# Analysis of Internal Gas Leaks in an MCFC System Package for an LNG-Fueled Ship
## CFD Simulation Method  
### Modeling and Boundary Conditions  
Figure 2 shows a 3D CAD model of the components inside the BOP, which is designed to operate the 300-kW MCFC stack. Inside the BOP is a pretreatment device used to provide fuel to the anode and oxidant to the cathode. The anode side of the BOP includes the pre-converter, polisher, humidifier, recycle blower, etc. The pre-converter converts the methane from the BOG to about 10% hydrogen to supply to the stack. The humidifier produces steam, which is supplied to the anode side of the stack for the electrochemical reaction in the stack. The polisher and recycle blower recirculate the exhaust gas at the end of the stack.  
The grid system of the package (without the external components) was created using the ANSYS Design Modeler [16] and ICAM-CFD [17]. An unstructured tetrahedron grid technique was efficiently applied to create the overall grid system. The grid cells with a prism shape were applied near a specific solid wall to resolve the relatively high velocity gradient. The uniform thickness ratios were maintained  
Figure 1: Scheme of boil-off gas (BOG) treatment system with fuel cell system for a liquefied natural gas (LNG)-fueled ship.  
Figure 2: Component locations in a molten carbonate fuel cell (MCFC) stack package.  
for the grid cell layers with different unit cells. Thus, in this analysis, approximately 20 million grid cells were used. The solution was independent from computational cell numbers.  
The louvers on the outer walls of the package room shown in Figure 3a were installed to assist in supplying air to the inside of the room to cool the equipment. The blue parts of the figure indicate the points where air is supplied to the room. The room air was set to atmospheric pressure and an ambient temperature of 25 \({}^{\circ}\)C. As shown in Figure 3b, the air heated by the devices inside the package was released through the exhaust fans installed on the roof. As shown in Figure 3b, in order to release the air at a speed of 10.3 m\(\cdot\)s\({}^{-1}\) through each exhaust pipe, the performance of the applied exhaust fan was 5000 m\({}^{3}\cdot\)h\({}^{-1}\) and the cross-sectional area of the exhaust pipes was 0.135 m\({}^{2}\). The heating surface (shown in blue in Figure 2) was set according to the specific heat fluxes for the heating area shown in Table 1. Since the package room is exposed to the outside, heat is transferred through the walls according to the surroundings; and the heat-transfer coefficient was set as 100 W\(\cdot\)m\({}^{-2}\)K\({}^{-1}\) to simulate the convective heat transfer of a weak wind. To identify the leakage in the system, fuel was modeled as leaked intentionally at the red points in Figure 4 with listed gas composition in Table 2. The leaked gas path line is traced by the CFD, and provides the supporting data to locate gas leak detectors.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Area [m\({}^{2}\)]** & **Total Heating Area [m\({}^{2}\)]** & **Heat Value [kW]** & **Heat Flux [W/m\({}^{2}\)]** \\ \hline
**Humidifier** & 1.189 & 1.515 & 1.00 & 660.1 \\ \hline
**EG-2012** & 0.326 & & & \\ \hline
**Polisher** & 1.134 & 2.651 & 2.426 & 915.1 \\ \hline
**EG-2011** & 1.517 & 7.281 & 4.00 & 549.3 \\ \hline
**Pre-converter** & 2.507 & & & \\ \hline
**FG-2008** & 1.959 & 8.368 & 2.00 & 239.0 \\ \hline
**FG-2009** & 3.902 & & & \\ \hline
**Recycle blower** & 1.865 & & & \\ \hline
**EG-4008** & 1.484 & 9.537 & 1.68 & 176.2 \\ \hline
**EG-4009** & 5.689 & & & \\ \hline
**Air heater** & 0.499 & & & \\ \hline
**Stack module** & 53.111 & 53.111 & 9.00 & 169.5 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Heat flux of the heating area of the stack package model.  
Figure 3: Conditions of the inlet and outlet of the balance-of-plant (BOP) package: (**a**) louver installation locations (inlet) and (**b**) exhaust pipe locations (outlet).