Note: Descriptions are shown in the official language in which they were submitted.
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PRODUCTION OF HARDENED COAL AGGLOMERATES
2 Field of the Invention
3 This invention relates to improvements in the
4 production of coal agglomerates which are suited to long-
term storage and/or transportation in the agglomerate form.
6 Back~round of the Invent1on
7 The formation of coal agglomerates from aqueous
8 slurries containing particulate coal and oil has been widely
9 practiced for many years. Many agglomeration processes have
been proposed requiring varying degrees of energy input and
11 oil consumption. Most processes having acceptable energy
12 input requirements and residence times produce relatively
13 oily or sticky coal agglomerates which, while being suitable
14 as as a feed stock for the immediate production of a coal-
oil mixture, have been found to be unsuitable for long-term
16 storage or transportation due to their stickiness and/or
17 poor physical strength.
18 Examples of prior art agglomeration processes may be
19 found in United States Patents Nos.4355999 Maso~ogites,
4302211 Verschun and Australian Patent 534563 (AU-B
21 54496/80) Dudt. In each of the above processes, long
22 residence times and/or multiple agglomeration stages are
23 required to achieve an acceptable coal agglomerate and even
24 then such products are not necessarily suited to
transportation in large bulk carriers of the type which
26 would make transportation of such agglomerates economically
27 viable. In the case of AU-B 54496/80, it will be noted that
28 a four stage process of increasing energy input is required
29 to produce an acceptable agglomerate. Although the
agglomerates produced by this process would be acceptably
31 dry (that is, not sticky), the agglomerates would be
32 unlikely to be of sufficient quality to survive
33 transportation without unacceptable production of fines
34 during the transportation process.
It is also well known to reduce the oiliness or
36 stickiness of particulate coal agglomerates by the
37 evaporative de-oiling of such agglomerates. However, such
38 processes haYe the obvious disadvantage of increasing the
3~
energy requirements of the production process since super
heated steam must usually be produced to provide the necessary
energy to cause evaporation of the oil coating the
agylomerates.
Summary of the Invention
It is an object of the present invention to provide an
improved coal agglomeration method which results in the
production of better quality agglomerates in lower residence
times.
The invention therefore provides a process for the
production of coal agglomerates comprising agitating an
aqueous slurry of coal particles in a first agitating zone in
the presence of oil to form coal agglomerates, further
agitating said agglomerates in either the first agitating zone
or a second agitating zone in the presence of a fresh coal
particle bearing slurry to improve the dryness and quality of
the agglomerates, characterised by the step of transporting
the slurry containing said agglomerates in a pipeline having a
length of 500m or longer and being in communication with
either the first agitating zone or the second agitating zone
to further improve the strength properties of the
agglomerates.
The agglomerates produced have been found to be well
suited for long-term storage and/or transportation in bulk.
In a preferred form of the invention, the step of
transporting the slurry containing the agglomerates in a
pipeline ~`ollows each of the agitation stages and the
transporting is preferably achieved in a pipeline loop.
The consolidation which occurs during formation and
circulation of the agglomerate bearing slurry through the
pipeline in combination with the two-step coal addition
operation permits the production of strong agglomerates having
a relatively dry surface. Agglomerates produced in this way
show little tendency for sticking together or for attrition
during handling operations. For these reasons, they are
eminently suited for long-term storage and/or for
transportation in bulk. The results achieved were not
,~ .
~2~53~
2a
predictable and the inventors found the improvement in
agglomerate quality by the circulation o~ the slurry in a
pipeline quite surprising. The inventors are not yet aware of
the physical reasons for the unexpected improvements
. ,~,,~, ~, ....
~53~
-- 3 --
1 achieved by the pipeline circulation, but it is clear that
2 the further contact between the agglomerates and the coal
3 particles in the slurry which occurs in the pipeline is most
4 beneficial.
In one preferred form of the present inYent;on, the
6 coal particles contained in the initial slurry are
7 preferably coated with oil and formed into small
8 agglomerates by introducing the slurry and the coating oil
9 into the inlet of a turbulent flow slurry pump. This method
of oil coating and formation of small agglomerates has been
ll described in our Australian Patent No. 529242 (AU-B
12 56D53/80). Of course it will be appreciated that acceptable
13 results may be obtained by the simple addition of oil to the
14 initial agitation stage in accordance with standard
practice, However, the use of a turbulent flow slurry pump
16 to achieve the initial oil coating and formation of small
17 agglomerates has the advantage of reducing the energy
18 requirements of the agglomeration process.
19 In the present specification the term "pipeline" should
be construed as a pipe of substantial length, for example,
2t at least 500m. Similarly, the term "oil" should be
22 construed to include all suitable hydrophobic liquids such
23 as kerosene, diesel oil, fuel, oill petroleum residue and
24 heavy aromatic materials such as coke oven tars and
bitumen and suitable mixtures thereof.
26 Br~ef Descr~ption of the Dra_ings
27 A preferred embodiment of the invention will now be
28 described with reference to the accompanying drawing in
29 which: -
Fig.1 is a schematic diagram showing an arrangement for
31 performing the process according to a preferred embodiment
32 of the invention.
33 Description of Preferred Embodiment
______ ____ __ _________ __________
34 Referring to Fig.l of the drawings, the arrangement
shown for performing the preferred embodiment of the process
36 according to the invention comprises a turbulent flow slurry
37 pump Pl into the inle~ of which suitable oil and a
38 particulate coal bearing aqueous slurry is introduced in the
3~3
.
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manner described in greater detail in our Australian ~atent
2 No.529242. While it may be convenient to inject the oil
3 directly into the inlet of the pump, it wil 1 be appreciated
4 that the oil may he added at any suitable position upstream
of the pump inlet.
6 The slurry general ly contains 30-50% by weight of
7 solids, including particulate coal which may result from a
8 grinding operationl washery or tailings pond. Any suitable
9 oil, such as a suitable grade of fuel oil, may be used to
achieve agglomeration and the 4uantity of oil introduced
11 into the inlet of the pump Pl is selected according to the
12 nature of the particulate COd 1 contained in the slurry (see
13 above Patent No.529242).
14 The pump Pl discharges into a first agitation tank 1 in
which the oil coated coal and partially formed agglomerates
16 produced in the pump Pl are further agglomerated~ A second
17 pump P2 is connected to the tank 1 and recirculates the
18 agglomerate bearing slurry produced in the tank 1 through a
19 pipeline loop Ll back into the agitation tank 1. During its
passage through the pipeline loop Ll, the agglomerates are
21 consolidated to increase their strength and the strengthened
22 agglomerates are recycled into the mixing tank 1 so that
23 further growth can occur by contact with fresh oil coated
24 coal particles. The length of the pipe loop L1 is selected
in conjunction with other operating parameters (such as oil
26 addition level, particle size distribution, residence time
27 in the tank/pipe loop) to achieve the required consolidation
28 and is preferably longer than 500 metres; for example 1600m
29 has been used in some pilot plant trials. rt has been
surprisingly found that the consol idation which occurs in
31 the pipe loop Ll in combination with the agitated tank 1, is
32 not readily achieved in the agitated tank 1 alone, certainly
33 not in the same overal 1 residence time. In addition, the
34 size of the agglomerates can be controlled by adjustment of
pipeline velocity and combined residence time in the tank 1
36 and pipe loop Ll~
37 If desired the pipeline may include flow disturbing
38 means which increase the mixing of the slurry in the
353~8
l pipeline as it is transported therethrough. See for example
2 our Australian Patent No. 529242 or United States Patent
3 No.3856668.
4 In an experimental pilot plant constructed to test the
viability of the process according to the present invention,
6 the following parameters have been found to be successful:
7 An agitated tank having a volume of 300 m3 has been
8 used in conjunction with a lOOmm diameter pipe loop. The
9 agitator is fitted with a 21 kW motor. The total length of
the pipe loop was l500m with bypasses fitted to allow use of
11 400m, 800m or 1600m lengths.
12 When using the 1600m length it was found necessary to
13 use more than one pipe loop pump to provide the necessary
14 head. Three 3/2 high head Warman slurry pumps were
installed for this purpose.
16 Various combinations of pipe loop length and combined
17 pipe loop-agitated tank residence times have been used to
18 successfully produce the desired agglomerates depending on
19 the nature o~ the ~eed slurry~
A typical set of conditions inc1ude a combined mean
21 residence time of three hours using a pipe loop length of
22 800m.
23 When processing small batches of material, (say 2-3
24 tonnas) a smaller agitated tank having a volume of
approximately 2m3 may be used in conjunction with the pipe
26 loop.
27 A third pump P3 continuously transfers agglomerate
28 bearing slurry from the tank 1 to a further tank 2 to which
29 fresh particulate coal bearing slurry is added. The second
mixing tank 2 operates in a similar manner to the first
31 mixing tank 1 and a fourth pump P4 circulates agglomerate
32 bearing slurry from the tank through a second pipeloop L2
33 and back into the tank 2 to further improve the strength of
34 the agglomerates. The addition of fresh slurry to the tank 2
improves the surface condition o~ the agglomerates reducing
36 their oiliness while the second pipeloop L2 consolidates the
37 agglomerates produced in the tank 2 and improves their
38 strength.
i3l~3
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1 A fifth pump P5 transfers the agglomerated product from
2 the tank 2 to a dewatering/classifying screen ~rom which any
3 small undersize agglomerates are returned to the tank 1
4 after separation of the waste mineral matter and water.
In a modification of the above embodiment, the second
6 mixing tank 2 is eliminated and the agglomerate bearing
7 slurry from the first mixing tank 1 is pumped directly into
8 the second pipe loop L2 for further conditioning in the
9 presence of fresh particulate coal bearing slurry, which may
be introduced into the inlet of pump P4 in any suitable
11 manner.
12 A batch of approximately 2.2 tonnes of agglomerates has
13 been produced using a pilot plant according to the preferred
14 embodiment described above and the batch subjected to
lS flowability tests.
16 In the pilot plant, the coal was processed through a
17 hammer mill and ball mill to generate a size distribution
18 similar to a typical pulverized fuel specification. The fuel
19 oil used to achieve agglomeration was heated to a
temperature of 30-35C before addition to the slurry and the
21 slurry was circulated through the pipe loop Ll for several
22 hours prior to the oil addition to increase the temperature
23 of the slurry to approximately 25C. The remainder of the
24 process was as described above and the resultant de-watered
agglomerates were found to be strong and well formed with a
26 top size of 2.3mm.
27 The following Table 1 summarises the results for this
28 run (d.b. = dry basis).
~2~3538~3
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1 Table 1: Summary of Results for Ag~lomerates Produced
_____ _ ___ __ __ _______ ___ _ _________ ________
2 by the Pil_t Plant
3 Feed Coal
4 Ash %d.b 20.1
Size analysis prior to agglomeration (% passing)
6 Agglomerated Product
7 Sizel mm
8 0.5 98.8
9 0.25 96.0
0.125 83.7
11 0.063 61.0
12 Fuel oil addition
13 (%by weight dry feed coal)16.7
14 Ash, %d~b 6.9
It may be concluded from the tests conducted to date
16 (as detailed further below) that the method of the invention
17 produces agglomerates which are stronger, less sticky and
18 have a lower (2%-3%) ash level than agglomerates produced by
19 the prior art methods. While detailed comparative tests
have not been conducted, qualitative observations have
21 indicated that the prior art methods would not be capable of
22 producing an agglomerate product of the same quality
23 without unacceptable residence times in stirred tanks. The
24 relatively short term circulation of the partly formed
agglomerates in the presence of fresh slurry causes additive
26 consolidation and further release of mineral matter, to a
27 greater extent than would be achieved by further stirred
28 tank processing for an equivalent time~ It is not clear why
29 pipeline circulation achieves these results although it is
clear that the agitation which occurs in a pipeline is
31 different in character to stirred tank agitation.
32 The batch of agglomerates produced by the pilot plant
33 was subjected to testing to determine the flow properties of
34 the agglomerates and their ability to withstand
transportation in bulk.
36 For the design and performance evaluation of material
37 handling facilities, it is necessary to examine samples of
38 the materials which are like1y to produce the most difficult
~L2853~
l flow conditions The conditions of moist~re content,
2 temperature and storage time relevant to the material under
3 actual operating conditions need to be duplicated in the
4 tests. However, since the main aim of the tests is to
obtain the characteristics of the agglomerates for
6 preliminary assessment of handling characteristics of the
7 agglomerate, particularly under sea transportation
8 conditions, oiled agglomerates having a moisture level
9 equivalent to that expected from a stock pile of the
material were tested.
11 Table 2 lists the properties o~ the oiled agglomerates
12 used in the tests (d.b. = dry basis a.d.b. = air dry basis).
35~8~3
1 Table 2 Propertles of Olled A~glomerates
2 Moisture % (a.d.b.) approximately 5
3 Oil ~ (d.b.) " 17
4 ~sh % (d.b.) " 6.9
Size Analysis:
6 Size, mm % Passing
7 2.0 68
8 1.0 4
9 0.5 0.5
Ag~lomerate Handlin~ Characteristics
________ _______ _______________
11 The ability of a bulk material to flow is dependent on
12 the strength developed by the material due to consolidation
13 and weathering. As a result of this strength, the material
14 may be able to form a stable arch or pipe. Free flowing
bulk materials have no cohesion and hence no strength.
1~ Tests have indicated that agglomerates manufactured in
17 accordance with the present invention, and at 5% moisture
18 level, behave essentially as a free flowing material.
l9 Although ~his free flow characteristic is slightly dif~erent
from a perfectly free flowing material such as dry sand
21 whose unconfined yield strength is always zero, energy coal
22 showed much greater strength than that of the agglomerates.
23 This means that the flowability of the agglomerates is much
24 better than that of typical Australian export coals.
Although there is some breakage of the agglomerates
26 under high stress conditions, tests have also shown that the
27 handling characteristics of the agglomerates are
28 satisfactory for ship load~ng transportation and unloading,
29 and for hopper storageO
Ship Transportation Tests
___ _____ ________ _____
31 Degradation of particles due to stress and to vibration
32 of the ship is not a serious problem for the ~ajority of
33 bulk solids as the particles are intrinsically strong.
34 However consolidation (or compaction) of the bulk solids can
create serious material handling problems if the bulk solids
36 contain a large proportion of fines or the bulk solids have
37 a cohesive characteristic.
38 The difficulty in handling compacted bulk solids is
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dependent on the degree of strength developed in the
2 compacted material and this important characteristic depends
3 on the proportion of fines, moisture content, consolidation
4 pressure, storage time and in the case of oi led
agglomerates the oil content.
6 Tests have been conducted to evaluate the effect of stress
7 on the compaction and degradation of our oiled agglomerates to
8 predict the degree of degradation and compaction of the
9 agglomerates which could be expected in the cargo hold of a
100,000 DWT bulk carrier. These tests have shown:
11 (1) During loading into the cargo hold of a ship,
12 aggl omerates are compacted~ by the weight of the material
13 during loading, but further compaction due to storage time
14 and ship vibration is small.
(2) At a stress above lOOkPa the agglomerates formed
16 into a consolidated cake although blocks of the cake were
17 easily broken into separate agglomerates. This means that
18 the compacted agglomerates near the bottom of the ship hold
19 would not come crumbling down easily when the agglomerates
are unloaded. However this is not essential if the material
21 is unloaded using a grab.
22 t3) At a stress of 150kPa (estimated stress for a
23 material depth of 20m in the cargo hold) the degradation of
24 agglomerates would be expected to result in an increase in
the 0.5mm size particles of about 5%. At the half depth of
26 the hold (lOm deep) the figure would be less than 1%. These
27 fines do not appear as discrete dry particles but are
28 a t t a c h ed t o t h e s u r ro un di n 9 1 a r ge r p a rti c 1 es o f
29 agglomerates~ Hence they do not form a dust problem in
handling.
31 Fu_ther ~xample of the Invention
32 To check the viability of the process embodying the
33 invention for lower grade feed material, further tests were
34 conducted using the pilot plant described above and are
detailed below.
36 Five tankers containing a waste thickener underflow
37 from a high volatile energy coal preparation plant were
38 transported to the pilot plant for testing.
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, 1
1 Following transfer of the slurry to a surge tank, the
2 solids concentration was adjusted to approximately 20% (by
3 weight) prior to desliming.
4 D~sliming was undertaken by pumping the slurry through
two 100mm KRT 2118 IV cyclones. An initial test was done
6 using a 20mm apex stopper diameter. However th;s was
7 subsequently enlarged to 25 mm diameter to give a cyclone
8 underflow solids concentration of approximately ~0%. A
9 cyclone inlet pressure of 250 kPa was used and the flowrate
to each cyclo,ne was approximately was 17m3/h. The u~derflow
11 was stored in temporary tanks during processing and returned
12 to the surge tank on completion of the desliming. Some
13 additional water was used to rinse the larger particles from
14 these tanks.
The deslimed slurry was circulated through a ball mill
16 closed circuit to grind the solids to a size distribution
17 close to that of typical pulverised coal (99% passing 300
18 microns). Approximately lOm3 of this slurry was reserved
19 ~or secondary addition to the agglomerates after initial
agglomeration.
21 After grinding, agglomerating oil was added to the
2Z slurry at the inlet to the ball mill sump pump whilst the
23 slurry was circulated through a 1 km long 100mm diameter
24 pipeloop and surge tank circuit~ The oil was added in
2~ several steps to ensure that excessive oil was not used.
26 A low sulphur furnace oil (0.4% sulphur) was used to
27 permit the production of agglomerates having a low sulphur
28 specification.
29 Circulation of the slurry was continued until the
agglomerates had reached 2-3 mm in diameter. At this stage
31 additional finely ground slurry was added to the surge tank
32 to absorb excessive oil on the agglomerate surface and
33 produce a "non sticky" transportable product. Circulation
34 was continued for a further two hours prior to dewatering
the agglomerates on a 0.5mm wedge wire vibrating screen.
36 A series of water sprays were used on the screen to
37 rinse off excessive clays and other mineral matter prior to
38 discharge of the ~gglomerates into the storage hopper.
~L285388
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1 Details of the various slurry and solids balances are
2 summarised below. These figures are approximate and are
3 based on best estimates from tank volumes and flows. Note
4 that there are some variations in volumes due to additional
water used for rinsing and pump gland seals.
6 Th~ck~ner Underflow total volume = 104m3
7 solids = 35t
8 after unloading to total volume = 154m3
9 surge tank slurry density = 1.108t/m3
solids concentration = 20,6%
11 solids = 35t
12 Size analysis and Ash distribution
13 Size fraction Weight Ash
14 mm Fraction % %d,b,
~0.5 3.9 22~6
16 -0.5 ~0.25 15.8 31,6
17 -0.25~0.125 16,0 47,7
18 -0.125~0.063 12.0 37,5
19 ~0.063 52,3 58.9
total 48.8
21 Cyclone Underflow
_ ____ _____ _ __
22 total volume = 47m3
23 slurry density = l.l99t/m3
24 solids concentration = 40.5%
solids = 23t
26 solids recovery yield
27 from cyclone fee, d.b. = 65.7
28 ~coal matter recovery
29 from cyclone feed, d.b. = 72.8%
~coal matter = solids - mineral matter; assuming mineral
31 matter = 1.1 x ash.
32 Size analysis and Ash distribution
33 Size fraction Weight Ash
34 mm Fraction % %d.b.
~0.5 7.0 21.7
36 -0.5 +0.25 22.3 29.5
37 -0.25~0.125 22.3 40.3
38 -0.125+0.063 16.2 33.4
~8~i3~3
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1 -0.063 32.2 67.8
2 Total ~4~3
3 Cyclone 0verflow
4 total volume = 122m3
S slurry density = 1.048t/m3
6 solids COnCntration = 9.55%
7 solids = 12t
8 Size analysis and Ash distribution
9Size fraction Weight Ash
mm Fraction % %d.b.
11 ~0.063 2.2 11.1
12 -0.063 +0.045 1.6 6.1
13 -0.045 +0.038 1.6 8.2
14 -0.038 94.6 58.7
Total 56.0
16 Crushed Slurry Prior to Agglomeratlon
17 tvtal vo1ume = 71m3
18 slurry density = 1.136t/m3
19 solids concentration = 28.8%
solids = 23t
21 Size Analysis
22 Size, mm %passing
23 0.5 99.9
24 0.25 99.3
0.125 94.3
26 0.063 75.1
27 Ash, % d.b. = 44.3
28 Agglomeration
__________ .
29 volume of initial slurry
used for agglomeration = 61m3
31 solids = 20t
32 total oil added = 3666kg
33 (assuming oil
34 density =
0.94t/m3)
36 oil added on initial
37 solids (d.b.) = 18.3% (by
38 weight)
~ ~ 53 ~ ~
l Additional solids added = 3.3t
2 during secondary
3 agglomeration
4 oil added on total = 15.7%
solids ~d.b.)
6 Product A~lomerates
_______ _ _________
7 Estimated agglomerated = 12.2t
8 product, dry, oil free
9 Estimated agglomerated = 17t
product including oil and
11 10% moisture
12 Product ash, %dry oil free = 5.9
13 Estimated product yield = 52.2
14 from ground deslimed slurry,
%d.b. (for tailings ash = 86.5%
16 d.b.)
17 Estimated product yield = 34.9
18 from original thickener
l9 underf1Ow, %d.b.
Estimated coal matter yield = 97
21 from ground slurry, %d.b.
22 Estimated coal matter yield = 70.6
23 from original thickener
24 underflow, %d.b.
Estimated oil based on = 21.6%
26 dewatered product basis
27 (including oil and 10% moisture)
28 Chemical Anal~sis: ~expressed on moisture free basis,
__ _ __ _ _ _ _ _ __ _
29 including oil)
Ash 5.0%
31 Vo 1 atile Matter 46.8%
32 Fixed Carbon 48.2%
33 Total Sulphur 0.42%
34 Specific Energy 33.9MJ/kg
- 15 -
1 The moisture of the agglomerates from the product hopper
2 after overnight drainage was approximately 12.5%.
3 Agglomeration and mineral matter separation of the
4 deslimed product was readily achieved in the above example.
The product ash was significantly lower than that
6 achieved in bench scale tests using conventional stirred
7 agglomeration techniques; this results from the higher
8 levels of consolidation and exclusion of mineral matter
9 achieved in the pipeline and agitated tank circulation
system. Petrographic examination of bench scale products
11 showed that the mineral matter in those agglomerates
12 contained approximately 25% pyrite. It is presumed that use
13 of the present invention results in elimination of the
14 majority of this pyrite, as long as it is ground to a size
1~ which a71Ows separation over the dewatering screen.
