FIELD OF INVENTION
This invention relates to integrated gasification based power generation;
especially pressurized fluidized bed gasification based systems used for any
grade of coals. More particularly, the invention relates to an improved bottom
ash extractor device for pressurized fluidized bed gasifier.
BACKGROUND OF THE INVENTION
Combined Cycle is increasingly being used to generate electricity through
integrated gasification. Such combined cycles are capable of using various
grades of low calorific value and high ash content coals.
In a refractory lined pressurized fluidized bed gasifier, a mixture of air and steam
is introduced through a distributor located at a bottom of the gasifier. Coal is
continuously injected to the gasifier through ejector using compressed air. Coal
gas also called 'fuel gas' is produced due to the chemical reaction of coal with air
and steam. The fly ash and unbumt carbon particles in fuel gas are separated by
a serially arranged cyclones. The coal gas at the exit of the cyclone is cooled in a
Heat Recovery Boiler (HRB). The gas is further cooled in the gas cooler while
superheating the saturated steam of HRB. Part of the superheated steam is
utilized for gasification process and the rest expands in the steam turbine to
generate electricity. The gas is further processed in a gas cleaning system and
admitted to a combustion chamber of a gas turbine to generate electricity.
During the gasification process, for a particular load, to maintain the bed
height/inventory, the bed ash is extracted from the bottom of the gasifier
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through the extractor. Maintaining the gasifier bed height is vital because it
greatly influences the fluidization velocity, better fluidization, better composition
of fuel gas having adequate quantity and reduction in the over loading of the
equipment located in the down stream gas path with fly ash.
In a pressurized fluidized bed gasifier the bed ash is removed by using rotary
bucket type extractors through ash coolers. The ash coolers having number of
smaller diameter tubes through which the required quantity of cold water is
caused to flow and the ash is flown between the tubes, and thus gets cooled. At
high pressure and at high temperatures problems are encountered when the
rotor of the extractor gets jammed due to accumulation of fine ash particles
between the rotor end and the casing provided on both the ends, further leakage
of gas through gland packing on both ends of the rotor shaft commences,
leading to maintenance problem particularly due to shorter length of support ribs
which results in stoppage of the extraction process.
An object of the invention is to provide an improved bottom ash extractor device
for pressurized fluidized bed gasifier which ensures removal of fine ash particles
between the rotor and the casing and rotor and end covers disposed on both the
ends.
Another object of the invention is to provide an improved bottom ash extractor
device for pressurized bed fluidized gasifier which eliminates the problem of
jamming of the extractor rotor, thereby allowing continuous removal of bottom
ash from the bed of the gasifier.
A further object of the invention is to provide an improved bottom ash extractor
device for pressurized fluidized bed gasifier which eliminates leakage of
poisonous/inflammable gas through gland packing of the rotor shaft thereby
ensures the safety and reducing the air pollution.
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A still further object of the invention is to provide an improved bottom ash
extractor device for pressurized fluidized bed gasifier which allows maintaining
an optimum bed height by efficient removal of the bed ash.
Yet another object of the invention is to provide an improved bottom ash
extractor device for pressurized fluidized bed gasifier which effectively
contributes to increase the operational life of the downstream equipment located
in the fly ash path of the gasification system.
Still another object of the invention is to provide an improved bottom ash
extractor device for pressurized fluidized bed gasifier which ensures an
environmental-friendly operation of the gasification system.
SUMMARY OF THE INVENTION
Accordingly there is provided an improved bottom ash extractor device for
pressurized fluidized bed gasifier comprising: a plurality of rotary buckets
interlocked by means of several keys on a solid shaft, the rotary buckets being
encased; by a cylindrical type casing having openings for ash inlet and outlet,
atleast two stator end covers releasably connected via a gasket to both sides of
said cylindrical casing; atleast two bearing housings provided at both ends of the
rotor shaft; a gas inlet pipe assembly disposed at both ends of the stator end
cover for gas purging; atleast two gland housings to avoid leakage of gas from
the device, the atleast two housings having a plurality of lantern rings disposed
at the central location of the housing for nitrogen/inert gas purging; and a
plurality of longer supporting ribs to support the atleast two bearing housings for
easy maintenance.
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BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Rgure 1- Shows an elevational and plan views of an improved bottom ash
extractor device according to the present invention.
Figure 2- Shows a gland housing configured for the improved bottom ash
extractor device according to the present invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF
THE INVENTION
Figure 1 shows the improved device wherein figure 2 illustrates the gland
housing of the device. While the plant is in operation, the bottom ash coming
from the bottom of the gasifier enters atleast one bucket (01) through a chute
(02). A solid shaft (03) rotates, filling and delivery of ash takes place
continuously and the ash is delivered to a receiver vessel (not shown) through
the chute (05). A plurality of rotary-buckets (01) are enclosed by a casing (18)
and atleast two number stator end covers (06) are bolted to the casing (18) with
a gasket (07) on both sides of the casing (18). Both the stator end covers (06)
has a gland housing (08) which consists of a plurality of graphited gland packing
(09), packed on both sides of the atleast two lantern rings (10), having a number
of holes on its periphery assembled at a center of the housing (08), for
nitrogen/inert gas purging through a plurality of nipples (11). A gland cover (12)
is disposed for tightening the plurality of graphited gland packing (09), to avoid
the leakage of gas from the extractor.
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For smooth running of the rotor shaft (03) both ends of the solid shaft (03) are
assembled with atleast two bearing housing (13), each one consists of a bearing
(14) and a cover (15). The bearing housings (13) are supported by a number of
longer supporting ribs ( 16) for easy maintenance.
A gas inlet pipe assembly (17) is arranged at both the stator end cover (06) for
gas purging to avoid accumulation of ash fines between the rotor shaft (03) and
the stator end cover (06) and to ensure smooth running of the rotary-buckets
(01).

We Claim
1. An improved bottom ash extractor device for pressurized fluidized bed
gasifier comprising:
- a plurality of rotary buckets (01) interlocked by means of several
keys (04) on a solid shaft (03), the rotary buckets (01) being
encased;
- a cylindrical type casing (18) having ash inlet and outlet ports;
- atleast two stator end covers (06) releasably connected via a
gasket (07) to both sides of the cylindrical type casing (18);
- atleast two bearing housings (13) provided at both ends of the
rotor shaft (03);
- a gas inlet pipe assembly (17) disposed at both ends of the stator
end cover (06) for gas purging; characterized by comprising:
- atleast two gland housings (08) to avoid leakage of gas from the
device, the atleast two gland housings (08) having a plurality of
lantern rings (10) disposed at a central location of the gland
housing (08) for nitrogen/inert gas punging; and
- a plurality of longer supporting ribs (16) to support the atleast two
bearing housings (13) for easy maintenance.
2. The device as claimed in claim 1, wherein the gland housing (08)
comprises a plurality of graphited gland packing (09) for packing the
lantern rings (10), and a gland cover (12) for tightening the glands to
avoid leakage of gas.
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3. The device as claimed in claims 1 or 2, wherein the nitrogen/inert gas is
purged via a plurality of nipples (11) configured on the gland housing
(08).
4. The device as claimed in claim 1, wherein the bearing housing (13)
comprises atleast one bearing (14) and a cover (15).
5. An improved bottom ash extractor device for pressurized fluidized bed
gasifier as substantially herein described and illustrated with reference to
the accompanying drawings.