Nitrogen trade-off during lignite chemical looping combustion using hematite as an oxygen carrier

The chemical looping combustion (CLC) of coal has attracted signification attention due to low CO2 and NOx emissions. In this paper, the lignite CLC and hematite used as an oxygen carrier (OC) were investigated. The thermodynamic behavior of NH3/HCN (NOx precursors) and Fe2O3 (the main component of hematite) were analyzed. Under different OC masses, the release characteristics of NH3 and HCN with temperature were studied using TG-MS. Using a fixed bed reactor, the nitrogen trade-off in the fuel reactor was investigated as a function of OC mass, changing reaction temperature, carrier gas flow rate, and type of OC (modified by K/Na/Ca/Ni/Cu/ Mn). Increasing the OC to lignite mass ratio led to a decrease of NH3 and HCN release. The release of HCN increased with the increasing temperature, while NH3 release decreased. An increased gas flow rate increased the emission of NH3 and HCN. Additionally, modifying the OC with Ni and Cu improved the oxidation performance and significantly reduced the emission of NH3 and HCN. To sum up, NH3 and HCN emission were lowest when the OC mass, temperature, and carrier gas flow rate were 10 g, 900 C, and 50 mL/min, respectively, and OC-Ni or OC-Cu was the OC.

Automated summary

The lignite chemical looping combustion and hematite as an oxygen carrier were studied in this paper. By analyzing the thermodynamic behavior and conducting experiments, it was found that increasing the oxygen carrier to lignite mass ratio could reduce the release of NH3 and HCN. The release of HCN increased with temperature, while NH3 release decreased. Increasing the gas flow rate resulted in higher NH3 and HCN emissions. Modifying the oxygen carrier with Ni and Cu improved oxidation performance and significantly reduced NH3 and HCN emissions.