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International Journal of Advances in Engineering &amp; Technology, May 2013.
©IJAET
ISSN: 2231-1963

SEPARATION CHARACTERISTICS OF FLY ASH PARTICLES IN
HYDROCYCLONE
Suresh1, Chandranath Banerjee2, A.K.Majumder2, S. N. Varma1
1

Department of Mechanical Engineering, University Institute of Technology, Rajiv Gandhi
Proudyogiki Vishwavidyalaya, Bhopal, India
2
Department of Mining Engineering, Indian Institute of Technology, Kharagpur, India

ABSTRACT
Graded fly ash particles have many useful industrial applications due to its fineness and spherical shape.
However, grading of fly ash in an industrial scale is a challenging task. The possibility of using hydrocyclones
for this purpose has been demonstrated here based on carefully conducted laboratory experiments. The primary
objective of this research is to study the effectiveness of a classifying hydrocyclone to produce graded fly ash
particles. To do this the principal challenge is on the optimization of the process and the design variables to
generate graded fly ash particles of various size ranges. The experimental data reveals that the ratio between
the underflow and the overflow discharge openings, popularly known as cone ratio, of a hydrocyclone actually
controls the particle size separation behavior in a hydrocyclone. Finally, the study reveals that the grading of
fly ash particles at desired size ranges is possible by properly controlling the cone ratio at an appropriate level
of feed inlet pressure.

KEYWORDS: fly ash, classification, hydrocyclone, cone ratio.

I.

INTRODUCTION

Fly ash is a by-product of thermal power plants resulting from the combustion of pulverized coal in
the coal-fired furnaces. Inorganic matter present in coal solidifies while suspended in exhaust gases
and ultimately gets collected through electrostatic precipitator. Due to this rapid solidification process
fly ash particles are generally spherical in shape. The fly ash is mainly considered to be a
ferroaluminosilicate element (El-Mogazi et al., 1988; Mattigod et al., 1990) although presence of char
and some amorphous and crystalline phases is common. Carbonates, silicates, sulfates, hydroxide and
oxides of calcium, iron, aluminum, and other metals in trace amount (Adriano et al., 1980) also exist
in flyash. The pH of flyash can vary from 4.5 to 12.0 depending largely on the S content of the parent
coal (Plank and Martens, 1975).The physical and chemical properties of fly ash depend on the nature
of the geo-morphological nature of coal deposit, mining technology, conditions of combustion, type
of emission control devices and storage and handling methods.
Fly ash particles usually belong to size range of 0.01 to 100 μm (Davison et al., 1974). Particle size
distribution of coal fly ash shows different size range (Mahlabaet al., 2011)which arebe classified as
clay-sized particles (particles greater than 1 μm and smaller than 5 μm), silt-sized particles (particles
greater than 5 μm but smaller than 75 μm) and sand-sized particles (particles greater than 75 μm but
smaller than 425 μm).
Material scientists from various fields have advocated that graded fly ash (very close size range
product) particles have excellent properties to find application in many potential areas. However, the
major challenge lies in the development of a commercially viable process capable of handling large
tonnages per unit time in grading of fly ash particles due to its fineness. Hydrocyclone is a very
popular unit operation in various engineering fields like chemical engineering, mineral engineering,
food processing etc. mainly for solid-solid and solid-liquid separations. It also finds applications in
solid-gas and liquid-liquid separation. Although hydrocyclone is a versatile unit operation due to its
apparent simplicity in operation, low floor space requirements and high throughput due to very low

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Vol. 6, Issue 2, pp. 1013-1025

International Journal of Advances in Engineering &amp; Technology, May 2013.
©IJAET
ISSN: 2231-1963
residence time requirement, the major challenges lie in the selection of an appropriate design for a
particular requirement and in the optimization of the process as well as design variables. However,
application specific designs of hydrocyclones are already commercially available.
The objective of this work is to study whether hydrocyclone can be effectively used for the generation
of closely sized particles of fly ash or not. To do this an in-depth study on how the partitioning
behaviors of solid particles are influenced by the process and design variables of the hydrocyclones is
a pre-requisite. Detailed experiments were carried out using a laboratory model closed-circuit
hydrocyclone test rig varying the important process and design variables.

II.

LITERATURE REVIEW

With increasing global population the demand for electricity is also increasing at an exponential rate.
The consumption of coal worldwide is projected to increase by 36% by the year 2020 (Jala and Goyal,
2006; Haynes, 2009). Therefore, the generation of fly ash is mounting at a high rate globally. Disposal
and proper utilization of fly ash are therefore, two very important issues. Fly ash disposal into the
environment causes air, water and soil pollutions. Primarily, fly ash is disposed off using either dry or
wet disposal scheme. In dry disposal, the fly ash is transported by truck, chute or conveyor at the site
and disposed off by constructing a dry embankment (dyke). In wet disposal, the fly ash is transported
as slurry through pipe line and disposed off in impoundment called &quot;ash pond&quot;. Coal fly ash caused
groundwater contamination has been reported worldwide. Dumped fly ash contaminates surface and
groundwater (Praharajet al., 2002), soils and vegetation due to the presence of hazardous metals
(Sikka and Kansal, 1995). It also contains many radioactive elements, which causes some harmful
diseases. Therefore, to overcome all these problems research work is continuing on its bulk utilization
and value added product development from it.
Globally, more than 30% of the total annual fly ash produced is utilized (Haynes, 2009) in highvolume-low-return areas like land filling, road making, cement making etc. at present and the rest of
the amount is being discharged in tailing ponds in the form of slurry. In the process large volume of
water is wasted as losses due to evaporation and the ground water is also getting contaminated due to
leaching of metals from the mineral substances present in fly ash. Large areas of valuable land in the
vicinity of power plants are also getting occupied to store enormous volume of fly ash particles in ash
ponds. This situation is worse in countries like India where the thermal coals generally have ash
contents in the range of 40-45% by weight. The percentage of flyash utilization is different in
different countries. In India, flyash production was 112 million tones in 2005–06 and it is expected to
generate about 150–170 million tons of flyash per year by end of the 2012 (MOEF, 2007).The
utilization of flyash in India has increased substantially in recent years from 13 million tons to51
million tons (MOEF, 2007). Research attention is, therefore, mounting to increase the utilization of
fly ash to partially overcome all those problems.
Many groups are working all over the world on fly ash utilization and many technologies have already
been developed and implemented. Fly ash in a bulk proportion is used mainly in the concrete and
cement manufacturing industries (Ecoba, 2002) due to its pozzolanic properties. Other bulk utilization
includes building roads, mine backfilling and land stabilization in mining areas (Jarvis and Brooks,
1996). There are a number of technical, economic, and legal barriers to the use of large quantities of
coal fly ash. In bulk utilization although high volume of fly ash can be utilized but net return on
investment is very low. On the other hand several value-added products have been developed where
less volume of flyash is utilized but return is very high.
Refractory bricks and ceramic products (Sevelius, 1997), heat and wear resistance ceramic products
(Vilches et al., 2001), cement substitute (Gao et al., 2008), porcelainised granite tiles, synthesis of
high cation exchange capacity (CEC) zeolites (Moreno et al., 2002), mullite as refractory aggregate
for refractory castables cordierite, additives for immobilization of industrial waste water treatment
(Dirk,1996),removal of heavy metal ions from wastewater (Somerset et al., 2008), ‘slash’ (fly
ash/sludge blend) production for soil amendment (Reynolds et al., 1999), sorbents for flue gas
desulfurization (Garea et al., 1997), filter material for the production of different products (Kruger,
1997) are some examples where less volume of fly ash is utilized but return is very high.
Fly ash particles can also be effectively utilized in many other sectors if the particles are graded
properly. For example, particle having the size greater than 45 micron is used as binders and the

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Vol. 6, Issue 2, pp. 1013-1025

International Journal of Advances in Engineering &amp; Technology, May 2013.
©IJAET
ISSN: 2231-1963
particles of 0.1 to 5 microns are used for making mineral filler (Styron et al., 1999). Particles in the
size range of 40-150 micron is reported to be used as reactive filler in grout packs, roll Crete, shot
Crete asphalt and lightweight foamed concrete (Kruger 1997). The filler fly ash have three different
particle sizes (25-45µm, 90-105µm &amp; 150-180µm).These particles can also be used in the cement,
concrete, bricks and polymer industries.
Therefore, one of the technical challenges lies in classifying the fly ash particles into different grades
conforming to various close size ranges.
In many engineering disciplines, hydrocyclones are effectively used as a dynamic particle separation
unit based on their size differences only. This is a continuously operating device, which utilizes
centrifugal force to enhance the relative settling velocity differentials between the particles. The
primary objective of this research was to study the effectiveness of a classifying hydrocyclone to
produce graded fly ash particles. To do this the principal challenge was on the optimization of the
process and the design variables to generate graded fly ash particles of various size ranges.

III.

EXPERIMENTATION

3.1 Material
Flyash was collected from a local power plant for experimentation purpose. The specific gravity of
the collected fly ash particles was measured to be 2.56. The size analysis of the sample was carried
out using a LASER particle size analyzer (Model MSX-14) and the data is shown in Figure 1 below in
a log-normal scale

volume % passing

Feed size distribution
100
90
80
70
60
50
40
30
20
10
0
0.1

1

10

100

1000

Particle size (in micron)
Figure1. Particle size distribution of fly ash

The measurement was repeated three times and the relative standard deviation was calculated to be
1.5 which ensures the reproducibility of the measurement technique. It may be observed from Figure
1 that the average size (d50) of the as-received fly ash sample is around 16 micron
A laboratory scale 76 mm diameter Mozley hydrocyclone made of polyurethane fitted in a closed
circuit test rig used for experimental purpose. Flexible arrangements, using flange, were made to fit
the units directly above the slurry tank. To transport the slurry (mixture of water and fly ash particles)
continuously from bottom of the tank to feed inlet of the cyclone a centrifugal pump (Type SP- 2H)
was used. The pump has rubber-lined impeller to minimize the abrasion of the solid particles. From
literature (Govindarajan, 1991 and Verghese, 1994) it was found that the slurry throughput in a 76
mm diameter cyclone varies from 0.5 to 4 liters/sec. Slurry feed rate to the separator and the pressure
at the inlet was adjusted by using the by-pass valve (gate valve). A heavy duty stirrer was fitted
horizontally at the bottom level of the slurry tank to keep the slurry in uniform suspension. The
schematic diagram of the closed circuit test rig is shown in Figure 2

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Vol. 6, Issue 2, pp. 1013-1025

International Journal of Advances in Engineering &amp; Technology, May 2013.
©IJAET
ISSN: 2231-1963

Figure2. Schematic diagram of the test rig

To collect the representative samples from the overflow and underflow streams for a desired duration,
a properly designed splitter system was fitted on the top of the slurry tank. The splitter consists of a
rectangular channel having a length of 1000 mm, width 500 mm and height 500 mm. A partition wall
of a height 400 mm was given to avoid mixing of overflow and underflow samples. In each
partitioned compartment an opening of 32 mm diameter was given to collect the samples separately.
Each opening was also connected with hose pipes having appropriate diameters to avoid free falling.
The entire arrangement of sample splitter was made up of stainless steel plates having thickness
around 5 mm. The dimensional detail of the sample splitter is shown in Figure 3.

Slider

Handle

Slide

TOP VIEW

FRONTVIEW

Figure3. Top and front view of the Sample splitter

3.2 Experimental Procedure
The collected fly ash samples were dried in a drying oven at 105 ± 5 oC for 4 hours to remove surface
and entrapped moisture. The dried samples were then mixed thoroughly and representative samples of
10 kg each were sampled out using the conventional coning and quartering method. Slurry having a

1016

Vol. 6, Issue 2, pp. 1013-1025

International Journal of Advances in Engineering &amp; Technology, May 2013.
©IJAET
ISSN: 2231-1963
fixed pulp density of 10% by weight was prepared by adding calculated amount of water with
measured quantity of fly ash sample for all the experiments. Slurry temperature was maintained at 40
°C during the experiments throughout. Initially, slurry is pumped into the separator by keeping the bypass valve fully open, and subsequently, the opening of the valve was adjusted to obtain required feed
inlet pressure. The system was then allowed to run for a few minutes to attain a steady state. The
attainment of steady state was confirmed once the measured slurry flow rates through both the streams
reached at a constant level.To collect samples separately but simultaneously from the overflow and
underflow streams the sample splitter assembly was used. Before starting the next experiment,
equivalent amount of water and fly ash sample collected from previous experiments were added to
maintain the constant slurry head in the tank. The slurry thus collected for a fixed duration was dried
in an oven to determine the distribution of water and fly ash in the respective streams. The respective
weights of slurry collected through each outlet i.e. overflow and underflow were recorded for further
analyses. The same procedure was followed in all the experiments.

IV.

RESULTS AND DISCUSSION

It was mentioned that following the experimental methodologies discussed in detail in previous
section, systematic experimental data was generated first for further analyses. The solid particles
collected through underflow and overflow of the hydrocyclone at different operating conditions were
subjected to particle size analyses. The experimental conditions and the data generated at those
conditions are presented in Table 1.
Table1. Experimental Conditions and the Data
Slurry wt.

1017

Solid wt.

Water wt.

Exp.
No.

P
(psi)

VFD
(mm)

SPD
(mm)

O/F
(kg)

U/F
(kg)

O/F
(kg)

U/F
(kg)

O/F
(kg)

U/F
(kg)

Collection
Time
(sec)

1

10

13

10

6.61

4.65

0.27

0.90

6.34

3.75

12.99

1R

10

13

10

6.92

4.74

0.27

0.90

6.64

3.85

13.44

1RR

10

13

10

6.52

4.48

0.26

0.84

6.26

3.64

12.92

2

10

13

15

3.42

9.46

0.13

1.16

3.29

8.30

12.97

2R

10

13

15

3.17

8.67

0.12

1.05

3.05

7.62

11.75

2RR

10

13

15

3.49

9.52

0.14

1.13

3.35

8.39

13.28

3

15

13

15

3.72

9.50

0.14

1.18

3.58

8.32

10.79

3R

15

13

15

3.80

9.86

0.15

1.23

3.65

8.63

11.32

3RR

15

13

15

3.70

9.56

0.15

1.17

3.55

8.39

10.97

4

15

13

10

4.39

6.61

0.81

0.26

3.57

6.35

11.11

4R

15

13

10

4.38

6.70

0.81

0.25

3.57

6.44

11.1

4RR

15

13

10

4.32

6.38

0.79

0.25

3.53

6.13

11.14

5

20

13

10

7.192

4.88

0.27

1.08

6.92

3.80

10.76

5R

20

13

10

7.60

5.04

0.29

1.03

7.31

4.00

11.42

Vol. 6, Issue 2, pp. 1013-1025

International Journal of Advances in Engineering &amp; Technology, May 2013.
©IJAET
ISSN: 2231-1963

1018

5RR

20

13

10

7.61

5.098

0.29

1.02

7.32

4.08

11.68

6

20

13

15

3.64

10.02

0.12

1.28

3.52

8.74

10.79

6R

20

13

15

4.044

10.15

0.13

1.29

3.92

8.86

10.99

6RR

20

13

15

4.06

10.35

0.13

1.30

3.93

9.05

10.48

7

10

18

15

8.00

7.76

0.27

1.24

7.74

6.52

12.36

7R

10

18

15

7.80

7.446

0.33

1.18

7.47

6.27

11.96

7RR

10

18

15

5.12

4.94

0.22

0.77

4.90

4.17

11.78

8

10

18

10

6.13

1.76

0.29

0.51

5.84

1.25

6.37

8R

10

18

10

7.23

2.03

0.37

0.58

6.86

1.45

7.57

8RR

10

18

10

6.88

1.96

0.33

0.55

6.55

1.41

7.43

9

15

18

10

7.74

2.10

0.34

0.68

7.40

1.42

6.61

9R

15

18

10

7.68

2.10

0.35

0.67

7.33

1.43

6.37

9RR

15

18

10

7.12

1.90

0.38

0.60

6.73

1.31

6

10

20

18

10

10.98

2.95

0.47

0.97

10.51

1.98

7.95

10R

20

18

10

9.63

2.56

0.40

0.76

9.23

1.80

7.82

10R

20

18

10

10.59

2.85

0.45

0.92

10.14

1.92

6.95

11

20

18

15

7.12

6.70

0.27

1.10

6.85

5.60

7.89

11R

20

18

15

9.41

8.72

0.35

1.41

9.06

7.31

9.75

11RR

20

18

15

9.77

9.09

0.36

1.45

9.40

7.64

10.27

12

15

18

15

7.68

7.24

0.31

1.21

7.37

6.04

9.52

12R

15

18

15

7.78

7.17

0.31

1.17

7.47

6.00

9.51

12RR

15

18

15

7.32

6.88

0.30

1.10

7.02

5.78

8.93

13

10

25

10

11.33

1.29

0.62

0.67

10.71

0.62

6.7

14

10

25

15

11.95

3.62

0.57

1.00

11.38

2.63

8.3

15

10

25

20

10.88

8.754

0.47

1.47

10.41

7.28

8.64

Vol. 6, Issue 2, pp. 1013-1025

International Journal of Advances in Engineering &amp; Technology, May 2013.
©IJAET
ISSN: 2231-1963
16

15

25

10

9.26

1.008

0.44

0.54

8.82

0.47

3.84

17

15

25

15

9.02

2.554

0.39

0.77

8.63

1.78

4.39

18

15

25

20

6.37

4.668

0.25

0.85

6.12

3.82

3.88

19

20

25

10

11.72

1.398

0.57

0.77

11.15

0.62

4.3

19R

20

25

10

16.77

1.87

0.81

1.02

15.96

0.85

5.93

20

20

25

15

12.45

3.476

0.52

1.09

11.94

2.38

5.31

20R

20

25

15

13.27

3.59

0.54

1.10

12.73

2.49

5.51

21

20

25

20

9.9

7.098

0.37

1.31

9.53

5.79

5.3

21R

20

25

20

9.77

6.786

0.36

1.25

9.41

5.54

5.23

Sometimes in a closed-circuit test rig that is used for the experimentation purposes the feed size
distribution changes because of abrasion and due to the improper design of the stirring system in the
slurry tank. Therefore, the comparative data at various experimental conditions generate misleading
information. To confirm the consistency in feed particle size distributions at various experimental
conditions, the reconstituted feed particle size distributions are compared with the actual feed particle
size distribution as presented in Figure 4. It is evident from this figure that the feed particle size
distribution remains unchanged throughout which reaffirms that the experimental data can reliably be
used for further comparison purposes.
Feed
Exp.10
Exp.16
&quot;Exp1&quot;

Exp.5
Exp.11
Exp.17
Exp 2

Exp.6
Exp.12
Exp.18
Exp3

Exp.7
Exp.13
Exp.19
Exp4

Exp.8
Exp.14
Exp.20

Exp.9
Exp.15
Exp.21

100
90

Volume %

80
70
60
50
40
30
20
10
0
0.1

1

10

100

1000

Particle size (in micron)

Figure 4: Comparative Plots for Feed Particle Size Distribution

In the first column of Table 1, ‘R’ and ‘RR’ denotes repeat test 1 and 2 respectively. It is evident from
the repeat tests that the variation in the data at a particular experimental condition is marginal. For
example, if we calculate the standard deviations at a 95% confidence level of slurry weights, solid
weights and water weights collected through overflow and underflow at experiment number 1, the

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Vol. 6, Issue 2, pp. 1013-1025

International Journal of Advances in Engineering &amp; Technology, May 2013.
©IJAET
ISSN: 2231-1963
values are 0.41, 0.27, 0.01, 0.07, 0.4 and 0.21 respectively. Marginal values of the standard deviations
data establish the reliability and the reproducibility of the experimental data generated. For further
analyses, the average values of the repeat data are considered.

4.1 Partitioning behaviours of Slurry, Solid and Water
The spigot diameter (SPD) and the vortex finder diameter (VFD) are the two most important design
variables which affect the classification performance of hydrocyclones. Instead of studying the effects
of the SPD and the VFD independently, cone ratio (ratio between SPD and VFD) has been used to
plot the data presented in Table 1 to understand the particle classification behavior at different
operating conditions. The graphical representations of the data are given in Figures 5 to 7 hereunder
which reflects the trends of the data.

Figure 5: Effect of Cone Ratio on Slurry Split

Figure 6: Effect of Cone Ratio on Solid Split

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International Journal of Advances in Engineering &amp; Technology, May 2013.
©IJAET
ISSN: 2231-1963

Figure 7: Effect of Cone Ratio on Water Split

From Figures 5 to 7 it is observed that with increasing cone ratio the slurry split, solid split and water
split decrease monotonically. This has happened due to the increased cross-sectional area in the
underflow discharge opening with increasing cone ratio which allows more slurry to pass through.
From the Figures 5-7 it is also interesting to note that at a fixed cone ratio all the three splits remain
almost identical at all feed pressures (P). This is probably signifying that the relative proportions of
slurry, solid and water reporting through a particular discharge opening remain unchanged with
increasing inlet flow rates, which is directly dependent on P, although their individual values will vary
considerably. This is a very significant observation which may be used as a scale-up factor for
hydrocyclones for industrial applications.
A close look at the Figures 5-7 also reveals that the absolute values of slurry split and water split at a
given operating condition are almost identical whereas the solid split values differ considerably. As
the solid concentration for all the experiments were kept at a constant level of 10 % by weight, the
density and the viscosity values of slurry are expected not to differ much from water and as a result
there is hardly any difference in their respective partitioning behaviors. The differences between the
solid split values and slurry split or water split values strongly signifies the classification of solid
particles at all the operating conditions.

4.2 Particle Classification Behavior
To understand the particle classification behavior at different operating conditions properly, the %
recovery of each particle size in underflow at each experimental condition has been calculated using
the following formula:
% Recovery in underflow = 100 x (weight of a particle size class in underflow) / (weight
of that particle size class in re-constituted feed)
% Recovery in underflow thus calculated has then been plotted as a function of individual particle
size, the curve thus generated is commonly known as partition curves in mineral processing literature
(Wills’ 1992). The partition curves generated for each experimental condition are then compared, as
shown in Figure 8.

1021

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International Journal of Advances in Engineering &amp; Technology, May 2013.
©IJAET
ISSN: 2231-1963
Expt. 1

Expt. 2

Expt. 3

Expt. 6

Expt. 5

Expt. 7

Expt. 8

Expt. 9

Expt. 10

Expt. 11

Expt. 12

Expt. 13

Expt. 14

Expt. 15

Expt. 16

Expt. 17

Expt. 18

Expt. 19

Expt. 20

Expt. 21

100
90
Type 1

% Recovery (Underflow)

80
70

60

Type 2

50
40

Type 3
30
20

Type 4

10
0
0.1

1

10

100

1000

Particle Size (micron)

Figure 8: Comparison of Partition Curves

Following interesting observations can be made from Figure 8:
(1) Partition curves in all experimental conditions do not follow the conventional ‘S’ shaped
pattern as mentioned in text books (refer wills’ book again), rather they have “Fish-hook”
patterns as described in recent literature (Nageswararao, 2000; Del Villar and Finch, 1992;
Finch, 1983 ; Flintoff, Plitt and Turak, 1987). This means that the recoveries of relatively
finer particle sizesare initially higher than the coarser particle sizes in underflow up to a
critical particle size and after that the recovery increases with increase in particle sizes.
(2) The changes in recovery patterns as mentioned above in point (1) are within a particle size
limit of 10 microns only in all the experimental conditions. The recoveries in all experimental
conditions are minimum at a very close particle size range of 4-6 microns and the recoveries
of 0.6 – 0.7 micron particles are almost equal to 9-10 micron particles. Although mechanistic
arguments behind this typical phenomenon in hydrocyclones have already been given by
Majumder et al. (2003, 2007) further in-depth studies are required in this direction which is
beyond the scope of this research work.
(3) From Table 1 it is obvious that the experimental conditions were different from each other
and hence, it was expected that the partition curves would be different for all the experimental
conditions. However, it is apparent from Figure 8 that all the partition curves can easily be
divided into only four types as shown in the same figure. This probably suggests that although
the experimental conditions were different from one another but the experiments carried out
which represent a particular type of partition curve are hydro-dynamically similar. To confirm
this observation further analysis of the partition curves are made as described hereunder.
The relevant experiment numbers belonging to each type of partition curve, as shown in Figure 8, are
first noted from Table 1. These are as follows:
 Type 1: Cone ratio is 1.15 for experiments 2, 3 and 6
 Type 2: Cone ratios are 0.77 for experiment numbers 1 and 5, 0.8 for experiment numbers 15,
18 and 21, and 0.83 for experiment numbers 7 and 12.
 Type 3: Cone ratios are 0.56 for experiment numbers 8, 9 and 10, and 0.6 for experiment
numbers 17 and 20.
 Type 4: Cone ratio is 0.4 for experiments 13,16 and 19
While looking at the experimental conditions representing each type of partition curves, as
mentioned above, interestingly it is observed that the ratios of SPD and VFD at those conditions
are either identical or within a very close range. These ratios are given hereunder.
 Type 1: Cone ratio is 1.15 for all the three experiments as mentioned above.

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©IJAET
ISSN: 2231-1963


Type 2: Cone ratios are 0.77 for experiment numbers 1 and 5, 0.8 for experiment numbers 15,
18 and 21, and 0.83 for experiment numbers 7 and 12.
 Type 3: Cone ratios are 0.56 for experiment numbers 8, 9 and 10, and 0.6 for experiment
numbers 17 and 20.
 Type 4: Cone ratio is 0.4 for all the three experiments as mentioned above.
It is interesting to note that at a fixed cone ratio the partition curves at different experiment numbers
are almost getting super imposed on each other. The overall standard deviations calculated between
the respective %recovery data amongst all size distributions at different experimental conditions are
1.46, 1.16, 1.7, 1.15, 2.08, 2.87 and 2.98 for cone ratios of 1.15, 0.83, 0.80, 0.77, 0.60, 0.56 and 0.40
respectively. As the standard deviation values are considerably low and may safely be assumed within
the range of experimental errors, it can be concluded that the cone ratio is the most significant variable
in a hydrocyclone which controls the particle classification behavior. It may further be concluded that
at a given cone ratio the pattern of the partition curves in a hydrocyclone does not change, at least
within the range of the variables studied, at all which means the hydrodynamic conditions inside are
mainly controlled by the cone ratio. This is a very significant observation from the designing and the
operational points of views of any hydrocyclone.
It can also easily be observed from Figure 8 that at experimental conditions representing type 1 and
type 4 curves there is hardly any particle classification. This has happened because the cone ratios are
either too large (1.15 for type 1) or too small (0.4 for type 4) in those experimental conditions. Too
large a cone ratio signifies a condition where the SPD is much bigger than VFD whereas too small a
cone ratio signifies a condition where VFD is much bigger than SPD. In both the conditions the
majority of the solids present in feed will escape through the relatively larger opening along with
water due to availability of more passage which will not yield any particle size separation inside the
hydrocyclone. However, type 2 and type 3 partition curves signify that the fly ash particle
classification at a d50 size of in between 5-12 micron is easily possible with a 76 mm diameter
hydrocyclone if the cone ratio is optimally selected in the range of 0.56 to 0.83.

V.

CONCLUSIONS

Based on the above the following conclusions may be drawn:
(1) It was found that at a fixed cone ratio all the three splits remain almost identical at all feed
pressures (P). This signifies that the relative proportions of slurry, solid and water reporting
through a particular discharge opening remain unchanged with increasing inlet flow rates,
which is directly dependent on P, although their individual values will vary considerably.
(2) At a fixed cone ratio the pattern of the partition curves in a hydrocyclone remains identical, at
least within the range of the variables studied, which means that the hydrodynamic conditions
inside are mainly controlled by the cone ratio.
(3) Hydrocyclones can easily be used to classify fly ash particles at desired size ranges if the cone
ratio is selected within the appropriate range.
The most important conclusion of this research is to to establish the technical viability of a specific
design of a hydrocyclone to produce graded fly ash particles of various specifications by properly
controlling its design parameters which can be applicable to classify various other industrial wastes,
apart from fly ash, for their utilization or safe disposal of polluted wastes concentrated into a
particular size range (for example organic pollutants deposition on the surfaces of 20 micrometer or
below particle sizes in dredged sediments).

VI.

FUTURE WORK

Bulk utilization of fly ash in various area are well established. A number of research articles have
been published till today based on utilization of fly ash. But utilization of graded fly ash is a new
research area. Most challenging is to grading the fly ash into closely size range product. Most of the
developments and usages are taking place in foreign countries. It became difficult to know the exact
status of technologies and its evaluation without physically carrying out a survey abroad. In India it is
still utilized in bulk application as mentioned above which is economically not profitable.

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©IJAET
ISSN: 2231-1963
Considerable experimentation and testing is going on to classify the spent flyash available after
mineral extraction so that different fractions could be supplied to different markets. But very few
organizations have been involved in this area and limited research is going on in this area.
Therefore the future research should be the detailed study on the grading of fly ash particle into
different size range by physical separation techniques like hydrocyclone or flotation and application
potential of graded fly ash in making value added products and to study the effect of various grain
size distributions on the reactivity of fly ash or on the strength characteristics of fly ash. This will
increase the utilization of fly ash in many folds and in future fly ash can be considered a potential
resources rather than industrial waste.

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BIOGRAPHIES
Suresh Boriah received his Bachelor of Technology in Mechanical Engineering and Master of
Technology in Mechanical Engineering. He is an Assistant Professor in Globus Engineering.
College, Bhopal. He is presently doing his Ph.D study in the Rajiv Gandhi Proudyogiki
Vishwavidyalaya, Bhopal, India. His area of research is hydrodynamic modeling of cyclone
separator.

Chandranath Banerjee received the Bachelor of Science degree in Chemistry and Bachelor of
Technology in Chemical Technology from Calcutta University and Master of Technology from
Indian Institute of Technology, Kharagpur where he is currently pursuing the Ph.D. He is
currently doing research on hydrodynamic modelling of Hydrocyclone, CFD analysis of
swirling flow and solid- fluid interaction in turbulence medium.
A. K. Majumder is presently working as an Associate Professor of Department of Mining
Engineering, IIT Kharagpur. He received his Ph.D degree from university of Queensland,
Australia in Mineral Processing. His area of research is Mineral Processing, Coal Washing,
Solid-Fluid Interactions and Fine Particle Processing. He has published more than 100 technical
paper in reputed international and National journal. Before joining IIT Kharagpur he worked as
a scientist in RRL Bhopal.

S. N. Verma is presently serving as a Professor in Mechanical Engineering Department in Rajiv
Gandhi Proudyogiki Vishwavidyalaya, Bhopal, India. He received his Bachelor of Engineering,
Master of Technology and Ph.D in Mechanical Engineering. His area of Specialization is Fluid
Mechanics and Operation Research.

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