New Method for Making Concrete May Eliminate Emissions

If cement producers were a country, they’d be the third-largest carbon emitter in the world, behind only China and the US. The manufacturing of cement used to make concrete produces an estimated 8% of global carbon emissions, which is nearly 3B tons of carbon dioxide per year.

In the epicenter of SoCal’s cement industry, San Bernardino County’s high desert in the Inland Empire—a region rich in limestone, the key ingredient of cement—two huge cement plants produce more combined carbon emissions than the Golden State’s aviation industry.

The plants, CalPortland’s Cemex facility in Oro Grande and a Mitsubishi Cement plant in Lucerne Valley, along with four other cement manufacturing facilities in CA have made significant gains in energy efficiency over the past two decades. According to the state Air Resources Board, the plants collectively have reduced emissions by about 17% compared to levels in 2000.

But California’s cement makers are going to have to more than double those emissions reductions to meet the state’s new requirement that cement manufacturing must cut carbon emissions by 40% by the end of 2035 and achieve net zero emissions by 2045.

If an experimental pilot program now underway involving a new form of renewable energy—a concentrated solar power installation known as a heliostat—is successful, they may be able to meet the emissions-reduction goal before the deadline.

A Pasadena-based startup named Heliogen was just awarded a $4.1M grant from the US Department of Energy to fund the pilot project in the Mojave Desert town of Lancaster, CA, that literally aims to solve the cement emission problem using smoke and mirrors.

At the site of an old driving range, a 55-foot tower equipped with black pipes and cameras glows with a light brighter than the sun. The light is beamed up to the tower from a field of mirrors—known as a heliostat—which have been programmed to follow the sun and beam concentrated sunlight up to a tower-top receiver, which is linked to a system that can capture and store intense heat.

Heliogen says the installation could be used to power a large number of energy-intensive industries that run 24/7 operations, but its first test will involve an effort to decarbonize cement production, according to a report in the Orange County Register.

The traditional way of producing cement involves grinding up limestone, combining it with other minerals and preheating the batch in a large tower to about 1,600 degrees F. The heated batch is then transferred to a rotary kiln, where the temperature reaches up to 2,800 degrees F.

The heating process, known as calcination, produces solid gray clumps known in the industry as clinker. Clinker is combined with gypsum and pulverized into cement powder that is combined with sand and sold to contractors who just have to pour it into cement mixers and add water to make concrete.

Heliogen’s pilot program is building a system with a vacuum that will suck powderized limestone and other minerals to the top of the tower, where the materials will be hit with the intense heat generated by the heliostat, instantly starting the chemical reaction that produces clinker.

The clinker at the Heliogen installation will move into a kiln that is powered by clean energy such as hydrogen—which also can be created using the concentrated solar power generated by the field of mirrors.

Heliogen aims to have the demonstration project for solar-powered cement calcination completed by 2025, followed by a commercial-scale installation by 2028—in time to provide a viable solution to meet the state’s 2035 carbon-reduction goal for cement manufacturing.