CA1041142A - Method of transporting waxy crude oils - Google Patents

Abstract

METHOD FOR TRANSPORTING WAXY CRUDE OILS

ABSTRACT

Hydrocarbon mixtures (e.g. "waxy" crude oils) are transported by first fractionating a mixture into at least a relatively low pour point fraction and a relatively high pour point fraction, congealing high pour point fraction into solid slugs (pipeline pigs), transporting or storing the slugs in the relatively low pour point fraction, pre-ferably in a pipeline, at a temperature below about the solution temperature of the slugs.

Description

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`' 1 BACICGROUND OF THE IN~7ENTION
i Field of the Invention:
~ This invention relates to transporting viscous hyclro-,~ ¦ carbon mixtures, e.g. crude oil, by frac~ionating the il hydrocarbon mixture lnto at least two fractions, congealin~
-~` one fraction into solid slugs and storing or transporting the slugs in the fluid fraction, preferably in a conduit.
Description of the Prior Art:
~! Examples of patents representative of the art includo:
Xells in U.~S. 271,080 separates wax Erom crude oils hy ~:
; ~ pumping the crude oil, e.g. in ~mall streams or jets, into ¦ the bottom oE a tank containing a brine at a temp~xa~ure $ ¦ sufficiently low to congeal the wa~. The congealed wax is ¦~ recovered in the brinc. ,;
; j Persch in U. S. 1,454,485 blasts air under pressure into crude oil to orm an emulsion of air ancl oil to incr~ase t th~ fluidity of the oil.

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1 Oberfe71 et al in U. S. 2,526,966 teaches transportinq

2 viscous cr~de oils by removing the light hydrocarbons

3 (including straight run gasoline), hydrogenating the resid~e

4 to increase the fluidity thereof and then combining the hydrogenated product and the light hydrocarbons a~d pumping 6 the mixture.
7 Chilton et al in U. S. 2,821,205 forms a film of wat~r 8 on the interior wall of the pipe to improve the pumpability 9 of viscous oil. In addition, a light petroleum or condensed : . .
`I 10 casing-head gas can be mixed with the crude oll to reduce 11 the viscosity. Agents such as phosphates and polyphosphat~s 12 can be added to increase the water's ability to selective].y 1. 13 adhere to the st.eel pipe and to displace oil from the sur-, 14 face of the pipe.
l 15 Scott et al in U. S. 3,269,401 teach facilitating flow .~l 16 of wax-bearing oil in a pipèline by dissolving in the oil, .~ 17 at superatmospheric pressure and while above its pour point, ~, 18 a gas such as N2, CO2, flue gas, and h~drocarbons containing l 19 less than 3 carbon atoms.
-$. 20 Kane in U. S. 3,425,429 transports VlSCOUS crude oils ~ 21 by forming an oil-in-water emulsion, the water containing ¦ 22 nonionic surfactant.
.~ 23 This technology, except -for prilling o:E thc high pour ,~ 24 point fraction for slurrying, heat transfer systems and .crude oil-water suspension systems, has generally proven to 26 be commercially unattractive. Prilling of a high pour point 27 fraction for transportation as a slurry w:ith a low pour ', 28 point fraction appears to be a particularly advantageous '3~: 29 method of transporting high pour point waxy crude oi.ls~
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1 Watanabe in U. S. 3,468,986 forms spherical particles 2 of wax by meltiny the wax, then dispersing same in a non-3 solvent liquid (e.g. water) maintained at a temperature 4 above the solidification temperature of the wax and there-

5 after cooling the dispersion to solidify the dispersed

6 droplets into discrete solid particles. The particles can

7 be coated with finely divided solids such as calcium car-; 8 bonate, etc. Watanabe teaches that it is known in the art 9 to disperse waxy particles by molding, prilling, spray 10 drying, extruding, etc.
11 Allen in U. S. 3,548,846 teaches transporting waxy 12 crude oils by incorporating propane or butane within the )i o 13 crude oil.
14 Vairogs in U. S. 3,618,624 transports viscous crude ' 15 oils by incorporating a miscible gas, e.g. CO2, methane, 16 ethane, into the crude to reduce the viscosity thereoE.
17 U. S. 3,846,279 to Merrill, Jr. teaches fractionating 18 waxy crude oils into a relatively low pour point fraction ~ 19 and a relatively high pour point fraction, prilling the 1 20 relatively high pour point fraction into spherical particl~s `i 21 or beads and then slurryiny the beads in the low pour point 22 fraction for transportation as a slurry.
23 The art has also used heat, e.g. tracer lines and large 24 heat exchangers placed intermittently along the pipeline, to x maintain the crude oil above its pour point and thus facilitate 26 pumping. The main disadvantaye of these methods is the 27 crude oil tends to "set-up" during shutdowns.
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~ever, the amount of prilled beads that can be efficiently trans-ported in the slurry is limited. In crude oil having extremely high wax contents, some other method has to be used to transport the excess high pour point fraction.

SUMM~RY OF THE INVENT I ON
The present invention may be bFoadly described as a pro-~axy cr~l~ c~; -cess for transporting a hydroear~e~ urQ in a conduit comprising:
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fractionating the hydrocarbon mixture into at least an overheads fraction and a bottoms fraction, molding at least a portion of -the bottoms fraction into solid slugs having an average diameter slightly smaller than the internal diameter of the conduit, recom-- bining the slugs with the overheads fraction, and transporting the . ~- . - ~
`combination at a temperature below about the solution temperature of the solid slugs in the overheads fraction.
PRE~ERRED EMBODIMENTS OF THE INVENTION :
`Hydrocarbon mixtures having an average pour point below the seasonably ambient temperature of the transportation system, e.g. a pipeline, are particularly applicable with this invention.
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~Examples of hydrocarbon mixtures include crude oil, shale oil, tar ,:
sand oil, fuel oil, gas oil, like hydrocarbon mixtures and mixtures of two or more of the same type or different hydrocarbon mixtures.
Crude oils are particularly useful with this invention and .
especially those classified as "waxy" crudc oils. Examples of the latter include crude oils which exhibit a "waxy gel" appearance at seasonably ambient temperature which contain about 1% to ..
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1 abo~t 80% wax (~ax i5 defined as the precipitate whi~h forms 2 after one part of crude oil is dissolved in 10 parts of 3 methyl ethyl ketone at about 80C. and the mixture chilled.
4 to -25C.) and preferably those which have an average pour 5 point above the average minimum temperature of the trans- . -6 porting systemr e.g. a pipeline. Examples of average pour 7 points of crude oils particularly useful with this invention

8 include about -25 to about 95C. and preferably about -20 to

9 about 65C. .
The hydrocarbon is first fractionated into at least 11 overheads having a density and viscosity at a given tempera-12 ture lower than the original hydrocarbon mix ure and bottoms 13 having a density and viscosity at a given temperature above :
.~ 14 that of the original hydrocarbon mixture. The bottoms :
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' 15 can be any portion of the hydrocarbon mixture but are usually -} 16 about 1~ to ahout 80~ and preferably about 20% to about 70%

17 and more preferably about 30% to about 60~ by weight of the 18 original hydrocarbon mixture. Fractions other than the 19 bottoms and overheads can be obtained and used in other ~l . 20 processing streams.

:~ 21 Fractionation can be .1ccomplished at atmospheric pres-:~ 22 sure, sub- or supera~mospheric pressure and at low and h.i.gh `31 ' .
23 temperatures by processes such as distillation, solvent 24 extraction, membrane fractionation and crystallization.

~ 25 .Optionally, an equivalent amount of up to 50%, preferably up ! 26 to 42~ and mo~e preferabl.y up to 33% by.volume of the bottoms 27. can be cracked (by thermal degradation, hydrogenation, : 28 catalytical degradation or combinations thereof) during 29 fractionation or before congelation.

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1 The overheads should have a pour point at least 1C.2 and preferably at least about 2C. and more preferably at 3 least about 5C. below the average temperature of the trans-4 porting system, such as a pipeline or a combination of pipeline and tank battery.
- 6 At least a portion of the bottoms is then congealed ; 7 into slugs conforming to the needs of the transportation g system, i.e. squares or rectangles for trucks and spheres or g cylinders for pipeline transportation. The bottoms are Jo cooled in appropriately shaped molds, preferably about 5 to 11 about 30C. below the average congelation temperature of the 12 bottoms, to form the slugs.
13 The slugs may be transported separately, e.g. by truclc, 14 trailer, barge or train, but are preferably transported with the overheads in a conduit, such as a pipeline. The slugs - 16 and overheads may be injected into a pipeline by means known 17 in the art. Alternatively, the slugs and the overheads may 18 be stored in a suitable storage area, e.g. in a storage tank 19 or barrel, for subsequent transportation. The slugs are sized to operate efficiently in the particular transportation i 21 or stora~e system, but will pre.~erably have an outsid~ dim~n-i 22 sion of at least 40 mm (millimeters), more preEerably at least `1 . 23 100 mm and most prefexably at least 200 mm. When the slugs 24 are to be transported with the overheads in a conduit, the slugs will preferably be slightly smaller than the internal d:iameter 26 of the conduit.
27 A liquid diluent, such as a straiyht-run gasoline, ;i 28 reservoir condensate or like hydrocarbon, can be mixed with i 29 the overheads before, during or af-ter recomhinin~ the slu~s ;l~ 30 with the low pour point fraction. Any diluent which is 31 miscible with the overheads and which preferably has a pour 32 point b~low the minimum temperature of the transportincJ
1 33 system is useful with this invention.

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1041~42 1 During or after congelation, the slugs can be coated 2 with gases, flexible membranes, rigid materials, or other 3 desired agents to inhibit sticking and distortion, and to 4 p~rmlt high temperatures during transportation. Examples of : 5 flexible membranes suitable for enclosing the sluys can be : 6 found in U. S. 3,225,787 to Gogarty et al and U. S. 3,473,572 : 7 to Nielson et al.
8 The congealed slugs can make up about 1% to about 90 9 and more preferably about 5~ to about 85~ and most pre-ferably about 10~ to about 80% by weight of the total . . 11 hydrocarbon transported. During transportation, the tem-12 perature of the overheads is preferably about 20C. below to 1:~ about 20C. above and more preferably ahout 10C. below to . 14 about 10C. above the minimum, seasonably ambient tempera-ture of the transportation system. Also, it is preferred ~ 16 that the temperature of the overheads during transportation .~ 17 be about 20C. and more preferably about 40C. below the ~ 18 solution temperature of the slugs in the overheads.
.;l 19 The slugs are preferably transported with the overheads , ! 20 in a conduit wherein the average maximum temperature of the 21 conduit in at leaqt its major initlal length i8 below the , 22 averaye solution temperature of the slugs in the overheads.

.~ 23 The average maximum temperature of the conduit is also pre-24 ferably at least about 1C. below and more preferably at ~ 25 least about 5C. below the average pour point of the slugs.

:~ 26 In addition, the average temperature of the col~duit should .~ 27 not be below the:average pour point of the overheads and 1 28 preferably is at least about 1C. and more preferably at 29 least about 5C. above this pour point.

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1 A gas miscible with the overheads can be incorporat~d 2 therein to faciliate pumpability. The gas is preferably 3 imrniscible with the slugs. Examples of such gases include 4 C02, hydrocarbons containing less than about 3 carbon atoms, N2, flue gas, and like gases. The gas can be injected into 6 the overheads under conditions such that the gas is present 7 in concentrations greater than saturation conditions at 8 atmospheric conditions--however, the gas should not be pre-9 sent at conditions such that a free gas phase is present.
The overheads ar~ preferably saturated with C02 at super-11 atmospheric pressures.
12 Chemical agents to faciliate integrity retention of the 13 slugs, e.g~ high molecular weight polymers, can be added to 14 the slugs prior to congelation. Also, viscosity reducing agents, pour point redLlcers, and drag reduction agents can 16 be admixed with the overheads to impart desired properties.

19 ~ "waxy" crude oil mixture having an average pour point of 45C. and an average ~PI gravity of about 50 is frac-21 tionat~d by distillation with 35% by weight being recovere~
22 as an overheads fraction (low pour point fraction, average 23 pour point about -10C.) and 65% beinc3 recovered as a 24 bottoms (average pour point about 55C.) The bottoms is heated to 70C. and then poured into molds forming cylindrical 26 slugs 23.5 inches in diameter and 24 inches in length. The 27 slugs are cooled to 30C. and are then injected into a 24 28 inch internal diameter pipeline containing flowing liquid .

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1 hydrocarbons at a temperature of 35C., the ambient tempera-2 ture. The slugs are transported through the pipeline a 3 distance of 200 miles and are then recovered. The slugs 4 show little or no physical distortion and little loss through solution in the hydrocarbon carrier.
6 It is intended that all equivalents obvious to those 7 skilled in the art be included within the invention of the 8 specification and appended claims.

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Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for transporting a "waxy" crude oil in a conduit comprising:
1) fractionating the crude oil into at least an over-heads fraction and a bottoms fraction, 2) molding at least a portion of the bottoms fraction into solid slugs having an average diameter slightly smaller than the internal diameter of the conduit, 3) recombining the slugs with the overheads fraction, and 4) transporting the combination in the conduit at a temperature below about the solution temperature of the solid slugs in the overheads fraction.

2. The process of Claim 1, wherein the "waxy" crude oil has an average wax concentration of about 1 to about 80%
by weight.

3. The process of Claim 1, wherein the "waxy" crude oil has an average pour point above about the average seasonally minimum temperature of the transporting system.

4. The process of Claim 1, wherein the solid slugs are cylindrical in shape.

5. The process of Claim 4, wherein the solid slugs are spherical in shape.

6. The process of Claim 1, wherein the bottoms fraction is equivalent to about 20 to about 70% of the weight of the hydrocarbon mixture.

7. The process of Claim 1, wherein the conduit has an average diameter of at least about 200 mm.