Process characteristics of catalytic thermochemical conversion of oily sludge with addition of steel slag towards energy and iron recovery

The improper disposal of oily sludge and converter steel slag can be of great environmental concerns, herein, we proposed an innovative methodology by coupling the catalytic thermochemical conversion of oily sludge with the high-temperature reduction of steel slag, where the gas energy and iron resources can be recovered simultaneously. It was found out that the gas yield, iron reduction efficiency, as well as the carbon conversion, were positively correlated with the temperature, the amount of steel slag added and slag particle fineness. With the addition of steel slag, the carbon conversion increased from 76.6 % to 90.1 %, and the iron reduction efficiency increased from 38.5 % to 70.6 %. The phase and microstructure characterizations revealed that the iron-bearing phases (RO phase, Ca2Fe2O5) in steel slag were reduced into metallic iron by pyrolytic gaseous intermediate products (600 - 800 degrees C) and solid char (800 -1000 degrees C). The in-situ reduced iron particles in turn acted as an efficient catalyst for cracking/reforming reactions, resulting in remarkable fuel gases, i.e. H-2, CO evolution. Hence, the reduction of steel slag and the catalytic cracking/reforming of oily sludge were both enhanced. Furthermore, the technical-economic analysis in terms of material and energy balances was performed. It revealed that the proposed process was favorable for energy recovery and high added material production.