CO₂ Capture from Atmospheric Air using the CaCO₃-CaO cycle

Motivation

Air remediation: IPCC scenarios predict that CO₂ capture from power-plant flue gases will not be enough to stabilize CO₂ concentration in the atmosphere and additional CO₂ capture from ambient air will become necessary in view of increasing emissions derived from transportation and other distributed sources.
Emissions: Use of solar energy for process heat eliminates CO₂ emissions produced during the energy-intensive capture process.
Logistics: CO₂ capture plant located next to the final storage site eliminates the need for CO₂ transportation

Background – A novel solar thermochemical carbonation-calcination cycle for the capture of CO₂ directly from air is depicted in Figure 1. The concentrated solar energy serves as the source of high-temperature process heat. The theoretical net energy requirements are estimated to be 2.5 MJ/mol CO₂ captured.

Energy and material flows for the CO2 capture form atmospheric air using the solar-driven carbonation and calcination reactions. — Fig.1. Energy and material flows for the CO₂ capture form atmospheric air using the solar-driven carbonation and calcination reactions.

The solar reactor concept is illustrated in Fig. 2. It features a fluidized bed that serves the functions of both the carbonator and calciner, eliminating the need for transportation of solids.

Carbonation step:
ambient air and steam is the fluidizing gas, CaO is transformed to CaCO₃,and CO₂-depleted air leaves the reaction site
Calcination step:
H₂O or CO₂ is the fluidizing gas, CaCO₃ is transformed to CaO, and pure CO₂ leaves the reaction site

Fig.2. Schematic of a solar fluidized-bed reactor for the consecutive conduction of the carbonation-calcination cycles using solar energy

A laboratory-scale solar fluidized bed reactor system shown on Fig. 3 was tested for performing both steps of a carbonation-calcination thermochemical cycle for the removal of CO₂ from ambient air using solar energy. Five consecutive cycles were experimentally demonstrated in a high-flux solar simulator. During all carbonation steps, CO₂ was practically completely removed from air since the off-gas contained less than 1 ppm CO₂ (Fig.4). During all calcination steps, CO₂ was released until reaction reached completion after about 500 s. The fluidized-bed system proved to be a suitable reactor concept for effecting both steps of the proposed thermochemical cycle for capturing CO₂ from ambient air.

Fig.3. Experimental setup at High-Flux Solar Simulator

Experimental demonstration: measured temperatures and CO2 concentration in the off-gas for five consecutive carbonation-calcination cycles — Fig.4. Experimental demonstration: measured temperatures and CO₂ concentration in the off-gas for five consecutive carbonation-calcination cycles

Objectives – Investigate and experimentally demonstrate the thermochemical cycle for CO₂ capture from air using concentrated solar power.

The research work includes:

Thermodynamic analyses of the proposed solar thermochemical cycle.
Exergy analysis for the open-material cycle that captures CO₂ from air while co-producing H₂.
Screening and comparison of the different sorbents for CO₂ capture from ambient air.
Kinetic analysis of the carbonation reactions by thermogravimetry.
Design, fabrication, and testing of a laboratory scale solar reactor system for performing carbonation-calcination thermochemical cycle.

Project-related Publications

CO2 Capture from Atmospheric Air using the CaCO3-CaO cycle

CO₂ Capture from Atmospheric Air using the CaCO₃-CaO cycle