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Marnoch Thermal Power: a new type of heat engine for tapping into lower temperatures

My latest Clean Break column on Ontario inventor Ian Marnoch and his new heat engine design that could make efforts at turning low-grade heat into electricity more economical.

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Tyler Hamilton

The Geological Survey of Canada put out a research paper in 2010 that concluded the country has enough geothermal heat to power itself many times over.

The big question is how much of that heat can be economically tapped?

As a general rule, the hotter and shallower the resource the more economical it is to exploit based on current technologies. The higher the temperature the easier it is to extract the volume of heat required to spin a turbine and generate electricity.

But there aren’t many places in Canada, beyond northern B.C., Alberta and the Yukon, that have that right combination of temperature and depth. Everywhere else, you’ll have to drill deep – as much as 10 kilometres down – to find enough heat. That’s a deal-breaker with respect to cost and risk.

It’s also a nut Ian Marnoch of Port Severn, Ont., is trying to crack. For the past seven years the Ontario inventor has been developing a new kind of “heat engine” that he says can generate electricity more economically from lower-grade heat. And that heat could come from anywhere: the ground, the sun, or an industrial waste process.

Not that the technology doesn’t already exist to do it. There are other heat-engine technologies out there, most notably those based on the Organic Rankine thermodynamic cycle. These systems transfer heat to a working fluid with a low boiling point, such as ammonia.

As the fluid heats up, expands and vaporizes it drives a turbine that generates electricity. The vapour is then cooled, condensing it back into a fluid which is recycled back through the process.

Marnoch’s heat engine works under a different principle. There is no vaporization of fluids. Instead, the Marnoch system relies on dry pre-pressurized air that expands and contracts as it is heated and cooled, causing pistons to turn that generate electricity.

This in itself may not be new, but it’s the way Marnoch has configured his machine that may give it an edge over other technologies. He says his thermal power engine can process heat much faster and at bigger volumes than Organic Rankine machines.

“It can process about three times as much heat by value as an Organic Rankine machine of the same size,” says Marnoch, adding that his heat engine can be designed to be much smaller and, therefore, less expensive.

That it operates more efficiently also means it can tap into lower temperatures that aren’t viable with other technologies. One area where Marnoch hopes to demonstrate the superiority of his design is in northern communities that currently rely on diesel generators for electricity production.

All he needs is the right temperature differential – that is, the gap between the heat source, such as the water in a deep mine shaft or temperature at the bottom of an old oil or natural gas well, and the heat sink, which would be the cool northern air.

If that gap is 20 degrees C or higher there’s potential to generate electricity. The system becomes more economical the wider the gap.

Marnoch has been working to perfect his patented heat engine with a team of PhD students and professors at the University of Ontario Institute of Technology, which has supported development of the machine for the past five years with funding from the federal and Ontario governments. The Ontario Power Authority and Ontario Centres of Excellence were also early funders.

The latest prototype of the machine is at the university’s new Clean Energy Research Laboratory, but Marnoch is eager to get the machine out in the field and tested in a real-world situation.

St. Marys Cement is one possible candidate. The company is exploring using the Marnoch engine to generate electricity from the waste heat of its Bowmanville cement plant.

“It is in very early discussions but we are very enthusiastic about the potential and what this can mean for industries with large volumes of low-grade waste heat,” says Martin Vroegh, environmental manager at St Marys.

Marnoch is hoping that the smaller size of his machine, relative to an Organic Rankine set-up, will make his technology more attractive to operators of industrial facilities, which often lack the real estate to host such equipment.

“It could open the door for us,” he says. “We just need to get out there and prove it works.”

If only it were that easy. Like any inventor or entrepreneur trying to bring a new clean technology to market, particularly one that directly challenges well-entrenched products, Marnoch knows he has many more hurdles to overcome and many years of trying.

It comes with the territory. But persistence is the soul of innovation, and Marnoch has plenty of it.

Tyler Hamilton, author of Mad Like Tesla, writes weekly about green energy and clean technologies. Contact him at tyler@cleanbreak.ca