A tripartite partnership between Japanese maritime companies has achieved a 93.8% reduction in methane slip from a marine gas engine operating at 100% load in onshore testing, clearing the way for trials at sea
The results from the research, which were verified by ClassNK through a statement of fact (SOF), were achieved on a testbed engine by using an exhaust gas recirculation (EGR) system in combination with a methane oxidation catalyst system. While the results were achieved on the testbed in December 2023, ClassNK presented the SOF in a ceremony held at Sea Japan 2024 in April.
Such results are encouraging for using LNG dual-fuel engine technology in ships to achieve CO2 and greenhouse gas (GHG) emissions reductions.
Backed by Japan’s National Institute of New Energy and Industrial Technology Development (NEDO), the ongoing research is being conducted by Hitachi Zosen Corp, Mitsui OSK Lines (MOL) and Yanmar Power Technology under the Development of Methane Slip Reduction Technology from LNG Fueled Vessels by Improving Catalysts and Engines project under the Green Innovation Fund Program. The six-year project, which runs from 2021 to 2026, aims to achieve a 70% reduction in methane slip in LNG-fuelled vessels.
Methane slip is a bugbear for LNG dual-fuel engines, particularly for two- and four-stroke engines based on the Otto cycle. Methane is a powerful greenhouse gas, with a global warming potential of 27-30 times that of CO2 on a 100-year timescale, according to the US EPA. Natural gas, which is used in LNG-fuelled engines, is composed mostly of methane. Methane slip is unburned natural gas that escapes out of the ship’s exhaust during combustion. This undermines the environmental benefits of using LNG as a marine fuel.
Depending on the type of engine technology, combusting LNG can reduce CO2 emissions by 20% to 25%, particulate and sulphur oxides by about 100%, and nitrogen oxides by about 80%.
In 2022, ClassNK issued an approval in principle for the concept of the methane oxidation catalyst system designed by Hitachi Zosen and Yanmar PT. The device is designed to reduce methane slip by placing a methane oxidation catalyst in the exhaust piping of an LNG-fuelled engine and oxidising the unburned methane on the catalyst.
Based on the test procedure submitted by Yanmar PT, ClassNK issued an SOF after confirming the methane slip reduction under LNG combustion conditions of marine dual-fuel engines equipped with a methane slip reduction system.
Next step: sea trials
Starting in Q4 2024, the methane slip reduction technology will be fitted on the 2023-built, LNG dual-fuel coal carrier Reimei to demonstrate the technology during sea trials. Managed by MOL and owned by Erica Navigation, the 95,792-dwt, Liberian-flagged bulk carrier was delivered in November to transport coal for Kyushu Electric Power. Plans call for the methane oxidation catalyst system to be fitted on Yanmar 6EY22ALDF engine technology.
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