How a high-tech twist on a 19th-century process could clean up steel and cement production?


Greenhouse gas emissions must virtually disappear in the coming decades to avoid the worst effects of climate change, and the hardest-to-erasure emissions may come from industries such as steel and cement that will play a major role in new, green infrastructure. Wind turbines, for example, are largely made of steel – but until now it was almost unheard of to make that steel with renewable energy.

That could change if a startup developing a “heat battery” can successfully move from the lab to the real world. That’s what Oakland, California-based Rondo Energy aims to do with $22 million in new funding from Bill Gates’ climate investment fund, Breakthrough Energy Ventures, and utility-backed investment firm Energy Impact Partners.

The heat battery should be able to supply heavy industry with extreme heat generated by renewable energy, a solution that could help clean up the pesky industrial activities that make up about a third of global greenhouse gas emissions. The company believes its technology could cut global emissions by 1 percent over the next decade

Until recently, many efforts to reduce CO2 emissions from planetary heating have focused on running the energy sector on clean energy and then electrifying other sources of pollution, such as cars and buildings. But that doesn’t necessarily reduce the pollution created by making many building materials, chemicals and fertilizers.

Those industries are called “difficult to decarbonize” because they often rely on coal, oil or gas to run kilns or kilns at extremely high temperatures. For example, when making steel, conventional coal is heated to about 1800 degrees Fahrenheit. As a result of this dirty process and the ubiquity of steel in construction, the steel industry alone accounts for about 8 percent of global greenhouse gas emissions.

To change that, Rondo Energy has found a new way to use old tricks. The battery uses renewable energy to heat up a type of brick similar to refractory bricks already used in steel blast furnaces.

Rondo Energy CEO John O’Donnell describes his company’s battery as a large “insulated shoebox full of bricks.” Electricity heats the stone quickly. As air passes through the string of rocks, it superheats — to about 2000 degrees Fahrenheit. That heat can be used directly or converted into high-pressure steam, which is often used in production.

“Because it’s simple and boring, [the technology] can go on a very large scale with economic drivers and tackle a big problem,” O’Donnell . tells us The edge

O’Donnell founded Rondo Energy in 2020 after starting a number of other companies that used solar energy to generate steam for industrial processes. Others have a slightly different approach to the problem. At least one company has attempted to harness the sun for cement and steel by concentrating sunlight to achieve extremely high temperatures. Earlier this year, Breakthrough Energy Ventures funded a company called Boston Metal that wants to decarbonize steelmaking using electrolysis. And some steel mills are already using electricity — often from coal-fired power stations — to transform scrap.

In addition to reducing pollution from heavy industry, Rondo Energy’s stone can also take advantage of excess renewable energy that would otherwise overload or be lost to the grid. In sunny California, daytime solar prices can sometimes drop so low — in negative territory — that utilities lose money on it. However, Rondo’s batteries can absorb and store the energy for later use. Much research is being done on large lithium batteries that can be plugged into the grid to perform a similar function.

The company has yet to figure out how to make its grand plans a reality. So far, the prototypes have just proven themselves in the lab. The $22 million in funding it received this month will go towards the first production lines to make the batteries on a large scale. This year, there will be some demonstration projects in Kern County, California. O’Donnell didn’t share what they will be used for, but county planning director Lorelei Oviatt told The Bakersfield Californian that the technology could potentially be used for “everything from green steel to conventional manufacturing and cement that needs both renewable energy and high-temperature heat.”

Crucially, the heat battery also offers an alternative to two controversial solutions to tackle the industrial emissions problem. Hydrogen fuel and technologies that capture carbon dioxide from chimneys have received the most attention to date for their potential to clean up heavy industry. But they have faced much resistance from skeptics who feared they would distract from efforts to turn away from fossil fuels. Most hydrogen today is made with gas, but it is also possible with renewable energy. Carbon capture technologies allow polluting facilities to continue burning fossil fuels and still claim to go green by reducing CO2 – even if other pollutants remain.

CO2 capture and hydrogen must also prove that they can be used on a large scale. They are currently very expensive and require much more investment in R&D and infrastructure, including a new network of pipelines to move hydrogen and captured carbon. Rondo’s technology is relatively simpler and cheaper to roll out, in part because it builds on older, established techniques, O’Donnell said.

“It’s cheaper because it’s boring,” O’Donnell says. “If you want to go fast, make it boring; use things you can count on.”

Rondo’s heat battery faces a similar challenge to other battery technologies: to become scrap at the end of its life cycle. The entire system has a 50-year lifespan, although O’Donnell says many of its individual components last for decades longer and can be recycled or discarded like similar materials already used in steelmaking.

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