4.1.2. IMO Conversion Emission Factor

At the 1997 MARPOL conference, research on the GHGs emitted by ships was presented via a discussion on "CO2 emissions from ships." The first GHG study performed by the IMO was presented at the 45th the Marine Environment Protection Committee [MEPC] conference. At the 56th MPEC conference, it was determined that a second IMO GHG study would be performed to examine atmospheric emissions caused by exhaust gas emissions, volatile fuel emissions, and refrigerant leaks.

One goal of this study is to calculate the CO2 emissions occurring when a hybrid power source is used in a ship. For this, only the exhaust gas emissions of the diesel engine and fuel cell were considered. Although the IPCC calculates GHG emissions by taking into account the ship type, fuel type, engine type, etc., this study used the CO2 mass conversion factor, a dimensionless constant, presented in the "Calculation of Energy Efficiency Operational Indicator Based on Operational Data" to calculate the CO2 emissions (IMO MEPC1/Circ 684 2009). GHG emissions were calculated by using the IPCC 2006 guidelines for CH4 and N2O in Table 5 (IPCC 2006), and the ISO 8217 Grades DMX conversion factor was used for CO2 [31–33].

**Table 5.** Fuel-based exhaust gas emission factors.


#### *4.2. Specifications of Components in the Fuel-Cell-Based Hybrid Power Source Test Bed*

The process flow diagram (PFD) of the fuel-cell-based hybrid power source test bed is shown in Figure 2. The test bed was composed of the following specific components: The MCFC system, energy storage system (ESS), diesel generator, load bank, and intelligent energy management system [34–37].

**Figure 2.** Process flow diagram of the test bed.

#### 4.2.1. MCFC System

The fuel cell used in the test bed was a 300 kW MCFC system composed of a stack module, an electric balance of plant (EBOP), and a machinery balance of plant (MBOP) [38]. The fuel cell system constituting the combined power source was operated with a rated capacity of 300 kW. However, a 100 kW output was used in a practical test bed. The MBOP was pretreated to make a better chemical reaction between the fuel gas and air, which concludes a pre-former, heater, humidifier, valves, pump, and blower [39]. The specifications are listed in Table 6.


**Table 6.** DFC300 MA system specifications.

The peripheral equipment needed by the fuel cell system is shown in Figure 3. It includes a fuel injection part for supplying natural gas, a potable water injection part for producing ultrapure water, a part for emitting drainage water resulting from the production of ultrapure water, and a nitrogen/mixed gas injection part for protecting the stack. The air injection and exhaust gas emission parts were at the top of the MBOP. Two exhaust fans were installed within the MBOP [40].

**Figure 3.** Configuration diagram of peripheral equipment for DFC300 MA.

The power generation concept of the fuel cell system is shown in Figure 4. The system was composed of a heat-up operating mode, which increases the initial temperature of the fuel cell stack module, a ramp-up operating mode, which increases the power to the rated output for actual power generation, and the operation mode, which produces the rated output.

**Figure 4.** Concept of Power generation for fuel cell system.

4.2.2. Energy Storage System (ESS)

The energy storage system is the electricity storage device, which uses electricity in the battery generated by the fuel cell stored. As shown in Figure 5, it is composed of a secondary battery and power conditioning system (PCS) [41].

**Figure 5.** Basic diagram for the energy storage system (ESS).

A lead-acid battery was used for the ESS in the test bed, and it was built using the bidirectional connection system, of which the specifications are listed in Table 7. The PCS has functions for checking the state of charging (SOC) of batteries in real time and controlling the temperature, current, and voltage to enable the system to be operated in a stable manner. It also has functions for surge protection, automated prevention of overcharging/overload, overvoltage alarms, and overvoltage prevention.


#### **Table 7.** ESS general battery and inverter specifications.

#### 4.2.3. Diesel Generator System (DGS)

The 50 kW synchronous generator used in the test bed is a revolving-field-type generator which uses a permanent magnet. Its specifications are given in Table 8.


**Table 8.** Hybrid test bed and generator specifications.

#### 4.2.4. Load Bank

The load bank is a forced air-cooled load bank with a rated capacity of 300 kW. It has high resistivity and experiences little change in resistance due to temperature increases. It uses an iron-chrome type 2 heating wire (FCHW-2). The load bank was used in the test bed to provide the electrical load for testing power sources, such as the generator or the uninterruptable power supply. The specifications

of the load bank are listed in Table 9. The resistance of the load bank was connected in parallel to allow the load capacity to be adjusted.


**Table 9.** Load bank specifications.
