Method of removing dissolved oil from produced water

A method of removing dissolved oil from water, the dissolved oil being comprised of hydrocarbon additives solvated by water molecules, the hydrocarbon additives having a hydrocarbon structure with an attached group for providing extra electrons for attaching the hydrocarbon additive to metal, the method comprising the steps of:

• turbulently contacting a first gas comprising dichlorodifluoromethane and a second gas with the water, the first gas comprising an effective amount of dichlorodifluoromethane to molecularly attract the dissolved oil particles through hydrogen bonding and dipole interactions, the second gas being sufficiently buoyant to promote movement of bubbles of the first gas to a surface of the water from which dissolved oil is being removed;
• the turbulent contacting occurring in a mixing tee to create bubbles that move dissolved oil particles to the surface of the water, the mixing tee comprising a chamber having a water inlet for the water, a gas inlet for the first and second gases, and an outlet through which the water and gas mixture is discharged, the gases being introduced through a conduit having a smaller diameter than the diameter of the water inlet, the conduit terminating adjacent the water inlet and propelling the gases against the inward flow of the water to create a counterflow of water and gas that enhances formation of bubbles in the chamber, an annular constriction being provided around the exterior of the conduit between the conduit's termination adjacent the water inlet and the remainder of the chamber;
• introducing the contacted water and gases tangentially into a flotation tank having an upper region and a lower region to create a circular flow therein;
• introducing the first and second gases into the flotation tank at the lower region which is below the level at which the water is tangentially introduced into the flotation tank;
• providing the flotation tank with an upper baffle and a lower baffle, both of which are substantially horizontally disposed in the interior of the tank between a level at which the water is tangentially introduced into the flotation tank and the lower region, the upper baffle having a central opening through which water flows downwardly and the second baffle being a substantially circular plate surrounded by a substantially annular opening through which water flows downwardly in the flotation tank, the lower baffle being provided with means for retaining beneath it bubbles created by the introduction of the first and second gases into the flotation tank at the lower level, and the upper baffle being provided with means for retaining beneath it bubbles created by the introduction of the first and second gases into the flotation tank at the lower level, the upper baffle being provided with an upper vent for venting bubbles from beneath the upper baffle to a position adjacent the surface of the water in the flotation tank, the lower baffle being provided with a lower vent for venting bubbles from beneath the lower baffle to a position adjacent the underside of the upper baffle and removing dissolved oil from said surface.

A method of removing dissolved oil from particulate matter contained in water, the dissolved oil being comprised of hydrocarbon additives solvated by water, the hydrocarbon additives having a hydrocarbon structure with an attached group for providing extra electrons for attaching the hydrocarbon additive to metal, the method comprising the steps of:

• introducing the water containing the particulate matter into a sump tank where the particulate matter accumulates on the bottom;
• introducing a gas comprising dichlorodifluoromethane into the sump tank and contacting it with the particulate matter, the gas comprising an effective amount of dichlorodifluoromethane to molecularly attract the dissolved oil particles through hydrogen bonding and dipole interactions, the gas promoting movement of the oil particles to a surface of the water in the sump tank;
• and
• skimming oil from the surface of the water.

A method of removing dissolved oil from water and sand contained in produced water having dissolved oil particles contained therein, the method comprising the steps of:

• mixing a first and second gas, the first gas being selected from the group consisting of nitrogen and dichlorodifluoromethane, the second gas being selected from the group consisting of natural gas, air and nitrogen;
• contacting in a mixing tee the first and second gases with water to create bubbles that move dissolved oil particles to the surface of the water, an effective amount of the first gas being added to attract the dissolved oil particles through hydrogen bonding and preferentially displace solvating water molecules, the mixing tee comprising a chamber having a water inlet for the water, a gas inlet for the first and second gases, and an outlet through which the water and gas mixture is discharged, the gases being introduced through a conduit having a smaller diameter than the diameter of the water inlet, the conduit terminating adjacent the water inlet and propelling the gases against the inward flow of the water to create a counterflow of water and gas that enhances formation of bubbles in the chamber, an annular constriction being provided around the exterior of the conduit between the conduit's termination adjacent the water inlet and the remainder of the chamber;
• introducing the contacted water and gases tangentially into a flotation tank to create a circular flow therein;
• introducing the first and second gases into the flotation tank at a lower level which is below the level at which the water is tangentially introduced into the flotation tank;
• providing the flotation tank with an upper baffle and a lower baffle, both of which are substantially horizontally disposed in the interior of the tank between a level at which the water is tangentially introduced into the flotation tank and the lower level, the upper baffle having a central opening through which water flows downwardly and the second baffle being a substantially circular plate surrounded by a substantially annular opening through which water flows downwardly in the flotation tank, the lower baffle being provided with means for retaining beneath it bubbles created by the introduction of the first and second gases into the flotation tank at the lower level, and the upper baffle being provided with means for retaining beneath it bubbles created by the introduction of the first and second gases into the flotation tank at the lower level, the upper baffle being provided with an upper vent for venting bubbles from beneath the upper baffle to a position adjacent the surface of the water in the flotation tank, the lower baffle being provided with a lower vent for venting bubbles from beneath the lower baffle to a position adjacent the underside of the upper baffle, wherein dissolved oil is removed from said surface, and said contacted water separates into a portion which is substantially free of sand, and a portion containing sand;
• introducing a portion of the contacted water, which is substantially free of sand, from the flotation tank, into a vacuum vessel to cause a liberation of a portion of the first and second gases dissolved in the water;
• and producing a water fraction in the vacuum vessel;
• removing the water fraction from the vacuum vessel;
• compressing the gases liberated in the vacuum vessel so that increased pressure condenses water out of the liberated gases;
• contacting the gases liberated in the vacuum vessel with a desiccant to remove water;
• reducing the temperature of the gases liberated in the vacuum vessel after they leave the desiccant until one of the gases liquifies, then separating the liquified gas from remaining gas;
• removing sand from the water in the flotation tank by introducing a portion of the contacted water, containing sand, from the flotation tank into a sump tank where the sand accumulates on the bottom;
• introducing the first and second gases into the sump tank and contacting it with the sand;
• and
• skimming oil from the surface of the water in the sump tank.