Experimental investigation on smoldering combustion for oil sludge treatment: Influence of key parameters and product analysis

Oil sludge disposal has recently become a challenge because of its large reserves and high toxicity. Smoldering combustion is a new approach for organic waste treatment where organic waste is efficiently destroyed with minimal energy input. This study aimed to explore the feasibility of smoldering combustion for oil sludge treatment with a low filling medium addition ratio. The influence of four key parameters (i.e., the moisture content of oil sludge, filling ratio, grain size, and airflow rate) on the smoldering combustion characteristics was explored. Reducing the moisture content of the oil sludge and increasing the airflow rate improved the smoldering robustness of oil sludge. The smoldering process could remain self-sustaining across sand-to-oil sludge filling ratios of 1:3-2:1, and a sand-to-oil sludge filling ratio of 2:3 was the most favorable. The oil sludge mixed with the medium-sized sand has a high air permeability, which brought about the maximum treatment rate. Detailed post-treatment analyses of smoldering products were conducted to evaluate the extent of oil sludge disposal. Smoldering combustion could completely remove volatile petroleum hydrocarbons (C10-C40) in the oil sludge, with a harmless carbon-based black residue after incomplete combustion under certain limiting conditions. Most of the metal elements in the oil sludge were concentrated in solid products after smoldering. The smoldering treatment of oil sludge has great advantages in resource recovery, and half of the petroleum hydrocarbons in oil sludge can be recovered by off-gas condensation.