Tri-combustion of multi-source solid wastes: Combustion behaviors, ash slagging characteristics, and gaseous pollutants emissions

Abstract

The huge production of sewage sludge (SS), combustible construction and demolition (C&D) waste, and waste logistics packaging challenges the sustainable development of our cities. Co-combustion is a promising way for multi-source solid waste management due to the efficient volume reduction, waste to energy, and easy operation in existing facilities. Pine sawdust (SD) and polyethylene (PE) were selected as representative components of combustible C&D waste and waste logistics packaging. Their combustion behaviors, ash slagging characteristics, and gaseous pollutants (HCl, NO_x, SO₂) emissions were investigated in the tri-combustion process. Results indicate that adding SD and PE reduces burnout temperature (T_h) by 188–230 °C and improves both the combustion stability index and comprehensive combustion index (CCI), enhancing SS combustion. The highest CCI value of SS-SD-PE was achieved at 0.5–0.3–0.2. Adding SD and PE elevates the ash fusion temperature, although a significant slagging tendency persists. Higher combustion temperature hinders chlorine fixation. The decrement of NO_x emission at high temperature correlates with the catalytic effect of metal oxides like Ca and Fe and the reduction by intermediates such as CO and soot particles. Tri-combustion can promote HCl emission. The lowest HCl emission of 0.274 mg·g⁻¹ is yielded at 0.4–0.3–0.3. The increase in SD and PE blending ratio leads to an increment of N conversion rate from 15.72 % to 24.5 % and from 2.47 % to 27.5 %, respectively. The increment of SD blending ratio promotes SO₂ emission, while PE can suppress it. These findings provide a better understanding of the interactions during the combustion of multi-source solid waste.