METHOD FOR MIXING A FIRST FLUID AND A SECOND FLUID

Technical field The present invention relates to injection-mixing devices and in particular such devices for use in systems for the treatment of oil, water and/or gas.

Background Injection-mixing systems are widely used in the oil and gas industry, covering a large range of applications, from well-head chemical injection to flow treatment at upstream processing facilities, transportation flowlines, and desalting systems in refineries, to name but a few. The efficiency of the injection-mixing systems deployed throughout the oil and gas production chain has great impact on the overall economic performance. Improving the efficiency and cost-effectiveness of injection-mixing technologies would add great value to the oil and gas industry.

The present invention is motivated by the need to improve the efficiency and cost- effectiveness of injection-mixing system used in the crude oil desalting process in refineries.

In most present crude oil desalting systems, fresh water is injected and mixed with the crude oil upstream of a desalter. The overall performance of the desalting system, including fresh-water demand, is greatly dependent on the efficiency of the fresh water injection-mixing system. Common crude oil desalting systems are typically equipped with an injection quill followed by a conventional mixing ball valve. Such fresh water injection-mixing systems have a high fresh-water demand and are not very efficient. A more complex fresh water injection-mixing system is described in patent application WO 03/072226 A2 marketed by ProSep Inc. Their injection-mixing technology is claimed to be more efficient than the more conventional systems described above. The goal of the present invention is to provide an injection-mixing device which avoids some of the disadvantages of the prior art.

Summary of the invention

The present invention is defined by the attached set of claims and in the following: In a first aspect, the present invention provides an injection-mixing device comprising a main pipe for a first fluid, an injection device and a swirl-generating element, wherein

the main pipe comprises an inlet for the first fluid and an outlet for a treated fluid;

the injection device comprises an inlet and at least one outlet for a second fluid, and the at least one outlet is arranged within the main pipe; and the swirl-generating element is arranged such that a centrifugal force is imparted or applied to the first fluid and the second fluid.

In one embodiment of the injection-mixing device, the first fluid is a fluid to be treated and the second fluid is a treatment fluid.

In an embodiment, the injection-mixing device comprises a treatment fluid line connected to the inlet of the injection device.

In an embodiment of the injection-mixing device, the injection device comprises at least one nozzle or a perforated or porous element. In yet an embodiment of the injection-mixing device, the at least one injection nozzle is arranged to provide a full/solid cone or a hollow cone spray pattern.

In yet an embodiment of the injection-mixing device, the perforated or porous element is a hollow conical, hemispherical, hemiellipsoid or cylindrical element.

In yet an embodiment of the injection-mixing device, the swirl-generating element is arranged upstream the outlet of the injection device.

In yet an embodiment of the injection-mixing device, the swirl-generating element is arranged between the inlet of the main pipe and the outlet of the injection device.

In yet an embodiment of the injection-mixing device, the swirl-generating element is arranged between the outlet of the main pipe and the outlet of the injection device.

In yet an embodiment of the injection-mixing device, the swirl-generating element comprises vanes arranged to induce a swirl motion to the fluid to be treated.

In yet an embodiment of the injection-mixing device, the at least one outlet of the injection device is arranged to provide a treatment fluid flow in a radial direction away from the centerline of the main pipe. In yet an embodiment of the injection-mixing device, the at least one outlet of the injection device is arranged to provide a treatment fluid flow at the inner wall of the main pipe. In yet an embodiment of the injection-mixing device, a section of the treatment fluid line is arranged through the swirl-generating element. The section of the treatment fluid line may form an integral part of the swirl-generating element.

In yet an embodiment of the injection-mixing device, the centerline of the section of the treatment fluid line arranged through the swirl-generating element is arranged at (i.e. coinciding with) the centerline of the main pipe and one end of the section is connected to the inlet of the injection device.

In yet an embodiment of the injection-mixing device, the main pipe comprises a pipe flange at the inlet and/or the outlet. The pipe flange(s) allows for easy connection of the injection-mixing device to for instance a pipe line, a second injection-mixing device, a separator section and/or a treatment section.

In a desalting system the separator section may separate (part of) the treatment fluid from the treated fluid and also part of the salt-containing water droplets that were already contained (dispersed) in the stream to be treated.

In yet an embodiment, the injection-mixing device comprises a flow straightener arranged downstream the at least one outlet of the injection device. The flow straightener may comprise vanes arranged to stop a swirl motion induced by the swirl-generating element at a position after the injection of a treatment fluid (i.e. the flow straightener is arranged between the outlet of the injection device and the outlet for a treated fluid). In a second aspect, the present invention provides a fluid treatment system comprising at least one injection-mixing device according to an embodiment of the first aspect.

In one embodiment, the fluid treatment system comprises an electrocoalescer arranged downstream the at least one injection-mixing device.

In one embodiment, the fluid treatment system comprises a separator section downstream of, or fluidly connected to, the outlet of the main pipe of the at least one injection-mixing device. The separator section is able to separate at least a part of the treated fluid from a treatment fluid, i.e. able to remove at least some of the treatment fluid which has been separated from the fluid to be treated due to the imposed centrifugal force. When the fluid treatment system is used for injecting a treatment fluid, for instance chemicals, solvents, extraction fluids etc., the separator section may be used for separating one phase of the treated fluid from another phase of the same treated fluid. The injected treatment fluid may enhance such separation of phases. For example, in a desalting system the separator section may separate (part of) the treatment fluid from the treated fluid and also part of the salt- containing water droplets that were already contained (dispersed) in the stream of fluid to be treated.

In yet an embodiment, the fluid treatment system comprises two injection-mixing devices fluidly connected in series, optionally separated by a separator section able to separate a treated fluid from a treatment fluid. The system may also comprise a further separator arranged downstream of the two injection-mixing devices.

Preferably, the vanes are radially arranged between a section of the treatment fluid line and the inner surface of the main pipe. In an embodiment, a section of the treatment fluid line is an integrated part of the mixing assembly.

In a third aspect, the present invention provides a method of mixing a first fluid and a second fluid, the method comprising the steps of: applying a centrifugal force to the first fluid by use of a swirl generating element, such that the first fluid obtains a swirl motion along the inner circumferential wall of a cylindrical vessel or pipe; injecting the second fluid downstream or upstream the swirl generating element, such that the second fluid is forced into contact with the first fluid by the centrifugal force.

In one embodiment, the method comprises the step of providing an injection mixing device comprising an inlet for the first fluid, an outlet for a treated fluid and an inlet for the second fluid.

In one embodiment of the method, the second fluid has a higher or lower density than the first fluid. In one embodiment of the method, the second fluid has a higher density than the first fluid, and is injected at a center section of the cylindrical vessel or pipe.

In one embodiment of the method, the second fluid has a lower density than the frst fluid, and is injected at the circumferential wall of the cylindrical vessel or pipe.

In one embodiment, the method comprises the step of: separating at least a part of a treated fluid from the second fluid, the treated fluid obtained from the first fluid after mixing with the second fluid. In one embodiment of the method, the first fluid is a fluid to be treated and the second fluid is a treatment fluid.

The injection-mixing device may also be defined in that the inlet of the main pipe is for a treatment fluid and the treatment fluid line is for a fluid to be treated.

The term "swirl-generating element" is intended to define any element able to induce a radial swirl motion providing a centrifugal force to a fluid entering the inlet of the main pipe of the injection-mixing device. In a preferred embodiment, the swirl-generating element comprises multiple vanes arranged to direct the fluid into a radial swirl motion, however the required centrifugal force may also be obtained by use of a tangential inlet, i.e. an inlet wherein the required centrifugal force or radial swirl motion is obtained by directing the fluid flow into a tangential relationship with a circular inner surface. The term "separation section" is intended to define any element able to remove and separate at least a part of the second fluid from the first fluid and/or part of the treated fluid from the same treated fluid (e.g. oil-water removal, gas-liquid, etc.).

The term "treatment section" is intended to comprise devices such as electrostatic coalescers, heat exchangers etc.

Short description of the drawings

The present invention is described in detail by reference to the following drawings:

Fig. l is a side view of an embodiment of an injection-mixing device according to the invention, wherein the injection device is a nozzle.

Fig. 2 is a side view of a further embodiment of an injection-mixing device according to the invention, wherein the injection device is a hollow cone in a porous or perforated material. Fig. 3 is a side view of an embodiment of an injection-mixing device according to the invention, wherein the injection device is a hollow cone in a porous or perforated material, the injection device is arranged to provide a treatment fluid upstream of the mixing assembly.

Fig. 4 is a side view of a fluid treatment system comprising two injection-mixing devices arranged in series or alternatively an embodiment of an injection-mixing device comprising two swirl-generating elements.

Figs. 5-7 are side views of various fluid treatment systems according to the invention.

Detailed description of embodiments of the invention

As mentioned above, the present invention was motivated by the need to improve the efficiency and cost-effectiveness of injection-mixing system used in the crude oil desalting process in refineries, and the embodiments of the invention is consequently described in that context. However, the disclosed injection-mixing device and fluid treatment system is equally advantageous in other processing applications involving injection of treatment fluids such as chemicals, solvents or extraction fluids for enhancing the effect of separation and processing equipment.

The most commonly injected treatment fluids (admixtures) includes

scavengers/irreversible solvents (liquid for removal of sour constituents, such as e.g. H ₂ S, Hg, thiols), corrosion inhibitors, hydrate inhibitors, scale inhibitors, wax inhibitors, drag reducers, desalters, de-emulsifiers, deoilers, defoamers,

antifoulants, flocculants (enhancing the coalescence rate of a dispersed phase), condensate/hydrocarbon (extraction fluids), gas (flotation or alleviation of slugging) and water (desalting or manipulation of the water cut of a multiphase flow mixture away from its critical value).

The respective treatment fluids (i.e. second fluid) are introduced into the flow of a pipe via the injection-mixing device upstream of processing equipment, such as upstream of a separator section. The flow (i.e. the first fluid or fluid to be treated) can be any multiphase mixture of gas and one or more liquids, a single gas or a combination of gases, any liquid or mixture of miscible liquid components or immiscible components such as hydrocarbon liquid and water. Hence, the flow may for example be an unprocessed well stream, produced water, processed oil-water flow, processed gas flow, produced water contaminated with dispersed and dissolved hydrocarbon, processed water flow contaminated with hydrocarbon liquid, or water subject to gas component removal (e.g. de-oxygenation). The range of surface tension, viscosity, pressure and temperature may vary considerably, and additional types of fluids or admixtures are also relevant. An injection-mixing device according to the invention is disclosed in fig. 1. The device comprises a main pipe 1, a nozzle 2 (i.e. an injection device), a treatment fluid line 4 (i.e. a line for a second fluid or second fluid line) and a swirl-generating element 10. The main pipe comprises an inlet 5 (or a first end) for a fluid to be treated (i.e. a first fluid) and an outlet 6 (or a second end) for a treated fluid. The main pipe may advantageously comprise pipe flanges (not shown) at the inlet and the outlet for easy connection of the injection-mixing device to a pipe line. In this particular embodiment, the treatment fluid line is arranged through the wall of the main pipe in a radial direction and along the centerline of the main pipe. The treatment fluid line is connected to an inlet 7 of the nozzle. In this embodiment, at least a section of the treatment fluid line constitutes an integral part of the swirl- generating element. The outlet of the nozzle is arranged downstream of the swirl- generating element, but may in other embodiment be arranged upstream of the swirl-generating element and provide the same advantageous effect. The swirl- generating element comprises a hollow cylindrical body providing a section of the treatment fluid line (or treatment fluid flow path) and vanes 3 arranged to induce a swirl motion to the fluid to be treated. In use, a fluid to be treated (for instance a crude oil process stream to be desalted) enters the inlet 5 of the main pipe.

Simultaneously, a treatment fluid (for instance freshwater for extracting salt present in the crude oil process stream) is injected via the fluid treatment line and the nozzle. Upon passing the swirl-generating element, the crude oil obtains a swirl motion. The swirl motion provides centrifugal force acting on the crude oil and the water, such that the water is mixed with the crude oil. Depending on the application and fluid conditions, the mixture of water and crude oil may subsequently be separated by migration of a water phase to the inner circumference of the main pipe. Thus, the induced swirl motion may provide a combined advantageous effect in some applications in that it both facilitates and improves an initial intimate mixing of the water (i.e. the treatment fluid, the second fluid) and the crude oil (i.e. the fluid to be treated, the first fluid) and further provides a subsequent separation of the water and the desalted crude oil (i.e. the treated fluid). However, a subsequent separation is not always desired and may be easily avoided by for instance having a short fluid pathway after the injection of the treatment fluid and/or by arranging a flow straightener (e.g. vanes arranged to stop the swirl motion shortly after the injection of the treatment fluid). For instance, in a desalter system comprising an electrostatic treatment section the role of the injection-mixing device (or fluid treatment system) is to maximize contact between freshwater droplets and salt- containing droplets, and generate a water-in-oil emulsion that is as homogeneous as possible (ideally all droplets having the same size). The emulsion created by the injection-mixing device should neither be too unstable (too large droplets) nor too stable (too small droplets). If droplets are too large they will be (partly) separated prior to reaching the electrostatic treatment (e.g. an InLine ElectroCoalescer plus settler and/or a conventional electrostatic coalescer). If the droplets are too small the emulsion will be too stable for the electrocoalescer/settler to work efficiently.

An alternative embodiment of an injection-mixing device is shown in fig. 2. In this embodiment the injection device is made up of a porous/perforated element 9 shaped as a hollow cone. The treatment fluid is injected to the main pipe through the pores/perforations in the hollow cone.

The size and shape of the outlet(s) of the nozzle 2 or the pores/perforations of the porous/perforated element may be adjusted to provide a desired range of droplet sizes suitable for the intended use.

A further embodiment of an injection-mixing device is shown in fig. 3. The device is similar to the one shown in fig. 2, but the porous/perforated element 9 (i.e.

injection device) is arranged upstream of the swirl-generating element 3. The swirl- generating element 3 is only schematically drawn, but may advantageously be similar to the one shown in figs. 1 and 2.

In an injection-mixing system (i.e. fluid treatment system), multiple injection- mixing devices may easily be arranged in series to improve the fluid treatment, e.g. by connecting the outlet 6 of a first injection-mixing device to the inlet 5 of a second injection-mixing device. Alternatively, as shown in fig. 4, the first and second injection-mixing devices are connected by a first separator section 1 1 in which the treatment fluid is separated from the fluid to be treated (or the treated fluid). In this embodiment, the separator section comprises perforations 12, through which the treatment fluid is removed due to the centrifugal force imposed by the swirl-generating element 3a, and an outlet 13. The outlet 13 may for instance be connected to any suitable vessel for storage, system for recycling the treatment fluid etc. A second separator section (not shown) may further be arranged after the swirl- generating element 3b of the second injection-mixing device. In this manner, the fluid to be treated may be subjected to multiple treatment regimes in series. The treatment regimes may be identical, for instance being two steps of desalting, or they may be different, in that for instance the fluid to be treated may be chemically treated in the first injection-mixing device and dehydrated in the second injection- mixing device. The injection-mixing system in fig. 4 may also be described as an injection-mixing device comprising two swirl-generating elements in series.

Further injection mixing devices or fluid treatment systems are shown in figs. 5-7. The injection-mixing device, or system, in fig. 5 comprises two swirl-generating elements, i.e. a first and a second swirl-generating element 3a, 3b, arranged in series. The swirl-generating elements are connected by a cylindrical pipe element 14 arranged through the center of the swirl generating elements. The second swirl generating element 3b comprises an end cone 15. The cylindrical pipe element is connected to the treatment fluid line 4. Further, at least one of the cylindrical pipe element and the end cone is perforated, or made in a porous material, such that a treatment fluid may be injected into the main pipe and mixed with a fluid to be treated entering the inlet 5 of the main pipe 1. When perforated or made in a porous material, the end cone corresponds to the porous/perforated element 9 described above. The device/system in fig. 5 may also comprise optional separation sections 11a, l ib, as described for the system in fig. 4, each comprising perforations 12 and an outlet 13. The separator sections are able to extract liquid which has coalesced on the inner surface of the main pipe 1.

The injection-mixing device, or system, in fig. 6 comprises a swirl-generating element 3 and an anti- swirl element 16 (or flow straightener). In this embodiment, the cylindrical pipe element is perforated, or made in a porous material, while the end cone 15 is fluid tight.

In some applications, the treatment fluid may have a lower density than the fluid to be treated. In those cases it may be advantageous or in fact necessary to inject the treatment fluid at the inner wall of the main pipe 1, such that the centrifugal force will provide the desired mixing of the treatment fluid and the fluid to be treated. An injection-mixing device, or system, suitable for the application of low-density treatment fluid is shown in fig. 7. In this embodiment, the treatment fluid is injected into the main pipe 1 via the outlets 8 of the radial injection device 17 arranged upstream the first swirl-generating element 3a. The applied centrifugal force will ensure that the treatment fluid will migrate from the inner wall of the main pipe towards the centerline of the main pipe, while the more dense fluid to be treated will migrate towards the inner wall of the main pipe. In this embodiment, the cylindrical pipe element is perforated and serves the same purpose as the separator sections 13 described above. The two fluids are mixed and at least parts of the treatment fluid are subsequently extracted through the cylindrical pipe element and the extracted fluid line 18 (similar to the treatment fluid line 4 in figs. 5 and 6, but having different function). The injection-mixing device may advantageously be used in any application wherein the mixing of a fluid to be treated with a treatment fluid is required. These applications include being arranged inside various processing equipment such as separators, used as a part of various processing systems, for instance arranged upstream, downstream or inside demisting cyclones, or hydrocyclones, inline equipment etc. The swirl-generating element 3 may also comprise an active driven swirl element disclosed in application PCT/EP2016/052876, a hydrocy clone element and/or several swirl-generating elements in series or parallel.