U.S. patent number 3,900,041 [Application Number 05/468,969] was granted by the patent office on 1975-08-19 for modification of particle hardness in waxy crude oil slurries.
This patent grant is currently assigned to Marathon Oil Company. Invention is credited to Dennis E. Drayer, Keith M. Kersch, George A. Pouska, James E. Tackett, Jr..
United States Patent |
3,900,041 |
Kersch , et al. |
August 19, 1975 |
Modification of particle hardness in waxy crude oil slurries
Abstract
Previously, waxy crude oils have been fractionated into a wax
fraction and a liquid fraction; the wax fraction formed into
particles and slurried into the liquid fraction for transportation
in pipelines. Particle stability is enhanced by extruding molten
wax without substantial crystalline structure into a hot wax
immiscible fluid flowing cocurrent to the extruded wax and under
conditions which will quickly form a smooth shell, and thereafter
cooling to form hard, smooth spheres which resist mechanical
degradation and which further approach a stabilized, or maximum,
pressure drop at a slower rate than non-hardened particles. This
treatment results in a particle which can be pumped in a pipeline
at heavier particle loadings or with less pressure.
Inventors: |
Kersch; Keith M. (Littleton,
CO), Pouska; George A. (Littleton, CO), Drayer; Dennis
E. (Littleton, CO), Tackett, Jr.; James E. (Littleton,
CO) |
Assignee: |
Marathon Oil Company (Findlay,
OH)
|
Family
ID: |
23861924 |
Appl.
No.: |
05/468,969 |
Filed: |
May 13, 1974 |
Current U.S.
Class: |
406/47; 264/9;
208/370; 406/197 |
Current CPC
Class: |
F17D
1/088 (20130101) |
Current International
Class: |
F17D
1/00 (20060101); F17D 1/08 (20060101); F17d
001/16 (); B65g 053/30 (); C10g 043/02 () |
Field of
Search: |
;137/1,13 ;264/5,9
;44/51 ;302/66 ;208/370,14,20 ;252/8.3 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Cohan; Alan
Attorney, Agent or Firm: Herring; Joseph C. Willson, Jr.;
Richard C. Hummel; Jack L.
Claims
We claim:
1. In a process for transporting waxy petroleum crudes by
fractionating the crude into at least a wax fraction and a liquid
fraction, forming substantially round particles of wax, slurrying
the wax particles in a liquid hydrocarbon comprised of the liquid
fraction and transporting the slurry, the steps comprising
introducing molten wax having no substantial crystalline structure
into a hot, wax immiscible fluid flowing cocurrent to the
introduction of the molten wax and at flow rates sufficient to form
substantially round particles having a substantially smooth outer
shell and thereafter introducing the wax particles into a colder
wax immiscible fluid at a sufficiently low temperature to
substantially solidify the wax particles.
2. The process of claim 1 wherein the immiscible fluids are
water.
3. The process of claim 1 wherein the liquid hydrocarbon is the
liquid fraction.
4. The process of claim 1 wherein the temperature of the molten wax
as it is introduced into the hot, wax immiscible fluid is about
0.degree. to about 175.degree.F. above its melting point.
5. The process of claim 1 wherein the temperature of the molten wax
is about 20.degree. to about 150.degree.F. above its melting
point.
6. The process of claim 1 wherein the temperature of the molten wax
is about 50.degree. to about 125.degree.F. above its melting
point.
7. The process of claim 1 wherein the hot, wax immiscible fluid is
at least about 5.degree. to about 150.degree.F. below the
temperature of the molten wax as the latter is dispersed
therein.
8. The process of claim 1 wherein the hot, wax immiscible fluid is
at least about 20.degree. to about 80.degree. below the temperature
of the molten wax as the latter is dispersed therein.
9. The process of claim 1 wherein in the temperature of the hot,
wax immiscible fluid is at least about 140.degree.F.
10. The process of claim 1 wherein the molten wax is under laminar
flow as it comes in contact with the hot, wax immiscible fluid.
11. The process of claim 1 wherein the hot, wax immiscible fluid
flowing cocurrent to the molten wax is under laminar flow.
12. The process of claim 1 wherein the concentration of the
solidified wax particles in the liquid hydrocarbon is within the
range of about 1 to about 60%.
13. The process of claim 1 wherein the concentration of solidified
wax particles in the liquid hydrocarbon is within the range of
about 20 to about 45% by weight.
14. The process of claim 1 wherein at least a major portion of the
wax particles is substantially solidified.
15. The process of claim 1 wherein the waxy hydrocarbon mixture has
an average pour point within the range of about 75.degree. to about
150.degree.F.
16. The process of claim 1 wherein the molten wax, before it comes
in contact with the hot, wax immiscible fluid, is heated to a
temperature sufficient to remove substantially all crystalline
structure in the molten wax and to obtain maximum durability of the
wax particles in the slurry.
17. The process of claim 1 wherein a diluent miscible with the
liquid hydrocarbon is admixed with the slurry to facilitate
transportation.
18. The process of claim 17 wherein the diluent is a liquid crude
oil containing less than 10% wax.
19. In a process for transporting waxy petroleum crudes having an
average pour point of about 75.degree. to about 150.degree.F. by
fractionating the crude into at least a wax fraction and a liquid
fraction, forming substantially round particles of wax, slurrying
the particles in the liquid fraction and transporting the slurry,
the steps comprising introducing molten wax fraction at a
temperature of about 20.degree. to about 150.degree.F. above its
melting point into hot water flowing cocurrent to the introduction
of the molten wax fraction and at flow rates sufficient to form
substantially round particles having a substantially smooth outer
shell and thereafter introducing the wax particles into a colder
water at a sufficiently low temperature to substantially solidify
the wax particles.
20. The process of claim 19 wherein the molten wax fraction is
about 50.degree. to about 125.degree.F. above its melting
point.
21. The process of claim 19 wherein the hot water is at least about
20.degree. to about 80.degree.F. below the temperature of the wax
fraction as the latter is dispersed therein.
22. The process of claim 19 wherein the temperature of the hot
water is at least about 140.degree.F.
23. The process of claim 19 wherein the molten wax fraction is
under laminar flow as it is introduced into the hot water.
24. The process of claim 19 wherein the hot water flowing cocurrent
to the molten wax fraction is under laminar flow.
25. The process of claim 19 wherein the concentration of solidified
wax particles in the liquid fraction is within the range of about
20 to about 45% by weight.
26. The process of claim 19 wherein a liquid crude oil containing
less than 10% wax is admixed with the slurry to facilitate
transportation.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention.
Waxy hydrocarbons are fractionated into at least two fractions. The
wax fraction is congealed and slurried in the fluid fraction prior
to storage or transportation.
2. Description of the Prior Art.
Pumping waxy hydrocarbon mixtures at temperatures below the pour
point is very difficult. Many methods have been tried to improve
the pumpability of waxy crudes, e.g. heat transfer methods,
chemical agents to improve fluidity of the mixture, pour point
depressants, diluents, etc., but in general these methods have not
been commercially acceptable. In addition, the oil has been
dispersed in water to form a water-external emulsion and the
combination pumped at temperatures below the pour point of the
crude oil.
Patents representative of the art include:
Kells, U.S. Pat. No. 271,080: Wax is separated from crude oil by
pumping the crude oil, e.g. in small streams of jets, into the
bottom of a tank containing a brine at a temperature sufficiently
low to congeal the wax which is recovered in the brine.
Oberfell, et al., U.S. Pat. No. 2,526,966: Viscous crude oils are
transported by removing the light hydrocarbons, hydrogenating the
residue, combining the hydrogenated product and the light
hydrocarbons and transporting the mixture.
Scott, et al., U.S. Pat. No. 3,269,601: The pumpability of waxy
crudes is improved by dissolving in the oil, at superatmospheric
pressure and while above its pour point, gases such as N.sub.2,
CO.sub.2, flue gas, and hydrocarbons containing 1-3 carbon atoms.
The "gas becomes associated in some way with wax crystals and
prevents the precipitated wax from agglomerating to form strong wax
structures".
Watanabe, U.S. Pat. No. 3,468,986: Teaches the formation of
spherical particles of wax by melting the wax, then dispersing the
spheres in water maintained at a temperature above the
solidification temperature of the wax and thereafter cooling the
dispersion to solidify the dispersed droplets. The particles can be
coated with finely divided solids such as calcium carbonate, etc.
Watanabe teaches that it is known in the art to disperse waxy
particles by molding, prilling, spray drying, extruding, etc.
Titus, U.S. Pat. No. 3,527,692: Crushed oil shale is transported in
a solvent such as crude oil, retorted shale oil, or fractions
thereof.
Dorsey, U.S. Pat. No. 3,321,426, teaches the formation of
freeflowing wax particles by agitating molten wax in water
maintained at a temperature above the melting point of the wax and
thereafter cooling the mixture and separating the congealed pellets
of wax. The wax is sheared as it is extruded into the water.
Allibone et al., U.S. Pat. No. 3,234,122: Waxy crudes are
transported by first precipitating the wax in the form of large
crystals and thereafter transporting the crude oil containing the
crystals. The crystals are formed, e.g., by heating the crude oil
to 200.degree.F. and then cooling at 1.degree.F/min to
60.degree.F.
Scott, U.S. Pat. No. 3,292,647, teaches transportation of waxy
crude oils in a pipeline by shearing the crude at a temperature
below its pour point to break down the wax and form a fine
dispersion, then introducing a gas, e.g. N.sub.2, CO.sub.2 and
natural gas, with the sheared crude to prevent regrowth of the wax
crystals and thereafter pumping the composition.
This technology, except for heat transfer systems, e.g. heat
exchangers to heat the crude oil, and crude oil-water suspension
systems, has generally proven to be commercially unattractive where
the crude oil contains relatively large concentrations of wax.
U.S. Pat. No. 3,804,752 to Merrill, Jr. et al teaches transporting
waxy crude oils by fractionating the crude into a high pour point
fraction and a low pour point fraction, thereafter slurrying the
congealed fraction in the low pour point fraction and pumping the
slurry.
SUMMARY OF THE INVENTION
Applicants have discovered an improved process of transporting
"waxy" hydrocarbon mixtures at seasonably ambient temperatures by
fractionating the hydrocarbon mixture into at least a relatively
high pour point (wax) fraction and a relatively low pour point
(liquid) fraction, introducing the wax fraction as droplets, at a
temperature above its melting point, into a hot wax immiscible
fluid flowing under laminar flow conditions and flowing cocurrent
to the wax fraction, and then into a colder wax immiscible fluid to
congeal the particles. Thereafter, the wax particles are separated
from the wax immiscible fluid and combined with a liquid
hydrocarbon and the resulting slurry transported, preferably in a
pipeline .
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a typical embodiment of the invention wherein the waxy
crude oil enters a distillation column and is separated into a low
pour point liquid fraction and a high pour point wax fraction. The
molten wax fraction is extruded into the bottom and comes in
contact with hot water introduced externally and concentric to the
wax through the nozzle. Colder water enters at the top and at the
bottom of the column. Water effluent exits at the bottom of the
column. The extruded wax congeals into beads before it reaches the
top of the column. The beads and some of the water flow out of the
column into a separator and the beads are recovered. Thereafter,
the beads are combined with the liquid fraction to obtain a
transportable slurry.
FIG. 2 compares the rate of stabilization of two different
slurries, one containing prills and the other beads.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
This invention is used to transport waxy hydrocarbon mixtures
having an average pour point above the ambient temperature of the
transportation system. Waxy hydrocarbon mixtures are mixtures
containing wax. Some asphaltenes can be tolerated. Wax is defined
as the precipitate formed by dissolving one part of hydrocarbon
mixture in ten parts of methyl ethyl ketone at about 80.degree.C.
and cooling the mixture to -25.degree.C. Examples of waxy
hydrocarbon mixtures include crude oils, shale oil, tar sand oil,
fuel oil, gas oil and other waxy hydrocarbon mixtures and mixtures
of two or more of the same type or different hydrocarbon mixtures.
Waxy crude oils are particularly useful in this invention. Examples
of average pour points of waxy hydrocarbon mixtures particularly
useful with this invention include about -10.degree. to about
200.degree.F., preferably about 0.degree. to about 150.degree.F.,
and more preferably 75.degree. to about 150.degree.F.
The hydrocarbon mixture is separated into at least two fractions, a
liquid overheads fraction which has a relatively low pour point
(referred to as the liquid fraction) and a wax bottoms fraction
which has a relatively high pour point (referred to as the wax
fraction). The wax fraction is about 1 to about 80% and preferably
about 5 to about 70% and more preferably about 10 to about 60% by
weight of the original hydrocarbon fraction. Fractions other than
the mentioned fractions can be obtained and used for other
purposes.
Fractionation can be by any process which separates the hydrocarbon
mixture into high and low pour point fractions. Optionally, a part
of the wax fraction can be cracked and/or hydrogenated during
fractionation or before congelation.
The molten wax is preferably about 0.degree. to about 175.degree.F.
and more preferably about 20.degree. to about 150.degree.F. and
most preferably about 50.degree. to about 125.degree.F. above its
melting point (as defined by "inverse cooling curve" in
Characterization of Petroleum Waxes, S. W. Ferris, Chapter 1 of The
Proceeding of the ASTM - TAPPI Symposium on Petroleum Waxes, Feb.
18-21, 1963, Special Technical Association Publication, STAP, No.
2) as it is dispersed into the column. Also, it is preferred that
the temperature of the molten wax be high enough that there is
substantially no crystalline structure (including hydrocarbons
other than wax) within the molten wax and that maximum durability
or integrity of the resulting wax particles is obtained--see
Example IV for working example of this preferred temperature range.
If the wax fraction has not been cooled to a temperature below the
above preferred temperature range since coming from the
distillation column, it can be introduced into the column and still
obtain durable wax particles.
Cooling
The molten wax is cooled in two stages. First, the wax is dispersed
into a hot wax immiscible fluid (coolant) at a temperature which
relatively slowly cools the wax to form smooth, substantially
round, preferably spherical, shells around the dispersed wax
particles. Then, the particles are passed into a colder coolant to
substantially complete the solidification of the particles.
The coolant should have a temperature above the pour point of the
wax, but below the wax temperature. Preferably the coolant is at
least about 5.degree. to about 150.degree.F. and preferably about
10.degree. to about 10.degree.F. and more preferably about
20.degree. to about 80.degree.F. below the molten wax temperature
as it is dispersed into the column. Examples of useful temperature
include at least 140.degree.F. and preferably about 180.degree.F.
when the coolant is water. The wax composition and equipment design
will control the amount of temperature differential between the
molten wax and the coolant. If the coolant is too cold, the
extruding wax will be filamentary and if the temperature is too
hot, the flow path required to form the spherical shell will be
excessive. Agglomeration indicates too little cooling and dimpling
indicates excessive coolant-to-wax temperature differential (i.e.
differential cooling temperature change is too sudden and too
large).
Superior results are obtained through the use of substantially
concentrically arranged nozzles wherein the wax is injected or
extruded into the coolant through a central orifice preferably
about 0.030 inch to about 0.5 inch and more preferably about 0.050
inch to about 0.100 inch in diameter. The coolant can be introduced
through an annular nozzle so that it flows cocurrent and concentric
to the wax. The velocity of the wax and coolant is preferably the
same and more preferably is within the laminar flow region.
Different flow rates can cause turbulence, reduce the size and
roughen the surface of the sphere. Single hole nozzles are useful
and with this type of nozzle the coolant can flow concentric and
cocurrent to the wax by thermal convection currents.
The cooled wax particles should have an average diameter of about
0.05 or less to about 20 or more mm. and preferably about 0.1 to
about 10 mm. and more preferably about 1 to about 8 mm. The
particles are preferably spherical, but can be elongated and can be
of either substantially uniform or random diameter sizes. The
physical shape and size is affected by the temperature and flow
rate of the hot coolant and the molten wax and by introducing the
coolant concentric to the nozzle(s).
The wax particles then come in contact with a colder wax immiscible
fluid (colder coolant) to obtain a substantially solidified
particle. The colder coolant can be about ambient temperature and
is preferably about 3.degree. to about 100.degree.F. below the
solidification temperature of the wax. The particles follow a
sufficiently long flow path to substantially solidify the wax
droplets. It is preferred that the temperature differential between
the inlet cold coolant and the outlet fluid in the column be large
enough to obtain maximum utilization of the enthalpy of the
liquid.
Temperature change from the hot coolant to the colder coolant can
be controlled by introducing the coolants at one or more places
within the tower and by regulating either heat input or output in
the column by heat exchangers, etc. The temperature change can be a
gradual change or a combination of a gradual change in the bottom
of the column and an abrupt change in the top of the column, or any
desired modification thereof. However, it is necessary that the
temperature change be sufficient to cool the average temperature of
the wax particles to a temperature below the average pour point of
the wax or that the transportation system be at a sufficiently low
temperature to complete solidification of the particles.
The coolant and/or the colder coolant can be any fluid that is
substantially immiscible with the wax at the extruding or
dispersing temperature. Examples include alcohols, ketones, esters,
and other polar or semipolar organic compounds. Preferably, the
coolants are water. Also, it can be a combination of two or more
coolants.
Solidification, as used herein, includes congealing, crystalization
and making into a consistency like jelly. Preferably the solidified
particle has at least a hard veneer on the wax particle. The
interior of the particle can be fluid, but is preferably
substantially solid.
A surfactant can be incorporated into the molten wax. Volume
amounts of 0.001 to about 20% and preferably about 0.01 to about
10% and more preferably about 0.1 to about 1%, by volume based on
the fraction, are useful. Examples of useful surfactants include
fatty acids, e.g. containing about 10 to about 20 carbon atoms and
preferably the monovalent cation-containing salts thereof. Sorbitan
monolaurate is an example of a useful surfactant. Preferably the
surfactant is a petroleum sulfonate and more preferably one
containing a monovalent cation, e.g. sodium or ammonium, and
preferably having an average equivalent weight of about 200 to
about 600, more preferably about 250 to about 500, and most
preferably about 350 to about 420.
At the top of the column, the solidified wax particles are removed.
This can be effected by removing the particles with the coolant and
thereafter separating the particles by means known in the art, e.g.
by mechanical means such as straining the coolant from the
particles, etc.
In a preferred embodiment, the liquid fraction or a liquid
hydrocarbon is introduced into the top of the column to physically
remove the wax particles. In this case, an interface between the
coolant and the liquid hydrocarbon is maintained at a point below
the elevation in the column at which the particles are removed. The
particles tend to accumulate at the interface.
Slurry Preparation
The liquid hydrocarbon (this term is defined to include the liquid
fraction) should be at least about 5.degree. and more preferably at
least about 30.degree. and most preferably at least about
70.degree.F. below the solution temperature of the solidified wax
particles when the liquid hydrocarbon is slurried with the
particles. Solution temperature is defined as that temperature at
which a major portion of the particles are in solution of the
liquid hydrocarbon.
During the slurrying operation, the temperature of the liquid
hydrocarbon is such that the resulting slurry temperature is
preferably about 5.degree. to about 10.degree.F. above and more
preferably 0.degree. to about 5.degree.F. above the minimum
seasonably ambient temperature of the transportation system. Also,
it is preferred that the temperature of the liquid hydrocarbon
during slurrying is about 30.degree.F. and more preferably about
70.degree.F. below the solution temperature of the particles in the
fraction.
The usual techniques and equipment for slurrying solids in liquids
are useful in our process. However, the liquid hydrocarbon should
be at least about 5.degree. and more preferably at least about
30.degree. and most preferably at least about 70.degree.F. below
the solution temperature of the particles in the liquid hydrocarbon
and have a pour point at least 1.degree. and preferably at least
5.degree.F. and more preferably at least about 15.degree.F. below
the average temperature of the transportation system.
Also, it is preferred that the temperature of the liquid
hydrocarbon be low enough during the slurrying operation to provide
a slurry temperature preferably about 10.degree.F. below to about
10.degree.F. above and more preferably at about the minimum
seasonably ambient temperature of the transportation system.
A liquid and/or gaseous diluent such as straight run gasoline,
reservoir condensate or light hydrocarbon can be admixed with the
liquid hydrocarbon before, during or after the slurrying operation.
Any diluent is useful as long as it is miscible with the liquid
hydrocarbon, has a pour point below the minimum temperature of the
transportation system and does not readily solubilize the wax
particles or cause any reaction to substantially increase the
solubility of the wax particles in the liquid hydrocarbon. Crude
oils can be used as the diluent, but preferably the crude oil has a
wax concentration less than about 10%--the wax can be in
crystalline form. Where a gaseous diluent is used, it is preferred
that it be dissolved in the slurry at transportation condition to
prevent cavitation of pumps.
Concentration of the wax particles in the slurry is preferably
about 1 to about 60% or more and preferably about 5 to about 55%
and most preferably about 20 to about 45% by weight.
Transportation of the Slurry
The temperature of the slurry during transportation is preferably
below the solution temperature of the wax particles at all times.
The slurry can stand temperatures higher than the solution
temperature of the wax for short periods of time so long as
substantial amounts of the wax particles are not reliquefied. But
if the temperature does exceed the solution temperature, the slurry
can still be effectively transported in a pipeline as long as the
temperature does not cycle more than preferably about
3.degree.-5.degree.F. below the highest temperature reached by the
slurry during transportation. Also, as long as the temperature is
increasing during the pipelining, even above the solution
temperature, there is no detrimental effect. However, when the
temperature decreases to more than about 10.degree.F. below the
highest transportation temperature, then large pressure drops occur
if the particle solution has been substantial.
Transportation system, as used herein, includes tanks, tank trucks,
tank trailers, tank barges, ships or tankers, pipelines, pipelines
and tank batteries, or holding tanks and combinations thereof.
Preferably the transportation system is a pipeline or a pipeline
plus tanks.
The slurry can be transported under laminar flow, transitional flow
(e.g. Reynolds Nos. about 2000 to about 4000) or turbulent flow
conditions in the conduit. It is preferably transported under
laminar and transitional flow conditions--turbulency within the
pipeline tends to break apart and solubilize the wax particles in
the liquid hydrocarbon of the slurry.
The slurry is preferably transported in a conduit wherein the
average maximum temperature of the conduit is below the average
solution temperature of the wax particle in the liquid
hydrocarbon.
In addition, the average temperature of the conduit is desirably
not below the average pour point of the liquid hydrocarbon and
preferably is at least about 20.degree.F. and more preferably at
least about 25.degree.F. above this pour point.
A gas soluble in the liquid hydrocarbon can be added to the slurry
to facilitate pumpability. Examples of gases include CO.sub.2,
hydrocarbons containing less than about 3 carbon atoms, N.sub.2,
flue gases and like gases. Preferably the gas is immiscible with
the wax particles.
The wax particles can also be coated with solid materials or other
agents to inhibit agglomeration and to permit higher slurry
transportation temperatures.
EXAMPLES
The following examples are presented to teach working embodiments
of the invention. Unless otherwise specified, the percents are
based on weight.
EXAMPLE I
A waxy crude oil (having an average pour point = 115.degree.F.) is
distilled into a liquid fraction (average pour point 17.degree.F.)
and a wax fraction (average pour point 125.degree.F., melting point
= 180.degree.F.). The wax fraction is stored at ambient temperature
and thereafter is heated to and maintained at 200.degree.F. for at
least 2 hours; it is then fed at a rate of 300 lbs/hr into a
manifold containing 37 nozzles positioned in the bottom of an 8 in.
dia. .times. 7 feet water column. The nozzles are spaced 1/2 inch
apart. Each nozzle is 1.375 inches long with a 0.08 inch diameter
hole drilled lengthwise 1.275 inches deep. Wax is fed into the side
of the nozzle from the manifold. Hot water is flowed cocurrent to
the wax and concentric to the nozzles at a rate of 0.75 gal/min and
at an initial temperature of 180.degree.F. Cold water at
45.degree.F. is introduced peripherally into the top of the column
and flows to the bottom of the column by free convection. Water may
be drawn off the bottom of the column if additional cooling is
needed. The cocurrent water and beads exiting the top of the column
have an average temperature of 80.degree.F. The average diameter of
the congealed beads is about 3/16 inch. A slurry is obtained by
stirring sufficient amounts of the beads into a holding tank with
the liquid fraction to obtain a bead concentration of 27.5%. The
slurry is then pumped through a 6 inches diameter pipeline at
38.degree.F. without difficulty.
EXAMPLE II
The wax of Example I that has been stored at ambient temperature is
prilled by introducing molten wax through 19 nozzles (inside
diameter = 0.035 inch) at 200.degree.F. and at a rate of 190 lbs/hr
into a prilling tower. The prills fall approximately 25 feet
through a 2 foot inside diameter prilling tower and are cooled with
a fine mist of water. The prills are collected at the bottom of the
prilling tower and separated from the water. Thereafter, a slurry
is obtained by combining the prills with the liquid fraction from
Example I at a concentration of 27.5%.
EXAMPLE III
Comparative Test of Beads vs. Prill
A slurry containing the liquid fraction of Example I and 27.5% of
the beads of Example I and the slurry of Example II are tested for
percent disintegration of the wax particles for periods of two and
3 hours by agitating the slurry at 40.degree.F. with an impeller
rotating at 650 rpm. The percent solids left in the slurry after
each test is determined by separating the solids from the slurry by
elutriation using acetone as the carrier fluid. The solids which
are not significantly changed after the disintegration tests are
separated from the slurry and weighed. Table 1 indicates results of
the test:
TABLE 1 ______________________________________ % Disintegration %
Disintegration after agitation after agitation Sample (Two Hours)
(Three Hours) ______________________________________ Slurry 1
(Beads) 74 82 Slurry 2 (Prills) 89 92
______________________________________
EXAMPLE IV
The procedure of Example I is repeated except the wax fraction is
heated to and maintained at 280.degree.F. for at least 2 hours and
then it is extruded at 220.degree.F. The beads obtained by this
example are then slurried in the liquid fraction of Example I to
obtain a slurry containing 27.5% of beads. This slurry is then
tested in the solids disintegration test and the following data are
obtained:
TABLE 2 ______________________________________ % Disintegration %
Disintegration after agitation after agitation Sample (Two Hours)
(Three Hours) ______________________________________ Slurry
containing beads obtained from Example IV 44 61
______________________________________
These data compared to slurry 1 of Example III (contains beads)
show that destruction of residual crystal structures in the melted
wax before congelation provides stronger beads.
EXAMPLE V
A slurry containing 27.5% of the prills of Example II and a slurry
containing 27.5% of the beads of Example I are tested for
stabilization--the hydrocarbon phase in both slurries is the liquid
fraction of Example I. Stabilization is defined as the transfer of
material between solid and liquid phases until equilibrium is
attained. As stabilization progresses, the appearance and apparent
viscosity of the slurry change. Stabilization is measured by the
pressure drop per unit pipe length as a function of time at
constant shear rate and slurry temperature. When stabilized, no
further change in pressure drop occurs. It is found that the
stabilization rates as indicated by a plot of .DELTA.P/L vs. Time
for the bead slurry is less than the prill slurry. FIG. 2
illustrates the data obtained by this example. These data are
obtained in a pipeline having an inside diameter of 2 inches and a
length of 150 feet and the slurries are run therethrough at the
same temperature. These data show that the prill slurry and the
bead slurry stabilize to the same pressure drop, but that the bead
slurry stabilizes at a slower rate than does the prill slurry. This
is significant in terms of slurry pumping horsepower
requirement.
It is intended that all equivalents obvious to those skilled in the
art be incorporated within the scope of the invention defined
within the specification and appended claims.
* * * * *