Ash fouling behavior during the combustion of bituminous coal and high-Ca pyrolytic biochar under air and oxyfuel atmosphere

Abstract

Co-combustion of coal and pyrolytic biochar under oxy-fuel atmosphere is a promising option for addressing CO2 problems in power plants, where the issue of ash fouling during combustion was considered in this study. A high-Ca pyrolytic biochar from pilot-scale trail and a high-Si Utah bituminous coal were selected for single- and co-combustion on a drop tube furnace (DTF) coupled with fouling sampling system under the atmosphere of air and oxy50 (CO2:O2 = 50:50 vol%) at 1300 ℃. The fouling deposits were collected and characterized by various techniques to investigate the formation mechanism of ash deposits. The results indicated that the combined effects of impaction and capture resulted in the different deposition propensity from coal and biochar combustion under both air and oxy50 conditions. Besides, co-firing can inhibit the formation of ash deposits during coal combustion under air atmosphere when the blended biochar was greater than 50%, while the deposition propensity of the blend with 80% biochar rapidly aggravated under oxy50 atmosphere. The fine particles act as “glue” to fix coarse particles from impaction were the main source of the inside deposits from coal combustion, whereas the inside deposits from biochar combustion were dominated by agglomerated and sintered fine particles. Co-firing can weaken the “glue effect” from coal combustion, and finally presented as mitigated deposition propensity of inside deposits. Switching to oxy50 condition, the enhanced sulfidation of deposits and scavenging of alkali metal suppressed the growth of inside deposits from coal combustion, while that had minor impact on biochar. The inhibitory effect of co-firing on inside deposits diminished with the increased biochar under oxy50, where the deposition propensity of the blend containing 80% biochar was higher than that in air-firing.