# Optimized Water Distillation Layout for Detritiation Purpose
## 3 Process Simulations
### Thermal Vapor Recompression
The entrainment ratio is corrected for the temperature difference between the suction and motive gases as follows:  
\[w_{b}w_{a}C=w_{b}w_{a}\sqrt{\frac{T_{a}}{T_{b}}} \tag{6}\]  
where \(w_{b}w_{a}C\) is the corrected entrainment ratio, and \(T\) is the absolute temperature. Thus, given the suction gas mass flow rate, \(w_{b}\), the outlet mass flow rate, \(w_{3}\), and the required motive gas mass flow rate, \(w_{a}\), are calculated as:  
\[w_{3}=\left(\frac{1}{w_{b}w_{a}C}-1\right)\times w_{b} \tag{7}\]  
Figure 2:0  
Referring to the EU-DEMO water CPS, the minimum motive steam flow rate can be evaluated and compared with the flow rate sent to the WDS derived from the preliminary design of the water CPS (1.72 kg h\({}^{-1}\)) [10]. The minimum motive steam flow rate, obtained with the maximum entrainment ratio of 20, is equal to 2174 kg h\({}^{-1}\), around three orders of magnitude higher than the WDS throughput. Therefore, the simplest configuration presented in Figure 3 cannot be adopted because a residual tritiated water flow rate would result. The solution could be to split the distillate flow rate exiting the top of the column in a smaller fraction used as motive steam and a larger fraction as suction flow rate. This solution, namely the Thermal Vapor Recompression with Compressor (TVR-CMP), is conceived to reduce the flow rate at the compressor and thus, the size of this component, compared to the MVR concept. The TVR-CMP system is presented in Figure 5, where the main results of the process simulations are also reported. The layout is the same of the MVR except for the compression system. A fraction of the distillate throughput is sent to the ejector as suction flow rate. The rest is compressed through the compressor to the conditions needed for the motive steam flow rate of the ejector. Although the benefit of a lower compressor flow rate compared to the MVR, the number of components increases (two regulation valves and the ejector), and higher temperature and pressure are achieved at the compressor outlet. Taking experience from the MVR simulation, in particular regarding the reboiler size, two ejector outlet pressures were considered for the simulations of the TVR-CMP: 30 kPa and 20 kPa. Per each case, a parametric analysis assessed the effect of different ejector area ratios on size and performance of the whole system. The main results for the case of 30 kPa are summarized in Table 3 (refer to Figure 4b for the subscripts' specification). One of the objectives of the TVR-CMP concept is the minimization of the flow rate through the compressor (i.e., the motive steam flow rate, \(w_{a}\)), in order to reduce the size of this component. This condition is accomplished with an ejector area ratio (\(A_{2}A_{t}\)) of 50 but, in this case, the pressure (\(p_{a}\)) and temperature (\(T_{a}\)) of the motive steam are too high for the CPS. In particular, the safety relevant condition of sub-atmospheric operation is lost. The issue of the high temperature could be solved with a staged compression with intercooler, although it would affect the thermal energy of the ejector outlet stream and thus the size of the reboiler. Focusing on the power saving, the most promising case is the \(A_{2}A_{t}\) equal to 5, allowing the minimization of the condenser and compressor power consumption while keeping acceptable reboiler size. In this case, around 70% of the distillate flow rate is routed into the compressor. The same parametric study was repeated, assuming an ejector outlet pressure of 20 kPa, and the main results are shown in Figure 2:1 Comparing the cases of 30 kPa and 20 kPa, the required motive flow rate is lower for the lowest ejector outlet pressure, and the thermodynamic conditions of that stream are less stringent. The power consumption is around 50% lower, whereas the required heat transfer area of the reboiler is around doubled in comparison with the 30 kPa case.