Evolution of Gases From the Pyrolysis of Raw and Torrefied Biomass and From the Oxy-Combustion of Their Bio-Chars

The current research assessed the evolution of gases from pyrolysis of biomass and from the subsequent combustion of bio-chars. Raw and torrefied biomass was pyrolyzed in nitrogen or carbon dioxide under high heating rates (10⁴ K/s) and high temperatures (1450 K). Pyrolyzates gases were monitored for carbon, nitrogen, and sulfur oxides. Subsequently, generated bio-chars were burned in both conventional (air) and simulated oxy-combustion (O₂/CO₂) gases. In principle, the oxy-combustion of renewable biomass coupled with carbon capture and utilization/sequestration can help remove atmospheric CO₂. Pyrolysis of biomass in CO₂ generated lower char yields, lower SO₂ and NO, and higher CO₂, CO, and HCN mole fractions, compared with pyrolysis in N₂. HCN was the most prominent among all measured nitrogen-bearing gases (HCN, NH₃, and NO) from biomass pyrolysis. Compared with their combustion in air, bio-chars burned more effectively in 30%O₂/79% CO₂ and less effectively in 21%O₂/79%CO₂. Emissions of CO were the lowest in 21%O₂/79%CO₂. Emissions of HCN were the highest in air combustion and decreased with increasing O₂ mole fraction in oxy-combustion; emissions of NO were highest in 30%O₂/79%CO₂, and emissions of NO were dominant during bio-char oxy-combustion compared with other N-compounds. In oxy-combustion, bio-chars released the lowest emissions of SO₂. Finally, the emissions of CO, NO, HCN, and SO₂ from the combustion of distiller's dried grains with solubles bio-chars were higher than those from rice husk bio-chars because of different physicochemical properties.