## 2 Materials and Methods  
### Thermodynamic Modeling and Validation  
The power plant considered in this study is an USC coal-fired power plant located in the Netherlands and commissioned in 2015. The 730 MW\({}_{e}\) power plant has a net electrical efficiency of 45%. The power plant is fed with coal that will be crushed in one of the four roller mills. When the particles of the coal are little enough they will be taken by the primary air to one of the four low-NO\({}_{x}\) burners in the burner row of that mill. Thus, there are four burner rows of four burners in an opposed-type arrangement in this 1550 MW\({}_{th}\) boiler. The combustion air is pressurized by two forced-draught (FD) fans and passes through a rotary air preheater to recuperate energy from the flue passes. After combustion, the flue gasses are forced through a state-of-the-art flue gas treatment (FGT) system by an induced draught (ID) fan. The FGT exists for a selective catalytic reduction (SCR) denitrification system, an electrostatic precipitator (ESP) to remove the dust, and a wet scrubber to reduce the SO\({}_{x}\) emissions. The USC boiler contains an economizer, three super heaters, and two reheaters, and the walls are the evaporator (\"evaporator \" is the customary term for the radiative heat exchanger in the furnace, although the cycle is supercritical in this case and, therefore, does not present an evaporation phase as such). The feedwater that arrives in the economizer comes from the condenser, and between the condenser and the economizer, the feedwater flows through five low-pressure preheaters, a deaerator, and three high-pressure preheaters. The feedwater is pressurized by several pumps after the condenser and after the deaerator. The steam, 252.2 bar and 600 \({}^{\circ}\)C, coming from the outlet of the super heaters, flows through a high-pressure steam turbine. In the reheaters, the steam still has a pressure of 61 bar and is upgraded to 620 \({}^{\circ}\)C before the steam is led to the intermediate pressure steam turbine. After the intermediate pressure steam turbine, the steam flows to one of the two double-flow low-pressure steam turbines. Afterwards, the used steam is condensed in one of the two water-cooled condensers. In total, there are nine extractions out of the steam turbines to heat the feedwater in the preheaters. The water steam cycle is visualized in a simplified overview in Figure 1.  
The power plant is modeled with Thermoflex(r). Thermoflex(r) is a high-fidelity fully flexible engineering software application for modeling and simulating the thermodynamic behavior of power production facilities (CCGT, CFPP, nuclear, renewables, etc.) and is the most flexible and adaptable package of Thermoflow(r). The software is state-of-the-art heat and mass balance software featuring a graphical user interface. In the design mode, the model can be made by using the over two hundred different predefined components. After component selection and connection, the default values of the components can be adapted and Thermoflex(r) computes the full heat and mass balance and the performances of the entire system, based on a series of thermodynamic design assumptions. Switching to the next mode, Thermoflex(r) translates the initial basic thermodynamic design assumptions into physical realistic components. Afterwards the model can be frozen in off-design mode and static simulations can be performed. The software calculates first all the pressures in the system, and when an equilibrium is reached, all the flows will be calculated followed by all the other parameters. With the ELINK application, the model can be made quasi-dynamic [23; 30; 37]. The basic model illustrated in Figure 1 corresponds to the current, coal-based operation, while the extended model illustrated in Figure 2 also comprises the additional steam extractions from the three tapping points (outlet HP, outlet IP, and LP turbines) to an intermediate closed loop via heat exchangers (elements 9 to 11) required for combined heat and power (CHP) production.