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FIELD OF INVENTION
the invention relates to pressurized fluidized bed combustion / gasification
systems. More particularly, the present invention relates to a fluidized bed char
combustion device adaptable to a fluidized bed gasification system.
BACKGROUND OF the INVENTION
Gasification of coal, lignite and other fuels in pressurized fluidized / entrained
bed systems are being adapted extensively for application in Integrated
gasification combined cycle. In these systems, the fuel is gasified in an oxygen
deficient environment. Hence the presence of un-burnt carbon-char in the fly ash
as well as in the bottom ash is high compared to the combustion system where
the oxygen required for reaction is provided. Even after recycling of these ash,
the carbon-char in the ash is high in fluidized bed systems where the
temperature of operation of the bed is influenced by the ash properties. To
improve the carbon utilization, combustion of these char in a separate device Is
adapted. In order to enable an easy handling and further to effect pressure seal,
the ash is generally cooled before taking it to the char combustor.
US patent no. 5666801 dated 16th September 1997 under the Combined cycle
power plant with integrated CFB devolatilizer and CFB boiler by Mr. Rohrer: John
W. discloses a method in which coal is de-volatalized in a Circulating fluidized
Bed devolatlliser / Thermal Cracker and the char is burnt in a CFB Boiler. the
fluidized bed could be a classical bubbling bed, a fast bed or a circulating bed
where generally high volatile and high reactive bituminous, sub bituminous or
lignite fuel is gasified in the gasifier to the maximum extent and un-burnt char

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along with the ash (either in full or partly) is burnt in conventional bubbling type
combustor.
The ash along with the char from the bottom of the bed and fly ash are removed
through a cooler, extractor (to control the rate of removal) and a lock system
consisting of vessels, isolation devices (ball valves), pressurizing / depressurizing
means, before discharging through a suitable means into the char combustor.
the char combustors mostly work at atmospheric pressure. This leads to a large
system for ensuring proper combustion especially for fly ash. Even when the
combustor is operating at elevated pressure, the ash is cooled to facilitate
extraction. Such a method not only requires the additional equipment, but also
cooling the ash / char results in tower efficiency of combustion / heat utilization.
It also requires support fuel to maintain the high bed temperature for efficient
combustion of char.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide a fluidized bed char
combustion device adaptable to a fluidized bed gasification system which
eliminates the disadvantages of the prior art.
Another object of the present invention is to provide a fluidized bed char
combustion device adaptable to a fluidized bed gasification system which ensures
efficient combustion of char present in the combustible material.
A further object of the present invention is to provide a fluidized bed char
combustion device adaptable to a fluidized bed gasification system which uses
the sensible heat of the ash / char to aid combustion without the need of any

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support fuel thereby making the fluidized bed gasification system efficient and
cost effective.
A still further object of the present invention to provide a fluidized bed char
combustion device adaptable to a fluidized bed gasification system which is
compact and does not require additional means for cooling the ash / char to
facilitate extraction.
SUMMARY OF THE INVENTION
Accordingly there is provided a fluidized bed char combustion device adaptable
to a fluidized bed gasification system, the system comprising a gasifier, atleast
one participate collection means retaining the ash and char particles separated
from the gas, and a bulk solid recirculator provided optionally for recycling the
solids into the gasifier, the device comprises a diversion means for diverting the
solid from the collection means to the gasifier via a parallel stream; a first
fluidized bed char combustor for inputting one of air and air-oxygen mixture n
the combustor, the first fluidized bed char combustor simultaneously controlling
the temperature of the input including the temperature of the fluidized bed
independently and/or combinedly thereby achieving combustion of the char
material present in the solids input; the generated flue gas including left-out char
being admitted to the gasifier, the resultant coarse ash including further left out
char particles being extracted from the bottom of the gasifier; a second fluidized
bed char combustor having atleast one heat transfer coil, and receiving the
coarse ash including further left-out char particles from the gasifier for
combustion therein, the flue gas generated being passed to a heat recovery
means, the coarse ash being disposed in two stages firstly via the bottom of the
combustor and secondly via the heat recovery means.

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BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 - Shows a block diagram of a fluidized bed char combustion device
adaptable to a fiuidized bed gasification system according to the
present invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF
THE INVENTION
The gasification system consists of a pressurized fluidized bed gasifier (1) where
the gasification is carried out to the maximum extent unlike only devolatilising /
cracking. In this system, the coal is fed either directly by pneumatic injection or
through a bulk solid recirculator into the gasifier bed being kept actively fluidized
by air, air-steam mixture distributed uniformly through the air distributor.
Gasification reaction takes place in the bed and the product gas along with finer
ash and char particles leave the gasifier vessel at the top. Relatively coarser ash
and char particles retained in the bed is extracted through the bottom. In a
particulate collection means (2) like cyclone (s), most of the particle carried by
the gas is separated. the gas leaving the collection means (2) is then cooled in a
heat recovery means (7) like steam generator and / or air heater and cleaned
further for removing the remaining dust such that the product gas is suitable for
applications like burning in a gas turbine combustor. the particles removed in
the collection means (2) is then recycled into the gasifier (1) with a bulk solid
recirculator (not shown). the device is provided with a parallel stream (Ps) to
divert the solid from the collection means (2) to the gasifier (1) through a
fluidized bed char combustor 4(1) by a diverting means (3) like cone valves or
siphon seal or loop seal or seal pot. the proportion of the material diverted could
be varied from 0 to 100%. Alternatively, the device may consist of a single

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stream (ss) to recirculate the entire material through a first fluidized bed char
combustor (4 (1)). the first fluidized bed char combustor 4(1) comprising a
vessel for ensuring proper fluidisation velocity and residence time, an air
distributor, an inlet connection from the separating means (3) and a return line
to the gasifier (1). By admitting required quantity or air, air-oxygen mixture and
controlling the temperature of the ash diverted, air supply, cooling coils and bed
segments independently or combinedly combustion of the char present in the
material is achieved. the flue gas formed along with the ash and any left out
char is admitted into the gasifier (1), provision is also made the ash
from the first combustor (4(1)) for disposal directly or through a second char
combustor 4(2) described below.
The coarse ash and char particles extracted from the bottom of the gasifier (1) is
taken to a second char combustor 4(2) for burning the char. the flue gas from
the combustor is cooled and cleaned in a heat recovery means (5(2), 6). When
the proportion of char in the ash extracted from the bottom is within acceptable
level for disposal- for some coals or certain operating conditions- the second
combustor 4(2) is used for cooling the material extracted. the gas can also be
used for pressurizing of locks. the material of construction of the components
have either the capability to withstand the temperature- in which case It is
insulated outside to prevent heat loss and for safety- or it may be cooled or
refractory lined. the fluidizing medium for the first char combustor 4(i) is air
and / or oxygen. By having heat transfer coils immersed in the bed of the second
char combustor 4(2) and controlling the ash/char feed and air/oxygen to the
bed, the temperature of the bed is maintained within a desired range.

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We Claim
1. A fluidized bed char combustion device adaptable to a fluidized bed
gasification system, the system comprising a gasifier (1), atleast one
paniculate collection means (2) retaining the ash and char particles
separated from the gas, and a bulk solid recirculator provided optionally
for recycling the solids into the gasifier (1), the device comprising:
- a separation means (3) for diverting the solid from the collection
means (2) to the gasifer (1) via a parallel stream (PS);
- - a first fluidized bed char cornbustor (4(1)) for inputting one of air
and air-oxygen mixture in the first combustor (4(1)), the first
combustor (4(1)) simultaneously controlling the temperature of the
input including the temperature of the fluidized bed independently
and/or combinedly thereby achieving combustion of the char
material present in the solids input, the generated Rue gas
including left-out char being admitted to the gasifier (1), the
resultant coarse ash including further left out char particles being
extracted from the bottom of the gasifier (1);
- - a second fluldized bed char combustor (4(2)) having atleast one
heat transfer coil, and receiving the coarse ash including further
left-out char particles from the gasifier (1) for combustion therein,
the flue gas generated being passed to a heat recovery means
(5(2),6), the coarse ash being disposed in two stages firstly via the
bottom of the combustor 4(2)) and secondly via the heat recovery
means (6).

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2. The device as claimed in claim 1, wherein the char combustors (4(1),
4(2)), the heat recovery means (5(2), 6), and the separation means (3)
are outwardly insulated to prevent heat loss.
3. The device as claimed in claim 1, comprising a single stream (SS) for
recirculating the entire solids via the first fluidized bed char combustor
(4(1)) instead of paralley diverting a portion via the bulk-solid recirculator.
4. A fluidized bed char combustion device adaptable to a fluidized bed
gasification system as herein substantially described and illustrated with
reference to the accompanying drawing.

Accordingly there is provided a fluidized bed char combustion device adaptable
to a fluidized bed gasification system, the system comprising a gasifier, atleast
one participate collection means retaining the ash and char particles separated
from the gas, and a bulk solid recirculator provided optionally for recycling the
solids into the gasifier, the device comprises a diversion means for diverting the
solid from the collection means to the gasifier via a parallel stream; a first
fluidized bed char combustor for inputting one of air and air-oxygen mixture n
the combustor, the first fluidized bed char combustor simultaneously controlling
the temperature of the input including the temperature of the fluidized bed
independently and/or combinedly thereby achieving combustion of the char
material present in the solids input; the generated flue gas including left-out char
being admitted to the gasifier, the resultant coarse ash including further left out
char particles being extracted from the bottom of the gasifier; a second fluidized
bed char combustor having atleast one heat transfer coil, and receiving the
coarse ash including further left-out char particles from the gasifier for
combustion therein, the flue gas generated being passed to a heat recovery
means, the coarse ash being disposed in two stages firstly via the bottom of the
combustor and secondly via the heat recovery means.