Why are we building gas ships ?

Calum Watson at BBC Scotland rightly asks “Why are we building gas-powered ships ?

Two “problem-hit” “green” ferries are three years late, designed to be fuelled by LNG – Liquefied Natural Gas.

Of course, Natural Gas has a shelf life, a sell-by date, a leave-it-in-the-ground date. Because it’s a fossil fuel, and at some point, even though we might use Natural Gas as a “bridge fuel” to the fully renewable future, as some point we will need to stop pumping it up and burning it. The climate demands it.

So, why are we building gas-fuelled ships, then ? Well, that’s because Renewable Gas is a-coming in. For now, Natural Gas combustion produces around half the carbon dioxide per unit of useful end energy than coal or the thickest petroleum-sourced “bunker fuel” marine oils.

And in addition, as Calum Watson at BBC Scotland points out, burning Natural Gas produces far less air pollution than burning the treacle tar that comes out of the bottom of the barrel and the bottom of the petrorefinery fractional distillation columns – almost too heavy to vaporise.

The model of shipping gas halfway round the globe, compressed and chilled as LNG, in a network of efficient trading routes, is something that can put cheap associated Natural Gas to good use in energy markets – associated with petroleum oil, that is – co-produced, or by-produced when the oils and the condensates are pumped up.

The same system can in the future be used to trade Renewable Gas – Renewable Methane, synthesised from Renewable Hydrogen and Renewable Carbon.

There’s no need to abandon gas-fuelled ships on climate change action grounds, when Renewable Gas is going to displace Natural Gas.

Calum Watson at BBC Scotland asks if hydrogen could be the shipping fuel of the future, but he rightly points out that if hydrogen were to be shipped in the same way as Natural Gas is now in the form of a liquid, the cryogenic demands on liquefying hydrogen would be extreme.

He discusses electric drive ships, and that’s going to be great for short hops – but for the long haul, shipping will still need energy denser material fuels. The question in my mind is if Renewable Methane as LRG – Liquefied Renewable Gas is the best option – as it is possible to synthesise fuels that are liquid at room temperature, starting with biomass and Renewable Hydrogen.

Combusting liquid Renewable Fuels made through synthesis might be shown to have the same kinds of air pollution implications as fossil marine fuels : perhaps Renewable Gas will work out to be the best choice for new ocean-going vessels. It won’t be the ammonia-made-from-hydrogen mentioned in the article – there are too many issues with using this in bulk. Renewable Gas, however, where it is Renewable Methane, will be almost identical to Natural Gas, which has a very high methane content.

Calum Watson at BBC Scotland ponders that, “it looks like shipyards will be building a lot more gas-powered ships – whether that will satisfy climate change concerns is another matter.” This is a valid issue when considering hydrogen made from Natural Gas – which is another dead end. But if we use, as he says, “The cleanest way of obtaining the gas is by splitting water molecules using electrolysis, a process which requires electricity”, and take Renewable Electricity as our power for this, then the product will automatically be climate sound.

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