FIELD OF INVENTION:-
Present invention relates to an improved system for flowability of material
collected in cyclone of large capacity Circulating Fluidized Bed Combustion
(CFBC) boilers.
BACKGROUND OF INVENTION:-
Circulating Fluidized Bed Combustion is an efficient method of burning
various fuels like anthracite coal, bituminous coal, high sulphur content lignite
and petcoke, etc. The fuel burns between 800°C - 950°C temperatures and at
high velocity in the combustor usually in the range between 4.0 m/sec and 7.0
m/sec. In conventional Circulating Fluidized Bed Combustion (CFBC) boilers, the
membrane water wall tubes present in the combustor with height between 32
and 40 meters, is top supported and provision to expand downward during
combustion. Primary air is admitted through distributor plate and secondary air
through several ports at an elevation between 2.0 and 5.0 meters for
combustion. Regulated quantity of fuel is admitted at lower elevation of
combustor through seal pot and limestone/dolomite is added along with fuel if
the fuel contains sulphur. The flue gas along with fine particles generated in
combustor is let out at top of combustor to cyclone where the particles are
separated from flue gas. Fly ash particles along with unburnt carbon and bed
material collected in cyclone are recycled back to the combustor through seal pot
for improving the combustion efficiency and effective capture of sulphur dioxide
through limestone added along with fuel. The flue gas let out from the cyclones
admitted to back pass of the boiler for recovering heat in various zones. The
particles collected in cyclone leave through bottom opening, large enough for the
quantity of material collected so that no accumulation of particle takes place.
Conical section of cyclone is made of an angle above 70° for free flow of
material. But, in few CFBC boiler installations, due to sintering nature of ash, the
bed material sinter with fly ash and the material do not flow freely to seal pot
circulation. The sintered material gradually builds up in cyclone and leads to
complete chocking in cyclone. If the material does not flow for circulation, the
bed temperature shoots up, inventory of material does not flow for circulation,
finally force to trip the entire boiler.
DETAILED DESCRIPTION OF PRIOR ART DRAWINGS:-
Schematic diagram of widely used Circulating Fluidized Bed Combustion
(CFBC) boiler is shown in Figure: 1.
In large capacity CFBC boilers, primary air (1) is admitted from bottom to
the water cooled combustor (2) through an air distributor and secondary air (3)
is admitted through separate ports at different elevation. The fly ash along with
bed material elutriate from the combustor are collected in cyclones (4) and the
collected particles are recycled to the combustor (2) through seal pot (5). A
separate fan/blower supplies air (6) for fluidizing the material in seal pot. The
fuel coal/lignite/pet coke is sized, stored in a bunker (7) gets admitted at a
regulated rate using a feeder (8) to the combustor (2) through outlet of seal pot
(5). A portion of material collected in the cyclone (4) is diverted to Fluidized Bed
Ash Cooler (9) for recovering heat from circulating material. A separate fan
supplies air (10) to the Fluidized Bed Heat Exchanger (9) for fluidizing the
material. Sorbent is sized, stored in sorbent bunker (11) for absorbing sulphur
dioxide in-situ. The sorbent is delivered along with the fuel to the combustor (2)
through outlet of seal pot (5). The fluidized bed material is also drained through
drain pipes (12) to maintain bed inventory.
The flue gas let out from the cyclones (6) is admitted to back pass (13) of
the boiler for recovering heat in various sections. The flue gas, exit from the
back pass (13) and enter into air preheater for heating the primary and
secondary air and finally leaves through fly ash separators to chimney.
The cyclone plays an important role in CFBC boilers for collecting fine size
range of particles elutriated from combustor and discharging them through its
bottom opening to seal pot for transferring the material to the combustor for
circulation. The cyclone gets chocked whenever ash with more sintering
tendency is fired during combustion.
An US Patent No: 6,997,973 entitled "Cyclone with plug prevention"
discloses the teaching of a vortex breaker which is placed at bottom of cyclone
for deagglomeration and in addition, the vortex breaker also contain two rotating
members with fingers extended radically placed from shaft, break up lump pieces
for aiding free flow of material. A rotary air lock feeder is placed below the
cyclone for discharging sized material/wood pieces to subsequent system.
A second US Patent No: 4,781,574 entitled "Method and system for
controlling cyclone collection efficiency and recycle rate in fluidized bed reactors"
explains a method and system for controlling the cyclone collection efficiency and
the recycle rate in a fluidized bed system. The invention also depicts inventory
control of fluidized bed.
The patents do not mention about plugging of cyclone in CFBC boilers due
to sintering characteristics of fuel ash. The present invention relates to a
Circulating Fluidized Bed Combustion system to overcome the above said
drawback. It has been the endeavor of the applicant to develop a cyclone with
special design features for eliminating/removing the ash agglomeration/choking
in cyclone for improving flowability of material from the cyclone and thereby
increasing the availability of CFBC boilers.
OBJECTS OF THE INVENTION:-
It is therefore, an object of the present invention to propose an improved
system for flowability of material in cyclone which prevents chocking of fly
ash/material in cyclone.
Another object of the present invention is to propose an improved system
for flowability of material in cyclone which uses compressed/high pressure air.
A still another object of the present invention is to propose an improved
system for flowability of material in cyclone which may improve free flow of
particles collected in cyclone.
An another objective of the present invention is to propose an improved
system for flowability of material in cyclone which does not alter or change the
configuration of the cyclone adopted in Circulating Fluidized Combustion boilers.
SUMMARY OF THE INVENTION:-
The present invention is provided with an improved system for flowability
of material in cyclone of large capacity Circulating Fluidized Bed Combustion
(CFBC) boiler comprising a plurality of cyclones attached on two sides of a CFBC
boiler wherein the flue gas and elutriated particles are separated. The cyclones
contain a plurality of air ports at different elevations at the hopper portion of the
cyclone for admission of high pressure air and the airports are placed at an angle
through which high pressure air is admitted in downward direction to the cyclone
for avoiding choking and the air inlet pipe of each port is connected with a
connecting header.
BRIEF DESCRIPTION WITH ACCOMPANYING DRAWINGS:-
Fig. 1 shows a schematic view of CFBC boiler as per Prior Art.
Fig. 2, 3 and 4 show an improved system CFBC boiler as per invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF
THE INVENTION:-
The equipment according to the invention will be described in detail by
means of a preferred embodiment illustrated in Figures 2, 3 and 4:
In circulating fluidized bed combustion (CFBC) system (Fig: 2) primary air
(1) is admitted to membrane water cooled combustor (2) from bottom through
air distributor plate and secondary air is admitted through number of ports (3) at
different elevations. Flue gas along with fly ash generated in combustor is
admitted to cyclone (4) where the flue gas and elutriated particles are separated.

The flue gas leave at top of cyclone and the particles collected in cyclone gets
discharged to seal pot (5) through a duct or pipe. The particles are fluidized in
seal pot through a fluidizing air (6) supplied to seal pot by a separate blower.
High density particles settled in combustor is drained through drain pipe (12) for
maintaining inventory of material in fluidized bed. The present invention can be
better described with reference to the accompanying Figs: 3. At hopper portion
of cyclone high pressure air is admitted through plurality of ports (14), at
different elevations for admitting secondary air for avoiding/reducing chocking of
material in cyclone. Fig: 4 depicts high pressure air delivered from connecting
headers (15), plurality of ports (14) and a common inlet pipe (16).
The header of compressed air is segmented at every 30° to 45° angle and with a
space in between 30°-45° are connected together at each elevation for admitting
compressed air through ports. The ports are fixed in cyclone hopper at an angle
between 50° and 70° for avoiding clogging of sintered material and the air leave
from ports are configured to penetrate the entire cross section of cyclone at the
corresponding elevation.
The ports are placed at an interval between 5° and 10° in each elevation of
cyclone-hopper.
The segments of header which consists of device for regulating air flow
measurement and pressure regulating device.
The pressure of compressed air admitted through each port is maintained
between 1.0 - 4.0 kg/cm2.

WE CLAIM:-
1. An improved system for flowability of material in cyclone of large capacity
Circulating Fluidized Bed Combustion (CFBC) boiler comprising:-
- a plurality of cyclones attached on two sides of a CFBC boiler wherein
the flue gas and elutriated particles are separated;
- a plurality of air ports (14) at different elevations are provided at the
hopper portion of cyclone for admission of high pressure air;
- the airports (14) are disposed at an angle through which high pressure
air is admitted in downward direction to the cyclone for avoiding
choking;
- the air inlet pipe (16) of each port is connected with a connecting
header (15);
characterized in that, the admission of high pressure air through the ports
(14) of the hopper flows in downward direction which prevents
agglomeration of fly ash deposited in cyclone and forces to drain out
through port (12) and controls inventory.
2. The system as claimed in claim 1 wherein the header of compressed air is
segmented at every 30°-40° angle and with a space between 30-45
degrees are connected together at each elevation for admitting
compressed air through ports.
3. The system as claimed in claim 1 wherein the ports are fixed in cyclone at
an angle between 50° and 70° for avoiding choking and the air leaves
from ports are configured to penetrate the entire cross section of cyclone
at that elevation.
4. The system as claimed in claim 1, wherein the ports are placed at an
interval between 5 and 10 degree in each elevation of cyclone-hopper.
5. The system as claimed in claim 1, wherein the segments of header which
consists of pressure regulating device and air flow measurement.
6. The system as claimed in claim 1, wherein the pressure of compressed air
admitted through each port is maintained between 1.0 kg/cm2 and 4.0
kg/cm2.

An improved system for flowability of material in cyclone of large capacity
Circulating Fluidized Bed Combustion (CFBC) boiler comprising a plurality of
cyclones attached on two sides of a CFBC boiler wherein the flue gas and
elutriated particles are separated and a plurality of air ports (14) at different
elevations are provided at the hopper portion of cyclone for admission of high
pressure air and the airports (14) are disposed at an angle through which high
pressure air is admitted in downward direction to the cyclone for avoiding
chocking and the air inlet pipe (16) of each port is connected with a connecting
header (15); characterized in that, the admission of high pressure air through
the ports (14) of the hopper flows in downward direction which prevents
agglomeration of fly ash deposited in cyclone and forces to drain out through
port (12) and controls inventory.