Patent Application
20080035586
It will be appreciated that the Figures are schematic illustrations that are not to scale or proportion, and, as such, some of the important parts of the invention may be exaggerated for illustration.
Non-limiting exemplary methods and apparatus described herein enhance the removal of a dispersed phase from a continuous phase intermixed therewith by means of the coalescing action of coalescing media in a vessel and the cyclonic action of at least one hydrocyclone in series therewith. The first vessel, also known as a coalescer herein, increases the size of the dispersed phase, while subsequently a separator hydrocyclone or batch of separator hydrocyclones separates the coalesced dispersed phase from the continuous phase at a higher removal efficiency. In one non-limiting embodiment, the dispersed phase may be a contaminant, such as oil in a continuous phase of produced water. A non-limiting application for the apparatus and methods herein is to separate the components of a wellbore fluid involved in hydrocarbon recovery, including, but not necessarily limited to, produced water from a subterranean formation. In a nonrestrictive instance, produced water on an offshore platform that has the contaminants sufficiently removed therefrom may be properly disposed of in the sea.
In more detail, one non-restrictive example includes utilization of this method to enhance removal efficiency of a produced water treatment, where existing hydrocyclones or degassers or flotation units do not meet oil and grease discharge requirements due to small size distribution of the contaminants. Indeed, hydrocyclone performance is a function of particle size. The larger the oil droplets' size, the better the oil removal efficiency becomes. The methods and apparatus herein will increase the oil droplet size by coalescing the smaller oil droplets into larger droplets in the coalescing vessel in order to enhance the performance of the downstream hydrocyclone.
Although conventional coalescers generally have an oil overflow outlet or port, it will be appreciated that the coalescer herein in an exemplary apparatus described herein does not have a conventional oil overflow port or outlet. In one sense, the method and apparatus herein “plugs” or eliminates the oil outlet from the first vessel and allows the coalesced oil droplets to flow through the vessel. In this process, the effluent from the coalescing vessel will contain much larger oil droplets so as to enhance the performance of the downstream hydrocyclone.
Thus, the coalescer vessel together with the downstream hydrocyclone are being used to remove the oil in the produced water. Due to the tighter regulations of lower permitted oil concentrations in the produced water for disposal, the effluent from the hydrocyclone must be polished by down stream equipment such as flotation, etc. However, it is expected that the methods and apparatus herein may permit the coalescer and the hydrocyclone combination only to be able to meet the required effluent standards in many cases.
Each coalescer or group of coalescers, or each hydrocyclone or batch of hydrocyclones may be contained within a single enclosure or vessel or may be housed within separate enclosures or vessels. For instance, in one non-limiting embodiment, the coalescer(s) may be housed or contained in one vessel while the separator hydrocyclone(s) may be contained or housed in a second vessel. In general, in another optional, alternative embodiment, the separator hydrocyclones have a conical section or profile followed by a tubular tail section which may or may not be tapered on the inside.
The first unit, vessel or coalescer contains at least some coalescing media therein to coalesce smaller dispersed droplets or particles into larger ones in the continuous phase. Some well-known and widely used systems employ corrugated plate interceptors and parallel plate interceptors, but these tend to be limited to oil emulsions where particle sizes are 30 μm or larger. The removal of oil emulsions where the diameter of the particles is less than 20 μm is very difficult with these devices because in many cases these smaller particles make up a high proportion of the total oil content, and it is difficult or impossible to reduce the level in the discharge to the permissible levels with conventional equipment.
Several media materials are used alone or together. Commonly used media include, but are not necessarily limited to, polymeric materials, sand, anthracite, and clay have also been used as separation and/or filtration media. When sand, anthracite and clay are used they are produced with a particular form or shape. These filtration technologies are generally limited however because of their sensitivity to the presence of viscous oils and/or suspended solids. It is not unusual that the materials used as a separation media become clogged with highly viscous oils or with suspended solids within 24 hours of operation, thus requiring replacement of the filtration media or backwashing with fresh or treated water, which results in even more oily wastes or more contaminated backwash liquids.
The coalescing media may, in particular, be an absorbent or adsorbent material. Absorbent or adsorbent materials which have relatively low absorption or adsorbent ability or capacity, such that coalesced droplets are readily released from the material are especially advantageous herein. In one non-limiting embodiment, the bulk of the mixture or dispersion is allowed to flow directly through the absorbent material, with the bulk of the dispersion flowing through an extensive network of passages between the filaments or strands and through the pores in the filaments or strands themselves. The absorbent may in one non-restrictive version have a limited capacity to temporarily trap the dispersed oil droplets due to its affinity for them but then also permits or allows the relatively larger, coalesced droplets to be released.
Due to this ability, the absorbent may thus also be an effective coalescing media. When an oily dispersion of fine droplets is passed through the coalescing media, some of the oil droplets will be temporarily retained, trapped or held within or on the pores of the absorbent due to their attraction for the absorbent. Here the non-aqueous droplets will be held until others find their way into the pores, and as more enter or accumulate they will eventually produce droplets that are sufficiently close to one another to contact and coalesce. This process will continue until the pores are relatively full and the larger droplets will be forced out by the flow of the liquid and because of their size to start rising. The relatively uniform nature of the absorbent filaments, strands and pores makes for the release of a substantially uniform size droplet.
In another non-limiting embodiment, the coalescing media used in the methods and apparatus herein has a high surface area and/or a substantially homogeneous porous mass, which may in one non-restrictive version be a polymeric matrix such as polyester, polystyrene, polypropylene, polyethylene, polyurethane, and mixtures thereof, which has the ability to absorb/adsorb fine oil emulsions within or on its relatively uniform and fibrous network structure. The physical separation phenomenon on the polymeric matrix that produces the coalescence of the oil droplets and the separation of the aqueous and non-aqueous phases on the polymer, may be a complex phenomenon and is likely to be a combination of absorption and adsorption followed by the coalescence of the small non-aqueous phase droplets into larger droplets, although the inventors herein do not wish to be limited to any particular theory.
Shown in more detail with respect to
In the known operation of coalescers, the produced water fluid mixture 20′ introduced through first inlet portion 22 of coalescer 20′ encounters coalescing media 26 (described in more detail above) that at least partially coalesces the dispersed liquid phase (e.g., contaminant droplets, oil, etc.).
As illustrated, coalescer 20′ does not include an oil overflow outlet or port 28 to permit the egress of oil 14 that is typically be found in a coalescer 20 of
It will also be appreciated that in another non-restrictive version of the invention the first vessel or coalescer 20′ may be backwashable, that is, may be designed to periodically have a fluid flowed, channeled or pumped therethrough in a direction opposite to that shown in
At least partially coalesced fluid mixture 16′ passes to separator hydrocyclone or second elongate hollow member 30 via a second inlet portion 32 at the larger (left) end of the hydrocyclone 30. In the known operation of hydrocyclones, the introduction of fluid mixture 16′ into second inlet portion 32 generates a swirling motion or vortex in the chamber, interior or enclosure that largely or at least partially separates the dispersed liquid phase (e.g., contaminant droplets, oil, etc.) from the continuous phase (e.g. water). In one non-restrictive embodiment of the method, the vortex is generated along the inner, interior or inside wall of the first hollow member or vortex 30. In one non-limiting embodiment the first inlet portion 32 has a greater cross-section diameter, taken transverse to a longitudinal axis of the hydrocyclone or elongate member 30, than the third underflow outlet portion 36.
Separator hydrocyclone 30 substantially separates the at least partially coalesced liquid phase, e.g., oily contaminants, from the continuous phase, e.g., water. By “substantially separate” herein is meant that at least a majority (greater than 50 volume %) of the coalesced liquid phase, which is larger than certain size (cut size) is separated, alternatively at least 80 vol. % of the coalesced liquid phase is separated, and in another non-limiting embodiment, at least 90 vol. % of the coalesced liquid phase present is separated. The cut size refers to a specific contaminant size from the size distribution of dispersed phase, which is substantially separated in accordance with operational and geometrical parameters of the hydrocyclone.
Separator hydrocyclone 30 also includes at least one overflow outlet or second overflow outlet portion 34 for discharging a relatively less dense coalesced liquid phase 18. Overflow outlet 34 may be coaxial with a vortex finder (not shown) in hydrocyclone 30 on the axis of separator hydrocyclone 30 typically found in a hydrocyclone, as is known in the art. In one non-limiting embodiment, the second inlet portion 32 has a greater cross-section diameter, taken transverse to a longitudinal axis (not shown) of the second elongate member or hydrocyclone 30, than the second outlet portion 34.
Separator hydrocyclone 30 further includes at least one underflow outlet or third outlet portion 38 on the other end of the second separation chamber 30 from the at least one overflow outlet 34 for discharging a relatively more dense liquid phase 40 (e.g., clarified water) of the fluid mixture. In another non-restrictive version, second inlet portion 32 is physically intermediate the second and third outlet portions, 34 and 36, respectively. Further in another non-limiting embodiment, second outlet portion 34 of the second elongate hollow member 30 is located toward one side of the inlet portion 32 of the second elongate hollow member 30. Third outlet portion 36 of the second elongate hollow member 30 may be located on an opposite side from the second inlet portion 32 of the second elongate hollow member 30 and the second outlet portion 34 of the second elongate hollow member 30.
This apparatus or system has at least one fluid communication, such as a pipe, tube, conduit or other pathway between the at least one outlet 24 of the coalescer 20 and the at least one second inlet 32 of the at least one separator hydrocyclone 30. In the non-limiting embodiment of
It will be understood that the vortex within the hydrocyclone 30 generates a G-force. In one non-limiting embodiment, the G-force may be in the order of tens or even hundreds of Gs. The G is defined herein as a unit measuring the inertial stress on a body undergoing rapid acceleration, expressed in multiples of the acceleration of one earth gravity.
In one optional embodiment, a chemical coalescing agent or demulsifier 38 may be introduced into the produced water 12 and/or or at least partially coalesced fluid mixture 16 through an opening, aperture, or other port (not shown) in the pipe, tubing or conduit through which these liquids pass. In one non-limiting embodiment, the chemical coalescing agent 38 is introduced upstream of first inlet 22, but may be introduced at other locations in addition to or alternative to this one. The optional chemical coalescing agent 38 aids in coalescing the particles or droplets of the dispersed phase (e.g., contaminant oil) together to form relatively larger particles or droplets. In one non-limiting embodiment such chemical coalescing agents or demulsifiers are polymers and are known in the art and may be used in dosages or amounts of about a few parts per million, based on the fluid or mixture treated. In other non-restrictive versions, if the produced water 12 contains solids, it may be necessary or helpful to pre-treat the water with a chemical coalescing agent or demulsifier of some type.
In the foregoing specification, the invention has been described with reference to specific embodiments thereof, and is expected to be effective in providing methods and apparatus for separating mixed liquid phases more efficiently. However, it will be evident that various modifications and changes can be made thereto without departing from the broader spirit or scope of the invention as set forth in the appended claims. Accordingly, the specification is to be regarded in an illustrative rather than a restrictive sense. For example, the coalescers and separators may be changed or optimized from that illustrated and described, and even though they were not specifically identified or tried in a particular apparatus, would be anticipated to be within the scope of this invention. For instance, the use of more coalescers and/or hydrocyclones in series would be expected to find utility and be encompassed by the appended claims. Different dispersed and continuous liquid phases, and different oily matter other than those described herein may nevertheless be treated and handled in other non-restrictive embodiments of the invention.
