Comparative reactivity of treated FBC‐ and PCC‐Fly ash for SO 2 removal

Two types of fly ash from fluidized bed (FBC) and pulverized coal combustors (PCC) were treated with calcium hydroxide (Ca(OH) 2 ) to produce reactive SO 2 sorbents. Treatment was performed using 28.6 mass% Ca(OH) 2 /fly ash mixtures slurried at 350 K for 8 h. Sulfation experiments were carried out in a thermogravimetric analyzer (TGA) at SO 2 concentration ranging from 0.11 to 0.67 vol% and 10(53–1153 K temperature range. At conditions close to those prevailing in an atmospheric FBC (1123 K, 3000 ppmv ami 20 vol% excess air), about 92% and complete conversion of CaO to CaSO 4 within 1 h reaction could be achieved with treated PCC and FBC fly ashes, respectively. Based on pore structural measurements for both sorbents, treatment enhanced the specific surface area (by about 8 times) as well as pore volume (by about 5 times). The shape of the N 2 ‐adsorption/desorption isotherms, specific pore area, and pore volume distribution curves remained unchanged. Study of the intrinsic kinetics of the reaction between treated fly ash and S02 indicated a first order reaction with respect to SO 2 concentration up to 0.31 vol% SO 2 (3.36 × 10 −8 mol/cm 3 ). Activation energies of 82.3 and 89.0 kJ/mol were calculated for treated PCC and FBC fly ashes, respsctively.