Integration of sludge combustion with treatment of hot blast furnace slags: pollution control and adding heating value

Combustion accounts for a dominant strategy for the harmless and volume reduction treatment of sludge while its low heating value challenges the combustion efficiency. High heating value and carbon-rich fuels like coal could improve the system's heating value but the carbon footprint could be increased as well. In this study, we proposed a novel sludge combustion method in the presence of hot blast furnace slags (BFS) considering both the heating value improvement and the pollution control. Process characteristics, kinetics, phase evolutions and heat balance were identified regarding this integrated strategy. TG-MS was first used to monitor the weight loss and the released gas signals with the adjusted weight ratio of sludge to BFS during the combustion process. The results showed that a weight ratio of 5 : 5 enabled better fixation of polluting gases released such as NH3 and NO, agreeing with the scale-up experiments that BFS had a fixation effect on nitrogen. The non-isothermal kinetic analysis revealed that the sludge combustion followed a diffusion model either with or without BFS, while BFS increased the activation energy and pre-exponential factor at the same time. A heat balance analysis showed that the heating value could be greatly increased to around 10 times of pure sludge with a sludge/BFS weight ratio of 5 : 5, i.e., from 110 to 1098 kJ kg−1, which could remarkably enhance the combustion efficiency. Our study thus provided an important guidance of sludge treatment by coupling industrial processes with pollution control and adding heating value.