(November 17, 2017 at 3:29 am)Fake Messiah Wrote: (November 17, 2017 at 1:16 am)Anomalocaris Wrote: The notion that 1 ship pollutes like 50 million cars is bullshit. Ships may use horrible fuel, but marine transportation is so fundamentally efficient in terms of fuel used per ton-mile achieved that the pollutants ship emits per ton-mile is a tiny fraction of any car, truck, or train.
Hey read it for yourself
https://www.theguardian.com/environment/...-pollution
A container ship with a 100,000 hp engine is very large indeed and likely transports up to 15,000-20,000 containers carries up to 200,000 tons of cargo at approximately 30 miles per hour and operates approximately 7000 hours a year, or achieve `~40,000,000,000 ton-miles a year.
If guardian article’s data is accurate, and that ship emits 5000 tons of SO2 during that time, then that ship emits about 0.1 grams of SO2 per ton-mile carried.
But here is a caveat, guardian appears to have assumed the ship’s engine operates at maximum output most of the time. This is never the case and increasingly less so. Even express containerships designed for 25-26 knots now routinely operate at 22 knots. This is because cutting a ship’s speed by 20% reduces propulsive power requirement by 50%. So in real life the SO2 emission of a ship with 100,000 hp marine engine is likely much lower than Gardian’s estimate. Perhaps half as much.
If the guardian article is again correct about cars, and a typical car emits ~100 grams of SO2 a year and travels 15000 miles, Then consider that typical car carries very little cargo, usually just one passenger. Let’s say on average the car carries 0.1 tons (220 lbs) of goods and passengers. This means the car still emits 0.07 grams of per ton-mile carried.
So cars are only somewhat less polluting in terms of SO2 emission per ton-mile than large containerships burning bunker fuel if the containerships routinely operates at maximum speed and engine output. Cars may still be more polluting if the container ship reduce speed to save fuel.
But keep in mind 99% of cars operates in the heart of population centers almost all the time.
Even small coastal feeder Container ships usually operates a substantial distance 20-50 miles out to sea, where as the large containerships with 100,000 hp engine we looked at above would like likely operate mainly on transoceanic routes from Asia to Europe or Asia to North America, and operate far from population centers at least half of the time.
So I am by no means convinced car really inflict less harm through their SO2 emission per ton-mile than ships.
Now let’s consider how we can reduce SO2 emission from ships. A major development already underway is to convert ships to burn compressed natural gas. One huge advantage of natural gas is they work with existing marine Diesel engines. Ships do not have to be built substantially differently to use natural gas s fuel than bunker fuel, and existing lines of marine Diesel engines will suffice as the power plant. Large commercial liquified natural gas carrier ships have used conventional marine Diesel engines to burn the boil off from their liquid cargo as their primary fuel for decades. Now coastal freight ships in Europe have also a gradual conversion to natural gas fuel. Natural gas is currently so cheap that in the electric power industry, natural gas fired power plant now have lower marginal variable cost than even very large and highly efficient nuclear power plants.
I would say in the face of the advantage of natural gas, small nuclear power plant has an almost impossible hurdle to overcome to become a viable emission reducing propulsion option for commercial sea going ships.
