Environmental impact is as ever at the heart of discussions on de-icing in aviation. Today, several solutions seek to mitigate the effects of glycol-based fluids – and some technologies that would eliminate the need to spray chemical de-icing agents entirely are now in development, as Megan Ramsay reveals
In terms of aircraft de-icing, one innovative product is of particular relevance as aircraft manufacturers move increasingly towards composite materials. James Tour, a chemist at Rice University in Houston, Texas, outlines: “We take a material and coat it with graphene nano-ribbons, which work as a de-icer. We now also have the capability to make it so that ice won’t form down to a certain temperature (-15°C). We can then pass a voltage through it and it still works at even lower temperatures.”
The nano-ribbons can be embedded in composite aircraft, which are made of carbon fibres woven and bound with an epoxy resin. A thin film of nano-ribbons is added to the topmost part of the epoxy. By applying electrodes at each end, the nano-ribbons can be heated (as high as 100°C if desired) so that any ice melts. Tour says that what he envisions for the aircraft industry is “to use this material either on the leading edge or over the whole aircraft. There is no need to spray chemical de-icers – once this film is on the aircraft, that’s it. Once it’s there, the aircraft’s surface is superhydrophobic. Below a certain temperature (for instance in-flight temperatures), you can flick a switch and melt any ice off.”
The coating itself, which is visually black, would be part of the composite moulding – the paint finish simply goes over the top. “Paints are designed to take quite high temperatures and we only need to heat the graphene nano-ribbons to a few degrees above the ambient temperature for the ice to start to slide off,” Tour notes. He also explains that there is a possibility of blending the nano-ribbons with paint; indeed, his team has sprayed on coatings before, but he believes that this process still needs development. A thin enough coat would appear visually transparent, with a negligible level of absorbence.
The obvious benefit of this technology is that it would do away with the need to spray ethylene glycol and propylene glycol. “It would mean aircraft would not have to sit on the tarmac for 30 minutes waiting to be de-iced before they can go. It has enormous environmental and cost savings – there’s no need for chemicals, equipment or the time delays that cost airlines a huge amount in fuel and personnel,” Tour sums up.
Another project that seeks to eliminate the use of chemical de-icers and reduce costs of melting snow and ice in the airside environment is the development of conductive concrete at the University of Nebraska-Lincoln. This involves adding steel shavings and carbon particles to a basic concrete mixture; when an electric current is passed through the material, it warms up sufficiently to melt any ice or snow on its surface.
Professor Chris Tuan, who is leading the research, says that phase one of the project has resulted in “a cost-effective concrete mix design that satisfied the mechanical requirements, durability requirements and effectiveness levels during tests performed in winter 2015”. The requirements specified in airport concrete pavement guidelines relate to the bending or flexing strength of the material, as it has to take the weight of a loaded aircraft.
The team is due to give a briefing and presentation at the Federal Aviation Administration (FAA) technical centre at Atlantic City International Airport, New Jersey, in August or September 2016.
“Next we want to propose the phase two study with an area of marked tarmac measuring 150ft by 50ft, hopefully next spring,” Tuan confirms.
The installation process is very simple, he observes. A steel rod is inserted into a layer of thermal insulation and connected to an electricity supply (a 10V socket is sufficient). The conductive concrete is then cast on top and left to harden. The components being inside the concrete, they are protected from damage and are maintenance-free. While conductive concrete costs round double the price of ordinary concrete, its installation cost is the lowest among the various heated pavement technologies, Tuan contends.
The upfront cost of the graphene nano-ribbons de-icing material, meanwhile, is not as easy to calculate at this point. The material itself is not expensive – and only a small amount is used because a very thin coat is sufficient – but the application process would increase the cost, according to Tour.
Furthermore: “This technology is very energy-efficient – about 95% efficient as opposed to 60-70%. Compared to using radiative heating with water passing through cables and then into the surface, here, the surface itself is the heating element, energised by two electrodes – so there are fewer steps. During the recent Winter Storm Kayla, which paralysed air traffic in the north-east of the US, it only cost between US$0.02 and $0.04 per square foot; that’s less than $0.25 per hour. Also, of course, there are no chemicals or salt that damage aircraft and the environment.”
Reality check
As with any new technology, it takes time and effort to bring an idea to a point where it becomes a commercially viable solution accepted by the industry and the regulatory authorities.
Tuan explains that since conductive concrete is a semi-conductor and an innovative product, tests, inspections and approvals are necessary to reassure potential customers that it is safe to use. Similarly: “For instance it took 25 years for microwave ovens to be widely used in the US,” he points out.
Although he believes conductive concrete will be implemented quickly in the US (and he also mentions interest from companies in Denmark, the Netherlands and Norway), there are stumbling blocks. “First, the concrete companies that could produce this stuff are a problem. It’s very new, and they’re a very conservative institution. We have to convince them it’s not going to damage their trucks or facilities. With every new technology you have to convince people to try it; once they’re comfortable with it, it will take off.
“Second, there’s the fear factor: manufacturers are nervous because they don’t know how it will turn out. Because they’re liable for it they tend to jack the price up, which can make the product cost-prohibitive.”
Tuan also observes that other research in this area is not always carried out thoroughly, leading to poor results that “give the technology a bad name, creating more fear”.
Back in Houston, Tour highlights other issues. “We have spoken to a few aircraft manufacturers but none of the big ones. Most of them want a retrofit – that is, an overcoat on their existing aircraft. This is a bit harder to envision for aluminium aircraft but easier for composite models. It needs some development and it needs a company that is committed to doing that; we do the research, but we need someone else to do the development.”
Right now: “There is already a sunk infrastructure in de-icing, plus we have to get approval, so people are not jumping into it. What makes things happen is government intervention – for instance, if EPA comes along and sets limits on glycol run-off. A decree of some sort stimulates investment,” and he is keen for his product to be ready for market as and when that happens.
Until then…
Both conductive concrete and the graphene-based de-icing material offer environmental benefits by eliminating the need for chemical de-icing agents. However, glycol fluids will remain in use until such time as alternative solutions become widely available and cost-effective.
One approach to dealing with de-icing fluid is the use of bacteria to break down run-off. This process is in use at Rhode Island’s T F Green Airport (PVD), where a de-icer and storm water management system constructed by Gresham Smith & Partners (GS&P) using anaerobic biological treatment went into full operation last year.
“De-icing fluid is critical to safe aircraft operation in wintry weather, but as an environmentally conscious organisation, we also want to keep it out of our streams, rivers and bays,” comments Rhode Island Airport Corporation’s interim president and CEO Peter Frazier. “PVD’s state-of-the-art de-icer management system allows aircraft to remain at the gate for de-icing in wintertime while protecting our nearby environment and streams.”
After a de-icing event, storm water run-off is piped to two storage tanks. It is then processed through two anaerobic fluidised bed reactor treatment trains where bacteria convert the propylene glycol into methane and carbon dioxide. The methane gas is recycled in the treatment building.
“The methane provides free fuel to heat the chemical-laden water, eliminating the costs associated with building a larger facility and purchasing natural gas,” explains senior environmental engineer and project designer for GS&P, Timothy Arendt.
In addition, the burning of methane – a powerful greenhouse gas – as fuel significantly reduces its impact on the environment.
The facility at PVD is one of only four of its kind in the world. The others are at Portland, Akron and Albany. Such solutions are not always practical, however. According to Wayne d’Entremont, system de-icing manager at Air Canada, for instance: “Given a typical Canadian winter, biological treatments are not as efficient as bacterial processes are slower in the winter and the typical glycol percentage is too high. Therefore the best way to protect the environment at our larger stations is to reclaim the spent glycol via a GRV (glycol recovery vehicle) or other means, and have it recycled or reused.”
This is precisely the service that Canada’s Inland Technologies offers. Roger Langille, president and CEO, outlines: “Inland provides re-manufactured propylene and ethylene glycol for use in various industrial applications in Canada and the US. We produce two grades of recycled glycol, a 50% raw-grade product and a 99% product, on both sides of the border. Each has specific markets and the reclaimed glycol is used in a variety of sectors including as automotive anti-freeze, as RV anti-freeze, as a paint additive, and in heat transfer products in HVAC (heating, ventilation and air-conditioning) systems.”
Inland has glycol recycling operations in both Canada and the US. Canadian carriers have opted to use ethylene glycol for its better freeze point protection and American carriers generally use propylene formats.
Last season, Inland began using its 99% glycol as a feedstock in Type I ADF in Halifax and now supplies the carriers at Halifax International Airport, including Air Canada. Similar plants are currently under development in Calgary, Alberta and in Portland, Maine. Final commissioning will take place in both plants this autumn; the Portland plant will be the first facility in the United States to produce Type I Aircraft De-icing Fluid (ADF) for local reuse.
Since 1995, Inland has processed 1 billion litres of fluid – enough glycol-contaminated storm water to fill almost 400 Olympic-sized swimming pools. “From that collected fluid we have recovered over 150 million litres of 50% product,” Langille says.
Inland manufactures its own glycol recovery vehicle, the Glyvac™, as well as its unique GlycolGuard™ drain block, which prevents unwanted run-off during de-icing operations or other situations where containment is essential. Its Starcevic Distillation System™ is a purpose-engineered plant that processes a 50% raw-grade glycol up to ±99.8% virgin-quality glycol product, Inland confirms. The company is also a certified manufacturer of Type I ADF, using a feedstock comprised entirely of re-manufactured glycol. With facilities typically located at or near an airport, it produces and distributes both ethylene and propylene glycol formats of Type I ADF.
Inland has also partnered with another ADF manufacturer at its Canadian sites, allowing for the continuous supply of Type I ADF to airlines. The Inland product is chemically equal to the virgin refined product produced by its partner, but completely formulated from recycled glycol, Langille says.
As for drawbacks to this approach, d’Entremont remarks: “A recycling programme has its unique challenges, especially in time, equipment and costs. The solution is to regroup all airlines in a consortium to manage a glycol mitigation programme. The cost is then shared amongst all the users resulting in overall best value.”
Air Canada has a group that attends the Society of Automotive Engineers’ aerospace committee bi-yearly meetings, where developments in sustainable de-icing are considered. “There are new possibilities such as infra-red technology that uses heat to melt ice or snow off an aircraft fuselage,” d’Entremont confirms.
However: “The energy and infrastructure costs are prohibitive compared to traditional glycol-based de-icing technology. Air Canada has also studied the possibility of adding icephobic coatings to its aircraft. As safety is of the utmost priority, Air Canada Flight Operations as well as our Maintenance and Engineering branches have considered the pros and cons due to the extra fuel required to carry around these coatings, which emit CO2 gases and may impact flight handling characteristics.”
