Flue gas-to-ash desulfurization of combustion of textile dyeing sludge: Its dependency on temperature, lignocellulosic residue, and CaO

Flue gas-to-ash controls on sulfur (S) species of the combustion of textile dyeing sludge (TDS) are pivotal in the achievement of circular and cleaner economies. This experimental study aimed to characterize S transformations in TDS as a function of temperature (600-1000 degrees C) and blend ratios of spent mushroom substrate (SMS) and calcium oxide (CaO) through thermodynamic equilibrium simulations. The conversion ratio of S to flue gas from the mono-combustion of TDS rose by 29.7% between 600 and 1000 degrees C and was 92.9% at 1000 degrees C. The increasing sulfur dioxide (SO2) emission with the high temperature occurred from the decomposition of sulfates. The conversion of S to SO2 decreased significantly with an increase in SMS from 10 to 50% and enhanced the S distribution in fly ash. Potassium and phosphorous in SMS appeared to play a significant role in the conversion of S. The addition of CaO exhibited a good desulfurization performance, with the S content of ash peaking at 5.2% at 800 degrees C with 7% CaO. The desulfurization efficiency of CaO highly depended on the temperature and blend ratios. The addition of SMS facilitated the agglomeration to form large particles at 1000 degrees C and formed more micro pores on their surfaces. Our equilibrium simulations pointed to the important role of CaO-assisted co-combustion versus mono-combustion of TDS in the S retention as well as to the enhanced decomposition of calcium sulfate (CaSO4) by SMS. Chlorine had a better affinity toward potassium to promote the release of gaseous potassium chloride (KCl) which in turn appeared to react with SO2 in flue gas and formed sulfates through sulfation reaction.

Automated summary

In the combustion of textile dyeing sludge, controlling sulfur (S) species through flue gas-to-ash processes is crucial for achieving circular economies. The experimental study found that temperature and blend ratios play significant roles in transforming S in TDS, with the addition of spent mushroom substrate (SMS) and calcium oxide (CaO) enhancing desulfurization efficiency. The results suggest that a combination of SMS and CaO can improve the retention of S and enhance the decomposition of calcium sulfate (CaSO4).