Glance up at the heavens on a clear day and you are bound to spot a passenger jet tearing across the sky. Let your gaze linger for just a moment longer and a few more planes will doubtless come into view, their vapour trails carving up the skyline.
It might be an unscientific snapshot, but the scene would nevertheless testify to one of the most pervasive societal trends of the past two decades: a boom in air travel.
At any one time, more than half a million people are speeding towards their destinations at 34,000 feet. The US, meanwhile, rarely has fewer than 5,000 aircraft simultaneously criss-crossing its airspace. The stratosphere will become even more crowded in future. Thanks to the increased wealth of the middle classes in emerging markets, our skies could be positively teeming with aircraft within a generation.
That’s a worrying prospect for several reasons. But perhaps the biggest concern of all is the impact air congestion might have on the environment. Currently, aircraft generate some 705 million tonnes of greenhouse gas emissions per year, or 12 per cent of the total produced by mechanised transport. According to the International Civil Aviation Organisation, however, jetliners could be belching out as much as seven times that amount by 2050.
Rather than embark on what would ultimately be a futile effort to stymie air travel, policymakers and the airline industry see improved technology as key to solving the pollution problem. Of all the innovations currently under development – aircraft re-design, solar cells, hydrogen-powered engines – it is biofuel, fuel that is extracted from organic matter, that represents perhaps the most feasible way of reducing aviation’s impact on the environment.
“Aircraft manufacturers constantly work to improve the fuel efficiency of their products and airlines push them to do so. However, there is only so much that can be done in this regard with today’s technologies, and given that aircraft are long-lived assets, quick turnover of aircraft fleets is not practicable,” says Nancy Young, vice president for environmental affairs at Airlines for America, an industry body.
Sustainable alternative jet fuel can bring a whole new source of emissions reduction to aviation.
“Thus, sustainable alternative jet fuel can bring a whole new source of emissions reduction to aviation – on top of the emissions reductions we get from the design and operation of the aircraft.”
The most established aviation biofuels are those produced from food crops such as maize, rapeseed, corn and grain, all of which are rich in essential vegetable oils. When these oils are combined with methanol, the chemical reaction that ensues produces a biofuel that can be used as an alternative to kerosene.
A similar process that makes aviation fuel from municipal waste has also recently come into commercial use.
In June, US flag carrier United Airlines made the industry’s biggest investment to date in waste-to-fuel technology, buying a USD30 million stake in Fulcrum Bioenergy, a California-based company. The UK’s British Airways, meanwhile, is currently constructing what will be the UK’s first waste-to-biofuel production plant in a joint venture with alternative fuel company Solena.
Biofuel currently offers airlines two potential benefits. The first is that it represents a relatively painless way for carriers to meet their emissions targets. Most energy crop biofuels qualify as “drop-in” fuels; in other words, they can be used in combination with, or as an alternative to, kerosene without needing to modify aircraft engines.
According to André Faaij, a professor of energy science at the University of Groningen in the Netherlands, using biofuel as a drop-in to either replace or complement kerosene can reduce aircraft emissions of harmful greenhouse gases – such as particulate matter and sulphur oxides – by as much as 90 per cent.
In tests carried out by German carrier Lufthansa two years ago, an Airbus A321 passenger jet running on 50 per cent biofuel produced 1500 fewer tonnes of CO2 emissions during 1200 flights between Frankfurt and Hamburg.
Airlines also like biofuels because they double up as an insurance policy against swings in the cost of kerosene. Fuel is by some margin the most volatile component of an airline’s costs. In the last decade, for instance, oil has traded within a range of USD40-USD140. So anything that can bring a bit more stability to an airline’s bottom line is welcome.
“Alternative fuels are not only good for the environment,” says Brett Hart, United’s executive vice president and general counsel. “Bio-fuels have the potential to hedge against future oil price volatility.”
But fuel produced from either food crops or municipal waste is unlikely to dethrone kerosene on its own. That’s because manufacturers would never be able to produce enough of it to bring down costs to competitive levels.
A constraint is land availability. Producing biofuels from crops such as maize and corn in particular eats up highly fertile arable land that would otherwise be used for food. Energy crop expansion is in constant conflict with the need to keep a growing world population fed – a trade-off that governments are understandably keen to avoid.
“Food crop biofuels can only be part of the solution.” says Prof Faaij. “For such fuels to gain critical mass and become more cost-effective in the long run, they would need to be produced in much higher volumes than is currently the case. But because they need higher-quality land, this limits their potential deployment.” This is where lignocellulosic, or “second generation”, biofuels could help.
Lignocellulosic biofuels are produced from non-food substances found in agricultural and timberland waste. Sourced from a wide range of organic matter such as trees, wild grasses and forest residues, these raw materials enjoy a considerable advantage over traditional food crops – they do not require additional nutrient-rich land.
“The beauty of the majority of lignocellulosic biofuels is you do not need high-quality soil to produce them,” Prof Faaij explains. “There are vast tracts of wasteland worldwide – in Eastern Europe, Latin America and Sub-Saharan Africa – that could yield enough lignocellulosic and residues to make this process commercially viable. What is more, these are perennial plants that can both improve soil quality and store more carbon food crops.”
The untapped potential is, it seems, considerable. According to the United Nations, there are some 700 to 1,400 million hectares of land that could be used to extract lignocellulosic biomass.
The International Panel on Climate Change (IPCC), meanwhile, estimates that the world could generate anywhere between 100-300 exajoules of energy per year from lignocellulosic biofuel alone by the second half of this century. To put that figure into context, the IPCC expects total world energy consumption to reach 1500 exajoules by 2080.
Experts believe lignocellulosic production could begin to reach industrial scale within five years. Canadian firm Iogen and Spain’s Abengoa Biotechnology are among the firms to have constructed lignocellulosic biomass-to-fuel conversion plants. Others, including Germany’s Choren and Sweden’s Chemrec, have developed new gasification processes to produce bio-diesel from lignocellulosic matter.
According to Prof Faaij, the technical barriers to the commercialisation of lignocellulosic fuel have already been overcome. “The biomass-to-fuel conversion technology already exists, and there is no need to change airline engine specifications to accommodate this fuel,” he says.
Getting costs down is more problematic, however. Producing biofuel from organic material is fairly expensive, particularly when compared to traditional aviation fuel. Complicating matters further is the explosion in shale oil and gas production in the US, which could put a lid on costs for traditional fuel, at least over the medium term.
At current prices, it costs around USD2500 to produce a tonne of biofuel from lignocellulosic substances – that’s about two and a half times more than it costs to manufacture a tonne of kerosene.
So for biofuels to compete on an equal footing, production needs to ramp up, and it can only do so with government support and increased financial backing from the airline industry. Investment focused on identifying sustainable sources of biofuels worldwide is crucial, as is the construction of biofuel depots at airports.
With such a framework in place, biofuels could displace kerosene as the aviation fuel of choice within decades.
“It is perfectly feasible to achieve large-scale deployment of second generation biofuels in the aviation sector and for prices to approach those of oil, or about USD80 a barrel,” says Prof Faaij.
“Biofuels could easily cover up to 20 per cent of the industry’s energy demands by 2030 at the latest. All we need for that to happen is a bit more financial and political commitment.”
