[0001] This invention relates to a process for converting coal or similar solid carbonaceous
materials. More particularly, this invention relates to an improved process for liquefying
coal and similar solid carbonaceous materials.
[0002] As is also well known, proven petroleum and gas reserves are shrinking throughout
the world and the need for alternative sources of energy is becoming more and more
apparent. One such alternative sourceis,of course, coal since coal is an abundant
fossil fuel in many countries throughout the world. Before coal will be generally
accepted by the ultimate consumer, however, it will be necessary to convert the same
to a form which will permit use in those areas where liquid or gaseous fuels are normally
required.
[0003] To this end, several processes wherein coal is either liquefied and/or gasified have
been proposed heretofore. Of these, the processes wherein coal is liquefied appear
to be more desirable since a broader range of products is produced and these products
are more readily transported and stored.
[0004] Of these several liquefaction processes which have heretofore been proposed, those
processes wherein coal is liquefied in the presence of a solvent or diluent, particularly
a hydrogen-donor solvent or diluent, and in the presence of a hydrogen-containing
gas appear to offer the greater advantages. In these processes, liquefaction is accomplished
at elevated temperatures and pressures and hydrocarbon gases are invariably produced
as by-products. For the most part, however, these and other liquefaction processes
yield a normally solid bottoms product containing relatively large quantities of carbon,
which bottom product cannot be discarded without further processing when an economic,
waste-free process is sought. Heretofore, several methods have been proposed in an
effort to avoid this deficiency. For example, the normally solid, bottoms product
can be subjected to further liquefaction in a separate stage or stages until such
time as the carbon content of the normally solid, bottoms product has been reduced
to a point where the carbon content thereof is sufficiently low such that discarding
thereof does not significantly and adversely affect the economics of the process.
Staged liquefaction, however, significantly increases both investment and operating
costs as a result of the additional equipment required and as a result of the energy
and other utilities required to effect the further liquefaction. It has also been
proposed, heretofore, to recycle all or a portion of the normally solid, bottoms product
to a single or plural liquefaction stage. When this is done, however, a large portion
of the material recycle is either unreactive (ash) or it is difficult to convert (fusinite).
These materials can amount to 60% of the recycle material and recycle of these materials
raises costs and lowers thermal efficiency. It has also been proposed, heretofore,
to simply burn the normally solid, bottoms product, directly, or to gasify the normally
solid, bottoms product to produce a gaseous product which can then be burned as a
fuel. Operation in this manner, however, reduces the yield of normally liquid products,
thereby reducing thermal efficiency, and increases both investment and operating costs
for essentially the same reasons already noted with respect to staged or further liquefaction.
Finally, it has been proposed, heretofore, to separate the unreactive and fusinite
portions of the bottoms from-the reactive portion thereof by extraction. Generally,
however, these operations depend upon the use of a relatively expensive solvent (such
as toluene) which must then be separated from the extract, generally, by vaporization.
This type of operation too has proven expensive due primarily to the high energy requirement
for separation of the solvent.
[0005] In light of the foregoing, the need for a liquefaction process which can be operated
in a mode requiring fewer liquefaction stages at an increased thermal efficiency to
yield a normally solid, bottoms product relatively low in carbon, which product may
be discarded, is believed readily apparent. More particularly, the need for a liquefaction
process wherein a significant portion of the carbon contained in the normally solid,
bottoms product can be efficiently recovered via extraction is believed to be readily
apparent.
[0006] It has now been discovered that the foregoing and other disadvantages of the prior
art processes can be reduced with the method of the present invention and an improved
liquefaction process provided thereby. It is, therefore, an object of this invention
to provide an improved liquefaction process wherein the yield of liquid product is
increased without further liquefaction at elevated temperatures and pressures and
without recycling the inactive and fusinite portions of the normally solid, bottom
product which preferably can be discarded,directly, after an extraction operation
with a reduced impact on process economics and thermal efficiency. Fusinite is the
woody material which was charred before being incorporated in the peat that ultimately
formed coal. The foregoing and other objects and advantages will became apparent fran
the description set forth hereinafter and fran the drawings appended thereto.
[0007] In accordance with the present invention, the foregoing and other objects and advantages
are accomplished by liquefying a coal or similar solid carbonaceous material in the
presence of a hydrogen donor solvent at elevated temperatures and pressures and thereafter
extracting at least a portion of the reactive bottoms from the normally solid bottoms
product. The extraction will be accomplished with a hydrogen donor solvent derived
from the solid carbonaceous material subjected to liquefaction. The raffinate from
the extraction, without separation of the solvent, will be recycled to the liquefaction
stage thereby increasing the overall liquid yield of the process. The normally solid
bottoms product remaining after extraction will contain less carbon than the feed
to the extraction step and may be discarded, directly, with less adverse impact on
economics than would be the case if the original, unextracted normally solid bottoms
product were discarded. As indicated more fully hereinafter, however, maximum conversion
of the solid carbonaceous material and maximum thermal efficiency will be realized
either by burning the remaining normally solid bottoms product or by further treating
the same to produce a useful fuel.
[0008] As indicated, supra, the present invention relates to an improved process for liquefying
coal and similar solid carbonaceous materials such as trash, coke and the like, wherein
the yield of liquid products is increased in a more thermally efficient manner and
a normally solid bottoms product containing less reactive carbon produced thereby..
The "liquefaction is accomplished at an elevated temperature and pressure and in the
presence of a hydrogen donor solvent which is prepared from a portion of the liquefaction
liquid product. At least a portion of the hydrogen donor solvent used during liquefaction
will be used to extract the normally solid bottoms product obtained from the liquefaction
and at least a portion of the carbonaceous materials extracted from the normally solid
bottoms product will be present during liquefaction.
[0009] In general, the method of the present invention can be used to liquefy any solid
carbonaceous material which can, effectively, be hydrogenated and liquefied. Such
solid carbonaceous materials include, but are not necessarily limited to, coal, trash,
biomass, coke and the like. The method of this invention is particularly useful in
the liquefaction of coal and may be used to liquefy any of the coals known in the
prior art including anthracite, bituminous coal, subbituminous coal, lignite, peat,
brown coal and the like.
[0010] In general, the solid carbonaceous material will be ground to a finely divided state.
The particular particle size or particle size range, actually employed, however, is
not critical to the invention and, indeed, essentially any particle size can be employed.
Notwithstanding this, generally, the solid carbonaceous material which is liquefied
in accordance with this invention, will be ground to a particle size of less than
1/4 inch and preferably to a particle size of less than about 8 mesh (M.B.S.Sieve
size).
[0011] . After the solid carbonaceous material has been sized, the same will be slurried
with a hydrogen donor solvent. As indicated more fully hereinafter, at least a portion
of the hydrogen donor solvent used in preparing the slurry will have been used to
extract the normally solid bottoms product from the liquefaction step. In general,
the solid carbonaceous material will be slurried with sufficient donor solvent to
produce a slurry containing a solvent: solid carbonaceous material ratio within the
range from about 0.8:1 to about 10:1 on a weight basis. As used herein the recitation
hydrogen donor solvent shall mean a hydrogen donor solvent produced from a portion
of the liquefaction liquid product and will include any non-donor species that might
be contained therein.
[0012] The hydrogen donor solvent used in the process of this invention may be any portion
of the liquefaction product from liquefaction containing at least about 0.8 weight
percent of donatable hydrogen based on the weight of total solvent or which can be
treated to contain at least about 0.8 weight percent of donatable hydrogen based on
the weight of total solvent. Particularly effective solvents are distillate fractions
cut from the liquefaction product and having an initial boiling point within the range
from about 350°F to about 425°F and a final boiling point within the range from about
700° to about 900°F. Generally, these fractions will not contain at least about 0.8
weight percent of donatable hydrogen based on the weight of total solvent but do contain
sufficient aromatic concentrations as to permit the production of a suitable hydrogen
donor solvent by hydrogenating at least a portion of the aromatics to a corresponding
hydroaromatic compound. In this regard, it should be noted that compounds capable
of donating hydrogen during liquefaction are well-known in the prior art and many
are described in U.S. Patent 3,867,275. Compounds capable of donating hydrogen during
liquefaction include the indanes, the dihydroflourines, the C
10-C
12 tetra-hydro- naphathalenes, the hexahydrofluorenes, the dehydro-, tetra- hydrohexahydro-,
and octohydrophenanthrenes, the C
12-C
13 acenaphthenes, the tetrahydro-, hexahydro-, and decahydro- pyrenes, the di-, tetra-,
and octahydroanthracenes, and other derivatives of partially saturated aromatic compounds.
As is also well-known in the prior art, hydrogenation of various coal liquefaction
liquid products will produce one or more of these known hydrogen donor compounds.
[0013] During start-up of the process of this invention and while solvent produced from
the solid carbonaceous materials subjected to liquefaction is not available the process
may be started-up or operated with any of the known hydrogen donor compounds mentioned
above. Either as a pure compound or as a mixture of such compounds either alone or
in combination with components which will not donate hydrogen at liquefaction conditions.
Hydrogenated creosote oil may also be used during start-up or at other times when
a solvent derived from the solid carbonaceous material subject to liquefaction is
not available.--Generally, the creosote oil will be hydrogenated in the same manner
as is the solvent derived from the solid carbonaceous materials subjected to liquefaction,
which method is described in further detail hereinafter. After the solid carbonaceous
material has been slurried, the slurry will then be subjected to liquefaction at a
temperature within the range from about 700 to about 950°F and at a pressure within
the range from about 800 to about 3000 psig. In general, from about 20 to about 100
weight percent of the total solvent used in preparing the slurry will have first been
used to extract reactive bottoms from the normally solid bottoms product produced
during liquefaction. This solvent will contain from about 5 to 50 weight percent reactive
bottoms. The liquefaction will, therefore, be accomplished in the presence of from
about 0.05 to 0.5 parts of reactive bottoms per part of coal, based on weight. During
liquefaction, the reactive bottoms will be converted to gaseous and liquid products
thereby increasing the total conversion of solid carbonaceous material and the yield
of normally liquid products.
[0014] During liquefaction, the solid carbonaceous material will be converted in part to
a normally gaseous product, and part to a normally liquid product, and in part, to
a normally solid bottoms product. In general, the normally solid bottoms product will
have an initial boiling point within the range of about 900°F to about 1100°F and
will contain unconverted carbonaceous material, inorganic material and high boiling
but converted carbonaceous material. Generally, the high boiling, but converted carbonaceous
material could be further reduced in molecular weight if the bottoms were subjected
to further liquefaction or if the entire bottoms were recycled. Similarly, at least
a portion of the unconverted material could be converted if the bottoms were subjected
to further liquefaction or if the bottoms were recycled to a liquefaction stage. The
more difficult to convert portion of the unconverted carbonaceous material (fusinite)
would not, normally, be converted through further liquefaction or recycle of the bottoms.
Similarly, the inorganic material (ash) would not be converted through further liquefaction
of the bottoms or via recycle thereof.
[0015] It has now surprisingly been discovered that a substantial portion of the reactive
material; i.e., normally solid carbonaceous material which could be converted to either
a gaseous or liquid product when subjected to further liquefaction or recycled to
a liquefaction stage, can be separated from the nohreactive portion of the normally
solid bottoms product; viz., the ash and fusinite, by extraction of the bottoms with
a donor solvent and particularly a donor solvent derived from the solid carbonaceous
material being subjected to liquefaction. The extraction may be accomplished at relatively
mild conditions and the extracted reactive portion of the normally solid bottoms product
further converted by recycling the same to one or more of the liquefaction stages.
The further conversion of the reactive portion of the normally solid bottoms product
will, then, be accomplished with less energy than would be required to subject the
normally solid bottoms product to further liquefaction in a separate stage and with
less energy than would be required to recycle the entire normally solid bottoms product.
The process of this invention is, therefore, more energy efficient than processes
heretofore proposed in the prior art.
[0016] In general, the extraction will be accomplished at a temperature within the range
from about 50 to about 600°F and at a pressure within the range from about 0 to about
750 psig. The extraction may be accomplished with any suitable means known in the
prior art to be effective for the extraction of a soluble or extractable portion of
a normally solid material with a liquid. In general, the extraction will be accomplished
in a well-mixed vessel so as to ensure good contact between the normally solid bottoms
product and the solvent used during extraction. The solvent containing the extracted-portion
of the normally solid bottoms product can then be separated from the relatively unreactive
portion of the normally solid bottoms product by any suitable means such as decanting,
centrifugation, filtration or the like. Of these, decanting after a gravitational
separation is most preferred since less energy is required for this particular mode
of separation. Following the separation, the solvent portion may be used directly
in the preparation of a slurry of the solid carbonaceous material to be subjected
to liquefaction. Any solvent that might be entrained in the ash and fusinite rich
raffinate stream could be removed by flash vaporization or by displacement with water.
The remaining bottoms, especially when the carbon content thereof is relatively low,
could be discarded. For maximum efficiency, however, it is believed most expedient
to either subject the ash and fusinite rich raffinate to combustion so as to recover
the fuel value thereof or to subject the same to gasification to produce a gas containing
hydrogen which could then be used to effect the liquefaction and hydrogenation of
the solvent fraction. When a partial oxidation process is used to effect the gasification,
displacement of entrained solvent with water would offer certain advantages.
[0017] As indicated previously, the liquefaction will, generally be accomplished at a temperature
within the range from about 700 to about 900°F and at a pressure within the range
from about 800 to 3000 psig. Any number of liquefaction stages or zones may be used
to effect the liquefaction but a single stage is generally preferred since this reduces
the initial investment cost and the energy requirement for effecting the liquefaction.
The total nominal holding time required is that sufficient to effect at least a partial
liquefaction of the solid carbonaceous material and will, generally, range from about
10 to about 200 minutes.
[0018] As also indicated previously, the liquefaction will result in the production of a
gaseous product, a normally liquid product and a normally solid bottoms product. After
liquefaction, these products may be separated into respective phases using conventional
techniques. For example, the gaseous products may be flashed overhead and the liquid
and solids then separated using filtration, centrifugation or distillation. Of these,
distillation is preferred.
[0019] After separation, the gaseous product may be upgraded to a pipeline gas or the same
may be burned to provide energy for the liquefaction process. Alternatively, all or
a portion of the gaseous product may be reformed to provide hydrogen for the liquefaction
process.
[0020] The liquid product may be fractioned into essentially any desired product distribution
and/or a portion thereof may also be used directly as a fuel or upgraded using conventional
techniques. In accordance with the present invention, a portion of the liquid product
will be separated and used as a solvent or diluent in the liquefaction process of
this invention. This portion of the liquid product will be hydrogenated to increase
the amount of donatable hydrogen therein prior to its use as a solvent or diluent.
Generally, a naphtha fraction will be recovered and the naphtha fraction will be further
processed to yield a high quality gasoline or similar fuel boiling in the naptha range.
[0021] Finally, in accordance with the improvement of this invention, at least a portion
of the normally solid bottoms product will be withdrawn, extracted by contacting with
at least a portion of the solvent separated from the liquid product and this solvent
containing the extracted components from the normally solid bottoms product will be
used in the preparation of a solid carbonaceous material slurry which is, ultimately,
subjected to liquefaction in the process of this invention. In general, from about
1 to about 6 parts of solvent or diluent per part of normally solid bottoms product,
by weight, will be contacted with the bottoms product in the extraction step. As a
result of this extraction, from about 20 to about 80 weight percent of the reactive
portion of the bottoms will be separated from the normally solid bottoms product during
extraction. Slurry preparation will then be controlled to provide from about 0.05
to about 0.5 parts of "reactive" components per part of solid carbonaceous material
fed to the liquefaction stage or zone.
[0022] In a preferred embodiment of the present invention, a coal will be liquefied in a
single stage liquefaction operation in a temperature within the range from about 80
to about 880°F, and at a pressure within the range from about 1500 to about 2000 psig.
In the preferred embodiment, the coal will be slurried with a solvent or diluent cut
from the coal liquefaction liquid product and hydrogenated such that the solvent contains
at least 45 weight percent hydrogen donor species and contains at least 1.25 weight
percent donatable hydrogen. All of the solvent used in preparing the slurry will have
been used to extract reactive material from the normally solid bottoms product produced
during liquefaction. The slurry after preparation will contain from about 0.1 to about
0.3 parts of reactive material from the bottoms per part of coal when fed to the liquefaction
stage or zone. The solvent to coal ratio in the slurry will-be within the range from
about 1:1 to about 5:1. The-nominal holding time during liquefaction will be within
the range from about 40 to about 140 minutes. In a preferred embodiment, the extraction
will be accomplished at a temperature within the range from about 100 to about 400°F
and at a pressure within the range from 0 to about 500 psig. The contacting between
the solvent and the normally solid bottoms product will be accomplished in a countercurrent
baffled contacting vessel at a solvent to normally solid bottoms product ratio within
the range from about 4:1 to about 8:1 (v/v). In the preferred embodiment, the baffled
contacting vessel will be disposed vertically with the solvent flowing upwardly-and
with the normally solid bottoms product settling downwardly. The solvent will then
be withdrawn at or near the top of the baffled contacting vessel and the normally
solid bottoms product free of extracted reactive material will be withdrawn at or
near the bottom.
[0023] It is believed that the invention will be better understood by reference to the attached
Figure 1 which illustrates a particularly preferred embodiment. Referring then to
Figure 1, a finely divided coal or similar solid carbonaceous material is introduced
into mixing vessel 10 through line 11 and slurried with a hydrogen donor solvent or
diluent introduced through line 12. In a preferred embodiment, the solvent will be
all or a portion of a distillate fraction cut from the liquefaction liquid product,
which fraction will be hydrogenated to produce a solvent containing at least 45 weight
percent hydrogen donor species and which will be used in the extraction of reactive
solid carbonaceous materials from the normally solid bottoms product. When all of
the solvent is not used in the extraction step, any additional solvent required to
effect the liquefaction may be recycled through line 13. During start-up, however,
or when a recycle solvent is not available, any of the known useful hydrogen donor
solvents or diluents may be introduced into line 13 through line 14.
[0024] In mixing vessel 10 and after normally solid bottoms product is available, the coal
or similar solid carbonaceous material will also be mixed with reactive material extracted
from said bottoms. In the embodiment illustrated, the reactive material will be contained
in the solvent fed into mixing vessel 10 through line 12. In the preferred embodiment,
the reactive material and solid carbonaceous material will be combined in a ratio
within the range from about 0.1:1 to about 0.3:1 by weight. The reactive material
and solid carbonaceous material will be combined with sufficient solvent including
that used in the extraction step and introduced into mixing vessel 10 through line
12 to produce a slurry wherein the solvent-to-solid carbonaceous material ratio is
within the range from 4:1 to about 8:1.
[0025] In the embodiment illustrated, the slurry is withdrawn from mixing vessel 10 through
line 16 and passed through preheater 17. In the preheater 17 the slurry will, generally,
be preheated to the desired temperature and generally to a temperature of about 50
to about 100°F below the temperature at which liquefaction is accomplished. When desired,
and particularly when the solid carbonaceous material has not been previously dried,
steam will be flashed overhead through line 18.
[0026] In general, the slurry of solid carbonaceous material will be combined with molecular
hydrogen. In a preferred embodiment, the molecular hydrogen will be added prior to
preheating through line 19. This is not, however, critical, and the hydrogen could
be added downstream of preheater 17 or added directly into the liquefaction vessel.
In any case, the hydrogen will be introduced after the steam is flashed overhead.
In the preferred embodiment, the hydrogen will be produced either by the steam reforming
of product gas from the liquefaction; by gasification of the nonreactive portion of
the solid bottoms product or by gasification of solid carbonaceous material in a separate
step, all in accordance with conventional technology. In general, sufficient hydrogen
will be introduced to provide from about 2 to about 10 weight percent, preferably
from about 3 to about 8 weight percent, molecular hydrogen based on dry, solid carbonaceous
material.
[0027] The slurry is withdrawn from the preheater through line 20 and passed directly to
liquefaction vessel 21. In the liquefaction vessel 21, the solid carbonaceous material
is at least partially liquefied and, generally, at least partially gasified, generally,
in the absence of any added catalyst. Preferably, the liquefaction vessel will be
sized so as to provide a nominal holding time within the range from about 40 to about
140 minutes and in a preferred embodiment, a single vessel will be employed. Also,
the temperature within the liquefaction zone-21 will, preferably, be within the range
from about 800 to about 880°F and the pressure will be, preferably, controlled within
the range from about 1500 to abou t 2000 psig.
[0028] In the embodiment illustrated, the combined product from liquefaction vessel 21 is
withdrawn through line 22 and passed to separating means 23. In the embodiment illustrated,
the separating means may be a combined atmospheric and vacuum distillation column
wherein gaseous products and products boiling below the naphtha boiling range are
withdrawn overhead through line 24 while a bottoms product comprising unconverted
solid carbonaceous material, mineral matter and converted materials having an initial
boiling point within the range from about 950°F to about 1050°F is withdrawn through
line 25. The liquid product is then fractionated into desired fractions and in the
embodiment illustrated, a naphtha product having an initial boiling point of about
150°F and a final boiling point within the range from about 350°F to about 425°F is
withdrawn through line 26; a middle distillate fraction having an initial boiling
point within the range from about 350°F to about 425°F and a final boiling point within
the range from about 650°F to about 850°F is withdrawn through line 27 and a vacuum
gas-oil fraction having an initial boiling point within the range from about 650°F
to about 850°F and a final boiling point within the range from about 950°F to about
1050°F is withdrawn through line 28.
[0029] In general, the overhead, gaseous material will comprise gaseous and lower hydrocarbons,
steam, carbon oxides, acid gases such as S0
2 and R
2S, any ammonia which may have been produced during liquefaction and any hydrogen not
consumed during liquefaction. This stream may be scrubbed and further divided to yield
a high Btu gas, lighter hydrocarbons and hydrogen. Generally, any hydrogen recovered
from this stream will be reused in either the liquefaction or hydrogenation step.
The naptha stream may be subjected to further upgrading to yield a good quality gasoline
and the heavier stream/withdrawn through line 28 may be upgraded to produce a heavy
fuel oil or hydrocracked and reformed to yield a gasoline boiling fraction. Generally,
the solvent boiling range material or at least a portion thereof will be catalytically
hydrogenated to increase the concentration of hydrogen donor species and at least
a portion of the hydrogenated fraction will then be used to extract reactive material
from at least a portion of the normally solid bottoms product withdrawn through line
25.
[0030] As indicated supra, the particular separation scheme employed is not critical to
the present invention and, indeed, any of the separation techniques known in the prior
art could be used to affect a separation of the gaseous, liquid and solid products.
For example, the gaseous product could be flashed directly after liquefaction and
the liquid-solid mixture then subjected to separation via distillation, filtration,
extraction, centrifugation or the like. In any case, however, a bottoms product containing
unreacted coal, mineral matter and high boiling hydrocarbons will be available for
extraction with.a solvent separated from the liquefaction product.
[0031] In the preferred embodiment, the solvent fraction withdrawn through line 27 will
be hydrogenated before the same is used either as the extraction solvent or the liquefaction
solvent or diluent. Preferably, the hydrogenation Will be accomplished catalytically
at conditions known to be effective for this purpose in the prior art. In the embodiment
illustrated, hydrogenation is accomplished in hydrogenation vessel 29 with molecular
hydrogen introduced through line 30. The hydrogen actually used may be from any source
but in a preferred embodiment will be produced either through the steam reforming
of at least a portion of the gaseous product from liquefaction, by gasification of
at least a portion of the normally solid bottoms product or by the gasification of
a portion of the solid carbonaceous material being subjected to liquefaction. In the
embodiment illustrated, unreacted hydrogen and the gaseous products of hydrogenation
are withdrawn through line 31. When desired, this gaseous product may be treated to
recover recycle hydrogen. Also in the embodiment illustrated, the hydrogenation product
is withdrawn through line 32. The hydrogenation product includes that portion of the
solvent to be used in the extraction step, that portion of the solvent, if any, to
be returned directly to mixing vessel 10 and any excess solvent that may have been
produced. That portion of the hydrogenation product to be used as a solvent during
extraction is withdrawn through line 39 and the remaining portion of the hydrogenation
product is withdrawn through line 32
1. Any excess solvent may be withdrawn through line 33 as product or stored for future
use during liquefaction. That portion of the solvent, if any, fed directly to mixing
vessel 10 is recycled through line 13.
[0032] Normally, the hydrogenation will be accomplished at a temperature within the range
from about 600°F to about 950°F and a pressure within the range from about 650 to
about 2000 psig, preferably 1000 to 1500 psig. The hydrogen treat rate during the
hydrogenation generally will be within the range from about 1000 to about 10,000 scf/bbl.
Any of the known hydrogenation catalysts may be employed but a nickel moly catalyst
is most preferred.
[0033] In accordance with the improved method of the present invention, the bottoms product
withdrawn through line 25 may be divided and all or a portion thereof subjected to
extraction. The portion to be subjected to extraction will be withdrawn through line
34 and fed to contacting vessel 40. In a preferred embodiment, the entire normally
solid bottoms product will be passed through contacting vessel 40. Any portion of
the bottoms product not subjected to extraction may be withdrawn through line 35 and
processed in accordance with conventional technology. In general, from about 80 to
about 100 weight percent of the bottoms product will be subjected to extraction.
[0034] In contacting vessel 40 the fraction of hydrogenated product from hydrogenation vessel
29 used as the extraction solvent is introduced at or near the bottom of contacting
vessel 40 and flows upwardly through the contacting vessel and is withdrawn at or
near the top thereof through line 41. The bottoms introduced through line 34 flow
generally downwardly and are withdrawn from the contacting vessel at or near the bottom
thereof through line 34'. In the embodiment illustrated, the solvent withdrawn through
line 41 containing the extracted reactive materials is then passed through knock-out
drum 42 to faciliate the separation of any unreactive materials contained-therein.
The unreactive materials will be separated from knock-out drum 42 through line 43'.
The unreactive materials separated in the knock-out drum may then be combined with
unreactive materials separated from the contacting vessel 40 in line 43 and introduced
into separator 46. In the separator, entrained solvent may be flashed overhead and
the remaining portion of the normally solid bottoms product withdrawn through line
48. The recovered solvent, though, not illustrated, may be combined with solvent withdrawn
from knock-out drum 42 or with solvent withdrawn from hydrogenation vessel 29 through
line 32. The solvent, generally free of unreactive materials, is withdrawn from knock-out
drum 42 through line 12 and fed to mixing vessel 10. The remaining portion of the
normally solid bottoms product withdrawn through line 48 may be directly discarded
or otherwise treated in accordance with conventional technology to recover the energy
value thereof.
[0035] As indicated, supra, and in a preferred embodiment, the extraction will be accomplished
at a temperature within the range from about 100 to about 400°F and at a pressure
within the range from about 0 to about 500 psig. In the embodiment illustrated, the
treat rate in contacting vessel 40 will be within the range from about 4 v/v/hour
to 8 v/v/hour. Though not illustrated, contacting vessel 40 could be a stirred vessel
and the entire solvent/normally solid bottoms product could be withdrawn and passed
to a gravity separator. The major portion of the solvent could, then, be separated
by withdrawing the same from the decanting vessel at a point above the solid level.
Solvent entrained in the remaining solids portion could then be separated in the same
manner as illustrated. When a stirred vessel is employed, space velocity is not important
but sufficient contacting time should be allowed to ensure that from about 20 to about
80 weight percent of the reactive material is separated from the normally solid bottoms
product. The reactive material thus separated is recovered with less energy than would
be required with the use of a more conventional solvent such as toluene or the like
which would, normally, be separated and reused in the extraction operation rather
than as a solvent in the liquefaction step.
[0036] Having thus broadly described the present invention and a preferred embodiment thereof,
it is believed that the same will become more apparent by reference to the following
examples. It will be appreciated, however, that the examples are presented solely
for purposes of illustration and should not be construed as limiting the invention.
EXAMPLE 1
[0037] In this example, a run was completed in a 100 pound per day continuous unit using
an Illinois seam coal (Illinois No. 6) as the solid carbonaceous material and a hydrogenated
recycle liquid having an initial boiling point of about 400°F and a final boiling
point of about 800°F and containing from about 40 to about 45 weight percent hydrogen
donor species was used as the extraction solvent and as the solvent or diluent for
liquefaction. The unit was operated in a mode similar to that illustrated in Figure
1. All of the solvent withdrawn from hydrogenation vessel 29 was used to extract bottoms
from the separation vessel. As withdrawn, the bottoms contain 40 weight percent of
toluene soluble material. The bottoms were extracted with the hydrogen donor solvent
at 300°F and 0 psig with a nominal contacting time of 5 minutes. After extraction,
the remaining portion of the normally solid bottoms product contained 10 weight percent
toluene soluble material. Use of the solvent intended for slurry preparation to extract
the bottoms therefore resulted in the recovery of about 75 weight percent of the reactive
material from the bottoms and the gaseous and liquid product yields were increased
accordingly.
EXAMPLE'2
[0038] In this example, a run was completed in a 100 pound per day continuous unit using
an Wyodak coal as the solid carbonaceous material and a hydrogenated recycle liquid
having an intial boiling point of about 400°F and a final bailing point of about 800°F
and containing from about 40 to about 45 weight percent hydrogen donor species was
used as the extraction solvent and as the solvent or diluent for liquefaction. The
unit was operated in a mode similar to that illustrated in Figure 1. All of the solvent
withdrawn from hydrogenation vessel 29 was used to extract bottoms from the separation
vessel. As withdrawn, the bottoms contain 50 weight percent of toluene soluble material.
The bottoms were extracted with the hydrogen donor solvent at 300°F and 0 psig with
a nominal contacting time of 5 minutes. After extraction, the remaining portion of
the normally solid bottoms product contained 10 weight percent toluene soluble material.
Use of the solvent intended for slurry preparation to extract the bottoms therefore
resulted in the recovery of about 80 weight percent of the reactive material from
the bottoms and the gaseous and liquid product yields were increased accordingly.
[0039] From the foregoing it will be apparent that the total conversion of the coal was
increased by about 10-15 weight percent and the yield of both gaseous and liquid products
was increased. This increase was, effectively, accomplished with less equipment and
less energy than would have been required if an additional liquefaction stage were
employed, if the entire bottoms were recycled or if a solvent had been used to extract
the bottoms which would then have been separated via distillation.