the benefit of lng is its actually usable for maritime power and its not nearly as destructive as any other fuels.
It's better than oil in both sustainability and lower carbon production while also having less societical or manufacturing setbacks than nuclear or electric. It is the least drastic change freighter companies could make while still changing.
ya, pure electric cargo ships probably won't be possible, certainly not ones that travel the distances we do right now. We'd have to have an economy that wasn't 100% reliant on transoceanic shipping which future automated manufacturing may brig
You seem to have no idea how "cryogenic fuels" actually work.
Liquid oxygen is not a fuel. It is an oxidizer. Fill a tank up with LOX and you know how much energy you get from burning it? Zero - oxygen can't burn. You could maybe use the temperature differential to drive some sort of heat engine... which wouldn't even provide enough energy to keep the liquid oxygen at liquid temperatures. To get something to burn, you need an oxidizer and a fuel.
Rockets, at least liquid-fueled ones, tend to have a separate oxidizer. Not always, there are monopropellants, but most of them use a separate oxidizer. Liquid oxygen is common because it's cheap and relatively safe, but there's also room-temperature oxidizers like nitrogen tetroxide or high-purity hydrogen peroxide.
What do they burn it with? Right now, the big two options for burning with LOX are RP-1 - a slight alteration to JP-1 jet fuel, with stricter limits on the types of contaminants that choke rocket engines - and liquid hydrogen, although liquid methane is used in a lot of upcoming designs. NTO is generally burned with some sort of hydrazine - room-temperature and self-igniting, but also super corrosive, super toxic, and carcinogenic in case the first two didn't kill you quickly.
All of those will burn in atmospheric oxygen. Hydrogen is infamously flammable. Jet fuel is flammable. Hydrazine is flammable. You get literally no benefit from lugging around a tank of cryogenic oxygen on a ship - any fuel you care to burn, will burn with the oxygen available in normal air.
So let's look at those fuels. RP-1 is for most purposes identical to kerosene - it's got really, really low sulfur content, because that tends to choke the regenerative cooling lines and coke the turbines, but in terms of how much carbon dioxide it emits by burning, it's identical to kerosene. Oh, and it's like ten times more expensive, because it's a low-volume product and not a lot of refineries make it, but if we somehow switched the main shipping fleets over to it that would drop.
Liquid methane, the up-and-coming fuel, is likewise basically liquified natural gas. You still get CO2 as a major product, you still have the hassle of keeping it liquid, and you still need tanks way bigger than you do for even gasoline, let alone bunker fuel.
Hydrogen is really unsafe and really hard to handle. It's extremely flammable. It leaks through everything - it's such a small molecule that it can go right through a lot of seals. Rocket scientists haven't managed to contain it perfectly, just figure out how to mitigate it. The Delta IV rockets literally light themselves on fire before launch to burn any leaked hydrogen in a controlled manner. It embrittles most metals - even stainless steel, exposed to a lot of hydrogen gas, will become brittle and fragile. It's extremely high-volume - you need massive tanks to store the same energy-equivalent of any room-temperature hydrocarbon. And, those tanks have to be insulated very, very heavily, because hydrogen is only a liquid at extremely low temperatures - 33K, -252C, or -423F, take your pick of units. It's so cold you usually have to insulate it from your liquid oxygen. The one good point to it is that it doesn't burn to CO2.
It's not cryogenic, but I mentioned it earlier so I'll discuss it now: hydrazine (and derivatives like monomethylhydrazine and dimethylhydrazine) is awful. This isn't some fuel you can schlep around in a drum. This is a fuel you need a full PPE suite for - full-body impermeable suit, face shield, goggles, and respirator. You have two-man-rule in effect. And, after all that, it still shits out a lot of CO2.
So, at best, you were saying "cryogenic fuels" instead of saying "liquid hydrogen", and grossly misunderstood the engineering challenges involved in working with liquid hydrogen. And insisted on burning it in a rocket engine instead of a turbine or a piston engine, for reasons I can't begin to fathom. (Why yes, you can burn hydrogen in a non-rocket engine - ULA is using a regular straight-six on the ACES upper stage to provide auxiliary power. I think some zeppelins used it too, since they had big bags full of it for lift anyways?)
At worst, you were seriously proposing liquid oxygen as a power source, which is a gross misunderstanding of chemistry, thermodynamics, and probably a few other fields.
The big issue here, even with a clean equivalent, is that ships are incredibly disruptive and destru tive due to the needed infrastructure of the modern pier system. Coastal landscape is incredibly important, especially at the mouths of rivers feeding into the ocean.
Our industrialized and urbanized lives have done inrepairable harm to the ocean which is far more important to the health of us and the planet.
And by most estimates,due in part to automation, more ships are going to be deployed and thus cause more damage.
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