Calcium Looping Implementation at Heavy Fuel Oil-Fired Power Plants: The Effect of Calcination/Carbonation Cycles on SO2 & CO2 Co-Capture By Two Structurally Distinct Limestones

Heavy fuel oil (HFO) is a low cost, highly sulfurous, unavoidable residual petroleum distillation byproduct representing 2-5% of refinery yield. Although phasing out HFO usage as a power source is unlikely while the world remains reliant on petroleum products, literature on CCS implementation at HFO-fired power plants is scarce. Calcium looping (CaL) is an advanced post-combustion CO₂ capture technology that utilizes limestone-derived calcium oxide as a CO₂ sorbent. Since CaO sulfation occurs at typical process conditions, CaL can simultaneously concentrate CO₂ and capture SO₂ from HFO flue gas. CaL typically utilizes two interconnected fluidized beds to cycle between: (1) CO₂ capture by CaO carbonation and (2) CaO regeneration by CaCO₃ calcination. As limestone is cycled, its capture capacity decays. The rate of decay is dependent on sorbent exposure to steam and deactivating impurities such as SO₂, which are present in HFO flue gas. In this study, samples of two structurally distinct limestones were cycled in the presence of: (1) steam, (2) both steam and SO₂. Relative limestone attrition, sintering, and deactivation rates were assessed. Samples at different stages of activity (X_max = 0.6, 0.3 and 0.1) were collected and used to explore the influence of sorbent cycling and CaSO₄ content on CO₂ and SO₂ co-capture from synthetic HFO flue gas during carbonation. Bubbling fluidized bed (BFB) reactors equipped with effluent line sampling for continuous CO₂, SO₂, and O₂ gas analysis were used. Sulfation and carbonation of cycled material was further explored by means of TGA analysis. Porosimetry and BET surface area analyses were performed on samples of the cycled limestones, and differences in CO₂ and SO₂ capture performance were correlated to differences in material surface structure and porosity.