Note: Descriptions are shown in the official language in which they were submitted.
~`
1138l~0
BAC~'G~OUND OF 'rl~E INVENTIO.~
.
FIELD O~ TIIE INV~NTIOr~
This invention relates to the li~uefaction of coal and
more specifically relàtes to the removal of unconverted coal,
ash, and other particulates from a coal liquefaction reaction
product.
DESCRIPTIO~ OF THE PRIOR ART:
Processes for the removal of particulate solids for example
unconverted coal and ash, from the coal-derived liquids by
the addition of a promoter or solvent liquid to produce precipi-
tation of such particulate solids are well kno~m in the prior
art.
U.S. Patent 3,687,837 discloses that the solids in a coal
liquefaction product can be caused to agglomerate, thereby in-
creasing ease of separation through fil;ration or centrifugation,
by adding a process derived solids-f~ee liquid boiling between
100F to 700F or an ash.containing liquid boiling a.bove 1000F.
The agglomerating agent boiling between 100F and 700F is pro-
duced by the do~stream hydrocracking of a clarified coal liquid.
The 1000F plus material is essentially bottoms liquefaction
product. The aforementioned process su~fers from the disadvan-
ta~es that the agglomerating agent (boiling between 100-700F)
must be produce~ by costly hydrogenation, while the 1000F plus
material is quite viscous and while promoting ag~lomeration,
makes separation by, for example,filtration or centrifugation,
~ore difficult. ~ similar process is disclosed in U.S.Patent
3,790,467.
U.S. Patent 3,791,956 to Gorin, et al., ~iscloses ~ coal
li~ucEaction process in ~Jhich ~ precipitatinq solvent which is
an aliphatic or naphthenic hydrocarbon solvent having ~ boilin~
~388~0
range of 75-200C, such as cycloll~xane, n-dccane,"DecaLi~'
etc., is add~d to a stirred agglomeration zone maintained at a
telllperat~lre between 250-370~C and a pressure bet~een 5-200 psig.
It is rccog~ ed thaL such liquid fracti~s ~o not normally occur
in the coal liquefaction product, but must be recovered following
'subsequent hydrocracking steps.
U.S.Patents 3,852,182 and 3,856,675 to Sze et al., disclose
the removal of solids derived liq~ids by a promoter liquid having
a characterization factor (K) of 9.75-11.0 and boiling between
0 250F and 750F. However, these processes required added pro-
cessing steps, such as hydrocracking to produce the promoter
liquid and the residence time for the solids to settle is rela-
tively long (0.5-6 hours). This re;quires large and expensive
pressurized settler vessels to æhieve satisfactory solids removal
from product liquid streams.
Because of these problems, the use of more effective solven~
liquid fractions, which can be conveniently derived from the coal-
liquefaction process and require significantly shorter settling
times, has been souc,ht. I
.
*Trademark for decahydronaphthalene
-- 2
3 8 ~
Sl~ 'u~R~ OF T~IE l~!VE~!TIOM
This invention per.ains to the removal by precipitation
of a~sll ~nd other insol~lble m~terials from coal-derived liquids,
and utilizes the addition of a~specific internally-generated
liquid fraction to promote solids precipitat-ion in the coal-
derived liquid and to achieve a higher percentage of solids
removal. The solids removal step uses a selected additive solvent
liquid which is derive~ from the coal liquefaction process through
simple fractionation and without need for further processing. The
,, solvent liquid used in this process is a coal-derived naphtha liquid
fraction, boiling between about 300-600~JF and having a characterized
factor (K) in the range of 9.5-11, as defined by the equation:
K = ~
wherein TB is the average molar boiling point of the liquid (K), and
G is the specific gravity of the liquid ( 60 F/60F) .
The solvent liquid used is preferably a 350-550F fraction o~
"H-Coal" process catalytic hydrogenation procesS naphtha fractionated
from the atmospheric still overhead liquid and mixed with the
hydrogenated coal liquid in sufficient amounts to produce the
:L~ precipitation of solids in a settling zone, but not in excessive
amounts or in a ràtio to produce exoessive settlina of val ~ le heavier
coal products. The'~-Coal"process is described in U.S.Patents
Re. 25,770 and 3,519,555.
ratio of solvent to coal liquid should be at least about 0.6/1
and preferably bet~7een 0.8/1 and 1.5/1. Also, because of the greater
effectiveness of this solvent fraction for causinn rapidprecipitation
of particulate solids in the settler, the required solids settling
time is relatively sllort, usually less than abou~ 45 minutes and
-- 3 --
*Tradem~rk
8~3~0 1~
. .
certain conditions, 10-30 minu~es. Such rapid precipîtation of
solids l~laterial permits the use o~ smaller and less expensive
vessels.
'lhe resulting cl~ri.ied o~erflow licl~lid ~Jithdrawll froln the
solids settler vessel contains less than 0.1 weight percent ash
~and unconverted insoluble coal solids. The remaining underflow
liquid portion contains increased solids of between about 40-50
weight percent. Such underflow liquid stream may be further
processed as desired, such as vacuum distillation, coking, or
~o gasification.
It is an important feature of this invention that the solvent
precipitating agent used is a special solvent fraction deri~ed
entirely from the coal liquefaction process, and that no further
hydrogenation treatment of this fraction, other than fractionation
recovery, is required. This solvent liquid fraction is usually
produced from atmospheric still overhead liquid and is also recovered
by fractionation from reduced solids overflow stream from the settler,
The conditions in the settler vessel should be maintained at
sufficient pressure to avoid evaporatilon of the light liquid fraction
and at suficient temperature to maintainthe liquid viscosity within
a desirable low range to facilitate solids settling. Usually the
settler pressure should be between about 50-200 psig and the
t~r~ atur~e should be a~out 500-6Q0F and preferably 530-580F.
DESCRIPTION OF THE DRAI~INGS
Fi~ure 1 is a schema'ic diagram showing tl~e essential proccss
stcps of the invcntion incor~orated into a coal liquefaction process.
-- 4 --
~388~0
Figure 2 is a graph of weight percent ash in coal
liquid against settling time for various ratios of solvent
to liquefaction product.
Figure 3 is a graph of weight percent solids
against ratios of solvent to liquefaction product.
DESCRIPTION OF THE PREFERRED EMBODIMENT
_ _ _ . _ _ . . .
This invention will now be described as employed
in a catalytic ebullated bed type coal hydrogenation process
and illustrated by Figure 1. As shown, a bituminous or
semibituminous coal enters the system at 10 and is first
passed through a preparation unit generally indicated at 12.
In such unit the coal is dried of substantially all surface
moisture, ground to a desired mesh size, and screened for
uniformity. For our purposes, it is preferable that the coal
have a particle size of about 50 to 375 mesh (U.S. Sieve
Series).
The coal fines are discharged into transfer line 13
and pass to slurry tank 14 where the coal is blended with a
slurrying oil indicated at 15, which is conveniently made in
the system. To establish an effectively transportable slurry,
it is found that the ground coal should be mixed with at
least about an equal weight of slurrying oil.
The resulting coal-oil slurry is pressurized by
pump 16 to superatmospheric pressure, such as 500-5000 psi,
and is then passed through heater 18 to bring the clurry to a
temperature in the order of 600F to 850F. The heated coal-
oil slurry is then discharged into reactor feed line 25,
wherein it is supplied with recycled hydrogen from line 19.
Fresh makeup hydrogen is added as needed at 17.
~f
i~388GO
.
The entire mi~ture o~ coal-oil slurry and hydrogen then
cnters reactor 20, passing upwarclly from the bottom at a rat~,
under pressure and at a temperature to accomplisll the desired
hydrogenation~ In addition, particulate hydrogenation catalyst
5may be added to reactor 20 at connection 21 in the ratio of
about 0.1 to 2.0 pounds of catalyst per ton of coal. Such a
catalyst would be from the class of cobalt, iron, molybdenum,
nickel, tin, or other hydrogenation catalysts kno~t in the art
deposited on a base of the class of al~nina~magnesia, silica,
o or similar materials.
By concurrently flo~ing liquid and gasiform materials up-
wardly through a vessel containing a mass of solid particles o~
a contact material, which may be a specific catalyst as indicated
above, and expanding the mass of solid particles at least 10%
and usually by 20-100% over the volume of the stationary mass,
the solid particles are placed in random motion within the vesse~
by the upflowing streams. A mass of solid particles in this
state of random motion in a liquid medium may be described as
"ebullated". The characteristics of the ebullated mass at a
~o prescribed degree of volume expansion can be such that finer,
lighter particulate solids ~ill pass up~7ardly thro~gh the ca~alyst
. m~ss, so that the contact p~rticLcs constit~lting the eb~llated
mass are retained in the reactor and the finer, lighter matexial
may pass from the reactor. The catalyst bed upper level 22
above which few, if any, contact particles ascend, is called the
uppcr level of ebullation.
In general, the gross density oE the stationary mass of con~tct
ma~erial ~i]l be bet~Jeen about 25 to 200 pounds per cu~ic foot, the
~lo~ rate of thc liquid will be between about 5 and 120 gallons p~r
minute pcr square foot of horizontal cross-section area of tlte
ebullatcd mass, ancl the e~panded volume o~ the ebullatcd mass
usually will be llOt more than double the volume of thc scttl~d
mass. To main~ain ~he desired superficial upward liquid velocity
113~8(~0
in the reactor, a portion of the liquid slurr~ is usually re-
cycled to the reactor, such as a portion of liquid stream 24
which is removed from about the upper level of ebullation 22
and recycled via conduit 38 and pump 39 to the bottom of the
reactor 20. Alternatively, thîs recycled liquid stream may be
located within the reactor, as will be understood by those
skilled in this art. Spent catalyst may be removed ~y drawoff
at connection 23 to maintain the desired catalytic activity
within the reaction zone.
Reactor operating conditions are in the range of
700-950F temperature and 1000-4000 psi partial pressure of
hydrogen, prefera~ly 750-900F and 1000-3000 psi hydrogen
partial pressure. Coal throughput or space velocity is at
the rate of 15 to 150 pounds coal per hour per cubic foot of
reactor volume, so that the yield of unreacted coal as char is
between 5 and 15 weight percent of the quantity of moisture
and ash-free coal feed. The relati~e size of the coal and
catalyst particles and condition of ebullation is such that
catalyst is retained in the reactor, while the ash and
unreacted char particles are carried out with the liquid
reaction products.
From reaction zone 20 and effluent stream 24, which
is virtually free of solid particles of contact material, is
withdrawn, cooled at 26: and then passed to a first phase
separator 28. From separator 28, a light gas stream is
removed at 29 and passed to hydrogen purification step 30.
A medium-purity hydrogen stream 32 is recovered from
purification step 30, warmed at 26, and recycled through
heater 34 to reactor 20 to proYide most of the hydrogen
requirements therein as heated hydrogen stream 19. Also, a
liquid stream 36 is recovered from separator 28 and is passed
- 7 -
, . . .. . . . , ., . .... . , ., . . ,, , ,, , ., . ,, .. , ~ ~, . . . .
~138~0
at reduced pressure to intermediate phase separator 40.
This separator operates at 500-650F temperature and permits
removal of a substantially gaseous stream at 41 and a liquid
stream at 42.
- 7a -
... ... . .... . . ..... . .
.
1~388~0
From phase separator 28, liquid stream 36 is
withdrawn and passed to phase separator 40. ~ hydrogenated
coal liquid is withdrawn at 42 containing unconverted or
insoluble coal and ash solids from the reaction step 20 and
is passed to hydroclone separation step 46. An overflow
liquid stream containing a reduced concentration of solids
is removed therefrom at 47 and returned to reactor 20 to
help control the solids concentration in the reactor. An
underflow liquid stream, containing an increased
concentration of solids, is withdrawn at 48. If desired, a
portion 49 may bypass hydroclone 46 for control purposes.
In addition, the hydroclone can be eliminated to permit
passage of stream 42 directly to settler 50.
This hydroclone underflow liquid stream 48 is mixed
at 44 with a solvent liquid 45 derived from the process by
fractionation. It has been found that the ratio of solvent
liquld 45 to stream 42 should be between 0.6/1 and 1.5/1.
The resulting mixed stream is then passed to settler 50,
which is maintained at a temperature between about 550-600F
and pressure conditions sufficient to avoid vaporization of
the precipitating solvent, generally about 50 psig and
usually not exceeding about 200 psig. Rotary rake 51 or
equivalent mixing means is used to provide sufficient mixing
and continuous agitation to prevent premature settling of
the precipitated solids component. Because of the
effectiveness of the combination of the liquids to produce
precipitation of solids, the residence time in the settler to
achieve significant solids settling is usually less than
about 45 minutes and is preferably 15-30 minutes.
From settler 50 r o~erflow liquid 52 is continuously
withdrawn and contains less than about 0.1 weight percent
- B -
.. , .. . ~ . .
1~388~0
solids and usually less than about 0.07 weight percent
solids comprising fine particles of uncon~erted coal and ash.
This overflow liquid 52 contains some sol~ent liquid fractions
and is passed to recovery
~0
- 8~ -
. . . . . .. . . ..
1~3~ 0
,
tower 51~:ror sut~;tantial recovery of the solvent mater:ial by
~list~ t:ion. 'rhe ~Inderrlo~! liq~lid strec~ 56, c~ontaitlin~, an
increased solids concentration, is removed from settler 50 by
pun-ping and with the aid o~ internal rotary 51, reduced in pressure
by passage to fla~h dr~m 58 which is maintained at a pressure of
at least 5 psig and a temperature of 550F which pr~vents vapor-
i~ation o~ solvent, and passed to vacuum distillation at 60. The
resulting overhead liquid 61 from the vacuum still is joined wit~h
stream 52 and passed to the recovery distillation tower 54. The
bottoms stream 62 from vacuum still 60 may be urther proeessed
by, ~or e~am~le, coliing or gasification to produce the makeup
hydrogen needed in the process.
The li.gllt fraction removed overllead at 55 from recovery tower
54 is a 350-600~F fraction, ~7hicll is ef~ective in produeing precipi
tation of ash and unconverte~l coal solids from the hyclrogenated
coal l~ uicl. Thi~; liquid ~raction is p<~ssed ~o holding tank 70
for recycl~. to tlle solvent preeipi.tat-ioll m:ixin~ ~ank as n~ecled.
Al~o froln ~o~er ~4 c~ ~uel oil Eraetion 56a is rcrnoved as produet.
If des-ire(l, a port:ion of stream 56a ean be used as slurry;ng oil
15.
Ret~lrn:i-nt, no~ to pllase seyarator l~0, overl~eacl streaTn 41 is
passcd Lo c~ )he2^;c d:ist:illclLioll to~Je-- G'~. The reslllt~ cr ~itluicl
product streanl is withdrawn at 66 and providcs an int~ mediate
liqu:id product. I:E desired, a portion 72 o~ ~his liqui~ stream
66 ca~ e used for slurrying oil 15. ri~l~e light overhead liquid
stream 65 is passecl to a fract~ionation tower 68 for production o~
a portion 69 oC t:he prccipitating solvent liqui~ needecl ~or tl~e
solverlt: pr~ci p.~ tC'ttiO11 step. This solvent liquicl ~r~c~ion renlovecl
c-lt 69 is passed to ilolding tanli 70. The coln~ined l~e~ solvent 69
arl(l recovere(l solvetlt 55 is withdra~n from tank 70 at the desire(l
rctte, to prov:id~ solvellt s~r~c-tm ~5 for aclclition to eoal-derived
~ r~c~ 2 clt lllix;~c, ~ int ~ cle~iir~d, cl cp~c:tal ~
: ( (
mi.xinr, Lanlc mcly be provic~ed at 44, desirned for achieving intimate
ie:i.t~ 0~ e sol~ent: alld l):ro<luc l: l:i.clui(ls s u:l~.L icicnt to a(:lLieveagglomer~tion and subseq~2n-t rapid settling of solicls in the
~settlinr vessel 50.
The invention will be lurther illustrated by reference to the
exan~ples which follo~
EX~MPLE I
~ continons run was made in accordance with the inventionin a
settler hav:i.ng a capacity for receiving 30 lbs of material per hour.
The settler utilized is a pipe 56 inches in length and 8 inches in
diameter. The feed ~Jas a hydroclone underflow containing 27 weight
percent solids, (1~ weigh, percent ash). The precipitating solvent
had the characteristics noted i.n Table 1 below.
_~`a
Gravlty, ~Pt 2
Dist:i.llcltion ~
P 300
~ , 3~,
3() , 350
S0 370
~96 ..
; 90 4l~8
~P 538
~ e res~llts of t~,is r;in are sho~n in Table 2 belo~/ whic~h sho~v
tl~at t-lle ash colltent~ .s red-lced to between .006 wei,llt percen~
and .093 ~ei.~ el^cent.
- 1 0 -
;
~13~380(1
;
. Tal)l~ 2
'
Coal l.iquid flow
Rate, lbs/hr 13.1
Precipitclting
Solvent Flow Rate, lbs/hr 11.9
Ratio Solvent to
Coal Liquid .91
Set-tler Conditions
Temperature F 550
~ressure, psig 200
Run Duration, hours 16
_____________________________________ _________ ___________________
__ __._____________________________________________________________
Set~ler Ovcrflow ~ettlcr Under~low
Ash,~ % - llour Flow Rate Flow ~a-te
8.9 7.2
1 0.016 6.91.
2 0.()28 0.76
3 0.0~.9 0.83
~ n. o/,o 1 2.32
~ 0.0~1 2.77
; 6 0.036 9.06
7 0.076 7.32
0.03~ _
9 0.006
lo n. 093 10 86
11 ~.0~.0 15.9
.2 0.0~ .9
01 ~.2.83
1(~ . 0. 0~ 13.26
0. 06 35.44
16 0. 07 29.60
18
19
22 1
2~
2?76
28
29
3n
31
'ro~ll, L~;. 138.
I~388QO
f'L~ I t
13c-se(l on the r~ sults in ~xallnle I, calculations for scale up
t:o 3¢)0 ~ ,c~re -n~?.d~ ~?roj ect:incr, the or)erclt;on in accord~nce
~:ith l i~ re 1. 'l`lle results ~re sho~Jn in Tabl~ .3 be:Low. ~e~erence
- to stream number in the ~able corresponds to Figu~e I.
Table 3
Cornponent:, Lbs/Hr
Stream Total Anti- Solid~
umber Lbs/llr Solvent Distillate F~es-iduum olicls I~TCr/o
llydroc lone
~`eed ~'~2 644.5 87.4 13.6
Ilydroclone
Over~low 47 394.5 39.8 10.
llydroclone
linderf1O~J L'~S 250.~'~ 3.2 118.~ 81.2 47.~ 19.0
Anti-Solvent
300-400I~ l~5222.1 222.1 0.0 0.0 0.0 0.0
Settler ~ccd ~72.5 225.3 118.~ 81.2 ~7.~ 10.
~et~lcr Overfl o;.~ 52 283.G 171.0 1 70.5 42.0 0.1 0.0
SJl~-cLltl-~É;0~7 56188.9 5~.3 ~7.9 39.2 ~7.5 25.
IJnclcr~lo~
l'`l~';h C)verl~r2acl 5059.2 S1.2 8.0 0.0 0.0 0.0
I'.ol:to~ . 591.~'). / 3.1 39 9 39. 2 ~/ . ', 3G.~'
Vacuuill ()verhead 6l3l~. 7 3.1 31.6 0.0 0 ~ o.o
~'acuum ~o~l:orns 6295.0 0.0 8.3 39.2 47.5 50.
I) i s t~ l. I. a t: ion
~ec-~d 52377.5 225.3 110.1 ~2.0 0.1 0.0
An ~ So lven~
l~ecovr ry 55222 .1 222.1 0. O O. O 0. O 0 O
~uel. ()i1 I'ro~uct: 56155.ll 3.2 110.O ~2.0 0.1 0.0
~ 1138800
EXAMPLE III
A one-liter capacity stirred autoclave unit was
used to determine solids settling rates for various mixtures
of separator bottoms liquid and selective sol~ent liquid
derived from coal. Numerous batch runs were made at
conditions of 550F temperature and 200 psig pressure, using
freshly produced hydroclone underflow slurry liquid mixed
with 350-600F "H-Coal"* process naphtha fraction as the
solvent liquid. Ratios of solvent~slurry liquid of 0.3 to
1.0 were tested. The operation consisted of charging the
autoclave with the desired quantity of slurry liquid and
solvent liquid, then heating and stirring the mixture until
the desired temperature and pressure was obtained. The
agitation was then stopped and liquid samples withdrawn
through an internal tube at a fixed level in the autoclave at
15 minute intervals for analysis to determine the solids
; concentration in the samples. Typical data obtained at
15 minute intervals after autoclave agitation was stopped
are shown in Figure 2.
It is noted that the weight percent ash in the coal
liquid sample declined with increased settling time from
8-11 weight percent initial to less than about one weight
percent solids after 30-90 minutes. With increased ratios
of solvent/slurry liquid, shorter settling times were
required to achieve desired low percent solids in the liquid
samples, with desired ratios exceeding about 0.3 and ratios
of 0.6 - 0.8 being the most effective. Surprisingly, where
the ratio of solvent to slurry liquid is at least or greater
than 0.8 a vast improvement in settling takes place.
- 13 -
* Trademark
EXAMPLE I~
To confirm the solids settlin~ data from the above
autoclave experiments by usin~ continuous process ~low runs,
an online continuous 30 lb~hr solvent precipitation step was
incorporated into an experimental "H-Coal" liquefaction
process handling about 250 lb/hr coal feed. The precipitation
equipment was used to produce solids settling and determine
the settling rate for mixtures of coal-derived liquid slurry
and selective solvent naphtha fraction additive liquid
produced in the "H-Coal" liquefaction process. The slurry
feed was hydroclone underflow liquid containing about 18
weight percent ash (27 W% total solids). The ratio of
solvent liquid to slurry liquid ranged between 0.3 and 1.1.
The resulting overflow liquid from the settler contained ash
concentration below 0.1 weight percent and ranged between
0.006 - 0.093 weight percent. The benzene-insoluble
material rejected in the underflow from the settler contained
as much as 30 weight percent ash (45W~ solids) on a
continuous basis. The liquid residence times in the settler
ranged from about 40 to 90 minutes. Results of average
weight percent ash in the overflow and underflow streams at
equilibrium settler conditions are shown in Figure 3.
It is noted that the average ash concentration in
the overflow liquid from the settler decreases from 0.11 to
0.03 weight percent as the ratio of solvent/slurry liquid
is increased from 0.4 to 0.9.
- 14
