CO2 capture performance of CaO–based pellets in a 0.1 MWth pilot-scale calcium looping system

• Ca-looping system was demonstrated for in situ CO2 capture using sorbent pellets.
• Testing campaign was conducted in CanmetENERGY's 0.1 MWth pilot dual-fluid beds.
• CO2-rich atmospheres were achieved by oxy-biomass combustion in the calciner.
• The results provided important insights into the behavior of sorbent pellets.

Post-combustion CO2 capture performance of CaO-based pellets tested in a pilot-scale calcium looping system is investigated. The pellets were prepared from two natural limestones with 10 wt.% cement as a binder. The pilot-scale system setup consists of a circulating fluidized bed calciner operating at 900 °C and a bubbling bed carbonator operating at 650°C. The flue gas was supplied to the carbonator from a natural gas-fired combustor, while the oxy-fuel combustion condition was established in the calciner using wood pellets as the fuel source. The test campaign results showed that CO2 capture efficiencies in the range of 80–90% can be achieved for each sorbent. The carbonation efficiency with limestone was steady throughout the ~ 5 h steady-state operation period, whereas efficiencies obtained with pellets exhibited a gradual decline over the duration of the test. An average carbonation conversion over the steady-state duration indicated the superiority of limestone with a conversion of 7.8%, compared to that of 6.0–6.8% achieved by pellets. Neither the limestone type nor the make-up mode showed any significant effect on the performance of the pellets. The inferior performance of pellets compared to that of limestone was attributed to the rapid and sever sintering of the pellets at the early stages of the test. It was concluded that, under the test conditions tested here, the use of CaO-based pellets in a pilot-scale calcium looping system does not seem to be a promising approach due to the significantly higher cost of production with comparable CO2 capture performance to that of limestone. Nonetheless, the test campaign provided important insights into the behavior of synthetic/modified sorbents under pilot-scale calcium looping conditions, which has not been reported elsewhere.

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