HELD OF INVENTION
This invention relates to the field of integrated gasification based power
generation & or for other uses; particularly pressurized fluidized bed gasification
based systems used for any grade of coals / bio mass. More particularly, the
present invention relates to a process for coal admission in gasification systems
through high temperature bulk-solids recirculator.
BACKGROUND OF THE INVENTION
Combined Cycle is increasingly being used to generate electricity through
integrated gasification. Such combined cycles are capable of using various low
calorific value and high ash content coals.
In a fluidized bed gasifier the air or mixture of air and steam is admitted
through a distributor located at bottom of the gasifier. Coal is continuously
injected to the gasifier. Coal gas is produced due to the chemical reaction of coal
with air and steam. The fly ash and unburnt carbon particles in fuel gas are
separated by a plurality of cyclones disposed in series. The coal gas at the exit of
the cyclone is cooled in a Heat Recovery Boiler (HRB). The gas is further cooled
in a gas cooler while superheating the saturated steam of HRB. Part of the
superheated steam is utilized for gasification process and the rest expands in a
steam turbine to generate electricity. The gas is further processed in a gas
cleaning system and admitted to the gas turbine combustion chamber to
generate electricity.
The collected ash having sizable amount of char/unburnt carbon is
recycled back to the gasifier through a non-mechanical High temperature bulk
solid recirculator to utilize the unburnt carbon in the fly ash.
%■

Typically, in pressurized fluidized bed gasifiers, during gasification process
air and steam are mixed prior to admission to the gasifier and admitted through
a distributor located at a bottom of the gasifier. Presently, adequate quantity of
crushed coal at ambient temperature is continuously fed to the gasifier through
an ejector using compressed air. The cold transport air supplied into the fluidized
bed disturbs the uniformity of the fluidized bed (temperature / fluidization) and
do not take active part in gasification in the fluidizing the bed. In the present
method coal is fed into the active fluidized bed by pneumatic transportation
where both the phases take place.
Accordingly it is an object of the present invention to provide a process for
coal admission in gasification system through a high temperature bulk-solid
recirculator which eliminates the disadvantage of prior art.
Another object of the present invention is to provide a process for coal
admission in gasification system through a high temperature bulk-solid
recirculator which eliminates the non-uniformity in the temperature, fluidisation
and gasification.
A further object of the present invention is to provide a process for coal
admission in gasification system through a high temperature bulk-solid
recirculator which eliminates the need for inputting air at a relatively higher
pressure and thus effects a saving.
A still further object of the present invention is to provide a process for
coal admission in gasification system through a high temperature bulk-solid
recirculator which increases the carbon conversion efficiency of the system
thereby increasing the overall efficiency of the plant.
Yet another object of the present invention is to provide a process for coal
admission in gasification system through a high temperature bulk-solid
recirculator which achieves quick conversion of coal gas by feeding preheated
crushed coal.

SUMMARY OF THE INVENTION
Accordingly, the invention eliminates the disadvantages of prior art by feeding
the coal through a seal pot. The bed is uniformly fluidized with sufficient
fluidization velocity with the help of bubble cap air nozzles. By the chemical
reaction, coal gas also called 'fuel gas' is produced with specific chemical
composition. The distributor helps to fluidize the bed and to mix the coal rapidly
and thoroughly. The bed ash is removed by ash extraction system. The fly ash
collection in cyclone having considerable amount of char/unburnt carbon is
recycled back to the gasifier through the non-mechanical type high temperature
bulk solid recirculator to utilize the unburnt carbon in the fly ash.
Accordingly, there is provided a process for coal admission in a gasification
system through a high-temperature bulk-solids recirculator, the recirculator
comprising a bubble cap distributor receiving clean coal gas/inert gas via a
plurality of gas inlet pipes , and a dual gas chamber , the coal gas /inert gas
being supplied at a pressure higher than the system pressure causing two
different fluidization velocities in two vertical limbs for fluidizing the bulk-solids,
ash particles being collected from the cyclone flow through a first inclined pipe ,
the fluidization velocities including disposition angle of the first inclined pipe

further causing the ash particles to overflow from the limb into the gasifier via a
second inclined pipe ;a coal admission pipe for feeding crushed coal from a
receiver in a preheated condition by means of a mechanical device; a plurality of
cooling water jacket pipes for cooling the hot pipes including two water inlet
pipes and an water outlet pipe ; and a plurality of nozzles arranged in the
middle of the bubble cap distributor so as to maintain the height of the
recirculator in a range from 0.8 d to 1.2 d, the process comprising the steps of:
feeding crushed coal from the receiver directly to a feeder for transferring the
fed coal via the coal admission pipe to the recirculator, the step of coal admission
through the high temperature bulk solid recirculator in fluidizing condition
causing the recirculator to act as a seal pot, allowing the coal heated in the seal
pot to overflow via the second inclined pipe which enables devolatization leaving
only char to reach the fluidized bed as solid material, thereby allowing one way
material transfer to the gasifier which achieves uniformity in the temperature,
fluidization and gasification.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Fig. 1 - shows a high-temperature bulk-solids recirculator adaptable to
carry-out the process of the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
Fig. 1 shows a high temperature bulk solid recirculator which consists of a
coal feeding pipe 01. When controlled quantity of clean coal gas/inert gas is
admitted to a bubble cap distributor 02 through a plurality of gas inlet pipes 03
and a dual gas chamber 04, at slightly more than the system pressure, the
pressurized gas cause fluidizing velocities in both left and right vertical limbs 05
& 06 of the recirculator. The limbs (5,6) having diameter 'd' ranging from 100mm
to 500mm and the bulk solids in both the limbs (05,06) start fluidizing and
raising up. The ash particles collected in atleast one cyclone of the system flow
through a pipe 07, having an angle a ranging from 40° to 120° which causes the
particles in the other limb (05) to over-flow into the gasifier through an inclined
pipe 08, having an angle θ ranging from 40° to 80°.
The process for coal admission in the gasification system includes feeding
of crushed coal from the receiver of the system into the pipe 01 by a suitable
mechanical device like rotary/screw feeder by gravity. The coal admission pipe
01 enables the fuel to enter into the gasifier in a pre-heated manner as it moves
along with the hot bulk solids (fly ash).
The entire system is enclosed by a plurality of cooling water jacket pipes
09,10,11 and 12 for cooling the hot pipes. The height between the plurality of
bubble cap nozzles 02 arranged in the middle of the distributor and entrance of
the delivery pipe 05 ranges from 0.8d to 1.2d. This process continues for the
entire operation and the unburnts in the fly ash are recycled back to the gasifier.
The cooling water enters through an inlet pipe 13 and hot water exit from an
outlet pipe 14.

The coal feeding arrangement through the high temperature bulk solid
recirculator in a fluidizing condition acts as a seal, allowing transfer of the
materials to the gasifier.
This invention has additional features in the fluidizing distributor nozzle
design, water cooling arrangement and the application for higher pressure.
Gasification takes part in two phases - viz, devolatilization in which the volatiles
are released and char is left out and this char takes part in
combustion/gasification. In the present method coal is fed into the active
fluidizing bed by pneumatic transportation where both the phases take place.
The cold air required for transporting the coal does not take active part in
fludizing the bed and further disturb the uniformity of the fluidized bed
(temperature / fluidization). According to the invention, this is avoided by
feeding the coal through the seal pot.
The sized coal from the receiver is fed directly to a feeder, which transfers
the coal to the coal feeding pipe 01. Due to such arrangement, no separate
transport device for the fuel is necessary. At the same time, the coal gets heated
up in the seal pot and over-flow the inclined pipe 08, which releases the volatile
gases and only the char is allowed to reach the bed as solid. The process avoids
non uniformity in temperature. The coal is fed just above the distributor and air
distribution is resorted to only through distributor. Uniform fluidization by
adjusting distributor air facilitates the new process.

WE CLAIM:
1. A process for coal admission in a gasification system through a high-
temperature bulk-solids recirculator, the recirculator comprising:
a bubble cap distributor (02) receiving clean coal gas/inert gas via a
plurality of gas inlet pipes (03), and a dual gas chamber (04), the coal gas
/inert gas being supplied at a pressure higher than the system pressure
causing two different fluidization velocities in two vertical limbs (05,06) for
fluidizing the bulk-solids, ash particles being collected from the cyclone
flow through a first inclined pipe (07), the fluidization velocities including
disposition angle of the first inclined pipe (07) further causing the ash
particles to overflow from the limb (05) into the gasifier via a second
inclined pipe (08);
a coal admission pipe (01) for feeding crushed coal from a receiver in
a preheated condition by means of a mechanical device;
a plurality of cooling water jacket pipes (09-12) for cooling the hot
pipes (05,06,07 & 08) including two water inlet pipes (13) and one water
outlet pipe (14); and

a plurality of nozzles arranged in the middle of the bubble cap
distributor (02) so as to maintain the height of the recirculator in a range
from 0.8 d to 1.2 d, the process comprising the steps of: feeding crushed
coal from the receiver directly to a feeder for transferring the fed coal via
the coal admission pipe to the recirculator, the step of coal admission
through the high temperature bulk solid recirculator in fluidizing condition
causing the recirculator to act as a seal pot, allowing the coal heated in
the seal pot to overflow via the second inclined pipe which enables
devolatization leaving only char to reach the fluidized bed as solid
material, thereby allowing one way material transfer to the gasifier which
achieves uniformity in the temperature, fluidization and gasification.
2. A process for coal admission in a gasification system through a high
temperature bulk-solids recirculator as substantially herein described and
illustrated with reference to the accompanying drawing.

The invention relates to a process for coal admission in a gasification system
through a high-temperature bulk-solids recirculator, the recirculator
comprising a bubble cap distributor (02) receiving clean coal gas/inert gas via
a plurality of gas inlet pipes (03), and a dual gas chamber (04), the coal gas
/inert gas being supplied at a pressure higher than the system pressure
causing two different fluidization velocities in two vertical limbs (05,06) for
fluidizing the bulk-solids, ash particles being collected from the cyclone flow
through a first inclined pipe (07), the fluidization velocities including
disposition angle of the first inclined pipe (07) further causing the ash
particles to overflow from the limb (05) into the gasifier via a second inclined
pipe (08); a coal admission pipe (01) for feeding crushed coal from a receiver
in a preheated condition by means of a mechanical device; a plurality of
cooling water jacket pipes (09-12) for cooling the hot pipes (05,06,07 & 08)
including two water inlet pipes (13) and one water outlet pipe (14); and a
plurality of nozzles arranged in the middle of the bubble cap distributor (02)
so as to maintain the height of the recirculator in a range from 0.8 d to 1.2 d,
the process comprising the steps of: feeding crushed coal from the receiver
directly to a feeder for transferring the fed coal via the coal admission pipe to
the recirculator, the step of coal admission through the high temperature bulk
solid recirculator in fluidizing condition causing the recirculator to act as a
seal pot, allowing the coal heated in the seal pot to overflow via the second
inclined pipe which enables devolatization leaving only char to reach the
fluidized bed as solid material, thereby allowing one way material transfer to
the gasifier which achieves uniformity in the temperature, fluidization and
gasification.