# Optimized Water Distillation Layout for Detritiation Purpose
## 3 Process Simulations
### Thermal Vapor Recompression  
The typical scheme of a TVR concept is presented in Figure 3. Exiting the top of the column, the distillate is sucked by the ejector, which is fed with a motive steam flow rate. Thermodynamic conditions of the mixture exiting the ejector are upgraded and used in the reboiler as a heat source. This configuration is particularly appropriate when using water, as the case of the EU-DEMO water CPS. However, focusing on the water CPS, a fundamental figure of merit in the assessment of this HPAD is the amount of the required motive steam flow rate. The best condition should be the case for which the flow rate would equal the bottom flow rate to be sent to WDS. In this case, the CPS itself accomplish with the refilling task. Instead, if the motive steam flow rate would be higher than the bottom throughput, unbalanced conditions would occur requiring the recirculation of some tritiated water that would increase complexity and tritium inventory of the system. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Compressor Outlet Pressure (kPa)** & **Compressor Outlet Temperature (\({}^{\circ}\)C)** & **Compressor Net Power Required (kW)** & **Condenser Power (kW)** & **Required Heat Transfer Area of Reboiler (m\({}^{2}\))** \\ \hline
15 & 92.25 & 55.19 & 55.40 & 81.12 \\
20 & 127.81 & 98.07 & 98.34 & 29.54 \\
25 & 156.94 & 133.28 & 133.57 & 19.36 \\
30 & 181.75 & 163.49 & 163.79 & 15.01 \\
35 & 203.45 & 190.12 & 190.41 & 12.56 \\
40 & 222.80 & 213.99 & 214.29 & 10.98 \\
45 & 240.28 & 235.99 & 236.27 & 9.92 \\
50 & 256.27 & 255.82 & 256.10 & 9.05 \\
55 & 271.01 & 274.50 & 274.78 & 8.42 \\
60 & 284.70 & 291.79 & 292.07 & 7.89 \\
65 & 297.49 & 307.98 & 308.27 & 7.44 \\
70 & 309.50 & 323.23 & 323.52 & 7.07 \\
75 & 320.83 & 337.66 & 337.95 & 6.75 \\
80 & 331.56 & 351.37 & 351.66 & 6.47 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: MVR CPS: parametric analysis over the compressor outlet pressure. Figure 2: CPS process simulator: scheme of the MVR and main results. The key component of the TVR concept is the ejector. Such a component is not included in the default model library of Aspen Plus; thus, an ejector model was developed using the momentum balance as described by [PERSON] (2017). The model, presented in Figure 4a, consists in two feed lines, SUCTION for the suction gas and STEAMIN for the motive gas, as well as a MIXER component, simulating the ejector itself, an outlet line, STEAMOUT, and the CALCULATOR. The latter implements the momentum balance model. Figure 4b presents a schematic view of the ejector, showing the main notation adopted in the modelling. It employs the design curves for optimum single-stage ejector, presented by [PERSON] and [PERSON] (2017) and reported by [PERSON] (2017). For different area ratios between nozzle throat (\(t\)) and mixing section (point 2), \(A_{2}A_{t}\), expressed as:  
\[A_{2}A_{t}=\frac{A_{2}}{A_{t}} \tag{2}\]  
where \(A\) is the flow area, and the design curves (2017, 2017) provide the ratio of suction (\(b\)) to motive pressure (\(a\)), \(p_{b}p_{a}\), over the entrainment ratio, \(w_{b}w_{a}\), and over the maximum compression ratio between suction and outlet (point 3), \(p_{3}p_{b}\). The three ratios are defined as:  
\[p_{b}p_{a}=\frac{p_{b}}{p_{a}} \tag{3}\]  
Figure 4: Steam ejector: (**a**) modelling; (**b**) main notation. Figure 3: Typical scheme of a TVR HPAD. \[w_{b}w_{a}=\frac{w_{b}}{w_{a}} \tag{4}\]  
\[p_{3}p_{b}=\frac{p_{3}}{p_{b}} \tag{5}\]  
where \(p\) is the pressure, and \(w\) is the mass flow rate. Given the desired ejector outlet pressure (\(p_{3}\)) and the suction gas pressure (\(p_{b}\)), the CALCULATOR computes \(p_{3}p_{b}\), and, employing the design curves, the \(p_{b}p_{a}\) is derived for a specific area ratio. From this ratio, the needed motive gas pressure is calculated and imposed to the STEAMIN feed line (see Figure 4a). Starting from the calculated \(p_{b}p_{a}\), and assuming the same area ratio, the CALCULATOR computes the \(w_{b}w_{a}\) employing the design curves reported in [29; 30].