FIELD OF INVENTION
This invention relates to an improved economizer hopper for segregating
lumps from fly ash. The hopper is provided in circulating fluidized bed
combustion boilers.
BACKGROUND OF THE INVENTION
The circulating fluidized bed process utilizes a fluidized bed combustor in
which crushed Lignite/coal and limestone are suspended in a stream of
upward flowing air. Due to the fine particle size of the coal feed and high
gas velocity, the bulk of the solids is carried out of the combustor along
with the flue gases, collected in a recycling cyclone and returned to the
combustor. Therefore, the process is called Circulating Fluidised Bed.
Combustion: The fuel Lignite/coal is ignited at a temperature of about
850 deg. C. Fuel is fed directly to the combustor without requiring costly
fuel preparation and distribution systems. The combustion air is fed in
two stages- Primary Air through the combustor and Secondary Air part
way up the combustor above the fuel feed point. The limestone required
for desulfurization is added near the bottom of the combustor.
The heat in flue gas leaving the cyclone is recovered in heat exchanger
coils located in the Back pass. The Economizer coils are placed in the
bottom portion of the back pass.
In CFBC boilers fired with high sulphur content (4 to 6%) lignite releases
SO2 in the range of 5000-7000 ppm. More quantity of limestone powder
is to be fed for the absorption of sulphur dioxide (SO2) from the flue gas.
In the process very small size limestone powder escapes to back pass and
settles over the tube surface and recarbonization takes place. The SO2
recombines with calcium oxide (CaO) and forms CaSO4 and CO2
recombines with CaO to form CaCO3. The above two products forms hard
deposits over the horizontal tubes and grows further and when soot
blower is operated detaches and falls down to economizer hopper along
with fly ash. The bigger size particles gets struck up at economizer ash
handling pump throat and fly ash evacuation process gets interrupted.
Automatic evacuation stops and manual mode of evacuation to be
adopted and in some occasion plant load needs to be reduced to tackle
the problem.
Reference may be made to the following known arts:
United States patent no. 5, 628, 259 Economizer Lump Breaker
describes the following:
A lump breaker apparatus mounted to an airlock of an economizer ash
hopper for breaking up ash clinkers accumulated on a grating disposed
in the airlock to maintain the passage of ash through the grating of the
air lock. The apparatus comprising of a pneumatic cylinder having a rod
extending there from with a ramming plate connected to a distal end
thereof and slidably disposed on the grating of the airlock, a mounting
assembly for mounting the cylinder to the airlock and a seal assembly for
providing a slidable seal about the rod. The ramming plate reciprocally
movable from a retracted position to an extended position along the
grating to impact the ash clinkers on the grating of the airlock with
sufficient force to fragment such ash clinkers and to permit the passage
of some ash clinkers through the grating.
United States patent No. 5, 599, 099 "Material blending apparatus
having pivotally mounted hopper" discloses the following:
A weigh batch blender including a hopper pivotally mounted within a
housing and having two compartments between which ingredient
materials which have been individually introduced into the hopper are
transferred to blend the ingredient materials as the hopper is pivoted
between two "mix" positions at the ends of the pivotal range of the
hopper. After blending, the hopper is moved to beyond one of the ends of
pivotal movement of the hopper to dump the blended ingredient material
contents of the hopper.
United States Patent No. 5, 222, 512 "Sparger system for discharge to
bulk material from hopper cars" is directed to the following:
A sparger system for removing sodium chlorate crystal and other
crystalline particulate material is slurry form from a tank car comprises
a plurality of spray nozzles from which water is expelled as a flat spray
initially to dissolve sodium chlorate so as to cavitate the mass of sodium
chlorate crystals, which break off in lumps into the cavity and then to
impact the walls and roof of the tank car to flush off residual sodium
chlorate crystal. The slurry is collected in a sump and is discharged there
from, with additional sprays agitating the sump to break up clumps of
sodium chlorate and to maintain the particular in suspension.
United States patent No. 4, 548, 342 "Flow control insert for hopper
bottom bins" is related to the following:
Solid particular material is moved through a hopper bottom bin in mass
flow inducted by a conical surface positioned within the hopper to
compensate for the shallowness thereof. Laminar mass flow movement
will occur in the uppermost region of the material within the vertical bin
walls. The hopper cross-section is separated into segregated flow
channels by the conical surface, and by webs extending therefore. The
conical surface and webs have overall dimensions small enough for
insertion through a bold ring on the bottom of the hopper. The
proportion of the material flowing through each channel is chosen to
achieve a desired discharge flow pattern by varying the relative cross-
sectional area of either the inlets or the outlets of the channels. This
results in changes in the velocity profile of the downwardly flowing
material in a zone above and adjacent to the separate flow channels.
United States patent no. 4, 030, 633 "System for controlling segregation
within a bin during material withdrawal" pertains to the following:
The system includes a plurality of material discharge spouts combined
with a blending device for use with a hoppered bin. Each spout opens to
the hopper at a location selected to draw material into the hopper at a
location selected to draw material into the hopper from substantially one
predetermined portion of a horizontal bin cross sectional plane in a first
in -first our segregation free manner. The blending device combines the
material discharge streams formed by the spouts in proportion to the
areas of the portions of the horizontal bin cross sectional plane from
which they are drawn, respectively, to form a common discharge stream
of uniform composition. The principles of the invention are applicable to
conversion of existing bins or bin bottoms, or to a bin withdrawal system
or process. Also discloses is a blending unit which includes a mass flow
hopper, the blending unit being particularly suited for bin or bin bottom
conversion application.
OBJECTS OF THE INVENTION
The primary object of the present invention is to propose an improved
economiser hopper for segregating lumps from fly ash which overcomes
disadvantages associated with the prior art.
Another object of the present invention is to propose an improved
economiser hopper for segregating lumps from fly ash which is efficient.
Further object of the present invention is to propose an improved
economizer hopper to segregate lumps from fly ash and ensure entry of
only fine ash into the fly ash evacuation system for trouble free operation
of the fly ash evacuation system.
Still another of the present invention is to propose an improved
economizer hopper to segregate large lumps or higher density materials
in any hopper system handling granular material.
SUMMARY OF THE INVENTION
The invention uses the principle of fluidization for segregation of lumps
or higher density material in a bed of granular solids. Fly ash material
collected in Economizer hopper is fluidized using fluidizing pads. The
larger (lumps) particles and higher density material fall through the bed
to the bottom, while the finer material is kept in suspension in a fluidized
state. The fly ash evacuation pneumatic handling system is connected
slightly at a higher elevation in the hopper. The larger lumps are
periodically drained. By this method entrance of large lumps is totally
eliminated.
STATEMENT OF INVENTION
According to this invention, there is provided an improved economizer
hopper for segregating lumps comprising of a hopper bifurcated into
atleast two parts for fly ash and heavier particles with fluidizing pads
provided on atleast three sides of the hopper to fluidize the fly ash which
is removed through a side chute connected to the hopper.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Further objects and advantages of this invention will be more apparent
from the ensuing description when read in conjunction with the
accompanying drawings and wherein:
Fig. 1 shows: general arrangement of CFBC boiler.
Fig .2 shows: schematic view of existing arrangement of economizer
hopper and the associated ash handling system equipments .
Fig. 3 shows: schematic view of improved economizer hopper for
segregating lumps.
DETAIL DESCRIPTION OF THE INVENTION WITH REFERENCE TO
THE ACCOMPANYING DRAWINGS;
Reference may be made to figure 2 showing the known arrangement of
the economizer hopper which does not segregate the lumps from the total
fly ash. It comprises of the Economizer hopper (1) and the pneumatic ash
handling system components (2). The disadvantage associated is that,
the pneumatic system gets choked and ceases to operate due to non
segregation of lumps.
In the modified arrangement, the hopper is bifurcated into two portions
for handling fly ash and heavier particles separately. The heavier particle
falls straight into the hopper and can be drained out manually at regular
intervals. Fluidizing pads are provided in three sides of the hopper to
fluidise the fly ash, so that the heavier particles and the fly ash are
segregated. The fly ash without lumps can be removed from the side
hopper and are evacuated by the pneumatic ash handling system.
Thus, the present invention discloses an improved economizer hopper as
shown in figure 3, in which the bottom portion of the economizer hopper
is fluidized with fluidizing pads (3). This fluidization aids in the
segregation of lumps and fines. The lumps travel down and are
discharged through the outlet gate (4) located at the bottom which is
periodically operated. The fine fly ash materials get fluidized and are
removed from the side chute (5) to be disposed by pneumatic fly ash
handling system.
Thus, the present invention can be used for segregating lumps or higher
density material from a hopper.
The fluidization arrangement segregates the large size or higher density
material from fine or low density material.
The bottom chute can be used to discharge large size lumps periodically.
The side chute is used to remove finer fly ash. The present invention can
also be used for other application where segregation of granular material
is required.
Further, the instant hopper can be used in boiler hoppers or any other
granular material handling hopper where separation of lumps is required
for the process or for handling the material.
It is to be noted that the present invention is susceptible to
modifications, adaptations and changes by those skilled in the art. Such
variant embodiments employing the concepts and features of this
invention are intended to be within the scope of the present invention,
which is further set forth under the following claims:-
WE CLAIM;
1. An improved economizer hopper for segregating lumps comprising
of a hopper bifurcated into atleast two parts for fly ash and heavier
particles with fluidizing pads provided on atleast three sides of the
hopper to fluidize the fly ash which is removed through a side
chute connected to the hopper.
2. An improved economizer hopper for segregating lumps as claimed
in claim 1, wherein the fly ash from the side chute is evacuated by
pneumatically ash handling system.
3. An improved economizer hopper for segregating lumps as claimed
in claim 1 or 2, wherein the hopper is connected to an outlet gate
at its bottom for removal of lumps.
4. An improved economizer hopper for segregating lumps
substantially as herein described and illustrated in the
accompanying drawings.

This invention relates to an improved economizer hopper for segregating
lumps comprising of a hopper bifurcated into atleast two parts for fly ash
and heavier particles with fluidizing pads provided on atleast three sides
of the hopper to fluidize the fly ash which is removed through a side
chute connected to the hopper.