Enrichment mechanism of arsenic in fine ash deposits during co-combustion of rice husk and coal

Arsenic is a harmful trace element and its behavior under several combustion conditions is of interest. Though the mechanisms regarding arsenic capture and transformation in combustion systems are well known, it is still worth investigating the dominant factors for particular fuels and combustion conditions. Considering the widely application of biomass resources for power generation and the advantages of oxy fuel combustion, this work explored the partitioning behavior of arsenic in ash deposits during co-combustion of high-Si rice husk (RH) and coal at air and oxyfuel condition. Results showed that arsenic was enriched in the inside ash deposits with smaller particle sizes. A larger proportion of arsenic partitioned into the particle phase in oxygen-rich condition than in air. Fe was found to be the key mineral for arsenic enrichment in RH fine ash particles. Combined with thermodynamic calculation, it was concluded that RH doping would change the transformation mechanism of arsenic in size-segregated ash particles during coal combustion. Particularly, the role of Fe on arsenic capture was more remarkable than Ca with RH addition. The enrichment of arsenic in fine ash particles weakened due to the interactions of Si with Ca/Fe. As a result, more arsenic was assumed to be left in the flue gas, which might cause potential emission risk to the environment.