Operation experience in a Calcium Looping plant using biomass as a fuel in a 2MWth oxy-fired circulating fluidized bed calciner

This study presents recent experimental results from the 1.7 MW_th “La Pereda” Calcium Looping pilot plant, following its upgrade to enable biomass combustion in the oxy-fired circulating fluidized bed combustor-calciner which is the main focus of this work. New steady-state trials were conducted under oxy-combustion conditions using biomass pellets in the calciner, accumulating >1500 h of additional experience. A key objective of the new experiments was to leverage the high reactivity of biomass as a fuel to enable combustion under conditions of low oxygen excess. This approach resulted in outlet oxygen concentrations in the CO₂-rich flue gas from the calciner close to zero, and nitrogen oxide (NOₓ) levels below 20 ppmv. These conditions have the potential to reduce the purification requirements downstream of the CO₂ capture system, while at the same time, the presence of unburnt fuel constituents and/or intermediate combustion products, such as CO and C_xH_yO_z, needs to be managed according to the configuration and boundary conditions of the entire CCS/U system. In particular, operation under sub-stoichiometric conditions (λ < 1) may lead to CO and unburnt hydrocarbon levels that could be incompatible with CO₂ transport for permanent storage. No adverse impacts of biomass firing were observed on sorbent performance or CO₂ capture efficiency, which reached up to 95% under standard conditions.