Investigation of the nitrogen migration characteristics in sewage sludge during chemical looping gasification

Abstract

Increasing attention has been given to the control of nitrogen pollutants during the process of using sewage sludge. In this paper, the gasification characteristics and the law of nitrogen migration in the process of chemical looping gasification (CLG) of sewage sludge were explored. Copper slag calcined at 1100 °C (1100CS), FeAl (Fe2O3+Al2O3), NiFeAl (NiFe2O4+Al2O3), and NiAl (NiO + Al2O3) were used as oxygen carrier. The addition of an oxygen carrier could increase the carbon conversion rate and decrease the low heating value. NOx precursors (HCN and NH3) were the main nitrogen-containing gas pollutants (∼40%). The sum yield of char nitrogen and tar nitrogen was only ∼10%. Nitrile nitrogen, heterocyclic nitrogen and amide nitrogen were the main nitrogenous compounds in tar nitrogen. Increasing the oxidative activity of the oxygen carrier could significantly promote the oxidative transformation of N2 from the NOx precursors, tar nitrogen, char nitrogen. Additionally, the migration of fuel nitrogen includes synchronous autothermal pyrolysis (stage Ⅰ) and oxidative pyrolysis of the three-phase product under the action of [O] (stage Ⅱ). Finally, this research realizes the energy utilization of sludge and reduces the release of nitrogen pollutants.