Welded Oil Collection Tanks with Floating Roofs - Skimming Without Losing Light Ends

Recovered oil streams - slop oil, skimmed oil, drain collections, interfacial emulsion - are the least predictable liquids on a refinery or terminal site. They arrive intermittently, they carry water and solids, they may be warm, and their composition changes with whatever happened upstream. A collection tank therefore has to do three jobs at once: separate, store, and avoid losing the light ends that make the recovered oil worth anything.

A floating roof addresses the third job directly. Engineered by Shijiazhuang Zhengzhong Technology Co., Ltd. (Center Enamel), a welded oil collection tank with a floating roof keeps the volatile fraction in the liquid instead of venting it, while the welded shell and the tank's internals handle separation and sediment removal.

1. What Is an Oil Collection Tank?

A welded atmospheric tank that receives intermittent recovered-oil streams, retains them long enough for gravity separation, and allows water and solids to be drawn off before the oil is pumped onward for recovery or reprocessing.

· Intermittent Inflow: Collection tanks are sized for the inflow pattern and the separation time the stream needs, not simply for volume.

· Gravity Separation: Retention allows free water to settle and light ends to stay in the oil phase.

· Water Draw-Off: A water draw-off and a bottom sump allow accumulated water to be removed routinely.

· Solids Management: Settled solids are removed at cleaning; access is designed around that task.

· Onward Pumping: Outlet arrangements avoid disturbing the separated layers when the tank is pumped out.

2. Why Put a Floating Roof on a Collection Tank?

Because recovered oil often carries a volatile fraction that a fixed roof would vent, and because the vapour from a mixed recovered stream is unpleasant, hazardous and increasingly regulated.

· Light Ends Retained: The deck keeps volatile components in the liquid rather than losing them to breathing.

· Odour and Emission Control: A covered liquid surface removes the vapour space that would otherwise vent to atmosphere.

· Fire Risk Reduced: No large vapour space means the credible fire scenario is a rim seal event rather than a surface fire.

· Regulatory Alignment: Vapour control on recovered-oil storage is increasingly the expected baseline.

· Product Value: Retained light ends are recovered value rather than a loss.

3. How Are Separation and Sediment Handled?

Through retention time, inlet and outlet arrangement, water draw-off and a bottom design that lets solids be removed. The floating roof's landing height has to be set with the sediment profile in mind, exactly as it is on a crude tank.

· Retention Time: Sized from the stream's separation characteristics, not from a rule of thumb.

· Inlet Arrangement: Inlet energy is dissipated so incoming flow does not re-mix separated layers.

· Water Draw-Off: Routine draw-off keeps the water layer from growing into the oil outlet.

· Bottom and Sump Design: The floor and sump are arranged so water and solids can be removed completely.

· Landing Height: Deck legs are set above the expected sediment depth so the deck can land level.

Engineering Assurance and Project Support

Every welded oil tank delivered by Shijiazhuang Zhengzhong Technology Co., Ltd. (Center Enamel) is designed to API 650 with shell courses sized by the one-foot method and checked for wind, seismic and hydrostatic load cases, or to EN 14015 and the Eurocodes where the site is European. Shell plate is shot-blasted to Sa 2.5 and coated to a documented dry film thickness, longitudinal and annular plate welds are examined by radiography or ultrasonic testing to the acceptance level written into the purchase order, and every tank is hydrostatically tested and dimensionally surveyed before hand-over. Collection tanks are supplied as welded steel shells to API 650 with the floating roof, internals, water draw-off, access and grounding engineered together, and delivered with hydrostatic test records and coating documentation.

"Recovered oil is worth what its light ends are worth. Vent them away and you are storing the least valuable part of the stream."

Frequently Asked Questions (FAQ)

What is the purpose of an oil collection tank?

It receives intermittent recovered-oil streams - slop, skimmed oil, drain collections - and holds them long enough for gravity separation so that water and solids can be drawn off before the oil is pumped onward. Sizing is driven by the inflow pattern and the separation time the particular stream needs.

Why does a collection tank benefit from a floating roof?

Because recovered oil usually contains a volatile fraction. A fixed roof vents those light ends through normal breathing, which is lost product, an odour and emission source, and a vapour inventory for fire. A floating deck keeps them in the liquid and reduces the credible fire scenario to a rim seal event.

How is sediment managed in a collection tank?

Through routine water draw-off, a bottom and sump arrangement that allows complete removal, and a cleaning interval set from the sediment accumulation rate. Where a floating roof is fitted, support leg landing height is set above the expected sediment depth so the deck can always rest level.

Can the tank be customised for our stream?

Yes. Capacity and geometry, deck type and buoyancy, seal specification, retention time, inlet and outlet arrangement, water draw-off and sump detail, heating where required, coating or alloy selection, access and grounding are all engineered to your stream characteristics and site conditions.