A method and system for crude oil dehydration and desalting and application thereof

Abstract

The application discloses a crude oil dehydration and desalination method, a system and application thereof, and belongs to the technical field of oil dehydration and desalination. The method comprises one-stage or multi-stage dehydration and desalination treatment, and each stage of dehydration and desalination treatment independently comprises the following steps: (1) introducing supercritical CO2 into a dehydration and desalination tank; and (2) mixing crude oil with optional water for extraction to form a material to be treated, and the material to be treated enters the dehydration and desalination tank from the top; meanwhile, optional backflushing water is introduced into the lower part or the bottom of the dehydration and desalination tank. The method has the characteristics of high crude oil dehydration and desalination efficiency, low cost, large processing capacity and low carbon environmental protection.

Description

Technical Field

[0001] This invention belongs to the field of crude oil pretreatment, and particularly relates to crude oil dehydration and desalting. Specifically, it relates to a method, system and application of crude oil dehydration and desalting. Background Technology

[0002] Crude oil extracted from the ground, especially high-viscosity heavy oil, often carries a large amount of water and salt. Even after oil-water phase separation, much of this water and salt remains in the oil phase as a water-in-oil emulsion. This water and salt can affect the smooth operation of subsequent crude oil distillation, corrode refining equipment and pipelines, and even lead to catalyst deactivation, poisoning, and reduced lifespan. Therefore, before distilling and refining crude oil, it is necessary to break up the water-in-oil emulsion and perform dehydration and desalting treatment.

[0003] Traditional crude oil dehydration and desalting methods involve mixing water, demulsifiers, and chelating agents with the crude oil. Water extracts the original water and salts from the crude oil, demulsifiers break up water-in-oil emulsions, and chelating agents convert high-valence metal ions (mainly calcium ions) in the oil phase into chelates insoluble in crude oil. Then, under a strong electric field, small water droplets coalesce into larger droplets, which are then separated from the oil phase. Some salts (mainly NaCl) dissolve in the water and are removed from the crude oil along with the aqueous phase. The remaining salts (mainly high-valence ions) form solid precipitates that settle at the bottom of the electrostatic desalting tank and are discharged with the wastewater through backwashing. This traditional method not only consumes a large amount of electricity but also requires the addition of large quantities of demulsifiers and chelating agents, leading to increased costs for chemicals and subsequent wastewater treatment. Summary of the Invention

[0004] To overcome the problems existing in the prior art, this invention provides a method for dehydrating and desalting crude oil and its application. This method features high efficiency, low cost, large processing capacity, and low carbon footprint for crude oil dehydration and desalting.

[0005] One of the objectives of this invention is to provide a method for dehydrating and desalting crude oil, the method comprising one or more stages of dehydration and desalting treatment, each stage of dehydration and desalting treatment independently comprising: (1) introducing supercritical CO2 into a dehydration and desalting tank; (2) mixing crude oil with optional extraction water to form a material to be treated, the material to be treated entering the dehydration and desalting tank from the top; and optionally introducing backflushing water into the lower part or bottom of the dehydration and desalting tank.

[0006] The extraction water in step (2) is used to extract the aqueous phase and salts from the crude oil, and the backwash water in step (3) is used to rinse the dirt at the bottom.

[0007] Through extensive experimental research, the inventors discovered that supercritical CO2 can disrupt the stability of the dispersed aqueous phase in crude oil, causing the aqueous phase to coalesce and separate, thereby achieving crude oil dehydration. Furthermore, CO2 can partially dissolve in crude oil, thus reducing its viscosity, accelerating the coalescence of water droplets and the separation of the aqueous phase, while simultaneously removing water-soluble salts (such as NaCl). The inventors also found that calcium ions in crude oil can react with CO2 to form CaCO3 precipitate and water-soluble Ca(HCO3)2, which then detach from the crude oil.

[0008] In a preferred embodiment, when the method includes multi-stage dehydration and desalination treatment, the crude oil obtained after the previous stage of dehydration and desalination treatment is used as the crude oil in the next stage of dehydration and desalination treatment step (2) for the next stage of dehydration and desalination treatment, and the crude oil product is obtained after the last stage of dehydration and desalination treatment.

[0009] In a further preferred embodiment, the method includes 1 to 10 stages of dehydration and desalination treatment, preferably 2 to 8 stages, more preferably 2 to 5 stages, such as 1 stage, 2 stages, 3 stages, 4 stages, 5 stages, 6 stages, 7 stages, 8 stages, 9 stages or 10 stages.

[0010] In a preferred embodiment, in step (1), based on 100% of the volume of the dehydration and desalination tank, the supercritical CO2 volume ratio is 80-20%, preferably 70-30%, after the start-up or stable operation.

[0011] For example, in step (1), based on the volume of the dehydration and desalination tank being 100%, the percentage of the supercritical CO2 volume after startup or stable operation is 80%, 70%, 60%, 50%, 40%, 30%, or 20%.

[0012] In a preferred embodiment, in step (2), when the extraction water is present, the extraction water accounts for 1%-20% of the mass flow rate of the crude oil, preferably 3%-13%.

[0013] For example, in step (2), when the extraction water is present, the proportion of the extraction water to the mass flow rate of the crude oil is 1%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, or 20%.

[0014] In a preferred embodiment, in step (3), when the backflushing water is introduced, the proportion of the backflushing water to the mass flow rate of the crude oil is 1%-20%, preferably 1%-8%.

[0015] For example, in step (3), when the backflushing water is introduced, the proportion of the backflushing water to the mass flow rate of the crude oil is 1%, 2%, 5%, 8%, 12%, 15%, 18%, or 20%.

[0016] In this invention, the flow rate of the crude oil is controlled to be 50-1000 t / h, preferably 100-800 t / h, more preferably 200-500 t / h; and / or, the flow rate of the extraction water is controlled to be 2.5-50 t / h, preferably 5-40 t / h, more preferably 10-25 t / h; and / or, the flow rate of the backflushing water is controlled to be 0.1-50 t / h, preferably 0.5-40 t / h, more preferably 1-25 t / h.

[0017] For example, the flow rate of the crude oil is controlled to be 50, 100, 200, 400, 600, 800 or 1000 t / h; and / or, the flow rate of the extraction water is controlled to be 2.5, 5, 8, 10, 15, 20, 25, 30, 35, 40, 45 or 50 t / h; and / or, the flow rate of the backflushing water is controlled to be 0.1, 0.5, 1, 2, 5, 8, 10, 15, 20, 25, 30, 35, 40, 45 or 50 t / h.

[0018] In a preferred embodiment, during the dehydration and desalination process, supercritical CO2 is continuously added to the dehydration and desalination tank, and a portion of hydrocarbon-rich supercritical CO2 is continuously discharged.

[0019] Through extensive experimentation, the inventors discovered that during the dehydration and desalination process, CO2 dissolves into the oil phase, and some high-valence ions, such as calcium ions, react with CO2 to form precipitates or soluble carbonates, thus consuming CO2. Therefore, it is preferable to replenish the dehydration and desalination tank with CO2. Simultaneously, the inventors also found that hydrocarbons in the oil phase (e.g., C1-C30, C1-C25, C1-C15, or C1-C5 hydrocarbons) can enter the CO2 phase, reducing the efficiency of CO2 dehydration and desalination. Therefore, it is necessary to discharge hydrocarbon-rich CO2. The hydrocarbon-rich CO2 enters a low-temperature cooling tower, where the hydrocarbon oil phase condenses and enriches from the CO2 into high-value-added condensate oil. The regenerated CO2 is then reinjected into the dehydration and desalination tank.

[0020] In a preferred embodiment, the crude oil, after being mixed with optional extraction water, enters the dehydration and desalination tank from the top through one or more nozzles.

[0021] Preferably, there are 1-100 nozzles, more preferably 1-50, and even more preferably 1-20, for example, 1, 2, 3, 4, 5, 10, 20, 40, 60, 80, or 100 nozzles. The nozzle types include, but are not limited to, conical, fan-shaped, circular, square, spiral, fine atomizing, and rotating types, with circular, conical, square, and atomizing types being preferred.

[0022] In a further preferred embodiment, the material to be treated is first subjected to pressure heating treatment, and then enters the dehydration and desalination tank through one or more nozzles.

[0023] In a further preferred embodiment, the material to be treated is heated to 20-300°C, preferably 30-200°C, and more preferably 35-150°C; the heater type includes, but is not limited to, electric heaters, tubular heat exchangers, plate heat exchangers, and heat pipe heaters, with electric heaters and tubular heat exchangers being preferred. The material to be treated is pressurized by a compression pump, and its flow rate ranges from 50-1000 t / h, preferably 100-800 t / h, and more preferably 200-500 t / h.

[0024] In a preferred embodiment, during the processing, the dehydration and desalination tank will stratify into an upper layer of supercritical CO2 phase, a middle layer of oil phase, and a lower layer of aqueous phase and solid precipitate; preferably, the dehydrated crude oil is extracted from the side of the dehydration and desalination tank (preferably the side of the oil phase portion).

[0025] In a preferred embodiment, the method further includes separating wastewater I from the bottom of the dehydration and desalination tank.

[0026] The wastewater I contains water, salt, and solid precipitates.

[0027] In a further preferred embodiment, the separated wastewater I is subjected to solid-liquid separation treatment to obtain a recovered aqueous phase and solid-containing wastewater II.

[0028] In a further preferred embodiment, the solid-liquid separation includes, but is not limited to, at least one of gravity sedimentation, centrifugal separation, electromagnetic sedimentation, filtration separation, and flotation separation, with gravity sedimentation and / or electromagnetic sedimentation being preferred for the solid-liquid separation.

[0029] In a preferred embodiment, the recovered aqueous phase is recycled back to step (2) after being mixed with optional fresh water for use as extraction water and / or as backflushing water.

[0030] Preferably, the ratio of recycled water to fresh water is 10:90 to 90:10, more preferably 20:80 to 80:20, and even more preferably 30:70 to 70:3, for example, 10:90, 20:90, 30:90, 40:90, 50:90, 60:90, 70:90, 80:90 or 10:90.

[0031] In a further preferred embodiment, the recovered aqueous phase is mixed with optional fresh water and then split into two streams: one stream is recycled back to step (2) as extraction water, and the other stream is recycled back to step (2) as backwash water.

[0032] In a preferred embodiment, the method includes: pressurized and heated crude oil and optional extraction water are introduced into a dehydration and desalination tank containing supercritical CO2 through one or more nozzles; the initially dehydrated crude oil enters the next stage dehydration and desalination tank to improve the dehydration and desalination rate, and finally obtains dehydrated crude oil; wastewater I flows out of the dehydration and desalination tank and enters a solid-liquid separation tank, and the separated aqueous phase is diluted with fresh water and recycled to the dehydration and desalination tank for backwashing and / or used as extraction water to co-inject with crude oil.

[0033] In a further preferred embodiment, the dehydration and desalination tank is provided with a feed inlet for the material to be treated (for introducing crude oil and optionally extracting water to mix and form the material to be treated), a crude oil discharge outlet, a supercritical CO2 inlet (for introducing supplemental supercritical CO2), a supercritical CO2 outlet (for discharging hydrocarbon-rich CO2), an optional backflushing water inlet (for introducing backflushing water), and a wastewater I outlet (for discharging the aqueous phase and solid precipitate). One or more nozzles are provided inside the dehydration and desalination tank and above the liquid level inside the tank, and the nozzles are connected to the feed inlet for the material to be treated.

[0034] In a further preferred embodiment, the dehydration and desalination tank has a heating and heat preservation function. The heating and heat preservation device is used to maintain a constant tank temperature, which is stable at 20-300℃, preferably 30-200℃, and more preferably 35-150℃. The number of dehydration and desalination tanks is 1-10, preferably 2-8, and more preferably 2-5.

[0035] In a preferred embodiment, the method includes:

[0036] (1) Crude oil and extraction water are compressed by a pump and a heater to reach the specified pressure and temperature, and then injected into a dehydration and desalination tank containing supercritical CO2 through one or more nozzles.

[0037] (2) After crude oil comes into full contact with supercritical CO2, oil and water phases are achieved. At the same time, water-soluble salts such as NaCl are fully extracted into the aqueous phase. High-valence ions such as calcium and magnesium react with CO2 to form carbonate precipitates or water-soluble bicarbonates, which are removed from the crude oil.

[0038] (3) After the unit starts up smoothly, the bottom of the dehydration and desalination tank contains the aqueous phase and solid precipitate, the middle contains the dehydrated crude oil, and the top contains the supercritical CO2 phase. The aqueous phase and solid precipitate at the bottom are discharged through the bottom wastewater outlet I and enter the solid-liquid separation tank. The recovered aqueous phase separated from the solid-liquid separation is diluted with optional fresh water and used as backflushing water and / or extraction water for the dehydration and desalination tank, and then reinjected into the dehydration and desalination tank. The dehydrated crude oil in the middle of the last stage dehydration and desalination tank is fed into the next stage dehydration and desalination tank or the subsequent crude oil refining unit through the discharge port. The supercritical CO2 phase at the top is replenished by the supercritical CO2 inlet to maintain a constant CO2 level. Some of the hydrocarbon-rich supercritical CO2 is discharged from the supercritical CO2 outlet and enters the CO2 purification and natural gas enrichment unit.

[0039] The second objective of this invention is to provide a system for dehydrating and desalting crude oil, preferably for carrying out the method described in the first objective of this invention. The system includes one or more dehydration and desalting tanks connected in series. Each dehydration and desalting tank is independently provided with a feed inlet for the material to be treated, a crude oil discharge outlet, a supercritical CO2 inlet, a supercritical CO2 outlet, a wastewater outlet, and an optional backflushing water inlet.

[0040] In a preferred embodiment, one or more nozzles are provided above the interior of the dehydration and desalination tank, and the nozzles are connected to the feed inlet of the dehydration and desalination tank via pipelines.

[0041] In a preferred embodiment, when the system includes multiple dehydration and desalination tanks connected in series, the crude oil outlet of the previous dehydration and desalination tank and the material inlet of the next dehydration and desalination tank are connected by pipelines along the material flow direction.

[0042] In a preferred embodiment, the supercritical CO2 inlet is located above the lower aqueous phase and solid precipitate of the dehydration and desalination tank (preferably above the middle oil phase), and the supercritical CO2 outlet is located at the upper part or top of the dehydration and desalination tank.

[0043] In a preferred embodiment, the system further includes a solid-liquid separation tank, which is provided with a wastewater I inlet, a recycled aqueous phase outlet, and a wastewater II outlet.

[0044] In a further preferred embodiment, the wastewater inlet I of the solid-liquid separation tank is connected to the wastewater outlet I of each dehydration and desalination tank via a pipeline; and / or, the wastewater outlet II of the solid-liquid separation tank is connected to an external discharge pipeline; and / or, the recovered water phase outlet of the solid-liquid separation tank is connected to pipeline I. A fresh water inlet pipeline is provided on pipeline I along the material flow direction. Then, pipeline I splits into two lines, namely pipeline II and pipeline III. Pipeline II is connected to the optional backflushing water inlet of each dehydration and desalination tank, and pipeline III is connected to the material inlet to be treated of each dehydration and desalination tank.

[0045] In a preferred embodiment, a heating device is provided on the pipeline connected to the feed inlet of the material to be processed.

[0046] In a preferred embodiment, the system further includes other commonly used components, such as a compression pump.

[0047] A third objective of this invention is to provide the application of the method described in one objective of this invention or the system described in another objective of this invention in crude oil dehydration and desalting.

[0048] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In the following, various technical solutions can, in principle, be combined with each other to obtain new technical solutions, which should also be considered as specifically disclosed herein.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] (1) The method described in this invention utilizes supercritical CO2 to separate the oil and water phases, while simultaneously removing water-soluble salts (such as NaCl). In addition, CO2 can react with high-valence ions such as calcium and magnesium to form carbonate precipitates and water-soluble bicarbonates, thereby removing high-valence ions from crude oil and achieving comprehensive deep desalting of crude oil.

[0051] (2) Compared with the prior art, the present invention does not require the addition of additional demulsifiers and chelating agents, saving on reagent and wastewater treatment costs; the present invention does not require a strong electric field, saving on power consumption; the present invention fully utilizes the characteristics of CO2, which can further achieve low carbon emission reduction. Moreover, the present invention has a simple process and features high dehydration and desalination efficiency and large processing capacity;

[0052] (3) This method has the characteristics of low cost, low carbon and environmental protection, high crude oil dehydration and desalting efficiency and large processing capacity. This invention is particularly suitable for the post-processing of CO2 flooding produced fluid and the pre-processing of CO2 oil separation technology, which can significantly reduce the cost of crude oil processing and improve the crude oil dehydration and desalting efficiency.

[0053] (4) The method described in this invention can control the water content in the crude oil after desalination to be below 0.5wt%, especially below 0.2%, and the salt content to be below 5ppm, especially below 3ppm. Attached Figure Description

[0054] Figure 1This illustration shows one embodiment of the system described in the present invention (the number of nozzles in the figure is only schematic and can be selected according to specific circumstances; the number of nozzles in the embodiment is as described in the text).

[0055] Figure 2 Another embodiment of the system described in this invention is shown (the number of nozzles in the figure is only schematic and can be selected according to specific circumstances; the number of nozzles in the embodiment is as described in the text).

[0056] a-Crude oil, 1-Dehydration and desalination tank, 11-Nozzle, 12-Supercritical CO2 inlet, 13-Supercritical CO2 outlet, 14-Package inlet for materials to be treated, 15-Backflushing water inlet, 16-Crude oil outlet after dehydration, 17-Wastewater I outlet; 2-Heater, 3-Compression pump, 4-Solid-liquid separation tank, 41-Wastewater I inlet, 42-Recovered aqueous phase outlet, 43-Wastewater II outlet, 5-Fresh water tank. Detailed Implementation

[0057] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0058] It should also be noted that the various specific technical features described in the following embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the various possible combinations will not be described separately in this invention.

[0059] Furthermore, various embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention. The resulting technical solutions are part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0060] Unless otherwise specified, the raw materials used in the examples and comparative examples are all disclosed in the prior art, such as those that can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0061]

Example 1

[0062] The properties of the crude oil to be treated, after dehydration and desalting of ordinary crude oil A, are shown in the table below:

[0063] Table 1

[0064]

[0065] use Figure 1The system shown is in operation. The number of nozzles in the diagram is for illustrative purposes only; the actual number of nozzles in this embodiment is based on the written description. The produced fluid from the oilfield enters the oil-water separator, and the properties of crude oil A after phase separation are shown in Table 1.

[0066] The dehydration and desalting tank is filled with supercritical CO2 at 14 MPa and 70°C. Crude oil A is pressurized to 15 MPa by a compressor pump and mixed with extraction water, also pressurized, to form the material to be treated. This material is then heated to 70°C by a heater. The pressurized and heated crude oil A is injected into the dehydration and desalting tank through six injection nozzles at a flow rate of 300 t / h. Based on the dehydration and desalting tank being 100% full, after stable start-up, the supercritical CO2 occupies the upper layer (50% by volume), the aqueous phase and fixed sediment settle to the bottom of the tank (lower layer), and the crude oil after the first dehydration occupies the middle layer. The crude oil after the first dehydration is pressurized to 15 MPa by a compressor pump, heated to 70°C by a heater, and then injected into the secondary dehydration and desalting tank through four injection nozzles at a flow rate of 245 t / h (based on crude oil mass). The crude oil after the second dehydration flows out of the secondary dehydration and desalting tank at a flow rate of 231 t / h (based on crude oil mass) and enters the subsequent crude oil refining unit. The aqueous phase and solids in the dehydration and desalination tank flow into the solid-liquid separation tank through the wastewater outlet I at the bottom of the tank. After gravity sedimentation separation, the wastewater II containing solid sediment at the bottom is discharged and enters the wastewater II treatment unit. The recovered aqueous phase is mixed and diluted with clean water (fresh water) and then reinjected into the bottom of the primary and secondary dehydration and desalination tanks at a rate of 10 t / h for backwashing. At the same time, it is injected into the primary and secondary dehydration and desalination tanks at rates of 15 t / h and 12 t / h, respectively, along with the crude oil before dehydration, as extraction water to extract the aqueous phase and salts from the crude oil.

[0067] During the dehydration and desalination process, supercritical CO2 is replenished from the supercritical CO2 inlet and continuously injected into the dehydration and desalination tank at a constant pressure of 14 MPa. Meanwhile, hydrocarbon-rich CO2 is discharged from the supercritical CO2 outlet at a flow rate of 1 t / h. The hydrocarbon-rich CO2 enters a cryogenic cooling tower, where hydrocarbon oil phases condense and enrich into high-value-added condensate oil. The regenerated CO2 is then reinjected into the dehydration and desalination tank.

[0068] The water content of the crude oil after desalination was measured to be 0.15 wt% using Karl Fischer potentiometric titration, and the salt content was measured to be 2.7 ppm using silver ion titration.

[0069]

Example 2

[0070] The properties of crude oil B before dehydration and desalting of high-viscosity crude oil are shown in the table below:

[0071] Table 2

[0072]

[0073] Process flow as follows Figure 2As shown in the figure, the number of nozzles is for illustrative purposes only; the number of nozzles in this embodiment is based on the textual description. The properties of crude oil B before stripping are shown in Table 2.

[0074] All dehydration and desalination tanks are filled with supercritical CO2 at 14 MPa and 40°C. Crude oil B is pressurized to 15 MPa by a compressor pump and heated to 40°C by a heater. The pressurized and heated crude oil B is injected into the dehydration and desalination tanks at a flow rate of 300 t / h through 10 injection nozzles. Based on the dehydration and desalination tanks being 100% full, after stable start-up, the supercritical CO2 occupies the upper layer, accounting for 40% of the volume. The aqueous phase and solid sediment settle to the bottom of the tank, occupying the lower layer. The crude oil after the first stage of dehydration occupies the middle layer. The crude oil after the first stage of dehydration is pressurized to 15 MPa by a compressor pump and heated to 70°C by a heater, then injected into the secondary dehydration and desalination tank at a flow rate of 210 t / h (based on crude oil mass) through 6 injection nozzles. The crude oil after the second stage of dehydration flows out at a flow rate of 175 t / h (based on crude oil mass), is pressurized to 15 MPa by a compressor pump, heated to 70°C by a heater, and then injected into the tertiary dehydration and desalination tank through 4 injection nozzles. After three stages of dehydration, the crude oil flows out at a rate of 161 t / h and enters the subsequent crude oil refining unit. The aqueous phase and solids in the dehydration and desalting tank flow into the solid-liquid separation tank through the wastewater outlet I at the bottom of the tank. After gravity sedimentation separation, the wastewater II containing solid sediment at the bottom is collected. The recovered aqueous phase is mixed and diluted with clean water (fresh water) and then reinjected into the bottom of the dehydration and desalting tank at a rate of 10 t / h for backwashing. It is then injected into the first-stage, second-stage, and third-stage dehydration and desalting tanks at rates of 15 t / h, 8 t / h, and 8 t / h, respectively, along with the crude oil before dehydration, to extract the aqueous phase and salts from the crude oil.

[0075] During the dehydration and desalination process, supercritical CO2 is replenished from the supercritical CO2 inlet and continuously injected into the dehydration and desalination tank at a constant pressure of 14 MPa. Simultaneously, hydrocarbon-rich CO2 is discharged from the supercritical CO2 outlet at a flow rate of 1 t / h. The hydrocarbon-rich CO2 enters a cryogenic cooling tower, where hydrocarbon oil phases condense and enrich into high-value-added condensate oil. The regenerated CO2 is then reinjected into the dehydration and desalination tank.

[0076] The water content of the crude oil after desalination was measured to be 0.20 wt% using Karl Fischer potentiometric titration, and the salt content was measured to be 2.1 ppm using silver ion titration.

[0077]

Example 3

[0078] Similar to Example 1, except that 30t / h and 24t / h of the crude oil before dehydration are injected together with the crude oil into the primary and secondary dehydration and desalting tanks as extraction water to extract the aqueous phase and salts from the crude oil. The crude oil after dehydration has a water content of 0.23wt% and a salt content of 2.2ppm.

[0079]

Example 4

[0080] Similar to Example 2, except that the crude oil was injected together with the pre-dehydration crude oil at rates of 30 t / h, 24 t / h, and 16 t / h into the primary, secondary, and tertiary dehydration and desalting tanks to extract the water phase and salts from the crude oil. The crude oil produced by this method had a water content of 0.25 wt% and a salt content of 2.0 ppm.

[0081]

Example 5

[0082] The process of Example 1 was repeated, except that extraction water was not used. The crude oil after this method had a water content of 4.5 wt% and a salt content of 600 ppm.

[0083] Comparative Example 1

[0084] Nitrogen gas was used instead of supercritical CO2, and the rest was the same as in Example 1.

[0085] Nitrogen gas has a virtually zero dehydration rate. Injected water, under vigorous agitation, may actually create new water-in-oil emulsions, increasing the water content of the crude oil. Therefore, using nitrogen instead of supercritical CO2 results in virtually zero dehydration and desalination rates.

[0086] Comparative Example 2

[0087] The process of Example 1 is repeated, except that multiple nozzles are not set at the feed inlet of the material to be processed, while other conditions remain the same.

[0088] In this embodiment, multiple nozzles are used to ensure thorough mixing and contact between crude oil and CO2, reaching reaction equilibrium within 1-10 minutes. Without nozzles, crude oil and CO2 can only mix through diffusion, which, due to the limited residence time (10-30 minutes) in the dehydration and desalination tank, results in insufficient mixing and a dehydration rate below 40%. Simultaneously, a significant amount of salt remains in the water-in-oil emulsion.

[0089] Comparative Example 3

[0090] The process of Example 1 is repeated, except that no supercritical CO2 is added or hydrocarbon-rich CO2 is discharged during the dehydration and desalination process. The water and salt content in the desalted crude oil output by this method gradually increases. After reaching equilibrium, the water and salt content in the output crude oil is the same as that in the input crude oil, that is, the water content is 19 wt% and the salt content is 2400 ppm.

[0091] Comparative Example 4

[0092] The process of Example 1 is repeated, except that backwashing is not performed at the bottom of the primary and secondary dewatering and desalination tanks. Solid sediments accumulate at the bottom of the dewatering and desalination tanks, eventually clogging the wastewater outlet.

[0093] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for dehydrating and desalting crude oil, the method comprising one or more stages of dehydration and desalting treatment, each stage of dehydration and desalting treatment independently comprising: (1) Supercritical CO2 is introduced into the dehydration and desalination tank; (2) Crude oil and extraction water are mixed to form a material to be treated, and the material to be treated enters the dehydration and desalination tank from the top; at the same time, backflushing water is introduced into the lower part or bottom of the dehydration and desalination tank; during the dehydration and desalination process, supercritical CO2 is continuously added to the dehydration and desalination tank, and some hydrocarbon-rich supercritical CO2 is continuously discharged.

2. The method according to claim 1, characterized in that, When the method includes multi-stage dehydration and desalination treatment, the crude oil obtained after the previous stage of dehydration and desalination treatment is used as the crude oil in the next stage of dehydration and desalination treatment step (2) for the next stage of dehydration and desalination treatment, and the crude oil product is obtained after the last stage of dehydration and desalination treatment.

3. The method according to claim 2, characterized in that, The method includes 1 to 10 stages of dehydration and desalination treatment.

4. The method according to claim 2, characterized in that, The method includes 2 to 8 stages of dehydration and desalination treatment.

5. The method according to claim 1, characterized in that, In step (1), based on the dehydration and desalination tank volume being 100%, the supercritical CO2 volume percentage is 80-20%; and / or, In step (2), when the extraction water is present, the extraction water accounts for 1%-20% of the mass flow rate of the crude oil; and / or, In step (3), when the backflushing water is introduced, the proportion of the backflushing water to the mass flow rate of the crude oil is 1%-20%.

6. The method according to claim 1, characterized in that, In step (1), based on the dehydration and desalination tank volume being 100%, the supercritical CO2 volume percentage is 70-30%; and / or, In step (2), when the extraction water is present, the extraction water accounts for 3%-13% of the mass flow rate of the crude oil; and / or, In step (3), when the backflushing water is introduced, the proportion of the backflushing water to the mass flow rate of the crude oil is 1%-8%.

7. The method according to claim 1, characterized in that, The crude oil and extraction water mixture is then introduced into the dehydration and desalination tank through one or more nozzles from the top of the tank.

8. The method according to claim 7, characterized in that, The material to be processed is first subjected to pressure heating treatment, and then enters the dehydration and desalination tank through one or more nozzles.

9. The method according to claim 8, characterized in that, The material to be processed is heated to 20-300℃.

10. The method according to claim 8, characterized in that, The material to be processed is heated to 30-200℃.

11. The method according to claim 8, characterized in that, The material to be processed is heated to 35-150℃.

12. The method according to claim 1, characterized in that, During the processing, the dehydration and desalination tank will separate into three layers: the upper layer is the supercritical CO2 phase, the middle layer is the oil phase, and the lower layer is the aqueous phase and solid precipitate.

13. The method according to claim 1, characterized in that, The dehydrated crude oil is extracted from the side of the dehydration and desalination tank.

14. The method according to any one of claims 1 to 13, characterized in that, The method further includes separating wastewater I from the bottom of the dehydration and desalination tank.

15. The method according to claim 14, characterized in that, The separated wastewater I was subjected to solid-liquid separation treatment to obtain the recovered aqueous phase and solid-containing wastewater II.

16. The method according to claim 15, characterized in that, The recovered aqueous phase is recycled back to step (2) after being mixed with fresh water for use as extraction water and / or as backflushing water.

17. The method according to claim 16, characterized in that, The recovered aqueous phase is mixed with fresh water and then split into two streams: one stream is recycled back to step (2) for use as extraction water, and the other stream is recycled back to step (2) for use as backwash water.

18. A system for dehydrating and desalting crude oil, used for the method described in any one of claims 1 to 17, the system comprising one or more dehydration and desalting tanks connected in series, each dehydration and desalting tank being independently provided with a feed inlet for the material to be treated, a crude oil discharge outlet, a supercritical CO2 inlet, a supercritical CO2 outlet, a wastewater I outlet, and a backflushing water inlet; the system further comprising a solid-liquid separation tank, which is provided with a wastewater I feed inlet, a recovered aqueous phase outlet, and a wastewater II outlet, the wastewater I feed inlet of the solid-liquid separation tank being connected to the wastewater I outlet of each dehydration and desalting tank via a pipeline; the wastewater II outlet of the solid-liquid separation tank being connected to an external discharge pipeline; the recovered aqueous phase outlet of the solid-liquid separation tank being connected to pipeline I, and a fresh water feed pipeline being provided on pipeline I along the material flow direction, after which pipeline I splits into two branches, namely pipeline II and pipeline III, wherein... Pipeline II is connected to the backflushing water inlet of each dehydration and desalination tank, and pipeline III is connected to the material inlet of each dehydration and desalination tank.

19. The system according to claim 18, characterized in that, One or more nozzles are provided above the interior of the dehydration and desalination tank, and the nozzles are connected to the feed inlet of the dehydration and desalination tank via pipelines; and / or, When the system includes multiple dehydration and desalination tanks connected in series, the crude oil outlet of the previous dehydration and desalination tank and the feed inlet of the material to be treated of the next dehydration and desalination tank are connected by pipelines along the material flow direction.

Images