Product property and environmental risk assessment of heavy metals during pyrolysis of oily sludge with fly ash additive

Abstract

Oily sludge is mainly engendered during crude oil exploitation, transportation and refining process. The effect of fly ash additive on the product distribution and property of oily sludge pyrolysis was studied by employing a fixed-bed reactor at 600 °C in this paper. The fly ash additives could enhance the yields of oil and gas from oily sludge pyrolysis. The highest pyrolysis oil and gas yields were achieved at 30.43 wt% and 11.56 wt% when the fly ash content is 50.0 wt%. The characteristic of the pyrolysis oil was determined by GC/MS and FTIR analysis. Hydrocarbon-type analysis showed that addition of fly ash to the oily sludge decreased the content of aromatic hydrocarbons and non-hydrocarbons (resins and heterocycles). The molecular weight of straight chain alkanes reduced with the increase of fly ash content (16.7–50.0 wt%). The lower heating value (LHV) of pyrolysis gas is in the range of 16.62–19.88 MJ/Nm3. The XRF results illustrated that pyrolysis char contains high concentrations of Fe, Ba, Si and Ca. The distribution of heavy metals (Pb, Zn, Cr, Cu, Ni, Cd, As and Hg) and the ecological risk related to the oily sludge and pyrolysis char were investigated by ICP. The results of this study showed that the potential ecological risk index values of oily sludge, fly ash and pyrolysis char without or with 50.0 wt% fly ash were 220.40, 246.99, 234.33 and 265.85, respectively. The heavy metals of oily sludge, fly ash and pyrolysis chars would be categorized as moderate risk.