FIELD OF APPLICATION
The present invention relates generally to an apparatus for deashing coal by dry
benefication. In particular, the invention relates to benefication of finer fraction
of coal, (of-1mm), using circulating fluidized bed
BACKGROUND OF THE INVENTION
The ash content of Indian coal is generally very high, at around 35 - 45 %. In
order to deash the coal or limiting the ash content of coal for its further use,
benefication of coal is required.
Finer fractions of coal (of -lmm) is treated through the wet benefication
process. The present invention proposes dry benefication of coal through
circulating fluidized bed (CFB) route.
SUMMARY OF THE INVENTION
Thus the main object of the present invention is to provide a method of deashing
of coal fines (- lmm) using circulating fluidized bed.

Gas-solid fluidization plays a central role in many chemical processes,
metallurgical and energy conversion processes. Passing a gas through a bed of
solids forms a gas-solid fluidized bed. When this happens, the bed of solids
takes on certain fluid-like characteristics. From a chemical processing point of
view, the fluidized bed is an excellent way of contacting gaseous reactants with
catalyst particles in a heterogeneous gas phase reaction.
For the purpose of the present invention, the mixing and segregation pattern in
circulating fluidized beds consisting of fine particles and coarse particles having
different density, size distributions and terminal settling velocity were
investigated using a 0.1016 m ID and 5.62 m height riser of circulating fluidized
bed system. Attention is focused on understanding the interaction and
mechanism between the particles and the conditions in which complete mixing or
segregation is possible in circulating fluidized beds. Effort is made to find out the
extent of ash from coal in the circulating fluidized bed at a typical gas velocity
and solids circulation rate.
Coal comprises lighter organic carbonaceous materials and heavier inorganic
inert material leaving behind on ignition what is called commonly as ash. On
fluidization heavier inert materials comprising heavier minerals segregates and
less lighter material moves up at the top resulting in the benefication process.

In the present invention the circulating fluidized bed system uses a blower for
blowing air into two air lines, a fast bed column and a slow bed column for
keeping the bed respectively in a fluidized condition and a minimum fluidized
condition.
A cyclone separator is provided at the end of the slow bed column for feeding
the solids carried over form the fast bed to be separated by the cyclone
separator and collected at its exit end. The heavier separated particles fall back
to the slow bed column and transferred to the fast bed column via a solid
transfer line for recycling.
The present invention thus provides an apparatus for deashing coal by dry
benefication, using a circulating fluidized bed loop comprises a fast bed column
and a slow bed column, each having a bed of solids and provided with a
distributor for blowing in air from a rotary air blower; a cyclone separator
provided at the distal end of said slow bed column for receiving and for getting
the solid separated from solid fines; and a solid transfer line provided for
circulating solids from said slow bed column to said fast bed column for recycling
the separated solids.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention can now be explained with the help of figures of the
accompanying drawings where

Figure 1 shows in schematic form the apparatus of the present
invention with the circulating fluidized bed arrangement.
Figure 2 shows the arrangement of the experimental
setup used for the present invention.
Figure 3 shows the percent change in ash composition of the
given coal sample along the riser length: Ug = 3 55 m/s.
Figure 4 shows the percent change in ash composition of the
given coal sample along the riser length: Ug = 4.02 m/s.
Figure 5 ~ shows the percent change in ash composition of the given
coal sample along the riser length- Ug = 2.82 m/s.
DETAILED DESCRIPTION
As shown in Figure 1, the circulating fluidized bed system used in the present
invention for dry benefication of coal comprises a blower 1, air lines provided
with orifice meters 4 a fast bed column or riser 7, a cyclone separator 10 with a
bag filter 11, a down comer with a butterfly valve 9, a slow bed column 8 and a
solids control valve fitted in a solids transfer line 12.

The fast bed column or riser 7 has at its bottom an air distributor 5. This can be
a perforated multi-hole distributor plate, for preventing heavier solid particles
from entering into the air lines from the bed, with a wire mesh netting fixed
below the distributor plate.
The slow bed column 8 is provided with an air distributor 6 and comprises a
multi-hole plate (with 47° angle) fitted at its bottom to allow for smooth passage
of air. Above this conical distributor 6 a wire mesh is arranged along with the
perforated air distributor plate to prevent solid particles from entering the air
line. The slow bed column 8 is connected to the riser 7 by means of a solid
transfer line 12 for circulating solid particles from the slow bed 8 back to the fast
bed 7. The solids transfer line 12 is made inclined with an angle of say 60° with
the vertical for smooth flow of solid particles. A specially made solids control
valve 12 can be installed for regulating the solids circulation rate.
The cyclone separator 10 can be made from mild steel and provided with a
feeding arrangement for feeding to the cyclone. The solids carried over from the
fast bed 7 enter into the cyclone separator 10 tangentially and get separated. At
the exit end of the cyclone separator 10 a bag filter 11, made of cloth, is fitted to
collect the fine particles. The separated particles fall back to the slow bed 8 and
can be re-cycled onto the fast bed 7 via the solid transfer line 12
In order to fluidize the solid particles, air is supplied to the circulating fluidized
bed system using a rotary blower 1 driven by an electric induction motor.

Air is supplied to the fast bed 7 through its air line and to the slow bed 8 through
the corresponding airline. The slow bed 8 is kept at a minimum fluidized
condition. The air lines can be made of mild steel. Two flow control gate valves
3, 3 and two globe valves 2, 2 are provided to regulate the airfow rate in the
two air lines.
The air distributors 5, 6 provided in the fast bed column 7 and slow bed column
8 for uniform gas flow into the beds of solids.
The distributor 5 fitted in the riser 7 and the other distributor 6 fitted in the slow
bed 8 comprise perforated plates covered by wire mesh netting.
The lower portion of the slow bed 8 is conical with a cone angle of about 47°
with the vertical axis.
Two orifice meters 4, 4 are provided for measuring the flow rates of air admitted
to the fast bed column (riser) 7 and the slow bed column 8. A circular steel plate
having a hole can be used as the orifice. Diameter of the hole (orifice) for the
slow bed column 8 is smaller than that for the fast bed column 7. The outer
diameter of the plate is the same as the inner diameter of the respective air line.
In both cases the upstream face of the orifice meter is sharp edged while at the
downstream end they are slightly tapered.

A specially designed butterfly valve 9 can be used below the cyclone separator
10 to measure the solids circulation rate through the circulating fluidized bed
loop.
Experimental set-up '_•'■'
.»
The experimental set-up used for the present invention is shown in Figure 2
The main elements of the circulating fluidized bed system of Figure 1 are
identified in Figure 2 with similar references.
For visual observation, the set up was made up of perspex. For the pressure
drop measurements, 22 pressure taps are installed along the circulating fluidized
bed loop that is connected to manometers. Along the whole riser 7 seven
sampling probes are installed at different locations. They are located at h = 0.67
m, 1.20 m, 1.57 m, 3.53 m, 4.3 m, 4.77 m and 5.09 m above the distributor
plate. The equipment characteristics are presented in Table 1.


Fast Bed Column (or Riser)
The riser 7 is a 0.1016 m column, having a height of 5.62 m, measured from the
distributor to the gas exit level. The air-distributor 5 comprises a multi-hole
distributor plate with 12 % open area. A 400-wire mesh is fixed below the
distributor 5 and thirteen number of pressure taps have been fitted along the
riser 7 column wall axially The inner end of the tap is covered with 400-wire
mesh while the outer end is connected to a polythene tubing and then to a
manometer.
Slow Bed Column
The slow bed column 8 is of 0.2032 m ID and 1.88 m height. At the bottom of
the slow column 8, an air distributor 6 comprising a multi-hole plate with 15 %
open area is used. Below the multi-hole plate, the air distributor 6 (with 47°
angle) is fitted to allow for smooth passage of air. Above the conical distributor
6, a 400-wire mesh is placed along with the perforated air distributor plate to
prevent solid particles, from entering into the air line. The slow bed 8 is
provided with a number of manometer tappings at fixed locations. 3.0.3 solid
transfer line 12.
Solid Transfer Line
The transfer line \s of 0.1016 m ID and 0.42 m length.

Cyclone Separator
The cyclone separator 10 is of 0.2032 m ID. The height of the cylindrical section
is 0.466 m and that of the conical bottom is 0.524 m.
Blower
The rotary blower is driven by a 7.5 KW induction motor at a rated speed of
1450 rpm with a capacity, of 550 Nm3 / hr. Air is supplied to the fast bed
through a 0.1016 m ID pipeline. Slow bed is kept at minimum fluidization
condition by supplying air through a 0.0508 m ID pipeline.
Air Distributor
The distributors 5 (made of perspex sheet) and 6 (made of GI sheet) consist of
perforated plates covered by 400-mesh wire netting. The holes are of about 3.2
mm diameter and are arranged in triangular pitch. Pressure taps have been
provided to measure the pressure drop across the distributor. The lower portion
of the slow bed is conical having a cdne angle 47° with the vertical axis and
height of 0.44 m.

Orifice Meter
For the fast bed, the diameter of the orifice used is two inch. Both theMjpstream
and down stream are four inch. The pressure tappings on each" side are located
5 cm away from the orifice. In the case of slow bed, the diameter of the orifice
used is one inch the corresponding pipe diameter being two inches. The
pressure drops across the orifice are measured with the help of manometers,
using water as the manometer-fluids.
Butterfly Valve
The butterfly valve 9 is made of perspex using a 0.1016 m ID plate. The plate is
drilled and covered with 400-wire mesh. The butterfly valve is placed below the
cyclone and about 0.95 m from the top of the slow bed in the down comer line.
Sampling Probe
To collect the solids sample at different axial and radial locations the sampling
probes are used. These probes are similar to the one used, by Rhodes and
Geldart's (1998) To collect sample, one end of the probe is made in the form of
a U-bend (commonly called as a U-bend probe) The probe is of 4 mm inner
diameter. The long horizontal end of the probe is threaded so that it can be
moved forward and backward into the bed.

Experimental Procedure
The experiment is carried out in three different steps, namely sample
preparation. Sample collection and sample analysis.
Sample Collection
Solid particles are fed into the column through a feed hopper. Initially, static
beds of solids are maintained in both fast and slow bed columns. Then, by
controlling the valve in the airlines, air is sent into the riser 7 to fluidize the solid
particles. The flow rate of an air in the slow bed is kept low enough so as to
maintain the bed just above the minimum fluidization condition. The solid
particles entrained from the riser 7 get separated from the carrying gas into the
cyclone 10. The particles from cyclone 10 fall back into the slow bed 8 through
the down comer and recycled to the riser 7 through the solid transfer line 12.

The mixing process is then monitored by continuous sampling at various
locations above the distributor plate at one radial position of r/R=0 i.e. on the
axis of the riser with the tip of the probe pointed downward to sample only the
upward flowing solids. The sample is collected in the sample collector with the
help of a suction pump. A rotameter is used in the system so that the sampling
can be done non-isokmetically. Figure 2 shows this arrangement. After the air
steady state is attained, the samples at different axial locations of the riser 7 are
collected. The static pressures at different sections of the circulating fluidized
bed also noted from the manometer readings.
The airflow rate to both the riser 7 and the slow bed 8, are measured from the
manometer readings. By controlling the valves in the airlines, the gas velocity in
the riser can be changed. Solids circulation rate can be controlled with the help
of the valve in the transfer line, which can be opened partially or fully. Solids
circulation rate is measured with the help of butterfly valve 9. This can be
achieved momentarily by closing the valve 9 and noting the solids accumulated
on the valve plate against time.

Results and Discussions
Raw data for high ash coal benefication are shown in Table 2. Since the set up
was entirely made up of perspex tube the nature of fluidization can be clearly
seen visually. It is observed that while a dense zone prevails at trfe* bottom of
the riser with low voidage but high solids hold up, at the top end of the riser 7 a
dilute zone prevails and in between a transition zone exists with gradual
decrease of the voidage. Reports published in the literature for other system
such as sand-air, FCC-air and also with other minerals show similar trends.
Figures 2-4 show the benefication curves for coal. At three different gas
velocities and solids circulation rates the solids samples were collected at
different position along the riser length and were analyzed at IIT Kharagpur
laboratory. The results as percentage ash in coal are plotted against riser length
in the above figures. While in Figure 2 the curves are drawn for gas velocity of
3.55 m/s and solids circulation rate between 6.87 and 10.11 kg/m2.s, in Figure 3
these are shown at a gas velocity of 4.02 m/s and solids circulation rates of 9.70
to 11.31 kg/m2.s. The other curves given in the Figure 4 are drawn for a gas
velocity of 2.82 m/s and solids circulation rate between 4.45-6.06 kg / m2 s.
The initial ash percentage in coal was 42 %. It has been found that ash
percentage at the bottom depending on gas velocity and solids circulation rate
decreases from 41-45 % at the bottom to a lower level of 33-35 % at the top.
That is there can be 7-8 % benefication or ash reduction in the dry benefication
process. When the gas velocity and solids circulation rate increase there is more
mixing and less segregation of material depending on their densities resulting in
less benefication of coal

The run indicates that there can be 7-8 % percentage benefication ~jn^a riser
column of 5.5 meter within the experimental runs explored.
In industrial scale the circulating fluidized bed system is of much larger diameter
and higher riser length. While larger diameter increases the throughput, the
increased riser length gives further improvement in coal ash benefication.
Moreover multiple riser in series may be used to further improve the benefication
efficiency and also, to increase the extent of deashmg.

WE CLAIM
1 An apparatus for deashing coal by dry benefication, using a circulating
fluidized bed loop comprises
a fast bed column (7) and a slow bed column (8), each having a bed of
solids and provided with a distributor for blowing in air from a
rotary air blower (1),
a cyclone separator (10) provided at the distal end of said slow bed
column (8) for receiving and for getting the solid separated from solid
fines, and
a solid transfer line (12) provided for circulating solids from said slow
bed column (8) to said fast bed column (7) for recycling the separated
solids
2 The apparatus as claimed in claim 1, wherein said distributor comprises a
perforated multi-hole distributor covered by mesh netting plate for
preventing heavier solid particles from the bed entering into the air lines
3 The apparatus as claimed in claim 1, wherein said solid transfer line is
attached between the slow bed column and the fast bed columns at an
inclination for easy transfer of solids from the slow bed column to the fast
bed column
4 The apparatus as claimed in claim 3, wherein the solid transfer line is
provided with a solid control valve for regulating circulation of solids
5 The apparatus as claimed in claim 1, wherein said cyclone separator is
provided with a feeding arrangement for feeding carried over solid
particles from said fast bed column to the cyclone.

6 The apparatus as claimed in claim 5, wherein a bag filter is provided at
the exit end of the cyclone separator for collecting the separated fine
particles
7 The apparatus as claimed in claim 1, wherein said slow bed column is
provided with a conical lower portion having a cone angle of about 47°
with the vertical axis
8 The apparatus as claimed in claim 1, wherein the air lines for said fast
bed column and slow bed column are each provided with an orifice meter
for measuring the flow rates there through and said orifice for the slow
bed column is smaller than that for the fast bed column.
9 The apparatus as claimed in claim 1, wherein a butterfly valve is provided
below said cyclone separator for measuring the solid circulation rates
through said circulating fluidized bed loop

Abstract

Title: An apparatus for deashing coal by dry benefication
using a circulating fluidized bed loop.
The present invention provides an apparatus for deashing coal by dry
benefication, using a circulating fluidized bed loop comprises a fast bed column
(7) and a slow bed column (8), each having a bed of solids and provided with a
distributor for blowing in air from a rotary air blower (1) A cyclone separator
(10) is provided at the distal and of said slow bed column (8) for receiving and
for getting the solid separated from solid fines, and a solid transfer line (12)
provided for circulating solids from said slow bed column (8) to said fast bed
column (7) for recycling the separated solids.