"A Comprehensive Comparison of Oil Sludge Treatment Techniques"

Keywords:

Pyrolysis treatment

Source: internal company

At present, there are nearly ten treatment methods for oily sludge, such as solvent extraction, solidification treatment, biological treatment, profile control treatment, drying and incineration, chemical hot washing, pyrolysis treatment, etc. In terms of treatment methods, these can be divided into physical and chemical methods and biological methods. Research hotspots mainly focus on solvent extraction, biological treatment, solidification treatment, incineration treatment and pyrolysis treatment, etc. The table below provides a comparison of various treatment methods in terms of economy and environmental protection.

Handling method	Core Principle	Advantages	Limitations	Applicable Scenarios
Solvent Extraction	Use organic solvents to enhance oil-solid separation selectivity; solvents are recycled for reuse after solid-liquid separation.	High oil separation efficiency (recovery rate >90%); solvent reuse enables resource recycling and high recovery.	Requires multiple extractions (cannot reach 100% recovery); high solvent consumption; safety risks and environmental issues of solvent storage.	High-oil, high-value sludge with high oil quality requirements.
Solidification Technology	Add cement, lime, etc. to oily sludge as solidifying agents to form stable aggregates, reducing harmful substance migration.	Simple operation, short process, fast treatment; lowers environmental risks; low labor costs.	No oil recovery; resource utilization is abandoned; volume increases by 30%-60% after solidification, occupying land.	Valueless, severely polluted oily sludge with solidification equipment.
Bioremediation	Use metabolism of microorganisms (e.g., petroleum-degrading bacteria) to decompose oily sludge into harmless substances (CO₂, water, etc.).	Good environmental protection (no secondary pollution); low operating cost; treated sludge can be used for soil improvement.	Long treatment cycle (7-30 days); greatly affected by temperature, pH, etc.; poor adaptability to high-oil sludge; only applicable to sludge with oil content <5%.	Harmless treatment of low-oil sludge and remediation of lightly polluted soil.
Conditioning Technology	Pre-treat oily sludge, then add it to oil wells as a conditioning agent to improve seepage channels and oil recovery.	Realizes resource utilization of oily sludge (no additional land occupation); assists in increasing oil production.	Strict requirements for sludge stability; needs to match reservoir conditions; easily leads to excessive oil production.	Oily sludge under specific reservoir conditions (requires prior precise matching of sludge properties and reservoir parameters).
Incineration Treatment	Incinerate sludge at high temperature to fully decompose oil and organics.	Fast treatment, significant volume reduction; removes toxic and harmful organics.	Extremely high energy consumption; incineration produces dioxins, etc.; complex supporting gas treatment equipment; high operating cost.	High-oil, valueless oily sludge with complete environmental protection facilities.
Chemical Washing	Use hot water as carrier, add surfactants, etc. to reduce oil-sludge adhesion and realize oil-water-solid separation.	Relatively simple operation; low equipment investment; good treatment effect for medium-oil sludge; suitable for promotion.	Generates large amounts of high-concentration oily wastewater; frequent water change; poor effect on aged, high-oil sludge.	Centralized low-to-medium oil sludge (e.g., oilfield joint stations) for small-to-medium-scale batch treatment.
Pyrolysis Treatment	Heat oily sludge in anoxic/oxygen-free environment to decompose organics into combustible gas, oil, and solid residues; collect oil and gas.	Oil recovery rate >90%; pyrolysis gas can be used for heating; low residual oil rate; better environmental protection than incineration.	Huge equipment investment (tens of millions of RMB); high requirements for process temperature control; high technical and operational costs.	Large-scale centralized treatment of oily sludge (e.g., oilfield/petrochemical enterprises with high oil recovery requirements).

Due to the high content of petroleum and other organic substances in oily sludge, the resource utilization of oily sludge has become a major development trend. In recent years, most of the researchers' studies on oily sludge have focused on the recovery of crude oil from oily sludge. As can be seen from the table:

① Although biological treatment, profile control treatment, solidification treatment and incineration treatment each have their own advantages, they cannot recover the oil in oily sludge. Biological treatment has a long processing cycle and poor treatment effect on naphthenic hydrocarbons, aromatic hydrocarbons and heterocyclic compounds; solidification treatment is mainly landfill at present, which will cause environmental pollution; incineration treatment wastes a lot of energy and causes secondary pollution.

② Solvent extraction and chemical hot washing can recover the oil in oily sludge, but they also have their drawbacks. The cost of the extractant is high, and the key to the current technology is to develop an extractant with high cost performance. In addition, the amount of remaining sludge after extraction is large, and there is a problem of secondary pollution treatment. Chemical hot washing has some industrial applications, but the degree of industrialization is limited. The amount of remaining sludge and wastewater is large, and there is also a problem of secondary pollution treatment. Moreover, both solvent extraction and chemical hot washing are only suitable for treating sludge with high oil content and have certain limitations.

③ Pyrolysis treatment can not only recover the oil in the sludge and realize the resource utilization of oily sludge, but also be applicable to all types of sludge. Moreover, the amount of wastewater and waste residue produced during the treatment process is small, and the waste residue can be recycled and reused, with almost no secondary pollution. Therefore, it has a wide range of applications. However, pyrolysis treatment technology consumes a lot of energy, and the key issue in industrial application is the lack of relatively mature pyrolysis reaction equipment.

Pyrolysis has become one of the important development technologies for the thermal treatment of oily sludge. Both domestic and foreign researchers are conducting extensive research and promotion. The pyrolysis treatment method not only meets the requirements of resource utilization of oily sludge, but also achieves harmless "zero discharge". In today's development of sustainable economy and increasing emphasis on environmental protection, this technology has great potential for development.