Note: Descriptions are shown in the official language in which they were submitted.
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1 BA~KGROUND OF THE INVENTION
2 This invention relates to an improved continuous
3 rotary drum filter means. More specifically, the sub~ect
4 invention is related to a continuous rotary drum filter for
the separati~n o petroleum liquids, such as lube oils,
6 from solids, such as paraffins.
7 The separation of mix,ures of compounds can be
8 accomplished by various unit operations including distil-
9 lation, solvent extraction and fractional crystallization.
Fractional crystallization is particularly well-suited to
ll the purification of many mixtures economically in a one-
12 stage operation. Frequently, the cry~tallization ~peration
13 is combined with another unit operation to produce an
14 improved separation process. In petroleum processing,
operations fractional crystallization is often utilized to
16 separate waxy compounds from the lube oil fraction.
17 Frequently, a solvent is added to the mixture to provide
18 more favorable conditions for crystal growth and to dilute
19 the resultant chilled slurry to thereby permit continuous
oil-wax separation.
21 One type of filter particularly well suited to
22 fractional crystallization, in general, and wax-lube oil
23 separation, in particular, is the rotary drum filter. In
24 this type filter, a filter drum continuously rotates within
a filter vat containing the mixture to be separated. In
26 one phase of the rotation, vacuum is applied to the filter
27 drum causing a major portion of filtrate to be drawn through
28 the filter cloth and fluid conduits, while the solids and
29 a minor amount of filtrate are trapped by the filter cloth
and build up to form a cake. A liquid solvent wash liquid
31 is often then sprayed over the cake and drawn through the
32 filter cloth and conduits to remove additional quantities
33 of filtrate from the cake. During another phase of the
34 rotation, high velocity gas is passed outwardly through the
fluid conduits to purge the li~uid filtrate and/or solv~nt
36 and break the filter cake away from the cloth. During this
37 purge cycle, liquid adhering to the walls of the conduits
f~
1 may be directed against sections of the filter cloth by
~ the high velocity gas, there~y causing erosion of the fil-
3 ter cloth. Filter cloth replacement necessitates complete
4 shutdown of the filter and is relatlvely expensive, since
S rotary filters frequently are thirty feet or more in
6 length.
7 One method for minimizing the erosive effects of
8 the liquid on the filter cloth has been to have an elongated
9 purge cycle in which the lead fluid conduit in the direction
of flow is evacuated while the lag conduit, or conauit im-
11 mediately following the lead conduit, is purged with high
12 velocity gas. Liquid purged out of the lag pipe is
13 directed into the lead pipe before it can strike the filter
14 cloth. At a predetermined point in the rotation, the vacuum
is discontinued and the purge gas and any remaining liquid
16 is directed outwardly. Extension of the time period during
17 which the combination of purge and evacuation is accom-
13 plished would decrease the amount of liquid remaining in
19 the lag fluid conduit when evacuation of the lead fluid is
discontinued. However, this would require a decrease in
21 the rotational speed of the filter drum and/or a decrease
22 in the other filter drum cycle times. Either of these
23 methods thus would decrease the filtration capacity of
24 the unit.
Yet another method of decreasing the erosive
26 effects of the liquid wouid be to use a thicker or more
27 erosion-resistant filter cloth. Use of a thicker filter
28 cloth would increase the filter cloth cost and also in-
29 crease the tendency of the filter cloth to bow while also
decreasing the filter capacity. In addition, the thicker
31 the filter cloth, the more difficult it is to remove the
32 wax fines from the cloth. Use of a more erosion-resistant
33 filter cloth may not be advantageous, since a more erosion-
34 resistant cloth may not have desirable filter cake dis-
charge characteristics.
36 Other methods for decreasing the amount of liquid
37 blown from the fluid conduits onto the filter cloth have
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3 -
1 been directed at the addition of liquid storage chambers
2 by the use of a series of capped pipes or the like attached
3 to the fluid conduits to trap the discharged liquid.
4 United States Patents 2,321,230; 3,262,575; and 4,032,~42
all are directed at individual liquid chambers attache!d
6 to each fluid conduit~ These devices have several dis-
7 advantages. Since the volume of residual liquid which may
8 remain in each fluid conduit may be significantt these
9 fluid chambers each should have a large capacity to trap
all the liquid discharged. However, entrapping this
11 residual liquid may result in undesirable deflection of the
12 chambers unless relatively complex support mechanisms are
13 provided. In addition, venting o~ the aforementioned
14 devices may not be sufficient, resultins in incomplete
drainage of the chambers during filter drum rotation. In
16 addition, the aforementioned devices may not be easily
17 retrofitted to rotary drum filters presently in use.
18 Accordingly, it is desirable to produce a
19 modified rotary filter in which erosion of the filter cloth
by entrained liquid is reduced or eliminated without
21 decreasing the ~ilter throughput or increasing the cost of
22 replacement filter cloths.
23 ` It is also desirable to have a rotary filter
24 design which effectively traps residual liquid and which is
relatively inexpensive and reliable.
26 It is also desirable to have a rotary filter de-
27 sign which is easily adaptable to rotary filters currently
28 in use for removing entrained liquid.
29 SUMMARY OF THE INVENTION
The subject invention is directed at an improved
31 rotary filter of the type comprising:
32 (a) a filter vat adapted to contain a filterable
33 slurry;
34 (b) a rotatable filter drum at least partially
disposed in said filter vat and adapted to accept a filter
36 cloth, said drum having circumferential openings therein in
37 substantial alignment with fluid conduits disposed in said
38 drum;
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1 ~c) means to rotate said drum in said filter
2 vat;
3 (d) fluid conduits disposed in said drum in sub-
4 stantial alignment with ~he circumferential openings in
said drum, said conduits communicating with a valve means
6 and with a liquid collection means; and
7 te) a valve means communicating with said fluid
8 conduits for xegulation of the fluid 10w through said
9 conduits and through the circumferentially disposed openings
in said filter drum, the improvement which comprises a
11 vented liquid collection means communicating with a
12 plurality of said fluid conduits, whereby,during one phase
13 of the rotation of said filter drum,liquid is directed from
14 said fluid conduits into said liquid collection means,
and, during another phase of the rotation of said filter
16 drum, the liquid is removed from said liquid collection
17 means. In a preferred embodiment of the subject invention
18 the liquid collection means comprises a pair of liquid
19 collection means, one being disposed at each end of the
filter drum. Each collection means comprises a series of
21 circumferentially disposed chambers, each chamber com-
22 municating with the terminus of a lag fluid conduit and
23 having a venting means.
24 BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is an exploded isometric drawing of a
26 typical rotary filter incorporating the subject invention.
27 Figure 2 is an enlarged simplified isometric
28 view showing fluid conduits and the liquid collection means
29 of the subject invention.
Figure 3 is a simplified cross-sectional view of
31 a rotary filter indicating the operations performed during
32 each rotation of the drum.
33 DETAILED DESCRIPTION OF T~E INVENTION
34 Referring to Figure 1, an exploded/ simplified
isometric assembly drawing of a typical rotary drum filter
36 is shown. The filter includes a filter vat, generally
37 indicated as 10 and a filter drum generally indicated as
63
1 20. Vat 10, having a substantially semicylindrical shape
2 is supported by columns 12 above base 14. An inlet 16
3 communicates with vat 10 and with the source of the slurry
4 to be separated (not shown). A level controller (not
shown) usually is added to control the level of slurry in
6 vat 10 by regulating valve 18 in inlet 16. A filter hood
7 90 having an overall semicylindrical shape has a plurality
8 of perforated spray headers or drip pipes 92 disposed
9 therein parallel to the axis of rotation of drum 20 to
wash the wax cake formed in the drum as hereinafter
11 described. Filter drum 20 is of a generally overall
12 cylindrical shape having a diameter slightly less than that
13 of the diameter of vat 10, such that drum 20 is rota-table
14 about its axis ~n vat 10 on a pair of trunions 22.. A
series of uniformly spaced channel sections 40 extenl
16 outwardly from the curvilinear surface of drum 20 parallel
17 to the axis of rotation. Terminal sections 42 disposed
18 near the ends of drum 20 connect each section 40 to an
19 adjacent channel section, to thereby define a series of
sgements 44 circumferentially disposed around drum 20.
21 Each segment 44 has two series of circumferential openings
22 through drum 20 evenly spaced along substantially the
23 entire axial length of each segment to form circumferential
24 rows with one series of openings 32 in general alignment
with fluid conduit 30 and with the other series of openings
26 34 in general alignment with fluid conduit 31. In each
27 segment 44 the leading opening 32 in the direction of
28 rotation hereinafter is referred to as the lead opening
29 while the immediately adjacent trailing opening 34 is
referred to as the lag opening. Similarly, fluid conduit
31 30, communicating with opening 32, is referred to as the
32 lead fluid conduit, while fluid conduit 31 communicating
33 with lag opening 34 is referred to as the lag fluid
34 conduit. One of the pair of trunions 22 has a plurality
of holes each of which communicates with lead and lag
36 fluid conduits 30, 31, respectively and with trunion valve
37 means 24 to perform varying operations during each revolu-
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1 tion of drum 20 as described hereina~ter. The other
2 trunion communicates with a conventional drum rotation
3 means (not shown) to rotate drum 20 in vat 10. Each con-
4 duit 30, 31 extends along substantially the entire axial
length of d~um 20 terminating in a liquid collection means
6 80.
7 A means for removing the filter cake from filter
8 cloth 60 such as doctor knife 100 disposed in a compart-
9 ment in vat 10 is shown discharging the filter cake into a
screw conveyor 102 which directs the filter cake out of
11 vat 10 through outlet 104. Within each segment 4~ is dis-
12 posed a filter grid 50 to maintain filter cloth 60 spaced
13 apart from drum 20. Filter cloth 60 is stretched over
14 channel sections ~0 and grids 50 and is retained in posi-
tion by caulking bar 70 compressingly inserted between
16 channel sections 40 and by circumferential wires (not
17 shown).
18 It has been found that the liquid remaining in
19 lag conduit 31 tends to be blown to the ends of the conduit
when blow gas is passed outwardly through the conduit while
21 flow to conduit 30 simultaneously is blocked by means of
22 trunion valve 24. Accordingly, liquid collection means 80,
23 shown in Figure 2, somewhat simplified for clarity, should
24 be in communication with at least a plurality of lag
conduits 31, preferably in communication with a majority of
26 lag conduits 31, and more preferably in communication with
27 all lag conduits 31 to decrease the erosive effects of
28 residual liquid on filter cloth 60 and to prevent residual
29 liquid from being blown back into the filter cake. Col-
lection means 80 preferably is disposed within drum ?0 in
31 communication with the termini of lag fluid conduits 31.
32 Although it is within the contemplation of this invention
33 that only one collection means 80 is utilized, it is
34 anticipated that a plurality of collection means typically
will be used, preferably having a substantially annular
36 or toroidal configuration. In the preferred embodiment
37 described herein, a pair of collection means 80 having an
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1 overall toroidal configuration are utilized, one disposed
2 in drum 20 adjacent to each drum wall 26. Collection
3 means 80 may ~e a separate body mounted in drum 20, or it
4 may be ~ormed by par~itioning the internal area adjacent
to wall 26 of drum 20. Where existing filters are to be
6 adapted to use of the subject invention, there may not be
7 sufficient room between the outermost circumferential rows
8 of openings 32, 34 and drum walls 26 for collection means
9 80. In that event, a sufficient number of rows of cir-
cumferential openings adjacent to each end may be blocked
11 off to provide sufficient room for installation of co].-
12 lection means 80, and lag conduits 31 may be modified to
13 communicate with collection means 80 as hereinafter des-
14 cribed.
The overall configuration of collection means 80
16 will be dependent upon the design of the filter means, the
17 required liquid storage capacity in the collection means,
18 and the space available within the filter drum 20 for
19 installing the collection means. To simplify construction,
collection means 80 preferably is of an overall annular
21 shape, more preferably of an overall toroidal configura-
22 tion.
23 Fiyure 2 shows collection means 80 comprising a
24 generally toroidal vessel 81 having individual chambers 82,
each chamber separated from the adjacent chamber by a
26 partition 86. Each chamber 82 communicates with a
27 ter~,inus of lag fluid conduit 31 through chamber opening
28 88. Each chamber 82 also is provided with a vent means
29 such as vent conduit 84 to permit alternate gas and liquid
residence in each chamber 82 during each revolution of drum
31 20. Chambers 82 should be sized such that each chamber
32 will contain all the r~sidual liquid discharged through the
33 respective terminus of lag fluid conduit 31 during each
34 revolution by the blow gas. It may be desirable to brace
vessel 81 to drum 20 by radially extending supports 100
36 communicating with vessel 81 and drum 20.
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1 The m~thod selected for venting chamber 82 is not
2 critical provided that the venting is sufficient during all
3 phases of filter operation. Adequate venting is particular-
4 ly important in allowing gas to displace liquid from each
chamber when the chamber is submerged in the slurry. One
6 particularly effective method for venting individual
7 chambers 82 is to connect each chamber, such as charnber 82A,
8 to the generally diametrically opposite chamber such ~s
9 chamber 82F, via the vent conduits 84 joined at 85,although
other means for venting chambers 82 also may be effective.
11 In this Figure, sections of all lag fluid conduits 31 and
12 all but two vent conduits 84 have been omitted for clarity.
13 A typical filter for the separation of wax from
14 lube oil has a filter drum 20, thirty feet in length and
eleven and one-half feet in diameter. This dxum has an
16 effective filtering area of approximately 1000 square feet
17 with thirty lag fluid conduits 31, 2 1/~ inches in diameter.
18 In this embodiment, liquid collection means 80 may comprise
19 two toroids fabricated from eight inch O.D. schedule 40
type 316 stainless steel approximately nine feet in dia-
21 meter. The rings are partitioned into 30 substantially
22 equivalent chambers 82, each chamber communicating with the
23 terminus of a lag fluid conduit 31 and with the diametrical-
24 ly opposite chamber via vent conduit 84, which may be
25 fabricated from small diameter thin-walled metal tubing,
26 such as half inch diameter stainless steel tubing.
27 Preferably tubing which is somewhat flexible should be
28 used, since all vent conduits 84 will pass near the center
29 of vessel 81.
The sectors of Figure 3 illustrate the varying
31 operations performed simultaneously by a typical rotary
32 filter such as that of Figure 1, which incorporate the sub-
33 ject invention. When a point on filter cloth 60 is in a
34 position included within sector A, that point is under
35 vacuum. Filtrate is drawn through filter cloth 60, cir-
36 cumferential openings 32 and 34 and fluid conduits 30 and
37 31, respectively, into a filtrate storage facility (not
3~63
1 shown). The solid wax crystals are ~etained on filter
2 cloth 60 and buildup to form a wax filter cake. Towards
3 the end of this phase, blow gas passes from chamber 82F
4 through vent conduit 84 into chamber 82A to pressurize
5 chamber 82A momentarily, thereby forcing liquid in chamber
6 82A out of the chamber through lag conduit 31 int~ filtrate
7 stoxage. As each point on filter cloth 60 rotates to
8 sector B, that point rises out of the slurry. Vacuum
9 continues to be applied to sector s to continue to draw any
10 remaining filtrate through circumferential openings 32 and
11 34 and fluid conduits 30 and 31, respectively, thereby
12 further drying the filter cake. Any remaining liquid in
13 chamber 82A is forced from the chamber through lag conduit
14 31 by the combination of the pressure in chamber 82A and
15 the vacuum in the lag conduit. When the point rotates
16 still further to a position within sector C, valve means
17 24 continues evacuation of fluid conduits 30 and 31, while
18 a wash fluid is sprayed through spray headers 92 in filter
19 hood 90 to wasn filtrate from the wax cake. At least a
20 portion of the filtrate remaining on the wax cake as well
21 as wash fluid passes through the wax cake, filtex cloth 60,
22 circumferential openings 32, 34 and fluid conduits 30, 31,
23 respectively, for removal from the filter. The wash fluid
24 generally comprises a liquid which is miscible with the
25 filtrate but not with the solids of the filter cake. In
26 the separation of lube oil from wax, this wash liquid
27 frequently is a mixture of ketones or ketone/toluene. When
28 the point on filter cloth 60 rotates to the position shown
29 by sector D, the filter cake is again dried by discontinu-
30 ing external wash flow and continuing to apply vacuum to
31 sector ~ which pulls wash from the wax cake through cir-
32 cumferential openings 32, 34, and fluid conduits 30, 31,
33 respectively. As the point rotates still further to sector
34 E, purge gas, typically having a velocity of about 100 feet/
35 second, is supplied to lag fluid conduit 31 communicating
36 with lag opening 34 while the i~mediately adjacent lead
37 opening 32 continues to be maintained under vacuum. This
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1 serves to cause some of the liquid remaining in lag fluid
2 conduit 31 communicating with lag opening 34 to flow into
3 fluid conduit 30 commllnicating with lead opening 32. As
4 the point rotates still further to sector F, lead opening
3~ is no longer evacuated. The purge gas which is called
6 blow gas at this point, forces at least a portion of the
7 rPmaining liquid in fluid conduit 31 into a chamber 82F
8 of 'iquid collection means 80~ Blow gas also passes through
9 vent con~uit 84 to pressurize the diametrically opposite
chamber 82A as previously described. Blow gas also contacts
11 filter cloth 60, causing the cloth to billow out slightly,
12 thereby facilitating the subsequent removal of the cake by
13 doctor knife 100. It should be noted that if li~uid col-
14 lection means 80 were not installed in the subject filter,
liquid remaining in conduits 31 would be conveyPd ~y the
16 high velocity purge gas against filter cloth 60 causing the
17 cloth to erode, particularly at the ends of drum 30 where
18 the liquid tends to collect.
19 The relative length of phases A-F is shown in
Figure 5 for a typical filter. It is to be understood that
21 the length of time that any given location on filter cloth
22 60 spends in a particular phase may be ad~uste~ by varying
23 the size of the sector devoted to that phase and by varying
24 the rate of rotation of drum 20. In addition to decreasing
the erosion rate of the filter cloth, use of the subject
26 invention also may permit a decrease in the time required
27 for phases E and/or F, thereby permitting an increase in
28 the filtration time in each revolution.
29 While the invention has been described with
respect to a specific embodiment, it will be understood
31 that this disclosure is intended to cover any variations,
32 uses and adaptations of this invention including such
33 departures from the present disclosure as come within
34 known or customary practice in the art to which the in-
vention pertains and as fall within the scope of the in-
36 vention.
