowering |
| FWP | = | Feed Water Pump |
| GT | = | Gas Turbine |
| h | = | Specific Enthalpy |
| HPFWH | = | High-Pressure Feed water Heater |
| HPHEX | = | High-Pressure Heat Exchanger |
| HPT | = | High-Pressure Turbine |
| HR | = | Heat Rate |
| HWBR | = | Hot Wind Box Repowering |
| IPT | = | Intermediate-Pressure Turbine |
| LHV | = | Lower Heating Value |
| LPFWH | = | Low-Pressure Feed water Heater |
| LPHEX | = | Low-Pressure Heat Exchanger |
| LPT | = | Low-Pressure Turbine |
| ṁ | = | Mass Flow Rate |
| P | = | Pressure |
| PFWHR | = | Parallel Feed Water Heating Repowering |
| PR | = | Partial Repowering |
| RC | = | Repowered Cycle |
| = | Heat Flow Rate | |
| r | = | Pressure Ratio |
| = | Heat Flow Rate | |
| s | = | Specific Entropy |
| SBR | = | Supplementary Boiler Repowering |
| ST | = | Steam Turbine |
| T | = | Temperature |
| TET | = | Turbine Exit Temperature |
| TIT | = | Turbine Inlet Temperature |
| Ẇ | = | Power |
| x | = | Molar Fraction |
| Greek Letters | = | |
| ρ | = | Density |
| η | = | Energy Efficiency |
| ε | = | Exergy Efficiency |
| Superscripts | = | |
| CH | = | Chemical |
| PH | = | Physical |
| Subscripts | = | |
| o | = | Reference Condition |
| a | = | Air |
| b | = | System Boundary |
| B | = | Boiler |
| c | = | Compressor |
| c.c | = | Combustion Chamber |
| c.v. | = | Control Volume |
| D | = | Destruction |
| e, out | = | Outlet |
| F, f | = | Fuel |
| f.g, g | = | Flue Gas |
| gen | = | Generation |
| i, in | = | Inlet |
| l | = | Losses |
| liq | = | Liquid |
| P | = | Production, Pressure |
| t | = | Turbine |
Acknowledgements
The authors are thankful to the deputy of engineering and planning of the Neka steam power plant for cooperating in recording the real data of the steam unit cycle.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Additional information
Notes on contributors
Jamshid Naeimi
Jamshid Naeimi received his bachelor's degree in mechanical engineering with a focus on heat and fluids from K.N. Toosi University of Technology in 1990. After that he worked at the Neka thermal power plant. After retiring, he obtained his master's degree in mechanical engineering majoring in energy conversion from Semnan University in 2017. He is currently a Ph.D. student in mechanical engineering at Semnan University. His fields of interests are energy, applied thermodynamics, and power plant technology.
Mojtaba Biglari
Mojtaba Biglari is associate professor of mechanical engineering at Semnan University. He received his B.S. degree from Sharif University of Technology and M.S. degree from Tehran University both in mechanical engineering and received his Ph.D. degree in cryogenic engineering from Moscow Power Engineering Institute (Technical University). His areas of interests are thermodynamics, refrigeration and cryogenics, direct energy conversion and renewable energies.
Saadat Zirak
Saadat Zirak is assistant professor of department of heat, fluid and energy conversion at Semnan University. In 1989, he received a bachelor's degree in mechanical engineering from Chamran University in Ahvaz. Then he received a master's degree in 1992 and a Ph.D. degree in mechanical engineering in 1999 from Isfahan University of Technology.
Iraj Jafari Gavzan
Iraj Jafari Gavzan is assistant professor of department of heat, fluid and energy conversion at Semnan University. In 1992, he received a bachelor's degree in mechanical engineering from Iran University of Science and Technology. Then in 1998 he received a master's degree from Tarbiat Modares University and in 2009 he received a Ph.D. in mechanical engineering from Sharif University of Technology.