الفهرس 
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Abstract
The unforeseeable growth in the global population needs growing technological advances in establishing power plants, it is a great challenge to overcome this critical issue by reducing greenhouse gases. Fuel supply due to political conflict and decarbonization is the most challenging standup for the energy sector and electricity generation. Through the second-law of thermodynamics, one could explore, analyze, and comprehend the energy quality of thermal systems other than the first law, which commits to energy quantities. In this regard, a deep investigation introduced in the present work shows the energy and exergy analysis of a supercritical steam power plant. Accordingly, thermodynamic analysis of a supercritical dual-fuel-fired steam power plant of a 670 MW-based natural gas fuel and 626 MW-based mazout oil fuel under different operating loads of 50%, 75%, 100%, and 105% at a sliding-pressure operation of 144, 199, 243, and 255 bar is conducted. The plant called South Helwan Supercritical Steam Power Plant and located 60 km in El-Kuriemat village south of Cairo, Egypt.
As well, a thermodynamic analysis of the main components, such as the boiler, multi-stage turbines, feedwater heaters, plant pumps, etc., is studied. Moreovere, expanding the sharing of solar energy with conventional steam power plants to keep pace with solutions to the crises facing the energy sector by boosting power or fuel saving. Based on the actual operation of the examined plant, energy and exergy analyses of the power plant-based mazout oil-fired are carried out to assess the system’s performance. The energy losses and exergy destruction are evaluated for each system component using real actual data. The results show that the condenser has the highest energy loss, while the boiler is the primary source of irreversibility with 88.62% of the total exergy destruction followed by the turbine and then the condenser. The intermediate pressure turbine maintains an exergy efficiency of 97% at 100% load, which is higher than high- and low-pressure turbines.
Moreover, the maximum thermal efficiency is achieved at 100% full load by 44.85% whereas, the maximum overall exergy efficiency of 40% is acquired at the maximum continuous rate condition of 105% load. A significant concern is introduced towards the steam generator since it has the largest exergy destruction percentage relative to other cycle components. The heat transfer sets inside a once-through steam generator are studied and analyzed. The exergy destruction in the combustion process represents 58.6% and 54% of the overall boiler exergy destruction at an operating load of 50% and 100%, respectively.
Also, it is crucial to form a complete understanding of the influence of fuel switching on the supercritical power plant’s performance to overcome the political issues. So, the influence of fuel switching between mazout oil and natural gas on the performance of supercritical steam power plant at a sliding-pressure operation is investigated via an energy and exergy analysis. The results indicate that the major exergy destruction that occurs in the boiler at a sliding-pressure of 255 bar equals 821 and 856 MW for natural gas and oil fuels, respectively. In addition, increasing the operating sliding-pressure from 144 to 255 bar enhances the overall energy and exergy efficiencies for natural gas, which are higher than for oil fuel. Moreover, at a sliding-pressure of 255 bar, the overall energy efficiency equals 47.79% and 44.85% for natural gas and oil fuel, respectively. While the overall exergy efficiency of the supercritical power plant due to using natural gas and oil fuel is 43.36% and 40%, respectively.
Solar energy is a clean and renewable source of energy that can help to reduce pollutant emissions from power plants. One way to integrate solar energy into a conventional power plant is through solar aided power generation. This system uses solar energy to supplement the output of the fossil fuel-fired plant, which can help to improve efficiency and reduce emissions. Therefore, the present study also introduces a thermodynamic analysis for a modeled solar aided supercritical steam power plant using two types of fuel at different operating loads, i.e., 50%, 75%, and 100%.
The proposed supercritical solar aided power plant is investigated in terms of energy, exergy, and steam flow rates. In the solar aided supercritical power plant, the condensate water passes into heat exchangers using a working fluid of Therminol VP-1. In the modeled solar aided power plant, the turbine extraction steam at 100% load is minimized, and it is eliminated at 50% and 75% loads. At a load of 50%, 75%, and 100%, the results show that the recovered amount of feedwater extraction increases the percentage of mechanical power by 16%, 21%, and 9.7%, respectively. As well, in the case of employing natural gas, the energy efficiency is optimized in comparison to the conventional supercritical power plant by 13.7%, 17%, and 1.9%, respectively. As well, for oil fuel, the mechanical power for a solar aided power plant increases by 25.7%, 27.6%, and 17.4%, respectively, while the energy efficiency is improved by 20.6%, 21.9%, and 7%, respectively.
However, the intermittent nature of solar radiation means that the solar aided power generation often operates under off-design conditions, which can reduce its efficiency. In the absence of a storage system, the turbine and boiler in a solar aided power generation may be forced to operate under off-design conditions for much of the time. Furthermore, in the present study, the performance of a solar aided supercritical steam generator system was simulated, analyzed, and optimized with various types of fuels at partial loads. The effect of preheating the economizer inlet temperature and varying the heat transfer fluid temperature is studied to obtain the optimum power plant performance of a partial load in fuel-saving operation mode.
The results show that at a half load condition and different heat transfer fluid temperatures of 340 °C, 350 °C, 360 °C, 370 °C, and 380 °C, the optimum economizer inlet temperatures equal 309 °C, 319 °C, 329 °C, 339 °C, and 349 °C when natural gas fuel is used. While when oil fuel is employed, the working fluid temperatures record 307 °C, 317 °C, 327 °C, 337 °C, and 347 °C, respectively. Moreover, heat transfer fluid temperatures at a 75% load are 340, 350 °C, 360 °C, 370 °C, 380 °C, and 390 °C, the efficient economizer inlet temperatures are 314 °C, 324 °C, 329 °C, 339 °C, 349 °C, and 359 °C, respectively, when natural gas fuel is employed, while in the case of utilizing oil fuel, they record 312 °C, 322 °C, 332 °C, 342 °C, 347 °C, and 357 °C, respectively. The results give a useful guide for the operation of a solar aided power plant with a storage system.