Decarbonisation Technology - May 2023 Issue

HFO, a thick viscous oil with a high sulphur content, is the primary fuel used within the shipping industry (72%) (Mallouppas & Yfantis, 2021). When combusted, HFO releases pollutants such as COx, NOx, and SOx, and PM (Mallouppas & Yfantis, 2021), (Wu, et al ., 2018), (Yeh, Shen, Cheruiyot, Nguyen, & Chang, 2022). PM 2 . 5 particles are of particular concern to human health, as they are small enough to lead to illnesses such as asthma, chronic obstructive pulmonary disease (COPD), coronary heart disease, stroke, and lung cancers (Taskforce for Lung Health, 2022), (Akhbarizadeh, et al ., 2021). Emissions of PM 2 . 5 from typical container ships are particularly high at 3.15 ± 0.39 g per kg of combusted HFO (Wu, et al. , 2018), which consume approximately 1,120 kg of fuel per hour at 25% engine power, emitting an estimated 3.53 kg of PM 2 . 5 particles into the atmosphere per hour (Aijjou, Bahatti, & Raihani, 2019). The shipping industry is estimated to be the source of 13% of the world’s SOx emissions (Balcombe, et al ., 2019). The use of LSFO can mitigate these emissions; however, this comes at an increased financial cost. Compounding the emissions of PM 2 . 5 are nitrous oxides, NOx, which are GHGs with a global warming potential (GWP) of GWP 20 = 30 – 33 when emitted from ground sources (Lasek & Lajnert, 2022). Furthermore, exposure to NOx has been linked to cardiovascular problems and higher rates of respiratory issues (Anenberg, et a l., 2017), (Faustini, Rapp, & Forastiere, 2014). In 2015, the International Maritime Organization (IMO) implemented stricter restrictions of a maximum of 0.10% m/m (mass by mass) sulphur content for ships operating in the Emission Control Areas (ECAs) as designated under Regulation 14 of MARPOL Annex VI (IMO, 2015), (IMO, 2023). This includes areas such as the North Sea, the Baltic Sea, the US/Canadian coast, and the US Caribbean area. Furthermore, controls on SOx emissions were expanded outside ECAs in 2020, with a new regulation limiting the sulphur content in fuel oil to 0.50% m/m (IMO, 2020). This regulation aims to reduce the overall SOx emissions from ships by 77%, leading to an annual reduction of approximately 8.5 million metric tonnes of SOx (IMO, 2020b). The industry’s response to these regulations has been varied (Cuong & van Hung, 2020),

(Saez Alvarez, 2021). Many companies transitioned to low-sulphur fuel oils, such as MGO and ultra-low-sulphur fuel oil (ULSFO), while others adopted alternative fuels like LNG, which produce fewer SOx emissions. Some chose to install exhaust gas cleaning systems, or scrubbers, on their vessels, enabling them to continue using high-sulphur fuel oil (HSFO). Additionally, several companies implemented slow steaming to lower fuel consumption and emissions (Faber, 2012), while others optimised their fleets by replacing older, less efficient vessels with newer, more environmentally friendly alternatives. These combined efforts have enabled the shipping industry to respond effectively to the IMO’s stringent SOx regulations. Alternative shipping fuels LNG makes up approximately 2% of fuel use in the shipping industry (see Figure 1). It is proposed as one of the fuels of the future for shipping, as it produces significantly lower pollutants than fuel oils such as HFO. When burnt, it has substantially reduced emissions: PM by more than 95%, NOx by more than 80%, and SOx by more than 90% (T&E, 2016). However, LNG is liquified methane with a GWP 28 times larger than CO 2 (T&E, 2016). A key issue with LNG ships is ‘methane slip’, the escape of unburned methane from marine engines. One study places methane slip at approximately 7 g per kg LNG burnt at higher engine loads, with a range of 23-36 g per kg at lower engine loads (Ahmadi Ghadikolaei, Cheung, Yung, & Shun Cheung, 2016). Transport and Environment (T&E), an NGO, highlighted that LNG might not effectively reduce GHG emissions due to methane slip, (Ricardo, 2016). One way to reduce methane slip is to use marine engines specifically designed for LNG, along with fuel storage tanks and pipelines tailored to handle this type of fuel. This is prohibitively expensive as a retrofit option, and even new ships have a significantly higher capital cost than HFO- fuelled ships (T&E, 2016). LNG-fuelled ships can be further decarbonised by using bio-LNG or biomethane (SEA-LNG, 2022). Hydrogen shows promise as a fuel of the future for shipping. The combustion of hydrogen is a cleaner process, producing only water as a byproduct. However, due to the higher