(Co-)combustion behaviors and products of spent potlining and textile dyeing sludge

Abstract

Abstract Co-combustion performances, ashes, gases and thermodynamics were quantified for spent potlining (SPL) and textile dyeing sludge (TDS) (with)out CaO. During the four decomposition stages of the blends according to the (D)TG experiments, the interaction among Na, Ca, F, Al, and S led to CaAl2O4, CaF2, and Na2SO4 which converted inorganic compounds into ash. Increased comprehensive combustion index, and decreased burnout temperature with 50% SPL indicated a better combustion and char burnout, and a shorter combustion process. CaO reduced the F volatilization and increased F− in the residual ash with 10% CaO. NaF was completely converted into CaF2 reducing the toxicity of soluble F− in the residual ash. The predom diagram of Na Ca F S using thermal simulations showed the stable existence regions of CaF2 and Na2SO4. The changed migration mechanisms of F− and S caused ash compositions to consist of Na2SO4 and CaF2 for the co-combustions, and of NaF and CaSO4 for the mono-combustions. 10% CaO promoted CaF2, Na2SO4, CaAl2O4, and to a lesser extent, Fe2O3. The main gases evolved from the co-combustion included HF, SO2, COS, CS2, HCN, NH3, NO, and NO2.