Effect of Hydrothermal Treatment on the Steam Gasification Behavior of Sewage Sludge: Reactivity and Nitrogen Emission

Abstract

Hydrothermal treatment not only reduces the cost of moisture removal but also improves the quality of the syngas from steam gasification for sewage sludge. However, the effect of the treatment on the gasification behavior, including the reactivity and emission of gaseous N compounds, was not clear. In this study, the kinetic analysis based on a thermogravimetric (TG) experiment was used to examine the reactivity of the hydrochars. In addition, the evolution of N functionalities in hydrochar with treatment conditions and the discharge of NH3 and HCN during gasification were also investigated. The result showed that the treatment lowered the activation energy of sludge in gasification of remaining char and effectively reduced the discharge of NH3 and HCN. CaO addition into raw sludge before treatment caused the shift of the peak temperature to the lower range in remaining char gasification and promoted the conversion of HCN to NH3.