Investigation of pyrolytic characteristics of three oily sludges with focus on properties of oil product

Pyrolysis is an important thermochemical conversion technology to recover the oily sludge resources and reduce the harmfulness of waste. This work aims to investigate the pyrolysis behaviors of three different oil sludges by using a thermogravimetric analyzer and two fixed-bed reactors. An attempt was made to determine a wide range of properties of liquid products. Three oily sludges included a tank bottom sediment (OS-1), an oil-water separator scum (OS-2), and a wastewater sediment concentrate (OS-3). OS-1 had a high content of oil, whereas OS-2 and OS-3 were characteristic of high contents of water and oxygen. The pyrolysis of as-received oily sludge in a vertical tubular reactor at 700 °C attained the oil yield up to 69.2 % for OS-1, against the oil yields ranged in 34.4–35.5 % for OS-2 and OS-3. These yields of pyrolysis oil were higher than or close to those of extraction oil. Through characterizing the molecular composition of pyrolysis oil and extraction oil, it was revealed that the pyrolysis promoted the cracking of long-chain alkanes and O/N-containing functional groups accompanied by the conjugation, cyclization and aromatization reactions. The analysis of the pyrolysis oils obtained from the horizontal tubular reactor showed that the liquid products derived from all three oil sludges had very low ash contents and viscosities, and the water-free pyrolysis oils had higher HHVs than the parent dried oil sludges.