Method for treating organic laden produced water

Abstract

An oil recovery process which utilizes chemical precipitation and complexation reactions to remove dissolved organics and silica from waste water streams. The process produces brine suitable for deep well injection and solids suitable for Class II landfill. The treatment process can be used in combination with a concentrator and in addition to producing brine suitable for deep well injection and solids suitable for Class II landfill, the concentrator also produces a clean water stream for reuse. By including a crystallizer for the brine processing the system has zero liquid discharge.

Claims

1. A method of treating a waste water stream having a pH >10 and comprising silica greater than 250 mg/L and an organic material, comprising: adding an acid to the waste water stream to produce a treated water stream; adding an alkaline earth oxide slurry comprising an alkaline earth oxide and water or brine, to the treated water stream to produce a floc stream; and separating the solids from the floc stream.

2. The method of claim 1 wherein the waste water stream is agitated after the addition of the acid.

3. The method of claim 1 wherein the acid is mixed with the waste water stream in a precipitator reactor.

4. The method of claim 1 wherein the acid is FeCl.sub.3.

5. The method of claim 1 wherein the alkaline earth oxide slurry is added to the treated water stream in a complexation reactor.

6. The method of claim 5 wherein the alkaline earth oxide slurry is agitated with the treated water stream in the complexation reactor at a temperature from 75 C. to 85 C.

7. The method of claim 5 wherein the complexation reactor has a cone bottom.

8. The method of claim 7 wherein the complexation reactor has a height to diameter ratio of between 1.0 and 1.7, the diameter being at an upper end of the cone.

9. The method of claim 1 wherein the solids are separated from the floc stream by a dewatering device.

10. The method of claim 9 wherein the dewatering device produces brine, and the brine is concentrated in a concentrator.

11. The method of claim 10 wherein the concentrator is an evaporator.

12. The method of claim 10 wherein the concentrator is a forward osmosis membrane system.

13. The method of claim 1 wherein the acid is a Lewis acid.

14. The method of claim 9 wherein the dewatering produces brine, and the brine is concentrated in a crystallizer producing a salt slurry.

15. The method of claim 14 wherein the salt slurry is dewatered.

16. The method of claim 1 wherein the alkaline earth oxide slurry comprises MgO.

17. The method of claim 1 wherein the alkaline earth oxide slurry comprises CaO.

18. The method of claim 1 wherein the waste water stream is produced after an oil-water separation process.

19. A system for treating a waste water stream having a pH >10 and comprising silica greater than 250 mg/L and an organic material, comprising: a precipitation reactor configured to mix an acid with the waste water stream to produce a treated water stream; a complexation reactor configured to receive the treated water stream and add an alkaline earth oxide slurry comprising an alkaline earth oxide and water or brine, to produce a floc stream; and a dewatering device to separate solids in the floc stream.

20. A method of treating a waste water stream having a pH >10 and comprising silica greater than 250 mg/L and organic matter, comprising: receiving an oil-water mixture; separating oil in the oil water mixture from water in the oil-water mixture to produce a produced water stream; purifying the produced water stream; generating steam from the produced water which produces a waste water stream containing organics; adding acid to the waste water stream to produce a treated water stream; adding an alkaline earth oxide slurry comprising an alkaline earth oxide and water or brine, to the treated water stream to produce a floc stream; and separating the solids from the floc stream.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is a schematic representation of an embodiment of the invention, showing an evaporation-based heavy oil recovery process with a backend precipitation, complexation and dewatering treatment process.

(2) FIG. 2 is a schematic representation of an alternative embodiment of the invention, showing a warm lime softening-based heavy oil recovery process with a backend precipitation, complexation and dewatering treatment process.

(3) FIG. 3a is a schematic illustration of an embodiment of a backend precipitation, complexation and dewatering treatment process according to the invention, including a concentration step.

(4) FIG. 3b is a schematic illustration of an alternative embodiment of the backend precipitation, complexation and dewatering treatment process according to the invention, including a crystallization step.

(5) FIG. 4 is a graph showing the relationship between filterability and chemical addition in the process according to the invention.

(6) FIG. 5 is a graph showing the relationship between TOC and chemical addition in the process according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(7) A detailed description of one or more embodiments of the invention is provided below along with accompanying figures that illustrate the principles of the invention. The invention is described in connection with such embodiments, but the invention is not limited to any embodiment. The scope of the invention is limited only by the claims and the invention encompasses numerous alternatives, modifications and equivalents. Numerous specific details are set forth in the following description in order to provide a thorough understanding of the invention. These details are provided for the purpose of example and the invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the invention is not unnecessarily obscured.

(8) The term invention and the like mean the one or more inventions disclosed in this application, unless expressly specified otherwise.

(9) The terms an aspect, an embodiment, embodiment, embodiments, the embodiment, the embodiments, one or more embodiments, some embodiments, certain embodiments, one embodiment, another embodiment and the like mean one or more (but not all) embodiments of the disclosed invention(s), unless expressly specified otherwise.

(10) A reference to another embodiment or another aspect in describing an embodiment does not imply that the referenced embodiment is mutually exclusive with another embodiment (e.g., an embodiment described before the referenced embodiment), unless expressly specified otherwise.

(11) The terms including, comprising and variations thereof mean including but not limited to, unless expressly specified otherwise.

(12) The terms a, an and the mean one or more, unless expressly specified otherwise. The term plurality means two or more, unless expressly specified otherwise. The term herein means in the present application, including anything which may be incorporated by reference, unless expressly specified otherwise.

(13) The term e.g. and like terms mean for example, and thus does not limit the term or phrase it explains.

(14) The term respective and like terms mean taken individually. Thus if two or more things have respective characteristics, then each such thing has its own characteristic, and these characteristics can be different from each other but need not be. For example, the phrase each of two machines has a respective function means that the first such machine has a function and the second such machine has a function as well. The function of the first machine may or may not be the same as the function of the second machine.

(15) Where two or more terms or phrases are synonymous (e.g., because of an explicit statement that the terms or phrases are synonymous), instances of one such term/phrase does not mean instances of another such term/phrase must have a different meaning For example, where a statement renders the meaning of including to be synonymous with including but not limited to, the mere usage of the phrase including but not limited to does not mean that the term including means something other than including but not limited to.

(16) Neither the Title (set forth at the beginning of the first page of the present application) nor the Abstract (set forth at the end of the present application) is to be taken as limiting in any way as the scope of the disclosed invention(s). An Abstract has been included in this application merely because an Abstract of not more than 150 words is required under 37 C.F.R. Section 1.72(b) or similar law in other jurisdictions. The title of the present application and headings of sections provided in the present application are for convenience only, and are not to be taken as limiting the disclosure in any way.

(17) Numerous embodiments are described in the present application, and are presented for illustrative purposes only. The described embodiments are not, and are not intended to be, limiting in any sense. The presently disclosed invention(s) are widely applicable to numerous embodiments, as is readily apparent from the disclosure. One of ordinary skill in the art will recognize that the disclosed invention(s) may be practiced with various modifications and alterations, such as structural and logical modifications. Although particular features of the disclosed invention(s) may be described with reference to one or more particular embodiments and/or drawings, it should be understood that such features are not limited to usage in the one or more particular embodiments or drawings with reference to which they are described, unless expressly specified otherwise.

(18) No embodiment of method steps or product elements described in the present application constitutes the invention claimed herein, or is essential to the invention claimed herein, or is coextensive with the invention claimed herein, except where it is either expressly stated to be so in this specification or expressly recited in a claim.

(19) Two embodiments of the general process of the present invention are illustrated schematically in FIGS. 1 and 2, respectively. Oil-water mixture 20 from an oil-water mixture collection 15 is directed to an oil-water separation process 25 which effectively separates the oil 30 from the water stream 40 (or 45 as shown in FIG. 2). This is commonly referred to as primary separation and can be carried out by various conventional processes such as gravity or centrifugal separation. Separated water may be subjected to a polishing de-oiling process where additional oil is removed from the water. Resulting water from the oil-water separation process is referred to as produced water. Produced water contains residual suspended silica solids, emulsified oil, dissolved organic material and dissolved solids. Following separation, the produced water stream 40 (or 45 as shown in FIG. 2) is directed by a line to a downstream purification process, such as an evaporation process 42 as shown in FIG. 1, or alternatively, a warm-lime softening with ion exchange process 47 as shown in FIG. 2. The downstream purification process purifies the produced water and produces a purified water stream 50 (or purified water stream 55 as shown in FIG. 2). Purified water 50 is directed to a steam generator, such as a boiler 58, where steam is generated and injected 60 into the oil bearing formation 65 to eventually form the oil-water mixture that is pumped to the surface 10 and collected at oil-water mixture collection 15 to repeat the process. Alternatively, as shown in FIG. 2, after the warm lime softening/ion exchange process 47, purified water stream is directed to steam generator 57, where steam is generated and injected 60 into the oil bearing formation 65 to eventually form the oil-water mixture that is pumped to the surface 10 and collected at oil-water mixture collection 15 to repeat the process.

(20) The evaporation purification process 42 also creates a waste stream 70. In the case of the warm-lime softening with ion exchange purification process 47, as shown in FIG. 2, waste stream 75 originates from the steam generator 57.

(21) The waste streams, either waste stream 70 or waste stream 75, as shown in FIGS. 1 and 2 respectively, from either exchange purification process, such as warm lime softening/ion exchange process 47 or evaporation process 42 respectively, have a pH >10 and contain high levels of silica (250-20,000 mg/L); suspended and dissolved organics, measured as Total Organic Carbon (TOC) (5,000-20,000 mg/L); and dissolved inorganic solids (10,000-150,000 mg/L). The suspended organics may include significant concentrations of oil if operational upset conditions fail to separate the oil from the water.

(22) Waste streams 70 and 75 are intended for use in deep well injection 65. However, the silica in these waste streams can precipitate in the disposal formation and reduce the capacity of the disposal well. Existing processes are directed towards removal of silica and generate a solid phase which is extremely difficult to separate from the aqueous phase and which scales and fouls equipment.

(23) The present invention provides for the removal of silica and organics from waste streams 70 or 75 and converts the silica and organics therein to a solid form that is easily separated from the aqueous phase. The method according to the invention includes a process which is focused on organic removal rather than silica removal. Each step of the process, by itself, removes silica, but does not produce a solid phase which is easily separated from the aqueous phase. A two-step process first precipitates the silica and organics and then produces a complex which is easily separated from the aqueous phase.

(24) In the present invention an acid, such as FeCl.sub.3, is used to lower the pH of the waste stream and cause acid insoluble organics and silica to precipitate from the waste water (other acids that could be used include hydrochloric acid (HCl), carbon dioxide (CO.sub.2), or aluminium chloride (AlCl.sub.3)). The precipitated organics and ferric hydroxide form a floc. In the case of using HCl or CO.sub.2 the floc is primarily precipitated acid insoluble organics. In this step, the majority (up to 95%) of the silica and the organics (up to 75%), are removed from the water. Using FeCl.sub.3 as an example, the chemical reaction in this step is as follows: Ferric chloride is a soluble acid that dissociates in aqueous solutions:
FeCl.sub.3.fwdarw.Fe.sup.3++3Cl.sup. When the ferric ions (Fe.sup.3+) encounter the high pH environment, insoluble ferric hydroxide (Fe(OH).sub.3) precipitates near instantaneously according to the reaction:
Fe.sup.3++3OH.sup..fwdarw.Fe(OH).sub.3

(25) The ferric hydroxide and precipitated organics form a floc, which adsorbs/absorbs silica. The removal mechanism for silica is adsorption of silica onto freshly precipitated organics and Fe(OH).sub.3. The removal of organics can be considered a destabilization of the colloidal material by the addition of a cationic charge and/or the precipitation of a complex formed by a partially hydrolyzed iron ion with an ionic functional group on the organic molecule. The organic constituents typically affected by this coagulant are colloidal or have a high molecular weight and high hydrophobicity (e.g. humic acids).

(26) If alternative acids, which do not form metal hydroxide precipitates, are used the chemical reactions are similar and result in precipitated organic flocs.

(27) FeCl.sub.3 coagulant demand may depend on the nature of the dissolved organic material, as measured by the Specific UV Absorbance (SUVA) or TOC concentration of waste water 70 or 75, as appropriate.

(28) The ferric hydroxide floc from this step has poor filterability characteristics. A filtration rate of less than 200 Liters/(m.sup.2-hr) (LMH) is typical. This is consistent with other studies which have shown that pH adjustment of high-silica, high organic concentration waters alone or adsorption of silica onto one hydroxide material, such as Mg(OH).sub.2, yield a material which does not easily separate from solution.

(29) The method according to the invention addresses the filterability problem by hydrolyzing an alkaline earth, such as MgO or CaO, in the presence of the floc formed from addition of acid. As an example, when mixed with water, calcium oxide hydrolyzes to calcium hydroxide (Ca(OH).sub.2) according to the reaction:
CaO+H.sub.2O.fwdarw.Ca(OH).sub.2
Calcium hydroxide will react with carbonate to form calcium carbonate according to the reaction:
Ca(OH).sub.2+CO.sub.3.sup.2.fwdarw.CaCO.sub.3+2OH.sup.
These reactions are a function of both time and temperature.

(30) In current Steam Assisted Gravity Drainage (SAGD) water treatment applications, the reaction is controlled such that the Mg(OH).sub.2 is formed over time and at elevated temperatures in the presence of dissolved silica. In such applications, the dissolved silica adheres to the Mg(OH).sub.2 crystals and is removed from the solution. The concentration of TOC in produced water from current SAGD applications is between 400 and 1,000 mg/L and the dosage of MgO is related to the concentration of silica. Typical magnesium dosages used in current silica removal treatment are in the range of ratios of 0.4 to 1.5 of the Mg ion to SiO.sub.2.

(31) In the method according to the invention, the acid removes the bulk of the silica and organics from waste water stream 70 or 75 and the alkaline earth, CaO for example, produces a calcium hydroxide-calcium carbonate-ferric hydroxide complex floc which can easily be dewatered. The addition of CaO is a function of the TOC concentration and not the silica concentration.

(32) The relationship between filterability and chemical addition is shown in FIG. 4. A filtration rate greater than 500 LMH with a differential pressure of 0.5 bar is generally commercially acceptable. The relationship between TOC and chemical addition to achieve commercially acceptable dewatering rates is linear and is shown in FIG. 5.

(33) The solids floc may contain between 2% and 8% solids (w/v) and has excellent filterability characteristics (LMH ranging from 1500 to 8000). The solids can be effectively separated by filtration or centrifugation. In the case of filtration, a thick solids cake does not impede the filtration rate and readily releases from a filter paper or filter cloth. In the case of centrifugation, the centrate is free of suspended particulates and may be rapidly separated from the solids in less than a minute at moderate RCF (relative centrifugal force) rate.

(34) Waste streams 70 or 75 with TOC concentrations below 6,000 to 8,000 mg/L may be treated as is and at temperatures ranging from 75-85 C. Waste streams 70 or 75 with higher TOC concentrations are diluted as necessary with brine 150 from within the process to reduce the TOC to approximately 8,000 mg/L. The resultant waste water 80, diluted or neat, can be allowed to cool and be reheated later, either directly or indirectly, to between 75-85 C.

(35) As shown in FIGS. 1 and 2, the waste water 80, diluted or undiluted, is submitted to the first of two chemical treatment steps. The first step is the addition of an acid 90, such as ferric chloride (FeCl.sub.3), to achieve approximately 2,000 mg/L as FeCl.sub.3 within the waste water 80. The FeCl.sub.3 addition can added be directly to the waste water 80 in such a way that there is thorough and complete mixing in a turbulent environment or may be added to a Precipitation Reactor Vessel 85 where the FeCl.sub.3-treated water is continuously agitated (50-100 rpm) during the addition for about 10 seconds. In this step, the majority of organics and dissolved silica are precipitated from solution, as described above.

(36) The acid treated, such as FeCl.sub.3-treated, water stream 100 is then submitted to the second chemical treatment which involves the complexation of the precipitates formed in the previous step with an alkaline earth hydroxide. The second chemical addition is an alkaline earth oxide slurry 110, such as magnesium oxide (MgO) or calcium oxide (CaO), to the Complexation Reactor 115. The alkaline earth oxide, such as MgO or CaO, is added as a slurry. The slurry is prepared by mixing the MgO or CaO powder with either a clean water source or recycled brine at temperatures not exceeding 30 C. The slurry mixture may be 10% (w/v) and can be premade up to one hour before addition. The slurry may be added in one bulk addition. The treated water is continuously agitated (50-100 rpm) during addition for about 30 seconds.

(37) After the alkaline earth oxide addition, the treated water is agitated slowly (approximately 20 rpm) in the complexation reactor 115 at elevated temperatures (70-85 C.) for 30-120 minutes. The agitator suspends the solids and creates contact between the alkaline earth hydroxide and acid hydroxide floc solids and the wastewater. The complexation reactor vessel 115 may have a cone bottom, preferably with a slope between 8-15. Vessel 115 may include baffles to ensure radial mixing. The reactor vessel 115 should have a height to diameter ratio of between 1.0 and 1.7. The ratio of agitator diameter to tank diameter may be between 0.3 and 0.5. This prevents solids from accumulating or settling in reactor vessel 115.

(38) The solids floc stream 120 is transferred with a pump to a dewatering device 125 which may be a centrifuge, series of centrifuges, filter press or other commercially available device for solids separation. The dewatering device separates the solids 130 from the brine 140. The resulting separated solids meet landfill Class II requirements and are suitable for disposal by trucking A portion of the filtered brine 150 can be used to dilute the incoming waste streams 70 or 75 prior to treatment. A portion of the brine 160 can disposed by deep well injection or further concentrated as described below. The brine has the following qualities: a. Silica concentration less than 150 mg/L; b. Substantial removal of suspended solids greater than 10 micron in size; and c. Hardness less than 500 mg/L as CaCO.sub.3.

(39) In another embodiment of the invention, as shown in FIG. 3a, the brine 160 from the dewatering device can be further concentrated at concentrator 165 to reduce the volume of disposed liquid. Concentrator technology is readily available and may be based on evaporation or membrane processes, such as forward osmosis, so that concentrator 165 may be an evaporator or a forward osmosis membrane system. Concentrators 165 produce brine 180, suitable for deep well injection, and a clean water stream 170 which is recyclable for beneficial reuse.

(40) In another embodiment of the invention, as shown in FIG. 3b, the brine 160 from the dewatering device can be further concentrated in a crystallizer 175 to nearly eliminate the volume of disposed liquid. Crystallizer 175 produces a clean water phase 170, which can be recycled for beneficial reuse, and a salt slurry 180. The salt slurry 180 is dewatered in a second dewatering device 185, such as a centrifuge or filter press, producing a salt cake 200, which is suitable for a landfill, and a centrate/filtrate 190, which may be recycled to the crystallizer 175. A portion of the centrate/filtrate 190 can be purged as stream 210 to prevent the accumulation of organics.

(41) Although a few embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications can be made to these embodiments without changing or departing from their scope, intent or functionality. The terms and expressions used in the preceding specification have been used herein as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding equivalents of the features shown and described or portions thereof, it being recognized that the invention is defined and limited only by the claims that follow

(42) As will be apparent to those skilled in the art, the various embodiments described above can be combined to provide further embodiments. Aspects of the present systems, methods and components can be modified, if necessary, to employ systems, methods, components and concepts to provide yet further embodiments of the invention. For example, the various methods described above may omit some acts, include other acts, and/or execute acts in a different order than set out in the illustrated embodiments. As another example the acid used could be another Lewis acid, such as magnesium chloride.

(43) Further, in the methods taught herein, the various acts may be performed in a different order than that illustrated and described. Additionally, the methods can omit some acts, and/or employ additional acts.

(44) These and other changes can be made to the present systems, methods and articles in light of the above description. In general, in the following claims, the terms used should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the invention is not limited by the disclosure, but instead its scope is to be determined entirely by the following claims.