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FIELD OF THE INVENTION
This invention relates to fluidized bed gasifiers, in particular pressurized Fluidized
bed gasifiers, and more particularly to a shutting down device adaptable to
pressurized fluidized beet gasifiers.
BACKGROUND OF THE INVENTION
Flujdized Bed Gasifiers are adopted to generate Syngas from coal for use in power,
process and chemical applications, in a fluidized bed gasifier, the bed of inert
material with coal is fiuidized by air and steam mixture is admitted from the bottom
of the bed through an air distributor During normal operation, a temperature of 900
to 1100 C is maintained in the fiuidized Bed by partial combustion of coal. In
steady operating conditions, tne coal and the un burnt char constitute about 5 -
25% of the inventory in the fluidized bed The balance is inert material like coal ash
In an emergency condition leading to instant shut-down of the gasifier, an inventory
of coal and unburot char particles at high temperature in the bed poses a safety
problem.
Presently steam is used to inhibit any combustion that may continue rising the bed
temperature even after the shut down However, such a system needs to ensure
availability of steam for this purpose, irrespective of the conditions prevailing
Besides, the steam condenses leading to heavy fouling of the down stream devices
like Heat Exchanger and Gas Pipes and makes the ash sticky and difficult to remove
and handle It further affects the surfaces of refractory lining provided on inside of
the gasifier.

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OBJECTS OF THE INVENTION
It is therefore, an object of the invention is to propose a shutting down device which
ensures a safe shut down of pressurized ftuidized bed gasifiers maintaining higher
carbon inventory.
Another object of the invention is to propose a shutting down device which rs
capable of creating an atmosphere of inert nitrogen inside the refractory lined
gasifier throughout the shut down period for protecting the refractory lining thus
ensuring better and longer life of the refractory,
A further object of the invention is to propose a shutting down device which as
capable of cooling the bed slowly and steadily with nitrogen.
A shal further object of the invention is to propose a shutting down device which
substantially eliminates fouling of down stream equipment of the pressurized
fluidized bed gasifier system
Yet another object of the invention is to propose a shutting down device which
ensures easy removal of bed ash by disallowing the bed ash to become sticky.
SUMMARY OF THE INVENTION
Accordingly, there is provided a shutting clown device adaptable to pressunzed
fluidized bed gasifier, the gasifrer operating at a bed temperature between 900°
to 1000°C; and being in a state of shutting down by cutting-off supply of feed

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coal followed by stoppage of the flow of arr and steam, the device compnang; a
liquid nitrogen storage vessel accommodating pressuned liquid nitrogen, a
plurality of vapounzer coils connected to the storage vessel via prping circuit
including control valves, the vaporizer cols converting the liquid nitrogen in
gaseous form by vaporization; a plurality of nitrogen gas holders receiving
nitrogen gas from the vaponzer coils and holding the nitrogen gas at ambient
temperature by maintaining a reduced pressure, and an auto pressure regulating
valve connected to the nitrogen gas holders which is set to adjust the pressure
of nitrogen ges higher than that maintained in the gasifier, the pressurized
nitrogen gas at ambient temperature being admitted to the gasifier via a piping
circuit provided with a non-return valve
The device according to the invention consists of a storage for liquid nitrogen,
vaporizer coils, gas holders for nitrogen gas, e pressure reglisting valve and
piping with a non return valve which is capable of admitting controlled quantity
of pressurized nitrogen gas at ambient temperature in a safe manner into the
bed of the pressurized fluidized bed gasffier to bring down the temperature of
the bed as and when needed
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure-1 - Shows a shutting down device adaptable to pressurized fluidized bed
gasifters

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DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
The device for Shutting Down of a Fluidized Bed Gasifier (07) comprises, a Liquid
Nitrogen Storage Vessel (01), Vaporizer coils (02) to convert liquid nitrogen into
gaseous form; Nitrogen Gas Holders (03) to hold nitrogen gas at pressures in the
range of 5 to 12 Kg/cm" and at ambient temperature; an Auto Pressure Regulating
Valve (04) to control the pressure of nitrogen gas at the required level before
admitting into the Fluidized Bed Gasifier, (07), and interconnecting piping circuit
(05), and a non return valve (06)
Dunrig any planned or emergency shut dwon of a gasifier operating with supply
of a mixture of arr and steam through the distributor and having coal above
the distributor, at a steady state with the bed temperature of the order of 900 to
1100 0 C the flow of feed coal is cut off first, followed by stoppage of air and
steam and simultaneously nitrogen gas is admitted to reduce the bed
temperature to a safe value depending on the nature of fuel being used for
gasification Prior to the admission of nitrogen, the pressure of nitrogen gas is
adjusted by setting the pressure regulating valve (04), to a pressure greater
then that of the gasifier (07) and the pressure of nitrogen in the gas holders (03)
is also correspondingly maintained by vaporization of liquid nitrogen from the
storage vessel (01) through the vaporizer coils (02).
Once bed temperature is reduced to the required level, the nitrogen gas flow is
cut off and air is again admitted for further cooling of the bed when the bed

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temperature reaches much below the ignition range of the fuel, the air supply JS
also cut off, Now the gasjfier is safely shut down although having high carbon
inventory in the bed. The use of nitrogen is also economized in this method and
only the required quantity of nitrogen is consumed
The device is capable of cooling the bed uniformly further the device reduces
the formation of carbon monoxide and hydrogen during the shut down of the
gasifier including reducing the carbon monoxide entrapment in the sub systems of
the pressurized bed system The device is also capable of reducing or eliminating
fouling of heat transfer surfaces and other areas. The device reduces or
eliminates steam condensation and the consequential effects like corrosion,
non sticky bottom ash handling.

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WE CLAIM
1. A shutting down device adaptable to pressurized fluldrzed bed gasifier, the
gasifior operating at a bed temperature between 9000 to 11000C, and
being in a state of shutting down by cutthng-off supply of feed coal
followed by stoppage of the flow of air and steam, the device comprising
- a liquid nitrogen storage vessel (01) accommodating pressured
liquid nitrogen;
- a plurality of vapounzed coils (02) connected to the storage
vessef (01) via piping circuit including control valves, the
vaporiser coils (02) converting the liquid nitrogen in gaseons form
by vaporization,
- a plurality of nitrogen gas holders (03) receiving nitrogen gas
from the vaporizer coils (02) and holding the nitrogen gas at
ambient temperature by maintaining a reduced pressure, and
- an auto pressure regulating valve (04) connected to the nitrogen
gas holders (03) which is set to adjust the pressure of nitrogen
gas higher than that maintained in that gasifier (07), the
pressurized nitrogen gas at ambient temperature being admitted
to the gasifier (07) via a piping circuit (05) provided with a non-
return valve (06).

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2. A shutting down device adaptable to pressurized fluidized beet gasifier, as
substantially described herein with reference to the accompanying
drawings.
Dated this 16th day of FEBRUARY 2006