- Calcium looping (CaL) is an emerging thermochemical process primarily developed for carbon capture, utilization, and storage (CCUS) applications, particularly from high-temperature industrial sources such as power plants, cement, and steel production.
- The core of the calcium looping process involves the reversible reaction between calcium oxide (CaO) and carbon dioxide (CO₂). In this cycle, CaO acts as a solid sorbent that reacts with CO₂ to form calcium carbonate (CaCO₃) in a carbonation reactor. The calcium carbonate is then transported to a calciner, where it is thermally decomposed at high temperatures (typically above 850°C) to release a concentrated stream of CO₂ and regenerate CaO for reuse in the next cycle.
- The carbonation reaction (CaO + CO₂ → CaCO₃) is exothermic and occurs at temperatures around 600–700°C, while the calcination reaction (CaCO₃ → CaO + CO₂) is endothermic and requires external heating. The energy required for the calciner is usually provided by oxy-fuel combustion or alternative heat sources, depending on the design and efficiency goals of the process. The high-temperature operating conditions of calcium looping make it especially compatible with industrial systems that already produce or handle hot flue gases, enabling integration without significant infrastructure modification.
- One of the major advantages of calcium looping is its ability to handle large volumes of CO₂ with relatively low sorbent cost. Calcium oxide is typically derived from natural limestone (CaCO₃), an abundant and inexpensive material. Additionally, the solid–solid reactions involved in the process avoid many of the issues associated with liquid absorbents, such as corrosion and solvent degradation. The cyclic nature of the process allows the solid sorbent to be regenerated and reused multiple times, although performance tends to degrade over time due to sintering, pore blockage, and loss of surface area.
- To counteract sorbent deactivation, researchers have developed various strategies including sorbent reactivation through hydration, the use of synthetic CaO-based materials, and process optimization to prolong the effective lifespan of the sorbent. Furthermore, calcium looping can be combined with other processes, such as chemical looping combustion (CLC) and integrated gasification combined cycles (IGCC), to enhance overall system efficiency and reduce greenhouse gas emissions.
- Beyond carbon capture, calcium looping has potential applications in energy storage, hydrogen production, and thermochemical cycles due to its ability to store and release heat during the carbonation and calcination reactions. This makes it a promising technology not only for decarbonization but also for supporting renewable energy systems that require thermal energy storage.
