written 11 June 2023
published 18 June 2023
What a week! The leading Republican presidential candidate whined about harassment as he was indicted again, this time in Federal court on 37 counts, including conspiracy to obstruct justice. Fox News stated the climate crisis is a hoax while MAGA faithful want to ban teaching about the climate crisis because "it scares children".
In the real world, where the rest of us live, 430 fires burning in Canada have created Martian like air quality in the New York city area, cancelling 600 flights because the toxic, smoky air was too opaque for safe landings. Killing heat is affecting Puerto Rico, torrential flooding savaged Italy, and the drought in Panama has reduced shipping through the Canal.
While complete economic decarbonization is essential, "Climate Restoration", by Fiekowsky and Douglis, says the only real possibility for a habitable planet is to also aggressively remove 1,000 billion tons of atmospheric CO2, returning to 300 ppm by 2050. Timely, effective solutions must sequester carbon for more than a century, already exist as demonstration projects capable of being scaled up to removing at least 25 billion tons annually, and be funded within current economic structures by providing marketable materials. The book identifies four possible candidates, all using natural geological or biological methods. The first creates synthetic limestone.
Dr. Brent Constantz, has been working for decades to use biological and geological systems to address the climate impact of the concrete industry, the second most widely consumed material, which uses cement to bind crushed rock aggregate. Manufacture of Portland cement is third largest source of atmospheric CO2, as ground limestone is heated to 2,700°F in a kiln. In 2007, he started Calera Corporation, which produces pure, powdered calcium carbonate (CaCO3) as a substitute for Portland cement, using a process based on that of clams and corals. Calera's main site uses carbon dioxide captured for the large power plant at Moss Landing.
He then turned his attention to the larger issue of concrete aggregate. Annual global concrete consumption is about 40 billion cubic yards, using 55 billion tons of rock, usually limestone, costing over $1 trillion, shipped an average of 200 miles from quarry to construction site. Limestone is mostly calcium carbonate, 44 percent carbon dioxide by weight, which is formed by living systems, drawing carbon dioxide out of the ocean over millions of years. This is one of the ways nature sequesters carbon dioxide, storing 50,000 times more carbon than we have in the atmosphere today.
Dr. Constantz developed a process for synthesizing high quality limestone using dilute CO2 from any source, including directly from the air. In 2012, he founded Blue Planet Systems, locate near Los Gatos, to commercialize and scale this process, to encourage the world to build with carbon-negative concrete. A cubic yard of concrete contains 3,000 pounds of aggregate. If Blue Planet Systems limestone is used, 1,320 pounds of carbon is sequestered in each cubic yard. If the CO2 is captured from the cement kiln, that adds another 600 pounds, or nearly a ton per cubic yard. Any CO2 source can be used.
Blue Planet Systems currently uses CO2 captured from fossil fuel plants. As we shift to renewables, other industrial sources can be used. Even direct capture for the air will add only 1 percent to the cost of Blue Planet limestone, and will allow limestone synthesis to be placed near to where concrete is consumed, further reducing emissions that would have been used in transportation, while avoiding the environmental destruction of quarry sites.
If all the annual aggregate use was all carbon-negative Blue Planet limestone, we could sequester about 40 billion tons of carbon dioxide a year. The more carbon negative concrete we use, the more we will sequester. Blue Planet expects to scale up to 5,000 plants by 2030, with the help of major industrial partners. This will require expanding capacity by 5 billion tons per year, with an annual investment of $250 billion. This will probably not need governmental subsidies, as the synthetic limestone market appears ready to take off on its own financial and green merits. But the government can help. In 2022, the US government required low-carbon concrete in all major federal projects.
According to Dr. Constantz, "Synthetic limestone takes concrete from an environmentally harmful material, with a large carbon footprint, to where we are sequestering the CO2. We are doing it profitably, not disposing it as a waste."
