U.S. patent number 3,726,784 [Application Number 05/116,373] was granted by the patent office on 1973-04-10 for integrated coal liquefaction and hydrotreating process.
This patent grant is currently assigned to Esso Research and Engineering Company. Invention is credited to Juan J. Correa, Jack M. Hochman.
United States Patent |
3,726,784 |
Correa , et al. |
April 10, 1973 |
INTEGRATED COAL LIQUEFACTION AND HYDROTREATING PROCESS
Abstract
A hydrotreated liquid product from coal is obtained by a process
in which liquefaction and hydrotreating zones are operated at
essentially the same moderate pressures (1000-2000 psig). Without
prior cooling, all the overhead vapor from the liquefaction reactor
is admixed with a portion of a light liquid fraction (700.degree.
F.) recovered from the liquefaction liquid product, giving a
hydrotreating feed having a temperature within a predetermined
range. The remaining portion of the light liquid fraction of the
liquefaction product is fed to the hydrotreating zone at quench
points in the hydrotreating zone downstream from the point of
introduction for the admixture, thus utilizing the heats of
reaction in the hydrotreating zone to heat the remaining liquid
portions (which provide quench to the hydrotreating zone).
Inventors: |
Correa; Juan J. (Parsippany,
NJ), Hochman; Jack M. (Boonton, NJ) |
Assignee: |
Esso Research and Engineering
Company (Linden, NJ)
|
Family
ID: |
22366787 |
Appl.
No.: |
05/116,373 |
Filed: |
February 18, 1971 |
Current U.S.
Class: |
208/412; 208/127;
208/401; 208/143; 208/431 |
Current CPC
Class: |
C10G
1/065 (20130101); C10G 1/002 (20130101); C10G
1/042 (20130101) |
Current International
Class: |
C10G
1/00 (20060101); C10G 1/06 (20060101); C10G
1/04 (20060101); C10g 001/04 () |
Field of
Search: |
;208/8,143 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gantz; Delbert E.
Assistant Examiner: O'Keefe; Veronica
Claims
Insofar as these changes and modifications are equivalent ways of
achieving the ends of this invention within the spirit and scope of
the appended claims, they are deemed within the invention, we
claim:
1. A process for producing hydrotreated liquid product from coal,
which comprises:
subjecting a slurry of coal particles in a hydrogen-donor solvent
to coal liquefaction in the presence of hydrogen for a sufficient
period of time and at a sufficient temperature to form a liquid
product and a vaporous product;
admixing all of said vaporous product with a portion of said liquid
product, without prior cooling of said vaporous product, to obtain
an admixture having a temperature within a predetermined range;
introducing said admixture into a hydrogenation zone having
essentially the same pressure as said liquefaction zone;
introducing a second portion of said liquid product into said
hydrogenation zone at a location downstream from the point of
introduction of said admixture where the temperature of said
hydrogenation zone exceeds said predetermined range by a specified
minimum, the quantity and temperature of said second portion being
correlated with the temperature at said location as as to cool the
hydrogenation zone downstream of said location to a temperature
within a predetermined range; and
recovering a hydrotreated liquid product from said hydrogenation
zone.
2. The process of claim 1 in which said predetermined range is
within the range from about 550.degree. F. to about 750.degree. F.
and said specified minimum is within the range from about 5.degree.
F. to about 75.degree. F.
3. The process of claim 2 in which said predetermined range is from
about 650.degree. F. to about 700.degree. F.
4. The process of claim 1 in which the pressure in said
liquefaction and hydrogenation zones is within the range from about
1000 psig to about 2000 psig.
5. The process of claim 1 in which all of said vaporous product is
admixed with a stream of hydrogen treat gas and a portion of said
liquid product, without prior cooling of said vaporous product, to
obtain an admixture having a temperature within said predetermined
range.
6. A process for producing a hydrogenated liquid product from coal,
which comprises:
in a coal liquefaction zone, liquefying coal slurried in a
hydrogen-donor solvent in admixture with from about 1 to about 6
weight percent hydrogen, under liquefaction conditions, to produce
a vaporous product, containing from about 1 to about 12 weight
percent hydrogen, and a liquid product, including a fraction
boiling within the range from about 300.degree. F. to about
700.degree. F.;
removing said vaporous product and said liquid product separately
from said liquefaction zone;
recovering said fraction from said liquid product and splitting
said fraction into a plurality of portions;
admixing all of said vaporous product with a first portion of said
fraction without prior cooling of said vaporous product, to produce
an admixture having a temperature in a predetermined range within
the range from about 550.degree. F. to about 750.degree. F.;
introducing said admixture at said temperature into a hydrogenation
zone having essentially the same pressure as said liquefaction
zone;
introducing a second portion of said fraction into said
hydrogenation zone at a location downstream from the inlet for said
admixture where the temperature of the hydrogenation zone exceeds
said temperature within said predetermined range by a specified
temperature within the range from about 5.degree. F. to about
75.degree. F., the quantity and temperature of said second portion
being correlated with the temperature at said location so as to
cool the hydrogenation zone downstream from said location to a
temperature within said predetermined range;
removing the effluent from said hydrogenation zone; and
recovering the hydrotreated liquid product from said effluent.
7. The process of claim 6 further comprising:
recovering a hydrogen treat gas from said effluent, and admixing
said vaporous product with said hydrogen treat gas and said first
portion of said fraction, without prior cooling of said vaporous
product, to obtain said admixture having a temperature within said
predetermined range.
8. The process of claim 6 in which the pressure in said
liquefaction and hydrogenation zones is within the range from about
1000 psig to about 2000 psig.
9. The process of claim 8 in which said liquefaction conditions
further include a temperature within the range from about
750.degree. F. to about 850.degree. F. and a liquid residence time
of from about 5 to about 60 minutes.
10. The process of claim 5 in which said predetermined range is
from about 650.degree. F. to about 700.degree. F.
11. A process for producing a hydrogenated liquid product from
coal, which comprises:
in a coal liquefaction zone, liquefying coal slurried in a
hydrogen-donor solvent in admixture from about 1 to about 6 weight
percent hydrogen, under liquefaction conditions including a
pressure within the range from about 1000 psig to about 2000 psig,
a temperature within the range from about 750.degree. F. to about
850.degree. F., and a liquid residence time of from about 5 to
about 60 minutes, to produce a vaporous product containing from
about 1 to about 12 weight percent hydrogen, and a liquid product
including a fraction boiling within the range from about
300.degree. F. to about 700.degree. F.;
removing said vaporous product and said liquid product separately
from said liquefaction zone,
recovering said fraction from said liquid product and splitting
said fraction into a plurality of portions;
admixing all of said vaporous product with a recycle stream of
hydrogen treat gas and a first portion of said fraction, without
prior cooling of said vaporous product, to obtain an admixture
having a temperature within a predetermined range from about
650.degree. F. to about 700.degree. F.;
introducing said admixture at said temperature into a hydrogenation
zone having essentially the same pressure as said liquefaction
zone;
introducing a second portion of said fraction into said
hydrogenation zone at a location downstream from the point of
introduction of said admixture where the temperature of the
hydrogenation zone exceeds said temperature within said
predetermined range by a specified maximum within the range from
about 5.degree. F. to about 75.degree. F., the quantity and
temperature of said second portion being correlated with the
temperature at said location so as to cool the hydrogenation zone
downstream from said location to a temperature within said
predetermined range;
removing the effluent from said hydrogenation zone;
recovering the hydrotreated liquid product and the hydrogen treat
gas from said effluent; and
recycling the hydrogen treat gas for admixture with said vaporous
product.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the hydrotreating of liquid product
produced by liquefying coal, and more particularly, to processes
wherein the liquefaction zone, in which coal is liquefied, and the
hydrotreating zone, in which liquefied coal is hydrotreated, both
are operated at essentially equivalent pressures.
2. Description of the Prior Art
In order to produce a coal liquid product of adequate hydrogen
content for use as a fuel product, the liquid product of coal
liquefaction is fed to a hydrotreating zone, which generally is
operated at substantially different pressures. It is usually
necessary to preheat the coal liquid to levels at which
hydrotreating occurs before introducing it into the hydrotreating
zone. Heretofore high furnace duties associated with preheating the
feed to the hydrotreating zone have been a highly difficult problem
to overcome. One approach for reducing high preheater furnace duty
has been to pass substantially all hydrogen gas needed for
hydrotreating the coal liquid into the liquefaction reactor in
which the coal liquid is produced, stripping off large amounts of
liquid from the liquefaction zone and thereby reducing the quantity
of liquid to be heated in the preheater. This approach involves its
own drawbacks, however, for it increases reactor costs, produces
serious heat balance problems, and requires a train of overhead
heat exchangers and high pressure vapor liquid separators for
separating and recovering hydrogen gases and vaporous and liquid
products from the liquefaction zone. Moreover, the required
exchanger-separator train is susceptible to stress cracking due to
the presence of corrosion precursors (hydrogen sulfide and
chloride) in the condensate, which makes the system even more
costly. In addition, a preheater is required for the hydrogen treat
gas fed to the hydrotreating zone.
SUMMARY OF THE INVENTION
The above-described problems in hydrotreating a liquid liquefaction
product are overcome by the present invention. In this invention,
all of an overhead vaporous product obtained from a coal
liquefaction zone is admixed, without prior cooling, with a portion
of a liquid product recovered from the liquefaction zone, thereby
heating that portion of the liquid product to a temperature within
a predetermined range desired for hydrotreatment of the liquid
product. Preferably, hydrogen treat gas, for hydrotreatment of the
liquid product, is also heated by admixing it with the vaporous
overhead and the light liquid portion, without prior cooling of the
vaporous product. The resultant admixture is introduced into a
hydrotreating zone having essentially the same pressure as the
liquefaction zone. The remaining portion of the liquid product is
fed into the hydrotreating zone at a location downstream from the
point of introduction for the admixture where the temperature of
the hydrotreating zone exceeds the predetermined hydrotreatment
temperature by a specified amount, the quantity and temperature of
the remaining portion being correlated with the temperature at the
location where it is introduced so as to cool the hydrotreating
zone downstream from that location to a temperature within the
predetermined range for hydrotreatment. The heats of reaction in
the hydrotreating zone thus serve to heat the remaining portion of
the liquefaction liquid product and such portions conversely
provide a liquid quench for the hydrotreating zone. The
hydrotreated liquid product is recovered from the effluent of the
hydrotreating zone, a hydrogen treat gas preferably also being
recovered from the effluent and recycled to admix with the feed to
the inlet of the hydrotreating zone, as above described. In the
present context, hydrotreating refers to all catalytic hydrofining
and hydrogenation reactions conducted at essentially non-cracking
temperatures and productive of exothermic heats of reaction.
By operating the liquefaction and hydrotreating zones at
essentially the same pressure level, a number of unique and
valuable advantages are obtained over the earlier processes. For
instance, one advantage, and an object of the invention, is the
elimination altogether of preheating furnaces for the liquid
product to the hydrotreating zone, and in a preferred form, the
further elimination of preheating furnaces for a hydrogen treat gas
to the hydrotreating zone. This is possible because all of the
overhead vaporous product from the liquefaction zone is used to
heat a portion of the liquid feed fed to the inlet of the
hydrotreating zone, and preferably, to also heat the hydrogen treat
gas fed to the hydrotreating zone.
Another advantage and object of this invention is the elimination
of overhead heat exchangers and high pressure liquid separator
trains for the effluent from the liquefaction zone. In the present
invention, the overhead vapor product from the liquefaction zone is
quenched by a portion of the liquid product recovered from the
liquefaction zone, and preferably also by a hydrogen treat
stream.
Another advantage and object of the invention is the use of
portions of the liquid liquefaction product not fed to the
hydrogenation zone inlet to provide quench to the hydrotreating
zone, eliminating more expensive and complicated quench systems
such as a recycle treat gas quench system.
Yet another advantage and object of this invention results from
utilizing all of the vaporous product from the liquefaction zone to
heat a portion of the liquid liquefaction product and preferably
also recycled treat gas. This is the advantage and objective of
minimizing movement of hydrogen gas in general. Since there is no
need in the present process to strip as much liquid as possible in
order to reduce the heat duty of a liquid preheater for the
hydrotreating zone, there is no need for treat gas recycle
facilities to be sized to pass all the hydrogen required for
liquefaction and hydrogenation to the liquefaction reactor.
A further advantage and objective of the invention, made possible
by operating the hydrogenation zone and the liquefaction zone at
essentially the same pressures, is a combination of the
liquefaction and hydrogenation treat gas recycling systems. This
constitutes a significant cost saving feature in treat gas recycle
facilities for such a system.
In accordance with this invention, a liquid product boiling above
about 200.degree. F. (at atmospheric pressure) and a vaporous
product are produced in a coal liquefaction zone. The vaporous
product includes hydrogen gas in concentrations of from about 0.5
to about 12 weight percent, preferably from about 1 to about 4
weight percent thereof. To produce the liquid product and vaporous
product, a coal liquefaction zone is charged with coal particles
having a size range of about 8 mesh (Tyler) and smaller slurried,
at a solvent-to-coal ratio of from about 0.8:1 to about 2:1, in a
coal-derived hydrocarbonaceous solvent nominally boiling within the
range from about 300.degree. F. to about 900.degree. F. The coal
feedstock is a solid particulate coal such as a bituminous coal,
subbituminous coal, lignite, brown coal, or a mixture thereof.
Although it is desirable to grind the coal to a particle size
distribution from about 8 mesh and finer, it has been found that
the coal suitably liquefies even if particles as large as
one-fourth inch on the major dimension are in the slurry. A typical
proximate and ultimate analysis of a suitable high volatile
bituminous coal is set forth in Table I, which follows:
TABLE I
Chemical Analysis of Coal Wt. % Dry Analysis Illinois No. 6 Coal
(With 95% Confidence Limit) Carbon 68.77 .+-. 0.22 Hydrogen 5.01
.+-. 0.03 Organic Oxygen 9.80 Nitrogen 1.13 .+-. 0.03 Organic
Sulfur 3.13 .+-. 0.78 Total Sulfur 4.51 .+-. 0.1 Ash 10.23 .+-.
0.13 Mineral Matter 11.7 .+-. 0.1 Volatile Matter 46.63 .+-.
0.47
Preferably, the coal is dried to remove excess water, either by
conventional techniques prior to mixing it with the coal-derived
solvent, or preferably by mixing the wet coal with hot solvent to
volatilize water in the mixer zone. Moisture in the slurry feed
preferably is less than about 2 weight percent. The coal-derived
solvent preferably is also a hydrogen-donor solvent, desirably one
containing at least 20 weight percent and preferably at least 50
weight percent of compounds which are known to be hydrogen donors
at the elevated temperatures used in coal liquefaction reactors,
that is, from about 700.degree. F. to about 950.degree. F. The
hydrogen-donor solvent streams suitably contain one or more
hydrogen-donor compounds in admixture with nondonor compounds or
with one another, suitably including compounds such as indane,
C.sub.10 -C.sub.12 tetrahydronaphthalenes, C.sub.12 and C.sub.13
acenaphthenes, di-, tetra- and octahydroanthracenes, and
tetrahydroacenaphthenes and other derivatives of partially
saturated aromatic compounds.
In the coal liquefaction process, the solvent stream preferably is
a hydrogenated recycle solvent fraction. The composition of such a
fraction will vary somewhat, depending upon the source of the coal
used as the feedstock to the system, the operating conditions and
the overall process, and the conditions used in hydrogenating the
solid fraction for recycle after liquefaction. However, a typical
description of a hydrogenated recycle solvent fraction will be
similar to that shown in Table II.
TABLE II
Solvent Properties
Typical Solvent Distillation
__________________________________________________________________________
Weight Average Weight Percent Specific Gravity Boiling Point
Vaporized of Fraction
__________________________________________________________________________
400 3.35 0.9120 442 8.61 0.9592 463 9.09 0.9729 488 9.09 0.9813 518
9.57 0.9933 549 9.57 1.0115 568 10.05 1.0473 596 10.05 1.0643 622
10.05 1.0613 674 10.04 1.0774 733 7.18 1.0942 775 3.35 1.1069
Overall specific gravity = 1.0229 Solvent Elemental Composition
__________________________________________________________________________
Element Weight Percent Carbon 90.42 Hydrogen 8.46 Oxygen 0.68
Nitrogen 0.36 Sulfur 0.075
In the liquefaction zone, conditions suitably include a pressure
within the range from about 1000 psig to about 2000 psig,
preferably from about 1000 psig to about 1500 psig, and a
temperature preferably within the range from about 750.degree. F.
to about 850.degree. F. Liquid residence time in the liquefaction
zone is suitably within the range from about 5 to about 60 minutes,
preferably from about 10 to about 40 minutes. Hydrogen suitably is
passed into the liquefaction zone in amounts of from about 1 to
about 6 weight percent (moisture and ash free coal basis),
preferably from about 1 to about 3 weight percent, in order to
replenish depleted hydrogen donor molecules in the solvent or to
provide such molecules in the solvent, if the solvent is not
already hydrogenated, by in situ hydrogenation in the liquefaction
zone. Conditions in the liquefaction zone are correlated to produce
sufficient liquid product to provide quench both for the vapor feed
to the hydrogenation zone and for the fluids passing through the
hydrogenation zone, at points in the zone, where quench is needed
to control hydrogenation temperatures.
The liquid product and the vaporous product produced in
liquefaction zone are separately removed from the liquefaction zone
and thereafter, a portion of the liquid product is heated to a
temperature within a predetermined range suitable for hydrotreating
by admixing it with all of the vaporous product, without prior
cooling of the vaporous product. The portion of the liquid product
which is so heated may be a part of the whole liquid product or a
part of a boiling range fraction of the whole liquid product.
Preferably, a recycled hydrogen treat gas stream recovered from the
effluent of the hydrotreating zone is also heated for passage into
the hydrogenation zone by admixing it, as well, with the vaporous
product without prior cooling of the vaporous product. The
proportions of the portion of liquid product and hydrogen recycle
gas, if any, mixed with the total vaporous liquefaction zone
product, are adjusted to obtain a temperature within a
predetermined range which is within the range from about
550.degree. F. to about 750.degree. F. suitable for hydrotreating
reactions.
In the hydrotreating zone, into which the admixture is fed,
pressure is maintained essentially the same as in the liquefaction
zone. Depending on the particular hydrotreating reaction employed,
space velocities, hydrogen treat rate and hydrotreating
temperatures will vary. In general, temperatures in the
hydrotreating zone are suitably within the range from about
550.degree. to 750.degree. F., space velocity within the
hydrotreating zone is suitably within the range from about 0.3 to 2
w/hr/w, and hydrogen treat rates are suitably within the range from
about 1,000 to about 12.000 SCF/B. Preferably the hydrotreating
zone is a solvent hydrogenation zone in which the mean
hydrogenation temperature is within the range from about
650.degree. to about 700.degree. F., liquid hourly space velocity
is within the range from about 1 to about 2 w/hr/w and hydrogen
treat rates are within the range from about 3,000 to about 8,000
SCF/B.
Hydrotreating temperatures are maintained at a predetermined range
within the aforesaid range of from about 550.degree. F. to about
750.degree. F. by introduction of the remainder of the liquid
liquefaction product into the hydrotreating zone at one or more
locations downstream from point of introduction of the admixture
where the temperature of the hydrotreating zone exceeds the
predetermined range of temperatures by a specified maximum within
the range from about 5.degree. F. to about 75.degree. F. The
quantity and temperature of the remaining liquid liquefaction
portion is correlated with the temperature at the one or more
locations to quench the temperature in the hydrotreating zone
downstream from the one or more locations to within the
predetermined range to be maintained in the zone. The range of
temperatures chosen for hydrotreatment, and to a lesser degree the
other hydrotreating conditions, will affect the maximum temperature
which can be permitted in the hydrotreating zone without runaway
reaction or undue shortening of catalyst life. Where hydrotreatment
is effected with a generally low range of temperatures, e.g., about
from 550.degree. F. to about 650.degree. F., as it may when a
liquid product of relatively low or moderate specific gravity and
low sulfur and nitrogen content is being hydrotreated (typical for
subbituminous and lower rank Western coals), it may be suitably
specified that the remaining portion of the liquid product is to be
introduced at the one or more locations in the hydrotreating zone
where the temperature is as much as 75.degree. F. greater than
650.degree. F. But where the hydrotreating temperatures are in a
higher range, e.g., from about 700.degree. F. to about 750.degree.
F., as they may be for hydrotreating of liquid product of heavier,
high sulfur and nitrogen content coal typical of Eastern bituminous
coal, the maximum temperature rise above that range suitably may be
no more than 25.degree. F.
The hydrotreating catalysts employed in the hydrotreatment are of
conventional nature. Without being limited to any particular
catalyst, these catalysts will typically comprise an alumina or
silica-alumina support carrying one or more iron group metals and
one or more metals of Group VI-B of the Periodic Table in the form
of the oxides or sulfides. In particular, combination of one or
more Group VI-B metal oxides or sulfides with one or more Group
VIII metal oxides or sulfides are preferred. For example, typical
catalyst metal combinations contemplated are oxides and/or sulfides
of cobalt-molybdenum, nickel-tungsten, nickel-molybdenum-tungsten,
cobalt-nickel-molybdenum, nickel-molybdenum, etc. As a typical
example, one catalyst will comprise a high metal-content sulfided
cobalt-molybdenum-alumina catalyst containing about 1 to 10 weight
percent cobalt oxide and about 5 to 40 weight percent molybdenum
oxide, especially about 2 to 5 weight percent cobalt and about 10
to 30 weight percent molybdenum. It will be understood that other
oxides and sulfides will be useful, such as those of iron, nickel,
chromium, tungsten, etc. The preparation of these catalysts is now
well known in the art. The active metals can be added to the
relatively inert carrier by impregnation from aqueous solutions
followed by drying and calcining to activate the composition.
Suitable carriers include, for example, activated alumina,
activated alumina-silica, zirconia, titania, etc., and mixtures
thereof. Activated clays, such as bauxite, bentonite and
montmorillonite, may also be employed.
The invention will be better understood by the detailed description
of a preferred embodiment of it, as depicted in the attached
drawing, and by provision thereafter of an example making use of
the process described in the preferred embodiment.
DESCRIPTION OF THE DRAWING
The drawing is a schematic flow diagram of an integrated
liquefaction-hydrogenation process for producing a recycle solvent
for a coal liquefaction reactor.
DESCRIPTION OF THE PREFERRED EMBODIMENT
A slurry of particulate coal (8 mesh Tyler and smaller) in a
hydrogen-donor solvent at a solvent/coal ratio within the range
from about 0.8:1 to about 2:1 and preheated to a temperature within
the range from about 750.degree. F. to about 850.degree. F. is
introduced by way of line 10 and admixed with a preheated hydrogen
recycle stream introduced by way of line 12 to produce a slurry
feed stream having from about 1 to about 6 weight percent of
hydrogen (MAF coal basis). The slurry feed stream is introduced
into a liquefaction reactor 14 maintained at liquefaction
conditions including a pressure within the range from about 1000
psig to about 2000 psig, e.g., about 1800 psig, and a temperature
within the range from about 750.degree. F. to about 850.degree. F.
Liquid residence time within the reactor 14 is suitably within the
range from about 10 to about 40 minutes. A vaporous product is
removed overhead from liquefaction 14 by way of line 16, and
suitably includes from about 0.5 to about 4 weight percent
hydrogen. A liquid product is separately removed from the
liquefaction reactor by way of line 18 and conducted into a low
pressure, temperature reduction gas-liquid separation zone 19 for
separation of flue gas constituents, primarily C.sub.1 -C.sub.4
hydrocarbons and hydrogen gases, removed by way of line 20, from
C.sub.5 and heavier liquid products, recovered by way of line 22.
The liquid products in line 22 are then alternatively conducted
either into a fractionator 24 or a fluid coker 26. Fluid coker 26
is preferably operated with a dense phase bed of coke particles
maintained in fluidized state by steam and by evolution of vapor
volatilization and cracking of the feed stream, as known in the
art. Within fluid coker 26, the liquid product hydrocarbons undergo
thermal cracking to produce vaporous coker products which pass
upwardly through a cyclone separator, for returning coke particles
back to the fluidized bed, and into a coker fractionator
conventionally located above the fluid coker and integrated
therewith. In the coker fractionator, the vaporous coker products
are liquefied and distilled according to boiling point, producing a
light coker fractionator stream boiling below 700.degree. F.,
recovered by way of line 28, and a heavy coker fractionator stream
boiling from about 700.degree. F. to about 1000.degree. F.,
recovered by way of line 30. Coker fractionator bottoms, including
char, is removed from coker 26 by way of line 32 for gasification
or other end use. Alternatively, if coking is unnecessary, line 22
is conducted directly to fractionator 24. Accordingly, fractionator
24 is operated to produce a gas stream boiling up to about
400.degree. F. for recovery by way of line 34. Fractionator 24
suitably fractionates the liquid product into a light fraction
boiling from about 400.degree. F. to about 700.degree. F., for
recovery by way of line 36, as well as a heavy fraction boiling
from about 700.degree. F. to about 1000.degree. F., recovered by
way of line 38. A bottom fraction from the fractionator is
withdrawn for further use such as gasification. A desired fraction
of the liquid product is removed from the fractionating zone by way
of line 42 for ultimate hydrotreating, either the
400.degree.-700.degree. F. fraction from line 36, the
700.degree.-1000.degree. F. fraction from line 38, by way of line
40, or a 400.degree.-1000.degree. F. fraction provided by combining
lines 36 and 38 through line 40. Or if fluid coker 26 is used, the
desired fraction is conveyed from lines 28 or 30, or both of them.
The liquid product fraction in line 42 is split into two or more
portions, as by suitable proportioning valve apparatus (not
illustrated), and a first portion, at a temperature, for example,
of about 300.degree. F., is admixed with all of the vaporous
liquefaction product from line 16 having, say, a temperature of
about 840.degree. F., thereby producing an admixture in line 48
with a resultant temperature within a range from about 650.degree.
F. to about 750.degree. F. suitable for hydrogenation, in the case
of the 400.degree./700.degree. F. fraction, preferably from about
650.degree. F. to about 700.degree. F. As illustrated, the
admixture is also preferably constituted with a recycle hydrogen
treat gas stream introduced by way of line 46 without prior
preheating passage through a preheater furnace, the quantity of the
first liquid portion from line 42 being adjusted with the quantity
of the recycle stream to provide the desired temperature range
consistent with the feed rates of each which is wanted.
The admixture in line 48 is then introduced into solvent
hydrogenation reactor 50, which is maintained at essentially the
same operating pressure as in liquefaction reactor 14.
Hydrogenation conditions within reactor 50 further include the
aforesaid temperature within the range from about 650.degree. F. to
about 750.degree. F., a hydrogen treat rate within the range from
about 1000 to about 12,000 SCF/B and an overall liquid hourly space
velocity within the range from about 0.3 to about 2 w/hr/w. A
remaining portion of the liquid product fraction recovered from
fractionator 24 (or fluid coker 26) is introduced into the solvent
liquefaction zone 50 by line 52 (and if necessary, by line 54) at
least at one location downstream from the inlet to the
hydrogenation reactor where the temperature of the hydrogenation
reactor exceeds the 650.degree. -750.degree. F. range by a
specified maximum within the range from about 5.degree. F. to about
75.degree. F., e.g., at most 75.degree. F. for the
650.degree.-700.degree. F. hydrotreating range used for the
400.degree./700.degree. F. fraction. The quantity and temperature
of the remaining portion or portions of the fraction used are
correlated with the temperature at the location in the solvent
hydrogenation reactor where such portion or portions are introduced
so as to cool the hydrogenation reactor downstream from said such
locations to a temperature within the range from about 650.degree.
F. to about 750.degree. F., or 650.degree.-700.degree. in the case
where the 400.degree./700.degree. F. fraction is used.
The effluent from the hydrogenation reactor 50 is removed by way of
line 56 and conducted into a high pressure temperature reducing gas
liquid separator 58, for separation of a gaseous hydrogen stream 60
from hydrocarbon vapors and liquids in line 59. The hydrogen gas in
line 60 is carried into a conventional scrubber 62 in which,
suitably, a monoethanol amine water solution is introduced, by way
of 64, for countercurrently contacting upflowing hydrogen gas, sour
water being removed by way of line 66 for ammonia recovery. The
scrubbed hydrogen gas is removed from scrubber 62 by way of line
68, purged by way of line 70, and made up with fresh hydrogen by
way of line 72, suitably to 80 percent hydrogen, for compression in
centrifugal compressor 74. The hydrogen recycle gas from compressor
74 is then, in part, admixed with the gaseous liquefaction product
16 and the liquid liquefaction product fraction in line 42, as
already described, and the remaining portion of the hydrogen
recycle stream is recycled by way of line 76 to line 12 for
introduction into liquefaction reactor 14 with the coal slurry from
line 10.
The hydrocarbonaceous vapors and liquids recovered from separator
58 by way of line 59 are introduced into a low pressure vapor
liquid separator 78, from which C.sub.1 -C.sub.4 fuel gas
constituents are removed overhead by way of line 80, C.sub.5 and
heavier liquid hydrocarbon constituents being removed by way of
line 82 and introduced into stripper 86 with liquid hydrocarbons
recovered from scrubber 62 by way of line 69. In stripper 86,
hydrocarbons boiling below about 400.degree. F. are stripped
overhead, and heavier boiling fractions are recovered by way of
line 90, either for recycle as hydrogen-donor solvent in making up
the coal slurry introduced by way of line 10, or for product use by
way of line 94, or for both such purposes.
The advantages of this invention will be apparent from this
embodiment of it. No preheating furnaces are necessary for the
liquid fraction or the recycle hydrogen treat stream passed into
solvent hydrogenation reactor 50. Heat for the hydrogen treat
stream and the portion of the liquid fraction passed into the
reactor inlet is provided by the vaporous product recovered from
the liquefaction zone. The other portions of the liquid fraction
are heated, while simultaneously quenching the catalyst beds in
reactor 50, by injection into the reactor downstream from the
inlet. This quench replaces the more costly recycle treat gas
quench. By not cooling the vaporous product, heat exchangers and
separation vessels for it are eliminated. Moreover, operation of
the liquefaction and hydrogenation zones at substantially the same
temperature permits a cost saving combination of the treat gas
recycling systems of the two zones. Finally, elimination of feed
preheat furnaces reduces the need for higher hydrogen throughputs
in the liquefaction reactor, reducing hydrogen hauling equipment
and liquefaction reactor costs.
The following example will more particularly illustrate the
invention.
Example
A slurry of Illinois No. 6 coal (9.52 weight percent ash) at a
solvent-to-coal ratio of 1:2 and preheated to 800.degree. F. is
admixed at a feed rate of 3,511 thousand pounds/hour with a
hydrogen treat recycle stream compressed to 1885 psig and
subsequently heated to 634.degree. F. in amounts of 462 thousand
SCF/SD (80 percent hydrogen), providing a hydrogen treat rate in
the liquefaction zone of 5.2 weight percent on a dry coal basis.
Conditions in the liquefaction zone include a mean temperature of
about 825.degree. F., a mean pressure of about 1810 psig, and a
liquid residence time of about 36 minutes, hydrogen uptake in the
zone being about 1.57 weight percent on a dry coal basis. About 519
thousand SCF/SD of vaporous product comprising 49 weight percent of
hydrogen is recovered from the liquefaction reactor, at a
temperature of 838.degree. F. and a pressure of about 1790 psig.
The vaporous liquefaction product is admixed with about 38.6
thousand barrels/SD of a 400.degree./700.degree. F. liquid product
fraction at a temperature of 285.degree. F. and about 200 million
SCF/SD of 80 percent hydrogen recycle gas at a temperature of
300.degree. F. to produce an admixture feed to the solvent
hydrogenation reactor having a temperature of about 700.degree. F.
The hydrogenation catalyst is conventional cobalt molybdate on a
silica-alumina bed. Total treat gas purity to the hydrogenation
reactor is 66.7 mol percent hydrogen for a treat gas rate of 4730
SCF/B. The liquefaction product fraction at 285.degree. F. is fed
at the rate of 20 thousand B/SD to the solvent hydrogenation
reactor as quench at locations downstream from the reactor inlet
where bed temperature rises to 50.degree. F. above the inlet
temperature. Reactor inlet temperatures at the start of the run are
662.degree. F. and at the end of the run are 739.degree. F., the
bed .DELTA. T being 22.degree. F. and the temperature increase rate
per day being 0.43.degree. F. Reactor inlet pressure is 1790 psig
and overall liquid hourly space velocity is 4.0 w/hr/w. Hydrogen
consumption in the solvent hydrogenation reactor is 630 SCF/B,
about 1.18 weight percent on a dry coal basis.
Having described in full our invention, in which coal liquefaction
and coal liquid hydrotreating zones are operated at essentially
equivalent temperatures and wherein one portion of the liquid
product from the liquefaction reactor is heated by means of the
vapor product from the liquefaction reactor for feed to a
hydrotreating zone, the other portion of the liquid product being
fed to the hydrotreating zone for quench of the zone, various
changes and modifications of the invention will now occur to those
skilled in the art.
* * * * *