The Out-of-Sight Pollutant - Shipping. Over the Horizon, bringing us all that Stuff we Buy - In a Way, we're Importing Pollution!
Out of sight, over the horizon, possibly out of mind as well - but still pumping out pollutants! There's one massive transport network that needs cleaning up, but which we might have forgotten - shipping.
There are 110,700 ships of over 100 gross tonnes ploughing through the world's oceans. Although mile for mile and ton for ton ocean shipping is be far the cheapest way to transport goods, a great deal of energy is needed to push them through the water. Though fitted with enormous, relatively efficient, diesel engines, the "bunker fuel" that most large ships use for fuel is basically the unrefinable junk that the petroleum discards - something like the tar that is used on roads. Not only is it black, sticky and unheathily dangerous, but it is rich in pollutants such as sulphur and produces clouds of black poisonous smoke full of dangerous micro-particles.
And that's before we even start worrying about the carbon dioxide that's emitted. This which adds up to more than 1 billion tonnes a year, roughly the same as aviation and the container ships are the worst offenders.
"Marine Diesel Oil" is a much cleaner fuel, and is often used when close to land or in harbour, but, although pollution is singnificantly reduced, there is little benefit in terms of efficiencience and thus in greenhouse gas emissions. There are some practical and operating changes that can help. For instance bow profiles could be altered to reduce hydrodynamic drag, more efficient packing of the containers, travelling only when full and rerouting to avoid bad weather. The simplest and most effective of all would simply be to reduce speed by 50% - which would reduce fuel use by two thirds.
Electric power of some sort would be an ideal solution of course, but with battery power this is only practical with short haul ferries with journies of less than 20 miles. Hydrogen plus fuel cells might be usable in the future but at the moment it remains inefficient, expensive and hampered by the fact that most hydrogen supplies come from methane steam reforming and this is even less green than using methane directly in diesel engines, which could well turn out to be a useful intermediate technology. It would produce about a quarter less carbon dioxide than either marine diesel oil or bunker fuel - and would be certainly a lot cleaner than the latter.
Natural gas, or methane, is, however, a very powerful greenhouse gas - although it persists in the atmosphere for a lot longer than carbon dioxide - and many shipping companies are concerned that leaks from tanks and pipeworks could make the problems worse. This consideration has led several to experiment with supplementing some of its bunker fuel with treated used cooking oil (UCO).
Eventually, as more surplus electricity arises from wind turbine farms, this could be usefully used to to produce hydrogen by hydrolising water, despite the inefficiency. Then the hydrogen, or, in another variant technology, ammonia, though toxic, could be used to generate electricity in fuel cells.
One way or another the carbon burden and pollution from shipping must both be reduced - and at a faster rate than the current piecemeal solutions described above are achieving!