Current Issue

As greenhouse gases emitted from ships were found to be one of the causes of global warming, regulations to reduce carbon dioxide, one of the greenhouse gases, were implemented led by the IMO. Therefore, in order to meet the strengthening regulatory standards, the shipping and shipbuilding industries are meeting regulations by converting ship fuel oil, installing Selective Catalytic Reduction (SCR) or Exhaust Gas Recirculation (EGR) systems, or Engine Power limit (EPL) system (Kim and Choi[2023a]; Carlo et al.[2013]). In addition, the Coast Guard manages ship emissions through onboard inspections for domestic ships, but actual measurements such as the operation of various emission devices and fuel standards require a lot of time and effort, and also depend on the ship's busy operation schedule. Due to restrictions, most inspections are carried out on paper, which limits management. In order to reduce greenhouse gases from ships, regulations have been strengthened to change air pollutant generation into actual inspections, and a monitoring system for each sea area using Coast Guard vessels has been established to conduct actual site inspections. Research was conducted to ensure data-based management, and that technological development and legal support are needed to introduce environmentally friendly ships in the short and long term. In addition to status surveys and research on actual reductions, various studies on technology and regulations were conducted. In addition to technical research, such as research on carbon dioxide reduction technology considering the operating mode of ships or research that can increase the ship energy efficiency index, it is also related to regulations (Kim and Choi[2023b]), so when the tonnage limit is lowered from the current carbon intensity regulation, it can be used on practice ships or domestic ships. There is also research showing that government ships may also be subject to regulation, and if exempt ships are included in the current regulations, regulation-related legislation or standards must be prepared, and research has also been conducted on the limitations of the current greenhouse gas reduction regulations. In a previous study (Lim et al.[2023], ro-ro passenger ships were selected among 11 regulated ship types for ships exempt from the ship energy efficiency index regulation and compared, and the comparison ship types were determined based on the purpose and shape of the ship. First, the type of ship that meets the purpose of the ship was selected as it corresponds to the SPS Code, one of the IMO Codes for ships performing official duties or ships operating for special purposes. In addition, in order to confirm the degree to which the shape of the ship is similar, ship types with similar square coefficients were identified through various dimensions of the ship, and finally, a ro-ro passenger ship was selected as the standard ship type, and the Required EEXI and Attained EEXI of the ships subject to study were compared to the Required EEXI. In connection with the studied cases of ways to satisfy EEXI, carbon intensity was calculated through IMO DCS data, which is the operation data of one of the ships under study, compared with Ro-Ro passenger ships of the same tonnage, and the carbon intensity index was reduced accordingly. That study to check what can be done(Lim et al.[2023]).

In its simplest form, the calculated annual Carbon Intensity Indicator (CII) (Kubilay[2024]) for an individual vessel refers to the ratio of the mass of carbon dioxide emitted to the total transport operations performed in a given year.

In Equation (1), "j" is the type f fuel oil, "FC_j" is the annual fuel consumption by oil type [ton], and "C_fi" is the conversion factor for each oil type to convert fuel consumption into carbon dioxide emissions [tCO₂/tFeul], and is specified EEDI (Energy Efficiency Designed ship Index) calculation guidelines (MEPC.308 (73rd)). Also representative values are 3.114 for Heavy Feul Oil (HFO), 3.206 for Marine Gas Oil (MGO), 3.151 for Light Fuel Oil (LFO), and 3.000 for Liquified Propane Gas (LPG). "Capacity" refers to ship capacity, and GT (Gross Tonnage) or DWT (Dead Weight Tonnage) is applied to each ship type. For ro-ro passenger ships, GT is used. And The IMO originally designed the CII regulation using 2008 as the reference year. However, due to the limited availability of 2008 data, the CII baseline was derived based on the operational carbon intensity performance of each ship type in 2019, and the baseline for ro-ro passenger ships was calculated through the capacity and parameters of individual ships calculated using 2019 IMO Data Collection System (DCS) data. The equation presented in the guideline is derived through regression analysis, where the collected data were used by setting the attained CII as the dependent variable and the ship's capacity as the independent variable. The parameters "a" and "c" were estimated based on the attained CII values and capacities of individual ships using the 2019 IMO DCS (Data Collection System) dataset. These parameters vary depending on the ship type and size. For the comparable ship type ro-ro passenger, the parameter values are 'a' is 7540 and 'c' is 0.578, which leads to the formulation of Equation (2) formula for calculating the 2019 reference value defined in the guidelines (G2) is as follows: Equation (2). (IMO [2021]; Resolution MEPC.333 (76) Guidelines on Operational Carbon Intensity Indicators and the Claculation Methods (CII GUIDELINES, G2).

Fig. 1. 
Grade range and Grade range Calculation formula.

In addition, in order to calculate the carbon intensity that must be met for the relevant year, the value of the reduction factor must be multiplied. This reduction factor is generally indicated as "Z" in Rule 28 of Chapter 6 of MARPOL Annex, and is defined as a coefficient that quantifies the decrease in carbon intensity compared to a designated baseline year. The annual carbon intensity of a ship's operations is a positive value representing a percentage of the required value. Based on this reduction factor, the vessel's annual operating CII allowable value is calculated as follows, and the reduction rate 'Z' has a value of 1% in 2020, 2% in 2021, and 3% in 2022. Equation (3) below is as follows, and the value calculated through this is called Required CII.

The operational carbon intensity level is based on the annual operational carbon intensity index achievement value among five grades (A, B, C, D, E) representing the highest, upper, middle, lower, and lowest grades. The rating is given through comparison of the vessel's annual operation CII achievement value and the boundary value, and the boundary is set based on the CII distribution of each individual vessel in 2019. The grade is classified through a grade range calculation formula using a vector (expressed as a dd vector) indicating the direction and distance deviating from the allowable value and the annual CII allowable value. Table 1 shows that four grade ranges can be calculated based on Ro-Ro passenger ships. The four ranges are largely divided into "Inferior boundary", "Upper boundary", "Lower boundary", and "Superior boundary" (IMO[2021];Resolution MEPC.333(76) Guidelines on Operational Carbon Intensity Indicators and the Claculation Methods (CII GUIDELINES, G1).

Similar to the previous study (Lim et al.[2023], Attained CII was calculated using the carbon intensity calculation formula for ro-ro passenger ships using data from one of the six ships under study, and ways to reduce carbon intensity accordingly were sought and confirmed. Training vessel A, the vessel subject to this study, was built in 2016 and is a vessel of over 5,000 tons that trainees board and sail in the ocean area as well as domestically. It is a ship of 5,000 tons or more and meets the carbon intensity regulation standards applied to ships sailing in the ocean area. Table 2 shows the main features of training ship A.

The carbon intensity was calculated for each year using the three years of operation information from 2020 to 2022 of training ship A. This was implemented in accordance with Chapter 6 of the Annex to the MARPOL Convention, and the degree of exhaust gas pollution was measured by measuring greenhouse gases generated from the ship. As a regulation for measurement, the annual fuel oil consumption of international sailing ships with a gross tonnage of 5,000 tons or more was calculated using Equation (1) through IMO DCS, a system that mandates reporting to the flag government. Table 3 calculates the operation data of training ship A from 2020 to 2022 and the amount of fuel consumed by the main engine and auxiliary engine according to Equation (1) and the conversion coefficient for each type of fuel. The calculated value at this time is Attained CII.

The reference CII was calculated using Equation (2), the carbon intensity calculation formula for Ro-Ro passenger ships selected as the standard ship type, and the Required CII was derived by reflecting the reduction rate for each year. The results are shown in the graph below.

As shown in the graph in Fig. 2, in 2020, a 1% reduction rate was applied in equation (2), and the Attained CII was 141.84 gCO₂/t∙nm, which was about 2.90 times higher than the Required CII of 48.84 gCO₂/t∙nm, and when calculating the grade. You can see that it is rated 'E'.

Fig. 2. 
Graph of Attained and Required CII data in 2020.

The Fig. 3 graph is data from 2021, and a reduction rate of 2% was applied for 2021. Attained CII was 143.97 gCO₂/t∙nm, Required CII was about 2.97 times higher than 48.35 gCO₂/t∙nm, and was rated 'E' when calculating the grade.

Fig. 3. 
Graph of Attained and Required CII data in 2021.

Fig. 4 applies data from 2022, and a reduction rate of 3% was applied in 2022. Attained CII was 132.49 gCO₂/t∙nm, Required CII was 2.76 times higher than 47.85 gCO₂/t∙nm, and was rated 'E' when calculating the grade. Overall, the Attained CII value is higher than the Required CII value, so the Attained CII value in 2020 and 2021 is 2.9 times higher than the Required CII value, and 2.7 times higher in 2022, confirming that the value of Attained CII is much higher than the Required CII.

Fig. 4. 
Graph of Attained and Required CII data in 2022.

Fig. 5 displays the Attained CII and Required CII for each year in a bar graph, and when calculating the grade for each year, it can be seen that all training ship A falls into the E grade. Currently, the training ship A is exempt from regulations, but if it becomes subject to regulations in the future, it will not be able to operate until a ship improvement plan is established and re-verification is performed, so preparation is needed(Li et al. [2023]).

Fig. 5. 
Comparison of CII (2020 to 2022).

Training ship A is currently not a ship subject to carbon intensity regulations in 2024, but in the future, as abnormal climates due to global warming continue to occur and in order to reduce greenhouse gases from a national perspective, carbon intensity regulations can be strengthened across all ship types in the ship field. Because there is a possibility, there is a need to reduce carbon intensity (Lim et al.[2023]). Ways to reduce the carbon intensity of ships include converting ship fuel oil to fuel with a low carbon conversion coefficient such as LNG or LPG (Jeong et al.[2024]), or reducing fuel consumption by reducing the speed of the ship, and reducing the ship's speed to the power of cube (Dan et al.[2020]). There is a way to lower fuel consumption by reducing the ship's load, which is proportional to. Among these, this study sought ways to reduce carbon intensity by considering the characteristics of training ship A. In Table 3, it can be seen that in the case of training ship A, the anchoring time is longer than the sailing time. If the anchorage time is relatively long and the voyage period is short, the voyage distance corresponding to the denominator is reduced, and the fuel consumption, which is a component in the numerator, is bound to increase because the generator and boiler are operated periodically during the anchorage period, so when calculating carbon intensity, it is high. The value comes out. Accordingly, we first compared the data with the data when the sailing distance increased.

Table 4 shows that the training ship A sailed 6,515 miles in 2023, which is 1.8 times more than in 2022, and the fuel consumption in 2023 was 821.4 tons for LSMGO and 51.5 tons for VLSFO. Based on this, the Attained CII values were compared and the Required values of the baseline Ro-Ro passenger ship were compared. When compared to CII, Attained CII was 81.66 gCO₂/t∙nm, which was 1.7 times higher than the required CII of 46.87 gCO₂/t∙nm, but it was confirmed that it was significantly reduced compared to Attained CII from 2020 to 2022, which had a relatively small sailing distance. In Fig. 6, it can be clearly seen that Attained CII has decreased. This means that Attained CII has decreased as the denominator in Equation (1) increases as the sailing distance increases.

Fig. 6. 
Comparison of CII (2020 to 2023).

According to IMO DCS Data from 2020 to 2023, training ship A has a short operating time and a long anchorage period, and even during the anchorage period, a large amount of carbon dioxide is generated due to the use of fuel due to the operation of the generator and boiler. Accordingly, this study attempted to calculate carbon intensity by applying a generator using LPG fuel with the characteristics shown in Table 5 instead of operating the generator of training ship A by LSMOG fuel using while at anchor (Lim et al.[2024]). Two LPG generators with a maximum output of 230 kW were operated to generate electricity during the berthing period, and carbon intensity was calculated by reflecting the amount of LPG consumed in the operation of the generators in fuel consumption while at berth. The biggest difference is that when a generator using diesel and LPG fuel, which is used as fuel for a generator on an existing training ship during the anchorage period, is installed, the carbon conversion coefficient is different. MGO has a value of 3.206, LFO has a value of 3.151, and propane LPG has a value of 3.000 (Lee and Nam[2017]).

According to the IMO DCS data, the average of the generator operation time while anchored in the training ship A is shown in Table 6, and the LPG consumption when operating two LPG generators was calculated by reflecting the fuel consumption per hour presented in Table 5.

Fig. 7 is a graph calculated based on the consumption in 2020. When an LPG engine is used when docking, the Attained CII is 104.85 gCO₂/t∙nm, and the Attained CII based on the consumption when using a generator using existing diesel oil when docking is It can be seen that there was a reduction of 36.99 gCO₂/t∙nm.

Fig. 7. 
Comparison of CII (Each fuel type, 2020).

Fig. 8 is a graph calculated based on the consumption in 2021. When an LPG engine is used at anchor, the Attained CII is 102.59 gCO₂/t∙nm, and the Attained CII is based on the consumption when a generator using existing diesel oil is used at anchor. It can be seen that there was a reduction of 41.38 gCO₂/t∙nm.

Fig. 8. 
Comparison of CII (Each fuel type, 2021).

Fig. 9 is a graph calculated based on the consumption in 2023. When an LPG engine is used at anchor, the Attained CII is 55.20 gCO₂/t∙nm, and the Attained CII is based on the consumption when a generator using existing diesel oil is used when at anchor. Compared to other years, it was reduced by 26.46 gCO₂/t∙nm and is calculated as 'D' compared to other years.

Fig. 9. 
Comparison of CII (Each fuel type, 2022).

When LPG Engine is used, it is significantly reduced from Attained CII from 2020 to 2023, but is still higher than Required CII, and is subject to regulation as 'E' grade from 2020 to 2022 and 'D' grade from 2023. do. This confirmed again that the carbon intensity of training ship A cannot be high because the voyage distance is short and the amount of fuel used during anchorage is large. In other words, Attained CII can be reduced by reducing the fuel consumption in the numerator part of Equation (1) or by adjusting the sailing distance in the denominator. In the case of domestic flights such as practice ship A, which has a long berth day and a relatively short sailing distance, There is a need to add new elements or adjust existing formulas. For example, the carbon intensity index is calculated by dividing the carbon intensity index while sailing and at anchor, and while at anchor, it is calculated as the fuel consumption generated per kW of the generator, or the part corresponding to the existing 'voyage distance' is calculated as the total generated output kW. Modification and supplementation of existing formulas, such as replacement calculations, are necessary.