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Going fishing... for a jet fuel breakthrough

Posted 17 May 2019 · Add Comment

Plans to produce sustainable bio-fuel in Abu Dhabi for airliners are nearing the next stage in the road towards full-scale production.

The small fenced compound in Abu Dhabi’s Masdar City scarcely attracts attention from anyone driving past to their jobs and homes in what is being developed to become the world’s most sustainable eco-city.
A few months ago, there would at least have been large patches of greenery to attract the eye of passing motorists. Today, however, the shrubbery has been harvested and hard-packed sand is once again the dominant theme, offset only by a few large metal water tanks and the sunken ponds of a small fish farm.
The site, however, is the starting point for what is hoped will become a major source of bio-fuel for Etihad Airways.
The search to find a ‘green’ substitute – or at least supplement – for fossil fuel-derived kerosene has been continuing for at least 15 years. Several promising plants have been tried as a source of oil that can be refined into fuel, but almost all have been ruled out because growing them competes with both agricultural land needed for food crops and water.
In the Gulf, of course, the latter is a particularly valuable commodity.
That is why considerable interest is being aroused by a small shrub, Salicornia bigelovii. A close relative of the native Salicornia in the UAE, this plant is indigenous to North America and is a member of a family called halophytes, which do not need agricultural-quality land on which to grow and, importantly, can thrive on salt water. This means sea water can be used as irrigation.
Salicornia’s tiny seeds produce an oil that can be converted to aviation fuel, while the rest of the plant can be used as bio-mass for energy creation.
Behind this initiative is a consortium consisting of the Khalifa University, ADNOC Refining, Etihad Airways, Boeing, Bauer Resources GmbH, plus engine manufacturers General Electric and Safran.
The plan is that seawater will be used in coastal fish farms. To eliminate one of the biggest problems surrounding such farms – disposing of the excreta from the fish – the contaminated water will be fed into the fields of Salicornia, which will absorb the fish waste from the water as fertiliser, boosting their growth.
Water and nutrients not taken up by the plants will be channelled into rows of mangroves, which absorb more of the waste material. By filtering through several bands of the fast-growing mangroves, the water that eventually passes back into the sea will be substantially cleaned.
As an added benefit, mangroves are excellent at locking up carbon dioxide, the ‘greenhouse gas’, in their massive root systems.
Initial tests of the proof-of-concept site at Masdar City have recently concluded and the experience is being studied. “The trials showed there weren’t really any problems,” said Linden Coppell, Etihad’s head of sustainability. “We’re making sure we distribute the water [to the plants] when it comes out of the fish ponds and we’re looking at the proportion of mangroves to Salicornia.”
Another offshoot of the proof-of-concept stage is a breeding programme to isolate the best versions of Salicornia for future planting.
The best time for planting is September/October so they are well-established before temperatures start to climb in the spring. The plants start to dry out naturally in early summer and are harvested in late July/early August.
After harvesting, the oil-bearing seeds are separated from the plant. They are so small that winnowing machines may have to be redesigned slightly to take this into account, said Coppell.
Despite that problem, the oil was extracted from the seeds and dispatched to ADNOC Refining. ADNOC worked with another local organisation, Abu Dhabi Vegetable Oil Company, which provided advice on the oil. It was initially a dark brown substance that undergoes some pre-treatment before going into ADNOC’s systems.
“ADNOC has never been given anything other than crude oil before,” explained Coppell. “Despite this, they are hugely enthusiastic about it. Clearly, we want them to be the ones to refine this in future. The quantity given to ADNOC was very small, measured in tens of litres. Depending on the quantities [in future], you would probably have to have some sort of add-on facility. It might be that they would take this through a whole separate process.”
Even if a separate refining route is necessary, the key requirement is that what emerges at the end of the process must be absolutely the same as ‘normal’ jet fuel, so that it can be used in aircraft engines with no adjustments to the powerplants.
That requirement is being put to the test. As Arabian Aerospace went to press, that initial small batch of Salicornia-derived fuel was due to be mixed with standard jet fuel and used in an Etihad Airways flight.
The next step is a demonstration plant, covering 200hectares, to scale up the cultivation and harvesting processes. This is likely to be situated in the west of the emirate.
“Although the site will require seawater for irrigation, it doesn’t have to be right next to the sea,” said Coppell. Water could be pumped inland to a site, as the actual coastline is prime land.
“At 200 hectares, the aquaculture element would be commercially viable, but for us, it’s all about how much oil we get.”
Salicornia seeds contain about 30% oil. That means that two tonnes of seeds would produce 600-700 litres of fuel per hectare, although this figure reduces as refining takes place to make the oil suitable as an aviation bio-fuel.
Meanwhile, naturally occurring sugars in the rest of the plant can be extracted and refined into ethanol, another type of fuel with multiple uses. Ethanol derived from sugar cane produces fuel for millions of cars in Brazil, for example, and new technologies have been developed to convert it into jet fuel.
Although the main focus of the Abu Dhabi project is, ultimately, on producing viable quantities of jet fuel, producing food for the UAE’s expanding population is another consideration.
Traditional farming is not particularly sustainable, as it requires a lot of water to be taken from underground aquifers, which are becoming increasingly salty as seawater gradually intrudes on them. So, fish farming is a favoured option.
At present, the species chosen for the project are tilapia and Indian white shrimp. Fish farm ponds tend to be warmed easily by the sun and the waters of the Gulf are saltier than most seas, factors that mean not all fish are suitable. “Tilapia is a hardy fish that can cope with extremes,” noted Coppell. Having said that: “When we scale up, we will look at commercial viability; we will look at other options.”
There is still some way to go. The demonstration scale 200ha plant has to be designed, with construction scheduled to start in 2020. The construction process is fairly simple, however, “and it should be operational in the next three to four years”.
Ultimately, if this pilot plant is a success, it is possible to envisage hundreds of thousands of hectares being planted with these shrubs that tend to grow naturally alongside many roads in the UAE. That very much depends on government policy. But it is a product that appears to have many upsides and no obvious disadvantages. Time will tell.
 

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