The agglomeration of CaO-based sorbent used to capture CO2 in fluidized bed

High temperature CO2 capture via a CaO-based sorbent was investigated in a fluidized bed. The sorbents tested included natural limestone, pellets made from powdered lime with a calcium aluminate cement binder, mixtures of natural limestone and alumina with a ratio of 1:1 and 2:1. Air-combustion flue gas with a composition of 15% CO2 + 6% H2O + 3% O2 + 76% N2 at 680°C and oxy-combustion flue gas with a composition of 80% CO2 + 16% H2O + 3% O2 + 1% N2 at 950°C were used as a carbonation and calcination atmosphere separately to simulate real CFB running conditions. Results showed that pellets have a lower carrying capacity (g CO2/g calcined limestone or pellets) than nature limestone for the first few cycles mainly due to the existence of calcium aluminate cement (CaAl2O4) binder, while pellets have better cyclic activity than natural limestone. Solids agglomeration was found to be a big problem in the application of using Ca-based sorbent to capture CO2. The solids was not powdery as original ones and tended to clump together after few cycles, making it difficult to fluidize and some dead areas form in the fluidized bed. Agglomeration became severer as cycle number increase and pellets had a much slighter agglomeration than nature limetone due to large particle size. The two mixtures were run in different conditions and H2O was speculated to accelerate agglomeration.