Method of producing fuel of relatively higher calorific value from low rank and oxidized coal

Low-rank or oxidized coal is processed to produce fuel of relatively higher calorific value by conditioning a slurry of the coal with an electrolyte, and then agglomerating the carbonaceous portion of the coal using a coal derived agglomerating oil. Agglomerates may be first formed in a high shear mixer and then larger agglomerates formed in a low speed mixer. The agglomerates may be processed in a coal liquefaction plant and a portion of the coal derived oil produced in the plant used as the agglomerating oil.

This invention relates to a method of producing fuel of relatively higher 
calorific value from low-rank and oxidized coal. 
It is known from, for example, "Physical Cleaning of Coal, Present and 
Developing Methods", edited by Y. A. Liu, 1982, "Selective Oil 
Agglomeration in Fine Coal Beneficiation", C. E. Capes and R. J. Germain, 
page 318, that lower-rank sub-bituminous coals, lignite, weathered high 
rank coals and other difficult to agglomerate coals are distinguished from 
other coals by their greater oxygen content and the hydrophilic nature of 
their surfaces relative to those of bituminous coals. The light oils which 
are used successfully to agglomerate the carbonaceous portions of 
bituminous coals are not able to wet the oxidized and/or hydrated 
carbonaceous portions of lower-rank coals and so form only emulsions with 
no discrete agglomerates when agitated with them in a water slurry. If 
heavier oils, such as coke oven tars and pitches as well as petroleum 
crudes and their higher boiling components, are used as conditioners with 
the light oils, however, then distinct agglomerates are formed with the 
lower-rank coals. Apparently the nitrogen, oxygen and sulfur functional 
groups of these complex oils are able to adsorb sufficiently well on the 
relatively hydrophilic surfaces of the lower-rank coals to form 
agglomerates. 
Ash rejection does occur when the heavier, complex oils containing multiple 
functional groups are used as conditioning agents. However, the amount of 
ash rejection is less than that might be expected if the lighter, more 
refined oils alone could be used for agglomeration. The procedure also 
produces a granular material from which a large portion of the surface 
moisture has been displaced. Unfortunately, the treatment is not able to 
reduce the internal moisture bound within the structure of the lower-rank 
coals without thermal drying. The consistent granular texture of the 
product is well suited to rapid thermal drying and the absorbed oil in the 
agglomerates reduces considerably the readsorption of moisture following 
thermal drying. 
A similar problem exists with other difficult to oil agglomerate coals such 
as oxidized (weathered) high-rank bituminous coals, for example, finely 
divided carbonaceous particles which have become oxidized or weathered in 
black-water ponds. 
There is a need for a process whereby low-rank and oxidized coals can 
readily be treated to produce a fuel therefrom of relatively higher 
calorific value. 
According to the present invention there is provided a method of producing 
fuel of relatively higher calorific value from low-rank and oxidized coal, 
comprising: 
(a) agitating to thoroughly mix electrolyte selected from the group 
consisting of concentrated sulphuric acid, concentrated hydrochloric acid 
and sulphur trioxide gas", with an aqueous slurry of the coal comminuted 
to the ash release particle size "essentially smaller than 35 mesh Tyler 
Standard Screen", to condition the coal slurry for oil agglomeration of 
the carbonaceous portion of the coal therein by a coal derived oil; then 
(b) adding coal derived agglomerating oil to the conditioned coal slurry, 
the coal slurry containing about 10 to about 40 wt % oil, and about 0.5 to 
about 5.0 vol % electrolyte; then 
(c) agitating the mixture of coal derived agglomerating oil and conditioned 
coal slurry to form agglomerates of carbonaceous material of the coal in 
the mixture, the agglomerates containing about 10 to about 50 wt % coal 
derived oil; then 
(d) separating the agglomerates from the remainder of the mixture, and then 
(e) washing the separated agglomerates with water. 
The mixture of coal derived agglomerating oil and conditioned coal slurry 
are preferably agitated at a mixing rate in the range of about 0.1 
hp/ft.sup.3 to about 6.0 hp/ft.sup.3 to form agglomerates of carbonaceous 
material of the coal in the mixture. 
Better still, the mixture of coal derived agglomerating oil and conditioned 
coal slurry are agitated at a mixing rate in the range of about 0.4 
hp/ft.sup.3 to about 4.0 hp/ft.sup.3 to form agglomerates of carbonaceous 
material of the coal in the mixture. 
Still better results may be obtained if the mixture containing agglomerates 
is further agitated at a relatively slower mixing rate in the range of 
about 0.05 hp/ft.sup.3 to about 0.5 hp/ft.sup.3 to form relatively larger 
agglomerates of carbonaceous material. 
The electrolyte may comprise a substance selected from the group consisting 
of concentrated sulphuric acid, concentrated hydrochloric acid and sulphur 
trioxide gas. 
In some embodiments of the present invention, finely divided carbonaceous 
coal solids are mixed by further agitation, with the mixture containing 
agglomerates to form even larger agglomerates from the carbonaceous 
material of the coal. 
A binder for carbonaceous material of the coal may be added to the 
conditioned coal slurry to assist in the formation of agglomerates of 
carbonaceous material of coal therein. 
The agglomerates may be processed in a coal liquefaction plant, and a 
portion of the coal liquefaction oil product from the coal liquefaction 
plant is used to provide the coal derived agglomerating oil. The 
agglomerates may be slurried with a portion of the coal liquefaction oil 
product before being processed in the coal liquefaction plant.

Referring now to FIG. 1 there is generally shown a conditioning vessel 1, a 
first agglomerating vessel 2, a second agglomerating vessel 4, a draining 
screen 6 and a washing screen 8. 
The conditioning vessel 1 has an aqueous coal slurry inlet connected to a 
feed pipe 10, an electrolyte inlet connected to a feed pipe 12 and a 
slurry outlet connected to slurry pipe 14. The mixing vessel, has a 
stirrer 15 coupled to an electric motor 16. 
The first agglomerating vessel 2 has an inlet connected to the pipe 14, an 
agglomerating oil inlet connected to a feed pipe 18 and an agglomerate, 
inorganic matter (ash) and water outlet 20. The first agglomerating vessel 
2 has a high shear mixing device 22 coupled to an electric motor 24. 
The second agglomerating vessel 4 has an inlet connected to the outlet 20 
and an agglomerated, inorganic matter (ash) and water outlet connected to 
a conveyor 26. The second agglomerating vessel 4 has an intermediate 
intensity mixing device 28 coupled to an electric motor 30 for operation 
at a relatively lower blade speed than that of the high shear mixing 
device 22. 
The draining screen 6 has a feed end for receiving agglomerates, inorganic 
matter (ash) and water from the conveyor 26, a drainage outlet connected 
to a pipe 32 and an agglomerate exit end for delivering agglomerates to a 
conveyor 34. 
The washing screen 8 has an agglomerate receiving end for receiving 
agglomerates from the conveyor 34, a drainage outlet connected to the pipe 
32, and an agglomerate exit end for delivering agglomerates to a conveyor 
36. A washing water spray device 38 is situated over the washing screen 8 
for spraying agglomerates thereon with washing water. 
In operation, an aqueous coal slurry of low-rank or oxidized coal is fed to 
the conditioning vessel 1 along the feed pipe 10, and electrolyte is fed 
into the conditioning vessel 1 along the feed pipe 12. The aqueous coal 
slurry and the electrolyte are thoroughly mixed in the conditioning vessel 
1 by the stirrer 15 coupled to the electric motor 16 to condition the 
carbonaceous portion of the coal slurry for oil agglomeration by rendering 
it more oleophilic. The conditioned coal slurry is then passed along the 
slurry pipe 14 to the first agglomerating vessel 2. 
Coal derived agglomerating oil is fed to the first agglomerating vessel 2 
along feed pipe 18. 
The coal derived agglomerating oil and the conditioned coal slurry are 
vigorously mixed in the first agglomerating vessel 2 by the high shear 
mixing device 22 to form agglomerates of carbonaceous material of the coal 
in the remainder of the mixture (inorganic matter and water). These 
agglomerates could be separated from the remainder of the mixture as a 
useful product. However, in this embodiment the agglomerates, together 
with the remainder (inorganic matter and water) of the mixture are fed 
along pipe 20 to the second agglomerating vessel 4. 
The agglomerates and the remainder (inorganic matter and water) of the 
mixture are agitated in the second agglomerating vessel 4 by the 
intermediate intensity mixing device 28 at a relatively lower blade speed 
than that of the high shear mixing device 22 until larger agglomerates are 
formed than those that were originally present. 
The larger agglomerates and the remainder (inorganic matter and water) are 
passed from the second agglomerating vessel 4 to the conveyor 26 which 
conveys them to the draining screen 6. 
The agglomerates with the remainder of the mixture (inorganic material and 
water) drained therefrom pass across the screen 6 to the conveyor 34 while 
the remainder is passed to the pipe 32. 
The agglomerates are conveyed by the conveyor 34 to the washing screen 8. 
As the agglomerates pass across the washing screen 8 they are washed by 
water from the spray device 38 to wash trapped inoragnic solids therefrom. 
The washed agglomerates are passed from the washing screen 8 to the 
conveyor 36 while the inorganic solids (ash, clay, gangue) and washing 
water are passed to the pipe 32. 
The agglomerates on the conveyor 36 may be used in, for example, fluidized 
or pulverized coal combustion, coal gasification, coal liquefaction, coal 
pyrolysis, coal/liquid fuel mixtures, coal/liquid pipeline mixtures. 
Clearly, since the agglomerating oil is a coal derived oil, using the 
agglomerates in a process that will derive such an oil from them will also 
provide a source of the agglomerating oil. 
It should be noted that while two agglomerating vessels 2 and 4 are shown 
in FIG. 1, and that this is the preferred embodiment, it is within the 
scope of the present invention to use any number of agglomerating vessels 
from one upwards. In some embodiments of the present invention, a common 
mixing and agglomerating vessel is used in which the coal slurry and 
electrolyte are first mixed and then the coal derived oil is mixed and the 
agglomeration is carried out, but in this case the system of necessity 
operates intermittently on a batch system. 
In some embodiments of the present invention, where handling of the 
agglomerates requires increased strength, a binder for the carbonaceous 
portion of the coal is fed to the agglomerating vessel 2 along a feed pipe 
40 (shown dotted). 
In tests to verify the present invention, using the apparatus shown in FIG. 
1, it has been found that attempting to agglomerate the finely divided 
carbonaceous portion of low-rank or oxidized coal from an aqueous slurry 
having from about 10 weight percent to about 40 weight percent solids, the 
solids comprising the finely divided carbonaceous solids of low-rank or 
oxidized coal and finely divided inorganic solids, by mixing the slurry 
with oil in an amount sufficient to produce agglomerates of the 
carbonaceous solids containing from about 10 weight percent oil to about 
50 weight percent oil and thereafter recovering the agglomerates as a 
product, in many instances the carbonacous solids of low-rank or oxidized 
coal are not agglomerated by such treatment. However, these 
non-agglomerating carbonaceous solids are readily agglomerated and 
recovered by mixing as a conditioning agent about 0.5 volume percent to 
about 5.0 volume percent of an electrolyte, such as concentrated sulphuric 
acid, concentrated hydrochloric acid or sulphur trioxide gas, with the 
aqueous slurry and then adding coal derived oil to it and agitating the 
mixture to produce agglomerates. Agglomerates are produced in a consistent 
and reliable manner containing from about 10 weight percent to about 50 
weight percent of the oil. In instances where handling of the agglomerates 
produced would require increased strength it was found that mixing an 
agglomerate strengthening agent such, as, for example, oleic acid or 
cresylic acids or creosote oil, or pine oil, or di-n-propyl ketone or 
1-hexanol, or sodium oleate, or naphthenic acid, or naphthylacetic and 
cyanamide or the like to the aqueous slurry, containing the said 
agglomerates of carbonaceous solids of low-rank coal or oxidized coal with 
oil and inorganic solids, readily produced the stronger agglomerates 
required for such handling. 
In the tests, Onakawana lignite from Ontario, Canada, was used with mineral 
contents varying from about 16 to about 32 wt % dry basis in a aqueous 
slurry containing about 10 to about 15 wt % solids. 
Suitable agglomerating oils are tar extracts and other oils derived from 
coal. Mixing rates range from about 0.1 hp/ft.sup.3 to about 6.0 
hp/ft.sup.3 were used in the vessels 1 and 2. The optimum degree of 
agitation is variable depending upon the particular solids being subjected 
to agglomeration, the types of coal derived oil used and the like, with 
values from about 0.4 hp/ft.sup.3 to about 4.0 hp/ft.sup.3 being common. 
Normally, a colour change occurs in the mixture in agglomerating vessel 2 
when the carbonaceous portion of the coal becomes coated with the coal 
derived agglomerating oil i.e., the bulk of the coal derived agglomerating 
oil is transferred from the aqueous medium to coat the carbonaceous 
portion of the coal and so the presence of oil is no longer observed in 
the vessel 2, although such a general rule of thumb is subject to 
qualification where an excessive amount of agglomerating oil is used. 
In the second agglomerating vessel 4 lower rates of agitation from about 
0.1 hp/ft.sup.3 to 0.5 hp/ft.sup.3 were used. The particle size of the 
coal solids charged to the vessel 1, were typically small, i.e., 
essentially smaller than 35 mesh Tyler Standard Screen (Sieve No. 40 in 
the U.S. Sieve Series) and preferably essentially smaller than 65 mesh 
Tyler Standard Screen (Sieve No. 70 in U.S. Sieve Series). For the tests 
the results of which are given in the following Table 1, in example 1, the 
particle sizes were in the range of minus 200 mesh plus 250 mesh Tyler 
Standard Screen (minus 200 plus 230 in U.S. Sieve Series); in examples 2 
and 3, minus 65 mesh plus 200 mesh Tyler Standard Screen, (minus 70 plus 
200 in U.S. Sieve Series); and in example 4 the particle sizes were 
smaller than minus 65 mesh Tyler Standard Screen (minus 70 in U.S. Sieve 
Series). Larger particles can, of course, be included depending on 
dissemination of ash (mineral matter) in the coal. 
TABLE 1 
__________________________________________________________________________ 
RESULTS 
Change in 
CONDITIONS Mineral 
ASH AGGLOMERATING BINDER ELECTROLYTE Content 
(MINERAL) 
OIL Amount Amount 
Carbonaceous 
from Coal 
CONTENT 
Coal Derived 
Amount WT WT. % 
Elec- 
Vol. % 
Recovery 
to Agglom- 
TEST 
COAL WT. % IN 
Agglomerat- 
% on Dry 
Binder 
on Dry 
trolyte 
in Percent 
erates 
NO. USED DRY COAL 
ing Oil Used 
Solids Used Solids 
Used 
Slurry 
Agglomerates 
WT. 
__________________________________________________________________________ 
% 
1 Onakawana 
31.9 Anthracene 
22 None None HCL 1.28 95 48 
Lignite Oil 
2 Onakawana 
16.6 Anthracene 
18 Cresylic 
1.46 H.sub.2 SO.sub.4 
0.58 93 54 
Lignite Oil Acid 
3 Onakawana 
21.5 Coal-Derived 
28 Oleic 
0.45 H.sub.2 SO.sub.4 
0.64 97 58 
Lignite Heavier Acid 
Distillate 
4 Onakawana 
25.4 Coal-Derived 
36 Cresylic 
1.59 H.sub.2 SO.sub.4 
0.77 99 56 
Lignite Heavier Acid 
Distillate 
__________________________________________________________________________ 
Referring now to FIG. 2, there is shown a flow diagram wherein oxidized 
coal from a source 42 is ground and conditioned as a slurry with an 
electrolyte at 44, the conditioned slurry is then agglomerated with coal 
derived agglomerating oil at 46. The coal agglomerates from 46 are formed 
into a coal/oil slurry at 48 and the coal/oil slurry is fed to a coal 
liquefaction plant at 50. At 50 the coal is subjected to hydrogenation and 
the resulting gases, oils and coal solids residues are separated, and the 
oil is fractionated. 
The hydrogen gas supply for the hydrogenation is derived from gaseous 
H.sub.2 production at 52 which receives gaseous O.sub.2 from 54 where 
oxygen is derived from air. At 52, gasification, shift conversion, gas 
clean up and H.sub.2 compression takes place, while residue produced by 
coal liquefaction is fed thereto. 
A portion of the coal derived oil produced at step 50 is used at step 46 as 
agglomerating oil and another portion is used at step 48 for slurring the 
agglomerates. At step 50 coal hydrogenation, gas/liquid/solid separation, 
H.sub.2 recovery and gas treatment, and fractionation occurs, giving as 
products naphtha, mid-distillate and heavy oil. 
Sour water from both the coal liquefaction step 50 and the H.sub.2 
production step 52 are fed for effluent control to an effluent treatment 
step 56 where NH.sub.3 recovery and phenol recovery is effected. 
Acid gases from the coal liquefaction step 50, the H.sub.2 production step 
52 and the effluent treatment step 56 are fed to an emission control step 
58 where sulphur is extracted and tail-gas clean-up occurs. 
Gases from the coal liquefaction treatment step are treated at step 60 by 
methanation, light end separation, and acid-gas removal to produce 
synthetic natural gas and liquefied petroleum gas leaving an acid gas 
residue.