By James Randerson
A new engine that generates electricity from waste hot water could reduce energy consumption and carbon emissions for thousands of different businesses, from cargo shipping to data centres. So says Exergyn, a firm based at DCU Alpha, Ireland, which plans to run the first industrial trials of its technology next year. Globally, Exergyn estimates that the heat lost in waste hot water from industrial processes amounts to around twice the energy in Saudi Arabia’s annual oil and gas output. “There’s just so much waste hot water in the world,” says Exergyn CEO Alan Healy. “In most cases [companies] are actually spending energy to cool it.”
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Cargo ships, for example, typically pump waste hot water from the engine around the vessel to cool it down. And in data centres, electricity-hungry fans are used to dissipate the heat generated by rows of servers. Finding an efficient way to capture and use this wasted energy would both reduce costs and cut carbon emissions.
The Exergyn Drive uses the quirky properties of an alloy of nickel and titanium called nitinol. You can bend nitinol out of shape, but when heated it undergoes a phase transition and reverts to its original crystal lattice structure. This “shape memory” property makes nitinol desirable in a wide range of applications, including medical devices, unbreakable sunglasses and NASA’s Mars rovers.
It also has another unusual quality. Unlike most materials, nitinol expands when cooled, rather like water does when it turns to ice (think of the mess in your freezer when you leave a bottle of beer to cool in there too long).
“There aren’t many materials in the universe that do that,” says Mike Langan, Exergyn’s head of product management.
These two properties drive the Exergyn engine. Inside the device, a bundle of metre-long nitinol wires are attached to a piston. Hot and cold water is alternately flushed over the wires every 10 seconds, which causes them to rapidly expand and contract by 4 centimetres, driving the piston up and down. A hydraulic system converts that forceful linear motion into rotary motion, which in turn drives a generator. The engine produces 10 kilowatts of electricity from around 200 kW of thermal energy in the waste hot water.
That might not be hugely efficient, but this is “free” energy that would otherwise be wasted. And often, money and energy would be spent actively cooling down the waste water.
The company has spent three years perfecting the design and modifying the material so that it will keep working for millions of cycles. It was awarded 2.5 million euros from the European Commission’s Horizon 2020 fund last year to help bring the technology to market and is now planning three industrial tests in 2017, at Dublin Airport and two landfill sites. In all three cases, the Exergyn technology will use warm water at 90 °C or less – from a gas engine at the airport and from biogas generators at the landfill sites – to produce electricity on-site.
In addition to harnessing waste heat from industry, the company hopes that the engine could expand the geothermal energy market. At the moment, generating electricity from geothermal sources in a cost-effective manner requires very hot water at high flow rates. That typically means digging very deep wells with a wide diameter, which hugely increases drilling costs. Langdon says that Exergyn’s technology makes a broader range of geothermal sites viable, as it works with water at a lower temperature and flow.
John Blowes, a past president of the Institution of Diesel and Gas Turbine Engineers, who has seen the technology but has no stake in the company, agrees there is a “massive” range of applications. But he says that only a small percentage of these will be viable unless the company can produce the technology cheaply. “It comes down at the end of the day, for me, to commercial viability,” he says.
Langan says the combination of no fuel costs and the mechanical simplicity of the machine means that Exergyn will be able to keep costs down. He says it can currently generate electricity at £40 per MWhr – cheaper than gas and coal.