Re: AGL LNG imports at Crib Point

AGL Employee

Hi @Eve0,


We agree that methane has a greater impact than carbon dioxide in the upper atmosphere. Both LNG production and coal production result in the fugitive emissions of methane to the environment. The amount of fugitive emissions for LNG production depends on the source of the LNG. Coal seam gas has a higher fugitive emissions than LNG sourced from traditional gas wells.


However, most of the gas produced in the world still comes from traditional sources, not coal seam gas.  We are most likely to buy gas from these traditional sources (such as from Qatar and Africa) because it is the same sort of gas that we use in Victoria which relied on traditional gas reserves in Bass Strait which are now in decline.


For the scope of Gas Import Jetty Project, the greatest potential of fugitive emissions comes from "Boil Off" of the LNG in the storage tankers. LNG is stored at very cold temperatures at atmospheric pressure in insulated tanks. Boil Off occurs when heat from the environment (ambient temperature) warms the LNG and some of the LNG becomes gas.


However, the “Boil Off” gas is captured and depending on the operating scenario it is either:

  • Recondensed back into storage,
  • Used to fuel the ships systems,
  • Compressed and mixed with the gas in the transmission pipeline


At a last resort the Boil Off is combusted in an unforeseen operating scenario, such as after an equipment failure.


The Boil Off rate is approximately 0.15% of the total LNG cargo.


When the boil off gas is burnt for fuel or combusted, carbon dioxide(CO2) is released to the atmosphere rather than methane molecules. For every methane molecule burnt, 1 molecule of carbon dioxide is released. There are other components in LNG like ethane and propane, but they are very small percentages of LNG. Ethane and Propane have a higher impact as they release 2 and 3 molecules of carbon dioxide respectively for every 1 molecule. Combustion is not 100%, so a small amount of the methane will make it through to the atmosphere.


All onshore pipelines, piping and equipment is leak tested before operation to make sure that there are exceptionally low losses.


There will also be losses of methane to the atmosphere during maintenance when equipment and piping is opened. The design of all facilities is done to minimise releases to the environment.