A novel demonstration underway at Technische Universität Darmstadt (TU Darmstadt), a research university in Darmstadt, Germany, has shown a calcium carbonate looping (CCL) technology retrofitted at existing power plants to curb emissions of carbon dioxide (CO2) released during the combustion of fossil fuels is nearly ready for the market.

The technology is part of Project SCARLET (“Scale up of Calcium Carbonate Looping Technology for Efficient CO2 Capture from Power and Industrial Plants”), a three-year research project funded by the European Union to obtain reliable information for the scale-up of CCL.

CCL is essentially a post-combustion carbon capture technology involving two chemical reactions continuously running in two interconnected fluidized bed reactors. “In the first fluidized bed reactor, the absorber, a powder of burnt lime or calcium oxide (CaO), is contacted with the CO2 in the power station exhaust to form calcium carbonate (CaCO3). The calcium carbonate then is transferred in the second of the two fluidized bed reactors, known as the regenerator, where high temperatures force out the CO2 bound as the calcium carbonate thereby producing burnt lime and CO2 once again,” the university said. “The released CO2 can then be used for other purposes or stored whilst the burnt lime is returned to the first fluidized bed reactor. The material needs to be replaced after several dozen cycles, but the depleted lime can then be used in cement production making it a valuable raw material rather than a waste product.”

So far, researchers at TU Darmstadt have developed the technical prerequisites for the industrial deployment for the CCL process through testing at a 1-MW experimental facility (Figure 1). Model calculations and computer simulations show that the new process is more cost-effective and energy efficient than competing processes, they claim. Project SCARLET will now embark on tests at a bigger 20-MW pilot project at the coal-fired Émile Huchet power plant in Saint-Avold, France.

Figure 4_Co2CarbonateLooping
1. The testing facility. Technische Universität Darmstadt’s Jochen Hilz, Jochen Ströhle, and Bernd Epple (from left to right) in the carbon dioxide testing facility, which houses the 1-MW calcium carbonate looping experimental pilot plant. Courtesy: Katrin Binner

“We need 80 kilograms of lime to capture one tonne of CO2,” explained Professor Bernd Epple of the TU Darmstadt’s Institute for Energy Systems and Energy Technology. “The current process costs amount to around 20 to 27 euro per tonne of CO2. Other processes are more expensive and less efficient. Through SCARLET we have succeeded in moving the [CCL] process a major step forward towards market readiness.”

The team is now evaluating concepts for the utilization of the recovered CO2. The university noted that the price per tonne of CO2 is currently very low on the global markets. “At this point, any power plant operators making use of the process would not be in a position to be able to sell the captured CO2 at a rate that would enable them to break even, let alone make a profit. It would have to be stored or reprocessed.”

According to Professor Epple, the possibilities are vast. “We’re considering using the CO2 directly for the production of methanol,” he said. “Global market prices for methanol are higher than those for CO2.”

Sonal Patel is a POWER associate editor