FIELD OF THE INVENTION
The present invention relates to a process of enrichment of reactive macerals in
coal.
BACKGROUND OF THE INVENTION
It is known that formation of coal takes place in two different stages for
example, biochemical and geochemical. During the biochemical stage, depending
upon the type of plant material and the extent of decomposition, different
petrographic components, known as macerals, are formed. Macerals upon
heating are grouped into two basic categories. Such as reactive and inerts. The
reactive macerals are Vitrinite, Semi—vitrinite, Exinite, wherein the inerts are
Inertinite and mineral matter. The first group of macerals is not only
petrographically distinct but also is characterized by chemical and physical
properties. For example, vitrinite is characterized by a relatively high oxygen
content compared to the other group-members. Vitrinite is rich is aromatic
structures. The aromaticity increases with rank from about 70%C in aromatic
bonding in sub bituminous coal to over 90% in anthracite. Vitrinite also contains
Various aliphatic groups. Vitrinite is derived from parenchymatous and woody
tissues of roots, stems, barks and leaves composed of cellulose and lignin.
Depending on the process of decomposition it undergoes, the degree of
gelification and rank, cell structures are preserved and visible to varying extents.
Being a major component of most of the coals, the properties of vitrinite largely
influence the industrial processes in which coal is utilized. In medium rank coals,
the vitrinite readily fuses during carbonization and this property interalia
influences both the process and the products of hydrogenation and combustion.

Oxidation during storage leads to deterioration of the quality of vitrinite including
thermoplasticity in the case of bituminous coal. Vitrinite is a major source of
natural gas of primary origin.
Vitrinite macerals are the most desired components in coking coal, and these
maceral is one of the substances in coal that produces its fluid characteristics
and also contribute to plasticity of coal. The reactivity in low rank coals means
they are readily hydrogenated. The range for density of vitrinite varies from 1.3
to 1.45 g/cm3. Density changes with rank, however, the minimum density can be
noted in the medium volatile bituminous rank range. Exinite macerals are
particularly rich in hydrogen, and as a result, yields high amounts of gas and tar
when carbonized. Hence coals with high liptinite content are the most suitable
for hydrogenation. An increased exinite content increases the strength of coal.
The density of exinite range from 1.0 to 1.25 g/cm3. Intertinite macerals are
generally very inert in carbonization and hydrogenation process. The specific
gravity of inertinites is in the range of 1.45 to 1.5. In coke making an enriched
vitrinite macerals can be used as blend in combination with coals which have low
coking properties.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a process for enrichment of
reactive materials in coal, especially which are non-coking in nature.
Another object of the invention is to propose a process for enrichment of reactive
materials in coal, in which the reactive materials in coal is enriched by specific
grinding and screening method.

SUMMARY OF THE INVENTION
Accordingly, there is provided a process for enrichment of reactive materials in
coal mainly which is non-coking in nature. This method is applicable for coking
coal also. In essence, the inventive process includes a specific grinding method
followed by a developed separation technique. Experimentation of the process
revealed that when non-coking coal is ground by a specific technique and
followed by separation of size fraction in a specific technique, it shows an
enrichment of the reactive macerals.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 shows a micrograph of a coal sample used in the invention.
DETAILED DESCRIPTION OF THE INVENTION
Selection of coal: For the disclosed invention, three types of non-coking coal and
one coking coal has been selected. The non-coking coals are known to be lacking
coking properties and used mostly for PCI (pulverized coal injection) purpose.
Characterization : The coals are characterized in terms of ash, volatile matter
(VM), crucible swelling number (CSN) and petrography. The details of the tests
are as follows :
Ash determination : Ash is determined by following ASTM standard D 3174-11.1
gm of 250 mm size sample is taken to a weighed capsule. Then the sample is
placed in a cold muffle furnace and heated gradually at such a rate that the
temperature reaches 450°C to 500°C by 1 hr. At the end of 2 hr, the sample
reaches the temperature of 950°C. After cooling the sample, the weight of the

sample is measured and ash-content in the coal is calculated by weight
difference.
VM determination : Ash is determined by following ASTM standard D 3175-11. In
this test, 1 gm of 250 mm size sample is taken in a covered platinum crucible
and heated in a furnace of 950°C for 7 min. The volatile materials is calculated
by weight difference.
Crucible swelling number : Crucible swelling number test has been done by
following ASTM D720-91 (2010), in which 1 gm of sample (-0.212 mm size) is
taken in a translucent squat shaped silica crucible and the sample is leveled by
tapping the crucible at least 12 times. The crucible is covered with a lid and
heated under standard conditions, either by a gas burner or a muffle furnace.
After the test is completed, the shape of coke button is compared with a
standard chart and accordingly, the crucible swelling number (0 to 9) is assigned
to the coal sample.
Petrography of coal: This is done by following ASTM standard D2797M-11a,
D2798-11 a and D 2799-1. For microscopic studies 5 kg coke sample is crushed
to minus 3 mm size and by using coning and quartering method, 100 gm sample
is prepared and mounted on carnauba wax. The mounted sample is polished
using silicon carbide coated grinding papers of 320, 400, 600 grids respectively,
followed by buffing on a blazer cloth using alumina polishing compounds (1.0
and 0.3 mm). The polished specimen is dried using an air dryer prior to
microscopic studies. The microscopic studies were done by Leica DMS 4000
microscope along with QW in software.

Grinding and separation method : Around 10-20 kg sample drawn from 100 kg
as received coal, by the coning-quartering method. Then it is passed through a
5 mm screen. After screening, it is subjected to grinding by shearing techniques.
The product is then screened with a 0.5 mm screen and the -0.5 mm fraction is
collected. It is then sent for further characterization as described hereinabove.
Results & Discussions :
Three types of non-coking coals, designated as A and B and C and one type
coking coal designated as D, are selected for the experimentation. Table 1 shows
the properties of these coals. After grinding and separation, the properties are
presented in Table 2 (designated as A1, B1, C1 and D1). It is observed that the
amount of reactive materials has been increased in each case. Crucible swelling
number also gets increased. This is due to orientation and size of different
macerals. The enrichment of macerals also depends on the locking of maceral
and mineral. By shearing it is possible to liberate the reactive macerals to a large
extent. Shearing and appropriate selection of size fractions of coal leads to
liberation of reactive (mostly vitrinite) maceral selectively.
In Coal grinding process, the grinding of solid matter occurs under exposure of
mechanical forces that trench the structure by overcoming of the interior
bonding forces. After grinding, the state of the solid is changed, for example, the
grain size, the grain size disposition and the grain shape. During shearing, the
major breakage of coal macerals and minerals takes place by attrition. Due to
the attrition, the liberation of reactive macerals are found to be higher.

Figure 1 shows the micrograph of a sample. For achieving higher liberation
during shearing, the maceral and mineral need to be interlocked in such a way
that by attrition more amount of reactive macerals is generated. This can be
linked with one of the properties of coal, namely hardgrove grindability index
(HGI). The HGI was developed in the 1930s to measure empirically the relative
difficulty of grinding coal. Coals with low values of HGI are more difficult to grind
and high values are much easier to grind. A 50 gm sample of coal, which has
been prepared in a specific manner and which has a limited particle size range,
1.18 x 0.6 mm, is placed in a stationary grinding bowl in which eight steel balls
can run in a circular path. A loaded ring is placed on top of a set of balls with a
gravity load of 284 N. The machine is run for 50 revolutions. The top of the
machine is removed and the ground coal removed. This coal is sized and a
quantity less than 75 microns is recorded. This is converted to a HGI value using
a calibration graph.
It is concluded from the present invention, that the coals having HGI greater
than 80 (coal A and D) are responding to shearing to a greater extent and hence
generating higher volume of reactives.

WE CLAIM :
1. A process for enrichment of reactive materials in coal, comprising the
steps of:
providing a coal sample having ash-content in a range of 7-16% on dry
basis and a crucible swelling number ranging between 0-6;
subjecting the coal sample to grinding through a shearing technique; and
separating the crusted coal by a 0.5 mm screen and collecting a size
fraction of 0.5 mm,
Wherein hardgrove grindability index (HGI) of the coal sample above 80
exhibits high responsiveness to shearing to generate large volume of
reactives.
2. The process as claimed in claim 1, wherein a multiple coal samples are
used in the process for characterization, wherein the original coal samples
having properties in terms of ash (8.7 to 16.99 db%), volatile materials
(13.74 to 21.25 db%), crucible swelling number (0 to 6.5) and total
reactive (33.5 to 42 vol%) wherein the products of the process from
multiple samples exhibit properties in terms of ash (8.08 to 15.15 db%),
volatile materials (12.70 to 21.9 db%), crucible swelling number (1.5 to
7), and total reactive (48.3 to 6 5.3 vol%).

3. The process as claimed in claim 1, wherein the ash-content, volatile
materials, crucible swelling number, and petrography of coal samples is
determined following ASTM standard D31744-11; D3175-11; D720-91
(2010); and D 2797M-11a, D2798-11a, and D2799-1, respectively.

ABSTRACT

The invention relates to a process for enrichment of reactive macerals in coal (both non-coking and coking), comprising the steps of : providing a coal sample having ash-content in a range of 7-16% on dry basis and a crucible swelling number ranging between 0-6; subjecting the coal sample to grinding through a shearing technique; and separating the crusted coal by a 0.5 mm screen and collecting a size fraction of 0.5 mm, wherein hardgrove grindability index(HGI) of the coal sample above 80 exhibits high responsiveness to shearing to generate large volume of reactives.