*2.3. Description of Steam Methanol Reforming-Based System*

Figure 3 shows the block diagram of the steam methanol reforming system combined with HT-PEMFC and CCS on board a ship. The integrated system consists of five main unit/sub-systems: Reformer for producing reformate gas, combustor for providing heat to the reformer, HT-PEMFC for power generation, CO2 capture unit, and CO2 liquefaction system for storage. Unlike the steam methane reforming system, the WGS reactor is not added because the hydrogen rich gas produced in steam methanol reforming includes CO contents tolerable to the HT-PEMFC in this study.

**Figure 3.** Block diagram of steam methanol reforming-based system.

As shown in Figure 4, methanol and water are mixed at 25 ◦C. The water and methanol mixture is preheated by the steam generated at the HT-PEMFC at HEX-1 and further vaporized by the reformate gas stream (stream R1) from the reformer at HEX-2. Then, H2 rich reformate gas is produced in the reformer. The main reactions that take place in the reformer are as follows [52]:

$$\text{CH}\_3\text{OH} + \text{H}\_2\text{O} = \text{CO}\_2 + 3\text{H}\_2 \quad \Delta\text{H}\_{298} = +49.7 \text{ kJ} \text{mol}^{-1} \tag{6}$$

$$\text{CO} + \text{H}\_2\text{O} = \text{CO}\_2 + \text{H}\_2 \quad \Delta \text{H}\_{298} = -41 \text{ kJ} \text{mol}^{-1} \tag{7}$$

$$\text{CH}\_3\text{OH} = \text{CO} + 2\text{H}\_2 \quad \Delta \text{H}\_{298} = +90.7 \text{ kJ} \text{mol}^{-1} \tag{8}$$

Equation (6) represents the steam methanol reforming reaction, Equation (7) represents the water gas shift reaction, and Equation (8) represents the methanol decomposition reaction. Only the WGS reaction is exothermic and the other two are endothermic. The operating temperature and pressure for the steam methanol reformer in this model are 200 ◦C and 3 bar, respectively. A S/C ratio of 1.5:1 was selected based on literature reviews [27,33]. Reformate gases containing H2, CO2, CO, and CH3OH exiting HEX-2 are further adjusted to 160 ◦C at HEX-3 and 1.1 bar by PCV-1. Then, the reformate gas is fed to the anode side of the HT-PEMFC for power generation. As off-gas (stream O1) from the fuel cell contains H2 unreacted in the fuel cell and CH3OH unconverted in the reformer, the fraction of these is supplied to the combustor to produce heat. The remaining is recycled to the anode inlet stream. The exhaust gas stream (E1) from the combustor preheat air is supplied to the combustor, and the remaining heat in the exhaust gas is recovered in HEX-5. The exhaust gas stream (E4), from which most water is removed in Sep-1, is fed to the CO2 capture unit, which is modeled as a "black box," in the same way as the steam methane reforming system.

**Figure 4.** Process flow diagram for steam methanol reforming-based system.

The captured CO2 stream (E5) is compressed to 14 bar by Comp-1, -2, and liquefied passing through HEX-7. Unlike the steam methane reforming system, a separate liquefaction cycle using ammonia as refrigerant was modeled. The liquefied CO2 is separated in Sep-2 and stored in a temporary tank on board the ship. The operating and design parameters of the steam methane and methanol reforming system combined with HT-PEMFC, CO2 capture, and liquefaction systems are presented in Table 3.


### **Table 3.** Base condition of simulations.

Note: For comparison purpose, the mass flow rate of total emitted CO2 of the steam methanol reforming-based system is adjusted to have the same value as that of the steam methane reforming-based system.
