Patent Description:
Once oil is produced it must be dehydrated and desalted to reduce the corrosion effect on production systems such as transportation carriers, pipelines, and refineries. The dehydration and desalting done at the oil producing facility is capable of removing the majority of the water and salts prior to delivery to a refinery. Once the oil is at the refinery it is desalted again to reduce the salts to even lower and less corrosive levels. In addition to the water and dissolved salts carried by the oil, there may be a large quantity of solids ranging in size from very small sub-micron particles or fines to larger particles such as sands. The larger particles are readily removed by the oil production facility leaving the finer particles to be removed at the refinery.

In general, the smallest particles may contribute to the stability of an oil-water emulsion by forming a barrier around the water droplets thus preventing droplet coalescence and separation. Water droplets that are surrounded by these fines may be large enough to settle in the electrostatic desalter, but they are hindered from coalescing by the fines. The effect is for this solid-laden water layer to accumulate at the oil-water interface as a "rag. " As this rag layer collapses the fines settle to the bottom of the vessel to form a "mud" layer where they must be removed periodically by a mud wash system.

This mud wash system consists of a set of spray nozzles that disperse a volume of fresh water into the desalter for the purpose of agitating the mud so it can be effectively removed from the desalter. Two primary methods for mud removal are practiced. One method is to do a timed mud wash where the vessel is washed only periodically as determined by the unit operator. The frequency depends on the solids (mud) loading and may be once per day or once per week, as examples. The disadvantage of periodic mud wash is that it sends high levels of oil wet solids to the water treatment facility where it must be handled for disposal. These periodic injections of oil wet solids can initiate an upset in the water quality.

The other method is a semi-continuous mud wash where sections of a vessel are washed sequentially. Upon the completion of all sections, the sequence is restarted. The advantage of a semi-continuous wash is to level the load of solids that are passed to the water treatment vessels. The disadvantage of both the semi-continuous and periodic methods is that solids are still allowed to settle in the bottom of the vessel where they can only be partially removed by each subsequent periodic washing.

While either method can handle the volume of fines in a refinery desalter, there remains a more significant problem that has not been properly dealt with before. This problem is the solid-laden rag that hangs at the oil-water interface. Once this interface mud accumulates at the interface it becomes quiescent and the rate of water and solids separation is slowed significantly. When the rate of collapse for interface rag is slower than the rate of accumulation, the interface volume increases and interferes with the desalter operation. While the exact nature of this interface rag cannot be readily determined, the effects are detrimental to the performance of the desalter in one of two ways.

If the interface rag floats on top of the water, then it can grow in height until it interferes with the integrity of the electrostatic field by increasing the current demand and reducing the field strength. The electric field does apply added energy to the top of the interface and can accelerate the rate of decay. If the interface sinks into the water layer it rapidly occupies the water volume of the desalter and reduces the water residence time. The effect is a decline in the water quality that is passed to the water treatment facility as the interface rag settles to the bottom of the vessel to form mud and mixes with the brine exiting to the brine heat exchangers and benzene recovery unit. This mixing accelerates the fouling and plugging of the heat exchangers and benzene recovery unit.

Because refineries have more complex and overlapping issues, system applications need to be expanded beyond the simple purpose of removing sludge and solids from the bottom of desalter vessels. A need exists, therefore, for a system that assists a refinery in meeting planned crude unit run-length expectations, does not put the desalter in an upset condition during operation, minimizes or eliminates sludge buildup at the bottom of the vessel, improves basic sediment and water (BS&W) reduction performance, improves salt reduction performance, minimizes emulsion and reverse emulsion buildup at the oil/water interface, keeps solids suspended in the brine until the solids exit to the process sewer, and protects process equipment ahead of the waste water treatment plant.

<CIT> discloses an emulsion treating apparatus including a tank partitioned internally into a separation chamber and a settling chamber. <CIT> discloses a method for separating oil from an oil and water mixture. The method includes using radial eductors to create a low pressure region where the oil attaches to air bubbles. <CIT> discloses the use of eductors in connection with pumping liquids which are at or near their boiling point.

<CIT> describes a desalter vessel with provision for controlling an interface emulsion layer which includes injecting a water flow through a plurality of nozzles arranged about a piping circuit located in the brine water layer. Each nozzle is oriented toward an interior space of the desalter vessel and is arranged oblique to the piping circuit. It is stated as preferred that each nozzle is oriented at an angle of about <NUM>° and <NUM>° in a horizontal plane and a downward angle of about <NUM>° and <NUM>° in a vertical plane. It is stated that water flow through the plurality of nozzles causes a horizontal and vertical rotation of a volume of water that is effective for suspending solids in the water and promoting a collapse of the interface emulsion layer.

A method for controlling an interface emulsion layer within an oil treatment vessel includes injecting a water flow into a brine water layer of the oil treatment vessel through a plurality of inlets arranged about a manifold oriented in a horizontal plane and located in the brine water layer. Each of the inlets is a radial eductor oriented in a vertical plane relative to the center line of the said manifold. The water flow through the eductors into the brine water layer causes a swirling flow pattern of a volume of water in the brine water layer around each radial eductor that agitates the lower surface of the interface emulsion layer residing above the brine water layer, helping to break down the interface emulsion layer and reducing its accumulation within the vessel.

A system for controlling an interface emulsion layer within an oil treatment vessel includes a plurality of inlets connected to a manifold located within the oil treatment vessel and oriented in a horizontal plane with the vessel configured for the manifold to be located in a brine water layer residing within the oil treatment vessel. Each inlet is a radial eductor oriented in a vertical plane relative to the center line of the radial eductor manifold. Water flowing through the radial eductors into the brine water layer creates a swirling flow pattern around each radial eductor to agitate a lower surface of the interface emulsion layer residing between the brine water layer and the oil layer in the oil treatment vessel. The system may further include a means for recycling a volume of the brine water layer to the radial eductor manifold, such as a recirculating pump and recycling piping.

A better understanding of the method and system for controlling the interface emulsion layer will be obtained from the following detailed description of the preferred embodiments taken in conjunction with the drawings and the attached claims.

The present invention provides a method and system for preventing mud build-up within a separator vessel by continuously agitating the lower surface of the interface emulsion layer so as to suspend solids in the water layer and promote the collapse of emulsion residing in the interface emulsion layer. Elements illustrated in the drawings are identified by the following numbers:.

Referring first to <FIG>, a separator vessel <NUM> is connected by conventional piping (not shown) to a crude oil source. Vessel <NUM> is of a type well-known in the art and commonly used in crude oil production and refining for dehydration and desalting of crude oil. A crude oil stream containing water and solid contaminants enters vessel <NUM> through the identified "oil inlet". Vessel <NUM> typically holds those components and processes them so that the oil is separated from the contaminants. The separated oil layer <NUM> is then removed from vessel <NUM> through an outlet <NUM> located at the top <NUM> of vessel <NUM>.

During the separation process, it is common for oil-coated solids, called mud <NUM>, to accumulate on a bottom <NUM> of vessel <NUM> and for a layer comprising a mixture of oil and water, called interface emulsion layer <NUM>, to form in an intermediate portion of vessel <NUM>. A solid-laden or brine water layer <NUM> accumulates between the layer of mud <NUM> residing on the bottom <NUM> and the layer of interface rag or emulsion <NUM>. To prevent the interface rag layer or emulsion <NUM> from accumulating until its presence begins to interfere with the performance of vessel <NUM>, a rag drain <NUM> may be provided (See <FIG>). The removal of the interface rag layer or emulsion <NUM> preferably occurs continuously and the removal rate may vary over time. Oil layer <NUM> accumulates above the interface emulsion layer <NUM> in the upper portion <NUM> of vessel <NUM>.

Some "rag," referred to as interface rag <NUM>, rather than settling to the bottom <NUM> of vessel <NUM>, may float on top of the water layer <NUM> and "hang" at the lower surface <NUM> of the interface emulsion layer <NUM> as shown in <FIG>. As this interface rag <NUM> accumulates it becomes quiescent and the rate of water and solids separation is slowed significantly. When the rate of collapse and settlement of interface rag <NUM> is slower than the rate of its accumulation, the volume of interface emulsion layer <NUM> increases and begins to interfere with the operation of vessel <NUM>. For example, interface rag <NUM> may sink into the water layer <NUM> and occupy water volume, thereby reducing water residence time, decreasing the quality of water passed to a treatment facility. Additionally, interface emulsion layer <NUM> may grow in height until it interferes with the integrity of an electrostatic field (not shown in the drawings) being applied to promote separation of components in the crude oil. Furthermore, as the interface rag <NUM> collapses it settles to the bottom <NUM> of vessel <NUM> and contributes to oil coated solids/mud <NUM> that accumulates in the vessel bottom. This oil-coated solids/mud <NUM> must be removed periodically, usually by way of a prior-art mud wash system <NUM> (see <FIG>).

A mud wash system <NUM>, as known in the prior art, includes piping <NUM> arranged in sections along a lower portion <NUM> of vessel <NUM> at a distance "h<NUM>" from the bottom <NUM> of vessel <NUM> (usually in the bottom third of water layer <NUM>). Piping <NUM> may include two outer pipes (not shown) that run near and along the interior wall surface <NUM> of vessel <NUM> and one middle pipe (not shown) spaced equidistant from, and running parallel to, each outer pipe. A series of spray nozzles <NUM> are connected to the piping <NUM> and oriented downward at a <NUM>° angle relative to a centerline line of piping <NUM>. The spray nozzles <NUM> disperse a volume of water into the desalter for the purpose of agitating the mud <NUM> so it can be effectively removed from the desalter by way of mud drains <NUM>. A recycle pump <NUM> and recycle piping <NUM> may be employed to recycle the mud wash water.

Prior-art mud wash system <NUM> does not prevent the build-up of mud <NUM>. This system also does not prevent episodic build-up of the interface emulsion layer <NUM>, nor does it reduce salt, reduce basic sediment and water (BS&W), eliminate interface rag <NUM>, or eliminate reverse emulsion migration from interface emulsion layer <NUM> to water layer <NUM>.

Referring to <FIG>, a system <NUM> is illustrated for slowly and continuously agitating the interface emulsion layer <NUM> to prevent or control the build-up of interface emulsion layer <NUM> and keep the fines that contribute to mud layer <NUM> suspended in the brine water layer <NUM>. System <NUM> (to be described) imparts enough velocity and motion into the water layer <NUM> to suspend solids therein until they are removed with water layer <NUM> as it is removed from vessel <NUM> and also creates a washing action under interface rag <NUM> to aid in water-wetting solids and recovery of oil to oil layer <NUM>. System <NUM>, which is capable of servicing desalter operations across a full range of API gravity crude oils, preferably utilizes no filters.

System <NUM> includes an oblong-shaped first piping circuit <NUM> that is located in a lower portion <NUM> of vessel <NUM>. The outer peripheral surface <NUM> of first piping circuit <NUM> is at distance "d" from the inner wall surface <NUM> of vessel <NUM>. The piping circuit <NUM> is also at a distance "h<NUM>" from the bottom <NUM> of vessel <NUM>. In a preferred embodiment, distance h<NUM> places first piping circuit <NUM> in the upper two-thirds of the height of water layer <NUM> in vessel <NUM>. First piping circuit <NUM> may be supported by a set of horizontal supports <NUM> as seen in <FIG>.

First piping circuit <NUM> produces a slow circulation of water layer <NUM> and, therefore, a slight water velocity across the lower surface <NUM> of the interface emulsion layer <NUM>. This slight velocity, which is established by a series of angled nozzles <NUM>, prevents build-up of interface rag <NUM> and reduces or eliminates mud <NUM>. Furthermore, the continuous circulation helps keep fines suspended in water layer <NUM> so that the fines are discharged directly with the discharge of water layer <NUM>, thus eliminating the need for frequent mud wash of vessel <NUM>.

Nozzles <NUM> are arranged and spaced about the inner periphery <NUM> of first piping circuit <NUM> (see <FIG>) and generally are pointed interiorly of vessel <NUM>. Nozzles <NUM> may be drilled passageways in first piping circuit <NUM> or may be, as illustrated, short length tubular members. Each nozzle <NUM> is preferably oriented at an angle of between about <NUM>° and <NUM>° in a horizontal plane relative to a line perpendicular to centerline <NUM> of first piping circuit <NUM> and at a downward angle of between about <NUM>° and <NUM>° in the vertical plane. The <NUM>° to <NUM>° angle translates to a <NUM>° to <NUM>° angle between a line drawn through the longitudinal centerline of the nozzle <NUM> and a line drawn perpendicular to centerline <NUM>. The preferred horizontal and vertical plane angle is <NUM>°. Alternatively, each nozzle <NUM> may be oriented at between about <NUM>° and <NUM>° in the horizontal plane, thereby promoting a clockwise (opposite) flow.

Referring to <FIG>, the water flow through each nozzle <NUM> is preferably at a low flow rate in the range of about. <NUM> (<NUM> to <NUM> feet) per minute. Once the flow from the nozzles <NUM> is established, the bulk of water layer <NUM> will begin to rotate slowly and in two directions, R<NUM> and R<NUM>. Rotation R<NUM> is in a horizontal plane coincident to the clockwise or counterclockwise orientation of nozzles <NUM>. Rotation R<NUM> is a toroidal-shaped rotation in a vertical plane. Rotations R<NUM> and R<NUM> continuously agitate the lower surface <NUM> of the interface emulsion layer <NUM> and keep the solids suspended in water layer <NUM> by lifting the fines from the bottom <NUM> of vessel <NUM>. The flow pattern created by R<NUM> and R<NUM> is substantially a rotating plane toroidal flow that consumes each sector S and looks like a series of large horizontal plane doughnut-shaped flows (see <FIG>).

Controls (not shown) may be provided to control the water flow through nozzles <NUM>, with first piping circuit <NUM> being controlled independent of second piping circuit <NUM>. The flow may be adjusted, for example, to bring the level or volume of the interface emulsion layer <NUM> within a predetermined range.

Water removed from vessel <NUM> through water outlet <NUM> may be routed to a recycling pump <NUM> for recycling the water back into the water layer <NUM>. Recycling pump <NUM> is preferably an ANSI/API centrifugal pump including duplex seals with barrier fluid and an expeller on the back of the impeller to protect seal integrity. No filtration is required in the recycle piping <NUM>.

In a preferred embodiment, after the initial lineout of desalter operation, the water flow rate through nozzles <NUM> is increased until interface rag layer <NUM> begins to upset. The water flow rate is then reduced until interface emulsion layer <NUM> begins to stabilize. Interface rag layer <NUM> is then monitored at the first tryline under the interface emulsion layer <NUM> and appropriate adjustments made to the water flow rate.

Referring now to <FIG> & <FIG>, an alternate embodiment of system <NUM> includes an oblong-shaped first piping circuit <NUM> and an oblong-shaped second piping circuit <NUM>, each equipped with nozzles <NUM>, <NUM> and independently controlled. The water flow through each nozzle <NUM>, <NUM> is preferably at a low flow rate in the range of about. <NUM> (<NUM> to <NUM> feet) per minute. First piping circuit <NUM> is placed below the interface emulsion layer <NUM> at a distance "h<NUM>" from the bottom <NUM> of vessel <NUM> in order to gently scrub the bottom of the interface emulsion layer <NUM>. Nozzles <NUM> are preferably oriented at an angle of between about <NUM>° and <NUM>° in a horizontal plane and in a vertical plane relative to centerline <NUM> of first piping circuit <NUM> (see <FIG> & <FIG>).

Second piping circuit <NUM> is placed at a distance "h<NUM>" from the bottom <NUM> of vessel <NUM> in order to gently fluidize the mud <NUM> from the bottom <NUM> of the vessel <NUM>. Unlike the arrangement of the prior art mud wash system <NUM> and its nozzles <NUM> (see <FIG>), second piping circuit <NUM> is an oblong-shaped circuit similar to that of first piping circuit <NUM>, with its nozzles <NUM> oriented oblique to the mud layer <NUM>. Nozzles <NUM> are preferably oriented at an angle of between about <NUM>° and <NUM>° in the horizontal plane relative to the centerline of second piping circuit <NUM> and at a downward angle of between <NUM>° and <NUM>° in the vertical plane. Preferably, there is no interference between the upper and lower toroids.

A system <NUM> as so far described above affects a number of performance issues typically associated with a separator vessel <NUM>. System <NUM> eliminates or minimizes episodic build-up of the interface emulsion layer <NUM>, reduces salt, reduces basic sediment and water (BS&W), eliminates rag layer separation, and eliminates reverse emulsion migration from the interface rag to the brine water layer.

Referring now to <FIG>, an embodiment of an interface emulsion control system <NUM> in accordance with this invention includes a radial eductor manifold <NUM> supporting a plurality of radial eductors <NUM>. The radial eductor manifold <NUM> is placed at a distance "h4 " from the bottom <NUM> of separator vessel <NUM>, below the interface emulsion layer <NUM>, and within the upper two-thirds portion of the water layer <NUM>. Each radial eductor <NUM> is oriented in a vertical plane relative to the radial eductor manifold <NUM> and the horizontal axis of the vessel <NUM> (see <FIG> & <FIG>). The embodiment also includes a recirculating pump <NUM> and recycle piping <NUM> to return a portion of the water removed from separator vessel <NUM> through water outlet <NUM> to the radial eductor manifold <NUM>, through the radial eductors <NUM>, and back into the water layer <NUM>. Recirculating pump <NUM> is preferably a centrifugal pump. Flow through the recycle piping <NUM> may be controlled by recycle valve <NUM>.

As shown in <FIG>, each radial eductor <NUM> has an outer eductor shell <NUM> that provides stability and support. A tubular eductor stem <NUM> is oriented vertically within the eductor shell <NUM> and has a plurality of tangential exit slots <NUM> that extend from the top to approximately the midpoint of the eductor stem <NUM>. The tangential exit slots <NUM> may be spaced at equal distances around the circumference of the eductor stem <NUM>. The radial eductors <NUM> may be spaced around the radial eductor manifold <NUM> so that the flow from each eductor <NUM> is independent of and does not affect the flow from the other eductors <NUM>. The radial eductors <NUM> may also be spaced so that they are separated from the interior wall of the separator vessel <NUM> by a distance of at least approximately <NUM> to <NUM> (<NUM> to <NUM> feet).

Water from the recycle piping <NUM> flows into each radial eductor <NUM> through the bottom of its inner bore <NUM>, up through the exit slots <NUM>, and leaves the radial eductor <NUM> through the exit portal <NUM> in the outer cap <NUM> of the radial eductor <NUM>. The water passes through the radial eductor <NUM> at a low flow rate, preferably in the range of about. <NUM> to <NUM> (<NUM> to <NUM> feet) per minute. As shown in <FIG>, the tangential exit slots <NUM> of the radial eductors <NUM> cause the water to exit the radial eductors <NUM> in a swirling flow pattern around each eductor <NUM>. This flow pattern gently agitates the lower surface of the interface emulsion layer <NUM>, helping to break down the interface emulsion layer <NUM> and reducing its accumulation within the vessel <NUM>. In a preferred embodiment, the water flow rate through radial eductors <NUM> is increased until the interface emulsion layer <NUM> begins to upset. The water flow rate is then reduced until interface emulsion layer <NUM> begins to stabilize.

Claim 1:
A method for controlling an interface emulsion layer (<NUM>) within an oil treatment vessel (<NUM>), the method comprising the step of:
injecting a water flow into a brine water layer (<NUM>) of the oil treatment vessel (<NUM>) through a plurality of inlets arranged about a manifold (<NUM>) oriented in a horizontal plane and located in the brine water layer (<NUM>);
characterised in that each of the inlets is a radial eductor (<NUM>) oriented in a vertical plane relative to the center line of the said manifold (<NUM>); and the water flow through the eductors into the brine water layer (<NUM>) causes a swirling flow pattern of a volume of water in the said brine water layer (<NUM>) around each radial eductor (<NUM>), the swirling flow pattern agitating a lower surface (<NUM>) of the interface emulsion layer (<NUM>) residing above the brine water layer (<NUM>).