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Description  |
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This invention relates to a distillation tower and method especially
adapted for use in rerefining modern-day additive-supplemented waste oils
in a manner to achieve virtually quantitative recovery of salable products
at relatively low operating costs and without complex and costly chemical
pretreatment of the waste oil to be distilled. More particularly, it is
concerned with such a tower and method wherein, in preferred forms, an
upright, cylindrical, two-stage tower having a tangential waste oil inlet
is provided, along with means for maintaining the temperature conditions
within the tower during processing for maximizing vaporization of the
hydrocarbons with a minimum of subsequent condensation thereof. This
increases the yield of valuable hydrocarbons from the waste oil, while at
the same time preventing undesirable decomposition or cracking of the oil.
However, the tower and method hereof are not limited to rerefining of
waste oil, but can be adapted for use in conjunction with various types of
distillation processes and equipment, including the treatment of virgin
oil and solvents, for example.
The waste oil rerefining industry has, in recent years, become only
marginally profitable. The industry has suffered from a variety of ills,
including relatively low product yields, low virgin oil prices,
restrictive governmental policies in connection with rerefined oil, and
increasingly stringent environmental pollution standards. These problems
have been so severe that the rerefining industry in the United States has
decreased from approximately 140 installations a few years ago to less
than 30 today. This decline has occurred in spite of the fact that
tremendous quantities of recoverable waste oil are produced annually in
the United States. Thus, the United States has been in the unseemly
position of paying exhorbitant prices for increasingly scarce virgin oil
on the one hand, while literally throwing away extremely valuable and
reusable waste oil on the other hand, simply because of a lack of means
for efficiently and effectively rerefining the waste oil.
A number of waste oil rerefining methods have been proposed in the past.
Principal among these are the socalled acid-clay, solvent
extraction/acid-clay, IFP propane clarification, distillation/clay and
hydrotreating processes. The acid-clay process has been used longer and is
more widely accepted than perhaps any of the other methods used for
rerefining used oils. In this process, the oil is first dehydrated and the
light ends removed by fractionation. This treated oil is next contacted
with sulfuric acid to remove a substantial proportion of the contaminants
from the lube oil. The acid treated lube oil is then generally "polished"
by contacting it with activated clay or diatomaceous earth for removing
suspended carbon and the remaining acid. The most significant problem
confronting rerefiners using this process is disposal of the "acid-sludge"
generated by the acid treatment. Specifically, this waste material
contains oil additives, ash, dirt and metals, sulfuric acid, and from 20
to 40% of the potentially reusable oil itself. As can be appreciated, this
conglomeration presents severe problems from the standpoint of
environmental pollution, therefore making disposal of the acid-sludge
costly and time consuming. This, in addition to the fact that a
significant quantity of the valuable and recoverable waste oil is lost
through the process, has detracted from the usefulness of the acid-clay
process.
The solvent extraction/acid-clay process is a relatively new concept and
involves pretreatment of the dehydrated waste oil feed stock with
relatively complex and costly solvents, followed by conventional acid
treatment and clay contacting. While the solvent treatment increases
product yields, the cost thereof is considerable and therefore little, if
any, overall economy is realized.
IFP propane clarification is not in and of itself a complete rerefining
process, but rather is a method of pretreating the dehydrated waste oil
feed stock. The method generally involves propane extraction, propane
separation, and propane recovery. In actual practice this method has not
been widely followed, by virtue of the complexity of the concept and high
costs, both in terms of original construction and in operation.
The distillation/clay process involves attempted removal of contaminants
from a solvent-treated waste oil feed stream by means of vacuum
distillation, followed by clay filtration as a polishing step. The primary
problem with this process involves the distillation tower itself.
Specifically, use of a conventional vacuum tower having internal trays or
bubble caps quickly results in plugging of the tower. Of course, the
inherent disadvantages described above of solvent pretreatment remain in
this process.
Finally, hydrotreating or hydrofinishing involves a polishing step
generally used in conjunction with one of the various rerefining methods.
This polishing process involves passing a stream of oil and hydrogen over
a catalytic bed to yield various grades of oil of good quality, with
little or no waste. Notwithstanding the theoretically desirable results
achievable with this process, it will be recognized that hydrotreating
does nothing to eliminate the problems associated with treatment of the
oil prior to polishing. Furthermore, the process requires significant
amounts of hydrogen, and this normally requires a substantial capital
expenditure or greatly increased operating costs. Moreover, use of
hydrogen necessitates complicated handling and storage procedures, and
creates safety hazards. Finally, the feed stream to the hydrotreating
stage must be virtually free of contaminants such as metallic compounds
and organic additives. Otherwise, these impurities may foul or destroy the
expensive catalyst in the hydrotreating reactors, thus detracting from the
quality of the end product and increasing maintenance expenses.
It is believed that a prime cause of many of the problems encountered with
prior rerefining methods stems from the presence of complex additive
packages in modern-day oils. For example, additives such as V.I.
improvers, detergents and/or dispersants are believed to interfere with
the usual chemical pretreatments, thus reducing the efficiency thereof.
In sum therefore, it will be appreciated that the prior methods of
rerefining have been deficient in one or more critical respects. Thus,
there is a real need in the art for a conceptual breakthrough which will
solve the problems of cost, complexity, adverse environmental effects, and
low yield in the rerefining industry.
The following patents are of background interest in connection with
rerefining processes and equipment: U.S. Pat. Nos. 2,162,195, 2,529,310,
3,607,731, 3,620,967, 3,625,881, 3,639,229, 3,791,965, 3,879,282,
3,930,988, 2,645,607, 3,544,428, 1,586,376, 2,061,666, 2,330,326,
2,477,595, 1,345,452, 1,413,327, 1,518,684, 1,799,530, 2,023,205,
2,112,360, 1,988,773, 2,162,195, 3,639,229, 3,763,036 and 4,021,333.
It is therefore the most important object of the present invention to
provide a distillation tower and method especially adapted for rerefining
of modern-day additive supplemented waste oils and which achieve
significant processing economies as compared with prior methods by virtue
of virtually quantitative yield of salable products, simplicity of
construction and operation, and elimination of environmental hazards, in
order that rerefining of waste oils is rendered economically feasible and
attractive. An additional object is to provide a novel distillation tower
and method usable in processes other than waste oil rerefining, e.g., in
treating virgin oil or solvent.
As a corollary to the foregoing, another object of the invention is to
provide a distillation tower which preferably includes an elongated,
cylindrical, enclosed chamber, means for supplying hot waste oil to the
chamber, and for imparting a whirling motion to the oil within the chamber
in order to enhance vaporization of a hydrocarbon fraction from the waste
oil, along with means for maintaining the proper temperature conditions
within the tower chamber, i.e., at a level for maintenance of a
substantial fraction of the vaporized hydrocarbons in the vapor state, but
below the temperature level sufficient to substantially decompose or crack
the oil at the prevailing pressure conditions within the tower chamber; in
alternate forms, the temperature-maintaining means can include peripheral
wall heating apparatus such as electrical heating tape or conventional
fluid heat-transfer apparatus, or appratus for flooding the chamber with
an excess of hot waste oil during processing whereby the tower temperature
conditions are maintained by virtue of the presence of the excess hot oil,
and means for recycling at least a portion of the excess waste oil passing
through the tower.
Another object of the invention is to provide a distillation tower which
includes an elongated, upright chamber divided into respective, vertically
adjacent first and second subchambers by means of an apertured partition,
along with means for equalizing pressures within the subchambers so as to
facilitate vapor-liquid separation within the tower.
Finally, another object of the invention is to provide a tower and method
of the type described which include a tangentially disposed waste oil
inlet adjacent the upper end thereof, along with internal baffle structure
adjacent the tangential inlet for directing vaporized hydrocarbon and
residual liquids around the confining sidewalls of the chamber and
imparting a desirable whirling or cyclone motion thereto; in preferred
forms, nozzle apparatus is provided within the inlet structure for
spraying of the waste oil into the tower as this has been found important
for maximum vaporization of hydrocarbons from the hot waste oil.
In the drawing:
FIG. 1 is a vertical sectional view of the preferred distillation tower in
accordance with the invention;
FIG. 1A is a fragmentary sectional view of a tower similar to that
illustrated in FIG. 1, but depicts the use of coil structure surrounding
the chamber wall for temperature maintenance purposes;
FIG. 2 is a sectional view with parts broken away for clarity and taken
along line 2--2 of FIG. 1;
FIG. 3 is an enlarged sectional view taken along line 3--3 of FIG. 1 and
depicting the preferred oil inlet nozzle structure; and
FIG. 4 is a schematic representation of the overall processing apparatus
used in the preferred method hereof.
Referring now to the drawing, a distillation tower 10 is illustrated in
FIG. 1. Broadly, tower 10 includes structure 12 serving to define an
elongated, enclosed, upright chamber 14 having a first upper outlet 16 for
vaporized hydrocarbons, along with a valve-controlled lower second outlet
18 for liquid bottoms. Means broadly referred to by numeral 20 is also
provided for supplying hot waste oil to the chamber 14, and for imparting
a whirling motion to the oil within the chamber 14 in order to enhance
vaporization of hydrocarbons from the hot oil. In addition, an
intermediate partition 22 is disposed within chamber 14 in order to divide
the latter into first and second, vertically adjacent subchambers 14a and
14b. Means 24 for allowing flow of oil from the first to the second
subchamber, and for equalizing pressures within the subchambers 14a and
14b, is also provided and includes a central aperture 26 through the
partition 22, and a pressure equalizing conduit 27 respectively in
communication with the first and second subchambers. Finally, means
referred to by the numeral 28 is included for maintaining the temperature
conditions within chamber 14, and particularly the upper first subchamber
14a thereof, at a level for maintaining a substantial fraction of
vaporized hydrocarbons therein in the vapor state in order to promote
efficient recovery thereof, but below the temperature level sufficient to
substantially decompose or crack the oil at the prevailing pressure
conditions within the chamber.
In more detail, the chamber-defining structure 12 includes an inner
metallic shell 30 comprising an elongated, upright, tubular, circular
cross section sidewall 32, along with concave top and bottom walls 34 and
36. Conventional thermal insulation 38 is disposed about the walls 32 and
34 in the manner shown, and an outer shell 40 is in covering relationship
to the insulation 38. Shell 40 is of the same configuration as shell 30,
as will be readily seen.
An elongated, centrally disposed, tubular pipe 42 extends through top wall
34 and downwardly into the upper subchamber 14a. Pipe 42 defines an outlet
for vaporized hydrocarbons and is connected to conventional recovery
apparatus to be described hereinafter. An annular baffle 44 is disposed
about pipe 42 in order to deflect falling, condensed hydrocarbons within
the upper subchamber to prevent entrainment thereof in the vaporized
hydrocarbons entering pipe 42. Lower subchamber 14b is provided with a
conventional bottoms outlet line 46 which is controlled by means of a
valve 48. In addition, a secondary removal line 50 extends through bottom
wall 36 and communicates with subchamber 14b, and is controlled by means
of a valve 52.
Oil-supplying means 20 includes a delivery line 54 for conveying hot,
dehydrated and previously fractionated waste oil to tower 10, in
conjunction with an inlet pipe 56. As best seen in FIGS. 1 and 2, the pipe
54 and inlet 56 are disposed adjacent the upper end of subchamber 14a and
are tangentially located relative to the sidewall 32. Referring
specifically to FIG. 3, it will be seen that nozzle structure generally
designated by the numeral 58 is provided with inlet pipe 56. In this
connection, oil delivery pipe 54 is connected to a first plate 60 having a
central opening therethrough of a diameter equal to that of the line 54. A
second plate 62 is located adjacent plate 60 and is provided with a
central bore therethrough having a frustoconical portion 64 and a
communicating cylindrical portion 66 of reduced diameter relative to the
line 54. Inlet pipe 54 on the other hand is provided with annular flange
structure 68; and the plates 60, 62 are interconnected to the flange
structure 68 by means of conventional bolts 70. Spray-forming apparatus in
the form of a bored insert 72 is located within inlet pipe 54 adjacent the
plate 62. Insert 72 is provided with an outwardly axially extending,
cylindrical bore 74 of expanded diameter relative to the bore portion 66
of plate 60, along with an outwardly diverging, frustoconical bore 76. In
this fashion, oil injected through the line 54 is in effect sprayed by
means of the nozzle structure 58 through the inlet pipe 56 and thence into
the interior of subchamber 14a. Of course, when tower 10 is operated under
appropriate vacuum conditions, a large proportion of the sprayed waste oil
is quickly or "flash" vaporized.
Internal, flow-directing, depending baffle structure 78 is located adjacent
the internal inlet opening 80 defined by inlet pipe 56. Baffle structure
78 is of annular configuration and includes a radially extending
connection lip 82, along with a depending circular wall portion 84 which
is in spaced relationship to the sidewall 32 as best seen in FIG. 1. It
will be understood that inlet pipe 56, nozzle structure 58 and baffle 78
cooperate during the operation of tower 10 for supplying oil to subchamber
14a, and imparting a whirling motion to the oil and vapors within the
tower. This desirable whirling motion is assured by virtue of the
tangential injection thereof and also because of the restricted annular
passage defined between the sidewall 32 and baffle wall 84. Oil thus
injected and directed (and the vapors evaporating therefrom) travel in a
circular path down the sidewall 32. This is important for purposes to be
made clear hereinafter.
Partition 22 is in the form of a concavo-convex plate 86 which includes a
central oil flow aperture 26. The plate 86 serves to divide the overall
chamber as noted above into subchambers 14a and 14b, and the aperture 26
allows flow of oil from first subchamber 14a into lower subchamber 14b. In
addition to the foregoing, the somewhat C-shaped pressure equalization
conduit 27 extends between the respective subchambers 14a and 14b and in
effect bridges the partition 86. Conduit 27 is insulated as at 90 and is
in the form of a simple, unobstructed tubular member serving to assure
equal pressure conditions within the respective subchambers.
Vortex-breaking means 92 is located adjacent wall 86 and includes a
circular, slightly downturned upper plate 94 supported by a plurality of
circumferentially spaced legs 96 which are in turn connected to the
sidewall 32. Vortex-breaking means 92 serves to prevent entrainment of
nonvaporized bottoms in the vaporized hydrocarbons produced within
subchamber 14a, and thus facilitates rapid and efficient separation of the
vapor fraction from the bottoms liquid fraction.
Temperature-maintenance means 28 preferably includes apparatus for heating
the defining sidewall of subchamber 14a. In the embodiment illustrated in
FIGS. 1-3, conventional electrical heating tape 98 is provided around
sidewall 32 for heating of the latter. Referring to FIG. 1A however, a
second embodiment is illustrated where coil structure 100 is disposed
about the wall 32. The coils are adapted to receive a fluid heat exchange
media in the usual fashion. This may include a conventional heat exchange
fluid or hot waste oil for example.
FIG. 4 is a schematic representation of the important components used in
conjunction with tower 10 in a rerefining process. In this regard, the
overall apparatus 102 includes a dehydration stage 104, a light ends
removal stage 106, a distillation stage 108, and an optional finishing or
polishing stage (not shown).
Dehydration stage 104 includes a conventional dehydrator 110 and the usual
separation equipment 112 for separating waste water for recoverable light
fuel oil. A dehydrated oil storage tank 114 is also provided along with
the necessary pumps 116 and heater 118.
Light ends removal stage 106 is likewise conventional and includes a
fractionation column 120. The overhead from column 120 feeds to separation
equipment 122 for separating fuel oil and light ends. A fractionated oil
storage tank 122, along with pumps 124 and heater 126, complete this
stage.
Distillation stage 108 includes the tower 10, an overhead line 128, and a
bottoms line 130. In most instances it is desirable to maintain vacuum
conditions within tower 10, and for this purpose an appropriate vacuum
pump 132 is operatively connected to tower 10. As will be more fully
explained hereinafter, the overhead from tower 10 is condensed by means of
a conventional condenser 134, and the distillate can either be used
immediately or polished by known techniques. On the other hand, the
bottoms line 130 is provided with a proportioning valve 136. Valve 136 is
coupled to a bottoms recovery line 138, and to a recycle line 140 which
leads back to fractionated oil storage tank 122. Line 140 and valve 136
are important for reasons to be made clear.
The operation of the overall rerefining apparatus 102, and particularly
distillation tower 10 forming a part thereof, will now be described in
detail. The following discussion pertains to the treatment of waste oil;
however, it is to be understood that the tower and method hereof are not
so limited, but can be used in a variety of separation processes. First of
all, waste oil as received is first directed to dehydration stage 104, and
particularly to dehydrator 110. In the dehydrator, the waste oil is heated
to remove the water and a portion of the undesirable particulates such as
dirt and suspended solids in the oil. Temperature conditions within
dehydrator 110 would typically be within the range of from about 150 to
300.degree. F., whereas pressure is generally maintained at atmospheric,
but vacuum conditions could be employed. In any event, the overhead from
the dehydrator comprising waste water and extremely light ends is directed
to separator apparatus 112 for recovery of the hydrocarbon fraction. The
bottoms from the dehydrator are sent to storage tank 114.
The essentially moisture-free oil from tank 114 is then heated in heater
118 to a temperature of from about 500 to 600.degree. F. at a pressure of
from about 3 to 5 p.s.i.g. Alternately, the fractionator can be under a
vacuum. This heated oil is then fed to steam-fed fractionation column 120
forming a part of stage 106. In the fractionation column 120, from about 1
to 10% of the waste oil is steam stripped overhead as light ends. These
light ends would typically include water, fuel oil, light lube oils
(spindle oils) and noncondensable gases. Preferably, the overhead is fed
to separation apparatus 122, where the light tube oils are condensed and
recovered, and the fuel oil and water are condensed and subsequently
gravity separated.
It will be appreciated that the steps involved in dehydration, stripping
and heating of the waste oil in the stages 104 and 106 are essentially
conventional, and those skilled in the art will understand that a number
of possible variations can be made in the above described steps.
The bottoms from column 120 are first fed to storage tank 122, and thence
to heater 126. At this point the dehydrated, stripped oil is heated to a
temperature of from about 650 to 850.degree. F., depending principally
upon the characteristics of the oil itself. Pressure conditions within
heater 126 are generaly from about 60 to 250 p.s.i.g.
In any event, the heated oil from the heater 126 is next fed to
distillation tower 10, and particularly through line 54 to inlet 56. This
oil, being under a positive pressure, is forced through the above
described nozzle structure 58 so that the oil is in effect sprayed into
subchamber 14a of the tower. This spraying, in conjunction with the vacuum
conditions within the tower, is believed to cause essentially
instantaneous or "flash" vaporization of a substantial portion of the
entering waste oil. In this regard, from about 50 to 95%, or more
preferably from about 85 to 95%, of the waste oil entering the tower is
vaporized in this fashion. In addition, the tangential orientation of the
inlet 56, in conjunction with baffle structure 78, assures that the
vaporized hydrocarbons and residual liquids within the tower 10 follow a
substantially circular whirling or cyclonic path of travel along the inner
surface of circular sidewall 32. These components flow down sidewall 32
and, during such passage the residuals are thrown radially outwardly,
impinge against the wall 32, and flow downwardly past vortex-breaking
means 92 and through aperture 26 into lower subchamber 14b. At the same
time, the whirling, vaporized hydrocarbons move generally towards the
center of the tower 10 with a portion thereof striking plate 94 in order
to "break" the vortex. The vapors are then drawn generally axially
upwardly into pipe 42 for recovery. The structure 92 is thus effective for
minimizing entrainment of the bottoms in the hydrocarbon vapors in the
central area of subchamber 14a. The bottoms fraction passing into
subchamber 14b comprises mainly extremely heavy hydrocarbons, metals, and
other impurities. Even flow of the bottoms fraction into subchamber 14b is
assured by virture of the pressure equalization conduit 27. Finally, the
valuable bottoms fraction is continuously withdrawn from chamber 14b
through line 46.
During the above described vapor-liquid separation sequence, the heating
means 28 is employed for heating the wall 32. This factor has been
discovered to be very important in achieving the high distillate yields
characteristic of the tower 10. In fact, it has been determined that
without the temperature maintenance afforded through the use of electrical
heating tape 98, or a functional equivalent thereof, an appreciable
quantity of the vaporized hydrocarbons will be recondensed within chamber
14a prior to passage thereof through pipe 42 for recovery. This of course
lessens the overall yield of distillate and is to be avoided. In practice
when waste lubricating oil derived from crankcases or the like is being
treated, the temperature of the waste oil directed to tower 10 should be
at a level of from about 650 to 850.degree. F., and the temperature of the
vaporized hydrocarbons within subchamber 14a should be maintained at a
level of from about 650 to 725.degree. F. Under these circumstances, it is
desirable to maintain the temperature of the tower sidewall at a level of
from about 675 to 750.degree. F. Furthermore, it is desirable to maintain
the absolute pressure within the tower 10 at a level of from about 0.5 to
3 inches of mercury.
Although use of heating tape 98 is preferred, it will be understood that
other expedients could be resorted to as long as temperature maintenance
is achieved. For example, FIG. 1A illustrates the use of coil structure
adapted to receive a separate heat exchange fluid or a portion of the
incoming hot oil. In addition however, it is possible in certain instances
to supply the necessary heat to distillation tower 10 without peripheral
heating apparatus. Referring specifically to FIG. 4, it will be noted that
the bottoms line 130 is provided with a proportioning valve 136 and
recycle line 140 back to tank 122. In this regard, it is sometimes
feasible to flood tower 10 with an excess of waste oil beyond the design
capability thereof so that the temperature conditions in the tower are
properly maintained simply by virtue of the presence of the excess hot
oil. This flooding technique of course results in passage of the excess
oil through tower 10 without complete distillation thereof. Accordingly,
in order that the valuable oil fractions therein are not lost, it is
advantageous to recycle the excess back to the tank 122 for ultimate
recycling through the distillation tower 10. It will be readily
appreciated by those skilled in the art that this recycling technique can,
after a given time, establish an equilibrium condition within the stage
108 wherein nonvaporizable bottoms would be continuously withdrawn through
line 138, while a recycle stream is continuously passed to the tank 122.
Of course, a combination of tower flooding and tower surface heating could
also be used if desired for proper temperature control.
It has been suggested in the past to employ gas/liquid cyclone separators
in the refining of virgin oil ("The Application of Gas/Liquid Cyclones in
Oil Refining", Transactions of the ASME, January 1958, by J. R. J. Van
Dongen and A. J. Ter Linden, and "The Separation of Liquid From Vapor,
Using Cyclones", Transactions of the ASME, January 1942, by Arthur Pollak
and L. T. Work). Flash vaporization techniques are also described in
"Flash Vaporization", Chemical Engineering Progress, February 1953 by R.
R. Hughes et al. However, these prior proposals do not deal with
rerefining of waste oil, nor do they in any way suggest the desirability
of maintaining proper temperature conditions within the tower for
enhancing production of distillate. As noted above, it has been found that
the temperature condition should be such that the hydrocarbon vapors
evolved from the whirling oil are maintained in a vapor state; on the
other hand, the temperatures should not be sufficient to substantially
decompose or crack the oil, since this interferes with the process. Hence,
it will be seen that the problem of temperature maintenance cannot really
be solved simply by preheating the oil prior to distillation to a level
greatly in excess of the desired distillation temperature, since this in
many instances will cause significant decomposition or cracking of the
oil. As can be appreciated, cracking can cause coking of the process
equipment and a decrease in ultimate yields.
In any event, as distillation proceeds, a bottoms fraction is drawn off
from line 138 and recovered. This valuable product can be used in asphalts
or greases, for example. Also, the vaporized hydrocarbons within
subchamber 14a are conveyed through line 128, condensed in condenser 134,
and recovered as a liquid.
The overhead from tower 10 can be condensed and used directly since a large
proportion of the undesirable contaminants are already removed. However,
if further purification is desired the distillate can be polished by any
one of a number of conventional procedures. For example, the distillate
can be filtered through clay or solvent extracted to give a clarified end
product. In the case of solvent extraction, solvents such as nitrobenzene
have proven to be highly successful in practice, although other organic
solvents can also be used to good effect.
The following examples illustrate the operation of a commercial waste oil
rerefinery using the tower and method of the present invention. However,
nothing in these examples is to be taken as a limitation upon the overall
scope of the invention.
EXAMPLE I
Approximately 10,800 gallons of waste oil derived from automotive
crankcases was treated in accordance with the present invention. The oil
was first dehydrated in a conventional dehydrator at about 230.degree. F.
and atmospheric pressure. The overhead (about 800 gallons) from this step
was condensed with tap water and contained 95 to 98% water and a minor
amount of gasoline and other light ends. The underflow oil had a
temperature of about 150.degree. F. and was directed to a settling tank.
The oil was next directed to a tube still heater and heated to a
temperature of from 570 to 600.degree. F., whereupon the heated oil was
fed to a conventional unheated bubble cap fractionator. The oil was then
treated in the fractionator at atmospheric pressure with countercurrent
steam injection (350.degree. F. saturated steam, 125 p.s.i.). The overhead
from this operation amounted to about 8 to 10% of the total and was at a
temperature of about 480 to 580.degree. F. The overhead was condensed with
tap water and contained about 3% H.sub.2 O, 95% No. 2 fuel oil and 2%
light spindle oil. These components were then gravity separated and
recovered. The fractionator bottoms were at a temperature of from about
480 to 520.degree. F. and were sent to an insulated run down tank.
The dehydrated fractionated oil was next directed to a tube still heater
and heated to a level of 680 to 720.degree. F. The heated oil was then
sent to the distillation tower described in detail herein. This tower was
equipped with surrounding plate coils as illustrated in FIG. 1A. A
fraction of the incoming waste oil was directed through the plate coil
structure in order to heat the walls of the distillation tower. These
walls were maintained at a level of about 600 to 620.degree. F. by this
means. This temperature was lower than desirable, and resulted in somewhat
lower yields of overhead. The oil to be treated was fed to the tower at a
rate of about 15 gallons per minute and was sprayed tangentially into the
tower in order to facilitate flashing thereof and to impart a whirling or
cyclone motion thereto. The conditions within the tower during processing
were a pressure of from about 1.6 to 2.0 inches of mercury, absolute, and
a hydrocarbon vapor temperature of from about 540 to 570.degree. F. During
processing, a substantial fraction of the oil was substantially
instantaneously flash vaporized. These and later evolved vapors were
maintained in the vapor state by virtue of the heating of the tower walls,
and the vapors were taken overhead and condensed. The condensed oil had a
viscosity of 45-47 ssu. at 210.degree. F., and 180-230 ssu. at
100.degree. F.; a viscosity index of 110-130; a color of No. 4 N.P.A.; a
flash point of 380-450.degree. F. C.O.C.; a pour point of from 0 to
-10.degree. F.; an A.P.I. gravity of 29.5 to 31.degree.; and a very slight
odor. The bottoms from the distillation tower were withdrawn at about
600.degree. F. and had a viscosity of 200-350 ssu. at 210.degree. F.; an
A.P.I gravity of 19-22.degree.; and a flash point of 525 to 575.degree. F.
The condensed overhead was next treated with Filtrol No. 20 activated clay
at 350.degree. F. in order to polish the distilled oil. This resulted in
about a 1 to 2% loss in oil. The final polished oil had an N.P.A. color of
2 to 2.5, no odor, and exhibited slightly increased viscosity, slightly
lowered pour point, and an increased flash point. This product was
eminently suitable for use as a lubricating oil.
EXAMPLE II
This example is similar to that of Example I, save for the fact that in the
distillation step | | |
