Note: Descriptions are shown in the official language in which they were submitted.
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001 -1-
002 BACKGROli~lD OF T~E IMVENTION
003 This invention relates to a gravity settling
004 apparatus and method for recovering a clarified liquid
005 from a slurry comprising a liquid and suspended solids.
006 In a particular asoect, the invention relates to the
007 design of internals for a gravity settler.
008 The need for an effective and economical appa-
009 ratus and method for removing suspended solids from a
010 liquid slurry containing them is a continuing problem in
011 the field of solid-liquid separation. The need is espe-
012 cially noticeable in the case of synthetic hydrocarbon
013 liquid processing, such as coal liquefaction, tar-sand oil
014 extraction and shale pyrolysis. Coal liquefaction
015 extracts, shale oils and the like usually contain appre-
016 ciable amounts of finely divided suspended solids. These
017 solids can seriously interfere with catalytic processing
018 for upgrading these oils to useful fuels due to catalyst
019 deactivation by poisoning active sites, pore plugging,
020 reactor plug~ing, etc. Ty2ically, all suspended, finely
0~1 divided solids have average diameters in the range below
022 100 microns.
023 ~hese solids are co~monly described in the art
024 as unfilterable because, as a practical ~atter, satis-
025 factory separation of them from the oil cannot be acco~-
026 plished by usual mechanical separation techniques such as
027 filtering, centriEugin~ and settling. Gravity settlers
028 are used to separate solids from a slurry of the solids
029 and the liquid, and they are especially useful in the
030 application of separating coal oil from coal fines and
031 ash. Examples of conventional gravity settlers include
032 the following:
033 U.S. Patent 4,075,080, which describes a process
034 for separating undissolved solids from coal oil. The
035 gravity settler described therein has a settling zone
035 above a washing zone in which descending agglomerated
037 solids are washed before they are withdrawn.
038 U.S. Patent 3,791,956, which describes a settler
039 comprising an upper quiet zone and a lowe agitated
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zone. The feed is discharged downwardly into a central vessel, clarified
liquid is withdrawn from an edge of the quiet zone, and solids are withdrawn
from the bottom of the agitated zone.
United States Patent 4,096,051, which describes a separator having
a central attrition zone surrounded by a sand separation zone and an outer
product recovery zone.
Settlers incorporating other arrangements of internals are shown
in United States Patents 3,184,065 and 1,104,051. In spite of the long
history of the use of gravity settlers, there ;s still room for improvement
in their design.
SU~ARY OF THE INVENTION
The present invention is an apparatus and a process for separating
a clarified liquid hydrocarbonaceous oil from a slurry of the liquid
hydrocarbonaceous oil and finely divided suspended solids.
In accordance with one aspect of this invention, there is provided
a gravity settler for settling finely divided suspended solids from a slurry
of a liquid hydrocarbonaceous oil and said solids, comprising in combination:
(a) a vessel containing a settling zone; (b) at least one duct with open
upper and lower ends within said vessel and spaced apart from the sides of
the vessel, said duct having a vertically extending portion, defining with
a bottom portion of said vessel a separating zone below said duct and in
communication with the interior of the duct and with said settling zone,
and defining with a side portion of said vessel a passageway so adapted and
arranged as to permit circulation of a portion of a partially settled
liquid hydrocarbonaceous oil from said separating zone upwardly into the
upper end of said duct, whereby incoming slurry within the duct is mixed
with partially settled liquid hydrocarbonaceous oil circulated into the
duct from the separating zone; (c) slurry inlet means discharging upwardly
into the interior of said duct; (d) settled solids removal means located
in a lower portion of said vessel; and (e) clarified
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liquid hydrocarbollaceous oil removal means located in an upper portion of
said settling zone.
In accordance with a preferred embodiment of the inventionJ the
settler is a vertically elongated vessel and the duct is an intermediate
portion thereof. Alternatively~ the settler can be a horizontally extending
vessel, and within the vessel a first baffle is positioned to one side
across a portion of the vessel and a side zone in the smaller resulting
portion of the vessel, said duct being spaced apart from the baffle and
defining with the baffle and side portion of the vessel said passageway.
In accordance with another aspect of the present invention, there
is provided a method for separating a clarified liquid hydrocarbonaceous oil
and an agglomeration agent from a slurry of said liquid hydrocarbonaceous oil
and finely divided suspended solids wherein said slurry is charged to a
settling zone and held there to allow said solids to agglomerate and separate
by gravitation, a clarified and essentially solids-free liquid comprising said
hydrocarbonaceous oil and said agglomerating agent is recovered from an upper
portion of said settling zone, and settled agglomerated solids are withdrawn
from a lower portion of said vessel, wherein the improvement comprises: (1)
discharging said slurry upwardly into a mixing zone within an intermediate
or upper portion of said vessel; (2) forming within said mixing zone a
mixture of said slurry with a downflowing recirculated liquid stream compris-
ing said hydrocarbonaceous oil and said agglomerating agent; (3) forming
from said mixture a first portion of agglomerated solids of a size large
enough to settle by gravitation and a partially settled liquid by circulating
said mixture downwardly into a separating zone positioned below said mixing
zone and separating said first agglomerate portion from said mixture by
gravitation; (4) forming from said partially settled liquid a second
portion of agglomerated so]ides of a size large enough to settle by
gravitation and a further settled liquid by circulating at least a portion
of said partially settled liquid upwardly through a quiet zone horizontally
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surrounding said mixing zone and there separating said second agglomerate
portion from said further settled liquid by gravitation; (5) providing at
least a portion of said recirculated liquid stream by circulating at least
a portion of said further settled liquid from said quiet zone into said
mixing zone; (6) circulating to said settling zone a portion of at least
one of the following: said partially settled liquid from said separating
zone and said further settled liquid from said quiet zone.
_SCRIPTION OF Tl-IE FIGURES_
Figure 1 is a vertical sectional view through a settler having a
spool-shaped duct in accordance with a preferred embodiment of the invention.
Figure 2 is a vertical sectional view through a settler having
two ducts formed by two concentric truncated cones in accordance with another
preferred embodiment of the invention.
Figure 3 is a vertical sectional view through a settler having a
settling zone positioned horizontally with respect to a spool-shaped duct,
in accordance with still another preferred embodiment of the invention.
DETAILED DESCRIPTION OF T~E INVENTION
The settler of the present invention is particularly useful in
-~ settling finely divided suspended solids from a slurry of the solids in a
liquid. In particular, the settler is useful in removing unfilterable
suspended solids from a slurry of the solids and a hydrocarbonaceous liquid
and especially a hydrocarbonaceous oil which is partially or completely
undistillable. Effective removal of finely divided solids from hydrocarbon-
aceous oils enables one thereafter to more easily catalytically upgrade the
oil, because prior distillation, which may involve a sub-
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001 ~5~
002 stantial loss of desirable product precursors with the
003 rejected solids, is no longer necessary.
004 As used herein, a "slurry" is a mixture com-
005 prising a liquid and unfilterable suspended solids. The
006 liquid may be any liquid or liquid mixture, aqueous or
007 organic, and preferably comprises a mixture of hydro-
008 carbonaceous oil and agglomerating agent.
009 As used herein, "unfilterable suspended solids"
010 means finely divided solids having an average diameter
011 below about 100 microns. Such solids suspend readily in
012 liquids, especially in unrefined synthetic oils. Sepa-
013 ration from the oil of these minutely sized solids by ordi-
014 nary techniques is not satisfactory in a practical eco-
015 nomic sense, because they readily obstruct the filter
016 medium and do not settle upon standing.
017 The term "nondistillable hydrocarbonaceous
018 liquid" (or "oil") as used herein refers to an oil which
019 cannot be distilled without decomposing or cracking, such
029 as coal liquefaction extract, shale oils and the like.
021 Such oils typically contain apr~reciable amounts (at least
02~ 5 wei~ht percent) of one or more components which under
023 ordinary distillation conditions thermally cracX or polym-
024 erize to form unsatisfactory degradation products such as
025 coke. Finely divided suspended solids in general are
026 effectively removed from the oil by the ap~aratus and
027 method of the invention.
028 Representative solids include mineral ash-
029 forming impurities, solid coal, coke, carbonaceous solids,
030 catalyst fines, solid oil shale and spent shale fines, tar-
031 sand solids such as clay and sand, natural and synthetic
032 mineral oxides, organic and inorganic salts, ~ixtures
033 thereof, and the like, in particulate for~, particularly
034 the finely divided solids having an average diameter belo~
035 about 100 microns and eseecially below 60 microns.
036 Representative solids-containing hydrocarbona-
037 ceous oils suitable for treatment by the present apparatus
03~ include shale-derived oil, coal liquefaction oils such as
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from extraction, hydrogenation, pyrolysis or other thermal treatment, and
combinations of them; tar-sand-derived oils; petroleum refinery decant oils
such as fractionator bottom oils from a fluid catalytic cracking process,
bottoms fractions of said oils and oils containing coke fines; mixtures of
any two or more of the above; and the like oils. Nondistillate hydrocarbon-
aceous liquids are preferred feeds, and coal-derived oils are especially
preferred.
The slurries suitable as feedstocks for the apparatus and process
of the present invention may contain, in addition to unfilterable suspended
solids, larger, but still finely divided particulate filterable solids, e.g.,
smaller than 200 microns. The total of solid components should represent
from at least 0.1 weight percent to as much as 60 weight percent or more,
and preferably from 1 to 50 weight percent, of the solids-coal oil slurry.
Especially preferred feedstocks have a finely divided solids content in the
range from 5 to 40 weight percent of the solids-oil slurry.
The liquid portion of the feedstock to the apparatus in the process
of the present invention may also contain an agglomerating agent. An espe-
cially useful agglomerating agent comprises a mixture of ketones and especial-
ly a mixture of acetone and 2-butanone in a proportion of at least 0.1 volume
and not more than 1.0 volume of ~-butanone for each volume of acetone. Pre-
ferred volumetric ratios of agglomerating agent to oil are from 0.05 to 3.
Agglomeration conditions for use in the process of the invention
will vary depending upon such process factors as the type and solids content
of the slurry, the size distribution of the solids and the properties of
the liquids being processed. Representative conditions are described in
my l)nited States Patent 4,094,770, issued June 13, 1978. In general, the
most satisfactory process temperature will range from 20 to 160C, and
satisfactory pressures will depend upon the temperatures employed and may
vary from 1 to 50 atmospheres absolute, and preferably from 1 to 5 atmospheres.
For removing solids from a coal oil, the preferred conditions are a
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temperature from 80 to 160C, more preferably from 120 to 160C, and a
pressure from 2 to 5 atmospheres.
The use of a washing zone is a preferred embodiment of the present
invention, even though in some applications the use of a washing zone may not
be desirable or practical. However, should a washing zone be employed, it
will preferably be operated at a temperature and pressure approximately the
same as those for the settler.
The present invention stems from the discovery that agglomerated
solids are very fragile and that disturbance or agitation of the liquid
within the settler should be minimized to reduce breakup of the agglomerated
solids. The duct surrounding an upwardly discharging inlet divides the
separator into a number of zones. These zones promote aggiomeration of the
suspended solids while minimizing disturbance of the contents of the remainder
of the vessel.
The Figures and Example will be discussed from the standpoint of
the preferred embodiment of separating coal fine and ash from a liquid
comprising coal oil and agglomerating agent.
Referring to Figure 1, there is shown settler 10 having a
converging bottom portion 11. The feed slurry to the settler enters through
line 12 and comprises a mixture of a coal oil containing suspended solids
and an agglomerating agent.
The slurry is discharged upwardly within spool-shaped vertically
oriented duct 13. Because the slurry is denser than the recirculated
partially clarified liquid ~specific gravity 1.0~ vs. 0.99), upon being
discharged
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001 -8-
002 into the duct, the slurry will reverse direction of flow
003 and begin to flow downwardly. As it ~lows downwardly, the
004 slurry mixes with a recycle portion of further settled
00S liquid entering the duct 13 through an upper opening there-
006 in. Deflector 15 prevents the feed from agitating the
007 clarified liquid above the duct, and duct 13 prevents dis-
008 turbance of the contents of the vessel alongside the
009 inlet. The mixture of feed and further settled liquid
010 circulates downwardly from mixing zone 16 through a diverg-
011 ing section of the duct and into separating zone 17. The
012 diverging section acts to decrease the down~ard velocity
013 of the mixture. In zone 17, a po~tion of the suspended
014 solids in the mixture agglomerates and separates by gravi-
015 tation. Agglomerated solids from SeQarating zone 17 and
~16 other zones are collected by downwardly converging bottom
017 portion 11 and passed into washing 20ne 18. In washing
018 zone 18, occluded product liquid is washed from the down-
019 flowing agglomerated soiids with an upflowing washing
020 liquid that is introduced into a lower portion of the
021 washing zone through line 19. The washing li~uid should
022 be a solvent for the clarified liquid and is preferably an
023 agglomerating agent, and more preferably the same agglom-
024 erating agent that is present in the feedstock. The
025 washed ag~lomerated solids are removed fro~ the bottom of
026 washing zone 18 via line 20.
027 After a portion of solids has agglomerated and
028 separated from the mixture in separating zone 17, the
029 resulting mixture, partially depleted of solids, is mixed
030 with upflowing washing liquid from washing zone 18 and
031 circulated into quiet zone 21. Further agglomeration
032 occurs in quiet zone 21, and a~glomerated solids settle
033 downwardly through opening 22, are collected on bottom
034 portion 11, and are passed to washing zone 18. Opening 22
035 is sized so that the velocity of the upflowing liquid`is
036 less than the terminal velocity of the settling agalom-
037 erated solids.
038 ~he further settled li~uid, further depleted of
039 solids, is circulated up~ardly from quiet zone 21. A
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001 _9_
002 portion of the liquid is circulated to the upper opening
003 of the duct as the partially clarified recycle liquid
004 which is admixed with the incoming slurry. ~ecycling a
OOS portion of the further settled liquid allows still more of
006 the solids suspended in it to agglomerate and separate
007 from the liquid. The remaining portion of the further
008 settled liquid from quiet zone 21 is circulated upwardly
009 into settling zone 23. Settling zone 23 is of sufficient
010 size to provide a residence time and liquid velocity suit-
011 able to allow the remaining solids to agglomerate and sepa-
012 rate by gravity. Generally, the residence time required
013 for liquids in the settling zone will be at least 1
014 minute, preferably from 2 to 60 minutes, and still ~ore
015 preferably from 2 to 5 ~inutes. Clarified liquid is with-
016 draw~ from the top of settling zone 23 via line 24.
017 Agglomerated solids from settling zone 23 settle by
018 gravity through quiet zone 21 or mixing zone 16 hefore
019 they are removed from the settler.
020 Another embodiment of the apparatus of the
021 present invention is illustrated in F~G. 2;
022 Referring now to FIG. 2, there is shown a
023 gravity settler 30 having two ducts in the form of a pair
024 of concentric cones 33 and 34 which have the base upper-
025 most. The feed is discharged upwardly through inlet 32,
026 changes direction to flow downwardly and is ~ixed with a
027 recycle portion of liquid which enters mixing zone 36 from
028 above. ~ portion of the solids agglomerates and continues
029 to settle downwardly in separating zone 37 onto converging
030 bottom portion 31. The collected ag~lomerates are then
031 passed into washing zone 38 and are there handled as
032 described in connection with FIG. 1. A portion of the par-
033 tially settled liquid from separating zone 37 is circu-
034 lated upwardly into annular space 35 between truncated
035 cones 33 and 34, and then is rec~/cled into ~ixing zone 36.
036 The remaining portion of partially settled
037 liquid from separating 20ne 37 is ~ixed with washing sol-
038 vent from washing zone 38 and circulated upwardly into
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002 quiet zone 41. Further agglomeration takes place in the
003 ~uiet zone. Agglomerated solids settle onto converging
004 bot,tom portion 31, and the partially settled liquid circu-
005 lates upwardly fro~ quiet zone 41. A portion of the
006 liquid from the quiet zone is circulated into mixing zone
007 36, and the re~aining portion is circulated to settling
008 zone 43. Further ag~lomeration of solids occurs in
009 settling zone 43, and a clarified liquid is withdrawn via
010 outlet 44.
011 Yet another embodiment of the settler of the
012 present invention is shown in FIG. 3.
013 Referring now to FIG. 3, there is shown a
014 gravity settler 50 having a converging bottom portion 51
015 for collecting agglomera~ed solids. Slurry inlet means 52
016 discharges upwardly within the duct defined by spool-
017 shaped wall 53. 8affle 54 mini.~izes disturbance of the
018 remainder of the contents in the cettler. In mixing zone
019 56, further settled liquid entering from the top is mi~ed
020 with the feed slurry and the resulting mixture is circu-
021 lated to separating zone 57, where a portion of the solids
022 agglomerate and settle by gravity onto converging bottom
023 portion 51 of the settler. A portion of the resulting par-
024 tiallyn settled liquid, partially depleted solids, circu-
025 lates from separating zone 57 upwardl~ into auiet zone 61,
026 where more solids agglomerate and settle by gravitation.
027 Lhe resulting further settled liquid is then circulated
028 over the top of duct 53 and into mixinq zone 56, where it
029 is mixed with the feed slurry.
030 The remaining portion of partially settled
031 li~uid from separating zone 57 is circulated under baffle
032 54 to settling zone 63. ~ore of the solids agglomerate
033 and settle by gravitation to collect on converging bottom
034 portion 51 and then are ~assed into washing zone 58. The
035 partially clarified liquid from settling zone 63 is circu-
036 lated to withdrawal zone 64 through passageway 65, located
037 above baffle 66. Baffle 66 minimizes possible agitation
038 of the contents of withdrawal zone 64. Substantially all
ilX~g
0 0 1
002 of the remaining solids in the liquid agglomerate and sepa-
003 rate from the liquid in zone 54. lhe agglomerated solids
004 settle by gravitation to converging portion 51 of the
005 settler, and pass out of withdrawal zone 64 through
OOG passageway 67 under baffle 66. Clarified liquid is
007 removed from withdrawal zone 64 via outlet 68.
00~ EXA~5PL~
009 ~he following illustrative example was carried
010 out using a glass settler of the design depicted in FIG.
011 1. ~he settler was 7.6 cm in diameter and 34 cm high, 4
012 cm of which is taken up by the converging bottom portion.
013 The washing zone has a 1 cm diameter and extends 8 cm
014 below the bottom of the settler. The spool was 5.4 c.~
015 long with the barrel portion taking 4.4 cm of that. The
016 barrel of the spool was 1.25 cm in diamter, the top was
017 flared to 2.5 cm in diameter, and the bottom was flared to
018 6.3 cm in diameter. The settler was initially filled with
019 a clear liquid so that the flow of the slurry could be
020 observed. A feed slurry co~prising a ~ixture of equal
021 parts coal oil containing suspended solids and agglom-
022 erating agent was passed upwardly into the center of duct
023 13 at 400 cc/min, providing an average liquid residence
024 time in the settler of less than four ~inutes. The feed
025 slurry had the following analysis:
026 Coal oil + suspended solids = 50 wt.~ of slurry
027 Specific gravity - coal oil ~ suspended solids = 1.04
02~ Coal oil
029 I~P = 149C
030 EP = approximately 533C
031 Solids = 30 wt.~ of weight of coal oil + solids
032 Particle size distribution: 1 to 60 ~icrons
033 iledian particle size: 5 microns
034 Composition: A mixture o' inorganic and
035 organic solids including one or
03G more of ash, residual coal, par-
037 tially hydrogenate~ coal, metal
038 oxides, sulfides and the like
039 Agglomerating agent = 50 wt.~ of slurry
040 2~Butanone = 12.5 vol.%
041 ~cetone = 37.5 vol.~
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The contents of the settler were maintained at room temperature
and atmospheric pressure. I-lowever, the preferred temperature is from 80 to
160C and the preferred pressure is from 1 to 5 atmospheres,absolute.
The feed was discharged upwardly into the center of duct 13, but
reversed directions and flowed downwardly through mixing zone 16 while mixing
with downflowing liquid from the settling zone. A sample taken at midspool
contained "Y" or "T" shaped chains of agglomerated solids from 10 to 30 microns
long, made of particles less than 1 micron in size. Agglomerated particles
settle onto the sloped surfaces of the duct (and onto the downwardly tapered
bottom portion of the vessel) where they contact each other, often sticking
together to increase in size or losing their charges (which facilitates
further agglomeration).
The resulting mixture circulated downwardly into separating zone
17. In the separating zone, solids agglomerated to form particles which
were from 20 to 30 microns in size, and these particles settled by gravitation
into washing zone 18. The size of the particles affects their residence time,
and the particles should agglomerate to a size sufficiently large, e.g.,
a~ove 10 microns in size, for settling to take place in minutes rather than
hours. In the washing zone, the agglomerated solids were washed by a stream
of agglomerating agent having the same composition as is in the feed. The
washing stream flowed upwardly at 40 cc/min. The partially settled liquid
from separation zone 17 mixed with the agglomerating agent from the washing
zone and the resulting mixture, which contained solids under 10 microns in
size, was circulated to quiet zone 21. More agglomerates formed in the quiet
zone and settled by gravitation, and the resulting further settled liquid
circulated out the top of the quiet zone.
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001 -13-
002 ~ portion of the further settled liquid circulated to the
003 mixing zone, and the remaining portion circulated upwardly
004 to the settling zone. A sample taken of the liquid 1-1/4
005 cm above the spool contained agglomerates 10 to 30 microns
006 in size. Samples taken of the clarified li~uid effluent
007 from the settler and of the liquid 9 cm below the top of
008 the settling zone were both free of solids over 0.5 micron
009 in size, and contained less than 0.05 wei~ht percent
010 solids. The clarified liquid had a specific gravity of
011 0.99. The particles discharged from the washing zone were
012 analyzed and found to contain less than 0.05 weight per-
013 cent coal oil.
014 Thus, the gravity settler of the present inven-
015 tion can be used to separate sus2ended solids from a
016 slurry of said solids and a liquid, to produce a clarified
017 liquid containing less than 0.1 weight percent solids, and
018 preferably less than 0.01 weiqht percent solids.
019 Other embodi~ents of the invention will be appar-
020 ent to those skilled in the art from a consideration of
021 this specification or practice of the invention described
022 therein. It is intended that the specification and
023 examples be considered as exe~plary only, with the true
024 scope and spirit of the invention being indicated by the
025 following claims.
