English
Mechanical cleaning of crude oil storage tanks generates large quantities of slop oil - a complex emulsion containing crude oil, water, mechanical impurities and light hydrocarbon vapours. Improper handling not only wastes valuable hydrocarbons but also creates serious environmental and safety risks. In 2018, our team delivered a complete on-site slop oil recovery and treatment project for Anqing Petrochemical, enabling the enterprise to convert tank-cleaning waste into a reusable refinery feedstock while meeting strict emission limits.
- Slop oil generated from mechanical cleaning of crude oil storage tanks is highly emulsified, with water and solid contents far exceeding refinery feedstock specifications.
- Conventional methods such as simple settling or off-site disposal are inefficient and costly, and raise HSE risks during transport.
- The recovered oil had to meet strict quality targets so it could be safely blended into the atmospheric-vacuum distillation (AVD) unit.
- All treatment had to be completed on site, with waste gas emissions controlled to regulatory levels.
A tailored process train was designed for on-site treatment:
- Thermochemical conditioning - demulsifiers combined with controlled heating break the stable oil-water emulsion.
- Physical solid removal - coarse solids and sludge are separated from the oil phase.
- Special mechanical dewatering unit - a decanter centrifuge (horizontal screw centrifuge) performs primary solid-liquid separation, followed by a disc-stack separator for fine dewatering and polishing.
- Drying - residual moisture in the solid residue is further reduced.
- Flue gas purification - off-gas from the treatment process is purified to meet emission standards.
The two-stage centrifugal separation configuration (decanter centrifuge + disc separator) was selected because it reliably handles the high solids load of tank-cleaning slop oil while achieving the low water and solid contents required for refinery blending.
| Parameter | Project Requirement | Achieved Result |
|---|---|---|
| Water content in recovered oil | < 1% | 0.03% |
| Solid content in recovered oil | < 1% | 0.0926% (mechanical impurities) |
| Water content of solid residue | ≤ 10% | Compliant |
| Non-methane total hydrocarbons (waste gas) | ≤ 120 mg/Nm³ | Compliant |
The recovered oil was delivered for blending in the atmospheric-vacuum distillation unit. Samples tested by the Anqing Petrochemical Laboratory showed a water content of 0.03% and a mechanical impurity content of 0.0926% - results that meet and exceed the project's technical specification requirements.
The project was executed in on-site recovery and treatment mode: all slop oil generated during tank cleaning was processed at the plant site, eliminating the cost, risk and environmental burden of off-site transport and disposal.
- Recovered valuable oil as refinery feedstock instead of disposing of it as waste.
- Recovered oil quality exceeded specifications (water 0.03%, mechanical impurities 0.0926%).
- Stable two-stage centrifugal separation with compact footprint and low operating cost.
- Full compliance with waste gas emission limits (NMHC ≤ 120 mg/Nm³).
- Minimised HSE risks through fully on-site treatment.
This project demonstrates a proven, reliable solution for the on-site recovery and treatment of slop oil generated from crude oil storage tank cleaning. By combining thermochemical conditioning with decanter and disc-stack centrifugal separation, drying and flue gas purification, the system delivers recovered oil that meets - and in practice exceeds - refinery blending specifications, creating measurable economic and environmental value for the customer.