FIELD OF THE INVENTION
This invention relates to integrated gasification Combined Cycle based power
generation; in particular pressurized fluidized bed gasification based systems capable of
using any grade of coal. More particularly, the invention relates to an Improved Syngas
cooling system with ease of maintenance in Pressurised Fluidized Bed Gasifiers.
BACKGROUND OF THE INVENTION
Pressurised Fluidized Bed gasification is increasingly being used in combine cycle plants
to generate electricity through integrated gasification and for other applications. Such
combined cycle plants are capable of using various grades of low calorific value and
high ash content coal.
In a refractory lined pressurized fluidized bed gasifier, air or a mixture of air and steam
is introduced through a distributor located at bottom of the gasifier, which is provided
with a plurality of bubble cap nozzles arrangement for fluidizing the bed. During
gasification process, coal is continuously injected to the gasifier through an ejector
using compressed air, coal gas also called 'syngas' is produced due to the chemical
reaction produced by the partial combustion of coal with air and steam. The fly ash and
unburnt carbon particles, if any, in the fuel gas are separated by serially arranged
cyclones. The hot coal gas at the exit of the cyclone is cooled in a Heat Recovery Boiler

(HRB). The gas is further cooled in a heat recovery unit to super heat the steam. Part of
the steam is utilized for gasification process and the rest expands in the steam turbine
to generate electricity. The gas is further processed in a gas cleaning system and
admitted to a combustion chamber of a gas turbine to generate electricity.
One of the known clean coal technology is the Integrated Gasification Combined Cycle
(IGCC) method of power generation. In such plants, to reduce heat loss and to improve
the efficiency, heat exchangers are added to recover heat and cool the gases. The
syngas from the gasifier leaving the cyclones at around 950°C -1050°C is cooled by the
syngas cooling system (heat recovery units) before the syngas is sent to a gas clean up
system and then to a gas turbine or for other uses. Generally an evaporator (boiler) is
arranged to face the hot gas, followed by a second heat recovery unit either to raise
the temperature of steam or to raise the feed water temperature.
The known heat recovery system includes; a double shelled gas entry chamber having a
conical shaped inner shell for hot gas flow, and a cylindrical shaped outer shell through
which the feed water enters. The hot gas absorbs heat from the inner shell and
transfers the heat to a shell & tube type heat exchanger in which gas flowing through
tubes and water / steam mixture on the shell side. A gas outlet channel for exiting the
cooled syngas is arranged and integrated as a single unit leading to complexity in
design, with insufficient access for removing, replacing or plugging of failed tubes and
welding during maintenance.

After a long period of operation, depending on the nature of ash, erosion and blockage
of the tubes occur, leading to shut down of the heat recovery system for cleaning and
plugging of tubes.
US Patent No. US20110162381A1 dated 2011-07-07, titled "SYSTEM AND METHOD FOR
COOLING SYNGAS PRODUCED FROM A GASIFIER" discloses a syngas cooler that
includes an outer wall defining a cavity. A first membrane water wall is positioned
within the cavity. A thermal siphon is positioned between the first membrane water wall
and the outer wall and is configured to channel a flow of syngas therethrough to
facilitate cooling the channeled syngas. The system comprising; three concentric,
vertically oriented membrane water walls, an outer wall that defines a cavity, a thermal
siphon positioned between the first membrane water wall and the outer wall to pass the
partially cooled syngas up between the first of the three membrane water walls and a
second of the three membrane water walls and then down between the third of the
three membrane water walls and the second of the three membrane water walls to
produce cooled output syngas.
US patent No: US2010/0031570 Al, Date: Feb. 11, 2010, Titled "METHOD AND SYSTEM
FOR AN INTEGRATED GASIFIER AND SYNGAS COOLER" teaches a method and system
for an integrated gasifier and syngas cooler. The system comprises a gasifier including

a reaction chamber, a syngas cooler integrally formed with the gasifier and having at
least one heat exchanger element, and a transition portion integrally formed with the
reaction chamber and the syngas cooler, and extending therebetween, the transition
portion further having a throat extending between the reaction chamber and the syngas
cooler, and a heat exchanger circumscribing the throat.
US Patent No. 5253703 dated Oct. 19,1993, titled 'WASTE HEAT EXCHANGER' describes
a heat exchanger particularly adapted to handle dusty hot waste gases and is of the
shell and tube type. This heat exchanger includes a vertically oriented shell through
which the waste gases flow longitudinally downward. The shell contains a tube
assembly of vertical tubes having external, longitudinally extending heat transfer fins
with the tubes being connected for fluid flow and support of their upper and lower ends
to a central vertical support/header assembly. This support /header assembly is a tube
divided into an upper header, a lower header and a center support tube section.
The ash particles may get deposited on the space between the fins; hence the ash
accumulated in the heat transfer surfaces will affect the heat transfer rate.
US Patent No: 4487611, Dated Dec. 11,1984 Titled "GAS COOLER FOR A SYNTHETIC
GAS" discloses a heat exchanger used to cool the syngas having heat transfer surfaces
in vertical position and a waterbath at the bottom portion of the heat exchanger.

OBJECTS OF THE INVENTION
An object of this invention is to propose an Improved Syngas cooling system with ease
of maintenance in Pressurised Fluidized Bed Gasifiers, which exchanges the sensible
heat of syngas that is flowing through the tubes to water / steam mixture flowing
around the tubes enclosed by a shell, to cool the syngas and generate saturated steam.
Another object of this invention is to propose an Improved Syngas cooling system with
ease of maintenance in Pressurised Fluidized Bed Gasifiers, which enables to detach the
bottom channel assembly from the shell and tube assembly for easy removing,
replacing or plugging of failed tubes and welding during maintenance, thus eliminating
the drawbacks of prior art.
A still another object of the invention is to propose an Improved Syngas cooling system
with ease of maintenance in Pressurised Fluidized Bed Gasifiers, which is reliable, easy
to operate and maintain.
A further object of the invention is to propose an Improved Syngas cooling system with
ease of maintenance in Pressurised Fluidized Bed Gasifiers, which generates saturated
steam for admission into the gasifier to generate coal gas.
SUMMARY OF THE INVENTION:
Accordingly, there is provided an Improved Syngas cooling system with ease of
maintenance in Pressurised Fluidized Bed Gasifiers, comprising; a bottom channel
assembly (gas inlet chamber) having a cylindrical shaped, horizontally positioned gas

inlet nozzle enclosed by castable refractory followed by castable insulate and an outer
pipe, a refractory lined inner shell
and an outer shell, vertically positioned and welded to top and bottom flanges, cooling
water inlet and. outlet pipe connections, and a refractory lined water jacketed ash
hopper, for hot syngas entry; a shell & tube type heat exchanger having : a plurality of
smaller diameter tubes vertically arranged' with suitable pitch and firmly welded to top
and bottom tube sheets to form as a tube bundle, through which the hot gas flows, a
cylindrical shaped shell which encloses the tube bundle having; a plurality of feed water
inlet pipe connections welded at the bottom of the shell through which feed water
enters, recovers heat from hot syngas and converts into saturated steam, a plurality of
riser and a vent riser pipe connections located and welded at the top of the shell
through which the water/steam flows to a steam drum; a gas outlet channel having: a
cylindrical shaped shell is placed vertically between a flange and the top tube sheet and
leak-proof welding is done on both top and bottom ends to form the top channel, a
nozzle-pipe is horizontally positioned and it's one end is welded to the shell and the
other end is welded to a flange, for exiting the cooled syngas for further processing, a
flat end cover is placed over the flange and tightened for easy maintenance, is capable
of cooling the syngas coming out of a pressurized fluidized bed gasifier to a
specified/required temperature and generating saturated steam, also which provides

necessary access for easy removing, replacing or plugging of failed tubes and welding
during maintenance, thus preventing the drawbacks of the current art.
The Improved Syngas cooling system with ease of maintenance in Pressurised Fluidized
Bed Gasifiers, comprising; a gas inlet chamber for hot syngas entry, a plurality of
smaller diameter tubes attached to top and bottom tube sheets to form as single
bundle, enclosed by a pressure vessel which is having feed water inlet and steam/water
outlet ports, a gas outlet channel, and a number of riser tubes capable of cooling the
syngas coming out of a pressurized fluidized bed gasifier and can generate saturated
steam.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig.I - Shows sectional elevation and plan views of an Improved Syngas cooling system
with ease of maintenance in Pressurised Fluidized Bed Gasifiers, according to the
present invention.
Fig.2 - Shows a cross-sectional elevation of the gas inlet chamber, according to the
present invention.
Fig.3 - Shows sectional elevation and plan views of the shell and tube heat exchanger,
according to the present invention.
Fig.4 - Shows a cross-sectional elevation view the gas outlet channel, according to the
present invention.

Fig.5 - Shows a plan view, illustrates the gas and feed water inlet nozzles orientations,
according to the present invention.
Fig.6 - Shows another plan view, illustrating the gas and water/steam outlet nozzles
orientations, according to the present invention.
Figs. 7, 8, 9, 10, 11 and 12 - show the various details of the Improved Syngas cooling
system with ease of maintenance in Pressurised Fluidized Bed Gasifiers, according to
the present invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION:
Figures 1,2,3 and 4 show the assembled sectional elevation and sectional plan views of
an Improved Syngas cooling system with ease of maintenance in Pressurised Fluidized
Bed Gasifiers, comprising; a bottom channel assembly (01) as shown in Fig.2 for hot
gas entry having; a larger diameter cylindrical shaped first outer shell (04) welded to
first outer hubs (06) of a plurality of specially designed first flanges (05) as shown in
Fig.10 (Detail-D) acts as cooling water jacket, a smaller diameter cylindrical shaped first
inner shell (08) welded to first inner hubs (07) of the plurality of specially designed first
flanges (05), a gas inlet nozzle (09) properly placed and welded to both first outer shell
(04) and first inner shell (08), through which the hot gas enters, an outer pipe (10), its
one end welded to the first outer shell (04) and the other end welded to a second
flange (11) acts as an enclosure, a plurality of first retainer plate

assembly (12) placed and welded with suitable pitch at the inner surface of the outer
pipe (10) for holding a first castable refractory (13) followed by a castable insulate (14)
intact, the second flange (11) enables to connect the gas inlet pipe from gasifier last
cyclone, forms the gas inlet chamber, a plurality of second retainer plates (15) placed
and welded with suitable pitch at the inner surface of the first inner shell (08) to firmly
hold a second castable refractory lining (16) cast at the inner surface of the first inner
shell (08) with suitable thickness to withstand high temperature and to protect the first
inner shell (08) from direct contact with the hot gas, a first cooling water inlet pipe (17)
welded at the bottom of the first outer shell (04) through which adequate quantity of
cooling water with required pressure is admitted which flows around the first inner shell
(08) through the annular gap that is provided between the first inner shell (08) and the
first outer shell (04) to maintain the water side wall temperature of inner shell (08)
below the saturation temperature of water corresponding to the cooling water inlet
pressure to avoid film boiling and heat transfer deterioration also to safe guard the first
inner shell (08) from high temperature oxidation, a first cooling water outlet pipe (18)
welded at the top of the first outer shell (04) enables the hot water to let-out, a conical
shaped second outer shell (19), its top end welded to a second outer hub (22) of a
specially designed third flange (21) as shown in Fig. 11 (Detail-E) and the other end
welded to a second outer hub (25) of a specially designed fourth flange (24) as shown
in Fig.12 (Detail-F) acts as cooling water jacket, a conical shaped second inner shell

(20) having a suitable included angle is properly placed and its top end welded to a
second inner hub (23) of the flange (21) as shown in Fig. 11 (Detail- E), the other end
welded to a second inner hub (26) of the flange (24) as shown in Fig. 12 (Detail-F), a
plurality of second retainer plates (15) placed and welded with suitable pitch at the
inner surface of the conical shaped second inner shell (20) to firmly hold the second
castable refractory lining (16) cast at the inner surface of the second inner shell (20)
with suitable thickness to withstand high temperature and to protect the second inner
shell (20) from direct contact with the hot gas and high temperature oxidation, a
metallic gasket (27) properly placed in between the flanges (05) and (21) fitted tightly
with a plurality of studs, washers and nuts (28,29,30) form the ash hopper for easy ash
removal, a second cooling water inlet pipe (31) properly placed and welded at the
bottom of the conical shaped second outer shell (19) and a second cooling water outlet
pipe (32) suitably located and welded at the top of the second outer shell (19) form the
cooling water circuit, through which adequate quantity of cooling water with required
pressure is admitted, which flows around the second inner shell (20) through the
annular gap that is provided between the second outer shell (19) and second inner shell
(20) to maintain the water side wall temperature of second inner shell (20) below the
saturation temperature of water corresponding to the cooling water inlet pressure to
avoid film boiling, heat transfer deterioration and also to safe guard the conical shaped

second inner shell (20) from high temperature oxidation, form the bottom channel
assembly for hot gas entry and easy ash removal;
a shell and tube type evaporator (02) as shown in Fig.I comprising; a top tube sheet
(33) having; a plurality of first holes (34) are drilled perfectly with a specified diameter
and pitch as shown in Fig.3, a first vent hole (35) drilled at center of the top tube sheet
(33) acts as a water/steam vent, a smaller diameter second vent hole (36) drilled at the
side of top tube sheet (33) and a first adopter (37) with suitable internal taper thread is
properly placed against the second vent hole (36) and welded, a second plug (38)
having corresponding external taper thread is screwed into the first adopter (37) as
shown in Fig.3 and Fig.7 (detail-A), for venting the water/steam whenever required, a
bottom hub (39) and a top hub (40) with suitable diameter, thickness and length are
machined at both sides of the top tube sheet (33) for shell connections, a bottom tube
sheet cum flange (41) having; a plurality of second holes (42) with same diameter,
pitch and number of holes as in top tube sheet (33) are drilled as shown in section-BB
of Fig.3, a smaller diameter drain hole (43) drilled at the side of the bottom tube sheet
(41) and a second adopter (44) with suitable internal taper thread is properly placed
against the drain hole (43) and welded, a second threaded plug (45) having
corresponding external taper thread is screwed into the second adopter (44) as shown
in Fig.3 for draining the water/steam whenever required, a plurality of third retainer
plates (46) are properly placed with suitable pitch at bottom of the bottom tube sheet

(41) and welded to hold a third castable refractory (47) which is cast with suitable
thickness as shown in Fig.9 (detail-C), a top hub (48) with suitable diameter, thickness
and length is machined at top of the bottom tube sheet (41) for shell connections, a
number of bolt holes (49) are drilled with suitable diameter and pitch at the periphery
of the bottom tube sheet (41) for connecting the bottom channel assembly (01) with
Shell and tube assembly (02) with gasket, studs, nuts and washers (27,28,29,30)
respectively, a plurality of smaller diameter tubes (50) are arranged vertically and
properly inserted into the holes (34A42) of top and bottom tube sheets ((33&41)
respectively, both the ends of the tubes (50) are contact expanded and leak proof
welding is done at both tube sheets to form a tube bundle, through which the hot
syngas flows and transfers heat thermodynamically to feed water and gets cooled to a
temperature above the dew point temperature of syngas at the working pressure, a
plurality of ferrules (51) partly inserted inside and partly protruded outside at top and
bottom ends of the tubes (50) are welded to the same tubes (50) as shown in Fig.8
(detail- B), and Fig.9 (detail-C), to protect both ends of the tubes (50) from direct
contact with hot syngas and high temperature oxidation, a cylindrical shaped pressure
vessel (52) with adequate thickness is properly positioned between both the tube
sheets (33 & 41) and its bottom end is welded to the top hub (48) of the bottom tube
sheet (41) and the other end is welded to bottom hub (39) of top tube sheet (33) to
form a shell which encloses the hot gas tubes (50) and capable of withstanding the
required quantity of feed water and steam mixture with high pressure, a plurality of

boiler feed water pipes (53) are properly positioned and welded at the bottom of the
third outer shell (52) as shown in Fig.5 and connected to downcomer pipes which are
supplying adequate quantity of boiler feed water with required pressure from a steam
drum (not shown), absorbs heat from hot tubes (50) and converted into water and
steam mixture, thus the syngas is cooled to a temperature much more than the dew
point temperature of syngas at the operating pressure, a plurality of water/steam riser
pipes (54) are welded at the top end of third outer shell (52) as shown in Fig.6, through
which the water and steam mixture are taken to the steam drum there the saturated
steam is separated, a plurality of supporting lugs (55) are properly located and welded
to the outer shell (52) as shown in Fig.5 for installing/hanging the Syngas cooling
system in position at gasifier plant;
a top channel assembly (03) as shown in Fig.I for hot gas exit having; a cylindrical
shaped shell (56) with suitable thickness is placed vertically between a fifth flange (59)
and the top hub (40) of the top tube sheet (33) and leak-proof welding is done on both
top and bottom ends to form the top channel, a pipe (57) is horizontally positioned and
its one end is welded to the shell (56) and the other end is welded to a sixth flange
(58) as shown in Fig.4, for exiting the cooled syngas for further processing, a flat end
cover (60) is placed over the flange (59) and tightened with a suitable metallic gasket
(61), a number of studs, nuts and washers (28,29,30) respectively, for easy
maintenance, a vent riser pipe (62) is positioned inside the top channel, its bottom end

is welded to the top tube sheet (33) and the tailing/rising end is welded to the steam
drum for venting the water and steam mixture, a shorter length support pipe (63) is
welded to the shell (56) and vent riser (62) with a suitable slope for supporting the vent
riser pipe (62) at the center, is capable of cooling the syngas coming out of a
pressurized fluidized bed gasifier to a specified/required temperature and can generate
saturated steam, also which provides necessary access for easy removing, replacing or
plugging of failed tubes and welding during maintenance.

WE CLAIM:
1. An Improved Syngas cooling system with ease of maintenance in Pressurised
Fluidized Bed Gasifiers, comprising:
- a bottom channel assembly (01) having; a gas inlet nozzle (09) covered with castable
refractory (13) including a castable insulite (14); an outer pipe (10); a refractory
lined first inner shell (08) and a first outer shell (04) vertically positioned and welded
to a plurality of top and bottom flanges (05) having first inner and outer hubs
(07,06); a cooling water inlet pipe (17) welded to the outer shell (04) to allow entry
of pressurized cooling water flowing around the first inner shell (08) through an
annular gap provided between the first inner shell (08) and the first outer shell (04)
to maintain the water side wall temperature of the inner shell (08) below a
saturation temperature of water to avoid film boiling and high temperature
oxidation; and an outlet pipe (18) welded to the outer shell (04) for exiting hot
water;
a refractory lined water jacketed ash hopper having a second outer shell (19) and a
second inner shell (20) welded to a third flange (21) and a fourth flange (24); a
plurality of second retainer plates (15) welded with inner surface of the second inner
shell (20) to hold a second castable refractory lining (16) cast at the inner surface of
the second inner shell (20) with suitable thickness to withstand high temperature and to
protect the second inner shell (20) from direct contact with the hot gas and high
temperature oxidation;

a second cooling water inlet and outlet pipes (31,32) welded to the second outer shell
(19) to form a cooling water circuit, through pressurized cooling water is admitted for
flowing around the second inner shell (20) through an annular gap provided between
the second outer shell (19) and second inner shell (20) to maintain the water side wall
temperature of the second inner shell (20) below a saturation temperature to avoid film
boiling and high temperature oxidation;
a shell & tube type heat exchanger assembly (02) having a plurality of tubes (50)
arranged vertically and inserted into holes (34&42) of top and bottom tube sheets
(33&41), both ends of the tubes (50) welded to the top and bottom tube sheets
(33&41) to form a tube bundle, through which the hot syngas flows and transfers heat
thermodynamically to the feed water, a pressure vessel (52) whose bottom end
welded to a top hub (48) of the bottom tube sheet (41) and the other end is welded to
a bottom hub (39) of the top tube sheet (33) to form a shell enclosing the hot gas tube
bundle (50), a plurality of feed water inlet pipe connections (53) welded at the bottom
of the shell (52) to allow entry of feed water to recover heat from hot syngas and
convert into saturated steam, the syngas being cooled to a temperature higher than
dew point temperature of the syngas at the operating pressure; a plurality of riser pipes
(54) and a vent riser pipe (62) welded at the top of the shell (52) through which the
water/steam flows to a steam drum; a plurality of supporting lugs (55)welded to the

outer shell(52) for installing/hanging the syngas cooling system form the shell and tube
assembly (02);
a gas outlet channel assembly (03)having; a shell (56) placed vertically between a
flange (59) and the top tube sheet (33) and welded on both top and bottom ends to
form a top channel, a nozzle (57) horizontally positioned with one end is welded to the
shell (56) and the other end welded to a flange (58), for exiting the cooled syngas,
a metallic gasket (61) placed over the flange (59), a flat end cover (60) placed over the
gasket (61) and tightened with studs and nuts, a vent riser pipe (62) positioned inside
the top channel with its bottom end welded to the top tube sheet (33) and the
tailing/rising end is welded to a steam drum for venting the water and steam mixture,
a shorter length support pipe (63) welded to the shell (56) with a slope for supporting
the vent riser pipe (62) at the center.
2. The syngas cooling system as claimed in claim 1, wherein the bottom channel
assembly (01) is provided with a first retainer plate assembly (12) welded at the
inner surface of the outer pipe (10) for holding a first castable refractory (13)
followed by a castable insulate (14) intact, the second flange (11) connecting the
gas inlet pipe from the gasifier last cyclone, to form the gas inlet chamber, a
plurality of second retainer plates (15) welded at the inner surface of the first inner
shell (08) to firmly hold a second castable refractory lining (16) cast at the inner

surface of the first inner shell (08) to withstand high temperature and to protect the
first inner shell (08) from direct contact with the hot gas.
3. The syngas cooling system as claimed in claims 1 or 2, wherein the top tube sheet
(33) having; a plurality of first holes (34), a first vent hole (35) drilled at center of the
top tube sheet (33) acting as a water/steam vent, a smaller diameter second vent hole
(36) drilled at the side of top tube sheet (33) and a first adopter (37) welded on the
second vent hole (36) , a second plug (38) screwed into the first adopter (37) for
venting the water/steam whenever required, a bottom hub (39) and a top hub (40)
constructed at both sides of the top tube sheet (33) for shell connections.
41 The syngas cooling system as claimed in claims 1 or 2, or 3,wherein the bottom tube
sheet (41) having : a plurality of second holes (42) corresponding to the holes in top
tube sheet (33), a smaller diameter drain hole(43) drilled at the side of the bottom tube
sheet (41) and a second adopter (44) welded on the drain hole (43),a second threaded
plug (45) screwed into the second adopter (44) for draining the water/steam whenever
required, a plurality of third retainer plates (46) welded at bottom of the bottom
tiibe sheet (41) to hold a third castable refractory (47), a top hub (48) constructed at
tap of the bottom tube sheet (41) for shell connections, a number of bolt holes (49) are
Grilled at the periphery of the bottom tube sheet (41) for connecting the bottom
channel (01) with Shell and tube assembly (02).

5. The syngas cooling system as claimed in one of claims 1 to 4,wherein a plurality of
ferrules (51) partly inserted inside and partly protruding outside at top and bottom ends
of the tubes (50).
6. The syngas cooling system as claimed in any of the preceding claims, wherein the
syngas coming out of the pressurized fluidized bed gasifier is cooled to a desired
temperature and generates saturated steam, which also provides necessary access for
easy removing, replacing or plugging of failed tubes and welding during maintenance.

The Improved Syngas cooling system with ease of maintenance in Pressurised Fluidized
Bed Gasifiers, comprising; a gas inlet chamber for hot syngas entry, a plurality of
smaller diameter tubes attached to top and bottom tube sheets to form as single
bundle, enclosed by a pressure vessel which is having feed water inlet and steam/water
outlet ports, a gas outlet channel, and a number of riser tubes capable of cooling the
syngas coming out of a pressurized fluidized bed gasifier and can generate saturated
steam.