Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTION
In the solvent dewaxing of lube oil stocks, for
example, using a rotary vacuum filter of the Oliver or
Eimco or Goslin-Birmingham type, there is a tendency for
small or micro wax crystals to be pulled through the filter
surface or canvas with the initial filtrate during the
first fcw seconds of immersion of the bare filter cloth into
the waxy oil-solvent slurry. This phenomenon is often
called "priming". These wax crystals frequently are
revealed as a cloudy, sometimes flocculent precipitate in
the final dewaxed oil. This cloudy condition is objectiona-
ble and has been tolerated because few, if any~ economical
methods of eliminating it are known. In the conventional
rotary vacuum filters as noted above, and concerning the
Oliver filter, for example, as illustrated and described in
the textbook Chemical Engineering Series by W. L. Badger and
W. L. McCabe9 McGraw-Hill Book Co., Inc., New York, 1936,
pages 485 - 490, the text teaches that "A low initial
pressure may mean that the first runnings from the press
will not be clear, but this is more than offset by the more
rapid filtration rate and consequently larger capacity.",
page 489, lines 19-22.
Accordingly, a primary object of this invention
is to provide a method for removing solid particles from
the filtrate that has passed through a filter prior to the
building up of a thick cake of the solid particles on the
outer surface as the filter rotates partially submerged in
a vat of slurry with solid particles suspended therein for
providing a solid particle free fil~rate.
Another primary object of this invention is to provide a rotary
continuous vacuum filter for carrying out or performing the method of remov-
ing solid particles from a filtrate that has passed through a filter prior
to the building up of a thick cake of the solid particles on the external
filter surface impervious to the solid particles as the filter rotates
partially submerged in a vat of slurry with solid particles suspended
therein for providing a solid particle free filtrate.
A further object of this invention is to provide a method for
removing micro wax crystals that have passed through the filter external
surface with the filtrate slurry prior to buildup of the wax cake impervious
to wax crystals for providing a wax-free filtrate.
A still further object of this invention is to provide a rotary
continuous vacuum dewaxing filter for removing micro wax crystals from a
filtrate that have passed through the filter prior to buildup of a wax
cake on the filter impervious to wax crystals for providing a clear and
wax-free filtrate or oil, increased filter rates, longer life insured for
the filter material, prevention of the formation of a flocculent precipitate
in the final dewaxed oil, and less operating problems are encountered than
with other corrective measures of removing cloudiness due to wax crystals.
A further object of this invention is to provide a rotary continu-
ous vacuum dewaxing filter that is easy to operate, is of simple configur-
ation, is economical to build and assemble, and is of greater efficiency
for the complete dewaxing of a waxy oil-solvent slurry.
According to one broad aspect of the present invention, there is
provided in a rotary continuous vaccum solid particle fil~er rotatable in
a vat of slurry with solid particles suspended therein that build up a
progressively thick cake of solid particles on the filter external surface
as the filter rotates partially submerged in the vat, a method for removing
solid particles that have passed through the external surface of the filter
~0 with the slurry prior to buildup of the solid particle cake for providing
solid particle free clear filtrate for output delivery comprising the steps
of passing the slurry with suspended solid particles therein through the
-2-
filter for a predetermined period of time until the solid particle cake is
formed thick enough to prevent further penetration of the solid particles
through the cake and filter, collectlng separately filtrate fractlons from
two adjacent sectors of the immersed part of the filter so that filtrate
from the second sector is the filtrate with the suspended solid particles
therein that has passed through the filter for the predetermined period of
time from the rest of the filtrate to leave a solid particle free and clear
filtrate, passing the filtrate from the first sector to a sampler for deter-
mining the existence of solid particles suspended therein, combining the
first sector filtrate with the solid particle free filtrate from the second
sector when no solid particles are dctected in the first sector filtrate
by the sampler, and recycli.ng the first sector filtrate to the vat of slurry
wi.th solid particles suspended therein when solid particles are detected in
the filtrate in thc sampler.
According to another broad aspect of the invention, there is
provided a rotary continuous vacuum filter for removing solid particles
from a filtrate that have passed through the filter prior to buildup of a
solid particle cake on the filter for providing a solid particle free
filtrate comprising~ a va~ of the slurry with solid particles suspended
therein, a cylindrical drum filter means having a longitudinal axis, having
a filter material on the peripheral surface thereof, and being molmted
partially submerged in said vat for rotation about i.ts longitudinal axis,
vacuum means internally of said filter means for drawing the slurry through
the submerged portion of said filter material for building up a progressively
thick cake of solid particles on the external surface of said filter material
as said filter means rotates partially submerged in said vat~ means for
collecting separately filtrate withdrawn from ~wo adjacent sectors of the
submerged part of the filter~ characterized by means for sampling filtrate
from the first sector to detect solid particles therein, clear filtrate
valve means responsive to the sampling means and adapted to pass, when no
solid particles are detected, such filtrate for combining with the solid
- particle free filtrate from the second sector, and solid particle filtrate
recycle valve means responsive to-the sampling means and adapted to pass,
when solid particles are detected in the filtrate from the first sec-tor,
such filtrate to means for recycling that filtrate to the vat.
The filter may be a dewaxing filter in which case the solid
particles are micro wax crystals.
Other objects and various advantages of the disclosed method of
removing solid particles, and a rotary continuous vacuum filter, will b~
apparent from the following detailed description, together with the accom-
panying drawings, submitted for purposes of illustration only and not intend-
ed to define the scope of the invention, reference being had for thatpurpose to the subjoined claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The drawings diagrammatically illustrate by way of example, not
by way of limitation, one form or mechanism for carrying out the methods of
the invention wherein like reference numerals have been employed to indicate
similar parts in the several views in which:
FIG. 1 is a schematic sectional view of the rotary continuous
vacuum dewaxing filter taken at 1-1 on FIG. 2;
PIG. 2 is a schematic longitudinal sectional view taken at 2-2
on FIG. l;
FIG. 3 is a schemati.c sectional view taken at 3-3 on FIG. 2; and
FIG. 4 is a schematic plan view of the discharge or recycle system
of the disclosed rotary continuous vacuum dewaxing filter for thc oil-solvent
filtrate with micro wax crystals prior to buildup of the wax cake on the
filter.
-3a-
DFSCRIPTION OF THE _NVENTION
The invention disclosed herein, the scope of
which being defined in the appended claims, is no~ limited
in its application to the details of construction and
arrangement of parts shown and described for carrying out
the disclosed methods, since the invention is capable of
other embodiments for carrying out other methods and of
being practiced or carried out in various other ways. Also,
it is to be understood that the phraseology or terminology
employed herein is for the purpose of description and not
of limitation. Further, many modifications and variations
of the invention as h~reinbefore set forth will occur to
those skilled in the art. Therefore, all such modifications
and variations which are within the spirit and scope of
the invention herein are included and only such limitations
should be imposed as are indicated in the appended claims.
This invention comprises a method for removing
solid particles that have passed through a filter, a method
for assembling a rotary continuous vacuum solid particle
filter, and a mechanism for practicing the first methods~
METHODS OF THE INVENTION
(A~ Method for Filtering Solid Particles from a Slurry
In a rotary continuous vacuum solid particle
cylindrical filter rotating in a vat of slurry with solid
` particles suspended therein, a vacuum is pulled from inside
- for pulling the slurry with the solid particles through
the filter surface to a chamber inside the cylindrical
filter. The longer the filter surface is submerged as it
rotates in the slurry in the vat, the thicker is a cake of
solid particles formed on the filter surface until after a
-4-
~$1 ~ b~ ~
predetermined period of time for that vat of slurry, no
more solid particles will flow through the cake and the
following slurry that is drawn through the cake and filter
is a clear filtrate free of solid particles. But, due to
passage of the solid particles with the slurry through the
filter at the beginning before the progressively thick cake
is formed, th~ total resultant filtrate is contaminated
with solid particles which eventually make the filtrate
cloudy~
Accordingly, a method for removing the solid
particles that have passed through the external filter
surface with the filtrate prior to buildup of the solid
particle cake for providing solid particle free and
clear filtrate for output delivery comprises the steps of,
(1) passing the slurry with the suspended solid
particles therein through the filter for a predetermined
period of time until the solid particle cake is formed
thick enough to prevent further penetration of the solid
particles through the cake and filter, and
(2) separating the filtrate with the suspended
solid particles therein that has passed through the
:.~ filter for the predetermined period of ~ime from the rest
of the filtrate to leave a solid particle ree and clear
filtrate.
An additional method step may comprise~
(1) passing the filtrate with the solid particles
suspended therein back into the vat for further filtering.
And another method step may comprise,
. (1) varying the predetermined period of time
for passing the slurry with the solid par~icles suspended
therein through the filter for vats of various slurries with
the solid particles therein whereby only clear and solid
particle free filtrate is left~
(B) Method for Filt~b~ La~5L~ EL~bE~
Also a rotary continuous vacuum dewaxing filter
is disclosed which is rotatable in a vat of waxy oil-
solvent slurry that builds up a progressively thick cake
of wax on the filter external surface as the filter rotates
partially submerged in the vat.
A method for removing the micro wax crystals
tha~ have passed through the filter outer surface with the
filtrate prior to buildup of the wax cake for providing
wax-free filtrate comprises the steps of,
(1) passing the waxy oil-solvent ~ urry with the
micro wax crystals therein through the filter for a pre-
determined period of time until the wax cake is formed
thick enough to prevent further penetration of the wax
crystals through the cake and filter, and
(2) separating the initial filtrate with the
micro wax crystals therein that has passed through the
filter for the predetermined period of time from the rest
of the filtrate to leave a wax-free clear filtrate.
An additional method step comprises~
(1) passing the filtrate with the miero wax
crystals therein back into the vat.
Another method step comprises,
(1) varying the predetermined period of time of
passing the waxy oil-solvent slurry through the filter for
L~
various vats of waxy oil-solvent slurries for insuring
receipt of all of the filtrate with the micro wax crystals
therein whereby only wax-free filtrate is left.
(C) Method for Assemblin~_a Solid Particle Filter
A method for assembling a rotary continuous vacuum
filter for removing solid particles from a filtrate slllrry
that have passed through the filter prior to buildup of a
solid particulate cake on the filter outer surface for pro-
viding solid particle free filtrate slurry comprising the
steps of,
(1) rotata~ly mounting a cylindrical drum filter
having a filter material on the peripheral surface thereof
about its longitudinal axis partially submerged in a vat
containing the slurry having the solid particles suspended
therein,
(2) connecting vacuum means to the cylindrical
drum filter for drawing the slurry with the solid particles
suspended therein through the submerged portion of the
: filter material for building up a progressively thick cake
of solid particles on the outer surface of the filter
material as the cylindrical drum filter rotates partially
submerged in the vat,
- (3~ forming the filter material sufficiently
permeable to permit some solid particles to pass there-
through with the slurry having the solid particles suspended
- therein until the filter has rotated through the vat for a
,. predetermined period of time until the solid particle cake
is formed thick enough to prevent further penetration of
the solid particles through the cake and filter material,
and
~7--
(4) connecting a trunnion means to the
cylindrical filter for collecting all of the filtrate with
the solid material therein only as the filter rotates for
the predetermined period of time whereby all the rest of
the slurry that passes through the filter material with the
solid material cake thereon is clear and solid material
free.
(D)_ Method for Assembling a Dewaxing Filter
A method for assembling a rotary continuous
- 10 vacuum dewaxing filter for removing micro wax crystals from
a filtrate that have passed through the filter prior to
. buildup of a wax cake on the filter for providing a wax
: free oil-solvent comprises the method steps of,
(1) rotatably mounting a cylindrical drum
filter having a filter material on the peripheral surface
; thereof about its longitudinal axis partially submerged in
a vat containing the waxy oil-solvent slurry,
(2) conn~cting vacuum means to the cylindrical
.
drum filter for drawing the oil-solvent slurry through the
submerged portion of the filter material for building up a
-. progressively thick cake of wax on the external surface of
the filter material as the cylindrical drum filter rotates
partially submerged in the vat,
,
(3) forming the filter material sufficiently
.. :` permeable to permit some micro wax crystals to pass there-
through with the oil-solvent slurry until the filter has
rotated through the vat for a predetermined period of time
~: until the wax cake is formed ~hick enough to become im-
: pervious to wax crystals to prevent further penetration of
the wax crystals through the cake and filter material, and
' _~_
:
~ 5~.~
(4) connecting a trunnion head means to the
cylindrical filter for collecting all of the filtrate with
the micro wax crystals therein only as the filter rotates
for the predetermined period of time whereby all the rest
of the oil-solvent slurry that passes through the filter
material with the wax cake thereon is clear and wax free.
Another method step comprises,
(L) connecting a trunnion head means to the
vat for passing only the filtrate with the micro wax
crystals therein back into the vat.
Further method steps comprise,
(1) mounting an adjustable block means on the
trunnion head means for varying the length of the predeter-
mined time, and
(2) forming the trunnion head means responsive
to the adjustable block means for receiving all of the oil-
filtrate with the micro wax crystals therein for the
particular vat of waxy oil-solvent slurry being filtered
whereby only wax-free and clear filtrate is left in the
trunnion head means for output delivery.
Clearly other filters may be assembled by the
above method than the filter disclosed hereinafter.
ROTARY CONTINUOUS VACUUM FILTER
FIG. 1, a cross-sectional view at 1-1 on FIG. 2,
;- illustrates details of the disclosed rotary continuous
; vacuum filter 10, FIGS. 1 and 2, which comprises basically
a horizontal filter cylinder 11 fixedly mounted on
trunnions 12, FIG. 2, (back trunnion not shown) for rotation
about its longitudinal axis in a vat 13 containing a waxy
oil-solvent slurry 15. The cylindrical filter 11 and
_9_
~.$~ ` 4
trunnion 12, FIG. 2, are rotatable in vat 13 to which is
fixedly secured hood 14 with suitable corresponding flanges
FIG. 1, on the two opposite sides of each.
The filter cylinder 11, FIG. 1, comprises a solid
cylindrical wall with a porous filter material 17 spa~ed
outwardly therefrom with dividing walls 18 which form cham-
bers or pans 19 completely around the periphery of the filter
cylinder 11. A suction or vacuum is applied to these
cham~ers with leading and trailing conduits, 20 and 21,
respectively, which extend forwardly through the forward
trunnion 12, FIG. 2, to the trunnion head 22.
Trunnion 12, FIG. 2, is rotatably mounted in
trunnion head 22 with wear plate 16 therebetween whereby
the flow of fluid in conduits 20 and 21 between the chambers
19 and the trunnion 12 is controlled by the trunnion head
.. _
22, FIG. 2 and particularly as illustrated in FIG. 3, an
enlarged view of the trunnion head and its control chambers.
As seen in FIG. 3, wear plate 16 with outer and
inner conduits 20, 21, respectively, terminating therein
all rotate counter-clockwise while being held flush up
against and in fluid tight contact with stationary trunnion
head 22. The four suction or vacuum pickup pipes 23, 24,
25, and 26, FIGS. 2 and 3, draw all fluids from the various
chambers 19, FIG. 1, around the periphery of the rotating
cylinder~ whether it be liquid or air. Three fixed blooks
27, 28 and 39 and the single adjustakle block 29 divide the
trunnion head 22 into the basic chambers. Fixed block 39
is mounted adjacent to and following fixed block 28 for
starting the filtering periods.
-10-
In operation, the vacuum pickup pipe 23, FIG. 3,
between blocks 29 and 27 draws all filtrate in the filter
cycle, from the corresponding submerged filter chambers 19,
illustrated in FIG. 1, which filtered the wax completely by
passing through the thickened wax cake 30 and the filter 17.
Vacuum pickup pipe 24, FIG. 3, between blocks 27 and 28 in
the cake wash period draws air and a solvent from cake
washing spray 31, FIG. 1, from the corresponding filter
chambers 19, FIG. 1, illustrated in this area. Vacuum pick-
up pipe 25, FIG. 3, between blocks 27 and 28 in the cakespray and wash period also draws air and solvent of cake
washing spray 32, FIG. 1, from the corresponding filter
chambers 19 illustrated in this area. Nozzle 33, FIG. 3,
in the cake drying period blows a drying inert gas outwardly,
such as a flue gas, to loosen the wax cake 30, FIG. 1, from
the filter material 17, FIGS. 1 and 2, so that guide or
scraper 34, FIG. 1, also loosens and guides the wax cake 30
into a wax transporter screw 35 which carries the wax cake
to a suitable container (not shown). This drying air is
blown out in reverse direction through the few conduits 20
and 21, FIG. 3, spaced between block portions 28a and 28b,
from the nozzle 33, FIG. 3, in the t:runnion head 22, FIG. 2,
back through the corresponding chambers 19, FIG. 1, and
through the filter. Flue gas, or an exhaust gas has low
oxygen content.
The following particularly, is the new mechanical
portion of the disclosed rotary continuous vacuum dewaxing
filter for carrying out the method of dewaxing. It com-
prises the adjustable block 29, FIG. 3, inserted and secured
with wedge 40 in the trunnion head 22, FIG. 2, between fixed
-11-
blocks 39 and 27. In this area as the initial waxy oil-
solvent slurry is drawn through the filter and as the micro
wax crystals pass through the filter into the filtrate,
an increasing number of the crystals lodge on the filter
material 17, FIG. 1, to gradually build up a tapered or
thickening cake of wax 30 as the cylinder with the submerged
filter material thereon rotates through the vat of waxy oil-
solvent slurry. For the particular waxy oil-solvent being
filtered, the adjustable block 29 is adjustably mounted with
wedge 40 for permitting rotation of the filter in this area
for a predetermined period of time through which the wax
` cake is formed thick enough to prevent further penetration
- of the wax crystals through the cake and filter material.
The resulting filtrate with the micro wax crystals therein
that is withdrawn by vacuum pickup 26 through the filter
prior to reaching the adjustable block 29 is drawn from
chambers l9a-19d, and is recycled to the waY~y oil~solvent
15, FIG. 1, in the vat 13. In actual operation this period
of time may be 3 to 5 seconds and the angle through which
the peripheral filter has passed may be about 24 degrees on
: a 30-foot diameter (9.144 meters) diameter cylinder. The
vacuum pickup 26 is thus re~uired in this initial filtering
period. Since the wax cake becomes thick enough at the
adjustable block 29 for filtering all wax crystals, the fil-
trate received in the next adjoining area from adjustable
block 29, FIG. 3, to fixed block 27 is clear and wax free
for providing an output of wax-free filtrate.
FIG. 4 illustrates a schematic plan view of the
discharge or recycle system of the rotary contimlous vacuum
filter. As illustrated, the waxy filtrate passes from the
vacuum pickup 26 to sampler 36 where it is determined that
-12-
,:,.
~ 4
wax exists in the filtrate. If no wax is present, the
valve 37 is opened and the wax-free filtrate is mixed with
the rest of the wax-free filtrate output. When wax crystals
are detected by sampler 36, valve 38 only is opened to re-
cycle the waxy filtrate with the vat of waxy oil-solvent
slurry.
Upon removal of the solvent, a wax-free oil re-
sults. The results are a clear oil of improved quality at
less cost, increased filter rates, longer life insured for
the filter material, prevention of the formation of a floccu-
lent precipitate in the final dewaxed oil, and less operating
problems are encountered than with other corrective measures
of removing cloudiness due to wax crystals.
Obviously other methods may be utilized for re-
moving solid particles that have passed through the outer
filter surface with the filtrate prior to buildup of a solid
particle cake for providing a solid particle free and clear
filtrate for output delivery and for assembling rotary con-
tinuous vacuum solid particle filters like the embodiment
of FIGS. 1, 2 than those listed above, depending on the
particular slurry desired to be used. Also, rotary con-
tinuous vacuum filters other than that disclosed above may
be assembled by the above method.
Accordingly, it will be seen that the disclosed
methods and rotary continuous vacuum solid particle filter
will operate in a manner which meets each of the objects
set forth hereinbefore.
While only one mechanism and two methods have
- been disclosed, it will be evident that various other
modifications and methods are possible in the arrangement
and construction of the disclosed solid particle filter
-13-
'.;
5~
without departing fr~m the scope nf the invention and it
is aceordingly desired to comprehend within the purview of
this invention such modifications as may be considered to
fall within the scope of the appended claims.
.~
~14-
