Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR RECOVERING
FINE GR~NULATED COAL BY FLOTATION
Background of the Invention
The present invention xelates to a method for
recovering fine granulated coal and more particularly to
a method for forming a water slurry of fine granulated
coal from a water slurry of fine powder coal containing
mineral matter and then recovering the fine granulated
coal from its water slurry by flotation.
The art of dressing coal from mineral matter
by flotation has been commercially completed for example
in the technology of dressing coal of a high coalification
degree for coke making, for example coking coal.
With so-called steam coal of a low
coalification degree in comparison to coking coal such
as bituminous coal of low rank, sub-bituminous coal,
brown coal and lignite~ the flotation method is incom-
plate technologically for the following reason: With
such coal, their hydrophillic properties increase with a
lowering in their coalification degrees, so that the coal
has the defects that a recovering efficiency for it by
flotation lowers and also inclusion of mineral matter by
froth more increases. As coal-dressing technologies by
flotation for fine powder-shaped steam coal having a
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particle si~e of about 80~ by weight of powder passing
through 200 meshes, there exist considerably the ones on
the course of development and such ones as may become
extinct in a short period of time after appearance, but
there are not yet existent comple~ed flotation
technologies for the steam coal that are free from the
above-mentioned defects.
On the other hand, as a coal-dressing
technology for fine powder~shaped steam coal, there can
be cited a so-called OA (Oil Agglomeration) method when
an economical efficiency is not taken into account. The
OA metnod is a method for agglomerating fine powder coal
to manufacture granulated coal, using as a binder at
least 20% by weight of hydrocarbon oil based on pure
coal weight with the amount of the hydrocarbon oil
varying with the quality of coal. Granulated coal of
size of 0.5 - 3 mm is obtained by the OA method and
separation of the granulated coal from the slurry mother
liquid and removal of mineral matter from the granulated
coal are both good. The OA method, however, can be said
to be lacking in economical efficiency today when
hydrocarbon oil is expensive, for it uses a large amount
of hydrocarbon oil expensive as compared with steam coal
as the binder.
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If an attempt to raise the economical
efficiency of the OA method is carried out by reducing
the amount of binder used to 10 - 15% by weight based on
the pure coal, only granulated coal of a size of about
100 - 200 ~m is obtained, so that problems arise that
the granulated coal cannot be separated or the separation
efficiency is only extremely low with use of a vibration
screen or screen-based type centrifugal mechanical dryers
utilized in the OA method.
Summar~ of the Invention
The first object of the present invention is
to provide a method for recovering fine granulated coal
by flotation.
The second object of the present invention is
to provide a method for recovering fine granulated coal
with good separation properties, using a reduced amount
of binder used.
The third object of the present invention is
to provide a method having an improved economical
efficiency in separation and recovery of fine granuiated
coal.
The fourth object of the present invention is
to provide a method for recovering fine granulated coal
that is applicable independent of the kind of coal.
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Such objects of the present invention are
achieved by stirring the water slurry of fine powder
coal with 5 20% by weight of a binder added based on
the weight of coal to manufacture the water slurry of
fine granulated coal of size of 100 - 250 ~m and then
adding 100 - 200 ppm of a frother or a flotation agent
with a frother base based on the weight of the above-
mentioned fine granulated coal to the water slurry of
the fine granulated coal to recover the granulated coal
by flotation.
Drawings
The drawings is a flow sheet showing an example
of the present invention.
The Preferred Embod _ nts
The present invention is described on the basis
of the flow sheet shown in the drawing hereinafter.
In the present invention, first, raw coal (1)
is pulverized with a mill (2) to manufacture fine powder
coal (3). As raw coal, bituminous coal, sub-bituminous
coal, brown coal and lignite can all be used independent
of the kind of coal.
Besides the raw coal, coal, coke, petroleum
coke and the like scattered on floors and devices (which
are termed coal to be swept hereinafter) are collected
for example with a dust collector and can be used for the
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present invention. Conventionally, the coal to be swept,
when collected, has simply been discarded as waste,
disadvantageGusly. According to the present invention,
however, the coal to be swept is put into u~e, usually
after nails, iron pieces and the like included have been
removed away with a magnet or the like.
The fine powder coal (3) is usuall~ pulverized
so as to have a particle size of 70 - 80% by weight of
coal powder passing through 200 meshes. If the raw coal
has such particle size as a result of pulverization which
may take place not mechanically but naturally during the
coal preparation or coal to be swept already has such a
particle size, it is unnecessary to further operate
pulverization.
The mill (2) is not specially restricted so far
as the resulting fine powder coal (3) has a particle size
within the above-mentioned range, and the mill (2) may be
a dry mill or a wet mill.
Next, in this process, the resultin~ fine
powder coal (3) is fed into a mixing tank (4) to form a
water slurry of the fine powder coal with a binder (5)
added. An order for adding water (6) and a binder (5)
is not specially restricted. For example, water (6) is
first added to the fine powder coal (3) to form a water
slurry of the fine powder coal and then a binder (5) may
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be added to the slurry. In contrast to this, after a
binder (5) has been added to the fine powder coal,
water (6) may be added to the fine powder coal.
As binder (5), normally use is made of
hydrocarbon oils, more specifically, petroleum-containing
oils such as crude oil, heavy oil and light oil, frac-
tions corresponding to the above-mentioned petroleum-
containing oils in liquid fractions resulting from
hydrogenation lique~action of coal, and vegetable oils
such as bean oils and cottonseed oils. Besides such
hydrocarbon oils, also ~seful are hydrophobic s~nthetic
polymers having a hydrophilic functional group, for
example polypropyleneglycol monomethyl ether, various
other oils such as lubricating oils and working oils for
hydraulic devices in factories, thermal power stations
and iron mills, and waste oils from factories.
Further, according to the present invention,
it is also possible to add a dispersing agent as an
auxiliary member to the above binder (5).
~he dispersing agent may be any of such as
alkanol amide type nonion (polyethyleneglycolether or
ester) surface active agent, sulfuric acid ester type
anion surface active agent and quaternary ammonium type
cation surface active agent, and the amount to be added
of the dispersing agent is preferably within the range
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of 200 to 800 ppm or, more preferably, 200 to 300 ppm
based on the weight of the pure coal in the fine powder
coal (3) A
The dispersing agent has a function to increase
the specific surface area of the binder (5).
The concentration of fine powder coal in a
water slurry (7) of the coal is 20 - 40% by weight and
may be appropriately selected within the range of concent-
ration.
Further, the amount of a binder (5) added is
5 - 20% by weight based on the amount of pure coal in raw
coal (1), and it is preferably 5 - 15% by weight if an
economical efficiency is taken into account. With an
amount to be added of the binder (5) less than 5% by weight
based on the amount of pure coal, the efficiency is adver-
sely affected of the separation of coal matter from mineral
matters in the slurry, and when the amount in reference
exceeds 20~ by weight, the economical efficiency is lowered
particularly when a hydrocarbon oil is used as the binder,
so that an amount of binder used exceeding 20% by weight is
not desirable.
Next, the water slurry (7) of fine powder coal
with a binder added is fed into a granulator (8) and is
stirred to granulate the fine powder coal, and thus the
water slurry (9) offine granulated coal is formed.
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As a granulator (8), the one used in the
conventional OA method can be adopted and, for example,
a horizontal cylindrical granulator having stirring
blades on its longitudinal shaft can be cited.
By this granulation opexation, fine powder coal
containing a binder agglomerates to form fine granulated
coal, and, on the other hand, since mineral matter in
fine powder coal is hydrophillic as compared with coal
matter, mineral matter transfers intowater, and thus most of
mineral matter is removed from coal. The amount of a
binder added in the present invention is less than in
the conventional OA method, so that the particle size of
the resulting granulated coal in the present invention
is usually 100 - 250 ~m and preferably 100 - 200 ~m.
The fine granulated coal has a muddy state in
the water slurry, in which the coal is suspended, and
when the slurry is let stand for a long time, the
granulated coal will precipitate with mineral matter.
Further, water (11) is preferably added to the
water slurry (9) of fine granulated coal to adjust the
concentration of the fine granulated coal in the slurry
at 10 - 15~ by weight. The concentration adjustment is
for facilitating the flotation of the fine granulated
coal that is to be mentioned later and it is not always
necessary. Such a concentration adjustment can be
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g
carried out after feeding the slurry (9) of fine
granula-ted coal into a tank, e.g., a conditioner (10)
for concentration adjustment.
Subsequently, a frother or a flotation agent
(12) with a frother base is added to the water slurry of
fine granulated coal having a concentration adjusted.
The function of the frother used in the present invention
is to froth the water slurry of the fine granulated coal,
and as the frother there can be cited higher alcohols,
e.g. methylisobutyl carbinol, octanol, pine oil,
terpineol, polyoxypropylene alkyl ether, and the like.
The flotation agent with a frother base means
a mixed agent of such a frother as mentioned above with
an auxiliary such as kerosine or a mixed agent of a
frother with a froth stabilizer such as alkylol amide.
The function of the auxiliary is to agglomerate
the fine granulated coal, and the function of the froth
stabilizer is to stabilize the fro~h. It is appropriately
determined according to the qualLty and ash content of
raw coal and to the particle size of fine granulated coal
that which should be used, a frother or a flotation agent
with a frother base. Further, those frother or flotation
agents are all available on the market.
The amount of such a frother or a flotation
agent with a frother base used in the present invention
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is 100 - 200 ppm based on the weight of fine granulated
coal, and the amount of an auxiliary or a froth
stabilizer in the flotation agent with a frother base
is 20 - 30% by weight based on the weight of the frother.
When the amount of a frother or a flotation
agent with a frother base used is less than 100 ppm of
the weight of fine granulated coal, frothing is
insufficient and the flotation and recovery of the fine
granulated coal become incomplete.
When the above-mentioned use amount exceeds
200 ppm, there is no difference in frothing and in the
efficiency of flotation and recovery of fine granulated
coal due to the use amount and also the economical
efficiency comes into question. Therefore, such a use
amount is not desired.
Such a frother or a flotation agent is usually
added to the water slurry of fine granulated coal in a
tank, e.g., a conditioner (10) used for adjustment of
the slurry concentration.
Finally, the water slurry of fine granulated
coal with a frother or a flotation agent added is fed
into a flotation machine (13) to separate and recover
the fine granulated coal by flotation.
The fine granulated coal (14) with a binder
added is more hydrophobic than the original powder coal,
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so that the coal (14) is raised by air bubbles resulting
from the frother or flotation agent and floats on the
water surface. On the other hand, as the mineral matter
tl5) in fine granulated coal is more hydrophillic than
the granulated coal (14), it does not float but
precipitates.
When the thus floating fine granulated coal
(14) is collected by the same method as in a conventional
flotation method, fine granulated coal (14) having a
small mineral matter content can be obtained. ~he thus
obtained fine granulated coal is suitable as a fuel in
boilers, thermal power stations and the like.
As mentioned above, according to the present
invention, fine granulated coal is formed using a small
amount of a binder as compared with a conventional OA
method and then the coal is separated and recovered by
flotation, so that the use amount of a hydrocarbon oil
binder expensive as compared with coal can be substan-
tially reduced, thus allowing the economical efficiency
2~ of the resulting fine granulated coal to be raised
markedly.
Further, the method of the present invention
can treat all kinds of coal and even coal to be swept
that has been wasted so far. In the conventional OA
method, even when a large amount o~ 20 - 30~ by weight
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of a binder, based on the pure coal matter of sub-
bituminous coal, brown coal or lignite, is used, only
granulated coal having a perticle size of about 500 ~m
at ut~ost can be obtained, so that the granulated coal
can hardly be separated by screeningu In the method of
the present invention, however, the fine granulated coal
of all kinds of coal can be floated and recovered as in
the cases of coal of a high coalification degree for
coke making such as coking coal, independent of the kind
of coal.
Further, the method of the present invention
does not require special devices for recovering of fine
granulated coal, but granulators and flotation machines
having been used from the past can be used without
alteration, so that the method of the present invention
has an extremely large industrial value.
The following describes the example of the
present invention.
EXAMPLE
Sub-bituminous coal having an ash content of
28% by weight was pulverized so as to have a particle
size of 80% by weight of powder coal passing through 200
meshes.
Next, 7% by weight of heavy oil C, based on the
amount of pure coal of the fine powder coal was added to
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the fine powder coal and then water was added to form
the water slurry of the fine powder coal having a
concentration of 31% by weight.
The water slurry was fed into a vertical
cylindrical granulator to agglomerate the fine particles
of coal and the water slurry of fine granulated coal was
manufactured. The fine granulated coal had a particle
size of 105 - 149 ~m.
The water slurry of the fine granulated coal
was fed into a conditioner and then water was further
added to adjust the concentration of the fine granulated
coal at 14% by welght.
Next, 150 ppm of a higher alcohol (octanol)
was added to the water slurry of the fine granulated coal,
which was fed into a flotatlon machlne, and then the
fine granulated coal was recovered by flotation.
The recovery ratio of combus-tible matter of
the resulting fine granulated coal was 96% and the ash
content of the coal was 8.3% by weight.
