The fate of mercury in fluidized beds under oxy-fuel combustion conditions

Among the different pollutant gases released from oxy-coal combustion, mercury is the responsible for important operational issues in the CO2 processing unit, being able to cause material corrosion. Some studies concerning the fate of mercury during oxy-coal combustion are referred to pulverized coal (PC) boilers. However, the fate of mercury emissions in fluidized bed (FB) combustors has yet to be elucidated. In this work, mercury emissions from a 3 kWth bubbling FB combustor operating under oxy-fuel combustion conditions have been evaluated. For this purpose, two Spanish Ca-based sorbents and two Spanish coals were used. The effects of type of Ca-based sorbent, the Ca/S molar ratio, temperature and recycled gases (NO, SO2 and H2O) typical in oxy-fuel combustion process on the distribution of mercury species have been analyzed. It was observed that the presence of Ca-based sorbents in the combustor favored mercury fixation as particle-bound mercury which exhibited a maximum at a temperature about 925 degrees C corresponding to the highest degree of limestone sulfation. SO2 recirculation inhibited the Hg-0 oxidation and thus the mercury fixation as particle-bound mercury decreased. However, neither NO nor steam recirculation affected mercury speciation. (C) 2015 Elsevier Ltd. All rights reserved.