Ca(OH)2 Superheating as a Low-Attrition Steam Reactivation Method for CaO in Calcium Looping Applications

Steam hydration of lime is an effective method for restoring CO2 capture activity but gives rise to high particle attrition rates in a fluid bed reactor This paper describes the phenomenon of Ca(OH)(2) superheating, also referred to as superheated dehydration (SD) The potential of an attrition-free lime reactivation process using this phenomenon is also investigated Attrition rates of the sorbent are measured when a reactivation step using steam hydration is implemented every three carbonation/calcination cycles It has been shown that the presence of CO2 during the dehydration step reduces attrition during subsequent cycles Experiments performed in a small fluid bed reactor show that the presence of 40-100% CO2 during the dehydration step increases the initiation temperature of the decomposition of Ca(OH)(2) from 445 to 618 degrees C The thermodynamic equilibrium water vapor pressure for the dehydration reaction at 618 degrees C is 516 kPa, whereas no water vapor was detected in the reactor during the dehydration step before the temperature reached 618 degrees C Under these circumstances it is proposed that the Ca(OH)(2) is in a nonequilibrium superheated state A CO2 capture cycling experiment, with a reactivation step every three carbonation/calcination cycles, maintained an average activity of 60%, creating only 3 25% of fines < 150 mu m after 28 carbonations The reactivation step consisted of hydrating the sorbent at a temperature of 270 degrees C and dehydrating it in 100% CO2 with a 23 min hold at 520 degrees C It is proposed that the SD phenomenon may be a key step in the development of an industrially feasible method of lime reactivation for use in CO2 capture and in thermal energy storage applications