Coal - jet fuel of the future?

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As the US Air Force continues engine testing in a drive to quench its huge thirst for fuel with synthetic blends, pioneering energy company Sasol of South Africa is nearing approval of a 100% synthetic jet fuel. Airlines are looking to coal-to-liquid and gas-to-liquid fuels as drop-in replacements for expensive and finite petrol­eum, and global development of facilities to produce these alternative jet fuels is well underway.

The approval process for Sasol's completely synthetic fuel started in 1999, following the seven-year effort to approve its 50/50 blend.

The Aviation Fuels Committee (AFC) is a joint civil/military body that advises the UK Ministry of Defence on aviation fuel and development of the specification. QinetiQ, an international defence and security technology company, manages the approval process on behalf of the AFC.  "The final decision for the 100% synthetic fuel [specific to Sasol] is expected this month," says Peter Brook, Principal Scientist for QinetiQ's Fuels and Lubricants Centre.  "No other companies have so far asked for approval to Defence Standard 91-91 for their synthetic fuels," Brook says, 91-91 being the specification most countries use.

Johan Botha, Sasol's general manager of product applications, says the 100% synthetic fuel will become part of the normal Jet A1 supply to the market. "Once the product is certified, it loses its identity as synthetic fuel and becomes Jet A1. No special arrangements are necessary to supply or use the fuel," he says.

Thorough investigation by the AFC is followed closely by industry standards setting body ASTM International. Today, only Sasol's 50/50 blend has AFC and ASTM approval for use in aircraft, says Stan Seto, the chair of ASTM subcommittee J on aviation fuels, but by year's end the door could open to other producers under new standards.

UK approval

"We have to wait for the UK Aviation Fuels Committee to approve the proposed changes in Defence Standard 91-91 before ASTM can move forward, because the ASTM changes reference back to the defence standard," says Steto. The subcommittee is debating language for a ballot, which will probably be posted for approval in the second half of 2008, he says.

Steto says the subcommittee is watching the USAF progressively test a 50/50 synthetic blend in each airframe and engine of its fleet. "Any approval by the Department of Defense of a blending product for JP-8, JP-5 or diesel fuel will eventually be requested for inclusion in the commercial aviation sector," he says.

Amending the ATSM fuel standards includes involvement by the Commercial Aviation Alternative Fuels Initiative (CAAFI), which is sponsored by the Air Transport Association, Aerospace Industries Association, Airports Council International-North America and the Federal Aviation Administration's Office of Environment and Technology. Participants hail from all corners of the international aviation industry.

CAAFI's timetable calls for certification of a 50% synthetic blend in 2008 (and a 100% fuel in 2010). "The bulk of the technical evaluation of the fuel is done," says Mark Rumizen, CAAFI's fuels specialist for aircraft certification. "Once you go through the technical evaluation, you have to update the industry specifications, which is primarily ASTM, and also the engine specifications and the international specifications. Once the specification is revised, any particular refinery will be allowed to make jet fuel from the process. They will have to offer supporting documentation that shows the process," Rumizen says.

Low-carbon fuel research supported by CAAFI (see P43), meanwhile, aims to calculate the "life-cycle environmental impacts of production and use of alternative fuels".

Broadly, synthetic fuel processing could become less polluting than typical jet fuel production. New carbon-capturing methods can store carbon dioxide that streams out of the coal or natural gas conversion plants, which use the 80-year-old process called Fischer-Tropsch. But exhaust of jet engines burning FT fuels have only marginally fewer greenhouse gasses than with today's kerosene. Some emissions tests measure just 1.6% less CO2, though they also show the almost complete elimination of oxides of nitrogen and sulphur. A slightly higher energy content than kerosene means 1% less fuel is needed for the same trip.

The synthetic fuel produces 50-80% less particulate matter, or soot, which is good for human health and helps military aircraft elude heat-seeking missiles. Conversely the contaminants in kerosene act as a lubricant inside the engine. Aromatics in particular help maintain elastomer seals in aircraft fuel systems, and when kerosene's 8-22% aromatic content by volume disappears in synthetic fuels it makes fuel leaks possible.

William Anderson, USAF assistant secretary for installations, environment and logistics says: "The real issue with Fischer-Tropsch fuel is it has no lubricity to it." With that problem solved, he says, there is nothing stopping blends up to 90%. "We know there are people out there looking for an additive," he says.

Sasol's 100% synthetic fuel does contain aromatics. "The lubricity properties of the fuel are similar to those of petroleum jet fuel," says Botha. Anderson says the USAF has had "numerous meetings with Sasol", and that the company could be one of many helping to achieve the goal of meeting half the USAF's domestic fuel need with synthetics by 2016. The USA spends $10 million on fuel per day, and each $10 per barrel price hike costs the USAF $600 million per year.

FT fuels are the first successor to kerosene and the USAF has quickened the pace to certify each engine in its fleet to run on a 50/50 blend. The Boeing B-52 bomber was certified in August 2007 after its first flight a year earlier. Certification of the Boeing C-17 airlifter in December brought increased commercial interest, as its Pratt & Whitney PW2000 engine also powers Boeing 757 airliners.

P&W helped with the tests. "In every case the FT fuel ran as well as kerosene, and in some instances it ran better," says Anderson. "We're speculating that the lesser qualities of contaminants are making it perform slightly better. When I say slightly, I mean really slightly, but it is noticeable."

Ground tests of the General Electric F101 engine have concluded and its flight tests on a Lancer B-1B bomber are set for March. As far as Anderson knows, those ground tests were the first time an afterburner has run using a synthetic fuel blend. Ground tests of the CFM56 engine were conducted at GE facilities near Cincinnati, Ohio, and will lead to flights of the Boeing KC-135R tanker. The CFM56 is one of the most widely-used engines in the world, powering the Boeing 737 series and Airbus A320 family as well as the A340-300.

Fighter tests

"We are currently working with the F-22, KC-135 and F-16. We anticipate the KC-135 will be first to fly, possibly in late spring/early summer," says the USAF. "The F-22 engine [F119] ground test is tentatively scheduled for the May/June timeframe at the Pratt & Whitney facility in West Palm Beach, Florida. The F-16 engine ground test [with the GE F110) will not be conducted until later this year."

These tests are fuelled by part of the 1.06 million litres (281,000USgal) of synfuel the DoD bought from Shell Malaysia. This year the DoD will accept bids to supply 500,000-750,000USgal. The soonest USAF expects commercial operations to be converting coal and gas for jet fuel in large amounts is 2012. Meeting half its domestic fuel needs by 2016, or 400 million USgal, is "highly dependent upon the alternative fuels industry".

"For what it's worth," Anderson says, "the air force efforts have got a lot of people interested in talking about this. Is that enough to get commercial capital and a developer and producer to put $2 billion into a plant? I honestly don't know. We are a customer that's establishing a market need, and that market need is to execute on the presidents' vision make sure we cover our national security concerns."

Air force documents claim the USA has enough fossil fuel reserves to become "the new Middle East" by tapping 1.4 trillion barrels of shale, 900 billion barrels of coal, 22.7 billion barrels of oil reserves and 100 million lb of pulp waste yearly. But between development and deployment is "the valley of death," when commercial investors will or will not support the technology.

Four years ago the FT process was economically feasible if oil rose above $40-50 a barrel, says Princeton University senior research scientist Robert Williams. "Today we think it will be competitive at $60-70 barrel," he says. Costs of building the immense conversion facilities are much higher now, largely due to the building boom in China pushing up the price of steel, cement, copper and other supplies.

Carbon dioxide capture

Williams analyses FT systems issues under Princeton's Carbon Mitigation Initiative. One key to economical facilities and minimised emissions under a carbon policy, he says, is CO2 capture and storage (CCS). This means pumping the huge amounts of CO2 produced as a byproduct of the conversion process into geological formations deep underground, for permanent storage or as a means of squeezing out extra crude oil after drilling (called enhanced recovery).

"If you only use coal and you don't do CCS, you're going to have a greenhouse gas emission rate that is almost twice that of crude oil-derived jet fuel," he says, "If you don't reduce the greenhouse gas emissions relative to crude oil, you're not going to get to first base."

CCS is pursued at a handful of industrial sites worldwide, and Williams believes FT facilities are ideal for helping prove the viability of CCS in widespread application. "The largest point sources of pure CO2 in the world are the two plants in South Africa that produce 150,000 barrels/day of FT liquids, and the rate at which pure CO2 is vented into the atmosphere is 20 million tons a year," he says.

That concentration means capturing CO2 during the conversion process is cheaper than off a smoke stack. To establish the widespread viability of CCS, at least six test sites are needed, each able to store a million tons a year or more, he says, and "If this is going to work, we're going to have to have literally thousands of projects around the world, each of them storing 1 to 10 million tons of CO2 per year".

The other key to profitable and environmentally-friendly FT fuels under a carbon trading policy is mixing the coal feedstock with biomass, such as waste from logging and agricultural operations. Pair that with CCS, he says, "then you require half or less as much biomass as with any conventional biofuel, like biodiesel or ethanol or cellulosic ethanol."

Williams says woodmill and logging residues "appear to be one of the cheapest sources of biomass", if the FT plant can be sited to exploit these feedstocks. As for whether to convert coal or natural gas into liquids, Williams says: "The only situation where you would consider making GTL is where you would have low-cost gas assets which can't be put into a pipeline for meeting other gas needs."

That is the case at the Pearl GTL plant in Qatar, where Royal Dutch Shell will produce 140,000 barrels a day of GTL products by 2011, as well as approximately 120,000 barrels a day of associated condensate and liquefied petroleum gas. How much will be directed to jet fuel has not been made public. "We can confirm that Shell is working with the regulatory bodies and OEMs to obtain approvals to use GTL kerosene in the aviation sector," Shell says.

The energy company continues to put 30 years of research to work converting gas in Malaysia, and is involved in joint studies with Shenhua Group and Ningxia, China's major coal producers, and with Anglo American in Victoria, Australia.

Qatar's gas is also tapped by Sasol,which is ramping up production at its Oryx GTL plant to 34,000 barrels a day by mid-2008. Botha says the company is looking at increased global exports. "The semi-synthetic Jet A1 is supplied from the Natref refinery as a fungible product to all oil companies in South Africa," he says. "Hence it is likely that product is supplied to Lanseria, Kruger Park and other smaller airports. Other airports have also been supplied on an ad hoc basis, including Windhoek [Namibia[, Gabarone [Botswana], etc."

Usually the blend is less than 50% synthetic, and it is always Jet A1. "It could be used for JP-8, but would then require the additional additives required by the JP-8 specification," Botha says. Sasol produces 43.8 million barrels each year at three plants.

Expansion plans

The company makes a variety of petroleum products from coal, and the USAF will require a range of aviation fuels from several suppliers. It says 23 CTL/GTL facilities have been built or planned overseas, and 14 are set for the USA. The largest are a Yankuang facility in China, planned to turn coal to 67 million barrels a year, an ExxonMobil GTL facility in Qatar set for 56.2 million barrels, and 54.8 million barrels from coal in a project led by the US state of Montana. The USAF is itself exploring the possibility of a CTL plant at the under-used Malmstrom AFB in Montana.

The Syntroleum plant in Tulsa, Oklahoma that provided the USAF's first test fuel is mothballed, but continues FT development. "The biggest to date would be the start-up of our plant with Tyson Foods in early 2010," says chief executive Edward Roth. It will use waste from turkey processing to produce diesel.

Rentech has plans to develop FT plants in California, Illinois and Mississippi. "We have the chemical layout of the plant done," says director of development Robert Freerks, now the facilities need designing. "A large-scale plant design is in the order of $100 million. It's an exceedingly expensive thing that you have to do before you can get financing for the plant."

Rentech is looking at USAF as a major customer, and ultimately plans to divert municipal wastewater into the feedstock. Rentech will sell its CO2 into a pipeline for enhanced oil recovery and storage, but first, paper recycling sludge will be mixed with coke and coal to make jet fuel.