The search for alternative aviation fuels: understanding the challenge
Jeff Gazzard, board member of the Aviation Environment Federation
Mon 10 Nov 2008 – Against a background of increasing pressure on the industry to do more to control and reduce its carbon emissions, alternative fuels have moved firmly onto and up the agenda as one way in which some or all of aviation’s greenhouse gas emissions might be further controlled and reduced, writes Jeff Gazzard.
It’s important to understand that alternative fuels have their own nomenclature, development specifications and pros and cons.
All alternative fuels must be technically compatible with current distribution networks and aircraft fuel systems; they must offer similar fuel density, energy efficiency and overall performance characteristics to current petroleum-derived aviation fuel; they must be safe at altitude with acceptable freezing point performance and must not corrode or degrade on-board fuel systems or aero engine components; and they should, from the industry’s viewpoint, cost the same, or less, than current jet fuel; and production quantities need to be ramped up quickly in order to make a clear and measurable reduction in the sector’s greenhouse gas emissions. The main question in climate change terms is whether such fuels have an overall benign or negative carbon balance.
Synthetic alternative fuels fall into two categories: coal-to-liquid (CTL) kerosene type products using the Fischer-Tropsch (F-T) process (German inventors of synthetic fuel process developed during World War 2) and natural gas-to-liquid (GTL) products also using the F-T conversion process.
Biofuels are the other route, using biomass material from sustainable sources as their feed stock that in an ideal world cause no additional competitive pressures on food production or agricultural resources, such as land for food and water supplies, which could produce an alternative fuel for aviation use, in a similar fashion to automotive biodiesel.
Commercial aviation faces competition from military needs for politically and economically secure sources of alternative fuel, although there may be some useful advances in developments in one field being directly transferable to the other. Current US research and development for military alternatives has a strong focus on both synthetic and biofuel routes and the potential for carbon sequestration.
So what is the current picture on the range of and progress towards commercial reality for alternative aviation fuels of all types?
US Air Force requirements developed by Darpa (Defense Advanced Research Projects Agency) programmes are currently out of the laboratory and into real life testing with CTL F-T synthetic jet fuel (Military specification Jet Propellant 8 alternative) having been tested on B52 and BI bombers and this past summer on the C17 military cargo aircraft.
Civilian F-T process jet fuel (kerosene Jet A alternative fuel) from coal has for some years been produced in South Africa by the state oil company, Sasol. Aircraft using Johannesburg airport can fill up on a 50/50 blend of normal kerosene and synthetic F-T fuel, although we understand this has just been certified for use in a 100% synthetic formula. The Sasol F-T plant is a legacy of the now dismantled apartheid regime facing international trade sanctions during the 1970s and 80s, including restrictions on oil supplies, which forced the state to turn to the F-T coal-to-liquid process for synthetic petroleum production, South Africa having plentiful coal reserves.
The synthetic CTL FT process can and does produce technically viable, safe aviation fuel in both civil, Jet A/Jet A-1, and military JP-8 forms. But there are large questions looming over the potential switch for the US military – where, how and at what cost can US-based CTL F-T JP-8 production be ramped up?
The whole question of security of supply naturally dictates homeland located production facilities. US military requirements alone will be in the region of the 4.5 billion (US) gallons of JP-8 fuel used by the US Air Force, US Army and NATO annually right now. This is a huge amount and even the declared goal of the US Air Force to use a 50/50 blend of synthetic and petroleum based fuel across its fleet by 2011 is both costly and ambitious. The US Air Force search for alternative military aviation fuel is governed by regulations that state that any new fuel must not have a carbon footprint worse than the standard petroleum derived fuels in use today.
But there is a significant environmental problem with CTL F-T fuel – the production process is hugely carbon intensive. Speaking in December 2007, the US Air Force Assistant Secretary overseeing the switch, James Anderson, said jet fuel from coal produced 1.8 times more carbon dioxide between production and consumption as jet fuel from oil, but added most of that additional amount could be captured during production of the synthetic fuel.
This last statement refers to the process of carbon capture and storage (CCS) for which, as far as we can tell, there are only small scale test or development programmes currently underway, although there is certainly a lot of chatter. CCS removes CO2during industrial refining or other processes, such as coal-fired power generation, or as in this case, the F-T process, by a chemical reaction or scrubbing; the gas is then collected or dissolved in solution and pumped away to containment areas in, for instance, suitable geological rock strata nearby, or put to other industrial uses, for example as a feedstuff for co-located algae biomass feedstock production plants. This last example is currently being promoted as an environmental win-win as the captured CO2 feeds the algae, which in turn yields a supposedly carbon neutral biofuel as the refined end product.
The only commercial scale application of CCS today is limited to parts of the oil industry where CO2is chemically separated/recovered from natural gas production flows, and then pumped under pressure into underground reservoirs to force out difficult to access oil or gas deposits.
The economics of CCS are somewhat opaque right now, with planned trial schemes on one minute and off the next, as they are hugely dependent on ‘will they, won’t they’ government grants or tax breaks by way of financial support. We also think CCS schemes will turn out to be very costly in and of themselves.
Because of this, our view is that would be unwise to commit to large scale investment in CTL or GTL synthetic aviation fuels without an absolute guarantee of effective simultaneous CCS systems being in place that sequester all production process related CO2 emissions.
Earlier this year, Airbus entered the alternative fuel race to gain column inches and green credentials by organizing a high profile test flight of an A380 aircraft from Bristol to Toulouse. This aircraft was powered by a Gas-to-Liquid F-T process synthetic kerosene fuel. The test is linked to a consortium of Qatar Airways, Qatar Petroleum, Qatar Fuels, Qatar Science & Technology Park, Rolls-Royce and Shell International Petroleum Company, which was set up in late 2007 to research the potential benefits of synthetic jet fuel processed from gas, as Qatar has huge reserves of natural gas.
This product is slightly cleaner than conventional fuel and CTL synthetic derivatives as it has almost no sulphur content and is also slightly more energy efficient than kerosene.
But labelling a fuel ‘green’ is inappropriate in this case because as with CTL, GTL aviation fuel uses the F-T process so it too has a larger carbon footprint than kerosene. Natural gas based aviation fuels have no climate change environmental benefits without CCS being deployed.
The conversion of fossil fuel feedstock, whether coal or gas, to synthetic aviation fuel is therefore currently environmentally unsustainable and we have severe reservations regarding the cost and timely development of CCS as a process and successful technology to deal with the excessive production of CO2 emissions inherent in using the F-T system.
Biofuel is the other alternative aviation fuel route under development. Biofuel from sustainable feed stocks are under consideration in various percentage mixes with either conventional or synthetic aviation fuel or as a 100% formula. The latter looks highly unlikely as most biofuels under consideration lack the energy density of kerosene so are significantly less efficient – their miles per gallon performance is much, much poorer with consequent range penalties for aircraft missions.
Commercial airlines including Virgin Atlantic, Continental Airlines and Air New Zealand all have headline-grabbing trials in place.
All commercial and military aviation projects are coordinated and reported on by the Commercial Aviation Alternative Fuels Initiative consortium, a US-based project. Its Executive Director, Richard Altman, laid out the content and timing, problems and opportunities for alternative aviation fuel R&D and end-use horizons in March 2007 in a presentation entitled ‘Alternative Fuels in Commercial Aviation - the Need, the Approach, Progress’ which is a clear and useful overview of the entire arena.
There are plenty of questions still to be answered but it is right and proper that all forms of aviation are looking at alternative fuels as CO2 emissions from aviation need to be controlled, stabilized and ideally reduced by the middle years of this century.
We don’t believe right now that any CTL/GTL derivatives should be manufactured without CCS being in place from day one – this doesn’t seem to us to be on the table in either a reasonable time frame, given the climate change greenhouse gas reduction policy imperatives worldwide, or at an acceptable financial cost.
Biofuel from future sustainable sources seems to us to be still ever-so-slightly in the realms of science fiction with talk from some proponents of algae production facilities on top of sewage works, claimed yields of fantastic proportions, and flexible conversion/ production/distribution networks situated wherever demand occurs.
We think a reality check is need is needed which is why the CAAFI information flow is the information source of choice.
To end on a positive note, we have identified a single R&D project as our ‘one to watch’. UOP, an Illinois-based Honeywell group company involved in refining industry processes, is currently researching biofuel technology for military jets. This type of research, which must be coupled with practical production means and CCS, is a way forward. But time is not on our side if we are to avoid the worst impacts of climate change. Our target for the commercial aviation industry would be 75% of aircraft fuel to come from completely sustainable biofuel production with refinery co-located CCS within 15 years. Any takers?