May 4, 2010
Artificial tree becomes carbon castle
Huge machines that suck millions of tonnes of carbon dioxide from the atmosphere each year are set to become weapons in the fight against climate change. That's the vision of scientists at Canadian company Carbon Engineering, which hopes to use existing technologies to scavenge the greenhouse gas on a massive scale. "It's not unobtanium, it's not magic, it's just heavy industry," said David Keith, a founder of the company.
Carbon Engineering was spun-out from the Energy and Environmental Systems Group at the University of Calgary, where Keith is director, in October 2009. Over the next three years, the company will spend at least $5 m raised from backers – including Bill Gates – to develop the largest "artificial tree" yet proposed.
"We're talking about building things that cost billions and we have millions," Keith told environmentalresearchweb. "So, we're going to build a facility that will operate outside [of a lab] for a year, so we can raise funding for a full industrial pilot. We want to come up with a design whose risk and cost estimates are believed."
The company is founded on a redesign of a scrubber originally tested by Keith's team in 2008. Far from resembling a tree, the equipment has the simplest structure that minimizes the overall energy and capital cost of "air capture". Whereas the Canadians' previous design resembled a cylindrical chimney, the latest incarnation is a rectangular slab, through which air is drawn sideways.
Within the scrubbers, Carbon Engineering absorbs carbon dioxide using sodium hydroxide solutions, recovering it later in the process. "In towers, the liquid flows down and the air blows up," Keith explained. "That geometry just doesn't allow you to get the air in and out at a low enough cost." While in a tower the solutions are pumped continuously, a horizontal orientation allows the liquids to rest until enough air has blown through almost to saturate them. Only then are the solutions pumped along. "That reduces the cost of pumping the fluid basically to zero," Keith said.
Delivering low costs is crucial because air capture is widely criticised as being expensive in comparison to capturing carbon dioxide directly from fossil-fuel-burning power plants. "Air capture will always cost more than power-plant capture if you build it at the same location, with the same construction and energy costs," Keith conceded. "But you don't have to do that, you can use the atmosphere as a free pipeline. We can be competitive because of the enormous economic freedom to take advantage of lower costs around the world."
Keith noted that the costs of air capture have been exaggerated by both its supporters and opponents, resulting in extreme estimates of $20 to $1000 per tonne of carbon dioxide. He says that his personal goal is to produce an "unequivocally industrial design" that can deliver a cost below $200/tonne. "I think that we can beat that, but even if it's up there I think people will say, 'Do you know what? This is doable.'"
Andy Extance is a contributing editor to environmentalresearchweb.