A.H. Lundberg is partnering with electrocoagulation vendors to solve the challenges faced by the oil & gas industry in treating wastewater. Contaminated water often contain high amount of silica and calcium, which traditionally required the addition of expensive chemicals for removal thus increasing the operating cost.
Electrocoagulation can efficiently remove contaminants such as suspended oil and grease, silica, calcium, magnesium, heavy metals and suspended solids from aqueous waste streams. A primary advantage of the process is high removal efficiency (90%-99%) of the contaminants with no chemical addition, minimum waste produced, low power operating cost (4-7 kWh/1000 gals treated) and minimal manpower requirements.
Electrocoagulation Process Description
Electrocoagulation process removes contaminants by applying an electric current through the aqueous solution that forms flocs, which has the ability to adsorb certain ionic constituents. The electric current provides the driving force necessary to stabilize the solution, which causes the oil to separate from the emulsions, and some entities to become hydrophobic, causing them to separate or precipitate easily.
Contaminated water feed from the SAGD process is transferred to a cell stack operating in a bipolar mode. In this mode the cells are arranged in series and require a higher voltage across the cell stack to drive a given current through each cell The feed is passed between two electrolyzed plates flowing up between the plates as the current passes through the solution perpendicular to the solution The positive side of the cell undergoes an oxidative reaction while the negative side undergoes cathodic reactions. The electrodes release ions into the solution as the current passes through the cell and dissolve (also known as sacrificial electrodes). The ions released into the solution neutralize the charges of particles in solution and causes coagulation and precipitation or floatation of unwanted material in the solution. At the same time as the charges are getting destabilized, water is getting electrolyzed generating some hydrogen and hydroxyl ions. The dissolving metals from the electrodes react with some of the stabilized ions to further destabilize them and causes them to precipitate.
The treated solution after passing through the cell stack is directed to a filtering/clarification process to remove the sludge and froth. The treated solution is then transferred to the Evaporators for further treatment.
Integrating Electrocoagulation with Evaporator
Feed from the electrocoagulation process is transferred to the Evaporation process. The evaporator comprises of two main sections, the heater (thermal body) and the vapour head (separator). Concentrated liquor flows around the evaporator at about 15 % w/w. The incoming feed combines with the circulating liquor that is transferred to the top of the evaporator and discharged onto a distributor, which spreads and discharges the liquor on the tubesheet around the tubes. The tubes stick out about 2 mm above the tubesheet. Liquor from the tubesheet overflows around the periphery of the tube evenly forming a thin film of liquid that falls down the tube. The liquor flowing down the tube is heated by the steam on the shell side generating vapours in the tube. The liquor and the steam discharges from the bottom of the thermal body into the vapour head. The liquid falls to the sump and the steam passes through the annulus of the evaporator, which houses the chevron mist eliminators to coalesce and separate moisture particle that are entrained with the vapours.
The steam from the evaporator vapour head is transferred to the Mechanical Vapour Compressor (MVR). The steam is compressed and utilized as a heat source on the shell side to vapourize more water. Steam discharging the MVR is superheated and has to be de-superheated prior to use in the Evaporator shell. A desuperheating station is supplied that sprays hot condensate discharging the shell to saturate the steam so that it releases its latent heat as soon as it comes in contact with the tubes in the Evaporator. Operating the Evaporator in this manner allows the unit to be used as a heater and a condenser for the water entering the system.
The condensate generated on the shell side discharges to a vertical condensate tank and from there its transferred to the boiler feed water tank.
Zero Liquid Discharge Process
The concentrated blowdown from the evaporator is transferred either to a disposal tank or further treated in a crystallizer to concentrate it more and generate crystals for disposal (Zero Liquid discharge ZLD Process).
A simple block diagram is provided below: