Biomass combustion with in situ CO2 capture by CaO in a 300 kWth circulating fluidized bed facility

Abstract

This paper reports experimental results from a new 300 kWth calcium looping pilot plant designed to capture CO2 “in situ” during the combustion of biomass in a fluidized bed. This novel concept relies on the high reactivity of biomass as a fuel, which allows for effective combustion around 700 °C in air at atmospheric pressure. In these conditions, CaO particles fed into the fluidized bed combustor react with the CO2 generated during biomass combustion, allowing for an effective CO2 capture. A subsequent step of regeneration of CaCO3 in an oxy-fired calciner is also needed to release a concentrated stream of CO2. This regeneration step is assumed to be integrated in a large scale oxyfired power plant and/or a larger scale post-combustion calcium looping system.

The combustor-carbonator is the key reactor in this novel concept, and this work presents experimental results from a 300 kWth pilot to test such a reactor. The pilot involves two 12 m height interconnected circulating fluidized bed reactors. Several series of experiments to investigate the combustor-carbonator reactor have been carried out achieving combustion efficiencies close to 100% and CO2 capture efficiencies between 70 and 95% in dynamic and stationary state conditions, using wood pellets as a fuel. Different superficial gas velocities, excess air ratios above stoichiometric requirements, and solid circulating rates between combustor-carbonator and combustor-calciner have been tested during the experiments. Closure of the carbon and oxygen balances during the combustion and carbonation trials has been successful. A simple reactor model for combustion and CO2 capture in the combustor-carbonator has been applied to aid in the interpretation of results, which should facilitate the future scaling up of this process concept.