Utilization of sludge templated carbide slag pellets for simultaneous desulfurization and denitrification: Low and moderate temperatures and synergetic mechanism

Abstract

Higher SO2 and NO removal requirements have been proposed for a low carbon, flexible power generation. In this study, a low-carbon, high-efficiency, and low-cost mixed pellet was prepared through synergistic utilization of carbide slag and sludge. Further, this work systematically explored its combustive properties and SO2 and NO removal capabilities. The results indicated that more efficient mass transfer and catalyzed reactions were integrated into the unique pellet structure. The sludge-added mixed pellets exhibited good denitrification ability, at low and moderate temperatures, and improved the desulfurization performance of carbide slag. The pellets with carbide slag to sludge mass ratio of 10:3 has a 12.3% higher desulfurization efficiency than 10:0 pellets, as sludge extended the duration of the chemical reaction control phase and reduced the diffusion resistance of the product layer during desulfurization. The sludge-added pellets had satisfactory denitrification efficiencies of up to 70% at 550 °C, primarily due to the homogeneous and heterogeneous reductions between NO, pyrolysis gas, and char, which formed in the pre-combustion phase of sludge; these NO reduction processes were significantly catalyzed through carbide slag-CaO surface reduction and reoxidation. Notably, more C(O) and C(N) groups formed on the char surfaces under trace atmospheric O2 concentration (≤1%), enhancing NO reduction. This pellet combustion process conforms to the three-dimensional diffusion reaction model. This study will provide a theoretical direction for high value waste utilization of carbide slag and sludge and facilitates the industrial application of thermal power flexible variable load pollutant control.