Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to an in-line method for
the beneficiation of coal and the formation of a coal-in-
oil combustible fuel therefrom.
I-t has already been proposed in United States
Patent No. 3,665,066, dated May 23, 1972, "Beneficiation
of Coals", Capes et al, to beneficiate a coal slurry
effluent by mixing a bridging liquid (light hydrocarbon
oil) with coal fines and agita~ing the formed mixture in
an aqueous medium to cause agglomeration of the coal
particles. The coal particle ayglomerates are then at
least partially dewatered and fed to a balling device,
together with balling nuclei of relatively coarse coal
particles and binding oil (heavy hydrocarbon oil) to form
a balled product in which each ball comprises at least one
balling nucleus in association with coal particles from
the agglomerates. The coal fines may contain significant
proportions of hydrophilic (or oleophobic) impurity or ash-
forminy particles a~sed of silica, alumina, pyrite, etc.
to which the functional groups of the light
hydrocarbon oil bridging liquid are incapable of attaching
themselves so that when the coal particle agglomerates are
formed, these particles remain suspended in the water and
are thus effectively separated from the coal particles.
While the process disclosed in the Capes et al
patent has proved to be useful for the production of
relatively coarse, balled coal products in the range 1/8
inch (3.2 mm) to 1 inch ~25.4 ~n) which are sufficiently stronq
to be transported in the balled form without the balls
disintegrating or releasing coal dust, there is a need
for a process for the production of relatively ~ine,
irnpurity liberated balled coal products having
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an average size no greater than of the order of 3 mm in
order that the balls will readily disperse in ~il to
form a co~bustible fuel comprising a coal-in-oil suspen-
sion. Impurity liberated coal-in-oil suspensions would
be a useful alternative fuel for existing oil fired
electrical generating facilities resulting in a saving
in the oil consumption. Other possible uses for these
suspensions are marine fuels, fuels for industrial boilers
and as injected fuels for blast furnaces.
In Canadian Patent No~ 1,020,880, dated November
15, 1977, "A method of displacing liquid suspendant of
a particulate material, liquid suspendant mixture by
micro-ag~lomeration" Capes et al, there is described an
in-line, one stage agglomerating process for producing
micro-agglomerates of coal fines which is particularly
useful for minimiæing the moisture content o coal-in-oil
suspensions for transportation along long distance
pipelines. ~hile this process is useful for the purpose
for which it was developed, there is still a need for this
process to be developed further to produce a combustible
fuel comprising an impurity liberated coal-in-oil suspension
wherein more accurate control of and larger amounts of the
residual moisture content remaining in the fuel from the
original coal-in-water slurry can be achieved. One reason
for this may be that the residual moisture content of
the coal-in-oil suspension explodes in a combustion chamber
and this possibl~r aids in dispersing the oil and coal and
thus in combustion efficiency.
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Controlled moisture content could also be useful
when the coal-in-oil suspension is subjected to vibratory
energy such as, for example, in burners which use vibratory
energy to increase the combustion efficieney in combustion
chambers.
Accordiny to the present invention there is
provided an in-line method for the benefielation of
coal and the ~o~ma-tion of a coal-i.n-oil combustible fuel
therefrom comprising:
a) comminuting coal in water to produce a
coal-in-water slurry comprising impurity liberated
coal particles at least as fine as 40 microns
weight mean particle size, then
b) m;xing the coal-in-water slurry with light
oil agglomerating liquid additive having a specifie
gravity of less than of the~.order of 1 g/cm3 to miero-
agglomerate the impurity liberated eoal partieles
and primarily dissoeiat~ inorganic impurities
and some watex therefrom,the light oil agglomera-
ting liquid additive being added at not more than of
the order of 20 wt % of the total weight of the
solids of the eoal-in-water slurry, then
e) separating the micro-agglomerated, impurity
- liberated eoal from the dissociated inorgan.ie
impurities and water, then
d) mixing - the separated~ micro-agglomerated,
impurity liberated eoal with heavy fuel oi~ having
a specific ~ravity greater than of the order ofi
0.~ g/cm3, as agglomerating liquid to produce
relatively larger agglomerates eomprising an
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average size no greater than of the order of
3 mm and primarily dissociate water with some
inorc~anic impurities which were present in the
micro-agylomera-ted, impurity liberated coal and
leave a residual amount of at least of the order
of S wt ~ water in the relatively larger
agglomerates, then
e) separating the relatively larger agglomerates
from the dissociated water and inorganic im-
purities, and then
f) mixiny -~he separated~ relatively larger
agglomerates with make-up heavy oil additive to
form a coal-in-oil combustible fuel.
In the accompanying drawing which illustrates,
by way of example, an embodiment oI` the present invention
there is shown a flow diagram of an in-line method for
t~-c be~eficiation of coal and the formation of a coal-in-
oil combustible fuel therefrom.
In Figure 1 there is shown an in-line method
for the beneficiation of coal and the formation of a coal-
in-oil combustible fuel therefromp comprising:
a) comminuting coal-in-water, in a ~et mill 1, to
produce a coal-in-water slurry 2 comprising im~
- purity li.berated coal particles at least as fine
as 40 microns weight mean particle size, then
b) mixing the coal-in-water slurry 2, in
three stlrring devices 4 to 6 arranged in cascade,
with ligh-t oil 8, having a specific ~ravity of
less than of the order of 1 g/cm3, as acJgIomerating
li~uid to micro-~.gglomerate the impurity liberated
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coal particles and primarily dissociate inorganic
impurities and some water tnerefrom, the light
oil agglomerati.ng liquid 8 being added at not
more than o the order of 20 wt % of the total
weight of the solids of the coal-in-water slurry
2, then
c~ separating, on a dewatexing screen 10 the
micro-agglomerated, impurity liberated coal
from the dissociated inorganic impurities and
water, then
d) mixlng the separated, micro-agglomerated~
impurity liberated coal 12, in a stirrer ].4,
with heavy fuel oil 16, having a specific gravity
greater than of the order of 0.9 g/cm3~ as agglo-
merating liquid to produce relatively larger
agglomerates comprising an average size
no greater than of the order of 3mm and
primarily dissociate water with some
inorganic impurities which were present in the
2Q micro-agglomerated, impurity li~erated coal and
leave a residual amount of at least of the
order of 5 wt % in the relatively larger agglome-
rates, then
e) separating the relatively larger agglomerates,
on a vibrating screen 18, from the dissociated
water and inorganic impurities, and then
P) mixing the separated, relati~ely larger
agglomerates i`0, in a mixe~ 22, with
make up heavy oil additive 24 to form a
coal-in-oil combustible fuel 26.
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The dry pulverizer 28 is used for the initial
stage of yrinding since this will generally pulverize coal
faster and in a smaller equipment volume than with wet methods,
although wet yrinding may be used throughout, if desired.
Coal to be pulverized is fed from a storage hopper 30 to
the dry pulverizer 28 which is s~ept wi-th air from a
supply 32. The swept air, with entrained pulverized coal,
is fed from the pulverizer 28 to a wet scrubber 34.
~ater containing the pulverized coal is fed from the wet
scrubber 34 to the wet mill 1 while air, which has been
scrubbed free from the pulveriæed coal in the wet scrubber
3~, is exhausted therefrom at 36.
As previously stated the coal-in-water slurry 2
from the wet mill 1 is stirred in three mixing devices
4 to 6 arranged in cascade. One mixing device could be
used provided that the residence time for the coal of the
coal-in-water slurry 2 therein to he micro-agglomerated
is tolerable. With the embodiment shown in Figure 1, a
residence time of four minutes was required and so the
three mixing devices 4 to 6 were provided.
The first mixing device 4 is a high shear
mixing device and may be a conventional turbine mixer.
The first mixing device 4 is used to disperse the light
oil agglomerating liquid 8 in the coal-in-water
slurry 2 and give an initial mixing.
The second and third mixing devices, 5 and 6
respectively, are relatively lower blade speed,
intermediate intensity mixing devices -to the mixing device
4 and are for producing the micro-agglomerates. It should
be noted that in dif~erent embodiments of the present invention,
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only one lower, intermediate inte-nsity mixing device is
necessary and in other em~odiments different mixing
devices may be used, such as, for example, one or more
emulsifying units with or without one or more lower,
intermediate intensity mixing devices.
The ligh~ oil agglomerating liquid additive 8
is fed to the first mixing device 4 from a storage tank 38.
As previously stated the micro-agglomerated,
impurity liberated coal is separated from the dissociated
components comprising primarily inorganic impurities
and some water on the screen 10~ which in this
embodiment is a stationary incli.ned screen down which the
separated, micro-agglomerated) impurity libera~ed coal
rolls and emerges as micxo-agglomerates 12 while the
dissociated inorganic impurit.ies and water, designated 40t
drain through the screen and are conveyed to a settling
pond 42. A vibrating screen separator or wet cyclone
separator could be used at this stage if the micro-
agglomerates possess suffici.ent streng~h not to break
up in such apparatus.
The embodiment shown in Figure 1 is arranged to
recycle most of the water from delivery 40 to the settling
tank 42, together with make-up water 44 which is fed
thereto. The water 46 from the settling tank provides
feed to the wet scrubber 34, wet mill 1 and the first
mixing device 4.
The micro-agglomerates 12 then pass to the mixing
device 14 which is also a re~atively lower blade speed,
intermediate intensity mixing device to the mixing
device 4.
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The relatively larger agglomerates are separated
from the dissoci~lted water and inorganic impurities on the
vibrating screen 18 because the relatively larger agglomer-
ates have suEficient strength no-t to break up on the vibrating
screen 18 r which is an e~ficient separator for the pur~pose.
A wet cyclone separa-tor, other types of screens, etc., could
also be used at this stage if desired.
The dissociated water and inorganic impurities,
designated 48, drain through the vibrating screen 18 and
are conveyed to a separation tank 50 from which a portion
52 of the ~ater is returned to the stirrer 14 while the
remaining water and inorganic impurities 54 are conveyed
to the settling pond 42.
The reason wh~ the water portion 52 is returned
to the mixing device 14 is to ensure that sufficient water
is delivered, ~ith the relatively larger agglomerates, to
the vibrating screen 18 to ensure that the inorganic impuri-
ties are thoroug~ly washed from the relatively larger agglo-
merates. This su~stantially reduces the possi~ility of inorganic
impurities ~eing carried over the ~i~rating screen 1~ with the
relatively larger agglomerates. In addition, the water in
mixing device 14 would usually be heated to about 60C to
reduce the viscosity of the heavy fuel oil 16. Recirculation of
water portion 52 avoids loss of thermal energy in discarded
hot water.
The mixer-22l to which the relatively larger
agglomerates 20 are conveyed in this embodiment is a
stationary, cylindrical vessel llaving a mixing device
rotating about a horizontal axis. Other types of mi~ers
may also be used such as, for example, a paddle type mixer.
The coal-in-oil combustible fuel 26 is stored
in an agitated holdin~ tank 56 from which it is with-
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drawn by a pump 58 ~t the desired rate ~o cons~nption asa co~bustible f-lel in, for example, an electrical
power generating ins-tallation (not shown). The method can
be matched to the desired rate of c~nsumption of the com-
bustible fuel so that the holding tank 56 is merely pro-
vided for storage to accommodate any fluctuations in the
production of the coal-in-oil combustible fuel or the
consumption thereof.
Details of an example using the method shown
in Figure 1 to bene~iciate coal mined from Minto,
New Brunswick, Canada and to form a coal-in-oil combust~ble
fuel therefrom will now be givèn.
A typical analysis of the Minto coal is given
below which shows that this is a coal having a high ash
and sulphur content.
Proximate Analysis (as fired) Norm Worst
Moisture 6.0% 12.0%
Volatile Matter 30.0% 24.2%
Fixed Carbon 46.0% 33.8%
Ash 18~0% 3n . o%
Sulphur 8.0% 10.0%
Btu/lb. (as fired) 11,300 8,400
(kj/kg1 (as fired)(26,284~ (19,540)
Grindability (Hardgrove)70 60
Ash Fusibility
Initial deformation, ~F ( C) 1,780 ( 970) 1,730 ( 940)
Softeningf F (C) 1,900 (1,040) 1,850 (1,010)
Fluid, F (C) 1,970 (1,080) 1,920 (1,050)
34
The weigh-t ratio of air to coal fed to the dr~
pulveriæer 28 was in the range 1.5:1- to 2:1. of the
order of 40 wt % coal and 60 wt % water were present in
the wet mill 1.
The first mixing device 4 was fed of the order
of 20 wt % coal, 3 wt ~ No. 2 fuel oil and 77 wt % water
The plant was a pilot plant desicJned to be capable
of treating 100 Imperial gallons/minO (455 l/min.) of slurry
2, which is equivalent to about 6 tons/hour(5.44 t~nnes/hour)
of coal solids (including impurities) based on the 20 wt %
slurry fed to the first mixing device 4.
The blades of the high shear mixing device 4, which
were driven by a 5 HP motor at 3,220 rpm, comprised two
groups of four ~igh shear impeller'blades, two of which
are shown for each ~roup and designated 60 to 63,'which
~a~er~n radi~ out~ardly to~ard~-trunca ed extr~itie.s. '
~ The high shear impeller blades 6~ and 62 ~r~re mounted
in an 18 inch ~0.46-m~ internal diameter tank 64
hav~ng a 35 inch CQ'.'8q' ml height with an annular
baffle 66 between the impeller blades 60 and 62 and four
vertical baffles, two of which are shown and designated
68 and 70, equally spaced therearound to enhance their
shearing effect on the coal-in-~ater slurry 2.
The four blades'of each of the relatively lower
blade speed, intermediate intensity mixing devices 5, 6
and 14, which were driven by a 5 HP motor at 280 rpm
comprised pitched, turbine impell'ér blades two of which
are shown and designated 72 and 74. The blades
72 and 74 were rnounted in a 40 in. (1.02 m) internal diameter
vessel having a 4G in~ (1.02 r,l) overflow heigh-t with
four vertical baffles, two of which are shown and designated
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76 and 78, equally spaced around the blades 72 and 74 to
enhance their shearing effect.
The dissociated inorganic impurities and ~tater,
designated 40, mainly comprised of the order of 96 wt %
water and 3 wt % ash and sulphur as the main inorganic
impurities together with oE the order of 1 wt % unagglomera-
ted combustible matter.
T~ relatively larger agglomerates produced by
mixer 14 comprised of the order of 70 wt % coal, 20 wt ~
oil and 10 wt % waker to which was added sufficient No. 6
fuel oil in the mixer 22 for the coal~in-oil combusti~le
fuel ~6 to comprise a coal~oil weight rat.io of 40/60b
Tests have shown tha~ using apparatus o the
type shown in Figure 1, then:
~) the preferred ~lade tip speed of the hig~ shear
impeller ~lades 60 to 63 is in the range of the
order of 10 m/sec. to of the order of 30 m/sec.
bet~er still of the order of 20 m/s~c. to of
the order of 25 m/sec.
ii) the preferred blade tip speed of the pitched,
turbine impeller blades 72 and 74 is up to of
the order of 15 m/sec.
Preferred light oils as-agglomerating lic~uid are
No~ 2 fuel oil and diesel o:il. Other light oils as agglomera-
ting liquid are, for example~ light petroleum fractions, kero-
sene, coke oven light oil and light crude and residual and
waste oils.
Preferred heavy fuel oils as agglomerating liquid
are No. 6 fuel oil and heavy residual oils. Other heavy
fuel oils as agglomerating liquid are, for example, crude
oi]s and coXe oven tar.
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The quantity of liyh-t oil agglomerating liquid
additive used will depend upon the type of coal being pro-
cessed and how finely the coal must ~e ground to produce
impurity liberated coal particles. Wnile a greater quantity
of light oil agglomerating liquid additive could be used
than of the order of 20 wt % of the -total weight of solids
of the coal-in-water slurry the desira~le thing according to
the present invention is that onl~ of the order of up to 20
wt % need ~e used so that the final coal-in-oil combustible
fuel will containS fox example, the maximum amount of heavy oil
ror which an oil fired installation was originally des.igned,
when the coal-in-oil com~ustible fuel i~ for use in this
manner.
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