Real-world study advances methane emissions abatement

One of LNG’s biggest challenges is methane emissions. Methane is an extremely powerful greenhouse gas (GHG) with a global warming potential (GWP) of 36 in a 100-year time horizon and 87 GWP on a 20-year cycle, making addressing methane slip and methane emissions top priorities.

This is where studies such as Total Methane and CO2 Emissions from Liquefied Natural Gas Carrier Ships: The First Primary Measurements, conducted in 2021 on board an LNG carrier during actual operations, are vital to measuring, managing and mitigating methane emissions from the sector. This study marks the first time methane emissions have been directly measured from an LNG carrier.

Dr Paul Balcombe, senior lecturer in chemical engineering, Queen Mary University of London, detailed the findings of the study at Riviera Maritime Media’s LNG Shipping & Terminals Conference in London in November. Conducted on board the 2021-built Gaslog Galveston, the research gathered information on emissions of methane and CO2 during the ship’s 10,000-nautical mile roundtrip voyage from Cheniere’s Corpus Christi LNG terminal to Zeebrugge, Belgium.

Dr Balcombe and his team physically measures emissions from Gaslog Galveston’s propulsion and generator engines, exhaust stacks, vents and any fugitive emissions. The research uncovered “some really good things and some items for improvement,” said Dr Balcombe.

Among those ‘good things’ were that venting and fugitive emissions were extremely low, accounting for about 0.1% of the total GHG emissions from the voyage. And, in a bit more good news, CO2 emissions from fuel usage were about one-third lower than previous estimates.

However, the study points out the bad, too. Methane slip averaged 3.8% across the ship’s propulsion and auxiliary LNG dual-fuel engines. In particular, the four-stroke auxiliary engines were a key cause of methane slip, with two of the four generators used almost all of the time on the voyage producing average slip rates of 7.9% and 8.5%. Essentially, this means that about 8% of all the fuel that was sent to the engines was released into the atmosphere. This clearly needs improvement.

By contrast, the ship’s pair of two-stroke, low-pressure, dual-fuel engines had average methane slips of 1.9% and 2.3%.

One way to dramatically improve the methane slip in the four-stroke auxiliary engines involves operating fewer engines at optimised loads, improving engine performance and efficiency, suggested Dr Balcombe.

As for the LNG carrier’s W5X72DF main engines, Swiss engine designer WinGD released its next-generation WinGD X-DF 2.0 model with iCER technology three years ago. This unit cuts methane slip by 50% and improves fuel efficiency in both gas and diesel modes, compared to the previous generation prime mover. These types of extremely efficient low-pressure, dual-fuel engines will be popular choices to power the next generation of LNG carriers for decades to come.

Organisations such as SEA-LNG and the Methane Abatement in Maritime Innovation Initiative (MAMII) are vital in bringing together industry players to help accelerate research, operational measures and technology advancements to address methane slip and emissions.

The LNG industry needs to continue to back this type of real-world study, to reduce methane slip and improve the global fleet’s environmental performance.