*4.1. Well to Tank Impact Assessment*

The level of GWP from the WtT phase is presented in Figure 11. Since there are no international pipelines in South Korea, the only way to import LNG and MGO fuel is by sea transport. The distances from the resource-export countries determine the sea transport distance and the emissions will vary accordingly.

**Figure 11.** GWP values from supply chain of LNG and MGO.

The simulation results have revealed that emissions from the ocean transport of fuels account for significant portions in this stage. In particular, the LNG carrier contributes to the largest portion of CO2 equivalent gas in the LNG supply chain. For oil tanker transportation, the route from Saudi Arabia to Korea is not the largest, but the MGO route from the US to Korea produces the largest GWP. LNG supply paths, on the other hand, typically generate less GWP than MGOs.

As explained in the LCA modelling part, crude oil tanker contains whole crude oil than refined MGO. It contributes to the GWP products from the tanker transport; however, it requires to be considered that the crude oil is refined to several energy sources.

Figure 12 illustrates the detail GWP value by LNG supply chain from Qatar to South Korea and MGO supply chain from Saudi Arabia to South Korea for each process.

**Figure 12.** GWP by LNG and MGO supply chain from Middle East to South Korea.

In the LNG supply pathway, next to the ocean transport process, purification and liquefaction process also emits considerable amount of GWP, 5.69 <sup>×</sup> 104 kg CO2 equivalent per 1.0 <sup>×</sup> 10<sup>7</sup> MJ of LHV. Energy usage and refrigerants losses in these processes contribute substantially to emissions. GHG emissions from utilities for LNG extraction, production and pipelines account for the third part, equivalent to 2.54 <sup>×</sup> <sup>10</sup><sup>4</sup> kg CO2 per 1.0 <sup>×</sup> <sup>10</sup><sup>7</sup> MJ LHV.

Diesel trucks emit GHGs from LNG terminals to bunkering ports. The ratio of GWP to total amount is not impressive, but the amount corresponds to more than 1 ton of CO2.

Methane slip during bunkering operation produces approximately 4 tons of CO2 equivalent energy per 1.0 <sup>×</sup> 107 MJ. In case of the MGO fuel, the production and transport process emits a significant amount of GWP, 1.60 <sup>×</sup> 105 kg CO2 equivalent per 1.0 <sup>×</sup> 107 MJ of LHV. Refining operation also produces considerable amount of the greenhouse gas, 7.5 <sup>×</sup> <sup>10</sup><sup>4</sup> kg CO2 equivalent per 1.0 <sup>×</sup> <sup>10</sup><sup>7</sup> MJ of LHV. The refining operation also produces a considerable level of GHGs equivalent to 7.5 <sup>×</sup> <sup>10</sup><sup>4</sup> kg CO2 per 1.0 <sup>×</sup> <sup>10</sup><sup>7</sup> MJ LHV. AP, PM, POCP and EP results are presented with Figure 12.

The results show that the dominant AP value in the LNG supply chain is attributed to the fuel production stage, whereas the ocean transport of the MGO produces the AP substantially. The result reveals that the dominant AP value in the LNG supply chain is to the fuel production phase. The PM emissions show same aspect with the AP. MGO-Refining process produces the SO2 equivalent and PM next to the ocean transport. POCP and EP pertinent to the LNG supply chain are relatively lower than the environmental potentials from MGO supply chain. For POCP, ocean transport of the MGO produces the most pollution and the MGO refining process makes a second contribution. Regarding EP, the largest contributor is still ocean transport however production process is second. Referring to the results in Figure 13, ocean transport is shown a key factor to control the local pollutants.

**Figure 13.** AP, PM, POCP and EP from the case study.

*4.2. Tank to Wake Impact Assessment*

Figure <sup>14</sup> shows GWP by the ship operation with 1.0 <sup>×</sup> 107 MJ of the LNG fuel and MGO fuel.

**Figure 14.** Global Warming Potential from Well to Tank Life Cycle.

GWP by the LNG combustion is approximately 1.08 times larger than MGO fuel's case. In case of LNG fuel combustion, methane slip from LNG fuel consumption raises the value of the CO2 equivalent considerably. Table 9 exhibits the amount of carbon oxides and methane emissions associated with the on-board fuel combustion process. It is found that the methane emission levels are significantly different in both cases. Although the CO2 emission is larger at MGO combustion, methane emission expressively contributes total amount of GWP during LNG fuel consumption.


AP, PM, POCP and EP during fuel consumption are presented in Figure 15. Values of AP, PM, POCP and EP from the MGO fuel consumption are remarkably larger than LNG fuel consumption case. The sulphur content of 0.1% in MGO contributes to the increase in the AP. It is possible to determine that LNG is clean energy based on the analysis results.

**Figure 15.** AP, PM, POCP and EP from Fuel Consumption [log scale].

#### *4.3. Well to Wake Impact Assessment*

Figure 16 shows the simulation results of the GWP from the WtW phase.

The overall GWP of MGO in the route of U.S.to South Korea is revealed the largest among the study cases due to the highest levels of the emissions from the supply chain and consumption. GWP during fuel consumption is lower in the MGO case, but the difference between GWPs in the fuel supply chain is much larger. The emission ratio between the supply chain and the onboard consumption is presented in Table 10.


**Table 10.** Ratio of emissions from the supply chain and consumption.

Table 10 shows that supply chain emissions are high in the U.S. to South Korea because the sea transport distance of fuel is longer than that in the Middle East to South Korea. In WtT analysis, ocean transport is a significant part of the supply chain.

Figure 17 provides the analysis results for AP, PM, POCP and EP emissions in WtW phase. Except for PM, emissions generated at the WtT stage are more dominant than the TtW stage. In particular, MGOs produce significantly more local pollutants than LNG. The level of GWP is similar between the two fuels, but AP, PM, POCP and EP are about 5–7 times larger in MGO cases than LNG cases.

**Figure 17.** AP, PM, POCP and EP by Well to Wake Analysis.
