FIELD OF THE INVENTION
The present invention relates to fluidized bed gasification/combustion based
systems operable with any grade of coal or other fuels. More particularly, the
invention relates to a device for lateral Extraction of ash from pressurized
fluidized bed gasifiers.
BACKGROUND OF THE INVENTION
Integrated Gasification Combined Cycle (IGCC) power generation systems
include a gasification system that is integrated with power producing turbine
systems. The gasifier converts a mixture of fuel, air or oxygen, and steam into a
partially combusted gas, referred to as "syngas". The hot combustion gases are
supplied to a combustor of the gas turbine engine, which powers a generator
that supplies electrical power to a power grid. Exhaust from the gas turbine
engine is thereafter admitted to a heat recovery steam generator that generates
steam for driving a steam turbine. Power generated by the steam turbine drives
an electrical generator that provides further electrical power to the power grid.
During the gasification process, the bed ash is extracted from the bottom of the
gasifier to maintain the bed height, which is critical to ensure better fluidization,
proper composition of the fuel gas, and a maximum conversion of carbon. A bed
ash extraction system uses auxiliary equipment like, ash cooler, rotary extractor,
receiver, lock, de-pressurizing vessel, ash hopper, and ash disposal system,
which not only add to the complexity, of the IGCC, apart from increase in the
capital expense and operational manpower of the system.
Figure 01 shows a typical refractory lined pressurized fluidized bed gasifier (01),
air or a mixture of air and steam is passed through a first distributor (02) which
is provided with a plurality of first bubble cap nozzles (03) arrangement to
fluidize the bed. In gasification process, the bottom ash is extracted at a desired
rate through a plurality of pipe (04) located at various points of the first
distributor (02), and a plurality of ash coolers (05) by using or a number of
rotary extractors (06), to maintain the bed height and ensure proper fluidization.
A plurality of bottom ash receiver (07) is disposed for temporary storing of the
bottom ash. The bottom ash is collected under high pressure is fed through a
plurality of valves (08) and a plurality of lock hoppers (09) to a bottom ash silo
(not shown), after isolating the receiver(s) (07) and depressurizing the lock
vessels. In order to ensure a free flow of the ash by gravity, the ash coolers
(05), extractors (06), receivers (07), valves (08), lock vessels (09) and the silo
are arranged one above the other. After providing a required clearance at the
disposal point from the silo, the height of each of the said equipment is add-up,
and the gasifier is located at a substantially high elevation from the total height
of said auxiliary equipment. This leads to a tall structure and abnormal levels of
coal silo. Moreover, in course of operation, formation of agglomerates due to non
uniform fluidization causes blockage in the bottom ash extraction pipes (04)
which creates difficulty in bed ash removal. Further, the buckets of the rotary
extractor get locked causing rotational interruption in rotation of the bucket
leading to stoppage in ash extraction.
U.S. Patent No. 6082442 entitled "APPARATUS FOR REMOVAL AND COOLING OF
ASH FROM THE BED OF A FLUIDISED BED FURNACE" discloses a device for
extracting and cooling dry ash from a fluidized bed furnace. This system consists
of a combustion chamber having a floor is provided with a number of ash
extraction pipes an intake and an outlet for cooling medium, a housing provided
with several floors, a chain conveyor, a motorized driving wheel and an ash
discharge port. The chain conveyor constitutes a drag conveyor and comprises
two parallel and circulating chains connected together at intervals by scrapers. In
case of leakage in the cooling system, water penetrates into the interior and
soaks the ash. The wet ash cakes up on the wall of the housing and clogs the
conveyor, which breaks down.
U.S. Patent No. 4601730 entitled "AIR SUPPLY GRATE AND ASH REMOVAL
SYSTEM FOR WOOD GASIFIER" discloses an air supply grate. According to the
configuration, the system comprises a reactor vessel provided with the several
ring sections and a floor section called ash plow, a vertical axis rotating ash plow
carried by a shaft, an ash extraction auger (screw conveyor) and a sealed ash
tank.
OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose a device for lateral
Ash Extraction from Pressurized Fluidized Bed Gasifiers to reduce the total
structural height of the gasifier.
Another object of the present invention is to propose a device for lateral Ash
Extraction from Pressurized Fluidized Bed Gasifiers to reduce the total structural
height of the gasifier which ensures maintaining a desired bed height level.
A further object of the present invention is to propose a device for lateral Ash
Extraction from Pressurized Fluidized Bed Gasifiers to reduce the total structural
height of the gasifier which ensures ash extraction at least from one of the
multiple ports located at various points along the height of the gasifier.
SUMMARY OF THE INVENTION
Accordingly, there is provided a device for ash lateral extraction of ash from
pressurised fluidised bed gasifiers, the gasifier comprising a refractory lined
gasifier for producing syngas with desired composition and calorific value by
maintaining the bed to a predetermined height at high temperature by allowing
easy bed ash removal; a water cooled flat plate first distributor for uniform flow
distribution of air and steam mixture, and uniform temperature distribution
above the bed level and hold the bed to said predetermined height at high
temperature; a plurality of first bubble cap nozzles to maintain uniform
fluidization velocity and minimize or avoid formation of agglomerates by rapid
and thorough mixing of the bed including ash extraction; the device comprising a
plurality of side ash extraction pipes located at various points along the height
of the gasifier with pre-determined height differential from the first distributor; a
plurality of first cooling water jacket pipes acting as enclosures to the ash
extraction pipes and to allow the cooling water to flow in the flow circuit; a
plurality of cooling water inlet pipes and cooling water outlet pipes disposed in
the cooling water inlet and outlet circuits; a loop seal assembly for over flowing
hot ash into a quench vessel ; a quench vessel means having a long ash inlet
pipe to allow the hot ash with gas to fall down into the quench vessel, a cooling
water inlet pipe with a spray nozzle to quench the hot ash coming from the ash
inlet pipe and maintain the water level in the quench vessel, a water jet pipe for
thorough mixing of ash with water to produce ash water slurry in a flowable form
for easy disposal, a high water level indicating probe, a low water level indicating
probe, an ash water slurry discharge pipe to dispose the ash water slurry into a
silo, and a steam/gas vent pipe to vent vapour formed, and return entrained
fluidizing medium from right leg into the gasifier.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.1 - shows an elevation of A Device for Ash Extraction from the bottom of
Pressurized Fluidized Bed Gasifiers according to the prior art.
Fig.2 - shows an elevation of A Device for Lateral Extraction of Ash from
Pressurized Fluidized Bed Gasifiers according to the present invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
PRESENT INVENTION
According to the present invention A Device for lateral Extraction of ash from
Pressurized Fluidized Bed Gasifiers comprising : (i) a loop seal means to extract
the bed ash from the gasifier; (ii) a quench vessel to cool and dispose of the bed
ash. The pressurized fluidized bed gasifier of the invention as shown in figure 2,
comprises a refractory lined gasifier (01) for producing syngas with desired
composition and calorific value; a water cooled flat plate first distributor (02)
positioned and supported in the refractory lined gasifier (01) having diameter
varying from 1000 mm to 4000 mm for uniform distribution of air and steam
mixture, and uniform temperature distribution above the bed which in turn
produces the desired composition of syngas. It also holds the bed to a particular
height with high temperature by allowing easy bed ash removal; a plurality of
first bubble cap air nozzles (03) to maintain uniform fluidization velocity and to
minimize or to avoid formation of agglomerates by rapid and thorough mixing of
the bed, a plurality of water cooled side ash extraction pipes (10) located along
the height of the gasifier (01) with pre-determined height differential from the
first distributor(02), and having diameter ranging from 100 mm to 250 mm, a
plurality of first cooling water jacket pipes (11) having diameter ranging from
200 mm to 400 mm; a number of cooling water inlet pipes (12) and cooling
water outlet pipes (13) allowing circulation of cooling water and the side ash
extraction pipes (10) to withstand high temperature; a second distributor (14)
with a number of second bubble cap nozzles (15) for uniform distribution of inert
gas or clean syngas, a controlled quantity of inert gas or syngas at ambient
temperature being admitted to the second distributor (14) through a plurality of
gas inlet pipes (17) and a dual gas plenum (16) maintained at a pressure higher
than the system pressure to generate two different fluidization velocities in the
vertical, limbs (19 & 20). The hot ash material in the second distributor (14)
fluidizing and raising up in both the left and right vertical limbs (19, 20). The
incoming ash particles from the gasifier cause the particles in the right limb (20)
to over flow into a quench vessel (25) through an inclined pipe (21), the left,
right limbs and the inclined pipe (19,20&21) above the second distributor (15) is
enclosed with a plurality of cooling water jacket pipes (22,23&24) and a plurality
of inspection ports (18). The quench vessel means comprising; a cylindrical
shaped long straight quench vessel (25) to accommodate the hot and
pressurized bed ash, a long inlet pipe (26) to allows the hot ash with gas to fall
down into the quench vessel (25), a cooling water inlet pipe (27) with a spray
nozzle and a valve to quench the ash coming from the inlet pipe (26), and
maintain the water level between "LOW" and "HIGH" limits in the quench vessel
(25), a water jet pipe (28) with valves for thorough mixing of ash with water and
make an ash water slurry in a flowable form for easy disposal, a water level
"high" indicating probe (29), a water level "low" indicating probe (30), an ash
water slurry discharge pipe (31) with a valve to dispose the ash water slurry
into the ash yard and a steam/gas vent pipe (32) with a suitable valve to vent
vapour, and return entrained fluidizing medium from right leg (20) into the
gasifier, to ensure smooth extraction of ash, a pressure balance is maintained in
the system by the items (27,28,29,30,31&32),
WE CLAIM
1. A device for ash lateral extraction of ash from pressurised fluidised bed
gasifiers, the gasifier comprising :
(a) a refractory lined gasifier (01) for producing syngas with desired
composition and calorific value by maintaining the bed to a predetermined
height at high temperature by allowing easy bed ash removal;
(b) a water cooled flat plate first distributor (02) for uniform flow distribution
of air and steam mixture, and uniform temperature distribution above the
bed level and hold the bed to said predetermined height at high
temperature;
(c) a plurality of first bubble cap nozzles (03) to maintain uniform fluidization
velocity and minimize or avoid formation of agglomerates by rapid and
thorough mixing of the bed including ash extraction;
the device comprising :
(i) a plurality of side ash extraction pipes (10) located at various
points along the height of the gasifier (01) with pre-determined
height differential from the first distributor(02);
(ii) a plurality of first cooling water jacket pipes (11) acting as
enclosures to the ash extraction pipes (10) and to allow the
cooling water to flow in the flow circuit;

(iii) a plurality of cooling water inlet pipes (12) and cooling water
outlet pipes (13) disposed in the cooling water inlet and outlet
circuits;
(iv) a loop seal assembly for over flowing hot ash into a quench
vessel (25);
(v) a quench vessel means having a long ash inlet pipe (26) to
allow the hot ash with gas to fall down into the quench vessel
(25), a cooling water inlet pipe (27) with a spray nozzle to
quench the hot ash coming from the ash inlet pipe (26) and
maintain the water level in the quench vessel (25), a water jet
pipe (28) for thorough mixing of ash with water to produce ash
water slurry in a flowable form for easy disposal, a high water
level indicating probe (29), a low water level indicating probe
(30), an ash water slurry discharge pipe (31) to dispose the
ash water slurry into a silo, and a steam/gas vent pipe (32) to
vent vapour formed, and return entrained fluidizing medium
from right leg (20) into the gasifier to ensure smooth extraction
of ash, a pressure balance is maintained in the system by the
items (27,28,29,30,31&32),
2. The device as claimed in claim 1, wherein the loop seal assembly
comprises a second distributor (14) with a number of second bubble cap
nozzles (15) for uniform distribution of inert gas or clean syngas, two
numbers of gas inlet pipes (17) through which controlled quantity of inert
gas or syngas at ambient temperature is admitted to a dual gas plenum
(16) with slightly more than the system pressure, cause two different
fluidization velocities in both the vertical, left and right limbs (19&20), and
inclined pipe (21) and the vertical, left, right limbs and the inclined pipe
(19,20&21) above the second distributor is enclosed with cooling water
jacket pipes (22,23&24), is capable of admitting the hot ash to the quench
vessel (25);

The invention relates to a device for lateral extraction of ash from pressurised
fluidised bed gasifiers, the gasifier comprising : a refractory lined gasifier (01)
for producing syngas with desired composition and calorific value by maintaining
the bed to a predetermined height at high temperature by allowing easy bed ash
removal; a water cooled flat plate first distributor (02) for uniform flow
distribution of air and steam mixture, and uniform temperature distribution
above the bed level and hold the bed to said predetermined height at high
temperature; a plurality of first bubble cap nozzles (03) to maintain uniform
fluidization velocity and minimize or avoid formation of agglomerates by rapid
and thorough mixing of the bed including ash extraction; the device comprising :
a plurality of side ash extraction pipes (10) located at various points along the
height of the gasifier (01) with pre-determined height differential from the first
distributor(02); a plurality of first cooling water jacket pipes (11) acting as
enclosures to the ash extraction pipes (10) and to allow the cooling water to flow
in the flow circuit; a plurality of cooling water inlet pipes (12) and cooling water
outlet pipes (13) disposed in the cooling water inlet and outlet circuits; a loop
seal assembly for over flowing hot ash into a quench vessel (25) ; a quench
vessel means having a long ash inlet pipe (26) to allow the hot ash with gas to
fall down into the quench vessel (25), a cooling water inlet pipe (27) with a
spray nozzle to quench the hot ash coming from the ash inlet pipe (26) and
maintain the water level in the quench vessel (25), a water jet pipe (28) for

thorough mixing of ash with water to produce ash water slurry in a flowable form
for easy disposal, a high water level indicating probe (29), a low water level
indicating probe (30), an ash water slurry discharge pipe (31) to dispose the ash
water slurry into a silo, and a steam/gas vent pipe (32) to vent vapour formed,
and return entrained fluidizing medium from right leg (20) into the gasifier.