WITHIN AN OIL-AND-WATER STREAM

BACKGROUND OF THE INVENTION

This invention generally relates to apparatuses, systems and methods used in crude oil desalting processes and, more specifically, to systems and methods used to inject dilution water into a crude oil stream in order to contact and coalesce entrained water within the stream.

The crude oil desalting process involves washing a crude oil stream with water having a low salt content (e.g. typically about 250 ppm or less) followed by electrostatic dehydration of the resulting mixture. The washing step involves mixing the low salt-content ("fresh" or "dilution") water with the crude oil stream so as to add energy into the stream and coalesce the dilution water with the brine water already entrained in the crude oil stream.

Mixing is accomplished through a mixing valve, static mixer, or some combination of the two. The degree of emulsification of the dilution water primarily depends on the pressure drop imparted by the valve. A normal design range for this pressure drop is in a range of 5 to 25 psi, with most valves or mixers operating below 15 psi. If too large of a pressure drop is created, the water droplets decrease to a size which makes them difficult to coalesce and remove in the downstream electrostatic dehydration process. A pressure drop control system, like that shown in FIG. 1, is used to control and operate the drop within the critical range.

Prior to the crude oil stream entering the mixing valve, it is advantageous to disperse the dilution water in the oil phase. This is typically done by way of a disperser which uses medium pressure spraying of the dilution water through holes on the dispersing tube of the disperser at a rate of 3-10% of oil flow rate . The spraying occurs in a direction perpendicular to the flow of the crude oil stream (see FIGS. 2A & B). Use of a static in-line mixer has also proved beneficial in accomplishing this dispersion.

One problem with the prior art dispersion system and method is, the dilution water droplets being sprayed or dispersed into the crude oil stream are greater than 1000 microns in size. In the invention described below, spray nozzles atomize wash water into the crude oil stream. The atomized water droplets are in a size range of 10 to 300 microns. This smaller wash water droplet size works to increase the contact efficiency with the brine droplets contained in the crude oil stream, thereby increasing desalting performance.

SUMMARY OF THE INVENTION

A system, method, and apparatus for desalting a crude oil stream includes an elongated, vertically oriented vessel that has an interior, piping structure arranged concentric to the vessel. The piping structure— which can be ring-shaped, cross-bar shaped, or any other shape preferable— has a plurality of spray nozzles oriented at a downward angle and receives wash water from a wash water inlet of the vessel. The piping structure may include more than one level of piping, and each level of piping may be fed by its own wash water inlet.

The spray nozzles may be located on different sides of the piping structure and, when more than one level is used, each level may have a different number of spray nozzles than the other levels. The spacing of the spray nozzles does not have to be even within or between levels and, if located on different sides of the piping structure, the nozzles do not have to be placed exactly opposite one another.

The pressure drop through each spray nozzle is preferably no greater than 300 psi and the nozzles preferably deliver a dilution water droplet preferably no larger than 300 microns in diameter.

An objective of this invention is to improve desalting performance by increasing the contact efficiency of the wash water with the brine droplets contained in the crude oil stream. Contact efficiency can be further increased by placing a mixing valve, static mixer, or some combination of the two downstream of the vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a prior art pressure drop control system.

FIG. 2A is a cross section view of a prior art mixing injector.

FIG. 2B is a view taken along section line 2B of FIG. 2A.

FIG. 3A is a preferred embodiment of a mixing vessel made according to this invention.

FIG. 3B is a view taken along section line 3B of FIG. 3A.

FIG. 4 is a front elevation view of a preferred embodiment of a nozzle spool made according to this invention.

FIG. 5 is a view of the nozzle spool taken along section line 5-5 of FIG. 4.

FIG. 6 is a top view of the nozzle spool of FIG. 4.

FIG. 7 is an isometric view of the nozzle spool of FIG. 4.

FIG. 8 is a schematic of a preferred embodiment of a system and method which makes use of a mixing vessel that houses the nozzle spool of FIG. 4.

FIG. 9 is top view of an alternate embodiment of the nozzle spool. The ring-shaped levels are replaced by a cross-bar shaped level.

Elements and Numbering Used in the Drawings and Detailed Description

5 Example of a commercial system

10 Mixing vessel

11 Spray nozzle

13 Centerline of 15

15 Spray pattern

17 Longitudinal centerline of 10

19 Inlet pipe

20 Nozzle spool

21 Spray nozzles

23 Wash water inlet

25 Wash water sub-stream

27 Wash water sub-stream

29 Wash water sub-stream

33 Flow meter

35 Wash water sub-inlet

37 Wash water sub-inlet

39 Wash water sub-inlet

45 Vertical pipe connected to 35

47 Vertical pipe connected to 37

49 Vertical pipe connected to 39

55 First or top level connected to 45

57 Second or middle level connected to 47

59 Third or bottom level connected to 49

61 Inner pipe or nozzle ring

63 Outer pipe or nozzle ring

65 Lateral pipe

67 Central longitudinal pipe

71 Spraying head or manifold

81 Crude oil inlet

83 Mixture outlet

85 Flow meter for 25

87 Flow meter for 27

89 Flow meter for 29

91 Flow meter

95 Valve for 25

97 Valve for 27

99 Valve for 29

103 Static mixer

105 Mixing valve

F Flow of oil-and-water stream in 10

P Positive displacement or centrifugal pump

S Interior space of 10 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 3A & B, a system and method for delivering dilution water within a crude oil stream includes a mixing vessel 10 with at least one spray nozzle 1 1 located within an interior space "S" of the vessel 10. The crude oil stream typically is an oil-dominant stream.

The spray nozzle 1 1 is arranged so that a centerline 13 of a spray pattern 15 of the dilution water droplets being delivered by the spray nozzle 1 1 is parallel to the longitudinal centerline 17 of the mixing vessel 10 (i.e., in a direction of flow "F" of the crude oil stream flowing through the mixing vessel 10). Therefore, the spray from each nozzle 1 1 is in a generally downward direction and into the downward flow F of the crude oil stream.

Mixing vessel 10 is a vertically oriented pipe located upstream of a mixing valve (not shown) and electrostatic dehydration process (also not shown). The spray nozzle 1 1 is plumbed to a horizontally oriented inlet pipe 19 which is in communication with a dilution water source (not shown). The spray nozzles 1 1 atomize the wash water from the dilution water source into the crude oil.

The spray nozzle 1 1 can be a first stage (or level) of spraying and at least one other spray nozzle 1 1 can be arranged downstream from and in an identical manner to the first-mentioned spray nozzle 1 1. The other spray nozzle 1 1 is a second stage (or level) of spraying. Multiple stages of spraying within the same mixing vessel 10 can be used as appropriate, as can multiple mixing vessels 10. Each stage within the vessel 10 preferably makes use of the same size of spray nozzle 1 1 and operates at the same pressures and rates. The number of spray nozzles 1 1 between inlet pipes 19 may be the same or vary as appropriate. The pressure drop through each spray nozzle 1 1 is preferably in a range of 50 psi to 300 psi, and more preferably in a range of 80 to 120 psi.

The spray nozzles 1 1 preferably deliver dilution water droplets in the range of 10 to 300 microns in diameter and, more preferably, in the range of 10 to 30 microns in diameter.

A preferred embodiment (FIG. 3A with a single nozzle) of the system was tested in a pilot unit and compared to similar tests run with a conventional disperser like a mix valve and a static mixer. The results show that, for the conventional mix valve and static mixer, the contact efficiency between the wash water droplets and the brine droplets contained in the crude oil stream is in the range of 40 to 50%. The contact efficiency for the system and method described above is in the range of 60 to 70%.

If the spray nozzle 1 1 is located upstream of a conventional disperser like a mix valve, the contact efficiency increases to 90%. Therefore, the spray nozzle 1 1 can be used along with a conventional mix valve, static mixer, or both to improve significantly improve contact efficiency (see e.g. FIG. 8 for an example commercial installation 5).

Referring now to FIGS. 4-7, an alternate embodiment of mixing vessel 10 includes a multi-level "nozzle spool" 20 having concentric inner and outer circular pipes or rings 61 , 63 on each level 55, 57, 59 of the spool 20. Other piping arrangements can include other shapes preferable, such as but not limited to a crossbar shaped arrangement like that shown in FIG. 9 in which lateral pipes 65 extend from a central longitudinal pipe 67 connected to a ring 63 and its respective wash water inlet 35, 37, or 39 (e.g., inlet 35 for first level 55). The spool 20 may also be a single level spool. Each level 55, 57, 59 is connected to three vertical pipes 45, 47, and 49, with one vertical pipe 45, 47 or 49 providing wash water to the level 55, 57, 59 and that level's rings 61, 63. Each ring 61, 63 supports a plurality of spraying heads or manifolds 71, each manifold 71 having a plurality of spray nozzles 21. Preferably, the first or top level 55 has 45% of the total spray nozzles 21, the second or middle level 57 has 30% of the total nozzles 21, and the third or bottom level 59 has 25% of the total nozzles 21.

Referring now to FIG. 8, the mixing vessel 10 has five ports: a crude oil inlet 81, three wash water inlets, 35, 37, 39, and a mixture outlet 83. Note that vessel 10 may have an internal pipe structure or arrangement other than that of nozzle spool 20 as shown in FIGS. 4-9. A positive displacement or centrifugal pump P pumps the wash water stream to the vessel 10 and guarantees the necessary working pressure for the spray nozzles 21. A flow meter 33 monitors the wash water stream.

Before entering the vessel 10, the wash water stream is divided into three sub- streams 25, 27, and 29 to allow a reasonable system turndown ratio. The sub-streams 25, 27 and 29 provide a wash water sub-stream to a respective vertical piping 45, 47 or 49 connected to the top, middle, or bottom level 55, 57, 59 (and the level's respective rings 61 ,63) of the nozzle spool 20.

Each inlet stream or piping 25, 27, 29 is equipped with a respective flow meter 85, 87, 89 and an on-off valve 95, 97, 99. The flow meter 85, 87, 89 monitors the sub-stream line 35, 37, 39 for plugged or leaking spray nozzles 21. The on-off valve 95, 97, 99 is used to direct the flow to each ring 61, 63 on the respective level 55, 57, 59 to maintain the pressure drop through the nozzles 21.

Similar to spray nozzle 1 1, spray nozzles 21 atomize the wash water from the dilution water source into the crude oil stream. The pressure drop through each spray nozzle 21 is preferably in a range of 50 psi to 300 psi, and more preferably in a range of 80 to 120 psi. The spray nozzles 21 preferably deliver dilution water droplets in the range of 10 to 300 microns in diameter and, more preferably, in the range of 10 to 30 microns in diameter. The spray from each nozzle 21 is in a general downward direction and into the crude oil flow as it flows in a downward direction through the vessel 10.

A crude oil stream enters the system through a crude oil inlet 81. The crude oil flow rate is monitored by a flow meter 91. The mixing vessel 10 could be bypassed when necessary to route the crude oil flow to static mixer 103 and mixing valve 105.

Vessel 10, when in use, represents the washing step located upstream of a separator vessel such as an electrostatic dehydration unit. The vessel 10 may replace the typical washing step described in the Background section or may be used in combination with it (see e.g., FIG. 8). One or more vessel 10's may be used prior to the mixed oil-and-water stream being routed to downstream equipment such as dehydrator or desalter vessel.

The preferred embodiments of the system and method described above are not all of the possible embodiments of the invention. The scope of the invention is defined by the following claims, including elements or steps which are equivalent to those recited.