Engineered treatment and recovery systems for refinery tank cleaning wastewater and tank bottoms with concentrated oil, sludge, and solids content.
Treat drilling muds, cuttings wash water and site runoff. Solid-liquid separation and water recycling for drilling operations.
Refinery wastewater treatment including API separators, DAF, advanced biological treatment and polishing for strict discharge.
Oil and gas wastewater treatment for produced water treatment.
Sour water and desalter effluent treatment for petroleum refineries.
Storage tanks, process vessels, and associated infrastructure accumulate sludge and sediments that require periodic removal, generating complex waste streams.
Petroleum storage and process tanks accumulate bottoms sludge over time as a natural consequence of gravity separation, corrosion, bacterial action, and the settling of solids from crude oil and refined products. This tank bottom sludge—often referred to as tank bottoms, slop oil, or basic sediment and water (BS&W)—represents one of the most challenging waste streams in the downstream oil and gas sector due to its high viscosity, variable composition, and regulatory classification as hazardous waste in many jurisdictions.
Tank cleaning operations, whether performed during routine maintenance, product changeovers, or statutory inspections, generate large volumes of wastewater contaminated with the accumulated sludge, residual hydrocarbons, cleaning chemicals, and wash water. The resulting waste stream is a three-phase mixture of oil, water, and solids (OWS) that cannot be discharged directly to the refinery wastewater treatment plant without pre-treatment, as the high concentrations of oil and solids would overwhelm conventional separation processes.
Reynolds & Bauhm provides purpose-engineered treatment and recovery systems that separate tank bottom sludge into its constituent phases, recover saleable oil, reduce waste volume through dewatering, and produce a clean aqueous phase suitable for discharge or reuse. Our approach prioritises resource recovery over disposal, delivering both environmental compliance and economic returns.
Crude oil storage tanks, product tanks, slop tanks, underground tanks, process vessels, and pipeline pigging operations
Oil content 10–70%, solids 5–40%, water 20–80%, with heavy metals, PAHs, and mercaptans often present
High viscosity (up to 50,000 cP), non-Newtonian flow behaviour, stable oil-water emulsions, and fine colloidal solids
EU Waste Framework Directive, EPA RCRA regulations, OSPAR guidelines for offshore installations, and national hazardous waste codes
Effective treatment requires addressing the complex multiphase nature and variability of tank cleaning residuals.
Tank bottom sludge contains significant quantities of recoverable hydrocarbons, ranging from light naphtha and diesel fractions to heavy fuel oil and asphaltenes. Oil concentrations can vary from 10% to over 70% by volume depending on the tank service, crude source, and cleaning methodology. The oil is frequently emulsified with water and bound to solids, requiring demulsification chemistry, heat, and mechanical energy to achieve efficient separation. Recovered oil must meet refinery crude unit or coker feed specifications to maximise value recovery.
The rheological properties of tank bottoms present significant handling challenges. Sludge may exhibit Bingham plastic or pseudoplastic behaviour, with yield stresses that prevent gravity flow and require positive displacement pumping. Asphaltene precipitation, wax crystallisation, and polymerisation of reactive hydrocarbons contribute to high viscosity and tenacious adhesion to surfaces. Thermal conditioning, dilution with lighter hydrocarbons, or mechanical shear are required to render the material pumpable and amenable to separation.
Inorganic solids in tank bottoms include sand, silt, rust particles, tank scale, and corrosion products, while organic solids comprise coke fines, asphaltenes, and biological slimes. Solids concentrations range from 5% to 40% and can abrade pumps, foul heat exchangers, and stabilise oil-water emulsions. Fine colloidal solids (particle size <10 µm) are particularly challenging to remove and require coagulation, flocculation, and high-efficiency solid-liquid separation technologies.
No two tank cleaning campaigns produce identical waste streams. Composition varies with crude slate, tank age, cleaning method (manual, robotic, high-pressure water), season, and the interval since the last cleaning. This variability demands flexible treatment systems with wide operating envelopes, real-time monitoring, and adaptive process control. Batch treatment configurations with analytical pre-characterisation are often preferred over continuous systems for handling highly variable tank bottom streams.
Our five-stage process maximises hydrocarbon recovery while minimising the volume of waste requiring off-site disposal.
Tank bottoms are pumped to heated reception tanks equipped with agitation to prevent phase separation and settling. Pre-screening removes debris, and samples are analysed to characterise oil, solids, and water content for process optimisation.
Demulsifying chemicals and heat (60–90°C) break oil-water emulsions. Decanting, centrifugation, or dissolved air flotation separate the liberated oil phase, which is polished and returned to the refinery crude unit or sold as recovered slop oil.
Coagulants and flocculants aggregate fine solids into settleable or floatable flocs. Lamella clarifiers, hydrocyclones, or decanter centrifuges remove solids from the aqueous phase, producing a concentrated slurry for dewatering.
Concentrated solids slurry is dewatered using screw presses, filter presses, or decanter centrifuges to achieve dry solids content of 25–45%. Polyelectrolyte conditioning optimises cake dryness and solids capture efficiency.
Dewatered cake is tested for hydrocarbon content. Material below hazardous waste thresholds is sent to landfill or used as fuel in cement kilns. Clean water phase is polished through filtration and routed to the refinery WWTP for final treatment.
Engineering data for typical mobile and fixed tank bottoms treatment systems supplied by Reynolds & Bauhm.
| Parameter | Feed Range | Product / Effluent | Performance | Equipment |
|---|---|---|---|---|
| Processing Capacity | 1 – 100 m³/h | – | – | Mobile or fixed plant |
| Oil Content (Feed) | 10 – 70% v/v | – | – | Reception tank |
| Recovered Oil Purity | – | < 2% BS&W | 85 – 95% recovery | Centrifuge / DAF |
| Solids Content (Feed) | 5 – 40% w/w | – | – | Screen / cyclone |
| Dewatered Cake Dryness | – | 25 – 45% DS | 80 – 95% solids capture | Screw press / centrifuge |
| Treated Water Oil Content | – | < 15 mg/L | 99.5% removal | DAF + polishing filter |
| Treated Water TSS | – | < 30 mg/L | 95 – 99% removal | Clarifier / filter |
| Operating Temperature | 10 – 90 °C | 20 – 40 °C | – | Heat exchangers |
| Chemical Consumption | – | – | – | 2 – 8 kg/m³ feed |
| Power Consumption | – | – | – | 5 – 25 kWh/m³ |
| Volume Reduction | – | – | 60 – 85% | Complete train |
| Residence Time | – | – | – | 4 – 24 hours batch |
Reynolds & Bauhm systems are deployed for cleaning and treatment operations across the full spectrum of refinery storage and process containment.
Atmospheric and floating roof crude oil storage tanks accumulate significant volumes of BS&W sludge, often exceeding 1,000 m³ in large diameter tanks. Cleaning campaigns generate massive waste streams requiring high-capacity mobile treatment units. Reynolds & Bauhm provides containerised and skid-mounted systems with processing rates up to 100 m³/h for major tank farm cleaning projects.
Storage TanksPetrol, diesel, jet fuel, and fuel oil storage tanks require cleaning during product changeovers, inspection cycles, or decommissioning. Product tank sludge is typically lower in solids and higher in recoverable light hydrocarbons than crude tank bottoms, making oil recovery particularly technically attractive. Treatment systems for product tanks emphasise vapour recovery and explosion-proof design.
Storage TanksRefinery slop oil tanks and waste oil recovery tanks collect off-spec products, drained pump seal oils, and miscellaneous hydrocarbon waste. These tanks contain the most variable and unpredictable sludge compositions, often containing mixtures of light ends, heavy residuals, chemical additives, and water. Flexible batch treatment systems are ideal for handling slop tank contents.
Explore Oilgas RefineryUnderground storage tanks (USTs) at refinery terminals, distribution depots, and retail stations present unique access and safety challenges. Sludge removal often requires vacuum trucks and confined space entry protocols. Reynolds & Bauhm provides compact, containerised treatment units that can be positioned above ground to receive and process UST cleaning waste on-site.
Explore Oilgas RefinerySeparators, coalescers, desalters, and knockout drums require periodic cleaning to maintain process efficiency. The waste from these vessels is typically more water-rich than storage tank bottoms but contains concentrated emulsified oil and fine solids. DAF units and high-speed disc stack centrifuges are particularly effective for processing vessel cleaning waste.
Explore Oilgas RefineryIntelligent and batch pigging operations for crude oil and product pipelines displace significant volumes of wax, asphaltene, and solids deposits. The pig receiver waste stream is a concentrated slurry that can be processed through Reynolds & Bauhm mobile treatment systems to recover hydrocarbons, separate solids, and produce clean water for disposal or reuse.
Explore Oilgas RefineryOur treatment solutions transform a costly waste disposal problem into a resource recovery opportunity.
Recover 85–95% of entrained hydrocarbons as saleable slop oil or crude unit feedstock. For a typical 10,000 m³ tank cleaning campaign, this can represent hundreds of thousands of pounds in recovered product value that would otherwise be sent for disposal.
Achieve 60–85% reduction in waste volume through efficient oil separation and sludge dewatering. Reduced disposal requirements translate directly to lower transport and landfill costs, particularly for hazardous waste classified materials.
Containerised and trailer-mounted treatment units can be deployed to any tank farm or terminal within days. Mobile systems eliminate the need for permanent infrastructure at sites with infrequent cleaning schedules.
Meet all applicable waste disposal regulations including EU Waste Framework Directive, EPA RCRA, and OSPAR requirements. Complete documentation, analytical testing, and waste tracking support regulatory audits and environmental reporting.
Pre-engineered modular systems can be mobilised, commissioned, and operational within 48–72 hours of arrival on site. This minimises tank downtime and accelerates return to service, critical for output-generating storage assets.
Reynolds & Bauhm provides project execution involvement including process design, equipment supply, chemical program management, operation supervision, and final waste characterisation. Single-point accountability reduces project risk and administrative burden.
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View PageCrude and product tank bottoms contain recoverable hydrocarbon hundreds of pounds per tonne.
Crude tank: 60–80% oil, 5–20% water, 5–25% solids (sand, scale, asphaltenes). Product tank: 70–90% oil. Sludge thickens over decades.
Fixed or floating mixers re-suspend bottoms before withdrawal. Sized for 8–15 W/m³ tank volume. Programmed mix-and-settle cycles avoid airborne mist.
Bottoms heating coils or steam lance raise viscosity. Maintain <90°C to avoid hydrocarbon flashing.
Continuous horizontal centrifuge: oil-out to slop / crude charge; solids cake to disposal; water back to BTU. Oil recovery 90–98% of incoming oil.
One 50,000-bbl crude tank can yield 200–500 t of recoverable hydrocarbon at decommissioning. Recovery centre project benefits typically 2–4 years.
Tank entry is high-risk: H₂S, benzene, pyrophoric iron sulphides, oxygen deficiency. Pre-mix with surface units before any internal work; LEL monitoring continuously.
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