water handling and treatment
Post on 20-Jul-2016
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Introduction
Necessary to handle waste water that include
Crude oil
Rain water
Washdown water
Offshore :HC that can be discharge
15mg/l to 50mg/l
Onshore : water cannot be disposed on surface ~ possible salt contamination
Water Handling and Distribution
Over time, water may be produced along with oil
This produced water has no commercial value therefore treat to remove oil and dispose to sea
Oil remains in water in 2 forms:
Emulsion
Oil droplets in water
Emulsion between oil and water
Main phase is water
Inject emulsion breaking chemicals upstream water treatment tank
Oil droplets in water
Oil droplets float freely in water
Settle out given enough time or use equipment/methods to assist removal of oil droplets – water treatment tank
Water Handling and Distribution
Oil floats to top of water treatment tank and skimmed off into the drain system
Water then disposed to sea through Closed Drain Caisson
Water sampling – Effluent Discharge Quality must be < 100ppm
Water Handling and Distribution
Produced water treatment equipment
Initial separation of oil and water
Gravity separators
Primary separation can be enhanced via
Heating of crude oil – separate water via reduced viscosity
Demulsification chemicals – break emulsions and let water droplets to settle
Electrostatic separation – reduce water content of dense, dry crude oil
Types of water treatment equipment
Corrugated Plate Interceptor (CPI)
Dissolved Gas Floatation Unit (DGF)/Dispersed Gas Floatation
Hydrocyclones
Produced water treatment equipment
Corrugated Plate Interceptor
Plate interceptors reduced distance required for oil droplet to migrate before it comes into contact with other oil droplets and coalesces
Interceptor packs consists of a series of closely spaced, parallel plates mounted at angle 45 degree
Plates have corrugated profile – allows large oil droplets to move upwards and collect at the high point
CPI works off because of short separation distance between the plates
Oil moves upwards through the water phase as the size increases
Oil layer formed then skimmed off by oil outlet weir
Configuration of water inlet and outlet arranged to minimise turbulence that causes re-mixing of small oil droplets
Remove up to 60micron
Dissolved/Dispersed Gas Floatation
Uses gas floatation to accelerate separation of oil from water
Via buoyancy effect caused by rising gas bubbles attached to oil droplets
Oil carried to surface coalesce and separate using oil weir
Gas injected in 2 manners
Inject into water and dispersed by rapidly rotating impeller
Dissolved in water under high pressure
Travels via pressure vessel and limited residence time causes gas to dissolve
Then reduce pressure rapidly, gas comes out in form of bubbles
Hydrocyclone
Use centrifugal force to increase effect of gravity
Oil-water feed flows tangentially into the upper, swirl section
Swirls around in circular path, then accelerate as flows enters taper section (reduced diamater)
Lighter oil moves up, heavier water exits out
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