Anthracite oxy-combustion characteristics in a 90 kWth fluidized bed reactor

• Anthracite oxy-combustion is experimentally characterized in a lab-scale FB reactor.
• Combustion efficiency is high for all tested oxy-conditions; most of values over 98%.
• Share of radiative heat transfer in the dense zone hardly increases when switching form air to O2/CO2 atmospheres.
• The higher the %O2 in the firing atmosphere, the lower both SO2 and NOx normalized emissions.
• An optimum temperature for SO2 capture is detected within 880–890 °C, for the 60/40% O2/CO2 test.
• The extent of gas staging to control NOx emissions is attenuated for the richest O2 atmospheres.

A comprehensive experimental characterization of Spanish anthracite oxy-combustion has been conducted, and the results are discussed in this paper, encompassing combustion efficiency, heat transfer, and pollutant emissions. The experimental work has been carried out in a 90 kWth bubbling fluidized reactor under a variety of O2/CO2 atmospheres and operating conditions (fluidization velocity, Ca:S ratio, and secondary oxidant supply). Combustion efficiency is improved under oxy-firing compared to air-firing, mainly due to the multiple-bubble regime and the lower fluidization velocities. The share of radiative heat transfer also rises, since O2/CO2 operation leads to an increase of the temperature in the dense zone of the reactor. Concerning SO2 emissions, the minimum values are found under the richest O2 atmosphere, yielding maximum values of sulfur capture efficiency in the temperature range of 880–890 °C. A decrease of NOx emissions is also observed under oxy-firing conditions, while the benefit of secondary oxidant supply has to be optimized for every specific O2 concentration.