# Performance Comparison of 500 MW Coal-Fired Thermal Power Plants with Final Feedwater Temperatures
## 2 Materials and Methods
### Performance Analysis of the Steam Cycle
#### 2.2.2 Design Conditions and Interpretation  
The reference condition for this study was based on the design conditions of an existing 500 MW class coal-fired power plant. Table 1 summarizes the reference conditions of performance analysis of the power plant. The assumptions are as follows: (1) The power plant is a supercritical coal-fired power plant. (2) All turbines are adiabatic. (3) The isentropic efficiency of each stage of the turbine is constant. (4) Except for No. 8 feedwater heater shell internal pressure and turbine extraction pressure connected to the feedwater heater, all other turbine extraction pressures and feedwater heater shell internal pressure are identical. (5) The ratio between the shell internal pressure of the No. 8 feedwater heater and the turbine extraction pressure connected to the feedwater heater is constant. (6) The design conditions of the feedwater heater (TTD and DCA) are identical. (7) The high-pressure turbine exhaust pressure and the hot reheat steam pressure are constant. (8) The heat transfer rate of the boiler (including the reheater) is constant. (9) The supplied exergy of the boiler is constant. (10) The CO\({}_{2}\) emission factor at the power transmission stage of a supercritical coal-fired power plant is 1.017 kgCO\({}_{2}\)/kWh [7]. (11) The ratio of transmission power output to the gross power output (\(R_{\text{Trans}}\)) is 0.94429 [41]. (12) The dead state temperature is 25 \({}^{\circ}\)C.  
The performance analysis model was established based on the heat balance diagram of an existing 500 MW class coal-fired power plant. The pressure of steam supplied to the No. 8 feedwater heater was changed by the extraction pressure of the high-pressure turbine. By changing the internal pressure of the No. 8 feedwater heater shell, the final feedwater temperature was changed. The same value as the mass flow rate of the main steam was applied to the mass flow rate of the feedwater flowing through the tube side of the No. 8 feedwater heater. According to the feedwater heater design conditions (TTD and DCA), the flow rate of steam extracted from the turbine was calculated under thermal equilibrium conditions, \begin{table}
\begin{tabular}{c c} \hline \hline
**Item** & **Conditions** \\ \hline Final feedwater temperature & 287.5 \({}^{\circ}\)C \\ Heat transfer rate of the boiler & 1,195,197 kJ/s \\ Exhaust pressure of low-pressure turbine & 5.1 kPa \\ Isentropic efficiency of condensate pump & 80\% \\ Efficiency of condensate pump motor & 95\% \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Reference conditions of performance analysis. and the steam excluding the extracted steam flows to the next stage of the turbine. The power consumption of the feedwater pumps was calculated by reflecting the flow rate of feedwater, and the steam consumption of the feedwater pump driving turbines required to drive the feedwater pumps was calculated according to the power consumption of the feedwater pumps. The required flow rate of the extraction steam to the deaerator was calculated considering the thermal equilibrium in the deaerator. The inlet steam flow rate of the low-pressure turbine was calculated by subtracting the steam demand of the feedwater pump driving turbines and the flow rate of the deaerator inlet steam from the flow rate of the medium-pressure turbine exhaust steam. The flow rate at the tube side of the low-pressure feedwater heater was calculated considering the sum of steam and water flowing into the condenser, such as the drainage of the low-pressure feedwater heater, the exhaust steam of the low-pressure turbine, and the exhaust steam of the feedwater pump driving turbine. The amount of steam extracted from the low-pressure turbine was calculated according to the design conditions of the low-pressure feedwater heater (TTD and DCA). The steam excluding the extraction steam flowed into the next stage of the low-pressure turbine. The heat transfer rate of the boiler changed according to the final feedwater temperature.