## 4 Modeling
### Integrated System Modeling
The 14.12 kg/s feedwater from CFPU enters the ECO of WTE boiler and is increased from 181.0 \({}^{\circ}\)C to 254.4 \({}^{\circ}\)C. The LMTD of SH and ECO is dropped after the system combination, leading to their heat transfer area expansion. The heat source of PAH1 and PAH3 in hybrid design remains unchanged, while that of PAH2 and SAH alters from the extraction steam of ST to the feedwater from the DEA of CFPU. The outlet air parameters of each section of APHs remain invariant. Thus, their parameters (cold side) are dismissed. The parameters of APHs in the new WTE system are described in Table 13. Since the working fluid mass flow of PAH1 and PAH3 varies, their operation state is changed. The variation in the heat transfer condition of APHs results in their LMTD reducing and area increasing. The mass flow variation of each extraction steam stage (stage 1-8) of CFPU before and after system combination is exhibited in Figure 4. With the system integration, the saturated steam from WTE boiler drum is transported to the extraction steam of RH2 of CFPU. Therefore, the second stage extraction steam flow reduces, and the power output increases. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{1}{c}{**Parameter**} & **Unit** & **PAH1** & **PAH2** & **PAH3** & **SAH** \\ \hline \multirow{4}{*}{Hot side} & Inlet/outlet fluid & - & Condensate/ & Feedwater/ & Steam/ & Feedwater/ \\  & Inlet/outlet pressure & MPa & 4.30/3.90 & 1.09/0.99 & 4.50/4.30 & 1.09/0.99 \\  & Inlet/outlet temperature & \({}^{\circ}\)C & 178.5/37.7 & 180.3/32.4 & 257.4/178.5 & 180.3/22.2 \\  & Mass flow & kg/s & 0.56 & 4.45 & 0.56 & 1.91 \\ \hline \multirow{4}{*}{Hot side} & LMTD & \({}^{\circ}\)C & 66.7 & 5.4 & 22.7 & 10.4 \\  & Heat load & MW & 0.33 & 2.79 & 1.13 & 1.28 \\ \hline \hline \end{tabular}
\end{table} 
Table 13: Variation in the APHs of WTEU in the integrated design. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{1}{c}{**Comparison**} & \multirow{2}{*}{**Unit**} & \multicolumn{3}{c}{**Initial Design**} & \multicolumn{2}{c}{**Integrated Design**} \\ \cline{3-6}  & & & **ECO** & **SH** & **ECO** & **SH** \\ \hline \multirow{4}{*}{Cold side} & Inlet/outlet fluid & - & Feedwater/ & \begin{tabular}{c} Saturated \\ steam/ \\ superheated \\ steam \\ steam \\ \end{tabular} & Feedwater/ & \begin{tabular}{c} Superheated \\ steam/ \\ feedwater \\ steam \\ \end{tabular} \\ \cline{2-6}  & Inlet/outlet pressure & MPa & 5.30/4.50 & 4.50/4.10 & 5.30/4.50 & 4.24/4.04 \\  & Inlet/outlet temperature & \({}^{\circ}\)C & 130.1/254.4 & 257.4/400.0 & 181.0/254.4 & 308.4/400.0 \\  & Mass flow & kg/s & 14.19 & 13.50 & 14.12 & 30.76 \\ \hline \multirow{4}{*}{Hot side} & Inlet/outlet fluid & - & \begin{tabular}{c} Flue gas/ \\ flue gas \\ \end{tabular} & \begin{tabular}{c} Flue gas/ \\ flue gas \\ \end{tabular} & \begin{tabular}{c} Flue gas/ \\ flue gas \\ \end{tabular} & \
\begin{tabular}{c} Flue gas/ \\ flue gas \\ \end{tabular} &
\begin{tabular}{c} Flue gas/ \\ flue gas \\ \end{tabular} \\  & Inlet/outlet temperature & \({}^{\circ}\)C & 382.7/189.9 & 513.5/382.7 & 342.3/189.9 & 513.6/342.3 \\  & Mass flow & kg/s & 35.61 & 35.61 & 35.61 & 35.61 \\ \hline \multirow{4}{*}{Hot side} & LMTD & \({}^{\circ}\)C & 89.7 & 119.3 & 34.50 & 65.9 \\  & Heat load & MW & 7.91 & 5.60 & 4.76 & 7.29 \\ \hline \hline \end{tabular}
\end{table} 
Table 12: Comparison of the ECO and SH between the initial and integrated designs.