Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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~OAI. HYD~OG~NATION PROCESS HAV~NG IMCREASED SOLIDS
RE~ENTION IN EBULLATED BED REACTOR
BACKGROUND OF INVENTI0~l
This invention pertains to improved catalytic hydrogena-
tlon of coal to produce increased percentages of lo~-boiling
hydrocarbon liquid products. It pertains particularly to
coal hydrogenation processes using an upflow ebullated cata-
lyst bed type reactor in which an increased percentage of
unconverted coal solids is retained in the reactor for
further conversion reaction therein, thereby producing
increased percentages of light hydrocarbon liquid and gas
products.
In conventional ebullated catalyst bed reaction pro-
cesses for the hydroconversion of hydrocarbon feedstocks, as
described in U. S. Patent No. 3,519,555 to Keith, et al, a
reactor liquid concentration of a desired equilibrium pro-
duct distribution is maintained as determined by the reac-
tants and process conditions. A continuous reaction process
exists with both internal and external recycled streams. In
a conventional ebullated bed hydrogenation reaction process
for coal, the reactor liquid solids concentration which
usually comprises about equal amounts oE unconverted coal
and ash may range from 10-25 W % fine particulate solids.
Such solids concentration in the reactor is usually main-
tained by ~rovidinga liquid-solid separation step downstream
of the reactor and recycling a liquid stream containing a
reduced concentration of solids to the reactor, as generally
taught by U. S. Patent 3,540,995 to Wolk, et al. However,
it is desirable to increase the percent hydroconversion of
coal solids and semi-solid materials in the reactor so as to
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provide for increased yields of light hydrocarbon liquid
products by using basically simpler solids separation proce-
dures within the reaction zone, and thereby minimize or
possibly avoid the need for providing an e~ternal liquid-
solids separation step in the process.
U. S. 3,188,286 to Van Driesen discloses a hydrocracking
process for heavy hydrocarbon oils, whlch uses inclined wall
mounted baffles or a cylindrical screen within an ebullated
bed catalytic reactor to help retain particulate catalyst
material within the reactor. Also, U.S, 3 677,71~ to Weber
et al discloses use of a phase separation device located in
the upper~portion of the ebullated bed catalyst reactor to
help retain catalyst in the reactor. However, a procedure
or means for desirably retaining ~ine unconverted coal
solids within an ebullated bed catalytic reactor for
achieving increased conversion of such coal solids to 'nydro-
carbon liquid products has apparently not been previously
disclosed or used.
SUMMARY OF INVENTION
The present invention provides an improved reaction pro-
cess and apparatus for catalytic hydrogenation of coal to
produce hydrocarbon liquld and gas products, wherein coal
solids are selectively retained in the reactor liquid for
prolonged hydrogenation reactions and improved conversion
therein. Such increased retention of coal solids in the
reactor is accomplished by deflecting solid coal particles
larger than about 30 microns which rise with the upflowing
liquid away from the opening jnto the effluent stream with-
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drawal conduit and back into the reactor liquid. Suchdeflecting of fine coal solids is accomplished by suitable
deflection means critically positioned in the upper portion
of the reactor vessel near and associated with the withdraw-
al conduit. This solids deflection means, such as a baf~le,
provides -for increased retention in the reactor of the
larger particle size least reacted coal solids and semi-
solids material for prolonged hydrogenation reaction at the
reaction conditions. The retention of such solids having
particle size usually larger than about 30 microns and pre-
ferably within the range of 40~200 microns prolongs the
residence -time and thus increases the hydrogena-tion reaction
and percentage conversion of these heavy hydrocarbon
materials to lower boiling components, such as light and
medium hydrocarbon liquid and gas products.
By using this reactor system having solids deflection
and retention means incorporated therein ~ the solids con-
centration in the reactor slurry llquid is increased to
exceed about 15 W % and may be increased up to about 30 W %
concentration or more in the liquid. Such higher solids
concentration in the reactor results in 10 - 2~ W % more
unconverted coal being retained in the reactor for ~urther
reaction therein, and provides improved yields of light and
medium liquid fraction products from the coal. A minor por-
tion of the reactor recycled liquid containing larger size
coal and ash particles is withdrawn from the reactor as
needed to maintain the solids concentration in the reactor
below an allowable level, such as about 30 W %.
Accordingly, this invention provides a significant increase
in coal conversion reaction efficiency and increased
throughput per unit reactor volume,
D~SCXIPTION OF INVEMTIO~
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In accordance with the invention, an ebullated bed
catalyst reactor for coal hydrogenation is provided with a
solids deflection baffle or retention device used within the
reactor, and such baffle is critically located within the
reactor upper portion to effect the increased solids con-
centrations desired in the reactor liquid. The baffle is
located so as to partially shield the inlet to the effluent
withdrawal conduit from upflowing coal solids and thereby
reduce the amount of particulate coal solids (unconverted
coal and ash) entering the conduit with the combined efflu-
ent liquid, and gas stream and selectively retain such
solids in the slurry liquid being recycled through the
ebullated catalyst bed.
The reactor deflection baf1e may be varied in position
and shape. The reactor baffle can be made any shape, such
as flat, curved downwardly, or conical-shaped, and is pre-
ferably attached to and supported by the withdrawal conduit.
The baffle can be oriented within the reactor either hori-
zontally or inclined with the horizontal plane at an angle
between 0 to about 45. The deflection baffle angle should
usualy not exceed about 45 with the horizontal, so that the
larger upflowing particles will be deflected back downwardly
into the reactor liquid. The center line distance between
the withdrawal conduit lower end and the upper surface of
the baffle should be at least equal to the conduit inside
diameter and is preferably 1.2-10 times the conduit dia-
meter. Also the baffle is sized relative to the inside
diameter of the reactor withdrawal conduit so that the hor-
izontal projection of the baffle area should exceed the in-
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side cross sectional area of the condui-t '~y about 2 to 2~
times the conduit area. These dimensional and area rela-
tionships provide for selectively retaining in the reactor
the desired increased concentration of unconverted coal
solids for further reaction. If desiredJ the position of
the solids deflection baffle in the reactor may be made
variable for process control purposes.
This invention is particularly applicable to catalytic
reaction systems having internal recycle of reactor liquid
to provide the desired amount of expansion and ebulla-tion of
the catalyst bed such as for H-Coal~ coal liquefaction pro-
cesses. Reaction conditions maintained in the reactor
should be within the broad range of 750-950F temperature
and 1000-4000 psi hydrogen partial pressure. Coal feed rate
or space velocity should be between about 5-60
pound/hr/ft3 reactor volume. The catalyst particle size
used should be sufficiently large for it to be reliably
retained in the ebullated bed and not be ~c-ar-~i~d--out--with
the recycled liquid. The catalyst particles are usually
larger than about 0.016 inch (400 microns) effective
diameter~ and preferably are in the range of 0.020 to 0.0~5
inch diameter (500-1600 microns). Such increased upflow
velocity of reactor liquid permits greater feedstream
throughput to be achieved for a particular size reactor.
For such ebullated catalyst bed reactors using internal
liquid recycle, the deflection baffle is also located suf-
ficiently removed from the top of the liquid-gas separation
device (recycle cup) so as to avoid any catalyst carryover
from the ebullated bed into the recycle cup. Such catalyst
carryover causes undesired recirculation of catalyst par-
ticles through the liquid recycle pump, which not only
causes increased attrition of the catalyst but can also
cause serious erosion damage to the pump, The reactor hav-
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ing deflectlon baffle means in its upper portion is usuallyand preferahly used for coal hydrogenation processes liti-
lizing upflow or ebullated type catalyst beds. However~ the
invention can also be advantageously used for coal hydroge-
nation processes without an externally added catalyst, in
which it is desired to maintain a high percentage of ash
solids in the reaction zone for their catalytic effect on
the hydroconversion reaction~
It is an additional feature of the invention that use of
this deflection baffle arrangement for providing increased
solids retention in the reactor permits selectively
withdrawing a low solids concentration liquid effluent
stream from the upper portion of the reactor, and also
withdrawing a high solids concentration minor stream from
the internal liquid recycle loop separately from the reactor
upper effluent stream Because a portion of the liquid-
solids separation for -the coal hydrogenation process occurs
within the reactor, this arrangement thereby reduces the
downstream liquid-solids separation requirements of the
process. The high solids concentrations stream-can usually
be successfully processed in a vacuum distillation step, and
the heavy vacuum bottoms portion containing high con-
centration of solids can be used either as fuel, or as feed
for producing the hydrogen needed in the process.
If the reactor is operated at high feed rates or space
velocities which results in more unconverted coal in the
product streams, it may be necessary to remove some o~ the
coal solids from the recycle liquid stream. Such solids
removal may be accomplished in a solvent precipitation step
instead of using expensive hydroclones for liquid-solids
separation.
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DESCRIP5'ION _ ~R~WIMGS
E'igure 1 is a schematlc diacJram showing the
principal elements of a liquid phase catalytic reaction
process for hydrogenating coal, using a reactor containing
a solids deflection means.
Figure 2 shows a typical reactor containing a
coni~cal-shaped solids deflection means.
Figure 3 shows a typical coal liquefaction process
utilizing a reactor containing solids deflection means, and
from which s-treams having varying solids concentration are
withdrawn from the reactor for further processing.
Figure 4 is a graph showing the typical
relationship between reactor liquid recycle flow rate and
weight percent coal solids in the reactor liquid.
DESCRIPTION OF PREFERRED EMBODIMENTS
As shown in Figure 1, coal at 10, such as
bituminous or sub-bituminous coal having an ash content of
5-12 W %, is usually ground, dried, and screened at 12, and
is sized to substantial]y all pass 30 mesh screen
(0.023 inch) and preferably is 40-32S mesh screen size
(0.0165-0017 inch) U.S. Sieve Series. The particulate coal
from conduit 13 is then slurried at 14 with a slurrying oil
15 to provide an oil/coal weight ratio ranging from about
1 to about 5. The resulting coal-oil slurry at 16 is
pressurized at 18 to elevated pressure and is combined with
a hydrogen-rich gas at 20. The coal-liquid-gas mixture is
then heated at heater 21 and introduced through flow
distributor 22 into the bottom of the upflow hydrogenation
reactor 24 containing ebullated catalyst bed 25,
usually having catalyst particle size of 0.020 to 0.065 inch
(500-1600 microns).
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The reactor 24 is adapted for providing a liquid-phase
reaction of the coal gas and a particulate hydrogenation
catalyst placed in random motion therein by the upflowing
liquid. Reaction conditions are preferably maintained
within the ranges of 780-900F temperature and 1500~3500 psi
hydrogen partial pressure. Coal feed rate should preferably
be about 10-40 pound/hr/ft3 reactor volume. The reactor
liquid is preferably recycled internally downward through
recycle cup 26 and downcomer conduit 27 to recycle pump 28
so as to maintain the desired extent of catalyst bed expan-
sion in the reactor, such as about 10 to 100 percent over
the bed settled height. Such reactor liquid recycle rate
usually ranges between about 20-50 gallons per minute per
ft2 reactor cross-sectional area. Fresh catalyst is added
at connection 23a and used catalyst is withdrawn at 23b as
needed to maintain the desired catalytic activity in the
reactor.
As also shown in Figure 1, a deflection means such as
baffle 30 is provided in -the vapor disengagement zone 26a
located above liquid recycle cup 26. The baffle 30 is solid
and oriented in such positlon so as to deflect upflowing
coal solids downwardly/and thus partially shield the opening
32a to effluent withdrawal condult 32. Baffle 30 thereby
provides for a partial separation of fine unconverted coal
and ash solids from larger sized solids in the reactor, and
thus selectively reduces the percentage of larger coal
solids entering the withdrawal conduit 32 along with com-
bined liquid and vapor portions. An increased concentration
of fine unconverted coal and ash solids having particle size
preferably within the range of about 40-300 microns is
retained in the reactor liquid for further reaction therein.
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~ne suitable deflec~or or baffle ~oni~Juration for thi.s
invention includes a flat plate oriented at an angle with
the horizontal of about 0 to 45 degrees, and usually haviny
a horizontally projected area equal to about 2 to 20 times
the cross-sectional area of the withdrawal conduit, as
generally shown in Figure 1. ~affle 30 is preferably
supported from conduit 32 by at least three structural rods
33, as is better shown in Figure 2. The conduit 32 and
connçcted baffle 30 are preferably made removable from the
upper end of reactor 24 through removable bolted flange 3~.
A catalytically reacted effluent stream
containing combined hydrocarbon liquid and gas components
is withdrawn through conduit 32, and passed to phase
separator 36. A gaseous stream is removed at 37, and liquid -
containing a minor concentration of fine solids is removed
at 39. Also, if desired, a portion 29a of recycle liquid
stream 29 containing increased concentration of coal and ash
solids can be withdrawn from the reactor for separate
processing.
Another suitable deflection baffle configuration
is conical-shaped baffle 3~ as shown in Fiqure 2, with the
cone apex oriented upwardly and centrally aligned with the
effluent conduit 32. The baffle conical surfaces are
usually oriented at an angle of 20 - 60 degrees with the
horizontal, and the diameter of the downwardly-facing base
of the cone can be about 2 to 10 times the inside diameter
of the withdrawal conduit. Although the flat inclined
baffle 30 conEiguration is suitable for use in reactors
having inside diameter up to about 1.5 feet, a conical-
shaped or a convex-shaped baffle is preferred for use in
larger diameter reactors.
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A further embodiment of this invention i5 shown in
Figure 3, which is an extension of the Figure 1 reactor
configuration. From ebullated catalytic bed reactor 24, an
effluent stream 41 containing liquid and vapor fractlons is
withdrawn from the upper part of the reactor through conduit
40 above catalyst bed level 25a and liquid level 31. As
shown, the lower end of the vertical withdrawal conduit 40
is bent by at least about 90, so that the lower surface 40a
of the conduit or an extension thereof acts as a solids
deflecting surface similarly to baffles 30 and 38. This
effluent stream 41 contains a lesser concentration of uncon-
verted coal and ash solids compared to the reactor liquid,
and is withdrawn through removable conduit 40 loca~ed near
the top of the reactor.
The effluent stream 41 is passed to hot phase separator
42, from which vapor portion 43 and liquid portion 44 are
removed separately. The resulting vapor portion 43 is
passed to hydrogen purification step 50, from which the
recovered hydrogen gas is repressured and recycled at 51 for
use as the hydrogen-rich gas at 20, along with any high
purity make-up hydrogen gas needed at 20a.
The liquid condensate stream at 44 is pressure-reduc~d
at 45 and passed to low pressure phase separator 46, from
which resulting vapor stream 47 is passed to fractionation
system 54. Also from separator 46, liquid portion 48 is
withdrawn and passed to liquid-solids separation step 52 t
which can comprise multiple hydroclones or a solvent preci-
pitation system. Overflow stream 53 containing a reduced
concentration of particulate solids is also passed to rac~
tionation system S4,where ~he material is usually separated
by fractional distillation into a gaseous and light ends
stream normally boiling up to about 450F removed at 55, a
distiLlate liquid fraction normally boiling bet~een about
450 and 650F removed at 56, and a bottom fraction removed
at 57 having a normal boiling range in excess o~ 6504F and
usually about 80~ to 975F. A,portion 56a of the relatively
solids-free oil at 56 is usually recycled as coal slurr~,finy
oil 15 to the system. The underflow liquid stream at 59~
containing an increased concentration of fine unconverted
coal and ash solids, is passed to a vacuum distillation step
60. Overhead liquid stream 61 is preferably added to
distillate stream 57 to provide heavy fuel oil product 58.
Vacuum bottoms stream 62 is withdrawn as a heavy product
material.
If desired, a portion of the liquid recycle stream 29
usually recycled directly to the reactor for maintaining the
desired ebullation of catalyst bed in the reactor 24, is
withdrawn at 63 as a solids-enriched liquid stream for
eparate processing. This liquid stream containing
coal
increased concentration of~solids, such as 20-40 W ~ solids,
is pressure-reduced at 65 and passed with underflow stream
59 to vacuum distillation at 60. Vacuum overhead stream 61
may be combined with liquid product 58, while bot-toms stream
62 may be passed to a coking step or serve as feedstock for
producing the hydrogen needed in the system.
It is an advantage of this invention that the solids
deflection means provided in the reactor upper end provides
sufficient solids separation that an external conventional
solids separation step such as by hydroclones centrifuge
filtration or solvent precipitation, is minimized or mav
even be eliminated depending upon the acceptable solids con-
centration level in the product oil streams. Thus~ elimina-
tion of such an external solids separation step reduces the
process cost and complexity.
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This invention will be further described by reference to
the following example of operations.
EX~LE
Illinois No. 6 bituminous coal having 50-300 mesh size
(U.S. Sieve Series) was fed as a coal/oil slurry with hydrogen
into a 6-inch diameter reactor containing an ebullated catalyst
bed, maintained at elevated temperatures and pressure conditions
to produce hydrocarbon liquid and gas products. The reactor
was provided with a flat metal baffle about 4-inch average
diameter, positioned at a 45~ angle with the horizontal plane
and having its center located about 1.3 inches upstream of a
1.125 inch inside diameter withdrawal conduit, similarly as
shown in Figure 1. The operating conditions and results for
the catalytic reaction step with and without the baffle and
for otherwise quite similar operating conditions are provided
in Table 1 below.
TABLE 1
EBULLATED BED REACTOR OPERATIONS WTTH AND WITHOVT
RETENTION OF COAL SOLID~S
Run No. 130-66 Run No. 30-67
Without Baffle With Baffle
In Reactor In Reactor
Coal Feed, W % Water 2.82 1.87
Coal Feed, W % Ash 11.07 10.93
Coal Feed Rate, Lbs/Hr 164 177
Hydrogen Makeup, SCFH 1890 1890
Catalyst Bed Expansion, %50 50 7
Recycle Gas SCFH 1075 1676
Recycle Oil, SCFH 410 451
Reactor Temperature, F 826 831
Reactor H? Pressure, psig2700 2700
Internal Slurry Recycle Rate,
Gpm/Ft2 Reactor (Average) 48 34
Start of Run 43 46
After 8 Hours 52 36
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It is noted that a si~niicantly lower internal s]urr~
recycle rate was required for producing the desired 50~
catalyst bed expansion in Run No. 130-67, using the internal
deflection baffle, actually reflecting a reduction of about
30% in the rate during the period of operationO ~he general
relationship between the reactor liquid recycle rate for 50~
catalyst bed expansion and the percent total solids in the
reactor liquid, i.e. unconverted coal and ash or mineral
matter, is shown in Figure 4, and is based on data sub-
sequently obtained for catalytic hydrogenation of coal.
Thus, this reduced liquid recycle rate required for Run No.
130-67 to achieve the same catalyst bed expansion indicates
increased density and viscosity of the reactor liquid. The
differences ln the operating conditions are not sufficient
to have any substantial effect on the internal recycle
liquid requirements. Thus, it is seen that the internal
deflection baffle means provides for increased viscosi.ty and=
coal solids concentration in the reactor liquid. This indi-
cates that increased conversion of the coal solids can be
achieved by use of such deflecting means critically located
upstream of the reactor effluent withdrawal conduit~ and
also that separation of unconverted coal and ash solids can
be achieved in the ebullated bed reactor system by such
solids deflection means.
It i~ recogni.zed that modifications and variations of
this invention can be made without departing from the
spirit and scope thereof, and which is defined solely by the
following claims.
