Well-to-wheel analysis on greenhouse gas emission and energy use with natural gas in Korea

In Korea, natural gas is widely used as city gas, fuel for electricity generation, and fuel for transportation (e.g., city bus). However, the environmental impact associated with the use of natural gas in Korea has not been paid much attention to. In this study, well-to-wheel (WTW) analysis on the greenhouse gas (GHG) emissions and energy uses associated with natural gas in Korea was performed by considering every step from feedstock recovery to final use in the vehicle operation.

The raw data used in the analysis were mainly provided by Korean natural gas industry and related associations. The additional information, especially for the processes in foreign countries, was also collected by literature survey. We adopted the GREET (Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation) model as a base WTW analysis tool, which was developed by the U.S. Argonne National Laboratory. However, the WTW analysis on natural gas in Korea is far different from that of the U.S, because ~99 % of natural gas used in Korea is imported from the oversea countries in the form of liquefied natural gas (LNG). For this reason, detailed parameters in GREET were changed for Korean situation, and especially, significant modifications were made on liquefaction, LNG transportation and storage, and re-gasification processes.

As a result of the analysis, the well-to-pump GHG emissions of city gas and compressed natural gas are calculated as 25,717–30,178 and 28,903–33,422 g CO₂ eq./GJ_{Fianl_fuel}, respectively. The WTW GHG emission of compressed-natural-gas-fueled city bus is calculated as 1,348–1,417 g CO₂ eq./km. These values are relatively larger than those of the U.S., because most of the natural gas used in the U.S. is transported by pipeline in a gaseous state, which typically takes less energy and associated GHG emissions, as compared to the import of LNG in Korea. Finally, sensitivity analysis is performed on the parameters, which have either range of values among various sources or uncertainties due to lack of accurate information.

The results show that further investigation on three parameters, i.e., CO₂ venting during natural gas processing, CH₄ leakage in Korea, and CH₄ leakage during recovery process, would be helpful to further improve overall accuracy of the analysis.