US20140238817A1

US20140238817A1 - Oil-water separator

Info

Publication number: US20140238817A1
Application number: US14/270,266
Authority: US
Inventors: Hassan M. Badr; Wael H. Ahmed
Original assignee: King Fahd University of Petroleum and Minerals
Current assignee: King Fahd University of Petroleum and Minerals
Priority date: 2012-07-09
Filing date: 2014-05-05
Publication date: 2014-08-28

Abstract

The oil-water separator is installed in a substantially horizontal crude oil pipeline for separating water from the oil and water mix. The separator includes a depending vortex and settling chamber depending from the pipeline, the segment of the pipeline and the separator defining a generally T-shaped configuration. Oil and water flowing through the pipeline drop into the chamber as it flows through the pipeline and over the chamber. The denser water tends to settle into the bottom of the chamber, while the lighter oil is entrained back into the flow through the pipeline. A sensor detects water collected in the bottom of the chamber and provides a signal to open a drain valve when sufficient water has been collected. While only a single separator serves to collect a substantial fraction of water, a series of separators may be installed along the pipe to remove more water from the oil.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent application Ser. No. 13/544,623, filed on Jul. 9, 2012.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to devices for separating dissimilar fluids from one another, and particularly to an oil-water separator comprising a vortex or swirl chamber depending from a delivery pipe.
2. Description of the Related Art
Virtually all output from oil wells comprises a mixture of three phases of material, i.e., solid particulates in the form of sand and the like, a liquid mix of crude oil and water, and gas or gases, primarily methane and carbon dioxide. (It should be noted here that in the petroleum industry, the term “phase” is used to describe a single type of liquid issuing from a well, i.e., oil and water are referred to as a liquid comprising an oil phase and a water phase.) The solids and gas are relatively easy to separate from the liquid fraction of the well output, as they comprise two separate physical phases. It is somewhat more difficult, and generally requires more energy, to separate materials belonging to a single physical phase (e.g., methane and carbon dioxide gas phase mix, or oil and water liquid phase mix) from one another. Thus, it is impracticable to separate oil and water from one another at a remote wellhead, given the present state of the art.
Accordingly, while gases and solid particulates are generally separated from the liquid phase at or near the wellhead in the petroleum field, the liquid phase (comprising a mixture of oil and water) is commonly transported via pipeline over some distance to a central refinery or processing plant where they are separated. The pumping of an oil and water mix through a pipeline demands relatively large amounts of energy, due to relatively high pressure drops in the line resulting from the oil and water mix. In any event, the movement of the mass of the water fraction through the pipeline requires additional energy over and above that required to move only the oil fraction of the mix. The alternative is to provide a settling pool or the like near the wellhead where the denser water will settle out beneath the lighter oil. However, the additional time that this requires is also impracticable.
Thus, an oil-water separator solving the aforementioned problems is desired.

SUMMARY OF THE INVENTION

The oil-water separator comprises a generally horizontal length of pipe having an inlet end and an opposite outlet end, and a vortex and settling chamber extending below the pipe. As the water and oil mixture encounters the chamber, it drops into the chamber. The dynamic energy of the water and oil mix is dissipated in the chamber in the form of turbulence and eddies. The denser water settles out of the lighter oil due to the force of gravity as their velocities slow. The lighter oil, being nearer the upper end of the chamber, is entrained into the moving horizontal stream of oil and any remaining water passing over the vortex and settling chamber. This configuration requires little more power than that required to pump the oil and water mix through the pipeline, and actually results in a net reduction of required power due to the removal of the water from the liquid phase mix.
The relative quantities of water and oil in the chamber may be determined by a conventional capacitance sensor or other conventional means. The output of the sensor is used to control a drain valve at the bottom of the chamber to release the collected water when it is determined that the water collected in the bottom of the chamber is substantially free of oil. The water may be dispensed as a waste product or may be used for other purposes, with or without some additional processing. In any event, any additional processing required to gain the water purity required for the desired use will be much easier to attain and will be much less energy intensive due to the initial removal of the greater majority of the oil by the vortex and settling chamber.
Although a substantial amount of water can be removed from the oil passing through the pipeline by means of a single vortex and settling chamber, it will be seen that the installation of two or more such chambers spaced along the length of the pipeline will result in additional incremental amounts of water being removed from the oil as it travels through the pipeline. As the vortex and settling chambers are relatively economical to install and operate, any number of such chambers may be installed along a length of pipeline in accordance with the degree of purification of the oil desired. The removal of the greater majority of the water from the oil has further benefits in that it not only reduces the energy required to pump the liquid through the pipeline, but it also reduces corrosion in the pipeline and other components (e.g., pumps, valves, etc.) by removal of the water.
In an alternative embodiment, gas is further removed from an oil-water-gas mixture. Water is first separated from the mixture of oil and gas, as described above, but in this embodiment an additional inverted vortex separation chamber is added. The inverted chamber extends above the pipeline and is positioned downstream from the corresponding combined vortex and settling chamber. The pipeline and the inverted vortex separation chamber form a substantially inverted T-shaped configuration. The inverted vortex separation chamber has an open lower end in fluid communication with the elongate, level pipeline such that the mixture of oil and gas remaining after separation of water from the flow enters the inverted vortex separation chamber, where it is separated into oil and gas. The gas has a density less than that of the oil, such that gas rises within the inverted vortex separation chamber, and the oil exits through the lower open end, back into the elongate, level pipeline
These and other features of the present invention will become readily apparent upon further review of the following specification and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side elevation view of a pipeline having a single oil-water separator according to the present invention disposed therein, illustrating its configuration.

FIG. 2 is a schematic side elevation view of a pipeline having a plurality of oil-water separators according to the present invention disposed therein for multi-stage phase separation in a single pipeline.

FIG. 3 is a schematic side elevation view of a three-phase oil-water-gas separator according to the present invention.

Similar reference characters denote corresponding features consistently throughout the attached drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The oil-water separator is a passive unit that serves to separate entrained water from crude oil being transported through a delivery pipeline. The device does not require any electrical or other power for its basic operation, other than for the operation of a low power sensor and the periodic operation of a water drain valve, and produces only a minimal pressure drop in the pipeline. The device is thus well suited for remote installation at or near a wellhead to separate the crude oil fraction from the oil-and-water liquid issuing from the wellhead, thereby providing greater economy in the transport of the crude oil.
FIG. 1 of the drawings provides a schematic elevation view of pipeline having an exemplary single oil-water separator 10 disposed therein. The separator 10 includes an elongate, substantially horizontal pipeline 12 having an inlet end 14 and an opposite outlet end 16. The inlet end 14 and the outlet end 16 are coaxial so that the section of the pipeline 12 shown in the drawing defines a straight or rectilinear flow path for the delivery of the liquids or fluids contained therein. It will be seen that the pipeline 12 may extend for some distance. The inlet and outlet ends 14 and 16 depicted in the drawings indicate only an inflow or upstream end and an opposite outflow or downstream end that would be connected in a much longer pipeline.
The pipeline 12 has a vortex and settling chamber 18 (also referred to as a separation chamber) depending therebelow (i.e., branching off the pipeline 12 normal thereto). The internal volume of the chamber 18 communicates with the internal volume of the pipeline 12. The longitudinal axis P of the pipeline 12 and the longitudinal axis C of the chamber 18 preferably form a right angle A, i.e., the chamber 18 is normal to the pipeline 12 to form a substantially T-shaped configuration for the pipeline 12 and chamber 18 assembly. However, the chamber 18 may be installed to the pipeline 12 with some other angle therebetween, if so desired. It will be noted that the vortex and settling chamber 18 may be formed by inserting a Tee connector in the pipeline 12, so that the oil-water separator 10 would have the same configuration shown in FIG. 1.
The vortex and settling chamber 18 has a substantially closed bottom end 20, with the exception of a selectively operable water drain valve 22 installed therein and discussed further below. The height or vertical depth of the chamber 18 may be adjusted as desired, depending upon the rate of flow of liquid through the pipeline 12, the width or diameter of the chamber 18 and pipeline 12, and other factors. In the exemplary separator 10 depicted in FIG. 1, the vortex and settling chamber 18 has a width or diameter D, with a vertical depth or height of 2+D, i.e., somewhat more than twice the diameter D. It will be noted that the vortex and settling chamber 18 is a cylindrical chamber, i.e., it has no conical or frustoconical portion, but is simply a closed (or closeable) cylindrical side arm that branches off the pipeline 12 or main flow line of a Tee connector.
The oil and water separator 10 operates automatically to collect water in the vortex and settling chamber 18 as the mixture or slurry of crude oil and water flows through the pipeline 12. As the oil and water mix encounters the chamber 18, the discontinuity of the open mouth of the chamber in the main pipeline 12 produces a turbulent swirl or vortex within the chamber 18. As water is more dense than oil, the denser water W will tend to flow to the outside of the vortex, i.e., closer to the bottom of the chamber 18 at the lower portion of the vortex. The lighter oil O will tend to rise, where it is again entrained by the oil and water mixture flowing through the pipeline 12. Thus, there are two physical principles in play to separate the water from the oil, i.e., the formation of a vortex within the chamber 18, and gravity acting on the denser water to cause it to settle to the lower portion of the chamber 18.
As the oil and water slurry or liquid flows through the pipeline 18 and over and into the vortex and settling chamber 18, water will collect in the lower portion of the chamber 18. Accordingly, some means must be provided for periodically draining any water that collects in the vortex and settling chamber 18. This is accomplished by an oil-water fraction sensor 24 that is disposed in the interior of the chamber 18, or at least communicates with the interior of the chamber 18. The sensor 24 is preferably a conventional capacitance-type sensor, but other sensors using other principles of operation may be used. Such two-phase sensors are well known in the art. As the output of the sensor 24 is an analog signal, an analog-to-digital electronic control 26 communicates electronically with the sensor 24 and sends a signal the drain valve controller 28 (e.g., a microcontroller circuit, digital signal processor circuit, etc.). The drain valve controller 28 controls the drain valve 22 (which may be a normally closed solenoid valve that can be opened and closed by applying the appropriate voltage or current to the coil) to open when the water collected in the bottom of the vortex and settling chamber 18 is determined to be substantially free of oil, in response to the signal from the sensor 24. When some predetermined or threshold fraction of oil is detected, the sensor 24 provides a corresponding signal and the controller 28 closes the water drain valve 22. The water drained from the drain valve 22 may be dispensed at the point of drainage, if it is sufficiently clean and no other environmental concerns exist. However, water is a somewhat valuable commodity in many oil production locales, and the water drained from the chamber 18 may be collected for further use or refinement by a water collection and delivery line 30 extending from the valve 22, if desired.
The oil-water separator 10, when configured in a single stage as shown in FIG. 1, may not be able to provide one hundred percent separation of the oil and water fractions typically found in the crude oil flowing through a pipeline. However, it does remove a large fraction of the water typically mixed with the crude oil as delivered from the well. Nevertheless, in many instances the removal of a larger fraction of the water from the oil is desired. Accordingly, an oil-water separator system comprising a series of mutually spaced apart vortex and settling chambers 18 installed along a pipeline 12 is illustrated schematically in FIG. 2 of the drawings, which shows three chambers 18 and the corresponding portions of the pipeline 12, comprising a plurality of oil- water separators 10 a, 10 b, and 10 c. Each of the oil- water separators 10 a, 10 b, and 10 c of FIG. 2 is substantially identical to the oil-water separator 10 of FIG. 1, discussed in detail further above. Accordingly, no further discussion of the structure and details of operation of the oil-water separators 10 a through 10 c need be provided here. The advantage of the plurality of oil-water separators 10 a through 10 c is that the second separator 10 b will remove a large part of any remaining water that passes by the first separator 10 a, and the third separator 10 c will remove a large part of the small fraction of water that still remains after passing the second separator 10 b. The illustration of FIG. 2 showing three such oil-water separators 10 a through 10 c is exemplary. It will be seen that any practicable number of such separators may be installed along a pipeline 12 to form a multi-stage separator, resulting in the removal of more of the water fraction from the oil and water mix or slurry flowing through the pipeline 12. The water collected in each vortex and settling chamber 18 may be drained into the environment, or collected and transported to another location for further use, purification, disposal, etc. by a common water collection and delivery line 30 that is connected to each of the drain valves 22 of the chambers 18.
In the alternative embodiment of FIG. 3, the oil-water separator 100 includes an additional gas separation portion. Similar to the embodiments described above, the oil-water separation portion includes an elongate, level pipeline 112 having an inlet end 114 for receiving an oil-water mixture and an outlet end 116, positioned opposite the inlet end 114. The outlet end 116 outputs oil separated from the oil-water mixture, as in the previous embodiments. At least one combined vortex and settling chamber 118 (also referred to as a separation chamber) extends normal to and below the pipeline 112. In FIG. 3, two such chambers 118 are shown, although it should be understood that any desired number of separate vortex separation chambers 118 may be used.
The pipeline 112 and each combined vortex and settling chamber 118 form a substantially T-shaped configuration. Each combined vortex and settling chamber 118 has an open upper end in fluid communication with the elongate, level pipeline 112 such that the oil-water mixture entering each combined vortex and settling chamber 118 is separated into oil O and water W. As in the previous embodiments, the oil O has a density less than that of the water W, such that the water W remains within each combined vortex and settling chamber 118 as the oil O exits through the open upper end, back into the elongate, level pipeline 112.
Also similar to the previous embodiments, each combined vortex and settling chamber 118 has a bottom end having a water drain valve 122 disposed thereon for draining the water through a delivery line 130. Further, an oil-water fraction sensor 124 is disposed in each combined vortex and settling chamber 118, or at least communicates with the interior of the chamber 118. The sensor 124 is preferably a conventional capacitance type sensor, but other sensors using other principles of operation may be used.
As the output of the sensor 124 is an analog signal, an analog-to-digital electronic control 126 communicates electronically with the sensor 124 and sends a signal to the drain valve controller 128. The drain valve controller 128 controls the drain valve 122 to open when the water collected in the bottom of the vortex and settling chamber 118 is determined to be substantially free of oil, in response to signals from the sensor 124. When some predetermined fraction of oil is detected, the sensor 124 provides a corresponding signal and the controller 128 controls the water drain valve 122 to close.
In addition to the above-described oil-water separation, the separator 100 further includes a gas separation portion for separating gas from the oil returned to pipeline 112, following water separation therefrom. As shown in FIG. 3, an inverted vortex separation chamber 140 extends normal to and upward from the pipeline 112 downstream from each vortex and settling chamber 118, i.e., there is one inverted vortex separation chamber 140 positioned downstream from each vortex and settling chamber 118 in alternating fashion. When the flow of fluid through the pipeline 112 passes by the open mouth of the inverted separation chamber 140, the opening in the wall of the pipeline and the shear forces of the fluid flow cause a vortex to form at the mouth of the inverted separation chamber 140, which at least partially rises in the chamber 140. Gas dissolved or otherwise mixed with the oil is separated from the oil within each inverted vortex separation chamber 140. Since gas is less dense than the oil, the gas rises within and escapes from the denser oil. The gas is collected in an upper portion of each inverted vortex separation chamber 140, as shown. The remainder of the fluid, primarily oil having smaller remaining quantities of water and gas entrained therein, continues to flow through the pipeline 112 past the inverted vortex separation chamber 140 to the next pair of separation chambers 118, 140, if any.
Similar to the operation of the oil-water separation portion, a gas drain valve 132 is disposed on the upper end of each inverted vortex separation chamber 140 for releasing the collected gas through a gas delivery line 142. Further, a multi-phase flow sensor or an oil-gas fraction or void fraction (the void fraction is the fraction of gas in the three-phase fluid) sensor 134 is disposed in each inverted vortex separation chamber 140, or at least communicates with the interior of the chamber 140, The sensor 134 is preferably a conventional capacitance type sensor, but other three-phase (oil, gas, water) or void fraction sensors known in the art using other principles of operation may be used.
As the output of the sensor 134 is an analog signal, an analog-to-digital electronic control 136 communicates electronically with the sensor 134 and sends a signal to the gas drain valve controller 138. The gas drain valve controller 138 controls the gas drain valve 132 to open when the fraction of gas separated from the fluid in the chamber 140 is determined to be above a predetermined threshold level according to the signal from the sensor 134, and to close otherwise.
It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.

Claims

We claim:

1. An oil-water separator, comprising:

a pipeline having an input end and an output end coaxial with the input end, the pipeline defining a rectilinear fluid flow path;

a cylindrical water separation chamber branching off the pipeline normal thereto, the water separation chamber having an interior, a first end opening into the pipeline, defining an open mouth of the chamber, and an opposing second bottom end;

a drain valve mounted at the bottom end of the chamber, the drain valve having an open position permitting a fluid to drain out of the separation chamber, and a closed position closing the second end of the separation chamber;

an oil-water fraction sensor communicating with the interior of the water separation chamber, the sensor generating a signal corresponding to the fractions of oil and water in the fluid in the water separation chamber; and

a drain valve controller connected to the drain valve and the oil-water fraction sensor, the controller controlling the drain valve to move to the open position when the signal from the sensor corresponds to a level below a threshold fraction of oil in the fluid, and to move to the closed position when the signal from the sensor corresponds to a level above a threshold fraction of oil in the fluid;

wherein the oil-water separator is adapted for installation with the pipeline extending horizontally and the water separation chamber extending downward from the pipeline, whereby a mixture of oil and water flowing through the pipeline forms a vortex at the open mouth of the water separation chamber, the oil and water separating in the chamber, the water falling into the water separation chamber towards the drain valve and the oil rising out of the water separation chamber to flow in the pipeline.

2. The oil-water separator as recited in claim 1, wherein the separation chamber has a width and a depth, the depth being at least twice the width.

3. A multi-stage oil-water separator, comprising a plurality of the oil-water separators according to claim 1, the oil-water separators being spaced apart in the pipeline for providing multiple successive stages of oil-water separation.

4. The oil-water separator according to claim 1, wherein said pipeline and said water separation chamber comprise an integrated Tee connector unit adapted for mounting in an oil transport and delivery line.

5. The oil-water separator according to claim 1, further comprising a gas separator for separating gas from two-phase oil-gas fluid flows and three-phase oil-water-gas fluid flows, the gas separator having:

a cylindrical gas separation chamber branching off the pipeline normal thereto spaced apart from and following said water separation chamber in the fluid flow path, the gas separation chamber being inverted and extending from the pipeline in a direction 180° opposite said water separation chamber, the gas separation chamber having an interior, a first end opening into the pipeline, defining an open mouth of the gas separation chamber, and an opposing second end closing the gas separation chamber;

a gas drain valve mounted at the second end of the chamber, the gas drain valve having an open position permitting a fluid to drain out of the gas separation chamber, and a closed position closing the second end of the gas separation chamber;

a multi-phase flow sensor communicating with the interior of the gas separation chamber, the sensor generating a signal corresponding to the fractions of oil and gas in the fluid in the gas separation chamber; and

a drain valve controller connected to the gas drain valve and the multi-phase flow sensor, the controller controlling the gas drain valve to move to the open position when the signal from the sensor corresponds to a level above a threshold fraction of gas separated from the fluid, and to move to the closed position when the signal from the sensor corresponds to a level below a threshold fraction of gas in the gas separation chamber;

wherein the oil-water separator is adapted for installation with the pipeline extending horizontally and the water separation chamber extending downward from the pipeline, followed by the gas separation chamber extending upward from the pipeline;

whereby a mixture of oil, water, and gas flowing through the pipeline forms a vortex at the open mouth of the water separation chamber, the water separating from the mixture in the water separation chamber, the water falling into the water separation chamber towards the drain valve and the oil-gas mixture rising out of the chamber to flow in the pipeline; and

whereby the oil-gas mixture flowing through the pipeline forms a vortex at the open mouth of the gas separation chamber, the gas separating from the mixture in the gas separation chamber, the gas rising into the gas separation chamber towards the gas drain valve and the remaining fluid from the mixture continuing to flow in the pipeline.

6. A multi-stage oil-water separator, comprising a plurality of the oil-water separators according to claim 5, said water separator chambers and said gas separator chambers being spaced apart and alternating in the pipeline for providing multiple alternating successive stages of oil-water and oil-gas separation.

7. The oil-water separator according to claim 5, wherein said pipeline, said water separation chamber, and said inverted gas separation chamber comprise an integrated unit adapted for mounting in an oil transport and delivery line.