US2780304A - Treatment of crude oil - Google Patents

Description

Feb. 5, 1957 Filed March 2, 1954 Fig.

J. E. PEW ET AL 2,780,304

TREATMENT OF CRUDE on 3 Sheets-Sheet l IN VEN TORS.

JAMES E. PEW BY CHARLES W. HAYES QMAT. s m

ATTOR EY Feb. 5, 1957 J. E. PEW ET AL 2,780,304

TREATMENT OF CRUDE OIL Filed March' 2, 1954 3 Sheets-Sheet 2 Fig. 3

, INVENTORS. JAMES E. PEW BY CHARLES w. HAYES q M26: EY cu! United States Patent TREATMENT OF CRUDE OIL James E. Pew, Malvern, Pa., and Charles W. Hayes,

Houston, Tex., assignors of one-half to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey, and one-half to Black, Sivalls and Bryson, Inc., Kansas City, Mo., a corporation of Delaware Application March 2, 1954, Serial No. 413,528

3 Claims. (Cl. 183-2.7)

This invention relates to the treatment of crude petroleum. It more particularly concerns method and apparatus for demulsifying crude petroleum and simultaneously removing therefrom certain light hydrocarbon constituents While retaining in the crude oil a major proportion of the next higher boiling hydrocarbon constituent.

Crude petroleum as obtained from oil wells generally contains water emulsified in the oil. It is customary practice to provide a treating system near the oil field which is adapted to remove water from the crude oil, so as to avoid the expense of transporting water along with the oil to the refinery. The conventional procedure for demulsifying the crude oil comprises heating it to. a temperature sufiicient to cause the emulsion to break and then ettling and separately withdrawing the water from the oil. During this operation normally gaseous hydrocarbon constituents are vaporized from the crude oil due to upwardly through the fractionating Zone.

the elevated temperature employed, thus requiring that suitable means be provided for collecting and recovering these lighter constituents.

The removal from the crude oil of the lightest hydrocarbons, such as methane, ethane and propane, duringthe deinulsification operation is generally desirable, since it obviates the necessity of transporting the crude oil to the refinery under substantially elevated pressure sufii cient to prevent volatilizati-on of these light components. Furthermore, these components generally are not required at the refinery and their removal decreases costs by reducing the volume of oil transported.

On the other hand, removal of butanes during the demulsification step generally is undesirable as both iso butane and n-butane usually are required for various purposes in refinery operations. For example, isobutane is needed as charge material for alkylation processes, while n-butane is desirable as blending stock for providing the desired vapor pressure for gasoline products or as charge stock for .isomerizat-ion. Conventional demulsification procedures, however, result in the removal of much of the butanes from crude oil along with the fighter hydro carbons. To recover the butanes removed with the other light hydrocarbons so that the butanes can be shipped to the refinery site, separate fractionating equipment must be provided at the location Where the demulsification step is conducted. This increases costs not only because the additional equipment for fractionation is required but also because of higher expense in transporting butanes as a separate product as compared to crude oil,

The present invention is directed to method and apparatus for demulsifying crude oil and simultaneously separating the lower boiling hydrocarbons therefromv while retaining most of the butane in the crude oil. In accordance with the invention, the crude oil to be treated is introduced into the upper part of a fractionating zone in which it flows downwardly countercurrent to upilowing vapors. From the fractionating zone the oil passes into a demulsitying zone where sufficient heat is provided to cause water to separate. The heat also causes vaporization of lower boiling hydrocarbons which pass into and "ice Conditions of temperature and pressure are maintained in the fractionating zone such that most of the butane is retained in the crude oil while the lower boiling hydrocarbons are withdrawn as gaseous phase from the top. Water and crude oil containing the butane are withdrawn as separate streams from the dem'ulsifying Zone.

The invention is more specifically described with reference to the accompanying drawings in which:

a Figure 1 is an elevation of a demulsifying-fraotionating device illustrating one embodiment of the invention;

Figure 2 is an enlarged elevational view, partly in section, of the fractionating portion of the device of Figure 1;

Figure 3 is an enlarged elevational view, partly in section, of the demulsifying portion of the device of Figure 1'; and

Figure 4 is a generally diagrammatic illustration of a process utilizing the invention in the treatment of crude petroleum from a high pressure oil field.

With reference now to the drawings, 10 is an elongated column which functions as both a fractionating and demulsifying device. The upper part of the column is provided with a series of conventional bubble cap trays, as illustrated in Fig. 2, which constitute the fractionating section. As shown for the uppermost tray 11, each tray is provided with bubble caps 12, an inlet weir 13, an outlet weir 14, a baffle 19 adjacent the outlet weir, and a downc'omer 15. The incoming crude oil, which is fed onto tray 11 from inlet line 16, flows across the tray and thence downwardly and across each succeeding tray in the column. 0n each tray the liquid after passing beyond the bubble caps 12 flows beneath the bafiie 19 before flowing over the outlet weir 14-. This arrangement prevents the accumulation of a layer of water on the tray as a result of separation of water loosely held by the incoming crude oil. As a general rule, about seven bubble cap trays should be provided to permit most of the butane to be retained in the crude oil while allowing the lighter hydrocarbons to be vaporized. The vapors are withdrawn from the top of column 10 through line 17 which is provided with pressure regulating valve 18 for maintaining the desired pressure within the column.

Beneath the lowermost bubble cap tray 20 a partition 21, shown in Fig. 3, divides the fractionating section of the column from .the lower portion herein referred to as the treater. Partition 21 has an opening communicating with a flue 22 through which vapors can pass from the treater to the upper section of the column, The crude oil which flows from tray 20 flows around flue 22 to an overflow weir 23, its liquid level being as illustrated at 24; and thence it passes to the treater portion through line 25.

The treater, constituting that portion of the column shown in Fig. 3 below partition 21, is provided with 'a heating section and an oil settling section; and its construction may be similar to that of known treating apparatus for effecting demulsification of crude petroleum, suchas the apparatus disclosed in U. S. Patent No. 2,546,269. As illustrated in Fig. 3, heating means such as gas fired tubes 30 are provided in a lower part of the treater, and the oil emulsion from line 25 enters the column through suitable distributing means 31 adapted to distribute the incoming stream along the length of tubes '30. Heating of the oil not only ensures demulsification but also causes vaporization of lower boiling hydrocarbon constituents, thus supplying vapors for the fractionating operation conducted in the upper part of the column. As

the emulsion is heated adjacent tubes 30, most of the water breaks out and settles into a lower water layer having an interface with the oil as indicated at 32 Oil and vapors evolved therefrom rise through an opening in partition plate 33 and pass upwardly through flume 34. At the top of the flume vapors escape and issue through flue 22 to the fra-ctiona-ting section of the column. The oil flows downwardly through an outer flume 35 and then into a settling zone. An annular bed of suitable contact material 36, such as sawdust or fiber glass, is positioned within the settling zone to ensure complete demulsification by causing coalescence of residual Water as the oil filters through the contact material. The oil which passes into the settling zone from outer flume 35 rises through contact material 36 and eventually passes over outlet weir 37 and out of the column via line 27. Water which separates from the oil in the settling zone can flow through line 38 to the water phase at the base of the column.

Removal from the system of water which has settled from the oil is effected through means providing an adjustable hydrostatic leg that permits regulation of the oilwater' interface 32 to the desired level. These means include pipe 40 which extends from within the water layer upwardly to a reservoir 41 containing an adjustable siphon 42 which regulates the liquid level 43 within the reservoir. An effluent water line 44 connects with a conventional automatic discharge valve 45 adapted to permit withdrawal of water without discharge of hydrocarbon vapor along with the water.

Operation of the above-described apparatus is as follows: Crude oil containing low boiling hydrocarbons and emulsified water is fed continuously to the upper part of column through line 16, and heat is supplied to the lower part of the column by means of heating tubes 30. The heat causes hydrocarbon vapors to evolve from the crude oil, and the vapors issue through flue 22 to the upper section and therein flow successively through the bubble cap trays in contact with the downflowing crude oil. Pressure within the column is regulated by means of valve 18 and the heat input to the lower part of the column is regulated so that the temperature and pressure conditions within the fraction-atin'g zone are effective to fractionate between propane and butane. In other words, the conditions maintained are such that most of the butane is retained in the crude oil and therefore leaves the system through line 27 a a component of the demulsified crude, while most of the propane is stripped from the crude oil and leaves the system through vapor line 17 in admixture with lower boiling hydrocarbons. Water settling from the heated crude forms a lower water layer and the oil-Water interface 32 is maintained at the desired level by adjusting siphon 42.

The temperature to which the oil emulsion is heated in the heating section of column 10 should be sufficient to ensure thorough demulsification. The temperature required may vary depending upon the source of the crude oil, but it generally will be within the range of 110-160 F. The pressure which should be maintained within the fractionating section to achieve the desired separation accordingly will depend upon the temperature selected for effecting the demulsification, as well as upon proportions of light hydrocarbons in the crude oil charged and the number of fractionating tray-s provided. At relatively low demulsifying temperatures relatively low pressures can be utilized; while higher pressures are required when the emulsion is heated to relatively high temperatures. In instances where the emulsion will break readily at low temperature, a pressure in the upper part of the fractionating zonewhich is just above atmospheric will cause substantial fractionation between propane and butane. When higher demulsifying temperatures are required, pressures ranging up to 60 p. s. i. g. or higher may be needed to ensure the desired retention of butane by the demulsifiedcrude oil. Any necessary variations in presure can readily be made by adjusting pressure regulating valve 18 at the top of column 10.

Fig. 4 schematically illustrates a system for handling crude oil from high pressure wells to stabilize the same by removal of propane and lighter constituents While effecting demulsification. The crude oil enters the system through line 50 and passes first to a high pressure separator 5 1 which effects separation of the incoming mixture into a gas phase, a liquid oil phase and an aqueou phase resulting from water which readily separates from the crude mixture. The gas phase is removed through line 52 while the water layer is withdrawn through valve 79 and line 180. The pressure in separator 51 may vary widely but typically may be within the range of 150-600 p. s. i. g. The ga stream removed via line 52 is composed mainly of methane, ethane and propane with small amounts of higher boiling constituents. A portion of it as needed for the heat exchange operation hereinafter described is withdrawn through valve 53 and line 54, while the remainder is removed from the system through pressure regulating valve 55.

The liquid phase from separator 51 is an oil-Water mixture containing minor amounts of propane and lighter constituents, and it requires both demulsifying and stabilizing. This is done by a combination fractionating-dcmulsifying operation similar to that described in connection with Figs. l-3. In Fig. 4, however, the fractionating section is shown as a separate tower 58 and the demulsifying section is illustrated as a horizontal drum 59. The oil emulsion passes from separator 51 through pressure reducing valve 56 and line 57 to the upper part of tower 58. The mixture entering the tower is relatively cold, its temperature generally being substantially below 110 F. The tower is provided with bubble plates, sieve plates, grid plates, packing or like fractionating means is illustrated by dotted lines 60. The relatively cold liquid descends through tower 58 countercurrent to hydrocarbon vapor which enters the base of the tower from drum 59 through line 61. Drum 59 is provided with a suitable tubular burner 62 to which fuel gas is fed by means of line 63 and from which the exhaust fumes pass via line 64. Drum 59 may be arranged to include a heating section and an oil settling section analogous to the arrangement shown for the apparatus of Fig. 3. Oil emulsion from the base of tower 58 is passed through line 65 into the heating section of drum 59. Water which breaks out of the emulsion is removed through line 66 having valve 67.

Sufficient heat is supplied to drum 59 by means of burner 62 to effect demulsification and to provide enough reboiling to provide the necessary volume of stripping vapors for the operation of tower 58. The pressure in the tower is adjusted by means of valve 68 in vapor exit line 69, and a pressure range of 10-50 p. s. i. g. for the operation of tower 58 is exemplary. Pressure and temperature conditions in the tower thus are regulated to effect fractionation between propane and butane, so

that most of the propane in the oil is driven out in the overhead vapor while most of the butane is retained in the demulsified oil.

The demulsified product, which is removed from drum 59 by means of line 70, needs to be cooled before being sent to storage to minimize vapor loss. In some oil field areas cooling water is not available for this purpose. The process illustrated in Fig. 4, utilizes gas from separator 51 as the coolant and hence dispenses with any necessity of a cooling medium from an outside source. This gas, which generally has a temperature substantially below 110 F., is fed from line 54 to a heat exchanger 71 wherein it passes in indirect heat exchange With the demulsified oil from line 70, following which it is removed from the system through line 72. The cooled oil product then flows through line 73 to tank 74, from which it is withdrawn whenever desired by means of line 75. Tank 75 also is provided with a gas vent line 76 containing a back pressure relief valve 77 through which any excess gas evolved in the tank is vented.

The following is a specific comparison between a fractionating-demulsifying operation conducted according to the present invention and a conventional dernulsifying operation conducted under similar conditions but without a countercurrent fractionating zone. In each of these operations crude oil directly from the wells was sent first to a high pressure separator operating at about 285 p. s. i. g. to remove the bulk of the light gases. The description which follows for each operation is based on a charge of 1000 bbls. of liquid hydrocarbon material from the high pressure separator, and yields are all reported in liquid bbls. at 60 F.

In the conventional operation the charge was passed to a continuous demulsifier maintained at a pressure of 20 p. s. i. g. and the temperature was therein raised to about 140 F. These conditions effected demulsification and drove off an amount of light hydrocarbons such that there was produced 748 bbls. of stabilized oil product having a Reid vapor pressure of 14 lbs. The charge of 1000 bbls. contained 95.4 bbls. of butanes While the stabilized oil contained 36.2 bbls. Hence, only about 38% of the butanes was recovered in the oil product and 62% was lost to the evolved gases. The gases also included 4.7% of the C5 and heavier hydrocarbon material present in the charge. These values are typical of conventional demulsifying practice in the field.

In the comparative operation conducted according to the invention, the charge was fed to a fractionator-demulsifier combination, similar to that described in Fig. 4, in which the fractionator was a bubble cap column having 7 trays. The pressure at the top of the fractionator was maintained at about 20 p. s. i. g. and the emulsion was heated to about 140 F. in the demulsification section. This likewise produced a stabilized demulsified oil product having a Reid vapor pressure of 14 lbs. but in this case the product yield increased to 887 bbls. as compared to the 748 bbls. obtained by the conventional method. The 1000 bbls. of charge contained 90.3 bbls. of butanes and 72.6 bbls. thereof were recovered in the stabilized oil. Hence, 80% of the butanes was recovered in the product and only 20% was lost to the evolved gases. Further, only 0.9% of the C5 and heavier hydrocarbons charged was lost to the evolved gases.

While the foregoing discussion has been confined mainly to the treatment of crude oil for the purpose of retaining most of the butane therein while removing most of the propane, it will be understood that the principles of the invention are applicable to crude oil treatment where it is desired to make a split between any two adjacent hydrocarbon components. For example, the invention can be utilized in similar manner if it is desired to retain most of the propane while removing most of the ethane from the crude, or if it is desired to make the split between butane and pentane. In such cases practice of the invention merely entails the adjustment of pressure and temperature conditions in the fractionator-demulsifier unit such that the lowest boiling desired hydrocarbon is mainly retained in the demulsified product while the next lower boiling hydrocarbon is mainly removed therefrom along with any still lower boiling hydrocarbons.

We claim:

1. Method for demulsifying crude petroleum and distilling therefrom a specified hydrocarbon constituent while retaining in the demulsified oil :a major proportion of the next higher boiling hydrocarbon constituent which comprises feeding the emulsified crude oil into the top of an elongated column having a series of vapor-liquid contacting sections separated by horizontal perforated trays, flowing downwardly through the column liquid consisting essentially of the emulsified crude oil constituents and passing such liquid into a demulsifying zone, heating the liquid constituents to effect separation of aqueous and hydrocarbon phases and to evolve hydrocarbon gas, passing evolved gas upwardly in said column for countercurrent contact with the downflowing liquid in said series of contacting sections, maintaining in said column conditions of temperature and pressure effective to fractionate between said specified hydrocarbon constituent and the next higher boiling hydrocarbon, withdrawing a gaseous stream containing said specified hydrocarbon constituent from the top of said elongated column and separately withdrawing water and demulsified oil containing said next higher boiling hydrocarbon from said demulsifying zone.

2. Method for demulsifying crude petroleum and distilling therefrom propane while retaining in the demulsified oil a major proportion oi the butane present in the emulsified crude oil which comprises feeding the emulsified crude oil into the top of an elongated column having a series of bubble trays, flowing downwardly through the column liquid consisting essentially of the emulsified crude oil constituents and passing such liquid into a demulsifying zone, heating the liquid constituents to effect separation of aqueous and hydrocarbon phases and to evolve hydrocarbon gas, passing evolved gas upwardly in said column for countercurrent. contact with the downflowing liquid on said bubble trays, maintaining in said column conditions of temperature and pressure effective to fractionate between propane and butane withdrawing a gaseous stream containing the propane from the top of said elongated column and separately withdrawing water and demulsified oil containing butane from said demulsifying zone.

3. An apparatus for treating a crude oil emulsion to obtain a stabilized oil product including, a treater having a heating section and an oil settling section thereabove, a bubble tower having connection with the settling section of the treater for passing hot vapors evolved in the heating section to the lower part of the bubble tower and having a series of bubble trays vertically spaced therein, means for admitting emulsion to be treated onto the uppermost tray of the bubble tower for countercurrent contact with said hot vapors, duct means connecting the bubble tower beneath the lowermost tray with the heating section of the treater for passing the vapor contacted emulsion directly into the heating section to effect separation of the oil and water components of the emulsion, means for removing the hot oil component from the settling section and separate means for removing the water component from a lower level of the treater, and means for removing vapors from the upper part of the bubble tower.

References Cited in the file of this patent UNITED STATES PATENTS 1,670,805 Gomory May 22, 1928 1,728,440 Otto Sept. 17, 1929 2,181,684 Walker Nov. 28, 1939 2,353,138 Beach July 11, 1944 2,528,032 Candler 'et al. Oct. 31, 1950 2,546,269 Lovelady Mar. 27, 1951 2,638,437 Ragatz May 12, 1953

Claims (1)

1. METHOD FOR DEMULSIFYING CRUDE PETROLEUM AND DISTILLING THEREFROM A SPECIFIC HYDROCARBON CONSTITUENT WHILE RETAINING IN THE DEMULSIFIED OIL A MAJOR PROPORTION OF THE NEXT HIGHER BOILING CONSTITUENT WHICH COMPRISES FEEDING THE EMULSIFIED CRUDE OIL INTO THE TOP OF AN ELONGATED COLUMN HAVING A SERIES OF VAPOR-LIQUID CONTACTING SECTIONS SEPARATED BY HORIZONTAL PERFORATED TRAYS, FLOWING DOWNWARDLY THROUGH THE COLUMN LIQUID CONSISTING ESSENTIALLY OF THE EMULSIFIED CRUDE OIL CONSTITUENTS AND PASSING SUCH LIQUID INTO A DEMULSIFYING ZONE, HEATING THE LIQUID CONSTITUENTS TO EFFECT SEPARATION OF AQUEOUS AND HYDROCARBON PHASES AND TO EVOLVE HYDROCARBON GAS, PASS-

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