CN117964180A - Oilfield produced water treatment system and treatment method - Google Patents
Oilfield produced water treatment system and treatment method Download PDFInfo
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Abstract
The invention belongs to the technical field of oilfield produced water treatment, and discloses an oilfield produced water treatment system and a treatment method, which combine an oil-oil extraction separation technology, an air flotation separation technology, a cyclone separation technology and a gravity sedimentation separation technology in terms of pretreatment, separate oil ions and solid suspended matters in a full particle size range, obtain the comprehensive effect of multi-effect coupling, greatly improve the separation efficiency and the operation reliability, and create conditions for the subsequent membrane separation.
Description
Technical Field
The invention belongs to the technical field of oilfield produced water treatment, and particularly relates to an oilfield produced water treatment system and an oilfield produced water treatment method, which are used for improving the stability and reliability of the oilfield produced water treatment system so as to improve the reinjection rate of oilfield produced water.
Background
The statements herein merely provide background information related to the present disclosure and may not necessarily constitute prior art.
The produced water (hereinafter referred to as "waste water") is a by-product in the oil field exploitation process, not only has a large water amount, but also contains a certain amount of floating oil, dispersed oil, emulsified oil and dissolved oil, and other solid suspended matters, dissolved salts, colloid substances and biological fungi with a certain concentration, and is one of the industrial waste water which is generally recognized in the world and is difficult to treat. The oilfield produced water is to be reinjected in situ in an oil extraction area, and firstly, the suspended matter concentration, the suspended matter particle size, the oil content, the oxygen content, the bacteria content and other technologies are required to be ensured to meet the quality requirements of reinjected water. The oil content index and the suspended matter content index are important indexes which are difficult to realize stably, and are core key points in the oilfield produced water treatment process.
The traditional process of oilfield produced water purification treatment in the petroleum industry is generally divided into three series treatment procedures of pre-sedimentation, coagulation sedimentation and pressure filtration fine treatment, and is commonly called as a three-stage treatment process. The pre-sedimentation process is relatively simple, the pressure filtration fine treatment process is complex, a multistage filter is required to be arranged to gradually filter residual emulsified oil from micro-particles to ultra-fine particles, and the oil content is reduced to the standard that the waste water can be reinjected or other recycling can be performed. The coarse filter medium adopts granular filter materials such as walnut shell, quartz sand, anthracite, etc., and the superfine filter adopts organic filter screen, metal filter screen, resin, etc. In practical applications, the above-mentioned various filtering modes are "dead-end filtering" mode. The filtering mode has the problems of easy blockage, short service life, large resistance, difficult cleaning and the like of the filtering medium, so that the quality stability of the treated oilfield produced water is poor, the reinjection rate of the oilfield produced water is low, and the ecological environment is adversely affected.
Disclosure of Invention
Aiming at the defects existing in the prior art, the invention aims to provide an oilfield produced water treatment system and a treatment method, wherein the treatment process focuses on a front-end pretreatment stage, adopts various oil-water separation technologies and solid-liquid separation technologies in the stage, realizes the cooperative coupling of various process technologies, furthest reduces the oil content and suspended matter content of wastewater, and achieves the inlet condition of the subsequent membrane treatment; in the technical aspect of back-end treatment, a modern membrane separation process is adopted as a core technology, so that a dead-end filtering mode adopting filter materials in the past is eliminated, and the reliability and stability of system operation are greatly improved. After the multi-effect coupling pretreatment and membrane separation process technology is applied, the reinjection rate of the oilfield produced water is obviously improved; meanwhile, the processing flow is greatly shortened, and energy-saving operation is realized.
In order to achieve the above object, the present invention is realized by the following technical scheme:
in a first aspect, the invention provides an oilfield produced water treatment system comprising an oil-oil extractor, a gas-liquid mixer, and a cyclone, wherein,
The oil-oil extractor is of a vertical tubular structure, a wastewater distributor, an oil-water extraction cavity and a liquid outlet are sequentially arranged from top to bottom, the wastewater distributor is connected with an oil-containing wastewater source, the oil-water extraction cavity is used for containing a light oil layer and a water layer, and the light oil layer is positioned above the water layer;
The liquid outlet is connected with a liquid phase inlet of the gas-liquid mixer, an aeration structure is arranged at the bottom of the gas-liquid mixer, and the aeration structure is connected with the air floatation fan; the liquid outlet is connected with the cyclone;
the cyclone is arranged in the inner sleeve tank, and the inner sleeve tank is arranged in the gravity settling tank;
The outlets at the bottoms of the cyclone and the inner sleeve tank are communicated with the outside through pipelines;
the top of the gravity settling tank is sealed, the set height of the gravity settling tank is respectively connected with an oil overflow pipeline and a water overflow pipeline, and the oil overflow pipeline is positioned above the water overflow pipeline.
In the experimental process, the inventor tries to adopt a mode of 'tank in tank', namely, a cyclone separator is arranged at the center of a gravity settling tank, and an inner sleeve tank is arranged at the periphery of the cyclone. The wastewater firstly enters the cyclone, and the wastewater is subjected to high-speed centrifugal rotation by liquid flow, so that various separation effects such as an oil particle collision polymerization effect, a layering effect of an oil phase and a water phase, a solid particle sinking effect and the like are generated, and the pretreatment effect is improved. The overflow of the cyclone is rich in oil particles, and after the overflow is further combined, an oil layer is formed in an overflow box above the cyclone, and the formed floating oil is continuously discharged downwards from a central pipe in the overflow box through a floating oil discharging device; the water phase and the bottom flow in the overflow enter an inner sleeve tank arranged at the periphery of the gravity settling tank; the solid slag contained in the underflow falls into the bottom of the inner sleeve tank, is discharged outwards through a slag discharge port, and the rest liquid phase flows upwards through the inner sleeve tank and enters the gravity settling tank. The gravity settling tank is provided with enough residence time to enable residual tiny oil particles in the water phase to slowly float, a layer of oil phase is formed above the water phase forming the gravity settling tank, and then the oil phase is discharged outwards through an oil phase overflow port. The process improves the old gravity settling tank process with single function to a certain extent, and improves the oil-water separation effect. However, the tank-in-tank process has relatively good treatment effect on floating oil and dispersed oil, but has poor treatment effect on emulsified oil and dissolved oil, and the treated oilfield produced water is difficult to meet the reinjection requirement.
The invention is provided with an oil-oil extractor, wherein a water layer and a light oil layer are contained in the oil-oil extractor, the water layer is positioned below the light oil layer and is used for buffering impact, and the upper light oil layer is floated. The waste water is sprayed from above and is contacted, mixed and collided with the light oil layer in the process of passing through the light oil layer, and oil particles with larger diameters, such as floating oil particles, dispersed oil particles and emulsified oil particles, in the waste water are directly fused into the light oil layer after contacting the light oil layer; the colloidal particles with smaller diameters in the wastewater and the dissolved oil are contacted with the light oil layer, a certain extraction effect occurs, so that the colloidal particles and the dissolved oil have a tendency of migrating from the water phase to the oil phase, thus the oil-oil extractor can intercept the oil particles with almost full particle size range in the wastewater, the oil removal rate is effectively improved, and the filter can intercept the oil particles with the diameter in a certain specific range. Moreover, the oil-oil extractor adopts a vertical container structure, so that the problem of blockage cannot occur.
After the wastewater is extracted by the oil-oil extractor, low-concentration solid suspended matters, escaped emulsified oil and dissolved oil still exist. The part of the wastewater flows through the water layer and is pumped to the gas-liquid mixer, the escaped oil particles and gas in the wastewater are combined to generate an air floatation effect, and then the wastewater is separated by the cyclone. The cyclone produces a high-speed cyclone so that most of air, oil particles and air-oil particle combinations with relatively low density enter an upper overflow area of the hydrocyclone to form an enriched oil layer, and then are discharged through the oil exhauster. By adopting the mode, the oil content escaping from the oilfield produced water after passing through the oil-oil extraction device can be effectively removed.
The water phase discharged from the underflow area at the lower part of the cyclone is discharged into the inner sleeve tank and overflows into the gravity settling tank through the upper edge of the inner sleeve tank. Because the size of the gravity settling tank is relatively large, in the process of long-time stay of the wastewater, residual dispersed oil and tiny oil particles of emulsified oil in the wastewater can slowly float, a layer of floating oil layer is formed on the water surface inside the gravity settling tank, and when the floating oil reaches a certain height, the floating oil can be discharged outwards in an overflow mode.
In some embodiments, the bottom of the distribution pipe of the wastewater distributor of the oil-oil extraction device is provided with an array of drop holes for dispersing the wastewater into small droplets. The waste water is dispersed into tiny liquid drops by utilizing the waste water distributor, so that the impact on a light oil layer can be reduced, the stability of the light oil layer is improved, the contact area with the light oil layer can be effectively increased, the extraction effect is further improved, and the treatment efficiency of oilfield produced water is effectively improved.
Preferably, the diameter of each drip hole in the drip hole array is 2-8 mm.
In some embodiments, the ratio of the thickness of the light oil layer in the oil-oil extractor to the height of the oil-oil extractor is 0.05-0.3: 1. the light oil layer has a sufficient thickness to ensure good extraction.
In some embodiments, the top of the oil-oil extractor is provided with an air outlet, the upper part is provided with an oil overflow port, and the air outlet and the oil overflow port are communicated through a pipeline. So as to realize internal pressure equalizing and prevent the flow from being influenced by pressure difference generated in the interior.
In some embodiments, a heater is disposed on the wastewater feed line of the oil-oil extractor. For heating the wastewater to adjust the optimum extraction temperature.
In some embodiments, the top of the gravity settling tank is air sealed. The inside of the oil extraction device, the hydrocyclone, the gravity settling tank and other equipment must be completely isolated from the external air, so that the external air is prevented from being dissolved in the wastewater after being invaded, the dissolved oxygen index of the wastewater exceeds the standard, and the consumption of the deoxidizer is increased, so that the equipment must be provided with natural gas as sealing gas to form micro positive pressure, and the external air is prevented from entering. The gas used by the air floatation device is also from sealing gas and is recycled.
In some embodiments, the bottom plate of the gravity settling tank is provided with a slope, and the lowest part of the bottom plate is provided with a cleaning outlet.
In some embodiments, an ultrafiltration membrane assembly is also included, the ultrafiltration membrane assembly being connected to the aqueous phase outlet of the gravity settling tank. The method is used for carrying out ultrafiltration treatment on the wastewater subjected to gravity sedimentation finally so as to remove a small amount of ultrafine suspended matters, emulsified oil and dissolved oil remained in the wastewater, and improve the treatment effect of oilfield produced water.
Preferably, the ultrafiltration membrane component further comprises a back flushing component, and a waste liquid outlet of the back flushing component is connected with the waste water distributor. The wastewater generated by back flushing is treated by using devices such as an oil-oil extractor and the like, so that the discharge of the wastewater is avoided.
In a second aspect, the invention provides a method for treating oilfield produced water, comprising the following steps:
Dispersing the oilfield produced wastewater into small liquid drops, then extracting oil-oil, and extracting and recycling oil particles in the oilfield produced water;
Mixing the wastewater subjected to oil-oil extraction with sealing gas, performing cyclone separation, and further separating and extracting oil particles in the wastewater; solid waste obtained by rotational flow is discharged;
the wastewater after rotational flow enters the inner sleeve tank, overflows into the gravity settling tank through the inner sleeve tank, and slowly floats up tiny oil particles in the wastewater in the residence process in the gravity settling tank, so that the third oil removal of the wastewater is realized.
In some embodiments, after the third degreasing of the wastewater, the method further comprises a step of performing ultrafiltration treatment on the wastewater, wherein the ultrafiltration adopts a cross-flow filtration mode.
In some embodiments, the oil-to-oil extraction time is 1-3 hours.
In some embodiments, the residence time of the wastewater in the gravity settling tank is 5-15 hours.
The beneficial effects achieved by one or more embodiments of the present invention described above are as follows:
(1) In the aspect of pretreatment, an oil-oil extraction separation technology, an air flotation separation technology, a cyclone separation technology and a gravity sedimentation separation technology are combined, oil ions and solid suspended matters in a full particle size range are separated, the comprehensive effect of multi-effect coupling is obtained, the separation efficiency and the operation reliability are greatly improved, and conditions are created for the subsequent membrane separation, which cannot be realized by the technologies such as a traditional tank-in-tank technology;
(2) In the aspect of core treatment, a modern membrane separation technology with high efficiency and low consumption is adopted, so that long-term fault-free operation can be realized, and the maintenance workload in the aspect of technology is greatly reduced;
(3) The process flow is greatly shortened, the traditional multi-stage filtration system is thoroughly replaced by adopting a membrane separation process, the operation process is simplified, and unmanned and intelligent operation is easier to realize.
(5) By running the process of the invention, the transformation and upgrading of the crude oil water treatment system can be conveniently realized.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention.
FIG. 1 is a schematic overall structure of an embodiment of the present invention;
FIG. 2 is a flow chart of a prior art membrane filtration process;
Fig. 3 is a flow chart at the time of backwashing.
Wherein, 1-a waste water feeding pipe; 2-a wastewater distributor;
a 3-oil extractor; 301. a light oil layer; 302. a water layer; 304. an oil level gauge; 305. an exhaust port; 306. an oil overflow port;
4-a feed pump; 5-a gas-liquid mixer; 6-a cyclone; 7-a cyclone underflow port; 8-a cyclone overflow box;
9-suspending an oil drain; 901. a guide rod; 902. an oil discharge pipeline;
10-a slag discharging pipeline; 11-an oil overflow pipe; 12-a water overflow pipe; 13-an inner sleeve pot; 14-a wire mesh filter; 15-a gravity settling tank; 16-air sealing the pipeline; 17-an air floatation air suction pipeline; 18-an air filter; 19-an air floatation fan; 20-an ultrafiltration membrane component water inlet pump; 21-an ultrafiltration membrane assembly water inlet pipeline; 22-an ultrafiltration membrane module; 23-a circulation pump; 24-an ultrafiltration membrane module circulation pipeline;
25-back flushing a water tank; 26-a backwash pump; 27-backflushing the water pipeline; 28-a purified water pipeline.
Detailed Description
It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the invention. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
The invention is further illustrated below with reference to examples.
The oilfield produced water treatment system comprises an oil-oil extractor 3, a gas-liquid mixer 5, a cyclone 6 and an ultrafiltration membrane component 22, wherein the oil-oil extractor 3 is of a vertical tubular structure, a wastewater distributor 2, an oil-water extraction cavity and a liquid outlet are sequentially arranged from top to bottom, the wastewater distributor 2 is connected with an oil-containing wastewater source, a light oil layer and a water layer are contained in the oil-water extraction cavity, and the light oil layer is positioned above the water layer; the waste water distributor 2 is a spraying device and is used for dispersing waste water into small liquid drops;
The liquid outlet is connected with a liquid phase inlet of the gas-liquid mixer 5, an aeration structure is arranged at the bottom of the gas-liquid mixer 5, and the aeration structure is connected with an air floatation fan; the liquid outlet is connected with the cyclone 6; the cyclone 6 is arranged in the inner sleeve tank 13, and the inner sleeve tank 13 is arranged in the gravity settling tank 15; the outlets at the bottoms of the cyclone 6 and the inner sleeve tank 13 are communicated with the outside through pipelines; the top of the gravity settling tank 15 is sealed, and an oil overflow pipeline 11 and a water overflow pipeline 12 are respectively connected to the top of the gravity settling tank at a set height, and the oil overflow pipeline 11 is positioned above the water overflow pipeline 12.
And an ultrafiltration membrane component water inlet pipeline 21 is connected with the water phase outlet of the gravity settling tank 15 and is used for carrying out ultrafiltration treatment on wastewater subjected to gravity settling.
The specific process is as follows:
(1) Oil-oil extraction process for pretreatment of the front stage
Oilfield produced water enters the wastewater distributor 2 of the oil-oil extractor 3 through the wastewater feed pipe 1 and the wastewater distributor 2. The upper part of the oil-oil extractor 3 is a light oil layer 301 for capturing oil particles in the wastewater; the lower part of which is a water layer 302 for cushioning impact and floating the upper oil layer. The wastewater is dispersed into fine droplets by the wastewater distributor 2 to reduce impact and increase contact area. In the process of passing through the light oil layer 301, the wastewater is contacted, mixed and collided with the light oil layer, and oil particles with larger diameters, such as floating oil particles, dispersed oil particles and emulsified oil particles, in the wastewater are quickly fused into the light oil layer after contacting the light oil layer; and colloidal particles with smaller diameters in the wastewater and dissolved oil are contacted with a light oil layer, a certain extraction effect occurs, so that the colloidal particles and dissolved oil migrate from the water phase to the oil phase, thus the oil-oil extractor 3 can intercept oil particles with the full particle size range in the wastewater, and the filter can only intercept oil particles with the diameter larger than a certain specific range.
As the oil particles in the wastewater continue to be intercepted, the light oil layer 301 in the oil-oil extractor 3 will gradually rise in level, and will be automatically discharged into the oil collection device when the oil level exceeds the oil overflow port 306. Colloids, suspended matter, dissolved salts, etc. in the wastewater will pass through the light oil layer 301 as the wastewater passes down into the water layer 302 for subsequent treatment. The oil-oil extractor 3 belongs to a cavity-type apparatus, in the interior of which no other internal components are provided, apart from the wastewater distributor 2 at the top, so that there is no problem of possible clogging.
The oil-oil extractor 3 adopts a vertical container form, the residence time of wastewater is controlled within 1-3 h, and usually the parameter needs to be adjusted by combining with field test data; the section flow speed of the oil-oil extractor is controlled within the range of 0.05-0.1 m/s, the overall height is controlled within the range of 5-10 m, and the wall thickness is controlled within the range of 10-20 mm.
The oil-oil extractor 3 is provided with a top seal gas port, a top vent 305, etc.; the side wall is provided with an oil overflow port 306, a liquid level meter interface, a drain port and the like, so that the installation of the oil liquid level meter 304 and a thermometer is facilitated; the bottom is provided with a sludge sedimentation bucket and a corresponding discharge port.
The oil-oil extractor 3 adopts a steel structure round normal pressure container, and the wall thickness is controlled within the range of 6-12 mm; the oil-oil extractor 3 should be provided with a temperature-reducing heat-tracing at the outer wall when it is placed in a cold area.
The thickness of an oil layer in the oil-oil extractor 3 is controlled within the range of 0.5-1.5 m; the distance between the wastewater distributor 2 and the light oil layer 301 is controlled within the range of 0.5-1.5 m; the waste water distributor 2 of the oil-oil extractor 3 adopts a distribution pipe form, the bottom of the pipeline is provided with a drip hole array, and the diameter of each drip hole is controlled within the range of 2-8 mm; the pipeline material of the waste water distributor 2 is made of PP material with better oil resistance.
The wastewater feed pipe 1 of the oil-oil extractor 3 is provided with an extracting agent, a flocculating agent, a corrosion inhibitor, a scale inhibitor, an deoxidizer, a demulsifier, an iron remover, a bactericide and other medicament adding devices and a pH adjusting medicament. The wastewater feed pipe 1 of the oil-oil extractor 3 is provided with a heater for regulating and controlling the optimal extraction temperature.
(2) Process for gas mixing and cyclone sedimentation in advanced pretreatment of front stage
After the oil particles contained in the wastewater pass through the oil-oil extractor 3, low-concentration solid suspended matters, emulsified oil and dissolved oil still exist. Because of the small diameter of these suspensions and oil particles, further forced separation means including air flotation, rotational flow and gravity natural sedimentation are required to achieve the inlet conditions for membrane separation. The traditional tank in the tank only comprises two technical means of rotational flow and gravity natural sedimentation, and the treated wastewater can not reach the inlet condition of membrane separation; the process of the invention adopts the oil-oil extraction technology firstly, and then adopts the synergistic treatment comprising three technologies of air floatation, rotational flow and gravity natural sedimentation on the basis, the separation effect is incomparable with the traditional tank-in-tank technology, and the inlet condition of membrane separation can be completely achieved.
The sealing gas (generally natural gas) at the upper part of the gravity settling tank 15 is sucked out by an air floatation blower 19, passes through a silk screen filter 14, an air floatation suction pipeline 17 and an air filter 18 at the upper part of the gravity settling tank 15, is pressurized by the air floatation blower 19, enters the gas-liquid mixer 5, is mixed with wastewater, combines oil particles in the wastewater with gas to generate an air floatation effect, and then is separated by a cyclone 6 by utilizing the density difference value of the oil-water-solid suspended matters. The wastewater from the gas-liquid mixer 5 enters the cyclone 6 in a tangential direction to generate high-speed rotational flow, so that most of air, oil particles and air-oil particle combination with relatively low density enter the cyclone overflow box 8 to form an enriched oil layer, and then pass through the suspension oil exhauster 9 to be discharged from the central oil discharge pipeline 902.
The top gas outlet of the gravity settling tank 15 is connected with the inlet of the air filter 18 through a gas pipeline; the outlet of the air filter 18 is connected with the inlet of the air floatation fan 19 through an air pipeline; the outlet of the air-float fan 19 is connected with the gas inlet of the gas-liquid mixer 5. The sealing gas is released from the top of the cyclone overflow box 8, passes through the screen filter 14 and the air filter 18 again, removes entrained liquid drops, enters the air floatation fan 19, is recycled, and prevents any outside oxygen-containing air from penetrating into the whole system, so that the oxygen content in the wastewater is controlled below a limit value.
Due to the high-speed swirling action of the cyclone 6, the bottom thereof will discharge the denser aqueous phase and solid slag. The solid slag will collect at the bottom of the inner jacket tank 13 and be discharged through the slag discharge pipe 10. The water phase at the bottom of cyclone 6 will flow upwards, over the upper edge of inner housing 13 and into gravity settling tank 15.
The gas-liquid mixer 5 adopts a vertical pipe structure, and a microporous aeration device is arranged at the bottom.
The flow speed of the gas-liquid mixer is controlled within the range of 0.2-0.5 m/s; the downstream pipeline of the gas-liquid mixer should have a certain length to ensure the mixing time of the gas-liquid two phases.
The microporous aeration device of the gas-liquid mixer adopts a disc-type appearance structure and is made of ceramic materials or organic materials with good oil resistance; the average pore is controlled within the range of 80-100 mu m; the aeration rate is controlled within the range of 0.05-0.25 m 3/m3 wastewater.
The cyclone adopts a conical shape, wastewater enters the cyclone from a tangential inlet at the upper part of the cone, and generates severe rotation in the cyclone, and the simultaneous separation of multiphase components such as gas-liquid mixture, oil, solid and the like is realized through the action of centrifugal force. Because gas-liquid mixing is performed in advance, part of oil particles carry micro bubbles, so that buoyancy is increased, and separation efficiency is improved.
Controlling the inlet pressure of the cyclone within the range of 0.05-0.2 MPa; the flow speed at the feed inlet is controlled within the range of 5-12 m/s; the cone angle is controlled within the range of 10-20 degrees; the cyclone material is made of corrosion-resistant and wear-resistant materials such as ceramics. When the wastewater treatment capacity is large, a plurality of cyclones can be used for parallel operation.
(3) Gravity sedimentation process for advanced pretreatment of the front stage
Because the size of the gravity settling tank 15 is relatively large, a long residence time is provided, so that tiny oil particles of residual dispersed oil and emulsified oil in the water phase can slowly float, a layer of floating oil layer is formed on the water surface inside the gravity settling tank 15, and when the floating oil reaches a certain thickness, the floating oil is discharged outwards through the oil overflow pipeline 11.
The gravity settling tank 15 is used as equipment for separating oil, water and solid slag in the system and is also used as a wastewater inflow buffer container.
The gravity settling tank 15 adopts a vertical steel structure tank body and is arranged as an arch tank top, has certain capacity of bearing internal pressure, is controlled within a range of 10-30 mm in design wall thickness, and is subjected to shock resistance calculation and verification.
The gravity settling tank 15 is provided with a breather valve for sealing gas at the top, and the sealing natural gas can be connected through the breather valve to maintain a certain positive pressure so as to stop the entry of external air.
The residence time of the gravity settling tank 15 is controlled within a range of 5-15 h.
The bottom plate of the gravity settling tank 15 is provided with a certain gradient, and the value of the gradient is controlled within the range of 0.003-0.01.
The upper area of the gravity settling tank is respectively provided with an oil overflow port and a water overflow port, the side wall is provided with a liquid level meter, and the bottom is provided with a cleaning port and the like.
For the wastewater with higher colloid content and suspended matter content, chemical flocculation dosing equipment can be additionally arranged, and a multi-stage gravity settling tank is arranged to ensure the separation effect.
(4) Ultrafiltration membrane separation process in post-stage finishing process
The wastewater from the gravity settling tank 15 still contains small amounts of ultra-fine suspended, emulsified and dissolved oils, for which case the separation technique using modern ultrafiltration membrane methods is the optimal process option. The membrane filtration adopts a high-flow cross-flow filtration mode, so that the high-efficiency interception of superfine solid particles and oil particles is realized.
The normal process flow diagram is shown in fig. 2.
The flow chart during back flushing is shown in fig. 3.
The final direction of the back flushing is the oil-oil extractor 3, i.e. it is returned to the beginning of the wastewater treatment and the pretreatment is carried out again, so that there is no wastewater discharge.
The membrane separation process mainly adopts a lateral filtration mode, and blocked large particulate matters are taken away by liquid flow flowing laterally and cannot be blocked on a filter screen, so that the stability and reliability of operation of the membrane separation process are far greater than those of various media filters adopting a dead-end filtration mode. The wastewater after the front-end multi-effect coupling pretreatment has greatly reduced oil content and solid suspended matter concentration, and can reach the inlet condition of membrane separation treatment.
The wastewater enters the ultrafiltration membrane component 22 for membrane filtration through the ultrafiltration membrane component water inlet pump 20, the ultrafiltration membrane component water inlet pipeline 21 and the ultrafiltration membrane component circulating pipeline 24. The filtered wastewater is sent through a clean water line 28 to a water injection station for reinjection or other use.
The ultrafiltration membrane separation process refers to an operation process of separating fine suspended matters, tiny oil particles, colloid and the like with the particle size of more than 10nm (0.01 mu m) in water by adopting an ultrafiltration membrane component device.
Materials selected for the ultrafiltration membrane device include, but are not limited to, a ceramic membrane, polyvinylidene fluoride (PVDF), polyethersulfone (PES), polypropylene (PP), polyethylene (PE), polysulfone (PS), and poly (acrylonitrile) (PAN).
The ultrafiltration membrane device is made of materials with high oil resistance, high oleophobicity, high flux and dirt resistance so as to ensure the stable operation of the ultrafiltration membrane device and prolong the time period of back flushing and chemical cleaning; the water yield of the single membrane is not lower than 1-1.5 m 3/h.
The diameter of the ultrafiltration membrane is controlled below 0.01 mu m, the pore diameter of the ultrafiltration membrane device at the level only allows water molecules and dissolved salts in water to pass through, and bacteria with the diameter of more than 0.2 mu m and colloid, rust, suspended matters, sediment, macromolecular organic matters and the like which are much larger than the volume of the bacteria are trapped, so that the purification treatment effect is ensured.
The oil content in the wastewater imported from the ultrafiltration membrane component is controlled below 2000ppm, and the concentration of solid suspended matters is controlled below 1000ppm, so as to ensure the long-term stable operation of the ultrafiltration membrane component.
The ultrafiltration membrane component water inlet pump adopts a stainless steel centrifugal pump, the lift is controlled within the range of 25-35 m, and a 10% flow allowance is reserved.
The ultra-filtration membrane component circulating pump adopts a stainless steel centrifugal pump, the lift is controlled within the range of 20-30 m, and the flow is controlled to be 5-10 times of the water inflow.
The ultrafiltration membrane component backwash water pump adopts a stainless steel centrifugal pump, the lift is controlled within the range of 25-35 m, and the flow is equivalent to the water inflow.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. An oilfield produced water treatment system, characterized in that: comprises an oil-oil extractor, a gas-liquid mixer and a cyclone, wherein,
The oil-oil extractor is of a vertical tubular structure, a wastewater distributor, an oil-water extraction cavity and a liquid outlet are sequentially arranged from top to bottom, the wastewater distributor is connected with an oil-containing wastewater source, the oil-water extraction cavity is used for containing a light oil layer and a water layer, and the light oil layer is positioned above the water layer;
The liquid outlet is connected with a liquid phase inlet of the gas-liquid mixer, an aeration structure is arranged at the bottom of the gas-liquid mixer, and the aeration structure is connected with the air floatation fan; the liquid outlet is connected with the cyclone;
the cyclone is arranged in the inner sleeve tank, and the inner sleeve tank is arranged in the gravity settling tank;
The outlets at the bottoms of the cyclone and the inner sleeve tank are communicated with the outside through pipelines;
the top of the gravity settling tank is sealed, the set height of the gravity settling tank is respectively connected with an oil overflow pipeline and a water overflow pipeline, and the oil overflow pipeline is positioned above the water overflow pipeline.
2. The oilfield produced water treatment system of claim 1, wherein: the bottom of the distribution pipeline of the wastewater distributor of the oil-oil extraction device is provided with a drop hole array for dispersing wastewater into small drops.
3. The oilfield produced water treatment system of claim 2, wherein: the diameter of each drip hole in the drip hole array is 2-8 mm.
4. The oilfield produced water treatment system of claim 1, wherein: the ratio of the thickness of the light oil layer in the oil-oil extractor to the height of the oil-oil extractor is 0.05-0.3: 1.
5. The oilfield produced water treatment system of claim 1, wherein: the top of the oil-oil extractor is provided with an exhaust port, the upper part of the oil-oil extractor is provided with an oil overflow port, and the exhaust port is communicated with the oil overflow port through a pipeline.
6. The oilfield produced water treatment system of claim 1, wherein: and the top of the gravity settling tank is sealed by air.
7. The oilfield produced water treatment system of claim 1, wherein: the device also comprises an ultrafiltration membrane component, and the ultrafiltration membrane component is connected with the water phase outlet of the gravity settling tank.
8. A method for treating oilfield produced water is characterized by comprising the following steps: the method comprises the following steps:
Dispersing the oilfield produced wastewater into small liquid drops, then extracting oil-oil, and extracting and recycling oil particles in the oilfield produced water;
Mixing the wastewater subjected to oil-oil extraction with sealing gas, performing cyclone separation, and further separating and extracting oil particles in the wastewater; solid waste obtained by rotational flow is discharged;
the wastewater after rotational flow enters the inner sleeve tank, overflows into the gravity settling tank through the inner sleeve tank, and slowly floats up tiny oil particles in the wastewater in the residence process in the gravity settling tank, so that the third oil removal of the wastewater is realized.
9. The oilfield produced water treatment method of claim 8, wherein: after the wastewater is deoiled for the third time, the method also comprises the step of carrying out ultrafiltration treatment on the wastewater, wherein the ultrafiltration adopts a cross-flow filtration mode.
10. The oilfield produced water treatment method of claim 8, wherein: the oil-oil extraction time is 1-3h; the residence time of the wastewater in the gravity settling tank is 5-15h.
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