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Патент USA US3098713

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Patented July 23,1963
I ,
Alfred L. Baker, .lr., Brinton Lea, Thornton, Pa., assignor
to Sun Oil Company, Philadelphia, Pa., a corporation
of New Jersey
N0 Drawing. Filed Oct. 26, 1960, Ser. No. 64,989
1 Claim. (Cl. 21-605)
low 35 ° \F., and is su?iciently dry to retain the water con
tent of petroleum oil within the range of 10 to 20 ppm.
during normal periods of storage. The air can be intro
duced continuosly or periodically. Usually, it is pre
ferred to circulate the air continuously over the surface
of the stationary oil under a forced draft. The mini
mum air flow rate is de?ned as that which will maintain
a slight positive pressure on the outlet vent.
The invention, while operable to the storage of some
This invention relates to the bulk storage of petroleum
oil. It particularly relates to the storage of electrical oils 10 volatile hydrocarbons, should be restricted to non-volatile
oils. Treatment of lower boiling fractions by the inven
whereby an increase in water content of the oil is pre
tion might cause excessive hydrocarbon losses, through
vented. It especially relates to an improved method of
and might cause hazardous operating condi
storing electrical oils in a storage vessel equipped with
breathing means.
The following examples illustrate the invention:
Example I
Particular non-volatile petroleum oils, that is, oils hav 15
ing a Saybolt viscosity above about 50 seconds at 100° F.
and which boil mainly above 400° F., such as turbine oils,
white oils, spindle oils, transformer oils and the like must
be essentially free from dispersed water if their quality is
Transformer oil having a Saybolt viscosity of 56 sec- -
onds at 100° F., boiling between 500 and 700° F., and
containing 17 p.p.m. moisture was pumped into a 2500
to be deemed satisfactory. It has been found that sus-' 20
barrel capacity storage tank which was equipped with
pended water imparts a cloudy appearance which reduces
marketability of the oil. More important, however, is the
standard breathing valves. After two weeks of storage,
fact that oils which are used for dielectric purposes must
the water content of the oil had increased to 31 p.p.m.
For these reasons, the transformer oils are treated under
essentially anhydrous conditions and are sent to bulk stor
age containing no dispersed water and containing from
31 ppm. of moisture is undesirable for dielectric use.
The above example illustrates the conventional method
be essentially free from dissolved water as well as sus
of storing oils. ‘It is clear that this method is unsatisfac
pended water. Otherwise, the dielectric strength and 25 tory
for storing transformer oils since an oil containing
other electrical properties of the oil are adversely affected.
Example 11
The oil from Example ‘I was pumped into a different
2500 barrel tank ‘which was equipped with an ambient air
blower. Ambient air was forced over the surface of the
less than 30 parts per million (p.p.m.) of dissolved mois
A transformer oil containing less than 30 p.p.m. dis
solved moisture, and preferably less than 20 p.p.m., will
oil for two weeks. At the end of this period, the stored
oil had increased in moisture content from 17 ppm. to
have a satisfactory dielectric value. However, it has been
found that an oil, upon storage in a vessel which has 35 37As
shown above, the mere passage of air through the
breathing means, will absorb moisture from the ambient
vapor space does not prevent the absorption of moisture
air that is breathed into the tank. It is not uncommon
by the stored oil. In fact, the example indicates that
‘p for oil under such storage conditions to increase in water
moisture absorption rate is increased by forcing ambient
a content 12-20 p.p.m. in one week or even 20-75 ppm. in
' two weeks.
air into the vapor space of the tank.
When, for example, transformer oil contains 40
Example III
' 30~75 ppm. of moisture or more it is unsatisfactory for
a dielectric uses. Excessive moisture in the oil shortens
The transformer oil from Example I was dumped into
the life of transformer insulation, causes sludging of the
another 2500 barrel capacity storage tank which was
oil, produces electrical losses and increases operating
equipped with a compressed air hose connected to one side
temperatures of the transformer.
of the tank. On the opposite side, an outlet vent was
\It is an object of the present invention to provide an
available. For two weeks, air was compressed to 80
improved method for storing non-volatile petroleum oils
p.s.i.g., cooled to 70° 'F., freed of condensed water by pas
whereby moisture absorption is minimized.
sage through a knockout pot, and introduced into the
The present invention applies to the storage of non
space above the surface of the oil. It was passed
volatile petroleum oils in bulk storage vessels which nor 50 under forced draft over the surface of the oil and re
mally would have breathing means.
moved under a slight positive pressure from the vent on
ing means” as used herein is de?ned as any means whereby
the opposite side of the tank. The stored oil, at the end
internal tank pressure is equilibrated to external changes
of the two week period, tested 17 ppm. water, which was
in atmospheric conditions, i.e., changes in temperature
the same as its original water content. The air entering
and leaving the tank had a dew point between 30 and
and pressure. ‘Normally, a non-volatile hydrocarbon
storage vessel contains valve mechanism whereby ambient
35 ° F.
air is passed into the vapor space of the tank when the ex
ternal air is warmer than the internal air. On the other
hand, the vapor space of the tank is partially exhausted
as the external air temperature cools below the internal
equilibrium temperature. In this manner, a storage ves
sel “breathes.” The term also includes those storage ves
sels having simply an open vent.
Thus, as shown in Example III the present invention
provides a simple, economical method of storing petro
leum oils having a susceptibility for moisture whereby the
absorption of moisture is prevented. The invention is a
combination method which comprises (1) con?ning the
petroleum oil as a stationary liquid in a storage vessel
equipped with breathing means; (2) compressing ambient
In accordance with the present invention, moisture ab
sorption by stored petroleum oils is prevented by passing
a stream of compresesd, dried air over the surface of the
oil in storage.
Thus, the present invention is based on the discovery
7 that ambient air compressed to between 30 and 500 pounds
per square inch gauge (p.s.i.g.), cooled to ambient tem 70
perature (e.g. 35 to 80° F.), and freed of condensed mois
ture will have a dew point of less than 50° F., usually be
air to a pressure between 30 and 500 p.s.i.g., cooling to
ambient temperature, and removing the condensed water
therefrom; (3) introducing the treated air into the vapor
space above the surface of the oil; (4) passing the treated
air over said surface; and (5) removing the air from the
storage vessel at a level above the surface of the oil.
-I claim:
The method of storing non-volatile petroleum oil con
taining less than 30 parts per million water which com
prises in combination: con?ning the petroleum oil as a
stationary liquid in a storage vessel equipped with breath
ing means; introducing a stream of hereinafter speci?ed
air into said vessel at a level above the surface of the oil;
compressing ambient air to a pressure Within the range
of 30 to 500 pounds per square inch gauge, cooling said
compressed air until a dew point of less than 50° F. is
attained, removing from said cooled air the condensed
water, and introducing the treated air into said vessel as 10
hereinabove speci?ed; passing said treated air over the
surface of the oil, and removing from said vessel at a level
above the surface of the stored oil the stream of air hav
ing substantially unchanged Water content.
References Cited in the ?le of this patent
2, 822,743
Colvin _______________ __ Feb. 11,
Germany ____________ __ Feb. 23,
Great Britain __________ __ Feb. 4,
Great Britain __________ __ Oct. 3,
Great Britain __________ __ May 3,
Great Britain __________ __ July 17, 1957
Perry, Chemical Engineers Handbook , 3rd ed., 1950,
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