thus it is more likely that SO2 will come into contact with CaCO3 than CaO. However, both reactions are possible, and are shown below. Indirect sulfation: CaO + SO2 + 1/2 O2 → CaSO4 Direct sulfation: CaCO3 + + 1/2 O2 → CaSO4 + CO2 Because calcium sulfate has a greater molar volume than either CaO or CaCO3 a sulfated layer will form on the outside of the particle, which can prevent the uptake of CO2 by the CaO further inside the particle. Furthermore, the temperature at which calcium sulfate dissociates to CaO and SO2 is relatively high, precluding sulfation's reversibility at the conditions present in CaL. Technical implications Calcium looping technology offers several technical advantages over amine scrubbing for carbon capture. Firstly, both carbonator and calciner can use fluidized bed technology, due to the good gas-solid contacting and uniform bed temperature. Fluidized bed technology has already been demonstrated at large scale: large (460MWe) atmospheric and pressurized systems exist, and there is not a need for intensive scaling up as there is for the solvent scrubbing towers used in amine scrubbing. Also, the calcium looping process is energy efficient. The heat required for the endothermic calcination of CaCO3 and the heat required to raise the temperature of fresh limestone from ambient temperature, can be provided by in-situ oxy-fired combustion of fuel in the calciner. Although additional energy is required to separate O2 from N2, the majority of the energy input can be recovered because the carbonator reaction is exothermic and CO2 from the calciner can be used to power a steam cycle. A solid purge heat exchanger can also be utilized to recover energy from the deactivated CaO and coal ashes from the calciner. As a result, a relatively small efficiency penalty is imposed on the power process, where the efficiency penalty refers to the power losses for CO2 compression, air separation and steam generation. It is estimated at 6-8 % points, compared to 9.5-12.5 % from post combustion amine capture. The main shortcoming of Ca-looping technology is the decreased reactivity of CaO through multiple calcination-carbonation cycles. This can be attributed to sintering and the permanent closure of small pores during carbonation. Closure of small pores The carbonation step is characterized by a fast initial reaction rate abruptly followed by a slow reaction rate (Figure 2). The carrying capacity of the sorbent is defined as the number of moles of