FIELD OF THE INVENTION
This invention relates to Pressurized Fluidized Bed Gasifiers, for generating
synthetic gas. More particularly, the invention relates to Pressurized Fluidized Bed
Gasifiers with shut down system operating without Inert Gas.
BACKGROUND OF THE INVENTION
Pressurized Fluidized Bed Gasifiers are adopted to generate Syngas from coal, lignite
or other carbonaceous solid fuels, for power, process and chemical applications. In a
refractory lined pressurized fluidized bed gasifier, during gasification process, the
crushed coal is continuously injected into the gasifier bed. Air or a mixture of air and
steam is introduced through a distributor located at the bottom of the gasifier, from
which a stream of high-pressure and high-temperature raw synthesis gas is
generated. During normal operation, the bed temperature is maintained at 900 to
1100 °C by partial combustion of coal. In steady operating conditions, the coal and
unburnt char constitute about 5 - 25% of the inventory in the fluidized bed. The
balance is inert material like coal ash. In an emergency condition or under a planned
shutdown leading to instant stoppage of the gasifier, the gasifier contains slow-
burning inventory. It is necessary to empty and degas or depressurize of the gasifier
in a controlled manner. Inventory of coal and unburnt char particles at high
temperature in the bed poses a safety problem.
Accordingly during the shutdown a controlled quantity of Nitrogen is supplied to
cool the inventory in a phased manner.
Figure 01 shows a pressurized fluidized bed gasifier with prior art safety system for
shutting down the gasifier.
In a typical pressurized fluidized bed gasifier (01), air or a mixture of air and steam
is passed through a distributor, which is provided with a plurality of bubble cap
nozzles arrangement to fluidize the bed. During gasification process, by the partial
combustion of carbonaceous materials such as crushed coal, petroleum or biomass
is converted into carbon monoxide (CO) and hydrogen (H2) by reacting the raw
material at high temperatures with a controlled amount of steam, oxygen and/or
air, the resulting gas mixture is called synthesis gas or 'syngas' and it is a fuel.
The prior art gasifier with safety system for Shutting Down of Pressurized Fluidized
Bed gasifiers comprises; a gasifier (01) to produce syngas from carbonaceous
materials, an air flow pipe line (02) provided with pressure and temperature
gauges to admit the process air to the gasifier (01), an auto air flow control valve
(03) coupled an orifice (05) to admit pre-determined quantity of air to the gasifier
(01), a bypass air pipe line (09) fitted with a manual valve (04) to supply air to
gasifier (01) during maintenance of auto air flow control valve (03), a plurality of
manual valves (04) provided on the pipe lines (02,09) to admit or stop flow of the
air to the gasifier (01), a drain pipe line (10) to drain the condensates in the pipe
line (02), a plurality of ON/OFF control valves (06) provided on the pipe lines
(02,10) to admit or stop the flow media in both the pipe lines (02&10), a non
return valve (07) provided on the pipe line (02) to admit air only to the gasifier
(01), a mixing vessel (08) to mix the air and steam during gasification process, a
nitrogen flow pipe line (11) fitted with pressure and temperature gauges to admit
nitrogen to gasifier (01) during shutdown period, an auto pressure regulating valve
(13) to control the pressure of nitrogen gas in the pipe line (11), a plurality of
manual valves (04) and an ON/OFF control valve (06) fitted in the pipe line (11)
to admit or stop flow of the nitrogen gas to the gasifier (01), a non-return valve
(07) provided in the pipe line (11) to admit nitrogen gas to the gasifier (01), a
bypass line (12) fitted with a manual valve (04) to admit nitrogen to the gasifier
(01) during maintenance of said auto pressure regulating valve (13) and an orifice
(14) with a transmitter fitted in the pipe line (11) to measure the nitrogen flow, is
capable of shutting down the gasifier during emergency or planned shutdown.
Indian patent no. IN 233778, Dt. 10 April 2009, entitled " A shutting down device
for fluidized bed gasifiers" discloses, during any planned or emergency shut down
of gasifier operating with supply of a mixture of air and steam through the
distributor and coal above the distributor, at a steady state with the bed
temperature of the order of 900 to 1100 ° C, the flow of feed coal is cut off first,
followed by stoppage of air and steam flow 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. Once the 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 temperature approaches much below the ignition
range of the fuel, the air supply is also cut off.
OBJECTS OF THE INVENTION
It is therefore, an object of this invention to propose a Pressurized Fluidized Bed
Gasifier with shut down system operating without Inert Gas, which eliminates the
disadvantages of prior art.
Another object of invention is to propose a Pressurized Fluidized Bed Gasifier with
shut down system operating without Inert Gas, which is enabled to maintain the
bed temperature within a permissible limit by allowing burning the residual
inventory and combustible gases in a controlled manner
A further object of invention is to propose a Pressurized Fluidized Bed Gasifier
with shut down system operating without Inert Gas, which is capable of slow,
steady and safe cooling of the bed with by maintaining a proportionate ratio of air
and steam.
A still further object of the invention is to propose a Pressurized Fluidized Bed
Gasifier with shut down system operating without Inert Gas which allows an easy
removal of the unsticky bed ash after the shut down.
SUMMARY OF THE INVENTION
Accordingly, there is provided a Pressurized Fluidized Bed Gasifiers with shut down
system operating without Inert Gas; a refractory lined gasifier (01) (refer Fig.02)
means for producing syngas from carbonaceous materials at desired composition
and calorific value; an air flow pipe line (02) provided with pressure and
temperature gauges to admit the process air to the gasifier (01); an auto air flow
control valve (03) coupled to an orifice (05) to admit a pre-determined quantity of
air to the gasifier (01); a bypass air pipe line (09) fitted with a manual valve
(04) to supply air to the gasifier (01) during maintenance of auto air flow
control valve (03); a plurality of manual valves (04) mean provided on the pipe
lines (02,09) to admit or stop flow of the air to the gasifier (01); a drain pipe line
(10) to drain the condensates in the pipe line (02); a plurality of ON/OFF control
valves (06) provided on the pipe lines (02,10) to admit or stop the air flow in both
the pipe lines; a non return valve (07) provided on the pipe line (02&16) to admit
air or steam only to the gasifier (01); a mixing vessel (08) to mix and admit the air
and steam during gasification and shutting down process; an auxiliary boiler
(15) provided to generate saturated steam to be used in gasification and shutdown
processes; a steam flow pipe line (16) fitted with pressure and temperature
gauges to admit steam to the gasifier (01); an orifice (17) coupled with an auto
steam flow regulating valve (18) to admit pre-determined quantity of steam to the
gasifier (01); a plurality of manual valves (04) and an ON/OFF control valve (06)
fitted on the steam pipe line (16) to admit or stop the steam flow to the gasifier
(01); )a non-return valve (07) provided on the pipe line (16) to admit steam only
to the gasifier (01); a bypass line (19) fitted with a manual valve (04) to admit
steam to the gasifier (01) during maintenance of the auto steam flow regulating
valve (18); and a drain pipe line (20) fitted with a steam trap (21) to drain the
condensates during operation.
According to the present invention the inventory in the gasifier is allowed to be
completely burnt in the presence of a predetermined proportion of air and steam
and then the bed is cooled in absence of inert gas for example nitrogen.
DETAILS DESCRIPTION OF THE INVENTION
As shown in figure 2, the pressurized Fluidized Bed Gasifier of the invention
comprising; a gasifier (01) to produce syngas from carbonaceous materials, an air
flow pipe line (02) provided with pressure and temperature gauges to admit the
process air to the gasifier (01) during the stages of combustion, gasification and
shutting down, an auto air flow control valve (03) coupled with an orifice (05) to
admit pre-determined quantity of air to the gasifier (01), a bypass air pipe line (09)
fitted with a manual valve (04) to supply air to the gasifier (01) during
maintenance of the auto air flow control valve (03), a plurality of manual valves
(04) provided on the pipe lines (02,09) to admit or stop the flow of air to the
gasifier (01), a drain pipe line (10) to drain the condensates in the pipe line (02), a
plurality of ON/OFF control valves (06) provided in the pipe lines (02,10) to admit
or stop the air flow in both the pipe lines (02&10), a non return valve (07)
provided on the pipe line (02) only to admit air to the gasifier (01), a mixing
vessel (08) to mix the air and steam and admit to the gasifier (01) during
gasification and shutting down process, an auxiliary boiler (15) provided with all
accessories to generate saturated steam, a steam flow pipe line (16) fitted with
pressure and temperature gauges to admit steam to the gasifier (01) during
gasification and shutdown period, an orifice (17) coupled to an auto steam flow
regulating valve (18) to admit a pre-determined quantity of steam to the gasifier
(01), a plurality of manual valves (04) and an ON/OFF control valve (06) fitted
on the steam pipe line (16) to admit or stop the steam flow to the gasifier (01), a
non-return valve (07) provided on the pipe line (16) only to admit steam to the
gasifier (01) and a bypass line (19) fitted with a manual valve (04) to admit steam
to gasifier (01) during maintenance of the auto steam flow regulating valve (18), a
drain pipe line (20) fitted with a steam trap (21) to drain the condensates during
operation.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.l - shows the schematic flow diagram of a shutting down system in a
pressurized fluidized bed gasifier according to the prior art.
Fig.2 - shows a schematic flow diagram of the shutting down system in a
pressurized fludized bed gasifier according to the present invention.
In a refractory lined pressurized fluidized bed gasifier (01) air or a mixture of air
and steam is introduced through a distributor located at the bottom of the gasifier.
The carbonaceous materials such as crushed coal, petroleum or biomass is
continuously injected to the gasifier through ejectors using compressed air as
transporting medium, by the partial combustion and chemical reaction of
carbonaceous materials with air and steam, syngas also called 'fuel gas' is
produced. At steady state gasification process the bed temperature in the order of
900 to 1100 °C is maintained.
During any scheduled or emergency shutdown of the gasifier (01), the fuel
feeding is cut off first, followed by air and steam flow is adjusted by the valves
(03&.18) respectively to burn the inventory available inside the gasifier (01) and
the bed temperature is maintained within the limits, when the bed temperature
starts falling (that means all the inventory burnt out) the steam flow is increased to
cool or to reduce the bed temperature, steam flow is cut off when the bed
temperature reaches a safe value of 400 to 500 °C and the air flow is continued for
further cooling the bed. When the bed temperature reaches a value of 100 tol50
°C. the air flow is cut off. Now the gasifier is taken a safe shut down with the
help of air and steam in the absence of inert gas.
WE CLAIM
1. A Pressurized Fluidized Bed Gasifier with shut down system operating
without Inert Gas;
a) a refractory lined gasifier (01) means for producing syngas from
carbonaceous materials at desired composition and calorific value;
b) an air flow pipe line (02) provided with pressure and temperature gauges to
admit the process air to the gasifier (01);
c) an auto air flow control valve (03) coupled to an orifice (05) to admit a pre-
determined quantity of air to the gasifier (01);
d) a bypass air pipe line (09) fitted with a manual valve (04) to supply air
to the gasifier (01) during maintenance of auto air flow control valve (03);
e) a plurality of manual valves (04) mean provided on the pipe lines (02,09)
to admit or stop flow of the air to the gasifier (01);
f) a drain pipe line (10) to drain the condensates in the pipe line (02);
g) a plurality of ON/OFF control valves (06) provided on the pipe lines (02,10)
to admit or stop the air flow in both the pipe lines;
h) a non return valve (07) provided on the pipe line (02&16) to admit air or
steam only to the gasifier (01);
i) a mixing vessel (08) to mix and admit the air and steam during
gasification and shutting down process;
j) an auxiliary boiler (15) provided to generate saturated steam to be used in
gasification and shutdown processes;
k) a steam flow pipe line (16) fitted with pressure and temperature gauges to
admit steam to the gasifier (01);
I) an orifice (17) coupled with an auto steam flow regulating valve (18) to
admit pre-determined quantity of steam to the gasifier (01);
m) a plurality of manual valves (04) and an ON/OFF control valve (06) fitted
on the steam pipe line (16) to admit or stop the steam Flow to the gasifier
(01);
n) a non-return valve (07) provided on the pipe line (16) to admit steam only
to the gasifier (01);
o) a bypass line (19) fitted with a manual valve (04) to admit steam to the
gasifier (01) during maintenance of the auto steam flow regulating valve
(18); and
p) a drain pipe line (20) fitted with a steam trap (21) to drain the
condensates during operation.
2. The gasifier as claimed in claim 1, wherein the gasifier is enabled to reduce
formation of carbon monoxide and hydrogen during the shut down of the
gasifier minimize the carbon Monoxide entrapment in the sub systems, and
cool the bed uniformly.
3. A Pressurized Fluidized Bed Gasifier with shut down system operating
without Inert Gas as substantially described and illustrated herein with
reference to the accompanying drawings.

A Pressurized Fluidized Bed Gasifier with shut down system operating without Inert
Gas; a refractory lined gasifier (01) means for producing syngas from
carbonaceous materials at desired composition and calorific value; an air flow pipe
line (02) provided with pressure and temperature gauges to admit the process air
to the gasifier (01); an auto air flow control valve (03) coupled to an orifice (05)
to admit a pre-determined quantity of air to the gasifier (01); a bypass air pipe line
(09) fitted with a manual valve (04) to supply air to the gasifier (01) during
maintenance of auto air flow control valve (03); a plurality of manual valves (04)
mean provided on the pipe lines (02,09) to admit or stop flow of the air to the
gasifier (01); a drain pipe line (10) to drain the condensates in the pipe line (02);
a plurality of ON/OFF control valves (06) provided on the pipe lines (02,10) to
admit or stop the air flow in both the pipe lines; a non return valve (07) provided
on the pipe line (02&.16) to admit air or steam only to the gasifier (01); a mixing
vessel (08) to mix and admit the air and steam during gasification and shutting
down process; an auxiliary boiler (15) provided to generate saturated steam to be
used in gasification and shutdown processes; a steam flow pipe line (16) fitted
with pressure and temperature gauges to admit steam to the gasifier (01); an
orifice (17) coupled with an auto steam flow regulating valve (18) to admit predetermined
quantity of steam to the gasifier (01); a plurality of manual valves
(04) and an ON/OFF control valve (06) fitted on the steam pipe line (16) to admit
or stop the steam Flow to the gasifier (01); a non-return valve (07) provided on
the pipe line (16) to admit steam only to the gasifier (01); a bypass line (19) fitted
with a manual valve (04) to admit steam to the gasifier (01) during maintenance of
the auto steam flow regulating valve (18); and a drain pipe line (20) fitted with a
steam trap (21) to drain the condensates during operation.