Experimental investigation of synergistic behaviors of lignite and wasted activated sludge during their co-combustion

- Combustion of lignite-WAS blend was conducted in a horizontal tube furnace.
- Synergistic effects existed between lignite and WAS during their co-combustion.
- High temperature and O2 concentration resulted in a high conversion ratio of fuel.
- The different factors played by temperature and O2 concentration were revealed.
- The changing trends of C, O, and Cl contents in the solid particles were studied.

To explore the feasibility of co-combustion of lignite and wasted activated sludge (WAS) and examine their synergistic effects, combustion of lignite-WAS blend at a mass ratio of 90:10 in a horizontal tube furnace was conducted. Results showed that the synergistic effects occurred between lignite and WAS during their co-combustion because the actual conversion ratio of combustible substances (CR) was higher than the theoretical prediction. Effects of furnace temperature and O2 concentration of inlet atmosphere on CR were also determined. High furnace temperature and O2 concentration of the inlet atmosphere resulted in high CR. In the early combustion stage, the furnace temperature played a major role. In the middle stage, the furnace temperature and O2 concentration of the inlet atmosphere exhibited a combined effect. In the late state, the O2 concentration of the combustion atmosphere played a key role. Scanning electron microscopy (SEM) photos indicated that the micro appearance of solid particles and their changing trends during the combustion of lignite-WAS blend were similar to those of lignite because of the high proportion of lignite (90%) in the blend. However, when compared to the case of lignite, the solid particles of the lignite-WAS blend were smaller, rougher, and looser in structure as the combustion progressed. In the solid combustion products of blend, carbon (C), oxygen (O), and chlorine (Cl) contents exhibited different evolution behaviors. The C content first increased and decreased, the O content first decreased and increased, and the Cl content continuously decreased to zero.