Crude Oil Dehydration
Water in Crude Oil
Crude oil leaves the well as a mixture of oil, water, gas and solid particles. Water and salt must be taken out before the crude can be transported or refined, because they corrode pipework, load the desalter and reduce the value of the barrel. Dehydration is the stage that brings the crude to a transportable and refinable condition.
Separation at High Water Cut
As the water cut rises, static desalters and gravity settlers lose effectiveness: residence time falls, short circuiting occurs and oil quality drifts. Centrifugal separation applies a force many times gravity to the same density difference, so separation continues at water cuts where a settler no longer holds specification.
Process Conditions
Water states in the feed
| Water state | Behaviour in the crude | Removal route |
|---|---|---|
| Free water | Separates under gravity given enough residence time | Removed in the first separation stage |
| Emulsified water | Fine droplets held in suspension, stabilised by asphaltenes and solids | Requires centrifugal force, heat, or a demulsifier |
| Dissolved water | In solution within the oil phase | Not removable by mechanical separation |
Conditions that govern separation
| Variable | Effect on separation |
|---|---|
| Water cut | Higher cut shortens residence time in static equipment and promotes short circuiting |
| Temperature | Raising temperature lowers viscosity so droplets migrate faster |
| Solids content | Solids stabilise emulsions and accumulate in the bowl, setting the discharge interval |
| Density difference | The wider the difference between oil and water, the faster the separation |
Salt and solids taken out here would otherwise report downstream. For the water phase see contaminated water treatment; for accumulated tank bottoms see crude oil sludge treatment.
Feed Introduction
The crude oil feed is introduced into the rotating bowl from the top via a stationary inlet pipe. It is then accelerated in a distributor before entering the disc stack.
Separation
Separation takes place between the discs of the disc stack. The oil phase moves through the disc stack towards the center of the bowl, while the solids are collected at the bowl periphery and continuously discharged through the nozzles along with some water.
Water Phase Separation
The water droplets move toward the periphery to the oil/water interface, where they coalesce to form a continuous water phase. The water that does not pass out through the nozzles is collected and pumped out under pressure.
Scope of Supply
Separation efficiency is held as the water cut rises, so short circuiting is avoided and the crude stays on specification through swings in the feed.
Water, salts and solids are drawn out of the crude, which lowers the load on the downstream desalter and refining train and raises the value of the delivered barrel.
Units handle a range of densities, viscosities and solids content, so the same equipment can be applied to difficult feedstocks without reconfiguration of the process.
Rental units for short and medium term projects, mobile and skid mounted, supplied with an operation manual. An experienced operator can be supplied with the unit. Ask for current rental availability.
Engineering FAQ
How is crude oil separated?
Crude oil leaves the well as a mixture of oil, water, gas and solid particles. Centrifugal separation applies a force many times gravity to the density difference between those phases, so water and solids are thrown outward and the oil is drawn off continuously.
Why use centrifugal separation instead of a settler?
As the water cut rises, residence time in a static settler falls and short circuiting occurs, so oil quality drifts. Centrifugal separation applies a force many times gravity to the same density difference, so it holds specification at water cuts where a settler no longer can.
What is taken out during dehydration?
Water and salt. Both corrode pipework, load the desalter and reduce the value of the barrel.
Where does dehydration sit in the chain?
It is the stage that brings the wellhead mixture of oil, water, gas and solids to a transportable and refinable condition.
Talk to an Engineer
Send the crude assay, the water cut and the required throughput. We will return a recommended configuration and a scope of supply. Adjacent duties are listed under applications.