The Effects of Repeated Cycles of Calcination and Carbonation on a Variety of Different Limestones, as Measured in a Hot Fluidized Bed of Sand

The capacity of calcined limestone to react repeatedly with CO2, according to CaO(cr) + CO2(g) = CaCO3(cr) (eq I), and also its regeneration in the reverse reaction have been studied in a small, electrically heated fluidized bed of sand, for five different limestones. The forward step of eq I is a promising way of removing CO2 from the exhaust of, for example, a coal-fired power station, ready for sequestration or as part of a scheme to generate H2 using an enhanced water−gas shift reaction. The reverse step regenerates the sorbent. The uptake of CO2 by CaO, produced by calcining limestone, was measured using a bed of sand fluidized by N2 at ∼1023 K. For each experiment, a small quantity of limestone particles was added to the hot sand, whereupon the limestone calcined to produce CaO. Calcination was completed in ∼500 s for particles of a mean diameter of ∼600 μm. Next, CO2 was added to the fluidizing nitrogen to carbonate the CaO for ∼500 s. Measurements of [CO2] in the off-gases enabled the rates of cal...