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

Abstract

Abstract 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.