Setting aside the ship’s own bunker fuel, does Liquid Natural Gas pose any ecological threat at all to the sea environment when a tanker is hit?
Obviously that amount of methane being released is not helpful to climate change. Would setting it on fire mitigate that problem? Yes, it would cause an explosion, but if the ship was out in the water where that was no issue - what chemicals would the LNG break down into if it were burned? Would those chemicals be less dangerous to the climate? How does it change the Sea environment threat?
I’ve been going in circles trying to research this, but I just don’t know enough chemistry to come to any conclusions.
AIUI, the only reason that it’s liquid is that it’s being held on the ship, in a tank, at a cryogenic temperature. If the tank is ruptured, it’d rapidly transition back to a gas, and escape into the atmosphere.
So, the environmental threat (largely methane, as you note) would be to the atmosphere, not to the ocean.
This article discusses a large land-based methane leak. Might give us some hints about what to expect. Aliso Canyon gas leak - Wikipedia.
As the methane escapes the ship there’s going to be local cooling of the seawater and also local absorption of some methane into the sea water.
But as said above, in fairly short order like minutes to hours substantially all of the ship’s leaked cargo will evaporate into the atmosphere. Methane is significantly lighter than air so the evaporating release will head skyward as a plume, not stagnate as a bubble of gas hugging the water surrounding the ship.
There’s also this bit that’s relevant: LNG carrier → spillage - Wikipedia. Even the largest of LNG carriers losing their entire cargo involves an amount of carbon release that’s trivial compared to any big city’s daily output. So not good news, but just one more micro-drop in the bucket of human-caused environmental damage.
Natural gas is mostly converted into carbon dioxide and water when it burns. Burning would reduce the methane release, but I think the challenge would be that it’ll be rapidly, and uncontrollably, evaporating once the tank is breached. Getting that to burn off, rather than just escape, might be difficult.
If you can figure out how to burn the escaping gas without burning the ship, I’m sure you’ll be very popular in marine salvage circles.
From my time in emergency management I learned that everything about an accident or disaster gets tens of times more difficult, and hundreds of times more polluting once anything is on fire.
I don’t know much about industrial uses of methane, but it seems to me that wherever that cargo was headed, it was going to be burned and/or released into the atmosphere eventually, right? How is it worse to release it before it gets to its destination?
Except that even if it’s burned either way, whatever facility that was going to burn it now burns a replacement cargo instead. It’s a drop in the bucket but in theory one more ship-full is burned than would otherwise have been.
If you can capture the escaping gas you can then reuse it as fuel; there’s no reason to just flare it off.
And if you can’t capture it, you can’t burn it in a controlled fashion. Just setting the ship afire and hoping some of the methane happens to get burned off before the ship sinks is simply wacky. Typical LNG tankers have several separate tanks. If one is holed (the most likely case from a collision) the others will hold their contents under pressure for awhile. Any fire sets the other tanks up for a Boiling liquid expanding vapor explosion - Wikipedia event. Which are catastrophic.
I was talking to some combustion experts who were working on the problem of complete combustion of natural gas in variable flow environments. In this case, flares in oil and gas fields. I told them “humans have been making fire for a long time; you’d think we’d be better at it.”
Depending on how the storage and transfer bits were damaged, it might be possible to transfer and flare it in a controlled fashion. But that’s challenging at sea. And it may not be safe to bring it to a transfer terminal.
BTW, to me, the idea of liquefying natural gas is kind of neat. It has to be cooled to −162 °C (−260 °F), which isn’t a temperature that any of us see on a normal day and then it takes up 1/600th of the volume of natural gas in the gaseous state. It’s kind of amazing the kinds of industrial processes that are possible today.
The last time I was on one I asked what the water spraying on the hull near the cargo manifold was for during loading thinking it must be done as some sort of fire precaution.
Nope. Kind of the opposite. It was to ensure that in case of a leak the steel was kept warm by the water because the cargo is so cold it can make steel brittle enough to undergo structural failure.
Of course “warm” in this context means “warm compared to -160°C”. Not what we usually think of as warm.