Capturing CO2 for cement production
The Calera technology, which uses aqueous minerals and CO2 emissions, has opened new avenues for the production of usable and valuable building products while relieving the economic burden of CO2 capture. Gulf Construction presents an exclusive report on this breakthrough technology, which was unveiled last month.
01 March 2009
IN A standing-room-only seminar at the “World of Concrete” Conference in Las Vegas last month, Dr Brent Constantz unveiled his company’s breakthrough carbon-negative cement and concrete mixes.
“By making a few changes in the concrete mix design, we can turn the carbon equation for construction and infrastructure on its head,” he explains.
The seminar, presented together with former president of the American Concrete Institute Terry Holland, covered US-based Calera Corporation’s basic technology innovations as well as the company’s “carbon calculator” for various mix designs that incorporate Calera products such as supplementary cementitious materials (SCMs) and synthetic sands and aggregates, all of which are carbon negative.
Calera has developed novel processes to produce building materials out of flue gas from power plants. By chemically converting carbon dioxide into carbonate minerals, Calera’s technology permanently sequesters CO2 into a broad product line of construction materials. The basic process is akin to the formation of coral reefs, utilising minerals dissolved in water. Several designs have been developed to work together with and enhance performance of desalination plants.
Solution for the Arabian Gulf
Aided by the connections of its main investor, venture capitalist Vinod Khosla, Calera is discussing projects in Australia, the Netherlands, Saudi Arabia, and the UAE, which is considering using the material in its Masdar City project, Constantz said.
“Is it possible with Calera technology to sequester billions of tonnes of carbon dioxide in the built environment? Absolutely!” declared Khosla on a recent trip to Abu Dhabi. “This give the construction industry a starring role in solving climate change. It’s stunning in scope and impact.”
Caldera has been actively pursuing opportunities in the Arabian Gulf region, claiming the triple benefit of carbon emissions reduction, green building materials and more efficient desalination. While the economics of the business are still closely held, Constantz is confident that Calera products will be able to compete on the basis of both product performance and price.
“Our capital costs and operating expenses will allow Calera to provide cost-effective, carbon-negative concrete blends to support the green construction boom in the Middle East,” Constantz states. “Our products are carefully designed to ASTM specifications and can be customised to local conditions. And, by the way, we solve the carbon footprint problem.”
Constantz speaks from a place of authority. Calera is his fourth company to produce cement products, the first three of which were focused on high-performance orthopedic cements, that is, synthetic bone materials. In addition, his PhD is in geology and he is currently a professor at Stanford University in California where he teaches carbonate sedimentology.
Impact on emissions
Calera uses a basic carbon calculator to find the carbon footprint of various concrete mixes. The method calculates the CO2 per pound of each ingredient, providing the total embodied CO2 in the cement mix. The entire system is considered, counting CO2 from production to the transportation of each material by rail or truck. The charts (left) illustrate the calculation for three different concrete mixes: The first is conventional concrete, the second is a carbon-neutral concrete, and the third is carbon-negative concrete.
When compared to the reference case of conventional concrete, Calera’s proposed carbon negative mix has a net carbon footprint reduction of over 1,600 lb of CO2 per cu yd of concrete.
Multiply this by the tonnes of cement and aggregate consumed around the world each year and the potential impact of Calera’s technology becomes apparent, says Constantz.
It is estimated that the 125 million tonnes of cement and 3 billion tonnes of aggregate are consumed in the US annually. Global estimates come in at 2.5 billion tonnes of cement and 60 billion tonnes of aggregate.
To put this in perspective with respect to greenhouse gas emissions, the Energy Information Administration (EIA) predicts that global CO2 emissions will reach 31.1 billion tonnes in 2010.
So, in rough terms, there is a good match in volume between the CO2 emitted globally and the market for products produced using Calera technology.
Carbon capture technology
The Calera technology uses aqueous minerals and CO2 emissions from power plants or other large point sources such as refineries.
The CO2 in the flue gas is dissolved in a reactor, where it becomes carbonic acid that is converted to carbonate ions, which in turn form a slurry containing suspended mineral carbonates. Solid-liquid separation and dewatering then produce a thicker slurry that can be handled for productisation.
Depending on the target product, the slurry is either dried to form reactive cements or otherwise processed to form sands and aggregates.
For each tonne of product produced, approximately half a tonne of carbon dioxide is captured using the Calera process. The production of usable and valuable building products helps to relieve the economic burden of carbon dioxide capture and sequestration for power plants. Another inherent advantage of Calera’s mineralogical CO2 sequestration process is that it does not require the separation of CO2 from the flue gas, which is a highly cost– and energy-intensive step.
Further, the Calera process allows the offset of Portland cement’s carbon footprint, he adds.
About Calera
Calera was founded in 2007 by Constantz, with the goal of reducing or eliminating the carbon footprint of the cement industry.
He later realised that the technology could be expanded to help reduce emissions in other carbon-intensive industries, including power production, oil refining, steel manufacturing and others. Over time, the product line also expanded beyond just cement.
Today, the company has a world-class research and development (R&D) laboratory and testing facilities to develop and certify cements, aggregates and concretes. Its corporate headquarters and primary laboratory facilities are located in Los Gatos, California.
Calera also has a pilot plant and process laboratory in Moss Landing, California, within the Monterey Bay Marine Sanctuary.
Calera carbon calculation table:
