Calcination of Ca-Based Sorbents in the Presence of Steam for Sorption-Enhanced Gasification Applications

The calcination kinetics of limestone and dolomite under conditions relevant to sorption-enhanced gasification (SEG) were investigated: mild temperature (775–850 °C), low CO2 partial pressure (0.05–0.10 bar), and a steam-rich (H2O balance) atmosphere. Experiments with two Ca-based sorbents (limestone and dolomite) were conducted in a fluidized bed reactor to assess both initial calcination kinetics and multicycle deactivation during 10 cycles under SEG carbonation conditions at 650 °C. Dolomite exhibited markedly higher calcination rates than limestone, which is consistent with the structural modifications induced by MgCO3 decomposition and the presence of MgO, resulting in a slightly lower apparent activation energy (115.96 kJ mol−1 for dolomite compared to 120.27 kJ mol−1 for limestone). Both sorbents showed a strong sensitivity to the deviation from the equilibrium CO2 partial pressure, with reaction orders near 2. The presence of steam was confirmed to have a significant catalytic effect, accelerating the first-cycle calcination rate compared to dry N2 conditions. Sorbent deactivation caused by sintering was more pronounced at higher temperatures and CO2 pressures. Dolomite showed significantly less deactivation, compared to limestone, which can be attributed to the increase in structural stability due to the presence of MgO. The kinetics obtained in this work contribute to the design of stable SEG based on dual fluidized bed reactors, particularly to assist in the selection of calcination operating conditions to minimize sorbent deactivation and in the development of stable CO2-sorbents.