Analysis of efficiency improvements for a coal-fired power plant by numerical investigation of the mill duct system and a geothermal power plant by evaluation of alternative evaporative cooling methods

Nearly over 62,000 power plants in the world are operating to produce people's electricity needs. Coal-fired power plants are being among the most common plants in electricity production. In contrast, geothermal plants can be considered to be the most reliable ones from the renewable energy sources aspect. As these power plants are planned to be operated based on their design data, their real-time electricity production can show variation from the designed values. In the present study, both a coal-fired thermal power plant (TPP) in Manisa, Turkey, and a geothermal plant in Aydın, Turkey, were investigated to identify efficiency losses and provide recommendations on efficiency improvements for these plants. Firstly, coal/air flow in the mill duct system in the Soma B TPP was numerically modeled to characterize the flow behavior of the coal particles and gas mixture. The two new design alternatives of the mill duct system, named ND-01 and ND02, were proposed to provide a better mixing at the duct system. It was realized that more homogenous particle disturbance was obtained in the mill duct system, especially for the particle sizes larger than 230 µm when ND-01 design is placed into the duct system. Secondly, the thermodynamical performance of a 21 MW geothermal plant with an aircooled two-level binary type organic Rankine cycle was numerically investigated based on its design and operating data. The study results show that when the ambient temperature rises from 5°C to 35°C, the power generation of the plant has a decrease of 6.8 MW at nominal load, energy efficiency has decreased from 13.5 percent to 9.98 percent and exergy efficiency is reduced from 54.65 percent to 38.67 percent. Furthermore, thermoeconomic analysis was carried out to determine the most profitable and economical evaporative cooling system for the plant by considering the payback period, internal rate of return (IRR), and net present value (NPV) methods. The payback periods of direct spray, wetted media, and ecomesh methods are calculated to be 8.4, 11.2, and 14.0 years, respectively. Besides, the direct spray system appears to be the most advantageous investment alternative among the others based on IRR and NPV results.