Even if our political leadership never recognizes climate change as a policy priority, pending federal legislation is forcing folks inside city-owned CPS Energy to consider places to hide politically volatile carbon dioxide emitted from their growing collection of coal plants.
One company Cris Eugster, the utility’s sustainability officer, mentioned in a conversation this week for the story
“CO2 Smackdown” is California-based
Calera, which boldly promises to not only keep coal cheaper than wind and solar, but to actually make it cleaner. “Instead of sequestration and storage of carbon, where you pump it in the ground, we’re probably a little more excited at this stage about reutilizing carbon. They’ve got a technology where they calcify the carbon,” Eugster said.
The process involves running flue gas (including carbon dioxide) over brackish water, creating a calcium bicarbonate solution. In the end the product becomes a mineralized solid which Eugster characterized as “a lot like limestone." Limestone, like cement, is a natural absorber of carbon dioxide. The material can then be used as road aggregate or turned into building materials, he said. “So you take all the carbon coming out of our coal plants and you basically making roads, infrastructure, buildings out of it. It’s a pretty cool concept.”
The company describes it this way on
their website:
The heart of the Calera process is the formation of novel, metastable calcium and magnesium carbonate and bicarbonate minerals, similar to those found in the skeletons of marine animals and plants, by capturing carbon dioxide from flue gas and converting the gas to stable solid minerals. We refer to this novel process as Mineralization via Aqueous Precipitation, or MAP for short. In its simplest form MAP involves contacting gas from the power plant with natural waters found in abundance on Earth. Many of the crystallographic forms Calera synthesizes are previously undescribed, or poorly known. These novel 'polymorphs' make it possible to produce high reactive cements, and aggregate precursors, with bulk chemistries that would usually be relatively inert.
Akin to portland cement and aggregate which derive from mining operations in quarries and subsequent processing, the precise stoichiometry of Calera's cements and aggregates will vary somewhat by site and will include other trace/minor components. In particular, many trace components will be captured from the flue gas such as sulfur oxides and mercury and will be incorporated into the solid phase as insoluble sulfates and carbonates. After removal from the water and appropriate processing, the solids have value in a number of construction applications. The versatility of MAP also allows the generation of bicarbonates, using half the amount of input materials but still mineralizing carbon dioxide into an aqueous solution that can be injected underground for storage without the possibility of leakage of carbon dioxide.
Depending on location and product offering, a Calera proprietary high-efficiency electrochemical process called Alkalinity Based on Low Energy (ABLE) is employed to produce NaOH and HCl using only salt and electricity:
NaCl + H2O -> NaOH + HCl
In locations with water shortage, the process water streams leaving the dewatering operations may be desalinated in a reverse or forward osmosis with reduced cost and energy demand, owing to the chemical removal of Ca/Mg (precipitated softening in the MAP process) as well as shared pretreatment and discharge operations. The salt-enriched RO concentrate can be utilized in the ABLE process operations.
Or if you’re a more visual person:
Of course, what CPS employees saw in California is only a demonstration plant. The challenge for Calera will be to recreate the model at a utility scale, making it tenable for an operating coal plant. “This is one we’re a little more excited about, but it’s really too early to tell which of these technologies will play out,” Eugster said.
Another company promising to likewise mineralize CO2 is
Skyonic.
“The problem with a lot of these technologies is you can prove them in the lab, but to scale the to something the size of 750-megawatt coal plant? It’s just not there at all. It’s almost premature because it’s not commercially viable at that scale,” Eugster said. “It’s innovative. It’s a little bit what this country’s about: innovation.”
In fact, Eugster said CPS is exploring at least three other “very different” carbon responses. What comes to market first will likely hinge on investment, federal favor, and, sadly, the pace and scale of destructive climate change in the United States.
