Calcium Looping Technology for CO2 Capture

This technology makes use of the idea that lime may be reused in a cyclic process to remove CO₂ from a mixture of gases where carbonate is calcined to generate a pure stream of CO₂ ready for sequestration. Flue gas from an existing power plant is introduced in the carbonator where the CO₂ reacts with CaO to form CaCO₃. This process must occur at elevated temperatures (600-650 ºC depending on CO₂ partial pressure). Removal rates around 80-90% seem to be a reasonable target for this technology.

The formed calcium carbonate is circulated to a different reactor where sorbent regeneration takes place. CaCO₃ is calcined and produces a concentrated stream of CO₂ suitable for capture and compression. Calcination step is highly energy demanding and it will likely occur at temperatures above 920 ºC. Heat requirements for sorbent calcination are covered by oxyfuel combustion in the second reactor itself. Once regenerated, the sorbent is returned to the carbonator to begin a new sorption cycle.

Because of the elevated temperatures, the entire cycle might be integrated in a steam cycle, reducing energy penalties of the capture system by several percentage points. The cost of natural sorbents for these cycles is significantly low, reducing operation costs.

This chapter examines the energy penalties of the Ca-looping CO₂ capture system, different types of sorbents and their performance subjected to repeated cycles of carbonation and calcination, the CO₂ capture efficiency and the possibility of integration of Ca-looping and power plants to reduce energetic penalties.

Keywords: Calcium looping, carbonation-calcination, high temperature sorbents, lime, cyclic sorbent degradation, energy integration, interconnected CFB, postcombustion, power plant, solid circulation, purge flow, pilot plants.