Combustion behavior of solid waste fuels in the vertical tube reactor under different oxy-fuel environments

Oxy-fuel combustion technology has been recognized as one of the promising ways for cost-effective CO₂ capture. The co-combustion characteristics of flax straw biomass/bituminous coal mixture (FS/BC) and flax straw biomass/sewage sludge mixture (FS/SS) under air, oxy-fuel (21 %/79 % O₂/CO₂) and oxygen-enriched oxy-fuel (30 %/70 % and 40 %/60 % O₂/CO₂) conditions were investigated in the vertical tube reactor. In particular, the study focused on the burning characteristics, the effect of blending ratio, and flue gas emissions. The findings indicated that flax straw biomass exhibited superior ignition performance compared to its blends with sewage sludge and bituminous coal. A higher O₂ concentration from 21 % to 40 led to a reduction in ignition delay time by 4 s at 850 ℃ and by up to 10 s at 950 ℃. Moreover, char combustion time was reduced by 50 % for FS/SS blends due to the lower fixed carbon content compared to FS/BC blends. Additionally, increasing the O₂ concentration resulted in lower emissions of CO by ∽40 % and N₂O by ∽45 % for both blends. However, this also led to a slight increase in SO₂ and NO emissions by ∽15 % and ∽26 %, respectively. The optimal conditions for the tested samples in oxy-fuel environment were found to be 30 % O₂/70 CO₂, which enhanced combustion performance while lowering flue gas emissions.