1. Field of the Invention
This invention relates to the removal and recovery of water soluble organics (WSO) from oil process water. In particular, the present invention relates to the removal and recovery of certain water soluble petroleum organics from crude oil production water and from aqueous streams used in removing water and/or inorganic salts, such as sodium chloride, from crude oil, residual oil, waste oils and the like.
In the removal of crude oil or production fluid from earth formations significant quantities of water are quite often removed along with the oil. In the Middle East, the production fluid can be virtually pure oil. However, it is not uncommon that oil well production fluids are composed of 90% or more of water and only 10% or less of crude oil. Such water is referred to as connate water and is produced along with the oil. Oil well production fluid typically comprises water, oil, water soluble substances (e.g., naphthenic acids, phenols and inorganic salts) and cations that tend to form scale (e.g., calcium, barium and strontium ions).
One of the first steps after removal of the oil well production fluid is to separate the oil from the water by phase separation techniques. The phrase "oil process water" refers to the water of such oil water production fluid as well as to the water phase produced by such phase separation.
Conventionally, separation is accomplished using a bulk separator or a free water knock out system. Virtually all of the hydrocarbon is conveniently recovered in this manner. Unfortunately, certain organic compounds, as well as inorganic salts and acids, are soluble in water; and mere phase separation will not remove the water soluble compounds from the aqueous phase. Water soluble organics include, among other things, certain naphthenates, phenols, lower fatty acids, etc. Water soluble inorganic salts include sodium chloride, sodium sulfate, calcium chloride, barium chloride, etc. While the amount of water soluble organics may be relatively small, up to 1,000 ppm, they nevertheless give rise to environmental problems, when the aqueous phase is discharged into the environment without the removal of the water soluble organics. Furthermore, the water soluble organics may be valuable substances. In order to meet present day strict environmental standards, a process to reduce the level of the water soluble organics in the discharged streams to 50 ppm or less is needed. The present invention provides a simple, economical procedure for accomplishing this end. While known methods can reduce the content of water soluble organics to the desired low level, they are relatively complex and/or expensive in comparison with the process of the present invention. For example, one could separate the water and water soluble organics by distillation or the use of biological treating ponds.
Use of certain petroleum fuel oils for specific purposes requires that such oils be treated in order to remove undesirable corrosive contaminants therefrom. For example, fuel oils used in the newer, high efficient, gas turbine power plants must meet certain strict requirements with respect to the presence of inorganic contaminants in the oil. The presence of sodium chloride and other similar inorganic salts renders the oil less than suitable as a fuel for use in gas turbine power plants. To upgrade fuel oil so that it is acceptable for use in the turbines, the fuel oil is commonly processed using a multi-stage electrostatic desalting facility. In such operation essentially complete removal of water soluble inorganic salts from fuel oil is accomplished by a counter-current water washing process in which a high electrostatic gradient is used to break the interim water-in-oil emulsion. Selective specialized chemical demulsifiers are normally used in such salt removal processes. While the process removes the inorganic salts from the fuel oil, unfortunately the wash water removes the water soluble organics from the fuel oil. In view of strict environmental standards, it is of considerable importance to remove these water soluble organics present in the wash water of the inorganic salt removal processes used to render the fuel acceptable for burning in turbines.
The invention is directed to a simple, straightforward method of removal of water soluble organics from oil well production fluids, as well as from aqueous streams used to render fuel oil acceptable for use as fuel for gas turbine power plants by the removal of inorganic salts therefrom.
2. Description of the Prior Art
U.S. Reissue Pat. No. 29,908 discloses recovery of oily waste in water by the use of a demulsification-flocculation separation process employing a combination acid-alum treatment. This process has no effect of removing water soluble oils.
U.S. Pat. No. 3,687,845 discloses removal of tramp oils from oil-in-water emulsions by the addition of a water soluble anionic polymer of high molecular weight and heat treatment of the emulsions so that the oils are coalesced and float to the surface of the liquid. Water soluble oils are unaffected by this treatment.
U.S. Pat. No. 3,707,464 discloses the addition of caustic or acid to adjust the pH of the liquid to about 8.0 to accelerate gravitational separation of oils and solids and the use of elevated temperatures to accelerate the separation process. Rather than being removed, water soluble organics in the solution would be stabilized by this treatment.
U.S. Pat. No. 4,035,289 discloses the use of microorganisms to reduce the presence of organic material in mineral oil drilling fluids. This is an example of the slow, expensive know methods involving biological treatments or use of absorbent materials, like charcoal and/or ion exchange resins.
U.S. Pat. Nos. 4,818,410 and 4,839,054 are directed to techniques for removing water soluble organics from oil process water by acidifying the water, contacting the acidified water with oil and thereafter separating the oil from the water. However, these patents recommend use of a mineral acid such as sulfuric acid, hydrochloric acid or phosphoric acid. Use of such acids involves in several drawbacks. Sulfuric acid and hydrochloric acid are corrosive to metal surfaces in the water to be treated. Phosphoric acid forms a precipitate with multivalent cations such as Ca.sup.+2 in the water, resulting in formation of scale and oil-wetting particles that tend to retain oil in the water phase. The agglomeration of oil onto such particles reduces the quality of phase separation and the particles carry the oil through the system, thereby fouling the system.