Gravity oil-water separator

Product Specification

Gravity-type oil-water separator | Purely physical separation · No reagents required · Stable operation

A gravity oil-water separator is a device that separates oil and water based on the density difference and hydrostatic pressure. It requires no chemical reagents and operates with little or no power. After oily wastewater enters the separator, optimized hydraulic channels and extended residence time allow suspended oil droplets to naturally rise to the oil collection area, while heavier particles sink to the sludge hopper, ultimately achieving three-phase separation of oil, water, and sludge. This equipment has a compact structure with no easily damaged moving parts and is widely used in oil separation of catering wastewater, pretreatment of industrial oily wastewater, and drainage of oil depots and gas stations.

core components

Inlet Rectification Zone: Water is evenly distributed using baffles or guide tubes to eliminate turbulence and improve separation efficiency.

Separation Zone: Utilizes inclined/corrugated plate coalescing modules (optional) or a horizontal flow design to increase the effective separation area and accelerate oil droplet buoyancy.

Oil Collection Zone: An oil drain trough or collection pipe is installed at the top for manual or automatic oil drainage.

Sludge Hopper: A conical structure at the bottom collects settled sludge, sand, and heavy oil (specific gravity > 1), which is periodically discharged.

 Outlet Regulating Device: An adjustable overflow weir or outlet control valve stabilizes the outlet water level.

Ventilation Pipe and Observation Port: Ensures safety and ease of maintenance.

Working principle

Oily wastewater enters the rectifying zone through the inlet, where its flow rate slows and becomes more uniform. It then flows upwards or horizontally through the separation zone. During the residence time (usually 30-60 minutes), tiny, dispersed oil droplets collide and merge, floating to the top oil collection zone due to their lower density than water. Solid particles with a specific gravity greater than water and some heavy oil settle to the bottom sludge hopper. The supernatant is discharged through the overflow weir. The floating oil in the oil collection zone can be periodically discharged by opening a valve or collected by an oil skimmer, while the sludge is discharged through the bottom drain outlet.

Main advantages

Energy-efficient or extremely low-energy consumption: Standard models rely entirely on gravity flow, requiring no chemical dosing or power; an automatic oil discharge mechanism (extremely low power) is optional.

High separation efficiency: With the coalescence module, oil droplet removal rates exceeding 90% for particles larger than 60μm are achieved, with effluent oil content ≤50mg/L.

No moving parts (basic model): High reliability, virtually maintenance-free.

Corrosion-resistant materials: Optional materials include epoxy-coated carbon steel, 304/316 stainless steel, FRP (fiberglass reinforced plastic), and HDPE (high-density polyethylene).

Flexible installation: Above-ground or underground design, customizable to suit site space.

High adaptability: Can handle vegetable oils, animal oils, mineral oils, and petroleum hydrocarbons.

Technical parameters

Processing flow rate: 0.5 – 100 m³/h (larger sizes can be customized)

Separation efficiency: ≥90% (oil droplets ≥60μm)

Residence time: 30 – 60 min

Operating temperature: 0 – 60℃

Inlet water oil content: ≤5000 mg/L (recommended for pretreatment of high concentrations, using in series)

Outlet water oil content: ≤50 mg/L (depending on oil properties and coalescence module)

Material: Corrosion-resistant carbon steel / 304/316 stainless steel / fiberglass / HDPE

Installation method: Above ground (bracket) or buried (thickened and reinforced)

Application areas

Oily wastewater separation from restaurant kitchens (upgrade and replacement of grease traps)

Rainwater and oily water from auto repair shops, car washes, and gas stations

Drainage pretreatment from steel, petrochemical, and machinery processing workshops

Primary separation of produced water from oil fields

Ballast water from ships and oily wastewater from ports. We can provide hydraulic calculations and coalescence module selection based on oil characteristics, flow rate, and discharge standards. We welcome on-site parameter requests for customized design solutions.