A system and method for removing dissolved contaminants, particulate contaminants, and oil contaminants from industrial waste water

FIELD OF THE INVENTION

0001This invention relates to a system and method for removing dissolved contaminants, particulate contaminants and oil contaminants from industrial waste water.

BACKGROUND OF THE INVENTION

0002The oil industry produces large amounts of waste water during exploration and production of petroleum. It has been estimated that approximately 800 gallons of water are used for the production of a barrel of oil of which approximately 80% is used for cooling in the refinery process. Oil wastes are classified depending on their origin, e.g., from oil production or from oil refining. Waste water from oil production is generally a mixture of drilling muds, salt water, free and emulsified oil and natural gas. Waste water from oil refineries includes, inter alia, free and emulsified oils from leaks, spills, and other sources. The combined refinery wastes or spills may contain crude oil and various fractions thereof, dissolved or suspended mineral and organic compounds discharged in liquors and sludges in various stages of processing.

0003Cleaning of industrial waste water from oil production and oil refining is important for both environmental and industry purposes. <patcit id="pcit0001" dnum="US6960294B"><text>US6,960,294</text></patcit> discusses a method of removing oil from water using dissolved gas floatation. There are many conventional processes for cleaning oil industrial waste water which include, for example, gravity separation, floatation, filtration, chemical treatments, electrochemical treatments, biochemical treatments, and the like. These systems are typically large, inefficient, and expensive to operate. The only known process which can achieve a final effluent with less than 5 p.p.m. oil contaminants is membrane filtration. However, membrane filtration is expensive and difficult to operate because the membranes quickly foul.

BRIEF SUMMARY OF THE INVENTION

0004It is therefore an object of this invention to provide a system and method for removing dissolved contaminants, particulate contaminants, and oil contaminants from industrial waste water.

0005It is a further object of this invention to provide such a system and method which removes dissolved contaminants, particulate contaminants, and oil contaminants from industrial waste water generated by oil production and oil refining processes.

0006It is a further object of this invention to provide such a system and method which removes dissolved contaminants, particulate contaminants, and oil contaminants from industrial waste water to an acceptable level required by the Environmental Protection Agency (EPA).

0007It is a further object of this invention to provide such a system and method which produces a final effluent which can be reused by oil production and oil refining processes.

0008It is a further object of this invention to provide such a system and method which provides a final effluent with less than 5 p.p.m. of oil contaminants.

0009It is a further object of this invention to provide such a system and method which provides a final effluent with less than 5 p.p.m. of particulate contaminants.

0010It is a further object of this invention to provide such a system and method which utilizes less space.

0011It is a further object of this invention to provide such a system and method which eliminates the problems associated with using membranes.

0012It is a further object of this invention to provide such a system and method which reduces costs.

0013It is a further object of this invention to provide such a system and method which recycles weighting agents.

0014It is a further object of this invention to provide such a system and method which is more effective.

0015The subject invention, however, in other embodiments, need not achieve all these objectives and the claims hereof should not be limited to structures or methods capable of achieving these objectives.

0016This invention features a system as defined in claim 1 for removing dissolved contaminants, particulate contaminants, and oil contaminants from industrial waste water, the system including a gas floatation and primary oil contaminant removal subsystem including a tank for receiving a flow of the industrial waste water and a flow of gaseous microspheres, wherein the gaseous microspheres combine with oil droplets in the waste water to form flocs which float to the surface and are removed to provide processed waste water with the majority of the oil contaminants removed, and a contaminant removal subsystem for removing dissolved contaminants, particulate contaminants, and any remaining oil contaminants from the processed waste water.

0017In a preferred embodiment, the gas floatation and primary oil contaminant removal subsystem may further include a floc removal subsystem for removing the flocs from the surface of the waste water. The subsystem may include a skimmer. The system may include a cooling subsystem for reducing the temperature of the waste water to an appropriate temperature for use with a desired flocculant. The system may further include a buffer tank for regulating the flow of waste water and removing coarse particulates in the waste water. The contaminant removal subsystem includes a coagulation mixing tank for receiving the processed waste water and introducing and mixing a coagulant with the processed waste water to precipitate the dissolved contaminants and form flocs of the precipitated dissolved contaminants and of the particulate contaminants. The system further includes a weighting agent mixing tank for receiving the processed waste water from the coagulation mixing tank and introducing and mixing a weighting agent with the processed waste water. The system may further include a flocculation subsystem for receiving the processed waste water from the weighting agent mixing tank and introducing and mixing a flocculant to form large flocs of the weighting agent and the microflocs of the particulate contaminants and/or large flocs of the weighting agent and the precipitated dissolved contaminants and/or large flocs of the weighting agent and any remaining oil particulates and/or large flocs of the weighting agent and any other particulates present in the waste water. The system may further include a separation subsystem for separating the large flocs from the processed waste water to form a clear effluent. The system may further include an oxidation subsystem for introducing an oxidation agent to the processed waste water for changing the electrical charges on one or more of the particulate contaminants and/or the oil contaminants. Oxidation agent may include hydrogen peroxide. The weighting agent may include magnetite. The weighting agent may include coal fines. The separation subsystem may include a clarifier. The separation subsystem may include a rapid settler. The separation subsystem may include hydrocyclone. The system may further include a weighting agent recovery subsystem for recovering the weighting agent. The weighting agent recovery system may include a high shear mixer subsystem. The weighting agent recovery subsystem may include a high gradient magnetic filter for removing fine magnetized weighting agents from the clear effluent. The weighting agent recovery subsystem may include a wet drum magnetic separator. The system may further include a recycling subsystem for recycling the weighting agent to the weighting agent mixing tank. The system may further include a re-circulation system for re-circulating sludge formed from large flocs of the weighting agent and the microflocs of the particulate contaminants and/or large flocs of the weighting agent and the precipitated dissolved contaminants and/or large flocs of the weighting agent and any remaining oil particulates and/or large flocs of the weighting agent and any other particulates present in the waste water. The flocculation subsystem may include a static mixer and/or a mixing tank. The oxidation subsystem may include a static mixer. The separation subsystem may include a skimmer disposed inside the clarifier for coalescing the oil contained in the processed waste water and driving the coalesced oil particulates to the surface of the clarifier. The clear effluent may have less than about 5 p.p.m. of oil contaminants, dissolved contaminants, and particulate contaminants.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

0018Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which: <ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Fig. 1</figref> is a schematic block diagram of one embodiment of the system for removing dissolved contaminants, particulate contaminants, and oil contaminants from industrial waste water of this invention;</li><li><figref idref="f0002">Fig. 2</figref> is a schematic block diagram of the system shown in <figref idref="f0001">Fig. 1</figref> incorporating a cooling subsystem in accordance with one embodiment of this invention;</li><li><figref idref="f0003">Fig. 3</figref> is a schematic block diagram of another embodiment of the system shown in <figref idref="f0002">Fig. 2</figref> utilizing coal fines as a weighting agent in accordance with this invention;</li><li><figref idref="f0004">Fig. 4</figref> is a schematic block diagram of another embodiment of the system shown in <figref idref="f0001 f0002 f0003">Figs. 1-3</figref> incorporating a buffer subsystem and also showing the primary components of one embodiment of the contaminant removal subsystem;</li><li><figref idref="f0005">Fig. 5</figref> is a schematic block diagram of yet another embodiment of the system for removing dissolved contaminants, particulate contaminants, and oil contaminants from industrial waste water of this invention; and</li><li><figref idref="f0006">Fig. 6</figref> is a schematic side view of one embodiment of a clarifier and oil skimmer that may be employed with the system shown in <figref idref="f0001 f0002 f0003 f0004 f0005">Figs. 1-5</figref>.</li></ul>

DETAILED DESCRIPTION OF THE INVENTION

0019As discussed in the Background section above, conventional processes for cleaning oil industry waste water, such as gravity separation, floatation, filtration, chemical treatments, electrochemical treatments, biochemical treatments, and the like, are inefficient, large, expensive to operate, and typically incapable of producing a final effluent with less than 5 p.p.m. of oil and/or particulate contaminants. Although membrane filtration systems can produce a final effluent with less than 5 p.p.m. of oil contaminants, these systems are expensive and difficult to operate because the membrane filter quickly fouls.

0020In contrast, system 10, <figref idref="f0001">Fig. 1</figref>, for removing dissolved contaminants, particulate contaminants, and oil contaminants from industrial waste water of this invention includes gas floatation and primary oil contaminant removal subsystem 12 which receives flow of industrial waste water 14, e.g., from oil production processes, oil refining processes, and the like. Subsystem 12, a dissolved air floatation (DAF) subsystem, receives flow of gaseous microspheres 16, e.g., from an air source with a bubble flow distribution subsystem. The flow of gaseous microspheres 16 combines with oil droplets in flow of industrial wastewater 14 in subsystem 12.

0021When oil is in an emulsified state, it exists as a colloidal suspension. When oil is in a free state, it is present as micro-droplets. The micro-droplets, when suspended in waste water, possess negative charge surfaces which creates repulsive forces between the droplets. The gaseous microspheres from flow of gaseous microspheres 16 are positively charged and are attracted to the oil droplets. The interaction of gaseous microspheres 16 with the oil droplets in industrial waste water 14 forms flocs. The flocs of the oil micro-droplets and the gaseous microspheres float to the surface of the waste water and are removed as recovered oil 18, e.g., with a skimmer or similar type device. This removes the majority of oil contaminants from the industrial waste water and is output as processed waste water by line 22.

0022Contaminant removal subsystem 20 receives the processed waste water from subsystem 12 by line 22 and removes dissolved contaminants, particulate contaminants, and any remaining oil contaminants from the processed waste water by line 22 to provide a final clear effluent by line 50 which preferably has a concentration of oil contaminants, particulate contaminants, and dissolved contaminants which are less than about 5 p.p.m. each, as discussed in detail below.

0023The contaminant removal subsystem 20 includes coagulation mixing tank 24 with mixer 26 which receives the processed waste water from subsystem 12, by line 22 and introduces coagulant 28, e.g., aluminum, FeCl₃, PAC (polyaluminum chloride), and the like, to tank 24. Mixer 26 mixes the coagulant and the processed waste water to precipitate the dissolved contaminants in the waste water and form microflocs of precipitated dissolved contaminants and particulates.

0024The contaminant removal subsystem 20 also includes weighting agent mixing tank 30 with mixer 32 which receives the processed waste water from coagulation mixing tank 24 by line 34 and introduces weighting agent or magnetic ballast 34, e.g., magnetite or similar type weighting agents known to those skilled in the art. Mixer 32 mixes the weighting agent 34 with the processed waste water in tank 30. As known by those skilled in the art, the weighting agent provides for rapid settling of flocs, as discussed below.

0025Subsystem 20 preferably includes flocculation mixing tank 36 which receives the processed waste water from weighting agent mixing tank 30 by line 40 and introduces flocculant 42. Mixer 38 mixes flocculant 42 with the processed waste water in tank 36 to form large flocs of the weighting agent and the microflocs of the particulate contaminants and/or large flocs of the weighting agent and the precipitated dissolved contaminants and/or large flocs of the weighting agent and any remaining oil particulates and/or large flocs of any other particulates present in the processed waste water received by line 40. The flocculant, e.g., a polymer, has an electrical charge (anionic or cationic) which attracts the weighting agent, the microflocs of the particulate contaminants, the precipitated dissolved contaminants, any remaining oil particulates, and any other particulates present in the waste water to form the large flocs which are separated using separation subsystem 44. The weighting agent provides for rapid settling of the flocs separation subsystem 44.

0026Separation subsystem 44 separates the large flocs of the weighting agent and the microflocs of the particulate, large flocs of the weighting agent and the precipitated dissolved contaminants and/or large flocs of the weighting agent and any remaining oil particulates and/or large flocs of any other particulates present in the processed waste water to provide a clear effluent on line 50, e.g., a final effluent having less than 5 p.p.m. each of oil contaminants, and particulate contaminants. As known to those skilled in the art, separation subsystem 44 may include a clarifier, a rapid settler, or a hydrocyclone.

0027In one design, system 10 may include recycling and re-circulating subsystem 46 which recovers and recycles weighting agent or magnetic ballast 34 from the processed waste water in separation subsystem 40 by line 48 and also re-circulates the sludge of the large flocs of the weighting agent and contaminants by line 48 (discussed below).

0028In one embodiment, system 10 includes an oxidation subsystem 29 for introducing an oxidation agent, e.g., hydrogen peroxide or similar oxidation agent known to those skilled in the art, to the processed water in coagulation mixing tank 24 in order to change the electrical charges of one or more of the particulate contaminants and/or the oil contaminants in the waste water and to improve the formation of flocs. Additional examples of contaminant removal subsystem 20 are disclosed in <patcit id="pcit0002" dnum="US6099738A"><text>U.S. Patent No. 6,099,738</text></patcit> by the inventors hereof.

0029The result is system 10 for removing dissolved contaminants, particulate contaminants, and oil contaminants from industrial waste water of this invention effectively and efficiently removes dissolved contaminants, particulate contaminants, and oil contaminants from industrial waste water, e.g., generated from oil production and/or oil refining processes. System 10 provides a final clean effluent, preferably having a level of oil contaminants and particulate contaminants less than about 5 p.p.m. each. Such a level is an acceptable level required by the EPA and can be reused by oil production and/or oil refining processes. Moreover, system 10 does not require the use of any membranes or filters, thus the problems associated therewith are eliminated. System 10 is less expensive and utilizes less space than conventional industrial waste water cleaning systems. The ability to recycle the weight agents further decreases processing costs.

0030In one embodiment, system 10', <figref idref="f0002">Fig. 2</figref>, where like parts have been given like numbers, includes cooling subsystem 52. Cooling subsystem 52 reduces the temperature of the waste water received from gas floatation and primary oil contaminant removal subsystem 12 by line 22 to an appropriate temperature on line 23, e.g., about 50° C, for use with a desired flocculant, e.g., a polymer such as Cytec A-130 or similar flocculant type known by those skilled in the art.

0031In one design, weighting agent 34', <figref idref="f0003">Fig. 3</figref>, where like parts have been given like numbers, may be coal fines. Using coal fines as the weighting agent generates a final sludge which can be filtered, dried, and used as a combustible.

0032In another design, system 10"', <figref idref="f0004">Fig. 4</figref>, where like parts have been given like numbers, includes gas floatation and primary oil contaminant subsystem 12 which receives flow of industrial waste water 14 and operates similar as discussed above with reference to <figref idref="f0001">Fig. 1</figref>. System 10' also preferably includes buffer tank 56 which regulates the flow of waste water, e.g., from cooling subsystem 52 by line 23 and removes coarse particulates from the waste water. Although, as shown in <figref idref="f0004">Fig. 4</figref> buffer tank 56 is located between cooling subsystem 52 and contaminant removal subsystem 20, this is not a necessary limitation of this invention, as buffer tank 56 may be located at any desired location in system 10.

0033In one design, contaminant removal subsystem 20' receives the cooled and regulated waste water from cooling subsystem 52 and buffer tank 56 by line 57. Static mixers 60 introduce and mix the coagulant via coagulant feed R1-82 by line 83 and/or the oxidation agent via oxidation feed R2-84 by line 85. The coagulant and/or oxidation agent interacts with plates 62 of static mixers 60 to effectively mix of the coagulant and/or the oxidizing agent with the processed waste water in line 57. The statically mixed coagulant and/or oxidizing agent with the processed waste water from subsystem 12 are fed into mixing tanks T-1 and T-2 by line 89. Tanks T-1 to T-2, e.g., weighting agent tank 30 with mixer 32 and flocculant mixing tank 36 with mixer 38 introduce and mix the waste water from static mixers 60 with weighting agents and flocculant to form large flocs of the weighting agent and the microflocs of particulate contaminants and/or large flocs of the weighting agent and the precipitated dissolved contaminants and/or large flocs of the weighting agent and any remaining oil particulates and/or large flocs of any other particulates present in the waste processed, similar as discussed above with reference to <figref idref="f0001">Fig. 1</figref>. Separation subsystem 44' includes clarifier 70 which removes the large flocs of the weighting agent and the microflocs of particulate contaminants, and/or the large flocs of the weighting agent and precipitated dissolved contaminants and/or large flocs weighting agent and any remaining oil particulates to provide a clear effluent on line 50', e.g., by rapid settling, as known by those skilled in the art.

0034In one design, contaminant removal subsystem 20' includes weighting agent recovery subsystem 46' for removing fine magnetized weighting agents from the clear effluent on line 50'. In one example, magnetic filter subsystem 72 and/or high shear subsystem 74 and/or magnetic wet drum separator 76 is used to remove and recover the weighting agent from the clear effluent in line 50'. Weighting agent recovery subsystem 70 recovers the weighting agent which is then recycled back to weighting agent mixing tanks, e.g., any of tank T-1 to T-2, by line 78. <i>See,</i> e.g., <patcit id="pcit0003" dnum="US6099738A"><text>U.S. Patent No. 6,099,738</text></patcit> cited <i>supra.</i>

0035Although, as discussed above with reference to <figref idref="f0001 f0002 f0003 f0004">Figs. 1-4</figref> above, gas floatation and primary oil contaminant removal subsystem 12 is located before contaminant removal subsystem 20, this is not a necessary limitation of this invention. In another embodiment, system 10^iv, <figref idref="f0005">Fig. 5</figref>, where like parts have been given like numbers, for removing dissolved contaminants, particulate contaminants, and oil contaminants from industrial waste water of this invention, may include gas floatation and primary oil contaminants removal subsystem 12 located after contaminant removal subsystem 20". In this embodiment, contaminant removal subsystem 20" receives flow of industrial waste water 14 by line 120. Subsystem 20' includes tanks 100 which receive coagulants 102 by line 103, weighting agents or magnetic ballast 104 by line 105 and a flocculant 106 by line 107. Mixing tanks 100 operate similar to coagulation mixing tank 24 with mixer 24, weighting agent mixing tank 30 with mixer 32, and flocculation mixing tank 36 with mixer 38, as described above with reference to <figref idref="f0001">Fig. 1</figref>. The output of mixing tanks 100 by line 103 is large flocs of the weighting agent and oil contaminants, large flocs of the weighting agent, and the microflocs of the particulate contaminants, and/or large flocs of the weighting agent and the precipitated dissolved contaminants, and/or large flocs of any other particulates present in the waste water. Clarifier 82 preferably removes the large flocs by rapid sedimentation. Clarifier 82, <figref idref="f0006">Fig. 6</figref>, may also include skimmer 170, disposed inside clarifier 82, which coalesces the oil contained in the processed waste water, e.g., as shown at 172, and drives the coalesced oil particulates to the surface of the clarifier for removal as shown by arrow 174. Clarifier 82 with skimmer 170 may be utilized in any of the embodiments of system 10 discussed above with reference to <figref idref="f0001 f0002 f0003 f0004">Figs. 1-4</figref>. Gas floatation and primary oil contaminant removal subsystem 12', <figref idref="f0005">Fig. 5</figref>, of similar design as gas floatation and primary oil contaminant removal subsystem discussed above with reference to <figref idref="f0001">Fig. 1</figref>, receives the clear effluent output by clarifier on line 123 and introduces gaseous microspheres which combine with any remaining oil droplets in the waste water to form flocs which float to the surface and are removed as recovered oil 18. The final clear effluent is output by line 50". Sludge 130 output by clarifier 82 by line 132 can the be re-circulated by line 110 to tanks 100 and/or processed by magnetic separator 114 which recycles the weighting agents by line 112 to mixing tanks 100. The final sludge 140 can be sent to filtration pond and incineration when the weighting agent is coal fines, indicated at 144. System 10^iv may also be combined with system 10, <figref idref="f0001 f0002 f0003 f0004">Figs. 1-4</figref>, such that gas floatation and primary oil contaminant subsystem 12, 12', is located at before and after contaminant removal subsystem 20, 21'. Such a design is useful for applications requiring more complete removal of oil contaminants.

0036Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words "including", "comprising", "having", and "with" as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments. Other embodiments will occur to those skilled in the art and are within the following claims.