FIELD OF INVENTION
The invention relates to integrated gasification based power generation,
in particular pressurized fluidized bed gasification based systems used
for any grade of coals. More particularly, the invention relates to an
improved water tube type heat recovery economiser for cooling and
recovering the heat from the syngas of pressurised fluidised bed
gasification systems.
BACKGROUND OF INVENTION
Pressurised Fluidised Bed Gasification is increasingly being used in
combined 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 coals.
In a refractory lined pressurized fluidized bed gasifier, a mixture of air
and steam is introduced through a distributor located at a bottom of the
gasifier. Coal is continuously injected to the gasifier through ejector
using compressed air. Coal gas also called fuel 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 serially arranged
cyclones. The coal gas at the exit of the cyclone is cooled in a Heat
Recovery Boiler (HRB). The gas is further cooled in the Economiser. 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 present international clean coal technology options is the
Integrated Gasification Combined Cycle (IGCC) method of power
generation.
In such plants, the syngas from the gasifier leaving the cyclones at
around 950-1000 C is cooled by heat recovery units before going to the
gas clean up system and supply to the gas turbine or for other uses.
Generally an evaporator (boiler) is arranged to face the hot gas, followed
by an economizer. The prior art systems adopts a shell type heat
exchanger with gas flow through tubes and water / steam mixture on the
shell side. With increase in size of the gasifier, the shell size increases.
With increase in pressure of the steam / water mixture (as proposed for
larger plants to improve efficiency), the shell thickness and hence weight
increases. In some cases it may lead to multiple units in parallel. The
thickness of tube sheets also increases considerably, leading to
complexity in design. Depending on the nature of ash, plugging of tube
and shut down for cleaning are also experienced.
The International Publication Number WO 2007/055930 A2 Titled
"RADIANT SYNGAS COOLER" discloses a heat exchanger particularly
used to cool the synthesis gas (Syngas) produced by coal gasification
process. In this syngas cooler the heat transfer surfaces are arranged in
vertical position which arrangement poses problems in maintenance or
repair work, the reason being that, in the water tube economiser the heat
transfer surfaces (tube bundles) are arranged in horizontal position. For

example, at least five tube bundles are arranged in series, so that any
bundle can be taken out and kept in a convenient place for repair work.
The 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 INVENTION
An object of this invention is to propose an improved water tube type
heat recovery economizer which is capable to effectively cool the main hot
syngas coming out of a pressurized fluidized bed gasifier.
Another object of the invention is to propose an improved water tube type
heat recovery economizer, which is reliable and easy to operate and
maintain.
A still another object of the invention is to propose an improved water
tube type heat recovery economizer which eliminates the problem to
plugging of tube and shutdown for cleaning.

Yet another object of the invention is to propose an improved water tube
type heat recovery economizer, which allows easy removal of the tube
bundle assembly from top of the economizer when required for
maintenance / repair work.
A further object of the invention is to propose an improved water tube
type heat recovery economizer which enables ingress and egress of
maintenance crews inside the Economizer through a number of man
holes provided.
SUMMARY OF INVENTION
According to the invention the improved water tube type heat recovery
economiser comprises a plurality of smaller diameter water tube coils
arranged in bundles enclosed by a pressure vessel having gas inlet and
outlet ports; a plurality number of man holes a water inlet /outlet header
and feed water pipes.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1- shows an elevation and plan view of the improved water tube
type heat recovery economizer according to the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
Figure 1 shows elevational and plan view of an assembled water tube
type heat recovery economiser according to the invention for integrated
gasification and combined cycle plant (IGCC). The economizer comprising
a plurality of tube bundles (01) arranged in series, and are supported by
a plurality of support members, the plurality of support member
constituting a plurality of gusset plates (02) welded on the inside wall of
a pressure vessel (03), a plurality of bottom plates (16) welded in the
gusset plates (02) and a pressure vessel (03), a plurality of hinged
supports (17) which on downward swiveling allow removal of the
assembly of the tube bundles from the top of the vessel (03), a plurality
of tube holding plates (18) welded with the tubes for holding the tube
bundle, a plurality of pins (19) for connecting the hinged plates (17) and
the tube holding plates (18). The tube bundles (01) are enclosed by the
pressure vessel (03), the pressure vessel (03) having a dished end (04)
with a flange (05) at an upper end of the vessel (03), and a hopper (06) at
the bottom end to collect the fly ash from the syngas. A feed water inlet
header (07) and a plurality of tubes (08) admitting feed water to the
economizer coils including a gas inlet pipe (09) located at the top of
economizer are provided. The hot syngas is admitted in the economizer
via the gas inlet pipe (09) and flows across the water tube bundles (01),
thereby loosing heat to the feed water and raising the water temperature.

A gas outlet pipe (10) located at the bottom of economizer is used to allow
exit of the syngas from the economises A plurality of raiser tubes (11)
and an outlet header (12) are provided at a top location to feed the hot
water to the drum. A plurality of man holes (13) are provided at various
locations on the pressure vessel (03) for facilitating inspection,
maintenance and repair work. To ensure uniform gas flow across the
water tube bundles (01), a plurality of baffle plates (14) are fixed around
the tube bundles (01), including a plurality of panto supports (15) to
positionally keep the water tube bundles are provided.
The water tube bundles (01) are configured to enable generating hot
water including withstanding very high pressure.
The pressure vessel (03) is used as an enclosure for the economizer tube
bundles (01) and allows the tube bundles to withstand high pressure.
The inlet headers (07) and the tubes (08) allow admitting of high-
pressure water to the economizer tube bundles.
The riser tubes (11) and the headers (12) feed the hot water to a drum,
(drum not shown in figure)
The baffle plates (14) are guiding the syngas to flow across the water tube
coils (01) with uniform velocity.

The plurality of support members (02,16,17,18,19) including the
pressure vessel (03) enable holding of the entire economizer tube
bundles (01) in position.
A number of man holes (13) enable the maintenance crew for ingress and
egress into the economizer when required for inspection, maintenance
and repair work.
The pluralities of panto supports (15) holding the water tube bundles
intact.

WE CLAIM
1. An improved water tube type heat recovery Economiser for cooling Syngas in
pressurized gasifiers / integrated gasification and combined cycle plant
comprising:
- a plurality of water tube bundles (01) interposed within a pressure
vessel (03);
- a plurality of support members (02,16,17,18,19) positionally holding
the economizer tube bundles(01) inside the pressure vessel (03),
- a plurality of inlet headers (07) and tubes (08) disposed at the lower
end of the pressure vessel (03) for allowing high-pressure water to
admit in the tube bundles (01);
- a plurality of riser tubes (11) and headers (12) disposed at the upper
end of the pressure vessel (03) for feeding hot water to a drum;

- a plurality of man holes (13) configured at different longitudinal
locations on the pressure vessel (03) to allow ingress and egress of the
maintenance crews;
- a hopper (06), and a dished end with flange (04, 05) respectively
disposed at the bottom end and the top end of the pressure vessel
(03); and
- a plurality of buffle plates (14) encircling the tube bundles (01) for
guiding the syngas with uniform velocity.
characterized in that the said hot syngas entering the pressure vessel
from the top end (9) and passing across the water tube bundles (1)
interposed and connected in series, transfers the heat to the water
passing through the tube and finally the syngas leaving the pressure
vessel through the outlet pipe (10) located just above the hopper (6)
at the bottom end.
2. The economizer as claimed in claim 1, wherein the plurality of support
members comprise a several gusset plates (02) welded on the inside wall of

the pressure vessel (03); a plurality of bottom plates (16) rigidly joined on the
gusset plates (02) and the pressure vessel (03); a plurality of hinged supports
(17) when swiveled in the downward direction enable removal of the tube-
bundles (01) in assembled condition via the head of the pressure vessel (03); a
plurality of holding plates (18) welded to the tubes of the tube bundles (01); and
a plurality of pins (19) connecting the hinged plates (17) and the tube holding
plates (18).
3. The device as claimed in claims 1, 2, wherein the pressure vessel (03) is
disposed as an enclosure for the economizer tubes (01), which is capable of
withstanding high pressure in the order of 80 bar.

ABSRACT

AN IMPROVED WATER TUBE TYPE ECONOMISER FOR COOLING AND
RECOVERING OF HEAT FROM SYNGAS IN PRESSURIZED FLUIDIZED BED
GASSIFIERS
This invention relates to an improved water tube type heat recovery Economizer for
cooling Syngas in pressurized gasifiers / integrated gasification and combined cycle
plant comprising a plurality of water tube bundles (01) interposed within a pressure
vessel (03) a plurality of support members (02, 16, 17, 18, 19) positionally holding
the economizer tube bundles (01) inside the pressure vessel (03), a plurality of inlet
headers (07) and tubes (08) disposed at the lower end of the pressure vessel (03)
for allowing high-pressure water to admit in the tube bundles (01); a plurality of
riser tubes (11) and headers (12) disposed at the upper end of the pressure vessel
(03) for feeding hot water to a drum; a plurality of man holes (13) to allow ingress
and egress of the maintenance crews; a hopper (06), and a dished end with flange
(04, 05) respectively disposed at the bottom end and the top end of the pressure
vessel (03); and a plurality of buffle plates (14) encircling the tube bundles (01) for
guiding the syngas with uniform velocity and characterized in that the said hot
syngas entering the pressure vessel from the top end and passing across the water
tube bundles interposed and connected in series, transfers the heat to the water
passing through the tube and finally the syngas leaving the pressure vessel through
the outlet pipe located just above the hopper at the bottom end.