Pollutant Formation under Nitrogen and Carbon Dioxide Atmosphere of Torrefied Poplar in an Entrained Flow Reactor

The release behavior of sulfur (S), chlorine (Cl), and nitrogen (N) compounds contained in torrefied poplar (TP) is investigated using an entrained flow reactor. Due to the binding forms of S, Cl, and N in biomass and the high volatile content, pollutants are released during the first stage of combustion, devolatilization. Detailed knowledge of this process is essential for understanding the release and formation of pollutants. In this study, the release is investigated in a nitrogen (N2) and carbon dioxide (CO2) atmosphere to investigate the influence of a CO2-rich environment on pollutant release. The experiments are carried out at three different temperatures (T = 900, 1000 and 1100 °C). The results show that the atmosphere and temperature have a significant influence on the formation of pollutants. Corrosive gases can be expected at low temperatures and corrosive deposits can be expected at high temperatures in both atmospheres. An increasing temperature reduces the formation of sulfur dioxide (SO2) and carbonyl sulfide (COS) at a residence time of 0.5 s in both atmospheres. In N2 atmosphere, no SO2 and COS are detected at the temperature of 1100 °C. However, both corrosive species can be expected at 1100 °C in CO2 atmosphere. A decreasing formation of hydrogen chloride (HCl) with increasing temperature is observed in both atmospheres and residence times (0.22 and 0.5 s). In CO2 atmosphere, less HCl is formed at temperatures of 900 and 1000 °C as in N2 atmosphere. The nitrogen contained in the fuel is predominantly released as hydrogen cyanide (HCN) and nitric oxide (NO). A high temperature favors the formation of HCN in a N2 atmosphere. The NO formation decreases with increasing temperature. Comparatively less HCN and NO are formed in a CO2 atmosphere. The nitrous oxide (N2O) concentration decreases with increasing temperature at a residence time of 0.5 s in a CO2 atmosphere, while the N2O concentration increases in a N2 atmosphere. In the CO2 atmosphere, a lower overall formation of nitrogen species is observed.