Note: Descriptions are shown in the official language in which they were submitted.
~ 2 ~ ~3~
THIS INVENTION relates to the refining of coal. It
relates in particular to a method of refining coal, and to
solvent refined coal (hereinafter also referred to as 'SRC').
According to the invention, there is provided a method
of refining coal, which includes, in a two-step process,
contacting coal with a solvent in a first step, thereby to
refine the coal partially in a first reaction,
removing some of the solvent; and
allowing9 in a second step, the partially refined coal from
the first step to remain in contact with the residual solvent,
for further refining of the coal in a second reaction.
The method may include9 after said second reaction,
removing at least some of the residual solvent, thereby tQ
produce solvent refined coal.
The solvent may be an oil. The oil may be a coal
derived oil-fraction, having a boiling range from about 80C to
about 450C, for example about 200C to about 450C.
The oil-to-oil coal ratio in the first step may be from
abQut 1:, to about 5:1 (on a mass basis), preferably about
3i~
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2:1, so that the oil an~ coal are in the form of an oil/coal
slurry in the first step.
The method may include adding a catalyst to the slurry.
The ratio of catalyst to coal in the slurry in the first s-tep,
may be about 1:50 (on a mass basis). The catalyst may be a
metal-based catalyst.
The contacting in the first step may be effected at a
temperature of about 350C tc about 480C, For example about
400C to 450C, and at a pressure of about 5x103 kPa to about
30x103 kPa, for example about 20x103 kPa. The reaction may be
effected in a hydrogen-rich atmosphere. The reaction time of the
first reaction may be less than 20 minutes, for example about 10
minutes or less.
The removal of the oil may be effected by means of
distillation. The volume of oil distilled off may be such that
the oil and coal residue are still in the form of a slurry in the
second step, and the concentration of the catalyst in the slurry
in the second step is at least twice the concentration of the
catalyst in the slurry in ~he first step.
The contacting in the second step may also be effected
at a temperature of about 350C to about 480C, for example about
400C to 450C, and at a pressure of about 5x103 kPa to about
30x103 kPa, for example ~bout 20x103 kPa. The reaction time of
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the second reaction may be between about 15 minutes and abou-t
150 minutes.
The invention extends also to solvent refined coal
when produced accordin~ to the method hereinbefore described.
Various aspects of this invention are as follows:
A method of solvent refining coal to produce normally
solid solvent refined coal which can be used as a feedstock for
the manufacture of high quality electrode coke, which includes
slurrying pulverized coal with a coal-derived solvent in a
slurrying stage to form a solvent/coal slurry;
subjecting the slurry to a first reactior~ in a first
reaction step;
maintaining the first reaction temperature at between 350C
and 4~0C, the first reaction pressure at between 5x103 kPa and
30xlO kPa, and the first reaction time at less than 20 minutes,
thereby to liquefy substantially all of the coal, and to refine
the coal partially;
removing some o~ the solvent in a solvent removal stage to
produce a residual slurry which comprises mainly residual solvent
and liquefied, partially refined coal, with no cooling of
hydrocarbon liquid effluent before or after the solvent removal
stage being effected, no hydrocarbon liquid solvent being added
to the slurry before or after the solvent removal stage and no
residual slurry being recycled back to the first reaction step;
subjecting the residual slurry to a second reaction in a
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second reaction step, under hydrogenative conditions;
maintaining the second reaction temperature at between 350C
and 480C with the temperature not being substantially lcwer tllan
that in the first stage, the second reaction pressure at between
5x103 kPa and 3nX103 kPa, and the second reaction time at between
15 and 150 minutes to refine the coal further; and
removing at least some of the residual solvent, thereby
producing, as a bottoms product, normally solid solvent refined
coal which is suitable as a coking feedstock capable of being
formed directly by coking and calcining into coke having a
coefficient of thermal expansion of less than 0,7xlO 6, with none
of this bottoms product being recycled to the first step.
A method OT producing a feedstock suitable for the
manufacture of high quality electrode coke, which includes
slurrying pulverised coal ~ith a coal-derived sol~ent in a
slurrying stage to form a solvent/coke slurry,
subjecting the slurry to a first reaction in a first
reaction step;
maintaining the first reaction temperature at between 350C
and 480C, the first reaction pressure at between 5X103 kPa and
30x10 kPa, and the first reaction time at less than 2Q minutes,
thereby to liquefy su~stantially all the coal~ and to refine the
coal partially;
removing some of the solvent in a solvent removal stage to
produce a residual slurry which comprises mainly residual solvent
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and liquefied, partially refined coal~ with no cooling of
hydrocarbon liquid effluent before or after the solvent removal
stage being effected, no hydrocarbon liquid solvent being added,
to the slurry before or after the solvent removal stage and no
residual slurry being recycled back to the first reaction stepi
subjecting the residual slurry to a second reaction in a
second reaction step, under hydrogenative conditions;
maintaining the second reaction temperature at between 350C
and 480C with the temperature not being substantially lower than
that in the first stage, the second reaction pressure at between
5x103 kPa and 30x103 kPa, and the second reaction time at between
15 and 150 minutes to refine the coal further~ and
removing at least some of the residual solvent, thereby
producing a bottoms product which is a suitable coking feedstoc~
capable of being formed directly by coking and calcining into
coke having a coefficient of thermal expansion of less than
0,7x10 6, with none of this bottoms product beiny recycled to the
first step.
The single FIGURE in the drawing shows a schematic flow
diagram of a process for producing solven-t refined coal,
utilizing the method of the present invention.
In the drawing, reference numeral 10 generally
indicates a process for produçing solvent refined coal.
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The process 10 includes a pretreatment stage 18. Into
the pretreatment stage 18 is fed, via a flowline 12, powdered
coal (for example, coal containing 36% (by mass) volatiles and
10% (by mass) ash). Into the pretreatment stage 18 is also fed,
via flowline 16, 2% (by mass3 Fe203 on coal, as an added
catalyst. Finally, to the pretreatment stage 18 is fed, via a
Flowline 14 9 ,ecycle solvent (the production of which is
described in more detail hereunder) comprising a coal-derived oil
fraction having a boiling range of from about 200C to about
420C. Sufficient solvent is added via the flowline 14 to form a
slurry having a solvent-to-oil ratio oF about 2:1 (on a mass
basis), in the pretreatement stage 18.
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The slurry is fed from ~he pretreatment stage, via a
flowline 19, into a first reaction step or stage 20. In the
reaction stage 20, the coal is contacted with the solvent in a
hydrogen-rich atmosphere for a short period up to 15 minutes at a
pressure of about 20x103 kPa and at a temperature of about 425C,
to liquefy or dissolve the coal and to refine it partially in a
first reaction.
The slurry from the stage 20 is then fed, via flowline
21, to a gas separation stage 22 in which gases (such as, C0~
C02, H20 and C1 3) evolved in the stage 20 are separated from the
slurry and removed via a flowline 23.
The slurry is thereafter fed, via a flowline 25, into a
distillation stage 24. In the distillation stage 24, sufficierlt
solvent is distilled off so that a residual slurry ~comprising
mainly partially refined coal, catalyst, undissolved matter and
solvent) having a catalyst concentration about three times higher
than the catalyst concentration in the slurry fed lnto the stage
20, is produced. The solvent distilled off is withdrawn from the
stage 24 and fed, via a flowline 26, into the flowline 14.
Hence, this solvent constitutes part of the recycle solvent to
the stage 18.
The residual slurry is withdrawn from the stage 24 and
fed, via a flowline 28, into a second reaction step or stage 30.
In this stage 30~ the partially refined coal is contacted with
th~ residual solvent for 60-120 minutes at a temperature of
425-445C and at a hydrogen pressure of about 20x103 kPa, to
refine the coal fur~her in a second reaction.
The slurry product from the stage 30 is then fed, via a
flowline 31, into a further gas separating stage 32. In the
stage 32, further gases evolved in the stage 30, are separated
from the slurry product, and removed via a flowline 33.
The slurry product is then fed, via a flowline 34, into
a solid remoYal stage 36. In stage 36, undissolved matter is
separated from the liquid product, and removed from the process
via a flowline 35.
Finally, the liquid product from the stage 36 is fed,
via a flowline 37~ into a further distillation stage 40. In the
stage 40, further solvent is distilled off and withdrawn from the
stage 40 via a flowline 38. A portion of this solvent is routed
to the flowline 14 so that sufficient solvent passes along the
flowline 14 to the pretreatment stage 18. The remaining solvent
is withdrawn from the process via the flowline 42 for external
use. SRC (which is a solid pitch-like material under ambient
conditions) is withdrawn from the stage 40, via a flowline 44,
and can be worked up further (not shown) to produce a superior
quality coke for the manufacture of electrodes.
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It is to be understood that, in the stages 24 and 40 a
liquid fraction having a boiling range of about 80C-200C is
also distilled off (not shown).
The invention will now be described by way of the
following non-limiting Examples:
EXAMPLE 1
1.1 A bituminous coal, containing 36X (by mass~ volatiles and
10% (by mass) ash, was powdered and slurried with 2 parts
(by mass) of a coal-derived oil fraction (solvent) having a
boiling range of from about 200C to about 420C. 1500 gms of
this slurry was reacted in a S litre autoclave with 2% (by mass)
Fe203 on coal as an added catalyst. In a first step, the coal
was contacted with the solvent in a hydrogen-rich atmosphere for
10 minutes at a pressure of about 20x103 kPa and a temperature of
425C, to refine the coal partially. Thereafter, sufficient
solvent was distilled off until a slurry having a catalyst
concentration which was about three times higher than the
catalyst concentration in slurry of the first step, remained in
the autoclave. The now partially refined coal (i.e. the coal
residu2) was allowed to remain in contact with the residual
solvent for a further 120 minutes in a second step at a
te~perature of 425C and a pressure of about 20x103 kPa, for
further refining. The autoclave ~as then cooled down and the
contents worked up to recover the solvent refined coal (eg
unreacted products removed and distillable oils recovered~.
~~23~ $
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1.2 1500 gms of the slurry of 1.1 was gain reacted in a 5 litre
autoclave with 2~ (by mass) Fe203 on coal as an added
catalyst. The reaction conditions were the same as for the first
step in 1.1. However, the reaction time in the first step was
increased to 130 minutes, and no solvent was thereafter distilled
off, ie the second step was not performed.
A comparison of the products obtained from 1.1 and 1.2
above (calculated as nett mass percentages on dry ash-free coal)
is as follows:
Ex~eriment 1.1 Ex~eriment 1.2
C0 + C02 3,1 2,0
H2 8,0 7,2
Cl - C3 8,2 11~7
C4 - ?00C 14 91 25,9
200 - 420~ 16,0 -17~
SRC ~420C plus) 42,2 67,9
Undissolved 2~3 3~2
The SRC obtained from both experiments was coked at 500C ~5
hours heating time and 4 hours coking time) and calcined for 30
minutes at 1 370C.
The coefficient of thermal expansion was determined for the
calcined coke by means of the X-ray diffraction method. The
coefficient of thermal expansion (CTE) was 0~4 x 10 6 for the
calcined coke obtained ~rom Experiment 1~1, and 0~7 x 10 6 for
the calcined coke obtained from Experiment 1.2.
From the above resul~s 9 it can be seen that a superior
quality coke is obtained from the two-step method of the present
invention. Furthermore, -the two-step method is self-sufficient
as regards solvent requirements. Experiment 1.2 gave coke of a
poorer quality and there was a large deficiency in process
solvent.
EXAMPLE 2
_________
1500 gms of the slurry of Example 1 was again reacted in a 5
litre autoclave with 2% (by mass) Fe203 on coal as an added
catalyst. In a first step, the coal was contacted with the
solvent in a hydrogen-rich atmosphere for 10 minutes at a
pressure of about 20x103 kPa and a temperature of 425C.
Thereafter, suf~icient solvent was distilled off until a slurry
having a catalyst concentration which was about 3 times higher
than the catalyst concentration of the slurry of the first step,
remained in the autoclave. The temperature of the autoclave was
raised to 445C, and the contactins continued for a further 60
minutes in a second step, at a pressure of about 20x103 kPa.
The following product spectrum was obtained (calculated as nett
mass percentages on dry ash-free coal):
C0 + C02 2,4
~ 8,5
~3~
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Cl - 3 13,2
C4 - 200C 20~9
200-420C 14,4
SRC (420C plus) 38,5
Undissolved 2,2
Calcined coke was produced from the SRC in the same way as in
Example 1, and was again of high quality, havin~ 2 CTE value of
0,4 x 10 6. This method yielded 35% liquid products in the
diesel and petrol boiling range ~C4-200C and 200C-420C
respectively).
EXAMPLE 3
_______
1500 gms of the slurry of Example 1 was again reacted in a 5
litre autoclave with 2% (by mass) Fe203 on coal as a catalyst,
under the same reaction conditions as in Example 2, in first and
second steps similar to those described hereinbefore with
reFerence to Example 2. The only difference was ~hat the
reaction time of the second step was increased from 60 to 120
minutes, thereby to increase the production of liquid fuels.
The following product spectrum was obtained (calculated as nett
mass percentages on dry ash-free coal):
~ + C~2 2,7
~2 ~,6
Cl - 3 13,5
~.~23~
C4 - 200C 20,4
200 - 420C 17,3
SRC (420C plus) 35,3
Undissolved 2,4
The total yield of liquid products was 37,7% while the CTE value
oF calcined coke produced from the SRC, was 0~3 x 10 6.
EXAMPLE 4
Again, 1500 gms of the slurry of Example 1 was used, and to this
was added 2% (by mass) Fe203 on coal as an added catalyst. Both
the first and second stPps were effected in a continuous flow
reactor. For the first step, a 1 litre autoclave was used, while
for the second step a vertical open tube reactor having a 25 mm
diameter was used. The reaction time was 15 minutes in the
autoclave and 120 minutes in the open tube reactor. The contact
temperature and pressure for both steps was 425C and 20x103 kPa
respectively. The following produc~ spectrum was obtained
(calculated as nett mass percentages on dry ash-free coal):
C0 ~ C02 2,8
~ 10,0
C1 - 3 8,4
C4 - 200C 19,3
200 - 420C 20,3
SRC ~420C plus~ 37/8
Undissolved 1,4
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Calcined coke wi~h a CTE value of 0,4 x 10 6 was produced from
the SRC as hereinbefore described.
The 200-420C fraction recovered after the first and
second steps can be recycled (ie used to form the slurry for the
first step). Excess oil can be used elsewhere, eg it can be
up-graded to diesel oil.
The Applicant is aware that SRC, which is a solid
pitch-like material under ambient conditions and which has
hitherto normally been obtained by direct hydrogenation of coal,
can be used as a feedstock for producing coke via a delayed
coking process. The so-produced green coke can be calcined and
can thereafter be used to manufacture electrodes.
The quality of the electrodes depends to a large extent
on the degree of depolymerisation of the original or raw coal
used.
The Applicant is aware of methods of depolymerizing
coal which comprises solvation of coal with a solvent in a single
step. During the solvation, the coal is depolymerised, but coal
fragments have a strong tendency to combine with solvent
molecules or fragments in side reactions, thus resulting in a
shortage in recycle solvent. To prevent or reduce the occurrence
of these unwanted side reactions, a good catalyst system and high
hydrogen pressure are normally used~ Prolonged reac~ion times,
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which are necessary to decrease the heteroatom content under
these conditions, lead to high yields of liquid and gaseous
products and subsequently low yields oF so!id SRC. If, on the
other hand, the SRC production is maximised by using short
reaction times, this product still contains too high a heteroatom
content to make it suitable for the manufacture of high quality
electrode coke.
During the depolymerization reaction~ gases such as
hydrogen sulphide, carbon dioxide~ carbon monoxide, ammonia and
water are evolved which indicates that the heteroatoms sulphur,
nitrogen and oxygen are liberated from the coal molecules during
polymerization.
Without wishing to be bsund by theory, the Applicant
believes that heteroatoms in the molecular structure of a coking
feed hinder the graphitisation thereof at higher temperatures, by
increasing the viscosity and decreasing the plastic range of the
mesophase (J Dubois, C Aquache and J L White - Metallography 3
(1970) 337-360. Hydrocracking is then needed to decrease the
hetero atom content of the solvent refined coal as far as
possible.
In US Patent 4 210 517 of the Mitsui ~ining Company
Limited and the Mitsui Coke Company Limited, the ratio of
N___S___0 is correlated with the quality of the calcined coke and
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it was shown that the lowest values correspond with the better
quality coke. This shows again that the hetero atom content or
the basic 'pitch' must be low and the carbon content high.
In the methods known to the Applicant, either a low
yield of good quality SRC or a high yield of poor quality SRC is
obtained.
The Applicant believes that in the two-step method
provided by this invention (in which said side reactions are
minimized or reduced as a result of the removal of some of th~
solvent of the first step), the reaction conditions can be chosen
so that (i) a high yield of high quality SRC (ie low hetero atom
content), and self-sufficiency as regards solvent requirements,
can be obtained, or (ii) a lower yield of high quality SRC with a
high yield of liquid products9 can be obtained. The SRC will be
suitable for thc manufacture of high quality electrode coke.
The Applicant further believes that large quantities of
high quality SRC and self-sufficiency as regards solvent
requirements can be obtained by means of the two-step method of
the invention, ~ithout the use of the added metal-based catalyst
(ie utilizing only the natural catalytic activity present in the
coal). However9 subs~antially equally large quantities of high
quality SRC and a similar degree of self-sufficiency as regards
solvent requirements can be obtained when a metal-based catalyst
is used, in which case a higher reaction temperature and shorter
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reaction time can be utili~ed to obtain a similar product
spec~rum. By using a metal-based catalyst and altering the
reaction conditions in the first and second steps, the amount of
liquid products obtained can be varied.
This process also has the advantage that a lower
initial catalyst concentration can be used (as compared with
known processes), resulting in lower overall catalyst usage than
is possible with said known processes.
