The domain of kerosene – Beppe Grillo’s Blog

Getting off kerosene-based aviation fuels will be one of the most difficult feats of achieving a carbon-neutral world. Aviation is responsible for only 2% of the global volume of emissions and 12% of those generated by the transport sector, but the transition to electric engines for airplanes is a much more complicated process than it is for cars and trains .

The aviation fuel we currently use – the most common type is known as Jet A-1 – has several advantages. Its energy density is very high, for each kilogram of weight it contains 42.8 megajoules; a value slightly lower than that of petrol, but unlike the latter it can remain in the liquid state up to 47°C below zero and is cheaper from the point of view of the cost than the loss due to evaporation because it is recorded at high altitudes and risk of catching fire when handled. Credible rivals are not yet visible on the horizon. Batteries that have enough capacity to carry hundreds of people on intercontinental flights are still the stuff of science fiction, and it will be some time before we see wide-body airplanes powered by liquid hydrogen. What we need is a fuel equivalent to kerosene but derived from plant material or organic waste.

Such an aeronautical biofuel would release, during the combustion process, a quantity of carbon equal to that which is absorbed by plants during their growth. The feasibility of the idea has been demonstrated: since 2007, test flights carried out using mixtures of Jet A-1 and biofuel have revealed that they can constitute an adequate alternative, at least for some flights, for modern aviation.

Passengers per airplane and fuel consumption. Passengers, in billions – Kerosene, in billions of litres

Since then, some 150,000 flights have been made using such blends, but only five of the major international airports offer regular distribution of biofuel (Oslo, Stavanger, Stockholm, Brisbane and Los Angeles), while its availability at other airports is only sporadic. The size of the biofuel consumption of the largest company United Airlines gives a perfect idea of ​​the discouraging proportions of this replacement work, albeit necessary: ​​the contract with a biofuel supplier provides for the supply of a quantity equal to 2% of the total fuel consumed annually by the company. True, airlines today are incredibly frugal: they burn about 50% less fuel per passenger-kilometer than they did in 1960. But the fuel savings have been offset by the continued expansion of the aviation industry, which has increased its overall annual consumption to exceed 250 million tons globally.

To meet such a fuel requirement, using mainly biofuel, we would have to go beyond organic waste and exploit oil-rich plants, seasonal (corn, soybean, canola) or perennial (such as oil palm), whose cultivation would require large plots of land and would lead to environmental problems. Oil crops in temperate climates have relatively low yields: with an average crop of 0.4 tons of aviation biofuel per hectare of soybean land, the United States would need to plant 125 million hectares – a land area larger than that of Texas, California and Pennsylvania combined, or slightly larger than the land area of ​​South Africa – to meet their fuel needs. Four times the 31 million hectares the country used to grow soybeans in 2019. Even the highest yielding plant – the oil palm, which can supply an average of 4 tons of aviation biofuel per hectare – would still require the exploitation of more than 60 million hectares of tropical forest in order to meet global demand for aviation fuel. It would mean quadrupling the land currently used for palm oil cultivation, causing the carbon dioxide accumulated during the natural growth of vegetation to be released into the atmosphere.

But why occupy vast lands when you can make biofuel from oil-rich algae? Intensive and large-scale cultivation of seaweed would require a relatively small area and offer a very large harvest. However, ExxonMobil’s experience shows us how difficult it would be to scale crops sufficiently to produce tens of millions of tons of aviation biofuel each year. In 2009, Exxon, in collaboration with Craig Venter’s Synthetic Genomics, set out to achieve a similar goal, but in 2013, after spending more than $100 million, it concluded that the obstacles were too great and decided to return to focus on pure long-term research.

As always, energy substitution would be an easier goal to achieve if only we reduced waste. For example, flying less. But considerable growth in air traffic is expected, particularly in Asia. Get used to the unmistakable smell of aviation kerosene, it will keep us company for a long time.

Based on the book by Vaclav Smil, “Numbers don’t lie”

Source: Il Blog di Beppe Grillo by

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