A data-driven study of IMO compliant fuel emissions with consideration of black carbon aerosols
Graphical abstract
Introduction
The world's economy relies heavily on maritime transportation since more than 90% of the global trade is facilitated by marine transportation (International Maritime Organization, 2019). Because of the extensive maritime transportation activities, there is a substantial impact on air pollution. The International Maritime Organization (IMO) has been working on reducing greenhouse gases (GHG) emissions and other pollutants such as sulfur oxides, nitrogen oxidizes. The latest Marine Environment Protection Committee (MEPC) regulation, Annex VI of the International Convention for the Prevention of Pollution from Ship (MARPOL), called “2020 Sulfur Cap”, is set to globally reduce the fuel sulfur content on board from 3.5% mass to 0.5% mass outside the emission control areas (ECA). The new ambitious convention brings many challenges and opportunities for each stage of the whole shipping fuel supply chain. Towards complying with the MARPOL convention, the shipping companies and oil refineries have made various improvements.
The current standard for shipping fuel is ISO 8217: 2017 and its latest revision, which was published on Sep. 18, 2019, named as ISO/PAS 23263:2019. It defines general requirements and serves to confirm the compliant fuels of ISO 8217:2017 with maximum of 0.50% sulfur content, and it addresses quality considerations and the range of marine fuels as well. A new category, very low sulfur fuel oil (VLSFO) with sulfur content range between 0.1% and 0.5%, was introduced to serve as the blended IMO fuel oil for non-ECAs in line with ISO 8217:2017. Besides, the proven IMO 2015 ECA grade distillate fuel, marine gas oil with maximum of 0.1% sulfur content is still an available option for shipowners to comply with the 2020 Sulfur Cap. The high sulfur fuel oil (HFSO), 3.5% maximum sulfur content, is considered as an attractive option for shipping industry because of the low fuel price, but the HFSO driven vessels should be equipped with pollutant reduction devices, mostly scrubbers, to continue serving for worldwide trade under the current MARPOL convention. As a clean fossil fuel, liquefied natural gas (LNG) has been applied to marine transportation for one decade. Many new vessels adopt this technique to meet the latest IMO rule and it is widely accepted as an effective way to comply with the IMO's long-term environment prevention strategy. So far, those four fuel solutions are the most common ones for decision-makers of the global commercial fleet.
The increasingly intense greenhouse effects have brought more concerns than ever before. Motivated by its mission of “safe, secure, clean and sustainable shipping”, IMO has implemented many strategies, regulations, and rules to reduce Greenhouse Gases (GHG) emissions from ships. The major Greenhouse Gases, CO2, CH4, N2O, and O3 have been studied for years to take effective measures to limit their emissions (Brynolf et al., 2014a; Comer et al., 2017; DNV GL, 2019a; IPCC Panel, 2014; Luo and Wang, 2017; Olmer et al., 2017; Pavlenko et al., 2020; Smith et al., 2014). The Global Warming Potential (GWP) was firstly proposed by Intergovernmental Panel on Climate Change (IPCC) and the 100-year GWP (GWP100) was adopted by the Nations Framework Convention on Climate Change and its Kyoto Protocol (IPCC Panel, 2014). However, black carbon aerosol (BCA) has not been widely considered by the shipping industry and related research. Among all particulate phase species, BCA has its uniqueness: stable at high temperature, strong absorption of solar radiation, and insolubility in water, alcohol and other liquids (AMAP, 2015). It is worth noting that an individual soot particle can be aggregated to form external structures, which is subject to forming a mixture of coated particles to reduce the albedo of the surface and to contribute to a continuous warming effect (AMAP, 2015). As the dominant form of light-absorbing particulate matter in the atmosphere, BCA emission has been linked with negative influences on earth's climate change, especially on the vulnerable Arctic region (IPCC Panel, 2014; Sharafian et al., 2019). One recent study (Olmer et al., 2017) pointed out that BCA is the second largest contributor to ship-induced GWP emissions, larger than CH4 and N2O; Moreover, black carbon is a major contributor to the human heart and lung disease as well (Bond et al., 2013). As a result, there is no reason to ignore BCA emissions, and this paper considers it as a major pollutant for the global warming potential consequence.
In assessing the environmental impacts of shipping fuels, it is necessary to adopt a life cycle assessment (LCA) approach for the whole supply chain of alternative fuels. Several studies (Bengtsson, 2011; Bengtsson et al., 2012; Brynolf et al., 2014b) have considered the extraction of raw material, fuel production, fuel transportation and storage, and bunkering as the well to tank stage and ship operation with the produced fuel as the tank to propeller stage. An important segment of the LCA is the tank to propeller (TTP) stage which is responsible for the bulk of emissions for carbonaceous fuels and is under the direct control of the shipping industry.
This manuscript will focus on the TTP segment to provide ship fleet manager a reliable reference to estimate the fuel consumption and air pollutant emissions, including both GWP gases and non-GWP gases, during the cruising mode in non-SECAs by adopting IMO 2020 compliant fuel options.
Section snippets
Relevant works
Accurate determination of shipping fuel emissions is critically important in benchmarking and accomplishing the long-term carbon reduction goal. To show a more reasonable estimation of the shipping fuel consumption and ship exhaust gas emissions, this work thoroughly searched the relevant works on the topic. The Marine Environment Protection Committee (MEPC), a subcommittee of IMO, has been working to streamline the process of collecting and calculating fuel combustion data. In one of the early
Description of methodology
As previously mentioned, the bottom-up approach is more reliable than the top-down method since it deals with more uncertainties. Fig. 1 is a flowchart showing the key tasks and collected data in the proposed methodology. We have compared all the milestone works of this field, and constructed the fuel consumption and shipping emission models by covering more operational uncertainties (adverse weather impacts for ship cruising, hull fouling effects for shipping fuel consumption and ship draught
Results and discussion
Fig. 2 shows the fuel consumption and shipping exhaust gas emissions contributing to global warming potential for the six ship types and five designated fuel options under IMO 2020 Sulfur Cap. In general, the total values of fuel consumption per nautical mile for container ships surpass those of the other five ship classes; while the GWP related gas emissions show the same trend as well. Focusing on emission amounts only, CO2 emissions consistently account for more than 90% among the four GWP
Case study
The proposed mathematical models for fuel consumption and GWP gas emissions are employed on a specific case for trans-ocean cruising from Houston (located in the North America ECA) to Rotterdam (located in North Sea SECA) from Oct. 1, 2019 to Oct. 31, 2019, aiming to find an optimized fuel option by minimizing the fuel consumption and environmental impacts.
Based on the AIS collected data, there were 234 ships navigating from Houston to Rotterdam during Oct. 1 2019 to Oct. 31 2019. The total
Conclusions
Towards enhancing the sustainable development of the shipping industry, fuel economy and safety concerns are among the most important factors to create future roadmaps for the operation and the growth of the global ship fleets. Focusing on optimizing calculations of shipping fuel consumption and ship exhaust gas emissions, this study provides a holistic bottom-up methodology by integrating and evolving several approaches to reduce the uncertainties. To our knowledge, this manuscript is the
CRediT authorship contribution statement
Chenxi Ji: proposed the approach, carried out the calculations, and developed the preliminary version of the manuscript. Mahmoud M. El-Halwagi: provided guidance to the development of the methodology and the analysis of the results. He also edited the manuscript.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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