FIELD OF INVENTION
The present invention relates to a venturi- nozzle for mixing solid particles with
pneumatically transported air stream.
BACKGROUND OF THE INVENTION
Venturi nozzles are used in pneumatic transportation system to feed solid
particles into high pressure air stream. It is also known as mixing nozzle since
the solids are mixed with air to transport material pneumatically. The venturi
nozzles (Fig:l) are extensively used in industries like cement, boilers, wheat flour
mill, etc, for pneumatic transportation of dry solids over a distance. High
pressure air for pneumatic transportation is admitted through a pipe (1) to the
venturi nozzle. The venturi nozzle contains a reducer (2) to create high air
velocity and thereby low pressure is created as per Bernoulli's principle. The
solids are drawn inside the venturi nozzle through a hopper (3) by the suction
pressure and mixed with air in a mixing chamber (4). The solids leave the mixing
chamber through a pressure recovery zone (5) at which velocity of the air is
gradually reduced and the pressure of air is gradually gained. The venturi nozzles
are manufactured either from a steel rod or machined from cast iron pieces. The
inlet and outlet pieces are welded with segments so as to match the design of
the venturi nozzle. The venturi nozzles are hard faced at the outlet of the mixing
chamber (6).

In the existing venturi nozzle design, inlet opening for flow of solid material is
more than sufficient to feed dry materials of maximum size range between 0 and
10 m.m. The pneumatic transportation air is admitted from left hand side and
the particle material are leaving from right hand side. The dry material for
transportation is drawn from a bunker and admitted to the venturi/mixing nozzle
at a regulated quantity through an air lock feeder. A series of such transportation
systems are incorporated in a Bubbling Fluidized Bed Combustion (BFBC) boiler
which is shown in Fig:2. Fuel, coal/ignite/char/coal washery rejects, etc, stored in
a bunker (7) and fed to the venturi feeder (9). The fuel and air mixture are
transported pneumatically and fed to the BFBC boiler (10). The flue gas is cooled
in heat recovery zones (11) and the pneumatic transportation air is heated in air
heaters (12). A forced draft fan (13) delivers required volume of air for
transportation and a booster fan (14) boosts the pressure to transport the fuel to
the BFBC boiler. The flue gas is cleaned in ash separator (15) and released to
atmosphere through an Induced draft fan (16).
But, to feed high moisture content clustered particles during rainy season, the
material inlet opening is found inadequate and consequently the particles do not
flow freely to the venturi nozzle. Hence, large size opening in venturi nozzle is
found essential for flow of clustered solid particles. Attempts for increasing the
diameter of the inlet opening results in poor low pressure in the mixing chamber
and at times back flow of air through the material inlet opening occurs which

prevents free flow of the material to the nozzles. Increase in velocity to the
pneumatic transportation air to obtain low pressure in mixing zone of venturi
nozzle with large size opening for material flow, results in high pressure drop.
Fuel, coal, lignite, char, washery rejects, etc, gets, wet, during rainy season, but
they are forced to feed to boilers for maintaining temperature of fluidized bed
combustion (BFBC) boilers. The wet and cluster material pose difficulties in
feeding in to the venturi/mixing nozzle and, consequently, impair the BFBC boiler
operation.
When the wet material enter inside the inlet hopper of the chute which connects
the venturi nozzle, the same gets choked and disallows an easy flow of the
particles into the nozzle. The pneumatic transportation line is starved of
materials and the air admitted for transportation of material cools the fluidized
bed. In order to increase the flow of wet material, the hopper outlet opening
connecting the venturi/mixing nozzle, is increased.
The wet particles of size range 0-10 m.m. fall into the mixing chamber of the
venturi/mixing nozzle with enlarged opening, and get mixed with the pneumatic
transportation air and looses its moisture in the mixing chamber so as to get
transported pneumatically to the fluidized bed boiler.
In the conventional venturi nozzles, used for pneumatic transportation of solids,
the material inlet is sufficient to allow required material for pneumatic

transportation when it is in dry condition. The pressure drop of the venturi nozzle
at a pneumatic transportation velocity of 11-14 m/sec, normally adopted for
coal/lignite/sand/char particle of size range between 0 and 10.0 m.m., is
between 350 - 450 mmwc.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a venturi nozzle
having a large inlet for solid material input without undergoing corresponding
increase in pressure drop across the nozzle.
Another object of the present invention is to propose a venturi nozzle having a
large inlet for solid material input, which prevents reduction in the average
particle size by attrition in the mixing chamber.
A further object of the present invention is to propose a venturi nozzle having a
large inlet for solid material input, which is adaptable in low pressure application
and capable of achieving weight ratio of material: Air as high as 3 thereby
reducing the operating power consumption of the forced draft fan.
A still further object of the present invention is to propose a venturi nozzle
having a large inlet for solid material input, which is capable to create low

pressure in the mixing chamber such that the solid materials from the chute can
be drawn.
Yet further object of the present invention is to propose a venturi nozzle having a
large inlet for solid material input, which sustains less erosion in the inside
surfaces and increase the life of the nozzle.
SUMMARY OF INVENTION
Accordingly, there is provided a venturi nozzle for mixing solid particles with
pneumatically transported air stream, comprising an angular air inlet reducer
configured to have an angle between 15 to 30°; a plurality of holes configured at
the outlet of the reducer to create a high velocity air stream, the air stream
having large cross-section of air flow with less air flow at the centre which forms
a low-pressure zone for smooth flow of the solid particles to the venturi nozzle; a
drain valve to drain-out the non-transportable large sized particles; a mixing
chamber enabling mixing of the solid particles and the air stream; a hopper
outlet hole through which the material for pneumatic transportation being
achieved; a convergent zone having a predetermined angle through which the
mixture of the solid particles and air stream is caused to pass from the solid
mixing chamber, and a divergent zone with a critical angle through which the
mixture of the solid particles and air stream is caused to pass from said
convergent zone.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure: 1- Schematic diagram of a prior art venturi nozzle.
Figure: 2 - Schematic diagram of a Bubbling Fluidized Bed Combustion (BFBC)
boiler incorporating a plurality of venturi/mixing nozzle.
Figure: 3 - Shows a schematic diagram of the venturi nozzle for transporting wet
clustered materials according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention can be better described with reference to the
accompanying drawing Fig: 3. The venturi nozzle or the mixing nozzle, can be
better described with reference to the accompanying drawing. The venturi
nozzle, essentially comprises an air inlet reducer (17) with an angle between 15
and 30 Deg (18) and have multiple holes (19) at the outlet so as to create a high
velocity air stream. The air stream emanating from the plurality of holes (19) has
large diameter of air flow with less air flow at the center so as to create a low
pressure zone (4) in the large cross section for flow of the particles from the
chute connecting the venturi nozzle. The solid particles are drawn through the
hopper outlet hole (20) of diameter more than the inside diameter of a pipe (21),
through which pneumatic transportation takes place. The venturi nozzle also

contain a drain valve (22) to drain large size particles that can be transported.
The solid particles and air stream are mixed in a mixing chamber (23) and pass
through a convergent zone (24) with a predetermined angle (25) being a critical
angle, between 40 and 60 Deg. The mixed particles then pass through a
divergent section (26) with a critical angle (27) between 3 and 8 Deg for
pressure recovery of air. A portion of mixing chamber (23) and a portion of the
convergent zone (24) are hard faced (28), to minimize erosion of the particles
stream. The pneumatic transportation air with the particles leave through the
pipe (21) for connecting to the down stream.
The invention provides an improved venturi nozzle for pneumatic transportation
of solids in lean phase transportation system which consist of an air inlet reducer
(17) with a specific angle (18), a plurality of holes (19) each having a diameter
(3) create high velocity of air stream for achieving a low pressure zone (4) at the
inlet of the venturi nozzle. The area of the low pressure zone (4) is high because
of the large area covered by the plurality of holes and thereby increase in the
inlet opening area of the feed particle to the venturi nozzle. The large opening
area or large diameter of opening in the venturi nozzle accommodates a cluster
of wet particles to feed to venturi nozzle and thereby avoiding chocking of
particles at the inlet of venturi nozzle which interalia improve availability of boiler
during rainy season.

The improved venturi nozzle has a mixing chamber (23) with large volume where
solid particles and air are mixed and hence attrition of particles are reduced
which restricts the size reduction in pneumatic transportation.
The venturi nozzle has less erosion prone area in the mixing chamber (23) and in
the air convergent zone (24) which are hard faced in select areas to increase the
life of operation. The venturi nozzle allows a less pressure drop of the
transportation air and thereby achieves transportation at a lesser air pressure.
The improved venturi nozzle can be manufactured in mass scale through welding
of machined and fabricated pieces through a manufacture friendly process.

WE CLAIM
1. A venturi nozzle for mixing solid particles with pneumatically transported
air stream, comprising:
- an angular air inlet reducer (17) configured to have an angle (18)
between 15 to 30°;
- a plurality of holes (19) configured at the outlet of the reducer (17)
to create a high velocity air stream; the air stream having large
cross-section of air flow with less air flow at the centre which forms
a low-pressure zone (4) for smooth flow of the solid particles to the
venturi nozzle;
- a drain valve (22) to drain-out the non-transportable large sized
particles;
- a mixing chamber (23) enabling mixing of the solid particles and
the air stream;
- a hopper outlet hole (20) through which the material for pneumatic
transportation being achieved;
- a convergent zone (24) having a predetermined angle (25) through
which the mixture of the solid particles and air stream is caused to
pass from said mixing chamber (23) and

- a divergent zone (26) with a critical angle (27) through which th3
mixture of the solid particles and air stream is caused to pass from
said convergent zone (24).
2. The venturi nozzle as claimed in claim 1, wherein the predetermined angle
of the convergent zone (24) is between 40° to 60°.
3. The venturi nozzle as claimed in claim 1, wherein said critical angle of the
divergent zone (26) is between 3° to 8°.
4. The venturi nozzle as claimed in any of the preceding claims, wherein the
mixing chamber (23) and the convergent zone (24) are partly hard faced
(28).
5. The venturi nozzle as claimed in claim 1, comprising a large inlet for solid
material input.
6. A venturi nozzle for mixing solid particles with pneumatically transported
air stream as substantially described and illustrated herein with reference
to the accompanying drawings.

The invention relates to a venturi nozzle for mixing solid particles with
pneumatically transported air stream, comprising an angular air inlet reducer
(17) configured to have an angle (18) between 15 to 30°; a plurality of holes
(19) configured at the outlet of the reducer (17) to create a high velocity air
stream; the air stream having large cross-section of air flow with less air flow at
the centre which forms a low-pressure zone (4) for smooth flow of the solid
particles to the venturi nozzle; a drain valve (22) to drain-out the non-transportable
large sized particles; a mixing chamber (23) enabling mixing of the
solid particles and the air stream; a hopper outlet hole (20) through which the
material for pneumatic transportation being achieved; a convergent zone (24)
having a predetermined angle (25) through which the mixture of the solid
particles and air stream is caused to pass from said mixing chamber (23) and a
divergent zone (26) with a critical angle (27) through which the mixture of the
solid particles and air stream is caused to pass from said convergent zone (24).