3.2.2. Tank to Wake Inventory Analysis

The case study vessel is the first LNG-fueled bulker, M/V *Ilshin Green Iris,* which was constructed by Hyundai Mipo Dockyard as a new generation of an environmentally friendly project in July 2016. The vessel obtained a dual class of Lloyd's Register and Korean Register in environmental engineering and complied with the International Gas Fuel (IGF) code [46]. The specification of the vessel is summarized in Table 5.


**Table 5.** Specification of the case study vessel.

The vessel is engaged in a regular domestic service in South Korea. Figure 6 illustrates the regular domestic route of the vessel. The sailing route is between the Donghae Port and Gwangyang Port and the distance between the two ports is 271 nautical miles (502 km). Based on the operating profile, four voyages on average are completed each month.

**Figure 6.** Sea Route of Case Study Vessel [42].

The ship can be operated using three types of fuels: LNG, HFO and MGO. Taking into account IMO sulfur regulation 2020, the LNG and MGO, not HFO, are possible sources of fuel. Emission factors from onboard fuel consumption were determined based on IMO GHG study as shown in Table 6 [47].


**Table 6.** Emission factors from LNG and MGO consumption. Data from [47].

Above table shows that the amount of CO2 from LNG is 14.3% lower than that of MGO, while LNG produces 833 times more methane (CH4) than MGO during combustion. Given the significant impact of CH4 on GWP, it can be perceivable that LNG may have a negative impact on GHG. On the other hand, emissions associated with NOX and PM from LNG are only about 16.0% and 18.6% of MGO respectively. SO2, which contributes to AP, is produced from MGO combustion only. The WtW analysis is determined by the combination between the WtT and TtW analyses.

Tables 7 and 8 show the emission data used for the analysis. Those data associated with the LNG production to the LNG carrier transport was adopted from a previous research by [13]. It was found that the production process has contributed to significantly emission of carbon dioxides (CO2) compared to other pollutants. The same trend was also found in purification and liquefaction processes. CH4 emission caused by the methane composition in the natural gas from the processes are notable. Methane slip was added to the bunkering operation by 0.0361% [14]. Emissions of the bunker truck are obtained from GaBi database. LNG carrier is considered to use the boil-off gas from the cargo LNG. Since the LNG does not contain sulphur, there is no SOX emission. Other emissions from the LNG carrier are determined along with the transport distance. Information of LNG terminal storage and bunkering operation was obtained from a research by [20].

Emissions by the MGO supply pathway between well and refinery were referred from a research by [19]. Since crude oil tanker is considered to use MGO fuel, NOX and SOX emissions are larger than LNG carrier. Refinery process also produce large amount of SOX and NOX emissions rather than LNG purification and liquefaction process. Emissions in MGO terminal storage and bunkering operation are the same as LNG but no methane loss was involved [20].



#### *J. Mar. Sci. Eng.* **2019** , *7*, 359


 **8.** Emissions from MGO supply pathway.

**Table**

*J. Mar. Sci. Eng.* **2019** , *7*, 359
