> First, the tank must be 'inerted' to eliminate the risk of explosion. An inert gas plant burns diesel in air to produce a mixture of gases (typically less than 5% O2 and about 13% CO2 plus N2). This is blown into the tanks until the oxygen level is below 4%.
> Next, the vessel goes into port to "gas-up" and "cool-down", as one still cannot load directly into the tank: The CO2 will freeze and damage the pumps and the cold shock could damage the tank's pump column.
> LNG is brought onto the vessel and taken along the spray line to the main vaporiser, which boils off the liquid into gas. This is then warmed up to roughly 20 °C (68 °F) in the gas heaters and then blown into the tanks to displace the "inert gas". This continues until all the CO2 is removed from the tanks. Initially, the IG (inert gas) is vented to atmosphere. Once the hydrocarbon content reaches 5% (lower flammability range of methane) the inert gas is redirected to shore via a pipeline and manifold connection by the HD (high duty) compressors. The shore terminal then burns this vapour to avoid the dangers of having large amounts of hydrocarbons present which may explode.
> Now the vessel is gassed up and warm. The tanks are still at ambient temperature and are full of methane.
> The next stage is cool-down. LNG is sprayed into the tanks via spray heads, which vaporises and starts to cool the tank. The excess gas is again blown ashore to be re-liquified or burned at a flare stack. Once the tanks reach about −140 °C (−220 °F) the tanks are ready to bulk load.
Wow, that's a whole lot of burning of hydrocarbons just to get the LNG into the tanker. How much does this overall add to the lifecycle carbon emissions of natural gas for electricity?
> Next, the vessel goes into port to "gas-up" and "cool-down", as one still cannot load directly into the tank: The CO2 will freeze and damage the pumps and the cold shock could damage the tank's pump column.
> LNG is brought onto the vessel and taken along the spray line to the main vaporiser, which boils off the liquid into gas. This is then warmed up to roughly 20 °C (68 °F) in the gas heaters and then blown into the tanks to displace the "inert gas". This continues until all the CO2 is removed from the tanks. Initially, the IG (inert gas) is vented to atmosphere. Once the hydrocarbon content reaches 5% (lower flammability range of methane) the inert gas is redirected to shore via a pipeline and manifold connection by the HD (high duty) compressors. The shore terminal then burns this vapour to avoid the dangers of having large amounts of hydrocarbons present which may explode.
> Now the vessel is gassed up and warm. The tanks are still at ambient temperature and are full of methane.
> The next stage is cool-down. LNG is sprayed into the tanks via spray heads, which vaporises and starts to cool the tank. The excess gas is again blown ashore to be re-liquified or burned at a flare stack. Once the tanks reach about −140 °C (−220 °F) the tanks are ready to bulk load.
Wow, that's a whole lot of burning of hydrocarbons just to get the LNG into the tanker. How much does this overall add to the lifecycle carbon emissions of natural gas for electricity?