Note: Descriptions are shown in the official language in which they were submitted.
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COAL WATER SLURRY AND METHODS FOR MAKING THE COAL WATER
SLURRY
BACKGROUND
This invention relates generally to coal water slurry and methods for making
the coal
water slurry. More particularly, this invention relates to particle size
distribution of coal
in coal water slurry and methods for making the coal water slurry.
In coal gasification fields, two types of methods are usually employed to
supply coal to a
gasifier for gasification. One is pneumatically transporting pulverized coal
with
pressurized nitrogen and spraying the coal into a gasifier. Another is
preparing a slurry
of coal and water, which hereinafter is referred to as "coal water slurry,"
and supplying
the coal water slurry to a gasifier. The "coal water slurry" method has been
widely used
because it is more reliable, easy transportable and adaptable to a higher
gasification
pressure than the method employing coal in a dry state.
Generally, higher coal concentration of a coal water slurry leads to higher
gasification
efficiency and lower consumption of coal and oxygen. Thus, during preparation,
it is
desirable to have higher concentration of the coal so as to economically
gasify the coal
water slurry.
There have been attempts to increase the coal concentration. For example,
particle size
distribution of coal in the coal water slurry may be modified to increase the
coal
concentration. However, in some current applications, the coal concentration
may not be
as high as desirable and may cause undesirable viscosity in the coal water
slurry with the
increase of the coal concentration in the water slurry concentration by
modification of the
coal particle size distribution.
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Therefore, there is a need for new and improved coal water slurry and methods
for
making the coal water slurry to increase the coal concentration and avoid
undesirable
viscosity.
BRIEF DESCRIPTION
A coal water slurry is provided in accordance with one embodiment of the
invention.
The coal water slurry comprises smaller and larger coal particles. The smaller
coal
particles are in a range of from about 20wt% to about 90wt% of the coal in the
coal water
slurry and comprise a mean particle size smaller than 26 m. The larger coal
particles are
in a range of from about l Owt% to about 80wt% of the coal in the coal water
slurry and
comprise a mean particle size in a range of from 50 m to 200 m.
A method for making a coal water slurry is provided in accordance with another
embodiment of the invention. The method comprises milling smaller coal
particles in a
range of from about 20wt% to about 90wt% of the coal in the coal water slurry
and
comprising a mean particle size smaller than 26 m, milling larger coal
particles in a
range of from about 10wt% to about 80wt% of the coal in the coal water slurry
and
comprising a mean particle size in a range of from 50 m to 200 m, and mixing
the
smaller coal particles, the larger coal particles, and water.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other aspects, features, and advantages of the present
disclosure will
become more apparent in light of the following detailed description when taken
in
conjunction with the accompanying drawings in which:
FIG. 1 is a schematic diagram of a coal particle size distribution in a coal
water slurry in
accordance with one embodiment of the invention;
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FIG. 2 is an experimental diagram illustrating comparison of correlations of
coal
concentration and viscosity with and without smaller coal particles in the
coal water
slurry; and
FIGS. 3-6 are schematic flow charts illustrating preparation of the coal water
slurry in
accordance with various embodiments of the invention.
DETAILED DESCRIPTION OF THE DISCLOSURE
Preferred embodiments of the present disclosure will be described hereinbelow
with
reference to the accompanying drawings. In the following description, well-
known
functions or constructions are not described in detail to avoid obscuring the
disclosure in
unnecessary detail.
FIG. 1 illustrates a schematic diagram of a particle size distribution of coal
for producing
a coal water slurry in accordance with one embodiment of the invention. As
used herein,
the term "coal water slurry" may indicate a mixture of certain amounts of
coal, water and
additives for producing energy used in generating electricity, heating,
support processing,
and manufacturing. In recent years, use of coal water slurry has become an
alternative to
use of conventional fuel oil and coal.
Typically, a coal water slurry may comprise from about 55wt% to about 70wt% of
coal
particles, from about 30wt% to about 45wt% of water, and less than about lwt%
of
additives. It should be noted that embodiments of the invention do not limit
to any
particular type of coal or additives for the coal water slurry. Non-limiting
examples of
additives include alkylnaphthelene sulfonate and polyoxyalkylene alkyl ether.
Generally, it is desirable to increase the coal concentration in the coal
water slurry so as
to improve gasification efficiency and reduce consumption of coal and oxygen.
Higher
coal concentration may be produced by pulverizing coal into a suitable
particle size
distribution while selecting suitable additives and appropriately mixing the
coal, water
and additives to manufacture the coal water slurry with suitable
concentration, viscosity,
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stability, and quality. In embodiments of the invention, the coal particle
size distribution
in the coal water slurry may be selected so that smaller coal particles are
dispersed into
spaces between larger coal particles so as to increase the coal concentration
in the coal
water slurry.
As illustrated in FIG. 1, the particle size distribution of the coal 10 for
producing the coal
water slurry may comprise smaller coal particles 12 in a range of from about
20wt% to
about 90wt% of a weight of the coal 10 and having a mean particle size smaller
than
about 26 m, and larger coal particles 11 in a range of from about IOwt% to
about 80wt%
of the weight of the coal 10 and having a mean particle size in a range of
from about
50 m to about 200 m. In some applications, the particle size distribution of
the coal
may comprise the small coal particles 12 in a range of from about 30wt% to
about 90wt%
and the larger coal particles 11 in a range of from about IOwt% to about 70wt%
of the
weight of the coal 10, respectively. As used herein, wt% means a weight
percentage.
In other applications, the particle size distribution of the coal 10 may
comprise the small
coal particles 12 in a range of from about 40wt% to about 90wt% and the larger
coal
particles 11 in a range of from about l Owt% to about 60wt% of the weight of
the coal 10,
respectively. In certain applications, the particle size distribution of the
coal 10 may
comprise the small coal particles 12 in a range of from about 50wt% to about
75wt% and
the larger coal particles 11 in a range of from about 25wt% to about 50wt% of
the weight
of the coal 10, respectively.
Additionally, in some examples, the smaller coal particles 12 may have a mean
particle
size smaller than about 25 m, about 20 m, or about 15 m. In other examples,
the
smaller coal particles 12 may have a mean particle size smaller than about I0
m or about
m. In certain examples, the smaller coal particles 12 may have a mean in a
range of
from about 5 m to about 15 m. Alternatively, the smaller coal particles 12 may
have a
mean in a range of from about 10 m to about 15 m, or from 5 m to about 10 m.
The
larger coal particles 11 may have a mean particle size in a range of from
about 50 m to
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about 70 m, from about 70 m to about 140 m, from about 90 m to about 140 m,
from
about 100 m to about 140 m, or from about 140 m to about 200 m.
Accordingly, after mixing, the smaller coal particles may be dispersed between
the larger
coal particles so as to increase the coal concentration of the coal water
slurry to be
produced. In some embodiments, the coal may comprise one or more of high rank
coal,
such as bituminous and anthracite, and low rank coal, such as sub-bituminous
coal and
lignite. In some examples, the coal particle distribution may comprise a
mixture of the
smaller low rank coal particles and the larger high rank coal particles, or
the smaller high
rank coal particles and the larger low rank coal particles. In one non-
limiting example,
both types of coal particles comprise low rank coal, such as the sub-
bituminous coal and
the lignite. Since the cost of low rank coal is lower, it may be cost-
effective in some
examples to produce the coal water slurry having higher coal concentration
using the low
rank coal.
Table-1 illustrates an experimental example of the coal particle size
distribution for
producing a coal water slurry in accordance with one embodiment. In this
example, the
coal comprises a low rank coal.
Table-1 Coal particle size distribution
Mesh Particle size ( m) Weight percentage (wt%)
>8 >2500 0
8-14 1400-2500 3
14-40 850-1400 12
40-325 45-850 60
325-540 26-45 12.5
<540 <26 50
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As can be seen from Table-1, the coal comprises about 50wt% of the smaller
coal
particles and about 50wt% of the larger coal particles. Particle sizes of the
smaller coal
particles are less than 26 m, and particle sizes of the larger coal particles
in the range of
from about 26 m to about 2500 m. For the embodiments of the invention, the
smaller
coal particles have a mean particle size smaller than 26 m. The larger coal
particles have
a mean particle size in a range of from about 50 m to about 200 m based on
distribution
of the weight percentages and the particle sizes thereof, as mentioned above.
FIG. 2 is an experimental diagram illustrating comparison of correlations of
the coal
concentration in the coal water slurry and viscosity with and without the
smaller coal
particles in the coal particle size distribution in accordance with one
embodiment. As
illustrated in FIG. 2, lines 13-14 illustrate the correlations of the coal
water slurry
concentration and the viscosity without and with the smaller coal particles,
respectively.
As can be seen from the line 13, at a point 15, in the initiation of
production of the coal
water slurry, the coal concentration in the coal water slurry is less than
46%. With the
amount of the coal increasing, the coal concentration reaches about 50% at a
point 16
where the viscosity there of is less than 600cp. However, during preparation
of the coal
water slurry without the smaller coal particles, the flowability of the coal
water slurry
becomes worse at the point 16 such that it becomes disadvantageous to increase
the coal
concentration further in the coal water slurry.
For the line 14, under the similar operating conditions as those for the line
13, in the
initiation, at a point 17, since the smaller coal particles are mixed with the
larger coal
particles, the coal concentration in the coal water slurry reaches about 54%.
With the
amount of the mixed coal increasing, the coal concentration reaches above 56%
at a point
18 where the viscosity thereof exceeds 1400cp. Then, a certain amount of the
additives
may be added to decrease the viscosity of the coal water slurry to about
1300cp at a point
19, which is suitable for the flowability of the coal water slurry.
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Accordingly, for the comparison of the lines 13-14 illustrated in FIG. 2, the
coal water
slurry having the mixture of the smaller coal particles and the larger coal
particles may
have the higher coal concentration and higher flowability than the coal water
slurry
without mixture of the smaller coal particles.
FIGS. 3-6 illustrate schematic flow charts illustrating preparation of the
coal water slurry
in accordance with various embodiments of the invention. As illustrated in
FIG. 3,
during preparation, according to a determined proportion of the smaller coal
particles and
the larger coal particles, certain amounts of starting coals 20, 21 are
introduced into a
coarse mill 22 and a fine mill 23 for milling, respectively.
It should be noted that in some applications, one or more coarse mills 22 and
one or more
fine mills 23 may be employed although one coarse mill 22 and one fine mill 23
are
illustrated in FIG. 3. The particle sizes of the starting coals 20, 21 may be
less than 3mm.
Although two starting coals 20, 21 are illustrated in FIG. 3, one or more
starting coal
supply sources (not shown) may be employed to provide one or more starting
coals 20,
21.
For the illustrated arrangement in FIG. 3, the coarse mill 22 is for wet
milling of the
starting coal 20 and the fine mill 23 is for dry milling of the starting coal
21. In non-
limiting examples, the coarse mill 22 and the fine mill 23 may comprise ball
mills, and
the particle sizes of the starting coals 20, 21 may be different and not less
than 3mm. In
certain applications, either or both of the starting coals 20, 21 may comprise
one or two
of the low rank coal and the high rank coal, and the starting coals 20, 21 may
be the same
or different from each other. In one non-limiting example, the starting coals
20, 21 are
the same low rank coal.
Accordingly, after the starting coals 20, 21 are introduced into the coarse
mill 22 and the
fine mill 23, respectively, according to determined particle size distribution
of the smaller
and larger coal particles, the fine mill 23 mills the starting coal 21 to
produce the dry
smaller coal particles having a mean particle size less than about 26 m.
Meanwhile, with
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introduction of the starting coal 20 into the coarse mill 22, determined
amounts of water
24 and additives 25 are also introduced into the coarse mill 22 to produce a
coarse coal
water slurry comprising the large coal particles having a mean particle size
in the range of
from about 50 m to about 200 m.
Subsequently, the dry smaller coal particles from the fine mill 23 and the
coarse coal
water slurry from the coarse mill 22 are introduced into a mixing vessel 26
for mixing to
produce the coal water slurry with higher concentration for further
processing, for
example, for introduction into a gasifier 27 to produce energy. For some
arrangements,
during mixing, a mixer (not shown) may be employed to mix the dry smaller coal
particles and the coarse coal water slurry within the mixing vessel 26, and
feed rates of
the dry smaller coal particles may be controlled into the mixing vessel 26 so
as to ensure
the water in the coarse coal water slurry to contact with the smaller coal
particles and the
smaller coal particles to disperse between the larger coal particles.
In certain applications, as illustrated in FIG. 3, before the coal water
slurry with higher
coal concentration is introduced into the gasifier 27 for processing, a filter
28 may be
employed to receive and filter the coal water slurry from the mixing vessel 26
to remove
impurities, such as rock in the coal water slurry, which is advantageous for
processing of
the coal water slurry in a gasifier. Alternatively, the filter 28 may not be
employed.
FIG. 4 illustrates a schematic flow chart of the preparation of the coal water
slurry in
accordance with another embodiment of the invention. The arrangement in FIG. 4
differs
from the arrangement in FIG. 3 in that the mixing vessel 26 in FIG. 3 is not
employed in
the arrangement in FIG. 4. For the arrangement in FIG. 4, the dry smaller coal
particles
from the fine mill 23 are introduced into the coarse mill 22 to mix with the
larger coal
particles, water and the additives while the starting coal 20 is milled in the
coarse mill 22.
In certain applications, a mixing vessel may also be employed behind the
coarse mill 22.
Again, a filter 28 may optionally be used before the coal water slurry is sent
to the
gasifier 27.
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FIG. 5 illustrates a schematic flow chart of the preparation of the coal water
slurry in
accordance with yet another embodiment of the invention. In the arrangement in
FIG. 5,
during preparation of the smaller coal particles in the fine mill 23, certain
amounts of
water 29 and optionally additives 30 are also introduced into the fine mill 23
while the
starting coal 21 is milled in the fine mill 23 to mix with the smaller coal
particles. In
some applications, one or more water supply sources and one or more additive
supply
sources may be employed to provide the water 24, 29 and the additives 25, 30
respectively. The water 24, 29 and the additives 25, 30 may be the same or
different
from each other. In some applications, the additives 25 and/or 30 may only be
introduced
into one of the mills or may be introduced into the mixing vessel 26.
In the arrangement of FIG. 6, all of the starting coal 31 is introduced into
the coarse mill
22 for wet milling. During milling, a certain amount of a coarse coal 32 from
the coarse
mill 22 is introduced into the mixing vessel 26, which acts as the larger coal
particles, and
another amount of the coarse coal from the coarse mill 22 flows into the fine
mill 23 for
further wet milling to produce the smaller coal particles. Then, the smaller
coal particles
are mixed with the larger coal particles from the coarse mill 22 in the mixing
vessel 26 to
produce the coal water slurry with higher concentration. In certain
applications, certain
amounts of water and additives may be added into either of the mills or into
the mixing
vessel.
In embodiments of the invention, from about 20wt% to about 90wt% of the
smaller coal
particles 12 having a mean particle size smaller than 25um may be mixed with
from
about I Owt% to about 80wt% of larger coal particles 11 having a mean particle
size in the
range of from about 50 m to about 140 m so as to produce the coal water slurry
with
higher coal concentration. In some applications, low rank coal may be used to
produce
the coal particle size distribution so as to produce the coal water slurry
with higher coal
concentration, which is cost effective. In addition, during preparation of the
coal water
slurry, wet milling and/or dry milling may be employed so as to improve system
flexibility to produce the coal water slurry.
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While the disclosure has been illustrated and described in typical
embodiments, it is not
intended to be limited to the details shown, since various modifications and
substitutions
can be made without departing in any way from the spirit of the present
disclosure. As
such, further modifications and equivalents of the disclosure herein disclosed
may occur
to persons skilled in the art using no more than routine experimentation, and
all such
modifications and equivalents are believed to be within the spirit and scope
of the
disclosure as defined by the following claims.
