FIELD OF INVENTION
The present invention generally relates to hydrocyclones, in particular
dense medium cyclones for carrying-out particle separation tests.
More particularly, the invention relates to a method of suppressing air
core in cyclones . The invention further relates to method and device
for conducting separation of particles in the cyclone having
suppressed air core.
BACKGROUND OF INVENTION
Hydrocyclone is an equipment that is used to separate particles
based on size and it uses water as the media for separating particles
into different size ranges.
The dense-medium cyclone, on the other hand is an equipment that
operates on the principle of gravity separation. Pure coal (specific
gravity 1.3) and pure ash (>2) have different specific gravities. When
the coal and ash particles are introduced into a medium whose
specific gravity is intermediate to that of coal and ash, the lighter
coal particles would float, and the heavier ash particles would sink. In
a dense medium cyclone, the medium for separation is fine
magnetite particles suspended in water.
A conventional cyclone as described hereinabove, is generally having a cylindro-
conical shape (fig 1). The magnetite slurry along with coal is introduced
tangentially into the equipment. The slurry as it descends down, the cyclone
forms a free vortex (1) in the periphery with a forced vortex (2) at the centre.
The particles that are introduced are forced to separate in the radial direction,
with the heavier ash particles thrown towards the periphery, and discharging
through the underflow (3), while the lighter coal particles are carried upward
along with the forced vortex (2), to discharge through the overflow (4). The
forced vortex (2) envelopes an air core (5) which is created due to a low
pressure zone, and is created at the centre. The air core (5) is sucked in through
the underflow (3) and extends all along the length of the cyclone uptill the
overflow (4).
However, experimentations have established that separation efficiency of
particles in a cyclone is substantially improved if the separation is carried-out
with a cyclone having suppressed air core.
US Patent US 4375411 describes a device (90) for limiting the vortex flow of a
fluid is disclosed. The device includes means (91) for securing the device to a
fixed position in a forced vortex environment at a location near the origin of the
vortex flow. Means (94-98) for redeveloping an interrupted vortex flow and
allowing the passage of the vortex air core therethrough is also provided but is
spaced apart from but connected to the securing means (91). Means (93) for
interrupting the vortex flow near its origin includes a passageway defined by the
securing means (91) and the means for redeveloping the vortex flow.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a method of suppressing air
core in a conventional cyclone which is simple, cost-effective and easy to
perform.
Another object of the invention is to propose a method of suppressing air core in
a conventional cyclone which is reproducible.
A further object of the invention is to propose a method of carrying out particle
separation tests in a cyclone having suppressed air core which is simple, cost-
effective, and easy to perform.
A still further object of the invention is to propose a method of carrying out
particle separation tests in a cyclone having suppressed air core which is
reproducible and user-friendly.
SUMMARY OF THE INVENTION
In a first aspect of the invention, there is provided a method in a cyclone with
suppressed air core to improve its particles separation efficiency, comprising the
steps of; providing a cyclone assembly having an inlet port and an outlet port;
providing means on the cyclone body for inserting a rod capable of suppressing
the air core; inserting the rod to reach the centre of the cyclone body when the
provisioning means being configured at a height in the central location;
alternatively inserting the rod till one forth of the height from the bottom when
the provisioning means being configured at the bottom of the cyclone .
In a second aspect of the invention, there is provided a method of determining
the separation efficiency in a cyclone with a suppressed air core. The method
comprising:
- connecting a cyclone to a water /slurry inlet through which water / slurry
is introduced into the cyclone at the desired flow rate, the flow rate being
measured by adapting a rotameter,
- pumping the slurry / water from a slurry tank having provisions for
bypass,
- providing control valves at the overflow and the underflow outlets of the
cyclone to vary the flow rates,
- providing pressure tapping at the inlet, overflow and underflow,
- connecting the pressure tapping to a series of manometers which can
measure the pressure drop across the cyclone,
- setting the inlet flow rate to the desired value, and varying the
underflow/overflow rate in a such a way so as to get a good air core,
- measuring the inlet and the underflow rate,
- stopping the flow to the cyclone,
- making an insertion in the centre/bottom of the cyclone body by inserting
a rod,
- inserting the rod at a height where the air core would disappear,
- continuing the insertion of the rod till the centre of the cyclone if the
provision is made for insertion at the centre of the cyclone body,
- alternatively inserting, the rod till one fourth of the height from the
bottom if the rod is inserted from the bottom using clamps placed below
and outside the bottom of the cyclone,
- selecting a rod for insertion having at least 50% of spigot diameter and a
length equal to 85% of the cyclone below the vortex flow, when the rod is
inserted from the bottom, alternatively, selecting a rod having a diameter
equal to 50% of the spigot diameter and inserting through an inserting
means configured at a height 67% below the cyclone root when inserted
through the side;
- varying the flow rates till such-time a good air core would be formed
extending from top to the bottom of the cyclone,
- introducing density tracers/coal particles,
- collecting the particles/slurry coming from the overflow and the underflow
- weighing the coal particles from the coal slurry coming from the overflow
and underflow after drying,
- carrying-out sink-float tests to find out the percentage of coal particles
reporting to the overflow and underflow,
- determining the percentage of lighter and heavier particles reporting to
the overflow and underflow, if the particles are density tracers,
- calculating the separation efficiency as the percentage of lighter particles
of the feed reporting to the overflow.
According to a third aspect of the invention, there is provided a cyclone with
suppressed air-core, comprising; a cyclone body made of Perspex or of any
material constituting a known cyclone body; an inlet port and an outlet port
configured at the top and bottom of the cyclone body, the inlet port allowing
delivery of water or slurry into the cycle, the outlet port being connectable to an
U-tube manometer; one each overflow and underflow outlets provided on the
cyclone body to remove the slurry and particles after separation; means housed
on the cyclone body to allow insertion and fixing of a rod either through the
bottom or at the centre of the cyclone body for suppressing air core.
In a fourth aspect of the invention there is provided an improved method to
determine the yields obtaining under ideal conditions at different levels of ash
when coal is washed. The method comprising: providing a dense-medium
cyclone in closed circuit with a slurry tank, a slurry pump, and a by-pass line, the
cyclone being disposed directly above the slurry tank such that the overflow and
the underflow get discharged directly into the tank when the testing samples are
not collected; the feed rate of the slurry to the cyclone including the feed
pressure is adjusted by providing a bypass valve in the bypass line; maintaining
the slurry in the tank in uniform suspension by recirculation and agitation of the
slurry by a heavy-duty stirrer; adding predetermined quantity of water,
magnetite, and coal in the slurry while the stirrer being kept running; pumping
the slurry into the cyclone and adjusting the bypass valve to obtain a required
pressure at the inlet of the cyclone; allowing the cyclone and the associated
means to operate till a steady state is reached; collecting overflow and underflow
slurry samples for a known period with the weights of the samples being
recorded; recovering separately the magnetite and coal samples
from the slurry and dried; the recovered coal samples are subjected to sink float
analysis at different specific gravities, and the magnetite samples from overflow
and underflow are size-analyzed; and calculating the flow rates of slurry coal
magnetite and water in the overflow and underflow streams, the analyses
establishing that the degradation of coal during the process is negligible.
The standard sink-float tests adaptable to the present invention can be described
as under:
The sink float test are a series of tests done to determine the yields obtainable
under ideal conditions at different levels of ash when coal is washed. It is a test
in which the coal is put initially in an organic liquid of specific gravity 1.3. The
coal is allowed sufficient time so that a clear distinction between the floating coal
and the sinking coal is visible. The coal that floats in the liquid is called the 'float'
and that sinks is the 'sink'. The float and the sink are weighed and are analyzed
for ash content. The rest of the sink is then put in a liquid of higher specific
gravity, say 1.4. This is continued until a specific gravity of 2.0 is reached. The
weights and ash content of the coal thus collected are used to plot curves from
which the yield of clean coal obtained at a particular ash content can be
determined.
The method by which a sink-float test is carried-out, and, the principle of which
is being adapted in the present invention can further be illustrated in reference
to a conventional dense-medium cyclone.
A dense-medium cyclone is illustrated in figure 1. The dense - medium cyclone
(8) is arranged in closed circuit with a slurry tank (6), a slurry pump (7) and a
by-pass line (9) as shown in Fig. 2.
The cyclone (8) is fitted directly above the slurry tank (6) so that when the
samples are not collected, the overflow (10) and underflow (11) streams are
discharged directly into the tank (6). A by-pass valve (9a) in the line (9) is used
for adjusting the feed rate of the slurry to the cyclone (8) and the pressure at
the feed inlet (12) of the cyclone (8). The recirculation of the slurry and the
agitation due to provision of a heavy duty stirrer (13) in the tank (6) are
sufficiently to keep the slurry in the tank (6) in uniform suspension. The cyclone
(8) is provided with facilities (19) to change the spigot and vortex finder. Before
the start of an experiment, the required spigot and vortex finder (19) are
inserted in the cyclone (8). Then, keeping the heavy-duty stirrer (13) running,
requisite quantities of water, magnetite and coal are added to the slurry tank (6).
The magnetite to coal ratio maintained in all the experiments is 4:1 by weight.
The slurry is pumped into the cyclone (8) keeping the bypass valve (9a) fully
open and then this valve (9a) is adjusted to obtain the required pressure at the
inlet (12) of the cyclone (8). The system is then allowed to run for some minutes
until a steady state is attained. Once the steady state is reached, the overflow
and underflow slurry samples (10,11) are collected for a known period and the
weights of these samples (10,11) are noted separately.
The coal is separated from the slurry samples (10, 11) collected from the
overflow and underflow (10, 11) by draining via a 100 mesh sieve with a water
spray (14). The magnetite along with water passed through the screen while the
coal particles are retained over the screen. The magnetite in each sample is
recovered from the slurry by filtration. The coal and magnetite samples thus
recovered are dried and weighed separately. The overflow and underflow
magnetite samples (10, 11) are size analyzed. The coal samples recovered are
subjected to sink float analysis at different specific gravities. The flow rates of
slurry, coal, magnetite and water in the overflow and underflow streams (10, 11)
are calculated. The size analyses are carried out to estimate the degradation of
coal during experimentation, which has been found to be negligible. This
procedure is followed in all the experiments conducted at different levels of
design and operating variables.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure-1 - Shows a schematic of a conventional cyclone,
Figure-2- A device for conducting seperation of particles in a
conventional cyclone according to prior art,
Figure-3- A device for conducting separation of particles in a cyclone
with suppressed air core according to the present invention.
Figure-4- Shows a method for suppression of air core from centre
according to present invention
DETAIL DESCRIPTION OF A PREFERRED EMBODIMENT OF
THE INVENTION
Figure-3 illustrates as to how the particle separation test is carried-
out in a cyclone having suppressed air core.
The cyclone ( c) is run with water to determine the conditions when a
full air core will be formed. Once the air core is formed, the overflow
and the underflow rates (10,11) and the pressure difference from the
manometer are noted down. The inlet water (12) is then stopped. A
rod (19) is then inserted in the cyclone ( c) (from
the top/sides/bottom, whichever way the provision is made) in such a
way so as to suppress the air core. The water flow is then started
and then the overflow and underflow rates (10,11) are adjusted in a
range where a good air core extending from top to bottom would be
formed. The density tracers of different specific gravities (in this case
108 particles are introduced; and the number of lighter and denser
particles. coming out of the overflow and underflow (10,11) are
counted. The separation efficiency is taken as % of lighter material of
feed reporting to overflow (10).
Fig 3 further shows the details as to how the provision for inserting
the rod at the centre for suppressing the air core is created.
The cyclone assembly ( c) is made of Perspex. In practice the cyclone
can be made of the standard material like Polyurethane/ any other
material of which industrial cyclones are made.
The inlet (12) and the outlet ports (16) are all M.S tubes; In practice,
the outlet ports (16) can be made of Perspex or of the same material
of which the cyclone ( c ) is made
The rest of the piping are all M.S. The insertion rod (19) is a M.S tub.
A U tube manometer assembly (17) is made of Perspex.
The cyclone assembly is made of non-reactive material and houses a
means (20) for inserting the rod (19) that can suppress the air core.
The invention is an integral/ core part of the cyclone assembly. The
cyclone assembly is used generally for studying the classification
efficiency or the separation efficiency of particles. The cyclone
assembly consists of the following parts serving the respective
functions.
The cyclone body can be conical or cylindro-conical in a shape and
has an iniet (12). The water or slurry is introduced into the cyclone (
c ) through the inlet (12). The overflow and the underflow outlets
(10,11) remove the slurry and the particles from the cyclone ( c )
after separation.
The water/slurry pipe lines (L) through which slurry or water flows
and are connected to the outlets (16) and inlets (12) of the cyclone
(c).
The pressure tappings connect the outlets (16) to the U tube
manometer (17) and are used to measure the pressure drop.
The U tube manometer (17) are manometer tubes filled with mercury
and are required for the measurement of pressure difference.
A rotameter (18) is provided for measuring inlet water flow rate, and
a slurry tank (6) is flowably connected to the cyclone (c ) via tubular
network.
WE CLAIM
1. A method in a cyclone with suppressed air core to improve its particles
separation efficiency, comprising the steps of:
- providing a cyclone assembly (c) having an inlet port (12) and an
outlet port (16);
- providing an inserting means (20) on the cyclone body for inserting
a rod (19) capable of suppressing the air core;
- inserting the rod (19) to reach the centre of the cyclone body when
the inserting means (20) being configured at a height in the central
location;
- alternatively inserting the rod (19) till one forth of the height from
the bottom when the inserting means (20) being configured at the
bottom of the cyclone (c).
2. A method of determining the separation efficiency in a cyclone with
suppressed air core, comprising the steps of :
- connecting a cyclone to a water /slurry inlet through which water /
slurry is introduced into the cyclone at a desired flow rate, the flow
rate being measured by adapting a rotometer;
- pumping the slurry / water from a slurry tank having a provision for
by pass;
- providing atleast one control valve at the overflow and the
underflow outlets of the cyclone to vary the flow rates;
- providing pressure tappings at the inlet, overflow and underflow;
- connecting the pressure tappings to a series of manometers which
can measure the pressure drop across the cyclone;
- setting the inlet flow rate to the desired value, and varying the
underflow/overflow rate in such a way so as to develop a
substantially effective air core;
- measuring the inlet and the underflow rate,
- stopping the flow to the cyclone;
- introducing density tracers/coal particles;
- collecting the particles/slurry coming from the overflow and the
underflow;
- weighing the coal particles from the coal slurry coming from the
overflow and underflow underflow after drying;
- determining the percentage of coal particles reporting to the
overflow and underflow by adapting sink float test;
- determining the percentage of lighter and heavier particles
reporting to the overflow and underflow, if the particles are density
tracers; and
- calculating the separation efficiency as the percentage of lighter
particles of the feed reporting to the overflow.
3. A cyclone with suppressed air-core, comprising:
- a cyclone body made of Perspex or of any material constituting a
known cyclone body;
- an inlet port (12) and an outlet port (16) configured at the top and
bottom of the cyclone body, the inlet port (12) allowing delivery of
water or slurry into the cycle, the outlet port (16) being
connectable to an U-tube manometer (17);
- one each overflow and underflow outlets (10,11) provided on the
cyclone body to remove the slurry and particles after separation;
means (20) housed on the cyclone body to allow insertion and
fixing of a rod (19) either through the bottom or at the centre of
the cyclone body for suppressing air core.
4. An improved method to determine the yields obtainable at different levels
of ash in course of washing the coal, the method comprising:
- providing a dense-medium cyclone in closed circuit with a slurry
tank, a slurry pump, and a by-pass line, the cyclone being disposed
directly above the slurry tank such that the overflow and the
underflow get discharged directly into the tank when the testing
samples are not collected;
- adjusting the feed rate of the slurry to the cyclone including the
feed pressure by providing a bypass valve in the bypass line;
- maintaining the slurry in the tank in uniform suspension by
recirculation and agitation of the slurry by a heavy-duty stirrer;
- adding predetermined quantity of water, magnetite, and coal in the
slurry while the stirrer being kept running;
- pumping the slurry into the cyclone and adjusting the bypass valve
to obtain a required pressure at the inlet of the cyclone;
- allowing the cyclone and the associated means to operate till a
steady state is reached;
- collecting overflow and underflow slurry samples for a known
period with the weights of the samples being recorded;
- recovering separately the magnetite and coal samples from the
slurry and dried;
- the recovered coal samples are subjected to sink float analysis at
different specific gravities, and the magnetite samples from
overflow and underflow are size-analyzed; and
- calculating the flow rates of slurry coal magnetite and water in the
overflow and underflow streams, the analyzes establishing that the
degradation of coal during the process is negligible.
5. A method in a cyclone with suppressed air core to improve its particles
separation efficiency as substantially described and illustrated herein with
reference to the accompanying drawings.
6. A method of determining the separation efficiency in a cyclone with
suppressed air core as substantially described and illustrated herein with
reference to the accompanying drawings.
7. A cyclone with suppressed air-core, as substantially described and
illustrated herein with reference to the accompanying drawings.
8. An improved method to determine the yields obtainable at different levels
of ash in course of washing the coal as substantially described and
illustrated herein with reference to the accompanying drawings.

The invention relates to a method in a cyclone with suppressed air core to
improve its particles separation efficiency, comprising the steps of providing a
cyclone assembly (c) having an inlet port (12) and an outlet port (16); providing
an inserting means (20) on the cyclone body for inserting a rod (19) capable of
suppressing the air core; inserting the rod (19) to reach the centre of the
cyclone body when the inserting means (20) being configured at a height in the
central location; alternatively inserting the rod (19) till one forth of the height
from the bottom when the inserting means (20) being configured at the bottom
of the cyclone (c).