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05/11/2007
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Could steam trains make a return to the tracks? Yes, if a chemical method of making steam takes off, writes Lou Reade
A new way of producing steam – in an exothermic chemical reaction, rather than heating water in a boiler – could open up new possibilities in powered machinery.
The method offers a quick and portable source of steam. At the same time, its temperature and pressure can be independently ‘tuned’ to specific values.
Oxford Catalysts, a UK company spun out of Oxford University, has developed a catalyst that causes two everyday chemicals – methanol and hydrogen peroxide – to react together and form ‘chemical’ steam. It has tested the concept by running a miniature steam engine, but believes the technology could be scaled up to power full-sized machines – be they petrol-free cars, futuristic steam trains or even rockets.
“Usually you make steam in a boiler and transport it,” says Terry Pollard of Oxford Catalysts. “Here, you just move the liquid.”
He points to a number of ways in which the 'chemical steam' is different.
“We can keep temperature and pressure separate,” he says. “Steam can be produced at 10 bar, or at atmospheric pressure – it depends how hard you push the liquid through the catalyst. But delivering this is an engineering problem, rather than a catalyst problem.”
The steam temperature of 500-800ºC is created by the chemical reaction. Pressure is created by pumping the fuel into the catalyst. But pumping the fuel, even at high pressure, does not use much energy because it is a liquid.
“In a normal system, the relationship between pressure and temperature is locked: so steam at 600ºC would need a pressure of 266 bar. We can create steam at 600ºC at atmospheric pressure,” says Pollard.
He adds that other elements of steam systems – the boiler itself, the piping, and the need to design parts to withstand high pressure – would no longer be necessary, as the source of steam can be moved directly to where it is needed.
“We think our steam generation device could be 25 times smaller than a conventional boiler system, for the same amount of steam,” says Pollard.
One potential application could be a 'green' car that replaces the standard engine with a steam turbine. Such a system would currently be impossible because it would mean fitting a boiler system into the car. But a turbine based on chemical steam would take up very little space.
“It is possible to imagine a turbine-type device that sits in a hub of each wheel and is steam-driven,” says Pollard. “We are looking at this type of technology. The catalyst is then part of the feed pipe to the turbine, so the only connection would be a fuel line. This would simplify the car by removing all but a fuel tank and pump.”
But for many engineers, the pinnacle of steam-driven transportation is the one that started it all: the train.
“By the end of their development, steam engines were very efficient – up to 40%,” says Pollard. “Our very hot steam plays to those efficiencies.”
And while steam trains may be seen as an anachronism, there is still considerable interest in this form of transport.
“We are talking to people who build steam engines – but they’re not in the UK,” says Pollard. “We want to get a feel for what they need. We've looked at the last 100 years of steam engines and are trying to understand how they work. One thing we can bring is that we have no constraints over temperature and pressure.”
And it is not only UK start-ups that are looking at this: Nasa has already begun looking into how it might power rockets using steam, while MIT.
“These are people we will look to talk to once we understand the potential of our technology in more detail,” says Pollard.
One way that Oxford Catalysts will develop the technology is by tailoring steam output to what the user requires. So the needs of a steam-cleaning machine – likely to be the first commercial application (see box story) – might be very different to that of a rocket.
According to Pollard: “For a good rocket propellant, you need high pressure and temperature, and fast-moving, light particles.”
Another potential use of the technology is as a source of hydrogen for fuel cells. By altering the proportion of the starting materials, and tweaking the catalyst, the reaction can be fixed to produce hydrogen gas.
Oxford Catalysts freely admits that its expertise is in chemistry rather than engineering. For this reason, it is looking for partners to help it develop specific applications.
“People need to tell us what kinds of problems they have,” says Pollard. “We are looking to license the technology in a range of different areas – with automotive and propulsion high on the agenda.
“In a way, all of this is too applied for us,” he says. “We are experts in catalysts, so will probably look to license the technology.”
Hot technology
Franck Letellier is a chemist working to optimise the performance of the catalyst. He takes a plastic spray bottle – the type you buy in a garden centre – that is filled with a colourless liquid, and pulls the trigger.
Steam pours out of the nozzle as it would from the top of a boiling kettle.
As demos go, it is hard to beat. But a few things should be pointed out: the colourless liquid is a mixture of water (around 50%), methanol and hydrogen peroxide; and the nozzle is fitted with a short metal tube that is packed with the catalyst.
This type of device is likely to be the first commercial application of the technology. Cleaning company Proventec is using it as the basis for a compact steam-cleaning machine that has no boiler. It will be far smaller and more portable than existing models, making it easier to transport. Later, it expects to move to sterilisation devices that would deliver a jet of steam for cleaning hospital wards, for example.
Although factories use vast quantities of steam, and most electricity is produced by steam turbines, this catalyst technology is unlikely to replace either of these applications. Instead, it is aimed at applications that call for instant steam on a smaller scale – but not the micro-scale.
The company says that 1.1kg of fuel – the aqueous methanol/peroxide mix – can produce 1kg of steam at 100-1,000[degrees]C. Around 1g of the catalyst is enough to make 50g of steam per minute.
“The catalyst is perfectly good for short-term applications,” says Letellier. “Further development is needed for something that lasts longer.”
POINTERS
Chemical steam is produced in an exothermic chemical reaction, and allows steam temperature and pressure to be selected independently
The technology could allow steam-based systems to be built without boilers, pipes and high-pressure vessels
First application is likely to be a steam-cleaning machine, but there is great promise for propulsion applications such as cars, rockets and trains
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Author
Tom Shelley
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