FIELD OF INVENTION
The present invention generally relates to the field of steam generation system.
The present invention in particular relates to pulverizers, feeding raw coal to the
boilers of steam generation system. More particularly, the present invention
relates to a motor-operated raw coal isolation device to prevent flowing of
ignited raw coal to the pulverizer from the storage bunker.
BACKGROUND OF THE INVENTION
Thermal power plants use Fossil fuels like coal to generate steam for Power
generation. The fuel coal is delivered from coal mines to the power plant through
rail, ship or by road transportation. The coal received at power plant is called raw
coal. This raw coal is stored in storage yards. The raw coal cannot be fired
directly in large capacity boilers / steam generators. The raw coal has to be
pulverized so as to make it burn efficiently in a boiler furnace. In modern utility
steam generating stations, the unit load is directly linked to the pulverizer. The
pulverizer dynamically responds to the load. Hence, the pulverizer operation
necessarily calls for a temporary storage arrangement. This storage arrangement
is called as raw coal bin or raw coal bunker. The raw coal is susceptible to a risk
of accidental ignition. If the coal is accidentally ignited, it will cause to develop a
big fire hazard. With this fire in the bunker, if raw coal is admitted to pulverizer it
will lead to catastrophic accident. To obviate this problem, it is desirable that an
isolation device capable of preventing the flow of burning coal from raw coal
bunker to the pulverizer, is provided. The raw coal bunkers are normally
designed for storage capacity of ten to fifteen hours of boiler operation.

As the raw coal is generally stored in a vertical column, any isolation device
when provided needs to move against such vertical column of raw coal. In
addition, monsoon brings more hardships by the way of increased moisture in
the raw coal which results in coal column compaction. Due to such, the existing
isolation devices available in market are suffering with the following setbacks.
i) When the bunker isolation device is operated, arch formulation takes
place which leads to mild to heavy choking of raw coal.
ii) The isolation device cannot be closed to its full capacity (100%) since
the entrapped coal between the isolation device plate (across the
section) and the wall on the opposite end acts as a barrier.
The opening size determines the flowabiiity of raw coal into the down stream.
Bigger the opening, smoother will be the raw coal flow. During monsoon season,
the flowabiiity of coal is very much affected due to increase in surface moisture.
The arch formulation at the bunker outlet is common phenomena which almost
interrupts the coal flow resulting starvation of coal into the pulverizer circuit.
During boiler operation the raw coal flows in to the down stream, therefore
during the normal condition, the isolation device can be easily closed as flowing
raw coal does not pose severe problems in piercing through column of coal.
However, when coal flow is interrupted due to reason beyond control, the
closure of isolation device to its full capacity is impossible. Power station
engineers resort a crude way of operation by manipulating the isolation device to
move forward and backward and there by inching towards complete closure of
the opening. Such a remedy is not reliable, safe and a technical solution.

Isolation device is used to Open / Close at the bunker outlet by moving from one
end to another. When the bunker outlet dimensions exceeds certain limit, the
force required to shear the vertical coal column increases exponentially which
may result halting the movement midway. Added to that, if the coal column is
established, it may further aggravate the situation.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to provide a motor-operated improved
raw coal isolation device which eliminates the disadvantages of the prior art.
Another object of the invention is to provide a motor-operated improved raw coal
isolation device which ensures free and smooth flow of moistured raw coal even
in monsoon periods.
A further object of the invention is to provide a motor-operated improved raw
coal isolation device which moves towards the center from the ends, and having
its moving parts with smaller overlapping such that a full closer of the device is
always ensured.
Yet another object of the invention is to provide a motor-operated improved raw
coal isolation device which does not require the coal column to be sheared in the
direction of the opening, thereby allowing a complete closure of the device.

A still further object of the invention is to provide a motor-operated improved
raw coal isolation device which prevents flow of burning coal from the raw-coal
bunker to the pulverizer thereby avoiding any catastrophic accident in a steam
generation system.
BRIEF DESCRIPTION OF THE INVENTION
The motor-operated improved raw coal isolation device comprises:
Corrosion resistant body: As the body of the device comes in contact
with coal, it is made of corrosion resistant steel. The corrosion resistant
steel body prevents rusting and withstands comparatively for a longer
period. The body is made of sufficient thickness to withstand the
corrosion. The isolation device is equipped with two access ports, each
having a molded gasket under a rigid cover, providing a dust-tight closure.
Covers are designed for easy removal. Inside surfaces of the covers flush
with the body, to assure good coal flow. The body of the coal isolation
device is a fabricated steel plate, with all joints in contact with the coal
flow welded inside and out, and ground smooth to eliminate any edges on
which coal could accumulate. The end cover, provided for isolation
removal and interior access, is equipped with molded gasket, assuring
dust-tight integrity of the isolation device. Two hand wheels are provided
for manual operation. Indicators are provided for the wheel to indicate the
'open" and "close" directions.

Corrosion resistant Isolator: There are atleast two isolators lined with
corresion resistant steel, The isolators are supported by "L" shaped racks.
The isolator is allowed to overlap each other at the center of the opening.
The isolator by its design keeps the supporting rollers completely away
from coal stream. The isolator edge is beveled so that the coal column is
easily sheared. This design minimizes the potential corrosion from
moisture in the coal, and contributed to reliable operation and long life.
Rack and Pinion: To assure closure of the isolator without choking,
pinions on the operating shaft engage "L" shaped racks which run down
each side of the isolator. As the pinions are located above the racks,
positive tooth engagement is ensured.
Drive systems: There are two actuators to drive the two isolators. The
actuators are synchronized to operate in tandem. The safe torque value is
set on the actuator so that the actuator trips when the torque level
exceeds. The actuators are operable remotely and locally.


rack (14) which run down each side of the isolator. As the pinions are suitably
located, positive tooth engagement is ensured.
A Drive means (18): The drive means comprises a plurality of actuators (18)
which drive the isolators (12). The actuators (18) are synchronized. Safe torque
value is set on the actuator. The actuator (18) trips when the specific level
exceeds. The actuators (18) are operable by an electric motor (not shown) from
the control room or near to its fixation.

WE CLAIM
1. An improved motor-operated raw coal isolation device adaptable to
open or close the outlet of a raw coal storage bunker dispose of
beneath the bunker in a thermal power plant, the device comprising
- a fabricated corrosion resistance body (06) having at least two
access ports with one molded gasket (07) and the other one
with rigid cover (08) and an end cover (03) for internal access
to the body (06) equipped with molded gasket (10) assuring
dust-tight integrity;
- at least two hand wheels (11) are provided on the body (06)
integrated with actuator (18) for manual operation with an
indicators to indicate open and close direction;
- at least two corrosion resistance lined (13) isolators (12) and
are supported by a plurality of suitable shaped racks (14) and a
plurality of rollers (15) resting away from coal stream and each
isolators is allowed to overlap the other at the centre of
opening;
- a plurality of pinions (16) are provided on an operating shaft
(17) such that a positive engagement is achieved between the
isolators (12) via the racks (14); and
- a drive means (18) for driving the insulators (12), the device
means being actuated by an electric motor from the control
room.

2. The device as claimed in claim 1, wherein the rigid covers (08) and the
end cover (09) each are respectively provided with molded gaskets
(07,10).
3. The device as claimed in claim 1, wherein the isolators (12) are
provided with corrosion resistant steel (13).

4. An improved motor operated raw coal isolation device adaptable to
open or close the outlet of a raw coal storage bunker in a thermal
power plant as substantially described herein with reference to the
accompanying drawings.

The present invention relates to an improved motor operated raw coal
isolation device adaptable to open and close the outlet of a raw coal storage
bunker disposed below the bunker in a thermal power plant. The device
comprising a fabricate corrosion resistance body (06) having at least two
accesss ports with one molded gasket (07) and other one with rigid cover
(08) and an end cover (09) for internal access to the body (06) equipped with
molded gasket(10) assuring dust tight integrity and at least two hand wheels
(11) provided integral with the body (06) and at least two corrosion
resistance lined (13) isolators (12) and are supported by a plurality of suitable
shaped racks (14) and a plurality of rollers (15)resting away from coal stream
and each insulator is allowed to overlap the other at the centre of opening
and a plurality of pinions (16) are provided on an operating shaft (17) such
that a positive engagement is achieved between the insulators (12) via the
rack (14) and a drive means (18) for driving the isolators(12), the drive
means being actuated by an electric motor from the control room.