Optimization of operating parameters for a 600MW Rankine cycle based Ultra Supercritical power plant

Abstract

Priority of any power generation plant is reduction in heat rate, improved conversion of low grade energy into high grade energy and increased thermal efficiencies. Increase in coal costs, Green environment protection and related global regulations led the researchers to invent new ways to improve the efficiency of power plants. This technical study aims at optimizing the various technical parameters for the selected 600MW Rankine cycle based Ultra Supercritical (USC) power plant. The energy and exergy destructions and efficiencies would be estimated by varying the number of feedwater heaters, bled steam pressures and deaerator pressures of power plant. Also aimed to optimize the number of feedwater heaters during this study. While carrying out this study, the operational constraints of the individual thermal equipment's are taken into consideration. Keywords: Ultra Supercritical, exergy analysis, energy analysis, feedwater heater, deaerator I. INTRODUCTION Based on the statistical data from International Energy Agency (Association, 2016) the Thermal energy is the highest source of power across world. With regeneration process or including the feedwater heaters, it is possible to increase the average heat addition of any steam power plant. Higher enthalpy which is available with the supercritical and ultra supercritical steam enables the thermal power plants to achieve higher efficiencies. So, there is a scope for the study to optimize the technical thermal parameters, in order to achieve the higher power plant efficiencies. Yuanyuan et.al[1]in his comprehensive study on USC Power plant, used a ten stage regenerative and double reheat system to optimize its parameters for higher efficiency. Power plant efficiency increase of 2% is observed i.e 44.78% to 46.83% by introducing double reheat instead of single reheat. Sandhya et. al[2], in her work analyzed a 422 MW power plant by using Lignite fuel, identified the highest exergy destruction in furnace (86%), 82% in Turbine, is reported. Zhi et. al[3], in his work investigated the influence of condenser pressure on power plant and exergy efficiency for which he considered a 500MW steam power plant,and concluded that, about 43.5% fuel cost reduction is possible by using the high grade coal(SA grade) instead of low grade (SM grade) coal. Rosen M.A et. al[4], conducted a study to compare the coal fired and nuclear power plants on the basis of exergy and energy. During which he considered a 500 MW power plant and derived and compared various exergitic and energetic losses. And it is observed that only 30% to 33% of exergy efficiency is being found in his research analysis. Rayudu et.al[5], in their study concluded that, the steam at elevated temperatures and pressures certainly improves the performances of rankine cycle. During the literature review, it is observed that, there is a significant scope to optimize the number of feedwater heaters, bled steam pressures and deaerator pressures of a power plant, for a better exergy and energy efficiencies when they operate at supercritical and ultra-supercritical conditions. A 600MW NTPC power plant is being considered, a simulated software model is developed by using Matlab software, in order to carryout the parametric optimization. Also these findings are validated with the realistic data available at an NTPC power plant. The following parameters are being considered for the study and optimized to achieve highest possible exergitic and energetic efficiencies. i. Turbine inlet pressure, ii. Turbine inlet temperature, iii. Reheat pressure ratio, iv. Reheat temperature ratio, v. Deaerator Pressure