Note: Descriptions are shown in the official language in which they were submitted.
D-1313
COAL SLURRY DRYING AMD DEOXYGENATIMG PROCESS,
FOR COAL LIQUEFACTION
BACKGROU~ID OF INVENTIOM
This invention pertains to drying and deoxygenating coal
by heating the coal in a hot slurrying oil It pertains
particularly to a process for drying and deoxygenating coal
in a coal slurry at 250-650~F temperature prior to feeding
the slurry to a coal liquefaction process
In coal liquefaction processes, the raw coal is ini-
tially crushed and dried to remove surface and contained
moisture down to Less than about 3 W % moisture remaining~
usually by using sensible heat such as by passing the coal
through a drying tunnel. Also, the raw coal usually con-
tains some undesired oxygen. A major disadvantage of high
oxygen content in coal feed for liquefaction processes is
that the oxygen cosnbines with expensive hydrogen to produce
water of no commercial value. Also oxygenated compounds
contained in the hydrocarbon liquid products from coal
liquefaction processes are not pre~erred in liquid fuels for
transportation uses. The oxygen compounds also contribute
to regressive reaction~ and producP unreactive insoluble
organic meterials.
Schafer has reported in Fuels 59, May, 1~80, pp. 295-
304, that coal dried by pyrolysis procedures decarboxylate,
i.e., rémovP COOH (carboxyl group), under increasing temper-
ature condition~ to yield carbon dioxide, carbon monoxide
and water. For each molecule of carbon dioxide produced,
one molecule of tightly bound water was also lost from the
dried coal. The effects of bound water and c~rbon dio~ide
are more profound in lower rank coals, since th~y contain
more carboxyl groups and hence more water than higher rank
coals. Physical and chemical properties of low rank coals,
as well as coal liquefaction process responses, are believed
to ~e adversely i~fluenced by the presence of tightly-held
water an~ carboxyl groups in the coal. These oxygen-
containing species are known to decrease hydrogen partial
pressure and coal conversion in the coal liquefaction
reac~or, increa~e hydrogen consumption, affect diffusion
properties, incr~ase separation and disposal requirements
and hence adversely affect th~ economics of coal liquefac-
tion processes.
In direct coal liquefaction processes a temperature
controlled mixing vessel i~ utilized for blending the par-
ticulate coal with a hot slurrying oil- The slurrying oil is
usually processed derived, then treat~d for removal of
gases, moisture and light naphtha, and cooled before being
recycled to the slurrying step~ V. S. Patent No. 4,209,911
to Weber disclose~ a process for drying coal in a ~lurry
mixing tank prior to coal li~uefaction. But Weber does not
di~close any deoxygenation of the coal or increase~ in
slurry reactivities at more severe drying conditions~as are
provided by the present invention.
SUMMARY OF IMVENTION
The invention provides a process for drying and deoxy-.
genating coal in a coal~oil ~lurry mixing vessel, maintained
at elevated temperatures. The invention compri~es a process
for drying .and deoxygenating particulate coal to remove
moi~ture and oxygen contained therein, comprisinq the steps
of mixing a particulate coal feed with a hydrocarbon slur~y-
ing oil in a mixing zone to provide a coal-oil slurry mix-
ture having an oil/coal ratio of from aoout 1.2 to about
2.5; heating said coal-oil slurry mixture to 230-650F tem-
perature to evolve moisture and oxygen vapors ~rom the coal;
and withdrawing a dried coal-oil slurry mixture containing
reduced moisture and oxygen contents. By using the inven-
tion, the water and oxygen content of the coal ~lurry are
lowered and the relative reactivity of coal slurries con-
taining bituminous and low rank sub-bituminous coals and
similar organic deposits are increased by raising the coal-
oil slurry temperature in tha slurry mixing vessel to at
least about 240F and usually not exceeding about 650F.
Moisture remaining in the heated coal oil slurry is reduced
to less than about 3 W ~, and the oxygen content is reduced
to less than about 7 W ~. Also, a more reactive slurry is
provided which produce~ a higher hydrogen partial pressure
in the reactor and increases coal total conversion to pro-
duct oils. At a given total reaction pressure, the inven-
tion will improve product quality, and decrease energy
requirements of cooling the recycle streams.
This coal drying and deoxygenation step is usually ac-
complished in a single mixing vessel, however if desired,
two or three staged mixing vessels can be use~ at increasing
temperature and pressure conditions. Although this coal
drying and deoxygenation step can be used to provide a dried
coal-oil slurry stream as a fuel, it is preferably used as
a pretreatment step for a coal feedstream to a coal
liquefaction process~ and more pre~erably provides a
feedstream to ~ catalytic coal liquefaction process.
Accordingly, when this coal drying and deox~genation
step is used in a coal liquefaction process, it is intended
to decrease H2 consumption, increase coal conversion, im-
prove product quality, decrease the energy requirements of
cooling the recycle streams, and thus improve the economics
of direct coal liquefaction or for lignin upgrading. ~ne
same beneits are also expected when processing coals con-
taining higher concentrations of mineral matter and which
contain clay water by decreasing or eliminating condensation
reaction products caused by evolution of steam vapor from
the clay.
8RIEF DESCRIPTION OF DRAWINGS
_ _ _ _
FIG. 1 shows a schematic flow diagram of a process for
drying and deoxygen~ting coal-oil slurry in accordance with
the invention.
FIG. 2 shows a schematic flow diagram of the coal slurry
dr~ing step operated upstream of a catalytic coal liquefac-
tion process.
FIG. 3 ~hows two graphs of coal deoxygenation and con-
version results from increasing slurry tank temperatures.
FIG. 4 shows a graph of decreasing yield of residual oil
(975F+ fraction) for increasing slurry mixing tank
temperature.
DESCRIPTION OF INVENTION
_ _
This invention will be further described as a coal pre~
treatment step for a coal liquefaction process. As shown in
FIG. 1, raw coal at 10 is crushed or ground and screened at
12 to provide a particle size range of 30 375 mesh ~U. S,
Sieve Serie-~). If desired, the coal can also be cleaned or
beneficiated to remove mineral matter. The particulate coal
a~ 13 is then fed into slurry mixing tank 14, where it is
mixed with a hydrocarbon slurrying oil 16 having a norm~l
boiling ran~e of about 500-750Fo The tank pressure is main-
tained at 0-150 psig and preferably at 0-50 psig pre~ure by
a portion of process-derived recycle gas stream. Th~ par-
ticulate coal at 13 can be fed to the ~ixing vessel 14
through a conventional pres~urized lock hopper or via a
screw or star type feeder (not show~)..
Effective mixing of the particulate coal and slurrying
oil is achieved by providing a liquid velocity within the
tank 14 of at least about 2 ft/sec. The coal and oil in the
atmospheric pressure or pressurized mixing tank can be mixed
by u~ing an angled agitator or mixer, baffle plate(s) and
recycle circulation lines or ~imilar mechanical devices o
provide a well mixed coal-oil slurry. Such mixing ~an be
effectively provided either by a rotary mixer 15 mounted in
the tank, or by the recycle to the tank of a portion 17a of
slurry stream 17 by pump 18, or by both arrangements.
The slurry temperature in mixing tank 14 is maintained
at 250-650F by recycling the hot slurryin~ oil 16 usually
at about 550-700F temperature. Th~ slurry tank temperature
is preferably 35Q-50QF. The tank 14 is usually provided
with ~ternal thermal insulation 14a to conserve heat and
heIp maintain the desired ~lurry temperature therein. The
re~idence time for the coal in tank 14 will depend on the
moi~ture content of th~ coal feed and the extent of drying
de~ir~d, and u~ually ranges from about 0.2 hours at high
drying.temper~ture of 650F and up to about 3 hours for high
-
moisture coals and lower drying temperature of about 2iO~7.
Longer residence times can be used if desir~d or process
control purposes. A vapor stream containing e~Jolv~d
moisture and oxygen is withdrawn at 19. The resulting
coal/oil slurry mixture at 17 which has appreciably reduced
moisture and oxygen content, is pressurized at 20 and passed
as stream 21 to a coal liquefaction process 24.
The temperature controlled slurry mixing tank 14 for
coal and recycle slurrying oils for direct coal liquefaction
is operated at 250-650F temperature and 0-150 psig pres-
sure. If desired, any fine inorganic solids which settle in
the slurry mix tank, such as clay soLids from which water
has been removed, can be withdrawn separately at 14b from
the tank 14. Such withdrawal is facilitat~d by having a
tapered bottom portion provided for the tank into which such
fine deposits can collect. Whenever the pressure of slurry
mix tank 14 is at or near atmospheric pressure, vapors
evolved from the tank at 19 may be removed by an eductor
device and are passed to a gas, oil and ~ater recovery
system (not shown).
The dried and deoxygenated slurry from the mixing tank
14 is then usually pa~sed through a preheater 22 into a coal
liquefaction process 24, which can be a catalytic or non-
catalytic process. In the process, the reacted effluent
material is separated into overhead and bottom streams, and
the overhead mat~rial is separated into recycle gas, naphtha
and distillate oil fractions. The bottoms are flashed iso-
thermally to 50-150 psig pressure and passed to a liquid-
solids separation step such as by a hydroclone device. A
gas stream is withdrawn at 25, light hydrocarbon liquid pro-
duct at 26, and heavy hydrocarbon liquid product at 27. A
liquid stream 16 having 250-650F temperature is recycled to
the slurrying tank 14 as the coal slurrying oil. ~ne ro~l-
oil mixing tank will usually be adequately heated by recycl-
ing the 'not 'nydroclone overflow stream to it as stream 16,
however, additional heat such as from electric heaters can
be provided as needed, such as for process start-up pur-
poses. A portion of recycle gas will be flashed at the
mixing tank presSurQ prior to pressuring the coal 'nopper and
mixing tank.
Although the coal drying and deoxygenating step is usu-
ally and preferably accomplished in a single mixing tank,
two or even more staged tanks could be used each operated at
increased temperature and pressure conditions. The coal-oil
slurry from the first mixing tank-would be pumped into the
subsequant tank for further heating, and the vapor streams
evolved from the tanks would be passed to a recovery system
(not shown).
The heating and drying coal-oil slurry step is pre-
ferably used with a catalytic coal liquefaction process as
shown in FIG. 2. In this preferred embodiment, the raw coal
is crushed and sized similarly as for FIG 1 and introduced
into hot slurry mix tank 14. From the hot slurrying mix
tanX 14, the heated coal-oil slurry is pressurized by pump
20 to elevated pressure, such as 500-S000 psi, and is then
passed through a preheater 22 into reac~or 30 containing
catalyst bed 32. Recycled hydrogen at 28 can be reheated at
29 and provided to the reactor 30, together with fresh
makeup hydrogen as needed at 28a, or alternatively can be
passed as stream 28b to heater 22.
The coal-oil slurry and hydrogen streams then enter re-
actor 30 contalning catalyst bed 32, passing uniformly up-
wardly from the bottom -through flow distributor 31 at a flow
rate and at temperature and pressure conditions to a~com-
plish the desired hydrogenation reactions The catalyst in
bed 32 should be selected from the group consisting of co-
balt, iron, molybdenum, nickel, tin, and other hydrocarbon
hydrogenation catalyst metals known in the art~ deposited on
a base material selected from the group consisting of alu-
mina, magnesia, silica, and similar materials. In addition,
particulate hydrogenation catalyst may be added to rPactor
30 at connection 33 in the ratio of about 0.1 to 3.0 pounds
of catalyst per ton of coal processed~
By concurrently flowing liquid and gasiform materials
upwardly through the reactor containing a bed of solid par-
ticles of specific catalyst as indicated above, and expand-
ing the bed of solid particles by at least about 10%, and
usually by 20 - 100~ over its settled height, the solid par-
ticles are placed in random ebullated motion within the
reactor by the upflowing streams. The characteristics of
the ebullated bed at a particular degree of volume expansion
can be such that finer, lighter particulate solids will pass
upwardly ~hrough the catalyst bed, so that the contact par-
ticles constituting the ebullated bed are retained in the
reactor and the finer, lighter material pass from the
reactor. The catalyst bed upper level 32a, above which few
if any contact particles ascend, is the upper level of
ebullation.
In general, the gross density of the mass of catalyst
will be between about 25 to 200 pounds per cubic foot, the
upward flow rate of the liquid will be between about 5 and
120 gallons per minute per square foot of horizontal cross-
section area of the reactor, and the expanded volume of the
ebullated bed usually will be not more t'nan double the
volume of the settled mass. To maintain the desired super-
ficial upward liquid velocity in the reactor, a portion of
the liquid slurry is us~lally recycled to the reactor, such
as llquid which is removed from above the upper level of
ehullation 32a and recycled via downcomer conduit 34 and
pump 35 to the bottom of the reactor 30, and then upwardly
through flow distributor 31. Spent catalyst may be removed
by drawoff at connection 36 to maintain the desired cataly-
tic activity within the reaction zone.
Reactor operating conditions are maintained in the broad
ranges o~ 700-930F temperature and 1000-5000 psi partial
pressure of hydrogen, and preferably at 750-900F and
1000-4000 psi hydrogen partial pressure. Coal throughput or
space velocity is in the range of 10 to 150 pounds coal per
hour per cubic foot of reactor volume, so that the yield of
unconverted coal as char is between about 4 and 10 W % of
the moisture and ash-free coal feed. ~he relative size of
the coal and catalyst particles and conditions of ebullation
is such that catalyst is retained in the reactor while ash
and unconverted coal or char particles are carried out with
the liquid reaction products.
From reactor 30, an effluent stream 37 which is vir-
tually free of solid catalyst particles is withdrawn, cooled
at 38, and then passed to phase separator 40. From separa-
tor 40, a light gas fraction stream is removed at 41 and
passed to hydrogen purification step 42. A medium-purity
hydrogen stream 43 is recovered from purification step 42,
and recycled as stream 28 through heater 2~ to reactor 30 to
provide a part of the hydrogen requirements therein as
heated hydrogen s-tream 29a.
From separ~tor 40 a liquid fraction stream 44 is with-
drawn, pressure-reduced at 45 and is passed to phase separa-
tor 46~ This separator operates at near atmospheric pres-
sure and 500-650F temperature and permits removal of a
light hydrocarbon liquid stream at 47 and a heavy hydrocar-
bon liquid ~tream at 48. Stream 47 contains naphtha and
light distillate fractions and is passed o fractionation
step 50, from which hydrocarbon gas p.-roducts are withdrawn at 51, light
distillate product at 52 and m~dium distillate product at 53. m e hydrogenated
f~ coal liquid fraction 48 u~ual~y having normal ~ iling range
above about $50F and preerably 6Q0-950F and containing
asphaltenes, preasphaltenes, unconverted coal and ash
solids, is passed to liquid solids separation step 54, such
as mult~ple hydroclones. An overflow 500F+ liquid stream
containing reduced concentration of solids is removed at 56.
A portion 57 of liquid ~tream 56 is pas~ed to fractionator
50, and the remainder 5~ i~ pres~urized to reactor pressure
at 59 and provides the slurrying oil 16 needed in slurry mix
tank 14.
~~ . From separation step 54 underflow liquid ~tream 62, con-
taining an incroased concentration of solids i~ removed and
passed to vacuum distillation at 64. The resulting overhead
liquid 65 from t~e vacuum still may be joined with stream 66
to provide a heavy distillate product stream 68. If
dPsired, a por~ion of stream 68 can be used for slurrying
oil 16. Also ~f desired, at least a portion 67 of the
~trealTI 66 can be passed to vacuum still 64. A he~vy vacuum
bottoms stream 69 containing some asphaltenes, preasphalte-
nes and unconverted coal and ash solids may be further pro-
~G cessed by coking to recover oil product~, or by gasification
to produce the makeup hydrogen need~d in the pr~cesC.
' ' 10
, .
4~
This invention will be further described 'cy reference f5
the following examples, which should not be construed as
limiting in scope.
EX~MPLE _
Wyodak sub-bituminous particulate coal having 50-325
mesh particle size (U.S. Sieve Series) and containing 10-25
W ~ moisture was fed into a slurry mix tank maintained at a
temperature range of 230-250F by hot hydrocarbon slurrying
oil recycled to the tank from a coal liquefaction process
unit. The initial moisture in the coal feed varied between
11 and 17.5 W ~, the residence time for the coal in the
slurry tank was about 2 hours, and the water contained in
the coal feed was substantially evaporated from the tanX as
vapor. Averaged results of the slurry tank drying opera-
tions over a period of several days are shown in Table 1.
TABLE 1
WATER VAPORIZATION FROM COAL FEED IN SLURRY MIX TANK
_ _
Avg. Tank Temperature, F
232239 246
Coal Feed Rate, lb/hx 211202 234
Slurrying Oil Feed, lb/hr 454429 428
Oil/Coal Weight Ratio 2.152.12 2.10
Initial Water in Slurry, W % Slurry6.5 5.S 4.0
Water in Slurry After Drying, W % Slurry 2.9 2.3 2.1
Water in Slurry, W % Coal 6.2 4.9 4.4
Water Removed by Slurry Tank, W % 45 42 52
These results show that even at the moderate slurry mix
tank temperatures of 232-246F, between 42 and 52% of the
moisture was removed from the coal feed initially containing
11-17,5 W % moisture down to about 4.4-6.2 W % of the dry
coal. This dried coal-oil slurry material is suitable as a
feedstream to a coal liquefaction process.
11
EX~PLE 2
A simulated slurry mixing tank stud~ of coal aeoxygena-
tion was conducted in which the slurry consisted of r~7yodak
coal containing 17-20 W % oxygen mixed with recycle oil
derived from the Wyodak coal. The coal-oil slurry was
treated in an autoclave at several temperatures between
350-500F and then analyzed. Results of coal deoxygenation
and conversion vs. slurry tank temperature are shown in FIG.
3. It was noted that as the slurry tank temperature was
increased from about 230F up to 500F, increased
deoxygenation and decarboxylation of the coal occurred and
the treated slurry became relatively more reactive, as indi-
cated by the increased coal conversion achieved. It is
believed that the more reactive slurry was produced due to
the loss of carboxyl and water molecules contained in the
coal. A more reactive slurry for direct coal liquefaction
not only increases coal conversion, but is believed to also
change the yield distribution favorably to produce more low
boiling hydrocarbon liquid fractions. Also, the hydrogen
partial pressure in a hydrogenation reactor would increase
due ~o the loss of carbon dioxide and water molecules from
the slurry mix tank instead of their remaining in the reac-
tor feed stream.
EX~MPLE 3
Illinois No. 6 bituminous coal initially containing
about io w ~ moisture and having particle size range of
50-200 mesh (U.S. Sieve Series) was mixed with a recycled
csal-derived oil in a ratio in the range of 1.~-1.8. The
recycled oil temperature was 450-600F. Initial mixing of
the coal and oil occurred in a tank at 160-200F temperature
for 3 hours average residence time to produce a slurr-
~source and to remove a substantial portion of the moisture
from the coal. The resulting coal/oil slurry was then
transferred into a second mixing tank maintained at a
constant slurry level and in which the mixing temperature
was maintained at 450F by electric heaters for an average
residence time of 1.9 hours. The remaining oxygen contained
in the coal was evolved from the second mix tank and a vapor
stream was removed containing moisture and oxygen. The re-
sulting coal/oil slurry stream containing reduced moisture
and oxygen content was withdrawn from -the lower end of the
tank.
The reactivity o the heated coal-oil slurry was deter-
mined by microautoclave analysis. Samples of the coal-oil
slurry were obtained before and after treatment in the hot
slurry mix tank, and the slurry material was then reacted
thermally in a microautoclave at 850F for 30 minutes. The
resulting reacted material was then extracted separat~ly
with cyclohexane, with toluene, and with tetrahydroEuran
(THF), and results are shown in Table 2.
T L 2
CONVERSION OF ILLINOIS NO. 6 COAL~OIL SLURRY,
W % SLURRY
Before After
Solvent Used Coal Treatment Coal Treatment*
Cyclohexane 57.9 64.3
Toluene ~1.0 66.5
THF 80.3 84.1
At 450F for 1.9 hours
Based on the above results, it is noted that an incrG~se
in slurry reactivity occurred with increased slurry ~ix tar.~
temperature of 450F. Thus, the solubility and reactivity
of the coal/oil slurry was increased, as shown by the
increased conversion of the coal achieved at otherwise
equivalent reaction conditions.
EX~MPLE 4
Illinois No. 6 bituminous coal similar to that in Exam-
ple 3 was mixed with a coal-derived hydrocarbon liquid or
slurrying oil in a coal/oil ratio in the range of 1.6-1. a .
The recycled oil temperature was 450-600F. Initial mixing
of the particulate coal and oil occurred in a tank at
160-200F temperature for 3 hours average residence time for
the coal. The resulting mixed coal/oil slurry was then
transferred into a second mixing tank in which the mixing
temperature was maintained at 450F by means of electric
heaters and in which the average residence time for the coal
was 1.9 hours. Moisture and oxygen originally contained in
the coal were evolved from the second slurry mixing tank and
a vapor stream was removed containing moisture and oxygen,
The resulting coal/oil slurry containing reduced moisture
and oxygen was withdrawn from the tank and passed to a bench
scale coal catalytic hydrogenation process. Operating con-
ditions for the process and results achieved are shown in
Table 3 and also in FIG. 4.
14
TABLE 3
COMPARATIVE LIQUEFACTION PROCESS PEP~ORMANCE ~JS.
_ . __ _
SLURRY MIX TANK TEMPERATURE
Conventional Operation Per
Operation This Invention
Slurry Mix Tank Temp. F 250 450
Moisture in coal, W % 10 10
Reaction Conditions
Temperaturë, F 850 850
Total Pressure, psi~2250 2250
Feed Rate, lb/hr/ft~31.2 31.2
Catalyst Age, lb coal/lb cat. 1400 1400
Yields, W % of Coal Feed
Cl-C3 Gas -- 8 . 5
C4-400F Naphtha - 20.3 20.5
400-975F Distillate 31.6 35 8
975F+ Residuum 14.6 10.8
Unconverted Coal 4.4 5.1
Ash 11.5 11.5
Water 8.9 9.4
CO~CO2 0.8 0.4
NH3~H2S 3.3 3 5
C4-975F Material 51.8 56.3
Coal Conversion, W % M.A.F. Coal 95.094.3
It is noted that as the-slurry mix tank temperature was
increased from 250F to 450F during an 8-day period of
operation, the yield of 400-975F fraction increased from
31.6 to 35.8 W %ras shown in Table 3. Also, during this
ime, the residual oil produc-t yield (975F+ fraction)
dry
decreased from 14.6 to 10.8 W % of/ coal feed for otherwise
equivalent operating conditions. Also, the decrease in CO
and CO2 in the product yields from the liquefaction at the
higher slurry mix tank temperature indicates that increased
oxygen was removed from the coal in the hot slurry mix tank.
S~ch decrease in residual oil yields with increasing slurry
mix tank temperature is further shown in FIG~ 4.
EXAMPLE 5
Wyodak sub-bituminous coal initially containing abou~
14-17 W % moisture ~nd 17-19 W % oxygen and having particle
si~e of 50~200 mesh (U.S. Sieve Series~ is mi~ed wi~h an
oil derived from the coal in a liquefac~ion and hydrogena-
tion process. The oil temperature used is ~50-600F and the
weigh~ ratio of oil to coal is 105-1.6, The coal/oil mix-
ture is maintained at a temperature of about 450F by elec-
tric heaters for an verage coal residence time of 1.9
0 hours.
Moisture and oxy~en contained in the coal re èvolYed
from the mix tank and a vapor strea~. removed containing
moi~ture and oxygen. The resulting coal/oil slurry csn7
taining a substantially reduced concentrat.ion of both mois-
ture and oxygen are withdrawn from the hot slurry mix tank
and fed to a coal liquefaction process for producing hydro-
carbon liquid product~ while requirin~ reduced hydrogen
consump~ion as compared ~o a liquefaction process having
conventional slurry mix tank temperature of ~00-250F.
Although this invention has been described broadly and
in terms sf certain preferred embodiments, it will be
understood ~at modifications and variations to the.process
can be made within the ~pirit and ~cope of the invention,
which is defined by the following claims.
16
