FIELD OF INVENTION
The present invention, generally relates to systems involving fuel feeding
arrangement for fluidized Bed system. Particularly the invention relates to Bubbling
Fluidised Bed Combustion (BFBC) Boiler. More particularly the invention relates to a
scrapper-assisted fuel feed nozzle device for feeding high moisture fuel in the
Bubbling Fluidised Bed combustion (BFBC) Boilers.
BACKGROUND OF THE INVENTION
Fluidised Bed Combustion boiler is a system consisting of fluidized bed enclosure,
where the solid particles are in a suspended state. The state is achieved by
controlling the amount of air passing through the bed. At low velocities, pressure
drop across the bed is negligible and buoyant force derived from low velocities is not
sufficient to suspend the particle in the bed. The bed remains static and undisturbed.
As the flow (velocity) is increased gradually, the buoyant force overcomes the
gravitational force exerted on the particle and suspends in the fluidized bed. The
pressure drop increases till a point, where it matches with the weight of particles per
unit area. At this stage, the bed particles are in suspended state and it is called
"minimally fluidized bed".
When the flow is increased further, the bed becomes highly turbulent as the
interstitial spaces between the bed particles increase allowing high velocity gas
streams promoting rapid mixing of the bed. At this stage the bed of solids attain
pseudo fluid properties.

In the BFBC boiler, the above mechanism is employed to suspend the solid coal
particles. The entire bed is preheated to ignition temperature of the fuel (coal). On
reaching the ignition temperature, the coal particles are fed. They undergo
combustion and release heat which is imparted to the whole volume of bed
uniformly due to high turbulence and rapid mixing characteristics of fluidizing
process.
The prior art of feeding the fuel in to the pressurized system is done in two different
methodologies for example, Under bed feeding and Over bed feeding. The
Methodologies differ from each other by the location of feeding into the bubbling
bed i.e., in the former case, the feed is from the underside of the bubbling bed
located in the distributor plate surrounded by air nozzles supplying the fluidizing air
for the bed; and in the latter case, the feed is from the sides of the bed - throwing
the fuel (pneumatically or using spreaders) on to the bed.
The under bed feeding requires that sufficient pressure be made available to
overcome the bed resistance and losses in the fuel feed line and genrally requires a
pressurized system. The over bed feeding system typically injects onto the surface of
the bubbling fluidized bed and therefore only requires a simple pneumatic feeding or
a spreader arrangement.
In the under bed feeding arrangement, the transfer of fuel (coal) at the atmospheric
pressure to the high pressure fuel transport line is effected by means of a fuel
mixing nozzle arrangement. In the mixing nozzle, the high pressure air is accelerated
to a high velocity thereby converting the pressure head to the velocity head and

bringing the static pressure to slightly below the atmospheric level for transferring
the fuel from the chutes. This high velocity air and fuel mixture is then collected by
the recovery nozzle and the pressure head is recovered by conversion of the high
velocity head to the static head in the diffuser part of the recovery nozzle. This static
head helps the fuel air mixture in overcoming, the line losses and the head of the
bubbling fluidized bed.
US Patent No 4,446,799 discloses a Fluidised Bed Fuel Feed System which uses a
movable nozzle on the furnace wall for feeding fuel on to the over bed of the
fluidised bed boiler. US Patent No 4,259,911 discloses a Fluidised Bed Boiler Feed
System which utilises a fuel pump arrangement for feeding the fuel / sorbent
mixture in dense phase transport with higher air pressures. US Patent No 4,203,391
discloses a Fluidised Bed Fuel Feeder which utilises T-Shaped nozzles for feeding the
coal into the fluidised bed boiler. US Patent No 5,868,083 describes a Method and
device for feeding fuel into a fluidised bed which USESa fuel pipe with storage vessel
for feeding the over bed. US Patent No 4,275,668 describes a Coal feed system for a
fluidized bed combustor which uses A separator with agglomerator for feeding onto
the surface of the bed of the Fluidised bed boiler.
The other prior art adapts an assembly of accelerating nozzle, which enables
creation of low pressure condition to enable transfer of coal (solids) into the
pressurized transport line. The coal-air mixture is then collected in the recovery
nozzle portion and the air pressure is then recovered in the recovery diffuser part of
the mixing nozzle arrangement.

This arrangement of fuel feed nozzle is prone to bridging at fuel mixing chamber
junction with the fuel feed line. This is due to the fact that the cross section of the
coal (solid) feed line is narrow promoting adhesion of the high moisture fuel (solids).
This system of feeding the fuel encounters difficulty in transfer of high moisture fuel
onto the transport line as the entry size of the system is narrow promoting formation
of bridging of fuel.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a scrapper-assisted fuel feed
nozzle device for feeding high moisture fuel in the Bubbling Fluidised Bed
combustion (BFBC) Boilers, in which the nozzle configuration is optimized such that
the low pressure air developed by fan system can be utilized.
Another object of the invention is to propose a scrapper-assisted fuel feed nozzle
device for feeding high moisture fuel in the Bubbling Fluidised Bed combustion
(BFBC) Boilers, which adapts a combination of nozzle to vary the fuel feed rate by
adjusting the transport velocity in achieving partial turn down.
Other objectives are elaborated in detail in the description provided hereinafter.
SUMMARY OF THE INVENTION
The device of the invention adopts a combination of nozzle and venturi nozzle
arrangement with a specific angle for acceleration, convergence and recovery for

utilizing the low pressure air (head developed by fans) to transport fuel (solids) for
feeding in to bubbling bed combustor (pressurized system).
The improved arrangement employs a coal feed line of identical cross section as that
of the transport line by optimizing the nozzle configuration to ensure the pressure
recovery. This is made possible due to the vertical nature of the walls at the entry of
the fuel on to the mixing nozzle.
In addition, one of the two alternate varieties of scrapping action is adapted to avoid
sticking of high moisture coal on to the vertical walls of the system, which eliminates
any chance of bridging any build up.
In a first embodiment, a unique arrangement of wire formed scrapper arrangement
is placed inside the transport line before the recovery nozzle extending up to the
coal feed line. This arrangement is mechanically connected to the driving
mechanism. The driving mechanism is then activated based on the frequency of
blockage experienced to ensure free flow of high moisture fuel. In normal scenario,
the wire formed scrapper is not activated thus operation can be optimized to suit the
fuel characteristics.
In a second embodiment, the scrapping arrangement consists of uniquely ventilated
disc (to provide scrapping action as well as provide suitable drainage of fuel (solid)
function) held in a specific position at the bottom near the drain point below the coal
feed line. The ventilated scrapper disc is guided up to coal feed line by a plurality of
guide rods. The disc is also connected to a cam arrangement in the driver unit. This
mechanism is used to release and compress the spring-disc arrangement.

The release of the spring attached disc enables a strong and sudden movement of
the ventilated disc with scrapping movement of the disc along the coal feed line.
This violent reaction force is sufficient to disturb any strong build up. This along with
the scrapping action of the ventilated disc provides a cleanup and transport
disturbed buildup of fuel (solid) particles.
According to the invention pressure recovery is optimized by altering the nozzle
configuration and appropriate placement of the scrapping mechanism. For scrapping
the bridging at fuel feed line throat is achieved by operating the scrapping
mechanism.
The scrapper means are configured depending the fuel characteristics (moisture/
surface adhesion, attrition), intensity, frequency and suitability of the drive means to
ensure trouble free feeding of the high moisture fuel.
The device which fuel feed to said fluidized bed is ensured by the device which
achieves a uniform feeding of the fuel and hence combustion efficiency.
The invented device is further adaptable to other similar applications utilizing low
pressure media for transportation of suitable solid particles.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - Shows a schematic view of an under bed feeding arrangement for
fluidized bed combustion boilers
Figure 2 - Shows a prior art arrangement of fuel feed nozzle device.

Figure 3 - Shows a first embodiment of a scrapper assisted fuel feed nozzle device
according to the invention.
Figure 4 - Shows a second embodiment of a scrapper assisted fuel feed nozzle
device according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE
INVENTION
A conventional arrangement of typical fuel feed nozzle device for transport of fuel
into bubbling fluidized bed boilers as shown in Figure 2 comprises a plurality of
accelerating nozzle (1), a coal feed line (2), a mixing chamber (3), a drain
arrangement (4) a recovery nozzle (5), a recovery diffuser (6) ,and a transport line
(7).
A first embodiment of the scrapper assisted fuel feed nozzle device is illustrated in
Figure 3. The device comprises a bed ash modified configuration of an accelerating
nozzle (8), a coal feed line (9), a mixing chamber (10), a drain means (11), a wire
mesh scrapper means (12), a drive means (13), a recovery nozzle (14), a recovery
diffuser (15), and a transport line (16).
A second embodiment of the scrapper assisted fuel feed nozzle device is illustrated
in Figure 4. The device comprises a bed ash modified configuration of an
accelerating

nozzle (8), a coal feed line (9), a mixing chamber (10), a drain means (11), a spring
loaded ventilated disc scrapper means (17), a drive means (13), a recovery nozzle
(14), a recovery diffuser (15) and a transport line (16).
The invention proposes a scrapper assisted fuel feed nozzle device utilizing a wire
mesh (12) and/or the spring loaded ventilated disc assembly (17) to overcome the
bridging problem associated with the feeding of high moisture fuel (solids). The
modus operandi for guiding this scrapper assembly (12) is by a plurality of guide
rods. The locating of the guide rods is made possible by the optimized mixing
chamber (10) and the fuel feed line (9) without sacrificing the efficiency of pressure
recovery. This assembly (17) is driven thorough the drive means (13) to rotate the
wire mesh (12) for scrapping action. The alternative ventilated disc assembly (17) is
activated through a mechanism of releasing the spring thorough the drive means
(13).
The scrapper assisted fuel feed nozzle device achieves a feeding of high moisture
fuel by altering the dimensional configuration of the fuel mixing chamber (10) in
combination with the fuel feed line (9) including an optimal pressure recovery by
adopting nozzle / diffuser configuration (14, 15). The surface adhesion of high
moisture fuel attenuated by the constrictive feed line (9) in prior art promotes
bridging phenomena at the throat of the feed line (9) at the mixing chamber (10).
This hindered the feeding operation rendering the fuel feed nozzle arrangement
ineffective in the prior art.
The advantage of the invention lies in fact that the pressure recovery process over
the entire device is not only affected by the improved nozzle configuration (8) and

also incorporates the affirmative measures to disturb the bridging thus ensures an
ideal scenario for operation of the transport line (16). This results in more uniform
bed temperatures improving fuel utilization and better control over thermal NOx
production as all the transport line to the boiler is actively in service without
hindrance to the fuel feeding operation.
The other benefits associated with scrapper assisted fuel feed nozzle device is the
better pressure recovery thus reducing the pressure to be developed by the fan
system and improves overall cycle efficiency.
A significant benefits stem from this unique control allows an adjustment for wide
varying fuel quality by going in for scrapper assisted fuel feed nozzle device for high
moisture fuel to ensure good combustion efficiency.

WE CLAIM
1. A scrapper-assisted fuel feed nozzle device for feeding high-moisture fuel in
Bubbling Fluidised Bed combustion (BFBC) boiler, comprising :
- at least one accelerating nozzle 98) for transferring fuel (coal) supplied
through a coal feed line (9), the nozzle (8) accelerating a low pressure
air supply to convert the pressure head to a velocity;
- a recovery nozzle and diffuser combination (14, 15) collecting the high
velocity air-fuel mixture and recovering the pressure head;
- an optimized mixing chamber (10) for promoting the mixing of the air-
fuel; and
- a transport line (16) for transportation of the air-fuel mixture for
feeding into the bubbling bed combustor,
characterized in that:
- the coal feed line (9) is having an identical cross-section as that of the
transport line (16) which is achieved by optimizing the configuration of
the atleast one accelerating nozzle (8), and
- a scrapper means (12, 17) disposed into the transport line (16)

before the recovery nozzle / diffuser (14, 15) which is connected to a
driving means (13), the driving means (13) being activated at a
predetermined frequency corresponding to the data relating to
frequency of blockage experience in the past.
2. The device as claimed in claim 1, wherein the scrapping means (16)
constituting a wire mesh scrapper which is enabled to eliminate the bridging
problem on the transport line (16).
3. The device as claimed in claim 1 or 2, wherein the scrapper means (16) is
guided by a plurality of guide rods.
4. A scrapper-assisted fuel feed nozzle device for feeding high-moisture fuel in
Bubbling Fluidised Bed combustion (BFBC) boiler, as substantially described
and illustrated herein with reference to the accompanying drawings.

The invention relates to a scrapper-assisted fuel feed nozzle device for feeding high-
moisture fuel in Bubbling Fluidised Bed combustion (BFBC) boiler, comprising at least
one accelerating nozzle (8) for transferring fuel (coal) supplied through a coal feed
line (9), the nozzle (8) accelerating a low pressure air supply to convert the pressure
head to a velocity; a recovery nozzle and diffuser combination (14, 15) collecting the
high velocity air-fuel mixture and recovering the pressure head; an optimized mixing
chamber (10) for promoting the mixing of the air-fuel; and a transport line (16) for
transportation of the air-fuel mixture for feeding into the bubbling bed combustor,
the coal feed line (9) is having an identical cross-section as that of the transport line
(16) which is achieved by optimizing the configuration of the atleast one accelerating
nozzle (8), and a scrapper means (12, 17) disposed into the transport line (16)
before the recovery nozzle / diffuser (14, 15) which is connected to a driving means
(13), the driving means (13) being activated at a predetermined frequency
corresponding to the data relating to frequency of blockage experience in the past.