US3527697A

US3527697A - Method of mixing and treating a hydrocarbon liquid to form a readily coalescing dispersion

Info

Publication number: US3527697A
Application number: US733662A
Authority: US
Inventors: Frederick D Watson
Original assignee: Petrolite Corp
Current assignee: Baker Petrolite LLC
Priority date: 1968-05-31
Filing date: 1968-05-31
Publication date: 1970-09-08
Anticipated expiration: 1987-09-08

Description

`vSept. 8, 1970 F. D. wATsoN METHOD QF MIXING AND TREATING A HYDROCARBON LIQUID TO FORM A READILY COALESCING DISPERSION 2 Sheets-Sheet 1 Fled lay 51. 1968 Sept. 8, 1979 F, D, WATSON 3,527,697

METHOD 0F MIXING AND TREATING A HYDROCARBON LlQUID To FORM A READILY COALESCING DISPERSION Filed May 3l, 1968 2 Sheets-Sheet 2 Heder/o4 l/l/aJof? m' www12.

ATTORNEY United States Patent O U.S. Cl. 208-267 4 Claims ABSTRACT OF THE DISCLOSURE This specification discloses: An orifice mixer and a method for intimately dispersing an aqueous treating liquid within a hydrocarbon liquid by their concurrent passage through a plurality of mixing stages. Each mixing stage has a certain shear effect on the fluids being mixed, and the number of stages provides a desired level of mixing energy. In each mixing stage, the liquids fiow through an open area formed by a plurality of like-size openings which have one dimension residing between 0.0312 and 0.250 inch. The total open area (and the number of openings) may be defined by formulas which are contingent upon the pressure differential, or head, which exists across each mixing stage. Preferably, the open area is provided by a plurality of like-size round openings.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to the dispersing of an aqueous treating liquid within a liquid hydrocarbon. More particularly, it relates to an orifice mixer and a method which provide mixing functions in response to the pressure differential created by the flow of fluids being mixed through small openings.

Description of the prior art A certain reaction between admixed immiscible liquids may require a large surface of contact and a very short contact time. In situations With a prolonged contact time, the desired reaction is accompanied by a multiplicity of undesired side effects such as polymerization, sludging, oxidation and carbonization. A minimum contact time and maximum surface of contact is particularly important in the treatment of liquid hydrocarbons with small amounts of acids, caustic and other aqueous treating liquids. Then, the resulting mixture, or dispersion, is separated by influence of an electric field. Reference may be taken to the patent to R. B. Perkins, Ir., U.S. No. 2,447,530 for a description of process situations of this tYP@ There are many mixers available for intimately contacting immiscible liquids. Examples of these mixers are: expansion valves, square-angle bends, orifice-plate columns, bafe-plate columns, perforated buckets, various mechanically driven paddle mixers, jet or nozzle mixers and pumps. The pressure-loaded expansion valve has been extensively utilized.

These mixers cannot be readily controlled in both the contact time between the immiscible liquids and the fineness (or contact surfaces) of the dispersed liquid droplets.

In the acid treatment and following caustic neutralization of residual acidity in liquid hydrocarbons, maximum utilization of the treating reagents and the complete neutralization of acid treated hydrocarbon have been diflicult to achieve. The rate of transference, or reaction, of a substance (acid, caustic, etc.) between droplets of ICC one liquid dispersed within an immiscible liquid, all things being equal, is proportional to the surface of contact between the liquids. In conventional mixers, the time of contact required to complete transference of the substance is therefore intimately associated with neness of the dispersion. As a result, a short time of contact is obtained only by very fine dispersions, which dispersions are diicult to resolve into their respective liquid phases.

In the present invention, droplet sizes in the dispersion are controlled by a novel orifice mixer and a method so as to be readily separated, especially Within an electric coalescer or treater. Repeated renewal of the surfaces of contact about these droplets produces an effective time of contact equivalent to using droplets of much ner sizes.

Orifice mixers have been employed for mixing immiscible liquids. However, these prior-art orifice mixers imparted a certain level of mixing energy to the liquids being mixed by controlling the orice sizes to obtain a desired pressure drop in liquids flowing through the orificeS. As a result, the orifice mixer had large openings for large-volume streams and small openings for smallvolume streams. While the mixing energies of these devices were comparable for the same time of contact, the surfaces of contact between the large and small opening versions were not.

SUMMARY OF THE INVENTION In accordance with this invention, an aqueous treating liquid is dispersed Within a liquid hydrocarbon in an orifice mixer. The liquids are passed concurrently in the mixer through a plurality of mixing stages which provide a certain level of mixing energy for intimately and successively contacting the liquids. The liquids fiow through each mixing stage under controlled shear conditions for dispersing the aqueous treating liquid into regulated droplet sizes within the hydrocarbon liquid. Each mixing stage has an open area (transverse to liquid How therethrough) which provides the shear conditions. The open area is formed by a plurality of like-size openings which have one dimension between 0.0312 and 0.250 inch. The open area has specific physical relationships encompassed Within formula definitions in certain embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a ow diagram of a hydrocarbon treating plant in which the orifice mixer and method of the present invention may be employed;

FIG. 2 is an enlarged elevation of the orifice mixer shown in FIG. 1;

FIG. 3 is a cross-section taken along line 3 3 of the orifice mixer shown in FIG. 2; and

FIG. 4 is a cross-section taken along line 4-4 of the orifice mixer shown in FIG. 2.

In these figures, like structures will be designated with identical referenced numerals.

DESCRIPTION OF SPECIFIC EMBODIMENTS Referring to the drawings, FIG. 1 illustrates a flow diagram of a hydrocarbon treating plant in which the present invention may be used to great advantage. However, the present invention may be used in other plants, if desired. The plant provides for acid and caustic treatment, in succession, of a liquid hydrocarbon stream at a refinery. More particularly, the feed to the plant is a liquid n-parain which is supplied through a pipe line 11. The n-parafn feed includes relatively light hydrocarbons which have a maximum boiling point of less than 500 F. and a viscosity of about 1 centipoise. The n-parafin passes through a flow control valve 12 into an acid mixer 14. The valve 12 is associated with a ilow controller and is operated by back pressure to regulate the ow of the n-paraffin stream to be treated. Concentrated sulfuric acid in a small amount of about by weight is introduced through line 13 into the n-paraffin feed upstream of the acid mixer 14. The n-parafiin and the sulfuric acid are intimately mixed within the acid mixer 14. The acid mixer 14 may be of conventional construction, and in one plant, was a motor-driven, impeller-type IIllXCI'.

The acid-hydrocarbon mixture iiows from the acid mixer 14 into an electric coalescer or treater 15 where it is resolved into separate hydrocarbon and acid phases. The electric treater 15 may be of any suitable design adapted to coalesce the dispersed acid droplets from the continuous hydrocarbon phase. More particularly, the electric treater 15 employs one or more energized electrodes 16 which produce an electric -field for resolving dispersions. In the electric iield, the dispersed acid coalesces and settles to the bottom of the treater 15. The settled acid is removed from the treater 15 through line 17. The relatively acid-free n-parain is removed from the treater 15 as an overhead product through line 18.

Although the electric treater 15 produces a substantially acid-free n-paraffin phase, an undesired residual amount of acid may yet remain in it. For example, the hydrocarbon overhead product from the electric treater 15 in one plant had a residual acidity of about 1000 parts per million (as sulfuric acid). It is most desirable that this acidity be removed from the n-paraiiin stream because of resulting corrosion problems, and for other reasons.

The excess acidity in the n-paran stream may be removed by intimate and thorough contacting with a caustic solution. For example, caustic solution is passed in a small amount of about 5% by weight through a pressure controlled valve 19 into the line 18 to commingle with the n-paraffn overhead from the electric treater 15. The necessary contacting of the caustic solution with the n-parafiin is obtained within a caustic mixer 21. The caustic mixer 21, in one plant, was a motor-driven, impeller-type mechanical mixer. For complete neutralization of the residual acidity, the caustic mixer 21 provided prolonged intimate mixing of the caustic solution and the n-parafiin stream. Although sufficient contacting between the immiscible liquids could eventually be obtained for neutralizing the residual acidity, the contact time or residence in the caustic mixer 21 became commercially excessive. In many instances, these mixing conditions also resulted in such a fine dispersion of the injected caustic solution in the n-parain that it is very difiicult to separate the mixed liquids.

In order to effect a separation of the intimately mixed liquids, they are passed through line 22 into an electric treater 23. The electric treater 23 is of any suitable design in which one or more energized electrodes 24 provide an electric field to resolve the dispersed caustic solution from the n-parafiin phase. The caustic-freed n-parafiin is removed as an overhead from the electric treater 23 through the line 26. The coalesced caustic solution is removed through the line 27. An automatic control valve 28 in the line 26 maintains a suitable back pressure on the n-parafiin efiluent from the treater 23. A manual control valve 28a may be used for this purpose, if desired. The n-parafl'in in the line 26 is sent to a suitable utilization such as to a product storage tank 29.

Mixing of an immiscible treating liquid into a liquid hydrocarbon may be obtained with greater facility by using an orlice mixer 31 of the present invention. The orifice mixer 31 having a plurality of mixing stages, is installed in parallel with the caustic mixer 21. Blocking valves 32 and 33 isolate the caustic mixer 21 from

lines

18 and 22 so that :Ilow may be directed only through the orifice mixer 31. Blocking valves 34 and 36 isolate the orifice mixer 31 so that fiow may be directed only through the caustic mixer 21. Pressure gauges 37 and 38, and

sample points

20, 30, 39, and 41, can be provided in

lines

18, 20, and 22 so that operation of the orifice mixer 31 may be monitored. The orifice mixer 31 is constructed to provide the desired intimate mixing of the caustic solution with the n-paraffin stream for substantially complete neutralization of residual acidity. In the orifice mixer 31, a very short contact time occurs during mixing of the caustic solution with the n-parafiin stream so that side reactions such as sludging, oxidation, etc., are reduced to a minimum. As a result, optimum low acidity is obtainable for the n-paratlin going to storage tank 29.

The orifice mixer 31 can be formed of any suitable construction as will be apparent from the present description and by reference to FIGS. 2, 3 and 4. In one embodiment the mixer 31 is formed of end-

members

42 and 43 which may be formed of pipe reducers. These

members

42 and 43 carry fianges 42a and 43a which are interconnected with the lines 18 and `22, respectively. 'Ihe ange members 42b and 43b, tive orifice discs 44, and four sealing rings 46, contain aligned openings in which studs 47 are received.

Nuts

48 and 49 are threaded over lock washers 48a and 49a onto the studs 47 to compress the sealing surfaces 46a of sealing rings 46 into fluid-tight engagement with the orifice discs 44 and the flanges 42h and 43b.

The orifice mixer 31 is usually provided with a body which has a cylindrical ow passageway extending between an inlet and outlet connectable to

lines

18 and 19. The orifice discs 44 are positioned transverse to the longitudinal axis of the flow passageway, and preferably, at equal spacings from one another. Each disc 44 contains a plurality of openings 49 which preferably are round and not aligned in adjacent discs. Substantially all of the liquids flowing through the mixer 31 pass through these openings 49. The openings 49 in the mixer 31 are arranged according to the present invention to have a particular dimension. Also, the openings 49 may have a total area open to liow which is defined by formulas to be hereinafter discussed.

The orifice discs 44 can be constructed of any suitable rigid material. They may be formed of a metal such as steel, or a plastic such as polypropylene. The like-size openings 49 may be round, formed of narrow slots or spiral cuts, or other shapes, in the orifice discs 44.

The openings 49 have one dimension, which is measured across the narrowest part of the openings, residing between 0.0312 and 0.250 inch. With openings 49 having these dimensions, the amount of shear applied in a mixing stage disperses immiscible aqueous treating liquid within a liquid hydrocarbon into regulated droplet-sizes which are readily separated or coalesced in an electric field. The dispersed droplets maintain their sizes upon passage through all subsequent mixing stages. As a result, the mixer 31 cannot produce the extremely fine dispersons which are so difiicult to separate. Thus, in the plant described relative to FIG. l, a very small amount of caustic solution can be readily dispersed into regulated droplet sizes in the n-parafiin stream. The resulting dispersion is readily coalesced in the electric treater 23 to produce a caustic-free hydrocarbon product.

The total open area of the openings 49 is correlated to the head developed across the orifice disc 44. The orifice mixer 31 operates with a pressure drop between its inlet and outlet which is equal to the total heads across all the orifice discs 44. More particularly, the open area, designated A, is taken in a plane normal to the liquid flow which passes through each orifice disc 44. 'I'he open area A is defined by the formulas:

Q=Ac\/: V=Q/A wherein:

Q=volumetric flow rate through each disc 44; A=tota1 area open to fiow through each dise 44; C=average orifice discharge constant for the open area A; h=fluid head developed across each disc 44;

,gr-acceleration of gravity; and V=the velocity of uid flow through each disc 44.

Where the openings 49 are round, the approximate number n of such openings may be determined from the formula n=A/a wherein A is the total area open to ow through each of the orifice discs 44 and a is the area of one opening 49.

In the mixer 31, each orifice disc 44 represents a mixing stage. The immiscible caustic solution is dispersed in one mixing stage into a certain range of droplet sizes within the n-parafin. Subsequent mixing stages do not change these droplet sizes. However, these mixing stages renew the surfaces of contact between the dispersed droplets and the hydrocarbon. The minimum number of mixing stages must provide renewal of the surfaces of contact sufficient to complete the utilization of the aqueous treating liquid. Additional mixing stages above such minimum number do not assist nor detract from the desired result.

The number of orifice discs 44 obviously is contingent upon the fluid head developed across each of them, and upon the operating pressure drop t between the inlet and outlet of the mixer 31. Stated in another manner, the orifice mixer 31 has at least two mixing stages which are provided by orifice discs 44; and additional mixing stages as required to produce a certain level of mixing energy for intimate contacting the droplets of a dispersed first liquid into an immiscible second liquid by their concurrent passage through subsequent orifice discs 44.

The number of mixing stages or discs 44 can be determined experimentally with the uids which are desired to be intimately contacted. Bench tests in the laboratory establish a minimum amount of the immiscible aqueous treating liquid to be mixed with a hydrocarbon for producing a desired result by employing a dise and cylinder mixing device. This device is conventional and used to intermix liquids. In this device, the liquids to be mixed are contained in a cylinder. A disc loosely fitting within the cylinder is carried on a stem. The stem is adapted to be reciprocated longitudinally within the cylinder. As a result, the liquids to be mixed are passed through a narrow opening between the disc and cylinder. The resultant shear of fluid flowing through the opening causes these liquids to be mixed. The opening between the disc and piston is selected within the range of the dimensions defined for the openings 49 in the orifice disc 44.

The disc is moved gently within the cylinder to start mixing of the immiscible liquids. Then, the disc is moved at a linear velocity through a stroke length l and produces a liquid fiow through the clearance opening at a velocity V. Generally, each mixing stage will operate at a head h not less than is produced by a 3 p.s.i. differential (a minimum for satisfactory operation) across each mixing stage. The Velocity V produced by the head h is determined from the formula: V=\/ghI wherein g is the acceleration of gravity constant. The disc is then moved, one or more times, through the stroke length l at the same linear velocity until the desired utilization of the aqueous treating liquid is obtained. The number of strokes required on the disc to complete a desired reaction is representative of the total mixing energy to produce the desired result. Thus, each stroke of the piston is related to the operation of each mixing stage of the mixer 31. Five strokes of the disc would represent five mixing stages in the mixer 31. If desired, the test may be repeated for several pressure differentials across each mixing stage until the pressure differential and number of mixing stages are optimized whereby the lowest amount of mixing energy is used to secure the desired utilization of aqueous treating liquid. Once the total mixing energy, and the number of stages that are required to produce it, are determined for a set of immiscible liquids, the total open area A of the openings 49 in the disc 44 can be determined from the aforementioned formulas for a given operating pressure drop t across the mixer 31.

The orifice mixer 31 of the present invention was tested in a field application in a plant which is represented in FIG. 1. The n-paraffin in the line 18 contained approximately 972 p.p.m. acidity as sulfuric acid. The caustic solution (aqueous sodium hydroxide) injected through the pressure valve 19 was of a strength between 1 and 4 weight percent. The caustic solution was introduced at a rate of approximately six gallons per minute. The resulting hydrocarbon and caustic solution stream Was passed through the orifice mixer 31 at about a 60 gallon per minute rate of flow. The orifice mixer 31, in this plant, was operated with an 18 pound per square inch pressure drop between its inlet and outlet. The mixing energy required for substantially complete neutralization of residual acidity indicated that five mixing stages should be present in the mixer 31. For convenience of manufacture, the flow passageway was designed with a 4 diameter. The following information tabulation, as applied in the formulas, for the mixer design was employed:

t=20 p.s.i. total (operating pressure differential t) Q=50 g.p.m.=0.lll6 tts/sec. C=0.72 (polypropylene, 1/2 thick) h=4 p.s.i./0.434 p.s.i./ft.=9.22 ft. per stage V=C\/2gh=0.72\/64.4 9.22\=l7.5 ft./sec. A=Q/V=(0.lll6 ft.3/sec.)

+(17.5 ft./sec.)=0.00637 ft? The largest size dimension, 0.250 inch, were used for openings 49. The openings 49 were round, and for 0.250 inch diameter, the vnumber of holes required per stage were:

0.917 in.2 0.049 ing/hole The number of openings 49 were increased to 20 in each disc 44 to insure operation of the mixer 31 Within the operating pressure differential t.

Operation of the orifice mixer 31 of this design was compared with the conventional caustic mixer 21. The conventional caustic mixer 21 intermixed a caustic solution of 1.6 weight percent at a rate of 5.7 gallons per minute into the n-paraflin stream which entered the electric treater 23. The n-parafiin overhead in line 26 had a residual acidity of between l8 and 20 p.p.m. as sulfuric acid. The orifice mixer 31 intermixed 1.3 weight percent of caustic solution at a rate of 5.6 gallons per minute into the n-parafiin stream which entered the electric treater 23. The n-parafiin overhead in line 26 had a residual acidity of between 7.5 and l0 p.p.m. Additionally, the orifice mixer 31 intermixed 1.8 weight percent of caustic at a rate of 5.6 gallons per minute with the nparaffin stream which entered the electric treater 23. The n-parafiin overhead in line 26 had a residual acidity of between 8.3 and 9.5 parts per million as sulfuric acid. The data indicated that with the orifice mixer 31, a completely neutralized n-paraffin overhead in line 26 could be produced if 5.0 weight percent of caustic was introduced in an amount between l0 and l2 percent by volume into the n-parafiin stream which was sent to the electric treater 23.

In operation of the orifice mixer 31, the liquids being mixed are passed concurrently through the flow passage through each orifice disc 44. The desired level of mixing energy for contacting these liquids to complete a desired reaction is produced solely by the fluid flow through the mixer 31 in response to this pressure differential t. The controlled shear exerted upon these liquids in each mixing stage disperses the aqueous treating liquid into regulated droplet sizes throughout the liquid hydrocarbon. This shear effect is obtained in each mixing stage by the open area A which is transverse to the liquid flowing :18.7 holes therethrough. This open area A, as previously defined, is provided by plurality of like-size openings having one dimension in the range between 0.0312 and 0.250 inch.

The average orifice discharge constant C which is employed in the formulas for defining the total area of the openings 49 in the orifice disc 44 is also termed a coefficient of discharge of a standard orifice. The coefficient of discharge is practically a constant of 0.61 for the sharp-edged orifice providing the diameter of the orifice is large compared to the thickness of the plate in which it is formed. This coefficient of discharge is 0.98 for the rounded orifice where the orifice is concentric to the pipe. The coefcient of discharge at 0.61 for the sharp-edged orifice is true only where the chamber on each side of the orifice is not less than five times the diameter of the orifice.

It has been found that in the present invention, the average orifice discharge constant C, will reside in the range of between about 0.7 and 1.0. For example, in the construction of the orifice disc 44 of 1/2 thick polypropylene, the average orifice discharge constant C has a value of about 0.72 for 1A diameter holes for the openings 49. Where the orifice disc 44 is formed of la" thick steel with 1A diameter holes for openings 49, the average orifice discharge constant C is equal to about 1.0. The numerical value for the average orifice discharge constant C can be determined from reference literature, or by laboratory evaluations considering the material, its thickness and the opening size for the openings 49 of the orifice disc 44.

In the orifice mixer 31 of thepresent invention, the use of multistages, and multishear in successive stages, insures the intimate mixing of immiscible liquids, and especially aqueous treating liquids with light-weight liquid hydrocarbon streams. The mixer 31 is adapted to provide a dispersion of one liquid in another liquid which has uniform characteristics throughout its volume. As a result, the degree of mixing is at an optimum for completion of a desired reaction, and for subsequent separation of the dispersed liquid from the continuous liquid in an electric coalescer or treater. Additionally, this intimate mixing within the mixer 31 occurs in the smallest amount of possible contact time, namely that time required for the fluids to flow through the mixer 31. The mixer 31 obviously has no moving parts, and the sole source of energy for the mixing is a function of the operating pressure drop across the mixer 31.

From the foregoing description, it will be apparent to one skilled inthe art, that various changes and alterations may be made to the orifice mixer and method of operation without departing from the spirit of the present invention. It is intended that such changes and alterations come within the present description which is taken as illustrative and not limitative of the present invention, whose scope is defined by the appended claims.

What is claimed is:

1. A method for mixing and treating a liquid hydrocarbon with an aqueous treating liquid comprising the steps of:

(a) mixing said aqueous treating liquid and said liquid hydrocarbon and passing the mixture through a rst of a plurality of mixing stages, each of said stages containing a plurality of small openings having one dimension residing between 0.0312 and 0.250

inch to produce droplets forming a readily coalescing dispersion of said aqueous treating liquid within said liquid hydrocarbon, and

(b) passing said dispersion from the first mixing stage through each of the remaining mixing stages until the aqueous treating liquid is substantially completely utilized in treating the hydrocarbon.

2. The method of claim 1 in which the hydrocarbon has a maximum boiling point below about 500 F.

3. The method of claim 2 in which the aqueous treating liquid is selected from the group consisting of acids and Ibases which are employed to treat liquid hydrocarbons.

4. A method for mixing an aqueous treating liquid with a hydrocarbon liquid by passing said liquids through a mixer which operates with a pressure differential t between its inlet and outlet, comprising the steps of (a) passing a mixture of said liquids through a flow passage in said mixer, which fiow passage extends between an inlet and an outlet and contains a plurality of mixing stages which provide a certain level of mixing energy for intimately contacting said liquids by the liuid `flow through said mixer in response to the pressure differential t,

(b) providing controlled shear to the liquids flowing through each of said mixing stages for dispersing the aqueous treating liquid into regulated droplet sizes within the hydrocarbon liquid, said shear being obtained in each of said mixing stages by an open area A transverse to liquid flow therethrough, and said open area A formed by a plurality of like-size openings having one dimension residing Ibetween 0.0312 and 0.250 inch, said open area A in each of said mixing stages being defined -by the formulas:

Q--volumetric ow rate through said mixer.

A=total opening area through which said liquids pass in said mixing stage, and such areas being taken in a plane transverse to liquid liow.

C=average orifice discharge constant for the open area A.

g=acceleration of gravity.

h=1iuid head developed across said mixing stage.

V=the velocity of fluid flow through said mixing stage.

References Cited UNITED STATES PATENTS 1,099,622 6/ 1914 Shiner 208-267 1,187,797 `6/ 1916 Allan 208-267 2,073,253 3/ 1937 Pfau et al 208-267 1,993,446 3/ 1935 Huff 208-298 2,751,425 6/ 1956 Rupp 208-177 FOREIGN PATENTS 613,971 2/ 1961 Canada.

DELB-ERT E. GAN'IZ, Primary Examiner G. J. CRASANAKIS, Assistant Examiner U.S. Cl. X.R. 20S-188, 270