Green Fuels For The Airline Industry  

David Strahan has an excellent post on alternative fuels for the airline industry, highlighting the scale of the problem and pointing to some interesting fuel from algae experiments underway - Green fuel for the airline industry ? (hat tip Carbonsink).

If airlines are to have any chance of staying aloft in a post-peak, carbon-rationed world, they must quickly find an alternative fuel with low emissions that also matches the stiff technical standards of jet kerosene. Because planes have to lift their fuel into the sky and carry it for the entire journey, this fuel has to be energy dense. Because they fly at high altitude, it needs to remain fluid at -50 °C. Because they fly long distances, chemically identical supplies must be available all over the world. And because airliners have long lives, the new fuel must be compatible with the existing fleet. What’s needed, in other words, is an exact replica of old-fashioned jet kerosene – a so-called “drop-in” replacement – that also emits substantially less CO2 per unit of energy. “Meeting all these conflicting demands is a very tall order,” says Mike Farmery, global fuel technical and quality manager at Shell Aviation. “There are lots of exciting ideas, but it will be hard to achieve quickly.” So what are our alternatives?

Until recently it was widely thought that using biofuels like bioethanol or biodiesel in aviation was a non-starter. Scientists have known since the 1940s how to turn vegetable oil into biodiesel using a process called transesterification, in which the oil is processed using alcohol and an acid catalyst. This produces fuels that work well on the ground but not at altitude: the natural freezing point of such oils is too high, so they would congeal at 33,000 feet. They also contain too much oxygen, which adds weight but not energy content.

However, it now seems those technical problems have been cracked. Finnish oil company Neste has devised a way to produce an oxygen-free biodiesel called NExBTL, which could in theory be used to make jet fuel. Neste already has two plants manufacturing NExBTL and has another two in the pipeline.
Meanwhile in February 2008, airline Virgin Atlantic conducted a test flight using a biofuel made from coconut and babassu oil produced by Imperium Renewables, a Seattle-based company that has developed a patented method of reducing the freezing point. A second test flight with an Air New Zealand plane is planned later this year.

The problem with so-called first-generation biofuels – made using conventional fermentation and distillation procedures from wheat, say – remains the amount of feedstock and land required. During Virgin’s test flight from London to Amsterdam, the Boeing 747 consumed 22 tonnes of fuel, of which only 5 per cent was neat biofuel. Producing even that much required the equivalent of 150,000 coconuts, says Brian Young, Imperium’s director of international business development. Had this single flight been run entirely on biofuel, it would have consumed 3 million coconuts – an astronomical number that highlights the scale of the problem. However, Virgin and its partners Boeing and GE stressed that the flight was simply a “proof of concept”, and accepted that producing useful amounts of fuel would require “next generation” feedstocks: those made from non-food crops, waste biomass or by converting existing fuels to liquid form.

One option, which Virgin’s Richard Branson suggested at the launch of his airline’s test flight, would be to produce fuel from the nuts of Jatropha curcas. This hardy bush grows in the tropics on relatively poor land with little water or fertiliser, so it needn’t displace food production. However, the amount of land required to fuel the world’s jet planes would still be prodigious

Aviation currently consumes around 5 million barrels of jet fuel per day, or 238 million tonnes per year. On current Jatropha yields – 1.7 tonnes of oil per hectare – replacing that would take 1.4 million square kilometres, well over twice the size of France. To put this in context, D1 Oils, the British company pioneering biofuel from Jatropha in countries such as India, Zambia and Indonesia, plans to plant 10,000 km2 over the next four years.

If vegetable oil looks likely to remain in short supply, another approach would be to make jet fuel from plant material using the Fischer-Tropsch chemical process developed in Germany in the 1920s. Originally designed to produce synthetic diesel from coal, the Fischer-Tropsch process also works with a wide range of organic matter. The feedstock is heated without oxygen to create a synthetic gas that is then converted to high-quality liquid fuels using high temperatures and iron-based catalysts. This makes it possible to create a synthetic jet fuel that is indistinguishable from conventional kerosene. Depending on the feedstock, the fuel could in principle have very low carbon emissions and not compete with food production. Unfortunately, though, all the feedstocks have significant drawbacks.

For example, Fischer-Tropsch jet fuel is already produced from coal by Sasol in South Africa, and planes refuelling in Johannesburg get a half-and-half blend of kerosene and coal-to-liquids (CTL) fuel. The problem with CTL is that life-cycle emissions are roughly double those of kerosene, making CTL-powered aviation even more damaging to the climate.

The Fischer-Tropsch process also works with natural gas. Gas-to-liquids (GTL) jet fuel was tested by Airbus and Shell earlier this year. Well-to-wing emissions are lower than CTL, yet no better than conventional kerosene, because the Fischer Tropsch process itself consumes so much energy. According to Airbus’s rival Boeing, GTL jet fuel emits 1.5 times as much CO2 as kerosene.

The only realistic hope of producing Fischer-Tropsch jet fuel with substantially lower emissions is to use some form of plant material such as wood or straw as the feedstock – so-called biomass-to-liquids, or BTL – as championed by the German company Choren, which plans to start full-scale production by 2012. The company boldly proclaims a vision of “potentially infinite production of renewable energy”, but a closer look at the numbers suggests the real outlook will be more modest.

In a presentation at the World Future Energy Summit in Abu Dhabi in January, Choren CEO Tom Blades said the company’s BTL fuel could reduce greenhouse gas emissions by up to 91 per cent, and insisted it would not compete with food production. One reason for this is that a large proportion of the feedstock will come from waste construction timber and existing forestry – initially. However, Blades acknowledged that further BTL expansion would require increasing amounts of specially grown “energy crops” such as willow or miscanthus. Supplies of waste timber aren’t expected to grow, so within 10 years, more than half of Choren’s feedstock will need to come from energy crops, again raising the issue of land use.

Blades cites the EU’s Biomass Action Plan report of December 2005, which suggests that Europe has the potential to produce around 100 million tonnes of energy crops annually by 2030, and that total available biomass, including waste and forestry contributions, could amount to 315 million tonnes. Since Choren’s BTL process takes 5 tonnes of dry biomass to produce a tonne of fuel, this would produce just over 60 million tonnes of fuel per year. That sounds a lot until you remember that in 2006 the EU consumed more than 700 million tonnes of crude. “We’re not replacing oil,” Blades admits, “just making it last a little bit longer.”

In the context of global aviation, the numbers are even more daunting. Meeting today’s global demand for jet fuel from BTL would require – assuming the average crop yields 10 tonnes of biomass per hectare – nearly 1.2 million km2. That’s well over three times the size of Germany, and makes no allowance for the predicted rapid growth in aviation. On the same assumptions, replacing all current transport fuel with BTL would require more than 10 million km2 – an area bigger than China. This demolishes any claim that second-generation biofuels wouldn’t have to compete with food production.

The one remaining alternative for low-emission jet fuel that doesn’t compete with agriculture are algae, which can be grown in ponds of seawater built on non-productive land. Given the right conditions, some species multiply quickly and produce oil, which can then be extracted and refined. It is widely agreed that such a system could take up less space and deliver much higher yields than oil crops such as palm or Jatropha – although quite how much higher is still controversial.

The technology itself is not new. Ami Ben-Amotz, a senior scientist at Israel’s National Institute of Oceanography in Haifa, has been farming algae commercially for more than 20 years to produce beta-carotene food supplements for the Japanese market. In 2004 he founded a new company, Seambiotic, to produce algae for biofuel at a coal-fired power station on the coast at Ashkelon.

It is an undeniably neat arrangement. Warm water from the power station’s cooling system is diverted through the ponds before returning to the sea. Meanwhile flue gas from the station’s chimney supplies CO2 to feed the algae, and energy for pumping and harvesting is available at minimal cost. The harvested algae are then reduced to a concentrated paste and mixed with solvents to separate the oil, which can be turned into biofuel by transesterification. Seambiotic is delighted with the results and aims to complete a larger, 50,000-square-metre pond on the site by the end of the year. Ben-Amotz says that refineries could offer similar opportunities.

Algae have stirred up huge excitement, not only because they have the potential to help mop up CO2 emissions, but also because of the sheer amount of fuel they might produce. Shell, which is building a pilot facility in Hawaii, claims algae could be 15 times as productive as traditional biofuel crops. Boeing believes algae could produce 85 to 170 tonnes per hectare per year (10,000 to 20,000 US gallons per acre per year), yielding all the world’s jet fuel in an area the size of Belgium. Yet the scientists who have done most research into algae production look askance at such claims.

The fundamental problem, explains Al Darzins, who coordinates alga research at the US National Renewable Energy Laboratory in Golden, Colorado, is that although algae grow very quickly, most of their biomass is usually carbohydrate. To trigger a higher proportion of oil, you have to stress the algae in some way – starve them of nutrients such as nitrogen, say – which in turn limits their growth rate. As a result, Darzins thinks 42 tonnes per hectare is a more realistic target.