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FEATURE: Today's rubbish, tomorrow's jet fuel

Dominic Bliss

'In order to make aviation sustainable, we have to make sustainable fuel. There is no other way to achieve it.' (Credit: Shutterstock)
'In order to make aviation sustainable, we have to make sustainable fuel. There is no other way to achieve it.' (Credit: Shutterstock)

One day, in the very near future, commercial aircraft will be fuelled by household rubbish. Yes, seriously.

A British technology company called Velocys is soon to build an industrial plant in Lincolnshire designed to convert household and office refuse – the stuff we throw away rather than what we send for recycling – into jet fuel. If all goes to plan, they could start production as soon as 2025. 

The plant, for which planning consent has already been granted, is called Altalto Immingham. It will sit on a 78-acre site beside the River Humber, near the town of Immingham, close to the east coast. So far Velocys, which is headquartered in Oxford, has raised £8.2m in funding, of which just under £1m is from government grants, and the rest from British Airways, Shell and its own coffers. The developers won’t put a final price on the project although they admit it will require “hundreds of millions of pounds”. They expect to hire a workforce of 130 people.

The wonder of this operation is that the raw materials are domestic and commercial rubbish – so there’s always a ready supply. Instead of using refuse that has already been separated for recycling, Velocys will accept any mixed rubbish – things we throw away at home and at work in black dustbin bags that normally end up in incinerators or landfill sites. Once up and running, they plan to process up to half a million tonnes of waste a year – enough to manufacture more than 60m litres of fuel, mostly jet fuel, but also a smaller amount of petrol for road vehicles. 

Clean burn

It will, they say, be enough to power around 1,000 commercial transatlantic flights a year. And, crucially, the fuels will work perfectly with existing jet and motor engines. “They require no changes to engines or infrastructure, meet all specifications and burn cleaner, cutting exhaust pollutants such as particulate matter,” Velocys states.

Neville Hargreaves is the company’s vice-president of waste-to-fuels. “In order to make aviation sustainable, we have to make sustainable fuel,” he says. “There is no other way to achieve it. It’s an absolute essential. There are no producers of sustainable aviation fuel in the UK today. So we are seen as part of the solution.”

Until now, garbage as aviation fuel was the stuff of sci-fi movies. The 1980s time-travel trilogy Back to the Future is a good example, where Marty McFly’s crazy professor friend fuels his flying DeLorean sports car with banana skins and beer that he roots out of a trash can.

The engineering behind Velocys’s plans is inevitably a little more complicated than this. Hargreaves explains how the first stage is to separate all the rubbish into its different constituents. Inorganic items such as stone, glass, metal and some plastics are separated off while the organic materials such as paper, cardboard, wood, food, most textiles and certain plastics are retained. It’s the carbon and hydrogen in these items that provide the raw materials for the eventual fuel.

The next stage is called gasification, where the materials are heated up (but, crucially, not burnt) and broken down into carbon monoxide, hydrogen and a little bit of carbon dioxide. This is known as syngas. The syngas is then washed to remove elements such as sulphur and chlorine, resulting in a clean version. 

The Velocys Fischer-Tropsch reactor

The Velocys Fischer-Tropsch reactor

Then follows something called the Fischer-Tropsch process, involving several chemical reactions that convert the carbon monoxide and hydrogen into liquid hydrocarbons – the building blocks of jet fuel and petrol. 

Finally, the hydrocarbons undergo a process known as hydrocracking, when the larger molecules are cracked into smaller ones. Rather like in a conventional fuel refinery, this produces the fuel itself. 

Seventy per cent of this fuel will be synthetic paraffinic kerosene, destined for the aviation industry, and 30% will be naphtha, to be used in road vehicles.

It’s the Fischer-Tropsch process that is perhaps the most intriguing aspect of the overall production. Developed in 1925 by two German chemists, Franz Fischer and Hans Tropsch, it uses metal catalysts, and very high temperature and pressure, to produce hydrocarbons. 

Handful of plants

There are only a handful of Fischer-Tropsch plants in operation. The Pearl GTL plant in Qatar is claimed to be the largest. Meanwhile energy companies Sasol and PetroSA operate plants in South Africa, and Shell runs a facility in Malaysia. Velocys is involved in two other Fischer-Tropsch projects – one in Mississippi, the other in Oregon – both of which will make fuel from the woody by-products of the forestry industry.

Hargreaves explains how all of the stages outlined above have already been demonstrated to work “at full commercial scale”, but only individually, not in combination, as he is proposing. Securing this combination, he admits, will be the greatest challenge for the new Altalto Immingham plant.

“We are taking technologies which have been demonstrated at scale and combining them in a new way,” he says. “A first-of-a-kind project such as ours will always have its challenges and complexities, but we are confident of our ability to deliver. This plant will have about 950 separate pieces of equipment within it. So it’s pretty complicated.”

Big enterprise

Indeed, plans of the plant show a central waste feed facility of over 15,000m2 with an adjacent gasification building of 5,630m2. Surrounding these are various generators, compressor shelters, substations, warehouses and office buildings. There will be stacks rising to around 80m in height, as well as pipelines, and new railway and road infrastructure. This is no small undertaking.

The site itself is currently vacant land, surrounded by industrial buildings. Velocys says it chose Immingham because it sits in the Humber region, “with a skilled local workforce, good infrastructure and a range of similar facilities nearby”. 

It has a point. The Humber estuary is home to one of the UK’s busiest ports complexes, and industrial businesses such as BP, Siemens Gamesa, Jesmond Engineering, Engie Fabricom, Drax Power, British Steel and ORE Catapult. 

The Immingham plant will cover a large area and will draw on a skilled local workforce

The Immingham plant will cover a large area and will draw on a skilled local workforce

On paper, Velocys’s green credentials look impressive. It says its engineering system guarantees a lower carbon footprint than if the waste was sent to incinerators or landfill sites. It also results in a fuel that massively reduces both the soot and sulphur oxide emissions from aircraft engine exhausts; a reduction of 90% of the former and almost 100% of the latter, the company claims. 

“The technology enables a net 70% reduction in greenhouse gas emissions for each tonne of sustainable jet fuel that displaces a tonne of conventional fuel,” the company states. “The greenhouse gas reductions achieved from the plant’s annual output are equivalent to up to 40,000 standard-size petrol engine cars.”

Ripe for conversion 

Hargreaves estimates that, in the UK, households and business premises produce between 10m and 15m tonnes of waste a year that is ripe for conversion into fuel. It’s not enough to manufacture all the sustainable jet fuel the country needs – to achieve this we would need agricultural waste added into the mix, he says. “But we do feel confident there’s enough to make a serious dent on the aviation fuel demand.”

Interestingly, Velocys won’t have to pay to obtain the waste. “We don’t buy it. We get paid to take it,” says Hargreaves. He explains how the supply chain starts with councils and businesses that are obliged to pay waste contractors to dispose of their waste. Those waste contractors then pay to incinerate the waste or send it to landfill sites. Velocys’s plant will simply act as an alternative disposal route.

Naturally, environmentalists would prefer aeroplanes to run on electricity rather than jet fuel (however sustainable that jet fuel might be). Hargreaves accepts this but worries that the technology for long-haul electric flight is too far off.

“I don’t see them being an option for long-haul flight before 2050,” he says. “Perhaps 2100. Who knows? There may be a technological breakthrough we haven’t thought of, but the laws of physics and chemistry get in the way. You need enormous energy density for long-haul flight and, at the moment, we don’t see any alternative to liquid hydrocarbons.”

Meanwhile, development of the Lincolnshire plant continues. Providing funding is secured, construction could start as early as 2022. 

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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.


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